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	claims	1. An extreme ultraviolet lithography process, comprising:receiving an extreme ultraviolet (EUV) mask including an absorption region and a reflective region;providing a radiation;providing an illuminator;illuminating the EUV mask by the radiation, the radiation being directed to the EUV mask by the illuminator and a first projection optics box (POB),wherein rays of the radiation incident on the EUV mask have an angle of incidence almost the same as a chief ray angle of incidence at the object side (CRAO) of less than three degrees;producing diffracted light and non-diffracted light, wherein the producing the diffracted light and the non-diffracted light further includes:reflecting the radiation by the reflective region of the EUV mask; anddiffracting the reflected radiation by the absorptive region of the EUV mask;removing at least partially the non-diffracted light by reflecting the non-diffracted light using the first POBwherein the first POB includes at least one of EUV refractive optics and EUV reflective optics; andcollecting and directing the diffracted light by a second POB to expose a target. 2. The process of claim 1, wherein the EUV mask comprises:a low thermal expansion material (LTEM) substrate;a reflective multilayer (ML) above one surface of the LTEM substrate;a conductive layer above an opposite surface of the LTEM substrate; anda patterned absorption layer above the ML. 3. The process of claim 1, wherein the CRAO directed by the illuminator is about zero degree. 4. The process of claim 1, wherein a first portion of more than 70% of the non-diffracted light is removed by the first POB,wherein a second portion of the non-diffracted light is collected and directed by the second POB to expose the target. 5. The process of claim 1, wherein collecting the diffracted light includes collecting light of −1st and +1st diffraction orders, andwherein the light of −1st diffraction order has a distance from a pupil center in a pupil plane that is the same as a distance between the light of the +1st diffraction order and the pupil center. 6. The process of claim 1, wherein directing the diffracted light includes directing light of −1st and +1st diffraction orders towards the target, andwherein the second POB includes a magnification of less than one. 7. An extreme ultraviolet lithography process, comprising:determining a chief ray angle of incidence at the object side (CRAO) of less than three degrees;receiving an extreme ultraviolet (EUV) mask, wherein the EUV mask comprises:a reflective multilayer (ML), wherein a first thickness of the ML is adjusted based on the CRAO; anda patterned absorption layer disposed above the ML and exposing reflective regions of the ML, wherein a second thickness of the patterned absorption layer is determined based on the CRAO;illuminating the EUV mask by a radiation from an illuminator, wherein rays of the radiation incident on the EUV mask have an angle of incidence almost the same as the CRAO;producing diffracted light and non-diffracted light, wherein the producing the diffracted light and the non-diffracted light includes:producing shadows in a first portion of the reflective regions of the ML by the patterned absorption layer;reflecting the radiation by a second portion of the reflective regions of the ML; anddiffracting the reflected radiation by the patterned absorption layer;directing the non-diffracted light to the illuminator using a first projection optics box (POB); andcollecting and directing the diffracted light by a second POB to expose a semiconductor wafer. 8. The process of claim 7, wherein collecting the diffracted light includes collecting light of −1st and +1st diffraction orders. 9. The process of claim 7, wherein directing the diffracted light includes directing light of −1st and +1st diffraction orders towards the target. 10. The process of claim 7, wherein the EUV mask comprises:a low thermal expansion material (LTEM),wherein the ML is disposed above one surface of the LTEM substrate,wherein the patterned absorption layer is disposed above the ML; anda conductive layer above an opposite surface of the LTEM substrate. 11. The process of claim 10, wherein the ML includes a plurality of molybdenum-silicon (Mo—Si) film pairs,wherein each of the plurality of Mo—Si film pairs has a thickness of about 7 nm, andwherein the ML has a reflectivity of about 70%. 12. The process of claim 10, wherein the ML includes a plurality of molybdenum-beryllium (Mo—Be) film pairs, andwherein a thickness of each of the plurality of Mo—Be film pairs depends on the CRAO. 13. The process of claim 10, wherein the patterned absorption layer includes a plurality of layers, andwherein each of the plurality of the layers includes at least one material selected from a group consisting of chromium, chromium oxide, chromium nitride, titanium, titanium oxide, titanium nitride, tantalum, tantalum oxide, tantalum nitride, tantalum oxynitride, tantalum boron oxide, tantalum boron nitride, tantalum boron oxynitride, aluminum, aluminum oxide, silver, silver oxide, palladium, copper, ruthenium, and molybdenum. 14. The process of claim 10, the EUV mask further comprising:a capping layer above the ML; anda buffer layer above the capping layer and below the absorption layer. 15. The process of claim 14, wherein the capping layer includes silicon, andwherein the LTEM includes TiO2 doped SiO2. 16. The process of claim 14, wherein the buffer layer includes at least one material selected from a group consisting of Ru, RuB, RuSi, Cr, Cr oxide, and Cr nitride. 17. The process of claim 14, wherein the capping layer and the buffer layer are a single layer. 18. An extreme ultraviolet lithography process, comprising:determining a chief ray angle of incidence at the object side (CRAO) of less than three degrees;receiving an extreme ultraviolet (EUV) mask, wherein the EUV mask comprises:a reflective multilayer (ML), wherein a first thickness of the ML is adjusted based on the CRAO; anda patterned absorption layer disposed above the ML and exposing reflective regions of the ML, wherein a second thickness of the patterned absorption layer is determined based on the CRAO;providing an extreme ultraviolet (EUV) radiation source;directing a radiation from the EUV radiation source to the EUV mask by an illuminator;illuminating the EUV mask by the radiation, wherein rays of the radiation incident on the EUV mask have an angle of incidence almost the same as the CRAO;producing diffracted light and non-diffracted light, wherein the producing the diffracted light and the non-diffracted light includes:producing shadows in a first portion of the reflective regions of the ML by the patterned absorption layer;reflecting the radiation by a second portion of the reflective regions of the ML; anddiffracting the reflected radiation by the patterned absorption layer;reflecting the non-diffracted light to the illuminator by a projection optics box (POB); andreusing the non-diffracted light reflected by the POB. 19. The process of claim 18, wherein the CRAO is about zero degree. 20. The process of claim 18, further comprising:collecting and directing the diffracted light by another POB to expose a target.
	abstract	Methods and systems are provided for developing radiation therapy treatment plans. A treatment template with radiation fields can be chosen for a patient based on a tumor location. Static radiation field positions can be adjusted for the patient, while arc radiation fields may remain the same. Static radiation field positions can be adjusted using dose gradient, historical patient data, and other techniques.
	description	The present invention relates to a lithographic apparatus with a special filter device, to the filter device per se, to a method for the production of such filter device and to a device manufacturing method. A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of one or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning” direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. In a lithographic projection apparatus, the size of features that can be imaged onto the substrate is limited by the wavelength of the projection radiation. To produce integrated circuits with a higher density of devices, and hence higher operating speeds, it is desirable to be able to image smaller features. While most current lithographic projection apparatus employ ultraviolet light generated by mercury lamps or excimer lasers, it has been proposed to use shorter wavelength radiation, e.g. of around 13 nm. Such radiation is termed extreme ultraviolet (EUV) or soft x-ray, and possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or synchrotron radiation from electron storage rings. The source of EUV radiation is typically a plasma source, for example a laser-produced plasma or a discharge source. A common feature of any plasma source is the production of fast ions and atoms, which are expelled from the plasma in all directions. These particles can be damaging to the collector and condenser mirrors which are generally multilayer mirrors or grazing incidence mirrors, with fragile surfaces. This surface is gradually degraded due to the impact, or sputtering, of the particles expelled from the plasma and the lifetime of the mirrors is thus decreased. The sputtering effect is particularly problematic for the radiation collector or collector mirror. The purpose of the collector is to collect radiation which is emitted in all directions by the plasma source and direct it towards other mirrors in the illumination system. The radiation collector is positioned very close to, and in line-of-sight with, the source of EUV in the plasma source and therefore receives a large flux of fast particles from the plasma. Other mirrors in the system are generally damaged to a lesser degree by sputtering of particles expelled from the plasma since they may be shielded to some extent. In the near future, extreme ultraviolet (EUV) sources will probably use tin (Sn) or another metal vapor to produce EUV radiation. This tin may be deposited on mirrors, e.g. a mirror of the radiation collector, and/or leak into the lithographic apparatus. A mirror of such a radiation collector may have a EUV reflecting top layer of, for example, ruthenium (Ru). Deposition of more than approximately 10 nm tin (Sn) on the reflecting Ru layer may reflect EUV radiation in the same way as bulk Sn. The overall transmission of the collector would decrease significantly, since the reflection coefficient of tin is much lower than the reflection coefficient of ruthenium. PCT Patent Application Publication No. WO 99/42904 discloses a filter that is, in use, situated in a path along which the radiation propagates away from the source. The filter may thus be placed between the radiation source and, for example, the illumination system. The filter includes a plurality of foils that, in use, trap debris particles, such as atoms and micro particles. Also, clusters of such micro particles may be trapped by these foils. These foils are oriented such that radiation can still propagate through the filter. The foils may be flat or conical and may be arranged radially around the path. The source, the filter and the projection system may be arranged in a buffer gas, for example, krypton at a pressure of about 0.5 torr. PCT Patent Application Publication No. WO 03/034153 discloses a contaminant barrier that includes a first set of foils and a second set of foils, such that radiation leaving the source first passes the first set of foils and then the second set of foils. The foils of the first and second set define a first set of channels and a second set of channels, respectively. The two sets of channels are spaced apart leaving between them a space into which flushing gas is supplied by a gas supply. An exhaust system may be provided to remove gas from the contaminant barrier. European Patent Application Publication No. EP 1 434 098 provides a contaminant barrier that includes an inner ring and an outer ring in which each of the foils is slidably positioned at least one of its outer ends in grooves of at least one of the inner ring and outer ring. By slidably positioning one of the outer ends of the foils, the foils can expand in a radial direction. The contaminant barrier may include a cooling system arranged to cool one of the rings to which the foils are thermally connected. In order to prevent debris from the source or secondary particles generated by this debris from depositing on an optical element, a filter device may be used, such as for instance described in United States Patent Application Publication No. US 2006/0186353. It is desirable, for example, to provide a lithographic apparatus with an alternative filter device, which filter device may be suitable for application in an EUV lithographic apparatus. It is also or alternatively desirable, for example, to provide such alternative filter device per se, a method for the production of such filter device, and/or a device manufacturing method. According to an aspect of the invention, there is provided a lithographic apparatus comprising a filter device, the filter device comprising a plurality of foils attached to a holder able to rotate around a rotation axis, the foils being arranged substantially parallel to the rotation axis and comprising a uni-directional carbon-fiber composite material selected from the group consisting of a carbon-carbon composite and a carbon-silicon carbide composite. In an embodiment, the lithographic apparatus comprises a source of radiation constructed to generate EUV radiation wherein the source of radiation is a Sn plasma source. Herein, the term “constructed to generate EUV radiation” refers to sources which are designed to generate EUV radiation and which are designed to be used in EUV lithography. In a variant, the source of radiation comprises a laser produced plasma source (LPP) or a discharge produced plasma source (Sn plasma source), respectively. The lithographic apparatus comprises, in an embodiment, an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate. In an embodiment, the lithographic apparatus is an EUV lithographic apparatus and comprises an EUV source of radiation to provide an EUV radiation beam. The lithographic apparatus may comprise a source of radiation constructed to generate the radiation beam, which in an embodiment is an EUV radiation beam, and the source of radiation is constructed to generate EUV radiation. In an embodiment, the direction of the fibers in the carbon-fiber composite material is perpendicular to the rotation axis. In an embodiment, the foils comprise one layer of uni-directional carbon-fiber composite material. In an embodiment, each of the foils comprises 2-5 layers of composite material. In the latter embodiment, the direction of the carbon fibers within the respective layer may differ from layer to layer. In an embodiment, the foils comprise a first layer of uni-directional carbon-fiber composite material and a second layer of uni-directional carbon-fiber composite material, wherein the direction of the fibers in the first layer is perpendicular to the direction of the fibers in the second layer. In an embodiment, the foils comprise a first layer of uni-directional carbon-fiber composite material and a second layer of uni-directional carbon-fiber composite material, wherein the direction of the fibers in the first layer have a first direction angle θ1 relative to a normal perpendicular to the rotation axis and wherein the direction of the fibers in the second layer have a second direction angle θ2 relative to the normal, and wherein the first and the second direction angles (θ1,θ2) are in the range of 0-10° and wherein the mutual angle between the direction of the fibers in the first layer and the second layer is larger than 0° and equal to or smaller than 10°. In an embodiment, the holder comprises a plurality of sleeves, wherein each foil comprises a tail part, wherein the sleeves are constructed to receive the tail parts, and wherein the sleeves are constructed to prevent release of the foils from the holder in a direction perpendicular to the rotation axis. In an embodiment, at least part of the holder may comprise a carbon-fiber composite material selected from the group consisting of carbon-carbon composite (C—C composite) and carbon-silicon carbide composite (C—SiC composite). In an embodiment, the holder may comprise uni-directional carbon-fiber composite material. According to a further aspect of the invention, there is provided a lithographic apparatus comprising a filter device, the filter device comprising a plurality of foils attached to a holder which is able to rotate around a rotation axis, the foils being arranged parallel to the rotation axis and comprising a material which does not substantially react with liquid Sn at a temperature of at least 1000° C. In an embodiment, the material does not substantially react with liquid Sn at a temperature up to about 2000° C. According to a further aspect of the invention, there is provided a device manufacturing method using a lithographic apparatus according to an embodiment of the invention. In aspect, there is provided a device manufacturing method, comprising: patterning a beam of radiation; projecting the patterned beam of radiation onto a target portion of a substrate; and filtering the beam of radiation using a filter device, the filter device comprising a plurality of foils attached to a holder able to rotate around a rotation axis, the foils being arranged substantially parallel to the rotation axis and comprising a uni-directional carbon-fiber composite material selected from the group consisting of a carbon-carbon composite and a carbon-silicon carbide composite. According to a further aspect of the invention, there is provided a filter device per se, the filter device comprising a plurality of foils attached to a holder which is able to rotate around a rotation axis, the foils being arranged substantially parallel to the rotation axis and comprising a uni-directional carbon-fiber composite material selected from the group consisting of carbon-carbon composite and carbon-silicon carbide composite. As mentioned above, in an embodiment, at least part of the holder, such as a holder upstream side, may comprise a carbon-fiber composite material selected from the group consisting of carbon-carbon composite (C—C composite) and carbon-silicon carbide composite (C—SiC composite). In a further aspect, there is provided a method for the production of a foil for a filter device, the method comprising: a. providing a resin containing pre-impregnated sheet; b. curing the resin; c. optionally reducing the thickness of at least part of the product obtained at b); d. carbonizing the product obtained at b) or c); e. optionally performing one or more times a densifying process, wherein the densifying process comprises infiltrating the carbonized product with a carbon-containing compound and subsequently carbonizing the infiltrated product; f. graphitizing the product obtained at d) or e); g. optionally reducing the thickness of at least part of the product obtained at f)wherein the method comprises reducing the thickness by process c), or by process g), or by both process c) and g), and wherein the foil comprises a uni-directional carbon-fiber composite material selected from the group consisting of carbon-carbon composite and carbon-silicon carbide composite. The carbon-containing compound may be, for instance, a phenolic resin. In an embodiment, the resin containing pre-impregnated sheet comprises a laminate of resin containing pre-impregnated sheets. In an embodiment, after the optional process c) and before process d) the method further comprises performing one or more times a laminating process, wherein the laminating process comprises: a1. arranging a further resin containing pre-impregnated sheet to the product obtained at b) or c) to obtain a laminate of the product obtained at b) or c) and the further resin containing pre-impregnated sheet; b1. curing the resin; and c1. optionally reducing the thickness of at least part of the product obtained at b1). A foil obtained with the method for production may be applied in the filter device of an embodiment of the invention. FIG. 1 schematically depicts a lithographic apparatus 1 according to an embodiment of the present invention. The apparatus 1 includes a source SO configured to generate radiation and an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or EUV radiation) from the radiation received from source, SO. The source SO may be provided as a separate unit and not be a part of the lithographic apparatus. A support (e.g. a mask table) MT is configured to support a patterning device (e.g. a mask) MA and is connected to a first positioning device PM configured to accurately position the patterning device MA in accordance with certain parameters. A substrate table (e.g. a wafer table) WT is configured to hold a substrate (e.g. a resist-coated wafer) W and is connected to a second positioning device PW configured to accurately position the substrate W in accordance with certain parameters. A projection system (e.g. a reflective projection mirror system) PS (also known as projection optics box POB) is configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, to direct, shape, or control radiation. The support MT holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support MT can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support MT may be a frame or a table, for example, which may be fixed or movable as required. The support MT may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix. The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”. As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask). Alternatively, the apparatus may be of a transmissive type (e.g. employing a transmissive mask). The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more patterning device supports). In such “multiple stage” machines the additional tables and/or supports may be used in parallel, or preparatory steps may be carried out on one or more tables and/or supports while one or more other tables and/or supports are being used for exposure. The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located, for example, between the projection system and the substrate during exposure. Referring to FIG. 1, the illuminator IL receives radiation from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation is passed from the source SO to the illuminator IL with the aid of a beam delivery system including, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The illuminator IL may include an adjusting device configured to adjust the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which projects the beam onto a target portion C of the substrate W. With the aid of the second positioning device PW and position sensor IF2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioning device PM and another position sensor IF1 (e.g. an interferometric device, linear encoder or capacitive sensor) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the patterning device support MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioning device PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioning device PW. In the case of a stepper, as opposed to a scanner, the patterning device support MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies. The depicted apparatus could be used in at least one of the following modes: a. In step mode, the patterning device support MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. b. In scan mode, the patterning device support MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the patterning device support MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. c. In another mode, the patterning device support MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed. The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components. The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength λ of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV or soft X-ray) radiation (e.g. having a wavelength in the range of 5-20 nm, e.g. 13.5 nm or 6.6 nm), as well as particle beams, such as ion beams or electron beams. Generally, radiation having wavelengths between about 780-3000 nm (or larger) is considered IR radiation. UV refers to radiation with wavelengths of approximately 100-400 nm. Within lithography, it is usually also applied to the wavelengths which can be produced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm; and/or I-line 365 nm. VUV is Vacuum UV (i.e. UV absorbed by air) and refers to wavelengths of approximately 100-200 nm. DUV is Deep UV, and is usually used in lithography for the wavelengths produced by excimer lasers like 126 nm-248 nm. The person skilled in the art understands that radiation having a wavelength in the range of, for example, 5-20 nm relates to radiation with a certain wavelength band, of which at least part is in the range of 5-20 nm. FIG. 2 shows the projection apparatus 1 in more detail, including a radiation system 42, an illumination system 44, and the projection system PS. The radiation system 42 includes the radiation source SO which may be a discharge plasma source. EUV radiation may be produced by a gas or vapor in the source, for example Xe gas, Li vapor or Sn vapor in which a very hot plasma is created to emit radiation in the EUV range of the electromagnetic spectrum. The very hot plasma is created by causing an at least partially ionized plasma by, for example, an electrical discharge. Partial pressures of, for example, 10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may be required for efficient generation of the radiation. In an embodiment, a Sn source as EUV source is applied. The radiation emitted by radiation source SO is passed from a source chamber 47 into a collector chamber 48 via an optional contaminant barrier 49 which is positioned in or behind an opening in source chamber 47. The contaminant barrier 49 may comprise a channel structure. Contaminant barrier 49 may comprise a gas barrier or a combination of a gas barrier and a channel structure. The contaminant barrier 49 further indicated herein at least comprises a channel structure. The collector chamber 48 includes a radiation collector 50 (herein also indicated as collector mirror) which may be formed by a grazing incidence collector. Radiation collector 50 has an upstream radiation collector side 50a and a downstream radiation collector side 50b. Radiation passed by collector 50 can be reflected off a grazing incidence mirror 51 to be focused in a virtual source point 52 at an aperture in the collector chamber 48. From collector chamber 48, a beam of radiation 56 is reflected in illumination system 44 via normal incidence reflectors 53, 54 onto a patterning device (e.g., a reticle or mask) positioned on patterning device support MT (e.g., a reticle or mask table). A patterned beam 57 is formed which is imaged in projection system PS via reflective elements 58, 59 onto substrate table WT. More elements than shown may generally be present in illumination system 44 and projection system PS. Grazing incidence mirror 51 may optionally be present, depending upon the type of lithographic apparatus. The grazing incidence mirror may be a grating spectral filter 51. Further, there may be more mirrors present than those shown in the Figures, for example there may be 1-4 more reflective elements present than elements 58, 59. Instead of or in addition to a grazing incidence mirror as collector mirror 50, a normal incidence collector may be applied. Collector mirror 50, as described herein in an embodiment in more detail as a nested collector with reflectors 142, 143, and 146, and as schematically depicted in, for example, FIG. 2, is herein further used as an example of a collector (or collector mirror). Hence, where applicable, collector mirror 50 as a grazing incidence collector may also be interpreted as collector in general and in a specific embodiment also as a normal incidence collector. Instead of or in addition to a grating spectral filter 51, as schematically depicted in FIG. 2, a transmissive optical filter may be applied that is transmissive for EUV and less transmissive for or even substantially absorbing of UV radiation. Hence, “grating spectral purity filter” is herein further indicated as “spectral purity filter” which includes gratings or transmissive filters. Not depicted in schematic FIG. 2, but also included as an optional optical element may be an EUV transmissive optical filter, for instance arranged upstream of collector mirror 50, or an optical EUV transmissive filter in illumination system 44 and/or projection system PS. In an embodiment (see also above), radiation collector 50 may be a grazing incidence collector. The collector 50 is aligned along an optical axis 0. The source SO or an image thereof is located on optical axis O. The radiation collector 50 may include reflectors 142, 143, 146 (also known as a Wolter-type reflector comprising several Wolter-type reflectors). These reflectors 142, 143, 146 may be nested and rotationally symmetric about optical axis O. In FIG. 2 (as well as in other Figures), an inner reflector is indicated by reference number 142, an intermediate reflector is indicated by reference number 143, and an outer reflector is indicated by reference number 146. The radiation collector 50 encloses a certain volume, i.e. the volume within the outer reflector(s) 146. Usually, this volume within outer reflector(s) 146 is peripherally closed, although small openings may be present. All the reflectors 142, 143 and 146 include surfaces of which at least part includes a reflective layer or a number of reflective layers. Hence, reflectors 142, 143 and 146 (more reflectors may be present and embodiments of radiation collectors 50 may have more than 3 reflectors), are at least partly designed for reflecting and collecting EUV radiation from source SO, and at least part of the reflector may not be designed to reflect and collect EUV radiation. For example, at least part of the back side of the reflectors may not be designed to reflect and collect EUV radiation. On the surface of these reflective layers, there may in addition be a cap layer for protection or an optical filter provided on at least part of the surface of the reflective layers. The radiation collector 50 is usually placed in the vicinity of the source SO or an image of the source SO. Each reflector 142, 143, 146 may comprise at least two adjacent reflecting surfaces, the reflecting surfaces further from the source SO being placed at smaller angles to the optical axis O than the reflecting surface that is closer to the source SO. In this way, a grazing incidence collector 50 is configured to generate a beam of (E)UV radiation propagating along the optical axis O. At least two reflectors may be placed substantially coaxially and extend substantially rotationally symmetrically about the optical axis O. It should be appreciated that radiation collector 50 may have further features on the external surface of outer reflector 146 or further features around outer reflector 146, for example a protective holder, a heater, etc. Reference number 180 indicates a space between two reflectors, e.g. between reflectors 142 and 143. All optical elements shown in FIG. 2 (and optical elements not shown in the schematic drawing of this embodiment) are vulnerable to deposition of contaminants (for instance produced by source SO), for example, Sn. This is the case for the radiation collector 50 and, if present, the spectral purity filter 51. Further, not only optical elements may be contaminated by deposition, such as Sn, but also construction elements such as walls, holders, supporting systems, gas locks, a contaminant barrier 49, etc. This deposition may not directly influence the optical properties of the optical elements, but due to re-deposition, this deposition may deposit (i.e. re-deposit) on optical elements, thereby influencing the optical properties. Hence, even deposition not deposited on optical elements may in a later stage due to re-deposition lead to contamination of surfaces of optical elements. This may lead to a decrease in optical performance like reflection, transmission, uniformity, etc. During use, deposition may be found on one or more of the outer 146 and inner 142/143 reflector(s). The radiation collector 50 may be deteriorated by such deposition (deterioration by debris, e.g. ions, electrons, clusters, droplets, electrode corrosion from the source SO). Deposition of Sn, for example due to a Sn source, may, after a few mono-layers, be detrimental to reflection of the radiation collector 50 or other optical elements, which may necessitate the cleaning of such optical elements. In order to diminish this deposition, a contaminant barrier 49 may be provided. In addition or instead to the contaminant barrier 49, a filter device may be provided as further discussed below. The contaminant barrier 49 is a static device, whereas the filter device according to an embodiment of the invention is a dynamic device, i.e. it is a rotating contaminant barrier, which may rotate during use of the lithographic apparatus. Therefore, a filter device, especially suitable for application in an EUV lithographic apparatus, especially for EUV with plasma based Sn sources, is provided. Referring to FIG. 3, the arrangement of the filter device 149 is schematically depicted. Source chamber 47 with source SO is depicted. Downstream from the source, the collector 50 is present (not depicted). Downstream from the source SO, but upstream from the collector 50, i.e. before the first (reflective) optics, optional contaminant barrier 49 is arranged, as described above. Further, downstream from source SO and upstream from the collector 50 (not depicted), and upstream from the optional contaminant barrier 49, filter device 149 is arranged. Schematically, a plurality of foils is depicted of the filter device 149 as further shown in FIG. 4. FIG. 4 schematically depicts the filter device 149 according to an embodiment of the invention. Only relevant details are shown; a filter device housing and a filter device motor to rotate the filter device 149 are for the sake of simplicity not indicated. The filter device 149 comprises a holder 201, for example in the form of a cone, with holder upstream side 220 (here a cone top), and foils 200 (of which only a few are depicted for clarity). During use, the filter device 149 may rotate along a rotation axis RA. In an embodiment, the rotation axis RA is substantially parallel to and substantially coincides with at least part of the optical axis O (as shown in FIG. 4). In an embodiment, the filter device 149 is rotationally symmetric about rotation axis RA (and in a an embodiment thus also optical axis O). The holder upstream side 220 is directed to the source SO (not depicted). The foils 200 may have an upstream front region 202, a top region 203, a downstream back region 204 and a bottom 205. The filter device 149 is a kind of “propeller” with foils 200 parallel to the rotation axis RA, e.g., parallel to and/or coinciding with the optical axis O. As seen in FIG. 4, the foils 200 are parallel to the rotation axis RA and are parallel to normals N perpendicular to the rotation axis RA. The planes of the foils intersect at the rotation axis RA. The foils 200 may have a maximum foil thickness d (see FIG. 5) in the range of 0.05-1.2 mm, or 0.1-0.4 mm. At larger thickness, too much radiation may be blocked, and a lower thickness may not be feasible with the carbon-fiber composite material described hereafter. The filter device 149 may comprise about 50-200 foils, or 150-200 foils. During use (i.e. during lithographic processing), the filter device 149 may rotate about rotation axis RA with a speed in the range of about 1,000-20,000 rpm, or in the range of 3,000-8,000 rpm. The foils 200 are oriented such that at least part of the radiation from source SO can still propagate through the filter 149. Specific embodiments are also described in PCT Patent Application Publication Nos. WO 99/42904 and WO 03/034153 and United States Patent Application Publication No. US 2006/0186353, which are incorporated herein in their entirety by reference. The filter device 149 is faced with ions and particles and especially with Sn (tin) particles. The Sn particles may, when they reach the filter device, have a temperature of up to about 2000-2500° C. Very robust materials like W (tungsten) or Mo (molybdenum) are not able to cope with these conditions. Surprisingly however, carbon-fiber composite material selected from the group consisting of carbon-carbon composites (C—C composites) and carbon-silicon carbide composites (C—SiC composites) are not only suitable to provide robust foils with the desired strength and thermal conductivity, but are also able to withstand Sn liquid under lithographic apparatus conditions. Such materials are especially suitable in coping with ions, particles and liquid Sn particles from a Sn based source of radiation. Uni-directional carbon-fiber composites appear to provide foils 200 which are suitable for application in the filter device 149. Carbon-fiber composite materials are known from the prior art, such as for instance from PCT Patent Application Publication No. WO 00/034629, U.S. Pat. No. 4,833,030, and U.S. Patent Application Publication Nos. US 2005/0151305, and US 2006/0019816. The term “uni-directional” refers herein to carbon fiber composite materials of the C—C or C—SiC type wherein the orientation of the carbon fibers is substantially in one direction (one orientation). This contrast with, for instance, 3D or woven type of carbon-fiber composites. In an embodiment, the lithographic apparatus 1 comprises the filter device 149, wherein the filter device 149 comprises a plurality of foils 200 attached to holder 201 which is able to rotate around the rotation axis RA, the foils 200 being arranged parallel to the rotation axis RA, wherein the foils 200 comprise the uni-directional carbon-fiber composite material selected from the group consisting of carbon-carbon composite (C—C composite) and carbon-silicon carbide composite (C—SiC composite). Thus, in an embodiment, the lithographic apparatus 1 comprises the filter device 149, wherein the filter device 149 comprises a plurality of foils 200 attached to holder 201 which is able to rotate around rotation axis RA, the foils 200 being arranged parallel to the rotation axis RA, wherein the foils comprise a material which does not substantially react with liquid Sn. The material, such as the herein described carbon-fiber composites, may have a thermal conductivity of at least about 50 W/mK, at least about 60 W/mK, at least about 100 W/mK, in the range of about 50-400 W/mK, in the range of about 60-400 W/mK, and/or in the range of about 100-400 W/mK. Note that this thermal behavior may be anisotropic. At least in one direction, in the direction of the orientation of the carbon fibers, the thermal conductivity may have the herein specified values. In an embodiment, the direction of the fibers in the carbon-fiber composite material is perpendicular to the rotation axis RA. Therefore, the tensile strength of the material is may be optimally applied and the centrifugal forces may be best resisted. The tensile strength in the direction of the fibers may be in the range of 200-900 MPa, or of about 400-800 MPa. Referring to FIG. 5, an embodiment of a foil 200 is shown, for clarity drawn separate from the holder 201. The foil 200 may have an upstream front region 202, top region 203, downstream back region 204 and a bottom 205. Towards the bottom 205, a tail part 206 is shown, which may be relatively thicker than the main part of the foil 200. This tail part 206 may better allow attachment of the foil 200 to the holder 201. The foil 201 has a maximum thickness d, which may be in the range of about 0.05-1.2 mm, or about 0.1-0.4 mm. The tail part 206 may have a maximum thickness in the range of about 0.2-2.5 mm, or about 0.6-1.5 mm. The tail part 206 may comprise about 0.2-5% of the total surface of the foil 200. In an embodiment, the maximum thickness d1 of the tail part is larger than the maximum thickness d of the foil. FIG. 5 schematically also depicts carbon fibers 210. The carbon fibers 210 may have an angle θ with a normal N perpendicular to the rotation axis RA. The smallest angle with the normal is selected. For clarity reasons, some of the carbon fibers 210 have been drawn as having an angle θ which is non-zero. The direction of the carbon fibers 210 is the mean value of angle θ for the carbon fibers 210 in the foil 200 (or layer comprised in the foil as discussed below). In a uni-directional carbon-fiber composite, the fibers 210 are arranged substantially parallel to each other and are arranged in substantially one direction. As mentioned above, the direction of the fibers 210 in the carbon-fiber composite material is in an embodiment perpendicular to the rotation axis RA, i.e. angle θ is substantially 0°, or in the range of 0-1°. FIG. 6a shows (in front view) an embodiment wherein the direction of the fibers 210 in the carbon-fiber composite material is perpendicular to the rotation axis RA, i.e. angle θ is substantially zero. For clarity reasons the tail part 206 is not shown, and only part of the foil 200 is shown. Note that schematically, the foil 200 herein is shown to have a constant thickness, however, there may be a variation in foil thickness over height or length of the foil 200, irrespective of the tail part 206. In FIG. 6a, schematically the optical axis O and rotation axis RA are shown in front view, i.e. the foil 200 of FIG. 5 is now seen from the front region 202 (upstream view). The foil in this embodiment essentially consists of one layer 300 of the carbon-fiber composite material. The fibers 210 in this embodiment are aligned parallel to the normal N (the normal perpendicular to the rotation axis RA), and (thus) perpendicular to the rotation axis RA, i.e. an angle θ with a normal N which is substantially zero. In an embodiment, the foils 200 comprise one layer 300 of uni-directional carbon-fiber composite material. However, another embodiment is possible, as schematically depicted in FIGS. 6b/6c/6d and 6e/6f (as well in FIG. 7a). The foils 200 may in an embodiment of the filter device 149 comprise 2-5 layers of composite material. In such an embodiment, the direction of the carbon fibers 210 within the respective layers may differ from layer to layer. FIG. 6b schematically depicts an embodiment of a foil 200, comprising two layers of carbon-fiber composite material. For the sake of clarity, the layers are drawn at a distance from each other. The foil 200 comprises in this embodiment a first layer 300(1) of uni-directional carbon-fiber composite material and a second layer 300(2) of uni-directional carbon-fiber composite material. The direction of the carbon fibers 210 relative to the normal (and thus relative to the rotation axis RA (not shown)) may differ from layer to layer. In FIG. 6b, the angles with the normal N to the rotation axis RA are indicated as θ1 and θ2, respectively. In an embodiment, not depicted, the foils 200 comprise first layer 300(1) of uni-directional carbon-fiber composite material and second layer 300(1) of uni-directional carbon-fiber composite material, wherein the direction of the fibers 210 in the first layer 300(1) is perpendicular to the direction of the fibers 210 in the second layer 300(2). When applying such a foil 200 in the filter device, in an embodiment, the direction of the fibers 210 of at least one of the layers is perpendicular to the rotation axis RA and the direction of the fibers 210 in the other layer is thus parallel to the rotation axis RA. Thus, in an embodiment, the direction of the fibers 210 in at least one of the layers is parallel to normal N, i.e. angle θ in this layer is substantially zero and perpendicular to the rotation axis RA, and the direction of the fibers 210 in at least one of the layers is perpendicular to normal N, i.e. angle θ in this layer is substantially 90°. In an embodiment schematically depicted in FIGS. 6b/6c, a foil 200 comprises first layer 300(1) of uni-directional carbon-fiber composite material and second layer 300(2) of uni-directional carbon-fiber composite material, wherein the direction of the fibers 210 in the first layer 300(1) have a first direction angle θ1 relative to normal N perpendicular to the rotation axis RA and wherein the direction of the fibers 210 in the second layer 300(1) have a second direction angle θ2 relative to the normal N, and wherein the first and the second direction angles (θ1,θ2) are in the range of 0-10° and wherein the mutual angle between the direction of the fibers in the first layer and the second layer is larger than 0° and equal to or smaller than 10°. For instance, the direction of the carbon-fibers 210 in the first layer 300(1) may have θ1 of 0° with normal N and the direction of the carbon-fibers 210 in the second layer 300(2) may have θ1 of 2.5° with normal N, thereby providing a mutual angle of 2.5°. In another embodiment, θ1 may be 2.5° and θ2 may be 2.5°, but the mutual angle may be 5° (opposite deviations of the directions in the respective layers). When two or more layers are applied in foil 200, in an embodiment, at least 2 layers have different directions of the carbon fibers, i.e. the carbon fibers in at least two layers are not parallel. When applying such a foil 200 with at least 2 layers in the filter device, in an embodiment, the direction of the fibers 210 of at least one of the layers is perpendicular to the rotation axis RA (i.e. angle θ with normal N is substantially zero). FIG. 6c schematically depicts a side view of this embodiment, wherein foil 200 comprises the two layers 300(1) and 300(2). In this schematic side view, the fibers 210 seem parallel, but are, as described above in an embodiment, not parallel. The deviation from parallelism is however in a plane perpendicular to the view. Each layer has a thickness, indicated as d(1) and d(2), respectively. FIG. 6d is a front or side view, but now schematically including the holder 201. Rotation axis RA, perpendicular to the plane of drawing, is also schematically indicated. For the sake of clarity, the filter device 149 is schematically depicted with only one foil 200. FIGS. 6e/6f schematically depict an embodiment of the foil 200, wherein the foil essentially consists of three layers, indicated with reference numbers 300(1), 300(2) and 300(3), respectively, with maximum thicknesses d(1), d(2) and d(3), respectively. The third layer 300(3) may comprise carbon-fiber composite material wherein the direction of the carbon fibers 210 is essentially parallel to the direction of the carbon fibers 210 in carbon-fiber composite material of the first layer 300(1). In an embodiment, as schematically depicted in FIGS. 6e/6f, foil 200 comprises a first layer 300(1) of uni-directional carbon-fiber composite material, a second layer 300(2) of uni-directional carbon-fiber composite material, and a third layer 300(2) of uni-directional carbon-fiber composite material, wherein the direction of the fibers 210 in the first layer 300(1) has a first direction angle (θ1) (not depicted) relative to a normal (N) perpendicular to the rotation axis (RA), wherein the direction of the fibers 210 in the second layer 300(2) has a second direction angle (θ2) relative to the normal (N), and wherein the direction of the fibers 210 in the third layer 300(3) has a third direction angle (θ3) (not depicted) relative to the normal (N), and wherein the first, second and third direction angles (θ1,θ2,θ3) are in the range of about 0-90° and wherein the mutual angle between the direction of the fibers 210 in the first layer 300(1) and the second layer 300(2) is, in an embodiment, substantially 90° and wherein the mutual angle between the direction of the fibers 210 in the first layer 300(1) and third layer 300(3) is, in an embodiment, substantially 0°. In other words, in an embodiment, foil 200 comprises first layer 300(1) of uni-directional carbon-fiber composite material, a second layer 300(2) of uni-directional carbon-fiber composite material, and third layer 300(2) of uni-directional carbon-fiber composite material, wherein the direction of carbon fibers 210 in adjacent layers are perpendicular to each other. In FIG. 6f, for clarity reasons, the respective layers 300(1), 300(2) and 300(3) are schematically drawn at a distance, but as schematically drawn in FIG. 6e, the three layers 300(1), 300(2) and 300(3) form a laminate and form adjacent layers 300(1), 300(2) and 300(3). As shown in the embodiment depicted in FIG. 6e, the middle layer 300(2) has carbon fibers 210 with a direction perpendicular to the plane of the drawing (upstream view), i.e. substantially parallel to the rotation axis RA and optical axis O, which layer is sandwiched between two layers 300(1) and 300(3) with substantially parallel directions of carbon fibers 210, and which directions are perpendicular to the direction of the carbon fibers of the middle layer 300(2). Likewise, stacks of layers, for example 2-5 layers, can be created wherein adjacent layers have carbon-fiber directions which are perpendicular to each other. In an embodiment, as schematically depicted in FIG. 8, the holder 201 comprises a plurality of sleeves 230, wherein each foil 200 comprises a tail part 206, wherein the sleeves 230 are constructed to receive the tail parts 206, and wherein the sleeves 230 are constructed to prevent release of the foils 200 from the holder 201 in a direction perpendicular to the rotation axis RA. FIG. 8 schematically depicts two embodiments A and B of sleeves. As will be clear to the person skilled in the art, more types of sleeve 230 may be possible. Further, as can be understood from FIGS. 4 and 5, a plurality of sleeves 230 corresponding to the plurality of foils 200 may be present, the former arranged to host the tail parts 206 of the latter. The holder 201 may have an external surface 212, which may at least partially be exposed to radiation of source SO during lithographic processing. In at least part of the holder 201, i.e. thus in at least part of the surface 212, sleeves 230 are arranged into which the tail part 206 can slide. They are constructed in such a way as not to allow release in a direction perpendicular to the surface 212, but only in a direction parallel to the surface 212. In an embodiment, the foils 200 have maximum foil thickness d and the tail parts 206 have maximum tail part thickness d1, wherein the maximum tail part thickness d1 is larger than the maximum foil thickness d. The sleeves 230 may be arranged to have different widths; one closer to the surface 212, which is chosen to host part of the foil 200 with maximum thickness d, and a part further from surface 212, deeper in the holder 201, with a larger width, which width is chosen to host the tail part with maximum thickness d1, as schematically depicted in FIG. 8. In this way, the large centrifugal forces to which the foils 200 may be exposed, may not lead to an undesired release of the foil 200. Further, the sleeves 230 and foils 200 with relatively thicker (d1>d) tail parts 206 may allow a relatively easy removal of a single foil from the filter device 149, for instance when after processing a foil 200 is damaged or when the Sn deposition on a foil 200 becomes too thick. The foil 200 may easily slide out of the holder 201 and be replaced by a new foil 200. In an embodiment, at least part of the holder 201, especially the top 220 directed to the source SO, may comprise a carbon-fiber composite material selected from the group consisting of carbon-carbon composite (C—C composite) and carbon-silicon carbide composites (C—SiC composite). This composite may be a uni-directional carbon-fiber composite material, but may however also be a woven or knitted or 3-dimensional carbon-fiber composite material. In this way, a relatively robust filter device 149 may be provided, which is surprisingly integrally able to cope with debris such as liquid Sn, ions etc., which may be released from the source SO. In an embodiment, the lithographic apparatus 1 comprises a source of radiation SO constructed to generate EUV radiation wherein the source of radiation SO is a Sn plasma source. The lithographic apparatus 1 comprises in, an embodiment, an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; and a projection system configured to project the patterned radiation beam onto a target portion of the substrate. In an embodiment, the lithographic apparatus 1 is an EUV lithographic apparatus. The lithographic apparatus comprises a source of radiation SO constructed to generate the radiation beam, which is, in an embodiment, a EUV radiation beam, and the source of radiation is constructed to generate EUV radiation. In an embodiment, the filter device 149, during operation (e.g., lithographic processing), may rotate about optical axis O (at high speed) to filter out at least part of the debris, such as liquid Sn particles, to help diminish deposition and/or deterioration of an optical element, such as a collector mirror 50. According to an aspect of the invention, there is provided a device manufacturing method using a lithographic apparatus 1 according to an embodiment of the invention, i.e. during lithographic processing, the filter device 149 is applied, removing by its rotation at least part of the debris ejected by source SO from the beam of radiation. A device manufacturing method may be provided, wherein, during lithographic processing, the filter device 149 rotates about rotation axis RA to filter out part of the debris emitted by source SO. According to an aspect of the invention, there is provided a filter device 149 per se, the filter device 149 comprising a plurality of foils 200 attached to holder 201 which is able to rotate around rotation axis RA, the foils 200 being arranged parallel to the rotation axis RA, wherein the foils 200 comprise a uni-directional carbon-fiber composite material selected from the group consisting of carbon-carbon composite (C—C composite) and carbon-silicon carbide composite (C—SiC composite). As mentioned above, in an embodiment, at least part of the holder 201, especially a holder upstream side 220, may comprise a carbon-fiber composite material selected from the group consisting of carbon-carbon composite (C—C composite) and carbon-silicon carbide composite (C—SiC composite). The filter device 149 may, as will be clear to the person skilled in the art, further comprise a mechanism to propel the filter device 149, such as a motor, and may further comprise a housing, wherein the filter device 149 may rotate, a gas source configured to provide a stream of gas through the filter device 149, i.e. through the open spaces between the foils 200. The filter device 149 may further or alternatively comprise a cooling mechanism, such as a Peltier element, to cool for instance the holder 201, one or more liquid cooling media channels inside the foils 200, one or more liquid cooling media channels external to the foils 200 (such as grooves in the foils 200), liquid tin guiding structures in the foils 200 or outside the foils 200 (such as grooves in the foils 200), IR emission enhancement structures (such as structures having dimensions in the order of 5 μm to 100 μm), foil spacing structures, and spacers between adjacent foils 200 (e.g., to prevent or diminish resonances during rotation), etc. In an aspect of the invention, there is provided a method for the production of the foils 200 for use in the filter device 149. The production of carbon-fiber composite materials is known from the prior art, such as for instance from PCT Patent Application Publication No. WO 00/034629, U.S. Pat. No. 4,833,030, and U.S. Patent Application Publication Nos. US 2005/0151305, and US 2006/0019816. Here, an embodiment of invention provides a method for the production of a foil for a filter device, the method comprising: a. providing a resin containing pre-impregnated sheet; b. curing the resin; c. optionally reducing the thickness of at least part of the product obtained at b); d. carbonizing the product obtained at b) or c); e. optionally performing one or more times a densifying process, wherein the densifying process comprises infiltrating the carbonized product obtained at d) with a carbon-containing compound and subsequently carbonizing the infiltrated product; f. graphitizing the product obtained at d) or e); g. optionally reducing the thickness of at least part of the product obtained at f) wherein the method comprises at least one process for reducing the thickness selected from the processes according to process c) and process g). Sub processes a), b) d) and f) are standard processes. However, an embodiment of the invention further provides, in an embodiment, at least a thickness reducing process, which is either process c) or process g) or both processes c) and g). The thickness may be reduced before the carbonizing process d) or after the graphitizing process f), or after both processes b) and f). By reducing the thickness, an optimal thickness (d and d1) of the foils 200 and tail part thereof may be obtained. The thickness may be reduced by polishing or other method known in the art, such as a grinding process. The phrase “providing a resin containing pre-impregnated sheet” refers to providing so called “prepregs” or pre-impregnated fiber reinforcement materials, known to the person skilled in the art, that after curing, carbonizing, optional densifying, and graphitizing forms (uni-directional) carbon-fiber composite material selected from the group consisting of carbon-carbon composite (C—C composite) and carbon-silicon carbide composite (C—SiC composite). Such sheets are commercially available, for instance from Toray or Nelcote. In an embodiment, the resin containing pre-impregnated sheet comprises a laminate of resin containing pre-impregnated sheets. In such an embodiment, one starts already with a laminate of sheets and performs the above process. Such laminate of sheets may be, for instance, arranged to provide, after processing, an embodiment of foil 200 as described above and as schematically depicted in FIGS. 6b-7a. In an embodiment, after the optional process c) and before the carbonizing process d) the method further comprises performing one or more times a laminating process, wherein the laminating process comprises: a1. arranging a further resin containing pre-impregnated sheet to the product obtained at b) or c) to obtain a laminate of the product obtained at b) or c) and the further resin containing pre-impregnated sheet; b1. curing the resin; and c1. optionally reducing the thickness of at least part of the product obtained at b1). In this embodiment, laminating is performed while processing. Above described embodiments may schematically be illustrated by FIGS. 7a and 7b. FIG. 7a shows a mold 400, with a depression 401 with depth d3. In an embodiment, depth d3 is substantially equal to ½ of d. Resin containing pre-impregnated sheets are arranged on top of each other. In FIG. 7a, these sheets are indicated as sheets 300(1)-300(5). These sheets will after performing the method for the production of the foils 200 form layers 300(1)-300(5), as described above. In the embodiment schematically depicted in FIG. 7a, the sheets are laminated in a sequence of large and small sheets, in the FIG. 7a large-small-large-small-large. In this way, after performing the production method, a piece 2000 may be provided, as schematically shown in FIG. 7b. The thicker part may have a thickness corresponding to d1 and the thinner part may correspond to the foil thickness d. This piece 2000 may be divided into 2 (substantially symmetric) parts, thereby providing a first foil 200(1) and a second foil 200(2). As will be clear to the person skilled in the art, piece 2000 may have such dimensions, as to provide n*2 (substantially symmetric) parts, thereby providing n first foil 200(1) and n second foil 200(2), wherein n is for instance in the range of 1-20. After an optional thickness reduction step and/or after an optional cutting step (thereby providing the desired shape of the foil(s) 200), the foil 200 may be ready for attachment in the holder 201 and then for application as filter device 149 in the lithographic apparatus 1. FIG. 7a schematically shows a stack/laminate of 5 layers, however, as indicated above, 1-5 layers may be used. As mentioned above, the process may for instance be performed in such a way that first sheets 300(1)-300(3) are arranged on the mold and then cured. Then, the product obtained might be at least partially reduced in thickness, as described above and as schematically indicated in FIG. 7a with the dashed line, and then sheets 300(4)-300(5) may be applied to the cured sheets 300(1)-300(3) and also subsequently be cured. Thereafter, if desired, the obtained product may also be reduced in thickness, as in an embodiment schematically depicted in FIG. 7b with the dashed lines (i.e. process c 1). Then, after obtaining the 5-layer laminate, this product may be further processed by carbonizing and graphitizing. Thereafter, if desired, the obtained product may also be reduced in thickness. The mold 400 is only a schematic embodiment of a possible mold. The term “substantially” herein refers in an embodiment to “completely” or “entirely”. In an embodiment, it may, for instance, refer to about 95-100%. The person skilled in the art understands the term “substantially”. Likewise, the term “at least partially” herein refers in an embodiment to “completely” or “entirely”. In an embodiment, it may, for instance, refer to about 95-100%. Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be appreciated that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, flat panel displays including liquid-crystal displays (LCDs), thin-film magnetic heads, etc. It should be appreciated that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers. Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured. While specific embodiments of the present invention have been described above, it should be appreciated that the present invention may be practiced otherwise than as described. For example, the present invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. This computer program may be used to control the removal of the deposition, control the pressures, etc. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the present invention as described without departing from the scope of the claims set out below. The present invention is not limited to application of the lithographic apparatus or use in the lithographic apparatus as described in the embodiments. Further, the drawings usually only include the elements and features that are necessary to understand the present invention. Beyond that, the drawings of the lithographic apparatus are schematic and not on scale. The present invention is not limited to those elements, shown in the schematic drawings (e.g. the number of mirrors drawn in the schematic drawings). Further, the present invention is not confined to the lithographic apparatus described in relation to FIGS. 1 and 2. It should be appreciated that embodiments described above may be combined.
	claims	1. A liquid level sensing apparatus which measures a liquid level in a liquid holding vessel based on temperature signals from a plurality of probes placed at fixed intervals in a vertical direction of the liquid holding vessel, wherein each of the probes includes a temperature sensor and a heater enclosed in the probe and the heater is placed in a neighborhood of a detecting point of the temperature sensor, the liquid level sensing apparatus comprising:a probe selection unit configured to select a probe whose heater is to be activated from among the plurality of probes;an input unit configured to receive an output of the temperature sensor of the probe selected by the probe selection unit, the output being received as a temperature signal directly in a form of an analog quantity;a signal processing unit configured to output a processing signal of the temperature signal in synchronization with activation of the heater;a calculation unit configured to arithmetically process the temperature signal and the processing signal and output a result;a gas/liquid discrimination unit configured to discriminate whether the detecting point exists in a gas phase or a liquid phase based on the output result of the arithmetic processing; anda display unit configured to indicate a discrimination result produced by the gas/liquid discrimination unit,wherein the calculation unit finds one of a difference and a quotient between the temperature signal and the processing signal and outputs a result, andthe signal processing unit is one of a hold circuit and a first order delay circuit, wherein the hold circuit holds the processing signal at a level of the temperature signal at a start time of the heat supply and the first order delay circuit outputs a first order delay response to the temperature signal. 2. The liquid level sensing apparatus according to claim 1, further comprising a liquid level determination unit configured to determine the liquid level based on the discrimination result produced by the gas/liquid discrimination unit. 3. A liquid level sensing method for measuring a liquid level in a liquid holding vessel based on temperature signals from a plurality of probes placed at fixed intervals in a vertical direction of the liquid holding vessel, wherein each of the probes includes a temperature sensor and a heater enclosed in the probe and the heater is placed in a neighborhood of a detecting point of the temperature sensor, the liquid level sensing method comprising:selecting a probe whose heater is to be activated from among the plurality of probes;receiving an output of the temperature sensor of the selected probe as a temperature signal directly in a form of an analog quantity;outputting a processing signal of the temperature signal in synchronization with activation of the heater;arithmetically processing the temperature signal and the processing signal and outputting a result;discriminating whether the detecting point exists in a gas phase or a liquid phase based on the output result of the arithmetic processing; anddisplaying a discrimination result based on at least one of the selected probes,wherein the arithmetically processing finds one of a difference and a quotient between the temperature signal and the processing signal and outputs a result, andthe outputting a processing signal utilizes one of a hold circuit and a first order delay circuit, wherein the hold circuit holds the processing signal at a level of the temperature signal at a start time of the heat supply and the first order delay circuit outputs a first order delay response to the temperature signal.
	description	The United States Government has rights to this invention pursuant to Contract No. W-31-109-ENG-38 between the U.S. Department of Energy and the University of Chicago, representing Argonne National Laboratory. 1. Field of the Invention This invention relates to a method for improving the imaging of a source of radiation and to a device for imaging a source of radiation, and more specifically, this invention relates to a method and device for producing a high spatial resolution three-dimensional image of a source of x-ray and gamma-ray radiation for medical and other applications by using a plurality of nearly perfect mechanically bent diffracting crystals which focus x-ray and gamma-ray radiation onto one or more detection devices. 2. Background of the Invention Cancer tumor cells have high rates of metabolism and multiply rapidly. Substances injected into the body tend to migrate to locations of such high growth and become incorporated in this new growth. If the injected substance is a short-lived radioactive isotope, the location of a tumor can be detected by locating the region of high radioactivity. Aside from pinpointing tumor location, an image of the tumor is also desirable to ascertain its shape, size, and juxtaposition with adjacent structures. For many medical applications it is imperative that a tumor be detected as early as possible, and early tumors are very small in size. Thus their detection and identification requires the ability to image very small sources. Also, medical research often uses small animals, with very small organs, and the availability of devices with very high spatial resolution is of the utmost importance. One method used to detect tumors is to first inject a body with radioactive compounds such as the Technetium isotope 99mTc, which is a 140.5 kiloelectron volt (keV) gamma emitter having a half-life of 5.9 hours. The gamma rays are detected by a large sodium iodide (NaI) scintillator crystal placed behind a collimator grid yielding at best an 8 millimeter (mm) resolution at the location of the source. The scintillator is viewed by a plurality of photomultiplier tubes and the location of a scintillation event is determined by a computer analysis of the relative intensity of the photomultiplier signals. The collimator/scintillator assembly is placed above and very close to the patient. Aside from this method yielding a low resolution of between approximately 8 mm and 1 centimeter (cm), the image produced is limited to the plane parallel to the surface of the scintillator. As such, the technique provides no depth information about the source. This deficiency can be remedied somewhat by adding another collimator/scintillator assembly below the patient, comparing the counting rate of the two scintillators, and thus estimating the position of the source along the line joining them. In the latest revision of this method the large NaI detector plus collimator is rotated around the patient, taking a plurality of images at different angles. This allows one to generate a three-dimensional image of the radiation emitting area. There are considerable additional costs associated with this method and the fact that this method has been introduced in spite of the additional costs underscores the importance of three-dimensional imaging. Another popular imaging technique is positron emission tomography (PET), used in diagnosis and medical research. In PET, a chemical compound containing a short-lived, positron-emitting radioisotope is injected into the body. The positrons (positively charged beta particles) are emitted as the isotope decays. These particles annihilate with electrons in surrounding tissue. Each annihilation simultaneously produces two 511 keV gamma rays traveling in opposite directions. After passing through collimators, these two gamma rays are detected simultaneously by scintillation detectors placed at 180 degrees to each other, and on opposite sides of the patient. The signals from the detectors' photomultiplier tubes are analyzed by a computer to facilitate the production of an image of the radiation-emitting region. Numerous drawbacks exist with scintillation detector tomography. For instance, the typical coarse resolution of no less than 8 mm often results in smaller structures being overlooked. This prevents early detection of cancerous tumors when they are least likely to have metastasized and when treatment is most likely to succeed. This is especially a disadvantage in the detection of breast cancer tumors wherein the tumors often become virulent before growing to a detectable size. Presently, mammography uses x-rays to detect tissue calcification. The assumption is made that this calcification is due to dead cancer cells and that there is a live cancer tumor in the immediate vicinity. Often however, there is no live tumor where calcification has been detected. In fact, the calcification may not have been due to a tumor at all. Unfortunately then, positive mammography results often lead to unnecessary surgical operations. Also, because poor spatial resolution often causes images of actual small tumors to be diffuse, variations in background radiation are often mistaken for actual tumors, leading to unnecessary surgical operations. This inadvertent incorporation of background radiation is an artifact of scintillation detector use wherein the detector must be large enough to cover a given area of the body. Aside from intercepting the radiation emanating from the source under observation, however, the large detectors also detect all ambient background radiation penetrating the scintillating region and this ambient radiation is analyzed as if it had been emitted by the source under observation. Another drawback to using imaging techniques incorporating scintillation detectors is that all of the various radiations emitted by the source are detected by the detectors. As such, a specific radiation having an energy indicative of a specific, injected isotope cannot be easily scrutinized. Lastly, because collimators allow for the detection of only the radiation that is emitted in a very narrow direction in space, the patient has to be injected with a relatively large amount of radioactive material. Recently, efforts have been made to improve scintillation detector tomography. Some PET instruments now achieve a resolution as small as 4 mm. Such improvements entail considerable expenditures and have the additional drawback that the improvement in resolution has come at the cost of a decrease in counting rate. This entails in turn either a longer examination time per patient or the injection of a stronger dose of radiation. Furthermore, the prospects for further improvements in resolution are limited by the fact that such improvements require collimators with ever smaller apertures, and therefore greater mass, together with lower count rates. This increase in collimator mass will increase the number of forward Compton-scattered photons in the collimators and these forward scattered photons are often indistinguishable from those emanating directly from the source. Significant improvements in spatial resolution and in detection efficiency as well as a three dimensional location of the source using a crystal diffraction method for focusing the radiation emanating from the source was disclosed in U.S. Pat. No. 5,869,841 (1999) (granted to the same inventor as the present invention and assigned to the same assignee) and incorporated herein by reference. Because of the focusing of the radiation emitted by the source, one requires the injection of much smaller amounts of radioactive substances at a site on the patient's body in order to locate features of interest. Experiments at the inventor's laboratory have demonstrated the effectiveness of this method and have achieved a spatial resolution of 7 mm. Modification of this crystal diffraction lens imaging system lead to improvements in the resolution, achieving a spatial resolution of 3.2 mm full width half maximum (FWHM), but with a reduction in sensitivity (counting rate). While this is adequate under many circumstances, and better than most present systems for imaging radioactive sources better spatial resolution with better sensitivity would provide significant advantages. U.S. Pat. No. 5,869,841 taught the use of diffracting crystals whose acceptance angle was increased by principally by means of a mosaic structure in the crystal possibly supplemented by bending the crystal. Thus a need exists in the art for an improved method and device for imaging x-ray and gamma-ray sources with sufficient spatial resolution, so as to obtain better sensitivity, to accurately observe and image structures smaller than 7 mm in size, even down to 0.3 mm in size or less. The invented method and the resulting device must have sufficient energy resolution to allow the imaging of radiation of a selected energy to the exclusion of others. The method and device also must limit the radiation to which the patient is exposed by incorporating a redirecting or “focusing” mechanism to detect radiation emanating from a tumor while disregarding ambient levels of radiation. It is an object of the present invention to provide a method and a device for high spatial resolution imaging sources of gamma-ray and x-ray radiation that overcome many of the disadvantages of the prior art. Another object of the present invention is to provide a small bulk device using crystal diffraction imaging of sources of gamma and x-ray radiation that features high detection efficiency. A feature of the present invention is the use of a plurality of non-coplanar assemblies each comprising one or more crystal diffraction lenses comprising nearly perfect mechanically bent crystals. An advantage of the invention is a much higher efficiency for the diffraction lenses. Another advantage of this invention is that the diffraction lenses can be made much smaller in diameter and with much shorter focal lengths. Still another object of the present invention is to provide a method for producing a high spatial resolution image of a radiation source located in a patient. A feature of the invention is the use of high purity and high quality mechanically bent diffracting crystals. An advantage of the invention is the ability to image sources as small as 0.3 mm into images of comparable size. A further object of the present invention is to provide a method for producing crystal diffraction lenses with short focal lengths. A feature of the present invention is that the spatial resolution of the system is not limited by the angle subtended by the radial thickness of a crystal element. An advantage of the present invention is that one can use shorter source-lens distances than heretofore without loss of sensitivity and resolution and thus obtain efficient shorter focal length system. Yet another object of the present invention is to provide a radiation imaging method that produces a magnified image of a radiation source located inside a patient. A feature of the invention is the ability to manufacture small size lenses with a short positive focal length. An advantage of this invention is the ability to produce an image with a magnification of at least a factor of four. In brief the present invention provides a method and a device for high spatial resolution imaging of sources of x-ray and gamma radiation comprising supplying one or more sources of radiation; focusing said radiation onto one or more detectors by means of mechanically bent nearly perfect diffracting crystals; analyzing said focused radiation to collect data as to the type and location of the sources of the radiation; and producing an image using the data. The invented device features lenses of short focal length that can produce images with a magnification by at least a factor factor of four. Also, the present invention provides a method for manufacturing mechanically bent crystals for use in high spatial resolution diffraction lenses and other applications. The method comprises: a) selecting a crystalline material and cutting from large single crystals single crystal slabs of desired thickness and with Miller indices orientation determined according to the radiation to be observed; b) forming sets of two or more juxtaposed plates, at least one of which plates is one of said crystal slabs, by contacting said plates with an uniform layer of glue that hardens only when it is activated; c) bending to a predetermined curvature one or more of said sets by means of a bending apparatus that allows in-situ measurements of the curvature of the plates; d) activating said glue while the set of plates is in the bending apparatus; and e) releasing said set from the bending apparatus. The present invention improves the imaging of sources of x-ray and gamma-ray radiation. The present invention provides a method and a device for high spatial resolution imaging of a source of radiation comprising using high purity and high quality mechanically bent diffracting crystals. Also, the present invention provides a method for manufacturing mechanically bent crystals for use in high spatial resolution diffraction lenses and other applications. The invented method can yield a detected image as small as 0.3 mm (Full Width at Half Maximum (FWHM) for a point source). Also, this invention provides the ability to produce an image with a magnification of at least a factor of four. The invented method results in a device, designated generally as numeral 10 in FIG. 1, that incorporates a plurality of lens/detector assemblies 17 to first focus and then detect radiation emanating from a radioactive source 15, such as a tumor 13 in a patient 12 that has incorporated some radioactivity. Each lens/detector assembly 17 comprises a plurality of high efficiency and high resolution crystal diffraction lenses 18 that focus onto detector arrays 19 only the radiation of a desired energy and origin. As disclosed infra, and with reference to FIG. 9, each lens 18 comprises a plurality of concentric rings 45, which in turn are comprised of very accurately mounted and bent perfect or nearly perfect diffracting crystals. These crystals are oriented with their principal radius of curvature in the same plane as the radiation, so that only radiation having a predetermined energy is focused onto a detector array 19. The detector arrays 19 of the device are shielded from unwanted radiation. The device 10 is designed to accommodate the detection of radiation from a myriad of sources. For clarity, the radiation source 15 in the exemplary embodiment shown in FIG. 1 is a tumor or other tissue that has absorbed a radio-isotope in vivo, whereby the tumor emits radiation of a predetermined wave length λ. However, other radiation sources are also appropriate, including radioisotope-impregnated fissures in a mineral or in a manufactured object, an x-ray or gamma-ray beam scattering from a target, x-rays or gamma rays produced by particle-beam bombardment of a target or emanating from either a terrestrial or astrophysical source. After emanating from the source 15, the radiation is focused by the diffraction lens 18. The lens 18 directs the radiation to a detector array 19. The output of the detector array is analyzed by a computer. The exemplary device 10 is a plane circular array of lens/detector assemblies 17 with the source 15 situated at the center 13 of the array, the detector arrays 19 positioned along the periphery of the array, and the focusing means 18 positioned approximately medially between the source 15 and the detector assemblies 19. As noted supra, the detector arrays 19 define the periphery of the plane circular array and therefore are distally placed relative to the center 13 of the circular array and the focusing lens 18. A three-dimensional scan of the source 15 can be accomplished with two lens/detector assemblies 17. FIG. 2 is an exemplary embodiment of a three-dimensional imaging system comprising two intersecting and concentric orthogonal arrays 10 of the lens/detector assemblies. The radiation source 15, resting on a movable platform 16, is located at the intersection of the two arrays at their common center 13 at the time of imaging. Prior to high resolution imaging operations, conventional scintillation counters 20 are provided for quick scan features of the radiating area to approximately locate the source's position. For the sake of additional clarity, FIG. 1 is an elevational view of FIG. 2 taken along lines 1-1. If the present invention is used as a medical imaging system, then the source 15 is a patient in whom a radioisotope has been injected. A reference source 14 of the same isotope is positioned at a suitable point on the patient's body and the location of the patient's tumor is measured with respect to the reference source 14. Imaging of an extended source is best accomplished by moving the movable platform 16 across the center 13 of the intersecting arrays 10. Alternatively, one could move the lens system relative to the source if means have been provided therefore. The positions of the lenses, detectors, and a platform 16 containing the source 15 and the reference source 14 are monitored by conventional electronic sensors (not shown) and recorded and analyzed by a computer (not shown). Lens/Detector Assembly Detail Each lens/detector assembly 17 incorporates a plurality of movable focusing lenses 18 and detector arrays 19. The positions of the lenses, detectors and a platform 16 containing the source 15 are monitored by conventional electronic sensors (not shown) and recorded and analyzed by computer (not shown). FIG. 3a is a cross sectional view of FIG. 1 taken along lines 3a-3a and presents a detailed depiction of the lens/detector assembly 17. Each lens/detector assembly 17 incorporates a plurality of movable diffraction lenses 18, detectors 19, and shielding around the detectors 19. Shielding is also placed along the longitudinal axis 23 of the assembly and longitudinally along the outside of the assembly. The axis and outside radiation shields 29, 30 respectively, are cone-shaped and mounted between the lens 18 and the source 15 and the lens and the detector array 19. Generally, the axis and outside shields can be any convenient configuration such as cone- or cylindrically-shaped. Lead, iron, and brass are suitable shielding materials. In FIG. 3a S and D denote the lens-source, and the lens-detector distances respectively. Lenses and detectors are mounted on tracks 22 equipped with electronic sensors. The tracks allow for independent axial movement of either or both the lens 18 and detector 19. For unit magnification, the detector array is moved in the same direction but twice as far as the lens. The present invention has the advantage of allowing the production of short focal length, focusing lens systems where the distance from the source to the lens is smaller than the distance from the lens to the detector, which magnifies the size of the image. See FIG. 3b. This in turn allows arrangements where the image is magnified. If F=lens focal length, then 1/F=1/S+1/D and the magnification M=D/S. FIG. 3b illustrates source/lens/detector arrangements with M=1, 2, and 4 respectively, with a source dimension being 27 and the corresponding image dimension 28. Note that for M=1 the total source/detector distance is 4F and for M=4 it is 6.25F, thus the importance of having a short F. A presently available copper lens as disclosed in U.S. Pat. No. 5,869,841 (1999) has a focal length of 50 cm and a distance from source to detector of 200 cm. A magnification of a factor of 2 would increase this source to detector distance to 225 cm and a magnification of a factor of 4, would increase the source to detector distance to 312.5 cm, which is very difficult to handle. A reduction in the focal length of the lens by a factor of 4 would reduce this source to detector distance to 56.3 cm. Detector Detail Generally, the detector array 19 comprises solid state detectors made of silicon or germanium or a composite material such as CdTe or CdZnTe. The detector array may include commercially available pixel detectors. The detectors are mounted a in movable housing 25 (See FIG. 3a). Scintillation detectors may also be used. A 3 by 3 detector array enables a determination as to whether the source being imaged is on the axis of the lens or off the axis of the lens and if off-axis, to determine in which direction it is off-axis. One may also use a 2 by 2 array, where the source is on axis when the counting rate in all four segments is equal. In the 3 by 3 array, the source is on axis when most of the radiation interacts with the central detector and the other detectors have equally weak count rates. The 3 by 3 array can also be used to obtain the lowest background possible. If the center detector is large enough to intercept all of the focused radiation when the source is on axis, then one can use the off-center detectors to estimate the background in the center detector. Furthermore, an energy sum coincidence can be made between the center detector and the outside detectors that can increase the efficiency for detecting the full energy of the detected photon ray, thus increasing the full energy count rate without increasing the background count rate. Thus in this latter arrangement one has the efficiency of a large detector for detecting the full energy of the gamma ray, while retaining the low background counting rate of only the central detector. An array comprising a large number of detector elements, or even a pixel detector, can also be used. In general terms, a point source is imaged into a spot equal in size to the cross section of the diffracting crystals in a direction orthogonal to the photon beam in prior art Bragg lens designs or lens designs using mosaic crystals but in the invented lens design using curved crystals, the detector image can be smaller than this dimension. Thus the size of an element in a detector array should be equal to or less than the desired spatial resolution. The present invention provides a spatial resolution of 0.3 mm. With a pixel detector array, the present invention allows nearly a one to one correspondence between source and image points, see infra. The size of the source that can be imaged directly on the detector by a single lens without moving the lens is determined by the amount of curvature in the crystal diffraction elements that make up the lens if the radial (orthogonal to the device axis) dimension of the crystal element is small. The larger the total curvature in the crystal element, the larger the area imaged. If the radial size of the crystal element is comparable to the source, then its radial size will also contribute to the imaged area. Once the response function of the lens is measured with a point source, a computer can be used to translate the image measured on a pixel detector to generate the an image of the source. The Crystal Diffraction Process In order to focus x-ray and gamma radiation, the present invention utilizes the phenomenon of crystal diffraction which is illustrated in FIGS. 4a and 4b. FIG. 4a depicts the phenomenon known as Laue diffraction, a volume effect that is most important with higher energy photons. The incident radiation beam 31 enters through one surface of a diffracting crystal. After interacting with a specific array of parallel atomic layers 34, the radiation beam is split into two beams, a transmitted beam 32, and a diffracted beam 33, with both beams exiting through a surface opposite to the one through which the radiation entered. Both the transmitted and the diffracted beams are produced by a coherent superposition of the scattering amplitudes of the radiation scattered by atoms in the parallel crystal layers. The angle 35 between the radiation beam and the crystal layers is designated as p. Typically between 104 and 107 atomic layers are suitable to approach 50% diffraction. The actual number of layers depends on the wavelength of the gamma ray. In practice, the maximum diffracted beam is less than 50% of the incident beam because some absorption of the beam occurs as it passes through the crystal. FIG. 4b depicts the phenomenon known as Bragg diffraction acting upon an incident beam 131. After multiple scatterings with the atoms comprising a specific array of parallel atomic layers 134 at the surface of the crystal, the net outcome for low energy photons is the emergence of a “diffracted” beam 133, which can contain nearly all of the incident photons. Some absorption of the radiation occurs during this process which continues until either the radiation is diffracted out of the crystal or is absorbed in the crystal. For photon energies similar to those used in medical imaging, the photons penetrate deep into the crystal resulting in an appreciable loss due to absorption. The angle 135 between the radiation beam and the crystal layers is designated as p. The diffracted beam exits through the same surface as the one through which the radiation entered. Again, the beam is produced by a coherent superposition of scatterings by atoms in the parallel crystal layers. Bragg diffraction is a surface phenomenon that is most effective for energies well below 30 keV and the fraction diffracted then can reach 90%. For both Laue and Bragg diffraction, diffraction occurs only when the Bragg condition is obeyed, (equation 1):λ=2dhkl sin p Eq. 1where λ is the radiation wavelength, dhkl the spacing between the atomic layers indicated by the Miller indices h,k,l, and p the angle between the direction of the radiation beam and the atomic layers (one can convert energy E in keV to wavelength λ in Angstrom units by using the relation λ=12.397/E). With perfectly parallel atomic layers, only rays within a few arc seconds of p will be diffracted (i.e., the “acceptance angle” is only a few seconds of arc), so that one can obtain a large diffraction efficiency only if the rays are nearly parallel, i.e. only if the source is very far away. Heretofore, several methods have been used to increase the acceptance angle. One method has been to utilize imperfections that are either naturally present or else artificially introduced within the crystal so that all the crystal planes are no longer parallel to each other. Methods previously employed for introducing imperfections include chemical doping, differential heating, stressing, bending beyond the elastic limit when heated and mechanically inducing dislocations. These imperfections in the crystal give rise to a three dimensional mosaic structure. The angle between the rays with the lowest angle p and those with the largest p is the acceptance angle (also known as the “rocking angle” which is the full width at one half maximum of this distribution). Ordinarily, rocking angles of between 100 and 800 arc seconds or larger can be obtained by the above methods. 800 arc sec is adequate for a first scan where a spatial resolution of 4 mm with a source to lens distance of 100 cm. A rocking angle of between 50 and 150 seconds of arc is required when a 1 mm spatial resolution is required. The use of crystals with a smaller rocking angle is not indicated unless other components of the system are adjusted so as to yield a better than 1 mm resolution (e.g. reduction of the sizes of the detectors and the source and detector apertures). FIG. 5 shows that for Bragg diffraction the acceptance angle for monochromatic radiation can be increased if the crystal is curved to form an arc coplanar with the radiation beam. Rays coming at different angles 139 will still find sets of planes 140 where the spacing between planes is such that the Bragg condition is obeyed. (The angle 41 between the rays 135 with the lowest angle p and the rays 139 with the largest p is the acceptance angle.) Thus, in the first place, the curved concave shape of the crystals can produce a significant focusing effect, i.e. an increase in the surface area that reflects radiation onto the detector, as is well known from geometrical optics. Furthermore, the stresses resulting in the bending of the crystal in the focusing geometry produces a lengthening Δl of the length l the convex surface of the bent crystal and a shortening or compression of the concave surface. This results in a continuous gradient in the spacing t of the planes parallel to the curved surface. The spacing between planes proximal to the concave face 143 is increased while the spacing between planes proximal to the convex face 144 is decreased. This results in an increase in the radial depth of the crystal from which radiation from the source is diffracted onto the detector. To a first approximation, the increase in the diffracting depth, typically a factor of three, is given by the absolute value of the inverse of what is known as the Poisson ratio P for the set of diffracting planes in question. (P is given by Δt/t)/Δl/l). The two effects (focusing and depth increase) combine to produce an enlarged volume of diffracting scattering centers, and, inasmuch as diffraction is a coherent phenomenon with the diffracted intensity proportional to the square of the number of scatterers, the resulting diffracted intensity with a bent crystal is much larger than that obtainable with an unbent crystal (see FIG. 4b). The fact that the spacing between planes proximal to the concave face 143 is increased while the spacing between planes proximal to the convex face 144 is decreased entails that the Bragg angle is larger for planes near the convex face than for planes near the concave face. While the above discussion is limited to Bragg diffraction, the same considerations apply to the Laue diffraction process. The Dual Focusing Properties of Bent Crystals. A bent diffraction crystal focuses gamma rays in two different ways (the following discussion focuses on Laue diffraction). The first method focuses the gamma ray by matching the curvature of the crystal to the opening angle of the incident gamma rays so that the Bragg angle between the incident radiation and the crystalline planes remains constant. This is illustrated in FIG. 5. The gamma ray from a point on the source passes through the crystal until it reaches a region where the Bragg condition is met, at which point it is diffracted, Because the crystal is curved the gamma ray will not encounter a second set of planes in the crystal where the Bragg condition is met so it will emerge from the crystal in the diffracted beam. This effect allows the diffraction efficiency to approach 100 percent. The only loss will be to atomic absorption in the crystal. Each point on the source will use an different part of the crystal to be diffracted. Thus the image of a point source is a narrow line on the detector. This line can be vary narrow approaching the radial width of the region that is generating the diffraction (typically 10 to 100 microns). The corresponding bent crystal on the opposite side of the lens will produce a similar line image. The ideal radius of curvature, r(Bragg), for the bent crystals for this kind of focusing is given by r(Bragg)=S/(sin p) where S is the distance from the source to the lens and sin p is the sine of the Bragg angle. The second kind of focusing that occurs in curved diffraction crystals results from the distortion of the crystalline planes due to the bending. The convex side of the crystal is stretched, while the concave side is compressed. The stretching causes the spacing between crystalline planes to decrease, while the compression causes the spacing to increase. This produces a uniform gradient in the spacing as a function of radial position. This gradient can compensate for the change in angle of the incident gamma rays in the radial direction and generate Laue focusing. This focusing is illustrated in FIG. 6. Again, the gamma ray passes through the crystal until it encounters crystalline planes with the right Bragg angle and is then diffracted. Because the crystalline planes are curved, the gamma ray will not encounter any further planes at the right Bragg angle so it will leave the crystal in the diffracted beam. The variation in the Bragg angle due to the variation in the spacing of the planes also results in the focusing at the detector of a broader cone of photons emanating from the source. As shown in FIG. 6 all the photons emanating from the source S between the angle 244, equal to the Bragg angle near the convex face 254, and the angle 245, equal to the Bragg angle near the concave face 255, are focused at one point D on the detector. One can achieve diffraction efficiencies approaching 100 percent in this arrangement. Again, the only loss is from atomic absorption. Again, a point source generates a narrow line image on the detector. The ideal radius of curvature, r(Laue) is given by r(Laue)=(S/sin p)×(Poisson's Ratio)=r(Bragg)×Poisson's Ratio. Poisson's ratio for crystals fall in the range of 0.2 to 0.5, thus the ideal radius for Laue focusing is smaller than for Bragg focusing, resulting in a greater curvature for the Laue focusing. The width of the source that the Bragg focusing can cover is limited by the radial size of the crystal. In Laue focusing the width of the source that can be focused is controlled by the total curvature of the crystal and can be much larger than for Bragg focusing. In practice for any arbitrary curvature the gamma ray passes through the crystal until it encounters a region where the Bragg angle is correct for diffraction and then is diffracted with a focusing properties that are a combination of the two types of focusing depending on the radius of curvature. As shown in FIG. 7, the variation in the Bragg angle due to the variation in the spacing of the planes also results in the focusing at the detector of a broad region of the source. Note that in FIG. 7 three source points 151, 152, and 153 are imaged onto separate detector points 191, 192, 193 respectively. Lens Design Detail The first step in determining the material and orientation of the diffracting crystals is to select the energy of the radiation that will be observed and the focal length F of the focusing means 18 one wants to achieve. In the simplest embodiment of the invention, a single lens is utilized, in a lens/detector array 17, but a lens/detector assembly 17 having a plurality of lenses is also suitable. Where lenses of focal length F1, F2, F3, etc. . . . are placed in close proximity or contact with each-other, the focal length of the combination is given by equations 2 through 6. Equation 2 gives the focal length for one lens, where p is the Bragg angle used in the lens and R is the radius of the crystal ring 45 (FIG. 7).F=R/(tan 2p) Eq. 2 Equation 3 gives the focal length for two lenses, where p1 and p2 are the Bragg angles used in the first and second lenses and R1 and R2 are the radii used in the first and second lens, respectively.F12=(R1−R2)/tan 2p1+R2/tan(2p1+2p2) Eq. 3 Equation 4 gives the focal length for three lenses, where p1, p2 and p3 are the Bragg angles used in the first and second and third lenses and R1, R2 and R3 are the radii used in the first, second and third lenses, respectively.F123=(R1−R2)/tan 2p1+(R2−R3)/tan 2(p1+p2)+R3/tan 2(p1+p2+p3) Eq. 4 If the lenses are very close together, then the R's become approximately equal and the approximate formula for the focal length is given by equation 5.F12 . . . n=R(Ave)/tan 2(p1+p2+p3 . . . pn) Eq. 5 If all of the Bragg angles are quite small, the focal length can be approximated by equation 6:1/(F12 . . . n)=1/F1+1/F2+ . . . +1/Fn Eq. 6 The set of atomic layers to be used for each ring 45 is determined by the condition that all the rings must have the same focal length F. For rays near the lens axis (small p) the relation between lens-source distance S, lens-detector distance D, and focal length F is given approximately by equation 7.(1/F)=(1/S)+(1/D) Eq. 7In practice S and D as shown in FIG. 3 are both chosen to be 2F, then the Bragg angle p is arctan[R/(2F)] where R is the radius of the ring. The Bragg condition yields the relation between the ring radius, focal length, radiation wavelength λ and atomic layer spacing d, given by equation (8).R/F=tan [2 arcsin(λ/2dhkl)] Eq. 8 For F>>R, i.e., for small angles, Equation 8 yieldsdhkl=λF/R Eq. 9 In practice, a gamma ray with a specific energy (and therefore wavelength λ) is selected. Then, the crystalline plane spacings of an available crystal are tabulated. This information is combined with the desired focal length F to arrive at the respective radii R for the crystal rings, pursuant to equation 10:R=dhkl/λF Eq. 10 Finally, the size of the crystals is chosen. (Alternately, λ is determined from the desired gamma ray energy, then F is chosen, and the available values of dhkl are identified, so that the values of R for the rings are suitable). Bent Crystal Manufacture Detail Each crystal diffraction lens 18 utilizes a plurality of nearly perfect diffracting crystals, where nearly perfect denotes high-quality grade commercially available crystals. Possible crystalline materials include, but are not limited to, silicon, quartz, tin, molybdenum, germanium, silver, gold, and copper. (Germanium, Silicon, Copper and Quartz have been found by the applicant to be suitable for the fabrication of x-ray and gamma-ray lenses for energies of around 150 keV.) The present invention provides a six-step method for repeatable, accurate, and economical production of thousands of bent crystal elements of the desired thickness and curvature. The optimum radius of curvature for the Bragg focusing is given by: radius(Bragg) r(B)=distance from the source to the crystal lens (S) divided by the sine of the Bragg angle p, or r(B)=S/sin p. The optimum radius for the Laue focusing is given by radius(Laue) r(L)=radius(Bragg)×Poisson's Ratio P for the crystalline planes being used. Since Poisson's Ratio in silicon and many other crystals tends to be in the range of 0.2 to 0.5, the desired radius for Laue focusing tends to be 2 to 5 times smaller than the desired radius for Bragg focusing. Thus the actual radius used in the crystal element will be a compromise between these two radii, depending on the desired characteristics of the lens. (Poisson's Ration for the [111] planes in silicon is 0.358, thus the ideal radius for Laue focusing is 2.8 times smaller that the ideal radius for Bragg focusing.) It is the presence of the Laue focusing that makes it relatively easy to obtain spatial resolution that is smaller than the radial dimensions of the crystal elements. Because in the present invention the spatial resolution is not limited by the angle subtended by the radial thickness of the crystal element, one can use shorter source-lens distances than heretofore without loss of sensitivity and resolution. With a shorter source-lens distances, one obtains a shorter focal length systems. The dimensions of the individual elements will vary depending of the desired characteristics of the lens. Typical dimensions could be 0.8 mm radial thickness, 20 mm length in the direction of the photon beam, and 2.5 mm wide. (See FIG. 6) Depending on the desired characteristics of the lens the radial thickness could be anywhere from 0.1 mm to 10 mm. The actual thickness being governed by the radius of the bend desired in the crystal. The dimensions of the length will also vary from a few mm to 10 or 20 cm or larger depending on the size of the lens. As the length of the crystal elements is increased the solid angle of the lens that sees the incident gamma rays is increased. This increases the efficiency of the lens. With a careful design the solid angle can match 80 percent of the area of the lens. The width of the crystals will vary from as small as 0.1 mm to a few cm, depending on the size of the lens and the desired resolution of the lens. First, single crystal silicon (or other appropriate crystal material) plates of the desired thickness (from 0.1 mm to 10 mm depending on the crystal's brittleness, desired resolution, and bending radius) and of the appropriate Miller indices orientation depending on the wavelength of the radiation are cut from perfect or nearly perfect single crystal boules or cylinders with an axis orientation perpendicular to the desired planes for short crystals and an axis parallel to the crystalline planes for long crystals. Then these plates are lapped and polished in the customary manner. Secondly, a set of two or more plates (or a plurality of sets side by side) is selected and the plates are contacted with glue between each layer and then either pressed or passed through a rolling apparatus to ensure a uniform glue thickness. (The glue must be such that it hardens only when activated by heat or other means.) Then the set is placed in a bending apparatus. This apparatus may be a four-point bender or one where the plates are pressed against a curved surface, so that the set is bent to the appropriate radius. The most accurate method is pressing against a curved surface. The curved surface often has a large radius, 5 to 100 m. This radius must be very uniform for the crystals to perform properly. These very precisely curved surfaces are made by first making the surface of an appropriately size block very flat and the applying a variable thickness coating to the surface that has the desired shape and thickness. Often the rise in the center of this curved surface will only be a few microns, so the curve needs to be accurate to a few hundredths of a micron. This variable thickness coating can be applied through selective evaporation techniques. The bending apparatus allows in-situ measurements so that one may check the curvature of the plates by optical or mechanical means. Frequently, one cannot bend a crystal into a pure cylindrical arc. This latter bending produces a deformation of the crystal in a direction orthogonal to the originally desired arc, so that one obtains a surface with two finite and approximately orthogonal planes of curvature. These planes of curvature and the associated radii can be controlled if one forms sets of dissimilar plates, choosing plates with different but appropriate orientations to form a set with bent crystal with tailored bending radii. The ideal shape of the bent crystals for magnifying lenses is ellipsoidal rather than cylindrical. Bent crystals with an ellipsoid like shape can be made with the same ease as ones with a cylindrical shape. Also, one can fashion hyperbolic, parabolic, and other shapes. One or more of the plates may be a non-crystalline material that provides rigidity to the set once it is bent. Third, while the set of plates is in the bending apparatus, the glue is activated by such means as heat or ultraviolet light. FIG. 9 shows two bent crystal elements cemented together into a crystal element 42 with the face 59 of the crystal set being the face through which the radiation enters the crystals. Fourth, the set is released from the bending apparatus and the radius is re-measured. Any deviation from the target radius at this step or future steps (due, for example, to the so-called spring back) must be detected and compensated for. Fifth, a number of such sets are placed on top of each other, with or without a separating layer such as wax, and then this assembly placed into a holder. Finally, sixth, the assembly is then cut, preferably in electron discharge machine (EDM) first in one and then in the orthogonal direction to produce a large number of smaller rectangular composite bent crystals of the desired shape, size, and orientation. This process (with variations obvious to persons skilled the art) can produce thousands of sets economically, reliably, and consistently. Such variables as crystal plate thickness, an additional backing plate, or the application of unequal moments can produce a variety of crystal profiles, including elliptical or parabolic profiles. This process can be employed for the production of bent diffracting crystals for a variety of non-lens connected applications. The same method can be used for any crystal diffraction apparatus where the wavelength of the photon, neutron, electron or other particles is comparable to the spacing of the crystal layers. Diffraction Lens Construction. Each crystal element needs to be placed at the right radial distance and with the right orientation (Bragg angle) in the lens frame. Thus the lens frame needs to allow one to adjust the Bragg angle while holding the radial distance constant. This is best done by supporting the crystal elements at two points in the photon diffraction plane. There many ways to generate a lens frame that supplies this kind of support. One example is the use of two identical thin plates with appropriate slots cut in them and appropriately spaced to support the different rings of crystals. FIG. 9 is a view of FIG. 3a along lines 9-9 giving a frontal view of a typical embodiment of a lens 18, while FIG. 10 shows a cross section of the lens along line 10-10 of FIG. 9 for an exemplary embodiment of a lens 18. Each lens 18 comprises two parallel support plates 43a, 43b (See FIG. 10) but under certain circumstances, as shown in FIG. 11, a single plate with the appropriate raised ridges 47 may be used for each crystal ring. The plates 43a, 43b comprise a low atomic number metal such as aluminum, beryllium, or magnesium but other materials are suitable. This is done so that the gamma rays can pass through these plates without being attenuated to any significant degree. Regions of the surface of the plates 43 define a series of apertures arranged as concentric rings 45. Each ring contains a plurality of diffracting crystal arcs 42 of the same material, radius, and crystal plane orientation. The material and orientation are determined according to the procedure described supra. For both Laue and Bragg diffraction, the diffracting crystals are mounted onto the plate in such a manner that once mounted, all the crystals in a given ring will be so oriented as to use the same set atomic layers to satisfy the Bragg condition. In a typical embodiment, the crystals in a given ring are all of the same material, orientation, and curvature but crystals in different rings may be of different materials, orientation, and curvature. Mounting of the crystals 42 onto the plates 43a, 43b can occur in a variety of ways. One method is to attach the two thin plates together with appropriate spacers and mount the frame in a rotating frame. A radioactive source of the energy to be focused is placed so that its radiation will be diffracted the crystals in one of the rings. A crystal is then placed in the lens frame and its diffracted beam is measured by an appropriately positioned detector. Slight adjustments are made to the position of the bent crystal in the lens frame by sliding in and out of the frame parallel to the axis of the lens until the best focus is obtained for that crystal element. When this is achieved the crystal element is glued in place. The lens frame is then rotated so that a new crystal element can be placed in the lens frame and tested in a similar manner. This procedure is repeated in this ring and in subsequent rings until the lens is completely filled with crystals. Only one crystal element is exposed to the radiation at a time through an appropriate shield. When this shield is removed it is possible to test the performance of the whole lens at any time during the assembly. Different rings may be used to focus sources of different energies. For very small diameter lenses, the lens frame may be replaced by thin spacers between the crystal element in adjacent rings. Scanning a Source and Formation of an Image The lens detector assembly achieves its best performance for sources located on or very near the axis of the assembly. When the source 15 is not situated on the axis of the assembly, the movable platform 16 is advanced until the source is positioned on the axis of the assembly. A straightforward method of source detection and imaging is scanning the relevant area. This is almost always necessary as a first step unless a possible source location has been determined by a previous scan or through another type of imaging system. In order to scan across the source 15, one may change the position of the body 12 using the means provided for moving the table 16. Alternatively, one may change the orientation of the lens/detector assemblies and adjust the source/lens and lens/detector distances as indicated by Equation 3 by means of the tracks 22 on which lenses and detectors are mounted. In yet another alternative, one can move the whole lens system relative to the source. Also, equation 5 shows the focal length's dependence on the wavelength of the radiation. The lens 18 and detector 19 are mounted on tracks 22 allowing the use of a given lens to detect radiation of a different wavelength by adjusting the lens-source and lens-detector distances as dictated by equation 3. Electronic sensors are mounted on tracks 22 and their signals are recorded and analyzed by the computer. For gamma rays with energies in the 150 keV range the focal length is proportional to the energy. Thus to focus a different energy one only needs to change the distance from the source to the detector and similarly, the distance from the lens to the detector. As long as the sine of the Bragg angle is close to the value of the tangent of the Bragg angle, this change in distances will result in a near perfect focus of the new energy radiation. Instead of relying on tracks 22, imaging of radiation of different wavelengths can also be accomplished by using different lenses, and keeping the elements of the assembly stationary. For example, a source having a first energy can be scanned in toto by moving the table 16 with respect to the center of the lens/detector arrays (see FIG. 1). If the device is to be used for gamma rays of a second energy, one can construct a plurality of different lenses using crystals with atomic spacings so chosen that one obtains the same focal length as the lenses used to focus the first source. Signals from the detector arrays 19 are analyzed by a computer in conjunction with the data from the detectors 20 and those from the sensors on the movable platform 16 and the lens and detector tracks 22. Device Apertures Restricting the area of the apertures in front of the detector array and in front of the source improves significantly the spatial resolution of the device when the latter is used in a scan mode. As shown in FIGS. 12a and 12b, a decrease in the detector array aperture 140 reduces the field of view, i.e. the area 196 of the source 15 that can be viewed at any one time. Restriction of the detector aperture also reduces the background seen by the detector array. Restriction of the source aperture 142 has a similar advantage in reducing the apparent size of the area viewed by the lens and in reducing the background radiation reaching the detector array. FIG. 13 illustrates the combined effect of narrow apertures in front of the detector array and in front of the source. This approach can reduce the background counting rate significantly. It is advisable that the size and position of the apertures be adjustable so that one may adapt the device to the specific requirements for a given observation. Use of a Multi-component Detector Array FIG. 14 depicts an alternate embodiment of the invention where using a many-component detector array presents the same spatial resolution advantages as the restriction of the detector aperture. In this case each pixel in the detector acts like a separate small aperture, allows one to take data in each aperture simultaneously. This approach avoids the loss of count rate that occurred with the use of a single aperture in front of the detector as mentioned above. FIG. 17 shows how points 151, 152, and 153 are imaged onto separate detectors 191, 192, 193. Such an array has obvious advantages in that it reduces the time necessary to acquire the necessary data. For instance, a 1 cm square array of 1 mm by 1 mm detectors produces a high spatial resolution (1 mm) life size image of a 1 cm object such as a tumor without having to scan the object. One Shot Imaging of an Extended Source. FIG. 7 shows the that a bent crystal element focuses gamma rays from separate source points to separate points on the detector. This effect is enhanced with a multi-plate element. (See FIG. 8) This generates a real and inverted image of the source on the detector and this with very high resolution. All the crystal elements on the lens may be set so that one has the x-ray and gamma-ray equivalent of an optical positive focal length (convex) lens generating a real and inverted image of a source on a detector If one is imaging the 140.5 keV gamma ray from Tc99m, then the maximum attenuation in a silicon crystal that is 2 cm long will be 22 percent. Theoretically any size source can be imaged at the detector to within a few percent of its actual size with bent crystals. This is quite different than with unbent crystals where one must use mosaic crystals to achieve reasonable sensitivities. With unbent crystals the resolution is limited to 1.6 times the radial thickness of the crystal element. The factor of 1.6 comes from the structure of the circular lens structure. With the bent crystal lens using perfect Laue focusing the resolution could be as small as 10 microns. The fact that the invented lens resembles a simple optical convex lens and has the capability of forming a magnified image of the source. (see FIG. 3b) confers special advantages. The magnified image makes a pixel detector more useful, in that the pixels will not have to be as small for the same resolution. A 1 mm×1 mm pixel can contain the energy from a 140.5 keV gamma ray from Tc99m, but a 0.1 mm×0.1 mm pixel is too small to contain the x-ray that is produced in the photoelectric absorption of the gamma ray or the Compton scattered gamma ray produced in a Compton event. In principle one could build a lens with a magnification of 8. This would magnify a 0.1 mm source to 0.8 mm at the detector and make the pixel detector efficient. The field of view of the lens without any scanning could be 2 to 3 mm in diameter giving and image at the detector with a spatial resolution of 0.1 mm over a 2 to 3 mm diameter area. With scanning this area could be expanded as much as one needed. The ability of reduce the size of the lens without losing efficiency or resolution, and in fact improving both of them combined with the understanding that one can now consider spatial resolution of 0.1 mm, suggests that one should consider using the power of the lens to magnify the image, just as one can use a simple convex lens for visible light can be used to magnify a light image. This will solve the pixel detector problem in that a magnified image can use large pixels for the same resolution. A 1 mm×1 mm pixel can contain the energy from a 140.5 keV gamma ray from Tc99m, but a 0.1 mm×0.1 mm pixel is too small to contain the x-ray that is produced in the photoelectric absorption of the gamma ray or the Compton scattered gamma ray produced in a Compton event. If one were to use magnification with the copper lens disclosed in U.S. Pat. No. 5,869,841 (1999), with a focal length of 50 cm and a distance from source to detector of 200 cm, a magnification of a factor of 2 would increase this source to detector distance to 225 cm and a magnification of a factor of 4, would increase the source to detector distance to 312.5 cm, which is difficult to handle. A reduction in the focal length of the prior art lens by a factor of 4 with a similar reduction in the size of crystal elements to a radial width of 1 mm, would reduce the source to detector distance to 56.3 cm (see FIG. 20) and generate an image on the detector of a point source of 2 to 3 mm in diameter. Magnification of this image would not improve the resolution. Thus one can see the advantages of going over to bent crystal lenses where the resolution can be as small as 0.1 mm. While the invention has been described with reference to details of the illustrated embodiment, these details are not intended to limit the scope of the invention as defined in the appended claims.
	claims	1. An inspection apparatus for inspecting jet pump beams of a nuclear reactor, the nuclear reactor comprising at least one jet pump with each jet pump comprising a jet pump beam and a jet pump beam bolt, said inspection apparatus comprising: a base straddlingly mountable on a jet pump beam, said base comprising a beam bolt opening sized to receive a jet pump beam bolt; a first transducer holder coupled to a first side portion of said base; and a second transducer holder coupled to a second side portion of said base, said first side portion opposite to said second side portion, each said holder comprising an adjustment cylinder, said adjustment cylinder configured to contact the jet pump beam when activated. 2. An inspection apparatus in accordance with claim 1 wherein each transducer holder comprises at least one ultrasonic transducer positioned to examine the jet pump beam. claim 1 3. An inspection apparatus in accordance with claim 2 wherein each transducer holder comprises two ultrasonic transducers positioned to examine the jet pump beam so that said ultrasonic transducers of said first transducer holder are oppositely disposed to said ultrasonic transducers of said second transducer holder. claim 2 4. An inspection apparatus in accordance with claim 1 further comprising at least one immersion ultrasonic transducer pivotally mounted to a third side portion of said base and at least one immersion ultrasonic transducer pivotally mounted to a fourth side portion of said base. claim 1 5. An inspection apparatus in accordance with claim 4 comprising one immersion ultrasonic transducer pivotally mounted to said third side portion and two immersion ultrasonic transducers pivotally mounted to said fourth side portion. claim 4 6. An inspection apparatus in accordance with claim 4 further comprising a first mounting member pivotally coupled to said third side portion of said base and a second mounting member pivotally coupled to said fourth side portion of said base. claim 4 7. An inspection apparatus in accordance with claim 6 wherein each said mounting member comprises at least one bore extending therethrough, each said bore sized to receive an immersion ultrasonic transducer. claim 6 8. An inspection apparatus in accordance with claim 1 further comprising a lift member coupled to said base, said lift member configured to couple to a lifting means. claim 1 9. An inspection apparatus in accordance with claim 1 wherein said adjustment cylinder comprises a pneumatic adjustment cylinder. claim 1 10. A method of inspecting a jet pump beam in a nuclear reactor, the reactor comprising at least one jet pump with each jet pump comprising a jet pump beam and a jet pump beam bolt, said method comprising: mounting an inspection apparatus on a jet pump beam; and scanning the jet pump beam with the inspection apparatus; said inspection apparatus comprising: a base straddlingly mountable on the jet pump beam, the base comprising a beam bolt opening sized to receive the jet pump beam bolt; a first transducer holder coupled to a first side portion of the base; and a second transducer holder coupled to a second side portion of the base, the first side portion opposed to the second side portion, each said holder comprising an adjustment cylinder, said adjustment cylinder configured to contact the jet pump beam when activated. 11. A method in accordance with claim 10 wherein mounting an inspection apparatus on a jet pump beam comprises: claim 10 positioning the inspection apparatus on the beam so that the beam bolt is received in the bolt opening of the inspection apparatus base; and activating the adjustment cylinders to contact the jet pump beam to prevent the inspection apparatus from rocking during the scanning step. 12. A method in accordance with claim 10 wherein each transducer holder comprises at least one ultrasonic transducer positioned to scan the jet pump beam. claim 10 13. A method in accordance with claim 12 wherein each transducer holder comprises two ultrasonic transducers positioned to scan the jet pump beam so that the ultrasonic transducers of the first transducer holder are oppositely disposed to the ultrasonic transducers of the second transducer holder. claim 12 14. A method in accordance with claim 10 wherein the inspection apparatus further comprises at least one immersion ultrasonic transducer pivotally mounted to a third side portion of the base and at least one immersion ultrasonic transducer pivotally mounted to a fourth side portion of the base. claim 10 15. A method in accordance with claim 14 wherein the inspection apparatus comprises one immersion ultrasonic transducer pivotally mounted to the third side portion and two immersion ultrasonic transducers pivotally mounted to the fourth side portion. claim 14 16. A method in accordance with claim 14 wherein the inspection apparatus further comprises a first mounting member pivotally coupled to the third side portion of the base and a second mounting member pivotally coupled to the fourth side portion of the base. claim 14 17. A method in accordance with claim 16 wherein each mounting member comprises at least one bore extending therethrough, each bore sized to receive an immersion ultrasonic transducer. claim 16 18. A method in accordance with claim 10 wherein the inspection apparatus further comprises a lift member coupled to the base, the lift member configured to couple to a lifting means. claim 10 19. A method in accordance with claim 10 wherein each adjustment cylinder comprises a pneumatic adjustment cylinder. claim 10 20. An inspection apparatus for inspecting jet pump beams of a nuclear reactor, the nuclear reactor comprising at least one jet pump with each jet pump comprising a jet pump beam, a jet pump beam bolt, and a beam lock assembly, the beam locking assembly comprising a locking sleeve and a lock plate, said inspection apparatus comprising: a base mountable on a jet pump beam, said base comprising a beam bolt opening sized to receive the jet pump beam bolt, said beam bolt opening comprising a recessed portion sized to receive the locking sleeve to permit said inspection apparatus to sit flat on the lock plate; a first transducer holder coupled to a first side portion of said base; and a second transducer holder coupled to a second side portion of said base, said first side portion opposite to said second side portion, each said holder comprising an adjustment cylinder, said adjustment cylinder configured to contact the jet pump beam when activated. 21. An inspection apparatus in accordance with claim 20 wherein each said transducer holder comprises two ultrasonic transducers positioned to examine the jet pump beam so that said ultrasonic transducers of said first transducer holder are oppositely disposed to said ultrasonic transducers of said second transducer holder. claim 20 22. An inspection apparatus in accordance with claim 20 further comprising at least one immersion ultrasonic transducer pivotally mounted to a third side portion of said base and at least one immersion ultrasonic transducer pivotally mounted to a fourth side portion of said base. claim 20 23. An inspection apparatus in accordance with claim 22 comprising one immersion ultrasonic transducer pivotally mounted to said third side portion and two immersion ultrasonic transducers pivotally mounted to said fourth side portion. claim 22 24. An inspection apparatus in accordance with claim 22 further comprising a first mounting member pivotally coupled to said third side portion of said base and a second mounting member pivotally coupled to said fourth side portion of said base. claim 22 25. An inspection apparatus in accordance with claim 24 wherein each said mounting member comprises at least one bore extending therethrough, each said bore sized to receive an immersion ultrasonic transducer. claim 24
	summary
	description	The present invention relates to a grating for X-ray imaging, to an X-ray imaging system and to a method for manufacturing a grating for X-ray imaging. In X-ray imaging, gratings are used, for example for differential phase contrast imaging or dark-field imaging. The gratings provide a repeated pattern of alternating areas, e.g. strips, of X-ray attenuating material and areas less X-ray attenuating. Another use of X-ray gratings are anti-scatter grids. In relation with higher image quality, a demand for large aspect ratios exists. A grating with a large aspect ratio and thin wall segments may have weakened mechanical stability and needs additional fixation. For example, WO 2012 055495 A1 describes a resist structure for producing an X-ray optical grating structure. There may thus be a need to provide a grating with a facilitated stabilization. The object of the present invention is solved by the subject-matter of the independent claims; further embodiments are incorporated in the dependent claims. It should be noted that the following described aspects of the invention apply also for the grating for X-ray imaging, for the X-ray imaging system and for the method for manufacturing a grating for X-ray imaging. According to the present invention, a grating for X-ray imaging is provided. The grating comprises a grating structure with a first plurality of bar members and a second plurality of gaps. The grating further comprises a fixation structure that is arranged between the bar members to stabilize the grating bar members. The bar members are extending in a length direction and in a height direction. Further, the bar members are spaced from each other by one of the gaps in a direction transverse to the height direction. The gaps are arranged in a gap direction parallel to the length direction. The fixation structure comprises a plurality of bridging web members that are provided between adjacent bar members. The web members are longitudinal web members that are extending in the gap direction and that are provided in an inclined manner in relation to the height direction. An inclination is provided in the gap direction. The inclined arrangement of the web members provides less artifact for the X-ray detector, i.e. the inclined web members have less affect, since the inclination takes place within the gap and in the gap's direction. The inclined arrangement also results in a facilitated manufacturing. The fixation structure comprises the plurality of bridging web members that are arranged in the gaps and that are provided between adjacent bar members. In an example, the bar members provide first grating members and the gaps provide second grating members. The web members provide bridging members that connect adjacent first grating members, wherein the bridging members protrude through, i.e. extend or span across, the second grating members, i.e. the bridging members cross the second grating members. The second grating members, i.e. the gaps, thus comprise space between the bar members that is arranged for providing a respective gap (or imaging) function (i.e. for providing an area or space with a different X-ray attenuation or absorption characteristic than the bar members). The second grating members, i.e. the gaps, also comprise space, in which the web members are located, that is arranged for providing a respective stabilizing (or mechanical) function. The bridging members thus each occupy a part of the gap, they each take away a small portion of the gap. The second grating members, i.e. the gaps, thus comprise the bridging members and a resulting net gap space. The space occupied by the bridging members can also be referred to as bridging or connection space. The first plurality of the bar members is thus interconnected by the web members bridging the second plurality of the gaps. The web members provide stabilizing elements for the bar members. According to an example, the web members and the bar members are made from the same material. In an option, the web members and the bar members are made as a one-piece structure. The term “same material” relates primarily to the X-ray attenuation properties of the material. In an option, the exact same material is used. In an alternative option, different materials are used, but with essentially equal X-ray attenuation properties. In an example, the web members and the bar members are made as one piece, e.g. by a common manufacturing process. The gap space, i.e. the resulting net gap space comprises a different material, i.e. different compared to the material of the bar members and the bridging members. The material of the gap space is at least different in terms of X-ray attenuation properties. According to an example, the bar members and the web members are made from structural material and an X-ray absorbing material is arranged in the gaps. The structural material is less X-ray absorbing than the X-ray absorption material. The first plurality of the bar members and the web members thus provide a constructive structural arrangement of the grating structure, i.e. a constructive or supportive structure of the grating structure. The second plurality of the gaps provides the X-ray absorbing arrangement of the grating structure, i.e. an X-ray absorptive or X-ray blocking structure of the grating structure. The “absorbing material” relates to a material that absorbs a major part of the X-ray radiation. For example, in view of X-ray imaging only a neglectable amount of X-ray is not absorbed. For example, the absorbing material comprises lead and/or gold. The absorbing material is provided in the resulting net gap space. The gaps thus comprise primary portions with the absorbing material and secondary (smaller) portions with the structural material of the web members. Thus, the X-ray absorbing material is arranged in a part of the gaps, when considering the gaps as the area between the bar members. When the term “gaps” is used for the resulting net gap space, i.e. the space between the bar members subtracted by the space occupied by the web members, the X-ray absorbing material is arranged in the gaps. In an example, the gaps (if understood as net gap space) are completely filled with the X-ray absorbing material. In another example, the gaps (if, again, understood as net gap space) are partly filled with the X-ray absorbing material. The other part can be filled with further material or can also be left empty. The “structural material” relates to a material that is capable of providing sufficient rigidity for the grating at least for the purpose of handling during manufacturing and assembling the grating. For example, the structural material comprises silicon or other suitable material for a grating in X-ray imaging. In an example, the structural material is configured to provide structural, i.e. mechanical stability of the grating. The structural material provides at least such stability that the absorbing material is fixedly attached and supported by the bar members and/or the web members. In an example, the bar members and the web members are made from the same material. In another example, two different materials are used for the bar members and the web members. According to an example, the grating is an absorber grating and the grating structure is made such that the gaps are filled with the X-ray absorbing material for X-ray absorption by the gaps. The bar members are provided to be less X-ray absorbing for X-ray radiation transmission in the bar members. The X-ray absorbing material in the gaps is more X-ray absorbent than the web members. The web members are provided along the gaps as a diagonal structure in relation to an X-ray viewing direction. The diagonal structure interrupts the absorbing structure along the gaps. Since the web members, in X-ray viewing direction only form a small part of the space of the gap, as a result, the gaps will always be more X-ray absorbent than the bar members. According to an example, the grating is an absorber grating and the grating structure is made such that the gaps are filled with the X-ray absorbing material for X-ray absorption by the gaps. The bar members are provided to be less X-ray absorbing for X-ray radiation transmission in the bar members, i.e. less absorbing for transmission of X-ray in the bar members. According to an alternative example, the grating is an absorber grating and the grating structure is made such that the bar members are made from X-ray absorbing material for X-ray absorption by the bar members. The gaps are provided to be less absorbing for X-ray radiation transmission in the gaps, i.e. for transmission of X-ray in the gaps. As an option, the gap part is less X-ray absorbent than the web segment part. The space of the gaps is less X-ray absorbent than the web members reaching through the gaps. The web members can be provided by X-ray absorbing material, e.g. the same material as used for the bar members. Since the web members, in X-ray viewing direction only form a small part of the space of the gap, as a result, the gaps will always be less X-ray absorbent than the bar members. The gaps may be provided with an X-ray transparent filler or may also be provided non-filled. Since the web members are provided in an inclined manner, the X-ray signal is improved due to more distributed attenuation by the web members in relation to the X-ray radiation direction. According to an example, the web members are arranged between the adjacent bar members such that the web members are connecting opposing portions of the bar members. According to another example, in a non-assembled state the web members are arranged parallel to each other. The grating may be configured to be bent for focusing during assembly. For example, the grating may be configured to be applied to a curved support structure or curved mounting surface. In an option, in a non-assembled state the web members are arranged in relation to a radiation direction of a fan-shaped X-ray beam; the web members are arranged with the same inclination angle to the radiation direction. Non-assembled state refers to a state where the grating is not mounted its final position within an X-ray imaging system. According to an example, in an X-ray radiation viewing direction, across the height at least one first gap part and at least one web segment part are provided. In an example, in a non-mounted state the grating is provided as a planar grating and in a direction transverse to the planar plane of the grating, e.g. normal or perpendicular to the plane, in a gap, across the height, at least one gap part is provided and at least one web segment part. According to an example, the web members are arranged such that, in an X-ray radiation viewing direction, a continuous degree of X-ray attenuation is provided along the gaps. This further improves the X-ray detector's signal and reduces the effort for post-processing of the signal. When the X-ray absorption is provided by the gaps, a continuous degree of rather high absorption is provided along the gaps. This high absorption is provided by the X-ray absorbing material arranged in the gaps, which material is provided in addition to the web members that are also arranged in the gaps but which themselves do provide a rather low attenuation (i.e. no or nearly X-ray absorption). Further, also a continuous degree of a rather or very low attenuation (for example X-ray transparent, i.e. with a neglectable X-ray attenuation in view of X-ray imaging) is provided along the bar members. When the X-ray absorption is provided by the bar members, a continuous degree of rather high absorption is provided along the bar members. This high absorption is provided by the X-ray absorbing material of the bar members. Further, also a continuous degree of a rather or very low attenuation (for example nearly X-ray transparent, i.e. with a neglectable X-ray attenuation in view of X-ray imaging) is provided along the gaps, members. Although the web members are also arranged in the gaps and the gaps themselves may provide X-ray attenuation due to a material providing X-ray absorption, but due to their small contribution in X-ray radiation direction, as a result they provide a rather low attenuation. According to an example, the web members are extending in a continuous manner from an upper edge of the bar members to a lower edge of the bar members. According to another example, the web members are arranged repeatedly in gap direction with a distance D over a gap height H. The web members have an inclination ratio in relation to the height direction R of D/H. According to an example, the web members are arranged at least as one of the following: i) as repeatedly arranged inclined web members with the same inclination angle; ii) as inclined segments with the same inclination angle value, but with alternating inclination directions, which results in a zig-zag web pattern along the gap; and iii) as repeatedly arranged inclined web segment portions that are provided in a crossing manner, which results in an X-type repeated web pattern. According to an example, the grating is an absorber grating for phase contrast and/or dark-field X-ray imaging. According to another example, the grating is an anti-scatter grid for X-ray imaging. According to the present invention, also an X-ray imaging system is provided. The X-ray imaging system comprises an X-ray source and an X-ray detector and a grating according to one of the above examples to be arranged in an X-ray radiation path between the X-ray source and the X-ray detector. According to an example, the X-ray source provides the X-ray radiation towards the X-ray detector in an X-ray viewing direction. The web members are provided in an inclined manner in relation to the X-ray viewing direction. The term “X-ray radiation” relates to X-ray radiation generated by the X-ray source that radiates towards the X-ray detector. The term “X-ray radiation path” relates to the propagation of the X-ray radiation. The X-ray radiation path thus describes the spatial area in which radiation is provided. For X-ray imaging, an object has to be arranged along the path to be able to generate X-ray image data. The X-ray radiation path can also be referred to as “X-ray radiation beam path”. In an example, the X-ray radiation is provided as a cone- or fan-shaped X-ray beam. The X-ray radiation thus provides a plurality of respectively arranged viewing directions. In another example, the X-ray radiation radiating the object is provided as coherent X-ray radiation with an essentially parallel arranged X-ray radiation. In an example, the X-ray source provides the coherent radiation. In another example, the X-ray source provides non-coherent radiation, which is then subject to a (source) grating structure to provide the coherent radiation. The term “X-ray viewing direction” relates to the direction of the X-ray radiation from the X-ray source to the X-ray detector. In case of a cone- or fan-shaped beam, the X-ray viewing directions vary respectively across the beam. In case of coherent, i.e. parallel X-ray radiation, the X-ray viewing directions across the beam are parallel to each other. In an example, the grating is provided as a flat grating where the web members are parallel to each other. When assembling the grating in an X-ray imaging system with a fan- or con-shaped beam, the grating is focused during assembly of the imaging system. For example, the grating is applied to a respectively shaped surface to bent when applying the grating to the shaped surface. In an example, the surface is curved, such as having a shape from a part of a concave spherical surface. According to an example, a grating arrangement for phase contrast and/or dark-field X-ray imaging is provided with the X-ray imaging system. At least partially coherent X-ray radiation is provided to irradiate an object. The grating arrangement comprises at least a phase grating and an analyzer grating. The grating is provided as an absorption grating forming the analyzer grating and/or a source grating to provide the at least partially coherent X-ray radiation. That is, the analyzer grating and/or a source grating, to provide the at least partially coherent X-ray radiation, is/are provided as an absorption grating, which is provided as a grating according to one of the examples above. According to the present invention, also a method for manufacturing a grating for X-ray imaging is provided. The method comprises the following steps: a) Generating a grating structure with a first plurality of bar members and a second plurality of gaps. The bar members are extending in a length direction and in a height direction, and are spaced from each other by one of the gaps in a direction transverse to the height direction. b) Generating a fixation structure arranged between the bar members to stabilize the grating bar members. The fixation structure comprises a plurality of bridging web members that are provided between adjacent bar members. The web members are longitudinal web members that are extending in the direction of the gaps and that are provided in an inclined manner in relation to the height direction. Grating-based phase-contrast and dark-field imaging is a promising technology to enhance the diagnostic quality of X-ray equipment e.g. in the areas of mammography, chest-radiography, and CT. According to an aspect, a solution is provided for a grating for a clinical system for grating-based phase-contrast and dark-field imaging. For example, an absorption grating G0 (“source grating”) or an absorption grating G2 (“analyzer grating”) is provided with a grating structure, for example in gold, with pitches in the order of a few μm to a few 10 μm, at heights of more than 200 μm, in order to achieve sufficient attenuation across the entire spectrum of the X-ray tube. For example, the so-called LIGA process is used for manufacturing such gratings. Due to the instruction of stabilizing structures, the gratings are stabilized and adhesion forces do not affect the geometrical precision of the grating. By providing inclined web members, for example as inclined bridges, the artifacts—registered by the sensor—caused by the fixation elements structure are decreased. When providing an even X-ray attenuation, an improved signal quality is achieved. As a further result of an example with continuous web members, only one mask is required in the manufacturing process. Additional undesired fringe pattern or additional noise are avoided or at least reduced. In an example, during a lithographic step, a mask with a bridge design is tilted around an axis perpendicular to the desired grating direction. This leads to tilted bridges or web members as mentioned above. The additional attenuation due to the bridges is distributed much more evenly across the grating area, which reduces the impact on image quality. In an example, for a given grating height H and a distance d between the web members along a trench, there is a dedicated tilt angle such that a homogeneous grating structure is achieved in transmission perpendicular to the grating area. In an example, this tilt angle α fulfils the relation tan α=d/H. At the same time, only a single illumination step is needed during lithography. The maximum length of the tilted bridge structure is correlated with the maximum achievable depth of the lithography process. The tilting angle has to be selected according to the lithography limitation as well as to the capability to electroplate the gold (or other material) under the bridge structure within the open volume of the parallelogram. Differential phase contrast imaging and dark-field imaging rely on the use of X-ray optical gratings. According to an aspect, to mechanically stabilize the grating structure, web members, for example as a bridge structure, are provided. The structure minimizes inhomogeneity without increasing lithography complexity for manufacturing. It is provided to rotate a web segment around an axis of rotation that is square to the grating direction. By doing so, a homogeneous grating can be obtained without increasing lithography complexity. Instead of tilting in the direction of α or −α, it is also possible to make double illumination steps and allow for example for V-shaped and W-shaped structures as well as X-shaped structures with a homogeneous distributed absorption of the stabilizing structure along the complete groove. In an example, the grating comprises multiple rotated web members to obtain an X-, V-, or XXX- or VVV- or combined X-V-pattern (when seen along the grating direction). In an example, the X-, XV- or VV-pattern is provided with a displacement such that a gap exists to be able to fill the lower part e.g. with X-ray absorbing material. For example, a distance is provided to achieve a V_V pattern; or a vertical displacement of the upper ends is provided such that a gap exists along a vertical direction. The filling may be provided, in an example, by electroplating. These and other aspects of the present invention will become apparent from and be elucidated with reference to the embodiments described hereinafter. FIG. 1 shows a grating 10 for X-ray imaging. The grating 10 comprises a grating structure 12 with a first plurality of bar members 14 and a second plurality of gaps 16. The grating 10 further comprises a fixation structure 18 arranged between the bar members 14 in order to stabilize the bar members 14. The grating bars, i.e. the bar members 14, are extending in a length direction 20 and in a height direction 22. The bar members 14 are spaced from each other by one of the gaps 16 in a direction transverse to the height direction 22, i.e. in a spacing direction. The spacing direction is indicated with a distance arrow 23. The gaps 16 are arranged in a gap direction 20′ parallel to the length direction 20. The fixation structure 18 comprises a plurality of bridging web members 24 that are provided between adjacent bar members 14. The web members 24 are longitudinal web members that are extending in the gap direction 20′ and that are provided in an inclined manner in relation to the height 22 direction. The inclination is provided in the gap direction 20′. FIG. 2 indicates a cross section along a gap with an inclined web member 24 that is provided inclined spanning across the length direction 20 and the height direction 22. An inclination angle is indicated with reference numeral 26. In an example, not further shown, the web members 24 are arranged parallel to the bar members 14 and are connected to the bar members 14 across the length on their side portions, i.e. across the length of the respective web member 24. In an example, not further shown, the web members 24 are arranged between the adjacent bar members 14 such that the web members 24 are connecting opposing and facing portions of the bar members 14. In other words, the web members 24 span transverse, preferably perpendicular to the gap's width direction, i.e. transverse, respectively perpendicular to the spacing direction 23. For example, the web members 24 are fixedly attached to opposite portions. In their cross-section transverse to their longitudinal direction, the web members 24 are spanning transverse to the gap direction, as mentioned. In other words, the web members 24 are connecting the bar members 14 in a direction perpendicular to the gap direction and perpendicular to the gap's depth, i.e. perpendicular to the viewing direction. In an example, the longitudinal web members 24 are provided as linear web members. The (first plurality of) bar members 14 and the (second plurality of) gaps 16 are forming a grating area. In an example, the grating area forms a grating plane. In another example, the grating area is provided bend on a cylindrical surface. The web members 24 are arranged in an inclined manner in relation to a main X-ray radiation direction, i.e. in an inclined manner to the viewing direction. In case of a radiation direction perpendicular to the grating, i.e. the grating extension within the grating area, the web members 24 are arranged in an inclined manner in relation to the perpendicular of the grating area. The web members 24 are arranged with a tilt angle in relation to the grating area or grating plane. The web members 24 stabilize the bar members 14 of the grating structure. Providing the web members 24 inclined results in a more distributed arrangement of the attenuation caused by the web members 24. The “bar members” 14 can also be referred to as bar elements or bar segments. The “web members” 24 can also be referred to as web elements or web segments or bridges or bridge segments. The web members 24 provide a stabilizing web that supports the bar members 14, i.e. bars. In an example not further shown, in an X-ray radiation viewing direction, across the height at least one first gap part is provided and at least one web segment part. In an example, the at least first gap part is X-ray transparent and does not provide X-ray attenuation. Only the part of the gap where the web segment is arranged, X-ray radiation is attenuated. The height direction is also referred to as a first direction or first height direction, and the length direction is referred to as second direction or second length direction. In an example, the grating is an absorber grating and the grating structure is made such that the bar members are made from X-ray absorbing material for X-ray absorption by the bar members. The gaps are provided to be less absorbing for transmission of X-ray in the gaps. Preferably, the gap part is less X-ray absorbent than the web segment part. For example, the web members 24 are provided in the same material as the bar members. In an example, the web members 24 are also made from X-ray absorbing material In a further example, the grating is an absorber grating and the grating structure is made such that the gaps are filled with X-ray absorbing material for X-ray absorption by the gaps. The bar members are provided to be less absorbing for transmission of X-ray in the bar members. In another example, the web members 24 are also made to be less absorbing for transmission of X-ray. In an example, as also indicated in FIG. 3 as an option, the web members 24 are arranged such that, in an X-ray radiation viewing direction 28, a continuous degree of X-ray attenuation is provided along the gaps. For example, the web members 24 are arranged such that in X-ray viewing direction, they X-ray radiation passes one web member while passing (i.e. radiating through) the gap of the grating. In another example, the radiation passes through two or three web members 24. The number of web members 24 that are passed is the same throughout the gaps, and also the same within the gaps in the gap direction. Providing a continuous degree of X-ray attenuation reduces the amount of artifacts in the X-ray signal provided by the detector. Advantage of this geometry is the single illumination step. However, instead of tilting in the direction of α or −α, it is also possible to make double illumination steps, for example for V-shaped and W-shaped structures as well as X-shaped structures. These can also provide a homogeneous distributed absorption of the stabilizing structure along the complete groove. In an alternative example, the web members are provided extending perpendicular to the gap direction. A number of web members is provided across the gap's height, which web members are displaced in direction of the gap. In an example, in a viewing projection, the same degree of X-ray attenuation is provided along the gaps. As an option, indicated in FIG. 3, the web members 24 are extending in a continuous manner from an upper edge 30 of the bar members 14 to a lower edge 32 of the bar members 14. As a result, only one mask has to be used for the manufacturing process and only one illumination is required in the lithography step. However, it also results in that a homogeneity is created in the grating that avoids that an additional undesired fringe pattern is created. The homogeneity is provided, in particular if the web members 24 are distributed regularly. The additional attenuation due to the web members 24 is distributed more evenly across the grating area, which reduces the impact on image quality. As a further option, although not shown in detail, the web members 24 are arranged at least as one of the following: i) repeatedly arranged inclined web members with the same inclination angle; ii) inclined segments with the same inclination angle value, but with alternating inclination directions, which results in a zig-zag web pattern along the gap; and iii) repeatedly arranged inclined web segment portions that are provided in a crossing manner, which results in an X-type repeated web pattern. In an example, the zig-zag pattern comprises portions that extend in gap's height only along a fraction of the height, but with the same inclination, which is still resulting in an even distribution of the attenuation. FIG. 3 shows a pattern of repeated inclined web members 24. The web members 24 are arranged repeatedly in the gap direction with a distance D over a gap height H. The web members 24 have an inclination ratio in relation to the height direction R of D/H. The distance D can also be referred to as pitch. In an example, for a given grating height H and a distance D between the bridges along a trench, there is a dedicated tilt angle such that a homogeneous grating structure is achieved in transmission perpendicular to the grating area. This tilt angle α fulfils the relation tan α=D/H, as shown in the option in FIG. 3. In an example, the grating is an absorber grating for phase contrast and/or dark-field X-ray imaging. The fixation structure addresses the manufacturing of the gratings in phase contrast X-ray imaging, in particular of the absorption gratings G0 (as source grating following the X-ray source) and G2 (as analyzer grating in front of the detector). For example, grating structures with pitches in the order of a few μm (micrometer) to a few 10 μm, at heights in gold of more than 200 μm are provided, in order to achieve sufficient attenuation across the entire spectrum of the X-ray tube. To build such gratings, a process including lithography, electroplating, and molding can be applied. The process in known as LIGA process (German for: Lithographie, Galvanoformung, Abformung). The fixation structure stabilizes the gratings that otherwise have the tendency to be unstable due to adhesion forces in particular for high aspect ratios. In another option, the grating is an anti-scatter grid for X-ray imaging. FIG. 4 schematically shows an X-ray imaging system 50 that comprises an X-ray source 52 and an X-ray detector 54. Further, a grating 56 is provided as an example of one of the above-mentioned gratings. The grating 56 is provided to be arranged in an X-ray radiation path 58 between the X-ray source 52 and the X-ray detector 54. FIG. 5 shows a system for phase contrast and/or dark-field X-ray imaging 50′ as an option of the X-ray imaging system. A grating arrangement 60 for phase contrast and/or dark-field X-ray imaging is provided. At least partially coherent X-ray radiation 61 is provided to radiate an object 62. The grating arrangement 60 comprises at least a phase grating G1 and an analyzer grating G2. As an option, a source grating G0, to provide the at least partially coherent X-ray radiation, can also be provided. The analyzer grating G2 and/or the source grating G0 are provided as an absorption grating which is provided as a grating according to one of the above examples. Further aspects, such as phase stepping etc. for differential phase contrast imaging are not described in further detail. FIG. 6 shows an example of a method 100 for manufacturing a grating for X-ray imaging. The method 100 comprises the following steps. In a first step 102, also referred to as step a), a grating structure is generated with a first plurality of bar members and a second plurality of gaps. The bar members are extending in a length direction and in a height direction, and are spaced from each other by one of the gaps in a direction transverse to the height direction. In a second step 104, a fixation structure is generated arranged between the bar members to stabilize the grating bar members. The fixation structure comprises a plurality of bridging web members that are provided between adjacent bar members. The web members 24 are longitudinal web members that are extending in the direction of the gaps and that are provided in an inclined manner in relation to the height direction. In an example, steps a) and b) take place at the same time. In an alternative example, steps a) and b) take place after each other. In an example, not further show, in a step a1), a mask for a radiation source is provided in order to shield radiation in a structure that is provided as a grating structure with a first plurality of bar members and a second plurality of gaps, and a fixation structure arranged between the bar members to stabilize the grating bar members. The bar members are extending in a length direction and in a height direction and are spaced from each other by one of the gaps in a direction transverse to the height direction. The fixation structure comprises a plurality of bridging web members 24 that are provided between adjacent bar members. The web members 24 are longitudinal web members that are extending in an inclined manner in relation to the height direction. In a step a2), a radiation sensitive photoresist substance is provided. In a step b′), the photoresist substance is illuminated with radiation while shielding the photoresist substance with the mask, which results in parts of the photoresist substance being fixated and other parts being non-fixated. In a step c), the non-fixated parts of the photoresist substance are removed while maintaining the fixated parts as a mold. In a step d), the grating structure is galvanically generated in the removed parts. In a step e), the fixated parts are removed. The illumination and hardening of the photo-sensitive substance is also referred to as lithography process. For example, the galvanic generation of the grating is provided by electroplating. In one example, the radiation used for radiating the photoresist substance is low-energy X-ray (e.g. 5 to 10 keV) from a synchrotron radiation source. In another example, the radiation used for radiating the photoresist substance is light from an ultraviolet light source. Advantage of the geometry of the grating is a single illumination step (see below). However, instead of tilting in the direction of α or −α, it is also possible to make double illumination steps, for example for V-shaped and W-shaped structures as well as X-shaped structures (see above). These can also provide a homogeneous distributed absorption of the stabilizing structure along the complete groove. In an example, only one mask is provided in step a) in only one illuminating step b). In an example, the mask is having a bridge design and the mask is tilted around an axis perpendicular to the desired grating direction. This leads to tilted bridges forming the web members 24 described above. The maximum length of the tilted web members 24 structure is correlated with the maximum achievable depth of the lithography process. In an example, the tilting angle is selected according to the lithography limitation as well as to the capability to electroplate the gold (or other material) under the web members 24 structure within the open volume of a parallelogram. It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application. However, all features can be combined providing synergetic effects that are more than the simple summation of the features. While the invention has been illustrated, and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.
	abstract	A method and combined video display and camera system are disclosed. In one embodiment, the system comprises a first sheet and a second sheet oriented parallel to the first sheet, the second sheet including a light diffuser. A light source is placed along an edge of the second sheet, wherein the second sheet diffuses light generated by the light source. One or more cameras are placed behind the second sheet to capture an image through the second sheet and the first sheet.
	summary
055457967	abstract	An article, such as a containment system (10), having sides (12) with walls (2) or (24) is made; in one method by using cast, cooled, melted, radioactive metal components where the melted metal has a specific activity over 130 Bq/g; or by providing a contaminated material in the form of a solid, liquid or mixture, and then mixing the contaminated material, to which no more than about 15 weight % of uncontaminated material has been reacted, with a binder, followed by forming the composition into a containment system and then curing it into a mass which contains both contaminated material, and uncontaminated binder acting as a matrix for the contaminated material. This article need not be a containment system but can be a wide variety of objects which are made out of radioactive waste, hazardous waste, and their mixtures.
	abstract	A water reactor fuel cladding tube (4) is described. The tube (4) comprises an outer layer (6) of a first zirconium based alloy and has metallurgically bonded thereto an inner layer (7) of a second zirconium based alloy. The inner layer protects (7) the cladding tube (4) against stress corrosion cracking. The second zirconium based alloy comprises tin as an alloying material, and each one of the zirconium based alloys comprises at least 96 percent by weight zirconium. The first zirconium based alloy comprises at least 0.1 percent by weight niobium. A method of manufacturing the cladding tube (4) is also described and comprises the step of co-extruding two tubes of different zirconium based alloys to produce the cladding tube (4).
	abstract	Nuclear reactor systems and methods are described having many unique features tailored to address the special conditions and needs of emerging markets. The fast neutron spectrum nuclear reactor system may include a reactor having a reactor tank. A reactor core may be located within the reactor tank. The reactor core may include a fuel column of metal or cermet fuel using liquid sodium as a heat transfer medium. A pump may circulate the liquid sodium through a heat exchanger. The system may include a balance of plant with no nuclear safety function. The reactor may be modular, and may produce approximately 100 MWe.
	abstract	A spacer grid for a fuel assembly in a light-water-cooled nuclear reactor, for providing the transverse retention of a bundle of fuel rods in mutually parallel arrangements, having an array of cells juxtaposed and placed in a regular lattice, each bounded and separated from neighboring cells by at least one peripheral wall which is open at two opposed ends, along the direction of an axis of the cell, so as to receive a fuel rod of cylindrical general shape passing along the cell along its axis parallel to the peripheral wall.
	summary
	description	The present invention claims priority from Japanese Patent Application No. 2006-318435 filed on Nov. 27, 2006, and No. 2006-318436 filed on Nov. 27, 2006, the entire content of which is incorporated herein by reference. 1. Field of the Invention This invention relates to an ion implantation apparatus configured to irradiate an ion beam in a ribbon-shape having a larger dimension in an X direction than a dimension in a Y direction substantially orthogonal to the X direction which has scanned in the X direction, or has not scanned in the X direction onto a target, for performing ion implantation. More particularly, the invention relates to an improvement of a means for narrowing the ion beam in the Y direction. 2. Description of the Related Art FIG. 16 shows a related art of this type of an ion implantation apparatus. The same ion implantation apparatus is described in JP-A-08-115701 (FIG. 1). In the specification and the drawings of the present application, a description is given by taking the case where ions forming an ion beam 4 are positive ions. In the ion implantation apparatus, an ion beam 4 having a small cross section (e.g., a circular or rectangular spot shape) which will be formed in a ribbon-shaped ion beam is generated from an ion source 2, and the ion beam 4 having the small cross section is mass-separated through a mass separator 6. The mass-separated ion beams are accelerated or decelerated through an acceleration/deceleration device 8, energy-separated through an energy separator 10, scanned in the X direction (e.g., in the horizontal direction) through a scanner 12, and converted into parallel beams through a collimator 14. Then, the ion beams are irradiated onto a target 24 (e.g., a semiconductor substrate) held in a holder 26 to perform ion implantation into the target 24. A path for the ion beam 4 between the ion source 2 and the target 24 is held in a vacuum atmosphere. The target 24 is mechanically scanned (reciprocatedly driven) along the Y direction (e.g., along the vertical direction) together with the holder 26 within the irradiation region of the ion beam 4 from a collimator 14 by a target driving device 28. In the specification and the drawings of the present application, a description is given that the traveling direction of the ion beam is referred to as a Z direction. In addition, two directions substantially orthogonal to each other in a plane substantially orthogonal to the Z direction are referred to as the X direction and the Y direction. In cooperation with the scanner 12 for scanning the ion beam 4 by a magnetic field or an electric field (in this example, a magnetic field), the collimator 14 bends the ion beam 4 scanned in the X direction so as to make it substantially parallel with a reference axis 16 by a magnetic field or an electric field (in this example, a magnetic field), and thus converts the ion beam 4 into a parallel beam. As a result, the ion beam 4 in a ribbon-shape having a larger dimension in the X direction than the dimension in the Y direction (see, FIG. 17, too) is led out. Though it is called as the “ribbon-shape”, it is not meant that the dimension in the Y direction is as thin as paper or cloth. For example, the ion beam 4 has a dimension in the X direction of about 35 cm to 50 cm, and a dimension in the Y direction of about 5 cm to 10 cm. The collimator 14 is referred to as a beam parallelizing magnet when a magnetic field is used as in this example. The ion implantation apparatus is an example of the case where the ion beam 4 in the ribbon-shape which has scanned in the X direction is irradiated onto the target 24. However, the ion beam 4 in the ribbon-shape may be generated from the ion source 2, and the ion beam 4 in the ribbon-shape may be irradiated onto the target 24 without having been scanned in the X direction. The transport path for the ion beam 4 is in a vacuum chamber not shown, and held in a vacuum atmosphere. However, gases such as residual gases or out gases are necessarily present though in small amounts. When the ion beam 4 collides against the gas molecules, neutral particles occur. Then, the neutral particles are incident to the target 24, so that a uniformity of an implantation amount distribution is degraded. As a result, an error in implantation amount is caused, or other detrimental effects are caused. Therefore, the ion beam 4 which is in an energy state to be irradiated onto the target 24 is deflected by an action of a magnetic field or an electric field by means of an ion beam deflector provided near the target 24. Thus, the deflected ion beam 4 and the neutral particles 18 going straight without deflection are separated from each other. As a result, the neutral particles 18 are prevented from being incident to the target 24. The collimator 14 also serves as the ion beam deflector. The ion beam 4 diverges due to a space charge effect during a travel. From viewpoints of enhancing a throughput of an apparatus, reducing an ion implantation depth in order to miniaturize a semiconductor device formed on the target 24, and the like, the ion beam 4 to be irradiated onto the target 24 is required to have a low energy and a large electric current. However, a divergence of the ion beam 4 due to the space charge effect increases with a reduction in energy and an increase in electric current of the ion beam 4. The divergence of the ion beam 4 occurs in both the X and Y directions. However, originally, the dimension in the X direction of the ion beam 4 is significantly larger than in the Y direction as described above. Therefore, the detrimental effect by the divergence in the Y direction is larger. When the ion beam 4 diverges in the Y direction, a part of the ion beam 4 in the Y direction is cut by the vacuum chamber surrounding a path for the ion beam 4 and a mask or the like for shaping the ion beam 4. As a result, a transport efficiency of the ion beam 4 to the target 24 is reduced. For example, a mask 20 having an opening 22 for passing the ion beam 4 and shaping the ion beam 4 may be disposed between the collimator 14 and the target 24, as shown in FIGS. 16 and 17, or as also disclosed in JP-B2-3567749. The mask 20 may cut an unnecessary bottom portion in the Y direction of the ion beam 4, thereby to shorten the distance L2 missing the target 24 from the ion beam 4. When the ion beam 4 diverges in the Y direction by the space charge effect, a rate of cutting to the ion beam 4 is increases by the mask 20. Accordingly, an amount of the ion beam 4 capable of passing through the mask 20 is reduced, resulting in a reduction of the transport efficiency of the ion beam 4. The problem is also present similarly in the case where a ribbon-shaped ion beam 4 is generated from the ion source 2, and the ribbon-shaped ion beam 4 is irradiated onto the target 24 without having been scanned in the X direction. As a means for compensating for the divergence in the Y direction due to the space charge effect of the ion beam 4, the following means may be considered. An electrostatic lens is provided in a vicinity on a downstream side or an upstream side of the collimator 14 in the path for the ion beam 4. As shown in FIG. 18, the electrostatic lens 30 includes an inlet electrode 32, an intermediate electrode 34, and an outlet electrode 36 spaced apart from one another in the traveling direction Z of the ion beam 4. The inlet electrode 32 and the outlet electrode 36 are held at a mutually equal electric potential (in FIG. 18, ground potential). The intermediate electrode 34 is applied with a positive or negative direct current voltage V1 from a direct current power source 38. Thus, it is held at a different electric potential from that of the inlet electrode 32 and the outlet electrode 36. The respective electrodes 32, 34, and 36 each individually has a shape corresponding to the shape of the ion beam 4 like a tube or a parallel plate. The electrostatic lens 30 acts as an einzel lens (which is also referred to as a unipotential lens) It has a function of narrowing the ion beam 4 in the Y direction without changing energy of the ion beam 4 even when the intermediate electrode 34 is applied with either direct current voltage V1 of positive or negative polarity. Incidentally, FIG. 18 shows the state in which the ion beam 4 has not been narrowed for simplification of showing. However, the ion beam 4 is narrowed in actuality. With the foregoing technique of narrowing the ion beam 4 by the use of the electrostatic lens 30, it is possible to compensate for the divergence in the Y direction due to the space charge effect of the ion beam 4, and to enhance the transport efficiency of the ion beam 4. However, unfavorably, energy contamination occurs like mixing of undesirable energy particles. When the intermediate electrode 34 of the electrostatic lens 30 is applied with a negative direct current voltage V1, the ion beam 4 is once accelerated in a region between the inlet electrode 32 and the intermediate electrode 34, and then, decelerated in a region between the intermediate electrode 34 and the outlet electrode 36 to return to the original energy. In this acceleration region, when the ion beam 4 collides with residual gases, and neutral particles are generated due to charge conversion, neutral particles having a higher energy than the energy of the incident ion beam 4 are generated. These neutral particles proceed toward the downstream side, which causes the energy contamination of a high energy component. When the intermediate electrode 34 is applied with a positive direct current voltage V1 as shown in FIG. 18, the ion beam 4 is once decelerated in a region between the inlet electrode 32 and the intermediate electrode 34, and then, accelerated in a region between the intermediate electrode 34 and the outlet electrode 36 to return to the original energy. In this deceleration region, when the ion beam 4 collides with residual gases, and neutral particles are generated due to charge conversion, neutral particles having a lower energy than the energy of the incident ion beam 4 are generated. These neutral particles proceed toward the downstream side, which causes the energy contamination of a low energy component. Consequently, energy contamination occurs even when the intermediate electrode 34 is applied with either direct current voltage V1 of positive or negative polarity. Whereas, when the intermediate electrode 34 is applied with a positive direct current voltage V1, as shown in FIG. 18, electrons 39 in an electric field-free drift space where an electric field doesn't exist space on the upstream side and on the downstream side of the vicinity of the intermediate electrode 34) are attracted to the intermediate electrode 34, and vanish. Therefore, when the amount of electrons in the drift space decreases, the divergence due to the space charge effect of the ion beam 4 is intensified. As a result, the transport efficiency of the ion beam 4 decreases. One or more embodiments of the invention provide an ion implantation apparatus capable of compensating a divergence in a Y direction due to a space charge effect of an ion beam, and the like, and enhancing a transport efficiency of the ion beam, and further inhibiting an occurrence of an energy contamination. In accordance with one or more embodiments of the invention, in an ion implantation apparatus of a first aspect of the invention, an ion beam formed in a ribbon-shape having a larger dimension in an X direction than a dimension in a Y direction substantially orthogonal to the X direction is irradiated onto a target. The ion implantation apparatus is provided with first and second magnets provided on an upstream side of the target, facing to each other in the Y direction across a path for the ribbon-shaped ion beam, and crossing a traveling direction of the ribbon-shaped ion beam. In the ion implantation apparatus, each of the first and second magnets has a pair of magnetic poles on an inlet side and on an outlet side of the ion beam, and polarities thereof are opposite between the first magnet and the second magnet. The first and second magnets generate magnetic fields in a direction so that an inward Lorentz force is applied to the ion beam between both the magnets, and the ion beam is narrowed in the Y direction. In the first aspect of the invention, the ribbon-shaped ion beam may be formed by scanning the ion beam in the X direction or by not scanning in the X direction. According to the ion implantation apparatus of the first aspect, it is possible to generate magnetic fields each having a component orthogonal to the traveling direction of the ion beam over an entire region in the X direction of the ribbon-shape ion beam by the first and second magnets (however, the magnetic fields generated by both the magnets are opposite from each other). By the magnetic fields, the ion beam receives inward Lorentz forces in the Y direction. As a result, the ion beam can be narrowed in the Y direction. According to a second aspect of the invention, in the ion implantation of the first aspect, the first and second magnets may be arranged substantially plane symmetrically with respect to a symmetric plane passing through a center in the Y direction of the path for the ion beam and substantially orthogonal to the X direction and the Y direction, except that the first magnet and the second magnet are opposite in polarity from each other. According to a third aspect of the invention, in the ion implantation apparatus of the first or second aspect, the first and second magnets may be arranged so as to obliquely cross the traveling direction of the ion beam. According to a fourth aspect of the invention, in the ion implantation apparatus of the first or second aspect, the first and second magnets may be provided on a path for the ion beam where the ion beam is scanned in a fan shape in the X direction, the first and second magnets may respectively have arc shapes protruding in the traveling direction the ion beam, such that an angle formed between the advancing direction of the ion beam at each scanning position in the X direction and a straight line connecting between the pair of the magnetic poles of each magnet at the shortest distance is invariably substantially constant. According to a fifth aspect of the invention, the ion implantation apparatus of the first or second aspect may include an ion beam deflector configured to deflect the ion beam which is in an energy state so as to be irradiated onto the target by a magnetic field or an electric field, and separate the ion beam and neutral particles. Further, in the ion implantation apparatus of the fifth aspect, the first and second magnets may be disposed in at least a vicinity on a downstream side of the ion beam deflector. In contrast, in the ion implantation apparatus of the fifth aspect, the first and second magnets may be disposed in at least a vicinity on an upstream side of the ion beam deflector. According to a sixth aspect of the invention, in the ion implantation apparatus of one of the first to fifth aspects, the first and second magnets may be permanent magnets. According to a seventh aspect of the invention, in the ion implantation apparatus of one of the first to fifth aspects, the first and second magnets may be electromagnets. In accordance with the first aspect of the invention, the ion beam may be narrowed in the Y direction by the magnetic fields generated by the first and second magnets. Therefore, it is possible to compensate for the divergence in the Y direction due to the space charge effect of the ion beam, or the like, and to enhance the transport efficiency of the ion beam. Further, the ion beam may be narrowed without acceleration and deceleration instead of the case using an electrostatic lens. Therefore, it is possible to inhibit the occurrence of energy contamination. Still further, the foregoing effect may be produced with a simple structure of the first and second magnets. In accordance with the second aspect of the invention, magnetic fields with good symmetry with respect to the symmetric surface may be generated by the first and second magnets. Therefore, it is possible to narrow the ion beam with good symmetry. In accordance with the third aspect of the invention, the magnetic component orthogonal to the traveling direction of the ion beam is made larger, which may narrow the ion beam in the Y direction more strongly. In accordance with the fourth aspect of the invention, the ion beam may be narrowed uniformly in the Y direction over the entire region of the ion beam to be scanned in a fan shape in the X direction. In accordance with the fifth aspect of the invention, the first and second magnets are permanent magnets. Therefore, the configuration may be more simplified. In accordance with the sixth aspect of the invention, the first and second magnets are electromagnets. It is easy to adjust the intensities of the magnetic fields generated from the first and second magnets. Accordingly, it is possible to control the degree to which the ion beam is narrowed in the Y direction with ease. Further, it is also possible to generate a more intense magnetic field than with a permanent magnet, and thereby to narrow the ion beam more strongly. Other aspects and advantages of the invention will be apparent from the following description and the appended claims. FIG. 1 is a plan view partially showing one exemplary embodiment of an ion implantation apparatus in accordance with the invention. Elements which are equal to or correspond to those of a related art shown in FIG. 16 are given the same reference signs and numerals. Below, points of difference from the related art will be mainly described. An ion implantation apparatus is disposed on an upstream side of a target 24. More specifically, the ion implantation apparatus is disposed in a vicinity of a downstream side of a collimator 14 also serving as an ion beam deflector for separating an ion beam 4 and the neutral particles 18 in FIG. 16. The ion implantation apparatus has a first magnet 50 and a second magnet 52 disposed so as to face each other in a Y direction across a path for a ribbon-shaped ion beam 4. In FIG. 1, the second magnet 52 (see, FIG. 3) is hidden under the first magnet 50, and does not appear. Therefore, a reference numeral 52 thereof is described in parentheses. Incidentally, on the downstream side of the collimator 14, the scanner 12 and the collimator 14 cooperate. Accordingly, the ion beam 4 is substantially scanned in parallel in the X direction, and the ion beam 4 has a ribbon-shape. The first and second magnets 50 and 52 are respectively permanent magnets substantially having straight shapes, in this exemplary embodiment. Both the magnets 50 and 52 are disposed as to cross a traveling direction Z of the ribbon-shaped ion beam 4. More specifically, the magnets 50 and 52 is disposed so as to obliquely cross the traveling direction Z, in this exemplary embodiment. Further, both the magnets 50 and 52 each has a length covering a dimension in the X direction of the ribbon-shaped ion beam 4, in this exemplary embodiment. Namely, both the magnets 50 and 52 each has a larger dimension in the X direction than the dimension in the X direction of the ribbon-shaped ion beam 4, and has a shape of a long narrow rod or plate. The wording “obliquely cross” means that the angle β formed between a normal 60 drawn to a long side 50a of the magnet 50 and the traveling direction Z of the ion beam 4 is other than 0 degree as shown in FIG. 2. The normal 60 is, in other words, a line parallel with a short axis or a magnetic axis of the magnet 50. When the angle β is 0 degree, as shown in FIG. 6, the magnet 50 crosses at substantially right angles with the traveling direction of the ion beam 4. The same applies to the second magnet 52. Both the magnets 50 and 52 each has a pair of magnetic poles which are N pole and S pole on an inlet side and on an outlet side of the ion beam 4. Namely, the two long sides 50a, 52a are respectively substantially magnetic poles over the overall length thereof. In other words, opposite sides in a direction of each short side of the magnets 50 and 52 are magnetic poles. In this regard, this exemplary example is largely different from a reference example in which short sides 80b, 82b are magnetic poles as shown in FIGS. 14 and 15. Further, the polarities of the magnetic poles are opposite between the first magnet 50 and the second magnet 52 as shown in FIG. 3. Further, in this exemplary embodiment, the first magnet 50 and the second magnet 52 are disposed substantially plane symmetrically with respect to a symmetric surface 58 passing through a center in the Y direction of the path for the ion beam 4, and substantially orthogonal to the X direction and the Y direction in FIG. 3. More specifically, the magnet 50 and the magnet 52 are configured to substantially have mutually equal shape and dimensions. Both the magnets 50 and 52 are disposed to substantially face each other in the Y direction. In other words, these magnets are overlapped one on another in the Y direction. In addition, the distances between the symmetric surface 58 and both the magnets 50 and 52 are set to be mutually substantially equal. Therefore, in a vicinity of the symmetric surface 58, the upper and lower magnetic fields cancel each other, so that the intensity of the magnetic field becomes substantially 0. Thus, the intensity of the magnetic field increases with an increase in distances upward and downward in the Y direction from the symmetric surface 58. The relationship between the setting sites and the polarities of the magnetic poles of both the magnets 50 and 52 are summarized in Table 1. The embodiment shown in FIG. 1 corresponds to Example 1 in Table 1. Example 2 will be described later. TABLE 1Polarity on thePolarity on theSetting site ofoutlet side ofoutlet side ofmagnetfirst magnet 50second magnet 52Example 1Downstream side ofN poleS polecollimator 14Example 2Upstream side ofS poleN polecollimator 14 The table 1 shows the case where the angle β is positive (however, smaller than 90 degrees) when the angle β is taken counterclockwise with respect to the incident ion beam 4 as shown in FIG. 2. Further, it shows the case where the angle γ shown in FIG. 6 is positive (however, smaller than 90 degrees) when the angle γ is taken clockwise with respect to the incident ion beam 4. Similarly, it shows the case where the angle shown in FIG. 8 is positive (however, smaller than 90 degrees) when the angle φ is taken clockwise with respect to the incident ion beam 4. When the angles β, γ, and φ are negative, the orientation of the orthogonal component BR described later is reversed. For this reason, it is essential only that the polarities of the magnets 50 and 52 are reversed from those shown in Table 1. In other words, in any case, the polarities of the magnetic poles of both the magnets 50 and 52 are set so as to cause magnetic fields in the direction in which Lorentz force is allowed to act on the ion beam 4 inwardly between both the magnets 50 and 52. This will be first described by reference to FIGS. 2 and 3. The first magnet 50 generates a magnetic field B in the direction crossing the ion beam 4 at the angle on the side of the path for the ion beam 4. The magnetic field B generated by the magnet 50 is schematically shown with a line of magnetic field 54 in FIG. 3. Distinct from the case of the reference example shown in FIG. 14 or 15, the magnetic pole of the magnet 50 is present in the direction of short side. Therefore, it is possible to generate the magnetic field B as described above. The magnetic field B has a component (orthogonal component) BR orthogonal to the traveling direction Z of the ion beam 4 due to the presence of the angle β. Such an orthogonal component BR occurs over the entire region in the X direction of the ion beam 4. By the orthogonal component BR, the ion beam 4 receives inward Lorentz force F in the Y direction (downward in FIG. 3). The second magnet 52 also generates the same magnetic field as the magnetic field B generated by the first magnet 50 except that the orientation is reverse. The magnetic field generated by the magnet 52 is schematically shown with a line of magnetic field 56 in FIG. 3. By the orthogonal component of the magnetic field, the ion beam 4 receives Lorentz force F acting inward in the Y direction (downward in FIG. 3). By the Lorentz force F, the ion beam 4 may be narrowed in the Y direction. The degree to which the ion beam 4 is narrowed is proportional to the magnetic flux density of the magnetic field B, and is inversely proportional to the energy of the ion beam 4. Therefore, when the magnetic flux density is constant, an ion beam 4 with a lower energy may be more strongly narrowed. One example of the state in which the ion beam 4 is narrowed is shown in FIG. 3. This is an example in which the incident ion beam 4 diverging in the Y direction is narrowed so as to converge. However, the state of the ion beam 4 shown is only one example (the same also applies to FIGS. 4, 9, 11, and 13). Adjustment of the degree to which the ion beam 4 is narrowed enables other narrowing techniques than the foregoing example. For example, it is also possible to lead out a parallel ion beam of which divergence is substantially 0 in the Y direction. The same also applies to other embodiments described later. Thus, with the ion implantation apparatus, the ion beam 4 may be narrowed in the Y direction by the magnetic fields generated by the first and second magnets 50 and 52. Therefore, it is possible to compensate for the divergence in the Y direction due to the space charge effect of the ion beam 4, and to enhance the transport efficiency of the ion beam 4 to the target 24. It is possible to narrow the ion beam 4 in the Y direction. Therefore, it is also possible to inhibit the divergence in the Y direction due to other factors than the space charge effect of the ion beam 4. Further, as described previously, by adjusting the degree to which the ion beam 4 is narrowed in the Y direction, it becomes also possible to lead out a parallel ion beam of which divergence is substantially 0 in the Y direction. Taking a more specific example, when the mask 20 is disposed on the downstream side of both the magnets 50 and 52 as with the example shown in FIG. 1, the following is possible: Between the collimator 14 and the mask 20, the divergence in the Y direction due to the space charge effect of the ion beam 4 is compensated. This increases the amount of the ion beam 4 to pass through the opening 22 of the mask 20, resulting in an increase in transport efficiency of the ion beam 4 to the target 24. Whereas, distinct from the case using an electrostatic lens, it is possible to narrow the ion beam 4 without acceleration or deceleration. Therefore, it is possible to inhibit the occurrence of energy contamination. Further, it is possible to exert the effect with a simple configuration of the first and second magnets 50 and 52. This exemplary embodiment further has the following advantage. Namely, both the magnets 50 and 52 are permanent magnets, and hence the configuration may be more simplified. Both the magnets 50 and 52 are arranged so as to obliquely cross with the traveling direction Z of the ion beam 4. Therefore, it is possible to make the orthogonal component BR larger, and to more strongly narrow the ion beam in the Y direction. Both the magnets 50 and 52 are disposed along the path for the ion beam 4 substantially parallelly scanned in the X direction. Therefore, it is possible to uniformly narrow the ion beam 4 in the Y direction over the entire region of the ion beam 4 substantially parallelly scanned in the X direction. The first magnet 50 and the second magnet 52 are substantially arranged plane symmetrically with respect to the symmetric surface 58, so that a magnetic field with good symmetry with respect to the symmetric surface 58 may be generated by the first and second magnets 50 and 52. Therefore, the ion beam 4 may be narrowed with good symmetry. Incidentally, between the magnetic poles of the first magnet 50 and the magnetic poles of the second magnet 52, strictly, magnetic fields B1 and B2 in the Y direction occur as with the example shown in FIG. 4. Both the magnetic fields B1 and B2 are mutually oppositely oriented. Further, these are intensified with a decrease in distance in the Y direction between both the magnets 50 and 52. By the magnetic fields B1 and B2, the ion beam 4 receives Lorentz forces F1 and F2 acting in the mutually opposite directions in the X direction. Thus, the ion beam 4 is bent in the X direction during passage through between both the magnets 50 and 52. As a result, a difference in orbit (orbit difference) ΔX in the X direction is caused between the inlets and the outlets of the magnets 50 and 52. When the intensities of both the magnetic fields B1 and B2 are made substantially equal to each other, the incident ion beam 4 and the irradiation ion beam 4 become substantially parallel to each other. Even when the orbit difference ΔX as described above is caused, the object of narrowing the ion beam 4 in the Y direction may be attained. Further, the orbit difference ΔX as described above is generally very small. Therefore, even when the orbit difference ΔX is caused, no particular inconvenience is caused. However, when inconvenience arises, it is possible to cope with it with other means. Incidentally, in FIG. 5, only one line of the ion beam 4 is shown as the typical one. However, the ion beams 4 at other sites are also the same as the one shown (the same also applies to FIGS. 6 and 12). Whereas, noticing that the ion beam 4 is bent in the X direction during passage through between both the magnets 50 and 52 as described above, as with the example shown in FIG. 6, the magnets 50 and 52 may also be disposed so as to cross substantially at right angles with respect to the traveling direction Z of the ion beam 4 (in other words, so that the angle β shown in FIG. 2 becomes substantially 0 degree). Also in this case, the angle γ formed between the ion beam 4 passing through between the magnets 50 and 52 and the magnetic field B is larger than 0 degree. Thus, the component (orthogonal component) BR orthogonal to the traveling direction Z of the ion beam 4 occurs. Therefore, by the orthogonal component BR, as with the case of the example of FIG. 2 or 3, the ion beam 4 receives Lorentz force acting inward in the Y direction (however, the magnitude thereof is generally smaller than in the example of FIG. 2 or 3). As a result of this, it is possible to narrow the ion beam 4 in the Y direction. The same phenomenon as this also occurs in the example of FIG. 2 or 3, to be exact, as indicated by reference to FIG. 5. Therefore, also noticing the angle γ, the angle formed between the ion beam 4 during passage through between the magnets 50 and 52 and the magnetic field B is β+γ. The magnet 50 may be formed of one permanent magnet. Alternatively, it may be formed by arranging a plurality of permanent magnets 68 of the same polarity in parallel as with the example shown in FIG. 7. The same also applies to the magnet 52. Further, the same also applies to the magnets 50 and 52 in the form of an arc (see, FIGS. 8 and 9) described later. Incidentally, it is not preferable that magnetic poles are disposed on the opposite sides in the longitudinal direction of a first magnet 80 and a second magnet 82, namely, on the two short sides 80b and 82b sides as with a reference example shown in FIGS. 14 and 15. When the magnetic poles are provided in such a configuration, between both the magnets 80 and 82, magnetic force lines 84 and 86 along the Y direction occur only in the vicinity of the magnetic poles on the opposite sides in the X direction as shown in FIG. 15. As a result, Lorentz forces F3 and F4 for diverging the ion beam 4 outward merely act on the vicinity of the opposite sides in the X direction of the ribbon-shaped ion beam 4. Thus, the ion beam 4 may not be narrowed in the Y direction. The first and second magnets 50 and 52 may be disposed in the vicinity of the upstream side of the collimator 14 in place of being disposed in the vicinity of the downstream side of the collimator 14 as in the above exemplary embodiment. With such a configuration, it is possible to increase the amount of the ion beam 4 entering the collimator 14, and passing therethrough. Therefore, it becomes easy to enhance the transport efficiency of the ion beam 4. The first and second magnets 50 and 52 may be disposed in at least one of, or may be disposed in both of the vicinity of the downstream side and the vicinity of the upstream side of the collimator 14. When these are disposed on both sides, it is possible to increase the amount of the ion beam 4 passing through the collimator 14. In addition, it is possible to inhibit the divergence in the Y direction of the ion beam passed through the collimator 14. Therefore, it is possible to more enhance the transport efficiency of the ion beam 4 to the target 24. However the sites at which the first and second magnets 50 and 52 are disposed are not limited to the foregoing sites. These may be disposed anywhere so long as the sites are on the upstream side of the target 24. Even so, the following is possible: the ion beam 4 is narrowed in the Y direction, and the divergence due to the space charge effect of the ion beam 4, and the like is compensated. Thus, the transport efficiency of the ion beam 4 is enhanced. However, when the ion beam 4 in a ribbon-shape which has scanned in the X direction is irradiated onto the target 24 as with the example shown in FIG. 16, the magnets 50 and 52 are disposed on the downstream side of the scanner 12 for carrying out the scanning. When the ribbon-shaped ion beam 4 is generated from the ion source 2, and the ion beam 4 in a ribbon-shape without having been scanned in the X direction is irradiated onto the target 24, the scanner 12 is unnecessary, and hence there is no limitation as described above. When the first and second magnets 50 and 52 are disposed in the path for the ion beam 4 to be scanned in a fan shape in the X direction by the scanner 12 (see, FIG. 16) as with the vicinity of the upstream side of the collimator 14, both the magnets 50 and 52 are each preferably formed in the one bent in an arc shape, namely formed in the following one in an arc shape. In other words, both the magnets 50 and 52 are each in an arc shape protruding in the traveling direction of the ion beam 4 as with the embodiment shown in FIG. 8 or 9. They are each preferably formed in an arc shape so that the angle φ formed between the traveling direction of the ion beam 4 at each scanning position in the X direction and a straight line 62 connecting between a pair of magnetic poles (N pole and S pole) of each of the magnets 50 and 52 at the shortest distance is invariably substantially constant. Specifically, two (i.e., the inlet side and the outlet side of the ion beam 4) arc-like sides 50c and 52c are each configured to be a part of a circle centering on a point b, where b denotes a point away at a distance L6 in the X direction from a center point a in which a denotes the center point of scanning of the ion beam 4 by the scanner 12. The arc-like sides 50c and 52c are respectively substantially magnetic poles over the overall length thereof. When both the magnets 50 and 52 are each formed in the foregoing arc shaper the angle φ substantially becomes constant regardless of the scanning position of the ion beam 4. By the angle φ (to be exact, with the angle γ described by reference to FIG. 6 added), the magnetic field B generated by both the magnets 50 and 52 has a component (orthogonal component) BR orthogonal to the traveling direction of the ion beam 4. By the orthogonal component BR, the ion beam 4 receives inward Lorentz force F in the Y direction. As a result, the ion beam 4 may be narrowed in the Y direction. The angle φ increases with an increase in the distance L6. Further, the angle φ substantially becomes constant regardless of the scanning position of the ion beam 4. Therefore, the ion beam 4 may be narrowed uniformly in the Y direction over the entire region of the ion beam 4 to be scanned in a fan shape in the X direction. Example 2 in the table 1 corresponds to the embodiment shown in FIGS. 8 and 9. When a ribbon-shaped ion beam 4 is generated from the ion source 2 (see, FIG. 16), and the ion beam 4 in a ribbon-shape is irradiated onto the target 24 without having been scanned in the X direction, the first and second magnets 50 and 52 each in a substantially straight form described by reference to FIGS. 1 to 7 described above may be disposed in the path for the ion beam 4. With such a configuration, it is possible to uniformly narrow the ion beam 4 in the Y direction over the entire region of the X direction of the ion beam 4. The first and second magnets 50 and 52 each in a straight or arc shape as described above may be formed of an electromagnet in place of being formed of a permanent magnet as with the embodiment. The embodiment of the case in which the magnets 50 and 52 are formed of an electromagnet will be described mostly for the differences from the embodiment in which the first and second magnets 50 and 52 are each formed of a permanent magnet. An embodiment in which the straight first and second magnets 50 and 52 are formed of an electromagnet is shown in FIGS. 10 and 11. This corresponds to the embodiment shown in FIGS. 2 and 3. Both the magnets 50 and 52 respectively have iron cores 70 having the shapes/arrangement corresponding to those of the magnets 50 and 52 shown in FIGS. 1 to 6, and coils 72 wound in the longitudinal direction of the respective iron cores 70. The two (i.e., the inlet side and the outlet side of the ion beam 4) long side 70a sides of each iron core 70 are respectively substantially magnetic poles over the overall length thereof. Both the magnets 50 and 52 receive exciting currents I1 and I2 supplied from direct current sources 74 and 76, respectively, and generate magnetic fields of the same polarities as those of the embodiment shown in FIGS. 1 to 6. Therefore, by the same action as that of the embodiment shown in FIGS. 1 to 6, the ion beam may be narrowed in the Y direction. Further, the first and second magnets 50 and 52 are electromagnets. Therefore, it is easy to adjust the intensity of the magnetic field generated thereby. Accordingly, it is possible to control the degree to which the ion beam 4 is narrowed in the Y direction with ease. For example, by changing the intensity of the magnetic field to be generated according to the energy of the ion beam 4, the ion beam 4 may be narrowed similarly at any energy. Further, by changing the intensity of the magnetic field to be generated, it is also possible to change the converging state (e.g., focal length) in the Y direction of the ion beam 4. It is also possible to control the beam dimension dt, the divergence angle α, and the deflection angle θ described later. Further, it is also possible to generate a more intense magnetic field than with the permanent magnet, and to more strongly narrow the ion beam 4. The same also applies to the embodiment shown in FIG. 12. The exciting currents I1 and I2 may have mutually the same magnitude or may have different magnitudes. When these have the same magnitude, one direct current electric source may be shared by both the magnets 50 and 52. Alternatively, the following configuration may be adopted. One of, or both of the direct current power sources 74 and 76 are set to be bipolar power sources, so that the orientations of the exciting currents I1 and I2 may be reversed. The same also applies to the embodiment shown in FIG. 12. An embodiment in which the arc-like magnets 50 and 52 are each formed of an electromagnet is typified by the first magnet 50, which is shown in FIG. 12. The cross section is the same as with FIG. 11, and hence reference should be made thereto. This corresponds to the embodiment shown in FIGS. 8 and 9. Both the magnets 50 and 52 respectively have iron cores 70 having the shapes/arrangement corresponding to those of the magnets 50 and 52 shown in FIGS. 8 and 9, and coils 72 wound in the longitudinal direction of the respective iron cores. The two (i.e., the inlet side and the outlet side of the ion beam 4) arc-like side 70c sides of each iron core 70 are respectively substantially magnetic poles over the overall length thereof. The coils 72 each may be wound straight in the longitudinal direction of the iron cores 70. However, as with the example shown, each coil 72 is preferably wound in an arc along the arc-like side 70c. With such a configuration, it is possible to generate uniform magnetic fields over both the arc-like sides 70c, i.e., substantially the overall lengths of both the magnetic poles. Both the magnets 50 and 52 receive exciting currents I1 and I2 supplied from direct current sources 74 and 76, respectively, and generate magnetic fields of the same polarities as those of the embodiment shown in FIGS. 8 and 9. Therefore, by the same action as that of the embodiment shown in FIGS. 8 and 9, the ion beam may be narrowed in the Y direction. Below, a description will be given to the case where, when the first and second magnets 50 and 52 are electromagnets, the beam dimension dt in the Y direction of the ion beam 4, the divergence angle α, and the deflection angle θ are controlled by using them. By reference to FIG. 1, on the upstream side of and on the downstream side of the target 24, a fore-stage multipoint Faraday 42 and a post-stage multipoint Faraday, each including a plurality of detectors for measuring the beam current of the ion beam 4 arranged in parallel in the X direction are provided, respectively. As with the technique described in, for example, JP-A-2005-195417, both the multipoint Faradays 42 and 44, and a shutter to be driven in the Y direction in front thereof are used in combination. Thus, based on the beam dimensions df and db in the Y direction of the ion beam 4 at two sites in the traveling direction Z of the ion beam 4, the distance L3 between both the sites, and the distances L4 and L5 between both the sites and the target 24, the beam dimension dt in the Y direction of the ion beam 4 at the site of the target 24, and the divergence angle α in the Y direction of the ion beam 4 may be measured according to the following equations. Alternatively, the following configuration or the like is also acceptable. In place of disposing the shutter in front of the fore-stage multipoint Faraday 42, the fore-stage Faraday 42 is disposed, for example, in the vicinity of the downstream side of the mask 20. Thus, the fore-stage multipoint Faraday 42 is driven in the Y direction.dt=(L5/L3)df+(L4/L3)db, (where L3=L4+L5) [Mathematical Expression 1]α=tan−1{(db−df)/2L3} [Mathematical Expression 2] Then, the direct current power sources 74 and 76, and further the exciting currents I1 and I2 may be feed-back controlled based on the measured data of the beam dimension dt and the divergence angle α by means of a control unit not shown. For example, when the beam dimension dt in the Y direction of the ion beam 4 or the divergence angle α thereof is large, it is essential only that control is accordingly carried out so as to increase the absolute values (magnitudes) of the exciting currents I1 and I2. As a result, the ion beam 4 is more strongly narrowed in the Y direction by both the magnets 50 and 52. Therefore, the beam dimension dt and the divergence angle α may be decreased. The following is also possible. The divergence angle α at the site of the target 24 is made substantially 0. Thus, the ion beam 4 having high parallelism in the Y direction is made incident upon the target 24 for carrying out ion implantation. To both the magnets 50 and 52, the exciting currents I1 and I2 having the mutually same magnitude are supplied. Thus, both the magnets 50 and 52 generate magnetic fields with the mutually same intensity. In this case, when the incident ion beam 4 is tilted in the Y direction due to some cause as with, for example, the example shown in FIG. 13, the outgoing ion beam 4 also has a deflection angle θ in the Y direction. The deflection angle θ is an angle formed between the central orbit of the ion beam 4 and the symmetric surface 58 within the YZ plane. This may be corrected in the following manner. The exciting currents I1 and I2 having mutually different magnitudes are supplied to both the magnets 50 and 52, respectively. Thus, magnetic fields having mutually different intensities are generated by both the magnets 50 and 52. For example, when the incident ion beam 4 is tilted upward in the Y direction as with the example shown in FIG. 13, it is essential only that at least on of the following are carried out: the exciting current I1 to be supplied to the magnet 50 on the side on which the ion beam 4 is tilted is increased; and the exciting current I2 to be supplied to the magnet 52 on the opposite side is decreased. As a result, the magnetic field generated by the magnet 50 on the side on which the ion beam 4 is tilted becomes more intense. Accordingly, the downward Lorentz force F becomes larger, which may reduce the deviation angle θ. The deviation angle θ may be substantially set to be 0 degree. When the deviation angle θ is reverse from the foregoing, it is essential only that the foregoing is reversed. By the use of the fore-stage multipoint Faraday 42, the post-stage multi-point Faraday 44, and the like, as with, for example, the technique described in JP-A-2005-195417, the deviation angle θ may be measured based on the central positions yf and yb in the Y direction of the ion beam 4 at two sites in the traveling direction of the ion beam 4, and the distance L3 between both the sites according to the following equation.θ=tan−1{(yb−yf)/L3} [Mathematical Expression 3] Then, based on the measured data of the deviation angle θ, the direct current power sources 74 and 76, and further the exciting currents I1 and I2 may be feed-back controlled by a control unit not shown so that the deviation angle becomes small (e.g., substantially 0 degree). While description has been made in connection with exemplary embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modification may be made therein without departing from the present invention. It is aimed, therefore, to cover in the appended claims all such changes and modifications falling within the true spirit and scope of the present invention.
048872830	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray mask for use in X-ray lithography in which a pattern is transferred to a substrate by the radiation of X-rays, and an exposure method employing the same. 2. Description of the Related Art Generally, X-ray lithography technology involves a process of transferring very fine patterns of about 0.3 .mu.m or less to a substrate. FIG. 1 is a plan view of a conventional X-ray mask employed to transfer the minute patterns to a substrate, and FIGS. 2 and 3 are sections taken along the line II--II of FIG. 1, respectively showing a state in which a supporting frame to be described later has not yet been etched and a state in which it has already been etched. An X-ray mask 2 shown in these figures has a membrane 4 made of a material, such as silicon nitride, which is highly transparent to X-rays, a mask pattern 6 made of a material, such as tungsten, which absorbs X-rays, the mask pattern 6 being formed on the upper surface of the membrane 4, a supporting frame 8 of Si formed on the lower surface of the membrane 4 for mechanically supporting the membrane 4, and an etching mask 10 provided on the lower surface of the supporting frame 8 to be used as a mask during etching of the supporting frame 8. In the thus-arranged conventional X-ray mask structure, the membrane 4 and the mask pattern 6 are sequentially formed as very thin films having a thickness of several .mu.m by vacuum deposition, sputtering, or the CVD method. In consequence, when the central portion of the disk-shaped supporting frame 8 is etched after the membrane 4 and the mask pattern 6 have been formed on the upper surface of the supporting frame 8 and after the etching mask 10 has been formed on the lower surface thereof, as shown in FIG. 2, the thin membrane 4 is deformed due to the reduction in the internal stress in the membrane 4 and in the mask pattern 6. As shown in FIG. 3, the mask pattern 6 formed on the upper surface of the membrane 4 is shifted from its predetermined correct position, thereby causing a distortion of the pattern. Further, the supporting frame 8, the membrane 4, and the mask pattern 6 may be thermally distorted, respectively, because of changes in an ambient temperature of the location where the X-ray mask 2 is placed, which may also lead to pattern distortion. FIG. 4 shows a mask pattern 6 in which such a pattern distortion has been generated. In FIG. 4, the outline of the mask pattern 6 as viewed from above is schematically represented by the square, which is divided into 25 pattern portions. The pattern portions A.sub.1, A.sub.2, A.sub.3 shown by the broken line represent those located at their correct positions, whereas the pattern portions B.sub.1, B.sub.2, B.sub.3 . . . shown by the solid line are those which have been displaced from their correct positions by pattern distortion. In particular, the hatched areas represent the mask pattern 6, which has been shifted from its correct position by pattern distortion. If an X-ray mask 2 with the mask pattern 6 which has been displaced from its correct position is employed to transfer the circuit patterns to the substrate, the accuracy with which the circuit patterns are aligned with the substrate reduced to a great extent, and this makes formation of the very fine patterns on the substrate with a high degree of accuracy difficult. In order to obviate this problem, Japanese Patent Laid-Open No. 62-122216 discloses an X-ray mask in which electrostriction or magnetostriction elements bonded to a supporting frame by an adhesive are deformed so as to correct the distortion in the mask. However, this X-ray mask structure suffers from a problem in that the adhesive is readily removed due to repeated vibrations of these electrostriction or magnetostriction elements. This in turn causes removal of the elements from the supporting frame, which leads to a reduction in the reliability of the mechanical structure of the mask. The X-ray mask also has a disadvantage in that it takes much time and trouble for the elements to be bonded to the supporting frame. SUMMARY OF THE INVENTION An object of the present invention is directed to obviating the aforementioned problems of the conventional X-ray mask by providing an X-ray mask which enables a mask pattern shifted from the correct position to be readily returned to its correct position, which is mechanically reliable, and which can be easily manufactured, as well as an exposure method employing such an X-ray mask. To this end, the present invention provides an X-ray mask which comprises a membrane formed of a material which transmits X-rays, a mask pattern formed on the surface of the membrane, the mask pattern being made of an X-ray absorbing material, and a supporting frame formed of a material which is mechanically deformed by the application of an external signal, the supporting frame serving to support the membrane. Further, the present invention provides an exposure method which comprises three steps. The first step is disposing an X-ray mask above a substrate in alignment therewith. The X-ray mask has a membrane formed of a material which transmits X-rays, a mask pattern formed on the surface of the membrane, the mask pattern being made of an X-ray absorbing material, and a supporting frame formed of a material which is mechanically deformed by the application of an external signal, the supporting frame supporting the membrane The second step is correcting the distortion caused in the mask pattern of the mask by the application of the external signal to the supporting frame of the mask. And the third step is irradiating the substrate with X-rays through the mask so as to transfer the mask pattern of the mask to the substrate.
039473228	description	DETAILED DESCRIPTION OF THE INVENTION The reactor pressure vessel 1 is substantially cylindrical with its axis vertical and within its core barrel 2, the reactor core (not shown) is positioned. The vessel has a top closure 3 normally bolted closed. An intercept ring 4 engages the periphery of the cover 3 and is held down by hooks 5 which pivot on hinges 6 secured to the upper portion of the cylindrical concrete containment 8 forming the pit in which the pressure vessel is positioned. The intercept ring and hook arrangement is disclosed and claimed by the Dorner et al U.S. application Ser. No. 315,932, filed Dec. 18, 1972. The bottom of the vessel 1 has a shoulder 9 at the periphery of its spherical bottom 10, and which is supported by the support arrangement 12 of the invention. Two identical steam generators 14 and 14' are connected with the upper portion of the vessel 1 by dual coolant pipes 15 and 15'. These pipes are in each instance divided by a horizontal partition so that the pipes provide coolant loops, respectively comprising hot legs 16 and 16' and cold legs 17 and 17'. The steam generators are of the type integrated or structurally combined with the main coolant pumps for the loops, the pumps being respectively shown at 20 and 20' driven by electric motors 21 and 21', the pumps being contained by concrete cylinders 22 and 22'. The substantially cylindrical steam generators extend upwardly from these motors and pumps within concrete containments 23 and 23' vertically held in compression by tie rods 24 and 24'. The arrangement 12 is shown on an enlarged scale by FIG. 2. Here, the short cylinder and cylindrical ring 26 is shown as being integral with the shoulder 9 of the vessel 1, although this ring 26 could be fixed to the periphery of the spherical bottom 10 of the vessel, by welding. This cylindrical ring 26 has substantially the same diameter as the vessel's bottom and is concentric with the axis of the vessel and its bottom. The bottom end of this ring 26 provides the inverted frusto-conical surface 27 which faces downwardly and is slidably supported by the upwardly facing upright frusto-conical surface 28 provided by a short cylinder or cylindrical ring 29 which is fixed as by welding to a flat steel base ring 30 resting on a shoulder 30a formed in the bottom of the concrete reactor pit and, therefore, capable of supporting the weight of the reactor vessel. In operation, if the diameter of the reactor vessel thermally increases, the surface 27 slides downwardly on the surface 28, and since at the same time the reactor vessel is elongated vertically, compensation for the vertical elongation is provided. The top portion of the vessel remains substantially unchanged as to its vertical position, vertical displacement of the pipes 15 and 15' being, therefore, avoided and eliminating vertical stressing. Furthermore, the pressure vessel, intercept ring 4 and hooks 5 may be designed so that when the vessel is at its normal operating temperature, the hooks 5 normally engage the intercept rings 4, thus placing the pressure vessel in compression between the hooks and its lower support points 9. The degree of this compression can be accurately calculated because via the present invention the vessel bottom is supported at differing heights which are dependent on the thermal expansion radially of the pressure vessel and which is, in turn, related to the vessel's vertical thermal expansion and contraction. As shown by FIG. 2, the supporting ring 29 may be made as a plurality of circumferentially interspaced segments 29b, this permitting air cooling of the lower cylindrical ring 29 and, in addition, reducing the risk that it might possibly change in diameter due to thermal expansion and contraction. The segments 29b should be strong and rigid and free from any spring action. The two surfaces 27 and 28 should retain their designed angularities at all times. Although the coolant pipes are relieved from vertical motion, they are still moved horizontally by the radial expansion and contraction of the vessel 1. Therefore, the steam generators 14 and 14' are supported on horizontally displaceable bearings 31 and 31' positioned as close as possible to the coolant pipes. This allows the steam generators to move in the axial or longitudinal directions of the coolant pipes and reduces stressing such as would occur if the steam generators were immovable horizontally. The pipe lines are provided with externally projecting shoulders 32 and 32' which are retained in annular recesses formed in the concrete construction 8 which has, of course, holes through which the coolant pipes extend to the steam generator. These recesses are formed around these holes. These recesses should provide enough space in the axial direction of the coolant pipes to permit their motion due to radial expansion and contraction of the vessel. However, the recesses should be proportioned so that in the event of a break in either coolant pipe or its connections between the shoulders and the vessel, the jet reaction will not result in excessive horizontal displacement of the steam generator having the pipe involved by the accident. Under normal conditions, the shoulders and their recesses serve to generally center the components of the installation.
047598972	abstract	An electromechanical measurement system for acquiring dimensional data from a nuclear fuel assembly includes an underwater measurement assembly, support means for mounting same on the edge of a spent fuel pool, and a control and data acquisition and processing unit. The underwater measurement assembly includes an elongated strongback disposable vertically along a pool wall, adjustment mechanism on a support assembly permitting accurate positioning of the strongback. A support plate carries hydraulic clamps for clamping the top nozzle of a fuel assembly while it is supported from overhead, a clamp carried by the lower end of the strongback being engageable with the bottom nozzle for holding the fuel assembly in a selected orientation with the faces of the top nozzle vertical. A chain/motor driven carriage moves vertically and carries a video camera and a plurality of measurement gauges movable in a horizontal plane for engaging each nozzle and grid of the fuel assembly at a plurality of points and measuring the distances of those points from fixed reference planes. A program-controlled computer calculates from the measurements the location of the center of each nozzle and grid in the measurement plane and processes this data to derive bow, twist and tilt measurements for the fuel assembly.
06058159&	abstract	A scanner apparatus comprises a tunnel housing having a top, two sides and entrance and exit openings; a bed assembly having a top and side portions wherein the side portions of the bed assembly are substantially fixed to the side portions of the tunnel housing to form a substantially enclosed area; an isolating device located at each of the entrance and the exit of the tunnel housing; a conveyor device for moving an object though the tunnel housing; and an analysis device for analyzing objects within the substantially enclosed area in the tunnel housing. The scanner apparatus has an essentially frameless structure which enhances its capability for scanning tall, wide items.
041561465	claims	1. A structure for replacably and sealingly mounting an operating member such as a glove, bag, and filter in a wall port of a radiation shielding box, comprising: a cylindrical fixed port member sealingly secured to a wall port of said shielding box and having a threaded portion on its inner periphery, a cylindrical replacement port member sized to fit within said fixed port member and having an operating member secured thereto, and an elastic member disposed on said replacement port member and having a threaded portion on its inner periphery corresponding to said threaded portion on the fixed port member and adapted to be threadingly inserted in a compressed and deformed stated between said fixed port member and said replacement port member. 2. A structure as claimed in claim 1, wherein said elastic member is fixedly provided on said replacement port member. 3. A structure as claimed in claim 2, wherein said replacement port member is made up of a first cylindrical portion larger in outside diameter and a second cylindrical portion smaller in outside diamter, said elastic member is fixedly provided on the outer wall of said first cylindrical portion, and said operating member is connected to said second cylindrical portion. 4. A structure as claimed in claim 3, wherein the inside diameter of said first cylindrical portion on which said elastic member is fixedly provided is larger than the outside diameter of said second cylindrical portion having said operating member. 5. A structure as claimed in claim 4, wherein the axial length of said first cylindrical portion is approximately equal to the axial length of said second cylindrical portion. 6. A structure as claimed in claim 5, wherein said first cylindrical portion is provided with a pin and a pin hole on its respective end faces. 7. A structure as claimed in claim 6, wherein said operating member is mounted on the outer periphery of said second cylindrical portion. 8. A structure as claimed in claim 6, wherein said operating member is provided on the inside of said second cylindrical portion. 9. A structure as claimed in claim 6, wherein said operating member is provided on the inside of said second cylindrical portion and is made of the same material as that of said second cylindrical portion. 10. A structure as claimed in claim 2, wherein said replacement port member and said operating member are integrally formed. 11. A structure as claimed in claim 2, wherein said fixed port member has a hole therein communicating with the outside, said replacement port member is composed of a cylindrical body having a reduced outside diameter at its central portion, an operating member constituting a filter is provided inside one end portion of said cylindrical body, an operating member constituting a sealing member is integrally provided inside the other end portion of said cylindrical body, and said central portion communicates with said hole. 12. A port section structure, comprising: a cylindrical fixed port member sealingly secured to a wall of a radiation shielding box and having a threaded portion on its inner periphery, a cylindrical replacement port member sized to fit within said fixed port member and having an operating member secured thereto, an elastic member disposed on said replacement port member and having a threaded portion on its outer periphery corresponding to said threaded portion on the fixed port member and adapted to be threadingly inserted in a compressed and deformed state between said fixed port member and said replacement port member, and a concave or convex section provided in at least one end portion of said replacement port member and engageble with a convex or concave portion of a like configured replacement port member. 13. A port section structure as claimed in claim 12, wherein said concave and convex sections comprise a pin and a pin hole, respectively. 14. A structure as claimed in claim 10, wherein a concave or a convex section is provided in at least one end face of said replacement port member and is adapted to be engaged with a convex or a concave section, respectively, provided in another replacement port member which can be screwed into said fixed port member. 15. A structure as claimed in claim 10, wherein said operating member comprises a bottom section of said cylindrical replacement port member.
	claims	1. A charged-particle beam writing apparatus for writing a predetermined pattern on a sample placed on a stage with a charged-particle beam, the apparatus comprising:a height measuring unit that measures a height of the sample by irradiating the sample with light and receiving light reflected from the sample; anda control unit that receives either height data acquired from a height data map prepared based on values measured by the height measuring unit before writing or height data measured by the height measuring unit during writing to adjust an irradiation position of the charged-particle beam on the sample. 2. The charged-particle beam writing apparatus according to claim 1, wherein the height measuring unit measures the height of the sample in real time concurrently with writing. 3. The charged-particle beam writing apparatus according to claim 1, wherein when an amount of the reflected light is equal to or larger than a threshold value, the control unit receives height data measured by the height measuring unit during writing, and when the amount of the reflected light is less than the threshold value, the control unit receives height data acquired from the height data map. 4. The charged-particle beam writing apparatus according to claim 1, wherein the control unit receives height data acquired from the height data map as height data of coordinates within a predetermined region. 5. The charged-particle beam writing apparatus according to claim 4, wherein the apparatus comprising:a support mechanism that is provided so as to surround the sample placed on the stage,a substrate cover that is provided on the support mechanism,wherein the substrate cover is grounded by connecting the support mechanism to ground,wherein the predetermined region is a region where the irradiated light is blocked by the substrate cover. 6. The charged-particle beam writing apparatus according to claim 1, wherein when a difference between height data measured by the height measuring unit during writing and height data measured previously is equal to or less than a threshold value, the control unit receives the height data measured by the height measuring unit during writing, and when the difference is larger than the threshold value, the control unit receives height data acquired from the height data map. 7. A charged-particle beam writing apparatus for writing a predetermined pattern on a sample placed on a stage with a charged-particle beam, the apparatus comprising:a height measuring unit that measures a height of the sample by irradiating the sample with light and receiving light reflected from the sample; anda control unit that receives a value obtained by adding an offset value, obtained from a difference between height data acquired from a height data map prepared based on values measured by the height measuring unit before writing and height data measured by the height measuring unit during writing, to the height data map to adjust an irradiation position of the charged-particle beam on the sample. 8. The charged-particle beam writing apparatus according to claim 7, wherein the height data map contains height data including measured values, and height data including values determined from the measured values by interpolation. 9. The charged-particle beam writing apparatus according to claim 7, wherein the offset value is updated only when the amount of light reflected from the surface of the sample is equal to or larger than a threshold value. 10. A charged-particle beam writing method for writing a predetermined pattern on a sample placed on a stage with a charged-particle beam, the method comprising:measuring a height of the sample by irradiating the sample with light and receiving light reflected from the sample; andusing either height data acquired from a height data map prepared based on values measured before writing, or height data measured during writing to adjust an irradiation position of the charged-particle beam on the sample. 11. The charged-particle beam writing method according to claim 10, wherein the measurement of height of the sample is performed in real time concurrently with writing. 12. The charged-particle beam writing method according to claim 10, wherein when an amount of the reflected light is equal to or larger than a threshold value, using height data measured during writing, and when the amount of the reflected light is less than the threshold value, using height data acquired from the height data map. 13. The charged-particle beam writing method according to claim 10, wherein height data acquired from the height data map is received as height data of coordinates within a predetermined region. 14. The charged-particle beam writing method according to claim 13, a support mechanism is provided so as to surround a mask placed on a stage, andproviding a substrate cover on the support mechanism,wherein the substrate cover is grounded by connecting the support mechanism to ground, andwherein the predetermined region is a region where the irradiated light is blocked by the substrate cover. 15. The charged-particle beam writing method according to claim 10, wherein the height data measured during writing is used when a difference between height data measured during writing, and height data measured previously is equal to or less than a threshold value, and using height data acquired from the height data map when the difference is larger than the threshold value. 16. A charged-particle beam writing method for writing a predetermined pattern on a sample placed on a stage with a charged-particle beam, the method comprising:measuring a height of the sample by irradiating the sample with light and receiving light reflected from the sample; andusing a value obtained by adding an offset value, obtained from a difference between height data acquired from a height data map prepared based on values measured before writing, and height data measured during writing, to the height data map to adjust an irradiation position of the charged-particle beam on the sample. 17. The charged-particle beam writing method according to claim 16, wherein the height data map contains height data including measured values and height data including values determined from the measured values by interpolation. 18. The charged-particle beam writing method according to claim 16, wherein the offset value is updated only when the amount of light reflected from the surface of the sample is equal to or larger than a threshold value.
	description	The following relates to the nuclear reactor arts, electrical power generation arts, nuclear reactor control arts, nuclear electrical power generation control arts, and related arts. A pressurized water reactor (PWR) employs a pressure vessel containing subcooled water as the primary coolant. Hot, subcooled water is circulated between the reactor core and one or more steam generators to transfer energy from the reactor core to the steam generator. In a conventional design, the steam generators are separate elements and the primary coolant is coupled between the pressure vessel and the steam generator via suitable high pressure fluid conduits. In an integral PWR design, the one or more steam generators are located inside the pressure vessel. An electrically heated pressurizer is used to control the reactor coolant system pressure. The PWR contains a steam region that controls the pressure and changes its volume to accommodate changes in liquid volume in the pressure vessel and coolant loop(s). A combination of heater operation and subcooled water spray in the steam region is used to increase or decrease the amount of steam in a steam “bubble” to maintain the pressure vessel at a constant pressure. It is desired to suppress or prevent over-pressurization of the PWR during operating transients and to preserve the subcooled margin of the reactor coolant inside the reactor core to ensure adequate heat transfer. In a typical PWR control paradigm, the water level in the pressurizer (that is, the pressurizer water level) serves as an indication of reactor coolant inventory. If the pressurizer water level drops below a predetermined level, additional makeup water is pumped into the reactor coolant system (RCS). On the other hand, if the pressurizer water level rises above another preset limit, water is letdown from the RCS. Reactor power control in a PWR is typically a complex process in which numerous control variables (for example, steam flow, feedwater flow, “gray” control rod positioning) are concurrently adjusted to maintain the desired operational state and to control transient behavior. These adjustments are constrained by the requirement to keep the pressurizer level within the preset limits so as to avoid overpressurization or underpressurization. To provide additional PWR reactivity control, it is known to add an effective amount of a soluble neutron poison, typically boron in the form of boric acid, to the primary coolant. The soluble boron poison reduces the magnitude of the moderator temperature coefficient. Thus, the boron concentration in the primary coolant provides yet another “adjustment knob” for controlling reactor power output. In some PWR's, the concentration of boric acid is varied over the fuel cycle to offset changes in reactor core reactivity as the nuclear fuel is consumed. The boron concentration is selected such that the moderator temperature coefficient and moderator void coefficient both remain negative. The magnitude of these coefficients is substantially reduced by the addition of the boron poison; however as a result, changes in water temperature inside the reactor have reduced impact on core power, thus simplifying control. With reference to FIG. 1, a typical relationship between the reactor coolant temperature (abscissa) and reactor power (ordinate) is shown. FIG. 1 plots the hot leg temperature (Thot) relationship, the cold leg temperature (Tcold) relationship, and the average temperature (Tave) relationship. The integrated control system simultaneously controls steam flow, feedwater flow, and the control rods in the reactor to alter core power output for transients. The soluble boron poison is typically reduced as the fuel burns to minimize the rod insertion into the reactor core. FIG. 1 plots the programmed reactor coolant temperatures inside the reactor pressure vessel using this approach. As power level increases, reactor inlet temperature drops and reactor outlet temperature rises to maintain a constant average temperature in the core and steam generator. The constant average temperature minimizes any volume changes in the reactor coolant as the power level changes. As a result, the pressurizer water level between the heated water and steam regions in the pressurizer remains essentially constant during changes in power level. Any deviation of the pressurizer water level that does exceed the upper or lower preset level limit causes water to be letdown or makeup water added to the RCS, in order to maintain the constant pressurizer water level setpoint. However, such corrective events are not common during normal operation, because the moderator temperature coefficient and moderator void coefficient are both small, and the control system maintains a nearly constant average water temperature. Disclosed herein are further improvements that provide reduced cost, simplified manufacturing, and other benefits that will become apparent to the skilled artisan upon reading the following. In one aspect of the disclosure, an apparatus comprises: an apparatus comprises a circuit or digital processor configured to adjust reactor power generated by a pressurized water reactor (PWR) by: (i) changing an average primary coolant temperature of primary coolant of the PWR, and (ii) adjusting a pressurizer water level setpoint of the PWR upward if the change (i) is to a higher average primary coolant temperature and downward if the change (i) is to a lower average primary coolant temperature. In another aspect of the disclosure, a pressurized water reactor (PWR) comprises: a pressure vessel; a reactor core disposed in the pressure vessel; an integral or external pressurizer; primary coolant disposed in the pressure vessel and heated by operation of the reactor core, the primary coolant not including a soluble boron poison in the primary coolant; and an apparatus as set forth in the immediately preceding paragraph. In another aspect of the disclosure, a method comprises: performing a pressurized water reactor (PWR) power adjustment; and adjusting a pressurizer water level setpoint based on a predicted direction and magnitude of change of a pressurizer water level of the PWR predicted to result from the performing the PWR power adjustment. In another aspect of the disclosure, a pressurized water reactor (PWR) comprises: a pressure vessel; a reactor core disposed in the pressure vessel; an integral or external pressurizer; primary coolant disposed in the pressure vessel and heated by operation of the reactor core, the primary coolant not including a soluble boron poison in the primary coolant; and a controller configured to perform a method as set forth the immediately preceding paragraph. In another aspect of the disclosure, a pressurized water reactor (PWR) comprises: a pressure vessel; a reactor core disposed in the pressure vessel; an integral or external pressurizer; primary coolant disposed in the pressure vessel and heated by operation of the reactor core; an integral steam generator disposed in the pressure vessel and configured to convert secondary coolant in the form of feedwater into steam by heat transfer from the primary coolant heated by operation of the reactor core to secondary coolant in the steam generator; and a controller configured to perform a PWR control method including the operations of (i) adjusting one or more parameters of the PWR and (ii) adjusting a pressurizer water level setpoint based on a predicted direction and magnitude of change of a pressurizer water level of the PWR predicted to result from the adjusting (i). As described herein with reference to FIG. 1, existing reactor control systems advantageously benefit from the suppression of pressurizer water level control transients due to reduced moderator temperature coefficient and moderator void coefficient values provided by the soluble boron poison. This effectively removes (or nearly removes) pressurizer water level as a controlled parameter during reactor power transient events. However, the inclusion of boric acid or another soluble poison in the primary coolant has substantial disadvantages. The boric acid can generate undesirable chemical reactions during reactor operation at elevated temperatures. Boric acid also presents environmental concerns and complicates waste disposal. Still further, using boric acid as a safety control, e.g. to suppress reactivity, can introduce safety concerns. For at least these reasons, there is interest in operating PWR nuclear power systems without using boric acid, and more generally without using a soluble neutron poison. However, a PWR operating without a soluble neutron poison has moderator temperature and void coefficients that are still negative, but with substantially larger absolute values over the fuel cycle as compared with a PWR operating with borated primary coolant. These larger (absolute) moderator temperature and void coefficients lead to substantial volume changes in the primary reactor coolant as the power level changes, which if left uncontrolled would lead to substantial changes in pressurizer water level during power transients. As a consequence, the PWR control system takes a more active role in maintaining the pressurizer water level setpoint, by performing coolant letdown to avoid overpressurization or coolant makeup to avoid underpressurization. These frequent pressurizer water level letdown/makeup control events further complicate the already-complex PWR reactor control, and generate additional radioactive waste in the form of additional contaminated primary coolant. It is recognized herein, however, that by employing a different control paradigm that allows constrained changes in the pressurizer water level during reactor power level changes, these changes can actually simplify reactor control during power transients. In effect, the disclosed approach for controlling reactor core power output actually relies on the larger (absolute) reactivity coefficients to simplify reactor control. With reference to FIG. 2, the disclosed control approaches are based on the observation made herein that the change of reactivity is in the “correct” direction to assist in reactor control. For example, consider a reactor operating at a steady state, into which a step increase in feedwater flow is introduced. The increased feedwater flow does not strongly impact the hot leg temperature (Thot), but does cause a substantial reduction in the cold leg temperature (Tcold) and consequently causes a substantial reduction in the average temperature (Tave). Because of the large negative moderator temperature and void coefficients, the reduced temperature of the primary coolant substantially increases the reactor core reactivity. In physical terms, the reduced temperature increases the water density which makes the denser water a more efficient neutron moderator which in turn increases the thermal neutron population and increases the reactivity. However, the reduction in water temperature also produces a concomitant reduction in the pressurizer water level in the absence of any pressurizer water level correction. Conventionally, the reduction in pressurizer water level would be detected as incipient low water inventory (a potential safety issue), and the pressurizer level control system would add makeup water to compensate. In the event of reduced feedwater flow, the sequence is reversed. The reduced feedwater flow increases the cold leg temperature (Tcold) and hence increases the average temperature (Tave) which in turn substantially reduces core reactivity due to the large negative moderator temperature and void coefficients while concurrently increasing the pressurizer water level. This increase would conventionally be detected as incipient excess water inventory (again, a potential safety issue), and the pressurizer level control system would letdown primary reactor coolant to compensate. The effect on reactivity of the water makeup or letdown event performed to maintain the pressurizer level setpoint is complex, since it can affect primary coolant temperature, pressure, and flow. Control therefore would entail complex modeling of the entire system including all these interactions. In all such cases, the control events would include undesirable water makeup or letdown events in order to maintain the pressurizer level setpoint so as to avoid overpressurization or underpressurization during load changes. The disclosed PWR control approaches are based on recognition that the pressurizer water level change resulting from a change in feedwater flow rate is not an indication of incipient overpressurization or underpressurization implicating a safety concern—rather, these pressurizer water level changes are a natural consequence of the change in feedwater flow rate, and moreover, the accompanying change in reactivity is advantageous for reactor control. The disclosed PWR control approaches allow for this natural change in pressurizer water level by relating the pressurizer water level setpoint with the feedwater flow rate. With continuing reference to FIG. 2, a suitable control process is as follows. The reactor primary coolant outlet temperature (that is, the primary coolant output from the reactor core, which is the hot leg temperature, Thot) is held to a constant value and as the reactor inlet temperature (that is, the cold leg temperature, Tcold, corresponding with steam generator outlet temperature) drops. This results in a decrease in the average temperature (Tave), which in turn leads to an increase in reactor core power output. Thus, instead of relying on a complex integrated control system to control the average reactor temperature, the PWR can be controlled by the feedwater control valve. Increasing feedwater flow will increase energy removal through the steam generator, causing reactor coolant temperature leaving the steam generator to decrease. The reduced reactor coolant temperature decreases average coolant temperature in the reactor core thus causing the reactor core fission rate to increase and produce more power due to the negative coolant temperature coefficient. A natural consequence of this approach is a change in reactor coolant volume as a function of power, due to changes in the cold leg temperature. The impact on the volume of water in the reactor coolant system (RCS) is as follows. When power increases due to a decrease in the steam generator outlet temperature and core inlet temperature, the average density of the reactor coolant increases. (This is because the colder primary coolant water is more dense). This increased average primary coolant density reduces the volume of coolant in the pressurizer causing the pressurizer coolant level to drop. It is recognized herein that this water level decrease is expected, and the control system accommodates this expected decrease in water level by lowering the pressurizer water level setpoint. Thus, as the power level (or, equivalently in this control paradigm, the feedwater flow rate) increases, the nominal pressurizer water level setpoint is decreased by the control system. The actual pressurizer level control parameters are an upper and lower limit, which in this approach are not preset values but rather are upper and lower limits that track with the change in water level setpoint so that the allowable band or range for the pressurizer water level moves with the setpoint (which, in turn, moves with the power level or feedwater flow rate). This eliminates (or at least reduces) the likelihood of a makeup when the power level increases or letdown flow when the core power is decreased. The control operations can thus be summarized as follows. To increase the power output, the feedwater flow rate is increased and concurrently the pressurizer water level setpoint is decreased. On the other hand, to decrease the power output, the feedwater flow rate is decreased and concurrently the pressurizer water level setpoint is increased. Increasing or decreasing feedwater flow rate is a straightforward procedure, as it merely entails adjusting the feedwater inlet valve setting. Accordingly, the foregoing PWR control approach is readily implemented. However, it will be recognized that another way the control approach can be implemented is to maintain a constant feedwater flow rate, and instead adjust the inlet feedwater temperature. In this case, a reduction in inlet feedwater temperature produces a reduction in the primary coolant temperature resulting in increased core reactivity and hence increased core output, with concomitant reduction in the pressurizer water level. Conversely, increasing inlet feedwater temperature produces an increase in the primary coolant temperature resulting in reduced core reactivity and hence reduced core output, with concomitant increase in the pressurizer water level. In this alternative approach, to increase the power output the inlet feedwater temperature is decreased and concurrently the pressurizer water level setpoint is also decreased. On the other hand, to increase the power output, the inlet feedwater temperature is increased and concurrently the pressurizer water level setpoint is also increased. Table 1 summarizes the PWR control operations. In this table: ΔTave is the direction of change of the average primary coolant temperature; Δ[Nthermal] is the direction of the change in the thermal neutron population; ΔPreactor is the direction of change in the reactor power output (or, equivalently, in the reactivity of the reactor); ΔVprimary is the direction of change in the volume of primary coolant in the reactor coolant system (RCS); and “Setpoint” is appropriate direction of adjustment of the pressurizer water level setpoint. TABLE 1Summary of PWR control operationsReactor poweradjustmentΔTaveΔ[Nthermal]ΔPreactorΔVprimarySetpointIncrease feed-DownUpUpDownDownwater flow rateDecrease feed-UpDownDownUpUpwater flow rateRaise inlet feed-UpDownDownUpUpwater temperatureLower inlet feed-DownUpUpDownDownwater temperature In considering the control operations set forth in Table 1, it will be appreciated that the feedwater flow rate and inlet feedwater temperature adjustments can be combined. For example, to raise the reactor power it is contemplated to raise the feedwater flow rate and also lower the inlet feedwater temperature. Both operations raise the reactor reactivity (ΔPreactor is adjusted upward) and both operations also decrease the primary coolant volume (ΔVprimary is downward)—accordingly, in addition to both raising the feedwater flow rate and also lowering the inlet feedwater temperature, the pressurizer water level setpoint is suitably decreased. Conversely, to lower the reactor power it is contemplated to lower the feedwater flow rate and also raise the inlet feedwater temperature, and the pressurizer water level setpoint is also suitably increased. More generally, it will be noticed that operations which increase the reactor power also decrease the primary coolant volume (so that the pressurizer water level setpoint should be decreased); whereas, operations which decrease the reactor power also increase the primary coolant volume (so that the pressurizer water level setpoint should be increased). An illustrative PWR employing an embodiment of the disclosed reactor control is next set forth. With reference to FIG. 3, a perspective sectional view an illustrative pressurized water nuclear reactor (PWR) including an integral steam generator is shown. A nuclear reactor core 10 is disposed inside a generally cylindrical pressure vessel 12, which contains primary coolant, which in the illustrative case of a light water reactor is water (H2O) which does not contain soluble boron (e.g., dissolved boric acid). Typically, the primary coolant does not include or contain any soluble neutron poison—however, it is contemplated to employ boric acid or another soluble neutron poison of a type and/or at a concentration for which the primary coolant retains substantial (negative) values for the moderator temperature coefficient and moderator void coefficient. Although light water (H2O) is preferred as the primary coolant, it is also contemplated to employ another primary coolant having substantial (negative) values for the moderator temperature and void coefficients, such as heavy water (D2O). The illustrative PWR includes an integral pressurizer 14 located at the top of the pressure vessel 12. The integral pressurizer 14 comprises a volume containing primary coolant residing in a lower portion and a steam bubble 16 in the upper portion of the volume, with a pressurizer water level 18 delineating between the steam bubble 16 and the water. A water level sensor (not shown) disposed in the pressure vessel 12 generates a measurement signal indicative of the pressurizer water level 18 which is received by a water level monitor 20. The diagrammatically illustrated water level monitor 20 is external to the pressure vessel 12; however, it is also contemplated for this monitor to be internal to the pressure vessel, for example embodied as a combined water level sensor/monitor. Moreover, in some embodiments the water level sensor may simply be an optical fiber passing through a pressure vessel penetration to optically observe the pressurizer water level 18, or a sensor external to the pressure vessel may monitor the water level by detecting an external characteristic such as a magnetoelectric characteristic. The water level monitor 20 generates a measured pressurizer water level value 22. The integral pressurizer 14 also includes suitable controls 24 (diagrammatically indicated in FIG. 3) for adjusting the pressure, such as one or more heaters for heating the steam in the steam bubble 16, or a subcooled water sprayer for cooling the steam bubble 16. The illustrative pressurizer 14 is an integral pressurizer in which heaters and water sprayers operate directly on the steam bubble 16. However, it is also contemplated to employ an external pressurizer instead of the illustrative integral pressurizer 14. In this alternative design, the steam bubble 16 is in fluid communication via a suitable pressure vessel penetration with an external volume (that is, external to the pressure vessel 12). Heaters or other control elements operate on the external volume to adjust its pressure, and the pressure adjustments are communicated to the steam bubble 16 via fluid communication with the external volume. In such alternative embodiments employing an external pressurizer, the water level 18 delineating the steam bubble 16 is still referred to herein as the pressurizer water level 18. Reactor coolant system (RCS) makeup/letdown valving 26 are configured to enable makeup water to be added to the RCS in the event of underpressurization, and to allow primary coolant to be let down in the event of overpressurization. Other valving and/or components (not shown) may also be provided for regulating the RCS. For example, although a high concentration of boric acid is not employed as a neutron poison in the primary coolant during normal operation, it is contemplated to provide a boric acid or other neutron poison reservoir arranged for rapid delivery into the RCS as an emergency measure, that is, to rapidly shut down core reactivity in the event of a loss of coolant accident (LOCA) or other abnormal event. Reactor control is provided by a control rod drive mechanism (CRDM) 30 that is configured to controllably insert and withdraw neutron-absorbing control rods into and out of the nuclear reactor core 10. The CRDM 30 may be divided into multiple units, each controlling one or more control rods, in order to provide redundancy or other benefits. The illustrative CRDM 30 is an internal system in which the drive motors and other components are disposed inside the pressure vessel 12 with only electrical power and control wiring extending outside the pressure vessel 12. Alternatively, external CRDM may be employed, in which (by way of illustrative example) control rod drive motors may be mounted above the pressure vessel with the control rods passing into the pressure vessel and extending (retractably) into the reactor core via suitable pressure vessel penetration. The pressure vessel 12 is also configured to define a desired primary coolant circulation. In the illustrative example, the circulation is defined by a hollow cylindrical central riser 32 disposed coaxially in the illustrative cylindrical pressure vessel 12. Primary coolant heated by the reactor core 10 flows upward through fluid conduits passing through the internal CRDM 30 and upward through the hollow central riser 32. The heated primary coolant discharges at the top of the hollow central riser 32 and is diverted downward by a diverter 34 (which optionally may define the bottom of the integral pressurizer 14). The diverted primary coolant flows downward through an annulus defined between the cylindrical central riser 32 and the walls of the cylindrical pressure vessel 12, and is then diverted upward by the bottom of the pressure vessel 12 to return to the reactor core 10. Optional primary coolant pumps 36 may be provided to drive the primary coolant circulation, or to assist natural circulation. Alternatively, natural circulation may be relied upon for circulating the primary coolant. The illustrative system of FIG. 3 is merely an illustrative example, and other primary coolant circulation paths and/or circulation control components are also contemplated. The pressure vessel 12 is suitably positioned substantially vertically. An optional skirt 40 may be provided to support the pressure vessel 12, or to bias against the pressure vessel 12 tipping over. The illustrative skirt 40 is positioned such that the lower portion of the pressure vessel 12 containing the reactor core 10 is located in a recess below ground. This optional arrangement is advantageous because it enables the lower region to be flooded for safety in the event of a LOCA or other accident. The described components ensure circulation of the primary coolant from the reactor core 10 upward through the hollow central riser 32, and back down the annulus surrounding the central riser 32 to return to the reactor core 10. The reactor core 10 heats the circulating primary coolant, which in the PWR design is superheated. To provide steam generation, this circulating superheated primary coolant is brought into thermal communication with a secondary coolant (typically light water, H2O optionally containing various additives, solutes, or so forth) flowing in a secondary coolant path that is in fluid isolation from the primary coolant path through which the primary coolant flows. In some embodiments (not illustrated), this is achieved by flowing the primary coolant out a relatively large-diameter vessel penetration and into a separate steam generator unit. There, the primary coolant flows through flow paths or a flow volume in close proximity to and hence in thermal communication with a secondary coolant flow path or volume containing the secondary coolant. Heat is thereby transferred from the primary coolant to the secondary coolant in the separate steam generator unit, and this heat transfer converts secondary coolant into steam. In the illustrative embodiment of FIG. 3, an integral steam generator is employed. An integral steam generator is a steam generator located in the same pressure vessel 12 containing the reactor core 10. In the illustrative example of FIG. 3, an integral steam generator 44 is located in the annulus surrounding the central riser 32, that is, in the annular space between the exterior of the central riser 32 and the inside walls of the pressure vessel 12. Secondary coolant in the form of feedwater is input via a feedwater inlet 50 into an annular feedwater inlet plenum 52 (or, alternatively, into a tubesheet) where it feeds into a lower end of the steam generator 44. The secondary coolant rises generally upward through the steam generator 44 in secondary coolant flow paths or volume that are in thermal communication with (but in fluid isolation from) proximate primary coolant flow paths or volume through which primary coolant flows generally downward. (Note that FIG. 3 does not show details of the steam generator). The steam generator configuration can take various forms. In some embodiments, the steam generator comprises tubes carrying primary coolant generally downward, while the secondary coolant flows generally upward in a volume outside of the tubes. Alternatively, the secondary coolant may flow generally upward through the steam generator tubes while the primary coolant flows generally downward outside of the tubes. The tubes may comprise straight vertical tubes, slanted vertical tubes, helical tubes wrapping around the central riser 32, or so forth. However arranged, heat transfer takes place from the superheated primary coolant to the secondary coolant, which converts the secondary coolant from the liquid phase to the steam phase. In some embodiments the steam generator may include an integral economizer in a lower portion of the steam generator. In some embodiments, the steam generator may comprise a plurality of constituent steam generators to provide redundancy. The resulting steam enters an annular steam plenum 54 (or, alternatively, into a tubesheet) and from there passes out one or more steam outlets 56. The resulting steam (whether generated by an integral steam generator such as the illustrative integral steam generator 44, or by an external steam generator unit) can be used for substantially any purpose suitably accomplished using steam power. In the illustrative example of FIG. 3, the steam drives a turbine 60 which in turn drives an electrical power generator 62 to provide electrical power. In the illustrative example of FIG. 3, the secondary coolant circulates in a closed path. Toward this end, a steam condenser 64 downstream of the turbine 60 condenses the steam back into a liquid phase so as to recreate secondary coolant comprising feedwater. One or more pumps 66, 68 and one or more feedwater heaters 70, 72 or other feedwater conditioning components (e.g., filters, components for adding additives, or so forth) generate feedwater at a desired pressure and temperature for input to the feedwater inlet 50. A feedwater valve 74 controls the inlet feedwater flow rate. With continuing reference to FIG. 3, the PWR further includes a digital processor(s) or electrical circuit(s) 80, 82, 90 configured to perform reactor power control including adjustment of the pressurizer water level setpoint. In the illustrative example, a reactor power control circuit or processor 80 operates the feedwater valve 74 to increase or decrease feedwater flow rate. In accordance with Table 1, increasing or decreasing feedwater flow rate produces a corresponding increase or decrease in reactor power. Additionally, in accordance with PWR control approaches disclosed herein, increasing or decreasing feedwater flow rate to produce a corresponding increase or decrease in reactor power also entails decreasing (in the case of feedwater flow rate increase) or increasing (in the case of feedwater flow rate decrease) the pressurizer water level setpoint. (This is seen in the rightmost column of Table 1). Toward that end, a feedwater flow rate monitoring signal 84 generated by a sensor integral with the feedwater valve 74 or by a separate feedwater flow meter (not shown) is input to a pressurizer water level control circuit or processor 82. The pressurizer water level control circuit or processor 82 performs conventional pressure water level control. That is, if the monitored pressurizer water level 22 rises above an upper pressurizer water level limit then the pressurizer water level control circuit or processor 82 causes the RCS makeup/letdown valving 26 to perform primary coolant letdown to reduce the pressurizer water level. Similarly, if the monitored pressurizer water level 22 decreases below a lower pressurizer water level limit then the pressurizer water level control circuit or processor 82 causes the RCS makeup/letdown valving 26 to add makeup water to increase the pressurizer water level. Additionally, however, the pressurizer water level control circuit or processor 82 includes a pressurizer water level setpoint adjustment circuit or processor 90 that adjusts the pressurizer level setpoint based on a predicted direction and magnitude of change of the pressurizer water level 18 predicted to result from the PWR power adjustment performed by the reactor power control circuit or processor 80. For example, if the reactor power control circuit or processor 80 performs a power adjustment by increasing the feedwater flow rate, then the corresponding predicted change in the pressurizer water level 18 is a decrease (see Table 1, first row). The magnitude of the decrease can be predicted based on simulations or empirical measurements, suitably embodied as a function of the magnitude of the feedwater flow rate increase. More generally, the magnitude of the change in pressurizer water level 18 can be predicted based on simulations or empirical measurements suitably embodied as a function of the magnitude of the corresponding change made by the reactor power control circuit or processor 80. The function may be embodied by a mathematical formula implemented by a digital processor or a suitable electrical circuit (e.g., an operational amplifier circuit configured to provide an analog implementation of the function). Typically, the adjusting of the pressurizer water level setpoint also entails adjusting the upper and lower pressurizer water level limits to track with the adjusted pressurizer water level setpoint. In some embodiments this tracking is a simple linear operation—for example, if the lower pressurizer water level limit may be set to a fixed distance in centimeters below the pressurizer water level setpoint, and the upper pressurizer water level limit may be set to a fixed distance in centimeters above the pressurizer water level setpoint. Alternatively, the upper and lower pressurizer water level limits can have another relationship with the pressurizer water level setpoint, such as the upper limit being 5% above the pressurizer water level setpoint and the lower limit being 5% below the pressurizer water level setpoint. The foregoing examples relate to power adjustment by adjusting the feedwater flow rate. As already discussed (see, e.g. Table 1), power adjustment by adjusting the temperature of the feedwater fed into the steam generator is also contemplated, as is power adjustment by a combination of feedwater flow and temperature adjustment. Toward this end, a temperature sensor 92 suitably measures the feedwater temperature at or near the feedwater inlet 50 (for example, in illustrative FIG. 3 the sensor is near or built into the feedwater valve 74). The temperature measured by the sensor 92 is also input to the pressurizer water level adjustment circuit or processor 90 to enable adjustments of the pressurizer water level setpoint based on the direction and magnitude of changes in temperature of feedwater input to the steam generator 44. With reference to FIG. 4, a suitable embodiment of the pressurizer water level control circuit or processor 82 of FIG. 3 is shown, including a suitable embodiment of the pressurizer water level adjustment circuit or processor 90. In the illustrative example of FIG. 4, the predicted effect of the feedwater flow rate and temperature on the pressurizer water level is a linear superposition combination of the individual flow rate and temperature effects. Accordingly, a first function 100 predicts the effect of feedwater flow rate on the predicted pressurizer water level, while a second function 102 predicts the effect of inlet feedwater temperature on the predicted pressurizer water level. A pressurizer water level setpoint 104 is then a linear (i.e., subtractive, due to the different polarities of the flow rate and feedwater temperature effects as seen in Table 1) combination of the outputs of the functions 100, 102. A difference block 106 computes the difference feedback signal between the monitored pressurizer water level 22 and the pressurizer water level setpoint 104, and suitable feedback control (a proportional-integral or PI control block 108, in the illustrative example of FIG. 4) generates a suitable control signal. The remaining circuitry 110 shown in FIG. 4 is designed to generate a single control signal 112 suitable for input to a “smart” embodiment of the RCS makeup/letdown valving 26, such as a reactor coolant inventory and purification system (RCIPS) embodiment. It is to be understood that the various control components 80, 82, 90 may be variously embodied. For example, in some embodiments a single digital processing device embodies all controller components 80, 82, 90. In other embodiments, these may be two or even three distinct processing devices or circuits. The various control components 80, 82, 90 may also be embodied by various combinations of digital processors and/or electrical circuits. The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
	abstract	A reactor pressure vessel (RPV) for a nuclear reactor that permits measurement of the flow through each reactor internal pump (RIP) is described. The reactor pressure vessel also includes at least one reactor internal pump that includes an impeller and a pump diffuser. At least two seal rings extend circumferentially around an outer surface of the diffuser housing outer wall and are located in circumferential grooves in the housing outer wall. At least one lateral bore extends through the housing outer wall into a diffuser housing longitudinal flow passage. Each lateral bore is located in an area between two adjacent seal rings, with each inter-seal ring area containing one lateral bore. At least one pressure tap bore extends from the outer surface of the RPV bottom head petal, through the pump deck to an inner surface of a pump deck opening. Each pressure tap bore is aligned with an area in the RIP containing a corresponding lateral bore.
048266469	claims	1. A method of confining positively charged particles comprising the steps of: (a) generating a magnetic field within a region wherein all the cusps of said magnetic field are point cusps; (b) injecting electrons within said region and using said generated magnetic field to confine electrons within said region and so to generate a negative potential well; and (c) injecting positively charged particles within said region and using said negative potential well to confine said positively charged particles within said region; and (d) maintaining the number of electrons greater than the number of positively charged particles; (a) generating a magnetic field within a region wherein all the cusps of said magnetic field are point cusps; (b) injecting electrons within said region and using said generated magnetic field to confine electrons within said region and so to generate a negative potential well; and (c) injecting positively charged particles within said region and using said negative potential well to confine said positively charged particles within said region; and (d) maintaining the number of electrons greater than the number of positively charged particles; (a) generating a magnetic field within a region wherein all the cusps of said magnetic field are point cusps; (b) injecting electrons within said region and using said generated magnetic field to confine electrons within said region and so to generate a negative potential well; and (c) injecting positively charged particles within said region and using said negative potential well to confine said positively charged particles within said region; and (d) maintaining the number of electrons greater than the number of positively charged particles; means for generating a magnetic field within a region, all the cusps of said magnetic field being point cusps; means for injecting electrons into the center of said region for forming a negative potential well within said region; means for injecting said positively charged particles into said negative potential well, said positively charged particles maintained within said region by said negative potential well; and means for maintaining the number of electrons greater than the number of positively charged particles; wherein said magnetic field generating means includes current carrying means for carrying an electric current, said current carrying means disposed on edges of one of an octahedron or a truncated regular polyhedron such that adjacent faces of said polyhedron have opposing magnetic polarities; wherein said magnetic field generating means generates only point cusps at positions corresponding to the centers of faces of said octahedron or truncated regular polyhedron; and wherein said electron injecting means is arranged to inject said electrons through one of said point cusps along a first line corresponding to an axis of said octahedron or truncated regular polyhedra. means for generating a magnetic field within a region, all the cusps of said magnetic field being point cusps; means for injecting electrons into the center of said region for forming a negative potential well within said region; means for injecting said positively charged particles into said negative potential well, said positively charged particles maintained within said region by said negative potential well; and means for maintaining the number of electrons greater than the number of positively charged particles; wherein said magnetic field generating means includes current carrying means for carrying an electric current, said current carrying means disposed on edges of one of an octahedron or a truncated regular polyhedron such that adjacent faces of said polyhedron have opposing magnetic polarities; wherein said magnetic field generating means generates only point cusps at positions corresponding to the centers of faces of said octahedron or truncated regular polyhedra; and wherein said electron injecting means is arranged to inject said electrons through one of said point cusps along a first line intersecting and axis of said octahedron truncated regular polyhedron at an angle. means for generating a magnetic field within a region, all the cusps of said magnetic field being point cusps; means for injecting electrons into the center of said region for forming a negative potential well within said region; means for injecting said positively charged particles into said negative potential well, said positively charged particles maintained within said region by said negative potential well; and means for maintaining the number of electrons greater than the number of positively charged particles; wherein said magnetic field generating means includes current carrying means for carrying an electric current, said current carrying means disposed on edges of one of an octahedron or a truncated regular polyhedron such that adjacent face of said polyhedron have opposing magnetic polarities; wherein said magnetic field generating means generates only point cusps at positions corresponding to the centers of faces of said octahedron or truncated regular polyhedron; and wherein said charged particle injecting means injects said particles in a beam along a line corresponding to an axis of said octahedron or truncated polyhedron. means for generating a magnetic field within a region, all the cusps of said magnetic field being point cusps; means for injecting electrons into the center of said region for forming a negative potential well within said region; means for injecting said positively charged particles into said negative potential well, said positively charged particles maintained within said region by said negative potential well; and means for maintaining the number of electrons greater than the number of positively charged particles; wherein said magnetic field generating means includes current carrying means for carrying an electric current, said current carrying means disposed on edges of one of an octahedron or a truncated regular polyhedron such that adjacent faces of said polyhedron have opposing magnetic polarities; wherein said magnetic field generating means generates only point cusps at positions corresponding to the centers of faces of said octahedron or truncated regular polyhedron/ and wherein said charged particle injecting means is arranged to inject said charged particles through one of said point cusps. means for generating a magnetic field within a region, all the cusps of said magnetic field being point cusps; means for injecting electrons into the center of said region for forming a negative potential well within said region; means for injecting said positively charged particles into said negative potential well, said positively charged particles maintained within said region by said negative potential well; and means for maintaining the number of electrons greater than the number of positively charged particles; wherein said magnetic field generating means includes current carrying means for carrying an electric current, said current carrying means disposed on edges of one of an octahedron or a truncated regular polyhedron such that adjacent faces of said polyhedron have opposing magnetic polarities; wherein said magnetic field generating means generates only point cusps at positions corresponding to the centers of faces of said octahedron or truncated regular polyhedron; wherein said charged particles injecting means injects said particles in a beam along a line corresponding to an axis of said octahedron or truncated polyhedron; and wherein said injection means includes means for injecting said beam with rotation. means for generating a magnetic field within a region, all the cusps of said magnetic field being point cusps; means for injecting electrons into the center of said region for forming a negative potential well within said region; means for injecting said positively charged particles into said negative potential well, said positively charged particles maintained within said region by said negative potential well; and means for maintaining the number of electrons greater than the number of positively charged particles; wherein said magnetic field generating means includes current carrying means for carrying an electric current, said current carrying means disposed on edges of one of an octahedron or a truncated regular polyhedron such that adjacent faces of said polyhedron have opposing magnetic polarities; wherein said magnetic field generating means generates only point cusps at positions corresponding to the centers of faces of said octahedron or truncated regular polyhedron; and wherein said charged particle injecting means is arranged to inject said charged particles along a second annulus through one of said point cusps, the central axis of said second annulus corresponding to an axis of said octahedron or truncated regular polyhedron. means for generating a magnetic field within a region, all the cusps of said magnetic field being point cusps; means for injecting electrons into the center of said region for forming a negative potential well within said region; means for injecting said positively charged particles into said negative potential well, said positively charged particles maintained within said region by said negative potential well; and means for maintaining the number of electrons greater than the number of positively charged particles; wherein said magnetic field generating means is further operable to generate a magnetic field conforming substantially in shape to a superposition of at least two polyhedra. (a) means for generating a magnetic field within a region, said means including magnetic field coils positioned on edges of a structure forming a polyhedral figure, each vertex of which is surrounded by an even number of faces, said field coils carrying currents such that adjacent faces of said polyhedral figure having opposing magnetic polarities, (b) means for injecting electrons within said region, said electrons having gyro radii effectively smaller than the radius of said region such that said electrons are trapped within said region by said magnetic field, said trapped electrons forming a negative potential well within a volum of said region; (c) means for injecting positively charged ions within said region, said ions having gyro radii effectively larger than a radius of said region, such that said positively charged ions are not trapped within said region by said magnetic field, said positively charged ions confined within said region by electric potential gradient forces resulting from said negative potential well, the number of electrons within said region maintained larger than the number of said positively charged ions, and said positively charged ions having energies sufficiently great within said region to produce collisional reactions. (a) generatiang a magnetic field within a region by passing current through magnetic field coils positioned on edges of a structure forming a polyhedral figure, each vertex of which is surrounded by an even number of faces, said currents such that adjacent faces of said polyhedral figure have opposing magnetic polarities, (b) injecting electrons within said region, said electrons having gyro radii effectively smaller than a radius of said region such that said electrons are trapped within said region by said magnetic field, said trapped electrons forming a negative potential well within a volume of said region; and (c) injecting positively charged ions within said region, said ions having gyro radii effectively larger than said radius of said region, such that said positively charged ions are not trapped within said region by said magnetic field, said positively charged ions confined within said region by electric potential gradient forces resulting from said negative potential well, the number of electrons within said region maintained larger than the number of said positively charged ions, and said positively charged ions having energies sufficiently great within said region to produce collisional reactions. 2. A method of confining positively charged particles comprising the steps of: 3. A method of confining positively charged particles comprising the steps of: 4. An apparatus for controlling positively charged particles comprising: 5. An apparatus as claimed in claim 4 further comprising a second electron injection means arranged opposed to said first mentioned electron injection means across said magnetic field generating means. 6. An apparatus for controlling positively charged particles comprising: 7. An apparatus for controlling positively charged particles comprising: 8. An apparatus as claimed in claim 7 wherein said means for injecting electrons includes means for generating an electron beam with rotation. 9. An apparatus for controlling positively charged particles comprising: 10. An apparatus as claimed in claim 9 further comprising a second charged particle injection means arranged opposed to said first mentioned charged particle injection means across said magnetic field generating means. 11. An apparatus for controlling positively charged particles comprising: 12. An apparatus for controlling positively charged particles comprising: 13. An apparatus as claimed in claim 12 wherein said charged particles form an annular beam and said injection means includes means for injecting said beam with rotation. 14. An apparatus for controlling positively charged particles comprising: 15. An apparatus as claimed in claim 14 wherein said current carrying means are disposed at positions corresponding to the edges of each polyhdedron. 16. An apparatus as in claim 15 wherein said current-carrying members are driven by alternating current supplies to produce 17. A device for producing collisional reactions comprising: 18. A device as recited in claim 17 wherein said gyro radii of said electrons are on the order of 10-100 times smaller than a diameter of said region. 19. A device as recited in claim 17 wherein said gyro radii of said electrons are on the order of 0.5-5 mm at energies of about 20-50 kev in a magnetic filed of 1-5 kilogauss. 20. A device as recited in claim 17 wherein said collisional reactions are nuclear fusion reactions. 21. A device as recited in claim 17 wherein said ions are selected from isotopes of an element taken from the group consisting of lithium, beryllium, helium, boron and hydrogen. 22. A device as recited in claim 17 wherein said electrons are injected at energies producing a sufficiently large negative potential well so as to cause nuclear fusion reactions among said positively charged ions. 23. A device as recited in claim 17 wherein said volume of said negative potential well is free of any tangible structure. 24. A device as recited in claim 17 wherein said region is free of any tangible structure. 25. A device as recited in claim 17 further including means positioned outside of said region for converting energy resulting from said reactions into one of thermal and electrical energy. 26. A method for producing collisional reactions comprising the steps of: 27. A method as recited in claim 26 wherein said gyro radii of said electrons are on the order of 10-100 times smaller than a diameter of said region. 28. A method as recited in claim 26 wherein said gyro radii of said electrons are on the order of 0.5-5 mm at energies of about 20-50 kev in a magnetic field of 1-5 kilogauss. 29. A method as recited in claim 26 wherein said collisional reactions are nuclear fusion reactions. 30. A method as recited in claim 21 wherein said ions are selected from isotopes of an element taken from the group consisting of lithium, beryllium, helium, boron and hydrogen. 31. A method as recited in claim 26 wherein said electrons are injected at energies producing a sufficiently large negative potential well so as to cause nuclear fusion reactions among said positively charged ions. 32. A method as recited in claim 26 wherein said volume of said negative potential well is free of any tangible structure. 33. A method as recited in claim 26 wherein said region is free of any tangible structure. 34. A method as recited in claim 26 further including the step of converting energy resulting from said reactions into one of thermal and electrical energy. 35. A method as recited in claim 26 further including the step of continuously increasing the number of electrons in said region to compensate for electron losses. 36. A method as recited in claim 26 further comprising the steps of periodically increasing the number of electrons in said region to compensate for electron losses.
	abstract	Provided is a method and an apparatus for inspecting a sample surface with high accuracy. Provided is a method for inspecting a sample surface by using an electron beam method sample surface inspection apparatus, in which an electron beam generated by an electron gun of the electron beam method sample surface inspection apparatus is irradiated onto the sample surface, and secondary electrons emanating from the sample surface are formed into an image toward an electron detection plane of a detector for inspecting the sample surface, the method characterized in that a condition for forming the secondary electrons into an image on a detection plane of the detector is controlled such that a potential in the sample surface varies in dependence on an amount of the electron beam irradiated onto the sample surface.
	description	This Application is a Continuation-In-Part of U.S. patent application Ser. No. 10/183,784 titled “Method and Apparatus for Forming Optical Materials and Devices” filed on Jun. 27, 2002, which claims the benefit of U.S. PROVISIONAL APPLICATION No. 60/302,152 titled “Novel Optical Materials Formed Using Electron Beam Irradiation and Method for Forming Optical Devices” filed on Jun. 28, 2001. The present invention relates generally to the fabrication of optical materials by electron beam radiation and more specifically to an apparatus and method for fabricating optical devices with a decreased birefringence while under tensile stress or a patterned birefringence under tensile stress utilizing electron beam radiation. An optical material, which has two different indexes of refraction in two different directions, will divide an incident light beam into two light beams, an ordinary ray and an extraordinary ray. The ordinary ray and the extraordinary ray are in different polarization states but not cross-polarized. This optical property is called birefringence. Halogenated optical materials are chemical compounds or chemical mixtures that contain halogen atoms, such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Halogenated optical materials typically have a single, uniform index of refraction. Halogenated optical materials also have a crystalline structure. When halogenated optical materials are stretched or otherwise placed under tensile stress, the halogenated optical material is birefringent. The halogenated optical material under stress forms a high index of refraction area in one direction and a low index of refraction area in a second direction. The high index of refraction of the halogenated optical material under stress is higher than the normal index of refraction of the halogenated optical material not under stress. The low index of refraction of the halogenated optical material under stress is lower than the normal index of refraction of the halogenated optical material not under stress. The difference in indexes of refraction between the high index of refraction and the low index of refraction in the halogenated optical material under stress is what causes the birefringence. It is an object of the present invention to provide an electron beam irradiation method and apparatus to decrease and pattern the birefringence of halogenated optical materials under tensile stress. The starting halogenated optical material is deposited on a substrate. The starting halogenated optical material is under tensile stress. The starting halogenated optical material is then exposed with the electron beam at an energy and dose, while the starting halogenated optical material is heated to the appropriate temperature, to decrease the birefringence of the halogenated optical material under stress or to pattern the birefringence of the halogenated optical material under stress. The optical material and substrate are preferably loaded into a vacuum chamber with a flood electron source to expose the upper surface of the substrate and a heating element to apply heat to the lower surface of the substrate. The method utilizes a large area electron beam exposure system in a soft vacuum environment. By adjusting the process conditions, such as electron beam total dose and energy, temperature of the selected optical material, and ambient atmosphere (devoid of oxygen), the birefringence of the halogenated optical material under stress can be altered. The electron beam imparts sufficient energy to the chemical bonds within the optical material to create scissions, which leads to the formation of additional networking bonds as these bonds recombine within the material. The decrease in birefringence is due to the process of scission and reformation within the optical material. Halogenated optical materials typically have a single, uniform index of refraction. Halogenated optical materials also have a crystalline structure. When halogenated optical materials are stretched or placed under tensile stress, the halogenated optical material is birefringent. The halogenated optical material under stress forms a high index of refraction area in one direction and a low index of refraction area in a second direction. The difference in indexes of refraction between the high index of refraction and the high index of refraction in the halogenated optical material under stress is what causes the birefringence. After electron beam irradiation and heating, the crystalline structure of the halogenated optical material layer has been randomized and made amorphous. The electron beam irradiation and heating will lower the high index of refraction of the halogenated optical material under stress and raise the low index of refraction of the halogenated optical material under stress. The differences in index of refraction between the high index of refraction area of and the low index of refraction area decrease which decreases the birefringence of the halogenated optical material under stress. The electron beam irradiation and heating can reduce the differences in index of refraction between the high index of refraction area of and the low index of refraction area until both areas have the same index of refraction eliminating the birefringence of the halogenated optical material under stress. The halogenated optical material under stress can be patterned with an apertured mask or an embossing structure by the electron beam irradiation and heating so that, under tensile stress, the halogenated optical material will have birefringent areas and decreased birefringent or non-birefringent areas. The foregoing has outlined, rather broadly, the preferred feature of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention and that such other structures so not depart from the spirit and scope of the invention is its broadest form. The exposure of selected optical materials to electron beam irradiation can convert the existing material into a new state, which exhibits more desirable optical and mechanical properties not present in the un-irradiated material. The introduction of extra bonds within solid halogenated optical materials, including polymers, results in decreased birefringence of the halogenated optical material under tensile stress. The electron beam imparts sufficient energy to the chemical bonds in the optical materials to create scissions, which leads to the formation of additional networking bonds as these reactive entities recombine within the optical material (crosslinking). Starting halogenated optical materials can be converted using this approach. These materials do not outgas significantly in soft vacuum (10-50 millitorr). Preferred optical materials include the following: Typical spin-on glass materials include methylsiloxane, methylsilsesquioxane, phenylsiloxane, phenylsilsesquioxane, methylphenylsiloxane, methylphenylsilsesquioxane, and silicate polymers. Spin-on glass materials also include hydrogensiloxane polymers of the general formula (H0-1.0SiO1.5-2.0)x and hydrogensilsesquioxane polymers, which have the formula (HsiO1.5)x, where x is greater than about 8. Also included are copolymers of hydrogensilsesquioxane and alkoxyhydridosiloxane or hydroxyhydridosiloxane. Spin-on glass materials additionally include organohydridosiloxane polymers of the general formula (H0-1.0SiO1.5-2.0)n(R0-1.0SiO1.5-2.0)m, and organohydridosilsesquioxane polymers of the general formula (HSiO1.5)n(RSiO1.5)m, where m is greater than 0 and the sum of n and m is greater than about 8 and R is alkyl or aryl. Typical polymer materials include halogenated polyalkylenes, preferred fluorinated an/or chlorinated polyalkylens, more preferred chlorofluoropolyalkylens, and most preferred are the fluorinated polyalkylenes among which are included: polytetrafluoroethane (ethylene), polytrifluoroethylene, polyvinylidene fluoride, polyvinylfluoride, copolymers of fluorinated ethylene or fluorinated vinyl groups with non-fluorinated ethylenesor vinyl groups, and copolymers of fluorinated ethylenes and vinyls with straight or substituted cyclic fluoroethers containing one or more oxygens in the ring. Also included in the most preferred polymers are poly(fluorinated ethers) in which each linear monomer may contain from one to four carbon atoms between the ether oxygens and these carbons may be perfluorinated, monofluorinated, or not fluorinated. Also included in the most preferred polymers are copolymers of wholly fluorinated alkylenes with fluorinated ethers, partly fluorinated alkylenes with wholly fluorinated ethers, wholly fluorinated alkylenes with partly fluorinated ethers, partly fluorinated alkylenes with partly fluorinated ethers, non-fluorinated alkylenes with wholly or partly fluorinated ethers, and non-fluorinated ethers with partly or wholly fluorinated alkylenes. Also included among the most preferred polymers are copolymers of alkylenes and ethers in which one kind of the monomers is wholly or partly substituted with chlorine and the other monomer is substituted with fluorine atoms. In all the above, the chain terminal groups may be similar to those in the chain itself, or different. Also among the most preferred polymers are included substituted polyacrylates, polymethacrylates, polyitaconates, polymaleates, and polyfumarates, and their copolymers, in which their substituted side chains are linear with 2 to 24 carbon atoms, and their carbon atoms are fully fluorinated except for the first one or two carbons near the carboxyloxygen atom such as Fluoroacrylate, Fluoromethacrylate and Fluoroitaconate. Among the more preferred polymers, one includes fluoro-substituted polystyrenes, in which the ring may be substituted by one or more fluorine atoms, or alternatively, the polystyrene backbone is substituted by up to 3 fluorine atoms per monomer. The ring substitution may be on ring carbons No. 4, 3, 2, 5, or 6, preferably on carbons No. 4 or 3. There may be up to 5 fluorine atoms substituting each ring. Among the more preferred polymers, one includes aromatic polycarbonates, poly(ester-carbonates), polyamids and poly(esteramides), and their copolymers in which the aromatic groups are substituted directly by up to four fluorine atoms per ring one by one on more mono or trifluoromethyl groups. Among the more preferred polymers, are fluoro-substituted poly(amic acids) and their corresponding polyimides, which are obtained by dehydration and ring closure of the precursor poly(amic acids). The fluorine substitution is effected directly on the aromatic ring. Fluoro-substituted copolymers containing fluoro-substituted imide residues together with amide and/or ester residues are included. Also among the more preferred polymers are parylenes, fluorinated and non-fluorinated poly(arylene ethers), for example the poly(arylene ether) available under the tradename FLARE(™) from AlliedSignal Inc., and the polymeric material obtained from phenyl-ethynylated aromatic monomers and oligomers provided by Dow Chemical Company under the tradename SiLK(™), among other materials. In all the above, the copolymers may be random or block or mixtures thereof. The method of creating new optical materials from these conventional solid halogenated optical materials, including polymers, according to the present invention, is depicted in FIGS. 1 and 2. A substrate 127 is placed in a vacuum chamber 120 at a pressure of 15-40 milliTorr and underneath an electron source at a distance from the source sufficient for the electrons to generate ions in their transit between the source and the substrate surface. The electrons can be generated from any type of source that will work within a soft vacuum (15-40 milliTorr) environment. A source particularly well suited for this is described in U.S. Pat. No. 5,003,178, the disclosure of which is hereby incorporated into this specification by reference. This is a large uniform and stable source that can operate in a soft vacuum environment. The cathode 122 emits electrons, which are accelerated by the field between the cathode and anode 126. The potential between these two electrodes is generated by the high voltage supply 129 applied to the cathode 122 and the bias voltage supply 130 applied to the anode 126. The electrons irradiate the starting optical material layer 128 coated on the substrate 127. The starting optical material layer 128 may be any of the halogenated optical materials previously mentioned. An electron energy is selected to either fully penetrate or partially penetrate the full thickness of starting halogenated optical material layer 128. For example, an electron beam energy of 9 keV is used to penetrate a 6000 angstrom thick film. Infrared quartz lamps 136 irradiate the bottom side of the substrate providing heating independent from the electron beam. A variable leak valve or mass flow controller, identified by reference 132, is utilized to leak in a suitable gas to maintain the soft vacuum environment. Referring to FIG. 2, electrons 145 traversing the distance 146 between the anode 126 and the substrate 127 ionize the gas molecules located in region 138 generating positive ions. These positive ions 143 are then attracted back to the anode 126 where they can be accelerated, as indicated at 142, toward the cathode to generate more electrons. The starting optical material layer 128 on the substrate 127 is an insulator and will begin to charge negatively, as indicated at 147, under electron bombardment. However, the positive ions near the substrate surface will be attracted to this negative charge and will then neutralize it. The IR quartz lamps 136 (FIG. 1) irradiate and heat the starting optical material layer or substrate thereby controlling its temperature. Since the starting optical material layer is in a vacuum environment and thermally isolated, the starting optical material layer can be heated or cooled by radiation. If the lamps are extinguished, the starting optical material layer will radiate away its heat to the surrounding surfaces and gently cool. In one embodiment of the invention, the starting optical material layer is simultaneously heated by the infrared lamps and irradiated by the electron beam throughout the entire process. In the present method, a halogenated optical material is deposited on substrate 127 by conventional means such as spin-coating or, alternatively, spray-coating or dip-coating to form starting optical material layer 128. Substrate 127 can represent any layer or stack of layers on a multiple-optical layer device. The coated substrate is continuously irradiated with electrons until a sufficient dose has accumulated to attain the desired change in the material and affect certain properties such as birefringence. A total dose of between 10 and 100,000 microCoulombs per square centimeter (μC/cm2) may be used. Preferably, a dose of between 100 and 10,000 μC/cm2 is used, and most preferably a dose of between about 2,000 and 5,000 μC/cm2 is used. The dose, however, can be as little as 1 microCoulomb if the electron beam is irradiating a very thin film, e.g. one nanometer. The electron beam is delivered at an energy of between 0.1 and 100 keV, preferably at an energy between 0.5 and 20 keV, and most preferably at an energy between 1 and 10 keV. The electron beam current ranges between 0.1 and 100 mA, and more preferably between 0.25 and 30 mA. The entire electron dose may be delivered at a single voltage. Alternatively, particularly for starting optical material layer thicker than about 0.25 μm, the dose is divided into steps of decreasing voltage, which provides a “uniform dose” process in which the starting optical material layer is irradiated from the bottom up. The higher energy electrons penetrate deeper into the starting optical material layer. In this way, the depth of electron beam penetration is varied during the electron exposure process resulting in a uniform energy distribution throughout the starting optical material layer. The variation allows for volatile components, such as solvent residues, to leave the film without causing any damage such as pinholes or cracks. This also attains uniformity throughout the layer exposed. Alternatively, the electron energy can be varied to achieve a precise dose and index change spatially within the starting optical material layer. During the electron beam exposure process, the starting halogenated optical material layer is kept at a temperature between 10 degrees Celsius and 1000 degrees Celsius. Preferably, the wafer temperature is between 30 degrees Celsius and 500 degrees Celsius. For some waxes and other low melting point materials low temperatures are utilized (25 degrees to 175 degrees Celsius). The infrared quartz lamps 36 are on continuously until the starting optical material layer temperature reaches the desired process temperature. The lamps are turned off and on at varying duty cycle to control the starting optical material layer temperature. Typical background process gases in the soft vacuum environment include nitrogen, argon, oxygen, ammonia, forming gas, helium, methane, hydrogen, silane, and mixtures thereof. For many starting halogenated optical materials, a non-oxidizing processing atmosphere is used. In addition to a near vacuum ambient atmosphere devoid of oxygen, the electron beam irradiation of the starting halogenated optical material and the heating of the starting halogenated optical material above the melt point will de-gas oxygen from the starting halogenated optical material. The degassing of oxygen increases the ratio of crosslinking to change scission under electron beam bombardment of halogenated optical materials. The optimal choice of electron beam dose, energy, current, processing temperature, and process gas depends on the composition of the starting halogenated optical material. The optical starting material may be deposited onto a suitable substrate. Typical substrates include glass, silicon, metal, and polymer films. Substrates can also be porous, textured or embossed. Deposition on substrates may be conducted via conventional spin coating, dip coating, roller coating, spraying, embossing, chemical vapor deposition methods, or meniscus coating methods, which are well known in the art. Spin coating on substrates is most preferred. Multiple layers of different materials are also preferred. Layer thicknesses typically range from 0.01 to 20 microns. 1 to 10 microns is preferred. In another embodiment of the invention, the optical starting material is formed into a supported layer similar to pellicles used in semiconductor applications. In this case, layers may be formed by casting, spin coating, and dip coating, lifted off the substrate and attached to a frame for handling. In addition, extruded layers can be attached to a frame, all of which are well known in the art. Casting, with lift-off and frame attachment is preferred. Single layers exhibit thicknesses ranging from 1 micron to 10 microns. Multiple layers of different materials are also possible. Once the article has been formed, the exposure equipment needs to be selected. Exposure of the material can be done with any type of low energy electron source, preferably in the range of 1 to 50 keV. Soft vacuum (15-40 millitorr) is also preferred for removal of volatiles and usage of low keV electrons. In the preferred embodiment of this invention, the optically useful material, either on a substrate or as supported layer, is selectively exposed to the electron beam and heated using the IR lamps. Selective heating is also preferred. The IR lamps typically operate from room temperature to 400 degrees Celsius. Most materials exhibit different e-beam irradiation responses depending on the temperature of the material. In addition, post annealing can eliminate charge gradients in electrodes formed during irradiation. Other functions such as transmission loss, polarization sensitivity, and back reflections can all be monitored during exposure and used in a feedback loop to the exposure parameters. In-situ feedback during exposure is an embodiment of this invention. Various gases can be introduced during the irradiation process. It has been shown that these gases can be reacted into the starting optical material layer depending on the material and exposure conditions. Introduction of a reactive or non-reactive gas into the starting optical material layer during exposure is a further embodiment of this invention. Radial exposure conditions, as well as other non-flat configurations, are embodiments of this invention as well as modification of the electron field using external means such as magnetic fields. Once the equipment is selected, the exposure conditions are selected. Typically the starting optical material layer is exposed to a sequential series of kinetic energies generating a particular distribution of bond densities within the optically useful material. Based on the material's particular e-beam response, temperature distribution within the material, kinetic energy distribution of the electrons, and density of the material, a range of new material states can be generated. These new material states exhibit properties not available in the un-irradiated state. Preferred property changes include decreasing or eliminating the birefringence of the halogenated optical material under stress or patterning the birefringence of the halogenated optical material under stress. Exposure can be done through an aperture mask above the starting halogenated optical material as known in the art or through an embossing structure directly on the starting halogenated optical material. Dual sided processing can be used. The mask can be either sacrificial or permanent depending on the application. Once the sample is exposed, fabrication can commence. As shown in FIG. 3A, the substrate 200 has an upper surface 202 and a lower surface 204. The starting halogenated optical material layer 206 has an upper surface 208 and a lower surface 210 and is a solid material. The starting halogenated optical material layer 206 will have an original index of refraction n0. The starting halogenated optical material layer 206 is positioned on the substrate 200. The lower surface 210 of the starting halogenated optical material 206 is deposited, bonded, coated, grown or otherwise positioned on the upper surface 202 of the substrate. The starting halogenated optical material will be under tensile stress. The starting halogenated optical material 206 can be deposited, bonded, coated or grown on the substrate 200 so the starting halogenated optical material is stretched along the length of the optical material layer, placing the starting halogenated optical material layer under tensile stress parallel to its upper and lower surfaces 208 and 210. The halogenated optical material under stress forms a high index of refraction area in one direction and a low index of refraction area in a second direction. The high index of refraction n1 of the halogenated optical material under stress is higher than the normal index of refraction n0 of the halogenated optical material not under stress. The low index of refraction n2 of the halogenated optical material under stress is lower than the normal index of refraction n0 of the halogenated optical material not under stress. The difference in indexes of refraction between the high index of refraction and the high index of refraction in the halogenated optical material under stress is what causes the birefringence of the halogenated optical material under stress. Alternately, the starting halogenated optical material layer 206 can be stretched to place the starting optical material under tensile stress before it is positioned on the substrate. Mechanical or electromechanical means known to those of ordinary skill in the art can be used to place the starting halogenated optical material under tensile stress. The starting halogenated optical material layer while still under tensile stress is removed from the mechanical or electromechanical stretching means and positioned on the substrate by deposition, bonding, coating, or growth. Alternately, the mechanical or electromechanical stretching means can be part of the electron beam apparatus inside the chamber to stretch the starting halogenated optical material layer on the substrate placing the starting optical material under tensile stress during electron beam irradiation and heating. As shown in FIG. 3B, a large area electron beam 212 is incident at a perpendicular angle to the upper surface 208 of the starting halogenated optical material layer 206 under tensile stress and irradiates the optical material layer under tensile stress. The depth of the penetrating electron beam and the resulting thickness of the altered refractive index layer are determined by the dose, voltage and duration of the electron beam and accordingly can vary from the upper surface of the starting halogenated optical material layer to the lower surface. The angle of incidence of the electron beam irradiation can vary from the perpendicular to the optical material layer. Infrared radiation beams 214 will heat the substrate 200 through the lower surface 204 and, by heat transfer through the substrate, will heat the starting halogenated optical material 206. The electron beam 212 fully penetrates the depth or thickness 216 of the halogenated optical material layer under tensile stress between the upper surface 208 and the lower surface 210 of the halogenated optical material layer 206. As shown in FIG. 3C, the entire halogenated optical material layer 206 under tensile stress, after electron beam irradiation and heating, will have its birefringence lowered. The electron beam imparts sufficient energy to the chemical bonds in the optical materials to create scissions, which leads to the formation of additional networking bonds as these reactive entities recombine within the optical material The introduction of extra bonds within solid halogenated optical materials, including polymers, results in decreased birefringence of the halogenated optical material under tensile stress. The electron beam irradiation and heating will lower the high index of refraction of the halogenated optical material under tensile stress and raise the low index of refraction of the halogenated optical material under tensile stress. The differences in index of refraction between the high index of refraction area of and the low index of refraction area decrease which decreases the birefringence of the halogenated optical material under tensile stress. The electron beam irradiation and heating can reduce the differences in index of refraction between the high index of refraction area and the low index of refraction area until both areas have the same index of refraction eliminating the birefringence of the halogenated optical material under tensile stress. The halogenated optical material layer can be removed from the substrate by conventional chemical, etching or physical means. Alternately, a release layer can be deposited on the substrate and the starting halogenated optical material layer can be deposited on the release layer. The electron beam radiation and heat radiation will pass through the release layer without effecting the release layer or the transformation of the starting halogenated optical material layer. After the transformation process, the halogenated optical material layer can be lifted off the substrate by dissolving the release layer. The halogenated optical material layer can be removed from tensile stress and returned to a non-birefringent state. If the halogenated optical material layer is placed under tensile stress subsequently, its birefringence is lowered or eliminated. The electron beam apparatus and method can provide a layer of one decreased birefringence or non-birefringence integral and adjacent to a layer of birefringence with both layers under tensile stress and formed of the same optical material. As shown in FIG. 4A, the substrate 300 has an upper surface 302 and a lower surface 304. The starting halogenated optical material layer 306 has an upper surface 308 and a lower surface 310. The lower surface 310 of the starting halogenated optical material layer is deposited, bonded, coated, or otherwise positioned on the upper surface 302 of the substrate. The starting halogenated optical material layer 306 will have an original index of refraction n0 and a thickness 312. The starting halogenated optical material layer 306 is under tensile stress. As shown in FIG. 4B, a large area electron beam 314 is incident at a perpendicular angle to the upper surface 308 of the halogenated optical material layer 306 under tensile stress and irradiates the halogenated optical material layer under tensile stress. Infrared radiation beams 316 will heat the substrate 300 through the lower surface 304 and, by heat transfer through the substrate, will heat the starting halogenated optical material layer 306. The electron beam 314 partially penetrates the halogenated optical material layer to a depth or thickness 318 from the upper surface 308 between the upper surface 308 and the lower surface 310 of the halogenated optical material layer. The penetration depth 318 is less than the thickness 312 of the halogenated optical material layer. As shown in FIG. 4C, the partial penetration of the electron beam irradiation divides the optical material into a first sub-layer and a second sub-layer. The optical material layer 306 has a first or upper sub-layer 320 having an upper surface 308 and a lower surface 322 and a second or lower sub-layer 324 having an upper surface 326 and a lower surface 310. The lower surface 322 of the upper sub-layer is on the upper surface 326 of the lower sub-layer. The lower surface 310 of the lower sub-layer is on the upper surface 302 of the substrate. Since the starting halogenated optical material layer is one layer, after electron beam irradiation, the second sub-layer is integral and positioned adjacent and on top of the first sub-layer within the halogenated optical material layer. As shown in FIG. 4C, after electron beam irradiation and heating, the first or upper optical material sub-layer 320 of the halogenated optical material layer 306 under tensile stress will have its birefringence lowered. The lower surface 322 of the upper sub-layer 320 is at the irradiation penetration depth 318 of the electron beam. The upper sub-layer will have a thickness equivalent to the penetration depth of the electron beam. The electron beam imparts sufficient energy to the chemical bonds in the optical materials in the second sub-layer to create scissions, which leads to the formation of additional networking bonds as these reactive entities recombine within the optical material. The introduction of extra bonds within solid halogenated optical materials, including polymers, results in decreased birefringence of the halogenated optical material under tensile stress. The electron beam irradiation and heating will lower the high index of refraction of the halogenated optical material under tensile stress and raise the low index of refraction of the halogenated optical material under tensile stress. The differences in index of refraction between the high index of refraction area of and the low index of refraction area decrease which decreases the birefringence of the first or upper sub-layer of the halogenated optical material under tensile stress. The electron beam irradiation and heating can reduce the differences in index of refraction between the high index of refraction area of and the low index of refraction area until both areas have the same index of refraction eliminating the birefringence of the first or upper sub-layer of the halogenated optical material under tensile stress. The second or lower optical material sub-layer 324 of the halogenated optical material layer 306 under tensile stress, which was not exposed to the electron beam irradiation, will have the original birefringence of the starting optical material layer. The lower sub-layer will have a thickness 328 equivalent to the original thickness 312 of the starting optical material less the thickness 318 of the upper sub-layer. Since the starting halogenated optical material layer is one layer, after electron beam irradiation, the first sub-layer of decreased birefringence or non-birefringence is integral and positioned adjacent to the second sub-layer of birefringence within the halogenated optical material layer. The halogenated optical material layer under tensile stress will have adjacent sub-layers of different birefringence but formed from the same halogenated optical material. The halogenated optical material layer under tensile stress will have adjacent sub-layers of different birefringence without fabrication by deposition, without an intervening adhesive layer between the two sub-layers, and with both adjacent sub-layers being formed from the same optical material. The depth of the penetrating electron beam and the resulting thickness of the altered birefringence layer are determined by the dose, voltage and duration of the electron beam and accordingly can vary from the upper surface of the starting halogenated optical material layer to the lower surface. The electron beam irradiation and heating can reduce the differences in index of refraction between the high index of refraction area and the low index of refraction area until both areas have the same index of refraction eliminating the birefringence of the second sub-layer halogenated optical material under tensile stress. The halogenated optical material layer can be removed from the substrate by conventional chemical, etching or physical means. Alternately, a release layer can be deposited on the substrate and the starting halogenated optical material layer can be deposited on the release layer. The electron beam radiation and heat radiation will pass through the release layer without effecting the release layer or the transformation of the starting halogenated optical material layer. After the transformation process, the halogenated optical material layer can be lifted off the substrate by dissolving the release layer. The halogenated optical material layer can be removed from tensile stress and returned to a non-birefringent state. If the halogenated optical material layer is placed under tensile stress subsequently, its birefringence is lowered or eliminated. An aperture mask can be used with the electron beam apparatus and method to provide a birefringence section integral and adjacent to a decreased birefringence or non-birefringence section with both sections formed of the same halogenated optical material. The aperture mask can be used with the electron beam apparatus and method to pattern a birefringence section integral and adjacent to a decreased birefringence or non-birefringence section with both sections formed of the same halogenated optical material. As shown in FIG. 5A, the substrate 400 has an upper surface 402 and a lower surface 404. The starting halogenated optical material layer 406 has an upper surface 408 and a lower surface 410. The lower surface 410 of the starting halogenated optical material layer is deposited, bonded, coated, or otherwise positioned on the upper surface 402 of the substrate. The starting halogenated optical material layer 406 will have an original index of refraction n0 and a thickness 412. The starting halogenated optical material layer 406 is under tensile stress. As shown in FIG. 5B, an aperture mask 414 is positioned between the electron beam source (not shown in this Figure) and the starting halogenated optical material layer 406 under tensile stress. The mask 414 has an upper surface 416 and apertures 418. A large area electron beam 420 is incident at a perpendicular angle to the upper surface 408 of the halogenated optical material layer 406 under tensile stress through the apertures 418 of the mask 414 and irradiates the halogenated optical material layer under tensile stress through the mask apertures 418. The electron beam 420 will be absorbed, or otherwise blocked, by the surface 416 of the mask 414 but will be transmitted through the apertures 418. Infrared radiation beams 422 will heat the substrate 400 through the lower surface 404 and, by heat transfer through the substrate, will heat the starting halogenated optical material 406. The electron beam 420 fully penetrates the depth or thickness 412 of the halogenated optical material layer 406 under tensile stress to the lower surface 410 of the halogenated optical material layer 406 and the upper surface 402 of the substrate 400 in the first sections 422 of the halogenated optical material layer 406 exposed to the electron beam through the apertures 418. Second sections 424 of the halogenated optical material layer 406 under tensile stress were not exposed to the electron beam 420 because the mask 414 absorbed or blocked the electron beam. As shown in FIG. 5C, the aperture mask 414 is removed. The halogenated optical material layer 406 is removed from the substrate 400 by conventional chemical, etching, physical means or the use of a release layer, as discussed previously. After heating and electron beam irradiation through the mask aperture, the first sections 422 of the halogenated optical material layer 406 under tensile stress will have its birefringence lowered. The electron beam imparts sufficient energy to the chemical bonds in the optical materials to create scissions, which leads to the formation of additional networking bonds as these reactive entities recombine within the optical material. The introduction of extra bonds within solid halogenated optical materials, including polymers, results in decreased birefringence of the halogenated optical material under tensile stress. The electron beam irradiation and heating will lower the high index of refraction of the first sections of the halogenated optical material under tensile stress and raise the low index of refraction of the first sections of the halogenated optical material under tensile stress. The differences in index of refraction between the high index of refraction area of and the low index of refraction area decrease in the first sections of the halogenated optical material layer, which decreases the birefringence of the halogenated optical material under tensile stress. The electron beam irradiation and heating can reduce the differences in index of refraction between the high index of refraction area and the low index of refraction area until both areas in the first sections of the halogenated optical material layer have the same index of refraction eliminating the birefringence in the first sections of the halogenated optical material under tensile stress. The second sections 424 of the halogenated optical material layer 406 under tensile stress, which was not exposed to the electron beam irradiation, will have the original birefringence of the starting optical material layer. Since the starting halogenated optical material layer is one layer, after electron beam irradiation, the first sections of decreased birefringence or non-birefringence are integral and positioned adjacent to the second sections of birefringence within the halogenated optical material layer. The mask serves to restrict the electron beam spatially limiting its irradiation to the apertured sections of the halogenated optical material layer. As shown in FIG. 5D, the apertures 418 in the mask 414 can form a pattern. Thus, after electron beam irradiation through the apertures in the mask, the halogenated optical material layer under tensile stress will have a pattern of decreased birefringence or non-birefringence in the birefringent halogenated optical material layer. Conversely, using a mirror or reverse pattern to the apertures in the mask, after electron beam irradiation through the apertures in the mask, the halogenated optical material layer under tensile stress will have a pattern of birefringence in the decreased birefringent or non-birefringent halogenated optical material layer. The patterned birefringence in the halogenated optical material layer under tensile stress has many practical applications including but not limited to identification markings or cards. By using the mask aperture, the halogenated optical material layer under tensile stress will have adjacent sections of different birefringence but formed from the same halogenated optical material. By using the mask aperture, the halogenated optical material layer under tensile stress will have adjacent sections of different birefringence without fabrication by deposition, without an intervening adhesive layer between the structure and layer or between adjacent sections, and with both adjacent sections being formed from the same halogenated optical material. The depth of the penetrating electron beam and the resulting thickness of the altered birefringence layer are determined by the dose, voltage and duration of the electron beam and accordingly can vary from the upper surface of the starting halogenated optical material layer to the lower surface. The aperture mask 414 of FIG. 5 can be used with the halogenated optical material layer 306 of FIG. 4 to provide a masked or patterned upper sub-layer 320 of decreased birefringence or non-birefringence. An embossing structure can be used with the electron beam apparatus and method to provide a birefringence section integral and adjacent to a decreased birefringence or non-birefringence section with both sections formed of the same halogenated optical material. The embossing structure can be used with the electron beam apparatus and method to pattern a birefringence section integral and adjacent to a decreased birefringence or non-birefringence section with both sections formed of the same halogenated optical material. As shown in FIG. 6A, the substrate 500 is a support ring with an upper surface 502 and a lower surface 504. The starting halogenated optical material layer 506 has an upper surface 508 and a lower surface 510. A small portion 512 of the lower surface 510 of the starting halogenated optical material layer is deposited, bonded, coated, or otherwise positioned on the upper surface 502 of the substrate support ring. A large portion 514 of the lower surface 510 of the starting halogenated optical material layer remains exposed. The support ring can substitute for a substrate layer in this and other embodiments of the present invention. The starting halogenated optical material layer 506 will have an original index of refraction n0 and a thickness 516. The starting halogenated optical material layer 506 is under tensile stress. As shown in FIG. 6B, an embossed structure 518 is formed of photoresist or wax has a pattern 520 (in FIG. 6C) on its upper surface 522. Returning to FIG. 6B, the lower surface 524 of the embossed structure 518 is flat and deposited or positioned on the upper surface 508 of the starting halogenated optical material layer 506. A large area electron beam 526 is incident at a perpendicular angle to the upper surface 522 of the embossed structure 518 and irradiates the embossed structure 518 and the starting halogenated optical material layer 506 under tensile stress. Infrared radiation beams 528 will heat the starting optical material 506 through the exposed portion 514 of the lower surface 510 of the starting halogenated optical material layer 506. The electron beam 526 fully penetrates the embossed structure 518 and fully penetrates the starting optical material layer 506 under tensile stress through the sections of the pattern 520 to the lower surface 510 of first sections 530 of the halogenated optical material layer 506. Second sections 532 of the halogenated optical material layer 506 under tensile stress were not exposed to the electron beam 526 because the pattern 520 absorbed or blocked the electron beam. As shown in FIG. 6D, the embossing structure 518 of photoresist is removed by conventional means. The optical material layer 506 is removed from the substrate support rings 500 by conventional chemical, etching, physical means or the use of a release layer, as discussed previously. After heating and electron beam irradiation through the embossing structure, the first sections 530 of the halogenated optical material layer 506 under tensile stress will have its birefringence lowered. The electron beam imparts sufficient energy to the chemical bonds in the optical materials to create scissions, which leads to the formation of additional networking bonds as these reactive entities recombine within the optical material. The introduction of extra bonds within solid halogenated optical materials, including polymers, results in decreased birefringence of the halogenated optical material under tensile stress. The electron beam irradiation and heating will lower the high index of refraction of the first sections of the halogenated optical material under tensile stress and raise the low index of refraction of the first sections of the halogenated optical material under tensile stress. The differences in index of refraction between the high index of refraction area of and the low index of refraction area decrease in the first sections of the halogenated optical material layer, which decreases the birefringence of the halogenated optical material under tensile stress. The electron beam irradiation and heating can reduce the differences in index of refraction between the high index of refraction area and the low index of refraction area until both areas in the first sections of the halogenated optical material layer have the same index of refraction eliminating the birefringence in the first sections of the halogenated optical material under tensile stress. The second sections 532 of the halogenated optical material layer 506 under tensile stress, which was not exposed to the electron beam irradiation, will have the original birefringence of the starting optical material layer. Since the starting halogenated optical material layer is one layer, after electron beam irradiation, the first sections of decreased birefringence or non-birefringence are integral and positioned adjacent to the second sections of birefringence within the halogenated optical material layer. The embossing structure 518 has a pattern 520 on its upper surface 522 which patterns the birefringence of the halogenated optical material layer. Thus, after electron beam irradiation through the patterned embossing structure, the halogenated optical material layer under tensile stress will have a pattern of decreased birefringence or non-birefringence in the birefringent halogenated optical material layer. Conversely, using a mirror or reverse pattern to the embossing structure, after electron beam irradiation through the pattern, the halogenated optical material layer under tensile stress will have a pattern of birefringence in the decreased birefringent or non-birefringent halogenated optical material layer. The patterned birefringence in the halogenated optical material layer under tensile stress has many practical applications including but not limited to identification markings or cards. By using the embossing structure, the halogenated optical material layer under tensile stress will have adjacent sections of different birefringence but formed from the same halogenated optical material. By using the embossing structure, the halogenated optical material layer under tensile stress will have adjacent sections of different birefringence without fabrication by deposition, without an intervening adhesive layer between the structure and layer or between adjacent sections, and with both adjacent sections being formed from the same halogenated optical material. The depth of the penetrating electron beam and the resulting thickness of the altered birefringence layer are determined by the dose, voltage and duration of the electron beam and accordingly can vary from the upper surface of the starting halogenated optical material layer to the lower surface. The embossing structure 518 of FIG. 6 can be used with the halogenated optical material layer 306 of FIG. 4 to provide a masked or patterned upper sub-layer 320 of decreased birefringence or non-birefringence. With the novel method and apparatus described in the present invention, birefringent materials can be altered to impart a three dimensional birefringence profile, which can be used in a number of useful optical components. Potential components which can be fabricated with this method are: compensation films for LCDs, birefringent optical devices for telecommunications, security devices (encoded security marks for currency, ID tags, liquor labels, cigarettes, DVDs, CDs, etc.). While there has been described herein the principles of the invention, it is to be clearly understood to those skilled in the art that this description is made only by way of example and not as a limitation to the scope of the invention. Accordingly, it is intended, by the appended claims, to cover all modifications of the invention, which fall within the true spirit and scope of the invention.
043022880	abstract	In a system, such as a water-cooled nuclear reactor, water level sensors provide signals to a control channel for control of feedwater flow and hence the water level in the pressure vessel. Rapid and fine level control is provided by comparing fluid outflow and inflow. Means are provided to block automatically the flow comparison signal from the control circuit in response to a signal characteristic of a faulted flow comparison signal. At least one redundant control channel is provided and level control is transferred thereto automatically upon excusion of the water level beyond predetermined normal upper and lower limits or in response to a rapid change in the water level control signal to avoid unnecessary shutdown in the event of a faulted channel.
	abstract	A control rod guide frame has a central passage of constant cross-section as a function of position along a central axis that passes through the central passage. The central passage is sized and shaped to guide a traveling assembly including at least one control rod as it moves along the central axis. The control rod guide frame comprises at least two radial guide frame sections secured around and defining the central passage. Each radial guide frame section may comprise an extruded radial guide frame section, which may be made of extruded steel. The central passage may include control rod guidance channels parallel the central axis and machined into the extruded radial guide frame sections. The at least two radial guide frame sections may be interchangeable. In some embodiments the at least two radial guide frame sections consist of between four and eight radial guide frame sections.
	abstract	A pressurized water reactor (PWR) includes a vertical cylindrical pressure vessel and a nuclear reactor core disposed in a lower vessel section. A hollow cylindrical central riser is disposed concentrically inside the pressure vessel. A downcomer annulus is defined between the central riser and the pressure vessel. A reactor coolant pump (RCP) includes (i) an impeller disposed above the nuclear reactor core and in fluid communication with the downcomer annulus to impel primary coolant downward through the downcomer annulus, (ii) a pump motor disposed outside of the pressure vessel, and (iii) a drive shaft operatively connecting the pump motor with the impeller. The PWR may include an internal steam generator in the downcomer annulus, with the impeller is disposed below the steam generator. The impeller may be disposed in the downcomer annulus. The RCP may further comprise a pump casing that with the impeller defines a centrifugal pump.
046474234	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention relates generally to fuel handling apparatus 10 (FIG. 2) for transporting fuel elements 12 into a nuclear reactor vessel 14 and withdrawing them therefrom, and for positioning fuel elements 12 in predetermined locations within the vessel 14. Referring particularly to FIG. 1, there is shown a high temperature gas-cooled reactor (HTGR) 16 which includes a vessel 14 defining an enclosed interior and a core 18 made up of a plurality of individual fuel elements 12 resting upon a support platform 20 within the interior of the vessel. The vessel includes inner and outer walls 15a and 15b respectively. A plurality of control rods 22 which may be inserted into the core 18 from beneath the support platform 20 are driven by control rod drives 24. An upper portion 26 of the vessel 14 encloses heat transfer apparatus (not shown). The vessel 14 includes a penetration or refueling port 28 which provides access to the interior of the vessel for the fuel handling apparatus 10 through the side 30 of the vessel. The vessel is surrounded by thick walls 32 made of concrete or the like which shield the surrounding environment from radiation emitted by the reactor 16. Referring now to FIG. 2, there is shown a transfer chute 34 for receiving spent fuel elements 12 and a conveyor 36 located at the terminal end of the chute 34. Spent fuel elements may be removed from the core 18 and lowered through the transfer chute 34 to the conveyor 36. New fuel elements may be brought to the bottom of the transfer chute 34 by the conveyor 36, lifted through the transfer chute 34 and placed in the core 18 by means of the fuel handling apparatus 10. The fuel handling apparatus 10 includes an outer support housing 38 defining a longitudinal axis extending through the penetration 28 and a support member 40 mounted for motion longitudinally or axially of the housing 38 within the housing. Lateral transportation of the support member 40 through the housing 38 is accomplished by longitudinal movement of the support member 40 within the housing 38 by lateral transport means 41. Heretofore, no known device has provided means for transporting fuel elements through a relatively small penetration in the side of a reactor vessel while also providing means for applying both upward and downward force to fuel elements within the vessel. In accordance with the present invention, the fuel handling apparatus 10 includes reversible lifting means 42 (FIG. 3) which are pivotal between a first orientation wherein the lifting means 42 may be used to lift or lower fuel elements 12, and a second orientation wherein the lifting means and a fuel element 12 supported thereby may be withdrawn from the vessel 30 through a relatively small penetration 28. The lifting means 42 preferably include an extendable member 44 which can positively transmit either upward or downward force to the fuel element 12. Grapple means 64 are mounted on the end of the extendable member 44 for detachably supporting a fuel element 12. Because the various fuel elements 12 are positioned directly adjacent other fuel elements 12 in the core 18 with their adjacent sides oriented vertically, it is desirable that the fuel handling apparatus 10 be capable of lifting and lowering the elements vertically. Accordingly, the fuel handling apparatus 10 should include means for positioning the lifting means 42 directly above any of the fuel elements 12. In addition, it is desirable that this be accomplished by fuel handling apparatus 10 extending through a single, relatively small penetration 42, and that the fuel handling apparatus 10 be capable of carrying the fuel elements 12 through this penetration and over a relatively long distance laterally to the transfer chute 34. In accordance with the present invention, the lateral transport means 41 preferably comprises a telescoping member 48 and suitable means (not shown) which may be of known design for extending and retracting the telescoping member 48 to transport the support member 40 laterally along the axis of the housing 38 to move the lifting means 42 between a first position within the vessel 14 and a second position within the housing 38 above the transfer chute 34. The support member 40 includes first pivot means 52 defining a vertical axis for pivotal mounting of a first arm 54. The first arm 54 includes second pivot means 56 defining a horizontal axis for pivotally supporting the second arm 58. The second arm 58 rigidly supports the lifting means 42. Suitable means 60 and 62 are provided for pivoting the first and second arms 54 and 58 respectively about the respective first and second pivot means 52 and 56. The lifting means 42 may be positioned above any desired fuel element 12 by a combination of longitudinal movement of the support member 40 and pivoting of the first arm 54 about the vertical axis defined by the first pivot means 52. At any position of the support member 40 within the vessel, the first arm 54 provides access to a range of positions transversely displaced from the longitudinal axis of the housing 38. When the apparatus 10 is used for moving a fuel element 12 vertically, the second arm 58 and lifting means 42 are placed in a first (vertical) position, shown in broken lines in FIGS. 2 and 3, and the extendable member 44 of the lifting means 42 is extended or retracted to lower or lift the element 12 as desired. When the element 12 is to be transported laterally through the penetration 28 or along the interior of the housing 38, the second arm 58 is placed in its second (approximately horizontal) position, shown in solid lines in FIGS. 2 and 3, with the fuel element 12 suspended in an upright position from the grapple means 64. In this position, the lifting means and fuel element 12 may pass through the penetration 28. The dimension of the lifting means 42 is greatest along its direction of movement. Accordingly, if the lifting means 42 were maintained in its first position with a fuel element 12 suspended therebeneath during passage through the penetration 28, a larger penetration would be required. Mounting the lifting means 42 in an arm 58 which may be pivoted from the vertical position prior to transportation through the penetration enables the lifting means 42 and fuel element 12 supported thereby to travel through a relatively small penetration 28. In the illustrated embodiment, movement of the lifting means 42 in a direction parallel to the axis of the housing 38 is accomplished by movement of the support member 40 longitudinally of the housing. Horizontal movement of the lifting means 42 transversely of the axis of the housing 38 may be accomplished by pivoting the first arm 54 about the vertical axis through the support member. Accordingly, the lifting means may be positioned directly above any location within the core for vertical access to such location by a combination of longitudinal movement of the support member 40 and pivotal movement of the first arm 54 about the first pivot means 52. Herein, the lifting means 42 are rigidly mounted on or within the second arm 58. The extendable member 44 of the lifting means 42 preferably comprises a storable tubular extendable member (STEM) which can be loaded either in tension or compression to apply either upward or downward force to a fuel element 12 during operation. Turning now to a more detailed description of the preferred embodiment of the present invention, the horizontal axis defined by the support housing 38 preferably extends through the center of the penetration 28. To avoid requiring the fuel handling apparatus 10 to be positioned directly adjacent the penetration 28, a tubular connector member 66 extends therebetween when the fuel handling apparatus 10 is in position for use, as shown in FIG. 2. The connector member 66 is supported by an annular support 68. The fuel handling apparatus 10 is preferably movable so that it can be removed from the position shown in the figures. To prevent or restrict release of radioactive matter or of radiation from the connector member 66 when the fuel handling apparatus 10 is not in position, an isolation valve 70 is provided at the outer end of the connector member 66 and may be closed when the fuel handling apparatus 10 is not in position. The valve 70 may be opened when the apparatus 10 is in position to enable access to the interior of the vessel 14. When the fuel handling apparatus 10 is in position, and the isolation valve 70 is open, an enclosed interior space is defined by the adjacent interiors of the support housing 38 of the fuel handling apparatus 10, the connector member 66, and the vessel 14. To prevent emission of radiation or contaminated matter from this interior space, suitable sealing means 72 such as inflatable seals are provided at the interfaces between the fuel handling apparatus 10 and the isolation valve 70. To facilitate transportation of the fuel handling apparatus 10 into and out of position, it is preferably supported movably. To this end, in the illustrated embodiment, suspension means 74 are provided for supporting the fuel handling apparatus 10 from above. The suspension means 74 herein comprise a pair of parallel I-beams 78 supported by a wall 32 above the housing 38, and two pair 80 of rollers 82, each pair 80 being rotatably mounted on opposite sides of an associated clevis 84 which is connected to the housing 38 and supported by the upper surface of the lower flange 86 of an associated I-beam so that each pair may roll along the length of its associated I-beam with one roller on each side of the web 86 of the I-beam. An annular support 88 extends about the housing 38 beneath each clevis 84 and is connected to its associated clevis by a link 89. It will be appreciated that various other means for movably supporting the fuel handling apparatus may be suitable. To provide a barrier to radiation during operation of the reactor in addition to the isolation valve, a suitable plug of known design may be removably inserted within the penetration 28 or connector member 66. As stated above, the preferred lifting means 42 includes a storable tubular extendable member (STEM) 44 which may be loaded longitudinally either in tension or in compression to apply force to fuel elements 12 during handling thereof. In the illustrated embodiment, the lifting means 42 employs two cooperating extendable members forming a single STEM and is known as a "BI-STEM" device. Referring particularly to FIGS. 5 and 6, the BI-STEM comprises two ribbons 90 made of metal or another suitable material which are stored on spools or reels 92. To extend the BI-STEM into a generally linear configuration, the ribbons 90 are curved or bent into overlapping, transversely curved configurations to form a single elongated, relatively rigid member 44 of generally circular cross section. The BI-STEM device is of known design. Devices of this type are obtainable from Spar Aerospace Products, Ltd. The BI-STEM device includes suitable means 91 for imparting curvature to the respective ribbons 90 and suitable drive means 93 for rotating the reels to extend or retract the extendable member 44. The grapple means 64 preferably comprises a grapple head which releasably supports a fuel element 12 by inserting a probe into a bore in the top of the fuel element and engaging lands formed on the internal surface of the bore as described in U.S. Pat. No. 3,383,286 to Paget. To enable the second arm 58 to pivot about the horizontal axis 56 with a fuel element 12 suspended from the grapple head 64 in an upright position, the grapple head is preferably pivotally supported by a pivot pin 94 extending through the end of the BI-STEM. In the illustrated embodiment, slots 96 are formed in the end of the second arm and when the STEM is fully retracted, the pivot pin 94 is pulled into the slots so as to be pivotally supported on the end of the second arm 58. In the alternative, it may be desirable to pivot the fuel element 12 into a horizontal orientation or another orientation other than the upright orientation illustrated to facilitate transportation of the fuel element 12 through the penetration 28. Accordingly, it may be desirable to provide means for constraining the grapple head 64 against pivoting with respect to the second arm 58. It will be appreciated that by allowing the fuel element 12 to be suspended in an upright position, as in the preferred embodiment, the magnitude of the moment which must be applied to the second arm 58 to pivot it upward to its second position need not be as great as would be required if the fuel element were to be angularly displaced simultaneously with the pivoting of the second arm. Turning now to FIG. 7, there is shown an alternative embodiment of the present invention wherein a telescoping lifting member 44a is used instead of a STEM device as described above. Otherwise, the fuel handling apparatus illustrated in FIG. 7 is essentially the same as that described above, and includes lateral transport means 41a comprising a telescoping member 48a having a support member 40a on its end. From the foregoing, it will be appreciated that the present invention provide a novel fuel handling apparatus for a nuclear reactor. While a preferred embodiment is illustrated and described herein, there is no intent to limit the invention to this or any other particular embodiment. The scope of the invention is defined by the spirit and language of the appended claims.
	claims	1. A process for the selective extraction of electrons from atoms or molecules or both or the selective insertion of electrons into atoms or molecules or both and the partial or complete decomposition of molecules and the composition of molecules, comprising:a. providing a means to control a field through adjustment of the net average charge per atom within a substance,b. providing a means for the extraction of electrons by the application of a controlled field over a substance,c. providing a means for the production of a field through any of or combination selected from the group consisting of electric, magnetic or electromagnetic sources,d. providing a means for the positive ionization of atoms or molecules permitted to enter the field or apertures of the substance,e. providing a means to produce a continuous supply of positive ions without the production of unwanted negative ions,f. providing a means to control the extraction of one or more electrons in order of their ionization potential from an atom or molecule for the production of +1, +2, +3 or greater positive ions,g. providing a means for the insertion of electrons by the application of a controlled field over a substance,h. providing a means to produce a continuous supply of negative ions without the production of unwanted positive ions,i. providing a means for the negative ionization of atoms or molecules permitted to enter the field or apertures of the substance,j. providing a means to control the insertion of one or more electrons into an atom or molecule for the production of −1 or greater negative ions,k. providing a means for the controllable simultaneous production of positive and negative ions,l. providing a means of control for one or more constituent atoms to be extracted from selected molecules,m. providing a means of control for larger molecules to be selectively decomposed into smaller molecules,n. providing a means to control the complete decomposition of selected molecules,o. providing a means to control the composition of selected molecules.
041475895	claims	1. A control rod assembly adapted for use in a nuclear reactor, said control rod assembly comprising a control rod having a shoulder, a drive shaft assembly, a coupling connecting said drive shaft assembly to said control rod and cooperating pin and cylindrical detent members connected to said drive shaft for operating said coupling to couple and uncouple said drive shaft assembly from said control rod, said cylindrical detent member being formed to captively hold said pin member in contact with said detent member in one of two axially spaced positions, one position creating coupling and the second position creating uncoupling of the drive shaft assembly from the control rod, said detent member being moved from one position to the other by a predetermined unidirectional rotation of said detent member which results from a lowering and subsequent lifting of said drive shaft assembly, said coupling including a plunger member and a radially biased resilient member having a shoulder cooperatively configured to engage said control rod shoulder, said resilient and plunger members being affixed to said drive shaft assembly and axially movable with respect to one another upon said movement of said detent member so as to radially move said resilient member shoulder into and out of engagement with said control rod shoulder. 2. The control rod assembly of claim 1, wherein said drive shaft assembly includes a rigid drive shaft, said detent member comprising a grooved cylinder which is mounted to said drive shaft for rotational movement thereon, a cylindrical member slidingly mounted onto said drive shaft, said cylindrical member having said pin member fixedly connected to the wall thereof, and a biasing member positioned to act on said cylinder member and said drive shaft such that said pin member is forcefully held in either of said two axially spaced positions in said detent member. 3. The control rod assembly of claim 2, wherein said grooved cylinder includes a pair of axially spaced arrays of grooves formed in said cylinder, with said pair of arrays of grooves being spaced by a portion of said grooved cylinder having its surface coplanar with the bottom surface of said grooves, said groove arrays being rotated relative to each other by an amount substantially equal to one-half the pitch distance between grooves, the entranceway to each groove from said spacing portion of the cylinder having a corner cut away so as to form a cammed surface, said grooves thereby being arranged to rotate said grooved cylinder one pitch distance by the force exerted by said pin member on said cammed surfaces during one lowering and lifting cycle of said drive shaft assembly, and during said lowering and lifting cycle, said pin member being positioned in one of said axial positions and then the other. 4. The control rod assembly of claim 3, wherein said pair of arrays of grooves in said grooved cylinder comprise a first array with each groove extending coextensively, and a second array with adjacent grooves extending alternately to one and then the other of said axially spaced positions of said pin member, said second array thereby having alternate grooves extending coextensively. 5. The control rod assembly of claim 1, wherein said detent member comprises a cylinder mounted to said drive shaft for rotational movement thereon and having two axially spaced arrays of grooves formed therein, said grooves serving to guide said movement of said detent member, said groove arrays being operationally interconnected by a portion of said detent cylinder having its surface coplanar with the bottom surface of said grooves, said groove arrays being rotated relative to each other by an amount substantially equal to one-half the pitch distance between grooves, and the entrance to each groove being cammed. 6. A control rod assembly adapted for use in a nuclear reactor, said control rod assembly comprising a control rod, a drive shaft assembly, a coupling connecting said drive shaft assembly to said control rod and cooperating pin and cylindrical detent members connected to said drive shaft for coupling and uncoupling said drive shaft assembly from said control rod, said detent member being formed to captively hold said pin member in contact with said detent member in one of two axially spaced positions, one position creating coupling and the second position creating uncoupling of the drive shaft assembly from the control rod, said detent member being unidirectionally rotatable such that said pin is positioned in one of said axial positions and then the other, said unidirectional rotation of said detent member resulting from a lowering and subsequent lifting of said drive shaft assembly, said coupling of the control rod with the drive shaft assembly including a shouldered indentation formed within the coupling end of said control rod, and a plurality of resilient members having a shouldered protrusion thereon for engaging with said shouldered indentation to couple the control rod with the drive shaft assembly, said plurality of resilient members being biasly formed radially so as to be normally disengaged from said shouldered indentation, the resilient members being mounted concentric with said drive shaft assembly, and such that an enlarged end of the drive shaft assembly having a cross-sectional configuration greater than an opening circumscribed by said resilient members is located axially adjacent the ends of said resilient members, whereby motion of the drive shaft assembly relative to the resilient members causes said enlarged end of the drive shaft to force the ends of said resilient members radially outward into engagement with said shouldered indentation in the control rod. 7. The control rod assembly of claim 6, wherein said resilient members are mounted to a cylinder member being concentrically mounted to said drive shaft and axially movable with respect thereto, and said axial position of the enlarged end of the drive shaft assembly so as to couple the control rod with the drive shaft by forcing the resilient members into engagement with the indentation in the control rod is fixed by the relative axial position of said pin member in said detent member. 8. A control rod assembly adapted for use in a nuclear reactor, said control rod assembly comprising a control rod, a drive shaft assembly, and a coupling connecting said control rod to said drive shaft assembly, said coupling including cooperating lug and detent means for connecting and disconnecting said control rod from said drive shaft assembly, said detent means including a cylinder mounted to said drive shaft assembly for unidirectional rotational movement thereon and being formed to hold said lug means in engagement therewith so as to connect said drive shaft assembly to said control rod, and to allow said lug means to be disengaged from said detent means so as to disconnect said drive shaft assembly from said control rod, said lug means being moved from engagement to disengagement with said detent means by a predetermined rotation of said detent means which results from a lowering and subsequent lifting of said drive shaft assembly, said detent cylinder further comprising three axially spaced arrays of grooves formed therein, with a first and second of said arrays of grooves being axially adjacent and serving to guide the movement of the lug means from engagement to disengagement with said detent means, and the third array of grooves being axially adjacent said second array and serving to allow axial separation of said lug means from said detent means, each of said arrays of grooves being operationally interconnected by portions of said detent cylinder having its surface coplanar with the bottom surface of said grooves, the first and second of said groove arrays having an equal number of grooves, said first and second groove arrays being rotated relative to each other such that each groove of each array is positioned along an axial line which lies between adjacent grooves in the opposite array, said third array of grooves having one half the number of grooves of said first and second arrays, with the grooves in said third array being aligned axially with every other groove in said second array, said first and said second arrays having the entranceway to each groove cammed such that movement of said lug means from a groove in one array to the other causes a rotation of said detent cylinder about its axis an amount corresponding to the pitch distance between opposite grooves in said first and said second arrays of grooves. 9. The control rod assembly of claim 8 wherein said lug means comprises at least one protruding member fixedly mounted to said control rod, and said control rod assembly further comprises a biasing member included with said drive shaft assembly positioned to hold said lug means against a shoulder formed within said detent cylinder so as to maintain connection of said drive shaft assembly with said control rod.
041772415	summary	BACKGROUND OF THE INVENTION This invention relates to a process and an apparatus for recovering nuclear fuel materials such as uranium oxide compounds from scrap materials containing such compounds. The residue (herein generally called "scrap" or "scrap materials") from many nuclear fuel processing operations can be in various forms and contain a sufficiently high concentration of the nuclear fuel to justify its recovery. Generally, one of the preliminary steps in a nuclear fuel recovery process comprises calcining scrap materials to remove the volatile matter and then dissolving the soluble portion of the resulting calcine in an acid. Such a process has been conducted using a calciner and a slab-shaped leaching apparatus. The prior art also includes dry processes for nuclear fuel recovery from scrap, with a representative process being disclosed in U.S. Pat. No. 3,578,419 in the name of Richard K. Welty and assigned to the same assignee as the present invention. This patent discloses a process for recovering hard scrap nuclear reactor fuel material in which the scrap is first oxidized in a fluidized bed and then comminuted, after which the oxidized material is reduced back to the original chemical form prior to the oxidation step with improved sintering characteristics. The foregoing processes are not suitable for the efficient recovery of enriched nuclear fuel, such as uranium compounds, from filter media used to filter the air drawn from nuclear fuel processing operations. Typically, these filters (e.g., High Efficiency Particulate Air or HEPA filters) are made of fiberglass or include some fiberglass in the filter media. When incinerated, the fiberglass forms a clinker that can encapsulate the uranium and is insoluble in most commonly used acids. In the past, ventilation filters have simply been disposed of by burial, or have been acid leached as a whole unit in a large tank. The leaching of filter media precludes complete recovery of the nuclear fuel and is, in addition, a manpower intensive operation that utilizes large volumes of acid. Typically, the materials other than filter media containing small amounts of enriched nuclear fuel result from the processing of the enriched nuclear fuel into a form, commonly oxide or carbide, suitable for utilization in nuclear reactors. In greater detail, such materials are rags, uniforms, gloves, plastic, oils, etc. It has been found that when such materials are incinerated, they form chunks of various sizes that need to be comminuted or ground to a smaller uniform size in order to be efficiently leached in an acid solution. Accordingly, it has remained desirable to have a system for the efficient recovery of nuclear fuel materials from filter media, incinerator ash and other particulate materials. OBJECTS OF THE INVENTION It is an object of this invention to provide a process for recovering nuclear fuel material from filter media and other scrap materials by converting these materials to a form suitable for leaching the nuclear fuel from these materials in an acid solution. Another object of this invention is to provide a process for recovering nuclear fuel materials from filter media and other scrap material designed to be totally safe from a consideration of nuclear criticality through all stages of operation. Still another object of this invention is to provide a process for recovering nuclear fuel from ventilation filters and other scrap materials in the form of a solution highly concentrated in the nuclear fuel through use of a recycle step for recirculating a portion of the solution to a leaching step. Other objects and advantages of this invention will become apparent from the following detailed description and the claims appended hereto and by reference to the attached drawings.
	description	The present application is a continuation application of International Application No. PCT/JP2015/081118 filed on Nov. 5, 2015. The content of the application is incorporated herein by reference in its entirety. The present disclosure relates to an extreme ultraviolet light generating device. Along with microfabrication of a semiconductor process in recent years, microfabrication of a transfer pattern in the photolithography of the semiconductor process has been progressing rapidly. In the next generation, microfabrication of 20 nm or smaller will be required. Accordingly, it is expected to develop an exposure device that has an extreme ultraviolet (EUV) light generating device that generates extreme ultraviolet (EUV) light having a wavelength of about 13 nm and a reflection reduction projection optical system in combination. As EUV light generating devices, three types of devices are proposed: an LPP (Laser Produced Plasma) type device that uses plasma generated when a target is irradiated with laser light, a DPP (Discharge Produced Plasma) type device that uses plasma generated by discharging, and an SR (Synchrotron Radiation) type device that uses orbital radiation light. Patent Literature 1: National Publication of International Patent Application No. 2007-528607 Patent Literature 2: National Publication of International Patent Application No. 2005-507489 Patent Literature 3: National Publication of International Patent Application No. 09-502254 An extreme ultraviolet light generating device, according to one aspect of the present disclosure, may include a chamber, a focusing mirror, a light source unit, and a light receiving unit. In the chamber, extreme ultraviolet light may be generated from a target supplied to a generation region. The focusing mirror may be configured to reflect the extreme ultraviolet light, generated in the generation region, by a reflection surface, and focus the light at a predetermined focal point farther from the reflection surface than the generation region. The light source unit may be connected with the chamber, and may be configured to output illumination light toward the target to be supplied to the generation region. The light receiving unit may be connected with the chamber, and may be configured to receive reflected light from the target, of the illumination light output toward the target, and capture an image of the target. The reflection surface of the focusing mirror may be formed in a spheroidal face that defines a first focus at the generation region and a second focus at the predetermined focal point. Assuming that a surface formed when an extended line, on the first focus side, of a line segment linking the outer peripheral edge of the reflection surface and the first focus is rotated about an axis passing through the first focus and the second focus, is a first limit surface, and assuming that a surface formed when the line segment linking the outer peripheral edge of the reflection surface and the first focus and an extended line, on the outer peripheral side, of the line segment are rotated about the axis passing through the first focus and the second focus, is a second limit surface, the light source unit and the light receiving unit may be disposed such that at least one of an optical path of the illumination light and an optical path of the reflected light passes through the first focus and is included in an internal space of the chamber located between the first limit surface and the second limit surface. Contents 1. Overall description of EUV light generation system 1.1 Configuration 1.2 Operation 2. Terms 3. Problem 3.1 Configuration of comparative example 3.2 Operation of comparative example 3.3 Problem 4. First embodiment 4.1 Configuration 4.2 Operation 4.3 Effect 5. Second embodiment 5.1 Configuration 5.2 Operation 5.3 Effect 6. Third embodiment 6.1 Configuration 6.2 Operation 6.3 Effect 7. Fourth embodiment 7.1 Configuration 7.2 Effect 8. Others Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The embodiments described below illustrate some examples of the present disclosure, and do not limit the contents of the present disclosure. All of the configurations and the operations described in the embodiments are not always indispensable as configurations and operations of the present disclosure. It should be noted that the same constituent elements are denoted by the same reference signs, and overlapping description is omitted. 1.1 Configuration FIG. 1 schematically illustrates a configuration of an exemplary LPP type EUV light generation system. An EUV light generating device 1 may be used together with at least one laser device 3. In the present application, a system including the EUV light generating device 1 and the laser device 3 is called an EUV light generation system 11. As illustrated in FIG. 1 and described below in detail, the EUV light generating device 1 may include a chamber 2 and a target supply device 26. The chamber 2 may be sealable. The target supply device 26 may be mounted so as to penetrate a wall of the chamber 2. The material of the target 27 to be supplied from the target supply device 26 may include, but not limited to, tin, terbium, gadolinium, lithium, xenon, or a combination of any two or more of them. A wall of the chamber 2 may have at least one through hole. The through hole may be provided with a window 21. Pulse laser light 32 output from the laser device 3 may penetrate the window 21. The inside of the chamber 2 may be provided with an EUV focusing mirror 23 having a spheroidal reflection surface. The EUV focusing mirror 23 may have a first focus and a second focus. On the surface of the EUV focusing mirror 23, a multilayer reflection film in which molybdenum and silicon are alternately layered may be formed. It is preferable that the EUV focusing mirror 23 is disposed such that the first focus is positioned in a plasma generation region 25 and the second focus is positioned at an intermediate focal point (IF) 292, for example. A center portion of the EUV focusing mirror 23 may be provided with a through hole 24 through which pulse laser light 33 may pass. The EUV light generating device 1 may include an EUV light generation control unit 5, a target sensor 4, and the like. The target sensor 4 may have an image capturing function, and may be configured to detect presence, trajectory, position, velocity, and the like of the target 27. The EUV light generating device 1 may also include a connecting section 29 that allows the inside of the chamber 2 and the inside of an exposure device 6 to communicate with each other. The inside of the connecting section 29 may be provided with a wall 291 having an aperture 293. The wall 291 may be disposed such that the aperture 293 is positioned at the second focus of the EUV focusing mirror 23. The EUV light generating device 1 may also include a laser light travel direction control unit 34, a laser light focusing mirror 22, a target collector 28 configured to collect the target 27, and the like. The laser light travel direction control unit 34 may include an optical element configured to define the travel direction of the laser light, and an actuator configured to adjust the position, posture, and the like of the optical element. 1.2 Operation Referring to FIG. 1, pulse laser light 31 output from the laser device 3 may pass through the laser light travel direction control unit 34, penetrate the window 21 as the pulse laser light 32, and may be made incident on the chamber 2. The pulse laser light 32 may travel inside the chamber 2 along at least one optical path of the laser light, may be reflected by the laser light focusing mirror 22, and may be radiated to at least one target 27 as the pulse laser light 33. The target supply device 26 may be configured to output the target 27 toward the plasma generation region 25 in the chamber 2. The target 27 may be irradiated with at least one pulse included in the pulse laser light 33. The target 27 irradiated with the pulse laser light 33 is made into plasma, and from the plasma, EUV light 251 may be radiated along with radiation of light having another wavelength. The EUV light 251 may be selectively reflected by the EUV focusing mirror 23. EUV light 252 reflected by the EUV focusing mirror 23 may be focused at the intermediate focal point 292, and output to the exposure device 6. It should be noted that one target 27 may be irradiated with a plurality of pulses included in the pulse laser light 33. The EUV light generation control unit 5 may be configured to preside over the control of the entire EUV light generation system 11. The EUV light generation control unit 5 may be configured to process image data or the like of the target 27 captured by the target sensor 4. Further, the EUV light generation control unit 5 may perform at least one of control of the output timing of the target 27 and control of the output direction and the like of the target 27, for example. Furthermore, the EUV light generation control unit 5 may perform at least one of control of the output timing of the laser device 3, control of the travel direction of the pulse laser light 32, and control of the focusing position of the pulse laser light 33, for example. The aforementioned various types of control are mere examples, and another type of control may be added when necessary. “Target” is an object to be irradiated with laser light introduced to the chamber. The target irradiated with laser light is made into plasma and emits EUV light. “Droplet” is a form of a target to be supplied to the chamber. “Plasma generation region” is a predetermined region in the chamber. Plasma generation region is a region where a target output to the chamber is irradiated with laser light, and the target is made into plasma. “Target trajectory” is a path on which a target output to the chamber travels. Target trajectory may intersect an optical path of the laser light introduced to the chamber in the plasma generation region. “Optical path axis” is an axis passing through the center of a beam cross section of the light along the travel direction of the light. “Optical path” is a path through which the light passes. Optical path may include the optical path axis. An EUV light generating device 1 of a comparative example will be described with use of FIGS. 2 and 3. The EUV light generating device 1 of the comparative example may be the EUV light generating device 1 including the target sensor 4. 3.1 Configuration of Comparative Example FIG. 2 is a diagram for explaining the configuration of the EUV light generating device 1 of the comparative example. The EUV light generating device 1 of the comparative example may include the chamber 2, the target supply device 26, and the target sensor 4. The chamber 2 may be a container in which the target 27 supplied to the inside by the target supply device 26 is irradiated with the pulse laser light 33 whereby EUV light 252 is generated, as described above. In the chamber 2, the laser light focusing mirror 22 and the EUV focusing mirror 23 may be provided. The laser light focusing mirror 22 may reflect the pulse laser light 32 passing through the window 21 and made incident thereon. The laser light focusing mirror 22 may focus the reflected pulse laser light 32 in the plasma generation region 25 as the pulse laser light 33. The EUV focusing mirror 23 may selectively reflect, by a reflection surface 231, light having a wavelength near a particular wavelength, of the EUV light 251 generated in the plasma generation region 25. The EUV focusing mirror 23 may focus the selectively reflected EUV light 251 at the intermediate focal point 292 that is a predetermined focal point, as the EUV light 252. The reflection surface 231 of the EUV focusing mirror 23 may be formed in a spheroidal face having a first focus F1 and a second focus F2. The first focus F1 may be located in the plasma generation region 25. The second focus F2 may be located at the intermediate focal point 292 that is farther from the reflection surface 231 than the plasma generation region 25. The target supply device 26 may be a device that melts the target 27 supplied to the chamber 2 and outputs it as a droplet 271 to the plasma generation region 25 in the chamber 2. The target supply device 26 may be a device that outputs the droplet 271 in a so-called continuous jet method. Operation of the target supply device 26 may be controlled by the EUV light generation control unit 5. The target supply device 26 may include a tank 261, a pressure regulator 262, a gas cylinder 263, and a biaxial stage 264. The tank 261 may contain the target 27 to be supplied to the chamber 2, in a molten state. The pressure regulator 262 may regulate the pressure when the inert gas in the gas cylinder 263 is supplied to the tank 261, to thereby regulate the pressure applied to the target 27 contained in the tank 261. Thereby, the pressure regulator 262 may regulate the velocity of the target 27 output from the inside of the tank 261 into the chamber 2 to a desired velocity. The biaxial stage 264 may move the tank 261 in a direction almost parallel to the X axis and the Y axis of a coordinate system described below with use of FIG. 4, to thereby regulate a target trajectory T of the target 27 output to the chamber 2 to be a desired trajectory passing through the plasma generation region 25. The target sensor 4 may detect the target 27 supplied to the plasma generation region 25. Specifically, the target sensor 4 may capture an image of the target 27 supplied to the plasma generation region 25, and measure the position, the velocity, or the target trajectory T of the target 27. Operation of the target sensor 4 may be controlled by the EUV light generation control unit 5. The target sensor 4 may include a light source unit 41 and a light receiving unit 42. The light source unit 41 may output illumination light toward the target 27 supplied to the plasma generation region 25. Specifically, the light source unit 41 may output illumination light to the first focus F1 located in the plasma generation region 25 and the vicinity of the first focus F1. The vicinity of the first focus F1 may be a region on the target trajectory T on the target supply device 26 side from the first focus F1. The light source unit 41 may be configured with use of a CW (Continuous Wave) laser that outputs continuous single-wavelength laser light, for example. Alternatively, the light source unit 41 may be configured with use of a lamp that outputs continuous light having multiple wavelengths, or the like. The light source unit 41 may be connected to a wall 2a of the chamber 2. The light source unit 41 may be disposed such that the emission port of the illumination light faces the first focus F1 located in the plasma generation region 25. The light receiving unit 42 may receive the reflected light from the target 27 to thereby capture an image of the target 27. The reflected light from the target 27 may be illumination light reflected by the target 27, of the illumination light output from the light source unit 41 toward the target 27 supplied to the plasma generation region 25. Specifically, the light receiving unit 42 may receive reflected light from the target 27 located at the first focus F1 in the plasma generation region 25 and the vicinity of the first focus F1, to thereby capture an image of the target 27. The light receiving unit 42 may be configured with use of an image sensor such as a CCD (Charge-Coupled Device), for example. The light receiving unit 42 may be connected with the wall 2a of the chamber 2. The light receiving unit 42 may be disposed on the optical path of the reflected light from the target 27. The light receiving unit 42 may be disposed such that an incident port of the reflected light from the target 27 faces the first focus F1 located in the plasma generation region 25. 3.2 Operation of Comparative Example Operation of the EUV light generating device 1 of the comparative example will be described. The target supply device 26 may output the target 27 contained in the tank 261 to the chamber 2. The output target 27 may travel on the target trajectory T toward the plasma generation region 25. The light source unit 41 may output illumination light to the first focus F1 located in the plasma generation region 25 and the vicinity of the first focus F1. When the target 27 output to the chamber 2 passes through the first focus F1, the illumination light output from the light source unit 41 may be radiated to the target 27. The light radiated to the target 27 may be reflected at the surface of the target 27. The reflected light from the target 27 may be received by the light receiving unit 42. The light receiving unit 42 may capture an image of the reflected light from the target 27. The light receiving unit 42 may acquire an image of the target 27. The light receiving unit 42 may measure the position, the velocity, or the target trajectory T of the target 27 from the acquired image. The light receiving unit 42 may transmit a signal representing the measurement result to the EUV light generation control unit 5. The EUV light generation control unit 5 may control the target supply device 26 based on the measurement result to thereby control the position, the velocity, or the target trajectory T of the target 27. 3.3 Problem FIG. 3 is a diagram for explaining the problem in the EUV light generating device 1 of the comparative example. The light receiving unit 42 of the target sensor 4 may receive reflected light from the target 27 and capture an image of the target 27, as described above. However, the light receiving unit 42 may capture an image of stray light, depending on the positions of the light source unit 41 and the light receiving unit 42. Stray light may be light unnecessary for measuring the position, the velocity, or the target trajectory T of the target 27, of the light received by the light receiving unit 42. Stray light may be light other than the reflected light from the target 27. In particular, illumination light output from the light source unit 41 may pass through the first focus F1 without being radiated to the target 27, and may be made incident on the reflection surface 231 of the EUV focusing mirror 23. In that case, the illumination light made incident on the reflection surface 231 may be reflected by the reflection surface 231, and reach the second focus F2 located at the intermediate focal point 292. The illumination light that reached the second focus F2 may be scattered by the wall 291 and the like existing around the second focus F2. At that time, part of the scattered light caused by the wall 291 and the like may be made incident on the reflection surface 231 again, and reflected by the reflection surface 231 again. In that case, the scattered light reflected by the reflection surface 231 may pass through the first focus F1, may be received by the light receiving unit 42, and may be captured as stray light. When the light receiving unit 42 captures an image of the stray light, the stray light may be reflected in an image acquired by the light receiving unit 42 such that it overlaps the image of the target 27, as illustrated in FIG. 3. Thereby, the light receiving unit 42 hardly recognizes the image of the target 27 correctly from the acquired image, and it is hard to measure the position, the velocity, or the target trajectory T of the target 27 correctly. Consequently, an error included in the measurement result may be large. Accordingly, it is desired to have a technology that enables the target 27 to be measured with high accuracy by suppressing the stray light that may be captured by the light receiving unit 42. An EUV light generating device 1 of a first embodiment will be described with use of FIGS. 4 to 6. The EUV light generating device 1 of the first embodiment may be different from the EUV light generating device 1 of the comparative example in the positions of the light source unit 41 and the light receiving unit 42. Regarding the configuration of the EUV light generating device 1 of the first embodiment, description of the same parts as the EUV light generating device 1 of the comparative example is omitted. FIG. 4 illustrates the internal space of the chamber 2 including the EUV focusing mirror 23, the first focus F1, and the second focus F2. In the coordinate system illustrated in FIG. 4, the first focus F1 located in the plasma generation region 25 is set to be the origin. In the coordinate system illustrated in FIG. 4, an axis passing through the first focus F1 and the second focus F2 is assumed to be the Z axis. The Z axis direction may be a direction from the first focus F1 toward the second focus F2. The Z axis direction may be a direction that the EUV light 252 is output from the chamber 2 to the exposure device 6. In the coordinate system illustrated in FIG. 4, an axis passing through the target supply device 26 and the plasma generation region 25 is assumed to be the Y axis. The Y axis direction may be a direction opposite to the direction that the target supply device 26 outputs the target 27 to the chamber 2. The Y axis may overlap the target trajectory T. In the coordinate system illustrated in FIG. 4, an axis orthogonal to the Y axis and the Z axis is assumed to be the X axis. Here, it is assumed that a line segment linking an outer peripheral edge 231a of the reflection surface 231 and the first focus F1 is a line segment K. An acute angle defined by the line segment K and the Z axis is assumed to be θm. θm may be 45° or larger but 90° or smaller, for example. Om may be any of 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, and 85°, for example. θm may be 84°, for example. An extended line on the first focus F1 side of the line segment K is assumed to be K1. An acute angle defined by the extended line K1 and the Z axis may be θm. An extended line on the outer peripheral edge 231a side of the line segment K is assumed to be K2. An acute angle defined by the extended line K2 and the Z axis may be θm. A face formed when the extended line K1 is rotated 2π [rad] about the Z axis is assumed to be a first limit surface Sf1. The first limit surface Sf1 may be in a form like a side face of a cone opened to the second focus F2 side, where the apex is the first focus F1 and the half vertical angle is θm. A face formed when the line segment K and the extended line K2 are rotated a [rad] about the Z axis is assumed to be a second limit surface Sf2. The second limit surface Sf2 may be in a form like a side face of a cone opened to the reflection surface 231 side, where the apex is the first focus F1 and the half vertical angle is θm. In the internal space of the chamber 2, a region of the second focus F2 side at least from the first limit surface Sf1 is assumed to be a first region Re1. In the internal space of the chamber 2, a region between the first limit surface Sf1 and the second limit surface Sf2 is assumed to be a second region Re2. Whether or not an image of stray light is captured in the light receiving unit 42 may depend on the positions of the light source unit 41 and the light receiving unit 42. FIG. 5 illustrates results of verifying the relationship between the positions of the light source unit 41 and the light receiving unit 42 and stray light under conditions 1 to 4. Condition 1 is the case where the optical path of the illumination light output from the light source unit 41 passes through the first focus F1 and is included in the second region Re2, and the optical path of the reflected light from the target 27 to be received by the light receiving unit 42 passes through the first focus F1 and is included in the first region Re1. In the case of condition 1, a verification result that an image of stray light was less likely to be captured by the light receiving unit 42 was obtained. Condition 2 is the case where the optical path of the illumination light output from the light source unit 41 passes through the first focus F1 and is included in the second region Re2, and the optical path of the reflected light from the target 27 to be received by the light receiving unit 42 passes through the first focus F1 and is included in the second region Re2. In the case of condition 2, a verification result that an image of stray light was less likely to be captured by the light receiving unit 42 was obtained. Condition 3 is the case where the optical path of the illumination light output from the light source unit 41 passes through the first focus F1 and is included in the first region Re1, and the optical path of the reflected light from the target 27 to be received by the light receiving unit 42 passes through the first focus F1 and is included in the second region Re2. In the case of condition 3, a verification result that an image of stray light was less likely to be captured by the light receiving unit 42 was obtained. Condition 4 is the case where the optical path of the illumination light output from the light source unit 41 passes through the first focus F1 and is included in the first region Re1, and the optical path of the reflected light from the target 27 to be received by the light receiving unit 42 passes through the first focus F1 and is included in the first region Re1. In the case of condition 4, a verification result that an image of stray light was likely to be captured by the light receiving unit 42 was obtained. This means that when at least one of the optical path of the illumination light output from the light source unit 41 and the optical path of the reflected light from the target 27 to be received by the light receiving unit 42 passes through the first focus F1 and is included in the second region Re2, an image of stray light is less likely to be captured by the light receiving unit 42. In other words, it is preferable that the light source unit 41 and the light receiving unit 42 are disposed such that at least one of the optical path of the illumination light and the optical path of the reflected light from the target 27 passes through the first focus F1 and is included in the internal space of the chamber 2 between the first limit surface Sf1 and second limit surface Sf2. Further, the internal space of the chamber 2 illustrated in FIG. 4 may be described with use of a polar coordinate system. In the polar coordinate system illustrated in FIG. 4, the first focus F1 located in the plasma generation region 25 may be the polar. In the polar coordinate system illustrated in FIG. 4, a distance from the first focus F1 that is the polar may be a radius vector, and an angle of the radius vector with respect to the Z axis may be a deflection angle θ [rad]. The deflection angle θ may be a rotation angle when the radius vector is rotated with respect to the Z axis, with the first focus F1, that is, the polar, being the center of rotation. In the case of describing the internal space of the chamber 2 illustrated in FIG. 4 with use of the polar coordinate system, the first region Re1 may be described as Expression 1, and the second region Re2 may be described as Expression 2. In that case, the light source unit 41 and the light receiving unit 42 may be disposed such that at least one of the optical path of the illumination light and the optical path of the reflected light from the target 27 passes through the first focus F1 and is included in the internal space of the chamber 2 described by the deflection angle θ satisfying Expression 2 representing the second region Re2.0<θ≤θm [Expression 1]θm<θ<(π−θm) [Expression 2] 4.1 Configuration FIG. 6 is a diagram for explaining the EUV light generating device 1 of the first embodiment. The light source unit 41 and the light receiving unit 42 of the first embodiment may be disposed so as to satisfy condition 1 of FIG. 5. The light source unit 41 of the first embodiment may be disposed such that the optical path of the illumination light output from the light source unit 41 passes through the first focus F1 and is included in the second region Re2. In more detail, the light source unit 41 of the first embodiment may be disposed such that the illumination optical axis of the light source unit 41 passes through the first focus F1 and is included in the second region Re2. The illumination optical axis may be an optical path axis of illumination light output from the light source unit 41. Further, the light receiving unit 42 of the first embodiment may be disposed such that the optical path of the reflected light from the target 27 received by the light receiving unit 42 passes through the first focus F1 and is included in the first region Re1. In more detail, the light receiving unit 42 of the first embodiment may be disposed such that the receiving optical axis of the light receiving unit 42 passes through the first focus F1 and is included in the first region Re1. The receiving optical axis may be an optical path axis of light to be received by the light receiving unit 42, of the reflected light from the target 27. The other parts of the configuration of the EUV light generating device 1 of the first embodiment may be the same as those of the EUV light generating device 1 of the comparative example. 4.2 Operation The light source unit 41 of the first embodiment may output illumination light from the second region Re2 toward the first focus F1 and the vicinity thereof. The light receiving unit 42 of the first embodiment may capture an image of the first focus F1 and the vicinity thereof from the first region Re1. When the illumination light is radiated to the target 27, the light receiving unit 42 may receive reflected light from the first focus F1 and the vicinity thereof toward the first region Re1, as reflected light from the target 27. When the illumination light output from the light source unit 41 is not radiated to the target 27, the illumination light may pass through the first focus F1. The illumination light passing through the first focus F1 may not be made incident on the reflection surface 231 of the EUV focusing mirror 23, and may be radiated to the wall 2a and the like of the chamber 2 and may be scattered. Regarding the light radiated to the wall 2a and the like of the chamber 2 and scattered, the light quantity is reduced. Accordingly, the light is less likely to reach the light receiving unit 42 and is less likely to become stray light. Even if it is received by the light receiving unit 42, the light radiated to the wall 2a and the like of the chamber 2 and scattered is less likely to affect measurement of the position, the velocity, and the target trajectory T of the target 27. The other operations of the EUV light generating device 1 of the first embodiment may be the same as those of the EUV light generating device 1 of the comparative example. 4.3 Effect The light source unit 41 of the first embodiment can be disposed such that stray light caused by the output illumination light is less likely to be generated. This means that the EUV light generating device 1 of the first embodiment can suppress generation of stray light itself to thereby suppress stray light to be captured by the light receiving unit 42. Thereby, the EUV light generating device 1 of the first embodiment can measure the target 27 supplied to the plasma generation region 25 with high accuracy. An EUV light generating device 1 of a second embodiment will be described with reference to FIG. 7. In the EUV light generating device 1 of the second embodiment, positions of the light source unit 41 and the light receiving unit 42 may be different from those of the EUV light generating device 1 of the first embodiment. The light source unit 41 and the light receiving unit 42 of the second embodiment may be disposed so as to satisfy condition 2 of FIG. 5. Regarding the configuration of the EUV light generating device 1 of the second embodiment, description of the same parts as the EUV light generating device 1 of the first embodiment is omitted. 5.1 Configuration FIG. 7 is a diagram for explaining the EUV light generating device 1 of the second embodiment. The light source unit 41 according to the second embodiment may be disposed such that the optical path of the illumination light output from the light source unit 41 passes through the first focus F1 and is included in the second region Re2. In more detail, the light source unit 41 of the second embodiment may be disposed such that the illumination optical axis of the light source unit 41 passes through the first focus F1 and is included in the second region Re2. The light receiving unit 42 of the second embodiment may be disposed such that the optical path of the reflected light from the target 27 to be received by the light receiving unit 42 passes through the first focus F1 and is included in the second region Re2. In more detail, the light receiving unit 42 of the second embodiment may be disposed such that the receiving optical axis of the light receiving unit 42 passes through the first focus F1 and is included in the second region Re2. The other parts of the configuration of the EUV light generating device 1 of the second embodiment may be the same as those of the EUV light generating device 1 of the first embodiment. 5.2 Operation The light source unit 41 of the second embodiment may output illumination light from the second region Re2 toward the first focus F1 and the vicinity thereof, similar to the case of the first embodiment. The light receiving unit 42 of the second embodiment may capture an image of the first focus F1 and the vicinity thereof from the second region Re2. When the illumination light is radiated to the target 27, the light receiving unit 42 may receive reflected light from the first focus F1 and the vicinity thereof toward the second region Re2, as the reflected light from the target 27. The illumination light output from the light source unit 41 is less likely to become stray light because, after passing through the first focus F1, it may be radiated to the wall 2a and the like of the chamber 2 and may be scattered, similar to the case of the first embodiment. The other operations of the EUV light generating device 1 of the second embodiment may be the same as those of the EUV light generating device 1 of the first embodiment. 5.3 Effect The light source unit 41 of the second embodiment can be disposed such that stray light caused by the output illumination light is less likely to be generated, similar to the case of the first embodiment. Thereby, the EUV light generating device 1 of the second embodiment can suppress generation of stray light itself to thereby be able to measure the target 27 supplied to the plasma generation region 25 with high accuracy, similar to the case of the first embodiment. An EUV light generating device 1 of a third embodiment will be described with use of FIG. 8. In the EUV light generating device 1 of the third embodiment, the positions of the light source unit 41 and the light receiving unit 42 may be different from those of the EUV light generating device 1 of the first embodiment. The light source unit 41 and the light receiving unit 42 of the third embodiment may be disposed so as to satisfy condition 3 of FIG. 5. Regarding the configuration of the EUV light generating device 1 of the third embodiment, description of the same parts as the EUV light generating device 1 of the first embodiment is omitted. 6.1 Configuration FIG. 8 is a diagram for explaining the EUV light generating device 1 of the third embodiment. The light source unit 41 according to the third embodiment may be disposed such that the optical path of the illumination light output from the light source unit 41 passes through the first focus F1 and is included in the first region Re1. In more detail, the light source unit 41 of the third embodiment may be disposed such that the illumination optical axis of the light source unit 41 passes through the first focus F1 and is included in the first region Re1. The light receiving unit 42 of the third embodiment may be disposed such that the optical path of the reflected light from the target 27 to be received by the light receiving unit 42 passes through the first focus F1 and is included in the second region Re2. In more detail, the light receiving unit 42 of the third embodiment may be disposed such that the receiving optical axis of the light receiving unit 42 passes through the first focus F1 and is included in the second region Re2. The other parts of the configuration of the EUV light generating device 1 of the third embodiment may be the same as those of the EUV light generating device 1 of the first embodiment. 6.2 Operation The light source unit 41 of the third embodiment may output illumination light from the first region Re1 toward the first focus F1 and the vicinity thereof. The light receiving unit 42 of the third embodiment may capture an image of the first focus F1 and the vicinity thereof from the second region Re2. When the illumination light is radiated to the target 27, the light receiving unit 42 may receive reflected light from the first focus F1 and the vicinity thereof toward the second region Re2, as reflected light from the target 27. When the illumination light output from the light source unit 41 is not radiated to the target 27, it may pass through the first focus F1. The illumination light passing through the first focus F1 may be made incident on the reflection surface 231 of the EUV focusing mirror 23. The illumination light made incident on the reflection surface 231 may be reflected by the reflection surface 231, and may be scattered by the wall 291 around the second focus F2, located at the intermediate focal point 292, and the like. Part of the scattered light caused by the wall 291 and the like may be made incident on the reflection surface 231 again and may be reflected, and may travel toward the light receiving unit 42. However, part of the scattered light caused by the wall 291 and the like is less likely to enter the view angle of the light receiving unit 42, and is less likely to be received by the light receiving unit 42. The scattered light deviated from the view angle of the light receiving unit 42 may be radiated to the wall 2a and the like of the chamber 2 and may be scattered. Regarding the light radiated to the wall 2a and the like of the chamber 2 and scattered, the light quantity is reduced. Accordingly, the light is less likely to reach the light receiving unit 42 and is less likely to become stray light. Even if it is received by the light receiving unit 42, the light radiated to the wall 2a and the like of the chamber 2 and scattered is less likely to affect measurement of the position, the velocity, and the target trajectory T of the target 27. The other operations of the EUV light generating device 1 of the third embodiment may be the same as those of the EUV light generating device 1 of the first embodiment. 6.3 Effect The light receiving unit 42 of the third embodiment can be disposed such that even if light that may cause stray light, such as scattered light by the wall 291 and the like, is generated, such light is less likely to be received. By allowing the light that may cause stray light to be less likely to be received by the light receiving unit 42, the EUV light generating device 1 of the third embodiment can suppress capturing of an image of stray light by the light receiving unit 42. Thereby, the EUV light generating device 1 of the third embodiment can measure the target 27 supplied to the plasma generation region 25 with high accuracy. An EUV light generating device 1 of a fourth embodiment will be described with reference to FIGS. 9 and 10. The EUV light generating device 1 of the fourth embodiment may be different from the EUV light generating device 1 of the first embodiment in the position of the light source unit 41. The light source unit 41 of the fourth embodiment may be disposed such that the optical path of the illumination light output from the light source unit 41 passes through the first focus F1 and is included in the second region Re2, similar to the case of the first embodiment. In more detail, the light source unit 41 of the fourth embodiment may be disposed such that the illumination optical axis of the light source unit 41 passes through the first focus F1 and is included in the second region Re2. However, the light source unit 41 of the fourth embodiment may be disposed in consideration of beam divergence of the illumination light output from the light source unit 41. Regarding the configuration of the EUV light generating device 1 of the fourth embodiment, description of the same parts as the EUV light generating device 1 of the first embodiment is omitted. 7.1 Configuration FIG. 9 is a diagram for explaining the light source unit 41 included in the EUV light generating device 1 of the fourth embodiment. FIG. 10 is an enlarged view illustrating the vicinity of the first focus F1 illustrated in FIG. 9. FIGS. 9 and 10 illustrate the case that when the light source unit 41 of the fourth embodiment outputs illumination light from the second region Re2 toward the first focus F1 and the vicinity thereof, the optical path of the illumination light passing through the first focus F1 intersects the outer peripheral edge 231a of the reflection surface 231. Here, the illumination optical axis of the light source unit 41 is represented by A. This means that the optical path axis of the illumination light output from the light source unit 41 is represented by A. An acute angle defined by the optical path axis A of the illumination light and the Y axis is represented by θ1. Regarding the divergence angle of illumination light, a half value thereof is represented by θd. Regarding the beam width of illumination light when passing through the first focus F1, a half value thereof is represented by W. The half value W of the beam width may be a value defined by 1/(e2) or 4σ. The half value W of the beam width may be a beam radius of the illumination light when passing through the first focus F1. The position where the optical path of the illumination light intersects the Z axis when passing through the first focus F1, on the reflection surface 231 side, is represented by x. A distance from the first focus F1 to the position x is represented by X. A line segment linking the outer peripheral edge 231a of the reflection surface 231 and the position x is represented by B. An acute angle defined by the line segment B and the Z axis is represented by θx. The distance from the outer peripheral edge 231a of the reflection surface 231 to the Z axis is represented by R. A distance from the outer peripheral edge 231a of the reflection surface 231 to the first focus F1 in the Z axis direction is represented by L. The distance L may be a distance from the outer peripheral edge 231a to the first focus F1, along the Z axis. A distance from the outer peripheral edge 231a of the reflection surface 231 to the position x in the Z axis direction is represented by La. Based on such a premise, when the optical path of the illumination light passing through the first focus F1 intersects the outer peripheral edge 231a of the reflection surface 231, the distance X, the distance La, and the distance L may have a relationship as Expression 3.X+La=L [Expression 3] First, the distance X of the left hand of Expression 3 will be considered. Referring to the triangle illustrated in FIG. 10, Expression 4 may be established from the sine theorem. W sin ⁢ ⁢ θ x = X sin ⁡ ( π 2 + θ d ) [ Expression ⁢ ⁢ 4 ] The angle θx may be described as Expression 5 from FIG. 10. θ x = π 2 - ( θ 1 + θ d ) [ Expression ⁢ ⁢ 5 ] The distance X may be described as Expression 6 when Expression 5 is substituted in Expression 4 and organized. X = W ⁢ ⁢ cos ⁢ ⁢ θ d ⁢ cos ⁢ ⁢ θ 1 ⁢ ⁢ cos ⁢ ⁢ θ d - ⁢ sin ⁢ ⁢ θ 1 ⁢ sin ⁢ ⁢ θ d [ Expression ⁢ ⁢ 6 ] The half value θd of the divergence angle may be minute. As such, a trigonometric function using θd as a variable may be approximated by the first-order term of Taylor expansion. Then, Expression 6 may be described as Expression 7. X = W ⁢ cos ⁢ ⁢ θ 1 - θ d ⁢ ⁢ sin ⁢ ⁢ θ 1 ⁢ [ Expression ⁢ ⁢ 7 ] Next, La of the left hand of Expression 3 will be considered. The distance La may be described as Expression 8 according to FIG. 9. L a = R tan ⁢ ⁢ θ x [ Expression ⁢ ⁢ 8 ] When Expression 5 is substituted in θx and organized, tan θx of the right hand of Expression 8 may be described as Expression 9. tan ⁢ ⁢ θ x = 1 - tan ⁢ ⁢ θ 1 ⁢ tan ⁢ ⁢ θ d tan ⁢ ⁢ θ 1 + tan ⁢ ⁢ θ d [ Expression ⁢ ⁢ 9 ] The half value θd of the divergence angle may be minute. As such, a trigonometric function using θd as a variable may be approximated by the first-order term of Taylor expansion. Then, Expression 9 may be described as Expression 10. tan ⁢ ⁢ θ x = 1 - θ d ⁢ tan ⁢ ⁢ θ 1 ⁢ tan ⁢ ⁢ θ 1 + θ d [ Expression ⁢ ⁢ 10 ] The distance La may be described as Expression 11 when Expression 10 is substituted in Expression 8 and organized. L a = R ⁢ tan ⁢ ⁢ θ 1 + θ d 1 - θ d ⁢ tan ⁢ ⁢ θ 1 [ Expression ⁢ ⁢ 11 ] Accordingly, Expression 3 may be described as Expression 12 when Expression 7 and Expression 11 are substituted in Expression 3 and organized. R ⁢ tan ⁢ ⁢ θ 1 + θ d 1 - θ d ⁢ tan ⁢ ⁢ θ 1 = L - W cos ⁢ ⁢ θ 1 - θ d ⁢ ⁢ sin ⁢ ⁢ θ 1 ⁢ [ Expression ⁢ ⁢ 12 ] By further organizing Expression 12, Expression 3 may be described as Expression 13.R(sin θ1+θd cos θ1)=L(cos θ1−θd sin θ1)−W [Expression 13] Here, the angle θ1 may be an angle defined by the optical path axis A of the illumination light and the Y axis. θ shown in Expression 1, Expression 2, and FIG. 4 may be an angle with respect to the Z axis. The Z axis and the Y axis may intersect at right angles. Accordingly, the angle θ1 may be described as Expression 14. θ 1 = θ - π 2 [ Expression ⁢ ⁢ 14 ] Accordingly, Expression 3 may be described as Expression 15 when Expression 14 is substituted in Expression 13 and organized.R(θd sin θ−cos θ)=L(θd cos θ+sin θ)−W [Expression 15] This means that when the optical path of illumination light passing through the first focus F1 is described with use of the deflection angle θ satisfying Expression 15, the optical path of the illumination light passing through the first focus F1 may intersect the outer peripheral edge 231a of the reflection surface 231. The distance R and the distance L according to the reflection surface 231 may be values preset by the design of the EUV focusing mirror 23. Accordingly, when the light source unit 41 outputs illumination light from the second region Re2 to the first focus F1 and the vicinity thereof, the light source unit 41 may output illumination light such that the optical path of the illumination light passing through the first focus F1, having the half values W and θd of the beam width and the divergence angle, is described with use of the deflection angle θ not satisfying Expression 15. Further, when the optical path of the illumination light passing through the first focus F1 does not intersect the reflection surface 231 including the outer peripheral edge 231a, the distance X, the distance La, and the distance L may have a relationship represented as Expression 16.X+La<L [Expression 16] By developing Expression 16 according to the same idea as Expressions 4 to 15, Expression 16 may be described as Expression 17.R(θd sin θ−cos θ)<L(θd cos θ+sin θ)−W [Expression 17] This means that when the optical path of illumination light passing through the first focus F1 is described with use of the deflection angle θ satisfying Expression 17, the optical path of the illumination light passing through the first focus F1 may not intersect the reflection surface 231 including the outer peripheral edge 231a even in consideration of the beam divergence of the illumination light. Accordingly, when the light source unit 41 outputs illumination light from the second region Re2 to the first focus F1 and the vicinity thereof, the light source unit 41 may output illumination light such that the optical path of the illumination light passing through the first focus F1, having the half values W and θd of the beam width and the divergence angle, is described with use of the deflection angle θ satisfying Expression 17. In other words, the light source unit 41 according to the fourth embodiment may be disposed such that the optical path of the illumination light output from the light source unit 41 passes through the first focus F1 and is included in the internal space of the chamber 2 described with use of the deflection angle θ satisfying Expressions 2 and 17. The other parts of the configuration of the EUV light generating device 1 of the fourth embodiment may be the same as those of the EUV light generating device 1 of the first embodiment. Regarding the operations of the EUV light generating device 1 of the fourth embodiment, description of the same operations as the EUV light generating device 1 of the first embodiment is omitted. 7.2 Effect The light source unit 41 of the fourth embodiment can be disposed such that stray light caused by the output illumination light is less likely to be generated, even in consideration of the beam divergence of the illumination light. Thereby, the EUV light generating device 1 of the fourth embodiment can suppress generation of stray light itself to thereby be able to measure the target 27 supplied to the plasma generation region 25 with high accuracy. It will be obvious to those skilled in the art that the techniques of the embodiments described above are applicable to each other including modifications. The description provided above is intended to provide just examples without any limitations. Accordingly, it will be obvious to those skilled in the art that changes can be made to the embodiments of the present disclosure without departing from the scope of the accompanying claims. The terms used in the present description and in the entire scope of the accompanying claims should be construed as terms “without limitations”. For example, a term “including” or “included” should be construed as “not limited to that described to be included”. A term “have” should be construed as “not limited to that described to be held”. Moreover, a modifier “a/an” described in the present description and in the accompanying claims should be construed to mean “at least one” or “one or more”.
042959357	summary	BACKGROUND OF THE INVENTION This invention relates to nuclear reactor fuel assembly grids, and, more particularly, to a bimetallic spacer means operative to resist the occurrence of in-reactor bowing of nuclear reactor fuel assemblies. The prior art is replete with a multiplicity of teachings of various forms of nuclear fuel assembly grids that have been proposed for use in nuclear reactor cores. One particularly striking aspect of the contents of these prior art teachings is the diversity of structural configurations that have been proposed for embodiment in such fuel assembly grids. Generally speaking, there are two major functions, which fuel assembly grids are intended to perform. First of all, such grids are used to provide the individual fuel rods, which collectively comprise a fuel assembly, with lateral support. The need for such support is occasioned in large measure by the very nature of the construction of a fuel rod. Namely, each fuel rod commonly consists of a multiplicity of fuel pellets that are arranged in a multiple layer configuration. Moreover, each fuel rod normally is of substantial length. Accordingly, even though the fuel pellets generally are to be found encased in a cladding tube, a need still exists to provide a fuel rod with the aforementioned support to insure that the latter will not undergo lateral displacement to an unacceptable degree, i.e., to a degree which potentially could adversely affect the operation of the nuclear reactor. The susceptiveness of the fuel rods to undergo lateral displacement stems from the nature of the forces to which the fuel rods are subjected. For instance, included in the forces to which reference is had here are the compression spring forces that are being exerted on the ends of the rods, the forces applied to the fuel rods as a consequence of the coolant flow in the fuel assembly, etc. The other major function, which is performed by the fuel assembly grid, is that of insuring that the desired spacing between the fuel rods, which collectively comprise the fuel assembly, is being maintained. The existence of proper spacing between the individual fuel rods is important, both from the standpoint of insuring that excessive flux peaking occasioned by the existence of improper spacing between fuel rods and the fuel assembly is prevented, and from the standpoint of insuring that proper coolant flow between the fuel rods and the fuel assembly is maintained. Unequal distribution of coolant flow between individual fuel rods can give rise to overheating and eventually cause hot spots to develop within the fuel assembly. Another important factor which must be borne in mind in proposing for use any particular design for a nuclear fuel assembly is that the support and spacing functions intended to be performed thereby must be capable of being accomplished in such a manner as to not interfere with the process of inserting and removing fuel rods into and from a fuel assembly. Namely, the nuclear fuel assembly grid must be operative to provide the desired lateral support to the individual fuel rods, which collectively comprise the fuel assembly, and to provide the desired spacing therebetween when the fuel rods are emplaced in a fuel assembly, and concomitantly must possess the capability to make possible the facile insertion and/or removal of the fuel rods into and/or from the fuel assembly, when such action is required. Apart from the need to provide support to the fuel rods themselves, some attention has been directed more recently to the desirability of improving the strength characteristics of the nuclear fuel assembly grid itself. Specifically, reference is had here to the recognition that has been given to the desirability of improving the strength of the fuel assembly grid per se so as to insure the ability of the fuel assembly to withstand the possible subjection thereof to seismic loading. As set forth in U.S. Pat. No. 4,058,436, which issued to the inventor of the subject matter of the instant application and which is assigned to the same assignee as the present invention, such seismic loading could give rise to the subjection of the fuel assembly to severe lateral stresses that, in turn, could adversely affect the operation of the nuclear reactor in which such a fuel assembly is contained. The nature of such adverse effects is clearly outlined in applicant's above-referred to earlier U.S. Patent. It can thus be seen that in proposing a design for a nuclear fuel assembly grid, another consideration which desirably should be taken into account in addition to the need to provide lateral spacing to the fuel rods and to establish the proper spacing between the fuel rods is that of the impact, which seismic loading might have on the fuel assembly. For the reason set forth in the aforereferenced U.S. Patent, it is important that the strengthening of the fuel assembly grid be accomplished in such a manner as to not detrimentally influence the operating efficiency of the nuclear reactor. That is, it is desirable that the fuel assembly grid be provided with additional rigidity in a manner which will not significantly increase the neutron absorption propensity of the grid. In this regard, as a material zircaloy is known to have a lower neutron capture cross-section than does stainless steel or inconel. On the other hand, as a material stainless steel and inconel are known to possess a higher degree of mechanical strength than does zircaloy. With the latter in mind, in accord with the teachings of the above-referred to U.S. Patent, a fuel assembly is provided, which has cooperatively associated therewith a multiplicity of all-zircaloy grids and one all-stainless steel grid. Each of the all-zircaloy grids embodies a unique construction that is operative to increase the strength characteristics thereof. Moreover, by employing such all-zircaloy grids, which are characterized by their superior crush strength, in combination with a suitably positioned all-stainless steel grid, a fuel assembly, which is so equipped, is provided that possesses sufficient overall strength to successfully resist the severe lateral stresses that are anticipated under conditions of seismic loading. In addition to the lateral stresses to which a fuel assembly may be subjected under seismic loading conditions, there are reasons to believe that under certain conditions fuel assemblies equipped with prior art forms of fuel assembly grids, may, for reasons of yet not totally explained, exhibit a susceptiveness to undergo bowing. The term bowing as used herein is intended to refer to that condition of a fuel assembly wherein one or more portions thereof have undergone lateral displacement. Although it has not been caused by seismic loading, such bowing of the fuel assembly is undesired equally as much as the lateral displacement which a fuel assembly undergoes as a consequence of seismic loading. In this regard, the reasons why such bowing of the fuel assembly is undesirable are basically the same as those which are to be found set forth in the U.S. Patent previously referred to hereinabove. Namely, by way of exemplification, such bowing can give rise to the permanent deformation of the fuel assembly. Moreover, the bowing of the fuel assembly may become sufficiently severe as to cause the fuel assembly to impact against adjacent fuel assemblies with adverse consequences. There are other types of damage that are equally likely to occur in the event that such bowing of the fuel assembly takes place with equally detrimental effects on the operation of the nuclear reactor. Consequently, there has been shown to exist in the prior art a need for a nuclear fuel assembly grid that in addition to possessing the capability of providing lateral support to the fuel rods that collectively comprise the fuel assembly and the capability of effecting the desired spacing between the fuel rods also possesses the capability of providing the fuel assembly with sufficient crush strength to withstand the severe lateral stresses imposed thereupon under seismic loading conditions as well as the ability to resist any susceptiveness on the part of the fuel assembly to undergo bowing. More specifically, a need has been shown to exist for such a grid, which would be operative to prevent the fuel assembly from undergoing lateral displacement that exceeds certain preestablished acceptable limits. Furthermore, a characteristic, which any such grid capable of fulfilling the above-stated objectives must also embody, is the fact that additionally it exhibits a relatively low propensity for neutron absorption. It is, therefore, an object of the present invention to provide a new and improved bimetallic spacer means particularly suited to be cooperatively associated with a nuclear fuel assembly of the type that is employable in the core of a nuclear reactor. It is another object of the present invention to provide such a bimetallic spacer means which includes means operative, when the bimetallic spacer means is cooperatively associated with a fuel assembly, to provide lateral support to the fuel rods that collectively comprise the fuel assembly. It is still another object of the present invention to provide such a bimetallic spacer means which includes means operative, when the bimetallic spacer means is cooperatively associated with a fuel assembly, to provide the proper spacing between the individual fuel rods that collectively comprise the fuel assembly. A further object of the present invention is to provide such a bimetallic spacer means, which is characterized by its improved crush strength, such that when the bimetallic spacer means is cooperatively associated with a fuel assembly, it is operative to enable the fuel assembly to withstand the severe lateral stresses imparted thereto under seismic loading conditions. A still further object of the present invention is to provide such a bimetallic spacer means, which is operative when cooperatively associated with a fuel assembly to enable the fuel assembly to resist any susceptiveness thereof to undergo inreactor bowing beyond certain specified preestablished acceptable limits. Yet another object of the present invention is to provide such a bimetallic spacer means, which is characterized in the fact that it exhibits a relatively low propensity for neutron absorption. Yet still another object of the present invention is to provide such a bimetallic spacer means, which is relatively inexpensive to manufacture, relatively easy to employ, and which is capable of providing effective and reliable operation. SUMMARY OF THE INVENTION In accordance with the present invention, there is provided a novel and improved bimetallic spacer means designed to be cooperatively associated with a fuel assembly and operative to resist in-reactor bowing of the fuel assembly when the latter is employed in a nuclear reactor core. In accord with one aspect of the invention, the bimetallic spacer means includes an all-zircaloy perimeter grid to which are attached a plurality of stainless steel strips. The plurality of stainless steel strips are mounted on the external surface of the perimeter grid and each has its major axis extending substantially perpendicular to the major axis of the perimeter grid. During power production the plurality of stainless steel strips expand outwardly to a greater extent than does the all-zircaloy perimeter grid. In their expanded state, the plurality of stainless steel strips function in the manner of stiff springs to effectively resist any tendency on the part of the fuel assembly to undergo in-reactor bowing. In accord with another aspect of the present invention, the bimetallic spacer means again includes an all-zircaloy perimeter grid to which a plurality of stainless steel strips are attached. However, in this instance the plurality of stainless steel strips are positioned on the external surface of the perimeter grid so that the major axis of each of the plurality of stainless steel strips extends substantially parallel to the major axis of the perimeter grid. Here also, the plurality of stainless steel strips function in the same manner as that described in the preceding paragraph. Namely, during power production, the plurality of stainless steel strips expand and function like stiff springs to limit any in-reactor bowing of the fuel assembly to within acceptable limits. In accord with still another aspect of the present invention, certain preselected rods, each having a zircaloy cladding associated therewith, are provided with a stainless steel strip. Those rods, which are selected to be provided with a stainless steel strip, are all located within the rows of fuel rods that define the perimeter of the fuel matrix of the fuel assembly. The stainless steel strips are positioned on the rods so as to be located on an outwardly exposed surface thereof. The stainless steel strips, in this instance also, function in the same manner as the stainless steel strips described in the two preceding paragraphs. Namely, the strips during power production expand and take on the characteristics of stiff springs having the ability to enable the fuel assembly to resist any susceptiveness on the part thereof to undergo in-reactor bowing beyond what is considered to be acceptable limits.
	abstract	A service condition, a cause of a malfunction, or another aspect of a device in a large group of devices to be managed can be analyzed in an accurate and efficient manner. A complete test involving the entire number of devices in a large group of managed devices (T) is periodically performed to determine whether the devices are operating normally or have a malfunction; a test result (Ic) is recorded for each cycle of the complete test, and a device that has been found to be malfunctioning is repaired or replaced; and analysis data G, E are created showing a malfunctioning frequency (N) of each of the managed devices (T) on the basis of the test result (Ic) of the complete test that spans a plurality of cycles.
051397358	description	MODE(S) FOR CARRYING OUT THE INVENTION As illustrated schematically in FIG. 1, an exemplary, natural circulation boiling water reactor 10 comprises a pressure vessel 12, a core 14, a chimney 16, a steam separator 18, and a steam dryer 20, all of which are conventional. Water flows, as indicated by arrows 22, into the core 14 from below. This subcooled water is boiled within the core 14 to yield a water/steam mixture which rises through the chimney 16 to a water level 22a from which the steam is dispelled upwardly. The steam separator 18 helps separate steam from water, and the released steam exits through a steam exit 24 near the top of the vessel 12. Before exiting, any remaining water entrained in the steam is removed by the dryer 20. The separated water is returned down a conventional peripheral downcomer 26 by the force of gravity. The steam in the vessel 12 is at a relatively high steam, or vessel, pressure P.sub.v of about 7.0 MPa, for example. Referring also to FIG. 2, an exemplary embodiment of the core 14 is illustrated and includes a plurality of vertically extending, conventional square fuel bundles 28 transversely spaced apart in a conventional radial matrix. In a conventional reactor core, vertically movable control rods or blades (not shown) are positioned between adjacent ones of the fuel bundles 28 and are selectively inserted into the core 14 or withdrawn from the core 14 for controlling reactivity therein. The conventional control rods require suitable control rod drives extending into the core from either the top head or the bottom head of the vessel, Which therefore requires relatively large penetrations therein. Referring to FIG. 1, a reactivity control system 30, in accordance with an exemplary embodiment of the present invention, is illustrated and has no moving parts within the vessel 12 and does not require large penetrations of the vessel 12 for controlling reactivity of the core 16. The control system 30 includes a plurality of fixed, or stationary, hollow control blades 32 which are transversely spaced apart between adjacent ones of the fuel bundles 28 as illustrated in FIG. 2. In this embodiment, the blades 32 extend vertically into the core 16 and are fixedly connected to a top perforated support plate 34 disposed at the top of the core 14. Each of the blades 32 includes a top end 36, a bottom end 38, and a fluid port 40 preferably disposed at the bottom end 38. The system 30 further includes at least one, and preferably a plurality of reservoirs 42 each containing a conventional liquid nuclear poison solution 44 such as sodium pentaborate in water. Each of the reservoirs 42 has a top end 46, a bottom end 48, and a fluid port 50 preferably disposed at the reservoir bottom end 48, and the reservoir 42 is preferably partially filled with the poison 44 to a vertical reservoir poison level R. A conventional poison conduit 52 is disposed in flow communication between respective ones of the reservoirs 42 and the blades 32 for channeling the poison 44 between the reservoir 42 and the blade 32. The core 14 includes a substantial number of the control blades 32, for example about 200 thereof, and each of the blades 32 may be provided with its own separate reservoir 42 and poison conduit 52. However, it is preferred that a plurality of transversely spaced apart blades 32 are joined in parallel flow communication through a respective poison conduit 52 and an individual reservoir 42 for reducing the total number of components of the system 30 while providing redundancy of operation therein so that any failure of an individual control system 30, including a respective reservoir 42 and respective control blades 32, will not prevent effective control of the core 14 by the remaining operable reservoirs 42 and control blades 32. Accordingly, the loss of the poison due to leakage in one of the systems 30 would be no worse than a stuck control rod in today's reactors. More specifically, FIG. 3 illustrates schematically the reactivity control system 30 in accordance with an exemplary embodiment including one of the reservoirs 42 operatively connected to a plurality of the control blades 32 in parallel flow communication therewith, with the poison conduit 52 including respective branches 52a and 52b joined to the control blades 32. The system 30 also includes means, shown schematically at 54, for controlling or varying the blade poison level B of the poison solution 44 in the blade 32 for selectively varying nuclear reactivity in the core 14. It is to be noted that the blades 32 are preferably positioned in the core 14 as illustrated in FIG. 1 for maintaining the bottom-up reactivity control typically found in current nuclear reactor plants, which is preferred in a boiling water reactor, but do so without bottom penetrations of the vessel 12. Since the control blades 32 are fixed in the core 14, they eliminate all moving components typically associated with a conventional control blade which is conventionally translated vertically into and out of the core 14 through conventional clearances. The present invention, therefore, makes the reactivity control system 30 even more immune to anticipated transient without scram (ATWS) than present nuclear reactor plants. Furthermore, the conventional control rod drives are no longer needed and thus eliminate congestion either under the vessel 12 or over the vessel 12 which would otherwise be required in a conventional control rod drive system. Yet further, the relatively large penetrations through the vessel heads are thusly eliminated since the conventional control rod drives are not used. In the embodiment of the invention illustrated in FIG. 1, the reservoirs 42 are preferably disposed outside the vessel 12 and the poison conduits 52 extend sealingly through the wall of the vessel 12 using conventional seals which allow the conduits 52 to channel the poison 44 through the vessel wall while preventing the pressurized water 22 inside the vessel 12 from leaking therefrom around the conduit 52 extending through the wall thereof. The resulting penetration of the vessel 12 for the conduit 52 is relatively small, and the sealing of the non-axially movable poison conduit 52 through the vessel wall may be conventionally relatively easily accomplished. This is in contrast to the conventional control rod drives which require relatively large penetrations through the vessel 12 and which must sealingly contain axially translatable shafts therein. However, as shown in phantom in FIG. 1, the reservoir 42, designated 42A and the poison conduits 52, designated 52A, may be alternatively disposed inside the vessel 12. In either embodiment, the reactivity control system 30 is preferably a substantially closed system in which the poison 44 in the reservoirs 42 and the blades 32 is maintained at a nominal pressure at least as high as the vessel pressure P.sub.v to prevent boiling of the poison 44 in the relatively hot vessel 12. Furthermore, by maintaining the nominal pressure in the blades 32 at least at the vessel pressure P.sub.v or slightly greater, differential pressure loads across the walls of the blades 32 are relatively small, which therefore reduces stress therein. The control system 30 may be maintained at the vessel pressure P.sub.v by a suitable conventional pressurizing pump (not shown) or by suitably pressurizing the blades 32 with an inert gas through a venting port 56, for example, disposed at the blade top end 36 as shown in FIG. 3. The level B of the poison 44 in the control blades 32 is analogous to position of conventional control rods in a conventional reactor. The system 30 is effective for variably draining the poison 44 from the reservoir 42 for variably filling the control blade 32, filling flow direction designated 44f, for variably reducing reactivity in the core 14. And, the system 30 is effective for variably draining the poison 44 from the control blades 32, drawing flow direction designated 44d, for variably filling the reservoir 42 for increasing reactivity in the core 14. As illustrated in FIG. 3, the level controlling means 54 are effective for varying the blade poison level B between poison minimum level B.sub.min adjacent to the blade bottom end 38 to a blade poison maximum level B.sub.max adjacent to the blade top end 36. Correspondingly, in the embodiment illustrated in FIG. 3, the reservoir poison level R varies from a maximum level R.sub.max to a minimum level R.sub.min. In a preferred embodiment of the invention, the level controlling means 54 include disposing the reservoir fluid port 50 at the reservoir bottom end 48, disposing the blade fluid port 40 at the blade bottom end 38, and positioning the reservoir 42 vertically relative to the blades 32 so that the poison 44 in the reservoir 42 may drain by gravity to selectively fill the blades 32 from the minimum level B.sub.min to the maximum level B.sub.max. For example, the vertical position of the reservoir 42 may be selected relative to the vertical position of the blades 32 so that the blade poison maximum level B.sub.max is equal to the reservoir poison minimum level B.sub.min, i.e. same vertical height relative to the blade bottom end 38, which will allow automatic shutdown of the core 14 in the event of a power failure or a loss of signal to the level controlling means 54, as well as allowing scram using at least gravity to fill the poison 44 in the control blades 32 to the maximum level B.sub.max. In this way, the poison 44 will flow by gravity to fill the control blades 32 to the maximum level B.sub.max corresponding to the top of the active fuel in the fuel bundles 28. The level controlling means 54 may include various configurations for suitably raising and lowering the level of the liquid poison 44 in the control blades 32 which is analogous to inserting and withdrawing conventional solid poison control rods. Illustrated in FIG. 4 is an exemplary embodiment of the level controlling means 54 including a conventional pump 58 disposed in series flow communication in the poison conduit 52 and operable for selectively pumping the poison 44 between the blade 32 and the reservoir 42. More specifically, a conventional controller 60 is operatively connected to the motor of the pump 58 for selectively varying its output pressure. The pump 58 may be activated for drawing by suction the poison 44 from the control blade 32, through the conduit 52, and pumping the poison 44 upwardly through the conduits 52 and the pump 58 and into the reservoir 42 for decreasing (draining flow 44d) the poison level in the blade 32. As long as the pump 58 is operated for balancing the pressure head of the poison 44 above the pump 58, the blade poison level B may be maintained at any desired level within the blade 32. By decreasing the output pressure of the pump 58, the poison 44 will be allowed by gravity to drain from the reservoir 42, through the pump 58, and into the blade 32 (filling flow 44f) for increasing the blade poison level B. In the event of a power failure to the pump 58, it will stop and the pressure head of the poison 44 in the reservoir 42 relative to the blade 32 will cause an automatic scram operation for raising the blade poison level to its maximum poison level B.sub.max. As illustrated schematically in FIG. 4, the pump 58 may be a conventional centrifugal pump, or may be a conventional fluid-driven eductor or jet pump. In the form of an eductor, the pump 58 would further include a conventional mechanical, for example centrifugal, pump 62 suitably disposed in flow communication between the reservoir 42 and the eductor pump 58 and operatively connected to the control 62. In this way, a portion of the poison 44 may be channeled from the reservoir 42, pressurized by the pump 62 and ejected as a jet in the eductor pump 58 for creating a variable-pressure suction at its inlet for drawing the poison 44 from the blade 32, and a pressure rise at its outlet to pump the poison 44 into the reservoir 42. In this embodiment, a venting conduit 64 is disposed in flow communication between the blade venting port 54 and the reservoir 42 for allowing the poison 44 to flow freely between the reservoir 42 and the blade 32 in response to operation of the pump 58. Illustrated in FIG. 5 is another embodiment of the level controlling means 54 which include means 66 for selectively moving the entire reservoir 42 upwardly relative to the blade 32 for allowing gravity to drain the poison 44 from the reservoir 42 and into the blade 32. The reservoir 42 is shown in its maximum upward position with the reservoir poison minimum level R.sub.min being at the same vertical height as the blade poison maximum level B.sub.max. The moving means 66 are also effective for moving downwardly the reservoir 42 relative to the blade 32 for allowing gravity to drain the poison 44 from the blade 32 and into the reservoir 42. The reservoir 42 is shown in phantom line designated 42a at its lowermost position with the poison 44 therein being disposed at the reservoir poison maximum level R.sub.max, which is at the same vertical height as the blade poison minimum level B.sub.min. The conduits 52 (e.g. 52a, 52b) and 64 are suitably flexible for moving with the reservoir 42. The reservoir moving means 66 may include a counterweight 68 operatively connected to the reservoir 42 and having a weight greater than the weight of the reservoir 42 and the poison 44 therein so that the counterweight 68 is effective for raising the reservoir 42 by gravity to fill the blade 32 with the poison 44 drained from the reservoir, for example during a scram operation or loss of power. The moving means 66 may include a suitable stationary support 70, a cable 72 fixedly joined between the counterweight 68 and the reservoir 42, pulleys 74 over which the cable 72 is suspended, and a conventional electrical drive motor 76 having a drive pulley 78 around which a portion of the cable 72 is positioned. The motor 76 is operatively connected to the controller 60 for rotating the pulley 78 in either of two opposite directions for moving the cable 72 and the reservoir 42 upwardly in one direction, and downwardly in the other direction. Upon a loss of power to the motor 76, the counterweight 68 is effective for rotating the motor 78 by gravity and lifting the reservoir 42 to its maximum elevation. Illustrated in FIG. 6 is another embodiment of the reservoir moving means 66 which include conventional racks 80 and pinions 82, with the pinions 82 being powered by conventional electrical motors 84 which are operatively connected to the controller 60. The motors 84 and pinions 82 are suitably fixedly connected to the reservoir 42 and are suitably rotated for raising and lowering the reservoir 42 as desired. Illustrated in FIG. 7 is another embodiment of the level controlling means 54. In this embodiment, the means 54 include the blades 32 having the venting ports 56 at the top ends thereof, and means 86 for selectively pressurizing the poison 44 in the blades 32 through the venting ports 56 for dispelling the poison 44 from the blades 32 and into the reservoir 42 through the conduits 52 for selectively varying the poison level in the blades 32. In an exemplary embodiment, the poison pressurizing means 86 is effective for selectively providing a non-poison displacing fluid 88 into the blade 32 through the venting port 56 at selectively varying pressure for displacing downwardly the poison 44 in the blade 32. The poison pressurizing means 86 are effective for selectively pressurizing the displacing fluid 88 from a minimum pressure, for example a zero gauge pressure, allowing the poison 44 in the blade 32 to reach the blade poison maximum level B.sub.max, and to a maximum pressure for displacing the poison downwardly in the blade 32 to reach the blade poison minimum level B.sub.min. The displaced poison 44 is channeled PG,14 through the poison conduit 52 and into the reservoir 44. Both the minimum and maximum pressures of the displacing fluid 88 are preferably greater than the vessel pressure P.sub.v to provide an over-pressure in the preferably closed system 30 illustrated in FIG. 7 to prevent boiling of the poison 44, so that boiling does not occur even during a severe accident. The reservoir 42 is preferably a container disposed external of the vessel 12 (see FIG. 1) and may be maintained at a pressure equal to or greater than the vessel pressure P.sub.v. As illustrated in FIG. 8, the poison pressurizing means 86 may include a conventional variable output pump 90 disposed in flow communication between the venting port 56 and a conventional source 92 for the displacing fluid 88. The pump 90 is operatively connected to the controller 60 for selectively varying the output pressure of the displacing fluid 88 from the pump 90. Illustrated in FIG. 9 is another embodiment of the poison pressurizing means 86. In this embodiment, the poison 44 is displaced from the blade 32 and into the reservoir 42 external of the vessel 12 (as shown in FIG. 1) by the displacing fluid 88 in the form of a gas such as nitrogen. Also in this embodiment, a conventional accumulator 94 is provided for storing the displacing gas 88 at a pressure substantially greater than the maximum pressure required for displacing the poison 44 downwardly in the blade 32 in order to store a large amount of the gas 88 in the accumulator 94. A conventional regulator 96 is disposed in flow communication with the accumulator 94 for selectively varying the pressure of the displacing gas 88 channeled from the accumulator 94 to the blade 32. A conventional control valve 98 is disposed in flow communication between the regulator 96 and the blade 32 for selectively joining the venting port 56 to the regulator 96 to provide the pressurized displacing gas 88 to the blade 32 for lowering the poison level therein. The control valve 98 is also operable for selectively joining the venting port 56 to a conventional low pressure dump 100 while interrupting flow of the displacing gas 88 from the regulator 96 to the venting port 56 for reducing, by venting, the pressure inside the blade 32 for raising the poison level up to the blade maximum poison level B.sub.max. The regulator 96 and the control valve 98 are operatively connected to the controller 60 for selectively varying the pressure of the displacing gas 88 inside the control blade 32 for controlling the level of the poison 44 therein. The control valve 98 preferably dumps the displacing gas 88 from the control blade 32 upon interruption of power or signal thereto for ensuring automatic scram operation. The control blades 32 indicated schematically in the several Figures described above may have any suitable transverse configuration or cross section. For example, as illustrated in FIG. 2, the control blade 32 may have a cruciform transverse configuration when used with the square fuel bundles 28. Furthermore, although the control blade 32 may be positioned between adjacent ones of the fuel bundles 28 as illustrated in FIG. 2, the blades 32 may alternatively be formed directly within an individual fuel bundle 28. For example, as illustrated schematically in FIG. 10, the fuel bundle 28 includes a plurality of conventional fuel rods 102, and the control blades 32 (one shown for example) may be fixedly positioned therein between adjacent ones of the fuel rods 102. In this exemplary embodiment, the control blade 32 has a circular transverse configuration. Illustrated in FIG. 11 is a hexagonal fuel bundle designated 28a, with the control blade, designated 32a having a Y-shaped transverse configuration and fixedly positioned between the fuel rods 102. Illustrated in FIGS. 12 and 13, is another embodiment of the square shaped fuel bundle 28 including the control blade 32 designated 32b, having an H-shaped transverse configuration fixedly disposed inside the fuel bundle 28. In this embodiment, the blade fluid port 40 extends from the bottom end 38 of the control blade 32b to the top end 36 for allowing easy access to fill or drain the blade 32b from the top thereof. The venting port 56 is again disposed at the blade top end 36. For the embodiment illustrated in FIGS. 12 and 13, the poison 44 may alternatively be selectively pumped into the control blade 32b through the port 56 to selectively fill the blade 32b, and be selectively withdrawn from the blade 32b by suction through the port 40 from a separate suction pump. Yet another embodiment may include a vertically moveable suction tube 104, shown schematically in FIG. 13, which can be hooked to a device similar to a conventional traversing incore probe (TIP) positioner 106 for drawing out the poison 44 from the blade 32b to control, or decrease, the level therein. The poison is selectively pumped into the blade 32b through the port 56 to control, or increase, the level therein. Yet further, a hexagonal fuel bundle can employ a fixed hollow-wall control element with a star shape. Yet another option would be a matrix of tubes similar to a pin-type control element. In other embodiments, control elements may comprise a series of tubes like the one shown in FIG. 10. In some embodiments, sufficient wall thickness may be used to withstand full reactor vessel pressure. In still further embodiments, control elements may have thin walls with structural reinforcing ribs to accommodate the pressure loads thereacross. Illustrated in FIGS. 14 and 15 is yet another embodiment of the invention which may be used for obtaining fine positioning of the poison level B in the control blades 32. The reservoir 42 is preferably disposed vertically below the blade 32 so that the poison 44 in the blade 32 may drain by gravity from the blade 32 and into the reservoir 42. The reservoir 42 includes a piston 108 for confining the poison 44 and against which the poison 44 exerts a pressure force upwardly due to the weight of the poison 44 in the blade 32. The piston 108 is selectively positionable vertically by a vertically positionable rod 110, in the exemplary form of a screw, having a distal end 110b disposed in contact with a top surface 108b of the piston 108 for controlling the vertical position of the piston 108 and the reservoir poison level R. A conventional motor 112, through which the screw 110 extends, rotates the screw 110 either clockwise or counterclockwise in response to the controller 60 operatively connected thereto. The reservoir includes a top fluid port 50b joined to a tee fitting 114 in flow communication with a conventional accumulator 116 containing a pressurized gas, such as the non-poison fluid 88, nitrogen for example. The tee 114 is also joined to a conventional, selectively positionable valve 118 operatively connected to the controller 60. The valve 118 is also operatively connected to the blade venting port 56 by the venting conduit 64, and includes an exhaust port 120 connected to atmosphere. In normal operation, the pressurized gas 88 flows from the accumulator 116 to the tee 114 and into the reservoir 42, and the valve 118 is positioned to channel a portion of the pressurized gas 88 from the tee 114 to the blade 32 for maintaining an equal pressure therein above the respective poison levels B and R to prevent boiling of the poison 44, as shown in FIG. 14. The screw 110 is selectively screwed downwardly for driving the piston 108 downwardly to force or pump the poison 44 out the port 50, through the conduit 52 and into the blade 32 to fill it. The screw 110 may also be screwed in the opposite direction, upwardly, for allowing the pressure head of the poison 44 to raise the piston 108 upwardly against the elevated screw distal end 110b for allowing the poison 44 to drain from the blade 32 into the reservoir 42. In this way, the poison level B in the blade 32 may be selectively varied from its minimum value B.sub.min to its maximum value B.sub.max while the piston 108 is moved vertically for changing the reservoir poison level R from its maximum level R.sub.max to its minimum level R.sub.min, respectively. In a scram operation, the valve 118 is positioned by the controller 60 to block flow from the tee 114, as shown in FIG. 15, and to join the conduit 64 to the exhaust port 120 to exhaust the gas 88 from the blade 32. The gas 88 continues to be discharged into the reservoir 42 from the tee 114 causing a pressure imbalance between the reservoir 42 and the blade 32. The gas 88 acts against the piston top surface 108b to drive the piston 108 downwardly for draining the reservoir 42 to fill the blade 32. In all of the embodiments of the invention disclosed above, the position, or level B of the poison 44 within the control blades 32 may be obtained by any suitable means, such as, for example direct measurement of the level of the poison 44 in the control blades 32. Or, alternatively, the level R of the poison 44 in the reservoir 42 may be measured to indicate the respective level B of the poison 44 in the control blades 32. In the embodiment of the invention illustrated in FIG. 4, the performance curves of the pump 58 may be used to determine the level of the poison 44 in the control blades 32 since the output pressure of the pump 58 determines the level R of the poison 44 in the reservoir 42 being elevated above the pump 58. For the embodiments of the invention illustrated in FIGS. 7-9, the pressure of the displacing fluid 88 may be conventionally sensed which is directly proportional to the level B of the poison 44 in the control blades 32 being displaced thereby. For conventional refueling of the core 16, the blades 32 are filled with the poison 44 to at least the maximum level B.sub.max, and the fluid ports 40 and 56 are conventionally plugged so that there is permanent suppression of the reactivity of the fuel bundles 28. In the embodiments of the blades 32 fixedly joined inside the fuel bundles 28, they may be removed together as a unit from the core 16. While there have been described herein what are considered to be preferred embodiments of the present invention, other modifications of the invention shall be apparent to those skilled in the art from the teachings herein, and it is, therefore, desired to be secured in the appended claims all such modifications as fall within the true spirit and scope of the invention.
	description	The present application is related to U.S. patent application Ser. No. 11/067,099, entitled SYSTEMS FOR PROTECTING INTERNAL COMPONENTS OF AND EUV LIGHT SOURCE FROM PLASMA GENERATED DEBRIS, filed on Feb. 25, 2005, which is and co-owned by the assignee of the present application, the disclosure of which is hereby incorporated by reference. The present invention related to a Laser produced plasma (“LPP”) extreme ultraviolet (“EUV”) drive laser beam transit system incorporating, e.g., a focusing lens, optics debris-mitigation, and a source chamber interface. In the above referenced patent application Ser. No. 11/067,099, there is discussed that an LPP EUV drive laser input window may consist of two windows: one for sealing, e.g., vacuum sealing, of the EUV Plasma production chamber and another one for exposure to the debris from plasma creation and that the cleaning of such debris inside the chamber may be accomplished, e.g., with a cleaning mechanism, which may incorporate, e.g., etching with a halogen-containing gas and/or by plasma etching. A laser produced plasma (“LPP”) extreme ultraviolet (“EUV”) light source and method of operating same is disclosed which may comprise an EUV plasma production chamber having a chamber wall; a drive laser entrance window in the chamber wall; a drive laser entrance enclosure intermediate the entrance window and a plasma initiation site within the chamber and comprising an entrance enclosure distal end opening; at least one aperture plate intermediate the distal opening and the entrance window comprising at least one drive laser passage aperture. The at least one aperture plate may comprise at least two aperture plates comprising a first aperture plate and a second aperture plate defining an aperture plate interim space. The at least one drive laser aperture passage may comprise at least two drive laser aperture passages. The laser passage aperture may define an opening large enough to let the drive laser beam pass without attenuation and small enough to substantially reduce debris passing through the laser passage aperture in the direction of the entrance window. The apparatus and method may further comprise a purge gas within the aperture plate interim space at a pressure higher than the pressure within the chamber. The apparatus and method may further comprise at least one laser beam focusing optic intermediate a source of the laser beam and the entrance window focusing a respective laser beam to the plasma initiation site within the chamber, which may comprise at least two laser beam focusing optics intermediate a source of a respective one of at least two laser beams and the entrance window and each focusing the respective laser beam to a respective plasma initiation site within the chamber. The apparatus and method may further comprise a respective focusing optic drive element for each of the at least two laser beam focusing optics. The apparatus and method may further comprise a purge gas supply providing purge gas to the aperture plate interim space and a purge gas discharge suction withdrawing purge gas from the aperture plate interim space. The entrance passage may comprise a tapering enclosure wherein the distal end opening comprises an opening large enough to permit the at least one laser beam to pass without attenuation and small enough to substantially prevent debris from entering the entrance passage. The apparatus and method of operating same may comprise an EUV plasma production chamber having a chamber wall; a drive laser entrance window in the chamber wall; a drive laser entrance enclosure intermediate the entrance window and a plasma initiation site within the chamber and comprising an entrance enclosure distal end opening; a protective window intermediate the entrance enclosure and the entrance window. The protective window may comprise at least two protective windows selectively interposable intermediate the entrance enclosure and the entrance window. The apparatus and method may comprise an interposing mechanism selectively interposing one of the at least two protective windows intermediate the entrance enclosure and the entrance window. The apparatus and method may further comprise a protective window cleaning zone into which at least one of the at least two protective windows is selectively positioned for cleaning when not interposed between the entrance enclosure and the entrance window, and a protective window cleaning mechanism cooperatively disposed in the cleaning zone. The apparatus and method may further comprise a cleaning gas supply mechanism supplying cleaning gas to the cleaning zone. The apparatus and method may further comprise a purge gas supply mechanism providing purge gas to a plenum intermediate the protective window and the entrance window. The cleaning gas supply mechanism and the purge gas supply mechanism may comprise the same gas supply mechanism. Applicants according to aspects of an embodiment of the present invention propose an LPP EUV drive laser source chamber with a laser beam transit system interface that also facilitates debris mitigation. A means is provided to deliver the drive laser beam, e.g., in the form of one or more drive laser beams, which in the case of a plurality are also merging and independently focusing into the source chamber while facilitating debris-mitigation features. As illustrated in FIG. 1 according to aspects of an embodiment of the present invention an LPP EUV light source laser input window system 10, may comprise an LPP EUV light source plasma initiation chamber 12, having an LPP EUV light source chamber side wall 14 in which may be mounted an LPP EUV light source drive laser light input window 16. The window 16 may be sealing attached to the side wall 14 by a laser light source input window attachment flange 18. Also attached to the side wall 14 may be an laser focus assembly chamber 20, which may have a cylindrical wall 22. Mounted inside the focus assembly chamber 20 may be, e.g., a drive laser beam delivery unit connection plate 24. Entering the focus assembly chamber may be a drive laser beam (not shown), which in some embodiments of the present invention may also include a second drive laser beam (not shown). Each of the drive laser beams may enter an optical path including, e.g., a drive laser beam focusing lens 42 and a drive laser beam focusing lens 44, each of which may be mounted on a drive laser beam focusing assembly 46 by way of being mounted in a drive laser beam focusing lens housing 48. Each lens may be held in the lens housing 46, 48 by a respective beam focusing lens mounting clamp 50, 52. The mounting clamps may each have respective mounting clamp engagement fingers 62 which hold the respective focus lens 42, 44. The focus assembly connection plate 24 may be attached to the side wall 14 by a mounting plate bracket 60. The respective focus lens housings 46, 48 may be attached to a respective mounting plate 58 by being attached to a respective mounting yoke 68. Each mounting plate 58 may be operatively connected to a respective driving mechanism, e.g., a respective PZT or other suitable drive unit 70, 72, depending on the need, if any, for the fine tuning, e.g., sub-micron movement, available from PZT actuation. Each drive unit may serve, e.g., to move the respective focus lens 42, 44 in the direction of the optical path to shift the focus point of the respective drive laser beam at the plasma initiation site (not shown) in the plasma initiation chamber 12. The PZT actuators 70, 72 may serve, e.g., to slide the respective lens housings 46, 48 on guide rails 74, 76 engaging guide tracks (not shown) attached to a respective translation plate 78, in order to adjust the focus of a respective drive laser beam at the plasma initiation site. Also in the optical path of the drive laser beam(s) may be a debris management outer aperture plate 80, having according to an embodiment of the present invention a first and second debris management beam aperture 82, 84. Further along the optical path of the drive laser beam(s) 30, 32 may be a debris management inner aperture plate 90 having, e.g., a first and second debris management aperture 92 (and not shown). The apertures may be positioned and selected in size and shape to be just big enough for the respective beam(s) 30, 32 to pass through the aperture depending on the focused size of the respective beam at the point of passage through the respective apertures, i.e., the aperture(s) 82, 84 are slightly larger than the apertures 92 (and not shown). It will be understood that there may also be built into the size and shape of the aperture(s) 82, 84 and the aperture(s) 92 (and not shown) room for largest size the respective beam(s) may be at the focusing position of the respective lens housing(s) 46,48, to allow for changes in the focusing of the respective beam(s) without attenuating beam energy at the respective aperture(s) 82, 84 or the respective aperture(s) 92 (and not shown). Intermediate the aperture plates 80, 90 may be formed an intermediate beam transit passage 96 forming a gas transit plenum. Further along the optical path(s) of the respective beam(s) may be positioned a beam debris management inner chamber enclosure assembly 100, extending into the plasma initiation chamber 12. The enclosure assembly 100, partly for ease of assembly and manufacture, may comprise according to aspects of an embodiment of the present invention a telescoping enclosure section 102, which may be attached to an inner chamber telescoping enclosure mounting flange 104, and on the opposite end also attached to another slightly smaller telescoping enclosure section 106, which may be fitted into a distal end of the section 102. This may be followed by additional respectively slightly smaller telescoped sections 108 and 110, followed still further by an elongated tapered enclosure section 120. the elongated tapered enclosure section 120 may terminate in a beam exit opening 122, or depending on the size of the focused beam(s) at that point, may have a beam(s) exit plate (not shown) with a respective beam exit aperture(s) not shown. A purge gas inlet pipe 130 may be provided, e.g., to supply purge gas, e.g., Ar, HBr, Br2, or mixtures thereof, under sufficient pressure, e.g., in the range of 0.1-10 torr to form, e.g., a stream of purge gas flowing through the gas transit plenum 96 to carry debris particles that manage to make it through either of the apertures 92 (and not shown) on the inner aperture plate 90, in order to, e.g., further reduce the amount of debris that reaches the outer aperture plate 80 apertures 82, 84 and thus further reduce the amount of debris reaching the window 16. The purge gas system may further comprise a purge gas inlet fitting 132 on the purge gas inlet line 130 and a purge gas inlet riser 134 connected between the purge gas inlet pipe 130 and the gas transit plenum 96. A purge gas inlet nozzle 136 may be connected to the riser 134 at the inlet to the plenum 96 to increase the velocity of the gas through the plenum 96. A purge gas exit riser 140 and a purge gas exit pipe 142 may serve to discharge the purge gas passing through the plenum 98 from the debris management assembly 100. Another purge gas inlet pipe (not shown) connected to a fitting 146 may serve to provide purge gas to the focus assembly chamber 20. A sealable wiring passage 148 may allow for the passage, e.g., of electrical cables through the back wall 150 of the focus assembly housing chamber 20. It will be understood by those skilled in the art that, according to aspects of an embodiment of the present invention, the laser beam(s) entrance window can be protected via a long tubular delivery “cone” approximated by the assembly 100, with a small exit opening or a small exit aperture(s) at far end, which can serve, e.g., to limit the cross sectional area that plasma can pass through in the direction of the window 12. In addition, the length of the tube facilitates debris contacting the tube inside walls and remaining there. Gas cross-flow between the plasma and window, e.g., through the plenum 96, which may be fed via Swagelock jointed plumbing to the plenum 96 and through to the outlet piping 140, 142. The upper end of the exit piping 142 may also be plumbed to a vacuum pump to evacuate gas and debris. The conduction path for the vacuum line is not very critical as it is desirable to have some purge gas flow down the length of the tube assembly 100, to further inhibit debris from entering and/or transiting the conical debris management assembly 100. The aperture plates 80, 90 according to aspects of an embodiment of the present invention can further limit the path of debris to the entrance window 12 and provide some capture of gas within the confines of the plenum 96, e.g., to provide a slightly higher gas pressure in this region, which can facilitate gas flow through the assembly 100 opposite the debris flow direction. It will be further understood that in addition one might include a fluid cooled nose cone assembly 10 2, 104, 106, 108 and/or 120 (which may be necessary in any event to cool the debris management assembly 100 due to its proximity to the plasma initiation site) in order that a cooled surface is provided to which the debris can more easily stick, in essence cryo-pumping. Additionally, the aperture plates may be cooled and/or an electro magnetic field coil(s) may be provided about the nose cone 102, 104, 106, 108 and/or 120 to influence the debris path and, e.g., steer it into inside walls of a respective one of the components 102, 104, 106, 108 and/or 120. In the process of operation of prototypes and test embodiments of the above referenced LPP EUV drive laser delivery system applicants have observed that good etching of, debris formed in an EUV creating plasma within the chamber, e.g., from the EUV radiation source material, e.g., Sn, from the surface of an optical element, e.g., a window by, e.g., HBr may be accomplished, and specifically accelerated at elevated temperature. Such a temperature may be, e.g., on the surface of the optical element and, e.g., on the order of 300-400° C. Applicants have concluded, therefore, that such optical elements, e.g., LPP EUV drive laser input (transit) windows may be cleaned in a halogen containing atmosphere, e.g., an HBr or H2 atmosphere, with heating to the desired specified temperature. However, heating of such optical elements, e.g., the laser transit window which is placed in optical path of the EUV drive laser beam may be complicated for several reasons. For example, one manner of such heating, i.e., thermoconductive heating from the side surface of the optical element, e.g., the drive laser transit window, e.g., can create a temperature gradient along the radius and thereby, e.g., distort the drive laser beam focus, e.g., which can cause, e.g., a loss of conversion energy, because, the drive laser beam is not properly focused at the target at the plasma initiation site within the chamber. Such distortion may be very difficult to compensate. Radiation heating from the front/rear surface, e.g., may be limited by the laser beam solid angle. Therefore, according to aspects of an embodiment of the present invention applicants propose apparatus and methods for the increase of the lifetime of optical elements, e.g., LPP EUV drive laser input transit window. According to aspects of an embodiment of the present invention applicants propose to provide a solution to, e.g., the above noted exemplary problems with, e.g., the protection of and cleaning of previously proposed LPP EUV optical element, e.g., LPP drive laser beam transit systems. Applicants propose, e.g., the separation of the heating zone from the laser beam zone, as shown, schematically and by way of example, in FIG. 3. As shown in FIG. 3, an LPP EUV light source laser input window system 10′ may comprise, e.g., an LPP EUV light source plasma initiation chamber 12, within which the LPP EUV light source laser input/transit window system 10′ may be mounted, e.g., to an LPP EUV light source chamber side wall 14, and contain an LPP EUV light source drive laser light input window 16. A protective window 148, which may be, e.g., is exposed to plasma formation debris, e.g., Sn debris from plasma, for certain number of pulses (e.g., 10M shots). This window 148 may, e.g., protect the vacuum containing window 16. After operation the protective window 148, which may, e.g., be mounted on a rotating wheel 150 (or turret) may be placed into a cleaning zone 152 and a clean substitute protective window 154 may thereby also be again placed into the laser beam transit zone 160. In the cleaning zone 152 the window may be, e.g., etched by an etchant specific to the debris, e.g., Sn, e.g., a halogen etchant, e.g., HBr, which may, e.g., be supplied to the cleaning cavity zone 154. A laser delivery and purge gas enclosure cone 120′ may be utilized, e.g., to protect the working window 148, 154 which is currently in use from, e.g., small micro-droplets of debris, e.g., Sn atoms and Sn ions easier to accomplish, e.g., by providing only a small opening at the tapered terminal end into which the debris can enter in route to the engaged window 148, 154. Such an opening, it will be understood, may form an exit aperture sized and shaped, e.g., to essentially match the size of the desired exit drive laser beam at the point of exit from the enclosure cone 120′. The pressure of HBr in the gas enclosure cone assembly 100′ may be, e.g., on the order of 0.1-10 torr. In the cleaning zone 154 the protective window, e.g., window 148 or 154 presently selected for cleaning may be relatively uniformly heated, e.g., by a radiation heater 155, e.g., made of a conductive metal, e.g., made of molybdenum, which may be, e.g., electrically or RF heated. The rotating wheel assembly 150 may contain according to aspects of an embodiment of the present invention several protective windows, e.g., 4, rather than just the two protective windows 148, 152. The clean window 152, e.g., rotated into the working zone 160 where the LPP drive laser beam transits into the chamber may operate at a temperature substantially lower than the 300-400° C. cleaning temperature, e.g., at room temperature, e.g., in order to therefore, e.g., reduce the possible optical distortions. Etching can still occur at fairly high pressure of HBr with uniform heating of the front surface of the protective window(s) in the cleaning zone 152, which can provide the ideal conditions for efficient cleaning of the window(s) in the cleaning zone 152, e.g., from Sn debris. Purge gas in the gas transit plenum 96′ between, e.g., the input window 16 and the actively engaged protective window 148, 154 currently in place to block debris, may serve to keep the input window 16 at a desired temperature and at the same time assist in cooling the delivery cone 100′ and also may flow into the cleaning zone 152 to cool the rotating wheel assembly 150 and the back side of the protective window(s) currently in the cleaning zone 152. It will be understood by those skilled in the art that a laser produced plasma (“LPP”) extreme ultraviolet (“EUV”) light source and method of operating same is disclosed which may comprise an EUV plasma production chamber having a chamber wall; a drive laser entrance window in the chamber wall; a drive laser entrance enclosure intermediate the entrance window and a plasma initiation site within the chamber and comprising an entrance enclosure distal end opening; at least one aperture plate intermediate the distal opening and the entrance window comprising at least one drive laser passage aperture. The at least one aperture plate may comprise at least two aperture plates comprising a first aperture plate and a second aperture plate defining an aperture plate interim space. The at least one drive laser aperture passage may comprise at least two drive laser aperture passages. The laser passage aperture may define an opening large enough to let the drive laser beam pass without attenuation and small enough to substantially reduce debris passing through the laser passage aperture in the direction of the entrance window. within the manufacturing tolerances allowed and depending on whether or not the need for blocking debris passage through a respective aperture or the need to allow for a range of focusing of the laser beam passing through the aperture and/or loss of beam energy and/or heating of the aperture is determined to be paramount, one skilled in the art can determine what large enough means in this context, whereby a significant amount of debris is blocked such that, along with any purge gas system employed the laser entrance window is assured a reasonable operating life while the drive laser beam is not so significantly attenuated in the aperture(s) that effective production of EUV in band light at the necessary wattage, e.g., at an intermediate focus where the light, e.g., passes into a tool using the light. The purge gas within the aperture plate interim space may be at a pressure higher than the pressure within the chamber and in this manner serve to assist in blocking debris passage, by, e.g., flowing in the opposite direction of the incoming debris entering the drive laser beam entrance enclosure. The apparatus and method may further comprise at least one laser beam focusing optic intermediate a source of the laser beam and the entrance window focusing a respective laser beam to the plasma initiation site within the chamber, which may comprise at least two laser beam focusing optics intermediate a source of a respective one of at least two laser beams and the entrance window and each focusing the respective laser beam to a respective plasma initiation site within the chamber. The apparatus and method may further comprise a respective focusing optic drive element for each of the at least two laser beam focusing optics. The apparatus and method may further comprise a purge gas supply providing purge gas to the aperture plate interim space and a purge gas discharge suction withdrawing purge gas from the aperture plate interim space. The entrance passage may comprise a tapering enclosure wherein the distal end opening comprises an opening large enough to permit the at least one laser beam to pass without attenuation and small enough to substantially prevent debris from entering the entrance passage, with large enough and substantially prevent being as defined above. The apparatus and method of operating same may comprise an EUV plasma production chamber having a chamber wall; a drive laser entrance window in the chamber wall; a drive laser entrance enclosure intermediate the entrance window and a plasma initiation site within the chamber and comprising an entrance enclosure distal end opening; a protective window intermediate the entrance enclosure and the entrance window. The protective window may comprise at least two protective windows selectively interposable intermediate the entrance enclosure and the entrance window. The apparatus and method may comprise an interposing mechanism selectively interposing one of the at least two protective windows intermediate the entrance enclosure and the entrance window. The apparatus and method may further comprise a protective window cleaning zone into which at least one of the at least two protective windows is selectively positioned for cleaning when not interposed between the entrance enclosure and the entrance window, and a protective window cleaning mechanism cooperatively disposed in the cleaning zone. The apparatus and method may further comprise a cleaning gas supply mechanism supplying cleaning gas to the cleaning zone. The apparatus and method may further comprise a purge gas supply mechanism providing purge gas to a plenum intermediate the protective window and the entrance window. The cleaning gas supply mechanism and the purge gas supply mechanism may comprise the same gas supply mechanism. It will be understood by those skilled in the art that the aspects of embodiments of the present invention disclosed above are intended to be preferred embodiments only and not to limit the disclosure of the present invention(s) in any way and particularly not to a specific preferred embodiment alone. Many changes and modification can be made to the disclosed aspects of embodiments of the disclosed invention(s) that will be understood and appreciated by those skilled in the art. The appended claims are intended in scope and meaning to cover not only the disclosed aspects of embodiments of the present invention(s) but also such equivalents and other modifications and changes that would be apparent to those skilled in the art. In additions to changes and modifications to the disclosed and claimed aspects of embodiments of the present invention(s) noted above the following could be implemented. While the particular aspects of embodiment(s) of the LPP EUV DRIVE LASER INPUT SYSTEM described and illustrated in this patent application in the detail required to satisfy 35 U.S.C. §112 is fully capable of attaining any above-described purposes for, problems to be solved by or any other reasons for or objects of the aspects of an embodiment(s) above described, it is to be understood by those skilled in the art that it is the presently described aspects of the described embodiment(s) of the present invention are merely exemplary, illustrative and representative of the subject matter which is broadly contemplated by the present invention. The scope of the presently described and claimed aspects of embodiments fully encompasses other embodiments which may now be or may become obvious to those skilled in the art based on the teachings of the Specification. The scope of the present LPP EUV DRIVE LASER INPUT SYSTEM is solely and completely limited by only the appended claims and nothing beyond the recitations of the appended claims. Reference to an element in such claims in the singular is not intended to mean nor shall it mean in interpreting such claim element “one and only one” unless explicitly so stated, but rather “one or more”. All structural and functional equivalents to any of the elements of the above-described aspects of an embodiment(s) that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Any term used in the specification and/or in the claims and expressly given a meaning in the Specification and/or claims in the present application shall have that meaning, regardless of any dictionary or other commonly used meaning for such a term. It is not intended or necessary for a device or method discussed in the Specification as any aspect of an embodiment to address each and every problem sought to be solved by the aspects of embodiments disclosed in this application, for it to be encompassed by the present claims. No element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element in the appended claims is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited as a “step” instead of an “act”.
	claims	1. An apparatus arranged to control a temperature of uranium material in a uranium material storage container, comprising:a thermal guide which wraps around an external surface of the uranium material storage container to cause a heat transfer medium inside the thermal guide to exchange heat energy with the uranium material storage container;a heat exchanger to heat or cool the heat transfer medium outside the thermal guide; andwherein the thermal guide comprises selectively releasable connections which attach the thermal guide to the uranium material storage container. 2. An apparatus according to claim 1, wherein the thermal guide forms a thermally conductive contact with the uranium material storage container to cause the exchange of heat energy by conduction. 3. An apparatus according to claim 1, wherein the thermal guide is configured to guide the heat transfer medium around an exterior of the uranium material storage container. 4. An apparatus according to claim 1, wherein the thermal guide surrounds the uranium material storage container. 5. An apparatus according to claim 1, wherein the thermal guide comprises a thermally conductive heat transfer surface for locating against the external surface of the uranium material storage container and through which heat energy is exchanged between the heat transfer medium in the guide and the uranium material storage container. 6. An apparatus according to claim 1, wherein the thermal guide comprises a heat insulating surface which is configured to prevent heat transfer between the heat transfer medium in the guide and the atmosphere around the uranium material storage container. 7. An apparatus according to claim 1, configured to controllably heat or cool the heat transfer medium in order to cause heating or cooling of the uranium material inside the uranium material storage container. 8. An apparatus according to claim 1, configured to detect the temperature of the uranium material storage container and to heat or cool the heat transfer medium in response to the detected value of the temperature of the uranium material storage container. 9. An apparatus according to claim 1, configured to heat or cool the heat transfer medium to obtain a predetermined target temperature for the uranium material storage container. 10. An apparatus according to claim 1, wherein the thermal guide comprises a plurality of sections which wrap around a corresponding plurality of regions of the uranium material storage container. 11. An apparatus according to claim 1 arranged to circulate the heat transfer medium between the thermal guide and the heat exchanger to heat or cool the heat transfer medium. 12. An apparatus according to claim 1, comprising a further thermal guide which wraps around an external surface of a further uranium material storage container to cause a heat transfer medium inside the further thermal guide to exchange heat energy with the further uranium material storage container, wherein the heat exchanger is configured to cause heat energy extracted from a warmer of the storage containers to be transferred to a cooler of the storage containers. 13. A uranium material storage container wrapped in a thermal guide of an apparatus according to claim 1. 14. A method of controlling a temperature of uranium material in a uranium material storage container, comprising:wrapping the uranium material storage container in a thermal guide of an apparatus arranged to control the temperature of uranium material in the uranium material storage container, wherein the thermal guide comprises selectively releasable connections which attach the thermal guide to the uranium material storage container; andusing a heat exchanger of the apparatus to heat or cool a heat transfer medium outside the thermal guide to cause the heat transfer medium to exchange heat energy with the uranium material storage container when inside the guide. 15. The apparatus according to claim 1, whereinthe thermal guide is flexible and configured to be wrapped around, and unwrapped from, a cylindrical surface of the uranium material storage container, and the thermal guide is connected to the heat exchanger by a circulation line. 16. The apparatus of claim 15, whereinthe uranium material storage container is one of a 48Y UF6 storage and transport cylinder or a 30B UF6 cylinder, andthe thermal guide is sized to extend around a full circumference of the uranium material storage container. 17. The method of claim 14, wherein the thermal guide is flexible, wherein the wrapping comprises wrapping the thermal guide around a cylindrical surface of the uranium material storage container, and further comprising:unwrapping the thermal guide from around a cylindrical surface of the uranium material storage container. 18. The method of claim 17, whereinthe uranium material storage container is one of a 48Y UF6 storage and transport cylinder or a 30B UF6 cylinder, andthe thermal guide is sized to extend around a full circumference of the uranium material storage container.
061309273	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates, in general, to grids used for placing and supporting fuel rods in a nuclear reactor fuel assembly and, more particularly, to a grid with nozzle-type coolant deflecting channels for use in such a nuclear fuel assembly, the grid being so designed as to effectively deflect coolant, thus mixing lower temperature coolant with high temperature coolant within the assembly and improving heat transferring effect between the fuel rods and the coolant, the grid also protecting the fuel rods from fretting wear due to a swirling motion or a lateral circulation of the coolant, and being reduced in the thickness of the intersecting grid strips while maintaining a desired buckling strength of said strips, thus allowing the coolant to more smoothly flow in the assembly and thereby reducing pressure drop of the coolant while effectively resisting laterally directed forces acting on the grids. 2. Description of the Prior Art In typical light water reactors, a plurality of elongated nuclear fuel rods 125 are regularly and parallelly arranged in an assembly 101 having a square cross-section in a way such that, for example, fourteen, fifteen, sixteen or seventeen fuel rods 125 are regularly arranged along each side of said square cross-section, thus forming a 14.times.14, 15.times.15, 16.times.16, or 17.times.17 array as shown in FIG. 1. In such a nuclear fuel assembly 101, the elongated fuel rods 125 are typically fabricated by containing a fissionable fuel material, such as uranium core, within a hermetically sealed elongated zircaloy tube 114, known as the cladding. In order to place and support such fuel rods 125 within the assembly 101, a plurality of spacer grids 110 are used. Each of such grids 110 is produced by welding a plurality of intersecting inner strips to each other into an egg-crate pattern prior to encircling the periphery of the grid 110 by four perimeter strips. The top and bottom of the fuel assembly 101 are, thereafter, covered with pallets 111 and 112, respectively. The assembly 101 is thus protected from any external loads acting on the top and bottom thereof. The spacer grids 110 and the pallets 111 and 112 are integrated into a single structure using a plurality of guide tubes 113. A framework of the assembly 101 is thus fabricated. Each of the above spacer grids 110 is fabricated as follows. As best seen in FIG. 2, two sets of inner strips 115 and 116, individually having a plurality of notches at regularly spaced portions, are assembled with each other by intersecting the two sets of strips 115 and 116 at said notches, thus forming a plurality of four-walled cells individually having four intersections 117. The assembled strips 115 and 116 are, thereafter, welded together at said intersections 117 prior to being encircled by perimeter strips 118, thus forming a spacer grid 110 with such four-walled cells. As shown in FIG. 3, a plurality of positioning springs 119 and a plurality of positioning dimples 120 are integrally formed on or attached to the inner strips 115 and 116 in a way such that the springs 119 and the dimples 120 extend inwardly with respect to each of said four-walled cells. In such a case, the dimples 120 are more rigid than the springs 119. In each four-walled cell, the positioning springs 119 force a fuel rod 125 against associated dimples 120, thus elastically positioning and supporting the fuel rod 125 at four points within each of said cells. In the typical nuclear fuel assembly 101, a plurality of grids 110 are regularly and perpendicularly arranged along the axes of the fuel rods 125 at right angles, thus placing and supporting the fuel rods 125 at multiple points. That is, the grids 110 form a multi-point support means for placing and supporting the fuel rods 125 within a nuclear fuel assembly 101. In such an assembly 101, the positioning springs 119 elastically and slightly force the fuel rods 119 against the dimples 120 in a way such that the fuel rods 125 are slidable on the support points of both the springs 119 and the dimples 120 when the fuel rods 125 are elongated due to irradiation induced growth during a circulation of the coolant within the assembly 101. When the fuel rods 125 are fixed to the grids 110 at the support points, the fuel rods 125 may be bent at portions between the support points of the grids 110, thus undesirably reducing the intervals between the fuel rods 125 of the assembly 101 as shown in FIG. 4. In some typical nuclear reactors using water as coolant, water receives thermal energy from the fuel rods 125 prior to converting the thermal energy into electric energy. During an operation of a nuclear fuel assembly 101 of such a reactor, water or liquid coolant is primarily introduced into the assembly 101 through an opening formed on the core supporting lower plate of the reactor. In the assembly 101, the coolant flows upwardly through the passages, defined between the fuel rods 125, and receives thermal energy from the fuel rods 125. In such a case, the sectioned configuration of the coolant passages provided in the fuel assembly 101 is shown in FIG. 4. Typically, the amounts of thermal energy generated from different nuclear fuel assemblies 101 are not equal to each other. Since the assemblies 101 individually have a rectangular configuration with the elongated, parallel fuel rods 125 being closely spaced apart from each other at irregular intervals, the temperature of coolant flowing around the fuel rods 125 is variable in accordance with positions. That is, the amount of thermal energy, received by water flowing around the corners 123 of each four-walled cell, is less than that received by water flowing around the fuel rods 125. The coolant passages of typical fuel assemblies 101 thus undesirably have low temperature regions. Such low temperature regions reduce the thermal efficiency of the nuclear reactor. The coolant passages of the fuel assemblies 101 may also have partially overheated regions at positions adjacent to the fuel rods 125 having a high temperature. Such partially overheated regions deteriorate soundness of the assemblies 101. In order to remove such partially overheated regions from a nuclear fuel assembly 101, it is necessary to design the grid in a way such that a uniform temperature distribution is formed in the fuel assembly 101. The grid is also designed to effectively deflect and mix the coolant within the assemblies 101. Such effectively mixed coolant makes uniform the increase in enthalpy and maximizes the core output. Typical examples of such designed grids are disclosed in Korean Patent Publication Nos. 91-1978 and 91-7921. In the grids disclosed in the above Korean patents, so-called "mixing blades" or "vanes" are attached to the upper portion of each grid and are used for mixing coolants within the fuel assembly. That is, the mixing blades or vanes allow the coolant to flow laterally in addition to normally longitudinally, and so the coolants are effectively mixed with each other between the channels and between the lower temperature regions and the partially overheated regions of the fuel assembly. On the other hand, a coolant mixing grid, comprising two sets of intersecting inner strips individually made up of two flat, narrow sheets deformed to provide channels for coolant, is disclosed in U.S. Pat. No. 4,726,926. In the above grid, the upper or lower portion of each channel is inclined relative to the axes of the fuel rods at an angle of inclination, thus producing a swirling motion of coolant at the inlet and outlet of said channels. Such a swirling motion of coolant improves the heat transferring effect between the fuel rods and the coolant within a nuclear fuel assembly. The above Korean or U.S. grids, designed to form a lateral flow of coolant or to deflect and mix the coolant within a nuclear fuel assembly, are somewhat advantageous in that they more effectively mix the coolant and improve the heat transferring effect between the fuel rods and the coolant within a nuclear fuel assembly. However, such a grid is problematic in that the lateral flow or mixing of coolant regrettably vibrates the elongated, parallel, closely spaced fuel rods within the assembly. As described above, the fuel rods 125 are supported by both the positioning springs 119 and the positioning dimples 120 within the four-walled cells of the grids 110. However, during an operation of a nuclear fuel assembly 101, the fuel rods 125 quickly and periodically interfere with the intersecting strips of the grids due to vibrations caused by the lateral flow of coolant. When the fuel rods 125 are so vibrated for a lengthy period of time, the claddings of the fuel rods 125 are repeatedly and frictionally abraded at their contact parts at which the fuel rods 125 are brought into contact with the springs and dimples of the grids. The claddings are thus reduced in their thicknesses so as to be finally perforated at said contact parts. Such an abrasion of the fuel rods is so-called fretting wear in the art. Such a fretting wear may be referred to Korean Patent Publication No. 94-3799 in detail. The laterally directed force caused by the mixing blades of the grids is in proportion to the coolant mixing effect and directly affects the thermal transferring effect of nuclear reactors. However, such a laterally directed force of the mixing blades also proportionally increases the amplitude of vibration of the fuel rods. This may cause damage to the fuel rods. The important factors necessary to consider while designing the grids for use in nuclear fuel assemblies are improvement in both the fuel rod supporting function of the grids and the buckling strength resisting of such a laterally directed force acting on said grids. During an operation of a nuclear reactor, the fuel assemblies may be vibrated laterally due to a load acting on the assemblies and this causes an interference between the assemblies. Therefore, the grids of the fuel assemblies may be impacted due to such an interference between the assemblies as disclosed in U.S. Pat. No. 4,058,436. In the prior art, the grid's buckling strength, resisting a lateral load acting on the grid, is reduced since the grid strips have to be partially cut away through, for example, a stamping process at a plurality of portions so as to form positioning springs and dimples within a fuel assembly. Such cut-away portions reduce the effective cross-sectional area of the grid capable of resisting impact, thus reducing the buckling strength of the grid. In a grid disclosed in U.S. Pat. No. 5,243,634, the positioning springs are individually integrated with an associated grid strip at one point, thus forming a cantilever structure. Such a cantilever spring is more flexible than a simple spring which is integrated with a grid strip at opposite ends thereof. In the mixing grid disclosed in the above-mentioned U.S. Pat. No. 4,726,926, the deformed portions, provided on the sheets of the intersecting grid strips for forming the channels for coolant, act as channel-shaped positioning springs used for placing and supporting the fuel rods within the four-walled cells. Since the sheets of the strips are not cut away but deformed to form such channel-shaped springs, flexibility of such channel-shaped springs is exceedingly less in comparison with the above-mentioned cantilever springs, thus failing to provide desired flexibility expected by conventional positioning springs. The channel-shaped springs thus act as dimples rather than springs. Therefore, the mixing grid, having such channel-shaped dimples, is problematic in that said dimples may cause the fuel rods to be undesirably bent when the fuel rods are elongated due to the irradiation induced growth during an operation of the reactor or to be scratched at the claddings when the fuel rods are inserted into the cells of the grids. SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a grid with nozzle-type coolant deflecting channels for use in nuclear fuel assemblies, which is so designed as to effectively mix low temperature coolant with high temperature coolant, thus preventing partial overheating of fuel rods and improving the thermal efficiency of a nuclear reactor, and which does not cause a swirling motion or a lateral circulation of the coolant within a fuel assembly, thus protecting the fuel rods from fretting wear. Another object of the present invention is to provide a grid for use in nuclear fuel assemblies, of which the intersecting inner strips are slightly reduced in the thickness, thus reducing resistance to the flow of coolant within the assembly, and are not cut away at any portion, thus maintaining a desired effective sectional area and thereby having a desired buckling strength capable of effectively resisting lateral load acting thereon. A further object of the present invention is to provide a grid for use in nuclear fuel assemblies, of which the intersecting inner strips have a reduced thickness and have channel-shaped positioning springs specifically designed to form a substantially longer interval between the fuel rod support points of grids, thus being increased in flexibility twice in comparison with typical grids having positioning springs and dimples, and which thus overcomes the problems experienced in typical channel-shaped dimples, for example, shown in U.S. Pat. No. 4,726,926. In order to accomplish the above objects, a grid with coolant deflecting channels for used in a nuclear fuel assembly in accordance with this invention, comprises: two sets of intersecting grid strips arranged in sets at an angle to each other prior to being encircled by a perimeter strip, thus forming a plurality of four-walled cells individually placing and supporting an elongated fuel rod therein, each of said grid strips being made up of two narrow sheets deformed to provide nozzle-type coolant deflecting channels, said channels individually having an upright Y-shaped or reversed Y-shaped configuration capable of so deflecting coolant as to mix low temperature coolant with high temperature coolant and to form a uniform temperature distribution within the fuel assembly. The coolant deflecting channels of this invention are specifically designed as follows. Each of the channels is gradually increased in the cross-sectional area within the region from the inlet to the middle portion, thus forming a diffuser. Each channel is, thereafter, gradually reduced in the cross-sectional area within the remaining region from the middle portion to the outlet, thus forming a nozzle. The middle portion of each channel thus acts as a positioning spring used for placing and supporting an elongated fuel rod within a four-walled cell of the grid. Due to the specifically designed configuration of the channels, the coolant flows through the middle portion of each channel at a low speed and at a high pressure, thus giving the middle portion an additional spring force. The outlet or the nozzle of each channel discharges the coolant from the channel at a high speed, thus improving the coolant mixing effect of the channel. In order to allow the channels of this invention to accomplish a desired operational function as expected from conventional positioning springs used for placing and supporting fuel rods within a fuel assembly, it is necessary to set the thickness of each sheet of the grid strip to about 0.15 mm-0.3 mm and the width of the middle portion of the channel to about 6 mm to 9 mm.
053496256	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS The x-ray diagnostics installation shown in FIG. 1 includes a pick-up unit composed of an x-ray radiator 1 having a gating stage 2, and a radiation receiver 3, which are held opposite one another by a holder 4. The holder 4 is constructed such that the pick-up unit is adjustable along a support 5 for an examination subject 6. Of course, such an x-ray diagnostics installation can also be executed such that the pick-up unit is stationary and the support 5 is adjustable. It is only necessary that the pick-up unit and the support 5 are adjustable relative to one another, so that a sequence of exposures of an examination region can be produced. The drive of the x-ray radiator I for 1 emission of a ray beam, the gating stage 2 for gating the ray beam, the adjustment of the pick-up unit or of the support 5 relative to one another, as well as the production of an image from the examination region of the examination subject 6 from the signals of the radiation receiver 3 on a display 7, ensue under the control of a control unit 8, the details of which shall be set forth in greater detail below with reference to FIG. 2. As shown in FIG. 2, the control unit 8 includes an operating unit 9 by means of which subject-related data, for example the size, the weight and the physique (thin, average, fat; short, average, tail) of an examination subject 6 can be supplied to an arithmetic unit 10. When, for example, the leg of the patient is to be examined, the arithmetic unit 10 calculates the average length of the leg on the basis of this data, and also calculates the number of exposures to be produced resulting therefrom, the step length of the relative adjustment of pick-up unit and support 5 relative to one another, the electrical parameters required for every exposure, and the diaphragm setting of the gating stage 2 arranged in the beam path of the x-ray beam that is required for every exposure. A pre-setting of the means for the relative adjustment of pick-up unit or support 5, the gating stage 2, and a voltage supply 11 which feeds the x-ray radiator 1, ensues by the arithmetic unit 10 on the basis of the calculated data for each of the successive exposures. Further apparatus-related parameters, for example the radiation receiver format as well as the apparatus geometry (focus-to-subject spacing and focus-to-image receiver spacing) and the desired section width and overlap, can be introduced into this calculation. These apparatus-related parameters can be input entered via the operating unit 9, insofar as they cannot be called as data of a memory of the control unit 8. If the x-ray diagnostics installation includes a digital image processing system, the subject-related data and the apparatus-related parameters can be supplied from the image processing system to the arithmetic unit 10 within the framework of the invention. The display 7 can be in the form of a monitor 12, a printer 13 or a display field of the operating unit 9, so that, as shown in FIG. 3, the subject contour 14, the individual exposure positions 15 through 21, the diaphragm settings in the exposure positions 15 through 21 (shown shaded) the image size in the subject plane, as well as the pick-up regions of the subject relative to the radiation field of the radiation beam calculated from the subject-related data and from the apparatus-related parameters are displayed. In addition, the entire presentation region 22 in the subject plane, the usable presentation region 23 in the subject plane, the section width 24 in the subject plane, the overlap 25 in the subject plane, the step length 26, the number of steps and the image format or formats related to the subject plane can also be indicated or displayed. The starting point for the calculation is a patient-related, anatomically typical, reproducible basic setting of the exposure unit, for example to the navel, that can be easily set under optical sighting supervision as the origin for the coordinates of the patient relative to the pick-up system. Of course, these presentations and data can also be displayed on an x-ray monitor on which an image of the examination region can also be portrayed. The data calculated by the arithmetic unit 10 can be supplied in subject-related fashion to a data memory 27, so that these can in turn be called in as needed. It is thus possible to produce repeatable, subsequent examinations under identical system conditions for a patient. Within the framework of the invention, the parameters of a contrast agent injector 28 required for the examination can likewise be calculated by the arithmetic unit 10 and can be pre-set via the control unit 8. The arithmetic operations implemented in the arithmetic unit 10 for the pre-setting of the x-ray diagnostics installation for the exposure sequence are set forth below, with reference to FIGS. 4 and 5. OF=(EF/FBA)FOA, or OF=EF/V; X=SW-r, with r=OF/2; since also X=r-U, then U=SW-ZX; Z=OF/2-U/2=r-U/2; SB=2[(OF/2).sup.2 -(OF/2-U/2).sup.2 ].sup.1/2 =2(r.sup.2 -Z.sup.2).sup.1/2 ; L.sub.1 =SZ.multidot.SW+OF; L.sub.2 =SZ.multidot.SW+OF-U+SZ.multidot.SW+2Z; and L.sub.3 =L.sub.2 +U/2; wherein; FOA=focus-to-subject distance FTA=focus-to-table distance FBA=focus-to-image intensifier distance in the plane of the blanking OF=subject field EF=input field of the image intensifier U=overlap SW=step width SZ=number of steps SB=section width L.sub.1 =overall subject length L.sub.2 =subject length between the section widths L.sub.3 =medically usable region V=magnification factor Z=pick-up field in the subject plane X and r are parameters shown in FIG. 5. According to a first exemplary embodiment of the invention, an image intensifier input field of 40 cm, a focus-to-image intensifier distance of 123 cm, a focus-to-subject distance of 100 cm, a step length of 20 cm, and a number of steps of 5, are to be entered into the arithmetic unit 10 via the operating unit 9, as a numerical example. On the basis of these inputs, the arithmetic unit 10 then implements the arithmetic operations 1 through 6 recited below: ______________________________________ 1. OF = (EF/FBA)FOA = (40 cm/123 cm)100 cm = 32.52 cm 2. r = OF/2 = 32.52 cm/2 = 16.26 cm 3. X = SW - r = 20 cm - 16.26 cm = 3.74 cm 4. U = SW - 2X = 20 cm - 2(3.74 cm) = 12.52 cm 5. SB = 2[(OF/2).sup.2 - (OF/2 - U/2).sup.2 ].sup.1/2 = 2[(16.26 cm).sup.2 - (16.26 - 12.52/2).sup.2 ].sup.1/2 = 25.64 cm 6. L.sub.3 = SZ .multidot. SW + OF - U + U/2 = 5 .multidot. 20 cm + 32.52 cm - 12.52 cm + 6.26 cm = 126.26 cm ______________________________________ The table recited below can be displayed on the display 7: ______________________________________ overlap = 12.52 cm section width = 25.64 cm usable examination region = 126.26 cm. ______________________________________ According to another exemplary embodiment of the invention, three keys (short, average, tall) are provided at the operating unit 9, which are to be operated in conformity with the physique of the patient to be examined. Upon actuation of a key, the arithmetic unit 10 interrogates a corresponding memory of a data store and, given examination of the leg of a patient as an example, thus obtains the following data for further calculation: ______________________________________ key "short" = 105 cm, key "average" = 115 cm, key "tall" = 130 cm. ______________________________________ Of course, it is also possible within the framework of the invention to enter the actual length/width of the overall examination region of the subject (leg) via the operating unit 9. Further data corresponding to the apparatus geometry can be stored in the data store as permanent values, these being interrogated by the arithmetic unit 10 and being capable of being utilized for the calculation. Permanent values for the apparatus geometry are the image intensifier input field, the focus-to-image intensifier spacing, the focus-to-subject spacing, the overlap and the section width. The arithmetic unit 10 thus calculates the optimum number of steps. According to a third exemplary embodiment of the invention, it is possible in an expansion of the second exemplary embodiment to prescribe the desired overlap and/or the section width via the operating unit 9, which then enters into the calculation. It is possible within the framework of the invention to define the subject contour via suitable separate means and to supply the subject-related data thus obtained to the arithmetic unit 10 on a disk or in some other stored form for further calculation. The pre-setting of the gating stage 2 likewise ensues on the basis of subject-related data, for example by the arithmetic unit 10--on the basis of subject-related data "short, average, tall; thin, average, fat)--interrogating corresponding data of a data store, so that the gating stage 2 is then correspondingly driven via the control unit 8. Data corresponding to the following table for gatings with reference to the example of exposure positions 15 through 21 can be contained in the data store: ______________________________________ Exposure Position 15 16 17 18 19 20 21 ______________________________________ thin 40 cm 40 cm 38 cm 33 cm 35 cm 30 cm 31 cm aver- 40 cm 40 cm 40 cm 35 cm 37 cm 32 cm 33 cm age fat 40 cm 40 cm 40 cm 38 cm 39 cm 36 cm 37 cm ______________________________________ The pre-setting of the voltage supply 11 likewise ensues on the basis of the entry of subject-related data. The arithmetic unit 10 for this purpose also interrogates a data store that contains data of electrical parameters corresponding to the subject-related data, so that the control unit 8 then correspondingly drives the voltage supply 11. A display or an output in some other form of the calculated data on a monitor or printer in tables and/or graphic presentation is possible in accord with all exemplary embodiments of the invention. Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
	abstract	A system for receiving and storing high level radioactive waste comprising: an enclosure comprising walls having inlet ventilation ducts, a roof comprising an array of holes, and a floor; an array of metal shells located in an internal space of the enclosure, the array of metal shells being co-axial with the array of holes in the roof so that containers holding high level radioactive waste can be lowered through the array of holes in the roof and into the array of metal shells; the array of metal shells acting as load bearing columns for the roof; and each of the metal shells comprising (i) an expansion joint for accommodating thermal expansion and/or contraction of the metal shells; and (ii) one or more holes at a bottom portion of the metal shell.
	description	This application claims priority of U.S. Provisional Application No. 60/457,958 filed on Mar. 25, 2003, entitled AUTOMATIC CLASSIFICATION OF DEFECTS USING PATTERN RECOGNITION APPLIED TO X-RAY SPECTRA, by Anne Testoni which is incorporated herein by reference in its entirety for all purposes. The present invention relates generally to inspection of semiconductor devices for the purpose of identifying defects thereon. Additionally, it relates to techniques for classifying defects found on integrated circuit devices. Semiconductor defects may include structural flaws, residual process material and other surface contamination which occur during the production of semiconductor wafers. Defects are typically detected by a class of instruments called inspection tools. Such instruments automatically scan wafer surfaces and detect, and record the location of optical anomalies using a variety of techniques. This information, or “defect map,” is stored in a computer file and sent to a defect review station. Using the defect map to locate each defect, a human operator observes each defect under a microscope and classifies each defect according to class (e.g., particle, pit, scratch, or contaminant). Information gained from this process is used to correct the source of defects, and thereby improve the efficiency and yield of the semiconductor production process. Problems with this classification method include the technician's subjectivity in identifying the defect class, and the fatigue associated with the highly repetitive task of observing and classifying these defects. One type of inspection or review tools that may be used to classify a defect are electron beam (ebeam) induced X-ray tools. An ebeam induced X-ray tool directs an e-beam towards the defect and X-rays are emitted from the defect as well as any surrounding material in response to the e-beam. The X-rays may then be analyzed to determine a composition of the defect. Typically, the X-rays are compared to X-rays emitted from a substrate having no defect. The X-ray spectra for the substrate without a defect is subtracted from the substrate having the defect to obtain the X-ray spectra for the defect. Although one can easily determine a composition of a defect when the substrate is formed from a single material, such as silicon, it becomes rather difficult to identify a defect's composition when the substrate is complex and formed from several different structures and materials. This technique would require obtaining reference X-ray spectra from multiple substrate specimens having no defects to thereafter compare to defects on such complex substrates. Additionally, one would have to determine the substrate type for each type of defect and then use the appropriate reference X-ray spectra to determine the defect's composition. Accordingly, there is a need for improved mechanisms for classifying defects using an e-beam induced X-ray inspection or review system or the like. Accordingly, mechanisms are provided for classifying defects based on X-ray spectrum obtained from the defects. In general terms, the present invention provides pattern recognition techniques for accurately and efficiently classifying a defect based on an X-ray spectrum obtained from such defect and its surrounding substrate and structures, no matter the complexity of such substrate and structures. A pattern recognition technique generally includes training a pattern recognition process to recognize particular types of X-ray spectrum obtained from specimens as belonging to a particular defect type or other specific characteristic of a specimen. Once a pattern recognition process is set up to recognize or classify particular X-ray spectrum, the pattern recognition process can then be utilized to automatically classify specimens as having a specific characteristic or defect type. In one embodiment, a method of classifying specimens based on X-ray data obtained from such specimens is disclosed. X-ray data is provided from a plurality of known specimens having known characteristics which are classified into a plurality of known classes. A pattern recognition process is set up to automatically classify the known characteristics of the known specimens based on the X-ray data from the known specimens. X-ray data can then be provided from an unknown specimen having an unknown characteristic of an unknown class. The pattern recognition process is utilized to automatically classify the unknown characteristic of the unknown specimen based on the X-ray data from the unknown specimen. In a specific implementation, the X-ray data from the known specimens is provided by directing a charged particle beam toward each known specimen and detecting X-rays emitted from the each known specimen in response to the charged particle beam. The detected X-rays form X-ray data have one or more intensity values at one or more energy levels. The X-ray data from the unknown specimen are provided in a similar manner. In one aspect, the unknown specimens and the known specimen are each a semiconductor device or test structure. In another aspect, the known and the unknown characteristic are each a defect and the known classes are known defect classes. In one embodiment, the known defect classes include defect compositions. In a further aspect, each known defect class includes one or more characteristics selected from the following: a particular defect composition, a defect location, an electrical type defect, an open type defect, etc. In a specific embodiment, setting up the pattern recognition process is accomplished by training a pattern recognition process to recognize particular types of X-ray data as belonging to one of the known classes. In a more specific embodiment, the pattern recognition process is a neural net algorithm, a natural grouping algorithm, or a wavelet algorithm. In yet another specific aspect, setting up the pattern recognition process is accomplished by (a) associating a feature vector having a plurality of parameters with each known specimen based on the each know specimen's X-ray data; (b) selecting a set of weight values for each variable in a class code equation; (c) inputting the selected weight values and the parameters of each feature vector into the class code equation to determine a plurality of class codes for the known specimens; (d) adjusting the weight values until the class codes for the known specimens having a same known class result in a same class code value; and (e) storing the weight values and class code values for the known specimens. In a further implementation, utilizing the pattern recognition process to automatically classify the unknown characteristic of the unknown specimen based on the X-ray data from the unknown specimen is accomplished by (a) associating a feature vector having a plurality of parameters with the unknown specimen; (b) inputting the stored weight values and the parameters of the feature vector of the unknown specimen into the class code equation to determine a class codes for the unknown specimen; (c) comparing the class code for the unknown specimen to the stored class codes for the known specimens; and (d) when the class code for the unknown specimen matches a one of the stored class codes, classifying the unknown specimen based on the matching class code. In a specific embodiment, the parameters of each feature vector of the known specimens and the unknown specimen include intensity values for each X-ray peak and its associated energy level and/or one or more ratios of X-ray intensity values. In another aspect, the invention pertains to an apparatus for classifying specimens based on X-ray data obtained from such specimens. The apparatus includes a beam generator operable to direct a charged particle beam towards a specimen, a detector positioned to detect X-rays from the specimen in response to the charged particle beam, and a processor operable to perform one or more of the above described method operations. These and other features of the present invention will be presented in more detail in the following specification of the invention and the accompanying figures which illustrate by way of example the principles of the invention. Reference will now be made in detail to a specific embodiment of the invention. An example of this embodiment is illustrated in the accompanying drawings. While the invention will be described in conjunction with this specific embodiment, it will be understood that it is not intended to limit the invention to one embodiment. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. Generally, the present invention applies to inspecting defects in or on wafers using X-ray emission techniques. X-ray emission analyses involves characterizing the composition of a specimen by exciting the atomic core electrons within a specimen and analyzing the resulting emitted X-rays. In the present invention, excitement of the atomic core electrons is achieved by bombarding the specimen with a focused electron beam (e-beam), although other techniques of inducing X-ray emission such as a focused ion beam can be used. Upon specimen bombardment, a transfer of energy occurs which excite the atomic core electrons into different electronic energy levels. Once in this excited state, the atoms have two possible modes of relaxation: emission of X-rays, or emission of Auger electrons. To illustrate these two possibilities, FIG. 1 illustrates a Bohr model of an atom with three electronic energy levels K, L and M (105, 115 and 117, respectively), with electrons in K having greater electronic binding energy than those in L, and electrons in L having greater binding energy than those in M. An incident electron 101 strikes an atom with enough energy to displace an atomic core electron 103, causing the ejection of a secondary electron 119 and producing a core hole or vacancy 107. With the vacancy in the core energy level, the atom is energetically unstable. The most probable stabilization mechanism is filling the vacancy with another electron in a higher energy level 109. That is, a second electron falls from a higher level into the vacancy with release of energy. The resulting energy may then be carried off by one of two mechanisms: Auger electron emission or X-ray emission. In Auger electron emission, the resulting energy is carried off when an Auger electron 111 from a higher energy level is ejected. In X-ray emission, the resulting energy is carried off in the form of emitted X-rays 113, leaving an ionized atom. Auger electron emission and X-ray emission are competitive processes. The present invention pertains to the detection and analysis of X-ray emissions of a specimen in accordance with the above description. Each element has its own characteristic electronic energy configurations and its own characteristic X-ray emissions. For example, copper has two dominant characteristic X-ray emissions: an Lα emission (emitted when an electron falls into the L electronic energy level) with an associated energy of about 0.93 kilo electron volts (keV); and a Kα emission (emitted when an electron falls into the K electronic energy level) with an associated energy of about 8.04 keV. Other elements will have their own characteristic associated energy transitions and X-ray emissions. The X-ray emissions of a specimen can be collected in the form of an X-ray emission energy spectrum. For example, FIG. 2 is an X-ray emission energy spectrum from a copper interconnect structure in an integrated circuit. The horizontal axis represents energy in keV and the vertical axis is the relative intensity. The oxygen Kα (O Kα) peak 201 has an energy of about 0.93 keV. The copper Lα (Cu Lα) peak 203 has a larger intensity than the 0 Kα and has an energy of around 1 keV. The silicon Kα (Si Kα) peak 205 has a larger intensity than the Cu Lα and 0 Kα peaks and has an energy of almost 2 keV. The copper Kα peak (Cu Kα) 207 has a lower intensity than the O Kα, Cu Lα and Si Kα peaks and has an energy of about 8.04 keV. The relative intensities of the peaks in this X-ray spectrum can be compared to spectra of the pure elements or other specimens of known composition to determine the elemental composition and amounts of each element within the specimen. In a preferred embodiment of the invention, X-ray emission is induced with an electron beam (e-beam). If the e-beam is of sufficient energy, bombardment of a specimen will result in an approximately “teardrop” shaped region, or volume, of excitation within the specimen. This teardrop volume is depicted in FIG. 3A. The figure illustrates a cross sectional view of a defect 304 on top of a silicon substrate 309 being bombarded by a focused e-beam 302. The defect in this example is composed of silicon dioxide. The e-beam bombardment results in a teardrop shaped volume 308 wherein electron trajectories travel, thereby causing X-ray emission from the defect and the silicon substrate, in the form of X-rays 310 and 312, respectively. This teardrop region is three-dimensional in that it covers a teardrop shaped volume within the specimen. An X-ray detector (not shown) is positioned to detect emitted X-rays from this teardrop region. Note that the incident e-beam will preferably have a high enough energy to generate X-rays from the defect and a portion of the substrate. This e-beam energy will depend on the specimen composition and thickness and on how deeply the defect to be examined lies or how deeply a defect can possibly lie. FIG. 3B is an X-ray emission energy spectrum obtained from the defect 306 and underlying substrate 306 of FIG. 3A. The horizontal axis represents energy in keV and the vertical axis is the relative intensity. As shown, the spectrum includes an oxygen Kα (O Kα) peak 350 and a silicon Kα (Si Kα) peak 352 that has a larger intensity than the O Kα peak. FIG. 3C is an X-ray emission energy spectrum from a reference silicon substrate having no defects. This spectrum only includes only a silicon Kα (Si Kα) peak 354 which has an energy of almost 2 keV. In conventional techniques, the relative intensities of the peaks in the X-ray spectrum obtained from the substrate having the defect can be compared to the spectrum obtained from the reference substrate having no defects to determine the composition of the defect. For example, subtracting the spectrum obtained from the substrate without a defect (of FIG. 3C) from the spectrum obtained from the substrate having a defect (of FIG. 3B) results in the spectrum of FIG. 3D. The resulting spectrum of FIG. 3D has a lower Si Kα peak intensity 356 than the Si Kα peak in the FIG. 3B spectrum and a same O Kα peak prior to the subtraction. One may determine that the defect of FIG. 3A is composed of silicon dioxide based on the presence of the Si and O peak within the resulting spectrum of FIG. 3D. However, this technique does not work when the substrate is more complex. By way of example, FIG. 4A illustrates a cross sectional view of a complex substrate 406 having a plurality of conductive copper structures 408, 410, and 414. In this example, X-rays are emitted from the copper structures 408, 410, and 414, as well as the silicon substrate 406 and defect 404, shown as X-rays 416, 420, 424, 422, and 418, respectively. As shown in FIG. 4B the spectrum for the complex substrate of FIG. 4A includes an oxygen Kα peak 454, a copper Lα peak 450a, a copper Kα peak 450b, and a silicon K peak 452. Subtracting the reference spectrum, for example, of FIG. 3C from the spectrum obtained from such a complex substrate does not facilitate determination of the defect's composition. Generating spectrum from a suitable number of reference substrates for comparison to the diverse number of complex substrates which could contain a defect would be a nearly impossible task. In general terms, the present invention provides pattern recognition techniques for accurately and efficiently classifying a defect based on an X-ray spectrum obtained from such defect and its surrounding substrate and structures, no matter the complexity of such substrate and structures. Accordingly, classification techniques of the present invention provide an efficient and accurate mechanism for automatically classifying unknown specimens. These techniques allow classification of defects on a wide range of complex substrates. FIG. 5 is a flowchart illustrating a procedure 500 for classifying defects and other characteristics of the specimen based on X-ray data in accordance with one embodiment of the present invention. Initially, X-ray data is provided from a plurality of known specimens that each have known characteristics or classes, such as known defect types, in operation 502. In one implementation, a charged particle beam (e.g., an electron beam) is directed toward each known specimen, and X-rays emitted from the each known specimen in response to the charged particle beam are detected. The detected X-rays are in the form X-ray data having one or more intensity values at one or more energy levels. Typically, the specimen is in the form of a semiconductor device or test structure. However, any suitable type of specimen which may be characterized using X-ray data may be used in the present invention. By way of examples, a thin film on a computer disk may be characterized by X-rays. The known characteristic of each known specimen may include any suitable parameter that may be characterized by X-rays. In one embodiment, the known characteristic is a defect class and corresponds to a particular defect composition, a defect location relative to the substrate, a via, or a trench, an electrical short type defect, an electrical open type defect, etc. The known characteristic or class may also correspond to other characteristics of the specimen, besides a defect class, such as film thickness. In this embodiment, X-ray data is provided from a plurality of specimens having known defect classes or compositions. A pattern recognition process is then set up to automatically identify or classify the characteristic of each known specimen based on the X-ray data from each known specimen in operation 504. Any suitable pattern recognition technique may be used to classify or identify characteristics of a specimen based on X-rays data. In general terms, a pattern recognition technique includes training a pattern recognition process to recognize particular types of X-ray spectrum as belonging to a particular defect type or other specific characteristic of a specimen. Example pattern recognition algorithms that may be modified for recognizing different X-ray spectrum as belonging to a particular class of defects include neural net, natural grouping, and wavelet algorithms. Several example pattern recognition techniques for classifying images are described further in U.S. Pat. No. 6,104,835, issued 15 Aug. 2000, by Ke Han (herein referred to as the '835 patent), which patent is herein incorporated by reference in its entirety for all purposes. These pattern recognition techniques may easily be modified and applied to X-ray spectrum, instead of images. For instance, the pattern recognition techniques described in the '835 patent utilize descriptor vectors that include image parameters that characterize the images. These descriptors may be modified to include X-ray data parameters, as well as other information relevant for characterizing a defect or other characteristic of a specimen. After a pattern recognition process is set up, X-ray data may then be provided from a unknown specimen having a unknown characteristic in operation 506. For example, the specimen may have a defect that has not been classified yet. The X-ray data from an unknown specimen may be provided in the same manner as described above with respect to providing X-ray data from a known specimen. The pattern recognition process is then used to identify or classify the unknown characteristic of the unknown specimen based on the X-ray data from unknown specimens in operation 508. Operations 506 and 508 may be repeated to classify any number and type of specimens. FIG. 6 is a flowchart illustrating the operation 504 of FIG. 5 for setting up the pattern recognition process in accordance with one embodiment of present invention. Initially, a feature vector is associated with each known specimen based on the each known specimens X-ray data in operation 602. The parameters of each feature vectors may include any information associated with the specimen, as well as any suitable X-ray data. By way of examples, the feature vector may include values for each X-ray peak intensity and its associated energy level, ratios of particular X-ray peak intensities (e.g., Si/O), defect size, etc. A set of weight values are then selected for each variable in a class code equation in operation 604. One example of a class code equation for a three parameter feature vector is:C=aA+bB+cC+dD+eAB+gAC+hBC+iA2+jB2+kC2[ 1]where a˜k are weight values, and A˜C are feature vector parameters. Of course, the class code and weight values will vary with different sized feature vectors. Additionally, different variables may be used depending on the particular requirements of the defect or specimen characteristic analysis application. The selected weights and the parameters of each feature vector are input into the class code equation in operation 606. After class code values are determined for the feature vectors from the known specimens, the determined class code values are then compared to each other in operation 608. It is then determined whether the class code values are equal for the feature vectors having a same class in operation 610. Using the above equation 1 in an example, a first defect class results in C equaling “1” for feature vectors obtained from specimens having the first defect class, and a second defect class results in C equaling “2” for feature vectors obtained from specimens having the second defect class. Each class value may correspond to a particular defect composition, a defect location relative to the substrate, a via, or a trench, an electrical short type defect, an electrical open type defect, etc. The class may also correspond to other characteristics of the specimen, besides a defect class, such as film thickness. In the above example, a class code equal to “1” may indicate a SiO2 particle defect, while a class code equal to “2” may correspond to a copper particle defect. If the class code values for a same class are not equal, the weight values are adjusted in operation 614 and operations 606 and 608 are repeated to obtain new class code values for the new adjusted weight values. If the class code values for the feature vectors having a same class have a same value, the weight values and the class code values and their associated known characteristics are stored for the pattern recognition process in operation 612. The procedure for setting up the pattern recognition process 504 then ends. FIG. 7 is a flowchart illustrating the operation 508 of FIG. 5 of using the pattern recognition process to identify or classify unknown specimens in accordance with one embodiment of the present invention. Initially, a feature vector is associated with the unknown specimen based on its X-ray data in operation 702. The feature vector preferably have the same parameters as the feature vectors used to set up the pattern recognition process of FIG. 6. Each parameter of the unknown feature vector and the stored weight values (determined and stored during the set up of the pattern recognition process of FIG. 6) are then input into the class code equation in operation 704. The class code value of the unknown feature vector is then compared to known class codes (determined and stored during the set up of the pattern recognition process of FIG. 6) in operation 708. It is then determined whether the class code of the unknown feature vector matches a known class code in operation 710. If there is a match, the unknown specimen is then classified based on the matching class code and its associated known characteristic or defect class in operation 712. In the above example, if the class code value equals “2”, it is determined that the specimen has the second type of defect, e.g., a copper particle defect. If there is no match found, a new class may then be defined based on the unknown specimen in operation 714. For instance, a new defect type may be manually classified by an operator and given a class code. The X-ray data from the new defect type may then be used to set up the weights for the class code equation so that it equals the new class code. As more defects of the same type are found, the weights of the class code equation can be adjusted based on the new X-ray data. After an unknown defect is classified, the pattern recognition process may then end or a new unknown specimen can then be analyzed. Any suitable electron beam induced X-ray microanalysis system may be utilized to practice and/or implement the techniques of the present invention. An eV300 automated e-Beam wafer inspection system available from KLA-Tencor Corporation of San Jose, Calif. may be used. FIG. 8 is a diagrammatic representation of a system utilizing an electron beam induced X-ray microanalysis test system according to one embodiment of the present invention. The system represented in FIG. 8 includes a beam generator 800, which directs an e-beam 801 at the specimen 803. The specimen 803 in the example depicted in FIG. 8 is a semiconductor wafer having a silicon substrate 809 upon which a silicon dioxide layer 811 is patterned with a plurality of trenches 813 filled with copper. The spot size of rastered beam may be any suitable size. Preferably, the spot size corresponds to approximately the area of the structure of interest. At least one X-ray detector is used to collect the X-rays emitted from the surface of the specimen. The system in FIG. 8 includes four X-ray detectors 805 positioned above the specimen. Any suitable number and type of detector for measuring X-rays at specific energy levels may be utilized. One type of detector is an energy dispersive system (EDS), which collects photons in a wide spectrum of energies. EDS systems are capable of collecting a greater range of signals. As a result however, EDS detectors also collect photons having energies surrounding the characteristic photon energies. This causes EDS detectors to have lower signal to noise ratios. Another type of detector is a wavelength dispersive system (WDS) X-ray detector. Several suitable embodiments of WDS X-ray detectors are described further in co-pending U.S. patent application Ser. No. 09/695,726, filed 23 Oct. 2000, which application is incorporated herein by reference in its entirety. In the system depicted in FIG. 8, each of the X-ray detectors is coupled with an analysis or processor unit 807. The analysis/processor unit 807 can be configured to analyze the data collected by the X-ray detectors 805 to generate X-ray ratio data of the elemental species in the specimen, such as the Cu Lα/Si Kα, Cu Kα/Si Kα and Cu Lα/Cu Kα described previously. The analysis/processor unit 807 may take the form of any suitable processing or computing system, such as a workstation, and include one or more processors and one or more memory devices. Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Therefore, the described embodiments should be taken as illustrative and not restrictive, and the invention should not be limited to the details given herein but should be defined by the following claims and their full scope of equivalents.
053735390	description	DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a schematic representation of a nuclear steam supply system 1 incorporating a typical pressurized water reactor (PWR) 3 in which the present invention is implemented to detect dropped control rods and malfunctioning thermocouples. The PWR 3 includes a reactor vessel 5 which forms a pressurized container when sealed by a head assembly 7. The reactor vessel 5 houses a reactor core 9 made up of a matrix of fuel assemblies 11. The fuel assemblies in turn contain a number of fuel rods 13 containing fissionable material. Fission reactions within the fuel rods 13 generate heat which is absorbed by a pressurized reactor coolant, for example light water, which is passed through the core 9. The reactor coolant enters the vessel 5 through inlet 15 and flows downward through an annular down-comer 17 and then upward through the fuel assemblies 11 where it is heated by the heat of the fission reactions. The heated reactor coolant flows upward out of the reactor core and through an outlet 19 into the hot leg 21 of a primary loop 23. The hot leg 21 delivers the heated reactor coolant to a steam generator 25 where feed water is converted into steam which is circulated in a secondary loop 27 to drive a turbine-generator 29 which generates electric power. Reactor coolant is returned to the inlet 15 through a cold leg 31 by a reactor coolant pump 33. Only one steam generator 25 in one primary loop 23 is shown in FIG. 1 for clarity; however, as is known, the typical PWR nuclear steam supply system I has two to four primary loops, each with its own steam generator 25 generating steam, and a comparable number of secondary loops 27 driving the single turbine-generator 29. The reactivity of the reactor core 9 is controlled by regulation of the concentration of a neutron absorber dissolved in the reactor coolant by a reactor chemical and volume control system CVCS 34 and by control rods 35 which are inserted into and withdrawn from the reactor core 9 by a rod control system 37 as discussed above. The rod control system 37 inserts and withdraws banks of control rods under the direction of a reactor control and protection system 39. Inputs to the reactor control and protection system 39 include hot and cold leg reactor coolant temperatures measured by temperature sensors such as RTDs 41 and 43, respectively. Additional monitored reactor parameters include core exit temperatures measured at selected fuel assemblies as discussed below by core exit thermocouples 45. An in-core detector system 47 maps power distribution in the core on a periodic basis. The dropped rod detection system 49 utilizes the signals generated by the hot leg and cold leg temperature sensors 41 and 43 and the core exit thermocouples 45 to detect a dropped control rod 35 and generate a signal which is applied to the rod control system 37 to block the withdrawal of control rods. The exemplary PWR 3 is an advanced system which, as discussed previously, is designed to load follow primarily through movement of the control rods rather than through regulation of the concentration of neutron absorber in the reactor coolant. Such reactors have in addition to control rods containing neutron absorbing material, gray rods with more moderate neutron absorbing materials which are provided to maintain appropriate power distribution in the core 9. FIG. 2 illustrates the arrangement of fuel assemblies 11 in the reactor core 9 of the exemplary PWR 3 with the conventional rods 35 depicted by the letter C, and the gray rods 35' indicated by the letter G. For purposes of this description, references to control rods 35 will include both the conventional control rods (C) and the gray rods (G) unless otherwise specified. The control rods 35 in a single fuel assembly form a cluster operated by a common mechanism, while groups of clusters are ganged together electrically to form banks of control rods, as is well known. The arrangement of the control rods into banks is not specified in FIG. 2 as it is not necessary to an understanding of the invention. The core exit thermocouples 45 are mounted in instrumentation thimbles provided in about a quarter of the fuel assemblies 11. As illustrated in FIG. 2, the core exit thermocouples are distributed in a regular pattern across the fuel assemblies 11 so that core exit thermocouples 45 are located in fuel assemblies that are laterally adjacent to every one of the conventional control rods clusters C and all but two of the gray rod clusters G. The only exceptions are two gray rod clusters G on the periphery of the core 9, each of which has one core exit thermocouple in a laterally adjacent fuel assembly. In addition, there are at least two, and more commonly, four core exit thermocouples 45 in fuel assemblies located a chess knight's move from each control rod C and gray rod cluster G location. Hence, a system divided into two completely independent trains of core exit thermocouples can readily be supported. However, the preferred embodiment of the invention adopts a four train system which requires an internal mutual exchange of information among the trains at one point in the computational process. The exemplary PWR 3 utilizes single core exist thermocouples distributed in four trains in the pattern indicated by the numerals 1-4 next to the thermocouples 45 in FIG. 2. In order for the dropped rod detection system of the invention to qualify as safety system grade, the entire system, including the core exit thermocouples 45, must be certifiable as meeting full Class IEEE-603 standards. The temperatures measured by thermocouples 45 are determined primarily by the power distribution. When thermocouple readings exhibit sudden changes, they may be caused by either: (a) a sudden change in the core condition; or (b) thermocouple malfunctions. In the former case, the thermocouple readings change and their spatial distribution must be governed by physical principles. However, in the latter case, a controlling physical principle is not applicable. In order to simplify the evaluation between these possibilities, a new parameter is introduced, the Relative Power Deviation, RD, which is defined by: ##EQU1## where: (L,M)=Thermocouple location .DELTA.T=Temperature rise in assembly PA1 .DELTA.T.sub.O =Temperature rise in assembly at reference condition PA1 .DELTA.T.sub.Avg =Temperature rise across reactor vessel PA1 .DELTA.T.sub.O.sbsb.Avg =Temperature rise across reactor vessel at reference condition PA1 a relatively high positive or negative CI value at the thermocouple location. PA1 smaller but still fairly large CI values (typically about one-fourth of the center CI value) and of opposite sign to the center CI value in most (frequently all) of the four laterally adjacent fuel assembly locations. PA1 noise level, random sign values of CI in the four diagonally adjacent fuel assembly locations. PA1 virtual disappearance of the relatively large, opposite sign values of CI in the four laterally adjacent fuel assembly locations if the RD value at the suspect thermocouple location is given a high lack of confidence value (i.e., ignored), the RD spline fit is rerun, and the CI's reevaluated. PA1 again, a relatively high positive or negative CI value at the location of a control rod or gray rod (in the exemplary reactor thermocouples and control or gray rods never share a common location). PA1 much smaller CI values of the same or opposite sign as the center CI value in the laterally and diagonally adjacent fuel locations. (Whether the CI values are of the same or opposite sign depends on which thermocouples are operational in the near vicinity, i.e., the values of nearby CI's are influenced to some degree by the spline fit algorithm.) It should be noted that although RD values are defined herein in terms of temperature, the definitions could also be cast in terms of enthalpy. While RD can be calculated by Eq. 1 only for those fuel assemblies 11 having core exit thermocouples, RD values for all fuel assemblies can be interpolated through use of a surface spline fit, as is well known in the art. Each thermocouple 45 measures an assembly exit temperature, which defines a temperature rise with respect to the inlet temperature. RD represents the percent change in the normalized power distribution, with respect to the reference shape. It is important to note that if the power spatial distribution is unchanged, RD remains at the value zero, regardless of power level. As the power distribution changes from the reference shape, RD values become non-zero. The spatial distribution of RD is governed by the neutron diffusion equation. When the power distribution experiences a large change, by insertion of control rods 35 for example, RD also changes by a large amount; however, its spatial variation is smooth, except at the rod insertion location. This is similar to the behavior of the neutron flux distribution. In order to quantify the smoothness of the distribution, another parameter, the Curvature Index, CI, is introduced. CI is defined as follows in an x-y array of assemblies indexed by the coordinates (i,j): EQU CI(i, 1j)=4*RD(i, j)-[RD(i-1, j)+RD(i+1, j)+RD(i, j-1)+RD(i, j+1)](Eq. 2) Mathematically, CI approximates the negative of the spatial second derivative of RD. When the power distribution changes due to control rod insertion, a large value of CI occurs only at the rodded location. In other locations, the value of CI should be small, in spite of a large variation of RD throughout a wide area. However, if a large value of RD is the result of a thermocouple malfunction, CI of the surrounding assemblies will also be large. In the validation of thermocouple signals, this is the principle used to distinguish true changes in the physical condition of the core from detector malfunctions. When looking for "bad thermocouple" signatures, the most meaningful CI values are those found in the location of the suspect thermocouple and in the four laterally adjacent fuel locations. The characteristics of a "bad thermocouple" signature are: The sign of the center CI value is indicative of the direction of the thermocouple signal error--positive indicates error high. The magnitude of the center CI value is roughly proportional to the magnitude of the signal error. If a moved (including "dropped") control rod is suspected, the CI values in all nine of the fuel locations in the 3.times.3 array centered on the rod location contribute to the signature pattern. The characteristics of the "moved control rod" signature are: The sign of the center CI value reflects the direction of movement of the control rod--a negative center CI value indicates rod insertion. The magnitude of the center CI value is roughly proportional to the amount of reactivity (positive or negative) inserted locally by rod movement. Important keys to the signature differentiation process are two: (1) is the maximum CI value at a thermocouple location or on a control rod/grey rod location? If at a control rod/grey rod location, almost certainly the rod has moved. (2) if the maximum CI value is at a thermocouple location, reprocessing the RD fit and CI evaluation with the suspect RD value discarded will show a recognizable change in the CI values at laterally adjacent fuel assembly locations. An example of the ability of the invention to distinguish between a dropped rod and a malfunctioning thermocouple is illustrated by FIGS. 3, and 4A and 4B which plot the values of CI for the fuel assemblies in the vicinity of a dropped rod, and in the vicinity of a failed thermocouple respectively. Each (-) and (+) represent an arbitrary unit of CI, while the dots represent partial units of random sign. As can be seen from FIG. 3, there is a large negative CI at the location of a dropped rod in the center of the figure in the fuel assembly 11 outlined in heavy line. It will be noticed that the CI's in the laterally and diagonally adjacent fuel assemblies are of either sign and are much smaller in magnitude than the CI of the assembly with the dropped rod. Also, it will be noted that the CI's of the fuel assemblies 360.degree. around and several assemblies away from the assembly with the dropped rod are affected. On the other hand, it can be seen in FIG. 4A that only the CI's for the fuel assemblies laterally spaced on the cardinal axes from the fuel assembly with a failed thermocouple are affected. Most importantly, it can be seen that the CI's for the laterally adjacent fuel assemblies are always of opposite sign from that of the fuel assembly with the failed thermocouple, and that the function falls off more rapidly than in the case of a dropped rod. FIG. 4B illustrates the distribution of CI values calculated from RD values generated from a surface spline fit in which the RD value for the suspect thermocouple is given a high lack of confidence factor. As can be seen, only very small disturbances even at the location of the suspect thermocouple are indicate. Again, the disturbances only extend to the four laterally adjacent fuel assembly locations. FIG. 5 is a block diagram of one of four trains 51 of the dropped rod detector system 49. The illustrated train 51 of the dropped rod detector system 49 includes a front end hot leg RTD signal processor 53. This processor digitizes ohm signals received from the hot leg RTD's 41 (typically three) in the train and converts the digital ohm signals to degrees Fahrenheit. The processor 53 then generates an average T.sub.hot temperature for the train. This average temperature T.sub.hot, is sent to all of the other trains. The processor 53 receives the average hot leg temperatures T.sub.hot generated by all of the other trains and generates therefrom an average, average T.sub.hot signal. Each train 51 also includes a front end cold leg RTD signal processor 54 which similarly digitizes ohm signals from the cold leg RTDs 43 in the train and converts them to degrees Fahrenheit. The processor 54 then generates train average T.sub.cold signal which is sent to all of the other trains. The processor 54 then generates an average, average cold leg temperature T.sub.cold from the T.sub.cold signals from all of the trains. A calculator 55 generates from the T.sub.hot and T.sub.cold signals a .DELTA.T.sub.core signal which is the average temperature rise across the core. The train 51 also includes a front end thermocouple (TC) signal processor 57 which, when the train is in service, digitizes voltage signals generated at each of the thermocouples in the train having coordinates L,M and converts them from millivolts to degrees Fahrenheit. The T/C signal processor 57 also identifies obviously failed thermocouples, both failed open and failed closed. In both cases, the processor 57 sets a lack of confidence, or tolerance, factor C (L,M) used in the surface spline fit to a large value (approximately 1,000, for example). As is well known, the lack of confidence factor C smooths out the surface spline fit by allowing the surface generated to deviate at a data point by an amount which is a function of the magnitude of the lack of confidence factor C at that point. The T/C signal processor 57 computes for each thermocouple a .DELTA.T.sub.T/C (L,M) which is the difference between the thermocouple reading and the average inlet temperature reading, T.sub.cold, provided by the processor 54. These .DELTA.T.sub.T/C L,M) values and C (L,M) values for the train are sent to all the other trains. Similarly, the processor 57 receives the same values from the other trains and outputs all of them to an RD and CI calculator 59. If the train 51 is not in service, because of train failure or because it is in the test mode, the front end T/C signal processor 57 sets all the .DELTA.T.sub.T/C (L,M) in the train to .DELTA.T.sub.core. In addition, all C (L,M) in the train are set to a large value (approximately 1,000). Again, these values are sent to all the other trains and the corresponding values from all the other trains are received to generate a complete set of values which is sent to the calculator 59. As will be discussed in more detail below, RD and CI calculator 59 utilizes the .DELTA.T.sub.T/C and C signals from the T/C signal processor 57 and the .DELTA.T.sub.core from the calculator 55 together with reference values for .DELTA.T.sub.T/C and .DELTA.T.sub.core to generate the CI values for all of the fuel assemblies 11 which are then used by a CI evaluator 61 which identifies any dropped rods. The dropped rod signal is applied to a safety system grade rod withdrawal stop generation module 63 which generates a rod stop signal for the train. The CI evaluator 61 also identifies failed thermocouples. The front end processor 57, in effect, throws out obviously failed thermocouples by setting their C values to a large number. As a result, the CI evaluator will essentially ignore such thermocouples and concentrate on the questionable thermocouples. This would include those which are not completely failed but are unreliable. The identification of malfunctioning thermocouples is stored in a library 65 together with the large C values for such failed thermocouples. The library 65 also stores the identification of failed thermocouples detected by the processor 57. As discussed previously, the structure 51 illustrated in FIG. 5 is provided for each of the four trains of the dropped rod protection system. As shown in FIG. 6, the rod stop signals generated by the stop generators 63-1 to 63-4 for each of the four trains is input to voting logic 67 which, as is well known in the art, generates a block rod withdrawal signal in the presence of a selected combination of train rod stop signals such as, for example, two out of four, or if one train is out of service, two out of three. The block rod withdrawal signal is applied to the rod control system 37 to prevent withdrawal of the control rods in response to a dropped rod. As shown in FIG. 7, a common reference transmitter 69 provides .DELTA.T.sub.core/REF and .DELTA.T.sub.T/C (L,M).sub.REF values for all thermocouple locations to each of the four trains of the dropped rod protection system. As the banks of control rods move, maps of the CI values across the core will show progressively greater symmetric distortion, reflecting the deviation of the current rod configuration from that under which reference conditions were established. This is perfectly normal, but none the less highly confusing to a computer. Accordingly, it is highly desirable to periodically update the reference values of .DELTA.T.sub.core/REF and .DELTA.T.sub.T/C (L,M).sub.REF. These references values are updated, utilizing a software core surveillance program such as BEACON, which is typically run at, for example, 15 minute intervals. BEACON, which is available from Westinghouse Commercial Nuclear Fuels Divisions, is an analytical tool which calculates a three dimensional nodal power distribution in the core utilizing either excore power range detectors and core exit thermocouples or fixed incore detectors. Since the reference transmitter 69, and BEACON which interfaces with it, are not safety system grade, the reference signals provided by the reference transmitters 69 are subject to human approval as shown functionally by the switch 71 in FIG. 5. If there is reason for the operator to believe that the reference values are not valid, approval of the reference values can be withheld. Also, as discussed in connection with FIG. 11 below, updating of the references can be prevented by a block indicated at 70 when misalignment of a control rod is detected. A method for updating the reference values is to (a) monitor the CI values at symmetric control rod locations of the controlling groups. These values will steadily increase in absolute magnitude as the control rods are moved farther and farther from the positions they were at when the last reference set of values was established. (b) when the monitored CI values reach a preselected absolute magnitude, display to the operator the bank position that corresponded to the still current reference values and an indication of the net direction of bank movement from that position. The operator must then attempt to confirm, using the rod position indicators, that the dropped rod protection septum has successfully tracked the trend of control bank movement. If no alarms to the contrary exist and if he is satisfied that the protection system is at least trending properly, he must authorize replacing the set of reference values that had been in use with the current set of those parameters. The key ingredient here is the operator's verification that the system is apparently working correctly. (c) if one of the "anomalous train behavior" or anomalous rod/bank movement type alarms is generated, an update "block" is activated and the current values can not be made reference values. If the operator is not satisfied that the system is trending properly he must withhold approval to update the reference values. In either event, and assuming that any system malfunctions have been corrected, the operator must verify that the BEACON core surveillance system is running correctly, i.e., no significant differences exist between various measurable aspects of core power distribution such as incore detector signals and the equivalent analytically predicted values. If BEACON is seen to be generating a reliable estimate of core power distribution, the operator can authorize the current BEACON estimates of .DELTA.T.sub.core and .DELTA.T.sub.T/C for all thermocouples to be established as the new set of reference values for the dropped rod protection system. Since BEACON runs continuously on-line it is always current with core operations. (d) if the reference values cannot be updated when needed, administrative controls, such as setting very conservative rod insertion limits to insure that the core will survive one or more dropped rods without damage, must be imposed until the situation is corrected. FIG. 8 illustrates a flow chart for the RD and CI calculator 59. Utilizing the information from the .DELTA.T calculator 55 and the T/C signal processor 57 as well as the reference information from the reference transmitter 69, the calculator 59 computes RD (L,M) at all thermocouple locations using equation 1 as indicated at 71. Using these RD values and the corresponding lack of confidence factors C for those locations, a surface spline fit is used at 73 to generate the relative power deviation RD for all fuel assemblies (i,j). These values are then used to calculate the curvature indices CI (i,j) for all fuel assemblies 11 using equation 2 as indicated at 75. The curvature indices are then ranked by magnitude at 77. The system, of course, also detects normal movement of the control rods. Periodically, such as for example, every 10 minutes, as determined at 79, the status of flags indicating rod movement is stored at 81, the flags are reset at 83 and a timer for the period is reset at 85. The flow chart for the CI evaluator 61 is shown in FIGS. 9A-9C with an insert which is FIG. 10. The CI evaluator cycles through the ranked CIs in descending absolute order as indicated at 87. Only those absolute CI values which are greater than a first limit as determined at 89 are examined. This limit 1 is selected so that only signals above the expected noise level need be examined. When all of the significant CIs have been examined, the CI evaluator is exited and the program transfers to the rod movement analyzer shown in FIGS. 11A and 11B. If the evaluator cycles through all of the CIs, indicating that all of the CIs are above the first limit, which is not a valid condition, "an anomalous train behavior" alarm is generated at 91. For those CI signals above the noise level at locations (i, j) at which there are thermocouples as determined at 93, the CI evaluator performs the routine shown in FIG. 10 which checks for a malfunctioning thermocouple at the cited location by eliminating the reading from the thermocouple. As shown in FIG. 10, the current lack of confidence factor C for the thermocouple in question, and the current curvature index CI array calculated with that thermocouple value, are stored at 97 and 99, respectively. The lack of confidence factor C for the thermocouple in question is then set to a high value at 101 and the surface spline fit for RD at all fuel assembly locations is regenerated at 103. The new RD values are then used at 105 to recalculate the CIs. The CIs in the local region around the thermocouple in question are then evaluated at 107 in the manner discussed above. If a bad thermocouple signature is detected at 107, the originally stored values of C and the CI array are restored at 109 and 111 and the program returns to FIG. 9A at the "yes" branch from the insert. If a bad thermocouple signature is not detected at 107, the C value for the location under examination and the original CI array are restored at 113 and 115 and the program returns to FIG. 9A and the "no" branch from the insert. Returning to FIG. 9A from the "yes" branch from the insert, if the location under examination is a location of a thermocouple in this train as determined at 117, then the confidence factor C for this fuel assembly is changed in the library 65 to a large value, such as for example, 1,000, and a "new bad T/C in this train" message is generated at 121. If the location under examination at 117 is not in this train, a "new bad T/C in another train" message is generated at 123. Whether the fuel assembly being examined has a thermocouple or not, if there is a control rod at this location, as determined at 125 in FIG. 9B, the CIs in the region surrounding this fuel assembly are examined at 127 to determine if they show a moved rod signature. If they do, the absolute value of the CI is examined at 129 in FIG. C to determine whether it is compatible with normal control rod movement or a dropped rod. As soon as a dropped rod is detected, a safety system grade rod withdrawal stop signal is generated at 131 and transmitted to the rod control system at 133 and a "rod withdrawal stop actuated" alarm is generated at 135. If the magnitude of CI at 129 is less than the limit 2, a rod movement flag for the rod at the coordinates R,S is set at 137. This flag contains the CI value and rod group assignment. The program then loops back to FIG. 9A to examine the next fuel assembly location. If the fuel assembly being examined has a CI value above the limit 1, but is not the location of a thermocouple or a control rod, a determination is made at 139 in FIG. 9B as to whether the fuel assembly is within a five by five assembly array of a control rod which has moved. If the fuel assembly is within the proximity of a moved control rod which would explain the CI value, the program loops back to FIG. 9A to examine the next fuel assembly. If this fuel assembly is not within the proximity of an identified moved control rod, or a moved control rod signature was not identified at 127, then a "anomalous train behavior" alarm is generated at 141 before the program loops back to 87. FIGS. 11A and 11B illustrate the flowchart for the rod movement analyzer. As indicated in connection with the description of FIG. 9A, when all the fuel assemblies with significant CI values have been evaluated, this routine is called to analyze detected rod movements. This is done by cycling through the rod banks in the order of insertion sequence as indicated at 143 in FIG. 11A to determine if there are any flags set indicating a movement of a control rod in the bank as indicated at 145. If only one rod movement flag is set in the bank as determined at 147, then an "apparent misalignment of rod (R,S) in bank X" message is generated at 149 and the "reference update" block is set at 151. This prevents changing of the references at 70 in FIG. 7. If the movement of more than one but not all of the rods in the bank have been detected at 153, then an "anomalous movement of bank X rods" message is generated at 155. If there are indications that all of the rods in the bank have moved at 153, and the time has arrived for a bank movement update as indicated at 157, the current rod movement flag data is compared on a rod by rod basis with the stored data on that bank. If recent bank movement is indicated at 159 in FIG. 11B and that movement is indicated as being a withdrawal at 161, a "bank X withdrawn during last minutes" message is generated at 163. For a rod insertion, a corresponding message is generated at 165. The rod movement analyzer does not provide precise information on rod movement, but rather, provides an indication of which rods have moved and in which direction which can be compared with the rod position indicator system. The rod analyzer functions primarily serve as a confidence builder for the operator by providing information on rod movement which can be cross-checked against other systems to provide an indication of the reliability of the system. While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.
048636720	claims	1. In combination with a nuclear reactor comprising an absorber rod control drive disposed above a bed of spherical fuel elements having an upper level and further comprising circulating cooling gas through said spherical fuel elements, an absorber rod comprising: a rod tip exhibiting a conically narrowing configuration; a lower rod segment comprising: an upper rod segment comprising: means for coupling said upper rod segment to said lower rod segment wherein said means for coupling is positively connected to an upper end of said lower inner rod element, a lower end of said upper inner rod element, and a lower end of said upper outer rod element; said means for coupling comprising a first portion having a diameter and a second portion having a smaller diameter than said first portion; a third annular gap axially disposed between said upper end of said lower outer rod element and said first portion of said means for coupling wherein said upper end of said lower outer rod element does not perform an axial support function and slides over said second portion of said means for coupling in response to thermal expansion; means for admitting cooling gas into an interior area of said absorber rod wherein said means for admitting comprises a plurality of circumferentially distributed, axially elongated slots arranged in said means for coupling; and means for releasably connecting said upper rod segment to said absorber rod drive, said means for releasably connecting comprising a claw body fixedly attached to said upper rod segment. means for spacing and holding rod guide cylinder from an interior surface of said lower inner rod element. 2. The combination according to claim 1, further comprising remotely actuable for releasing said means for releasably connecting said upper rod segment, wherein said means for releasably connecting is a plurality of deflectable claw members and said means for releasing is an axially displaceable ring configured to deflect said claw members upon displacement. 3. The combination according to claim 2, wherein said upper rod segment comprises sub-segments axially connected to one another wherein at least two sub-segments are coupled by a coupling exhibiting circumferentially distributed axially elongated slots. 4. The combination according to claim 3, further comprising a holding rod connecting said rod tip to a safety holder fixed to said means for coupling wherein said holding rod is attached within a holding rod guide cylinder abutting said rod tip; and 5. An absorber rod according to claim 1 wherein said rod tip further exhibits a lower spherical recess.
	claims	1. A passive containment building cooling system, comprising:a containment building;an emergency fluid storage section positioned outside the containment building and configured to store heat exchange fluid therein;a plurality of plate-type heat exchanger positioned inside the containment building, each plate-type heat exchanger comprising containment atmosphere flow path channels configured to flow containment atmosphere along one side of a plate of the heat exchanger and fluid flow path channels configured to flow the heat exchange fluid along the other side of the plate of the heat exchanger; anda line passing through the containment building and configured to supply the heat exchange fluid from the emergency fluid storage section to the fluid flow path channels of the plurality of plate-type heat exchangers and return the heat exchanger fluid to the emergency fluid storage section,wherein the plurality of plate-type heat exchangers are connected in parallel along the line via an inlet header connected between the line and an inlet region of each fluid flow path channel and an outlet header connected between an outlet region of each fluid flow path channel and the line,wherein the plurality of plate-type heat exchangers are connected in parallel to an inside of the containment building and each plate-type heat exchanger comprises an inlet guide configured to receive the containment atmosphere from the inside of the containment building and direct the containment atmosphere to the containment atmosphere flow path channels and an outlet guide configured to return the containment atmosphere from the atmosphere flow path channels to the inside of the containment building, andwherein the plurality of plate-type heat exchangers are arranged adjacent to one another and each plate-type heat exchanger further comprises a casing configured to cool containment atmosphere passing through an intermediate flow path defined by spaces between adjacent plate-type heat exchangers. 2. The passive containment building cooling system of claim 1, wherein each of the fluid flow path channels further comprises:a main heat transfer region connected between the inlet region and the outlet region, and having a flow resistance smaller than that of the inlet region. 3. The passive containment building cooling system of claim 2, wherein the inlet region is formed with a smaller width than that of the main heat transfer region, and has a length greater than a straight length of the main transfer region in a longitudinal direction of the plate type heat exchanger. 4. The passive containment building cooling system of claim 1, wherein the heat exchange fluid comprises atmosphere outside the containment building, and the passive containment building cooling system is configured to cool atmosphere within the containment building in an air cooling manner using the atmosphere outside the containment building. 5. The passive containment building cooling system of claim 1, wherein a longer direction of the plate corresponds to a longitudinal direction of the plate type heat exchanger, and a shorter direction of the plate corresponds to the lateral direction of the plate type heat exchanger,at least one of the inlet header and the outlet header is positioned at a first side surface of the plate type heat exchanger, parallel to the longitudinal direction thereof or positioned at a second side surface of the plate type heat exchanger facing away from the first side surface, andthe passive containment building cooling system further comprises a common header which is connected to the inlet header and all the channels, or connected to the outlet header and all the channels. 6. The passive containment building cooling system of claim 1, whereina longer direction of the plate corresponds to a longitudinal direction of the plate type heat exchanger, and a shorter direction of the plate corresponds to the lateral direction of the plate type heat exchanger, andthe atmosphere flow path channels comprise:a first atmosphere flow path channel connected between a top surface and a bottom surface of the plate type heat exchanger orthogonal to the longitudinal direction thereof; anda second atmosphere flow path channel connected between a first side surface of the plate type heat exchanger parallel to the longitudinal direction thereof and a second side surface of the plate type heat exchanger facing away from the first side surface to intersect with the first atmosphere flow path channel. 7. The passive containment building cooling system of claim 1, wherein the passive containment building cooling system further comprises:a coolant storage section installed below the plate type heat exchanger to collect condensate formed by the plate type heat exchanger, and connected to a safety injection line to inject the collected condensate to the reactor coolant system; anda condensate return line extended from the plate type heat exchanger to the coolant storage section to allow atmosphere within the containment building to transfer heat from the plate type heat exchanger to the fluid and guide condensate formed by condensation to the cooling water storage section. 8. The passive containment building cooling system of claim 1,wherein a longer direction of the plate corresponds to a longitudinal direction of the plate type heat exchanger, and a shorter direction of the plate corresponds to a lateral direction of the plate type heat exchanger,wherein the atmosphere flow path channels or the fluid flow path channels are formed in the longitudinal direction of the plate type heat exchanger, andthe plate type heat exchanger further comprises an open type flow path that is formed on the plate type heat exchanger in the lateral direction thereof and wherein said flow path is configured to communicate with the channels to allow atmosphere or heat exchange fluid passing through the open type flow path to join atmosphere or heat exchange fluid passing through the channels.
043226221	claims	1. A device for the achromatic magnetic deflection of a beam of charged accelerated particles, comprising at least one electromagnet having pole pieces delimiting air gaps in which are created magnetic fields having the same direction and specific values so as to obtain paths of particles having the form of loops whose lengths are a function of the momentum of the particles, said pole pieces forming a first, a second and a third magnetic sector disposed one after the other and joined together, the whole of these magnetic sectors having a plane of symmetry perpendicular to the plane of the mean path of said beam of particles, and intersecting this plane along an axis XX, forming an axis of symmetry, and magnetic deflection device presenting successively to the beam of particles a flat input face E, a first curved face F.sub.1, a second curved face F.sub.2 and a flat output face S, said input E and output S faces forming therebetween an angle 2.alpha., said identical curved faces F.sub.1 and F.sub.2 as well as said axis of symmetry XX being substantially orthogonal to the different paths of said particles, the values of said magnetic inductions created in the first and third magnetic sectors being respectively equal to KB.sub.o, B.sub.o being the value of the magnetic induction in the second magnetic sector and K a numerical co-efficient less than 1. 2. A magnetic deflection device as claimed in claim 1, wherein the radius of curvature r.sub.1 of the paths of the particles in the first and third magnetic sectors and the radius of curvature r.sub.2 of the paths in the second intermediate magnetic sector are bound by the relationship: ##EQU5## r.sub.1 and r.sub.2 depending, for specific magnetic induction values in the different magnetic sectors, on the momentum of said particles, b being the distance separating the mean incident path from the intersection point I of input face E with the axis of symmetry XX of the magnetic deflection device, .theta. being the total angle of deflection of the particles in the first and third magnetic sectors, this angle .theta. depending on the momentum of said particles, for specific values of the magnetic induction, R being the radius of curvature of curved faces F.sub.1 and F.sub.2 respectively common to the first and second magnetic sectors, and to the second and third magnetic sectors, and wherein the deflection angle 2.phi. of the particles in the second magnetic sector is equal to 2[.pi.-(.alpha.+.theta.)]. 3. A magnetic deflection device as claimed in claim 2, wherein a pair of pole pieces is provided whose form and dimensions are such that they delimit three successive contiguous magnetic sectors M.sub.1, M.sub.2, M.sub.3, in which are respectively created magnetic inductions of value (B.sub.o /2), B.sub.o, (B.sub.o /2), the ratio K=(r.sub.2 /r.sub.1) being substantially equal to 0.5, wherein angle 2.alpha. is substantially equal to (.pi./2), and wherein the radius of curvature R of the intermediate faces F.sub.1, F.sub.2 is substantially equal to 2b. 4. A magnetic deflection device as claimed in claim 3, wherein the air gap of the magnetic sector M.sub.2 has a height equal to half of the height of magnetic sectors M.sub.1 and M.sub.3. 5. A magnetic deflection device as claimed in claim 3, wherein the angles .theta. corresponding to the different paths are between 60.degree. and 110.degree.. 6. A magnetic deflection device as claimed in claim 2, wherein a pair of pole pieces are provided whose form and dimensions are such that they delimit three successive contiguous magnetic sectors M.sub.10, M.sub.20, M.sub.30, in which are created respectively magnetic fields of values substantially equal to 0.36 B.sub.o, B.sub.o, 0.36 B.sub.o, the ratio (r.sub.2 /r.sub.1) of the radius of curvature r.sub.2 of the paths in magnetic sector M.sub.20 and of the radius of curvature r.sub.1 of the paths in magnetic sectors M.sub.10 and M.sub.30 being substantially equal to 0.36, said angle .alpha. being substantially equal to .pi./3, and said radius of curvature R.sub.10 of the intermediate faces F.sub.10, F.sub.20 being substantially equal to 1.58 b. 7. A magnetic deflection device as claimed in claim 6, wherein the height of the air gap of magnetic sector M.sub.20 is substantially equal to a third of the height of magnetic sectors M.sub.10 and M.sub.30. 8. A magnetic deflection device as claimed in claim 6, wherein the angles of rotation .theta. of the particles of different energies in magnetic sectors M.sub.10 and M.sub.30 are between 55.degree. and 100.degree.. 9. A magnetic deflection device as claimed in 3, wherein each of the pole pieces is formed by a first element a.sub.1, made from a magnetic material on which is fixed a second element c placed so as to reduce the air gap of the pole pieces corresponding to said intermediat magnetic sector and having the form of the intermediate magnetic sector. 10. A magnetic deflection device as claimed in claim 6, wherein each of the pole pieces is formed by a first element a.sub.1 made from a magnetic material on which is fixed a second element c placed so as to reduce the air gap of the pole pieces corresponding to the intermediate magnetic sector and having the form of said intermediate magnetic sector.
047643331	claims	1. An end closure for a container, in particular an end closure for a nuclear fuel transport flask, comprising means defining an end opening for a container, a gate movable laterally across said end opening between open and closed positions, the gate having first and second portions and means continuously urging said portions apart, a door, means releasably mounting the door on the gate, the door including means sealingly engageable with said opening, the door having upper and lower cooperable wedge-shaped members releasably mounted on the first and second gate portions respectively for movement therewith between the open and closed positions, the assembly including means arranged such that a lateral displacement of the gate into or out of its fully closed position effects movement of the second gate portion only and corresponding movement of the associated lower wedge-shaped door member, with the first gate portion and its associated upper wedge-shaped door member remaining laterally stationary whereby to effect a vertical displacement of the upper wedge-shaped door member into or out of sealing engagement with said opening. 2. An end closure according to claim 1 including respective cooperable stop members on the first and second gate portions to determine the extent of sole movement of the second gate portion independently of the first gate portion. 3. An end closure according to claim 1 wherein said sealingly engageable means includes a first sealing ring in the upper wedge-shaped door member, and further comprising a second sealing ring about said opening cooperable with the first sealing ring. 4. An end closure according to claim 1 wherein said continuous urging means includes spring-loaded means for continuously urging apart the first and second gate portions. 5. An end closure according to claim 4 in which the spring-loaded means comprises a pair of spring-loaded mechanisms positioned symmetrically at opposite sides of the centre line of the gate, each mechanism having a compression spring in one of the gate portions and a plunger slidable in said gate portion and secured at its end remote from the spring to the other of the gate portions.
056087764	claims	1. A twin beam computed tomography scanner for performing a helical scan, comprising: an x-ray source for generating an x-ray to be projected generally towards, and at least partially through, an object; a detector array comprising a plurality of detector cells, said cells arranged to form at least two cell rows; a beam splitter positioned so that the x-ray projected from said x-ray source is substantially split to form at least two beams prior to being projected at least partially through the object; a data acquisition system coupled to said detector array; and a controller coupled to said data acquisition system and to said beam splitter for controlling said beam splitter so that the x-ray beams from said beam splitter do not substantially impinge on edge regions of said detector cells. projecting an x-ray beam from the source towards the object and through the beam splitter as the source rotates around the object and as the object moves axially relative to the source along a z-axis; detecting whether any beam impinges upon an edge region of a detector cell; and if a beam impinges upon the edge region of a detector cell, then adjusting the beam splitter so that the beams do not substantially impinge upon the detector cell edge region. 2. A scanner in accordance with claim 1 wherein said detector cells are arranged so that a first edge of a first cell in a first cell row is adjacent a first edge of a first cell in a second cell row. 3. A scanner in accordance with claim 2 wherein each of said detector cells comprises at least a first edge region in which the sensitivity response of said detector cell is lower than the sensitivity response with respect to at least one other cell location. 4. A scanner in accordance with claim 3 wherein a collimator is positioned so as to substantially block x-rays from impinging on said first edges of said first and second cells. 5. A scanner in accordance with claim 1 wherein said beam splitter comprises a beam splitting member configured to cause a first input beam to be split into at least two output beams. 6. A scanner in accordance with claim 5 wherein said beam splitting member is constructed of x-ray absorbing material. 7. A scanner in accordance with claim 5 wherein said beam splitter further comprises first and second collimating members, said beam splitting member at least partially positioned in a beam path which extends between said first and second collimating members. 8. A scanner in accordance with claim 7 wherein said beam splitting member is movable relative to at least one of said collimating members. 9. A scanner in accordance with claim 5 wherein said beam splitting member has an elongate elliptical shape and is rotatable relative to at least one of said collimating members. 10. A scanner in accordance with claim 5 wherein said beam splitting member has a triangular shape. 11. A scanner in accordance with claim 5 further comprising first and second spaced collimating members, the relative orientations of said first and second collimating members and said beam splitting member being selectively adjustable based on a helical pitch. 12. A method of generating projection data for an object using a scanner having a beam splitter, an x-ray source and an x-ray detector array having at least two rows of detector cells, each detector cell having at least one edge region, said method comprising the steps of: 13. A method in accordance with claim 12 wherein the beam splitter includes first and second collimating members and a beam splitting member, and the relative orientation of the first and second collimating members and the beam splitting member is selected substantially based on helical pitch. 14. A method in accordance with claim 12 further comprising the step of collimating the x-ray beam prior to the beam being at least partially projected through the object. 15. A computed tomography system for performing a helical scan and for generating an image of an object, said system comprising an x-ray source, an x-ray detector array having adjacent rows of detector cells positioned to receive x-rays emitted from said x-ray source, and a pre-patient collimator positioned so that the x-ray projected from said x-ray source is substantially split to form at least two beams prior to being projected at least partially through the object to be imaged, said system further comprising an offset detector data acquisition system, a reference detector data acquisition system, a motor controller and a motor, said data acquisition systems coupled to said detector array, outputs from said data acquisition systems coupled to said motor controller, said motor being coupled to said pre-patient collimator and configured to control said pre-patient collimator so that the x-ray beams from said pre-patient collimator do not substantially impinge on edge regions of said detector cells. 16. A computed tomography system in accordance with claim 15 wherein said pre-patient collimator comprises a housing, a beam splitting member, and first and second collimating members. 17. A computed tomography system in accordance with claim 16 wherein said beam splitting member is movable relative to said collimating members.
056446144	description	DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIGS. 1 and 2, a computed tomograph (CT) imaging system 10 is shown as including a gantry 12 representative of a "third generation" CT scanner. Gantry 12 has an x-ray source 14 that projects a fan beam of x-rays 16 toward a detector array 18 on the opposite side of gantry 12. Detector array 18 is formed by detector elements 20 which together sense the projected x-rays that pass through a medical patient 22. Each detector element 20 produces an electrical signal that represents the intensity of an impinging x-ray beam and hence the attenuation of the beam as it passes through patient 22. During a scan to acquire x-ray projection data, gantry 12 and the components mounted thereon rotate about a center of rotation 24. Rotation of gantry 12 and the operation of x-ray source 14 are governed by a control mechanism 26 of CT system 10. Control mechanism 26 includes an x-ray controller 28 that provides power and timing signals to x-ray source 14 and a gantry motor controller 30 that controls the rotational speed and position of gantry 12. A data acquisition system (DAS) 32 in control mechanism 26 samples analog data from detector elements 20 and converts the data to digital signals for subsequent processing. An image reconstructor 34 receives sampled and digitized x-ray data from DAS 32 and performs high speed image reconstruction. The reconstructed image is applied as an input to a computer 36 which stores the image in a mass storage device 38. Computer 36 also receives commands and scanning parameters from an operator via console 40 that has a keyboard. An associated cathode ray tube display 42 allows the operator to observe the reconstructed image and other data from computer 36. The operator supplied commands and parameters are used by computer 36 to provide control signals and information to DAS 32, x-ray controller 28 and gantry motor controller 30. In addition, computer 36 operates a table motor controller 44 which controls a motorized table 46 to position patient 22 in gantry 12. Particularly, table 46 moves portions of patient 22 through gantry opening 48. Referring to FIG. 3, and with respect to operation of x-ray source 14, x-ray beam 16 emanates from a focal spot 50 of source 14. X-ray beam 16 is collimated by collimator 52, and collimated beam 16 is projected toward detector array 18 along a fan beam axis 54 centered within fan beam 16. As shown in FIG. 4, detector array 18 is generally curved at a fixed radius from focal point 50. A distance (d) between focal spot 50 and the center of any detector element 20 at a fan beam angle (.alpha.) is the same. Particularly: EQU d(.alpha..sub.o)=d(.alpha..sub.n) where: .alpha..sub.o =fan beam angle at vertical; and PA1 .alpha..sub.n =fan beam angle at any angle offset to vertical. PA1 .alpha..sub.o =is the fan beam angle at vertical; and PA1 .alpha..sub.n =fan beam angle at any angle offset to vertical. PA1 .alpha.=fan beam angle; PA1 Z=position of beam on detector; PA1 f=position of focal spot in z axis; PA1 c=position of collimation point in z axis; PA1 d=source to detector distance; and PA1 s=source to collimation distance. PA1 .alpha.=fan beam angle; PA1 Z=position of beam on detector; PA1 f=position of focal spot in z axis; PA1 c=position of collimation point in z axis; PA1 d=source to detector distance; and PA1 s=source to collimation distance. As described above, known collimators have rectangular, or linear, apertures, or slots. A distance (s) between x-ray source 14 and the collimator aperture changes as a function of fan beam angle (.alpha.). Particularly: EQU s(.alpha..sub.o)<s(.alpha..sub.n) where: As shown in FIG. 5, collimated fan beam 16 collimated by collimator 52 with a rectangular slot or aperture 56 is generally convex as indicated at 58. Particularly, each x-ray in beam 16 impinges upon detector cells 20 in detector array 18 at a z axis location, Z(.alpha.), according to the equation: EQU Z(.alpha.)=(c-f)d(.alpha.)/s(.alpha.)+f where: However, since detector elements 20 are generally rectangular, portions of convex fan beam 16 do not impinge detector elements 20. This unused portion 60 (shaded), however, has been attenuated by patient 22. Patient 22 was thus unnecessarily subjected to the full convex fan beam. Referring to FIG. 6, and in accordance with one embodiment of the present invention, a collimator 70 has a contoured aperture 72 therein. Contoured aperture 72 is curved and receives x-ray beams from x-ray source and emits a generally rectangular beam 74 which impinges upon detector elements 20 in detector array 18. As shown, rectangular beam 74 directly overlaps the rectangular detector element 20. Therefore, in one embodiment, contoured aperture 72 prevents any unused portions of fan-beam 16 from impinging on detector elements 20, and thus eliminates patient exposure to unnecessary x-ray dose. In accordance with another embodiment of the present invention, a collimator aperture is curved according to the following equation: EQU c(.alpha.)=(Z-f)s(.alpha.)/d(.alpha.)+f, where: In accordance with yet another embodiment of the present invention a collimator aperture is contoured for each slice configuration and focal spot size. For example, a cam collimator, as hereinafter described in more detail, may be used to continuously change aperture shape as a function of the aperture size. In accordance with still yet another embodiment of the invention, as shown in FIG. 7, collimator 80 has a collimator aperture 82 that is contoured with a fixed linear ramp. The fixed linear ramp approximates the curvature for a nominal slice configuration. For example, where a distance between x-ray source 14 and patient 22 is 541 mm, a distance between x-ray source 14 and detector element 20 is 949 mm, and a vertical distance between x-ray source 14 and collimator is 162 mm, a ramp slope of 0.2 mm per 100 mm may be used. Linear ramp aperture 82 provides similar patient dose savings and is believed to be easier to manufacture than multiple curved or linear contours. FIG. 8 is a top view of a double cam collimator 100 in accordance with yet another embodiment of the present invention. Collimator 100 includes cams 102 and 104. Cams 102 and 104 are shown as being spaced and generally define edges 106 and 108, respectively, for restricting a beam passing therebetween. Cams 102 and 104 each include bosses 110A, 110B, 110C and 110D extending therefrom. A stepper motor (not shown) would be coupled to at least one boss 110A,110B and 110C,110D of each cam 102 and 104 to control relative movement of such cams 102 and 104. The collimators with contoured apertures as described above restrict collimated fan beam 16 to more closely approximate the size of detector cells 20. By so restricting collimated fan beam 16, unused portions of x-ray beams attenuated by patient 22 are reduced, yet the integrity of data received at detector cells 20 is maintained. From the preceding description of various embodiments of the present invention, it is evident that the objects of the invention are attained. Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. For example, the CT system described herein is a "third generation" system in which both the x-ray source and detector rotate with the gantry. Many other CT systems including "fourth generation" systems wherein the detector is a full-ring stationary detector and only the x-ray source rotates with the gantry, may be used. Moreover, the linear ramp contoured aperture described herein has a ramp slope of 0.2 mm per 100 mm. Many other ramp slopes can be used. Furthermore, the aperture contour may be prefabricated with a specific curvature or slope or, alternatively, the aperture contour may be modified during a scan. Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims.
	claims	1. An apparatus for improving ion beam quality comprising:an ion source for generating an ion beam, the ion source comprising a faceplate with an aperture for the ion beam to travel therethrough; anda set of extraction electrodes comprising at least a suppression electrode and a high-transparency ground electrode having an overall height H comprising a base height y and a slot height x where the base height y is at least two times less than the slot height x, and a spacing between the suppression electrode and the base of the high-transparency ground electrode in a direction of travel of the ion beam is greater than 70% of the slot height x, and wherein the set of extraction electrodes extract the ion beam from the ion source via the faceplate, and wherein the high-transparency ground electrode together with the spacing is configured to optimize gas conductance between the suppression electrode and the high-transparency ground electrode for improved extracted ion beam quality. 2. The apparatus of claim 1, wherein the high-transparency ground electrode is configured with a base angle θ, and a slot angle δ. 3. The apparatus of claim 2, wherein the base angle θ is 20°. 4. The apparatus of claim 2, wherein the base angle θ is greater than 20°. 5. The apparatus of claim 4, wherein the base angle θ is 40°. 6. The apparatus of claim 1, wherein the high-transparency ground electrode is a single-slot high-transparency ground electrode or a double-slot high-transparency ground electrode. 7. The apparatus of claim 1, wherein the ion source is encased in a housing having a tapered configuration. 8. The apparatus of claim 1, wherein the faceplate is a protruded faceplate in which the faceplate protrudes toward the set of extraction electrodes. 9. The apparatus of claim 1, wherein the suppression electrode is a protruded suppression electrode. 10. The apparatus of claim 1, wherein the high-transparency ground electrode further comprises one or more anchor portions protruding into one or more extraction slots of the high-transparency ground electrode for defining stable plasma boundaries inside of the high-transparency ground electrode. 11. A method for improving ion beam quality comprising:providing an ion source comprising a plasma generator for generating an ion beam and a faceplate with an aperture for the ion beam to travel therethrough; andproviding a set of extraction electrodes comprising at least a suppression electrode and a high-transparency ground electrode having an overall height H comprising a base height y and a slot height x where the base height y is at least two times less than the slot height x, and a spacing between the suppression electrode and the base of the high-transparency ground electrode in a direction of travel of the ion beam is greater than 70% of the slot height x, wherein the set of extraction electrodes extract the ion beam from the ion source via the faceplate, and wherein the high-transparency ground electrode together with the spacing is configured to optimize gas conductance between the suppression electrode and the high-transparency ground electrode for improved ion beam quality. 12. The method of claim 11, wherein the high-transparency ground electrode is configured with a base angle θ, and a slot angle δ. 13. The method of claim 12, wherein the base angle θ is 20°. 14. The method of claim 12, wherein the base angle θ is greater than 20°. 15. The method of claim 14, wherein the base angle θ is 40°. 16. The method of claim 11, wherein the high-transparency ground electrode is a single-slot high-transparency ground electrode or a double-slot high-transparency ground electrode. 17. The method of claim 11, wherein the ion source is encased in a housing having a tapered configuration. 18. The method of claim 11, wherein the faceplate is a protruded faceplate in which the faceplate protrudes toward the set of extraction electrodes. 19. The method of claim 11, wherein the suppression electrode is a protruded suppression electrode. 20. The method of claim 11, wherein the high-transparency ground electrode further comprises one or more anchor portions protruding into one or more extraction slots of the high-transparency ground electrode for defining stable plasma boundaries inside of the high-transparency ground electrode.
	summary
	claims	1. A method of irradiating a layer (3) including:directing and focusing a radiation beam (7) to a spot (11) on said layer (3) by means of at least one optical element (59);causing relative movement of the layer (3) relative to said at least one optical element (59) so that, successively, different portions of the layer (3) are irradiated and an interspace (53) between a surface of said at least one optical element (59) nearest to said layer (3) is maintained; andmaintaining at least a portion of said interspace (53) through which said radiation irradiates said spot (11) on said layer (3) filled with a liquid (91) supplied via a supply conduit;characterized by directing gas (71-73) to said layer (3); andremoving supplied liquid (91) from said layer (3) in the vicinity of a flow of said gas (71-73). 2. A method according to claim 1, wherein said gas (71-73) is supplied at a pressure sufficiently high to cause a net gas flow (71-73) in a direction along said layer (3) opposite to the direction (30) of said movement of said layer (3). 3. A method according to claim 1 or 2, wherein the flow of said gas (71-73) is entered into an interspace between said layer (3) and a boundary surface (83) having a width of at least 2 μm and preferably at least 5 μm and at most 100 μm and preferably 30 μm. 4. A method according to claim 3, wherein the liquid (91) forms a film on said layer (3) having a thickness, and wherein an interspace (86) between said layer (3) and a surface (87) facing said layer (3) upstream of an area where the liquid is discharged is larger than the thickness of said film. 5. A method according to any one of the preceding claims, wherein liquid (91) and gas are drawn away from said layer (3) at a higher flow rate than the sum of the flow rates of said gas flow (71-73) and the supply of said liquid (91). 6. A method according to any one of the preceding claims, wherein said gas (71-73) is air. 7. A device for directing radiation to a layer (3) including:at least one optical element (59) for focusing a beam (7) of radiation originating from a radiation source (33) to a spot (11) on said layer (3);a displacement structure for causing relative movement of the layer (3) relative to said at least one optical element (59) so that, successively, different portions of the layer (3) are irradiated and an interspace (53) between said layer (3) and a surface of said at least one optical element (59) nearest to said spot (11) is maintained; andan outflow opening for supplying liquid (91) to at least a portion of said interspace (53) through which, in operation, said radiation irradiates said spot (11) on said layer (3);characterized by a gas outflow opening (70) for directing a gas flow (71-73) to said layer (3); anda discharge channel (76) having an inlet (77) in the vicinity of said gas outflow opening (70) for drawing away liquid (91) from the layer (3). 8. A device according to claim 7, wherein said gas outflow opening (70) for directing said gas flow (71-73) is a slit. 9. A device according to claim 7 or 8, wherein said discharge channel (76) communicates with a vacuum source (81). 10. A device according to any one of the claims 7-9, wherein said gas outflow opening (70) and said inlet (77) of said discharge-channel (76) extend about said interspace (53).
	summary
052934160	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to an x-ray apparatus of the type used to produce an x-ray shadowgraph. 2. Description of the Prior Art It is known to prepare x-ray shadowgraphs using a slotted diaphragm by scanning a line-shaped detector array with a fan-shaped x-ray beam, by causing the x-ray beam to move across a predetermined measurement field while also moving the detector array. An x-ray shadowgraph of a subject in the scanned measuring field can then be reconstructed from the electrical output signals of the detector array. A disadvantage of this known technique is that a relatively large number of mechanical parts must be moved in synchronism with each other, including at least the detector array as well as a slotted diaphragm for gating the x-ray beam. In order to retain an optimum anode angle in the image-effective beam path, the x-ray radiator is usually also moved, i.e., rotated. SUMMARY OF THE INVENTION It is an object of the present invention to provide a radiography apparatus with which x-ray shadowgraphs can be produced which permits an x-ray shadowgraph of a subject to be reconstructed in a predetermined measuring field with a minimum of mechanically moved components, while using a detector array. The above object is achieved in a radiography apparatus which includes means for moving the x-ray source in a direction perpendicular to the line direction of the detector array, so that the detector array is irradiated by an x-ray beam which scans the measuring field from different directions. In the radiography apparatus disclosed herein, the only component which must be moved for scanning the x-ray field is the x-ray radiator. The detector array remains at rest. In an embodiment of the invention, a screen or slotted diaphragm having diaphragm shafts aligned to the detector array is disposed preceding the measuring field in the direction of radiation propagation. This screen diaphragm assures that a fan-shaped x-ray beam is incident on the detector array for each measuring position of the x-ray radiator. In a further embodiment of the invention, the radiography apparatus can be combined with or in a computer tomography apparatus, having a measuring unit consisting of an x-ray radiator and a CT detector array curved around the focus of the x-ray radiator. The measuring unit can be rotated around a system axis, and the detector array for generating the x-ray shadowgraphs is oriented perpendicularly to the CT detector array. In a computer tomography apparatus, the x-ray radiator is already capable of being mechanically moved in order to create computer tomograms. This same mechanical motion, and the structure for generating the mechanical motion, are used for preparing x-ray shadowgraphs in accordance with the principles of the present invention.
061635901	abstract	A sample cell for use in x-ray imaging, including structure defining a chamber for a sample and, mounted to the structure, a body of a substance excitable by an appropriate incident beam to generate x-ray radiation, the cell being arranged so that, in use, at least a portion of the x-ray radiation traverses the chamber to irradiate the sample therein and thereafter exits the structure for detection.
	description	This application is a continuation of U.S. patent application Ser. No. 11/545,638 entitled “Methods of Using and Making Radiopharmaceutical Pigs” filed on 10 Oct. 2006 (still pending), which is a continuation of U.S. patent application Ser. No. 11/486,197 entitled “Radiopharmaceutical Pig” filed on 13 Jul. 2006 (now U.S. Pat. No. 7,495,246), which is a continuation of U.S. patent application Ser. No. 10/527,301 entitled “Polymer Pharmaceutical Pig and Associated Method of Use and Associated Method of Production” filed on 9 Mar. 2005 (now U.S. Pat. No. 7,165,672), which claims priority to PCT Application No. PCT/US03/31823 filed on 7 Oct. 2003, which claims priority to U.S. Provisional Patent Application No. 60/419,161 filed on 17 Oct. 2002, the entire disclosures of which are hereby incorporated by reference in their entireties. A pharmaceutical pig is used for transportation of liquid radiopharmaceuticals. A radiopharmacy typically dispenses a liquid radiopharmaceutical into a syringe, which is then placed in a pharmaceutical pig for transport to a medical facility. The pharmaceutical pig reduces unwanted exposure from the radioactive material and protects the syringe from damage. After delivery, the pharmaceutical pig is opened, the syringe is removed and the radiopharmaceutical is administered to a patient. The used syringe is put back in the pharmaceutical pig and returned to the radiopharmacy for disposal. Some radiopharmacies are independently owned and others are owned and operated in nationwide networks by Cardinal Health, Inc., having a place of business at 7000 Cardinal Place, Dublin, Ohio 43017 and Mallinckrodt Inc., a business of Tyco International, Ltd. Conventional pharmaceutical pigs are used on a daily basis by radiopharmacies across the country. Many of the conventional pigs in current use are formed from plastic and lead. Of course, the lead is used as shielding material for the radiopharmaceutical. Conventional plastic/lead pharmaceutical pigs are typically configured in a two-part or a three-part design, discussed in greater detail below. Other conventional pharmaceutical pigs are formed from plastic and tungsten. The tungsten is an alternative shielding material to lead, but it is much more expensive. The pharmaceutical pigs that are currently used with syringes are elongate devices sized to enclose a single syringe that holds a dose for a single patient. Conventional two-part pharmaceutical pigs are available from Biodex Medical Systems, Inc. of Shirley, N.Y. (“Biodex”) and are commonly used in the Mallinckrodt system of radiopharmacies. Conventional three-part pharmaceutical pigs are produced by Cardinal Health, Inc. and are shown in U.S. Pat. No. 5,519,931. These conventional three-part pharmaceutical pigs are believed to be in widespread use in the Cardinal Health, Inc. system of radiopharmacies to transport conventional syringes. The Biodex two-part pharmaceutical pig is formed from: a) an outer plastic shell having a removable plastic top that threadibly engages a plastic base; and b) an inner shield having an upper lead section that fits in the plastic top and a lower lead section that fits in the plastic base. Conventional syringes are transported in this two-part pharmaceutical pig. However, because of the possibility of contamination, the lower section of the pharmaceutical pig is washed and disinfected after each use in the Mallinckrodt system of radiopharmacies. There is a three-part pharmaceutical pig disclosed in U.S. Pat. No. 5,519,931, assigned to Syncor International Corp., which is formed from the following components: a) an outer shell having a removable plastic top that threadibly engages a plastic base; b) an inner shield having an upper lead section that fits in the plastic top and a lower lead section that fits in the plastic base; and c) an inner disposable liner having a removable plastic cap that connects to a plastic base. A conventional syringe is contained in the disposable plastic liner, which fits into the lead portion of the pharmaceutical pig. There is also a pharmaceutical pig disclosed in U.S. Pat. No. 6,425,174, which is also assigned to Syncor International Corp., that includes an upper shield and a lower shield that nest within an upper outer shell and a lower outer shell, respectively. There is a separate sharps container, having an upper cap and a lower housing, that nests within the upper shield and the lower shield, respectively. John B. Phillips is listed as the inventor on several patents for a three-part pharmaceutical pig having: a) an outer plastic shell; b) an inner lead shield; and c) a removable inner liner to hold a syringe. The Phillips' patents are as follows: U.S. Pat. Nos. 5,611,429; 5,918,443; and 6,155,420. The removable inner liner in the Phillips' design has a flared hexagonal shaped section sized to surround the finger grip of the syringe and hold it securely in place during transit. Conventional three-part lead/plastic pharmaceutical pigs, such as the Syncor design or the Phillips design described above, rely on a removable inner liner having a cap and base to contain the syringe and prevent contamination of the lead shielding material with the radiopharmaceutical. However, both the two-part lead/plastic pharmaceutical pig and the three-part lead/plastic pharmaceutical pig have exposed lead on the interior. There is a need for a new design that protects the lead from inadvertent contamination by the liquid radiopharmaceutical. Lead is a very porous material that can absorb the radiopharmaceutical. Moreover, lead, as a material, might be construed as being hygienically challenging. Many conventional three-part lead/plastic pharmaceutical pigs use a threaded design to connect the cap and the base. Some of these prior art designs require several turns to connect the cap and the base. In a busy radiopharmacy, there is a need for a faster and easier way to attach the cap to the base. However, the cap is typically not locked into place, therefore, rough transportation and a failure to provide the requisite number of turns can result in the cap untwisting slightly from the base during transit with a potential spill of radioactive pharmaceutical fluid resulting therefrom. Another issue is that the base of a conventional pharmaceutical pig is generally cylindrical making the pharmaceutical pig prone to tipping and falling over on its side. The present invention is directed to overcoming one or more of the problems set forth above. These deficiencies and shortcomings include, but are not limited to, exposed lead, numerous turns required to attach the cap to the base, absence of a locking mechanism to secure the cap to the base and a cylindrical base where the bottom portion of the base has substantially the same diameter as the top portion of the base so that the pharmaceutical pig is prone to tipping and falling over on its side. A pharmaceutical pig is sized and arranged to transport a single syringe containing a unit dose of a radiopharmaceutical from a radiopharmacy to a medical facility such as a doctor's office, clinic or hospital. After the radiopharmaceutical has been administered to a patient, the used syringe is put back into the pharmaceutical pig and returned to the radiopharmacy for proper disposal. The present invention may be used with conventional syringes or safety syringes. In one aspect of this present invention, a polymer pharmaceutical pig is disclosed. The polymer pharmaceutical pig includes an elongate polymer base having a base shell that completely encloses a base shielding element and having a first hollow center section and an elongate polymer cap that is removably attached to the elongate polymer base, the elongate polymer cap, having a second hollow center and a cap shell that completely encloses a cap shielding element. Moreover, for convenience and ease of use, the amount of rotation of the elongate polymer cap in relation to the elongate polymer base for removably attaching the elongate polymer base to the elongate polymer cap is minimized, i.e., preferably less than three hundred and sixty degrees (360°), more preferably less than one hundred and eighty degrees (180°) and optimally less than ninety degrees (90°). Preferably, a locking detent is located in the threaded interconnections to secure the elongate polymer base to the elongate polymer cap. The polymer material utilized in the base shell and the cap shell can include virtually any type of plastic and is preferably polycarbonate resin, e.g., LEXAN® material, while the base shielding element and the cap shielding element can be made of virtually any type of material that blocks radiation emitted from the radiopharmaceutical. This material preferably includes lead as well as tungsten and metallic-filled polymers, with lead being the most preferred material due to the low cost and ease of manufacturing. Preferably, the elongate polymer cap is substantially cylindrical and the bottom portion of the elongate polymer base is substantially bell-shaped. Moreover, the elongate polymer base of the pharmaceutical pig preferably includes a top portion having a first diameter, a middle portion having a second diameter and a bottom portion having a third diameter, where the second diameter of the middle portion is less than the first diameter of the top portion and is less than the third diameter of the bottom portion. The elongate polymer cap of the pharmaceutical pig preferably includes a top portion having a fourth diameter and a bottom portion having a fifth diameter, where the fourth diameter of the top portion is less than the fifth diameter of the bottom portion. In the preferred design, the top portion of the elongate base includes a plurality of flattened portions, where at least one flattened portion of the plurality of flattened portions includes an arch-like portion and the bottom portion of the elongate base includes a plurality of flattened portions, wherein at least one flattened portion of the plurality of flattened portions includes an arch-like portion. The bottom portion of the elongate cap base includes a plurality of flattened portions, where at least one flattened portion of the plurality of flattened portions includes an arch-like portion. Optimally, at least one flattened portion of the plurality of flattened portions in the top portion of the elongate base is substantially aligned with the at least one flattened portion of the plurality of flattened portions in the bottom portion of the elongate cap. In another aspect of this present invention, an assembly including a pharmaceutical pig sized and arranged to transport a syringe is disclosed. The assembly includes a syringe having a needle, a barrel, a pair of wing-shaped finger grips, and a plunger, and a pharmaceutical pig including an elongate polymer base that completely encloses a base shielding element. The elongate polymer base having a first hollow center section that is sized to surround the needle and at least a portion of the barrel of the syringe and an elongate polymer cap that is removably attached to the elongate polymer base. The elongate polymer cap completely encloses a cap shielding element and the elongate polymer cap includes a second hollow center section that is sized to surround at least a portion of the plunger of the syringe. In still another aspect of this present invention, a method for transporting a syringe in a pharmaceutical pig, the syringe having at least a needle, a barrel, a pair of wing-shaped finger grips, and a plunger is disclosed. The method includes placing a syringe containing a liquid radiopharmaceutical in a pharmaceutical pig having an elongate polymer base that completely encloses a base shielding element. The elongate polymer base having a first hollow center section that is sized to surround the needle and at least a portion of the barrel of the syringe and an elongate polymer cap that is removably attached to the elongate polymer base. The elongate polymer cap completely encloses a cap shielding element and the elongate polymer cap having a second hollow center section that is sized to surround at least a portion of the plunger of the syringe. This is followed by transporting the pharmaceutical pig containing the syringe to a medical facility and then transporting the pharmaceutical pig and the used syringe back to the radiopharmacy for disposal of the used syringe. In yet another aspect of this present invention, a method for producing a pharmaceutical pig is disclosed. The method includes molding a base shielding element in a first mold, molding a cap shielding element in a second mold. This is followed by inserting the base shielding element within a third mold and injecting molten polymer material into the third mold so that when the polymer material hardens, the base shielding element is completely enclosed by the polymer material to form an elongate base. This is then followed by inserting the cap shielding element within a fourth mold and injecting molten polymer material into the fourth mold so that when the polymer material hardens, the cap shielding element is completely enclosed by the polymer material to form an elongate cap. These are merely some of the innumerable illustrative aspects of this present invention and should not be deemed an all-inclusive listing. These and other aspects will become apparent to those skilled in the art in light of the following disclosure and accompanying drawings. FIG. 1 is a perspective view of the embodiment of the pharmaceutical pig of the present invention that is generally indicated by numeral 10. There is an elongate base 12 and an elongate cap 14. The elongate base 12 and the elongate cap 14 of the pharmaceutical pig 10 can be formed in any of a wide variety of shapes and sizes, however, a substantially cylindrical shape is preferred. Preferably, the elongate base 12 includes a top portion that is generally indicated by numeral 16 having a first diameter, a middle portion that is generally indicated by numeral 18 having a second diameter and a bottom portion that is generally indicated by numeral 20 having a third diameter. The elongate cap 14 includes a top portion that is generally indicated by numeral 22 having a fourth diameter and a bottom portion that is generally indicated by numeral 24 having a fifth diameter. In the preferred embodiment, the second diameter of the middle portion 18 of the elongate base 12 is less than the first diameter of the top portion 18 of the elongate base 12. The second diameter of the middle portion 18 of the elongate base 12 is also less than the third diameter of the bottom portion 20 of the elongate base 12 to create a bell-shape. Also, in the preferred embodiment, the fourth diameter of the top portion 22 of the elongate cap 14 is less than the fifth diameter of the bottom portion 24 of the elongate cap 14. The elongate base 12 for the pharmaceutical pig 10, preferably includes a first plurality of flattened portions 28, e.g., four (4), that each include an arch-like portion 30 located on the bottom portion 20 of the elongate base 12 of the pharmaceutical pig 10. The bottom portion 20 of the elongate base 12 is preferably bell-shaped to prevent tipping and includes a domed, bottom surface 32 to reduce material cost, as shown in FIGS. 4 and 5. Referring again to FIGS. 1 and 2, the top portion 16 of the elongate base 12 for the pharmaceutical pig 10, preferably and optionally, includes a second plurality of flattened portions, e.g., four (4), that preferably alternate between rectangular portions 36 and rectangular portions that each have a downwardly extending arch-like portion 34. The elongate cap 14 for the pharmaceutical pig 10, preferably and optionally, includes a third plurality of flattened portions 40, e.g., four (4), that each include an arch-like portion 41. The top portion 22 is preferably circular and includes a flat top surface 42, as shown in FIG. 1, which can be labeled as well as easily transported within a delivery case that can hold a multiple number of pharmaceutical pigs 10. There is a plurality of threaded interconnections, which is generally indicated by numeral 44, as shown in FIG. 2. Preferably, but not necessarily, there are four (4) threads 45. Preferably, with the present pharmaceutical pig 10 of the present invention, the amount of turns required to secure the elongate base 12 to the elongate cap 14 is minimized. The preferred amount of turning being one turn (360°) or less, with a more preferred amount of turning being one-half of a turn (180°) or less and the most preferred amount of turning being one-quarter of a turn (90°) or less. The pitch of the threads 45 can vary greatly depending on the parameters of the pharmaceutical pig 10, with the most preferred value of pitch being 1.38 for the threads 45. Referring now to FIG. 3, there is a series of locking detents 46 that secure the elongate base 12 to the elongate cap 14. These locking detents 46 lock the elongate base 12 to the elongate cap 14 when the threads 45 of the elongate cap 14 and the elongate base 12 are completely engaged. The elongate cap 14 is flush against the elongate base 12 after having completed the maximum amount of turning, e.g., one-quarter of a turn (90°) to seal the elongate cap 14 against the elongate base 12 in fluid-tight relationship. This seal is present without the presence of an additional component that requires replacement and maintenance, such as an o-ring. Located within the elongate cap 14 and elongate base 12 is a cap shielding element that is generally indicated by numeral 48 and the base shielding element that is generally indicated by numeral 54, respectively, as shown in FIGS. 4 and 5. These shielding elements 48 and 54 are typically formed from lead because it is relatively inexpensive and easy to form. Moreover, these shielding elements 48 and 54 can be formed from any material that blocks the radiation that is emitted from the radiopharmaceutical. For example, tungsten is a suitable shielding element, but it is more expensive than lead and more difficult to form or mold. Metallic-filled polymer composite materials such as the ECOMASS® compounds produced by Engineered Materials, a M. A. Hanna Company having a place of business in Norcross, Ga. can also be used as shielding material. The cap shielding element 48 has a closed end 52 and an open end 50. The walls 56 of the cap shielding element 48 are of generally uniform thickness. The base shielding element 54 has a closed end 58 and an open end 60. The walls 62 of the base shielding element 54 are of generally uniform thickness. As shown in FIG. 5 and best illustrated in FIG. 6, the walls 62 of the base shielding element 54 form a protrusion 64, which is preferably but not necessarily triangular, which forms an angle T when measured against the inside wall of the base shielding element 54. The base shielding element 54 includes a ledge near the open end 60 that forms a shoulder 66. Referring again to FIGS. 4 and 5, the cap shielding element 48 of the elongate cap 14 is completely enclosed by a cap shell 70 having an outer cap shell portion 72 and an inner cap shell portion 74. Also, the base shielding element 54 of the elongate base 12 is completely enclosed by a base shell 76 having an outer base shell portion 78 and an inner base shell portion 80. The cap shell 70 and base shell 76 are preferably made of polymer material. This can include virtually any type of plastic, however, the most preferred type of material is a polycarbonate resin. A specific type of polycarbonate resin, which can be utilized with the present invention, can be purchased under the mark LEXAN®, which is a federally registered trademark of the General Electric Company, having a place of business at One Plastics Avenue, Pittsfield, Mass. 01201. LEXAN® is very lightweight, but is also known for its impact resistance, clarity, stability and heat resistance. The preferred method of forming the cap shell 70 and base shell 76 so that the cap shell 70 and base shell 76 enclose and seal the cap shielding element 48 of the elongate cap 14 and the base shielding element 54 of the elongate base 12, respectively, is by the process of molding. Although the polymer material can be molded in two parts and then melted or welded to provided the complete enclosure of the cap shielding element 48 of the elongate cap 14 and the base shielding element 54 of the elongate base 12, the preferred method of molding the polymer material is by a “two-shot” or “overmolding” process. Examples of this “two-shot” or “overmolding” process are described in: U.S. Pat. No. 4,750,092, which issued to Werther on Jun. 7, 1988 and was assigned to Kollmorgen Technologies Corporation, which is incorporated herein by reference; U.S. Pat. No. 6,381,509, which issued to Thiel et al. on Apr. 30, 2002; and was assigned to Mattec, Inc, which is incorporated herein by reference; and U.S. Pat. No. 6,405,729, which issued to Thornton on Jun. 18, 2002, which is incorporated herein by reference. A significant advantage of the present invention is that no inner liner is utilized. This is a significant advantage since inner liners are typically discarded after each use. This reduces cost and eliminates waste. As also shown in FIG. 5, there is a syringe 83, having: a needle 87 shown in phantom; a barrel 86; a plunger 85; and finger grips 93 which are sometimes called wings. The finger grips 93 may be hexagonal, circular or polygonal; they may fully or partially surround the barrel 86. The finger grips 93 are captured between the previously described shoulder portion 66 formed in the inner base shell portion 80 of the base shell 76 and the inner cap shell portion 74 of the cap shell 70. The syringe 83 is therefore prevented from lateral movement inside the pharmaceutical pig 10 during transit. The needle 87 and at least a portion of the barrel 86 are positioned in a first hollow center section 91 of the elongate base 12. At least a portion of the plunger 85 is positioned in a second hollow center section 89 of the elongate cap 14. The pharmaceutical pig 10 is believed to comply with the revised Bloodborne Pathogens Standard (29 C.F.R. Sectional 1910.1030(d)(2)) promulgated by the Occupational Safety and Health Administration by fully meeting their definition of a “sharps container” by providing a container that is: puncture resistant; capable of being labeled or color-coded; leakproof on the sides and bottom; and does not require a healthcare provider to reach by hand into the container where the sharp has been placed. Method of Use for the Pharmaceutical Pig 10 A prescription is called in, faxed in, or otherwise given to a radiopharmacy. The pharmacist enters the prescription in a computer and prints out the labels. A self-adhesive label can be attached to the pharmaceutical pig 10 in a conventional fashion. In the alternative, a label can be attached to the pharmaceutical pig with the flexible sleeve (not shown), without the need for adhesives. A separate label is affixed to a safety syringe or a conventional syringe. The syringe 83 is filled with a radiopharmaceutical in accordance with the prescription. The filled syringe 83 is assayed. In other words, the activity of the radiopharmaceutical in the syringe 83 is measured in a dose calibrator to verify that it complies with the prescription. The filled syringe 83 is put in the pharmaceutical pig 10 and then closed. The pharmaceutical pig 10 is wipe tested for contamination. If the pharmaceutical pig 10 passes the wipe test, it is placed in a delivery container. The delivery containers used by some Mallinckrodt Inc. pharmacies have interior padding of rubber foam. Several pharmaceutical pigs 10 may be placed in a single delivery container. Before leaving the radiopharmacy, the delivery container and the pharmaceutical pigs 10 are wipe tested and surveyed. If the delivery container passes, a DOT label is affixed to the outside of the delivery container and it is delivered to a medical facility. The pharmaceutical pigs 10 are then opened and the syringe 83 is placed in an injection shield. The radiopharmaceutical is administered to the patient. The delivery case with the pharmaceutical pigs 10 and used syringes 83 are then returned to the radiopharmacy. The syringe 83 is removed from the pharmaceutical pig 10 and placed in a disposal bin. The pharmaceutical pig 10 is then washed and dried. The pharmaceutical pig 10 is then ready to be reused. Method of Producing the Pharmaceutical Pig 10 This involves first molding the base shielding element 54 by pouring molten, nuclear shielding, material into a first mold (not shown). The preferred substance is lead, as opposed to tungsten or metallic-filled polymers, due to cost considerations and ease of molding. When the base shielding element 54 has solidified, the base shielding element 54 is then placed into an injection molding machine (not shown). The polymer material, e.g., polycarbonate resin, is then injected and flows into a third mold, having a mold cavity, which surrounds the base shielding element 54. After an application of temperature and pressure, a solidified elongate base 12 is released from the mold. This elongate base 12 includes the base shielding element 54, which is now completely enclosed by a base shell 76. The base shell 76 includes an inner base shell portion 80 that is adjacent to the needle 87 and barrel 86 of the syringe 83 and an outer base shell portion 78 that forms the outer surface of the elongate base 12. In the same manner, the cap shielding element 48 is created by pouring molten, nuclear shielding, material into a second mold (not shown). As with the base shielding element 54, the preferred substance is again lead. When the cap shielding element 48 has solidified, the cap shielding element 48 is placed into an injection molding machine (not shown). The polymer material, e.g., polycarbonate resin, is then injected and flows into a fourth mold, having a mold cavity, which surrounds the cap shielding element 48. After an application of temperature and pressure, a solidified elongate cap 14 is released from the mold. This elongate cap 14 includes the cap shielding element 48, which is now completely enclosed by the cap shell 70. The cap shell 70 includes an inner cap shell portion 74 that is adjacent to the plunger 85 of the syringe 83 and an outer cap shell portion 72 that forms the outer surface of the elongate cap 14. Although a preferred embodiment of the pharmaceutical pig 10, a method of use of the pharmaceutical pig 10 and a method of production for the pharmaceutical pig 10 have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it is understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit for the invention as set forth and defined by the following claims.
041522877	description	DETAILED DESCRIPTION OF THE INVENTION In the process of this invention, concentrated highlevel wastes are continuously injected into a fluidized bed of glass frit or similar material which serves as a reaction site for the decomposition, dehydration, and calcination of the wastes to solid oxides, water vapor, and decomposition gases. The solid oxides are calcined on the glass frit, which is present in the fluidized bed, and the coated material is continuously removed via elutriation and/or bed overflow. The glass frit bed material acts as diluent for the radioactive calcine being formed in the reactor and, thus, reduces the decay heat problem which would otherwise result from high inventory of fission products in the bed. The use of a non-radioactive bed material permits a wide range of waste compositions, including those relatively high in sodium concentrations, to be calcined without caking. The invention involves creating a heated fluidized bed of glass particles fluidized by a gaseous medium such as air, nitrogen, or steam. Heated air is used to pre-heat the system until the bed reaches the autoignition temperature of kerosene, at which time kerosene is introduced through a spray system. Other means for heating the bed, such as with electric heaters or circulating fluids, would also suffice. The waste material is atomized with a gas and sprayed into the fluidized bed which is operated at temperatures sufficiently high to decompose any unstable salts in the radioactive material, forming principally oxides, but below the melting temperature of the bed material. The temperature may vary between about 300.degree. C. and 1200.degree. C. but generally will be between about 350.degree. C. and 700.degree. C. The atomized waste solution, which is mostly metallic nitrates and nitric acid, is dehydrated and decomposed to metallic and fission product oxides, which coat or are intimately mixed with the bed particles and gaseous products. The gaseous products and entrained particles are swept from the reaction zone with the fluidizing gas. As in known fluidized bed processes, the glass frit bed material is continuously added to the bed to replace the bed material which is constantly removed by elutriation and/or bed overflow. Bed material is added to adjust the mean diameter of the bed material to between about 100 to 400 microns. The use of the non-radioactive glass frit material as the bed material insures a low bed inventory of heat producing fission products. The calcined material which is entrained with the gases exiting the reactor is filtered from the gases and together with the calcine, which overflows from the reactor, is introduced to a melter wherein the calcine-containing glass frit is melted. The melt is then poured into a receptacle, degassed, and allowed to solidify or is further processed, for example, into glass beads. Alternatively, the mixture may be melted directly in the receptacle, which is later allowed to cool. The practice of the process is described in detail with reference to the figure in which the number 10 generally represents the vessel for conducting a fluidized bed process. The smaller diameter or constricted portion 11 contains the particulate medium 32 forming the fluidized bed and the larger idameter in the disengaging portion 12 which is substantially free of the fluidized bed. Portion 11 is heated by the combustion of fuels such as hydrogen, kerosens, butane, natural gas or other hydrocarbon fuels or, alternatively, by external heating, not shown, such as coiled electric resistance wiring placed adjacent to portion 11. In operation, fluidizing gas, such as air, is introduced into the portion 11 through line 13 which is connected to source 22 of the fluidizing gas. Fuel, such as kerosene, is introduced in the atomized form into portion 11 through line 14 which is connected to source 23 of the fuel. An oxidant, such as oxygen is introduced into portion 11 either through line 14, line 15 or through an alternate line not shown. The liquid waste is introduced in an atomized form to portion 11 of reactor 10 through line 15 which is connected to source 24 of the radioactive waste feed. The radioactive waste feed is atomized by introducing an atomizing gas from source 33 through line 34 which is connected with conduit 15. Alternatively, the waste feed may be injected under pressure through a spray nozzle. Intermittent or continuous withdrawal of the larger particles which settle to the bottom of portion 11 is conducted through line 19. Overflow line 18 provides a means for removal of a portion of the calcine material from the fluidized bed. The expanded portion 12 of reactor 10 is a disengaging portion which is of greater diameter than the cross-sectional areas of the lower portion 11 to permit disengaging particles from the gases. Gases and entrained particles exit reactor 10 by way of line 17 to the gas-solid separtor 35. Separator 35 is arranged for gas removal with filters 20 serving to retain any fine solids being carried with the gaseous medium exiting reactor 10 through line 17. The gas filters may be any convenient filter such as sintered metal filter elements with an nominal 3 micron retention capability or other gas-solid separators. The solid particles removed from the gaseous medium exiting reactor 10 are removed from separator 35 through line 26. Line 18 and line 19 from reactor 10 are interconnected with line 26 such that the solid particles overflowing from portion 11 through line 19 are intermixed in line 26 with the solid particles from separator 35 and the mixture is then introduced into melter 27. The calcine-coated glass bed material is melted in melter 27. The melt is then removed from melter 27 through line 36 to a receptacle 28 wherein the melt is allowed to solidify. In the event of the loss of fluidization, valve 29 would permit the flow of bed material through line 30 into receiver receptacle 31. In the alternative, line 30 could be connected to the melter 27. Instead of using a separate melter, the receptacle 28 may be heated to a temperature sufficient to melt the glass frit. In the practice of this invention, the fluidizing gases pass into portion 11 at a velocity sufficient to effectively fluidize the material to desired level by known art means. In general, the fluidizing gas is introduced at a controlled flow rate of about 0.9 to about 1.1 feet per second. An initial charge of particles having a size range of about 100 to 600 microns form the bed which is easily fluidized by a fluidizing medium. The bed material at start-up may be other than glass frit, such as alumina or silica, if temperatures higher than the melting point of the glass frit would be produced upon ignition of the fuel. Once operating temperature of the fluid bed is attained, glass frit would be added to replace the original bed material. The feed solution containing the radioactive waste is fed in atomized form into the fluidized bed at a rate appropriate to the calcination capacity of the calciner. When the radioactive waste material calcines on the particles in the fluidized bed, the particles are withdrawn from the fluidized bed at a rate controlled by the operator of the process. The glass frit particles forming the fluidized bed can be of various glass compositions. The glass should be selected in order to provide the characteristics of the end product desired. Generally, borosilicate glass frit is the preferred material for forming the fluidized bed. Since the invention is directed to the calcination of liquid waste containing radioactive materials, the fluidized-bed reactor for such a process must be mounted in a shielded space with a controlled atmosphere and equipped with remote controls for handling the materials. Various known materials for constructing fluidized bed reactors may be used for construction of reactor 10. Novel equipment design is not required for conducting the process of this invention. The advantages of utilizing glass material as the bed material in a fluidized bed for the calcination of radioactive wastes include reducing decay heat removal problems due to reduced inventory of fission products, simplifying particle size and bed level control, eliminating mechanical equipment for mixing calcined waste and glass frit, and permitting a broader range of radioactive waste materials to be handled. In this process, the ratio of glass to waste material may be varied as desired to meet operating and product form specification. Preferably, the ratio of bed material to waste material to be calcined should be from about 1.5 to 1 to about 5 to 1. In one embodiment of the invention, the calcining vessel is a 6.75-inch square fluidized bed section with a 9-inch square disengaging section. A 12-inch diameter filter chamber, containing seven 36-inch long by 2.3-inch diameter sintered-metal filters, is used to remove entrained fines from the process off-gas. The filters are blown back periodically by a pulse of high pressure air to disengage the particulate matter. The filtered off-gas is then passed through a condenser and scrubber system for cleanup. During operation of this invention, the bed of borosilicate glass frit of about 300 microns is fluidized while process heat is supplied by the combustion of air and kerosene directly in the bed. Waste feed is introduced through an air-atomized nozzle and the calcination reaction occurs. Bed material is continuously added. A temperature of 500.degree. C. is maintained in the bed. The calcine-coated particles are permitted to overflow and/or elutriate from the bed to maintain the proper bed inventory. The rate of bed solids addition is dependent on the glass forming step and needs to be in an excess of about 1.5 parts glass bed material to 1 part calcine. The calcine product ranges from about 100 to 400 microns in mean diameter. The size of the calcine product is controlled by the rate of addition of the bed material, varying the feed rates, adjusting the atomizing gas rates, and varying the rate the bed material is removed from the reactor. Having described above a preferred embodiment according to the present invention, it will occur to those skilled in the art that modifications and alternatives to the disclosed structure and process may be implemented within the spirit of the invention. It is accordingly intended to limit the scope of the invention only as indicated in the following claims.
	abstract	The present invention relates to solar absorptive coatings including a ceramic material. In particular, the coatings of the invention are laser-treated to further enhance the solar absorptivity of the material. Methods of making and using such materials are also described.
	summary
	summary
051805448	abstract	In the field of commercial nuclear reactors, there is an increasing demand for long-life control blades in order to meet the requirements of higher economy and reduction in the disposal of radioactive wastes. A control blade proposed by the invention stands a long use by virtue of the use of a long-life neutron absorber which is typically made of hafnium. Despite the use of hafnium which has a large specific weight (13.3 g/cm.sup.3), the size, shape and weight of the control blade are substantially the same as those of conventional control blades which employ boron carbides B.sub.4 C as the neutron absorber, so that the control blade can be back-fitted in existing boiling water reactors without difficulty. The control blade of this invention is a flux-trap-type control blade in which long-life neutron absorber plates or sheets are arranged to oppose each other in the thicknesswise direction of the wing within the sheath plate such that a water gap is preserved between the opposing neutron absorber plates, so that the weight of the hafnium, which occupies most part of the total weight of the control blade, is reduced by an amount corresponding to the volume of the water gap. The thickness of the neutron absorber plates or sheets is increased at the upper portion of the control blade where the neutron exposure is specifically high and where a large neutron absorption power or capacity is required for ensuring a sufficient reactor shut-down margin, while the thickness is reduced in other portions so as to increase the size of the water gap. In consequence, the weight of the control blade incorporating heavy hafnium as the neutron absorber is reduced almost to the same level as that of ordinary control blades, without being accompanied by any reduction in the reactivity worth.
	abstract	An apparatus for holding radioactive objects includes a base and a central pillar extending upwardly between a bottom end coupled to the base and a top end above the base. A plurality of inner segments are spaced around the central pillar, and a plurality of outer segments are spaced around the inner segments to form pairs. The inner segments, the outer segments and the central pillar may be coupled together to permit limited radial movement of at least one of the segments of each pair. Each pair may define a generally vertical, object-receiving channel arranged between the inner and outer segment of the pair. The segments of each pair may be adapted to bear against an object in the channel of the pair to laterally restrain the object and facilitate heat transfer from the object.
	claims	1. A passive core decay heat transport system for water cooled reactors comprising a device in a reactor core, wherein the device comprises:at least one coolant channel containing a fuel assembly;at least one collet joint connecting a fuel in the fuel assembly to a shield plug;at least one thermo-siphon containing a liquid metal for transporting of decay heat from the fuel;at least one other thermo-siphon containing a liquid metal for transport of the decay heat from the at least one thermo-siphon; andat least one assembly of heat dissipating fins for transport of the decay heat from the at least one other thermo-siphon to an ultimate heat sink with atmosphere air;wherein thermal expansion of the liquid metal in the at least one thermo-siphon and the at least one other thermo-siphon establishes a conductive heat transfer path and a convective heat transfer path and transfers the decay heat from the fuel to the at least one thermo-siphon, and the at least one thermo-siphon transports the decay heat to the at least one other thermo-siphon and then to the at least one assembly of fins, whereby the at least one assembly of fins dissipates the decay heat by natural circulation of air within the passive core decay heat transport system into an atmospheric air. 2. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the fuel assembly is coupled to at least one lower end fitting connecting the fuel assembly to the coolant channel. 3. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the shield plug provides shielding from radiation and guides a flow within the at least one coolant channel. 4. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, further comprises at least one seal plug coupled to the at least one collet joint for pressure sealing a water coolant. 5. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the at least one assembly of heat dissipating fins comprises:an isolation enclosure in a reactor closure deck;a flow guide;at least one inlet duct connected to the at least one assembly of fins;at least one outlet duct;a means to connect to a containment; andat least one air cooling duct surrounding the containment for cooling hot air from the at least one assembly of fins;wherein the conductive heat transport path and the convective heat transport path are activated by the melting of a metal to create the liquid metal, which transfers the decay heat to the ultimate heat sink in closed circuit, through the conductive heat transport path and the convective heat transport path the at least one assembly of heat dissipating fins, the flow guide, the inlet duct, the outlet duct, the containment, and the cooling duct; andwherein the at least one assembly of heat dissipating fins communicated with external air for cleansing and initiating the passive core decay heat transport system. 6. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the at least one assembly of heat dissipating fins may have either of a rectangular, a circular or a spiral configuration. 7. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the at least one assembly of heat dissipating may be detachable or compact staggered. 8. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein the at least one assembly of heat dissipating fins are made of a material suitable for an operating temperature of about 300° C. or more. 9. The passive core decay heat transport system for water cooled reactors as claimed in claim 1, wherein a metal coolant of lead is adapted to pass the decay heat from the reactor core to the ultimate heat sink. 10. A method for passive core decay heat transport in the passive core decay heat transport system for water cooled reactors of claim 1 comprising:i. melting of metal due to rise in temperature of the fuel above the melting point of the metal;ii. activation of the conductive heat transport path and the convective heat transport path due to the melting of the metal;iii. transfer of the decay heat by the conduction heat transfer path and the convective heat transfer path between the fuel assembly, the at least one thermo-siphon and the at least one other thermo-siphon;iv. transfer of the decay heat from the at least one other thermo-siphon to the at least one assembly of heat dissipating fins; andv. transfer of the decay heat by the air from the at least one assembly of heat dissipating fins to the ultimate heat sink. 11. The method for passive core decay heat transport for water cooled reactors as claimed in claim 10, wherein the metal is lead. 12. The method for passive core decay heat transport for water cooled reactors as claimed in claim 10, wherein a metal coolant passes the decay heat from the fuel to the ultimate heat sink. 13. The method for passive core decay heat transport for water cooled reactors as claimed in claim 10, wherein the method is operated passively. 14. A passive core decay heat transport device for water cooled reactors comprising:at least one lower end fitting coupled to a fuel assembly producing heat;at least one coolant channel containing the fuel assembly surrounded by primary water coolant to cool a fuel within the fuel assembly;at least one thermo-siphon containing liquid metal for transport of the heat;at least one shield plug for radiation shielding and guiding a flow within the at least one coolant channel;at least one collet joint connecting the fuel in fuel assembly to the shield plug;at least one other thermo-siphon containing liquid metal for transport of the heat; andat least one seal plug coupled to at least one assembly of heat dissipating fins, wherein the at least one seal plug comprises at least one of the at least one collet joints coupled to the at least one other thermo-siphon;wherein the fuel assembly transfers the heat to the at least one thermo-siphon using a conductive heat transfer mode and a convective heat transfer mode, and the at least one thermo-siphon transfers the heat to the at least one other thermo-siphon and then to the at least one assembly of fins, which results in cooling of the reactor core by natural circulation of air in closed circuit within the passive core decay heat transport device into an atmospheric air.
	abstract	An ignition system has a plurality of spark igniters for the recombination of hydrogen in a gas mixture. The ignition system provides and ensures reliable early ignition of an ignitable gas mixture, even in the case of comparatively fast gas displacement. Each spark igniter is, according to the invention, configured as a high-speed igniter with an operating frequency in excess of about 10 Hz. In order to ensure reliable ignition of the ignitable gas mixture both in the event of a temporary failure of external units, and when the ignition system has a particularly long operating time, the spark igniters are advantageously connected together in groups for supplying them with energy. Each group of spark igniters is connected to an intermediate energy store common to them, and the intermediate energy stores are connected to a central energy supply unit.
047972483	abstract	During the dismantling of a nuclear reactor fuel assembly, there is a simultaneous gripping of all the rods (a) arranged in square grid form in said assembly using a device (10) which effects a clamping or locking at the end of the rows of rods. For this purpose, device (10) has passageways (26) penetrated by the ends of two adjacent rows of rods (a). In said passage ways are trapped mobile members (34, 34') arranged in such a way that each rod is placed between two adjacent members. By applying a locking force on the mobile end members in each passageway (26), each rod is gripped between two members (34, 34'). Preferably, the mobile members (34, 34') are provided with abutments limiting the locking or clamping force individually applied to each rod. For filling the gaps of the grid of rods (a) corresponding to the locations occupied by the guide tubes in the assemblies, rollers (78) are placed in the passageways (26) at the corresponding locations.
	summary
	description	FIG. 1 and FIG. 2 of the accompanying drawings illustrate an x-ray technique-based nonintrusive inspection apparatus 8 according to an embodiment of the invention. The inspection apparatus 8 includes a support frame 10, a loading tunnel section 12, an inspection tunnel section 14, an unloading tunnel section 16, a loading conveyor apparatus 18, and inspection conveyor apparatus 20, an unloading conveyor apparatus 22, first, second, third and fourth shielding arrangements, 24, 26, 28 and 30 respectively, a stationary x-ray line scanner subsystem 32, a rotating CT scanner subsystem 34, and a controller 36. The support frame 10 includes a base frame 38 and an arch 40 which arches in a plane perpendicular to the drawing and which is secured to the base frame 38 on opposing sides of the arch 40. The x-ray line scanner subsystem 32 is mounted on one side of the arch 40 and the CT scanner subsystem 34 is mounted to the arch 40 for rotation in a plane perpendicular to the drawing on a side of the arch 40 opposing the x-ray line scanner subsystem 32. Referring now in particular to FIG. 2, each tunnel section 12, 14 or 16 has a respective first end 42 and a respective second end 44 opposing the first end thereof. The inspection tunnel section 14 is located in line after the loading tunnel section 12 so that the second end 44 of the loading tunnel section 12 is adjacent the first end 42 of the inspection tunnel section 14. The unloading tunnel section 16 is located in line after the inspection tunnel section 14 so that the second end 44 of the inspection tunnel section 14 is located adjacent the first end 42 of the unloading tunnel section 16. All the tunnel sections 12, 14 and 16 are mounted to the base frame 38. Each conveyor apparatus 18, 20 or 22 is located within a respective tunnel section 12, 14 or 16. Each conveyor apparatus 18, 20 or 22 includes a respective front conveyor roller 46 near a respective first end 42 of a respective tunnel section 12, 14 or 16, a respective rear conveyor roller 48 near a respective second end 44 of a respective tunnel section 12, 14 or 16, and a conveyor belt 50 which runs over the conveyor rollers 46 and 48 and a supporting bed (not shown). Although not shown in FIG. 2 so as not to obscure the drawing, it should be understood that each conveyor roller 46 and 48 of each conveyor apparatus 18, 20 and 22 is rotatably mounted to a respective bracket assembly and that each bracket assembly is secured to the base frame 38. It should also be understood that one of the conveyor rollers 46 or 48 of each conveyor apparatus 18, 20 and 22 is rotated by a respective motor which is mounted to the base frame 38 but which is not shown in FIG. 2 so as not to obscure the drawing. Each shielding arrangement 24, 26, 28 and 30 includes a respective curtain roller 54 and a respective radiation resistant curtain 56 secured to the curtain roller 54. Although not shown in FIG. 2 so as not to obscure the drawing, it should be understood that each curtain roller 54 is rotatably mounted to a respective support structure and that each support structure is secured to the base frame 38. It should also be understood that each curtain roller 54 is rotated by a respective motor which may also be mounted to the support structure but which is not shown in FIG. 2 so as not to obscure the drawing. The curtain rollers 54 are positioned so that each curtain 56 is located near an end 42 or 44 of one or more of the tunnel sections 12, 14 and 16. Rotation of the curtain roller 54 in one direction causes the curtain 56 to be rolled from the curtain roller 54 which causes the curtain 56 to drop, and rotation of the curtain roller 54 in an opposite direction raises the curtain 56 by rolling the curtain 56 onto the curtain roller 54. When the curtain 56 is raised, the curtain 56 is moved into an xe2x80x9copen positionxe2x80x9d wherein the end or ends 42 or 44 are open, and when the curtain is dropped the curtain is moved into a xe2x80x9cclosed positionxe2x80x9d wherein the curtain 56 doses the end or ends 42 or 44. For example, when the curtain 56 of the first shielding arrangement 24 is moved into its open position, the first end 42 of the loading tunnel section 12 is open, and when the curtain 56 of the first shielding arrangement 24 is moved into its closed position, the first end 42 of the loading tunnel section 12 is closed. Similarly, when the curtain 56 of the second shielding arrangement 26 is moved into its open position, the second end 44 of the loading tunnel section 12 is in communication with the first end 42 of the inspection tunnel section 14, and when the curtain 56 of the second shielding arrangement 26 is moved into its open position, communication between the loading and inspection tunnel sections 12 and 14 is substantially closed off. Similarly, when the curtain 56 of the third shielding arrangement 28 is moved into its open position, the second end 44 of the inspection tunnel section 14 is in communication with the first end 42 of the unloading tunnel section 16, and when the curtain 56 of the third screening arrangement 28 is moved into its closed position, communication between the inspection and unloading tunnel sections 14 and 16 is substantially closed off. Similarly, when the curtain 56 of the fourth shielding arrangement 30 is moved into its open position, the second end 44 of the unloading tunnel section 16 is open, and when the curtain 56 of the fourth shielding arrangement 30 is moved into its closed position, the second end 44 of the unloading tunnel section 16 is closed. Detectors (not shown) are positioned to detect the positioning of each curtain 56 independently. More detectors (not shown) are positioned to detect the positioning, speed and acceleration of each conveyor belt 50 independently. More detectors (not shown) are positioned to detect the positioning of containers at various locations within the inspection apparatus 8. The controller 36 is in communication with the detectors. A disk or other computer readable medium may be provided on which an executable program is stored. The controller 36 may, for example, be a computer which is capable of reading the program on the disk and may include memory in the program is stored. The program, once executed may automatically synchronize movement of the curtains 56 and the conveyor belts 50 in a manner which is generally referred to as xe2x80x9cradiation lockingxe2x80x9d. Radiation locking is further described hereinbelow with reference to FIG. 3a to FIG. 3j. The controller 36 also controls other aspects of movement of containers through the inspection apparatus 8 which are further described hereinbelow with reference to FIG. 4a(i) to FIG. 4c(ii). It can generally be noted that this stage that radiation locking provides adequate shielding of x-ray radiation from people that may be located in an area around the inspection apparatus 8. The controller 36 controls power supplied to the motors which drive the conveyor apparatus 18, 20 and 22 so as to control the positioning, speed and acceleration of the conveyor belts 50 of the conveyor apparatus 18, 20 and 22. The controller 36 also controls power supplied to the motors which drive the curtain rollers 54 of the first, second and third shielding arrangement 24, 26, 28 and 30 so as to control the positioning, speed and acceleration of the curtain rollers 54 of the first, second and third shielding arrangement 24, 26, 28 and 30. One advantage of the inspection apparatus 8 illustrated in FIG. 2 is that, because of adequate shielding due to radiation locking, there is no need for locating the conveyor apparatus 18, 20 and 22 so that they define an elaborate undulating pathxe2x80x94the conveyor belts 50 are all linearly aligned with one another, and are located within the same horizontal plane (if, of course, the inspection apparatus 8 is located on a horizontal floor). When a technician has to enter any one of the tunnel sections 12, 14 or 16, the technician may easily enter the tunnel section without the need for the technician to climb up an inclined conveyor apparatus, as is often the case in certain prior art apparatus. A further advantage of the fact that the conveyor belts 50 are all linearly aligned is that the height of the overall apparatus can be minimized. In one example the inspection apparatus 8, ones enclosed by a housing, has an overall height of about 223 centimeters. A further advantage is that the maximum speed of objects passing through the inspection apparatus 8 is not constrained by the existence of discontinuities in the belt path. A further advantage of the inspection apparatus 8 is that the curtains 56 are xe2x80x9cactive curtainsxe2x80x9d in the sense that each curtain 56 opens to allow for a container to pass 56 without obstruction by the curtain 56. The curtain 56 does therefore not create a volume of xe2x80x9cdead spacexe2x80x9d by lying on top of the container. Larger objects can therefore be moved into a respective tunnel section 12, 14 or 16 although each conveyor apparatus 18, 20 or 22 may have a smaller footprint. Larger containers are typically about 110 centimeters in length and in one example the loading tunnel section 12 has a length of about 135 centimeters and the unloading tunnel 16 has a length of about 135 centimeters. Because dead space is minimized, the overall length of the apparatus is thus decreased. Active curtains also have the advantage that they may allow for passing through of heavier containers, which may for example be as much as one meter in height, but that very light weight containers may also pass through without being obstructed, there being no absolute minimum weight requirement for passing through the active curtains. Larger light objects in particular may pass through easier than through prior art passive curtains. It should also be noted that the x-ray line scanner subsystem 32 and the CT scanner subsystem 34 operate within the same tunnel section, namely the inspection tunnel section 14, without an intermediate radiation resistant curtain or other shielding device. By locating the x-ray line scanner subsystem 32 and the CT. scanner subsystem 34 within the same tunnel section, the overall length of the inspection apparatus 8 is reduced. As will be described in more detail hereinbelow, collimators prevent, or limit, interference between x-rays of the x-ray line scanner subsystem 32 and the CT. scanner subsystem 34. Furthermore, it should be noted that the x-ray line scanner subsystem 32 and the CT scanner subsystem 34 are both mounted to the same upwardly extending support structure, namely the arch 40. By mounting the x-ray line scanner subsystem 32 and the CT scanner subsystem 34 both to the same support structure, the orientation of the x-ray line scanner subsystem 32 and the CT scanner subsystem 34 relative to one another can be more accurately controlled. In particular, the x-ray line scanner subsystem 32 may scan in a first plane and the CT scanner subsystem 34 may scan in a second plane which is parallel to the first plane to a much tighter tolerance. Parallelism between the first and second planes is important because it greatly reduces the complexity of software used for coordinating images received from the x-ray line scanner subsystem 32 and the CT scanner subsystem 34. It should also be noted that the same conveyor belt, namely the conveyor belt 50 of the inspection conveyor apparatus 20, transports containers while being scanned respectively by the x-ray line scanner subsystem 32 and the CT scanner subsystem 34. There is thus no transition from one conveyor belt to another between the x-ray line scanner subsystem 32 and the CT scanner subsystem 34. Because of the use of a single conveyor belt for transporting containers from the x-ray line scanner subsystem 32 to the CT scanner subsystem 34, the orientation and predictability of positioning of the containers are insured. As will also be evident from the description that follows, many features of the inspection apparatus 8 provide for high speed inspection of containers. The features providing for high speed inspection of containers in combination generally make provision for inspection of at least 600 containers per hour. The concept of radiation locking is now described by way of an example illustrated in FIG. 3a to FIG. 3j. In the description that follows, the curtain of the first shielding arrangement 24 is referred to as xe2x80x9cthe first curtain 56Axe2x80x9d, the curtain of the second shielding arrangement 26 is referred to as xe2x80x9cthe second curtain 56Bxe2x80x9d the curtain of the third shielding arrangement 28 is referred to as xe2x80x9cthe third curtain 56Cxe2x80x9d, and the curtain of the fourth shielding arrangement 30 is referred to as xe2x80x9cthe fourth curtain 56Dxe2x80x9d. (Compare FIG. 2 with FIG. 3a). In the following discussion of FIG. 3a to FIG. 3j it can also be inferred that the confines of the inspection tunnel section 14 are continuously radiated, unless specifically stated otherwise. First, as illustrated in FIG. 3a, a number of closed containers 60, 62 are lined up, utilizing conventional airport conveyor belts, in front of the first curtain 56A. The first curtain 56A is raised. The second curtain 56B remains in a down position so that radiation from the inspection tunnel section 14 is prevented from reaching the loading tunnel section 12. Next, as illustrated in FIG. 3b, a first of the containers 60 is moved through the first end of the loading tunnel section 12 into the loading tunnel section 12. The second curtain 56B remains in a down position. Next, as illustrated in FIG. 3c, the first curtain 56A is lowered, thus xe2x80x9clockingxe2x80x9d the first container 60 between the first curtain 56A and the second curtain 56B and hence the concept of xe2x80x9cradiation lockingxe2x80x9d. Radiation locking merely serves to ensure that the first curtain 56A is down before the second curtain 56B is raised and generally lasts only for a fraction of a second. Next, as illustrated in FIG. 3d, the second curtain 56B is raised. Although radiation from the inspection tunnel section 14 may enter the loading tunnel section 12, the radiation is prevented by the first curtain 56A from leaving the loading tunnel section 12. It can already be seen from the discussions of FIG. 3a to FIG. 3d that at least one of the first curtain 56A and the second curtain 56B is always in a down position, at least when the confines of the inspection tunnel section 14 are radiated. Radiation is therefore prevented from leaving the inspection apparatus from a container entry side. The controller (see reference numeral 36 in FIG. 2) may be programmed so that the line scanner 32 and the CT scanner subsystem 34 are switched off when, for whatever reason, both the first curtain 56A and the second curtain 56B are at least partially open (or when both the first curtain 56A and the second curtain 56B are not entirely closed). Sensors may for example be provided which detect the positioning of the curtains 56A and 56B and which forward the detected information to the controller. Next, as illustrated in FIG. 3e, the first container 60 is moved (utilizing the first and second conveyor apparatus 18 and 20xe2x80x94see FIG. 2) from the loading tunnel section 12 into the inspection tunnel section 14. Once the first container 60 is located entirely within the inspection tunnel section 14, the second curtain 56B is again lowered, as illustrated in FIG. 3f. Next, as illustrated in FIG. 3g, the third curtain 56C is raised and the first container 60 is moved (utilizing the second and third conveyor apparatus 20 and 22xe2x80x94see FIG. 2) from the inspection tunnel section 14 into the unloading tunnel section 16. The fourth curtain 56D remains in a down position so as to prevent radiation, which may enter the unloading tunnel section 16 from the inspection tunnel section 14, from leaving the inspection apparatus through the second end of the unloading tunnel section 16. In the meantime, a second of the containers 62 may be moved into the loading tunnel section 12 in a manner as hereinbefore described with reference to FIG. 3a to FIG. 3d. Further movement of the second container 62 is similar to the movement of the first container 60 as hereinbefore and hereinafter described and should further be evident from the drawings. Once the first container 60 is located entirely within the unloading tunnel section 16, the third curtain 56C is again lowered, as illustrated in FIG. 3h. The first container 60 is thus locked between the third curtain 56C and the fourth curtain 56D, again illustrating the concept of radiation locking, this time after exit of the first container 60 from the inspection tunnel section 14. Again, radiation locking of the first container 60 within the unloading tunnel section 16 may last only for a fraction of a second. As with the first and second curtains 56A and 56B, at least one of the third curtain 56C and the fourth curtain 56D is always in a down position, at least when the confines of the inspection tunnel section 14 are radiated. Radiation is therefore also prevented from leaving the inspection apparatus from a container exit side. The controller (see reference numeral 36 in FIG. 2) may be programmed so that the line scanner 32 and the CT scanner subsystem 34 are switched off when both the third curtain 56C and the fourth curtain 56D are at least partially open. Sensors may for example be provided which detect the positioning of the curtains 56C and 56D and which forward the detected information to the controller. Next, as illustrated in FIG. 3i, the fourth curtain 56D is raised and the first container 60 is moved out of the unloading tunnel section 16 through the second end of the unloading tunnel section 16. The third curtain 56C remains in a down position, thus preventing radiation within the inspection tunnel section 14 from reaching the unloading tunnel section 16. For a complete discussion, FIG. 3j illustrates the inspection apparatus after the fourth curtain 56D is lowered. The second container 62 may at this stage be located within the inspection tunnel section 14. FIG. 3j is thus similar to FIG. 3f. The above described steps may then be repeated for a third and following containers. It should be evident from the aforegoing description of FIG. 3a to FIG. 3j that one advantage of the inspection apparatus is that the confines of the inspection tunnel section 14 can be continuously radiated, i.e. without having to turn off a radiation source accompanied by delay in inspection of containers. Referring briefly to FIG. 3e to FIG. 3g, the container 60 is scanned while moving into (FIG. 3e), while located within (FIG. 3f) and while moving out of (FIG. 3g) the inspection tunnel section 14. The manner in which the container 60 is scanned and certain related features are now described with reference to FIG. 4a to FIG. 4c which correspond to FIG. 3e to FIG. 3g, respectively. In the following description of FIG. 3e to FIG. 3g, detailed aspects relating to software used in the inspection apparatus, are not described in detail since the patents of Peschmann, referenced previously, teaches the general principles and techniques whereby objects of interest, such as explosives hidden in a closed container, are nonintrusively detected utilizing certain existing x-ray technique-based nonintrusive inspection apparatus. The Peschmann patents teach many details of the general and specific implementation of the present invention wherein the x-ray line scanner may be used to form a convention x-ray projection image, and in which software programs residing in the memory of a computer may be used to analyze the x-ray line scanner images, and to identify locations within a container being scanned that may deserve more detailed x-ray technique-based nonintrusive inspection. Peschmann teaches further that upon identifying such locations in the container, the container may be positioned with respect to the imaging plane of a CT scanner subsystem, such that a sequence of cross-sectional images of the container may be acquired at the locations so specified. Peschman further teaches that additional software programs that may reside in the memory of a computer may be used to analyze the cross-sectional images formed by the CT scanner subsystem, and that additional software programs that may reside in the memory of a computer may analyze all of the data available from both the x-ray line scanner subsystem and the CT scanner subsystem to render decision as to the likely presence of an object of interest such as an explosive hidden in the container. As previously mentioned, the x-ray line scanner subsystem and the CT scanner subsystem (reference numerals 32 and 34 in FIG. 2) are located relatively dose to one another. In addition to such a set of general and specific details of implementation provided by the Peschman patents, the present invention now provides particular scanning methods that enable the inspection apparatus 8 to be designed more compactly by permitting imaging planes of the x-ray line scanner subsystem and the CT scanner subsystem to be located closer to one another than would be otherwise possible, while still being capable of achieving a high rate of inspection of containers. What should be understood, however, is that the controller (reference numeral 36 in FIG. 2) is programmed to carry out the steps illustrated in FIG. 4a(i) to FIG. 4c(ii). Referring to FIG. 4a(i), the container 60 is illustrated as it passes from the loading tunnel section 12 into the inspection tunnel section 14. An imaging plane of the x-ray line scanner subsystem is represented by the line 32 and an imaging plane of the CT scanner subsystem is represented by the line 34. The imaging plane 32 of the x-ray line scanner subsystem may be spaced from the second curtain 56B by a distance which is less than the length of the container 60 so that the container 60 starts moving to the imaging plane 32 of the x-ray line scanner subsystem before being entirely located within the inspection tunnel section 14. FIG. 4a(ii) is a view of the container 60, illustrating the container 60 after a first front portion 70 has been moved past the imaging plane 32 of the x-ray line scanning subsystem. Inspection software analyzing the image formed by the x-ray line scanning subsystem represents the first front portion 70 of the container 60, and may at this stage detect a location 72A within the first front portion 70 which may contain an object of interest 72B. Alternatively, the inspection software may determine, based on other rules, that the specific location 72A within the first front portion 70 of the container 60 requires further measurements by the CT scanner subsystem. Acquisition of the x-ray line scanner image continues whenever the container progresses past the imaging plane 32 of the x-ray line scanner subsystem. This image acquisition does not necessarily require the container to move continuously, nor does it necessarily require the container to move at a constant speed or in a single direction. Once the location 72A has been identified, the speed at which the container 60 moves may then be progressively reduced and the container 60 may be brought to a standstill, as illustrated in FIG. 4b(i) and FIG. 4b(ii), with the location of interest 72A located in the imaging plane 34 of the CT scanner subsystem. Movement of the container 60 and acquisition of the x-ray line scanner image is thus position dependent as opposed to, for example, time dependent. Once the container 60 has stopped, the CT scanner subsystem 34 may scan the location of interest 72A. In the time between identifying the location of interest 72A and the time at which the container is stopped with the location of interest 72A within the imaging plane 34 of the CT scanner subsystem, the x-ray line scanner subsystem may scan a second front portion 74 for of the container 60. A second object of interest 76 may be detected by the x-ray line scanner subsystem 32. Note that the imaging plane 32 of the x-ray line scanner subsystem and imaging plane 34 of the CT scanner subsystem may be spaced from one another by a distance which is less than the overall length of the container 60 so that the container 60 passes through the imaging plane 34 of the CT scanner subsystem before a rear portion 78 of the container 60 passes through the x-ray line scanning plane 32. The container 60 may then be advanced until the second object of interest 76 is located in the imaging plane 34 of the CT scanner subsystem, as illustrated in FIG. 4c(i) and FIG. 4c(ii). The imaging plane 34 of the CT scanner subsystem may be spaced from the third curtain 56C by a distance which is less than the overall length of the container 60 so that the container 60 is already partially located within the unloading tunnel section 16. In the meantime, the x-ray line scanner subsystem 32 may scan the rear portion 78 of the container 60. Note that the container 60 may therefore be moved through the inspection tunnel section 14 without altering the direction of movement of the container 60 relative to the x-ray line scanner subsystem 32 and the CT scanner subsystem 34. Because the first curtain 56B, the imaging plane 32 of the x-ray line scanner subsystem, the imaging plane 34 of the CT scanner subsystem, and the third curtain 56C are spaced from one another by relatively small distances, the overall length of the inspection tunnel section 14 is relatively short. In one example the imaging plane 32 of the x-ray scanner subsystem is spaced from the first curtain 56B by a distance of about 34 centimeters, the imaging plane 34 of the CT scanner subsystem is spaced from the imaging plane 32 of the x-ray line scanner subsystem by a distance of about 87 centimeters, the third curtain 56C is spaced from imaging plane 34 of the CT scanner subsystem by a distance of about 65 centimeters, and the overall length of the inspection tunnel section 14 is therefore about 186 centimeters. FIG. 5 is a perspective view illustrating only the support frame 10 and the CT scanner subsystem 34. The base frame 38 is of monocoque design. Monocoque designs are frequently used, for example, in the design of the hulls of ships and in the design of the bodies of aircraft. In the present example, the base frame 38 generally has the shape of the hull of a ship in that the base frame 38 generally has a channel shape. Other components also form part of the base frame 38 which are similar to a bulkhead of a ship. More specifically, the base frame 38 includes a first monocoque section 82, a second monocoque section 84, and a third monocoque section 86. It should be understood that the first monocoque section 82 is located in the region of the loading tunnel section, the second monocoque section 84 is located in the region of the inspection tunnel section, and the third monocoque section 86 is located in the region of the unloading tunnel section. (See reference numerals 12, 14 and 16 in FIG. 2). The second monocoque section 84 has a base plate 88, first and second side walls 90 and 91 respectively, and first and second end walls 92 and 93 respectively. The side walls 90 and 91 are secured to the base plate 88 and extend upwardly from the base plate 88 and away from one another so that the base plate 88 and the first and second side walls 90 and 91 jointly define a channel shape which is wider at the top than at the bottom, similar to the hull of a ship when viewed in cross section. The end walls 92 and 93 are secured at spaced locations within the channel shape defined by the base plate 88 and the side walls 90 and 91, with edges of the end walls 92 and 93 secured to the base plate 88 and the side walls 90 and 91. Each end wall 93 or 94 is similar to a bulkhead of a ship. The channel shape of the second monocoque section 84 is extremely resistant to bending, and the channel shape together with the end walls 93 and 94 also provide torsional resistance to the second monocoque section 84. Further components may be provided which give added support to the base frame 38. For example, a horizontal deck 95 may be secured to upper edges of the side walls 90 and 91 and the end wall 93, between the end wall 93 and the CT scanner subsystem 34. An additional vertical component 96 may be located on a side of the deck opposing the end wall 93 and have an upper edge secured to the deck, side edges secured to the side walls 90 and 91, and a bottom edge secured to the base plate 88. The deck and the additional vertical component are preferably located in the region of the arch 40 to provide additional rigidity to the base frame 38 in that region. The first and third monocoque section 82 and 86 are similar to one another in design. Only the first monocoque section 82 is further described. It should however be understood that the description of the first monocoque section 82 that follows may also hold true for the third monocoque section 86. The first monocoque section 82 has a base plate 97, first and second side walls 98 and 100, and an end wall 102. The side walls 98 and 100 are secured to the base plate 97 and extend upwardly from the base plate 97 and away from one another so that the base plate 97 and the first and second side walls 98 and 100 jointly define a channel shape which is wider at the top and at the bottom. The base plate 97 and the side walls 98 and 100 are positioned against the side walls 90 and 91 of the second monocoque section 84 and secured thereto. The end wall 102 is secured within the channel shape defined by the base plate 97 and the side walls 98 and 100 and on a side thereof opposing the end wall 93 of the second monocoque section 84. The channel shape of the first monocoque section 82 provides the first monocoque section 82 with resistance to bending and the end walls 93 and 102, together with the channel shape, provide torsional resistance to the first monocoque section 82. The arch 40 has opposing ends 104 and 106 which are secured to the side walls 90 and 91, respectively, of the second monocoque section 84. A bearing (not shown) is located within the arch 40 and the CT scanner subsystem 34 is mounted to a rotational portion of the bearing. In use, the CT scanner subsystem 34 may rotate at a rate of about 120 revolutions per minute. Furthermore, it may be required that the CT scanner subsystem 34 be relatively large. One reason for the size requirement of the CT scanner subsystem 34 is so that larger containers may pass through the CT scanner subsystem 34. The CT scanner subsystem 34 may, for example define an opening 110 which is about 113 centimeters in diameter. Another reason for the size requirement of the CT scanner subsystem 34 deals with the compatibility of the inspection apparatus with conveyor belts found within airports. Airport conveyor belts are typically about one meter wide. If the conveyor belts used within the inspection apparatus are less than one meter wide, additional channeling devices may have to be provided to reorient and channel containers from the airport conveyor belts to the conveyor belt of the loading tunnel section. (See reference numerals 50 and 12 in FIG. 2). For example, containers may be oriented on the airport conveyor belts so as to be oriented such that their longest the dimension lies transverse to the direction of motion of the conveyor belts. With smaller aperture apparatus, channeling devices may then have to be located between the airport conveyor belts and the inspection apparatus to reorient the containers so that their longest dimensions line up in a direction which is more or less parallel to the direction of motion of the conveyor belts so that the containers fit into the inspection apparatus and onto the conveyor belts used in the inspection apparatus. Such channeling devices may add to the overall length of the inspection apparatus and are preferably avoided. The conveyor belts used within the inspection apparatus 8 are therefore preferably about one meter wide, which means that a one-meter wide conveyor belt should be able to pass through the CT scanner subsystem 34. However, the relatively large diameter of the CT scanner, together with its high rotational rate, may cause very strong forces to be applied to the base frame 38. The forces may occur inadvertently due to an unbalanced operating condition arising from any cause. Furthermore, the relatively large diameter of the CT scanner subsystem together with a requirement to accelerate quickly to a high rate of revolution, or decelerate quickly, may cause very strong torsional forces on the base frame 38 when rotation of the CT scanner subsystem 34 is started or stopped. It should be evident from the aforegoing description that the base frame 38 is designed to deal with the high forces which may tend to bend or induce vibration in the base frame 38 when the CT scanner subsystem 34 is in an unbalanced condition, for example, and resist the relatively high torsional forces which act on the base frame 38 when rotation of the CT scanner subsystem 34 is started or stopped. It should be evident from the aforegoing description that the design of the base frame 38 is related to the width of the conveyor belts that are used within the inspection apparatus and that the conveyor belts may be sufficiently wide so that reorienting of containers may be avoided. The containers may thus enter the inspection apparatus while being oriented with their longest dimensions transverse to the direction of motion of the conveyor belts. Because the containers may be oriented in such a manner, a container may therefore be oriented so that the width of the container may be located in a direction approximately parallel to the direction of motion of the conveyor belts, thus potentially permitting container inspection to be completed with a smaller number of CT scanning slices than would be required to complete an equally effective inspection were the container to be oriented differently. FIG. 6 illustrates a portion of the arch 40, the inspection tunnel section 14, the x-ray line scanner subsystem 32, and the CT scanner subsystem 34. The inspection tunnel section 14 includes a first tunnel portion 120, a second tunnel portion 122, and a third tunnel portion 124 which are all nonrotatably mounted to the base frame. (See reference numeral 38 in FIG. 2). The first tunnel portion 120 is located on a side of the x-ray line scanner subsystem 32 opposing the CT scanner subsystem 34 and has a first end 126 which is also the first end 42 of the inspection tunnel section 14, and a second end 128, opposing the first end 126, against the x-ray line scanner subsystem 32. The second tunnel portion 122 is located between the x-ray line scanner subsystem 32 and the CT scanner subsystem 34 and has a first end 130 against the x-ray line scanner subsystem 32, and a second end 132, opposing the first end 130, at the CT scanner subsystem 34. The third tunnel portion 124 is located on a side of the CT scanner subsystem 34 opposing the x-ray line scanner subsystem 32 and has a first end 134 at the CT scanner subsystem 34 and a second end 136, opposing the first end 134, which is also the second end 44 of the inspection tunnel section 14. The x-ray line scanner subsystem 32 is nonrotatably mounted to the arch 40 and includes a partial gantry enclosure 138 and a radiation tube 140. Other features of the x-ray line scanner subsystem 32 are similar to those of the CT scanner subsystem 34 and the CT scanner subsystem 34 is described in more detail hereinbelow. The arch 40 is located around the second tunnel portion 122 and defines a bearing housing 142 around the second tunnel portion 122. The bearing housing 142 is open towards the CT scanner subsystem 34. A bearing 144 is located within the bearing housing 142. The CT scanner subsystem 34 includes a gantry enclosure 148, an x-ray tube 150 which is secured to the gantry enclosure 148, and a ring 152 which is secured to the gantry enclosure 148. The ring 152 extends into the bearing housing 142 and is located on a rotating portion of the bearing 144, thus mounting the CT scanner subsystem 34 rotatably to the arch 40. The CT scanner subsystem 34 rotates around the inspection tunnel section 14. FIG. 7 illustrates the gantry enclosure 148 and the ring 152 of the CT scanner subsystem 34 in more detail. The gantry enclosure 148 includes first and second spaced gantry plates, 154 and 156 respectively, first, second, and third spacers 158, 160, and 162 respectively, a collimator face 164, and a hollow, substantially frustum pyramidal collimator component 165. The first gantry plate 154 has a gantry aperture 166 formed therein and the second gantry plate 156 also has a gantry aperture 168 formed therein. The ring 152 is mounted to the first gantry plate 154 around the gantry aperture 166 in the first gantry plate 154. The collimator face 164 is curved and a hole 170 is formed in the collimator face 164. The collimator component 165 has a base 172 which is slightly larger than the hole 170 in the collimator face 164. The collimator component 165 also has an apex 174 which is smaller than the base 172 and which is formed so as to fit snugly against the x-ray tube. (See reference numeral 150 in FIG. 6). When the base 172 of the collimator component 165 is positioned over the hole 170 and the collimator component 165 is mounted to the collimator face 164, the hole 170 may only be accessed through the apex 174 of the collimator component 165. The first and second gantry plates 154 and 156 are secured to the spacers 158, 160, and 162, with the spacers being located between the gantry plates and around the gantry apertures 166 and 168. The first and second spacers 158 and 160 may be made of a material such as aluminum. The third spacer 162 has a curved shape and may also be made of a material such as aluminum. The collimator face 164 may also be made of a material such as aluminum and is shorter than the third spacer 162. The spacers 158, 160, and 162 and the collimator face 164 are positioned in a trapezium-like shape with the third spacer 162 and the collimator face 164 respectively forming a long side and a short side of the trapezium and the first and second spacers 158 and 160 connecting edges of the third spacer 162 and the collimator face 164 so that the first and second spacers 158 and 160 are spaced closer to one another at the collimator face 164 and further from one another at the third spacer 162. The gantry enclosure 148 is so partially defined by the first and second gantry plates 154 and 156, the spacers 158, 160, and 162, and the collimator face 164. The only areas of the gantry enclosure 148 which are open are due to the gantry apertures 166 and 168 in the first and second gantry plates 154 and 156 respectively, and due to the hole 170 in the collimator face 164. The gantry enclosure 148 includes lead lining which prevents radiation from escaping from the gantry enclosure 148. Lead tiles 176 are mounted to the third spacer 162 within the gantry enclosure 148. Lead plates 178, 180 are also secured to the first spacer 158 and the second spacer 160, respectively, within the gantry enclosure 148, and a lead plate 182 is secured to the collimator face externally of the gantry enclosure 148. A lead liner 184 is also secured to the first gantry plate 154 on a side thereof facing into the gantry enclosure 148, and another lead liner 186 is secured to the second gantry plate 156 on a side thereof facing into the gantry enclosure 148. The lead liners 184 and 186 conform to the internal dimensions of the gantry enclosure 148. In addition, the collimator component 165 is made of the lead. It can thus be seen that the entire gantry enclosure 148 is lead lined and thus resistant to transmission of x-ray radiation. The only areas through which x-ray radiation may pass into or out of the gantry enclosure 148 are the apex 174 of the collimator component 165 and the gantry apertures 166 and 168 in the first and second gantry plates 154 and 156, respectively. Referring again to FIG. 6, the x-ray tube 150 fits snugly on the apex 174 of the collimator component 165. A lead lining 188 covers all inner surfaces of the x-ray tube 150, except an area of the x-ray tube 150 directly over the apex 174 of the collimator component 165. The entire area including the x-ray tube 150 and the collimator component 174 is thus enclosed by lead. It should now the evident that, when the x-ray tube 150 is activated, x-rays are transmitted from the x-ray tube 150 through the collimator component 165 into the confines of the gantry enclosure 148. X-ray radiation may only escape through the gantry apertures 166 and 168 in the first and second gantry plates 154 and 156 respectively. Detector arrays 190 are located within the gantry enclosure 148 on a side of the gantry enclosure 148 opposing the x-ray tube 150. The detector arrays 190 may for example be mounted to the lead tiles 176. Conductors 192 are connected to the detector arrays 190 and extend through the lead tiles 176 and the third spacer 162 so as to provide an electrical connection between the detector arrays 190 and externally of the gantry enclosure 148. The x-ray line scanner subsystem 32 may have a similar construction to the CT scanner subsystem 34 and is lead lined in a manner similar to the CT scanner subsystem 34. Lead linings 196, 198 and 200 are also formed on the internal dimensions of the first, second and third tunnel portions 120, 122 and 124, respectively. Lead linings 196 and 198 of the first and second tunnel portions 120 and 122 are sufficiently dose and overlapping the lead linings of the x-ray line scanner subsystem 32 so that interfaces between the x-ray line scanner subsystem 32 and the first and second tunnel portions 120 and 122 are, in a radiation sense, substantially sealed. The second end 132 of the (stationary) second tunnel portion 122 extends into the gantry aperture 166 in the first gantry plate 154 of the (rotatable) CT scanner subsystem 34. The lead lining 198 on the second tunnel portion 122 is located relatively dose and overlapping the lead liner 184 on the first gantry plate 154 and is separated therefrom only by a gap which is necessary to allow for rotation of the CT scanner subsystem 34 relative to the second tunnel portion 122. And interface between the second tunnel portion 122 and the CT scanner subsystem 34 is thus, in a radiation sense, substantially sealed. Similarly, the first end 134 of the third tunnel portion 124 extends into the gantry aperture 168 of the second gantry plate 156, and the lead lining 200 is located relatively close to the lead liner 186 so that an interface between the third tunnel portion 124 and the second gantry plate 156 is, in a radiation sense, substantially sealed. Referring again to FIG. 2, the internal dimensions of the loading and unloading tunnel sections 12 and 16 are also lead lined. Each curtain 56 is made of a number of layers which are located over one another, including a number of layers containing significant amounts of lead. It should be evident that the entire inspection apparatus 8 is self shielded against in the sense that it effectively attenuates leaking of radiation therefrom and that no extraneous radiation resistant shielding members have to be provided for purposes of radiation containment. Because no extraneous radiation shielding members have to be provided, much less lead lining is requiredxe2x80x94see for example how the x-ray tube 150 is lead lined with the minimal amount of lead. The lead on the CT scanner subsystem 34 does make it somewhat heavier, with corresponding consequences as far as stresses and strains on the base frame are concerned. (See reference numerals 38 in FIG. 5). The base frame is, as described with reference to FIG. 5, however designed to deal with relatively large forces. Although self shielding has been specifically described with reference to an x-ray technique-based nonintrusive inspection apparatus for inspection of containers, the principles of self shielding may also find application in related technologies such as CT scanning of people and other patients. A self shielded CT scanner may be located within a room and be used for inspecting and diagnosing of a patient. Since the CT scanner is self shielded, the patient may be inspected, utilizing the CT scanner, while people are located around the CT scanner within the same room. Furthermore, such self-shielded apparatus would obviate the need and cost of providing special rooms with walls, floors, and ceilings which are capable of providing such radiation shielding FIG. 8 illustrates in end view the CT scanner subsystem 34 and a driving arrangement 210 forming part of the x-ray technique-based nonintrusive inspection apparatus and which is used for rotating the CT scanner subsystem 34. It should be evident from the aforegoing description that the CT scanner subsystem 34 is rotatably mounted to the arch of the support frame. (See for example reference numerals 10 and 40 in FIG. 2 and FIG. 5). The CT scanner subsystem 34 has a circular outer surface 212 which may, for example, be on a ring which may be secured to the gantry enclosure. (See reference numeral 148 in FIG. 6). The driving arrangement 210 includes first, second and third pulleys 214, 216 and 218, respectively, an electric motor 220, and a flexible member 222, such as a flexible belt or a chain, forming a closed loop. The pulleys 214, 216 and 218 are located at various locations around the C.T. scanner subsystem 34. The first and second pulleys 214 and 216 are rotatably mounted to the support frame. (See reference numeral 10 in FIG. 2). The electric motor 220 is also mounted to the support frame and the third pulley 218 is directly coupled and mounted to a shaft of the electric motor 220 so as to be rotated by the electric motor 220 when the electric motor 220 is operated. The flexible member 222 encircles and runs over the first, second and third pulleys 214, 216 and 218, respectively. When stationary, or at any given moment while moving over the pulleys 214, 216, and 218, the flexible member 222 has a first section 224 running from the first pulley 214 to the second pulley 216 in a first direction 226 around and over the circular outer surface 212. The flexible member 222 also has a second section 228 returning from the second pulley 216 over the third pulley 218 back to the first pulley 214 in a second direction 230, which is opposite to the first direction 226, around the circular outer surface 212. In use, when the third pulley 218 is rotated by the electric motor 220, the flexible member 222 progresses over the pulleys 214, 216 and 218, for example in an anti-clockwise direction. Because of progression of the flexible member 222, the CT scanner subsystem 34 is rotated in a clockwise direction. It can thus the seen that a complete revolution of the flexible member 222 does not entirely encircle the CT scanner subsystem 34. Because of the positioning of the flexible member 222, it may be engaged with the circular outer surface 212 without having to be positioned so that it surrounds the CT scanner subsystem 34, the inspection tunnel section, or the inspection conveyor apparatus. The flexible member 222 may thus be installed without obstruction from the CT scanner subsystem 34 itself or obstruction from the inspection tunnel section of the inspection conveyor apparatus which are mounted to the base portion in the vicinity of the CT scanner subsystem 34. (See reference numerals 14, 20 and 38 in FIG. 1). Maintenance due to failure of the flexible member 222 is thus greatly simplified. In other embodiments more pulleys may be used serving various purposes such as tensioning of the flexible member 222, or the flexible member 222 may be driven by a separate device. FIG. 9 illustrates one of the shielding arrangements 24, 26, 28 or 30 of FIG. 2 in more detail. The shielding arrangement 24, 26, 28 or 30 forms part of a larger shielding apparatus which includes support structures 240 which are mounted to the base frame and which form part of the support frame of the x-ray technique-based nonintrusive inspection apparatus of the invention. (See reference numerals 8, 10 and 38 in FIG. 2). Each shielding arrangement 24, 26, 28 or 30 includes, in addition to the curtain roller 54 and the radiation resistant curtain 56, also an electric motor 242, a tensioning roller 244, a flexible sheet 246, and a torsion spring 248. The curtain roller 54 is rotatably mounted between the support structures 240, and the curtain 56, as previously mentioned, is secured to the curtain roller 54 so as to be rolled onto or from the curtain roller 54 upon rotation of the curtain roller 54. The electric motor 242 is also secured to one of the support structures 240. A driving belt 250 couples the electric motor 242 to the curtain roller 54 so that the curtain roller 54 is rotated upon operation of the electric motor 242. The rotational positioning of the curtain roller 54, and therefore also the height of the curtain 56, is also determined by the electric motor 242. The sheet 246 has one portion attached to the curtain roller 54 and a second portion attached to the tensioning roller 244. The sheet 246 is rolled onto the tensioning roller 244. The tensioning roller 244 is also rotatably mounted between the support structures 240. The torsion spring 248 is located between one of the support structures 240 and that tensioning roller 244. The torsion spring 248 is under torsion, i.e. the torsion spring 248 is torsionally biased, thus tending to rotate the tensioning roller 244. The tensioning roller 244 is, however, prevented from rotating because the tensioning roller 244 is connected by the sheet 246 to the curtain roller 54 and the rotational position of the curtain roller 54 is determined by the electric motor 242. It should thus be evident that the sheet 246 is under tension between the curtain roller 54 and the tensioning roller 244 because of the tendency of the tensioning roller 244 to rotate and the predetermined rotational positioning of the curtain roller 54. FIG. 10 illustrates the arrangement of FIG. 9 in end view. The curtain 56 hangs from one side of the curtain roller 54. The tensioning roller 244 is located on the same side of the curtain roller 54 as the side of the curtain roller 54 from which the curtain 56 hangs, with the curtain 56 being located between the curtain roller 54 and the tensioning roller 244. The sheet 246 passes from under the tensioning roller 244 over and onto the curtain roller 54. The sheet 246 therefore extends clockwise around the tensioning roller 244 and anti-clockwise around a portion of the curtain roller 54. The tensioning roller 244 has a tendency to rotate in an anti-clockwise direction 251. Because of the tendency of the tensioning roller 244 to rotate in an anti-clockwise direction, and the connection between the tensioning roller 244 and the curtain roller 54, the curtain roller has a tendency to rotate in a clockwise direction. Rotation of the curtain roller 54 in an anti-clockwise direction results in rolling of the curtain 56 onto the curtain roller 54 and rotation of the curtain roller 54 in a clockwise direction results in rolling of the curtain 56 from the curtain roller 54. The tensioning roller 244 thus tends to roll the curtain 56 from the curtain roller 54. The tensioning roller 244 and the sheet 246 ensure that the curtain 56 is rolled tightly and in a controlled manner onto the curtain roller 54. The tensioning roller 244 and the sheet 246 also ensure that the curtain 56 remains tightly on the curtain roller 54 when rotation of the curtain roller 54 in an anti-clockwise direction is decelerated. The tensioning roller 244 and the sheet 246 also ensure that the curtain 56 remains tightly on the curtain roller 54 when the curtain roller 54 is rotated in a clockwise direction. For example, FIG. 11 illustrates the arrangement of FIG. 10 when the curtain 56 is rolled onto the curtain roller 54 by rotation of the curtain roller 54 in an anti-clockwise direction 252. The sheet 246 is rolled together with the curtain 56 onto the curtain roller 54 with the sheet 246 being located on an outer surface of the curtain 56. Due to the tension present in the sheet 246, the sheet 246 creates a force 254 on the curtain 56 which is radially inward towards the curtain roller 54. Because of the force 254, the curtain 56 is maintained in close contact with the curtain roller 54 and preceding layers of the curtain 56 when the curtain 56 is rolled onto the curtain roller 54. When the curtain roller 54 is rotated in an anti-clockwise direction, the curtain 56 has momentum. When the curtain roller 54 is brought to a halt, after being rotated in an anti-clockwise direction, the momentum of the curtain 56 will tend to lift the curtain 56 from the curtain roller 54 or preceding layers of the curtain 56 on the curtain roller 54. The tendency of the curtain 56 to lift is, however, counteracted by the force 254. When the curtain roller 54 is accelerated in a clockwise direction, lack of momentum of the curtain 56 will attend tend to cause the curtain 56 to lift, which tendency is again counteracted by the force 254. By correctly positioning the tensioning roller 244, the trajectory of the curtain 56 when it rolls off the curtain roller 54 can also be controlled. The trajectory of the curtain 56 is preferably substantially vertically downwardly. Vertical downward movement of the curtain 56 is preferred because waves within the curtain 56 or whiplash-like oscillations of the curtain 56 can so be avoided and the curtain 56 can thus the brought to standstill much quicker. Referring again to FIG. 10, it should also be noted that the curtain roller 54 has an outer surface which has a shape which is generally in the form of a spiral having a step 260. An end of the curtain 56 is secured to an inner portion 262 of the spiral with a edge of the curtain 56 adjacent the step 260. A surface 264 of the curtain 56 opposing the inner portion 262 is substantially in line with an outer portion 266 of the spiral. When the curtain 56 is rolled onto the curtain roller 54, as illustrated in FIG. 10, up to the point where the curtain 56 starts rolling onto itself (the sheet 246 being located between layers of the curtain 56) a smooth transition is ensured. A smooth transition is important because waves within or whiplash-like oscillations of the curtain 56 may be avoided, and the power demanded of the drive motor is made more uniform in time. When the curtain 56 is rolled from the curtain roller 54 a smooth transition is also ensured which, in addition to the positioning of the tensioning roller 244, further prevents waves within or whiplash-like oscillations of the curtain 56. It can thus be seen from the aforegoing description that the curtain 56 may be lowered and raised quickly and in a controlled manner both because of the tensioning roller 244 and the spiral shape of the curtain roller 54. FIG. 12a(i) to FIG. 12c(ii) illustrate a method of making a collimator for a detector array of the CT scanner. (See reference numeral 34 in FIG. 2). FIG. 12a(i) illustrates a die 310 which may be used for injection molding of such a body of a collimator. The die 310 includes a cup 312 and a shape defining element 314. The shape defining element 314 includes a substructure 316 and a plurality of fins 318 which are secured to the substructure 316. The fins 318 define a plurality of septa gaps 320 between them. Referring to FIG. 12a(ii), the shape defining element 314 also includes delimiting portions 322 secured to the substructure 316 on opposing sides of the fins 318. The fins 318 are slightly longer than the delimiting portions 322. FIG. 12b(i) illustrates the die 310 after the shape defining element 314 is inserted into the cup 312. The fins 318 extend all the way to a base of the cup 312. In FIG. 12b(ii) it can be seen that L-shaped support structure gaps 324 are formed between opposing surfaces of the fins 318 and the delimiting portions 322, and between the delimiting portions 322 and the base of the cup 312. In another section through FIG. 12b(i), one will be able to see that the support structure gaps 324 and the septa gaps 320 are in communication with one another. A material is injected into one of the support structure gaps 324 so that the material fills the support structure gaps 324 and the septa gaps 320. The material preferably comprises about 86 percent lead, 3 percent tin, and 11 percent antimony. The lead provides the material with x-ray radiation shielding capabilities, while the purpose of the alloy between the elements is to provide the material with the strength that lead, by itself, lacks. The material is then allowed to set within the die 310 to form a body of a collimator which is then removed from the die 310 as will be further described hereinbelow with reference to FIG. 14. FIG. 12c(i) illustrates the body 330 of the collimator 332. The body 330 has a plurality of septa 334, formed in the septa gaps 320, which are located next to one another. Referring to FIG. 12c(ii), it can be seen that support structures 336 are formed within the support structure gaps 324 and that the septa 334 are secured between and supported by the support structures 336. The support structures 336 include mounting portions 338 which are coplanar with one another, and walls 340 extending from the mounting portions 338 parallel to one another. FIG. 13 is a perspective view of the collimator 332. Registration notches 341 are formed within sides of the mounting portions 338. The registration notches 341 allow for positioning and securing of a plurality of collimators such as the collimator 332 simply, reliably, and accurately in a modular fashion. It can be seen from the aforegoing description that an effective and easy method is provided for forming the body 330 of the collimator 332. More importantly, the body 330 has superior strength characteristics because of the materials used for forming the body and because of the manner in which the septa 334 are secured between the support structures 336. The collimator 332 may be located on a detector array of the CT scanner subsystem (see reference numeral 34 in FIG. 2) wherein the detector array rotates at a relatively large radius. The CT scanner subsystem may, in addition, rotate at a relatively high rate of revolution. The radius of rotation of the detector array, together with the relatively high rate of revolution of the CT scanner subsystem may cause large centrifugal forces to act on the collimator 332. The strength characteristics of the body 330 of the collimator 332 are thus important for dealing with the centrifugal forces. FIG. 14 illustrates in much exaggerated detail an x-ray tube 150 which is used in the CT scanner subsystem (see reference numeral 150 in FIG. 6), and a view of the septa 334 when the collimator 332 of FIG. 12 and FIG. 13 is installed on a detector array (not shown). Each septum 334 has first and second opposed surfaces 342 and 344, respectively, and a center line 346 between the surfaces 342 and 344. The center lines 346 converge towards one another in a direction 348 and meet at the x-ray tube 150. Because of the orientations of the center lines 346 relative to one another, x-rays 350 which are emitted by the x-ray tube 150 may pass through collimator apertures 352 between the septa 334 in a manner wherein the x-rays 350 are correctly collimated. Surfaces 342 and 344 of two of the septa 334 which face one another do, however, not converge in the direction 348. As shown in the drawing, it may be possible that the opposing surfaces 342 and 344 of two of the septa 334 located next to one another may diverge from one another in the direction 348. The reason for the orientations of the opposing surfaces 342 and 344 relative to one another is so that the fins (see reference numeral 318 in FIG. 12b(i)), when the septa 334 are manufactured, may be removed. Each fin will therefore have opposing surfaces which are substantially parallel to one another or which taper towards one another in a direction from the substructure (see reference numeral 316 in FIG. 12a(i)) towards tips of the fins. As mentioned, FIG. 14 is in greatly exaggerated detail. The angles between the center lines 346 of the septa 334 are, in practice, much smaller than indicated in FIG. 14. Removal of the fins is therefore not substantially hampered because of the angles of the center lines 346 relative to one another. In practice, for example, sixteen of the septa 334 may be provided, a lower tip of a first of the septa may be spaced from a lower tip of a sixteenth of the septa by a distance of about 50 millimeters, and an upper tip of the first septum may be spaced from an upper tip of the sixteenth septum by a distance of about 49 millimeters. FIG. 15 illustrates one of the conveyor apparatus 18 or 22 and its interaction with the base frame 38. (Compare FIG. 15 with FIG. 2). Rails 410 are located on opposing sides of the base frame 38. A lever 412 is pivotally mounted to a portion 414 of the base frame 38. Handles 416 are mounted to ends of the lever 412. A pin 418 is secured to the lever 412 intermediate a pivot axis 420 of the lever 412 and one of the handles 416. The conveyor apparatus 18 or 22, in addition to the front conveyor roller 46, the rear conveyor roller 48, and the conveyor belt 50 (compare with FIG. 2), further includes a conveyor slider plate 424 and a number of bracket assemblies 426. The bracket assemblies 426 are mounted directly to the conveyor slider plate 424 and the front and rear conveyor rollers 46 and 48 are, in turn, rotatably mounted between respective sets of the bracket assemblies 426. The conveyor apparatus 18 or 22 as shown in FIG. 15 may be preassembled by a subcontractor. The subcontractor may also tension the conveyor belt 50 of the conveyor apparatus 18 or 22 before the conveyor apparatus 18 or 22 is supplied to another entity which mounts the conveyor apparatus 18 or 22 to the base frame 38. A slot 428 is formed through the conveyor slider plate 424. The slot 428 extends in a direction transverse to the direction of motion of the conveyor belt 50, and therefore substantially parallel to the front and rear conveyor rollers 46 and 48. The arrows 430 indicate mounting of the conveyor apparatus 18 or 22 onto the base frame 38. The conveyor slider plate 424 nestles between and on the rails 410 so as to be movable only in a direction 432 in which the rails 410 extend. The pin 418 is aligned with the slot 428 so that the pin 418 extends through the slot 428 when the conveyor slider plate 424 is located on the rails 410. An operator may move one of the handles 416 so that the lever 412 rotates about the pivot axis 420. Rotation of lever 412 causes rotation of the pin 418 about the pivot axis 420. The pin 418 engages within the slot 428 within the conveyor slider plate 424 so that the conveyor apparatus 18 or 22 is moved backward or forward along the rails 410. The pin 418 also slides along the slot 428 when the lever 412 is rotated. Movement of the pin 418 along the slot 428 is limited by the length and positioning of the slot 428 so that movement of the conveyor apparatus 18 or 22 along the rails 410 is also limited. Although only one of the conveyor apparatus 18 or 22 is shown in FIG. 15, it should be understood that both of the conveyor apparatus 18 and 22, as shown in FIG. 2, have a design similar to that shown in FIG. 15. The conveyor apparatus 20 is rigidly mounted to the base frame 38, so that only the conveyor apparatus 18 and 22 are able to be moved by moving its respective lever 412. In use, the conveyor apparatus 18, 20 and 22 are mounted to the rails 410 in such a manner that adjacent front and rear rollers 46 and 48 thereof are located fairly close to one another. By so locating the to -conveyor apparatus 18, 20 and 22 relative to one another, smooth transition of containers from one conveyor apparatus to another is ensured. It may, however, happen from time to time that parts of containers, such as belts on luggage, become jammed between adjacent ones of the front and rear conveyor rollers 46 and 48 of two of the conveyor apparatus which are located sequentially one after the other. One of the conveyor apparatus 18 or 22 may then be moved away from the conveyor apparatus 20 by moving the handle 416 thereof, so as to part adjacent ones of the front and rear conveyor rollers 46 and 48 of the two conveyor apparatus. The jammed parts of containers can then be released from between the adjacent conveyor apparatus. Ideally, the conveyor apparatus 18 or 22 should not, under normal operating conditions, be able to float freely on the rails 410. An additional mechanism may be provided which may lock the lever 412 releasably into a number of predetermined positions. Other mechanisms may also be provided for controlling movement of the conveyor slider plate 424 along the rails 410, and for controlling the orientation of the conveyor slider plate 424 relative to the rails 410. Such mechanisms are known in the art. FIG. 16 of the accompanying drawings illustrates the inspection apparatus 8 which further includes paneling around all the components heretofore described with the exclusion notably of the controller (see reference numeral 36 in FIG. 2) and the base frame 36. The paneling, in particular, is located around the tunneling which is formed by the loading tunnel section 12, the inspection tunnel section 14, and the unloading tunnel section 16, and around the x-ray line scanner subsystem 32 and the CT scanner subsystem 34. The paneling includes a plurality of contiguous panels 510 which match up with one another and which, together with the base frame 38, define a housing 512 around the other components of the inspection apparatus 8. One of the panels 510A is located at the first end 42 of the loading tunnel section 12. The panel 510A has an entry aperture 514 which is in close proximity to the first end 42 of the loading tunnel section 12. Another one of the panels 510B is located at the second end 44 of the unloading tunnel section 16. The panel 510B has an exit aperture 515 which is in close proximity to the second end of the unloading tunnel section 16. More of the panels 510C and 510D are sliding doors which are slidably mounted to the base frame 38 to provide access to the x-ray line scanner subsystem 32 and the CT scanner subsystem 34. When the panels 510C and 510D are closed, a fairly tight interface 516 is formed between the panels 510C and 510D. From the aforegoing can generally be noted that a housing 512 is relatively airtight. FIG. 17 is a view of the inspection apparatus 8 which further illustrates an air-conditioning apparatus 520 forming part of the inspection apparatus 8. The housing 512 is shown to have an air inlet opening 522 and an air outlet opening 524. The gantry enclosure 148 is also shown together with the ring 152 and the bearing 144 which mount the gantry enclosure 148 rotatably to the arch 40. The air-conditioning apparatus 520 includes an air inlet duct 526, an air-conditioning unit 528, an air supply duct 530, a plenum 532, a radiator 534, and an air return duct 536. The air-conditioning unit 528 is located externally of the housing 512 and includes a fan 538. The plenum 532 is nonrotatably mounted to the support frame of the inspection apparatus (see reference numeral 10 in FIG. 2) and is in the form of a ring which is located around the ring 152. The plenum 532 a located externally of the gantry enclosure 148 next to the first gantry plate 154 of the gantry enclosure 148. The plenum 532 has a recessed shape which is open towards the gantry enclosure 148. A number of air passages 542 are formed through the first gantry plate 154. The (non-rotating) plenum 532 is located over the air passages 542 so that the confines of the plenum 532 are in communication with the confines of the (rotating) gantry enclosure 148. The radiator 534 is mounted on an outer surface of the gantry enclosure 148 and holes (not shown) are formed in the gantry enclosure 148 which place the confines of the gantry enclosure 148 in communication with the radiator 534. Note that no fan is mounted within the gantry enclosure 148. The air inlet duct 526 has one end at atmospheric pressure and another end connected to, and in communication with, the air-conditioning unit 528. The air supply duct 530 extends through the air inlet opening 522 and has one end connected to, and in communication with, the air-conditioning unit 528 and an opposing end connected to, and in communication with, the confines of the plenum 532. The air return duct 536 has one end connected to, and in communication with, the air outlet opening 524 and an opposing end connected to, and in communication with, the air-conditioning unit 528. In use, air flows into the air-conditioning unit 528 when the fan 538 rotates. The air enters the air-conditioning unit 528 substantially at atmospheric pressure and atmospheric temperature. The air then passes through the air-conditioning unit 528. The air-conditioning unit 528 lowers the temperature of the air to substantially below atmospheric temperature. The fan 538 also increases the pressure of the air to above atmospheric pressure. The air is then drawn into the housing 512 through the air supply duct at above atmospheric pressure and below atmospheric temperature. The air then flows through the air supply duct 530 into the plenum 532 from where the air flows through the air passages 542 into the gantry enclosure 148. A window 543 is located between the gantry apertures 166 and 168 so that a confined volume is defined by the window 546, the gantry plates 154 and 156, and the spacer 160. A number of plates (not shown) are located at selected angles around a revolution of the gantry enclosure 148 and extend radially outward so that individual confined volume pockets are defined around a revolution of the gantry enclosure. The air enters selected ones of these pockets through selected ones of the air passages 542, notably a pocket at the radiator 534 and a pocket in which the detectors (190 in FIG. 6) are located. Air then flows from each pocket through holes (not shown) out of the gantry enclosure 148. The air flows from one pocket through some of the holes in the spacer 160 to the radiator 534. The air then passes through the radiator 534. The radiator 534 is used for cooling the x-ray tube (see reference numeral 150 in FIG. 6) and, when operated, is at a temperature substantially above atmospheric temperature. The air is used to cool the radiator 534. When the air flows through the radiator 534, the temperature of the air increases somewhat, but still remains below atmospheric temperature. The air also remains above atmospheric pressure. Referring now to FIG. 16 and FIG. 17 in combination, once the air passes through the radiator 534, the air is located within a volume 540 which is externally of the tunneling provided by the loading, inspection and unloading tunnel sections 12, 14 and 16, respectively, externally of the x-ray line scanner subsystem 32, and externally of the gantry enclosure 148, but still contained within the housing 512. As mentioned, the housing 512 is in close proximity to and therefore seals relatively tightly on the loading and unloading tunnel sections 12 and 16, at least to an extent sufficient to maintain the above atmospheric pressure of the air within the housing 512. As also mentioned, the interface 516 is also relatively airtight. The housing 512, in all other respects, is formed to maintain the above atmospheric pressure within the housing 512. The air then flows from the housing 512 through the air outlet opening 524 and the air return duct 536 back to the air-conditioning unit 528. The air-conditioning unit 528 may control the ratios of air flowing respectively from the air inlet duct 526 and the air return duct 536 so that the air within the volume 540 remains above atmospheric pressure. Because the air within the volume 540 remains above atmospheric pressure, and therefore above the pressure of the air externally of the housing 512, the air may leak slightly from between adjacent panels 510 of the housing 512 in a direction from within the housing 512 to an area around the housing 512. Because of the direction of leaking of air, ingress of dirt, moisture, and other contaminants into the housing 512 may be avoided. The positive pressure within the housing 512 thus protects the components within the housing 512 from dirt, moisture, and other contaminants. It should be evident from the aforegoing description that the temperature of the air in the volume 540 is still below atmospheric temperature, as required for improved, more stable, and more reliable operation of components such as detector arrays which are used within the inspection apparatus 8. What should also be noted from FIG. 17 is the positioning of the fan 538. The fan 538 is located externally of the gantry enclosure 148. The fan 538 is thus protected from gyroscopic forces which may otherwise act on the fan 538 should the fan 538 be located on the gantry enclosure 148. By so locating the fan 538, the gantry enclosure 148 can be rotated at higher speeds that would otherwise be possible. The gantry enclosure 148 can also be made larger without being limited by possible malfunctioning of the fan 538. As previously mentioned, the invention is described by way of example only. In the aforegoing description and example is given of apparatus and a method for inspecting closed containers before being loaded into a loading bay of an airplane. Such use may, for example, be for the detection of explosives within closed containers. It should however be understood that the invention is not to be limited to the inspection of a closed containers before being loaded into a loading bay of an airplane. Various aspects of the invention may for example find application in the detection of contraband and illicit materials generally, applications beyond those linked to aviation, such as rail travel, the inspection of mail or parcels, materials testing and characterization, and the inspection of patients, in particular those applications utilizing CT technology.
052951677	summary	FIELD OF THE INVENTION This invention generally relates to an apparatus which is supported by and transportable along a refueling bridge of a nuclear reactor. In particular, the invention is directed to an apparatus for storing and coupling extension poles used to manipulate a tool at a remote location inside a boiling water reactor and supporting the coupled poles during assembly, transport and manipulation of the tool. BACKGROUND OF THE INVENTION During disassembly and servicing of a boiling water reactor, some activities must be performed underwater at depths of 40 to 60 feet. These activities are typically performed from the refueling bridge which spans the reactor cavity. Hollow, thin-walled poles are frequently used to reach the reactor components. These poles (each about 10 feet long and 2 to 4 inches in diameter) are usually stored on the refueling bridge. In order to reach the desired depth underwater, a number of poles are connected in series until the total length of the assembly is sufficient to allow one end of the assembly to be manipulated while the other end supports the tool at the desired depth. These poles are conventionally assembled on the bridge. Different diameter poles are used, with the larger-diameter poles being for high-torque activities. This system for storing, assembling and manipulating service poles on a refueling bridge suffers from a number of disadvantages. First, in order to reach the desired depth underwater, a number of poles need to be available to be coupled. The poles are usually stored by laying them down on the refueling bridge walkway prior to assembly and after disassembly. Poles stored in this way can obstruct other activities, present a hazard to personnel walking on the bridge, become tangled with ropes and lines, and spread contamination on the refueling bridge. Second, small-diameter, lightweight poles, which are typically used for underwater work, are very flexible and difficult to position when connected in long assemblies. Also, they cannot transmit the significant amount of torque which is required for some tools and operations. The poles also become very contaminated on the inside and are difficult to clean. Third, assembly and disassembly of a multiple-pole assembly requires much handling and holding of the pole sections. Holding and handling the weight of the pole assembly is tiring for operating personnel. During assembly or disassembly of the poles, it is possible for a pole to slip out of the operator's hands and into the cavity. Fourth, when using poles for a torquing operation, either a T-bar or a second person is required to hold the pole steady. Lastly, some underwater servicing operations require three or more people working along side each other in close proximity on the refueling bridge walkway. The close proximity of the workers causes congested working conditions and reduces individual visual observation of the underwater work. SUMMARY OF THE INVENTION The present invention is a service pole caddy system which overcomes the foregoing disadvantages of the conventional apparatus. This service pole caddy system was designed to provide a convenient means to store, assemble and disassemble service poles and to provide an auxiliary platform to perform the underwater work. In addition, the system provides a standard set of poles to perform most of the tasks and eliminates many of the problems historically experienced by servicing crews. In accordance with the preferred embodiment of the invention, the service pole caddy system comprises a rail truck-mounted rigid frame which supports a pole storage caddy, a set of standard service poles, a pole assembly work station and a motorized monorail pole hoist. A detachable auxiliary personnel work platform can be mounted on the rigid frame adjacent to the pole assembly work station. The hoist is used to convey the pole sections back and forth from the storage caddy to the work station for assembly and disassembly as required. The hoist is also used to support the weight of the pole assembly for in-vessel work. The entire rigid frame can be rolled along the refueling bridge to a desired location. The service pole caddy system provides a convenient vertical storage rack for storing service poles away from other servicing activities. The stored poles are easily accessible for assembly. Since the rack is positioned over the pool of coolant inside the reactor cavity, any excess water on the poles drains back into the pool, thereby keeping contaminated liquids off of the refueling bridge. Also, storing the service poles in a dedicated rack hanging off of the refueling bridge avoids the undesirable condition wherein the work area on the bridge walkway becomes cluttered with service poles. The service pole caddy system further comprises a passive pole support and assembly work station having means adapted to couple with a neck on a pole end connector of each of the service poles. In particular, these means comprise a two-position slotted keyway plate. A first position allows the pole to be lowered by the hoist until the next pole connector is lined up in the keyway. The operator then manually pushes the pole into a second position where the neck of the pole can be rested on a tapered support seat. The operator then causes the hoist to slacken, thereby transferring the load of the multi-pole assembly to the keyway plate, and removes the pole handling connector. The next pole is then removed from the caddy and connected to the pole supported by the keyway plate of the assembly station. Without disengaging the hoist from the last-assembled pole, the operator raises the multi-pole assembly to take the load off the keyway plate, pushes the multi-pole assembly until the pole intersecting the keyway is aligned in the first position. The operator then lowers the multi-pole assembly until the neck of the last-assembled (i.e., top) pole is lined up with the keyway and pushes the last-assembled pole into the support (i.e., second) position. This process is repeated until the pole assembly is complete. This feature eliminates the need for any mechanical latches, collars, or clamp devices. The pole assembly cannot be easily dropped, since it is either hooked to the hoist or supported in the assembly station keyway. The pole assembly work station on the service pole caddy system has a guided keyway feature to provide lateral restraint during torquing operations. The pole is vertically located in the guided keyway such that the full body diameter of the pole is within the key. The pole is thus prevented from moving laterally, allowing one-man torquing capability without the use of a T-bar. The service pole caddy system features a detachable auxiliary personnel platform. When used, the platform allows workers to position themselves adjacent to and/or across from each other when performing underwater work. Less congestion and more working room allows more efficient performance with less visual interference around the work area.
046684441	claims	1. In a process for the production of a substantially isotropic spherical fuel or absorber element of high strength for a high temperature reactor by molding a mixture of graphite molding powder containing a resin binder with coated nuclear fuel or absorber particles to a spherical nucleus, pressing on a shell of the same graphite molding powder, carbonizing the resin binder and vacuum calcining at a temperature up to about 2000.degree. C., the improvement comprising employing as the graphite molding powder a mixture of graphitized coke particles having substantially isotropic properties and a hardenable binder resin, first preliminarily pressing from this graphite molding powder at 80.degree. to 120.degree. C. two ellipsoidally shaped shell halves successively in a first cylindrical steel molding die having a smooth ellipsoidal hollowing of the lower die and a smooth ellipsoidally shaped front surface of the upper die adjusted to it, also preliminarily pressing from another portion of the graphite molding power and coated particles likewise at 80.degree. to 120.degree. C. in a second steel molding die which also has smooth surfaces and relative to the shell halves, appropriately ellipsoidally shaped spherical nucleus whereby the pressing is to such an extent that the density of the graphite matrix in the preliminarily pressed nucleus and in the preliminarily pressed shell halves is between 1.1 and 1.4 g/cm.sup.3, then putting together the nucleus and the two shell halves to form an ellipsoidally shaped body and finally completing the molding in the plastic temperature range of the resin binder to form a final sphere and removing it from the mold. 2. A process according to claim 1 wherein there is employed graphitized soft coal secondary pitch coke as the graphite powder and that the density of the preliminary pressed portions is between 1.1 and 1.3 g/cm.sup.3. 3. A process according to claim 2 wherein the resin binder is hardened in the molding die in the final molding process and the molded body is discharged from the die at molding temperature. 4. A process according to claim 1 wherein the resin binder is hardened in the molding die in the final molding process and the molded body is discharged from the die at molding temperature. 5. A process according to claim 4 including the step of preheating the preliminarily pressed portions to a temperature just below the final molding temperature and inserting it in the preheated mold. 6. A process according to claim 3 including the step of preheating the preliminarily pressed portions to a temperature just below the final molding temperature and inserting it in the preheated mold. 7. A process according to claim 2 including the step of preheating the preliminarily pressed portions to a temperature just below the final molding temperature and inserting it in the preheated mold. 8. A process according to claim 1 including the step of preheating the preliminarily pressed portions to a temperature just below the final molding temperature and inserting it in the preheated mold. 9. A process according to claim 8 comprising carrying out the final molding in a floating matrix. 10. A process according to claim 5 comprising carrying out the final molding in a floating matrix. 11. A process according to claim 1 comprising carrying out the final molding in a floating matrix.
046577220	claims	1. An ion accelerating device comprising: a cathode, an anode, said anode comprising tubular conducting means having its centerline along the centerline of the beam, a target, means for accelerating a beam of electrons from the cathode through the anode to the target, including means for placing a potential difference between the cathode and the anode, means for supplying ions to the beam so that the ions are accelerated toward the target, the improvement wherein: the target being positioned across the end of the tubular anode that is farthest from the cathode, a return path for the electrons reaching the target for conducting the electrons that reach the target, said anode comprising means for forming a potential trough that collects and accelerates ions toward the target. said tubular conducting means has a diameter that increases along at least a limited portion thereof adjacent the end thereof closest to the cathode. said tubular conducting means includes a dielectric sleeve surrounding said tubular conducting means, and a bulkhead around said sleeve, said sleeve preventing said bulkhead from shorting said tubular conducting means. a limited portion adjacent that end of said tubular conductive means that is closest to the cathode being composed of graphite, so that a spark-over to the anode will not be a sustained one. providing a cathode spaced from said anode, establishing a beam of electrons that leaves said cathode and enters said tubular anode and then passes through said tubular anode to the target, positioning the target adjacent the end of the anode that is farthest from the cathode, providing a return path for the electrons reaching the target, adding ions to the beam, forming a potential trough in said beam to move ions toward the target, and intensifying said potential trough while the beam is traveling in said anode and toward the target, whereby to collect and move at least some of said ions towards the target. 2. An ion accelerating device as defined in claim 1 in which the tubular conducting means is made of material resistive to flow of electrons and the cross-section of the tubular conducting means being sufficiently small so that the tubular conductive means will intercept some electrons that have strayed from the beam and so that the flow of such electrons along the tubular conductive means will sustain an electrical field. 3. An ion accelerating device as defined in claim 2 in which: 4. An ion accelerating device as defined in claim 2 in which said limited portion flares outwardly as it approaches said end thereof closest to the cathode, said tubular conductive means being composed of material resistive to the electrical current so that there will be a potential drop across it and so that an electric field will be created that accelerates the beam. 5. An ion accelerating device as defined in claim 4 in which: 6. An ion accelerating device as defined in claim 2 comprising: 7. The method of accelerating ions through a tubular anode to a target comprising: 8. The method of claim 7 in which said anode has an electric field which intensifies said potential trough and collects and moves at least some of said ions towards the target. 9. The method of claim 8 in which said anode has high resistivity and has a current flowing along the same whereby said anode has said electric field. 10. The method of claim 7 comprising providing substantial electrical resistivity for the anode, and conducting an electric current along said anode whereby said anode has an electric field that intensifies said potential trough. 11. The method of claim 10 in which said electric field is maintained in intensity along the path starting at the end of the anode farthest from the target and extending to the end of the anode closest to the target.
	abstract	A position determination system and method is provided that may be used for obtaining position and orientation information of a detector in a contaminated room. The system includes a detector, a sensor operably coupled to the detector, and a motor coupled to the sensor to move the sensor around the detector. A CPU controls the operation of the motor to move the sensor around the detector and determines distance and angle data from the sensor to an object. The method includes moving a sensor around the detector and measuring distance and angle data from the sensor to an object at incremental positions around the detector.
054406005	summary	BACKGROUND OF THE INVENTION Annular linear flow electromagnetic induction pumps for impelling liquid metals generally comprise an annular flow channel or duct which is surrounded by a column composed of a multiplicity of alternating annular stator coils and magnetic stator iron. This type of electromagnetic pump, commonly known as a single stator, annular linear flow induction pump, and its use in a liquid metal cooled nuclear fission reactor, is disclosed in U.S. Pat. No. 4,859,885, issued Aug. 22, 1989, and No. 4,882,514, issued Nov. 21, 1989. However, a more versatile linear flow electromagnetic induction pump design than those shown in the above patents comprises a double stator system. This electromagnetic pump system comprises the single stator arrangement as shown in the aforesaid patent, which is additionally provided with a second or inner stator arrangement concentrically contained and enclosed within the pump's central linear liquid flow duct or channel. A second stator column is also composed of a multiplicity of alternating annular stator coils and stator iron. In combination, the outer and inner, or double stators act upon the liquid linearly passing through the annular flow duct. This double stator arranged pump design provides greater pumping capacity per pump unit size, or alternatively equal capacity provided by a smaller pump unit. Accordingly the double stator pump has the advantages of greater efficiency and versatility, among others. The disclosures and contents of U.S. Pat. No. 4,508,677, No. 4,859,885 and No. 4,882,514, are incorporated herein by reference. SUMMARY OF THE INVENTION A stator core for an electromagnetic pump includes a plurality of circumferentially abutting tapered laminations extending radially outwardly from a centerline axis to collectively define a radially inner bore and a radially outer circumference. Each of the laminations includes radially inner and outer edges and has a thickness increasing from the inner edge toward the outer edge to provide a substantially continuous path adjacent the circumference.
044773773	description	DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION The process of the invention relates to the recovery of cesium ions from mixtures thereof with other metal ions. Nuclear waste represents a rich source of cesium but it is admixed with many other metals closely related in molecular weight and/or chemical properties which make separation difficult by conventional separation procedures. The present invention accomplishes this separation effectively and efficiently. The separation procedure of the invention involves the transport of cesium ions from a separate source phase to a separate recipient phase through a liquid membrane containing the calixarene which interfaces with the two separate phases. The cyclic octamer of FIG. 2, the cyclic hexamer of FIG. 3 and the cyclic tetramer of FIG. 4 all exhibit the property of selectively complexing with Cs+ under basic conditions. A suitable apparatus in which the process of the invention can be carried out is shown in FIG. 1 in which 10 is an open-top outer container, 12 is an open-ended inner container located within container 10 with its open bottom spaced above the closed bottom of the outer container, 14 is a layer of liquid membrane containing the calixarene deep enough to cover the open bottom end of the inner container 12, 16 is a body of aqueous solution of the metal ions to be separated located in the inner container 12 and 18 is an aqueous recipient phase located in the outer container 10 above the level of the liquid membrane. A stirring means, e.g., a magnetic stirrer 20 may be included, if desired. In this apparatus the source phase is separated from the recipient phase by the liquid membrane phase and by a physical barrier, the open-ended inner container. The containers may be made of any suitable material such as metal, glass, plastic and the like. In the use of this apparatus the cesium ions are selectively removed from the body 16 of aqueous solution containing them by the calixarene in phase 14 across the interface between phases 14 and 16 and are delivered from the calixarene to the aqueous recipient phase 18 across the interface between phases 16 and 18. The process of the invention is not dependent upon this apparatus, however, because the process can be carried out in any apparatus which provides means for holding (1) a separate aqueous phase containing the metal ions to be separated, (2) a separate aqueous recipient phase and (3) a membrane phase which separates and interfaces with the other two phases. For example the phases may be in any kind of container as an emulsion of the two separate phases as dispersed phases in a continuous organic liquid phase containing the ligand. In such apparatus the source phase is separated from the recipient phase only by the liquid membrane phase. The separate aqueous phase containing the metal ions to be separated may be prepared in any suitable manner from any starting material having metal values which it is desired to recover in whole or in part. A starting material of great potential value is nuclear waste which contains a plurality of degradation products of uranium splitting and which have molecular weights about half of the molecular weight of the uranium, including cesium. The membrane phase containing the ligand in a suitable hydrophobic organic solvent may be prepared in any suitable manner from liquids known in the art to be useful for this purpose, e.g., any of those mentioned in J. D. Lamb, J. J. Christensen, J. L. Oscarson, B. L Nielsen, B. W. Asay and R. M. Izatt, J. Am. Chem. Soc., 102, pages 6820-6824 (1980). The recipient phase may be distilled, deionized water. The three liquid phases, after preparation, are placed in the apparatus in which the process is to be carried out. In the apparatus without barrier separation between the source and recipient phases, the source phase and the recipient phase are emulsified with the membrane phase in any suitable container for the emulsion. In the apparatus illustrated in FIG. 1 the membrane phase is first introduced into container 10 until it covers the lower end of tube 12, as illustrated in FIG. 1, the source phase is introduced into the tube 12 and the recipient phase into the container, both floating on the membrane phase and separated by the tube 12. The transport of the cesium ion from the source phase to the recipient phase then takes place through the membrane phase by means of the selective ligand over a long enough period of time for substantially complete removal of the cesium ion from the source phase and its delivery to the recipient phase. WORKING EXAMPLES Three liquid membranes are prepared by dissolving enough of each calixarene in an organic liquid membrane solvent containing the various percentages of methylene chloride and carbon tetrachloride set forth in TABLE I to form a 1.0 mM solution. TABLE I __________________________________________________________________________ CALIXARENE PERCENTAGE METHYLENE CHLORIDE PERCENTAGE CARBON TETRACHLORIDE __________________________________________________________________________ 1. Tetramer 25 75 2. Hexamer 18 82 3. Octamer 16 84 __________________________________________________________________________ Into each of three 4-dram vials 10 mL of each solution is poured, which is enough to cover the lower end of glass tube 12. Atop this organic liquid are placed (1) in the tube 12 0.8 mL of a source phase containing the ions to be separated, including cesium and other ions indicated in TABLE II, and (2) in the space in container 10 outside tube 12 5.0 mL of distilled, deionized water. After 24 hours the recipient phase is sampled and analyzed for cation concentration by atomic absorption spectrometry. Three runs are made of each calixarene and the results averaged. The standard deviation among the values in each run is less than 15%. The results are given in TABLE II. TABLE II ______________________________________ Transport Rate Source (moles .times. 10.sup.7 /24 hours) Phase 1 2 3 ______________________________________ LiOH c 4.4 + 0.5 0.9 + 0.1 NaOH 0.9 + 0.1 1.4 + 0.7 1.5 + 0.1 KOH 45 + 12 28 + 7 1.7 + 0.6 RbOH 35 + 13 70 + 40 22 + 5 CsOH 61 + 2 360 + 50 130 + 15 Ca(OH) 0.3 + 0.03 c 0.5 + 0.1 Sr(OH) 0.11 + 0.7 0.3 + 0.1 0.13 + 0.03 Ba(OH) 0.7 + 0.3 1.4 + 0.7 0.17 + 0.02 ______________________________________ c = less than 0.4 moles .times. 10.sup.7 /24 hours TABLE II demonstrates that the calixarene ligands are effective carriers of the heavier monovalent alkali metal cations. All three gave selective transport of Cs+ over all other cations. The tetramer is least selective for Cs+ and shows greater affinity than either of the other ligands for K+. While the invention does not depend on the reason or hypothesis for the differences in selectivity it may be noted that the three ligands vary considerably in the size of their central cavity. Comparison of the relative magnitudes of the radii for the cations and these ligands makes it apparent that the selectivities seen in TABLE II are determined by factors other than relative sizes. CPK models indicate that the cavity radii of the ligands are: tetramer 1.36-1.84 .ANG.; hexamer 4.3-5.6 .ANG.; octamer 8.0-8.8 .ANG.. The radii of Cs+, Rb+ and K+ are 1.70, 1.49 and 1.38 .ANG., respectively, R. D. Shannon and C. T. Prewitt, Acta Crystallogr., B25, pages 969 et seq. (1969). It is likely that M+ selectivity is related to the relative hydration energies of the cations studied, since partial or complete dehydration of the cation will occur in the complexation process. This hypothesis is supported by the fact that srongly hydrated divalent cations show almost no transport, while among the monovalent cations the least strongly hydrated cation, Cs+, is selected. Experiments were carried out using calix[8]arene to measure the rate of Cs+ transport under conditions of varying source pH to demonstrate the exchange of a proton for the cation at the source phase interface. Mixtures of CsNO.sub.3 and CsOH were used as the source phase. The relative amounts of the two solutes were adjusted to maintain the total Cs+ concentration at 1.00M in each case. The values of the transport rate are small below pH of 12 but rise rapidly beyond this point. This result confirms that a proton is removed from the ligand in the complexation process and that for appreciable transport to take place, the source phase must be quite basic. Although the invention has been described and illustrated by reference to certain specific calixarenes, additional analogs of these calixarenes are within the scope of the invention and with groups other than butyl in the para position of the phenol moiety which may serve to alter the acidity of the phenolic OH and thus the cation binding characteristics of the ligand.
	description	This application is a 35 U.S.C. §371 national phase filing of International Application No. PCT/US12/67217, filed on Nov. 30, 2012, which claims priority under 35 U.S.C. §119(e) from U.S. Provisional Application No. 61/566,584 filed on Dec. 2, 2011, the disclosures of which are hereby incorporated herein by reference in their entireties. This section of this document introduces various pieces of the art that may be related to or provide context for some aspects of the technique described herein and/or claimed below. It provides background information to facilitate a better understanding of that which is disclosed herein. This is a discussion of “related” art. That such art is related in no way implies that it is also “prior” art. The related art may or may not be prior art. The discussion in this section is to be read in this light, and not as admissions of prior art. Detection of the stress in and resulting strained states of thin film materials and small volume samples of material are difficult to resolve by looking at diffraction patterns/shadowgraphs in 2D angle space. The detection of such diffraction pattern shifts between strained conditions, uses X-ray, electron, and neutron diffraction techniques that require careful sample preparation. Furthermore, preferred orientations may not always be available for investigation of novel materials and structures in situ. The presently claimed subject matter is directed to resolving, or at least reducing, one or all of the problems mentioned above. The presently disclosed technique provides a method and apparatus for use in modulated X-ray harmonic detection and identification. In a first aspect, a method comprises: modulating an X-ray signal with as first radio frequency and with a second radio frequency; transmitting the modulated X-ray signal into a field of view containing a sample; receiving backscatter of the transmitted X-ray signal reflected from the sample; and processing the received backscatter to identify the sample from the pattern of the detected harmonics of the first and second radio frequency signals. In a second aspect, an X-ray RADAR apparatus comprises: means for modulating an X-ray signal with a first radio frequency and with a second radio frequency; means for transmitting the modulated X-ray signal into a field of view containing a sample; means for receiving backscatter of the transmitted X-ray signal reflected from the sample; and means for processing the received backscatter to identify the sample from the pattern of the detected harmonics of the first and second radio frequency signals. In a third aspect, a computer-implemented method, comprising: receiving data representative of backscatter of a radio frequency modulated X-ray signal reflected from a sample, the X-ray signal being radio frequency modulated with a first frequency and with a second frequency; and processing the received backscatter to identify the sample from the pattern of the detected harmonics of the first and second radio frequency signals. In a fourth aspect, a program storage medium encoded with instructions that, when executed by a processor, perform a software implemented method, the software implemented method comprising: receiving data representative of backscatter of a radio frequency modulated X-ray signal reflected from a sample, the X-ray signal being radio frequency modulated with a first frequency and with a second frequency; and processing the received backscatter to identify the sample from the pattern of the detected harmonics of the first and second radio frequency signals. In a fifth aspect, a computing apparatus, comprises: a processor; a bus system; a storage communicating with the processor over the bus system; and an application residing on the storage that, when invoked, by the processor, performs a software implemented method, comprising: receiving data representative of backscatter of a radio frequency modulated X-ray signal reflected from a sample, the X-ray signal being radio frequency modulated with a first frequency and with a second frequency; and processing the received backscatter to identify the sample from the pattern of the detected harmonics of the first and second radio frequency signals. In a sixth aspect, an X-ray RADAR apparatus, comprises: a transmitter capable of: modulating an X-ray signal with a first radio frequency and with a second radio frequency; and transmitting the modulated. X-ray signal into a field of view; a receiver capable of receiving backscatter of the transmitted X-ray signal reflected from a sample within the field of view; and a processing unit capable of processing the received backscatter to identify the sample from the pattern of the detected harmonics of the first and second radio frequency signals. The above presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later. While the invention is susceptible to various modifications and alternative forms, the drawings illustrate specific embodiments herein described in detail by way of example. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-Specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. Turning now to FIG. 1, a modulated X-ray signal 100 is directed toward a sample 110. The signal 100 may be modulated as discussed further below and as disclosed in the applications incorporated by reference below. The sample 110 reflects and, in the illustrated embodiment, diffracts the signal 100 into a diffraction pattern 120. The diffraction pattern elements 130 (only one indicated) contain not only the carrier the signal 100), but also various harmonics thereof. The scattering patterns therefore contain additional information in the frequency domain to identify which patterns contain information scattered from a thin film or small volume region. This additional information identifies the strained state and indicates stress in the material. Modulated x-ray energy is scattered from a sample of material, the scattered x-ray energy containing nonlinear frequency domain response from the photocurrent stresses generated by the x-ray flux. More particularly, the scattered energy contains the fundamental modulation of the x-ray energy, plus additional second and third harmonics and their mixing products with the fundamental or “carrier” x-ray modulation frequency. The amounts of energy in the scattered harmonic products provide additional information on the state of the sample under x-ray examination. Note, however, the presently disclosed technique is not limited to diffraction. The illustrated embodiment shows how lattice changes would show up in the “blur spot” intensity changes, without having to show a “blur” image. The nonlinear material response in the detected x-ray intensity would be a combination/superposition of diffraction shadows, transmissivity changes and reflectivity changes in and along surfaces that change in a nonlinear way with the x-ray signal. FIG. 1 includes a depiction of a rendered image 140. It is not necessary to render or even use images, but one can do harmonic detection on selected “pixels” in an image, as long as the pixels are co-sighted/aligned with the harmonic x-ray signal detector. Most applications would benefit by having knowledge of an x-ray image and location of given harmonic content in certain parts of the x-ray image. (The harmonics can be detected separately from the imager system.) The knowledge of relative location and harmonic content (nonlinear material locations) would be useful in some embodiments. FIG. 2 illustrates one particular embodiment of an apparatus 200 by which the method of the presently disclosed technique may be performed. This system images the received backscatter from the sample although, as set forth above, imaging is not necessary in all embodiments. More particularly, FIG. 2 conceptually illustrates one particular embodiment of an X-ray microscopy imaging system 200. The system 200 is shown subjecting a target volume, or specimen, 203 to a plurality of X-rays 206 (only one indicated) generated and radio-frequency modulated as discussed further below. The system 200 comprises, in general, an X-ray source 209 and a sensor 212. The X-ray source 209 is capable of emitting the plurality radio-frequency modulated X-rays 206 toward the target volume 203 when in operation. The sensor 212 is capable of imaging a plurality of X-rays 215 (only one indicated) reflected from the target volume 203 and radio-frequency modulating the image when in operation. Radio frequency modulating the image impresses the image with a radio-frequency modulation. Upon imaging the X-rays 215, the sensor 212 then outputs the radio-frequency modulated image 218. In general, the X-ray source 209 of the illustrated embodiment includes a filament, a radio-frequency modulated tube, and a high power microwave source, none of which are shown. The filament generates an electron beam output to the radio frequency modulated tube. The radio frequency modulated tube comprises a pair of cavity resonator structures and a high power (e.g., 2 joules/pulse) microwave source that give rise to the magnetic or electric fields that deflect the electron beam and impart the intensity modulation of the electron beam at radio frequency and an electron beam dump. The rotator then imparts the radio frequency modulated x-rays 206 toward the target 203. The radio-frequency modulated tube is a high voltage, high energy tube. The radio-frequency modulated tube may be, for example, a Klystron, such as is known in the art. Suitable implementations for the X-ray source 209 are commercially available off the shelf. For example, the NIR MCP-PMT and X-Ray Scintillator line of products offered by Hamamatsu Corp. offer several suitable alternatives. Hamamatsu Corp. can be reached in the United States at: 360 Foothill Rd. Bridgewater, N.J. 08807, ph. 908-231-0960; fax: 908-231-1218. Additional information can be obtained through those contacts or at www.hamamatsu.com over the World Wide Web of the Internet. The sensor 212 of the illustrated embodiment comprises three parts as shown in FIG. 3A. It includes a layer of a scintillating material 227 capable of intercepting the X-rays 215 emanating from the target volume 203 and fluorescing light (not shown) correlated thereto. A radio-frequency modulated microchannel plate 230 is located behind the scintillating material 227 to detect and amplify the fluoresced light. The microchannel plate 230 may also be referred to as a “phase plate”. The amplification of the fluoresced light may also be described as “intensifying” the image, and so the microchannel plate 230 may be considered an “image intensifier”. A detector array 233 is placed to detect the amplified fluorescent light output by the radio-frequency modulated microchannel plate 230. Again, suitable implementations are commercially available off the shelf, including the X-Ray Scintillator line of products offered by Hamamatsu Corp. mentioned above. Furthermore, information regarding imaging with such sensors and their fabrication is available from U.S. Pat. Nos. 6,531,225 and 6,762,420. In the particular embodiment illustrated in FIG. 3B, the detector array 233 is not large enough to cover the entire back of the microchannel plate 230 simultaneously. The illustrated embodiment therefore includes a scan drive 236 that scans the detector array 233 from one position 300, shown in FIG. 3B in solid lines, to other positions 303 (only one indicated), shown in broken lines, across the back 231 of the microchannel plate 236. Such scan drives are known to the art and the scan drive 236 can be implemented using any suitable scan drive known to the art. The X-ray source 209 receives a modulation signal 239 from a radio-frequency (“RF”) modulator 242. The sensor 212 receives a modulation signal 238 from the RF modulator 244. The signals 238, 239 are “synced” by the sync 245 in that they are harmonically related to one another. Such a harmonic relationship can be achieved many ways and so the sync 245 may be implemented in many ways. Some embodiments may use a direct digital synthesizer (“DDS”) for this function, but those skilled in the art having the benefit of this disclosure will appreciate that any suitable technique known to the art may be employed. The radio frequency modulation can include modulation of amplitude, phase and/or frequency from a few kilohertz (e.g., 3 KHz) through 300 GHz and is applied across the two faces of the microchannel plate 230. Those in the art will recognize that, practically, the state of art in x-ray fluorescent imaging materials is at ˜10 GHz, but “direct detection” of x-ray energy by new solid state detectors may very well have growth to 300 GHz. Typically, modulation will hold on one center frequency and amplitude/phase modulate, although some embodiments may modulate all three at once. This creates a biasing of the microchannel plate 230 that changes the recorded intensity of the image 218 as a function of the transmitted radio frequency modulated X-ray energy. In operation, the source 209 generates the X-rays 206. The radio frequency amplitude modulated X-rays 206 have a preferred conical angle α of radiation from the tube volume toward the desired target volume 203 to be examined. The expanding cone α of X-rays 206 from the virtual point source of the source 209 provides a means for casting a magnified shadow of an object placed in the path between the X-ray source 209 and a scintillator material 227. The reflected X-rays 215 through the target volume 203 will also contain this radio frequency modulation, containing energy modified by the materials in the object to be X-ray imaged. The microwave modulation of the X-Rays 215 allows detection of second and third harmonics and their products. The X-Rays 215 induce photocurrents/fields generated by the nonlinear material of the sample 203. The photocurrents induce stress/strain on material lattice at frequency and the strained lattice induces x-ray diffraction pattern changes at frequency. The X-ray detected ratio of harmonics to carrier power can then be used to identify diffraction pattern elements originating from the nonlinear thin film. The mechanics of these phenomena are further discussed in Y. H. Yu, et al., “Measurement of Thin Film Piezoelectric Constants Using X-ray Diffraction Technique”, Phys. Scr. T129 (2007) 353-357 (2007); and A. B. Kozyrev, et al., “Nonlinear Behavior of Thin Film SrTiO3 Capacitors at Microwave Frequencies”, 84 J. App. Phys. 3326-3332 (1998). Both of these papers are incorporated by reference below. The reflected X-rays 215 intercept the scintillation material 227 in front of the radio frequency modulated microchannel plate 230. The scintillation material 227 fluoresces across an optical frequency range that the microchannel plate 230 is designed to amplify. The scintillation material 227 has a time constant small enough that the amplitude of the fluorescence follows the radio frequency modulation rate. The resulting modulated microchannel plate light (not shown) is detected by the detector array 233 and recorded as the digital image 218. More particularly, scintillator materials have 100 ps (10 GHz) fluorescence response. The fluorescence typically peaks in the near IR to visible and IR to Visible wavelength detector diodes with bandwidths >10 GHz are commercially available off the shelf. Some embodiments may use “soft” x-ray detectors rather than scintillator materials. Soft x-ray detectors ˜10 keV have 100 ps (10 GHz) direct detection response. This approach trades higher frequency x-ray resolution for smaller detection receiver (no fluorescence layer, no high voltage micro channel plate) and easier to produce x-ray sources. Direct detection X-ray detectors with 10 μm×10 μm pixel resolution arrays are commercially available off the shelf. Returning to FIG. 2, the resulting amplitude image 218 is a set of ordered data. As those in the art having the benefit of this disclosure will appreciate, the image 218 may be rendered for human perception by means of printed hardcopy or electronic display. However, such rendering can be omitted in some embodiments. The processing and analysis can therefore be performed directly on the image 218 regardless of whether it is rendered. In practice, a series of images 218 are captured over time, each representing a sampling of the reflected X-rays 215. The image 218 may be stored, rendered for human perception, processed for some further use, or any combination thereof depending upon the particular embodiment. The X-ray microscopy imaging system 200 shown in FIG. 2 will typically be deployed in association with a computing apparatus 400, shown in FIG. 4. The computing apparatus 400 in the illustrated embodiment is a stand-alone work station. In alternative embodiments, the computing apparatus may be embedded in the apparatus 200 or may be part of a larger computing system. Instead of a workstation, the computing apparatus could be implemented in a desktop, laptop, notebook, etc., in other embodiments. The present invention admits wide variation in the implementation of the computing apparatus 400. In one aspect, the present invention is a software implemented method for generating and analyzing an X-ray image. FIG. 4 shows selected portions of the hardware and software architecture of the computing apparatus 400 such as may be employed in some aspects of the present invention. The computing apparatus 400 includes a processor 405 communicating with storage 410 over a bus system 415. The present invention admits wide variation in the implementation of the processor 405. Certain types of processors may be more desirable than others for some embodiments. For instance a digital signal processor (“DSP”) or graphics processor may be more desirable for the illustrated embodiment than will be a general purpose microprocessor. Other video handling capabilities might also be desirable. For instance, a Joint Photographic Experts Group (“JPEG”) or other video compression capability and/or multi-media extension may be desirable. In some embodiments, the processor 405 may be implemented as a processor set, such as a microprocessor with a graphics co-processor particularly for server architectures. The storage 410 may be implemented in conventional fashion and may include a variety of types of storage, such as a hard disk and/or random access memory (“RAM”) and/or removable storage such as a magnetic disk (not shown) or an optical disk (also not shown). The storage 410 will typically involve both read-only and writable memory. The storage 410 will typically be implemented in magnetic media (e.g., magnetic tape or magnetic disk), although other types of media may be employed in some embodiments (e.g., optical disk). The storage 410 may also employ various virtual memory and other memory management techniques. The present invention admits wide latitude in implementation of the storage 410 in various embodiments. In the illustrated embodiment, the storage 410 is internal memory implemented in a hard disk main memory, RAM, and in cache. The bus system 415 will also vary widely by implementation. Depending upon the implementation, the bus system 415 may comprise an internal bus, a network backbone, or some combination thereof. For example, if the computing apparatus 400 is instead embedded with the X-ray microscopy imaging system 200, the bus system 415 may be implemented as an internal bus. On the other hand, if the computing apparatus 400 is but a part of a larger computing system across which the computing functionalities are distributed, then some type of external bus—i.e., a network backbone—will be employed. Either way, the bus system 415 may be implemented using conventional technologies. The storage 410 is also encoded with an operating system (“OS”) 430, user interface software 435, and an application 465. The user interface software 435, in conjunction with a display 440, implements a user interface 445. The user interface 445 may include peripheral input/output devices such as a keypad or keyboard 450, a mouse 455, or a joystick 460. The processor 405 runs under the control of the operating system 430, which may be practically any operating system known to the art. The application 465 may be invoked by the operating system 430 upon power up, reset, or both, depending on the implementation of the operating system 430. The application 465, when invoked, performs the method of the present invention. The user may also invoke the application 465 in conventional fashion through the user interface 445. The storage 410 is also encoded with two data structures 425, 426. The data structure 425 contains the images 218 (only one indicated) that are acquired as described above. The data structure 426 contains the resultant images 427 (only one indicated) generated by the application 465 through the process generally described above. The resulting images 427 are “angle only” radiograph images with intensity proportional to signal strength of the difference between the transmitted and received modulation frequencies and their harmonics. The images now give a standard radiograph with the benefit of referencing the detected harmonic signals to the appropriate angle/pixel location in the image. The data structures 425, 426 may be implemented in any suitable type of data structure known to the art, such as a database, a list, or a queue. The data structures 425, 426 may be designed for long term storage of the images 218, 427 or to temporarily buffer them, depending on the implementation. As mentioned above, the hardware and software architecture shown in FIG. 4 is exemplary only, and may find wide variation across numerous alternative embodiments. A good example of such variation is the implementation of the data structures 425, 426 described immediately above. Another good example is in the application 465. In other embodiments, the functionality residing in the application 465 may instead repose in some other kind of software component, such as a script, a daemon, etc. There similarly may be variation in the suns of the various elements of the software aspects of the architecture. For example, there is no need for the images 218, 427 to reside on the same computing apparatus 400 or to reside on the same computing apparatus 400 as the application 465 by which they are processed and created. Some embodiments of the present invention may be implemented on a computing system comprising more than one computing apparatus. Such computing system may employ a network client/server architecture. In a networked client/server architecture the images 218, 427 (only one of each indicated) may, for example, reside on a data structure (not shown) residing on a server while the application by which they are processed resides on a workstation. Furthermore, there is no requirement that the images all reside together. The images 218 might reside on the server while the resultant images 427 might reside on a workstation. The invention admits wide variation in this respect. Note that there is no requirement such a computing system be networked. Alternative embodiments may employ, for instance, a peer-to-peer architecture or some hybrid of a peer-to-peer and client/server architecture. The size and geographic scope of the computing system 500 is not material to the practice of the invention. The size and scope may range anywhere from just a few machines of a Local Area Network (“LAN”) located in the same room to many hundreds or thousands of machines globally distributed in an enterprise computing system. As is apparent from the discussion above, some portions of the detailed descriptions herein are consequently presented in terms of a software implemented process involving symbolic representations of operations on data bits within a memory in a computing system or a computing device. These descriptions and representations are the means used by those in the art to most effectively convey the substance of their work to others skilled in the art. The process and operation require physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical, magnetic, or optical signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated or otherwise as may be apparent, throughout the present disclosure, these descriptions refer to the action and processes of an electronic device, that manipulates and transforms data represented as physical (electronic, magnetic, or optical) quantities within some electronic device's storage into other data similarly represented as physical quantities within the storage, or in transmission or display devices. Exemplary of the terms denoting such a description are, without limitation, the terms “processing,” “computing,” “calculating,” “determining,” “displaying,” and the like. Note also that the software implemented aspects of the invention are typically encoded on some form of program storage medium or implemented over some type of transmission medium. The program storage medium may be magnetic (e.g., a floppy disk or a hard drive) or optical (e.g., a compact disk read only memory, or “CD ROM”), and may be read only or random access. Similarly, the transmission medium may be twisted wire pairs, coaxial cable, optical fiber, or some other suitable transmission medium known to the art. The invention is not limited, by these aspects of any given implementation. Furthermore, portions of this disclosure include discussion of “images”. These images are shown in a human-perceptible form, i.e., in a hard copy. Note that this presentation is for the sake of illustration. The images are actually collections or sets of ordered data. In the illustrated embodiments, the data is three-dimensional. The images may be rendered to make them perceptible by image analysts in some embodiments. For example, the images may be rendered for output in hard copy, or they may be rendered and displayed electronically. However, some embodiments of the invention may be practiced automatically, that is, without human interaction. Thus, some embodiments may be practiced without the images being so rendered. In operation, the application 465 of the illustrated embodiment executes the process 500 shown in FIG. 5. The process 500 may be performed in two parts—image acquisition and image processing in some embodiments. In this particular embodiment, all acquisition occurs prior to processing. Alternative embodiments may “process on the fly”, or process the images 218, shown in FIG. 2, as they are acquired. The difference will create some differences in handling having both advantages and disadvantages relative to the illustrated embodiment. Those in the art having the benefit of this disclosure will appreciate not only these relative advantages and disadvantages, but also the differences in handling and will be able to implement such alternatives should they wish to do so. As mentioned, in one aspect, the present invention provides a method, such as the method 500 illustrated in FIG. 5. The method 500 comprises modulating (at 510) an X-ray signal with a first radio frequency and with a second radio frequency. The modulated X-ray signal is then transmitted (at 520) into a field of view. Backscatter from the transmitted X-ray signal is received (at 530) and processed (at 540) to determine a prior known or expected spurious products—e.g., sum and/or difference products for the first and second frequencies with which the X-ray signals 206 are modulated. This is done by performing a time series analysis to detect image change across the time series of images that represent pixels changing at the rate of the difference frequency of the RF frequency and the a priori signature harmonic patterns. More particularly, because the first and second frequencies are known, it is known what harmonic patterns of spurious products might be expected. Examples of spurious products include 2ƒ1+3ƒ2 and/or 3ƒ2−2ƒ1, as well as other permutations in sums and differences. The spurious products that are detectable and detected will form a pattern characteristic of the material of the sample under inspection. Such patterns can be determined for materials of interest and, for example, stored electronically for later matching with images acquired from the sample as described above. The material can thus be identified. The invention admits some latitude in the implementation of both the apparatus and method of the invention. For example, a suitable handled X-ray device suitable for modification to implement the presently disclosed technique is the LEXID™ X-ray Imaging Device available from Physical Optics Corporation, at 0600 Gramercy Place, Torrance, Calif. 90501-1821 Phone: 310-320-3088, Fax: 310-320-5961. In particular, the device would be modified to implement the modulation technique disclosed herein. Additional information is available over the World Wide Web of the Internet at their website <http://www.poc.com/default.asp>, Principles of operation, construction, and design are also disclosed in U.S. Pat. No. 7,231,017. Using such a handheld device, however, the computing apparatus 400 of FIG. 4 will more typically be embodied in a laptop. The laptop will receive the received backscatter from a sensor through a peripheral connection from a handheld sensor. The processing may even be performed in the handheld sensor itself in some embodiments. Such an acquisition is shown in U.S. application Ser. No. 12/541,539, entitled “X-Ray Explosive Imager”, in the name of the inventor J. Richard Wood, and filed Aug. 14, 2009, commonly assigned herewith, and incorporated by reference below. The technique can be used to identify electronics under examination. Some materials may have a unique harmonic response, that given some it priori knowledge about the target sample being x-ray interrogated, may give a unique identifying signal. While the technique disclosed herein will produce a very low rate of false alarms, it also will generally suffer form a low signal to noise ratio. However, under even very good condition, the signal to noise ratio will be ˜0.5 with conventional RF detection. Accordingly, this is not a strong negative relative to conventional techniques. The following applications, patents, and papers are hereby incorporated by reference in their entirety and for all purposes as if set forth herein verbatim: U.S. Provisional Application Ser. No. 61/566,584, entitled “Modulated X-Ray Harmonic Detection”, in the name of the inventor J. Richard Wood, and filed Dec. 2, 2011, and commonly assigned herewith; and U.S. Provisional Application Ser. No. 61/089,140, entitled “X-Ray Explosive Imager”, in the name of the inventor J. Richard Wood, and filed Aug. 15, 2008, and commonly assigned herewith; and U.S. Provisional Application Ser. No. 61/107,924, entitled “X-Ray RADAR”, in the name of the inventor J. Richard Wood, and filed Oct. 23, 2008, and commonly assigned herewith; and U.S. application Ser. No. 12/604,548, entitled “X-Ray RADAR”, in the name of the inventor J. Richard Wood, and filed Oct. 23, 2009, and commonly assumed herewith. U.S. application Ser. No. 12/541,539, entitled “X-Ray Explosive Imager”, in the name of the inventor J. Richard Wood, and filed Aug. 14, 2009, and commonly assigned herewith. Y. H. Yu, et al., “Measurement of Thin Film Piezoelectric Constants Using X-ray Diffraction Technique”, Phys. Scr. T129 (2007) 353-357 (2007). A. B. Kozyrev, et al., “Nonlinear Behavior of Thin Film SrTiO3 Capacitors at Microwave Frequencies”, 84 J. App. Phys. 3326-3332 (1998). In the event of conflict between the present disclosure and any incorporated reference, the present disclosure controls. The phrase “capable of” as used herein is a recognition of the fact that some functions described for the various parts of the disclosed apparatus are performed only when the apparatus is powered and/or in operation. Those in the art having the benefit of this disclosure will appreciate that the embodiments illustrated herein include a number of electronic or electro-mechanical parts that, to operate, require electrical power. Even when provided with power, some functions described herein only occur when in operation. Thus, at times, some embodiments of the apparatus of the invention are “capable of” performing the recited functions even when they are not actually performing them—i.e., when there is no power or when they are powered but not in operation. This concludes the detailed description. The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
06212255&	description	DESCRIPTION OF THE INVENTION The present invention provides an apparatus for insuring dose uniformity for a blood contained in a transfusion bag that receives X-ray beam radiation from X-ray tubes. Referring to FIGS. 1-3, the inventive X-ray system 11 comprises a suitably shielded apparatus or machine 12, which may be portable. The machine 12 includes a first X-ray tube or source 15 which is oriented to provide a beam of X-rays downwardly, indicated by the dotted lines 16, to a chamber 19 which is adapted to receive a cannister or container 18 for the blood plasma bag. The cannister 18 has an oval shaped interior for receiving the transfusion bag 20, and includes a cover or top 21, see FIG. 2. The cannister 18 is dimensioned and positioned to maintain the blood plasma transfusion bag 20 at a precise distance and position relative to the X-ray tube 15, see FIG. 3. Cover 21 controls the depth or thickness of the blood bag 20 within cannister18. Importantly, the cannister 18 is dimensioned to receive the cover 21 to maintain the thickness of 4 cm throughout the bag. The system includes suitable radiation security switches so that X-ray exposures can be initiated only when all the radiation doors have been closed, as is known. In the embodiment shown, X-ray tube 15 has an output of 160 kV and the X-ray beam output port of tube 15 is designed to provide a relatively wide X-ray beam of 40-50 degrees in order to provide a beam with a sufficiently large diameter to fully cover the cannister 18 and the included bag 20, as will be discussed. The X-ray tube is positioned relatively close, that is 23 cm, from the upper surface of cannister 18 to assure that maximum energy is delivered to the bag 20. As is known, the closer an X-ray source is to object to be irradiated, the higher the energy delivered to the object; that is, the level of the energy delivered to the object is dependent on the distance between the two components. As is also known, the object can be irradiated faster when more energy is delivered to the object. It is of particular importance that the irradiation received by the blood plasma in bag 20 be uniform. That is, the blood in the bag must be uniformly irradiated; that is, irradiation energy within a specified range must be provided to the blood for the same period of time to meet Federal regulations. For this purpose of providing an efficient uniform irradiation of the blood plasma bag, in the embodiment of FIGS. 1-3, a second X-ray tube 17 is provided on the opposite side of the cannister 18. The X-ray tube 17 is essentially identical to X-ray tube 15 and provides energy to the opposite surface or side of the bag 20. Tube 17 is positioned the same distance from the cannister as is tube 15, that is at 23 cm from the lower surface of cannister 18. Hence, the transfusion bag 20 is concurrently irradiated from two separate X-ray sources for a precise time. In the embodiment of FIG. 1, the two X-ray tubes 15 and 17 are powered by the same power supply from an AC source connected through adapter 29. Two separate power sources may be provided. It is clear from FIG. 2, that the irradiation energy from X-ray tube 17 complements the irradiation energy from X-ray tube 15. Since the energy level varies as the beam penetrates the 4 cm thick bag of blood; the energy provided changes with the depth or thickness of the blood in bag 20. (As stated above, the thickness of the bags is a maintained at 4 cm by the cannister.) The energy from tube 15 is maximum at the top surface of blood bag 20 and decreases as it penetrates the bag 20, and is effectively at a minimum level at the lower surface of bag 20. Conversely, the radiation energy from X-ray tube 17 is maximum at the lower surface of bag 20 and decreases to a minimum at the top surface of bag 20. The relation of the irradiation energy at any level or depth of bag 20 is a sum of the energy developed by the two tubes. In practice it has been found that irradiation of a blood plasma bag for about six minutes with the apparatus disclosed complies with Federal regulations. The blood in bag 20 becomes a factor in controlling the dose distribution for the irradiation. The kV, mA, time and filtration of the beam are carefully controlled to assure that the applicable dose delivered to all parts of the bag is similar. Transfusion bags vary in both size and configuration and the cannister 20 accommodates the different varieties while maintaining a maximum thickness of 4 cm or less. As is known, X-ray energy is absorbed in a particular item as a function of density of the material and depth to be penetrated. In the particular embodiment of FIG. 1, the energy level of the X-ray tubes is 160 kV. It has been found that to maintain uniformity of radiation to all parts of the bag, the tubes must provide each at least 150 kV output to comply with the FDA specifications that the irradiation be within a range of 1500-2500 rads. The X-ray tubes 15 each irradiate the bag 20 with a surface dose of 2500 rads and an exit dose of 1500 rads. Present requirements are that the bag be irradiated for a six minutes. Ideally, the irradiation dose effective at the center of the blood plasma in bag 20 is the same as the dose at the blood plasma adjacent the opposite (upper and lower) surfaces of the bag. Further, it has been found that the output port of each of the X-ray tubes 15 and 17 should preferably have a diameter to provide a 45 degree beam such that the beam has at least a diameter of 15.5 cm at 23 cm distant from the tube. This permits the tubes to be placed closer to the bag, since as is known, the effective radiation is dependent on the distance of the object from the source. It has also been found important to provide an efficient ion pump to maintain a good vacuum in the X-ray tube. An ion pump is preferred since the tube is used frequently for short periods, and hence any impurities in the vacuum can not be purged merely by usage and heating of the tube. Thus an efficient ion pump is used. In the embodiment shown the tubes both have a rating of 160 kV; however, theoretically the tubes could have different outputs rating. The 160 kV tubes are commercially available tubes with known characteristics and are manufactured by various reliable sources. The bags 20 used in blood transfusion bags vary in both size and configuration. The cannister 18 accommodates the different varieties of bags while maintaining the bag at a maximum thickness of 4 cm or less. This insures the dose delivered to any part of the blood will be no more than 2500 rads and no less than 1500 rads, all per FDA specifications. The size of the chamber is related to the minimum width of the variety of blood bags to be accommodated. As depicted in FIG. 2, in one embodiment the dimensions of cannister are 15.5 cm.times.12 cm.times.4 cm, and cannister contains the bag 20 in a snug tight position. An important concept in this application is that the transfusion bag 20 is held at a maximum thickness of 4 cm throughout. As mentioned above, X-ray energy is absorbed in a particular material as a function of density and depth to be penetrated. As alluded to above it is important in system 11 that the distance from the X-ray source 15 to the upper surface of bag 20 is 23 cm, and the distance to the lower surface of the bag 20 is 27 cm. The configuration is symmetrical; that is, the distance from the X-ray source 17 to the lower surface of the bag 20 is 23 cm, and the distance to the upper surface of the bag 20 is 27 cm. FIG. 5 shows an embodiment of the inventive system 11 wherein the machine 12A includes a door 29 mounted on a pivot to slidably close the irradiation chamber 19. FIG. 6 shows an embodiment of the invention wherein the machine 12 includes a hinged door 31 with a plug 32 for closing the irradiation chamber 19. FIG. 4 depicts a second embodiment of the invention wherein a blood plasma bag 20 is positioned to be irradiated by a single X-ray tube 15A. In this embodiment, the plasma bag 20 is mounted in a vertical orientation, that is its longest length is vertical and its 4 cm thickness is positioned vertically as contrasted to the horizontal orientation of the bag 20 shown in FIGS. 1-3. A first surface or side of the plasma bag 20 is irradiated for a preselected time period. Next, rotatable support 28 rotates the bag about its vertical axis, and the opposite surface of the bag 20 irradiated for an equal period of time. The cumulative irradiation provided to the opposite surfaces or sides is thus effective to provide a uniform irradiation to the blood contained in the bag. While the invention has been particularly shown and described with reference to a particular embodiment thereof it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.
051026155	claims	1. A container for storing and transporting radioactive material comprising: a vessel, having an upwardly open cavity for accommodating said radioactive material, said vessel having walls with a core of concrete shielding material enveloped and isolated within a continuous metal lining; and a cap, covering the top surface of said vessel sealing said cavity, said cap having a core of concrete shielding material enveloped and isolated within a continuous metal lining, the lower outer peripheral edge of said cap being continuously welded to the upper outer peripheral edge of said vessel. an upwardly open internal liner the inner surfaces of which define said cavity, having side and bottom walls; an external vessel liner, spaced outward from said internal liner having side and bottom walls; and a top vessel plate, having a central opening defining said cavity, an inner portion of said top vessel plate adjacent said central opening being continuously welded to an upper portion of said internal liner and an outer portion of said top vessel plate being continuously welded to an upper portion of said external vessel liner, said concrete shielding material filling the internal space defined by said internal and external vessel liners and said top vessel plate. a bottom cap plate; a top cap plate, spaced upward from said bottom cap plate; and an external cap liner having side walls the top and bottom portions of which are continuously welded respectively to the outer portions of said top and bottom cap plates, said concrete shielding material filling the internal space defined by said bottom and top cap plates and said external cap liner. a vent pipe communicating between an upper portion of said cavity and the exterior of the container; and venting control means within said vent pipe for sealing said vent pipe and for enabling fluid to pass between said cavity and the exterior of the container. a drain pipe communicating between a lower portion of said cavity and the exterior of said container; and drain control means within said drain pipe for sealing said drain pipe and for enabling fluid to pass between said cavity and the exterior of said container. a vent pipe communicating between an upper portion of said cavity and the exterior of the container; venting control means within said vent pipe for sealing said vent pipe and for enabling fluid to pass between said cavity and the exterior of the container; a drain pipe communicating between a lower portion of said cavity and the exterior of said container; and drain control means within said drain pipe for sealing said drain pipe and for enabling fluid to pass between said cavity and the exterior of said container. aligning pins connected to the top surface of said vessel; and aligning sockets within the lower surface of said cap corresponding to and mating with said aligning pins to align said cap upon said vessel. a gasket ring, between the top surface of said vessel and the lower surface of said cap, adjacent said cavity, sealing said cavity. 2. A container according to claim 1 wherein said vessel, cavity, and cap are of substantially rectangular transverse cross-section, said vessel and cap having rounded longitudinal edges. 3. A container according to claim 1 wherein said vessel has a continuous metal lining comprising: 4. A container according to claim 1 wherein said cap has a continuous metal lining comprising: 5. A container according to claim 1 wherein said concrete shielding material comprises aggregates selected from the group consisting of magnetite and specularite. 6. A container according to claim 1 wherein said continuous metal lining comprises material selected from the group consisting of copper, titanium, and carbon steel plate. 7. A container according to claim 1 wherein outer surfaces of said container are coated with epoxy paint to facilitate radioactive decontamination. 8. A container according to claim 1 wherein said vessel includes two diametrically opposing lifting lugs attached to its outer side walls for lifting said vessel and container. 9. A container according to claim 1 wherein said cap includes a lifting eyelet attached to its top surface for lifting said cap. 10. A container according to claim 1 comprising: 11. A container according to claim 1 comprising: 12. A container according to claim 1 comprising: 13. A container according to claim 1 comprising: 14. A container according to claim 1 comprising:
055815928	claims	1. An anti-scatter x-ray grid for medical diagnostic radiography, the grid comprising: a substrate having channels therein, the substrate comprising material that is substantially non-absorbent of x-radiation; and absorbing material in the channels, the absorbing material comprising material that is substantially absorbent of x-radiation, the substrate comprising plastic material capable of remaining stable at the melting temperature of the absorbing material. a substrate having channels therein, the substrate comprising material that is substantially non-absorbent of x-radiation; and absorbing material in the channels, the absorbing material comprising material that is substantially absorbent of x-radiation, wherein the ratio of the height of the absorbing material and the distance between channels ranges from 2:1 to 16:1 and wherein the line rate of the channels per centimeter ranges from 30 to 300. 2. The grid of claim 1, wherein the absorbing material comprises material capable of being melted and removed from the substrate. 3. The grid of claim 1, wherein the substrate is a material selected from the group consisting of polyetherimides, polyimides, and polycarbonates. 4. The grid of claim 3, wherein the substrate further comprises filler material. 5. The grid of claim 1, wherein the absorbing material comprises a lead-metal alloy. 6. The grid of claim 5, further including an adhesion promoting material between the substrate and the absorbing material, the adhesion promoting material is a material selected from the group consisting of copper, nickel, and iron. 7. The grid of claim 1, wherein the absorbing material comprises a metal alloy including material selected from the group consisting of lead, bismuth, gold, barium, tungsten, platinum, mercury, thallium, indium, palladium, silicon, antimony, tin, and zinc. 8. The grid of claim 1, wherein the absorbing material comprises a range of 60% to 50% bismuth and a corresponding range of 40% to 50% lead. 9. The grid of claim 1, further including a protective layer over at least one surface of the substrate, the protective layer comprising material that is substantially non-absorbent of x-radiation. 10. The grid of claim 9, wherein the protective layer comprises a plastic. 11. The grid of claim 1, wherein at least some of the channels are angled such that the channels are aligned to an x-radiation source. 12. The grid of claim 1, further including an adhesion promoting material between the substrate and the absorbing material. 13. An anti-scatter x-ray grid for medical diagnostic radiography, the grid comprising: 14. The grid of claim 12, wherein the line rate of the channels per centimeter ranges from 120 to 300.
	description	The present invention relates, generally speaking, to the field of the inspection of the tubes of a tube heat exchanger. More precisely, the invention relates to a method for evaluating the clogging of the passages of a tube support plate of a tube heat exchanger, said passages being made along the tubes and serving for the circulation of a fluid in said heat exchanger through said plate. A steam generator is generally composed of a bundle of tubes in which hot fluid circulates and around which circulates the fluid to be heated. For example, in the case of a steam generator of a PWR type nuclear power plant, the steam generators are heat exchangers that use the energy of the primary circuit from the nuclear reaction to transform the water of the secondary circuit into steam, which will supply the turbine and thus produce electricity. The steam generator brings the secondary fluid from a liquid water state to the steam state just at the saturation limit, using the heat of the primary water. Said primary water circulates in tubes around which the secondary water circulates. The outlet of the steam generator is the highest point in temperature and pressure of the secondary circuit. The exchange surface, physically separating the two circuits, is thus constituted of a tubular bundle, composed of 3500 to 5600 tubes, according to the model, in which circulates the primary water taken to high temperature (320° C.) and high pressure (155 bars). These tubes of the steam generator are maintained by tube support plates generally arranged perpendicularly to the tubes that pass through them. In order to allow the fluid which vaporises to pass, the passages of these tube support plates are foliated, that is to say that their shape has lobes around the tubes. Since the water goes from the liquid state to the vapour state, it deposits all the materials that it contains. If the depositions of material take place in the lobes, they reduce the free passage: this is clogging, which is thus the progressive closing up, by depositions, of the holes intended for the passage of the water/steam mixture. FIG. 1 schematically illustrates a top view of a foliated passage in a tube support plate 10, through which passes a tube 11. The lobes 12a and 12b enable water to pass through the tube support plate 10 along the tube 11, thereby enabling the circulation of water in the steam generator. A deposition 13 is visible at the lobe 12b, clogging said lobe 12b. The deposition may be situated on the tube side and/or on the plate side. The clogging leads to modifications of the flow of water in the steam generator, and thus favours the onset of excessive vibrations of the tubes, as well as inducing significant mechanical stresses on the internal structures of the steam generator. This degradation thus has effects both on the safety and on the performances of the installations. It is thus indispensable to have good knowledge of the nature and the evolution of this degradation. At present, the only non-destructive examination system that is capable of accessing the totality of the tube/tube support plate intersections of steam generators is the axial eddy current probe (SAX probe). Eddy currents appear in a conductive material when the adjacent magnetic flux is varied. A multifrequency eddy current probe is passed through a tube of said exchanger and a measurement signal is measured with said probe according to the environment in which the probe is situated, from which it is possible to extract information regarding anomalies in the heat exchanger. A variation of the magnetic induction, typically by a coil in which an alternating current circulates, generates eddy currents, of which the variation induced by the magnetic field is detected. Typically, the voltage difference generated by the variation of impedance of the coil is measured. The exploitation of the measurement signals of this eddy current probe does not result in a lengthening of the shutdown of the steam generator, since said eddy current probe is already used during unit shutdowns, particularly for inspecting the integrity of the tubes of the steam generator. Said eddy current probe, initially intended for the detection of damage to the tubes, is also sensitive to clogging. Furthermore, the interpretation of this signal is at present performed manually by specialised operators, which is very long, of the order of around a week of processing for the analysis of a single steam generator. Furthermore, the intervention of an operator to plot measurements from analysis software often gives rise to a bias that is difficult to quantify. Moreover, the measurement signal is not calibrated and is noisy, such that its exploitation may prove to be difficult. The evaluation of the clogged aspect of a foliated passage by an operator from the measurement signal is moreover very unreliable, being generally carried out empirically given the signal received and its comparison with other signals corresponding to other passages, the condition of which is known, for example by televisual inspection. A general aim of the invention is to overcome all or part of the defects of the methods of the prior art for evaluating the clogging of foliated passages around tubes in tube support plates. A method is in particular proposed for evaluating the clogging of the passages of a tube support plate of a tube heat exchanger, said passages being made along the tubes for a fluid to pass through the tube support plate, in which an eddy current probe is passed through a tube of said exchanger and a measurement signal is measured with said probe according to the environment in which the probe is situated, characterised in that in order to evaluate the clogging at the downstream edge of a tube support plate: a lower edge signal corresponding to the probe passing the downstream edge of the tube support plate is determined from the measurement signal; an upper edge signal corresponding to the probe passing the upstream edge of the tube support plate is determined from the measurement signal; the impulse response of the probe is estimated; the lower edge signal is deconvolved by means of said impulse response estimation; the clogging is evaluated by analysing the lower edge signal thus deconvolved. This method is advantageously completed by the following characteristics, taken alone or in any of the technically possible combinations thereof: the probe acquires at least in part the measurement signal in differential mode; the measurement signal is a multifrequency signal composed of at least two signals at different frequencies, and the lower edge signal and the upper edge signal result from linear combinations of at least two signals at frequencies different to said measurement signal; the linear combination involves a complex coefficient optimised to minimise the signal power along the tube outside of zones where plates are present; the impulse response of the probe is estimated from the upper edge signal; the deconvolution of the lower edge signal by means of the impulse response estimation of the probe is realised using a filter constructed from said impulse response estimation; the frequency response of the filter is an approximation of the inverse of the Fourier transform of the impulse response of the probe; the filter is a Wiener filter and the deconvolution is a Wiener deconvolution; the frequency response of the Wiener filter is of the form: G ⁡ [ f ] = H * ⁡ [ f ]  H ⁡ [ f ]  2 + B ⁡ [ f ] S ⁡ [ f ] with the exponent * designating the complex conjugation, H[f] the Fourier transform of the impulse response of the probe, S[f] the power spectral density of the signal to be estimated and B[f] the power spectral density of the noise; the impulse response of the probe h[n] is estimated from the response of the probe zupp[n] to the passage of the upstream edge of the tube support plate by the probe according to:h[n]=−zupp[−n] a filtering by a low pass filter is applied to the deconvolved lower edge signal, the cut-off frequency of said low pass filter being determined by means of a standard deviation of a Gaussian function constituting an approximation of the real part of an impulse of the signal corresponding to the probe passing a clean edge of a tube support plate; the analysis of the deconvolved lower edge signal comprises the analysis of the real part and the imaginary part of said deconvolved lower edge signal; the analysis of the deconvolved lower edge signal comprises the definition of indicators corresponding to pairs of extremes of physical quantities of the imaginary part of the lower edge signal. The invention also relates to a computer programme product comprising programme code instructions for the execution of the steps of the method according to the invention, when said programme is run on a computer. Extraction of the Useful Parts of the Measurement Signal In order to carry out the evaluation of the clogging of the foliated passages 12a, 12b of the tube support plates 10, the measurement signal preferably undergoes a pre-processing aiming in particular to extract therefrom the parts corresponding to the probe passing the tube support plates. The extraction of these useful parts of the measurement signal may be done in different ways. French patent application no 1256584 discloses a preferential embodiment for determining the position of the tube support plates, the principles of which are recalled hereafter. A multifrequency eddy current probe is passed through a tube 11 of said exchanger and a measurement signal is measured with said probe according to the environment in which the probe is situated. The measurement signal is thus acquired by the axial eddy current probe during its movement in the tube 11 of the steam generator. This measurement signal is multifrequency, and is in complex form, with real and imaginary components. Within the scope of this description, a signal will be considered with complex components according to three frequencies from three acquisition channels, of which two in differential modes noted z1[n] and z3[n] and one in absolute mode noted zA[n]. The frequencies are for example comprised in the range 100-600 kHz. The probe carrying out a back and forth journey in the tube, preferably the signals corresponding to the movement phase are chosen where the probe is pulled by the mechanism which moves, typically during its return. In fact, this results in a better mechanical stability of the probe, and consequently a more regular velocity thereof. The selection of the part of the signal of the probe corresponding to the return of the probe is based on the detection of an important drop of the voltage measured at the moment where the probe switches round to travel the tube in the return direction. The selection of a measurement signal limited to a single direction of the probe also makes it possible to limit the quantity of data to save and to process. Given the sensitivity of the acquisitions of the eddy current signals to the acquisition conditions, at the switching over of the probe and in order to standardise the signals analysed, a prior step of calibration is preferably implemented. This involves calibrating the signals with respect to reference signals, known as calibration signals. The latter correspond to defects established on the calibration tube, and the characteristics (amplitude and phase) of which are known. The calibration (step S0) takes place in the same manner whatever the acquisition frequency considered, with, in reference to FIG. 2, for each tube controlled: identification (step S20) of the parts of the measurement signal corresponding to known defects of the tube of the heat exchanger, estimation (step S21) of the phase and the amplitude of the parts of the measurement signal corresponding to the known defects, determination (step S22) of a transformation to apply to the measurement signal from said parts of the measurement signal corresponding to known defects to calibrate the measurement signal, application (step S23) of the transformation to the measurement signal. Let zuntreated(f)=x+jy (where j is the imaginary number) derived from an acquisition at frequency f, and zcalib(f)=xcalib+jycalib the complex impedance measured for a calibration defect given at the same frequency. A calibration defect is characterised by two parameters A0 and θ0 which are respectively the amplitude and the phase of the max-min vector (maximum amplitude vector on the representation according to Lissajous). These are the characteristics that the calibration defect should have after calibration. Before calibration, these two parameters are respectively equal to A and θ. The calibration of the signal z then consists in a rotation of angle δϕ=θ0−θ and a homothetic transformation of the h=A0/A parameter as described by the following equation:z=hz0ejδϕ Actually, use is not made of the geometric configuration of the tube or the heat exchanger to detect the zone of the defect, but uniquely the characteristics of the signal (phase and amplitude). A calibration is thus available that is independent of the problems of handling the probe or sampling the signal, which are capable of falsifying the assessment of the position of the part of the signal corresponding to the defect. Once the measurement signal has been calibrated, it remains to determine the parts of the multifrequency measurement signal corresponding to the passage at the tube support plates 10 of the eddy current detecting probe acquiring said measurement signal in the tube of the heat exchanger. The measurement signal is very noisy and cannot be used directly to detect the tube support plates 10. In order to facilitate this detection, a detection signal, noted d[n], is constructed by linear combination of components of the measurement signal of different frequencies to minimise the energy of the detection signal between the tube support plates 10, while taking a high value at the passage of tube support plates 10. The signals available at the input of the algorithm are the three calibrated complex signals zA[n], z1[n] and z3[n] corresponding to the return of the probe in the tube. Only the signals corresponding to the differential mode (z1 and z3), more sensitive to the probe passing by a plate, are used in this part. The respective real and imaginary components of the signal zi[n] are noted xi[n] and yi[n]. Firstly the set of available measurements is filtered by a high pass filter in order to delete the small variations of signals due to the horizontal movement of the probe in the tube. For each signal available a high pass filter (for example a Butterworth filter) is applied, for example of 0.01 reduced cut-off frequency. The signals resulting from the filtering of the signals z1 and z3 are noted z1f and z3f. The real and imaginary parts of these signals are thus noted:z1f[n]=x1f[n]+jy1f[n]z3f[n]=x3f[n]+jy3f[n] This first filtering operation makes it possible to construct signals having a constant and zero average base line. To then construct a detection signal that is the weakest possible between the plates, an observation window is firstly searched for expressed in number of samples of signal which limits the impact of the passage of a tube support plate 10. To do so, information is available on the average velocity v of the probe, as well as on the sampling frequency fe. Knowing the velocity of the probe and its sampling frequency, each distance may be converted into a number of signal samples according to the formula: N sample = distance × f e v It is possible for example to search for an observation window corresponding to a length of M samples less than the number of samples between two successive tube support plates 10 Npe,pe, for example M = N pe , pe 2 . This search is carried out for example on the signal x3f·x3f having a high variance during the passage of the probe at a tube support plate 10. It suffices to find such a window to search for the portion of the signal of length M where the variance of x3f is minimal. By noting m0 the first index of this window, this leads to: m 0 = argmin m ⁢ { ∑ n = m m + M - 1 ⁢ ( x 3 ⁢ f ⁡ [ n ] - 1 M ⁢ ∑ n = m m + M - 1 ⁢ x 3 ⁢ f ⁡ [ n ] ) 2 } However, the portions of signal corresponding to the passage by the tube support plates 10 are not known, since this is precisely what it is sought to determine. Thus, if a tube support plate 10 was found in the observation window, it could significantly impact the remainder of the method. In order to limit the impact of the passage of a tube support plate 10 in the calculation, a sufficiently large window is preferably chosen. For example, the observation window may correspond to an estimated number of samples of the measurement signal representing the distance between consecutive tube support plates 10 along the tube 11, that is to say of size M=Npe,pe. In order to limit the impact of the passage by a tube support plate 10, it is also possible to choose the set of indices of the signal n such that \|x3f[n]\| is below a certain threshold. This threshold may be for example the standard deviation of the signal x3f. Different components of the measurement signal are then combined to determine a detection signal, the combination thereby made being chosen to minimise the energy of the detection signal. The combination of the different components of the measurement signal is an adaptive linear combination, the values of the weighting coefficients used for this combination being determined, for one sample of the detection signal, by minimisation of the variance of the detection signal on the observation window of the measurement signal around this sample. Preferably, the different components of the measurement signal combined to determine the detection signal are real and imaginary components of the measurement signal. Similarly, different components of the measurement signal combined to determine the detection signal are components of different frequencies. Weighting coefficients α, β and γ are thus sought such thatx3f[n]≈α·x1f[n]+β·γ3f[n]+γ·y1f[n]in order to construct the detection signal d[n] defined byd[n]=x3f[n]−α·x1f[n]−β·y3f[n]−γ·y1f[n] Furthermore, to manage the considerable non-stationarity of the components of the measurement signal, the coefficients α, β and γ are updated for each signal sample. More precisely, the triplet {α[n], β[n], γ[n]} chosen at an instant n is that which minimises the power of the reconstruction error on a signal window centred on the n-th sample: { ∝ [ n ] , β ⁡ [ n ] , γ ⁡ [ n ] } = argmin α , β , γ ⁢ { ∑ k = n - M / 2 k = n + M / 2 - 1 ⁢ ( x 3 ⁢ f ⁡ [ k ] - ∝ x 1 ⁢ f ⁡ [ k ] - β ⁢ ⁢ y 3 ⁢ f ⁡ [ k ] - γ ⁢ ⁢ y 1 ⁢ f ⁡ [ k ] ) 2 } The optimisation of {α[n], β[n], γ[n]} is carried out by means of the least squares algorithm. It will be noted that the number of coefficients may be changed. A detection signal d[n] chosen by adaptive linear combination of real and imaginary components of the measurement signal is thereby obtained. Such a construction of the detection signal has several advantages: an automatic estimation of the optimal coefficient of combination of frequencies (i.e. search for the coefficient minimising the energy of the outside of plate signal); the combination may take place between all the components (real and imaginary parts) of the different frequencies; the combination coefficients are not constant along the tube, but vary in order to adapt to the tube. Variations of the condition of the tube are thus managed. Once the detection signal has been constructed, it remains to detect the peaks of the detection signal likely to correspond to the passage of tube support plates 10, by comparison with a detection threshold. In fact, the detection signal thereby created contains different peaks, which correspond to the probe passing the different plates, and not only the tube support plates 10, and other elements of structures. These signal peaks may be identified by only retaining signal peaks above a detection threshold s. Preferably, the detection threshold for detecting the peaks of the detection signal is a function of the minimum value that the standard deviation σ of the detection signal takes over a part of the signal corresponding to a number of samples less than the estimated number of samples between two consecutive tube support plates 10. The standard deviation σ may be determined in the following manner: σ = min m ⁢ { 1 M - 1 ⁢ ∑ n = m m + M - 1 ⁢ ( d ⁡ [ n ] - 1 M ⁢ ∑ n = m m + M - 1 ⁢ d ⁡ [ n ] ) 2 } The detection threshold must then be a compromise between the risk of false detections (a too low threshold leads to the detection of numerous peaks not corresponding to the probe passing a tube support plate 10) and the risk of not detecting a tube support plate 10. It may for example be comprised between 5 and 15 σ, preferably 10 σ. It may be that the probe passing a tube support plate results in several passages of the signal above the detection threshold. To only retain a single peak per plate, to then pinpoint the peaks corresponding to the tube support plates 10, the following test is carried out on successive pairs of peaks: if n1 and n2 are two indices of successive peaks, it will be said that n2 is a “secondary peak” of n1 if d[n1]>d[n2] and if the number of samples between n1 and n2 is considerably below the minimum distance estimated between two peaks of plates. Thus, prior to the step of selection of the peaks, the peaks detected are restricted to the peaks corresponding to a local maximum of the detection signal over a range of the detection signal corresponding to a number of samples on either side of the local maximum less than or equal to the minimum of the following three values: 0.5 times an estimated number of samples between two tube support plates, 0.8 times an estimated number of samples between the tube support plate of the hot branch the closest to the cold branch of said heat exchanger and the tube support plate of the cold branch the closest to the hot branch of said heat exchanger, 0.8 times an estimated number of samples between a first of the tube support plates and another preceding plate in the direction of circulation of the probe. The secondary peaks being deleted, it then remains to select the peaks of the detection signal corresponding to the passage of the tube support plates 10 by a determination of the peaks of the signal having a regular spacing. Ideally, if the probe has a known and constant velocity v, then the number of samples between two plates is exactly proportional to the distance between plates: N pe , pe = distance ⁢ ⁢ between ⁢ ⁢ plates × f e v In this ideal case, it would suffice to identify the indices of the corresponding samples to only retain the peaks for which the indices are exactly spaced by Npe,pe. In practice, the velocity of the probe is not exactly constant nor precisely known and may vary along the tube. The gap between two peaks corresponding to tube support plates 10 is thus not exactly equal to Npe,pe and it may be different from one pair of tube support plates 10 to another. This average gap between tube support plates 10 may however be estimated. To do so, the peaks of the detection signal corresponding to the passage of the tube support plates 10 are selected by the selection of at least one sub-set of peaks minimising the difference between the number of samples of the detection signal between two successive peaks of said sub-set and a median value of the number of samples of the detection signal between two successive peaks. A tube of a heat exchanger extends along it through two parts, generally designated cold branch and hot branch, according to the direction of flow of the fluids realising the heat exchange, separated by a structure without tube support plate 10 designated as the curve. Consequently, such a structure breaks the regularity of the spacing of the tube support plates. It suffices to call on the following method for one branch, then for the other, to select all of the peaks corresponding to the tube support plates 10. ik designates the index of the k-th peak detected, Δ[k]=ik+1−ik the gap between the successive peaks k and k+1, and Npe,pe,real the average number of samples between two tube support plates 10. Since the tube support plates are the majority plates along the tube, the majority of the values taken by Δ[k] is situated around Npe,pe,real. An estimation of Npe,pe,real is thus provided by the median value of the set of values taken by Δ[k]:Npe,pe,real=median{Δ[k]} It then remains to find, among the set I of peak indices, the sub-set Ipeak of indices corresponding to the number of tube support plates NbPe, such that the gaps between two successive indices are always more or less equal to Npe,pe,real: I peak = argmin I ⁢ ∑ i ∈ I ⁢ ( Δ ⁡ [ i ] - N pe , pe , real ) 2 . The indices of samples of the signal corresponding to the passage of tube support plates 10 are thus obtained. Once the set of indices corresponding to the probe passing the tube support plates 10 has been estimated, it is then possible to carry out at a subsequent step of verification in which the positions of the peaks of the detection signal corresponding to the passage of the tube support plates 10 are compared with known data on the geometry of the heat exchanger. Two criteria are used: the length of the tube support plates 10 and the length of the curve. The first verification criterion relates to the length of the curve: for each tube, the number of samples between the final plate of the hot branch and the final plate of the cold branch is compared to the known distance according to the plans. A margin is allowed, in order to take account of the uncertainty on the velocity of the probe. The second validation criterion makes it possible to verify the length of the set of plates detected. The detection algorithm having made it possible to estimate the indices of the tube support plates 10 uses the positive peaks of the detection signal. However the probe passing a tube support plate 10 generates on the signal at least one positive peak and one negative peak (the two peaks correspond to the probe passing the edges of plates). A new estimation of the indices of the tube support plates 10 may thus be obtained by detecting this time the negative peaks of the detection signal, without taking into account the first peaks detected. In practice, it suffices to recall the detection algorithm of the peaks by taking the opposite of the detection signal (d[n] becomes −d[n]). The method may thus comprise a final step of verification in which the opposite of the detection signal is taken, the steps of detection S2 and of selection S3 of the positions of the peaks of the detection signal corresponding to the passage of the tube support plates 10 are applied and a check is made that the gaps between the positions of the peaks on the detection signal and on its opposite correspond to the edge to edge distance of a tube support plate 10. Two sets of estimated indices are then thus available, for each branch. If these two sets of indices are correct, the difference between the two estimations of a same tube support plate 10 must be of the order of magnitude of the size of a tube support plate 10. Taking account of imprecisions on the velocity of the probe and plate edge effects, a margin is allowed to validate the estimation. Since the positions of the tube support plates are known in the measurement signal, it is thus possible to extract therefrom the useful parts relative to the probe passing the tube support plates. Evaluation of the Clogging The useful signal relative to the passage of the tube support plates 10 is thus available after its extraction from the set of the measurement signals emitted by the SAX probe. To do so, methods other than that described previously may be envisaged. At this stage, for each tube support plate 10, a signal corresponding to the probe passing the downstream edge of the tube support plate 10, and a signal corresponding to the probe passing the upstream edge of the tube support plate 10 has thus been extracted from the measurement signal. A lower edge signal corresponding to the probe passing the downstream edge of the tube support plate 10, and an upper edge signal corresponding to the probe passing the upstream edge of the tube support plate 10 are then determined from the measurement signal. Thus, as explained above, the probe acquires at least in part the measurement signal in differential mode, and the measurement signal is a multifrequency signal composed of at least two signals at different frequencies. Preferably, only signals corresponding to the differential mode (z1 and z3) are used because they are more sensitive to the passage of the tube support plate 10. These signals are acquired at different frequencies, and the lower edge signal is determined as the linear combination of at least two signals at frequencies different to said measurement signal, in this instance z1 and z3. This linear combination involves a complex α coefficient optimised to minimise the signal power along the tube 11 outside of the tube support plate zones 10. Thus, the lower edge signal zlow is determined from the signals obtained in differential mode over the frequencies f3 and f1, such thatZlow[n]=z3low[n]−α·z1low[n], with ∝=argmin∥z3[n]−∝×z1[n]∥2,for the indices n corresponding to the signal outside of the tube support plate zones 10, and z3low corresponding to the response of the probe in differential mode on the frequency f3 during the probe passing the downstream, that is to say lower, edge of the tube support plate 10, and z1low corresponding to the response of the probe in differential mode on the frequency f1 during the probe passing the downstream, that is to say lower, edge of the tube support plate 10. The same is done with the upper edge signal, with preferably the same coefficient α, such that zupp[n]=z3upp[n]−α·z1upp[n], with z3upp corresponding to the response of the probe in differential mode on the frequency f3 during the probe passing the upstream, that is to say upper, edge of the tube support plate 10, and z1upp corresponding to the response of the probe in differential mode on the frequency f1 during the probe passing the upstream, that is to say upper, edge of the tube support plate 10. Two complex signals are thus obtained. The lower edge signal zlow may be expressed as:zlow[n]=xlow[n]+i·ylow[n]with xlow and ylow respectively the real and imaginary components of the lower edge signal and i the imaginary unit such that i2=1. Similarly, the upper edge signal zupp may be expressed as:zupp[n]=xupp[n]+i·yupp[n]with xupp and yupp respectively the real and imaginary components of the upper edge signal and i the imaginary unit such that i2=1. It thus remains to implement an appropriate processing of these signals in order to evaluate the clogging of the passage of the tube support plate 10. This processing is implemented on the lower edge signal, which is a complex signal. In fact, the clogging of the foliated passages, that is to say the lobes 12a, 12b, in the tube support plates 10 takes place at the lower edge of the tube support plates 10, upstream of the passage for the flux of fluid passing through the tube support plate 10. It is thus from the lower edge signal that the level of clogging may be estimated. More precisely, the lower edge signal is deconvolved by the complex impulse response of the probe. Actually, in an ideal case of a perfect SAX probe, the signal should only contain a series of complex impulses, corresponding to the passage by an edge of tube support plate 10, on meeting a deposition, and the study of the single lower edge signal should be sufficient to quantify the clogging. However, in practice, the response of the SAX probe to an impedance variation is not perfect. It is known as the impulse response of the probe. It is thus necessary to restore the lower edge signal to recover the response of the probe representative of the clogging state of the foliated passage in the tube support plate 10. To this end an impulse response estimation of the probe is determined, preferably corresponding to the probe passing a clean edge of the tube support plate 10 in the tube 11, for example from the upper edge signal. It is then sought to deconvolve the lower edge signal zlow[n] by a signal h[n] corresponding to the impulse response of the probe at the passage of the tube support plate. To do so, it is possible to use a filter. Such a filter is designated deconvolution filter or instead restoration filter. The deconvolution filter is calculated from the impulse response estimation, and the lower edge signal is deconvolved by means of said deconvolution filter (step S30). The deconvolution filter may be an approximation of the inverse of the impulse response of the probe. It may also be a Wiener filter and the deconvolution may thus be a Wiener deconvolution, which constitutes a preferential embodiment of the method described. Other deconvolution methods exist and may be used. For example, the deconvolved lower edge signal zlow,id[n] that best corresponds to the lower edge signal zlow[n] that has been observed may be searched for:zinf,id[n]=argminz[n]{J1(zinf[n]−z[n]⊕h[n])+λ×J2(z[n])}with J1 the data fit criterion (for example an L2 norm, a squared L2 norm, an L1 norm, etc.) and J2 a criterion reflecting a characteristic a priori known on the signal that it is sought to reconstruct (for example an L2 norm, a squared L2 norm, an L1 norm, a function of the gaps between neighbouring samples z[n]−z[n−1]). The term λ makes it possible to accord more or less importance to the a priori on the solution (J2) compared to the data fit (J1). This criterion may also be written in the frequency domain. There are thus several variants of deconvolution criteria J1 and J2 that may be used, and, for each variant, several resolution methods, for example by filtering or by optimisation methods. In the case where the deconvolution filter is a Wiener filter, the frequency response of the Wiener filter is of the form: G ⁡ [ f ] = H * ⁡ [ f ]  H ⁡ [ f ]  2 + B ⁡ [ f ] S ⁡ [ f ] with the exponent * designating the complex conjugation, H[f] the Fourier transform of the impulse response of the probe, S[f] the power spectral density of the signal to be estimated and B[f] the power spectral density of the noise. A zero-padding, that is to say an addition of zeros within the signals, may be carried out during the calculation of the discrete Fourier transforms in order to increase the frequency resolution. The impulse response h[n] of the probe may be estimated from the response of the probe at the passage of the upstream edge of the tube support plate 10 by the probe, that is to say by means of the upper edge signal, according to the formula:h[n]=−zupp[−n]. For example, from processing operations carried out to extract the useful parts of the measurement signal, the indices ilow and iupp of the measurement signal corresponding respectively to the passages of the lower and upper edges of the tube support plate 10 are known. For a sampling frequency Fe=1000 Hz, a velocity of the probe v=0.5 m·s−1 and a length of tube support plate 10 of 30 mm, there are 60 samples of signal corresponding to the tube support plate 10, and an impulse response of around 20 samples. It is then possible to choose for the range of values of the upper edge signal zupp[n] the 60 samples following the centre of the tube support plate 10 determined at around 0.5×(ilow+iupp), i.e. a margin of 20 samples on each side of the impulse response. These figures are obviously indicated as a non-limiting example of the use of the upper edge signal zupp[n] for the impulse response estimation of the probe. Several approaches are possible for estimating the signal to noise ratio corresponding to the ratio of the power spectral density of the noise B[f] and the power spectral density S[f] of the signal to be estimated. One of these approaches consists in approximating this ratio by a constant. In fact, the signal to be estimated corresponds to an ideal lower edge signal which would show a series of impulses corresponding to the variations of complex impedance encountered by the probe in the vicinity of the tower edge of the tube support plate 10. Consequently, the power spectral density S[f] of this signal may be considered as a constant. The power spectral density of the noise B[f] may be determined on the portions of the signal between the tube support plates 10. This may be assimilated with a white noise, and thus this power spectral density of the noise B[f] may be considered as a constant. Thus the ratio of the power spectral densities of the noise and of the signal to be estimated may be considered as a constant. This constant may be adjusted empirically, by taking for example: B ⁡ [ f ] S ⁡ [ f ] = 10 × σ 2 ,with σ2 the power of the noise, calculated on an out of plate zone. Once the deconvolution filter has been determined, it is then possible to carry out the deconvolution of the lower edge signal by means of said deconvolution filter. The deconvolution filter g is then applied to the lower edge signal zlow to obtain a complex deconvolved lower edge signal zlow id introduced by the impulse response of the probe:zlow id=zlow*g. In practice, this operation may be carried out in the frequency domain:zlow id=TF−1{Zlow[f]×G[f]},with Zlow[f] the Fourier transform of the lower edge signal zlow, G[f] the Fourier transform of the deconvolution filter g, and TF−1 indicating the inverse Fourier transformation. In order to avoid amplifying too substantially certain frequencies only corresponding to the measurement noise, a filtering (step S31) by a low pass filter is applied to the deconvolved lower edge signal, the cut-off frequency of said low pass filter being determined by means of a standard deviation of a Gaussian function constituting an approximation of the real part of an impulse of the lower edge signal corresponding to the passage of an edge of tube support plate 10. In fact, the real or imaginary part of an impulse of the lower edge signal corresponding to the passage of an edge of tube support plate 10 has forms very similar to Gaussian functions or derivatives thereof. For example, it is possible to assimilate to a Gaussian function the impulse 0 in the real part of the lower edge signal corresponding to the passage of the lower edge of the tube support plate 10 in a configuration without clogging, and to a linear combination of derivatives of the Gaussian function the impulses in the imaginary part of the lower edge signal corresponding to the passage of the lower edge of the tube support plate 10 in a clogged configuration. If σ is the standard deviation of this Gaussian function, generally of the order of 3 or 4 samples, the Fourier transforms of the signals to be deconvolved no longer contain energy above a maximum frequency fmax: f ma ⁢ ⁢ x = 3 2 ⁢ π ⁢ ⁢ σ . This maximum frequency fmax may thus be chosen as cut-off frequency of the low pass filter. Once the deconvolved lower edge signal thereby filtered, it remains to analyse said signal to evaluate the clogging. This analysis is preferably based on the analysis of the profile of the real part and the imaginary part of the lower edge signal. These profiles are compared to the ideal profiles expected for several configurations in order to identify the configuration to which the deconvolved lower edge signal corresponds. Several examples are given hereafter, for the case of a probe entering via the lower edge of the plate. The same configurations would be obtained in the case of a probe exiting via the lower edge of the plate. The ideal temporal response of the probe passing through a clean edge of a tube support plate 10, that is to say free of clogging or fouling, is illustrated by FIG. 5. In this figure, the curve 50 represents the complex impedance in absolute mode during the passage of an edge of a clean tube support plate 10. This comprises a first part 51 corresponding to an impedance characteristic of the tube 11 in the absence of tube support plate 10, noted Ztube, and a second part 52 corresponding to an impedance characteristic of the presence of the plate Zplate. Curve 53 represents the complex impedance in differential mode during the passage of an edge of a clean tube support plate 10, in correspondence with curve 50. The passage of the rim of tube support plate 10 results in an impulse 54 characteristic of the passage of the impedance from the tube 11 to that of the tube support plate 10, and corresponding to Zplate-Ztube. FIG. 6 shows the Lissajous signal, with the real part of the deconvolved lower edge signal on the X-axis and the imaginary part on the Y-axis. FIG. 7 shows in a temporal manner, at the top the real part of the deconvolved lower edge signal, and at the bottom the imaginary part of the deconvolved lower edge signal. The deconvolved upper edge signal is also represented, this being considered as reference representing a clean edge of a tube support plate 10. However, in these figures, the lower edge signal and the upper edge signal are superimposed, indicating that the lower, or downstream, plate edge is clean, in the same way as the edge of the upper plate. FIGS. 8 to 11 illustrate a configuration in which the lower plate edge is clogged by a deposition of magnetite situated at the same level as the lower plate edge. The ideal temporal response of the probe passing through a clogged edge of a tube support plate 10 is illustrated by FIG. 8. In this figure, curve 80 represents the complex impedance in absolute mode during the passage of a clogged edge of a tube support plate 10. This comprises a first part 81 corresponding to an impedance characteristic of the tube 11 in the absence of tube support plate 10 and clogging, noted Ztube, a second part 82 corresponding to an impedance characteristic of the presence of clogging of magnetite between the tube 11 and the tube support plate 10, noted Zmagn, and a third part 83 corresponding to an impedance characteristic of the presence of the tube support plate 10 without magnetite, noted Zplate. Curve 84 represents the complex impedance in differential mode during the passage of an edge of a clogged tube support plate 10, in correspondence with curve 80. The start of clogging of magnetite results in a first impulse 85 characteristic of the passage of the impedance from the tube to that of the deposition of magnetite, and corresponding to Zmagn-Ztube. The end of the deposition of magnetite results in a second impulse 86 characteristic of the passage of the impedance from the deposition of magnetite to that of the plate and corresponding to Zplate-Zmagn. FIG. 9 shows a representation in Lissajous that an ideal signal representative of clogging should show. It shows a first signature 95 characteristic of the passage of the impedance from the tube to that of the deposition of magnetite, and corresponding to Zmagn-Ztube. It also shows a second signature 96 characteristic of the passage of the impedance from the deposition of magnetite to that of the plate and corresponding to Zplate-Zmagn. The dotted line signature 97 corresponds to the signature of the passage characteristic of the passage of the impedance from the tube to that of the tube support plate in the absence of clogging, and corresponding to Zplate-Ztube. It will moreover be noted that the sum of the first signature 95 and the second signature 96 corresponds to the dotted line signature 97. In fact, Zmagn-Ztube+Zplate-Zmagn=Zplate-Ztube. FIGS. 10 and 11 illustrate the deconvolved lower edge signal in the case of clogging by a deposition of magnetite. FIG. 10 shows a representation in Lissajous of this deconvolved lower edge signal. It shows a first signature 105 characteristic of the passage of the impedance from the tube to that of the deposition of magnetite, and corresponding to Zmagn-Ztube. It also shows a second signature 106 characteristic of the passage of the impedance from the deposition of magnetite to that of the plate and corresponding to Zplate-Zmagn. The third signature 107 corresponds to the signature of the deconvolved upper edge signal, assumed clean. A very good correlation is observed between the profile of the deconvolved lower edge signal and the profile of an ideal signal. Consequently, it is easy to deduce the clogging state of the foliated passage from the deconvolved lower edge signal. FIG. 11 shows in a temporal manner, at the top the real part of the deconvolved lower edge signal 110, and at the bottom the imaginary part of the deconvolved lower edge signal 111, in the same configuration. The real part 112 and the imaginary part 113 of the deconvolved upper edge signal are also represented, the upper edge signal being considered as reference representing a clean edge of a plate. It may be deduced from FIGS. 10 and 11 that the lower edge signal, after deconvolution, indeed contains two complex impulses, which represent the two variations of impedance corresponding to the probe passing by the ends of the deposition clogging the foliated passage. FIGS. 12 to 15 illustrate a configuration in which a deposition formed of a ring of magnetite is present on the tube, below the lower edge of the tube support plate. The ideal temporal response of the probe in the vicinity of this ring of magnetite and this edge of tube support plate is illustrated by FIG. 12. In this figure, curve 120 represents the complex impedance in absolute mode. This comprises a first part 121 corresponding to an impedance characteristic of the tube in the absence of tube support plate and clogging, noted Ztube, a second part 122 corresponding to an impedance characteristic of the presence of a ring of magnetite along the tube, noted Zmagn, a third part 123 corresponding to the part of the tube between the deposition and the plate, and the impedance of which is Ztube, and finally a fourth part 124 corresponding to an impedance characteristic of the presence of the tube support plate 10 without magnetite, noted Zplate. Curve 125 represents the complex impedance in differential mode during the probe passing in the vicinity of this ring of magnetite and this edge of tube support plate, in correspondence with curve 120. The start of deposition of magnetite results in a first impulse 126 characteristic of the passage of the impedance from the tube to that of the deposition of magnetite, and corresponding to Zmagn-Ztube. The end of deposition of magnetite results in a second impulse 127 characteristic of the passage of the impedance from the deposition of magnetite to that of the tube, and corresponding to Ztube-Zmagn. The rim of the tube support plate results in a third impulse 128 characteristic of the passage of the impedance from the tube to that of the tube support plate, and corresponding to Zplate-Ztube. FIG. 13 shows a representation in Lissajous that an ideal signal representative of this configuration should show. It shows a first signature 136 characteristic of the passage of the impedance from the tube to that of the magnetite deposition ring, and corresponding to Zmagn-Ztube. It also shows a second signature 137 characteristic of the passage of the impedance from the magnetite deposition to that of the tube, and corresponding to Ztube-Zmagn. It should be noted that, logically, the second signature 137 is the opposite of the first signature 136. Finally it shows a third signature 138 characteristic of the passage of the impedance from the tube to that of the plate, and corresponding to Zplate-Ztube. FIGS. 14 and 15 illustrate the deconvolved lower edge signal in the configuration with a magnetite deposition ring. FIG. 14 shows a representation in Lissajous of this deconvolved lower edge signal. It shows a first signature 146 characteristic of the passage of the impedance from the tube to that of the magnetite deposition ring, and corresponding to Zmagn-Ztube. It also shows a second signature 147 characteristic of the passage of the impedance from the magnetite deposition to that of the tube, and corresponding to Ztube-Zmagn. It should be noted that logically, the second signature 147 is the opposite of the first signature 146. Thus, two peaks are observed, that is to say signatures, of zero sum with a considerable energy on the imaginary part. Finally it shows a third signature 148 characteristic of the passage of the impedance from the tube to that of the plate, and corresponding to Zplate-Ztube. The fourth signature 149 corresponds to the signature of the deconvolved upper edge signal, assumed clean. It may here be noted that the proximity of the ring of magnetite with the lower edge of the tube support plate leads to a mixture between the second signature 147 and the third signature 148. A very good correlation is observed between the profile of the deconvolved lower edge signal and the profile of an ideal signal. Consequently, it is easy to deduce from the deconvolved lower edge signal the configuration of the clogging of the foliated passage. FIG. 15 shows in a temporal manner, at the top the real part of the deconvolved lower edge signal 150, and at the bottom the imaginary part of the deconvolved lower edge signal 151, in the same configuration. The real part 152 and the imaginary part 158 of the deconvolved upper edge signal are also represented, the upper edge signal being considered as reference representing a clean edge of a plate. It shows for the real part of the deconvolved lower edge signal a peak 153 corresponding to the passage of clean plate, and two peaks 154, 155, of zero sum, revealing the presence of the ring of magnetite. Two corresponding peaks 156, 157 for the imaginary part of the deconvolved lower edge signal are reproduced. The expected absence of peak corresponding to the passage from the edge of clean plate should be noted for the imaginary part. FIGS. 16 to 19 illustrate a configuration in which a tube fouled over this length by a deposition of magnetite has a fouling break below the lower edge of the tube support plate. The ideal temporal response of the probe in the vicinity of this fouling break and this edge of tube support plate is illustrated by FIG. 16. In this figure, curve 160 represents the complex impedance in absolute mode. This comprises a first part 161 corresponding to an impedance characteristic of the tube fouled by magnetite, noted Zfoul, a second part 162 corresponding to an impedance characteristic of the tube in the absence of magnetite, noted Ztube, at the break of the fouling of the tube, and a third part 163 to an impedance characteristic of the presence of the tube support plate 10 without magnetite, noted Zplate. The curve 165 represents the complex impedance in differential mode during the probe passing from this fouling break and the edge of tube support plate, in correspondence with curve 160. The fouling break by the magnetite results in a first impulse 166 characteristic of the passage of the impedance from the fouled tube to that of the tube free of magnetite, and corresponding to Ztube-Zfoul. The passage of the rim of the tube support plate results in a second impulse 167 characteristic of the passage of the impedance from the tube to that of the tube support plate, and corresponding to Zplate-Ztube. FIG. 17 shows a representation in Lissajous that an ideal signal representative of this configuration should show. It shows a first signature 176 characteristic of the passage of the impedance from the fouled tube to that of the tube free of magnetite, and corresponding to Ztube-Zfoul. It also shows a second signature 177 characteristic of the passage of the impedance from the tube to that of the plate, and corresponding to Zplate-Ztube. FIGS. 18 and 19 illustrate the deconvolved lower edge signal in the configuration of the tube with a fouling break. FIG. 18 shows a representation in Lissajous of this deconvolved lower edge signal. It shows a first signature 186 characteristic of the passage of the impedance from the fouled tube to that of the tube free of magnetite, and corresponding to Ztube-Zfoul. It also shows a second signature 187 characteristic of the passage of the impedance from the tube to that of the plate, and corresponding to Zplate-Ztube. A very good correlation is observed between the profile of the deconvolved lower edge signal and the profile of an ideal signal. Consequently, it is easy to deduce from the deconvolved lower edge signal the presence of a fouling break of the tube. FIG. 19 shows in a temporal manner, at the top the real part of the deconvolved lower edge signal 190, and at the bottom the imaginary part of the deconvolved lower edge signal 191, in the same configuration. The real part 192 and the imaginary part 193 of the deconvolved upper edge signal are also represented, the upper edge signal being considered as reference representing a clean edge of a plate. It shows for the real part of the deconvolved lower edge signal a positive peak 194 corresponding to the passage of clean plate, and a negative peak 195 corresponding to the presence of a fouling break. A negative peak 196 is reproduced for the imaginary part of the deconvolved lower edge signal. The expected absence of peak corresponding to the passage from the edge of clean plate should be noted for the imaginary part. The examples could again be multiplied. It may be deduced therefrom that the method according to the invention makes it possible to interpret physically the profiles of the deconvolved complex signal. Simple indicators may be put forward to deduce the condition of the foliated passages of a tube support plate. Actually, the deconvolved complex signal represents directly the condition of the tube support plate through the different types of variation of impedance that it highlights. For a clean tube support plate, the imaginary part of the deconvolved complex signal has zero power. In the presence of a clogged lower edge of plate: the imaginary part of the deconvolved lower edge signal has high power; the imaginary part of the deconvolved lower edge signal does not have a constant sign; the imaginary part of the deconvolved lower edge signal contains as much power in its positive as in its negative values. Other configurations may also be detected. For example, in the case of a fouled tube, a fouling break in the vicinity of the tube support plate may be detected by the fact that: the imaginary part of the deconvolved complex signal has considerable power; the imaginary part of the deconvolved complex signal is of constant sign. Thus, the method according to the invention makes it possible to considerably improve the evaluation of the condition of clogging of foliated passages, by making it possible in particular to distinguish different configurations, for example a fouling break which could pass for clogging with less precise methods. More precisely, indicators may be defined to facilitate the analysis of the lower edge signal. The analysis of the deconvolved lower edge signal may thus comprise the definition of indicators corresponding to pairs of extremes of physical quantities of the imaginary part of the lower edge signal. For example, the following indicators may be used for the estimation of clogging or fouling: If y+ (respectively y−) designates the positive (resp. negative) values taken by the imaginary part of the signal obtained in the vicinity of the lower edge of the plate after deconvolution, and if the following different quantities are defined: EY+/Ey−: energy of y+ and y− PY+/Py−: power of y+ and y− MY+/My−: maximum value of y+ and \|y−\| ΓY+/Γy−: standard deviation of the values taken by y+ and by y.For each pair of physical quantities, XY+/Xy−, with X corresponding to E, P, M or Γ, a minimal indicator and a maximal indicator are defined: Xmin=min {XY+, Xy−} Xmax=max {XY+, Xy−}According to the preceding interpretations, there is a simple correspondence between the indicators Xmin, Xmax and the condition of the plate: Clean tube support plate: Xmin and Xmax are low; Fouling break in the vicinity of the lower edge: Xmin is low, Xmax is high; Lower edge clogged: Xmin and Xmax are high and approximately equal.Other indicators can also be used, by regarding the projection of the deconvolved lower edge signal over a family of functions (Gaussian functions for example). The invention also relates to a computer programme product comprising programme code instructions saved on a support that can be used in a computer for the execution of the processing steps of the method for evaluating clogging, when said programme is run on a computer. Actually, the measurement signal is transmitted from the eddy current probe to a memory to be stored therein with a view to its processing. Said processing of the measurement signal on which the present invention is based is implemented by a processing unit equipped with a calculator, typically a computer provided with display and communication means, through which it acquires the measurement signal and transmits the results of the implementation of the method for evaluating clogging, said computer being configured to implement the method according to the invention.
	description	The following describes the micro-manipulation method concerned with this invention. FIG. 1 illustrates a general relationship between the effective accelerating voltage Va, which is determined by the electron beam accelerating voltage and the object""s potential, and the electron emission ratio Iout/Iin, which is the ratio of electrons emitted by the micro-object. FIG. 2 illustrates xcex4+xcfx84, that is, the sum of the secondary electron emission ratio and the transmitted electron emission ratio. FIG. 3 is a table that shows the relationships between the accelerating voltages and charge polarities. In FIG. 1, when the electron emission rate equals 1, this means that the object emits exactly the same quantity of electrons as the beam of electrons that have passed the object. Electrons entering an object are generally emitted from the object in the form of secondary electrons or transmitted electrons. As the effective accelerating voltage Va becomes larger, the secondary electron emission ratio xcex4 first increases sharply, then exceeds 1 and reaches the maximum value. Thereafter, the ratio xcex4 drops rapidly, then slowly decreases nearly to 0. The transmitted electron emission ratio xcfx84, on the other hand, increases gradually as Va becomes larger, then the ratio increases nearly to 1. Because secondary electrons are generated on the very surface layer of the matter, they are hardly affected by the object""s size. The transmitted electrons are affected exponentially by the object""s size. The broken line in FIG. 1 indicates the transmitted electron emission ratio of an ordinary object of 10 xcexcm in size. With such a large object, the transmitted electrons are almost negligible in the accelerating voltage range (about 30 kV) of an ordinary SEM. At this time, electrons entering the object are not significantly released as secondary electrons or transmitted electrons, so the object is charged negatively. For this reason, conventional techniques enable manipulation of large objects with good repeatability. The solid curve in FIG. 1 shows the transmitted electron emission ratio of an ordinary object of 300 nm in size. The influence of transmitted electrons is not negligible with such a small object. FIG. 2 indicates xcex4+xcfx84, that is, the sum of the secondary electron emission ratio and the transmitted electron emission ratio. In this case, the charge polarity of the object varies with the effective accelerating voltage Va. In FIG. 2, xcex4+xcfx84 becomes 1 at three points. Assuming that the effective accelerating voltage Va has values V1, V2 and V3 at these three points, objects carry no charge when the accelerating voltage is set to one of these values. At other values, objects are charged either positively or negatively. The accelerating voltage equals the effective accelerating voltage Va only when it is V1, V2 or V3 because objects have a potential of 0 V at these values. In any other circumstances, the accelerating voltage differs from the effective accelerating voltage Va. FIG. 3 shows the relationship described above. To control the charge state of an object, an effective accelerating voltage can be selected from this table. The actual V1, V2 and V3 values vary with the materials and shapes of objects. However, these values can be easily learned from the way secondary electron images appear at different accelerating voltages. Images suddenly darken when the charge turns positive or lighten when the charge turns negative. These values can also be easily learned from responses to manipulation. Such responses are characteristics of adhesion to or release from the handling tool while a voltage is applied. By utilizing the above-noted general properties of objects and selecting the electron beam accelerating voltage, handling tool potential and work substrate potential in the proper combination, this invention makes possible the highly repeatable pick-up and release of micro-objects sized several micrometers or less with a micro-handling tool. Referring to FIG. 4, the following describes an example of a micro-sphere having a predetermined size, multi-layer arrangement work performed for optical experimentation under a SEM. FIG. 4 is a schematic drawing of the SEM. In the SEM used here, the accelerating voltage can be selected from a range up to 30 kV. The work substrate 1 is made of a conductive glass substrate 2 that is coated with a thin polymer film to increase the adhesion force between the object and the substrate. In a further embodiment, a thin ITO film 3 (189 nm thick), or a transparent conductive electrode, is evaporated on the glass substrate 2, which is then dip-coated with a thin polystyrene film 4 (15 nm thick) to increase the adhesion force between the object and the substrate. As long as similar structures are available, various other methods may be used to make the glass substrate conductive and various types of polymer film may be applied to increase the adhesion force. The object of manipulation in this example is a polyvinyltoluene micro-sphere 5 with a diameter of 2 xcexcm. The micro-sphere is manipulated with a micro-handling tool 6, which is a tapered glass pipette that is sputter-coated with a gold layer and has a tip diameter of 0.7 xcexcm. The substrate 1 is attached to the specimen stage and the micro-handling tool 6 is attached to the work arm of the manipulator. The operator controls the manipulator with a joy stick, while viewing SEM images on a monitor. Because the micro-handling tool 6 and the work substrate 1 are individually connected to a variable power source via a protective resistor (1 Mxcexa9), the operator can control their potentials arbitrarily. In this experiment, with an accelerating voltage of 10 KV used for ordinary work, the micro-sphere could not be picked up from the substrate even when positive voltages ranging up to 70 V or a negative voltage was applied to the micro-handling tool 6 even though the substrate was grounded. This is partly because the substrate surface is covered with a coating to increase adhesion with the micro-sphere 5. Another reason is that the V3 value is about 10 KV for the micro-sphere 5, so the sphere carries little charge when 10 KV is applied. When the accelerating voltage was increased to the maximum 30 kV and xe2x88x9235 V was applied to the micro-handling tool 6, the micro-sphere 5 could be picked up from the grounded substrate with an about 50% probability of success. To release the micro-sphere 5 from the micro-handling tool 6 and place it on the work substrate 1, it was only necessary to simply ground the micro-handling tool 6 again and bring the micro-sphere 5 in contact with the substrate. Manipulation could be performed as desired with an about 90% probability of success. At this time, the same result was obtained when the handling tool was grounded and +35 V was applied to the work substrate. These results indicate that the sphere was charged positively. Lowering the accelerating voltage to 25 KV resulted in a pick-up failure when the micro-handling tool 6 and the work substrate 1 were at the same potentials. It is understood from this fact that the accelerating voltage clearly exerts an influence and plays an important role in determining the success and failure of manipulation. It is difficult to manipulate micro-objects of several micrometers or smaller only by controlling the potentials of the micro-handling tool and the work substrate. As stated above, this invention easily realizes the pick-up and release of such small micro-objects with excellent repeatability, simply by controlling the accelerating voltage. The work substrate used in the aforementioned embodiment may of course be replaced with a work substrate having similar functions. Various other embodiments are also possible within the spirit and scope of this invention. The embodiments noted previously are merely examples and they not to be interpreted in a restricted manner. All modifications and alterations within a range equivalent to the scope of the following Claims are meant to be included in this invention. Industrial Field of Application As described above in detail, to enable effective micro-manipulation performed by a micro-manipulator attached to an SEM or a TEM for the purpose of micro-matter analysis or microstructure assembly, this invention makes possible the desired manipulation of micro-objects as small as several micrometers or less in size and it does so with excellent repeatability.
	claims	1. Radiation-attenuation underwear shorts, comprising:a plurality of radiation-attenuating material panels adapted to conform to the contours of a body, having a plurality of attaching mechanisms on one side;a front portion, made of a compression material and having a plurality of attaching mechanisms disposed on one side of the front portion, the front portion including a first pocket for retaining a first radiation attenuating material panel; anda back portion, made of a compression material and having a plurality of attaching mechanisms disposed on one side of the back portion, the back portion including second pocket for retaining a second radiation attenuating material panel,wherein the front portion and the back portion are secured together to form underwear shorts, such that the attaching mechanisms and the first and second pockets are disposed within the underwear shorts,wherein the first radiation-attenuating material panel is removably disposed within the first pocket and the plurality of attaching mechanisms of the first radiation-attenuating material panel are removably coupled to the plurality of attaching mechanisms of the front portion,wherein the second radiation-attenuating material panel is removably disposed within the second pocket and the plurality of attaching mechanisms of the second radiation-attenuating material panel are removably coupled to the plurality of attaching mechanisms of the rear portion. 2. The radiation-attenuation underwear shorts of claim 1, wherein the radiation attenuating panels are comprised of lead. 3. The radiation-attenuation underwear shorts of claim 1, wherein the radiation attenuating panels are comprised of lead alloy. 4. The radiation-attenuation underwear shorts of claim 1, wherein the radiation attenuating panels are covered in a removable, machine washable material.
	description	This application is a continuation of U.S. patent application Ser. No. 13/565,678, filed Aug. 2, 2012, which claims the benefit of U.S. patent application Ser. No. 12/575,312, filed Oct. 7, 2009, now U.S. Pat. No. 8,247,769, which claims the benefit of U.S. Provisional Patent Application No. 61/195,639, filed Oct. 9, 2008, U.S. Provisional Patent Application No. 61/236,745, filed Aug. 25, 2009, and U.S. Provisional Patent Application No. 61/240,946, filed Sep. 9, 2009, which are commonly assigned, the disclosures of which are hereby incorporated by reference in their entirety. U.S. patent application Ser. No. 12/575,285, now U.S. Pat. No. 8,203,120 was filed concurrently with U.S. patent application Ser. No. 12/575,312 and the entire disclosure of U.S. patent application Ser. No. 12/575,285 is hereby incorporated by reference into this application for all purposes. The U.S. Government has certain rights in this invention pursuant to Grant No. GM081520 awarded by the National Institutes of Health, Grant No. FA9550-07-1-0484 awarded by the Air Force (AFOSR) and Grant No(s). CHE0549936 & DMR0504854 awarded by the National Science Foundation. Electrons, because of their wave-particle duality, can be accelerated to have picometer wavelength and focused to image in real space. With the impressive advances made in transmission electron microscopy (TEM), STEM, and aberration-corrected TEM, it is now possible to image with high resolution, reaching the sub-Angstrom scale. Together with the progress made in electron crystallography, tomography, and single-particle imaging, today the electron microscope has become a central tool in many fields, from materials science to biology. For many microscopes, the electrons are generated either thermally by heating the cathode or by field emission, and as such the electron beam is made of random electron bursts with no control over the temporal behavior. In these microscopes, time resolution of milliseconds or longer, being limited by the video rate of the detector, can be achieved, while maintaining the high spatial resolution. Despite the advances made in TEM techniques, there is a need in the art for improved methods and novel systems for ultrafast electron microscopy. According to embodiments of the present invention, methods and systems for 4D ultrafast electron microscopy (UEM) are provided—in situ imaging with ultrafast time resolution in TEM. Thus, 4D microscopy provides imaging for the three dimensions of space as well as the dimension of time. In some embodiments, single electron imaging is introduced as a component of the 4D UEM technique. Utilizing one electron packets, resolution issues related to repulsion between electrons (the so-called space-charge problem) are addressed, providing resolution unavailable using conventional techniques. Moreover, other embodiments of the present invention provide methods and systems for convergent beam UEM, focusing the electron beams onto the specimen to measure structural characteristics in three dimensions as a function of time. Additionally, embodiments provide not only 4D imaging of specimens, but characterization of electron energy, performing time resolved electron energy loss spectroscopy (EELS). The potential applications for 4D UEM are demonstrated using examples including gold and graphite, which exhibit very different structural and morphological changes with time. For gold, following thermally induced stress, the atomic structural expansion, the nonthermal lattice temperature, and the ultrafast transients of warping/bulging were determined. In contrast, in graphite, striking coherent transients of the structure were observed in the selected-area image dynamics, and also in diffraction, directly measuring the resonance period of Young's elastic modulus. Measurement of the Young's elastic modulus for the nano-scale dimension, the frequency is found to be as high as 30 gigahertz, hitherto unobserved, with the atomic motions being along the c-axis. Both materials undergo fully reversible dynamical changes, retracing the same evolution after each initiating impulsive stress. Thus, embodiments of the present invention provide methods and systems for performing imaging studies of dynamics using UEM. Other embodiments of the present invention extend four-dimensional (4D) electron imaging to the attosecond time domain. Specifically, embodiments of the present invention are used to generate attosecond electron pulses and in situ probing with electron diffraction. The free electron pulses have a de Broglie wavelength on the order of picometers and a high degree of monochromaticity (ΔE/E0≈10−4); attosecond optical pulses have typically a wavelength of 20 nm and ΔE/E0≈0.5, where E0 is the central energy and ΔE is the energy bandwidth. Diffraction, and tilting of the electron pulses/specimen, permit the direct investigation of electron density changes in molecules and condensed matter. This 4D imaging on the attosecond time scale is a pump-probe approach in free space and with free electrons. As described more fully throughout the present specification, some embodiments of the present invention utilize single electron packets in UEM, referred to as single electron imaging. Conventionally, it was believed that the greater number of electrons per pulse, the better the image produced by the microscope. In other words, as the signal is increased, imaging improves. However, the inventor has determined that by using single electron packets and repeating the imaging process a number of times, images can be achieved without repulsion between electrons. Unlike photons, electrons are charged and repel each other. Thus, as the number of electrons per pulse increases, the divergence of the trajectories increases and resolution decreases. Using single electron imaging techniques, atomic scale resolution of motion is provided once the space-charge problem is addressed. According to an embodiment of the present invention, a four-dimensional electron microscope for imaging a sample is provided. The four-dimensional electron microscope includes a stage assembly configured to support the sample, a first laser source capable of emitting a first optical pulse of less than 1 ps in duration, and a second laser source capable of emitting a second optical pulse of less than 1 ns in duration. The four-dimensional electron microscope also includes a cathode coupled to the first laser source and the second laser source. The cathode is capable of emitting a first electron pulse less than 1 ps in duration in response to the first optical pulse and a second electron pulse of less than 1 ns in response to the second optical pulse. The four-dimensional electron microscope further includes an electron lens assembly configured to focus the electron pulse onto the sample and a detector configured to capture one or more electrons passing through the sample. The detector is configured to provide a data signal associated with the one or more electrons passing through the sample. The four-dimensional electron microscope additionally includes a processor coupled to the detector. The processor is configured to process the data signal associated with the one or more electrons passing through the sample to output information associated with an image of the sample. Moreover, the four-dimensional electron microscope includes an output device coupled to the processor. The output device is configured to output the information associated with the image of the sample. According to another embodiment of the present invention, a convergent beam 4D electron microscope is provided. The convergent beam 4D electron microscope includes a laser system operable to provide a series of optical pulses, a first optical system operable to split the series of optical pulses into a first set of optical pulses and a second set of optical pulses and a first frequency conversion unit operable to frequency double the first set of optical pulses. The convergent beam 4D electron microscope also includes a second optical system operable to direct the frequency doubled first set of optical pulses to impinge on a sample and a second frequency conversion unit operable to frequency triple the second set of optical pulses. The convergent beam 4D electron microscope further includes a third optical system operable to direct the frequency tripled second set of optical pulses to impinge on a cathode, thereby generating a train of electron packets. Moreover, the convergent beam 4D electron microscope includes an accelerator operable to accelerate the train of electron packets, a first electron lens operable to de-magnify the train of electron packets, and a second electron lens operable to focus the train of electron packets onto the sample. According to a specific embodiment of the present invention, a system for generating attosecond electron pulses is provided. The system includes a first laser source operable to provide a laser pulse and a cathode optically coupled to the first laser source and operable to provide an electron pulse at a velocity v0 directed along an electron path. The system also includes a second laser source operable to provide a first optical wave at a first wavelength. The first optical wave propagates in a first direction offset from the electron path by a first angle. The system further includes a third laser source operable to provide a second optical wave at a second wavelength. The second optical wave propagates in a second direction offset from the electron path by a second angle and the interaction between the first optical wave and the second optical wave produce a standing wave copropagating with the electron pulse. According to another specific embodiment of the present invention, a method for generating a series of tilted attosecond pulses is provided. The method includes providing a femtosecond electron packet propagating along an electron path. The femtosecond electron packet has a packet duration and a direction of propagation. The method also includes providing an optical standing wave disposed along the electron path. The optical standing wave is characterized by a peak to peak wavelength measured in a direction tilted at a predetermined angle with respect to the direction of propagation. The method further includes generating the series of tilted attosecond pulses after interaction between the femtosecond electron packet and the optical standing wave. According to a particular embodiment of the present invention, a method of operating an electron energy loss spectroscopy (EELS) system is provided. The method includes providing a train of optical pulses using a pulsed laser source, directing the train of optical pulses along an optical path, frequency doubling a portion of the train of optical pulses to provide a frequency doubled train of optical pulses, and frequency tripling a portion of the frequency doubled train of optical pulses to provide a frequency tripled train of optical pulses. The method also includes optically delaying the frequency doubled train of optical pulses using a variable delay line, impinging the frequency doubled train of optical pulses on a sample, impinging the frequency tripled train of optical pulses on a photocathode, and generating a train of electron pulses along an electron path. The method further includes passing the train of electron pulses through the sample, passing the train of electron pulses through a magnetic lens, and detecting the train of electron pulses at a camera. According to an embodiment of the present invention, a method of imaging a sample is provided. The method includes providing a stage assembly configured to support the sample, generating a train of optical pulses from a laser source, and directing the train of optical pulses along an optical path to impinge on a cathode. The method also includes generating a train of electron pulses in response to the train of optical pulses impinging on the cathode. Each of the electron pulses consists of a single electron. The method further includes directing the train of electron pulses along an imaging path to impinge on the sample, detecting a plurality of the electron pulses after passing through the sample, processing the plurality of electron pulses to form an image of the sample, and outputting the image of the sample to an output device. According to another embodiment of the present invention, a method of capturing a series of time-framed images of a moving nanoscale object is provided. The method includes a) initiating motion of the nanoscale object using an optical clocking pulse, b) directing an optical trigger pulse to impinge on a cathode, and c) generating an electron pulse. The method also includes d) directing the electron pulse to impinge on the sample with a predetermined time delay between the optical clocking pulse and the electron pulse, e) detecting the electron pulse, f) processing the detected electron pulse to form an image, and g) increasing the predetermined time delay between the optical clocking pulse and the electron pulse. The method further includes repeating steps a) through g) to capture the series of time-framed images of the moving nanoscale object. According to a specific embodiment of the present invention, a method of characterizing a sample is provided. The method includes providing a laser wave characterized by an optical wavelength (λ0) and a direction of propagation and directing the laser wave along an optical path to impinge on a test surface of the sample. The test surface of the sample is tilted with respect to the direction of propagation of the laser by a first angle (α). The method also includes providing a train of electron pulses characterized by a propagation velocity (vel), a spacing between pulses ( λ 0 ⁢ v el c ) ,and a direction of propagation tilted with respect to the direction of propagation of the laser by a second angle (β). The method further includes directing the train of electron pulses along an electron path to impinge on the test surface of the sample. The first angle, the second angle, and the propagation velocity are related by sin ⁡ ( α ) sin ⁡ ( α - β ) = c v e ⁢ ⁢ 1 . According to another specific embodiment of the present invention, a method of imaging chemical bonding dynamics is provided. The method includes positioning a sample in a reduced atmosphere environment, providing a first train of laser pulses, and directing the first train of laser pulses along a first optical path to impinge on a sample. The method also includes providing a second train of laser pulses, directing the second train of laser pulses along a second optical path to impinge on a photocathode, and generating a train of electron pulses. One or more of the electron pulses consist of a single electron. The method further includes accelerating the train of electron pulses and transmitting a portion of the train of electron pulses through the sample. Numerous benefits are achieved by way of the present invention over conventional techniques. For example, the present systems provide temporal resolution over a wide range of time scales. Additionally, unlike spectroscopic methods, embodiments of the present invention can determine a structure in 3-D space. Such capabilities allow for the investigation of phase transformation in matter, determination of elastic and mechanical properties of materials on the nanoscale, and the time evolution of processes involved in materials and biological function. Depending upon the embodiment, one or more of these benefits may be achieved. These and other benefits will be described in more detail throughout the present specification and more particularly below. These and other objects and features of the present invention and the manner of obtaining them will become apparent to those skilled in the art, and the invention itself will be best understood by reference to the following detailed description read in conjunction with the accompanying drawings. Ultrafast imaging, using pulsed photoelectron packets, provides opportunities for studying, in real space, the elementary processes of structural and morphological changes. In electron diffraction, ultrashort time resolution is possible but the data is recorded in reciprocal space. With space-charge-limited nanosecond (sub-micron) image resolutions ultrashort processes are not possible to observe. In order to achieve the ultrafast resolution in microscopy, the concept of single-electron pulse imaging was realized as a key to the elimination of the Coulomb repulsion between electrons while maintaining the high temporal and spatial resolutions. As long as the number of electrons in each pulse is much below the space-charge limit, the packet can have a few or tens of electrons and the temporal resolution is still determined by the femtosecond (fs) optical pulse duration and the energy uncertainty, on the order of 100 fs, and the spatial resolution is atomic-scale. However, the goal of full-scale dynamic imaging can be attained only when in the microscope the problems of in situ high spatiotemporal resolution for selected image areas, together with heat dissipation, are overcome. FIG. 1 is a simplified diagram of a 4D electron microscope system according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. As illustrated in FIG. 1, a femtosecond laser 110 or a nanosecond laser 105 is directed through a Pockels cell 112, which acts as a controllable shutter. A Glan polarizer 114 is used in some embodiments, to select the laser power propagating in optical path 115. A beam splitter (not shown) is used to provide several laser beams to various portions of the system. Although the system illustrated in FIG. 1 is described with respect to imaging applications, this is not generally required by the present invention. One of skill in the art will appreciate that embodiments of the present invention provide systems and methods for imaging, diffraction, crystallography, electron spectroscopy, and related fields. Particularly, the experimental results discussed below yield insight into the varied applications available using embodiments of the present invention. The femtosecond laser 110 is generally capable of generating a train of optical pulses with predetermined pulse width. One example of such a laser system is a diode-pumped mode-locked titanium sapphire (Ti:Sapphire) laser oscillator operating at 800 nm and generating 100 fs pulses at a repetition rate of 80 MHz and an average power of 1 Watt, resulting in a period between pulses of 12.5 ns. In an embodiment, the spectral bandwidth of the laser pulses is 2.35 nm FWHM. An example of one such laser is a Mai Tai One Box Femtosecond Ti:Sapphire Laser, available from Spectra-Physics Lasers, of Mountain View, Calif. In alternative embodiments, other laser sources generating optical pulses at different wavelengths, with different pulse widths, and at different repetition rates are utilized. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. The nanosecond laser 105 is also generally capable of generating a train of optical pulses with a predetermined pulse width greater than that provided by the femtosecond laser. The use of these two laser systems enables system miniaturization since the size of the nanosecond laser is typically small in comparison to some other laser systems. By moving one or more mirrors, either laser beam is selected for use in the system. The ability to select either laser enables scanning over a broad time scale—from femtoseconds all the way to milliseconds. For short time scale measurement, the femtosecond laser is used and the delay stage (described below) is scanned at corresponding small time scales. For measurement of phenomena over longer time scales, the nanosecond laser is used and the delay stage is scanned at corresponding longer time scales. A first portion of the output of the femtosecond laser 110 is coupled to a second harmonic generation (SHG) device 116, for example a barium borate (BaB2O4) crystal, typically referred to as a BBO crystal and available from a variety of doubling crystal manufacturers. The SHG device frequency doubles the train of optical pulses to generate a train of 400 nm, 100 fs optical pulses at an 80 MHz repetition rate. SHG devices generally utilize a nonlinear crystal to frequency double the input pulse while preserving the pulse width. In some embodiments, the SHG is a frequency tripling device, thereby generating an optical pulse at UV wavelengths. Of course, the desired output wavelength for the optical pulse will depend on the particular application. The doubled optical pulse produced by the SHG device propagates along electron generating path 118. A cw diode laser 120 is combined with the frequency doubled optical pulse using beam splitter 122. The light produce by the cw diode laser, now collinear with the optical pulse produced by the SHG device, serves as an alignment marker beam and is used to track the position of the optical pulse train in the electron generating path. The collinear laser beams enter chamber 130 through entrance window 132. In the embodiment illustrated in FIG. 1, the entrance window is fabricated from materials with high transparency at 400 nm and sufficient thickness to provide mechanical rigidity. For example, BK-7 glass about 6 mm thick with anti-reflection coatings, e.g. MgF2 or sapphire are used in various embodiments. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. An optical system, partly provided outside chamber 130 and partly provided inside chamber 130 is used to direct the frequency doubled optical pulse train along the electron-generating path 134 inside the chamber 130 so that the optical pulses impinge on cathode 140. As illustrated, the optical system includes mirror 144, which serves as a turning mirror inside chamber 130. In embodiments of the present invention, polished metal mirrors are utilized inside the chamber 130 since electron irradiation may damage mirror coatings used on some optical mirrors. In a specific embodiment, mirror 144 is fabricated from an aluminum substrate that is diamond turned to produce a mirror surface. In some embodiments, the aluminum mirror is not coated. In other embodiments, other metal mirrors, such as a mirror fabricated from platinum is used as mirror 144. In an embodiment, the area of interaction on the cathode was selected to be a flat 300 μm in diameter. Moreover, in the embodiment illustrated, the frequency doubled optical pulse was shaped to provide a beam with a beam waist of a predetermined diameter at the surface of the cathode. In a specific embodiment, the beam waist was about 50 μm. In alternative embodiments, the beam waist ranged from about 30 μm to about 200 μm. Of course, the particular dimensions will depend on the particular applications. The frequency doubled optical pulse train was steered inside the chamber using a computer controlled mirror in a specific embodiment. In a specific embodiment, the optical pulse train is directed toward a front-illuminated photocathode where the irradiation of the cathode by the laser results in the generation of electron pulses via the photoelectric effect. Irradiation of a cathode with light having an energy above the work function of the cathode leads to the ejection of photoelectrons. That is, a pulse of electromagnetic energy above the work function of the cathode ejects a pulse of electrons according to a preferred embodiment. Generally, the cathode is maintained at a temperature of 1000 K, well below the thermal emission threshold temperature of about 1500 K, but this is not required by the present invention. In alternative embodiments, the cathode is maintained at room temperature. In some embodiments, the cathode is adapted to provide an electron pulse of predetermined pulse width. The trajectory of the electrons after emission follows the lens design of the TEM, namely the condenser, the objective, and the projector lenses. Depending upon the embodiment, there may also be other configurations. In the embodiment illustrated, the cathode is a Mini-Vogel mount single crystal lanthanum hexaboride (LaB6) cathode shaped as a truncated cone with a flat of 300 μm at the apex and a cone angle of 90°, available from Applied Physics Technologies, Inc., of McMinnville, Oreg. As is often known, LaB6 cathodes are regularly used in transmission and scanning electron microscopes. The quantum efficiency of LaB6 cathodes is about 10−3 and these cathodes are capable of producing electron pulses with temporal pulse widths on the order of 10−13 seconds. In some embodiments, the brightness of electron pulses produced by the cathode is on the order of 109 A/cm2/rad2 and the energy spread of the electron pulses is on the order of 0.1 eV. In other embodiments, the pulse energy of the laser pulse is reduced to about 500 pJ per pulse, resulting in approximately one electron/pulse Generally, the image quality acquired using a TEM is proportional to the number of electrons passing through the sample. That is, as the number of electrons passing through the sample is increased, the image quality increases. Some pulsed lasers, such as some Q-switched lasers, reduce the pulse count to produce a smaller number of pulses characterized by higher peak power per pulse. Thus, some laser amplifiers operate at a 1 kHz repetition rate, producing pulses with energies ranging from about 1 μJ to about 2 mJ per pulse. However, when such high peak power lasers are used to generate electron pulses using the photoelectric effect, among other issues, both spatial and temporal broadening of the electron pulses adversely impact the pulse width of the electron pulse or packet produced. In some embodiments of the present invention, the laser is operated to produce low power pulses at higher repetition rates, for example, 80 MHz. In this mode of operation, benefits available using lower power per pulse are provided, as described below. Additionally, because of the high repetition rate, sufficient numbers of electrons are available to acquire high quality images. In some embodiments of the present invention, the laser power is maintained at a level of less than 500 pJ per pulse to prevent damage to the photocathode. As a benefit, the robustness of the photoemitter is enhanced. Additionally, laser pulses at these power levels prevent space-charge broadening of the electron pulse width during the flight time from the cathode to the sample, thus preserving the desired femtosecond temporal resolution. Additionally, the low electron count per pulse provided by some embodiments of the present invention reduces the effects of space charge repulsion in the electron pulse, thereby enhancing the focusing properties of the system. As one of skill in the art will appreciated, a low electron count per pulse, coupled with a high repetition rate of up to 80 MHz provided by the femtosecond laser, provides a total dose as high as one electron/Å2 as generally utilized in imaging applications. In alternative embodiments, other suitable cathodes capable of providing a ultrafast pulse of electrons in response to an ultrafast optical pulse of appropriate wavelength are utilized. In embodiments of the present invention, the cathode is selected to provide a work function correlated with the wavelength of the optical pulses provided by the SHG device. The wavelength of radiation is related to the energy of the photon by the familiar relation λ(μm)≈1.24÷v (eV), where λ is the wavelength in microns and v is the energy in eV. For example, a LaB6 cathode with a work function of 2.7 eV is matched to optical pulses with a wavelength of 400 nm (v=3.1 eV) in an embodiment of the present invention. As illustrated, the cathode is enclosed in a vacuum chamber 130, for example, a housing for a transmission electron microscope (TEM). In general, the vacuum in the chamber 130 is maintained at a level of less than 1×10−6 torr. In alternative embodiments, the vacuum level varies from about 1×10−6 torr to about 1×10−10 torr. The particular vacuum level will be a function of the varied applications. In embodiments of the present invention, the short duration of the photon pulse leads to ejection of photoelectrons before an appreciable amount of the deposited energy is transferred to the lattice of the cathode. In general, the characteristic time for thermalization of the deposited energy in metals is below a few picoseconds, thus no heating of the cathode takes place using embodiments of the present invention. Electrons produced by the cathode 140 are accelerated past the anode 142 and are collimated and focused by electron lens assembly 146 and directed along electron imaging path 148 toward the sample 150. The electron lens assembly generally contains a number of electromagnetic lenses, apertures, and other elements as will be appreciated by one of skill in the art. Electron lens assemblies suitable for embodiments of the present invention are often used in TEMs. The electron pulse propagating along electron imaging path 148 is controlled in embodiments of the present invention by a controller (not shown, but described in more detail with reference to certain Figures below) to provide an electron beam of predetermined dimensions, the electron beam comprising a train of ultrafast electron pulses. The relationship between the electron wavelength (λdeBroglie) and the accelerating voltage (U) in an electron microscope is given by the relationship λdeBroglie=h/(2m0eU)1/2, where h, m0, e are Planck's constant, the electron mass, and an elementary charge. As an example, the de Broglie wavelength of an electron pulse at 120 kV corresponds to 0.0335 Å, and can be varied depending on the particular application. The bandwidth or energy spread of an electron packet is a function of the photoelectric process and bandwidth of the optical pulse used to generate the electron packet or pulse. Electrons passing through the sample or specimen 150 are focused by electron lens assembly 152 onto a detector 154. Although FIG. 1 illustrates two electron lens assemblies 146 and 152, the present invention is not limited to this arrangement and can have other lens assemblies or lens assembly configurations. In alternative embodiments, additional electromagnets, apertures, other elements, and the like are utilized to focus the electron beam either prior to or after interaction with the sample, or both. Detection of electrons passing through the sample, including single-electron detection, is achieved in one particular embodiment through the use of an ultrahigh sensitivity (UHS) phosphor scintillator detector 154 especially suitable for low-dose applications in conjunction with a digital CCD camera. In a specific embodiment, the CCD camera was an UltraScan™ 1000 UHS camera, manufactured by Gatan, Inc., of Pleasanton, Calif. The UltraScan™ 1000 CCD camera is a 4 mega-pixel (2048×2048) camera with a pixel size of 14 μm×14 μm, 16-bit digitization, and a readout speed of 4 Mpixels/sec. In the embodiment illustrated, the digital CCD camera is mounted under the microscope in an on-axis, below the chamber position. In order to reduce the noise and picture artifacts, in some embodiments, the CCD camera chip is thermoelectrically cooled using a Peltier cooler to a temperature of about −25° C. The images from the CCD camera were obtained with DigitalMicrograph™ software embedded in the Tecnai™ user interface, also available from Gatan, Inc. Of course, there can be other variations to the CCD camera, cooler, and computer software, depending upon the embodiment. FIG. 2 is a simplified perspective diagram of a 4D electron microscope system according to an embodiment of the present invention. The system illustrated in FIG. 2 is also referred to as an ultrafast electron microscope (UEM2) and was built at the present assignee. The integration of two laser systems with a modified electron microscope is illustrated, together with a representative image showing a resolution of 3.4 Å obtained in UEM2 without the field-emission-gun (FEG) arrangement of a conventional TEM. In one embodiment of the system illustrated in FIG. 2, the femtosecond laser system (fs laser system) is used to generate the single-electron packets and the nanosecond laser system (ns laser system) was used both for single-shot and stroboscopic recordings. In the single-electron mode of operation, the coherence volume is well defined and appropriate for image formation in repetitive events. The dynamics are fully reversible, retracing the identical evolution after each initiating laser pulse; each image is constructed stroboscopically, in seconds, from typically 106 pulses and all time-frames are processed to make a movie. The time separation between pulses can be varied to allow complete heat dissipation in the specimen. Without limiting embodiments of the present invention, it is believed that the electrons in the single electron packets have a transverse coherence length that is comparable to the size of the object that is being imaged. Since the subsequent electrons have a coherence length on the order of the size of the object, the electrons “see” the whole object at once. To follow the area-specific changes in the hundreds of images collected for each time scan, we obtained selected-area-image dynamics (SAID) and selected-area-diffraction dynamics (SADD); for the former, in real space, from contrast change and for the latter, in Fourier space, from changes of the Bragg peak separations, amplitudes, and widths. It is the advantage of microscopy that allows us to perform this parallel-imaging dynamics with pixel resolution, when compared with diffraction. As shown below, it would not have been possible to observe the selected temporal changes if the total image were to be averaged over all pixels, in this case 4 μmillions. As illustrated in FIG. 2, a TEM is modified to provide a train of electron pulses used for imaging in addition to the thermionic emission source used for imaging of samples. Merely by way of example, an FEI Tecnai™ G2 12 TWIN, available from FEI Company in Hillsboro, Oreg., may be modified according to embodiments of the present invention. The Tecnai™ G2 12 TWIN is an all-in-one 120 kV (λdeBroglie≈0.0335 Å) high-resolution TEM optimized for 2D and 3D imaging at both room and liquid-nitrogen temperatures. Embodiments of the present invention leverage capabilities provided by commercial TEMs such as automation software, detectors, data transfer technology, and tomography. In particular, in some embodiments of the present invention, a five-axis, motor-driven, precision goniometer is used with computer software to provide automated specimen tilt combined with automated acquisition of images as part of a computerized tomography (CT) imaging system. In these embodiments, a series of 2D images are captured at various specimen positions and combined using computer software to generate a reconstructed 3D image of the specimen. In some embodiments, the CT software is integrated with other TEM software and in other embodiments, the CT software is provided off-line. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. In certain embodiments in which low-electron content electron pulses are used to image the sample, the radiation damage is limited to the transit of the electrons in the electron pulses through the sample. Typically, samples are on the order of 100 nm thick, although other thicknesses would work as long as certain electrons may traverse through the sample. Thus, the impact of radiation damage on these low-electron content electron pulse images is limited to the damage occurring during this transit time. Radiation induced structural damage occurring on longer time scales than the transit time will not impact the collected image, as these damage events will occur after the structural information is collected. Utilizing the apparatus described thus far, embodiments of the present invention provide systems and methods for imaging material and biological specimens both spatially and temporally with atomic-scale spatial resolution on the order of 1 nm and temporal resolution on the order of 100 fs. At these time scales, energy randomization is limited and the atoms are nearly frozen in place, thus methods according to the present invention open the door to time-resolved studies of structural dynamics at the atomic scale in both space and time. Details of the present computer system according to an embodiment of the present invention may be explained according to the description below. Referring to FIG. 2, a photograph of a UEM2 in accordance with embodiments of the present invention is illustrated, together with a high-resolution image of graphitized carbon. As illustrated, two laser systems (fs and ns) are utilized to provide a wide range of temporal scales used in 4D electron imaging. A 200-kV TEM is provided with at least two ports for optical access to the microscope housing. Using one or more mirrors (e.g., two mirrors), it is possible to switch between the laser systems to cover both the fs and ns experiments. The optical pulses are directed to the photocathode to generate electron packets, as well as to the specimen to initiate (clock) the change in images with a well-defined delay time Δt. The time axis is defined by variable delay between the electron generating and clocking pulses using the delay stage 170 illustrated in FIG. 1. Details of development of ultrafast electron microscopy with atomic-scale real-, energy-, and Fourier-space resolutions is now provided. The second generation UEM2 described in FIG. 2 provides images, diffraction patterns, and electron-energy spectra, and has application for nanostructured materials and organometallic crystals. The separation between atoms in direct images, and the Bragg spots/Debye-Scherrer rings in diffraction, are clearly resolved, and the electronic structure and elemental energies in the electron-energy-loss spectra (EELS) and energy-filtered-transmission-electron microscopy (EFTEM) are obtained. The development of 4D ultrafast electron microscopy and diffraction have made possible the study of structural dynamics with atomic-scale spatial resolution, so far in diffraction, and ultrashort time resolution. The scope of applications is wide-ranging with studies spanning diffraction of isolated structures in reactions (gas phase), nanostructures of surfaces and interfaces (crystallography), and imaging of biological cells and materials undergoing first-order phase transitions. Typically, for microscopy the electron was accelerated to 120 keV and for diffraction to 30 keV, respectively, and issues of group velocity mismatch, in situ clocking (time zero) of the change, and frame referencing were addressed. One powerful concept implemented is that of “tilted pulses,” which allow for the optimum resolution to be reached at the specimen. For ultrafast electron microscopy, the concept of “single-electron” imaging is fundamental to some embodiments. The electron packets, which have a well-defined picometer-scale de Broglie wave length, are generated in the microscope by femtosecond optical pulses (photoelectric effect) and synchronized with other optical pulses to initiate the change in a temperature-jump or electronic excitation. Because the number of electrons in each packet is one or a few, the Coulomb repulsion (space charge) between electrons is reduced or eliminated and the temporal resolution can reach the ultimate, that of the optical pulse. The excess energy above the work function determines the electron energy spread and this, in principle, can be minimized by tuning the pulse energy. The spatial resolution is then only dependent on the total number of electrons because for each packet the electron “interferes with itself” and a coherent buildup of the image is achievable. The coherence volume, given by:Vc=λdeBroglie2(R/a)2ve(h/ΔE)establishes that the degeneracy factor is much less than one and that each Fermionic electron is independent, without the need of the statistics commonly used for Bosonic photons. The volume is determined by the values of longitudinal and transverse coherences; Vc is on the order of 106 nm3 for typical values of R (distance to the source), a (source dimension), ve (electron velocity), and ΔE (energy spread). Unlike the situation in transmission electron microscopy (TEM), coherence and image resolution in UEM are thus determined by properties of the optical field, the ability to focus electrons on the ultrashort time scale, and the operational current density. For both “single electron” and “single pulse” modes of UEM, these are important considerations for achieving the ultimate spatio-temporal resolutions for studies of materials and biological systems. Atomic-scale resolution in real-space imaging can be achieved utilizing the second generation ultrafast electron microscopy system (UEM2) of FIG. 2. With UEM2, which operates at 200 keV (λdeBroglie=2.507 μm), energy-space (electron-energy-loss spectroscopy, EELS) and Fourier-space (diffraction) patterns of nanostructured materials are possible. The apparatus can operate in the scanning transmission electron microscope (STEM) mode, and is designed to explore the vast parameter space bridging the gap between the two ideal operating modes of single-electron and single-pulse imaging. With these features, UEM2 studies provide new limits of resolution, image mapping, and elemental analysis. Here, demonstrated are the potential by studying gold particles and islands, boron nitride crystallites, and organometallic phthalocyanine crystals. FIG. 2A displays the conceptual design of UEM2, which, as with the first generation (UEM1—described generally in FIG. 1), comprises a femtosecond laser system and an electron microscope modified for pulsed operation with femtosecond electron packets. A schematic representation of optical, electric, and magnetic components are shown. The optical pulse train generated from the laser, in this case having a variable pulse width of 200 fs to 10 ps and a variable repetition rate of 200 kHz to 25 MHz, is divided into two parts, after harmonic generation, and guided toward the entries of the design hybrid electron microscope. The frequency-tripled optical pulses are converted to the corresponding probe electron pulses at the photocathode in the hybrid FEG, whereas the other optical pump beam excites (T-jump or electronic excitation) in the specimen with a well-defined time delay with respect to the probe electron beam. The probe electron beam through the specimen can be recorded as an image (normal or filtered, EFTEM), a diffraction pattern, or an EEL spectrum. The STEM bright-field detector is retractable when it is not in use. The laser in an embodiment is a diode-pumped Yb-doped fiber oscillator/amplifier (Clark-MXR; in development), which produces ultrashort pulses of up to 10 μJ at 1030 nm with variable pulse width (200 fs-10 ps) and repetition rate (200 kHz-25 MHz). The output pulses pass through two successive nonlinear crystals to be frequency doubled (515 nm) and tripled (343 nm). The harmonics are separated from the residual infrared radiation (IR) beam by dichroic mirrors, and the frequency-tripled pulses are introduced to the photocathode of the microscope for generating the electron pulse train. The residual IR fundamental and frequency-doubled beams remain available to heat or excite samples and clock the time through a computer-controlled optical delay line for time-resolved applications. The electron microscope column is that of a designed hybrid 200-kV TEM (Tecnai 20, FEI) integrated with two ports for optical access, one leading to the photocathode and the other to the specimen. The field emission gun (FEG) in the electron-generation assembly adapts a lanthanum hexaboride (LaB6) filament as the cathode, terminating in a conical electron source truncated to leave a flat tip area with a diameter of 16 μm. The tip is located in a field environment controlled by suppressor and extractor electrodes. The gun can be operated as either a thermal emission or a photoemission source. The optical pulses are guided to the photocathode as well as to the specimen by a computer-controlled, fine-steering mirror in an externally-mounted and x-ray-shielded periscope assembly. Each laser beam can be focused to a spot size of <30 μm full width at half maximum (FWHM) at its respective target when the beam is expanded to utilize the available acceptance angle of the optical path. Various pulse-energy, pulse-length, and focusing regimes have been used in the measurements reported here. For UEM measurements, the cathode was heated to a level below that needed to produce detectable thermal emission, as detailed below, and images were obtained using both the TEM and the UEM2 μmode of operation. For applications involving EELS and energy-filtered-transmission-electron microscopy (EFTEM), the Gatan Imaging Filter (GIF) Tridiem, of the so-called post-column type, was attached below the camera chamber. The GIF accepts electrons passing through an entrance aperture in the center of the projection chamber. The electron beam passes through a 90° sector magnet as shown in FIG. 2A, which bends the primary beam through a 10 cm bending radius and thereby separates the electrons according to their energy into an energy spectrum. An energy resolution of 0.87 eV was measured for the EELS zero-loss peak in thermal mode operation of the TEM. A retractable slit is located after the magnet followed by a series of lenses. The lenses restore the image or diffraction pattern at the entrance aperture and finally it can be recorded on a charge-coupled device (CCD) camera (UltraScan 1000 FT) at the end of the GIF with the Digital Micrograph software. The digital camera uses a 2,048×2,048 pixel CCD chip with 14 μm square pixels. Readout of the CCD is done as four independent quadrants via four separate digitizing signal chains. This 4-port readout camera combines single-electron sensitivity and 16-bit pixel depth with high-speed sensor readout (4 Mpix/s). Additionally, for scanning-transmission-electron microscopy (STEM), the UEM2 is equipped with a bright-field (BF) detector with a diameter of 7 mm and an annular dark-field (ADF) detector with an inner diameter of 7 mm and an outer diameter of 20 mm. Both detectors are located in the near-axis position underneath the projection chamber. The BF detector usually collects the same signal as the TEM BF image, i.e., the transmitted electrons, while the ADF detector collects an annulus at higher angle where only scattered electrons are detected. The STEM images are recorded with the Tecnai Imaging & Analysis (TIA) software. To observe the diffraction pattern, i.e., the back focal plane of the objective lens, we inserted a selected area aperture into the image plane of the objective lens, thus creating a virtual aperture in the plane of the specimen. The result is a selected area diffraction (SAD) pattern of the region of interest only. Adjustment of the intermediate and projector lens determines the camera length. Diffraction patterns are processed and analyzed for crystal structure determination. Several features of the UEM2 system are worthy of note. First, the high repetition rate amplified laser source allows us to illuminate the cathode with 343 nm pulses of energies above 500 nJ, compared with typical values of 3 nJ near 380 nm for UEM1. Thus, a level of average optical power for electron generation comparable to that of UEM1 operating at 80 MHz, but at much lower repetition rates, was able to be delivered. The pulse energy available in the visible and IR beams is also at least two orders of magnitude greater than for UEM1, allowing for exploration of a much greater range in the choice of sample excitation conditions. Second, the hybrid 200-kV FEG, incorporating an extractor/suppressor assembly providing an extractor potential of up to 4 kV, allows higher resolving power and greater flexibility and control of the conditions of electron generation. Third, with simple variation of optical pulse width, the temporal and spatial resolution can be controlled, depending on the requirements of each experiment. Fourth, with variation of spacing between optical pulses without loss of pulse energy, a wide range of samples can be explored allowing them to fully relax their energy after each excitation pulse and rewind the clock precisely; with enough electrons, below the space-charge limit, single-pulse recording is possible. Finally, by the integration of the EELS spectrometer, the system is empowered with energy resolution in addition to the ultrafast time resolution and atomic-scale space resolution. The following results demonstrate the capabilities of UEM2 in three areas: real-space imaging, diffraction, and electron energy resolution. Applications of the present invention are not limited to these particular examples. First discussed are the images recorded in the UEM mode, of gold particles and gold islands on carbon films. FIGS. 2Ba-f are UEM2 images obtained with ultrafast electron pulses. Shown are gold particles (a, d) and gold islands (c, f) on carbon films. UEM2 background images (b, e) obtained by blocking the photoelectron-extracting femtosecond laser pulses. For the UEM2 images of gold particles, we used the objective (contrast) aperture of 40 μm to eliminate diffracted beams, while no objective aperture was used for the gold-island images. FIGS. 2Ba and 2Bd show gold particles of uniform size dispersed on a carbon film. From the higher magnification image of FIG. 2Bd, corresponding to the area indicated by the black arrow in FIG. 2Ba, it is found that the gold particles have a size of 15 nm, and the minimum particle separation seen in the image is 3 nm. It should be noted that FIGS. 2Bb and 2Be were recorded under identical conditions to FIGS. 2Ba and 2Bd, respectively, but without cathode irradiation by the femtosecond laser pulses. No images were observed, demonstrating that non-optically generated electrons from our warm cathode were negligible. Similar background images with the light pulses blocked were routinely recorded and checked for all cathode conditions used in this study. The waffle (cross line) spacing of the cross grating replica (gold islands) seen in FIG. 2Bc is known to be 463 nm. The gold islands are observed in FIG. 2Bf, where the bright regions correspond to the amorphous carbon support film and the dark regions to the nanocrystalline gold islands. It is found that the islands may be interconnected or isolated, depending on the volume fraction of the nanocrystalline phases. To test the high-resolution capability of UEM utilizing phase contrast imaging, an organometallic compound, chlorinated copper phthalocyanine (hexadecachlorophthalocyanine, C32Cl16CuN8), was investigated. The major spacings of lattice fringes of copper of this molecule in projection along the c-axis are known to be 0.88, 1.30, and 1.46 nm, with atomic spacings of 1.57 and 1.76 nm. FIGS. 2Ca-b are high-resolution, phase-contrast UEM images. Shown are an image in FIG. 2Ca and digital diffractogram in FIG. 2Cb of an organometallic crystal of chlorinated copper phthalocyanine. The diffractogram was obtained by the Fourier transform of the image in FIG. 2Ca. The high-resolution image was taken near the Scherzer focus for optimum contrast, which was calculated to be 90.36 nm for a spherical aberration coefficient Cs of the objective lens of 2.26 mm. The objective aperture was not used. FIG. 2Da exhibits the lattice fringes observed by UEM, where the black lines correspond to copper layers parallel to the c-axis. The Fourier transform of FIG. 2Da is shown in FIG. 2Db, discussed below, and the clear reciprocity (without satellite peaks in the F.T.) indicates the high degree of order in crystal structure. FIG. 2D shows high-resolution, phase-contrast UEM image and structure of chlorinated copper phthalocyanine. The high-resolution image shown in FIG. 2Da is a magnified view of the outlined area in FIG. 2Ca. The representation of the crystal structure shown in FIG. 2Db is shown in projection along the c axis, and the assignment of the copper planes observed in FIG. 2Da is indicated by the gray lines. The spheres are the copper atoms. FIG. 2Da is an enlargement of the area outlined in FIG. 2Ca, clearly showing the lattice fringe spacing of 1.46 nm, corresponding to the copper planes highlighted in gray in FIG. 2Db, in which a unit cell is shown in projection along the c-axis. Regions without lattice fringes are considered to correspond to crystals with unfavorable orientation, or amorphous phases of phthalocyanine, or the carbon substrate. It is known that in high resolution images, the lattice fringes produced by the interference of two waves passing through the back focal plane, i.e., the transmitted and diffracted beams, are observed only in crystals where the lattice spacing is larger than the resolution of the TEM. In the profile inset of FIG. 2Da, it should be noted that the FWHM was measured to be approximately 7 Å, directly indicating that our UEM has the capability of sub-nanometer resolution. The digital diffractogram obtained by the Fourier transform of the observed high-resolution image of FIG. 2Ca is shown in FIG. 2Cb. In the digital diffractogram, the peaks represent the fundamental spatial frequency of the copper layers (0.69 nm−1), and higher harmonics thereof. A more powerful means of obtaining reciprocal-space information such as this is the direct recording of electron diffraction, also available in UEM. FIGS. 2Ea-f show measured and calculated electron diffraction patterns of gold islands and boron nitride (BN) on carbon films, along with the corresponding real-space images of each specimen, all recorded by UEM. Shown are images and measured and calculated electron diffraction patterns of gold islands (a,b,c) and boron nitride (BN) (d,e,f) on carbon films. The incident electron beam is parallel to the [001] direction of the BN. All diffraction patterns were obtained by using the selected-area diffraction (SAD) aperture, which selected an area 6 μm in diameter on the specimen. Representative diffraction spots were indexed as indicated by the arrowheads. In FIG. 2Eb, the electron diffraction patterns exhibit Debye-Scherrer rings formed by numerous diffraction spots from a large number of face-centered gold nanocrystals with random orientations. The rings can be indexed as indicated by the white arrowheads. The diffraction pattern of BN in FIG. 2Ee is indexed by the hexagonal structure projected along the [001] axis as shown in FIG. 2Ef. It can be seen that there are several BN crystals with different crystal orientations, besides that responsible for the main diffraction spots indicated by the white arrowheads. In order to explore the energy resolution of UEM, we investigated the BN specimen in detail by EELS and EFTEM. FIG. 2F shows energy-filtered UEM images and spectrum. FIG. 2F shows a zero-loss filtered image (FIG. 2Fa), boron K-edge mapping image (FIG. 2Fb), thickness mapping image (FIG. 2Fc), and corresponding electron-energy-loss (EEL) spectrum (FIG. 2Fd) of the boron nitride (BN) sample. The 5.0- and 1.0-mm entrance aperture were used for mapping images and EEL spectrum, respectively. The thickness at the point indicated by the asterisk in FIG. 2Fc is estimated to be 41 nm. ZL stands for zero-loss. The boron map was obtained by the so-called three-window method. In the boron map of FIG. 2Fb, image intensity is directly related to areal density of boron. In the thickness map of FIG. 2Fc, the brightness increases with increasing thickness: d (thickness)=λ(β)ln(It/I0), where λ is the mean free path for inelastic scattering under a given collection angle β, I0 is the zero-loss (ZL) peak intensity, and It is the total intensity. The thickness in the region indicated by the asterisk in FIG. 2Fc was estimated to be 41 nm. In the EEL spectrum of FIG. 2Fd, the boron K-edge, carbon K-edge, and nitrogen K-edge are observed at the energy of 188, 284, and 401 eV, respectively. In the boron K-edge spectrum, sharp π* and σ* peaks are visible. The carbon K-edge spectrum is considered to result from the amorphous carbon film due to the existence of small and broad peaks at the position π* and σ, being quite different from spectra of diamond and graphite. With the capabilities of the UEM2 system described herein, structural dynamics can be studied, as with UEM1, but with the new energy and spatial resolution are achieved here. Specimens will be excited in a T-jump or electronic excitation by the femtosecond laser pulses (FIG. 2A) scanned in time with respect to the electron packets which will probe the changes induced in material properties through diffraction, imaging, or electron energy loss in different regions, including that of Compton scattering. Also planned to be explored is the STEM feature in UEM, particularly the annular dark-field imaging, in which compositional changes are evident in the contrast (Z contrast). Such images are known to offer advantages over high-resolution TEM (relative insensitivity to focusing errors and ease of interpretation). Electron fluxes will be optimized either through changes of the impinging pulse fluence or by designing new photocathode materials. In this regard, with higher brightness the sub-angstrom limit should be able to be reached. The potential for applications in materials and biological research is rich. FIG. 3 is a simplified diagram of a computer system 310 that is used to oversee the system of FIGS. 1 and 2 according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many other modifications, alternatives, and variations. As shown, the computer system 310 includes display device 320, display screen 330, cabinet 340, keyboard 350, and mouse 370. Mouse 370 and keyboard 350 are representative “user input devices.” Mouse 370 includes buttons 380 for selection of buttons on a graphical user interface device. Other examples of user input devices are a touch screen, light pen, track ball, data glove, microphone, and so forth. The system is merely representative of but one type of system for embodying the present invention. It will be readily apparent to one of ordinary skill in the art that many system types and configurations are suitable for use in conjunction with the present invention. In a preferred embodiment, computer system 310 includes a Pentium™ class based computer, running Windows™ NT, XP, or Vista operating system by Microsoft Corporation. However, the system is easily adapted to other operating systems such as any open source system and architectures by those of ordinary skill in the art without departing from the scope of the present invention. As noted, mouse 370 can have one or more buttons such as buttons 380. Cabinet 340 houses familiar computer components such as disk drives, a processor, storage device, etc. Storage devices include, but are not limited to, disk drives, magnetic tape, solid-state memory, bubble memory, etc. Cabinet 340 can include additional hardware such as input/output (I/O) interface cards for connecting computer system 310 to external devices external storage, other computers or additional peripherals, which are further described below. FIG. 4 is a more detailed diagram of hardware elements in the computer system of FIG. 3 according to an embodiment of the present invention. This diagram is merely an example, which should not unduly limit the scope of the claims herein. One of ordinary skill in the art would recognize many other modifications, alternatives, and variations. As shown, basic subsystems are included in computer system 310. In specific embodiments, the subsystems are interconnected via a system bus 375. Additional subsystems such as a printer 374, keyboard 378, fixed disk 379, monitor 376, which is coupled to display adapter 382, and others are shown. Peripherals and input/output (I/O) devices, which couple to I/O controller 371, can be connected to the computer system by any number of means known in the art, such as serial port 377. For example, serial port 377 can be used to connect the computer system to a modem 381, which in turn connects to a wide area network such as the Internet, a mouse input device, or a scanner. The interconnection via system bus allows central processor 373 to communicate with each subsystem and to control the execution of instructions from system memory 372 or the fixed disk 379, as well as the exchange of information between subsystems. Other arrangements of subsystems and interconnections are readily achievable by those of ordinary skill in the art. System memory, and the fixed disk are examples of tangible media for storage of computer programs, other types of tangible media include floppy disks, removable hard disks, optical storage media such as CD-ROMS and bar codes, and semiconductor memories such as flash memory, read-only-memories (ROM), and battery backed memory. Although the above has been illustrated in terms of specific hardware features, it would be recognized that many variations, alternatives, and modifications can exist. For example, any of the hardware features can be further combined, or even separated. The features can also be implemented, in part, through software or a combination of hardware and software. The hardware and software can be further integrated or less integrated depending upon the application. Further details of the functionality, which may be carried out using a combination of hardware and/or software elements, of the present invention can be outlined below according to the figures. Embodiments of the present invention enable ultrafast imaging with applications in studies of structural and morphological changes in single-crystal gold and graphite films, which exhibit entirely different dynamics, as discussed below. For both, the changes were initiated by in situ femtosecond impulsive heating, while image frames and diffraction patterns were recorded in the microscope at well-defined times following the temperature-jump. The time axis in the microscope is independent of the response time of the detector, and it is established using a variable delay-line arrangement; a 1-μm change in optical path of the initiating (clocking) pulse corresponds to a time step of 3.3 fs. FIG. 5 illustrates both time-resolved images and diffraction. In this example, the images in FIGS. 5A and 5B were obtained stroboscopically at several time delays after heating with the fs pulse (fluence of 1.7 mJ/cm2). The specimen is a gold single crystal film mounted on a standard 3-mm 400-mesh grid. Shown are the bend contours (dark bands), {111}twins (sharp straight white lines) and holes in the sample (bright white circles). The insets in FIG. 5B are image-difference frames Im(tref′; t) with respect to the image taken at −84 ps. The gold thickness was determined to be 8 nm by electron energy loss spectroscopy (EELS). FIG. 5C illustrates the time dependence of image cross-correlations of the full image from four independent scans taken with different time steps. A fit to biexponential rise of the 1 ps step scan is drawn, yielding time constants of 90 ps and 1 ns. FIG. 5D illustrates the time dependence of image cross-correlations at 1 ps time steps for the full image and for selected regions of interest SAI #1, #2, and #3, as shown in FIG. 5A. FIGS. 5E and 5F are diffraction patterns obtained using a single pulse of 6×106 electrons at high peak fluence (40 mJ/cm2) and selected-area aperture of 25 μm diameter. Two frames are given to indicate the change. Diffraction spots were indexed and representative indices are shown as discussed below. FIGS. 5A and 5B illustrate representative time-framed images of the gold nanocrystal using the fs excitation pulses at a repetition rate of 200 kHz and peak excitation fluence of ˜1.7 mJ/cm2. In FIG. 5A, taken at −84 ps, before the clocking pulse (t=0), typical characteristic features of the single crystal gold in the image are observed: twins and bend contours. Bend contours, which appear as broad fuzzy dark lines in the image, are diffraction contrast effects occurring in warped or buckled samples of constant thickness. In the dark regions, the zone axis (the crystal [100]) is well aligned with the incident electron beam and electrons are scattered efficiently, whereas in the lighter regions the alignment of the zone axis deviates more and the scattering efficiency is lower. Because bend contours generally move when deformation causes tilting of the local crystal lattice, they provide in images a sensitive visual indicator of the occurrence of such deformations. At positive times, following t=0, visual dynamical changes are observed in the bend contours with time steps from 0.5 ps to 50 ps. A series of such image frames with equal time steps provide a movie of the morphological dynamics. To more clearly display the temporal evolution, image-difference frames were constructed. Depicted as insets in the images of FIG. 5B, are those obtained when referencing to the −84 ps frame; for t=+66 ps and +151 ps. In the difference images, the regions of white or black directly indicate locations of surface morphology change (bend contour movement), while gray regions are areas where the contrast is unchanged from that of the reference frame. It is noted that the white and black features in the difference images are nm-scale dynamical change, indicating the size of the induced deformations. Care was taken to insure the absence of long-term specimen drifts as they can cause apparent contrast change. To quantify the changes in the image the following method of cross-correlation was used. The normalized cross correlation of an image at time t with respect to that at time t′ is expressed as: γ ⁡ ( t ) = ∑ x , y ⁢ C x , y ⁡ ( t ) ⁢ C x , y ⁡ ( t ′ ) ∑ x , y ⁢ C x , y ⁡ ( t ) 2 ⁢ ∑ x , y ⁢ C x , y ⁡ ( t ′ ) 2 where the contrast Cx,y(t)=[Ix,y(t)−Ī(t)]/Ī(t); Ix,y(t) and Ix,y(t′) are the intensities of pixels at the position of (x,y) at times t and t′, and Ī(t) and Ī(t′) are the means of Ix,y(t) and Ix,y(t′), respectively. This correlation coefficient γ(t) is a measure of the temporal change in “relief pattern” between the two images being compared, which can be used as a guide to image dynamics as a function of time. Two types of cross-correlation plots were made, those referenced to a fixed image frame before t=0 and others that show correlation between adjacent time points. (Another quantity that shows time dependence qualitatively similar to that of the image cross-correlation is the standard deviation of pixel intensity in difference images). FIGS. 5C and 5D show the cross-correlation values between the image at each measured time point and a reference image recorded before the arrival of the clocking pulse. The experiments were repeated, for different time-delay steps (500 fs, 1 ps, 5 ps, and 50 ps), and similar results were obtained, showing that morphology changes are completely reversible and reproducible over each 5 μs inter-pulse interval. The adjacent-time cross-correlations reveal the timescales for intrinsic changes in the images, which disappear for time steps below 5 ps, consistent with full-image rise in time. Over all pixels, the time scale for image change covers the full range of time delay, from ps to ns, indicating the collective averaging over sites of the specimen; as shown in FIG. 5C the overall response can be fit to two time constants of 90 ps and 1 ns. The power of selected area image dynamics (SAID) is illustrated when the dynamics of the bend contours are followed in different selected areas of the image, noted in the micrographs as SAI #1, 2, and 3. The corresponding image cross-correlations (FIG. 5D) have different shape and amplitude from each other and from the full image correlation. The large differences observed here and for other data sets, including onsets delayed in time and sign reversals, indicate the variation in local deformation dynamics. In FIGS. 5G-L, a time-resolved SAI at higher magnification is depicted. A broad and black “penguin-like” contour is observed as the dominant feature of this area. As shown in the frames, a colossal response to the fs heating is noted. The gray region inside the black contour appears and broadens with time. Also, a new black contour above the large central white hole begins to be evident at 1200 ps, and gains substantial intensity over the following 50 ps. All frames taken can be used to construct a movie of SAID. The observed SAID changes correspond to diffraction contrast (bright-field) effects in bend contours, as mentioned above. It is known that the shape of bend contours can be easily altered by sample tilting or heating inside the microscope. However, here in the ultrafast electron microscope (UEM) measurements, the changes in local tilt are transient in nature, reflecting the temporal changes of morphology and structure. Indeed, when the experiments were repeated in the TEM mode of operation, i.e., for the same heating laser pulse and same scanning time but with continuous electron probe beam, no image change was observed. This is further supported by the change in diffraction observed at high fluences and shown in FIGS. 5E and 5F for two frames, at negative time and at +50 ns; in the latter, additional Bragg spots are visible, a direct evidence of the transient structural change due to bulging at longer times. Whereas real-space imaging shows the time-dependent morphology, the selected area diffraction dynamics (SADD) patterns provide structural changes on the ultrashort timescale. Because the surface normal of the film is parallel to the [100] zone axis, the diffraction pattern of the sample was properly indexed by the face-centered-cubic (fcc) structure projected along the [100] zone axis at zero tilt angle (see FIG. 5E). From the positions of the spots in FIG. 5F, which are reflections from the {113} and {133}planes, forbidden in the [100] zone-axis viewing, we measured the interplanar spacings to be 1.248 and 0.951 Å, respectively. With selected area diffraction, Bragg peak separations, amplitudes, and widths were obtained as a function of time. The results indicate different timescales from those of image dynamics. FIG. 6A illustrates structural dynamics and heat dissipation in gold and FIG. 6B illustrates coherent resonance of graphite. Referring to FIG. 6A, SADD for fs excitation at 1.7 mJ/cm2 peak fluence (519 nm) is illustrated. The Bragg separation for all peaks and the amplitude of the {042}peaks are shown in the main panel; the inset gives the 2.2 μs recovery (by cooling) of the structure obtained by stroboscopic ns excitation at 7 mJ/cm2. The peak amplitude has been normalized to the transmitted beam amplitude, and the time dependence of amplitude and separation is fit as an exponential rise, and a delay with rise, respectively. Referring to FIG. 6B, resonance oscillations are observed for the Bragg (1 22) peak in the diffraction pattern of graphite; the amplitudes are similar in magnitude to those in FIG. 6A. The sample was tilted at 21° angle to the microscope axis and the diffraction pattern was obtained by using the SAD aperture of 6 μm diameter on the specimen. The graphite thickness is 69 nm as determined by EELS; the oscillation period (τp) is measured to be 56.3 ps. For a thickness of 45 nm, the period is found to be τp=35.4 ps. FIGS. 6D-G illustrate, for selected areas, time dependence of intensity difference (dark-field) for graphite. The image change displays the oscillatory behavior with the same τp as that of diffraction. The dark-field (DF) images were obtained by selecting the Bragg (1 22) peak. In FIG. 6H, each line corresponds to the difference in image intensities, Im(t−30 ps; t), for selected areas of 1×100-pixel slices parallel to contrast fringes in the DF image. The average amplitude of {042}diffraction peaks drop significantly; the rise time is 12.9 ps, whereas the change in separations of all planes is delayed by 31 ps and rises in 60 ps. The delay in the onset of separation change with respect to amplitude change is similar to the timescale for the amplitude to reach its plateau value of 15% reduction in the case of the {042}amplitude shown. In order to determine the recovery time of the structure, we carried out stroboscopic (and also single-pulse) experiments over the timescale of microseconds. The recovery transient in the inset of FIG. 6A (at 7 mJ/cm2) gives a time constant of 2.2 μs; we made calculations of 2D lateral heat transport with thermal conductivity (λ=3.17 W/(cm K) at 300 K) and reproduced the observed timescale. For this fluence, the maximum lattice spacing change of 0.08% gives the temperature increase ΔT to be 60 K, knowing the thermal expansion coefficient of gold (α=14.2×10−6 K−1). The atomic-scale motions, which lead to structural and morphological changes, can now be elucidated. Because the specimen is nanoscale in thickness, the initial temperature induced is essentially uniform across the atomic layers and heat can only dissipate laterally. It is known that for metals the lattice temperature is acquired following the large increase in electron temperature. The results in FIG. 6A give the temperature rise to be 13 ps; from the known electron and lattice heat-capacity constants [C1=70 J/(m3 K2) and C2=2.5×106 J/(m3 K), respectively] and the electron-phonon coupling [g=2×1016 W/(m3 K)] we obtained the initial heating time to be ˜10 ps for electron temperature T1=2500 K, in good agreement with the observed rise. Reflectivity measurements do not provide structural information, but they give the temperature rise. For bulk material, the timescale for heating (˜1 ps) is shorter than that of the nano-scale specimen (˜10 ps), due to confinement in the latter, which limits the ballistic motion of electrons in the specimen, and this is evident in the UEM studies. Because the plane separation is 0.4078 nm, the change of the average peak separation (0.043%), at the fluence of 1.7 mJ/cm2, gives a lattice constant change of 0.17 μm. Up to 30 ps the lattice is hot but, because of macroscopic lattice constraint, the atomic stress cannot lead to changes in lateral separations, which are the only separations visible for the [100] zone-axis probing. However, the morphology warping change is correlated with atomic (lateral) displacements in the structure as it relieves the structural constraint. Indeed the time scale of the initial image change is similar to that of plane separations in diffraction (60-90 ps). This initial warping, which changes image contrast, is followed by longer time (ns) minimization of surface energy and bulging, as shown in FIG. 5D. Given the picometer-scale structural change (0.17 pm), the stress over the 8-nanometer specimen gives the total expansion to be 3.4 pm over the whole thickness. Considering the influence of lateral expansion, the maximum bulge reaches 1 to 10 nm depending on the lateral scale. Finally, the calculated Debye-Waller factor for structural changes gives a temperature of 420 K (ΔT=125 K), in excellent agreement with lattice temperature derived under similar conditions, noting that for the nanoscale material the temperature is higher than in the bulk. Graphite was another study in the application of the UEM methodology. In contrast to the dynamics of gold, in graphite, because of its unique 2D structure and physical properties, we observed coherent resonance modulations in the image and also in diffraction. The damped resonance of very high frequency, as shown below, has its origin in the nanoscale dimension of the specimen and its elasticity. The initial fs pulse induces an impulsive stress in the film and the ultrafast electron tracks the change of the transient structure, both in SAID and SADD. In FIG. 6B, the results obtained by measuring changes of the diffraction spot (1 22) are displayed and in FIGS. 6D-G those obtained by dark-field (DF) imaging with the same diffraction spot being selected by the objective aperture and the specimen tilted, as discussed below. For both the image and diffraction, a strong oscillatory behavior is evident, with a well defined period and decaying envelope. When the transients were fitted to a damped resonance function [(cos 2π/τp)exp(−t/τdecay)], we obtained τp=56.3±1 ps for the period. The decay of the envelope for this particular resonance is significantly longer, Tdecay=280 ps. This coherent transient decay, when Fourier transformed, indicates that the length distribution of the film is only ±2 nm as discussed in relation to the equation below. The thickness of the film was determined (L=69 nm) using electron energy loss spectra (EELS). In order to test the validity of this resonance behavior we repeated the experiments for another thickness, L=45 nm. The period indeed scaled with L, giving τp=35.4 ps. These, hitherto unobserved, very high frequency resonances (30 gigahertz range) are unique to the nanoscale length of graphite. They also reflect the (harmonic) motions due to strain along the c-axis direction, because they were not observed when we repeated the experiment for the electron to be along the [001] zone axis. The fact that the period in the image is the same as that of the diffraction indicates the direct correlation between local atomic structure and macroscopic elastic behavior. Following a fs pulse of stress on a freely vibrating nanofilm, the observed oscillations, because of their well-defined periods, are related to the velocity (C) of acoustic waves between specimen boundaries, which in turn can be related to Young's modulus (Y) of the elastic stress-strain profile: 1 τ p = nC 2 ⁢ ⁢ L = n 2 ⁢ ⁢ L ⁢ ( Y ρ ) 1 / 2 ,where n is a positive integer, with n=1 being the fundamental resonance frequency (higher n are for overtones). Knowing the measured r, and L, we obtained C=2.5×105 cm/s. For graphite with the density ρ=2.26 g/cm3, Y=14.6 gigapascal for the c-axis strain in the natural specimen examined. Pyrolytic graphite has Y values that range from about 10 to 1000 gigapascal depending on the orientation, reaching the lowest value in bulk graphite and the highest one for graphene. The real-time measurements reported here can now be extended to different length scales, specimens of different density of dislocations, and orientations, exploring their influence at the nanoscale on C, Y, and other properties. We note that selected-area imaging was critical as different regions have temporally different amplitudes and phases across the image. Uniting the power of spatial resolution of EM with the ultrafast electron timing in UEM provides an enormous advantage when seeking to unravel the elementary dynamics of structural and morphological changes. With total dissipation of specimen heat between pulses, selected-area dynamics make it possible to study the changes in seconds of recording and for selected pixels of the image. In the applications given here, for both gold and graphite, the difference in timescales for the nonequilibrium temperature (reaching 1013 K/s), the structural (pm scale) and morphological (nm scale) changes, and the ultrafast coherent (resonance) behavior (tens of gigahertz frequency) of materials structure illustrate the potential for other applications, especially when incorporating the different and valuable variants of electron microscopy as we have in our UEM. Embodiments of the present invention extend ultrafast 4D diffraction and microscopy to the attosecond regime. As described herein, embodiments use attosecond electron diffraction to observe attosecond electron motion. Pulses are freely generated, compressed, and tilted. The approach can be implemented to extend previous techniques including, for example phase transformations, chemical reactions, nano-mechanical processes, and surface dynamics, and possibly to other studies of melting processes, coherent phonons, gold particles, and molecular alignment. As described herein, the generation of attosecond resolution pulses and in situ probing through imaging with free electrons. Attosecond diffraction uses near mono-energetic attosecond electron pulses for keV-range of energies in free space and thus space charge effects are considered. Additionally, spatiotemporal synchronization of the electron pulses to the pump pulses is made along the entire sample area and with attosecond precision. Diffraction orders are shown to be sensitive to the effect of electron displacement and conclusive of the four-dimensional dynamics. A component of reaching attosecond resolution with electron diffraction is the generation of attosecond electron pulses in “free space,” so that diffraction from freely chosen samples of interest can take place independent of the mechanisms of pulse generation. Electrons with energies of 30-300 keV are ideal for imaging and diffraction, because of their high scattering cross sections, convenient diffraction angles, and the appropriate de Broglie wavelength (0.02 to 0.07 Å) to resolve atomic-scale changes. Moreover, they have a high degree of monochromaticity. For example, electrons accelerated to E0=30-300 keV with pulse duration of 20 attoseconds (bandwidth of ΔE≈30 eV) have ΔE/E0≈10−3-10−4, making diffraction and imaging possible without a spread in angle and resolution. Optical attosecond pulses have typically ΔE/E0≈0.5 and because of this reach of ΔE to E0, their duration is Fourier-limited to ˜100 attoseconds. Free electron pulses of keV central energy can, in principle, have much shorter duration, down to sub-attoseconds, while still consisting of many wave cycles. Pulses with a large number of electrons suffer from the effect of space charge, which determines both the spatial and the temporal resolutions. This can be avoided by using packets of single, or only a few, electrons in a high repetition rate, as demonstrated in 4D microscopy imaging. FIG. 7A depicts the relation of single electron packets to the effective envelope due to statistics. Each single electron (blue) is a coherent packet consisting of many cycles of the de Broglie wave and has different timing due to the statistics of generation. On average, multiple single electron packets form an effective electron pulse (dotted envelope). It will be appreciated that there is high dispersion for electrons of nonrelativistic energy. The small but unavoidable bandwidth of an attosecond electron pulse causes the pulse to disperse during propagation in free space, even when no space charge forces are present. For example, a 20-attosecond pulse with ΔE/E0=10−3 would stretch to picoseconds after just a few centimeters of propagation. Embodiments of the present invention provide methods and systems for the suppression of dispersion and the generation of free attosecond electron pulses based on the initial preparation of negatively-chirped electron packets. As described herein, femtosecond electron pulses are generated by photoemission and accelerated to keV energies in a static electric field. Preceding the experimental interaction region, optical fields are used to generate electron packets with a velocity distribution, such that the higher-energy parts are located behind the lower-energy ones. With a proper adjustment of this chirp, the pulse then self-compresses to extremely short durations while propagating towards the point of diffraction. To achieve attosecond pulses, the chirp must be imprinted to the electron pulse on a nanometer length scale. Optical waves provide such fields. However, non-relativistic electrons move significantly slower than the speed of light (e.g. ˜0.3 c for 30 keV). The direct interaction with an optical field will, therefore, cancel out over time and can not be used to accelerate and decelerate electrons for compression. In order to overcome this limitation, we make use of the ponderomotive force, which is proportional to the gradient of the optical intensity to accelerate electrons out of regions with high intensity. By optical wave synthesis, intensity profiles can be made that propagate with less than the speed of light and, therefore, allow for co-propagation with the electrons. FIG. 7B illustrates a schematic of attosecond pulse generation according to an embodiment of the present invention. A synthesized optical field of two counter-propagating waves of different wavelengths results in an effective intensity grating, similar to a standing wave, which moves with a speed slower than the speed of light. Electrons can, therefore, co-propagate with a matched speed and are accelerated or decelerated by the ponderomotive force according to their position within the wave. After the optical fields have faded away, this velocity distribution results in self-compression; the attosecond pulses are formed in free space. Depending on the optical pulse intensity, the electron pulse duration can be made as short as 15 attoseconds, and, in principle, shorter durations are achievable. If the longitudinal spatial width of the initial electron pulse is longer than the wavelength of the intensity grating, multiple attosecond pulses emerge that are located with well-defined spacing at the optical minima. This concept of compression can be rigorously described analytically as a “temporal lens effect.” The temporal version of the Kapitza-Dirac effect has an interesting analogy. Some of our initial work was based on an effective ponderomotive force in a collinear geometry. In order to extend the approach to more complex arrangements, here we generalize the approach and consider the full spatiotemporal (electric and magnetic) fields of two colliding laser waves with an arbitrary angle and polarization. The transversal and longitudinal fields of a Gaussian focus were applied. We simulated electron trajectories by applying the Lorentz force with a fourth-order Runge-Kutta algorithm using steps of 100 attoseconds. Space charge effects were taken into account by calculating the Coulomb interactions between all single electrons for each time step (N-body simulations). FIG. 7B illustrates temporal optical gratings for the generation of free attosecond electron pulses for use in diffraction. (a) A femtosecond electron packet (blue) is made to co-propagate with a moving optical intensity grating (red). (b) The ponderomotive force pushes electron towards the minima and thus creates a temporal lens. (c) The induced electron chirp leads to compression to attosecond duration at later time. (d) The electron pulse duration from 105 trajectories reaches into the domain of few attoseconds. FIG. 7C depicts the compression of single electron packets in the combined field of two counter-propagating laser pulses with durations of 300 fs at wavelengths of 1040 nm and 520 nm. The pulse is shown just before, at, and after the time of best compression; the center along Z is shifted for clarity. The plotted pulse shape is a statistical average over 105 packets of single electrons. The beam diameter of the initial electron packet was 10 μm and the beam diameters of the laser pulses were 60 μm; the resulting compression dynamics is depicted before, just at, and some time after the time of best compression to a duration of 15 attoseconds (see FIG. 7C(b)). These results show that an optical wave with a beam diameter of only several times larger than that of the electron packet is sufficient to result in almost homogeneous compression along the entire electron beam. The characteristic longitudinal spread after the point of best compression, as depicted in FIG. 7C is the result of an “M”-shaped energy spectrum of the electrons after interactions with the sinusoidal intensity grating. Coulomb forces prevent concentration of a large number of electrons in a limited volume, and a compromise between electron flux and laser repetition rate must be found to achieve sufficiently intense diffraction. The laser pulses for compression have energies on the order of 5 μJ and can, therefore, be generated at MHz repetition rates with the resulting flux of 106 electrons/s, which is sufficient for conclusive diffraction. Nevertheless, having more than one electron per attosecond pulse is beneficial for improving the total flux. In order to investigate the influence of space charge on the performance in our attosecond compression scheme, we considered electron packets of increasing electron density and evaluated the resulting pulse durations and effective electron density per attosecond pulse. Two findings are relevant with the results shown in FIG. 8. First, the duration of individual attosecond electron pulses increases relatively insignificantly with the number of electrons contained within. Even for 40 electrons in a single pulse, the duration increases only from 15 to 25 attoseconds (see FIG. 8(a)). The reasons for this are the highly oblate shape of the electron pulses, and the approximate linearity of space charge forces in the longitudinal direction, which are compensated for by somewhat longer interaction in the ponderomotive forces of the optical waves. Secondly, for a train of pulses, there is an effect on synchronization. When the initial femtosecond electron packet covers several optical cycles of the compression wave, a train of attosecond pulses results as shown in FIG. 7B. Perfect synchronization to the optical wave is provided, because all attosecond pulses are located at the same optical phase of the fundamental laser wave. This phase matching relation, which permits attosecond resolution, despite the presence of multiple pulses, is altered under space charge conditions. The attosecond pulses repel each other and a temporal spreading of the comb-like train results. For a train of near 10 attosecond pulses, FIG. 8(b) displays the difference in timing for an adjacent attosecond pulse in relation to the central one, which is always locked to the optical phase because the space charge forces cancel out. The total timing mismatch is the product of the plotted value with the number of attosecond pulses in the entire electron packet (near 10 for this example). In order to keep the total mismatch to the optical wave below 20 attoseconds, 10 electrons per attosecond electron pulse represent an optimum value. The total pulse train then consists of 200 electrons for that group of pulses; of course the total flux of electrons is determined by the repetition rate. Note that mismatch to the compression wave is absent with isolated attosecond electron pulses, which are generated when the initial uncompressed electron packet is shorter than a few femtoseconds, or with optical fields of longer wavelength. Numerous imaging experiments have been successful with single electron packets. In state-of-the-art electron crystallography experiments, typically 500 electrons per pulse were used at a repetition rate of kHz to produce the needed diffraction. This is equivalent to having 5 electrons per attosecond pulse at 100 kHz, which is a convenient repetition rate for optical wave synthesis, and provides enough time for letting the material under investigation to cool back to the initial state. Laser systems with MHz repetition rates will provide even higher fluxes. Applications of attosecond electron pulses for diffraction and microscopy use synchronization of events in the pump-probe arrangement with an accuracy that is equal or better than the individual pulse durations. In contrast to recompression concepts that are based on time-dependent microwave fields, the application of laser waves for attosecond electron pulse generation provides exact temporal synchronization when the pump pulses are derived by phase-locking from the same laser system. Many common optical techniques, such as nonlinear frequency conversion, continuum generation in solids, or high-harmonic generation, all provide a phase lock in the sense that the outcome has the same relative phase and timing in relation to the incoming optical wave for each single pulse of the laser. A second requirement for reaching into the temporal resolution of attoseconds is the realization of spatial delay matching along extended areas of the diffraction. The use of large samples, for example with up to millimeters in size in some electron diffraction experiments, provides enhanced diffraction efficiency and offers the possibility to use electron beams with large diameter, in order to maximize the coherence and flux. In this case, the time resolution is limited by differences in the arrival times of pump and probe pulses at different points within the involved beam diameters (group velocity mismatch). Electron pulses at keV energies travel with significantly less than the speed of light (e.g. vel=0.3 c for 30 keV electrons) and are, therefore, “overtaken” by the laser wave. Embodiments of the present invention provide two arrangements for matching the group velocity of electrons with the phase velocity of optical pulses. Both arrangements are suitable for applications in noncollinear, ultrafast electron microscopy and diffraction. FIG. 9(a) presents a concept for the transmission geometry of diffraction and microscopy in which two angles are introduced, one between the laser beam and the electron beam (β), and another one (α) for the tilt angle of the sample (black) to the phase fronts of the laser wave. Total synchrony is achieved if the relative delay between the optical wave and the attosecond electron pulses is made identical for all points along the entire sample surface. Each small volume of the sample is then subject to an individual pump-probe-type experiment with the same time delay. The above condition is found when we match the coincidence along the entire width of the specimen. The effective surface velocity vsurface of the laser and of the electron pulses must be identical. From FIG. 9A, this requirement is expressed by the following equation: sin ⁡ ( α ) sin ⁡ ( α - β ) = c v el . ( 1 ) It follows that an angle of β=10°, for example, results in an optimum angle for the sample tilt of α=14.8°, which are both easily achievable angles in a real experiment. The effective tilt of the sample with respect to the electron direction is then α−β=4.8°. Naturally, if this value is not coincident with a zone axis direction, a complete rocking curve should be obtained in order to optimize α and β with tilt requirements. Although different portions of the laser wavefront impinge on the surface of the sample at different times, this behavior is matched by the electron pulse, resulting in all portions of the surface of the sample being phase matched. As illustrated in FIG. 9(a), the laser beam, also referred to as a laser wave, is used to activate the sample, for example, to heat the sample, cause motion of the sample, or to effect the chemical bonds present in the sample. The timing of the laser wave and the electron pulses are synchronized using the delay stage discussed in relation to FIG. 1. The train of electron pulses can be generated using the configuration illustrated in FIG. 10(a). Another option for synchronization along extended surfaces is the use of tilted electron pulses, for that the electron density makes an angle with respect to the propagation direction. Tilted optical pulses have been used for reaching femtosecond resolution in reflection geometry, but here tilted electron pulses are introduced for effective spatiotemporal synchronization to the phase velocity of the excitation pulses along the entire sample surface. FIG. 9B depicts the concept. If an angle γ is chosen between the laser (red) and the attosecond electron pulses (blue), the electron pulses need to be tilted likewise. The sample is located parallel to the optical phase fronts and its entire surface is illuminated by the attosecond electron pulse at once and at the same time of incidence relative to the optical pulse wave. Because the incidence is delay-free for all points along the surface, velocity matching is provided for the whole probed area. The generation of tilted attosecond electron pulses is outlined in FIG. 10(a). The introduction of an angle between the intensity grating (red) and the electron beam (blue) leads to formation of electron pulses with a tilt. As described above, a femtosecond electron packet (blue) is first generated by conventional photoelectron generation and accelerated in a static electric field. By intersecting the counter-propagating intensity grating at an angle, tilted electron pulses result with attosecond duration. The ponderomotive force accelerates the electrons towards the planes of destructive interference in the intensity wave and they form attosecond pulses that are compressed along the optical beam axis; but the pulses propagate in the original direction. Only a slight adjustment of the electrons' central energy is required to achieve phase matching to the moving optical grating. Based on this concept, we simulated the tilting effect by using 31-keV electron pulses with an initial duration of ˜15 femtoseconds and a spatial beam diameter of ˜10 μm. FIG. 10(b) illustrates the simulation results for an initial packet of 15-femtosecond duration (left) and an intersection angle of 5°. The tilted attosecond pulses have duration of ˜20 attoseconds when measured perpendicular to the tilt (note the different scale of Z and X). The optical intensity wave is synthesized by two counter-propagating laser pulses of 100-fs duration and wavelengths of 1040 and 520 nm. The angle between the electron beam and the laser wave is 5°. The results of compression are shown in FIG. 10(b): The attosecond electron pulses are formed at the minima of the optical intensity wave and, therefore, are tilted by 5° with respect to the electron propagation direction. For other incidence angles of the laser, the electron pulses are tilted accordingly. Perpendicular to the attosecond pulses, the measured duration is ˜20 attoseconds, given as the full width at half maximum. Based on the methodology for generation and synchronization of attosecond electron pulses described above, the diffraction and manifestation of electron dynamics in the patterns are described. By way of two different examples, embodiments of the present invention are utilized to observe electronic motions in molecules and materials with attosecond electron packets. We consider first the physics of electron scattering and the change in scattering factors which characterize individual atoms and the electron density involved. Diffraction from molecular crystals or other crystalline structures provides two distinct advantages over that obtained for gas phase ensembles. First, the sample density is many orders of magnitudes higher (1021 molecules/cm3 as compared to 1010 to 1016/cm3 in gas jets); diffraction is, therefore, more intense. Second, the crystalline order results in Bragg scatterings and they are concentrated into well-defined “spots” for ordered crystals; the patterns become rods for surfaces and narrow rings for amorphous substances. The diffraction results in intensities which are proportional to the square of the diffraction amplitude. As discussed below, coherence in diffraction is used in observing the changes of interest. The diffraction from molecular crystals, or other crystalline materials of interest, is defined by the summation over the contributions of all scatterers in a unit cell. The intensity I of a Bragg spot with the Miller indices (hkl) is determined by the positions (xyz) of the scatterers j in the unit cell: I ⁡ ( hkl ) ∝  ∑ j ⁢ ⁢ f j ⁢ exp ⁡ [ - 2 ⁢ π ⁢ ⁢ i ⁡ ( hkl ) · ( xyz ) j ]  2 , ( 2 ) where fj are the atomic scattering factors. Electron diffraction is the result of Coulomb interaction between the incoming electrons and the potential formed by nuclei and electrons. The factors fj account for the effective scattering amplitude of atoms and are derived from quantum calculations that take into account the specific electron density distribution around the nuclei, including core electrons. The scattering we are considering here is the elastic one. In order to estimate the influence of electron dynamics on contributions to time-resolved diffraction patterns, we consider typical densities of electrons in chemical bonds, and the possible change. Static electron density maps show that typical covalent bonds consist of about one electron/Å3 and that this density is delocalized over volumes with diameters in the order of 1 Å. For estimating an effective scattering factor of such electron density, we consider a Gaussian sphere with a diameter of 1 Å, consisting of one electron. The electric potential is derived by Gauss' law and results in a radial dependence that is represented in FIG. 11, dotted line. The total scattering amplitude of free charges diverges at small angles, because of the long-range behavior of the potential. Since in real crystals the potential is localized in unit cells, we use a Gaussian distribution of the same magnitude in order to restrict the range to about +1.5 Å. For potential of spherical symmetry, an effective scattering factor can be calculated from the radial potential Φ(r) according to f el ⁡ ( s ) = 8 ⁢ π 2 ⁢ m e ⁢ e h 2 ⁢ ∫ 0 ∞ ⁢ r 2 ⁢ Φ ⁡ ( r ) ⁢ sin ⁡ ( 4 ⁢ π ⁢ ⁢ sr ) 4 ⁢ π ⁢ ⁢ sr ⁢ ⁢ ⅆ r , ( 3 ) where S=sin(ν/2)/λel is the scattering parameter for a diffraction angle ν and λel is the de Broglie wavelength of the incident electrons. The result for our delocalized electron density is shown in FIG. 11(b); for comparison we plot also the tabulated scattering factor of neutral hydrogen. Both have comparable magnitude, which is expected because of their similar sizes. Here, we consider the iodine molecule as a model case and invoke the transition from a bonding to an anti-bonding orbital. The crystal structure of iodine consists of nearly perpendicular iodine pairs with a bond length of ˜2.7 Å. Two electrons contribute to the intramolecular σ bond; the intermolecular bond is weaker. FIG. 12 depicts the system under study and the two cases considered. The effect of antibonding excitation is made by comparing the Bragg intensities for the iodine structure, including the binding electrons, to a hypothetical iodine crystal consisting only of isolated atoms (see FIG. 12(a)). In Table 1, we give the results of the calculations following equation 2 with the values off tabulated for iodine atoms and from equation (3) for the electronic distribution changes. Despite the large difference in f of the iodine nuclei and the electron (about 50:1), the changes of Bragg spot intensity are significant, being on an order of 10-30%. TABLE 1Effects of Electron Motion on Selected Molecular Bragg SpotsMiller Indices (hkl)(a) ΔITransition(b) ΔIMovement (0.08 Å)100, 010, 001(forbidden)(forbidden)200, 400, 60000002−35%0020 (weak)+100% −17%40000040−18%+13%00400111+15% −2%331−20%+15% In column (a), the magnitude of Bragg spot intensity change ΔI of crystalline iodine as a result of bonding to antibonding transition is given. In column (b), the magnitude of Bragg spot intensity change as a result of field interaction with charge density, also in iodine. This large change is for two reasons. First, the bonding electrons are located in-between iodine atoms and contribute, therefore, strongly to the enhancement or suppression of all Bragg spots that project from the inter-atomic distances of the molecular units. Second, the large effect is result of the intrinsic “heterodyne detection” scheme of diffraction; the total intensity of a Bragg spot scales with the square of the coherent sum of individual contributions (see equation (2)). Although the total contribution to the intensity of a Bragg spot from bonding electrons is lower by a factor of several hundreds than the intensity contributions from the iodine atoms, the modulation is on the order of several percents as a result of the coherence of diffraction on a nanometer scale. Symmetry in the crystal is evident in the absence of change in certain Bragg orders. From measurements of the dynamics of multiple spots, it follows that electron density movies could be made. This is best achieved in an electron microscope in diffraction geometry; however conventional diffraction is also suitable to simultaneously monitor many Bragg spots and is advantageous for the study of ordered bulk materials. The example given is not far from an experimental observation made on a metal-to-insulator transition for which a σ-type excitation was induced with a femtosecond pulse. As a second model case we consider the reaction of bonded electron density to external electric fields, such as the ones from laser fields. Depending on the restoring force and the resonance, an electron density will oscillate with the driving field in phase or with a phase delay. This charge oscillation re-radiates and is responsible for the refractive index of a dielectric material. In order to estimate the magnitude of charge displacement, we must take into account the polarizability, β, and the electric field strength, Elaser. In the limit of only one moving charge, the displacement D is approximately given by D ≈ α e ⁢ E laser . The polarizability of molecular iodine along the bond is α≈130 ∈0Å3 (˜70 a.u.) in the static limit and a similar magnitude is expected for the crystal for optical frequencies away from the strong absorption bands; the anisotropy of polarizability indicates the role of the bonding electrons. With femtosecond laser pulses, a field of Elaser=109 V/m is possible for intensities below the damage threshold. With these parameters, one expects a charge displacement of D≈0.08 Å, or about 3% of the bond length. FIG. 12(b) is a schematic for the change in charge distribution by an electric field. We assume an active role of only the bonded electrons, and take the polarization of the laser field to be along the b axis of solid iodine. This axis is chosen because it has the least symmetry; a is perpendicular to the bonds. Table 1 gives the intensity changes of selected Bragg spots; the change is in the range of ±20% for some of the indices. The total energy delivered to the molecular system by the laser field is only on the order of 0.01 eV. Nevertheless the changes of charge displacements on sub-angstrom scales are evident. This marks a central advantage of electron diffraction over spectroscopic approaches, which require large energy changes in order to have projections on dynamics. In contrast, diffraction allows for the direct visualization of a variety of ultrafast electron dynamics with combined spatial and temporal resolutions, and independent of the resolution of internal energy levels. The “temporal lens” concept can be used for the focus and magnification of ultrashort electron packets in the time domain. The temporal lenses are created by appropriately synthesizing optical pulses that interact with electrons through the ponderomotive force. With such an arrangement, a temporal lens equation with a form identical to that of conventional light optics is derived. The analog of ray diagrams, but for electrons, are constructed to help the visualization of the process of compressing electron packets. It is shown that such temporal lenses not only compensate for electron pulse broadening due to velocity dispersion but also allow compression of the packets to durations much shorter than their initial widths. With these capabilities ultrafast electron diffraction and microscopy can be extended to new domains, but, as importantly, electron pulses are delivered directly on the target specimen. With electrons, progress has recently been made in imaging structural dynamics with ultrashort time resolution in both microscopy and diffraction. Earlier, nuclear motions in chemical reactions were shown to be resolvable on the femtosecond (fs) time scale using pulses of laser light, and the recent achievement of attosecond (as) light pulses has opened up this temporal regime for possible mapping of electron dynamics. Electron pulses of femtosecond and attosecond duration, if achievable, are powerful tools in imaging. The “electron recombination” techniques used to generate such attosecond electron pulses require the probing electron to be created from the parent ions (to date no attosecond electron pulses have been delivered on an arbitrary target) and for general applications it is essential that the electron pulse be delivered directly to the specimen. In ultrafast electron microscopy (UEM), the electron packet duration is determined by the initiating laser pulse, the dispersion of the electron packet due to an initial energy spread and electron-electron interactions. Since packets with a single electron can be used to image, and the initiating laser pulse can in principle be made very short (sub-10 fs), the limiting factor for the electron pulse duration is the initial energy spread. In photoelectron sources this spread is primarily due to the excess energy above the work function of the cathode, and is inherent to both traditional photocathode sources and optically-induced field emission sources. Energy-time uncertainty will also cause a measurable broadening of the electron energy spread, when the initiating laser pulse is decreased below ˜10 fs. For ultrafast imaging techniques to be advanced into the attosecond temporal regime, methods for dispersion compensation and new techniques to further compress electron pulses to the attosecond regime need to be developed. As described herein techniques for compressing free electron packets, from durations of hundreds of femtoseconds to tens of attoseconds, using spatially-dependent ponderomotive potentials are provided by embodiments of the present invention. Thus, a train of attosecond pulses can be created and used in ultrafast electron imaging. Because they are generated independent of the target they can be delivered to a specimen for studies of transient structures and electronic excitations on the attosecond time scale. The deflection of electrons (as in the Kapitza-Dirac effect) by the ponderomotive potential of intense lasers and the diffraction of electrons in standing waves of laser light have been observed, and so is the possibility (described through computer modeling) of spatial/temporal focusing with combined time-dependent electric and static magnetic fields. The “temporal lens” description analytically expresses how ponderomotive compression can be used to both compensate for the dispersion and magnify, in this case compress, the temporal duration of electron packets. We obtain simple lens equations which have analogies in optics and the results of “electron ray optics” of temporal lenses allows for analytical expressions and for the design of different schemes using geometrical optics. Here, we consider two types of temporal lenses, thin and thick. For the realization of the temporal thin lens, a laser beam with a Laguerre-Gaussian transverse mode, radial index ρ=0 and azimuthal index l=0 (or, in common nomenclature, a “donut” mode, is utilized. In the center of the donut mode, electrons will experience a spatially-varying ponderomotive potential (intensity) that is approximately parabolic. This potential corresponds to a linear spatial force which, for chirped electron pulses, can lead to compression from hundreds of fs to sub-10 fs. The second type, that of a thick lens, is based on the use of two counter-propagating laser beams in order to produce a spatially-dependent standing wave that co-propagates with the electrons. A train of ponderomotive potential wells are produced at the nodes of the standing wave, leading to compression but now with much “tighter focus” (thick lens). Because the electron co-propagates with the laser fields, velocity is matched. Analytical expressions are derived showing that this lens has the potential to reach foci with attosecond duration. Finally, we discuss methods for creating tunable standing waves for attosecond pulse compression, and techniques for measuring the temporal durations of the compressed pulses. Space-charge dispersed packets of electrons that have a linear spatial velocity chirp may also be compressed with the temporal lenses described here. All electron sources, both cw and pulsed, have an initial energy spread. For pulsed electron sources this is particularly relevant as electron packets created in a short time disperse as they propagate. The initial energy spread leads to an initial spread in velocities. These different velocities cause the initial packet to spread temporally, with the faster electrons traveling a further distance and the slower electrons traveling a shorter distance in a given amount of time. The dispersion leads to a correlation between position (along the propagation direction) and electron velocity as described in relation to FIG. 14. The linear spatial velocity “chirp” can be corrected for with a spatially-dependent linear impulsive force (or a parabolic potential). Thus, if a pulsed, spatially-dependent parabolic potential can be made to coincide appropriately with the dispersed electron packet, the slow trailing electrons can be sped up and the faster leading electrons can be slowed down. The trailing electrons, now traveling faster, can catch the leading electrons and the electron pulse will thus be compressed. FIG. 13 illustrates dispersion of an ultrashort electron packet. At t=to the packet is created from a photocathode and travels with a velocity v0. As it propagates along the x-axis it disperses, with the faster electrons traveling further, and the slower ones trailing for a given propagation time t. At t=0 a parabolic potential is pulsed on, giving an impulsive “kick” to the dispersed electron packet. After the potential is turned off, t>τ, the trailing electrons now have a greater velocity than the leading electrons. After a propagation time t=ti, the pulse is fully compressed. Consider a packet of electrons, propagating at a speed v0 along the x-axis, with a spread in positions of Δxo=v0Δto, at time t=to. At t=0, a potential of the form U(x)=½Kx2 interacts with the electron packet for a duration t in the lab frame. The waist, or spatial extent of the potential (temporal lens) is chosen to be w, while the duration r is chosen such that it is short compared to w/v0. When this condition is met the impulse approximation holds, and the change in velocity is Δv=−τ/m(dU(x)/dx)=−τKx/m, for \|x\|<w, where m is the electron mass. After the potential is turned off, t>τ, the electrons will pass through the same position, xf−x=(v0+Δv)tf, at the focal time tf=−x/Δv=m/(Kτ). To include an initial velocity spread around v0 (due to an initial ΔE), consider electrons that all emanate from a source located at a fixed position on the x-axis. An electron traveling exactly at v0 will take a time t0 to reach the center of the potential well at x=0. Electrons leaving the source with other velocities v0+vk will reach a location x=vkto at t=0. The image is formed at a location where electrons traveling with a velocity v0 and a velocity v0+vk intersect, this is, when v0ti=x+(v0+Δv+vk)ti. The image time ti is then t=−x/(Δv+vk). FIG. 14 illustrates ray diagrams for spatial and temporal lenses. The top figure in FIG. 14 depicts three primary rays for an optical thin spatial lens. The object is located at yo, and the spatial lens has a focal length, f. A real image of the object is created at the image plane, position y. The bottom figure in FIG. 14 is a ray diagram for a temporal thin lens. The diagram is drawn in a frame moving with the average speed v0 of the electron packet. The slopes of the different rays in the temporal diagram correspond to different initial velocities that are present in the electron packet. As shown in the diagram, a temporal image of the original electron packet is created at the image time ti. The initial packet (object) is created at a time to with Δto=Δxo/v0, where the spatial extend of the pulse is directly related to the temporal duration of the object. The lens is pulsed on at t=0 and the temporal focal length of the lens is tf. The lens represents the ponderomotive potential and in this case is on for the very short time r. For the object time, to=x/vk, image time t=−x/(Δv+vk) and the focal time tf=x/Δv, the temporal lens equation holds, 1 t o + 1 t i = 1 t f . ( 4 ) Ray tracing for optical lenses is often used to visualize how different ray paths form an image, and is also useful for visualizing how temporal lenses work as shown in FIG. 14. As derived in later sections, the magnification M is defined as the ratio of the electron pulse duration (Δti) at the image position to the electron pulse duration (Δto), and is directly proportional to the ratio of the object and image times (−ti/to) and distances (−xi/xo). In polar coordinates, a Laguerre-Gaussian (LG01) mode has a transverse intensity profile given by, I(r, φ)=I0exp(1)2r2exp(−2(r/w)2)/w2 where w is the waist of the focus and I0 the maximum intensity. This “donut” mode has an intensity maximum located at r=√{square root over (2)} with a value of I0=2EP(√{square root over (ln 2/π3)}/(w2τ) where EP is the energy of the laser pulse and τ is the full-width-at-half-maximum of the pulse duration, assuming a Gaussian temporal profile given by exp(−4 ln 2(t/τ)2). The ponderomotive energy UP(x) is proportional to intensity, U P ⁡ ( x ) = 1 2 ⁡ [ e 2 ⁢ λ 2 ⁢ exp ⁡ ( 1 ) ⁢ I 0 2 ⁢ π 2 ⁢ m ⁢ ⁢ ɛ 0 ⁢ c 3 ⁢ w 2 ⁢ ln ⁢ ⁢ 2 π ] ⁢ x 2 ≡ 1 2 ⁢ Kx 2 , ( 5 ) where m is the electron mass, e is the electron charge and X the central wavelength of the laser radiation and replacing r with x. Near the center of the donut mode focus (or x<<w) the intensity distribution is approximately parabolic, and hence the ponderomotive energy near the donut center is also parabolic. In analogy with a mechanical harmonic oscillator, the quantity in the square brackets of equation (5) can be referred to as the stiffness K; it has units of J/m2=N/m, and at 800 nm has the numerical value of, K≈3.1×10−36EP/(w4τ). For this parabolic approximation to be applicable, the spatial extent of the dispersed electron pulse, at t=0, Δx(0)=v0Δto+Δvoto must be much smaller than the laser waist, where the object velocity spread is Δvo=ΔE/√{square root over (2mE)}. The effect of this parabolic potential on an ensemble of electrons emitted from a source will now be analyzed. The velocity distribution of the ensemble is centered around v0, with an emission time distribution centered on −to, where all electrons are emitted from the same location xo=−v0to. Assuming a single donut-shaped laser pulse is applied at t=0, and centered at x=0, the electron ensemble is then influenced by the potential U(x)=½Kx2. The kth electron in the ensemble has an initial velocity v0+vk and emission time −to+tk. Using a Galilean transformation to a frame moving with velocity v0, the propagation coordinate x (lab frame) is replaced with the moving frame coordinate {tilde over (x)}=x−vot. At t=0 the potential exists for the ultrashort laser pulse duration r, giving the electron an impulse (or “kick”) dependent on its instantaneous position in the parabolic potential. In both frames, the position of the electron at t=0 is xk(0)={tilde over (x)}k(0)≡v0tk+vkto−vktk, where xk(t) and {tilde over (x)}k(t) are in the lab and moving frames, respectively. Using the impulse approximation the electron trajectory immediately after the potential is turned off becomes,{tilde over (x)}k(t)=vkt+{tilde over (x)}k(0)(1−t/tf), (6)where tf=m/(Kτ) is the focal time. The electron trajectories, before and after t=0, can be plotted in both frames to give the equivalent of a ray diagram as illustrated in FIG. 15. Electrons emitted at the same time, i.e. tk=0, but with different velocities, will meet at the image position, {tilde over (x)}k=0 in the moving frame at the image time ti. The image time is found by setting {tilde over (x)}k(ti)=0, from equation (6), with tk=0, {tilde over (x)}k(ti)=vkti+vkto(1−ti/tf)=0 which is equivalent to the lens equation, equation (4): to−1+ti−1=tf−1. An expression for the magnification can be obtained when electrons that are emitted at different times tk and different velocities vk are considered. If the magnification is defined as M=−ti/to then the temporal duration at the image time becomes,Δti=MΔto (7)where Δto and Δti are the duration of the electron packet at the object and image time, respectively. Durations achievable with a thin temporal lens follow from equation (7). An experimentally realistic temporal lens would use a 50 fs, 800 nm laser pulse with 350 μJ energy, focused to a waist of w=25 μm. These values result in a stiffness of K=5.5×10−8 N/m and a focal time of t=0.3 ns; tf=m/(Kτ). If the lens is applied 10 cm from the source, electrons emitted at v0=c/10 (3 keV) would have an object time of to=xo/v0=0.1/(c/10)=3.0 ns. Using the temporal lens equation, equation (4), ti is obtained to be 0.33 ns. Hence, a magnification of M=−ti/to=0.1. Consequently, a thin temporal lens can compress an electron packet with an initial temporal duration of Δto≈100 fs, after it has dispersed, to an image duration of Δti≈10 fs. While the example presented here is for 3 keV electrons, the thin lens approximation holds for higher energy electrons as long as r is chosen to be short compared to w/v0. Experimentally, the thin temporal lens can be utilized in ultrafast diffraction experiments which operate at kHz repetition rates with lasers that typically possess power that exceeds the value needed for the ponderomotive compression. Referring to FIG. 15, thin lens temporal ray diagrams for the lab and co-propagating frames are illustrated. The upper left panel is a ray diagram drawn in the lab frame showing how different initial velocities can be imaged to a single position/time. The gray lines are rays representing electrons with different velocities. The lower left panel is a ray diagram drawn in a frame moving with the average velocity v0 of the electron packet. The rays represent velocities of v0/67, v0/100 and 0. In the co-propagating frame, the relationship between Δto and Δti can be visualized as Δti=−Δtoti/to. One major difference between the lab frame and the moving frame is that in the latter the position of the object and image are moving. The lines representing the object and the image positions are drawn with slopes of −v0. The upper right panel depicts the experimental geometry for the implementation of a thin temporal lens. Note that the laser pulse and electron packet propagate perpendicular to each other, and that the interception point between the electrons and photons is at x=0 and t=0. The lower right panel shows how the parabolic (idealized) potential compares to the experimentally realizable donut potential. The colored dots indicate the position of electrons following the rays indicated in the left bottom diagram. Above, it was analytically shown that free electron packets can be compressed from hundreds to tens of femtoseconds using a temporal thin lens, which would correspond to a magnification of ˜0.1. Co-propagating standing wave can be created by using two different optical frequencies, constructed by having a higher frequency (ω1) optical pulse traveling in the same direction as the electron packet and a lower frequency (ω2) traveling in the opposite direction. When the optical frequencies ω1, ω2, and the electron velocity v0 are chosen according to v0=c(ω1−ω2)/(ω1+ω2), a standing wave is produced in the rest frame of the electron as illustrated in FIG. 16. If the electron has a velocity v0=c/3, and ω1=2ω2 then the co-propagating standing wave has a ponderomotive potential of the form, U P ⁡ ( x ) = 1 2 ⁢ ( e 2 ⁢ λ ~ 2 ⁢ E 0 2 8 ⁢ π 2 ⁢ mc 2 ) ⁢ cos 2 ⁡ ( k ~ ⁢ x ) , ( 8 ) where E0 is the peak electric field, {tilde over (λ)} the Doppler shifted wavelength. The envelopes of the laser pulses are ignored in this derivation, but they can be engineered so that the standing wave contrast is optimized. The standing waves can be provided outside the microscope housing or inside the microscope housing. The presence of the standing wave copropagating with the electron pulse or packet inside the microscope housing can produce a series of attosecond electron pulses as illustrated in FIG. 7B and FIG. 16. Depending on the geometry with which the laser beams interact, the standing wave and the electron pulse can overlap adjacent to the sample, providing attosecond electron pulse generation at distances close to the sample. The attosecond electron pulses can be single electron pulses. To find an analytic solution in the thick lens geometry, each individual potential well in the standing wave is approximated by a parabolic potential that matches the curvature of the sinusoidal potential, UP(x)=½[e2E02/(2mc2)]x2=½Kx2. Using the exact solution to the harmonic oscillator the focal time is,tf=cot(ωPτ)/ωP+τ (9)where ωP=√{square root over (Km)} and τ is the duration that the lens is on. For τ→0, tf→m/(Kτ), which is identical to the thin lens definition. The image time, ti, has a form,ti=(1/ωP2+totf−tfτ+τ2)/(to−tf+τ), (10)and after the two assumptions, τ→0 and to>>1/(tfωP2) becomes equivalent to equation (4), the lens equation: to−1+ti−1=tf−1. The standard deviation of the compressed electron pulse at arbitrary time to is, Δ ⁢ ⁢ t a = t f 2 ⁡ ( λ ~ 2 + 4 ⁢ ⁢ t a 2 ⁢ Δ ⁢ ⁢ v o 2 ) + t a 2 ⁢ λ ~ 2 - 2 ⁢ ⁢ t f ⁢ t a ⁢ λ ~ 2 48 ⁢ ⁢ t f 2 ⁢ v 0 2 , ( 11 ) which is valid for an individual well. The time when the minimum pulse duration occurs is t=tf{tilde over (λ)}2/({tilde over (λ)}2+4tf2/Δvo2)≈tf and for experimentally realistic parameters is equal to tf. This implies that the thick lens does not image the initial temporal pulse; it temporally focuses the electrons that enter each individual well. Since there is no image in the thick lens regime, the minimum temporal duration is not determined by the magnification M as in the thin lens section, but is a given by, Δ ⁢ ⁢ t f = t f 2 ⁢ λ ~ 2 ⁢ Δ ⁢ ⁢ v o 2 12 ⁢ ⁢ v o 2 ⁡ ( λ ~ 2 + 4 ⁢ ⁢ t f 2 ⁢ Δ ⁢ ⁢ v 0 2 ) ≅ t f ⁢ Δ ⁢ ⁢ v o v o ⁢ 2 ⁢ 3 ( 12 ) It should be noted that neither the temporal focal length nor the temporal duration are directly dependent on the Doppler shifted wavelength {tilde over (λ)}, as long as the condition to<v0Δto/Δvo is met. An example illustrates what temporal foci are obtainable. A source emits electrons with an energy distribution of 1 eV and a temporal distribution of 100 fs. Electrons traveling at v0=c/3 and having an energy E=31 keV gives a velocity distribution of Δvo=1670 m/s. If the distance between the source and the temporal lens is 10 cm, to=1.0 ns is less than v0Δto/Δvo≈6.0 ns, satisfying the condition to<v0Δto/Δvo and equation (12) is then valid. If the two colors used for the laser beams are 520 nm and 1040 nm, the Doppler-shifted wavelength is {tilde over (λ)}=740 nm. For a laser intensity of 3×1012 Wcm−2 (available with repetition rates up to megahertz), the oscillation frequency in the potential well is ωp≈2×1012 rad/s, which gives a focal time of tf≈1 ps. With these parameters, equation (12) gives a temporal duration at the focus of Δtf≈5 as. To support this ˜5 as electron pulse, time-energy uncertainty demands an energy spread of ˜50 eV. The ponderomotive compression imparts an energy spread to the electron pulse which can be estimated from ΔE˜mv0λ(2tf), giving ˜50 eV similar to the uncertainty limit. This ΔE is very small relative to the accelerating voltage in microscopy (200 keV) and only contributes to a decrease of the temporal coherence. In optical spectroscopy such pulses can still be used as attosecond probes despite the relatively large ΔE when the chirp is well characterized. Combining the anharmonicity broadening of 15 as, we conclude that ultimately temporal pulse durations in the attosecond regime can be reached. In the temporal thick lens case, the use of ω and 2ω to create a co-propagating standing wave requires v0=c/3. However, the velocity of the electrons, v0, can be tuned by changing the angle of the two laser pulses. A co-propagating standing wave can still be obtained by forcing the Doppler-shifted frequencies of both tilted laser pulses to be equal. A laser pulse that propagates at an angle θ with the respect to the electron propagation direction has a Doppler-shifted frequency w=γω(1±(v/c)cos θ), where ω is the angular frequency in the lab frame, {right arrow over (v)}=v{circumflex over (x)} is the electron velocity, and γ=1/√{square root over (1−v2/c2)}. When the two laser pulses are directed as shown in FIG. 16, a co-propagating standing wave occurs for an electron with a velocity v0=c(k1−k2)/(k1 cos θ1+k2 cos θ2), where the laser pulse travelling with the electron packet has a wave vector of magnitude k1 and makes an angle of θ1 with the electron propagation axis; the second laser pulse traveling against has a wave vector magnitude of k2 and angle θ2, in the lab frame. An electron moving at v0 will see a standing wave with an angular frequency, ω ~ = 2 ⁢ ( cos ⁢ ⁢ θ 1 + cos ⁢ ⁢ θ 2 ) 2 ⁢ ⁢ cos ⁢ ⁢ θ 1 + cos ⁢ ⁢ θ 2 ⁢ γω ⁡ ( 1 - β ) , ( 13 ) where 2k=k1=2k2 for experimental convenience, ω=kc, and the wavelength is {tilde over (λ)}=2πc/{tilde over (ω)}=2π/{tilde over (k)}. The standing wave created with arbitrary angles θ1 and θ2 will be tilted with respect to the electron propagation direction, which will temporally smear the electron pulse. This tilting of the standing wave can be corrected for by constraining the angles θ1 and θ2 to be: θ2=arcsin(2 sin θ1). For θ1=150 (forcing θ2≈31°), electrons with velocity v0=0.36c (E≈33 keV) see a standing wave. A 1 eV electron energy distribution at the source gives a velocity distribution of Δv0≈1630 m/s, at 33 keV. Using the same laser intensity as in the thick lens case, and the new v0 and Δvo, the condition to<v0Δto/Δvo is still satisfied, allowing equation (13) to be used, resulting in a duration at the focus of Δtf≈4.6 as. Using the tunable thick lens makes the experimental realization more practical, allowing for easy optical access and electron energy tuning, while at the same time keeping Δtf approximately the same. For additional tunability, an optical parametric amplifier can be used so that the laser pulse frequencies are not restricted to ω and 2ω. The ability to create electron pulses with duration from ˜10 fs to ˜10 as raises a challenge regarding the measuring of their duration and shape. Two different schemes are presented here for measuring pulses compressed by thick and thin temporal lenses. For measuring the thin lens compressed electron packet, the focused packet could be intersected by a laser pulse with a Gaussian spatial focus as illustrated in FIG. 17. An optical delay line would control the time delay between the measuring laser pulse and the compressed electron packet. As the time delay, Δt, is varied, so is the average energy of the electrons, as shown in FIG. 17. If the delay time is zero, then the average electron energy will be unaffected, as there is no force. If the delay line is changed so that the Gaussian pulse arrives early (late), then the average energy will decrease (increase). The change in the average energy is dependent on the duration of the electron pulse, and the intensity of the probing laser pulse. If the electron pulse is longer than the duration of the measuring laser pulse, then the change in the average energy will be reduced. The steepness of the average energy as a function of delay time, Ē(Δt), is a direct measure of the electron pulse duration, and using fs-pulsed electron energy loss spectra this scheme can be realized. For the thick lens a similar method is described here. At the focal position and time of the compressed temporal electron packet, a second co-propagating potential is introduced. The positions of the individual wells in the second co-propagating standing wave can be moved by phase shifting one of the two laser beams that create the probing potential (FIG. 17). By varying the phase shift, the potential slope (and hence the force) that the electrons encounter at the focus is changed. If no phase shift is given to the probing standing wave, no average energy shift results. When a phase shift is introduced, the electrons will be accelerated (or decelerated) by the slope of an individual well in the standing wave, and as long as the phase stability between the electrons and the probing standing wave is appropriate, attosecond resolution can be achieved. As the electron pulse duration becomes less than the period of the standing wave, the average electron energy change increases. The electron temporal duration of the compressed electron packet can be determined directly by the steepness of the Ē(φ) curve. Diffraction with focused electron probes is among the most powerful tools for the study of time-averaged nanoscale structures in condensed matter. Embodiments of the present invention provide methods and systems for four-dimensional (4D) nanoscale diffraction, probing specific-site dynamics with ten orders of magnitude improvement in time resolution, in convergent-beam ultrafast electron microscopy (CB-UEM). For applications, we measured the change of diffraction intensities in laser-heated crystalline silicon as a function of time and fluence. The structural dynamics (change in 7.3±3.5 ps), the temperatures (up to 366 K), and the amplitudes of atomic vibrations (up to 0.084 angstroms) are determined for atoms strictly localized within the confined probe area of 50-300 nm; the thickness was varied from 2 to 100 nm. A broad range of applications for CB-UEM and its variants are possible, especially in the studies of single-particles and heterogeneous structures. In fields ranging from cell biology to materials science, structures can be imaged in real-space using electron microscopy. Atomic-scale resolution of structures is usually available from Fourier-space diffraction data, but this approach suffers from the averaging over the selected specimen area which is typically on the micrometer scale. Significant progress in techniques has enabled localization of diffraction to nanometer and even angstrom-sized areas by focusing a condensed electron beam onto the specimen. Parallel illumination with a single electron wavevector is reshaped to a convergent beam with a span of incident wavevectors. This method of convergent beam electron diffraction (CBED), or electron microdiffraction, and with energy filtering, has made possible determination of structures in 3 dimensions with highly precise localization to areas reaching below one unit cell. The applications have been wide-ranging, from revealing bonding charge distribution and local defects and strains in solids to detecting local atomic vibrations and correlations. Today, aberration-corrected, atomic-sized convergent electron beams enable analytical probing using electron-energy-loss spectroscopy (EELS) and scanning transmission electron microscopy (STEM). In order to resolve structural dynamics with appropriate spatiotemporal resolution, femtosecond (fs) and picosecond (ps) electron pulses are ideal probes because of their picometer wavelength and their large cross section, resulting from the effective Coulomb interaction with atomic nuclei and core/valence electrons of matter. Typically, ultrafast electron diffraction is achieved by initiating the physical or chemical change with a pulse of photons (pump) and observing the ensuing dynamics with electron pulses (probe) at later times. By recording sequentially delayed diffraction frames a “movie” can be produced to reveal the temporal evolution of the transient structures involved in the processes under study. FIG. 18 is a simplified schematic diagram of a CB-UEM set-up (top), and observed low-angle diffraction discs according to an embodiment of the present invention. Femtosecond electron pulses are focused on the specimen to form a nanometer-sized electron beam. Structural dynamics are determined by initiating a change with a laser pulse and then observing the consequences using electron packets delayed in time. Insets (right) show the CB-UEM patterns taken along the Si [011] zone axis at different magnifications. At the high camera length used, only the ZOLZ discs indexed in the figure are visible; the kinematically-forbidden 200 disc appears as a result of dynamic scattering. In the reciprocal space representation of the diffraction process (bottom) the Ewald sphere has an effective thickness of 2α, the convergence angle of the electron beam. The diamond structure of Si forbids any reflections from odd numbered Laue planes when the zone axis is [011]. Embodiments of the present invention provide CB-UEM methods and systems with applications in the study of nanoscale, site-selected structural dynamics initiated by ultrafast laser heating (1014 K/s). Because of the femtosecond pulsed-electron capability, the time resolution is ten orders of magnitude improved from that of conventional TEM, which is milliseconds; and because of beam convergence, high-angle Bragg scatterings are visible with their intensities being very sensitive to both the 3D structural changes and amplitudes of atomic vibrations. The CB-UEM configuration is shown in FIG. 18; our chosen specimen is a crystalline silicon slab, a prototype material for such investigations. From these experiments, it is found that the structural change within the locally probed site occurs with a time constant of 7.3±3.5 ps, which is on the time scale of the rise of lattice temperature known for bulk silicon. For these local sites, the temperatures measured at different laser fluences range from 299° K to 366° K, corresponding to vibrational amplitude changes from 0.077 Å to 0.084 Å, respectively. The reported results would be impossible to obtain with conventional, parallel beam diffraction. The electron microscope is integrated with a fs oscillator/amplifier laser system. The fundamental mode of the laser at 1036 nm was split into two beams: the first was frequency doubled to 518 nm and used to initiate the heating of the specimen, whereas the second, which was frequency tripled, was directed to the microscope for extracting electrons from the cathode. The time delay between pump and probe was adjusted by changing the relative optical path lengths of these two pulses. The pulses were sufficiently separated in time (5 μs) to allow for cooling of the specimen. The electron packets were accelerated to 200 keV (corresponding to a de Broglie wavevector of 39.9 Å−1), de-magnified, and finally focused (with a 6 mrad convergence angle) to an area of 50-300 nm diameter on the wedge-shaped specimen, as shown in FIG. 18. A wide range of thicknesses, starting from ˜2 nm was accessible simply by moving the electron beam laterally. The silicon specimen was prepared by mechanical polishing of a wafer along the (011) planes, followed by Ar ion-milling for final thinning/smoothing; the wedge angle was 2°. In the microscope, Kikuchi lines were observed and used as a guide to orient the specimen with the [011] zone axis either parallel or tilted relative to the incident electron beam direction. FIG. 18 display the typical high-magnification (high-value camera length) CB-UEM patterns of Si obtained when the specimen is unexcited and the zone axis is very close to [011]; the magnification (>10×) cab be seen by comparing the disc length scale in FIG. 18 and ring radius in FIG. 19. Unlike parallel-beam diffraction which yields spots, convergent-beam diffraction produces discs in reciprocal space (back focal plane of the objective lens) with their diameter given by the convergence angle (2α) of the electron pulses. These discs form the Zero Order Laue Zone (ZOLZ) of the pattern; they show white contrast with thin specimens and exhibit the interference patterns displayed in FIG. 18 when the thickness is increased. In the reciprocal space, the effective thickness of the Ewald sphere is 2α (bottom panel of FIG. 18), giving rise to multiple spheres that can intersect with Higher Order Laue Zones (HOLZ) reflections, the focus of this study (see FIG. 19) and the key to 3D structural information; the first and second zones, FOLZ and SOLZ, are examples of such zones or rings. The interference patterns in the disks are the result of dynamical scattering in silicon and are reproduced in our CB-UEM patterns (FIG. 18). The scattering vectors of HOLZ rings (R) are related to the inter-zone spacing in the reciprocal space (hz in Å−1) by the tilt angle from the zone axis (η) and by the magnitude of the incident electron's wavevector (k0). In the plane of the detector and for our tilt geometry, the HOLZ ring scattering vector is given by (equation (14)):R≅(k02 sin2 (η)+2k0hz)1/2−k0 sin(η), (14)where, for our case of the [011] zone axis, hz=n/(μ√{square root over (2)}) with n=1, 2, 3 . . . for the different Laue zones. Additionally, for this zone axis, k+l=n, where (hkl) are the Miller indices of the reciprocal space. When k+l=1, for FOLZ, k and l must have different parity, which is forbidden by the symmetry of the diamond Si structure. Therefore, the FOLZ along the [011] zone axis should be absent and the first visible ring should belong to SOLZ; in general, all odd numbered zones will be forbidden. Here, HOLZ indexing is defined according to the fcc unit cell and not to the primitive one [1]. FIG. 19 illustrates temporal frames obtained using CBUED. In FIG. 19(a) high angle SOLZ ring obtained for a tilt angle of 5.15° from the [011] zone axis are shown. Besides SOLZ, Kikuchi lines and periodic bands (due to atomic correlations) are visible. The ZOLZ discs are blocked (top left) to enhance the dynamic range in the area of interest; the disc of the direct beam (the center one in FIG. 18 discs) is indicated by a circle. The intensity scale is logarithmic. In FIG. 19(b,c,d) time frames of the SOLZ ring are shown by color mapping for visualization of dynamics. The intensity of the ring changes within picoseconds, but the surrounding background remains at the same level. FIG. 19(a) presents the HOLZ ring taken with the CB-UEM. In order to reduce the strong on-zone-axis dynamic scattering (and to bring the high scattering angles into the range of the recording camera), the slab was tilted 5.15° away from the [011] zone axis, along the [022] direction. The scattering vector of the Bragg points of the ring, from the direct beam position, was measured to be 2.2 Å−1, close to the value of 2.22 Å−1 obtained by using equation (14) for n=2, which identifies the spots shown as part of the SOLZ. From this value, the know lattice separation of 5.4 Å was obtained for silicon. In addition to the SOLZ ring, Kikuchi lines and some oscillatory bands are also visible in the CB-UEM, as seen in FIG. 19(a). Kikuchi lines arise from elastic scatterings of the inelastically scattered electrons, whereas the oscillatory bands in the thermal diffuse scattering (TDS) background result from correlations between the atoms. We also observed deficit HOLZ lines and interference fringes in ZOLZ discs for a two-beam condition. The temporal behavior is displayed in FIG. 19, with three CB-UEM frames taken at time delays of t=−14.8 ps, +5.2 ps, and +38.2 ps, together with a static image; the zero of time is defined by the coincidence of the pump and probe pulses in space and time. The frame at negative time has higher ring intensity than that observed at +38.2 ps, whereas the +5.2 ps frame shows an intermediate intensity value. It is clear from the results that the intensity change is visible within the first 5 ps of the structural dynamics. For quantification, the intensities in each frame were normalized to the area of azimuthally integrated background. The normalization of the HOLZ ring intensities to the TDS background makes the atomic vibration estimations insensitive to the thickness changes of the probed area, which may result from slight beam jittering. FIG. 20 illustrates diffraction intensities at different times and fluences. Normalized, azimuthally-integrated intensity changes of the SOLZ ring are shown with time ranging from −20 ps to +100 ps, for two different laser powers. Whereas the 10 mW response does not show noticeable dynamics, the 107 mW transient has a clear intensity change with a characteristic time of 7.3±3.5 ps. The range of fluences studied was 1.7 to 21 mJ/cm2 (see FIG. 21). The red curve is a mono-exponential fit based on the Debye-Waller effect. The red dashed line through the 10 mW data is an average of the points after +20 ps. The dependence on fluence is given in FIG. 21. FIG. 20 depicts the transient behavior of the SOLZ ring intensity for two different laser power, 10 mW and 107 mW, corresponding to pulse fluence of 1.7 and 19 mJ/cm2, respectively; the heating laser beam diameter on the specimen is 60 μm. The intensities were normalized to the average value obtained at negative times. Whereas the intensity change is essentially absent in the 10 mW data, the results for the 107 mW set shows a transient behavior with a characteristic time of 7.3±3.5 ps, obtained from the mono-exponential fit shown in red in the figure. The temporal response of UEM-2 is on the fs time scale, as obtained by EELS, and it is much shorter than the 7 ps illustrated here. The local heating of the lattice is responsible for the SOLZ intensity change with time. A pump laser, in our case at 518 nm (2.4 eV), excites the valance electrons of Si to the conduction band; one-photon absorption occurs through the indirect bandgap at 1.1 eV, and multi-photon absorption excites electron-hole pairs through the direct gap. The excited carriers thermalize within 100 fs, via carrier-carrier scatterings, and then electron cooling takes place in ˜1 ps, by electron-phonon coupling. During this time lattice heating occurs through increased atomic vibration, reducing SOLZ intensity. The effective lattice temperature is ultimately established with a time constant of a few picoseconds depending on density of carriers or fluence. However, in CB-UEM measurements the lattice-temperature rise could be slower than in bulk depending on the dimension of the specimen relative to the mean free path of electrons in the solid. The dynamical change can be quantified by considering a time-dependent Debye-Waller factor with an effective temperature describing the decrease in the Bragg spot intensity with time. If the root-mean-square (rms) displacement of the atoms, ux21/2, along one of the three principle axes is denoted by ux for simplicity, and the scattering vector by s, then the HOLZ ring intensity can be expressed as (equation (15)):IRingF(t)=I0(t_)exp[−4π2s2ux2(t)], (15)where IRingF(t) is the measured intensity for a given fluence, F, and the vibrational amplitude is now time dependent. Note that ux is 1/3 of the total, utotal. In the Einstein model of atomic vibrations, which has been used successfully for silicon, the atoms are treated as independent harmonic oscillators, with the three orthogonal components of the vibrations decoupled. As a result, a single frequency (ω) is sufficient to specify the energy eigenstates of the oscillators. The relationship of the vibrational amplitude to temperature can be established by simply considering the Boltzmann average over the populated eigenstates. Consequently, the probability distribution of atomic displacements is derived to be of Gaussian form, with a standard deviation corresponding to the rms (ux) of the vibration involved (equation (16)):ux=[(ℏ/2ωm)cot h(ℏω/2kBTeff)]1/2 (16)where ℏ is Planck's constant, kB the Boltzmann constant, Teff in our case the effective temperature, and m the mass of the oscillator. In the high temperature limit, i.e. when ℏω/2kBT<<1, eq. 3 simplifies to mω2ux2=kBT, which is the classical limit for a harmonic oscillator; the zero-point energy, which contributes almost half of the mean vibration amplitude at room temperature, is included in equation (16). The value of ℏω is 25.3 meV. Despite its simplicity, the Einstein model in equation (16) was remarkably successful in predicting the HOLZ rings and TDS intensities by multi-slice simulations. FIG. 21 illustrates the amplitudes of atomic vibrations (rms) plotted against the observed intensity change at different fluences. The inset shows the mono-exponential temporal behavior, with the asymptotes highlighted (circles) for their values at different fluences. The fluence was varied from 1.7 to 21 mJ/cm2. This comparative study of the effect of the fluence was performed at a slightly different sample tilt (corresponding to s=2.7 Å−1), corresponding to a thickness of ˜80 nm. For each fluence, the temperature represents the effective value for the lattice structural change. The error bars given were obtained from the fits at the asymptotes shown in the inset, and they are determined by the noise level of temporal scans. In FIG. 21, we present the change in the asymptotic intensity with fluence (inset), and the derived vibrational amplitudes for the different temperatures. The amplitudes are directly obtained from equation (15), as s is experimentally measured. The relative temperature change (from t_ to t+) is then derived from equation (16), taking the value of ux at room temperature (297° K) to be 0.076 Å. The amplitude of atomic vibrations, and hence the temperature, increases as the fluence of the initiating pulse increases. Although the trend is expected for an increased ux with temperature, the absolute values, from 0.077 to 0.084 Å, correspond to a large 3.2% to 3.6% change in nearest neighbor separation; these values are still well below the 15% criterion for a melting phase transition. The linear thermal expansion coefficient has been accurately determined for silicon, and for a value of 2.6×10−6K−1 at room temperature the vibrational amplitudes reported here are much higher than the equilibrium thermal values at the same temperature. This is because the effective temperature applies to a lattice arrested in a picosecond time window; at longer times, the vibrations equilibrate to a lower temperature. As such, measuring nanoscale local temperatures on the ultrashort time scale enhances the sensitivity of the probe thermometer by orders of magnitude. Moreover, the excitation per site is significantly enhanced. For a single-photon absorption at the fluence used, we estimate, for a 60 nm-thick specimen, the number of absorbed photons per Si atom (for the fs pulse employed) to be ˜0.01, as opposed to 10−9 photons per atom if the experiments were conducted in the time-averaged mode. The achievement of nanoscale diffraction with convergent-beam ultrafast electron microscopy opens the door to exploration of different structural, morphological, and electronic phenomena. The spatially focused and timed electron packets enable studies of single particles and structures of heterogeneous media. Extending the methodology reported here to other variants, such as EELS, STEM and nanotomography, promises possibilities for mapping individual unit cells and atoms on the ultrashort time scale of structural dynamics. With 4D electron microscopy, in situ imaging of the mechanical drumming of a nanoscale material is measured. The single crystal graphite film is found to exhibit global resonance motion that is fully reversible and follows the same evolution after each initiating stress pulse. At early times, the motion appears “chaotic” showing the different mechanical modes present over the micron scale. At longer time, the motion of the thin film collapses into a well defined fundamental frequency of 0.54 MHz, a behavior reminiscent of mode locking; the mechanical motion damps out after ˜200 ps and the oscillation has a “cavity” quality factor of 150. The resonance time is determined by the stiffness of the material and for the 53-nm thick and 55-μm wide specimen used here we determined Young's modulus to be 0.8 TPa, for the in-plane stress-strain profile. Because of its real-time dimension, this 4D microscopy has applications in the study of these and other types of materials structures. Structural, morphological, and mechanical properties of materials have different length and time scales. The elementary structural dynamics, which involve atomic movements, are typically of picometer length scale and occur on the time scale of femto (fs) to picoseconds (ps). Collective phenomena of such atomic motions, which define morphological changes, are observed on somewhat longer time scale, spanning the ps to nanosecond (ns) time domain, and the length scale encompasses up to sub-micrometers. These microscopic structures are very different in behavior from those involved in the mechanical properties. On the nanoscale, when the membrane-like mechanical properties have high frequencies and complex spatial-mode structures, imaging becomes of great value in displaying the spatiotemporal behavior of the material under stress. Utilizing embodiments of the present invention, we have visualized nanoscale vibrations of mechanical drumming in a single-crystalline graphite film (53-nm thick). To study the transient structures, in both space and time, our method of choice has been 4D ultrafast electron microscopy (UEM). This microscope enables investigation of the atomic structural and morphological changes in graphite on the fs to ns time scale and for nm-scale resolution. Additionally, mechanical properties can be determined in real time, which are evident on the ns and microsecond (μs) time scale. The stress is introduced impulsively using a ns laser pulse while observing the motions in real space (in situ) in the microscope using the stroboscopic electron pulses. Remarkably, at times immediately following the initiating pulse the motion appears “chaotic” in the full image transients, showing the different mechanical modes present in graphite. However, after several μs the motion of the nanofilm collapses into a final global resonance of 0.54 MHz. From this resonance of mechanical drumming of the whole plate, we obtained the in-plane Young's modulus of 0.8 terapascal (Tpa). The reported coherent resonance represents the in-phase build up of a mechanical drumming, which is directly imaged without invasive probes. Graphite was chosen because of its unique material properties; it is made of stacked layers of 2D graphene sheets, in which the atoms of each sheet are covalently bonded in a honeycomb lattice, and the sheets separated by 0.335 nm are weakly held together by van der Waals forces. It displays anisotropic electromechanical properties of high strength, stiffness, and thermal/electric conductivity along the 2D basal planes. More recently, with the rise of graphene, a new type of nano-electromechanical system (NEMS) has been highlighted with a prototypical NEMS being a nanoscale resonator, a beam of material that vibrates in response to an applied external force. With the thicknesses reaching the one atomic layer, graphene remains in a high crystalline order, resulting in a NEMS with extraordinary thinness, large surface area, low mass density, and high Young's modulus. Briefly, the setup for ultrafast (and fast) electron imaging involves the integration of laser optical systems into a modified transmission electron microscope (TEM). Upon the initiation of a structural change by either heating of the specimen or through electronic excitation by the laser pulses, an electron pulse generated by the photoelectric effect is used to probe the specimen with a well-defined time delay. A microscopy image or a diffraction pattern is then taken. A series of time-framed snapshots of the image or the diffraction pattern recorded at a number of delay times provides a movie, which displays the temporal evolution of the structural (morphological) and mechanical motions, using either the fs or ns laser system. Because here the visualization is that of the mechanical modes with resonances on the MHz scale, the ns resolution was sufficient. The electrons are accelerated to 200 kV with a de Broglie wavelength of 2.5079 pm. Two laser pulses were used to generate the clocking, excitation pulse at 532 nm and another at 355 nm for the generation of the electron pulse for imaging. The time delay was controlled by changing the trigger time for electron pulses with respect to that of clocking pulses. The delay can be made arbitrarily long and the repetition rate varies from a single shot to 200 kHz, to allow complete heat dissipation in the specimen. The experiments were carried out with a natural single crystal of graphite flakes on a TEM grid. Graphite flakes were left on the surface, covering some of the grid squares completely. The observed dynamics are fully reversible, retracing the identical evolution after each initiating pulse; each image is constructed stroboscopically, in a half second, from typically 2500 pulses of electrons and completing all time-frames (movies) in twenty minutes. FIG. 22 illustrates images and the diffraction pattern of graphite. (A), an image shows features of fringes in contrast (scale bar: 5 μm). Sample thickness was measured to be 53 nm using electron energy loss spectroscopy (EELS). (B) Magnified view of the indicated square of panel A (scale bar: 1 μm). (C) Diffraction pattern obtained by using a selected area diffraction aperture (SAD), which covered an area of 6 μm in diameter on the specimen. The incident electron beam is parallel to the [001] zone axis. Bragg spots are indexed as indicated for some representative ones. Panels A and B of FIG. 22 show the UEM (bright field) images of graphite, and in panel C, a typical electron diffraction pattern is given. The Bragg spots are indexed according to the hexagonal structure of graphite along the [001] zone axis, with the lattice dimension of a=b=2.46 Å (c=6.71 Å). In FIG. 22A, and at higher magnification in FIG. 22B, contrast fringes are clear, typically consisting of linear fringes having ˜1 μm length and a few hundred-nm spacing. These contrast fringes are the result of physical bucking of the graphene layers by constraints or by nanoscale defects within the film. In the dark regions, the zone axis (the crystal [001]) is well aligned with the incident electron beam and electrons are scattered efficiently, whereas in the lighter regions the alignment of the zone axis deviates more and the scattering efficiency is lower. With these contrast patterns, changes in image provide a sensitive visual indicator of the occurrence of mechanical motions. The black spots are natural graphite particles. FIG. 23 illustrates representative image snapshots and difference frames. (A) Images recorded stroboscopically at different time delays, indicated at the top right corner of each image (t1, t2, t3, t4, and t5), after heating with the initiating pulse (fluence=7 mJ/cm2); t1=200 ns; t2=500 ns; t3=10 μs; t4=30 μs; t5=60 μs; and the negative time frame was taken at −1000 ns. Note the change in position of fringes with time, an effect that can be clearly seen in FIG. 23B. (B) Image difference frames with respect to the image taken at ˜1 μs, i.e., Im(−1 μs; t), which show the image change with time. The reversal in contrast clearly displays the oscillatory (resonance) behavior. In FIG. 23(A), we display several time-framed images of graphite taken at a repetition rate of 5 kHz and at delay times indicated with respect to the clocking (heating) pulse with the fluence of 7 mJ/cm2. At positive times, following t=0, visual changes are seen in the contrast fringes. With time, the contrast fringes change their location in the images, and with these and other micrographs of equal time steps we made a movie of the mechanical motions of graphite following the ns excitation impulse. To more clearly display the temporal evolution on the nanoscale, image-difference frames were constructed. In FIG. 23(B), depicted are the images obtained when referencing to the −1 μs frame, i.e., Im(−1 μs; t). In the difference images, the regions of white or black indicate locations of surface morphology change (contrast pattern movement), while gray regions are areas where the contrast is unchanged from that of the reference frame. Care was taken to insure the absence of long-term specimen drifts as they can cause apparent contrast change; note that in the difference images, the static features are not present. The image changes, reported in this study, are fully reproducible, retracing the identical evolution after each initiating laser pulse, as mentioned above. The reversal of contrast with time in FIG. 23(B) directly images the oscillatory behavior of the drumming. The image change was quantified by using the method of cross-correlation. The normalized cross correlation of an image at time t with respect to that at time t′ is expressed as γ ⁡ ( t ) = ∑ x , y ⁢ C x , y ⁡ ( t ) ⁢ C x , y ⁡ ( t ′ ) ∑ x , y ⁢ C x , y ⁡ ( t ) 2 ⁢ ∑ x , y ⁢ C x , y ⁡ ( t ′ ) 2 ( 17 ) where the contrast Cx,y(t) is given by [Ix,y(t)−Ī(t)]/Ī(t), and Ix,y(t) and Ix,y(t′) are the intensities of pixels at the position of (x,y) at times t and t′; Ī(t) and Ī(t′) are the means of Ix,y(t) and Ix,y(t′), respectively. This correlation coefficient γ(t) is a measure of the temporal change in “relief pattern” between the two images being compared, which can be used as a guide to image dynamics as a function of time. Shown in FIG. 24 are cross-correlation values between the image at each measured time point and a reference image recorded before the arrival of the clocking pulse. FIG. 24 illustrates the time dependence of image cross correlation. The whole scan for 100 μs is made of 2000 images taken at 50-ns steps. Also depicted are the zoomed-in image cross-correlations of three representative time regimes (I, II, and III). In each zoomed-in panel, the selected-area image dynamics of five different regions are included. Note the evolution from the “chaotic” to the global resonance (drumming) behavior at long times. Over all pixels, the time scale for image change covers the full range of time delays, from tens of ns to hundreds of μs, indicating the collective averaging over the sites of the specimen. Upon impulsive heating at t=0, the image cross-correlation changes considerably with an appearance of a “chaotic” behavior, in the ˜5 μs range (regime I in FIG. 24). After 10 μs, e.g., regime II, the cross correlation change begins to exhibit periodicity (regime II), and at longer time, a well-defined resonance oscillation emerges (regime III). This is also evident in the selected-area image dynamics (SAID) in several regions (noted as 1 to 5) where the temporal behavior is of different shapes at early time but converges into a single resonance transient after several tens of μs. The shape of image cross correlation dynamics was robust at different fluences, from 2 to ˜10 mJ/cm2, but the amplitude varies. The overall decay of the transients is on a time scale shorter than the separation between pulses. In fact, we have verified the influence of repetition rate and could establish the full recovery at the time intervals indicated. Heat transfer must occur laterally. With an initial z-independent heat profile by absorption of the heating pulse in graphite, we estimated, using a 2D heat diffusion in a homogeneous medium, the time scale for an in-plane transfer, with thermal conductivity λ=5300 W/(m·K), density ρ=2260 kg/m3, and specific heat cV=707 J/(K·kg). For the radius at half height of the initial pulse heat distribution r0=30 μm, t1/2, the time for the axial temperature to drop to a half of its initial value, is deduced to be ˜720 ns, certainly much shorter than the 200-μs time interval between pulses. It follows that the decay of the oscillation [Q/(π·f0)], as derived below, is determined by the damping of mechanical motions. When the specimen absorbs intense laser light, the lattice energy, converted from carriers (electron energy) by electron-phonon coupling, in a few ps, builds up in the illuminated spot on the surface within the duration of the laser pulse. As a consequence, the irradiated volume will expand rapidly following phonon-phonon interaction on the time scale of tens of ps. The resulting thermal stress can induce mechanical vibration in the material, but a coherent oscillatory behavior, due to the thermoelastic stress, will only emerge in the image if the impulsive stress is on a time scale shorter than the period; probing of images should be over the entire time scale of the process, in this case 100 μs. On the ultrashort time scale we have observed the structural and morphological elastic changes. FIG. 25 illustrates resonance dynamics and FFT of graphite. (Left) Time dependences of image cross correlation of full image (A) and image intensity on the selected area of 4×6 pixels as indicated by the arrowhead (B) in FIG. 24. (Right) Fast Fourier transforms of image cross-correlation (C: 0-100 μs; D: 60-100 μs) and image intensity (E: 0-100 μs; F: 60-100 μs). Asterisks in the panels indicate overtones. Note the emergence of the resonance near 1 MHz in panel F. The resonance modes in graphite are highlighted in FIG. 25 by taking the fast Fourier transform (FFT) of image cross-correlation in the time regime of 0-100 μs. The FFT (FIG. 25C) shows several peaks of different frequencies, among which the strongest one around 2.13 MHz is attributed to the overtone of 1.08 MHz. The overtones, due to the truncated nature of cross-correlation close to the value of 1, are greatly reduced in the FFT of image intensity change (FIGS. 25E and 25F). In a few tens of μs, various local mechanical modes observed at early time damp out and one global mode around 1 MHz survives. The peak when fitted to a Lorentzian yields a resonant frequency of 1.08 MHz, and a “cavity” quality factor Q (=f0/Δf)=150±30. This dominant peak gives the fundamental vibration mode of the plate in graphite. For a period of vibration, the contrast pattern of image would recur twice to its initial feature giving the observed frequency to be twice that of structural vibration; the fundamental frequency is, thus, obtained to be 0.54 MHz. A square mechanical resonator clamped at four edges without tension has a fundamental resonance mode of f0 which is given by f 0 = A ⁢ d L 2 ⁡ [ Y ( 1 - v 2 ) ⁢ ρ ] 1 / 2 + f ⁡ ( T ) ( 18 ) where f(T) due to tension T is zero in this case. Y is the Young's modulus; ρ is the mass density; v is the Poisson's ratio; L is the dimension of a grid square; d is the thickness of the graphite; and A is a constant, for this case equal to 1.655. We measured d to be 53 nm from EELS. Knowing ρ=2260 kg/m3 (300 K), v=0.16 for graphite, and L=55 μm, we obtained from the observed resonance frequency the Young's modulus to be 0.8 TPa, which is in good agreement with the in-plane value of 0.92 TPa, obtained using stress-strain measurements. This value is different by more than an order of magnitude from the c-axis value we measured using the microscope in the ultrafast mode of operation. Thus, using embodiments of the present invention, we have demonstrated a very sensitive 4D microscopy method for the study of nanoscale mechanical motions in space and time. With selected-area-imaging dynamics, the evolution of multimode oscillations to a coherent resonance (global) mode at long time provides the mapping of local regions in the image and on the nanoscale. The time scale of the resonance is directly related to materials anisotropic elasticity (Young's modulus), density, and tension, and as such the reported real-time observation in imaging can be extended to study mechanical properties of membranes (graphene in the present case) and other nanostructures with noninvasive probing. The emergent properties resolved here are of special interest to us as they represent a well-defined “self-organization” in complex macroscopic systems. The function of many nano and microscale systems is revealed when they are visualized in both space and time. Here, four-dimensional (4D) electron microscopy provided in accordance with an embodiment of the present invention is used to measure nanomechanical motions of cantilevers. From the observed oscillations of nanometer displacements as a function of time, for free-standing beams, we are able to measure the frequency of modes of motion, and determine Young's elastic modulus, the force and energy stored during the optomechanical expansions. The motion of the cantilever is triggered by molecular charge redistribution as the material, single-crystal organic semiconductor, switches from the equilibrium to the expanded structure. For these material structures, the expansion is colossal, typically reaching the micron scale, the modulus is 2 GPa, the force is 600 μN, and the energy is 200 pJ. These values translate to a large optomechanical efficiency (minimum of 1% and up to 10% or more), and a pressure of nearly 1,500 atm. We note that the observables here are real-material changes in time, in contrast to those based on changes of optical/contrast intensity or diffraction. As the physical dimensions of a structure approach the coherence length of carriers, phenomena not observed on the macroscopic scale (e.g., quantization of transport properties) become apparent. The discovery and understanding of these quantization effects requires continued advances in methods of fabrication of atomic-scale structures and, as importantly, in the determination of their structural dynamics in real-time when stimulated into a configuration of a nonequilibrium state. Of particular importance are techniques that are noninvasive and capable of nanoscale visualization in real-time. Examples of the rapid progress in the study of nanoscale structures are numerous in the field of micro and nanoelectromechanical systems (i.e., MEMS and NEMS, respectively). Recent advancements have resulted in structures having single-atom mass detection limits and binding specificities on the molecular level, and especially for biological systems. Beyond mass measurement and analyte detection, changes in the dynamics of these nanoscale structures have been shown to be sensitive to very weak external fields, including electron and nuclear spins, electron charge, and electron and ion magnetization. The response to external stimuli is manifested in deflections of the nanoscale, and a variety of techniques have been used to both actuate and detect the small-amplitude deflections. Optical interference is often used for measurement purposes, wherein the deflections of the structure cause a phase shift in the path-stabilized laser light thus providing detection sensitivities that are much less than the radius of a hydrogen atom. High spatiotemporal resolutions (atomic-scale) can be achieved in 4D ultrafast electron microscopy (UEM). Thus it is possible to image structures, morphologies, as well as nanomechanical motions (e.g., nanogating and nanodrumming) in real-time. Using embodiments of the present invention, we direct visualized nano and microscale cantilevers, and the (resonance) oscillations of their mechanical motions. The static images were constructed from a tomographic tilt series of images, whereas the in situ temporal evolution was determined using the stroboscopic configuration of UEM, which is comprised of an initiating (clocking) laser pulse and a precisely-timed packet of electrons for imaging. The pseudo-one-dimensional molecular material (copper 7,7,8,8-tetracyanoquinodimethane, [Cu(TCNQ)]), which forms single crystals of nanometer and micrometer length scale, is used as a prototype. The optomechanical motions are triggered by charge transfer from the TCNQ radical anion (TCNQ−) to copper (Cu+). More than a thousand frames were recorded to provide a movie of the 3D movements of cantilevers in time. As shown below, the expansions are colossal, reaching the micrometer scale, and the spatial modes are resolved on the nanoscale in the images (and angstrom-scale in diffraction) with resonances of megahertz frequencies for the fixed-free cantilevers. From these results, we obtained the Young's modulus, and force and energy stored in the cantilevers. Here, different crystals were studied and generally are of two types: (1) those “standing”, which are free at one end (cantilevers), and (2) those which are “sleeping” on the substrate bed; the latter will be the subject of another report. For cantilevers, the dimensions of the two crystals studied are 300 nm thick by 4.6 μm long and 2.0 μm thick by 10 μm long (see FIG. 26). As such, they define an Euler-Bernoulli beam, for which we expect the fundamental flexural modes to be prominent, besides the longitudinal one(s) which are parallel to the long axis of the crystal. Our interest in Cu(TCNQ) stems from its highly anisotropic electrical and optical properties, which arise from the nature of molecular stacking in the structure. As illustrated in FIG. 26, Cu(TCNQ) consists of an interpenetrating network of discrete columns of Cu+ and TCNQ−running parallel to the crystallographic μ-axis. The TCNQ molecules organize so that the ie-systems of the benzoid rings are strongly overlapped, and the favorable interaction between stacked TCNQ molecules makes the spacing between the benzoid rings only 3.24 Å, significantly less than that expected from purely van der Waals-type interactions. It is this strong π-stacking that results in the pseudo-one-dimensional macroscale crystal structure and is responsible for the anisotropic properties of the material. With electric field or light, the material becomes mixed in valence with both Cu+(TCNQ−) and Cu° (TCNQ°) in the stacks, weakening the interactions and causing the expansion. At high fluences, the reversible structural changes become irreversible due to the reduction of copper from the +1 oxidation state to copper metal and subsequent formation of discrete islands of copper metal driven by Ostwald ripening. The methodology we used here for synthesis resulted in the production of single crystals of phase I. FIG. 26 illustrates atomic to macro-scale structure of phase I Cu(TCNQ). Shown in the upper panel is the crystal structure as viewed along the a-axis (i.e., π-stacking axis) and c-axis. The unit cell is essentially tetragonal (cf. ref. 19) with dimensions: a=3.8878 Å, b=c=11.266 Å, α=γ=90°, β=90.00(3)°; gray corresponds to carbon, blue corresponds to nitrogen, and yellow corresponds to copper. The hydrogen atoms on the six-membered rings are not shown for clarity. The lower panel displays a typical selected-area diffraction pattern from Cu(TCNQ) single crystals as viewed down the [011] zone axis along with a micrograph taken in our UEM. The rod-like crystal habit characteristic of phase I Cu(TCNQ) is clearly visible. FIG. 27 illustrates a tomographic tilt series of images. The frames show images (i.e., 2D-projections) of the Cu(TCNQ) single crystals acquired at different tilt angles of the specimen substrate. The highlighted region illustrates a large change in the position of the free-standing mircoscale crystal relative to another, which is lying flat on the substrate, as we change the tilt angle. The scale bar in the lower left corner measures two micrometers. The tilt angle at which each image was acquired is shown in the lower right corner of each frame in degrees. The tilt angle is defined as zero when the specimen substrate is normal to the direction of electron propagation in the UEM column. The tilt series images shown in FIG. 27 provide the 3D coordinates of the cantilevers. The dimensions and protrusion angles of these free-standing crystals were characterized by taking static frames at different rotational angles of the substrate. By placing the crystal projections into a laboratory frame orthogonal basis and measuring the length of the projections in the x-y (substrate) plane as the crystal is rotated by an angle α about the x-axis, the measured projections were obtained to be Θ of 37.8° and φ of 25.3°, where Θ is the angle the material beam makes with respect to substrate-surface normal and φ is the azimuthal angle with respect to the tilt axis, respectively. Note that the movie of the tilt series clearly shows the anchor point of the crystal to be the substrate. The dimensions and geometries of the crystals are determined from the tilt series images with 5% precision. To visualize real-time and space motions, the microscope was operated at 120 kV and the electron pulses were photoelectrically generated by laser light of 355 nm. The clocking optical pulses (671 nm laser), which are well-suited to induce the charge transfer in Cu(TCNQ), were held constant at 3 μJ, giving a maximum fluence of 160 mJ/cm2. Because the relevant resonance frequencies are on the MHz scale, the ns pulse arrangement of the UEM was more than enough for resolving the temporal changes. The time delay between the initiating laser pulse and probe electron pulse was controlled with precision, and the repetition rate of 100 Hz ensured recovery of the structure between pulses. A typical static image and selected-area diffraction are displayed in FIG. 26. From the selected-area diffraction and macroscopic expansion we could establish the nature of correlation between unit cell and the crystal change. The 4D space-time evolution of cantilevers is shown in FIGS. 28 and 29. The referenced (to negative time, tref=−10 ns; i.e., before the arrival of the clocking pulse) difference images of the microscale (FIG. 28) and nanoscale (FIG. 29) free-standing single crystal clearly display modes of expansion on the MHz scale. Each image illustrates how the spatial location of the crystal has changed relative to the reference image as a function of the time delay, elucidating both the longitudinal and transverse displacements from the at-rest position. In order to accurately measure the positions in space we used a reference particle in the image. These reference particles, which are fixed to the surface of the substrate, do not appear in frame-reference images if drift is absent or corrected for. This is an important indication that the observed crystal dynamics do not arise from motion of the substrate due to thermal drift or photothermal effects. Moreover, there is no significant movement observed in images obtained before the arrival of the excitation pulse, indicating that, during the time of pulse separation, the motion has completely damped out and the crystal has returned to its original spatial configuration. The thermal, charging, and radiation effects of the electron pulses are negligible here and in our previous studies made at higher doses. This is evidenced in the lack of blurring of the images or diffraction patterns; no beam deflection due to sample charging was observed. Lastly, no signs of structural fatigue or plasticity were observed during the course of observation, showing the function of the cantilever to be robust for at least 107 pulse cycles. Shown in FIG. 30 is the displacement of the microscale single crystal as a function of time, in both the longitudinal and transverse directions, along with the fast Fourier transforms (FFT) of the observed spatial oscillations for the time range shown (i.e., 0 to 3.3 is). The motions in both directions of measurement are characterized by a large initial displacement from the at-rest position. The scale of expansion is enormous. The maximum longitudinal expansion possible (after accounting for the protrusion angle) for the 10 μm crystal would be 720 nm or over 7% of the total length. For comparison, a piezoelectric material such as lead zirconate titanate has typical displacements of less than 1% from the relaxed position, but it is known that molecular materials can show enormous optically-induced elastic structural changes on the order of 10% or more. The large initial motion is transferred into flexural modes in the z and x-y directions, and these modes persist over the microsecond (or longer) scale. The overall relaxation of the crystal to its initial position is not complete until several milliseconds after excitation. From the FFTs of the measured displacements, we obtained the frequency of longitudinal oscillation to be 3.3 MHz, whereas the transverse oscillations are found at 2.5 and 3.3 MHz (FIG. 30). We note that the motion represents coupling of modes with dephasing, so it is not surprising that the FFT gives more than one frequency. In fact, from an analysis consisting of a decomposition of the motion via rotation of a principle axes coordinate system relative to the laboratory frame, we found that the plane of lateral oscillation of the crystal was tilted by 18° relative to the plane of the substrate. The nature of contact with the substrate influences not only the mode structure but also the damping of cantilevers. Because of the boundary conditions of a fixed-free beam, the vibration nodes are not evenly spaced and the overtones are not simple integer multiples of the fundamental flexural frequency (f1), but rather occur at 6.26, 17.5, and 34.4 for f2, f3, and f4, respectively. This is in stark contrast to the integer multiples of the fundamental frequency of a fixed-fixed beam. Taking 3 MHz to be the main fundamental flexural frequency of the microscale crystal, we can deduce Young's elastic modulus of the crystal. The expression for the frequencies of transverse (flexural) vibrations of a fixed-free beam is given by, f n = η ⁢ πκ 8 ⁢ ⁢ L 2 ⁢ c ≡ η ⁢ πκ 8 ⁢ ⁢ L 2 ⁢ Y ρ ( 19 ) where fn is the frequency of the nth mode in Hz, L is the beam length at rest, Y is Young's modulus, and ρ is the density. The radius of gyration of the beam cross section is κ and is given as t/12, where t is the thickness of the beam with rectangular cross section. The value of η for the beam is: 1.1942; 2.9882; 52; 72; . . . ; (2n−1)2, approaching whole numbers for higher q values. The overtones are not harmonics of the fundamental, and the numerical terms for f1 and f2, which result from the trigonometric solutions involved in the derivation, must be used without rounding. For the longitudinal modes of fixed-free beam, fn=(2n−1)c/4L. From the above equation, and knowing ρ=1.802 g·cm3, we obtained Young's modulus to be 2 GPa, with the speed of sound, therefore, being 1,100 μm·s−1; we estimate a 12% uncertainty in Y due to errors in t, L, and f This value of Young's modulus (N·m2) is very similar to that measured for TTF-TCNQ single crystals using a mm-length vibrating reed under an alternating voltage. Both materials are pseudo-one-dimensional, and the value of the modulus is indicative of the elastic nature along the stacking axis in the direction of weak intercolumn interactions. Young's modulus slowly varies in value in the temperature range of 50 to 300 K but, when extrapolated to higher temperatures, decreases for both TTF-TCNQ and K(TCNQ). From the absorbed laser pulse energy (30 nJ), the amount of material (7.2×10−14 kg), and assuming the heat capacity to be similar to TTF-TCNQ (430 J·K−1·mol−1), the temperature rise in the microscale crystal is expected to be at most 260 K. Finally, we note that for the same modulus reported here, the frequency of longitudinal mode expansion [f=c/4L; n=1] should be nearly 25 MHz, which is not seen in the FFT with the reported resolution, thus suggesting that the observed frequencies in the longitudinal direction are those due to cantilever motion in the z direction; the longitudinal expansion of the crystal is about 1 to 2% of its length, which in this case will be 100 to 200 nm. The potential energy stored in the crystal and the force exerted by the crystal at the moment of full extension along the long axis just after time zero [cf. FIG. 30(A)] can be estimated from the amplitudes and using Hooke's law: V = 1 2 ⁢ ( YA L ) ⁢ Δ ⁢ ⁢ L 2 ( 20 ⁢ ⁢ a ) F = ( YA L ) ⁢ Δ ⁢ ⁢ L ( 20 ⁢ ⁢ b ) where V and F are the potential energy and force, respectively, and A is the cross-sectional area of the crystal. The bracketed term in equation (20) is the spring constant (assuming harmonic elasticity, and not the plasticity range), and by simple substitution of the values, we obtained 200 pJ and 600 μN for the potential energy and force, respectively, considering the maximum possible expansion of 720 nm; even when the amplitude is at its half value [see FIG. 30(A)], the force is very large (˜300 μN). For comparison, the average force produced by a single myosin molecule acting on an actin filament, which was anchored by two polystyrene beads, was measured to be a few piconewtons. In other words, because of molecular stacking, the force is huge. Also because of the microscale cross-section, the pressure of expansion translates to 0.1 GPa, only a few orders of magnitude less than pressures exerted by a diamond anvil. Based on the laser fluence, crystal dimensions, and absorptivity of Cu(TCNQ) at 671 nm (3.5×106 m−1), the maximum pulse energy absorbed by the crystal is 30 nJ. This means that, of the initial optical energy, a minimum of ˜1% is converted into mechanical motion of the crystal. But in fact, it could reach 10 or more percent as determined by the projection of the electric field of light on the crystal. In order to verify the trend in frequency shifts, the above studies were extended to another set of crystal beams, namely those of reduced dimensions. Because the resonant frequencies of a fixed-free beam are determined, in part, by the beam dimensions [cf. equation (19)], a Cu(TCNQ) crystal of different length than that shown in FIG. 30 should change the oscillation frequencies by the κ/L2 dependence. With a smaller cantilever beam we measured the oscillation frequencies for a crystal of 300 nm thickness and 4.6 μm length, using the same laser parameters as for the larger crystals, and found them to be at higher values (FIG. 31). This is confirmed by the FFTs of the displacement spanning the range 0 to 3.3 μs [FIGS. 31 (C) and (D)]; a strong resonance near 9 MHz with another weaker resonance at 3.6 MHz in the longitudinal direction [FIG. 31 (C)] is evident. Within a few microseconds, the only observed frequency in the FFT was near 9 MHz. This oscillation persists up to the time scans of 30 μs, at which point the amplitude was still roughly 40% of the leveling value near 2 is. By taking this duration (30 μs) to be the decay time (τ) required for the amplitude to fall to 1/e of the original value, the quality factor (Q=πfτ) of the crystal free oscillator becomes near 1,000. However, on longer time scales, and with less step resolution, the crystal recovers to the initial state in a few milliseconds, and if the mechanical motion persists, Q would increase by an order of magnitude. It is clear from the resonance value of the flexural frequency at 9 MHz that as the beam reduces in size, the frequency increases, as expected from equation (19). However, if we use this frequency to predict Young's modulus we will obtain a value of 30 GPa, which is an order of magnitude larger than that for the larger microscale crystal. The discrepancy points to the real differences in modes structure as we reach nanometer-scale cantilevers. One must consider, among other things, the anchor-point(s) of the crystals, the frictional force with substrate and other crystals, and the curvature of the beam (see movie in supporting information). This curvature will cause the crystal to deviate from ideal Euler-Bernoulli beam dynamics, thus shifting resonance frequencies from their expected positions. Interestingly, by using the value of 30 GPa for Young's modulus, the minimum conversion efficiency increases by a factor of 15. These dependencies and the extent of displacement in different directions, together with the physics of modes coupling (dephasing and rephasing), will be the subject of our full account of this work. Thus, with 4D electron microscopy it is possible to visualize in real space and time the functional nanomechanical motions of cantilevers. From tomographic tilt series of images, the crystalline beam stands on the substrate as defined by the polar and azimuthal angles. The resonance oscillations of two beams, micro and nanocantilevers, were observed in situ giving Young's elastic modulus, the force, and the potential energy stored. The systems studied are unique 1D molecular structures, which provide anisotropic and colossal expansions. The cantilever motions are fundamentally of two types, longitudinal and transverse, and have resonance Q factors that make them persist for up to a millisecond. The function is robust, at least for 107 continuous pulse cycles (˜1011 oscillations for the recorded frames), with no damage or plasticity. With these imaging methods in real-time and with other variants, it is now possible to test the various theoretical models involved in MEMS and NEMS. Electron energy loss spectroscopy (EELS) is a powerful tool in the study of valency, bonding and structure of solids. Using our 4D electron microscope, we have performed ultrafast EELS, taking the time resolution in the energy-time space into the femtosecond regime, a 10 order of magnitude increase, and for a table-top apparatus. It is shown that the energy-time-amplitude space of graphite is selective to changes, especially in the electron density of the π+σ plasmon of the collective oscillation of the four electrons of carbon. Embodiments of the present invention related to EELS enable the microscope to be used as an analytical tool. As electrons pass through the specimen, each type of material (e.g., gold, copper, or zinc) will have a different electron energy. Thus, it is possible to “tune” into a particular element and study the dynamic behavior of the material itself. In microscopy, EELS provides rich characteristics of energy bands describing modes of surface atoms, valence- and core-electron excitations, and interferences due to local structural bonding. The scope of applications thus spans surface and bulk elemental analysis, chemical characterization and electronic structure of solids. The static, time-integrated, EEL spectra do not provide direct dynamic information, and with video-rate scanning in the microscope could changes be recorded only with a time resolution of millisecond or longer. Dedicated time-resolved EELS apparatus, without imaging, have obtained millisecond resolution, being determined primarily by detector response and electron counts. However, for studies of dynamics of electronic structure, valency and bonding, the time resolution must increase by at least nine orders of magnitude. We have performed femtosecond resolved EELS (FEELS) using our ultrafast electron microscope (UEM), developed for 4D imaging of structures and morphology. Embodiments of the present invention are conceptually different from time-resolved EELS (termed TREELS) as the time resolution in FEELS is not limited by detector response and sweep rate. Moreover, both real-space images and energy spectra can be recorded in situ in UEM and with energy filtering the temporal resolution can be made optimum. We demonstrate the method in the study of graphite which displays changes on the femtosecond (fs) time scale with the delay steps being 250 fs. Near the photon energy of 2.4 eV (away from the zero energy loss peak), and similarly for the π+σ plasmon band, the change is observed, but it is not as significant for the π plasmon band. Thus it is possible to chart the change from zero to thousands of eV and in 3D plots of time, energy and amplitude; the decrease in EELS intensity at higher energies becomes the limiting factor. This table-top approach using electrons is discussed in relation to recent achievements using soft and hard (optical) X-rays in laboratory and large-scale facilities of synchrotrons and free electron lasers. According to embodiments of the present invention, the probing electrons and the initiating light pulses are generated by a fs laser, and the EEL spectra of the transmitted electrons are recorded in a stroboscopic mode by adjusting the time delay between the pump photons and the probe electron bunches. The concept of single-electron packet used before in imaging is utilized in this approach. When each ultrafast electron packet contains at most one electron, “the single-electron mode,” space-charge broadening of the zero-loss energy peak, which decreases the spectrometer's resolution, is absent. FIG. 32 is a schematic diagram of a microscope used in embodiments of the present invention. A train of 220 fs laser pulses at 1.2 eV was frequency doubled and tripled and then split into two beams. In other embodiments, a range of laser pulse widths could be used, for example from about 10 femtoseconds to about 10 microseconds. The frequency tripled light at 3.6 eV was directed to the microscope photocathode, and the photoelectron probe pulse was accelerated to 200 keV. The 2.4 eV pulses were steered to the specimen, and provided the excitation at a fluence of 5.3 mJ/cm2. In other embodiments, a fluence ranging from about 1 mJ/cm2 to about 20 mJ/cm2 could be utilized. By varying the delay time between the electron and optical pulses, the time dependence of the associated EEL spectrum was followed. The electrons pass through the sample and a set of magnetic lenses to illuminate the CCD camera, forming either a high resolution image of the specimen, a diffraction image, or they can be energy dispersed to provide the EEL spectra. The apparatus is equipped with a Gatan imaging filter (GIF) Tridiem, of the postcolumn type, which is attached below the transmission microscope camera chamber. The energy width of near 1 eV was measured for the EELS zero-loss peak and it is comparable to that obtained in thermal-mode operation of the TEM, but increases significantly in the space-charge limited regime. The experiments were performed at repetition rates of 100 kHz and 1 MHz, and no difference in the EEL spectra or the temporal behavior was observed, signifying a complete recovery of electronic structure changes between subsequent pulses. The reported temporal changes were missed when the scan resolution exceeded 250 fs, and the entire profile of the transient is complete in 2 μs. The electron beam passes through the graphite sample perpendicular to the sample surface while the laser light polarization was parallel to the graphene layers. Finally, the zero of time was determined to the precision of the reported steps, and was observed to track the voltage change in the FEG module of the microscope. The semi-metal graphite is a layered structure, which was prepared as free-standing film. The thickness of the graphite film was estimated from the EEL spectrum to be 106 nm (inelastic mean-free path of ˜150 nm), and the crystallinity of the specimen was verified by observing the diffraction pattern which was indexed as reported. FIG. 33 shows a static EEL spectrum of graphite taken in UEM. The distinct features are observed in the spectrum and indeed are typical of the electronic structure bands of graphite; the in-plane π plasmon is found near 7 eV, while at higher energy, the peak at 27 eV is observed with a shoulder at 15 eV. These latter peaks correspond to the π+σ oscillation of the bulk and surface plasmons, respectively. The results are in agreement with those of literature reports. The bands displayed in different colors (FIG. 33) are the simulations of the profiles with peak positions reproducing the theoretical values near 7, 15 and 27 eV. The 3D FEELS map of the time-energy evolution of the amplitude of the plasmon portion of the spectrum (up to 35 eV) is shown in FIG. 34, together with the EEL spectrum taken at negative time. The spectra were taken at 1 MHz repetition-rate, for a pump fluence of 5.3 mJ/cm2 at room temperature and for ts=250 fs for each difference frame. The map reflects the difference for all energies and as a function of time, made by subtracting a reference EEL spectrum at negative time from subsequent ones. The relatively strong enhancement of the energy loss in the low energy (electron-hole carriers) region is visible and the change is near the energy of the laser excitation. This feature represents the energy loss enhancement due to the creation of carriers by the fs laser excitation in the ππ* band structure, as discussed below. At higher energy, the 7 eV π plasmon peak remains nearly unperturbed by the excitation, and no new features are observed at the corresponding energies. For the 27 eV π+σ bulk plasmon an increased spectral weight at positive time is visible as a peak in the time-resolved spectrum. In order to obtain details of the temporal evolution of the different spectroscopic energy bands, we divided the spectrum into three regions: the low energy region between 2 and 5 eV, the π plasmon region between 6 and 8 eV, and the π+σ plasmon region between 20 and 30 eV. The 3D data are integrated in energy within the specified regions of the spectrum, and the temporal evolution of the different loss features are obtained; see FIG. 35. For regions where changes occur, the time scales involved in the rise and subsequent decay are similar. In FEELS, the shortest decay is 700 fs taken with the steps of 250 fs. The duration of the optical pulse is ˜220 fs, but we generate the UV pulse for electron generation through a non-linear response, and it is possible that the pulses involved are asymmetric in shape and that multiphotons are part of the process; full analysis will be made later. We note that the observed ˜700 fs response indeed reflects the joint response from both the optical and electron pulses and it is an upper limit for the electronic change. It is remarkable that, in FIG. 35, the temporal evolution of the interlayer spacing of graphite obtained by ultrafast electron crystallography (UEC) at a similar fluence, i.e. 3.5 mJ/cm2, the timescale of the ultrafast compression corresponds well to the period in which the bulk plasmon is out of equilibrium; in this plot the zero of time is defined by the change of signal amplitude. In graphite, the characteristic time for the thermalization of photo-excited electrons is known to be near 500 fs at low fluences (a few μJ/cm2). When excited by an intense laser pulse, a strong electrostatic force between graphene layers is induced by the generated electron-hole (carrier) plasma. This causes the structure to be out of equilibrium for nearly 1 ps; a stressful structural rearrangement is imposed on the crystal, which, at very high fluences (above 70 mJ/cm2), has been proposed as a cause of the phase transformation into diamond. Because graphite is a quasi two-dimensional structure, distinct spectral features are visible in EELS. The most prominent and studied peaks are those at 7 eV and the much stronger one at 27 eV. From the solution of the in-plane and out-of-plane components of the dielectric tensor it was shown, for graphite, that the 7 eV band is a π plasmon, resulting from interband ππ* transitions in the energy range of 2-5 eV, whereas the 27 eV band is a π+σ plasmon dominated by σσ* transitions beyond 10 eV (FIG. 5). We note that in this case the plasmon frequencies are not directly given by the ππ* and σσ* transition energies as they constitute tensorial quantities. For example ϖ π + σ 2 = ϖ p 2 + 1 4 ⁢ ( Ω π 2 + 3 ⁢ Ω σ 2 ) ,where ωp=npe2/∈0m)1/2 is the free electron gas plasma frequency; Ωπ and Ωσ are the excitation energies for ππ* and σσ* transitions, respectively. For ωp, the electron density is np, n is the number of valence electrons per atom and p is the density of atoms, and ∈0 is the vacuum dielectric constant. It follows that the density of occupied and empty (π, σ, π, and σ) states is critical, and that the it Plasmon is from the collective excitation of the π electrons (one electron in the p-orbital, with screening corrections) whereas the π+σ plasmon is the result of all 4 valence electrons collectively excited over the coherent length scale of bulk graphite; there are also surface plasmons but at different energies. Recently it was demonstrated, both theoretically and experimentally, that the π and π+σ plasmons are sensitive to the inter-layer separation, but while the former shows some shift of peaks the latter is dramatically reduced in intensity, and, when reaching the grapheme limit, only a relatively small peak at ˜15 eV survives. This is particularly evident when the momentum transfer is perpendicular to the c-axis, the case at hand and for which the EEL spectrum is very similar to ours. With the above in mind, it is now possible to provide, in a preliminary picture, a connection between the selective fs atomic motions, which are responsible for the structural dynamics, and changes in the dielectric properties of Plasmon resonances, the electronic structure. The temporal behavior, and coherent oscillation (shear modes of ˜1 ps), of c-axis expansion display both contraction and expansion on the picometer length scale per unit cell. The contraction precedes the expansion, as shown in FIG. 35, with velocity that depends on the fluence, i.e., the density of carriers. With fs excitation, the electronic bands are populated anisotropically, and, because of energy and momentum conservation, the carriers transiently excite large-momentum phonons, so called strongly coupled phonons. They are formed on the fs time scale (electron-phonon coupling) but decay in ˜7 ps. The initial compression suggests that the process is a cooperative motion and is guided by the out-of-equilibrium structure change dictated by the potential of excited carriers; in this case ππ* excitation which weakens c-axis bonding. The initial atomic compression, when plotted with transient EELS data (FIG. 35), shows that it is nearly in synchrony with the initial change, suggesting that the spacing between layers (c-axis separation) is the rate determining step, and that in the first 1 μs, the compressed ‘hard graphite’ effect is what causes the increase in the amplitude of the π+σ plasmon peak. In other words, the decrease of the spectral weight due to the change of electronic structure upon increasing the interlayer separation (to form graphene) becomes an increase when the plates are compressed, because of the enhanced collectiveness of all four valence electrons of carbon. The change involves shear motions and it is not surprising that the π+σ peak (dominated by σσ* excitation) is very sensitive to such changes. The π peak is less influenced as only one electron is involved, as discussed above, and the amplitude change is relatively small. The faster recovery of EEL peaks in 700 fs is, accordingly, the consequence of expansion which ‘decouples’ the π and σ system. Lastly, the relatively large increase in EEL near the photon energy is due to carrier excitation (π*) which leads to a loss of electron energy at near 3 eV, possibly by electronic excitation involving the cy system (FIG. 36). The created carriers cause an increase in the Drude band as evidenced in the decrease in optical transmission. The demonstration of ultrafast EELS in electron microscopy opens the door to experiments that can follow the ultrafast dynamics of the electronic structure in materials. The fs resolution demonstrates the ability of UEM to probe transients on the relevant sub-picosecond time scale, while keeping the energy resolution of EELS. Moreover, the selectivity of change in the collective electron density (for graphite) suggests future experiments, including those with changes in polarization, shorter optical pulses, core excitation and oxidation sites. We believe that this table-top UEM-EELS should provide the methodology for studies which have traditionally been made using synchrotrons (and free electron lasers) especially in the UV and soft X-ray regions. Chemical bonding dynamics are important to the understanding of properties and behavior of materials and molecules. Utilizing embodiments of the present invention, we have demonstrated the potential of time-resolved, femtosecond electron energy loss spectroscopy (EELS) for mapping electronic structural changes in the course o nuclear motions. For graphite, it is found that changes of milli-electron volts in the energy range of up to 50 electron volts reveal the compression and expansion of layers on the subpicometer scale (for surface and bulk atoms). These nonequilibrium structural features are correlated with the direction of change from sp2 [two-dimensional (2D) grapheme] to sp3 (3D-diamond) electronic hybridization, and the results are compared with theoretical charge-density calculations. The reported femtosecond time resolution of four-dimensional (4D) electron microscopy represents an advance of 10 orders of magnitude over that of conventional EELS method. Bonding in molecules and materials is determined by the nature of electron density distribution between the atoms. The dynamics involve the evolution of electron density in space and the motion of nuclei that occur on the attosecond and femtosecond time scale, respectively. Such changes of the charge distribution with time are responsible for the outcome of chemical reactivity and for phenomena in the condensed phase, including those of phase transitions and nanoscale quantum effects. With convergent-beam electron diffraction, the static pattern of charge-density difference maps can be visualized, and using x-ray absorption and photoemission spectroscopy substantial progress has been made in the study of electronic-state dynamics in bulks and on surfaces. Electron energy loss spectroscopy (EELS) is a powerful method in the study of electronic structure on the atomic scale, using aberration-corrected microscopy, and in chemical analysis of selected sites; the comparison with synchrotron-based near-edge x-ray absorption spectroscopy is impressive. The time and energy resolutions of ultrafast electron microscopy (UEM) provide the means for the study of (combined) structural and bonding dynamics. Here, time-resolved EELS is demonstrated in the mapping of chemical bonding dynamics, which require nearly 10 orders of magnitude increase in resolution from the detector-limited millisecond response. By following the evolution of the energy spectra (up to 50 eV) with femtosecond (fs) resolution, it was possible to resolve in graphite the dynamical changes on a millielectronvolt (subpicometer motion) scale. In this way, we examined the influence of surface and bulk atoms motion and observed correlations with electronic structural changes: contraction, expansion, and recurrences. Because the EEL spectra of a specimen in this energy range contain information about plasmonic properties of bonding carriers, their observed changes reveal the collective dynamics of valence electrons. Graphite is an ideal test case for investigating the correlation between structural and electronic dynamics. Single-layered grapheme, the first two-dimensional (2D) solid to be isolated and the strongest material known, has the orbitals on carbon as sp2 hybrids, and in graphite the π-electron is perpendicular to the molecular plane. Strongly compressed graphite transforms into diamond, whose charge density pattern is a 3D network of covalent bonds with sp3 hybrid orbitals. Thus, any structural perturbation on the ultra-short time scale of the motion will lead to changes in the chemical bonding and should be observable in UEM. Moreover, surface atoms have unique binding, and they too should be distinguishable in their influence from bulk atom dynamics. The experiments were performed on a nm-thick single crystal of natural hexagonal graphite. The sample was cleaved repeatedly until a transparent film was obtained, and then deposited on a transmission electron microscopy (TEM) grid; the thickness was determined from EELS to be 108 nm. The fs-resolved EELS (or FEELS) data were recorded in our UEM, operating in the single-electron per pulse mode to eliminate Boersch's space charge effect. A train of 220 fs infrared laser pulses (λ=1038 nm) was split into two paths, one was frequency-doubled and used to excite the specimen with a fluence of 1.5 mJ/cm2, and the other was frequency-tripled into the UV and directed to the photoemissive cathode to generate the electron packets. These pulses were accelerated in the TEM column and dispersed after transmission through the sample in order to provide the energy loss spectrum of the material. The experimental, static EEL spectra of graphite in our UEM, with grapheme for comparison, are displayed in FIG. 37A; FIG. 37B shows the results of theoretical calculations. The spectral feature around 7 eV is the π Plasmon, the strong peak centered around 26.9 eV is the π+σ bulk plasmon, and the weaker peak on its low energy tail is due to the surface Plasmon. The agreement between the calculated EEL spectra and the experimental ones is satisfactory both for graphite and grapheme. Of relevance to our studies of dynamics is the simulation of the spectra for different c-axis separations, ranging from twice as large as naturally occurring (2c/a; a and c are lattice constraints) to 5 times as large. This thickness dependence is displayed in FIG. 37B. As displayed in FIG. 37, the surface and bulk Plasmon bands (between 13 and 35 eV) can be analyzed using two Voigt functions, thus defining the central position, intensity, and width. At different delay times, we monitored the changes and found that they occur in the intensity and position; the width and shape of the two spectral components are relatively unchanged. FIGS. 37C and 37D, show the temporal changes of the intensity for both the surface and bulk plasmons. As noted, the behavior of bulk dynamics is “out of phase” with that of the surface dynamics, corresponding to an increase in intensity for the former and a decrease for the latter. Each time point represents a 500-fs change. Within the first 1 ps, the bulk Plasmon gains spectral weight with the increase in intensity. With time, the intensity is found to return to its original (equilibrium) value. At longer times, a reverse in sign occurs, corresponding to a decrease and then an increase in intensity—an apparent recurrence or echo occurring with dispersion. The intensity change of the surface plasmon in FIGS. 37C and 37D, shows a π phase-shifted temporal evolution with respect to that of the bulk plasmon. The time dependence of the energy position of the different spectral bands is displayed in FIG. 38. The least-squares fit converges for a value of the surface plasmon energy at 14.3 eV and of the bulk plasmon at 26.9 eV. The temporal evolution of the surface plasmon gives no sign of energy dispersion, whereas the bulk plasmon is found to undergo first a blueshift and then a redshift at longer times (FIGS. 38A and 38B). The overall energy-time changes in the FEEL spectra are displayed in FIG. 39. To make the changes more apparent, the difference between the spectra after the arrival of the initiating laser pulse (time zero) and a reference spectrum taken at −20 μs before time zero is shown. The most pronounced changes are observed in the region near the energy of the laser itself (2.39 eV), representing the energy-loss enhancement due to the creation of carriers by the laser excitation, and in the region dominated by the surface and bulk plasmons (between 13 and 35 eV). Clearly evident in the 3D plot are the energy dependence as a function of time, the echoes, and the shift in phase. A wealth of information has been obtained on the spectroscopy and structural dynamics of graphite. Of particular relevance here are the results concerning contraction and expansion of layers probed by diffraction on the ultra-short time scale. Knowing the amplitude of contraction/expansion, which is 0.6 μm at the fluence of 1.5 mJ/cm2, and from the charge of plasmon energy with interlayer distance (FIG. 37), we obtained the results shown in FIG. 38C. The diffraction data, when now translated into energy change, reproduce the pattern in FIG. 38A, with the amplitude being within a factor of two. When the layers are fully separated, that is, reaching grapheme, the bulk plasmon, as expected, is completely suppressed. The dynamics of chemical bonding can now be pictured. The fs optical excitation of graphite generates carriers in the nonequilibrium state. They thermalize by electron-electron and electron-phonon interactions on a time scale found to be less than 1 μs, less than 500 fs, and −200 fs. From our FEELS, we obtained a rise of bulk plasmons in ˜180 fs (FIG. 39). The carriers generated induce a strong electrostatic force between grapheme layers, and ultrafast interlayer contraction occurs as a consequence. In FIG. 37D, the increase of the bulk plasmon spectral weight on the fs time scale reflects this structural dynamics of bond-length shortening because it originates from a denser and more 3D charge distribution. After the compression, a sequence of dilatations and successive expansions along the c axis follows, but, at longer times lattice thermalization dephases the coherent atomic motions; at a higher fluence, strong interlayer distance variations occur, and grapheme sheets can be detached as a result of these interlayer collisions. Thus, the observations reported here reflect the change in electronic structure: contraction toward diamond and expansion toward grapheme. The energy change with time correlates well with the EELS change calculated for different interlayer distances (FIG. 37). We have calculated the charge density distribution for the three relevant structures. The self-consistent density functional theory calculations were made using the linear muffin-tin orbital approximation, and the results are displayed in FIG. 40. To emphasize the nature of the changes observed in FEELS, and their connection to the dynamics of chemical bonding, we pictorially display the evolution of the charge distribution in a natural graphite crystal, a highly compressed one, and the extreme case of diamond. Once can see the transition from a 2D to a 3D electronic structure. The compressed and expanded graphite can pictorially be visualized to deduce the change in electron density as interlayer separations change. With image, energy, and time resolution in 4D UEM, it is possible to visualize dynamical changes of structure and electronic distribution. Such stroboscopic observations require time and energy resolutions of fs and meV, respectively, as evidenced in the case study (graphite) reported here, and for which the dynamics manifest compression/expansion of atomic planes and electronic sp2/sp3-type hybridization change. The application demonstrates the potential for examining the nature of charge density and chemical bonding in the course of physical/chemical or materials phase change. It would be of interest to extend the scale of energy from ˜1 eV, with 100 meV resolution, to the hundreds of eV for exploring other dynamical processes of bonding. The following articles are hereby incorporated by reference for all purposes: 4D imaging of transient structures and morphologies in ultrafast electron microscopy, Brett Barwick, et al., Science, Vol. 322, Nov. 21, 2008, p. 1227. Temporal lenses for attosecond and femtosecond electron pulses, Shawn A. Hibert, et al., PNAS, Vol. 106, No. 26, Jun. 30, 2009, p. 10558. Nanoscale mechanical drumming visualized by 4D electron microscopy, Oh-Hoon Kwon, et al., Nanoletters, Vol. 8, No. 11, November 2008, p. 3557. Nanomechanical motions of cantilevers: direct imaging in real space and time with 4D electron microscopy, David J. Flannigan, et al., Nanoletters, Vol. 9, No. 2 (2009), p. 875. EELS femtosecond resolved in 4D ultrafast electron microscopy, Fabrizio Carbone, et al., Chemical Physics Letters, 468 (2009), p. 107. Dynamics of chemical bonding mapped by energy-resolved 4D electron microscopy, Fabrizio Carbone, et al., Science, Vol. 325, Jul. 10, 2009, p. 181. Atomic-scale imaging in real and energy space developed in ultrafast electron microscopy, Hyun Soon Park, et al., Nanoletters, Vol. 7, No. 9, September 2007, p. 2545. It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.
	abstract	A nuclear reactor includes a pressure vessel and a nuclear reactor core comprising fissile material disposed inside the pressure vessel at the bottom of the pressure vessel. A secondary core containment structure includes a containment basket comprising insulation with a maximum stable temperature of at least 2200K cladded by steel. The bottom of the pressure vessel and the nuclear reactor core are disposed inside the containment basket with the containment basket spaced apart from the bottom of the pressure vessel by a clearance gap. The containment basket may comprise zirconia insulation cladded by steel. In some embodiments the clearance gap between the containment basket and the bottom of the pressure vessel is no larger than one meter. The secondary core containment structure may further comprise conduits arranged to inject water into the clearance gap between the containment basket and the bottom of the pressure vessel.
059149957	abstract	A nuclear reactor fuel assembly includes a fuel assembly base, a fuel assembly head and mutually parallel fuel rods containing nuclear fuel and extending between the fuel assembly head and the fuel assembly base. A water tube having first and second open ends extends parallel to the fuel rods. The first end of the water tube grips and is held at the fuel assembly base. An elongated extension body has first and second ends. The second end of the extension body grips and is held at the fuel assembly head. The second end of the water tube is screwed into the first end of the elongated extension body, or the first end of the elongated extension body is screwed into the second end of the water tube. The elongated extension body has two mutually coaxially disposed partial bodies. One of the partial bodies has the second end of the extension body and the other of the partial bodies has the first end of the extension body. One of the partial bodies is screwed into the other of the partial bodies. A check nut may be seated on the one partial body which is screwed into the other partial body and the check nut is braced against the other partial body.
054421861	summary	FIELD AND BACKGROUND OF THE INVENTION This invention relates to a radioactive isotope source, and more particularly to an encapsulated radioactive isotope source which is designed to permit re-encapsulation and reuse of the radioactive isotope. Various types of analytical instruments use a radioactive isotope source in order to obtain measurements of the physical characteristics or properties of a test specimen. For example, there are commercially available instruments which use a radioactive isotope source for measuring properties such as density, composition, moisture content, thickness, etc. Examples of such test instruments are described in the following United States patents owned by applicants' assignee: U.S. Pat. Nos. 4,525,854; 4,542,472; 4,587,623; 4,766,319; 4,874,950; 4,979,197; and 5,155,356. In nuclear instruments of the general type illustrated by the above patents, the radioactive isotopes are typically contained in a capsule. For example, where the isotopes are americium and beryllium, small pellets of the americium and beryllium are packaged in a stainless steel capsule. Even though the radioactive half-life of these isotopes is very long (e.g. over 400 years) it is often recommended that the instruments be returned to the manufacturer periodically so that the radioactive isotope source can be reconditioned or replaced. This is because the weld in the stainless steel capsule may lose strength or become brittle after a number of years. In the past, used radioactive isotope source capsules were collected and sent to a disposal site for radioactive materials. However, it has become increasingly difficult to find disposal sites which will accept such radioactive materials. SUMMARY OF THE INVENTION The present invention provides a way to re-encapsulate and thus reuse radioactive isotope source capsules. Specifically, in accordance with the present invention a source capsule containing a radioactive isotope is put inside of an outer protective jacket or capsule and the outer jacket is sealed. The outer protective jacket is so designed that it can be reopened without disturbing the radioactive isotope source capsule contained therein. Thus, when it becomes necessary to recondition the source capsule, the inner source capsule can be removed from the outer protective jacket and it can be re-encapsulated in another outer protective jacket. Because of the long radioactive half-life of the isotopes employed, the source capsules can be re-encapsulated as many times as may be needed, thus avoiding the problems associated with disposal of the radioactive isotopes. Furthermore, the ability to reuse the radioactive isotope source allows for recycling and thus an overall reduction in the number of sources produced. In accordance with one embodiment of the present invention, there is provided a re-encapsulated radioactive isotope source which comprises an outer protective jacket in the form of a can having a side wall, an integrally formed bottom wall and an open upper end. A source capsule containing a radioactive isotope is received within this outer protective jacket. A jacket cap is received within the outer protective jacket so as to close the open end of the jacket, with the source capsule thus located within the outer protective jacket. The jacket cap has its outer peripheral edge positioned in close fitting relation to the inner peripheral surface of the jacket side wall to form a narrow gap between the jacket cap and the jacket side wall. A seal, such as a weld, extends along the narrow gap, joining the jacket cap to the jacket and sealing the source capsule within the protective jacket. In a preferred embodiment, the axial length of the jacket is greater than the axial length of the source capsule and a removable spacer is positioned within the jacket filling the space between the source capsule and the jacket cap. A score line is provided on the outside surface of the jacket in the region of the underlying spacer to facilitate reopening the outer jacket without risk of damage to the original source capsule. When it becomes necessary to recondition the source by re-encapsulation, the protective outer jacket is reopened and the original source capsule is removed from the jacket. The source capsule and a new spacer are then positioned within another outer protective jacket in the form of a can having a side wall, an integrally formed bottom wall and an open upper end. Another jacket cap is positioned within the outer protective jacket so as to close the open end of the jacket with the source capsule being located within the jacket. The jacket cap has its outer peripheral edge positioned in close fitting relation to the inner peripheral surface of the jacket side wall to form a narrow gap between the jacket cap and the jacket side wall. A seal is formed extending along the narrow gap to join the jacket cap to the jacket and to seal the source capsule within the protective jacket.
	description	The present invention relates to a control technique for controlling electrification. This electrification turns out to become a problem when observing an insulating-substance sample in devices which use a charged particle beam as the probe. Examples of such devices are a scanning electron microscope (SEM) and a focused-ion-beam (FIB) machining and observation device. Also, it is highly likely that electric charges will be accumulated on glass-substrate samples by irradiation with the charged particle beam. Examples of such glass-substrate samples are a reticle (i.e., mask) and a quartz wafer. Accordingly, in particular, the present invention relates to a technique for allowing a pattern configured on the glass-substrate samples to be stably length-measured using the charged particle beam devices. In the SEM observation of an insulating-substance composed sample by using a charged particle beam, the main object and concern has been placed on elimination or neutralization of the electrification which turns out to become the problem. In order to accomplish this object, the following techniques and units have been disclosed so far, for example: A technique for converting an insulating-substance sample into electrically conductive property by forming an electrically conductive layer on the insulating-substance sample by a method such as evaporation (Patent Document 1), a technique for neutralizing the electrification on the insulating-substance sample by providing an irradiation unit of beams such as an electron beam or positive and negative ion beams independently of a primary charged particle beam which is irradiated onto the sample for forming the image (Patent Documents 2 and 3), a technique for neutralizing the electrification by providing a plasma irradiating unit inside a sample chamber or outside the sample chamber (Patent Document 4), a unit for maintaining the inside of the sample chamber under low vacuum (Patent Documents 5, 6, and 7), a technique for neutralizing the electrification by providing a gas locally-introducing unit (Patent Document 8) to ionize the gaseous molecules by the primary charged particle beam, and further, a technique for converting the insulating-substance sample into the electrically conductive property by irradiating short-wavelength light such as ultraviolet rays onto the electrified area (Patent Documents 9 and 10). Any of the above-cited techniques and units, however, has the following drawbacks: An on-the-spot observation is impossible to make, the throughput is low, the device control is complicated, the resolution is low, the maintenance is difficult and the period is short, a photosensitive material such as resist is unsuitable therefor, and the like. Meanwhile, as a technique similar to the configuration of the present invention, a defect inspection method for an insulating-film sample in the SEM has been disclosed in Patent Document 11. This defect inspection method is as follows: Namely, an electrode is located in a manner of being directly opposed to the sample, then applying an appropriate electric voltage thereto. This voltage allows low-energy secondary electrons generated from the sample to be fed back to the sample, thereby making it possible to stabilize the electrification at a constant potential. Accordingly, it has been publicly known that the electrification can be relaxed by using the secondary electrons via the operation of the electrode. This technique, however, is an invention belonging to the era where the device size was larger. Moreover, the electron-beam irradiation area in question is also larger than the one in the present invention. Namely, the effect which this technique brings about is, after all, an effect of roughly suppressing an in-elapsed-time increase in positive electrification on the insulating film. This technique is also a one which was used afterwards for the potential contrast control over a circuit inspection device called “EB tester”. After all, this technique differs from the present invention in its objects and effects. In the present invention, controls to be implemented are as follows: A control over local displacement of the electrification charges, a control over the beam drift whose velocity is equal to a few nm/s and which is caused by the potential gradient on the insulating-substance sample, and a dynamic control over the electrode voltage where attention is focused on an intentional control over the potential barrier. These controls and phenomena turn out to become problems when making a high-magnification and high-accuracy length-measurement just like in the present invention. Also, in Patent Document 12 and Patent Document 13, disclosures have been made concerning observation methods for the insulating-substance sample. The observation methodologies described in the above-described Documents are as follows: Here, in general, the retarding method is a high-resolution implementation methodology for the SEM where a primary electron beam with high energy supplied is caused to pass through within a lens field which functions as a deceleration potential against the primary electron beam. In the device where the retarding method is used for a sample or a sample stage, an electrode is located at a position above the sample or in such a manner as to cover the sample, then applying thereto a voltage which is equal to the retarding voltage. This voltage allows the sample to be positioned within an electric-field-absent environment, thereby controlling the insulating-substance sample surface at an arbitrary potential. Otherwise, in the device which uses the retarding method, an auxiliary electrode is added with an object of improving yield quantity of the secondary electrons. These methodologies, however, differ from the present invention in the following points: Namely, the control over the electrification and a reduction in the beam drift are not regarded as their object, and such an effect itself cannot be expected. Moreover, in Patent Document 14, a disclosure has been made concerning the following configuration: In the SEM which uses the retarding method, an objective-lens polar segment is located, and also an intermediate electrode is located at a position above the objective-lens polar segment. The intermediate electrode is a technique for neutralizing the electrification of a sample by applying a negative bias to the objective-lens polar segment to cause the secondary electrons generated from the sample to be fed back to the sample. However, the present configuration itself has been disclosed in the above-described Patent Document 13. Also, the principle and the phenomena have been disclosed in the above-described Patent Document 11. Accordingly, since the effect of the sample stage lacks in the conventional techniques, it is impossible to make uniform the potential gradient on the sample surface. Simultaneously, with the contents disclosed as the present configuration, it is difficult to implement the stabilization of the electrification on the insulating-substance sample, and the inspection and length-measurement in the high magnification where the beam drift turns out to become the problem. Consequently, no concrete solving unit or method has been disclosed for these problems. Patent Document 1: JP-A-8-68772 Patent Document 2: JP-A-8-222176 Patent Document 3: JP-A-10-172493 Patent Document 4: JP-A-2002-131887 Patent Document 5: JP-A-9-304040 Patent Document 6: JP-A-5-174768 Patent Document 7: JP-A-2002-203774 Patent Document 8: US-P-6555815B2 Patent Document 9: JP-A-2000-36273 Patent Document 10: JP-A-10-312765 Patent Document 11: JP Pat.2130001 Patent Document 12: JP-A-09-171791 Patent Document 13: JP-A-2001-026719 Patent Document 14: JP-A-2002-250707 Non-Patent Document 1: A DATABASE OF ELECTRON-SOLID INTERACTIONS David C Joy, EM Faculty, University of Tennessee, and Oak Ridge National Laboratory Problem To Be Solved By The Invention It is an object of the present invention to perform a high-resolution, excellent-accuracy, and excellent-reproducibility length-measurement of a structure on a sample by using a charged particle beam. This sample is assumed to be a kind of sample on the surface of which an insulating substance is partially exposed, or whose substrate is formed of an insulating substance. Accomplishing this object requires that the following problems be overcome: The first problem is the so-called “a reduction in the beam drift”. The beam drift is the following phenomenon: Namely, when observing an insulating-substance sample using a charged particle beam, electrification is induced. Moreover, this electrification makes a sample surface potential nonuniform within a charged-particle-beam irradiation area surface. This nonuniformity causes a potential gradient to occur. Eventually, the orbit of the charged particle beam is deflected by this potential gradient. Also, as is known as a physical phenomenon, because of the electrification which has occurred on the sample, if this electrification assumes a positive polarity, a potential will be formed directly above an electrified location. This potential turns out to become a potential barrier which is exerted against energy of secondary electrons generated from the electrified location. As a result, there occurs the self-relaxation effect that the low-energy secondary electrons emitted from the electrified location will be fed back to the sample surface then to lower the electrification quantity. Even if the length-measurement location or the sample to be length-measured has been changed, as long as the electrification quantity can be reduced enough as compared with an initial electrification quantity, it is possible to reduce an error of the length-measurement accuracy down to a level which is of no problem from the practical standpoint. Also, if the electrification has been vanished completely, it becomes impossible to clarify differences in the material and structure by using the potential contrast. Accordingly, controlling the electrification quantity is also important. It is highly unlikely, however, that the secondary electrons will be fed back to the electrified area uniformly. Also, unless the self-relaxation effect itself is under an appropriate condition, the electrification quantity remains large even if a considerable long time has elapsed. As a result, the sample surface potential remains nonuniform. Consequently, the second problem is to provide a unit and a condition which allow the self-relaxation effect of the electrification to be performed effectively. Moreover, after overcoming the first and second problems, the third problem is to provide a device which allows implementation of a high-resolution image observation. Means For Solving The Problems Energy of the charged particle beam to be irradiated onto the sample is set so that generation efficiency of the secondary electrons generated from the sample becomes equal to 1 or more. Configuration of the device is as follows: A flat-plate electrode is located in such a manner as to be directly oppose to the sample. Here, the flat-plate electrode is an electrode to which a voltage can be applied independently, and which is equipped with a hole through which the primary charged particle beam can pass. Moreover, a voltage can be applied independently to a sample stage on which the sample is mounted. Here, the sample stage's surface directly opposed to the sample is formed into a planarized structure with no projections and depressions thereon. Also, diameter D of the hole provided in the flat-plate electrode and distance L between the flat-plate electrode and the sample are set such that a relation of D/L≦1.5 is satisfied. Furthermore, a positive voltage which is equal to a few V to a few tens of V relative to the sample surface potential is applied to the flat-plate electrode so that the induced electrification will not be accumulated in excess, and so as to perform the detection of the secondary electrons. In addition, as a pre-stage for the length-measurement, the voltage to be applied to the flat-plate electrode is changed from the predetermined initial value to an a-few-V to a-few-tens-of-V negative voltage while irradiating the primary charged particle beam. After that, the length-measurement is performed. Advantages Of The Invention According to the device configuration of the present invention, it becomes possible to eliminate the potential gradient on an insulating-substance sample surface, and to perform high-speed relaxation and stabilization of the electrification induced when a charged particle beam is irradiated onto the insulating-substance sample. Even in the high magnification under which the length-measurement is performed, it becomes possible to stabilize the S/N ratio and contrast, and to eliminate the beam drift as well. As a result, it becomes possible to perform the length-measurement of an insulating-substance sample with a high resolution, an excellent accuracy, and an excellent reproducibility. Moreover, it is possible to automatically set the flat-plate electrode voltage for stabilizing the electrification. This characteristic allows optimum conditions to be set even in various types of samples whose electrification quantities differ from each other, thereby making it possible to perform length-measurements of the insulating-substance samples regardless of the differences in the samples or technical competencies of operators. The other objects, characteristics, and advantages of the present invention will become apparent from the following description of embodiments of the present invention accompanied by the accompanying drawings. Best Mode For Carrying Out The Invention First, referring to FIG. 1, the explanation will be given below concerning a representative embodiment of the present invention. The present embodiment is of the basic configuration of a scanning electron microscope (SEM) which uses the retarding method. The whole or a part of configuration components 1 to 12 of the present embodiment is contained within a vacuum container. The electron source 1 is the so-called “Schottky electron source”, i.e., an electron source where zirconium oxide is coated and diffused on a needle-shaped-machined tungsten thereby to decrease the work function of an electron emission portion at the electron source front-end. The electron source 1 is heated at a proper temperature by a constant current power-supply 15 which is kept floating over an electron-gun acceleration power-supply 18 for applying an electron-beam initial acceleration voltage −3 kV to the electron source. Then, electron emission is performed at an extraction electrode 3 to which an extraction voltage power-supply 17 for performing the electron electric-field emission is connected. This makes it possible to acquire an emitted electron beam whose energy distribution width is narrow and whose emission current quantity is stable. Also, a power-supply 16 capable of applying a negative voltage to the electron-gun acceleration power-supply 18 is connected to a suppression electrode 2 set up in proximity to the electron source. This makes it possible to increase or decrease the emission current quantity. A magnetic-field lens 4 and a magnetic-field lens 5, which have an effect of converging the electron beam, are set onto an optical condition which is preferable for the present embodiment. A deflection coil 8 allows the electron beam to scan on a sample 11 with a desired FOV (: Field Of View). Secondary electrons generated from the sample 11 are accelerated in the electron source 1's direction by an effect of magnetic field of an objective lens 9, and by effects of negative voltages which are respectively applied to a control electrode 10 and a metallic sample stage 12 by a control electrode power-supply 20 and a retarding power-supply 21. The secondary electrons are finally captured by a secondary-electron detector 13, then being electrically amplified thereby. After that, the amplified secondary electrons are subjected to an A/D conversion at an image processing unit 19. This makes it possible to display, on an image output terminal 14, a raster image which is synchronized with an electron-beam scan signal at the deflection coil. Although, in the present embodiment, an Everhart-Thornley type detector including a scintillator, a light guide, and a secondary-electron multiplier tube is used as the secondary-electron detector 13, a semiconductor detector or a micro channel plate may also be used. Also, in the present embodiment, there is provided a conversion electrode 6 at the pre-stage of the secondary-electron detector 13. The conversion electrode 6 allows the secondary electrons or reflection electrons accelerated and ascending from the sample 11 to be converted into the low-speed secondary electrons once again. Simultaneously, there is provided an EXB filter 7. The EXB filter 7 exerts no influences on the orbit of the primary electron beam, and is capable of deflecting only the low-speed secondary electrons in the secondary-electron detector 13's direction. The set-up of the conversion electrode and the EXB filter configures the detection system whose secondary-electron collection efficiency is high. A potential-blockage type energy filter (not illustrated) is provided within the EXB filter 7. This energy filter uses one or more pieces of mesh-like metallic electrodes, then applying thereto a voltage which is at basically the same level as the voltage applied to the sample stage 12 by the retarding power-supply 21. This voltage allows the energy filter to generate a potential barrier which is exerted against the energy of the secondary electrons generated and accelerated from the sample 11. On account of this potential barrier, it becomes possible to make the distinction between the reflection electrons and the secondary electrons, of course. In addition thereto, by providing a plurality of secondary-electron detectors 13, it also becomes possible to simultaneously acquire the reflection electrons and the secondary electrons, and to display them in a manner of being added to the SEM image with arbitrary proportions. Furthermore, by making the blockage potential of the energy filter variable, it also becomes possible to measure the surface potential on the sample 11 caused by the electrification which is induced when the primary electron beam is irradiated on the sample 11. This allows a change in the optical magnification to be calculated using both an operation condition of the optical system and the surface potential. Consequently, if, from this result, resetting deflection current of the deflection coil 8 is carried out, accurate magnification setting becomes executable regardless of the electrification on the sample surface. The configuration explained so far is the basic configuration as the SEM in the present embodiment. It is the object of the present invention to perform the stable length-measurement without being influenced by the electrification even if the sample 11 is a sample on the surface of which an insulating substance is partially exposed, or a sample whose substrate is formed of an insulating substance., e.g., a reticle (i.e., mask) or a liquid-crystal substance. Accordingly, the explanation will be given below concerning a configuration therefor. The number of secondary electrons which are generated if a single electron enters the sample is defined as the secondary-electrons emission ratio δ. Then, in the case of SiO2, as illustrated in FIG. 2, the secondary-electrons emission ratio δ changes depending on incident energy of the primary electron beam. Here, it has been known that the sample surface will be positively electrified if δ is larger than 1, and that the sample surface will be negatively electrified if δ is smaller than 1. In the present embodiment, using substantially 1-KeV energy used in the ordinary low-acceleration SEM, the energy of the electron beam to be irradiated onto the sample is set so that the generation efficiency of the secondary electrons generated from the sample becomes equal to 1or more. Although the incident energy which is close to 50 eV may also be selected, the change in the secondary-electrons emission ratio relative to the incident energy is large and difficult to control. This is disadvantageous from the viewpoint of the resolution as well. Moreover, as will be described later, the selection of the incident energy corresponding to δ which is close to 1 will prove advantageous in points as well of stabilization of the electrification quantity and automatization of voltage setting to be applied to the control electrode 10. Also, consider the case where an insulating-substance sample or in particular, a sample whose substrate is formed of glass, is located at an intermediate position between the control electrode 10 formed into a flat-plate electrode and the sample stage 12. Then, in this case, vacuum and the glass turn out to exist between the control electrode 10 and the sample stage 12. As a result, if a hole is large enough up to a degree that the potential generated by the components positioned in the electron source 1's direction of the control electrode 10 can permeate into a proximity to the sample from the hole, the potential turns out to penetrate into the sample whose permittivity is larger than that of the vacuum. Here, the above-described hole is a hole which is provided in the control electrode 10 and through which the primary electron beam can pass. This potential's penetration causes a warp in an equipotential surface to occur on the sample surface, thereby resulting in occurrence of a potential gradient within the sample surface. In addition thereto, when the electrification charges are induced on the insulating-substance sample, the above-described potential gradient causes a displacement of the charges to occur. This charges' displacement further changes the potential gradient on the sample surface, thereby resulting in occurrence of the beam drift of the primary electron beam. This is a conceivable explanation of the reason for occurrence of the beam drift. In the present embodiment, the control electrode 10, i.e., the flat-plate electrode, is located in such a manner as to be directly opposed to the sample 11. Here, the flat-plate electrode is an electrode to which the voltage can be independently applied by using the control electrode power-supply 20, and which is equipped with the hole. Also, the hole is the one through which the primary electron beam can pass, and which is located on an axis coinciding with the central axis of an objective-lens magnetic pole hole. Moreover, the retarding power-supply 21 makes it possible to independently apply the voltage to the sample stage 12 on which the sample 11 is mounted. Here, the sample stage's surface directly opposed to the sample 11 is formed into a planarized structure with no projections and depressions thereon. This allows the sample 11 to be sandwiched between the control electrode 10 and the sample stage 12. On account of this configuration, the electric field between the control electrode 10 and the sample 11 becomes a parallel electric field. This condition permits the sample surface to be caused to coincide with the equipotential surface, thereby allowing elimination of the warp in the equipotential surface on the sample surface. Simultaneously, it becomes possible to arbitrarily set the equipotential surface by the voltages applied to the control electrode 10 and the sample stage 12. Consequently, in the insulating-substance sample or in particular, in the sample whose substrate is formed of glass, it becomes possible to set the sample surface at a voltage. Here, this voltage can be accurately calculated using an electric-field simulation which uses the sample's permittivity, the voltages applied to the control electrode 10 and the sample stage 12, and their respective sizes. Next, referring to FIG. 3A and FIG. 3B, the more detailed explanation will be given below concerning the formation of the equipotential surface. In addition to the retarding method, as one of the high-resolution implementation methodologies for the SEM, the boosting method exists. This boosting method is as follows: Namely, a positive high voltage is applied to the whole of a magnetic path or a part of the magnetic path which is isolated. This positive high voltage causes the electron beam to pass through within the lens field at a high speed, thereby reducing chromatic aberration. In FIG. 3A, a 5-kV boosting voltage is applied to the objective lens 9 by a boosting power-supply 25, and the retarding voltage is applied to the sample stage 12 by −2 kV. Also, a control electrode 22 is set at −1.9 kV. FIG. 3A illustrates the control electrode 22. However, if there is provided none of the control electrode 22, or if a hole, which is provided in the center of the control electrode 22 and through which the primary electron beam can pass, is rather large as in the control electrode 22, the boosting voltage penetrates into the sample 11 from the hole, then forming an equipotential-line distribution 23. This indicates that the distribution 23 formed will cause a potential gradient to occur on the surface of the insulating-substance sample 11. Meanwhile, FIG. 3B illustrates a state where the boosting voltage applied to the objective lens 9 is lowered, and where the hole diameter of the control electrode is made smaller as in a control electrode 26. In this case, as is indicated from an equipotential-line distribution 27, the distribution 27 has been planarized. This condition permits the surface of the sample 11 to be caused to coincide with the equipotential surface. Even if the boosting voltage continues to be set at the high voltage, this effect can also be acquired by making the hole diameter of the control electrode 26 even smaller, or by making the distance between the control electrode 26 and the sample 11 larger. These methods, however, result in an increase in the deflection curvature of the primary electron beam, or an exceeding lowering in the resolution. Also, as an important element for allowing the present invention to be effectively carried out, structure of the sample stage 12 can be mentioned. FIG. 4A is a cross-sectional diagram of structure of a metallic sample stage 28 including the control electrode 10 when the reticle is selected as the sample. This is the case of a configuration where the insulating-substance sample 11 is embedded in the sample stage 28, and where the upper surface of the sample 11 and that of the sample stage 28 are configured to exist on one and the same flat plane. Support stages 24 are spacers for preventing the reticle from being brought into directly contact with the sample stage 28 so as not to damage the reticle. The support stages 24 are formed of a material which generates no foreign substances. Height of the support stages 24 exerts influences on a change ratio in the voltage which is exerted on the sample 11 at the time of a voltage change in the control electrode 10, i.e., the sensitivity. This will be explained later. Accordingly, there must not exist a variation in the height among the devices. FIG. 4B, which is a part of FIG. 4A, illustrates an equipotential-line distribution in the case of observing an end portion of the sample 11. This is the case where a primary electron beam 29 is irradiated on a place which comes inwards by 5 mm from the sample end-portion. Incidentally, the condition is based on an example including a combination of the retarding voltage and the control-electrode voltage and the control-electrode location, i.e., a preferable example for carrying out the present invention effectively. Here, the retarding voltage is equal to −2100 V, the control-electrode voltage is equal to −2000 V, the distance between the control electrode 10 and the sample 11 is equal to 1 mm, the hole diameter of the control electrode 10 is equal to 1 mm, and the height of the support stages 24 is equal to 0.5 mm. The resultant equipotential-line distribution turns out to become a distribution like an equipotential-line group 30. Then, if a dimension 31 is of basically the same order as thickness of the sample, a large difference will occur between a potential density formed between the control electrode 10 and the sample stage 28 and a potential density formed by the control electrode 10 and the sample 11. This will cause a large potential gradient to occur in the electron-beam irradiation location at the sample end-portion. Meanwhile, FIG. 5A is a cross-sectional diagram of another embodiment of the sample stage. As illustrated in FIG. 5B, the dimension 31 is made smaller like a dimension 33. As a result, the resultant equipotential-line distribution turns out to become a distribution like an equipotential-line group 34. Accordingly, it becomes possible to eliminate the potential gradient which has occurred at the end portion of the sample 11, thereby being capable of suppressing the displacement of the electrification charges into a minimum value. Incidentally, basically the same processing as the dimension 33 is applicable not only to the depth of the illustrated depression of a sample stage 32, but also to heights of structures to be located on the periphery of the sample 11 on the sample stage 32. In view of the factors preferable for the present invention, such as the voltage condition, the position of the control electrode 10, and the height of the support stages 24, it is desirable that the dimension 33 be made smaller than one-half of the sample thickness. As having been described so far, based on the consideration of the potential distribution which occurs in the structural manner, it is possible to reduce the potential gradient on the insulating-substance sample surface, and thereby to eliminate one of the factors for the beam drift. Actually, however, none of the problems can be solved unless some countermeasure is taken against the potential variation on the sample surface caused by the accumulation of the electrification charges which are induced when irradiating the electron beam onto the insulating-substance sample. Hereinafter, the explanation will be given below concerning embodiments of a control method for the electrification charges. According to the present invention, even if the electrification is induced on the surface of the insulating-substance sample 11 by the irradiation with the primary electron beam, a positive voltage which is equal to a few V to a few tens of V relative to the sample surface potential has been already applied to the control electrode 10 so that the induced electrification will not be accumulated in excess. Consequently, even if the accumulation of the electrification charges has been developed, the development will be stopped with an electrification quantity which is lower than the potential difference between the control electrode 10 and the surface of the sample 11. As a result, it becomes possible to limit the initial accumulation of the electrification charges down to the electrification quantity in which the electrification charges can be reduced enough by the self-relaxation effect on the electrification. In the present embodiment, if a quart wafer is selected as the sample, the preferable voltage applied to the control electrode 10 is equal to about 50 V relative to the sample surface potential. Furthermore, the electrification, which has been induced on the sample by the irradiation with the primary electron beam, exhibits the above-described tendency to be settled down to the constant electrification quantity by the self-relaxation effect in elapsed time. It is highly unlikely, however, that the secondary electrons generated from the electrified area will be fed back to only the electrified area uniformly. Accordingly, the electrification quantity cannot be said to be small enough yet, and the charge distribution within the area is still in the nonuniform state. At this point-in-time, however, in the voltage already set to the control electrode 10, the potential barrier directly above the electrified area (which was described in [Problem to be solved by the Invention] as well) has become small enough down to a degree that the secondary electrons can pass therethrough. FIG. 6A, FIG. 6B, FIG. 7A, and FIG. 7B illustrate the above-described phenomena. These are about the case where the irradiation area of the primary electron beam is equal to about 70 μm per side. FIG. 6A illustrates an equipotential-line distribution at the time when the initial voltage applied to the control electrode 10 is set at −1610 V, and the retarding voltage is set at −1700 V. The incident energy of the primary electron beam at this time becomes equal to about 1 KeV, where δ is slightly larger than 1. When the primary electron beam has been irradiated on the insulating-substance sample 11, positive charges equal to a few V to a few tens of V are swiftly electrified on an electrified area 42 which substantially coincides with the irradiation area of the primary electron beam. Then, the resultant equipotential-line distribution turns out to become a distribution like an equipotential-line group 41. FIG. 6B is a diagram acquired by locally enlarging the electrified area 42 in FIG. 6A, where the equipotential-line interval is equal to 1V. A potential barrier 44, which is negative with reference to the electrification potential, will be formed directly above the electrified area 42. As a result, the following self-relaxation effect will occur: Namely, about 2-eV secondary electrons, which are the most common of the secondary electrons' energy distribution, are caused to be fed back by the potential barrier 44, thereby re-entering a proximity to the electrified area 42 then to cancel out the positive electrification charges. FIG. 7A and FIG. 7B illustrate the state where the electrification quantity has been reduced by the self-relaxation effect in FIG. 6A and FIG. 5B. The reduction in the electrification quantity changes the equipotential-line distribution into a distribution like an equipotential-line group 45 in FIG. 7A. When watching the equipotential-line group 45 locally, the equipotential-line group 45 is changed to a distribution like an equipotential-line group 48 as illustrated in FIG. 7B. Namely, the potential barrier directly above the electrified area 46 is relaxed. Consequently, the about 2-eV low-energy secondary electrons 47 are accelerated in the electron source 1's direction, thereby becoming capable of being detected by the secondary-electron detector 13. This phenomenon also coincides with a phenomenon that, immediately after the primary electron beam irradiation on the sample 11, brightness of the SEM image is decreased instantaneously, and becomes brighter once again. Also, the potential stabilization on the electrified portion by this self-relaxation effect usually requires a long-time electron beam irradiation which ranges from a few tens of seconds to a few minutes, although it depends on the irradiation current quantity as well. However, here, the voltage applied to the control electrode 10, while irradiating the primary electron beam, is changed to a negative voltage which is equal to a few V to a few tens of V relative to the initial voltage value. This makes it possible to intentionally generate a potential barrier on the electrified area which remains nonuniform, thereby allowing the secondary electrons to be fed back to the electrified area. Accordingly, it becomes possible to stabilize the electrification quantity by reducing the electrification quantity down to a degree that the magnification error presents no problem. This allows the potential gradient to be eliminated over a wide range in cooperation with the effects by the control electrode 10 and the sample stage 12 described earlier. Moreover, there will occur none of the unstable displacement of the charges caused by the potential gradient. This makes it possible to form a potential-stabilized area on the insulating-substance sample surface. As a result, there exist no hindrance factors for the secondary electrons. Consequently, it becomes possible to acquire an excellent-S/N-ratio SEM image, and to eliminate the beam drift of the primary electron beam. It is important, however, that the voltage change in the control electrode 10 be made in a continuous manner or a step-by-step manner. The reason for this condition is as follows: On account of this condition, in the process where the potential barrier is being gradually formed by the voltage change, quantity of the secondary electrons having the energy which allows the electrons to be fed back to the sample, and positions at which these secondary electrons are fed back to the sample also change gradually. This also allows the electrification quantity to be relaxed in a continuous manner. Accordingly, unlike the case where an instantaneous switching of the voltage change is performed, there will occur none of steep charges' concentration gradient or steep potential gradient. This permits diffusion of the charges to be suppressed down to the smallest possible degree, thereby making it possible to perform the stabilization of the electrification swiftly. It is possible to illustrate the above-described process as is illustrated in FIG. 8A, FIG. 8B, FIG. 9A, and FIG. 9B. In the state illustrated in FIG. 8A and FIG. 8B, since there still exits much of the electrification quantity, an unexpected maladjustment occurs in the diffusion caused by the charges'concentration gradient or the length-measurement magnification. Then, the voltage applied to the control electrode 10 is changed by about −20 V from the initial voltage value. As illustrated in FIG. 8B, this voltage change allows an about 1-V potential barrier 52 to be re-formed directly above an electrified area 49 in FIG. 8A. As a result, secondary electrons having energy lower than about 1 eV are caused to be fed back to the electrified area 49. This reduces the electrification charges even further. The self-relaxation effect at the steps in FIG. 8A and FIG. 8B reduces the charges on an electrified area 54 in FIG. 9A. Accordingly, the equipotential-line distribution is planarized in proximity to the sample like an equipotential-line group 53. As illustrated in FIG. 9B, even when watching the electrified area 54 locally, no potential barrier exists against low-energy secondary electrons 55 in an equipotential-line group 56. Accordingly, it becomes possible to detect the secondary electrons with an excellent S/N ratio. Moreover, since there exists almost no potential gradient on the primary electron beam irradiation area, there occurs no large displacement of the electrification charges. Also, the electrification quantity is small. These conditions result in no occurrence of the beam drift of the primary electron beam. FIG. 10 schematically illustrates the relationship between the voltage applied to the control electrode 10 and the electrification quantity induced on the sample 11 when the control-electrode voltage 10 is changed. The A area in FIG. 10 corresponds to a time-zone within which not a long time has elapsed since the irradiation on the sample 11 with the primary electron beam. Here, as is indicated by a graph 38, the positive electrification will be developed swiftly, and thus the electrification quantity will also be increased swiftly. The voltage applied to the control electrode 10 remains an initial value 35, and the SEM image becomes darker. In the B area corresponding to a time-zone up to which a further time has elapsed, as is indicated by a graph 39, the electrification quantity will be reduced by the self-relaxation effect. The voltage applied to the control electrode 10 remains the initial value 35, and the SEM image becomes brighter. However, even if the voltage applied to the control electrode 10. is maintained at the initial value 35, the electrification quantity will be reduced as is indicated by the graph 39. As a result, it takes quite a long time until the electrification quantity has been stabilized, and the beam drift will not be settled down. In the C area, the voltage applied to the control electrode 10 is changed in a continuous manner as is indicated by a graph 36, or in a step-by-step manner where the change is divided into several parts or times as is indicated by a graph 37. This change allows the electrification quantity to be reduced swiftly as is indicated by a graph 40, thereby making it possible to stabilize the electrification quantity in a short time. At this time, the SEM image becomes brighter after it has become darker to some extent. If the voltage applied to the control electrode 10 is controlled as is illustrated in FIG. 10, the following operation is conceivable: Namely, it becomes possible to automatically terminate the voltage change in the control electrode 10 by detecting the brightness change in the SEM image or the secondary-electron current quantity. Also, in some cases, the electrification quantity differs depending on the type or configuration of the sample, and thus detection quantity of the secondary electrons decreases. Accordingly, the initial value of the voltage applied to the control electrode 10 has a possibility of being able to be changed. Consequently, it is evident that it becomes possible to automatically determine the optimum initial value by sweeping the voltage applied to the control electrode 10 over a wide range using basically the same methodology. When trying to detect the brightness change in the SEM image or the secondary-electron current quantity, concretely, the following method is simple and convenient: Namely, the voltage applied to the control electrode 10 is changed while irradiating the primary electron beam, then determining the relationship between digital gradation of the SEM images grabbed on each constant time-period basis and the pixel number belonging thereto. If the gradation and the pixel number become larger or smaller than threshold values determined in advance, it is possible to terminate the voltage change in the control electrode 10, or it is possible to use the electrode voltage at that time as the initial value of the voltage applied to the control electrode 10. Now, as having been explained previously, the beam drift refers to the phenomenon that the orbit of the primary electron beam undergoes the deflection effect by the potential gradient in proximity to the sample surface. Here, this force field is formed by the potential difference between the primary electron beam irradiation area and its peripheral portion. Accordingly, the following condition is important: Namely, the potential gradient which becomes the cause for formation of the force field is made uniform in a range which is sufficiently wider than a high-magnification charged particle beam irradiation area where the length-measurement is to be performed (e.g., a few μm per side). As described earlier, there has existed the following method: The voltage to be applied to the flat-plate electrode is changed from the initial value to the negative voltage which is equal to a few V to a few tens of V, thereby reducing the electrification quantity and eliminating the potential gradient simultaneously. From the importance of the uniformity, in the case of using this method, it is effective that the length-measurement with the high magnification set thereto be performed after this method has been carried out with the low magnification set in advance. If the above-described solving methods are employed and applied to the first and second problems described in [Problem to be solved by the Invention], it turns out that the voltage applied to the control electrode 10 causes a deceleration potential to occur against the primary charged particle beam within the lens field between the objective lens and the sample. The higher the energy of the primary charged particle beam becomes which will pass through within the lens field, the more capable it becomes to reduce the chromatic aberration of the lens. Accordingly, it becomes important to locate the control electrode 10 in a manner of being made as close as possible to the sample surface. In the control electrode 10, however, there is provided the hole through which the primary electron beam can pass. As a result, as described earlier, there exists the possibility that the potential's penetration from the hole will cause the potential gradient to occur on the sample surface. Accordingly, it is impossible to make the distance between the control electrode 10 and the sample 11 arbitrarily close. Typically, the degree of this potential's penetration can be considered to be an order of the radius of the hole. Also, the electric-field simulation has indicated that the potential gradient on the sample surface can be reduced enough if the relation between the diameter D of the hole and the distance L between the flat-plate electrode and the sample satisfies D/L≦1.5. Consequently, a method for solving the third problem is as follows: The diameter of the hole is set at D, which satisfies the above-described relation with respect to L that allows the lens aberration to be reduced to satisfy the performance of the device. The above-described description has been given concerning the embodiments. To those who are skilled in the art, however, it is apparent that the present invention is not limited thereto, and that various modifications and amendments can be made within scopes of the spirit of the present invention and the scope of the appended claims. 1 electron source 2 suppression electrode 3 extraction electrode 4 magnetic-field lens 5 magnetic-field lens 6 conversion electrode 7 EXB filter 8 deflection coil 9 objective lens 10 control electrode 11 sample 12 sample stage 13 secondary-electron detector 14 image output terminal 15 constant current power-supply 16 power-supply 17 extraction voltage power-supply 18 electron-gun acceleration power-supply 19 image processing unit 20 control electrode power-supply 21 retarding power-supply 22 control electrode 23 equipotential-line distribution 24 support stages 25 boosting power-supply 26 control electrode 27 equipotential-line group 28 sample stage 29 primary electron beam 30 equipotential-line group 31 dimension 32 sample stage 33 dimension 34 equipotential-line group 35 control-electrode voltage initial value 36 graph for control-electrode voltage control 37 graph for control-electrode voltage control 38 graph for electrification-quantity change 39 graph for electrification-quantity change 40 graph for electrification-quantity change 41 equipotential-line group 42 electrified area 43 secondary electrons 44 equipotential lines representing potential barrier 45 equipotential-line group 46 electrified area 47 secondary electrons 48 equipotential-line group 49 electrified area 50 equipotential-line group 51 secondary electrons 52 equipotential lines representing potential barrier 53 equipotential-line group 54 electrified area 55 secondary electrons 56 equipotential-line group
050230441	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is generally related to nuclear reactors and more particularly to nuclear reactor control mechanisms. 2. General Background In nuclear reactors, control mechanisms are required to prevent excessive reactivity, to maintain specific levels of reactivity during operations, and to provide power shaping within the core for the most efficient operation. A second independent control mechanism is usually employed for emergency shutdown. Control mechanisms may be put into four general categories depending upon their basic operating principle: 1) insertion/removal of a fissile, poison, or moderator material into or from the active core region; 2) reflection of leaking neutrons back into the system by variable reflectors, shutters, or rotating drums; 3) geometry changes as in a split core or "godiva" type reactor; and 4) flux shadowing by moving internal parts made of alternating regions of different neutronic materials such as fuel, moderator, or absorber. This movement results in isolation of some core active region from the rest. Patented devices for controlling reactors by the flux shadowing principle of which applicant is aware include the following. U.S. Pat. No. 2,852,458 discloses coaxial cylinders designed to move rotatably and translatably relative to each other. The cylinders have circumferential sections of material having different neutron absorbing characteristics whereby the movements change the neutron flux shadowing effects. U.S. Pat. No. 2,898,281 discloses control rods disposed adjacent and parallel to each other with each rod having equal length sections of neutron absorbing and permeable materials and means for longitudinally positioning the rods relative to each other. U.S. Pat. No. 3,103,479 discloses a control rod formed from different layers of neutron absorbing material. U.S. Pat. No. 3,347,747 discloses the use of hollow tubes that house neutron absorbing balls wherein the distribution of the balls in the tubes is controlled by fluid flow through the tubes. U.S. Pat. No. 3,485,717 discloses the use of a cruciform control element formed from tubes having different cross-sectional neutron absorption properties. U S. Pat. No. 4,707,329 discloses a control rod with inner and outer cylindrical members movable relative to each other and each having alternating poison and nonpoison regions. Existing control mechanisms are configured in the vertical direction only and most provide only local reactivity changes. No control mechanism exists that divides the core region into halves to provide global power control. SUMMARY OF THE INVENTION The present invention addresses the above need in a straightforward manner. What is provided is an assembly for controlling the release of neutrons in a nuclear reactor formed from at least two disks. The disks are machined with identical surface hole patterns such that rotation of one of the disks relative to another causes the hole pattern to open or close. The assembly is positioned at the center of the reactor core such that the disks are coaxial with the reactor core and divide it into two halves. The disks may be made of absorber, moderator, or neutronically transparent material(material that allows the passage of neutrons therethrough), with the holes being a void or having fissile material therein. Rotation of the disks relative to each other to open or close the hole pattern results in a variable attenuation of the incident neutron current resulting in a flux shadowing effect.
047132124	abstract	Apparatus and process for supervising and controlling the operations of loading and unloading of fuel of a nuclear reactor comprising an information processor 30 formed from several units. A treatment unit 31 receives control signals giving notably the position, the speed, the load of machines 7 and 16 operating the loadings and unloadings of groups in the core 2, the reactor pool 3, and the spent fuel pit 14. A programmable unit 34 furnishes command signals, previously recorded, representing the loading sequence. The command and control signals are treated in a central calculating unit 35 which, while considering the information furnished by the permanent memory unit 32 and by the temporary memory unit 33 gives on one hand the coordinates of all sites for the groups, and on the other hand the coordinates of the places of the movable elements as well as the identification marks and positions of each group, compares the different signals received, and according to their coincidence, authorizes or arrests the directed movement. The temporary memory unit 33 saves the last position acquired while erasing the previously occupied positions, while the control box 37 records all of the movements executed.
	description	This application is based upon and claims the benefit of priority from Japanese Patent Application Nos. 2017-22319 filed on Feb. 9, 2017 and 2017-217136 filed on Nov. 10, 2017; the entire contents of all of which are incorporated herein by reference. The embodiments of the present invention relate to a fuel assembly, a core design method and a fuel assembly design method of a light-water reactor. Generally, a nuclear reactor is operated such that fuel excess reactivity becomes zero at the EOC (End of Cycle) in a light-water reactor fuel assembly and a light-water reactor core. In a boiling water reactor (BWR), concentration control is performed such that the neutron absorption capacity of a burnable poison such as gadolinium oxide (gadolinia) is fully burned out at the EOC. There are cases where thermal characteristics of the core are improved for an initial loading core, which is a first cycle core of the BWR plant, by intentionally making the burnable poison of a minor proportion of the fuel unburned, while compensating lack of excess reactivity with the remaining fuel. In a pressurized water reactor (PWR), concentration control is performed such that a boric acid concentration in chemical shim is zero at the EOC. Fissile material enrichment is controlled according to a target discharging burnup (same meaning as “achievement burnup”) etc., and thus excessively high enrichment is not used. Further, when spent nuclear fuel is recycled, the above-mentioned light-water reactor fuel and the fuel used in the light-water reactor core are discharged from the core and then reprocessed. Then, uranium and plutonium isotopes are extracted for reuse, and minor actinides are disposed of as high-level radioactive waste. The minor actinides have high toxicity, so that particularly harmful minor actinides are separated by a reprocessing method called partitioning. The separated minor actinides are added to MOX (Mixed Oxide) fuel and burned in a fast reactor or subjected to irradiation in an accelerator with the minor actinides as a target to be transmutation into a nuclide with low toxicity. As described above, so-called “partitioning and transmutation” is considered to be performed. When once-through cycle is adopted (that is, nuclear fuel recycling is not performed), spent fuel is subjected to final disposal as it is. In the once-through cycle, a process like the above-mentioned “partitioning and transmutation” is not performed, so that the toxicity of the minor actinides is not reduced. On the other hand, an intentional use of high-enrichment uranium fuel allows reduction of the production of the minor actinides. This is because using uranium fuel having a high uranium 235 enrichment increases the rate of nuclear fission reaction by uranium 235 to reduce the rate of absorption reaction caused by uranium 238 to thereby reduce reduction of the production of the minor actinides. However, an increase in the uranium 235 enrichment increases excess reactivity, with the result that the excess reactivity may exceed a reactivity worth given by a reactivity control devices such as control rods, which may make it hard to control the reactivity. The increase in the excess reactivity to be brought about by the increase in the uranium enrichment can be suppressed by using a burnable poison. The burnable poison can also be used effectively for a fuel assembly whose uranium enrichment is increased for reduction of the toxicity of the minor actinides. However, a large number of complicated calculations need to be performed for determination of the concentration or the number of the burnable poison-containing fuel rods, and thus effective design has heretofore not been made. The embodiments of the present invention have been made to solve the above problems, and the object thereof is to reduce the excess reactivity when the uranium enrichment is increased in a light-water reactor. According to an embodiment, there is presented a design method for a fuel assembly of a light-water reactor, which includes a plurality of fuel rods arranged in parallel separated by a distance in a direction perpendicular to the longitudinal axis of the fuel rods, the fuel rod including a fuel clad and a fuel in the fuel clad, the fuel containing material based on uranium dioxide containing enriched uranium 235, some of the fuel rods including a burnable poison in the fuel, the method comprising: accumulating a determined fuel data investigated by analyses or experiments, showing that each of a combination of p·n/N and e is feasible as the core or is not approved as the core, wherein N is an integer equal to or greater than 2 and a number of the fuel rods in the fuel assembly, n is a number of the fuel rods containing the burnable poison and an integer equal to or greater than 1 and less than N, p is a ratio wt % of the burnable poison in the fuel, and e is an enrichment wt % of the uranium 235 contained in all of the fuel rods in the fuel assembly; formulating a criterion formula which determines whether a combination of p·n/N and e is feasible as a core or is not feasible as a core and is formulated based on the determined fuel data; and determining whether a temporarily set composition of the fuel assembly is approved as a core or is not approved as a core based on the criterion formula. According to an embodiment, there is presented a design method for a core of a light-water reactor, which includes a plurality of fuel assemblies arranged in parallel and arranged into a square lattice array separated by a distance in a direction perpendicular to the longitudinal axis of the fuel assemblies, a reactivity control device in the distance between the fuel assemblies, a plurality of fuel rods arranged in parallel separated by a distance in a direction perpendicular to the longitudinal axis of the fuel rods in the fuel assembly, the fuel rods including a fuel clad and a fuel in the fuel clad, the fuel containing material based on uranium dioxide containing enriched uranium 235, some of the fuel rods including a burnable poison in the fuel, the method comprising: accumulating a determined fuel data investigated by analyses or experiments, showing that each of a combination of p·n/N and e is approved as the core or is not approved as the core, wherein N is an integer equal to or greater than 2 and a number of the fuel rods in the fuel assembly, n is a number of the fuel rods containing the burnable poison and an integer equal to or greater than 1 and less than N, p is a ratio wt % of the burnable poison in the fuel, and e is an enrichment wt % of the uranium 235 contained in all of the fuel rods in the fuel assembly; formulating a criterion formula which determines a combination of p·n/N and e is approved as a core or is not approved as a core and is formulated based on the determined fuel data; and determining whether a temporarily set composition of the fuel assembly is approved as a core or is not approved as a core based on the criterion formula. According to an embodiment, there is presented a fuel assembly of a light-water reactor comprising: a plurality of fuel assemblies arranged in parallel and arranged into a square lattice array separated by a distance in a direction perpendicular to the longitudinal axis of the fuel assemblies; a plurality of fuel rods arranged in parallel separated by a distance in a direction perpendicular to the longitudinal axis of the fuel rods in the fuel assembly; a fuel clad included in the fuel rods; a fuel included in the fuel rods and covered by the fuel clad and containing material based on uranium dioxide containing enriched uranium 235, wherein some of the fuel rods contain a burnable poison in the fuel, and p, n, N and e satisfy a formula: 0.57 e−1.8<p·n/N<0.57 e−0.8, wherein N is an integer equal to or greater than 2 and a number of the fuel rods in the fuel assembly, n is a number of the fuel rods containing the burnable poison and an integer equal to or greater than 1 and less than N, p is a ratio wt % of the burnable poison in the fuel, and e is an enrichment wt % of the uranium 235 contained in all of the fuel rods in the fuel assembly. Hereinafter, fuel assemblies, core design methods, and fuel assembly design methods of a light-water reactor according to embodiments of the present invention will be described with reference to the accompanying drawings. While the following description will be given mainly targeting a boiling water reactor, the present invention is applicable also to a pressurized water reactor. FIG. 1 is a plan cross-sectional view illustrating one control rod, four fuel assemblies surrounding the control rod, and the surrounding thereof in a BWR core according to an embodiment of the present invention. In FIG. 1, a detailed structure of each fuel assembly is omitted. FIG. 2 is a view illustrating in detail an example of the internal configuration of the fuel assembly in the BWR core according to the embodiment of the present invention. More specifically, FIG. 2 is a detail schematic view of part II of FIG. 1. FIG. 3 is a view illustrating in detail another example (different from the example of FIG. 2) of the internal configuration of the fuel assembly in the BWR core according to the embodiment of the present invention. More specifically, FIG. 3 is a detail schematic view of part II of FIG. 1. FIG. 4 is a plan cross-sectional view illustrating the structure of a fuel rod constituting a BWR fuel assembly according to the embodiment of the present invention. In the BWR core of the embodiment, several hundreds of fuel assemblies 10 are arranged in a square grid in a horizontal plane. The enrichment of uranium is, e.g., 3.8% on average in normal uranium fuel assemblies. In Japan, for example, facilities for conventional normal uranium fuel assemblies are designed assuming that the uranium enrichment is less than 5.0%. On the other hand, in the light-water reactor fuel assemblies 10 of the present embodiment, the uranium enrichment is 5.0% which is higher than that in the normal uranium fuel assemblies. In the following description, the uranium enrichment is assumed to be 5.0%, but this is not limitative. As described later, the uranium enrichment may be higher or lower than 5.0% as long as effects can be obtained. In each fuel assembly 10, a plurality of fuel rods 11 and 12 vertically extending in parallel to each other are arranged in a square grid (9 by 9 in the examples of FIGS. 2 and 3) in a horizontal plane. The outer periphery of the fuel assembly 10 is surrounded by a substantially square-cylindrical channel box 13 which extends in the vertical direction. Two water rods 14 (marked by “W” in FIGS. 2 and 3) are disposed at the center of the fuel assembly 10. The water rods 14 each have a hollow cylindrical shape extending in the vertical direction inside of which water flows. Although the water rods 14 are two circular tubes in the examples of FIGS. 2 and 3, the number of the water rods 14 may be one or three or more, and the shape thereof may be a square-cylindrical tube. Each of the fuel rods 11 and 12 includes a circular cladding tube 20 extending vertically and nuclear fuel material 21 enclosed in the cladding tube 20. The nuclear fuel material 21 contains uranium oxide containing enriched uranium. The nuclear fuel material 21 is normally formed into a plurality of columnar pellets, and the pellets are axially stacked in the cladding tube 20. The fuel rods 12 are a fuel rods containing burnable poison (marked by “G” in FIGS. 2 and 3), and the nuclear fuel material 21 in the fuel rod 12 contains a burnable poison (e.g., gadolinia). The fuel rods 11 are fuel rods not containing burnable poison (marked by “R” in FIGS. 2 and 3), and the nuclear fuel material 21 in the fuel rods 11 do not contain burnable poison. Control using a control cell core is considered as reactivity control for the BWR. This is core design in which the number of unit cells into each of which a control rod is inserted at normal operation time is made small. Each of the control rods used for power control at normal operation time is surrounded by four fuel assemblies to obtain one control cell. Specifically, in the control cell, a control rod (reactivity control device) 30 having a cross shape in the horizontal cross section and extending vertically is disposed at the center of mutually adjacent 2 by 2 arrayed fuel assemblies 10. At normal operation of the nuclear reactor, light water is filled outside the channel boxes 13. The control rods 30 are inserted and withdrawn in the vertical direction in/from the water outside the channel boxes 13 so as to be able to control nuclear reactor power. A local power range monitor (LPRM) 31 as a nuclear instrumentation device is disposed outside the channel boxes 13 at a diagonal position with respect to the center of the control rod 30. In general, the thermal conductivity of burnable poison such as gadolinia is lower than that of uranium oxide. Thus, the enrichment of uranium 235 in the nuclear fuel material 21 enclosed in the burnable poison-containing fuel rod 12 is made lower than the maximum value of the enrichment of uranium 235 in the nuclear fuel material 21 included in the fuel assembly 10. With this configuration, it is possible to avoid the thermal power of the burnable poison-containing fuel rods 12 from being greater than thermal power of the other fuel rods to thereby prevent the burnable poison-containing fuel rods 12 from being excessively heated. As illustrated in FIGS. 2 and 3, in the fuel assembly 10, the burnable poison-containing fuel rods 12 may not be disposed at positions adjacent to the control rod 30. This configuration prevents reduction in the absorption rate that the control rod 30 absorbs thermal neutrons, which are likely to contribute to nuclear fission reaction, whereby a core can be designed without involving a reduction in reactivity worth of the control rod 30. Further, as illustrated in FIGS. 2 and 3, preferably, in the fuel assembly 10, the burnable poison-containing fuel rods 12 are not disposed adjacent to the nuclear instrumentation device 31. With this configuration, a core can be designed without involving a reduction in accuracy of the nuclear instrumentation device 31. Further, as illustrated in FIGS. 2 and 3, in the fuel assembly 10, at least one burnable poison-containing fuel rod 12 may not be adjacent, on at least its one surface of the four surfaces corresponding to four directions along which the square-grid shaped fuel rods are arranged, to the other fuel rods 11 or 12. That is, at least one burnable poison-containing fuel rod 12 is disposed adjacent to, e.g., the water rod 14 or the channel box 13 at the outermost peripheral portion of the assembly. With this configuration, thermal neutrons by which the burnable poison is likely to undergo absorption response often collide with the burnable poison, thereby increasing the rate of the neutrons absorbed by the burnable poison. This increases the reactivity worth of the burnable poison to thereby significantly suppress the excess reactivity. Further, as illustrated in FIGS. 2 and 3, in the fuel assembly 10, at least some burnable poison-containing fuel rods 12 may be disposed adjacent to each other. By adjacently disposing the burnable poison-containing fuel rods 12, the number of collisions of the burnable poison on adjacent surfaces with thermal neutrons is reduced. This decreases the burning speed of the burnable poison, with the result that the reactivity of the burnable poison continues longer than in a case where the burnable poison-containing fuel rods 12 are not disposed adjacent to each other. FIG. 5 is an example of a graph illustrating results of feasibility of the core which is determined for various combinations of burnable poison average mass ratio and uranium enrichment in the BWR fuel assembly according to the embodiment of the present invention by applying analysis calculation thereto. The burnable poison average mass ratio is represented by (burnable poison concentration p)·(burnable poison-containing fuel rod number ratio). The burnable poison-containing fuel rod number ratio is represented by (the number n of burnable poison-containing fuel rods/total number N of the fuel rods included in the fuel assembly). Accordingly, the burnable poison average mass ratio is represented by (p·n/N). The criterion for the feasibility of the core is whether the fuel excess reactivity can be controlled by a reactivity control device such as a control rod, which may make it hard to control the reactivity or not. The fuel is feasible when its excess reactivity is less than, or equal to the reactivity which the control rods can control. The fuel is not feasible when its excess reactivity is more than the reactivity which the control rods can control. In the nuclear characteristics evaluation analysis of FIG. 5, the same configuration as that of the fuel assembly illustrated in FIGS. 2 and 3 is assumed. By assuming that an infinite number of fuel assemblies are arranged in a grid in horizontal directions, feasibility of the core can be determined. The burnable poison is assumed to be gadolinium. In the nuclear characteristics evaluation analysis of FIG. 5, the fuel rods in the fuel assembly are arranged in a 9 by 9 grid. However, nuclear characteristics (neutron spectrum) of the fuel assembly have a large influence on core characteristics, so that substantially the same results as those of FIG. 5 are obtained irrespective of the number of the fuel rods in the fuel assembly if a hydrogen-uranium ratio of the fuel assembly is the same. For example, even when the fuel rods in the fuel assembly are arranged in a 10 by 10 grid or an 11 by 11 grid, substantially the same results as those of FIG. 5 are obtained. In the example of FIG. 2, the number n of burnable poison-containing fuel rods 12 is 24, and the total number N of the fuel rods included in the fuel assembly is 74; and in the example of FIG. 3, the number n is 36, and the number N is 74. The uranium enrichment is assumed to be “e”. In this case, whether the core is feasible or not was determined for various combinations of the burnable poison average mass ratio (p·n/N) and uranium enrichment e by performing analysis. As a result, two straight lines were obtained as the boundary condition determining whether the core is feasible or not as illustrated in FIG. 5. That is, a range where the burnable poison average mass ratio (p·n/N) is larger than (0.57 e−1.8) and smaller than (0.57 e−−0.8) is the optimum ratio of burnable poison addition. That is, a criterion formula (1) indicating a requirement for making the core feasible in this case is represented by the following expression:0.57e−1.8<(p·n/N)<0.57e−0.8 (1) Thus, actual design of the fuel assembly can be made using the criterion formula (1). In order to design various types of fuel assemblies different in conditions, whether the core is feasible or not is determined for a sufficient number of various combinations of burnable poison average mass ratio (p·n/N) and uranium enrichment e by performing analysis or experiment meeting the individual conditions, whereby data (results) according to the individual conditions are accumulated, and thus the graph as illustrated in FIG. 5 can be obtained. Based on the obtained graph, criterion formulas corresponding to the criterion formula (1) in individual conditions can be obtained. The following criterion formula (2) is considered to be more appropriate in general.a1·e−b<(p·n/N)<a2·e−c (2)In the above expression, a1, a2, b, and c are each a positive constant, and a1≥a2. Although the above criterion formulas (1) and (2) are linear expressions, they may be quadratic expressions or other type of expressions. FIG. 6 is a graph illustrating an example of an analysis result on the relationship between a cycle burnup and excess reactivity when the fuel assembly falling within the optimum range of the burnable poison average mass ratio of FIG. 5 is burned in a BWR. FIG. 7 is a graph schematically illustrating a change in a fuel assembly infinite multiplication factor when the uranium enrichment is increased in a design of the fuel assembly according to the embodiment of the present invention. FIG. 8 is a graph schematically illustrating a change in the number of burnable poison-containing fuel rods corresponding to a change in the reactivity of the burnable poison in the design of the fuel assembly according to the embodiment of the present invention. Although a straight line is shown in FIGS. 7 and 8 each, these graphs are schematic, and the change may not be represented by straight lines. FIG. 10 is a graph illustrating values of top ten control rods in terms of the reactivity worth in a control cell core of a typical conventional BWR. As illustrated in FIG. 10, the control rod reactivity worth of the control cell is somewhat above 0.1% Δk at a maximum. In an advanced boiling water reactor (ABWR), up to 29 control cells are provided, so that the excess reactivity that can be controlled by the control cell is 3% Δk or less. By designing a combination of the burnable poison average mass ratio (p·n/N) and uranium enrichment e of the fuel assembly 10 so as to satisfy the criterion formula (1) or (2), the excess reactivity during a nuclear reactor operation cycle can be designed to be 0 to 3.0% Δk which is a range achievable under the control of the control rod, as illustrated in FIG. 6. This is because a reactivity variation (ΔS(Δe)) when the uranium enrichment e of FIG. 7 is changed to (e+Δe) coincides with a reactivity variation (ΔS(ΔGd)) of FIG. 8 as an absorbing material changed with respect to the number n of burnable poison-containing fuel rods in the fuel assembly and the average added mass ratio. That is, by changing the total amount of the burnable poison by ΔGd, the change Δe of the uranium enrichment e can be compensated. Next, a method of designing a light-water reactor fuel assembly using the above-described investigation results will be described referring to FIG. 9. FIG. 9 is a flowchart illustrating a procedure of the fuel assembly design method according to the embodiment of the present invention. First, the configuration of the light-water reactor fuel assembly is assumed within a predetermined range, and feasibility of the core is determined for various combinations of burnable poison average mass ratio (p·n/N) and uranium enrichment e by performing analysis calculation or experiment, whereby core feasibility determination data are accumulated as illustrated in FIG. 5 (step S10). Then, like the above criterion formula (1) or (2), a core feasibility criterion formula is decided for various combinations of burnable poison average mass ratio (p·n/N) and uranium enrichment e based on the core feasibility determination data obtained in step S10 (step S11). Then, a specific combination of a burnable poison average mass ratio (p·n/N) and a uranium enrichment e of the light-water reactor fuel assembly is assumed (step S12), and the feasibility of the core is determined for the assumed combination based on the core feasibility criterion formula obtained in step S11 (step S13). When the determination result in step S13 is “NO” (unfeasible), the combination of the burnable poison average mass ratio (p·n/N) and the uranium enrichment e is changed, and steps S12 and S13 are executed again. On the other hand, when the determination result in step S13 is “YES” (feasible), design of the fuel assembly is determined by the combination of the burnable poison average mass ratio (p·n/N) and the uranium enrichment e at that time (step S14). According to the above-described design method, the excess reactivity when uranium enrichment is increased in a light-water reactor can be reduced. Further, by deciding the core feasibility criterion formula in advance, the feasibility of the core can be easily checked when various parameters are changed in specific design of the fuel assembly, making it possible to speed up design work while saving manpower. In the embodiment, the burnable poison to be added to nuclear fuel material is preferably a compound containing gadolinium, a compound containing erbium, or a compound containing boron. When the burnable poison to be added to nuclear fuel material is gadolinia, the maximum mass ratio thereof is preferably lower than 20 mass %. This is because when the maximum mass ratio of gadolinia is equal to or higher than 20 mass %, a mixture of gadolinia and uranium oxide is less likely to form a solid solution. As the burnable poison in the embodiment, gadolinium obtained by concentrating gadolinium with odd mass number (e.g., 155 or 157) is preferably used. This increases the absorption cross-sectional area of gadolinium, making it possible to reduce the additive amount of the burnable poison. Further, by installing the fuel assembly in the light-water reactor core including the control cell, a reactivity change range due to operation of the control rod can be reduced, making it possible to easily satisfy thermal soundness of the fuel assembly in the light-water reactor core. While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
046831142	summary	The present invention relates to nuclear fuel pellets containing a boron-containing burnable absorber as a glazed coating thereon and a composition and method for forming such a glazed coating. BACKGROUND OF THE INVENTION It is well-known that the incorporation, in various manner, of a burnable absorber with nuclear fuel pellets, which enables the use of excessive amounts of fuel in a reactor during the initial life of the fuel, can extend the life of the fuel elements. In some instances, the burnable absorber is mixed directly with the fuel and integrated therewith, while in other instances, a burnable absorber coating may be applied to the surface of fuel pellets, or discrete forms of a burnable absorber may be interspersed between conventional fuel pellets, or otherwise located within the cladding for the nuclear fuel. In U.S. Pat. No. 3,122,509, for example, coherent nuclear fuel elements are disclosed where conventional base glass compositions are admixed with a nuclear fuel or other nuclear material, as a binder glass. Boron carbide, for example, may be blended with a base glass of conventional glass-making materials, and the blended mixture placed in a metal cladding tube and compacted. The compact is then heated to sinter the glass and boron carbide together in a coherent form. The coherent conventional glass-boron carbide cylinders formed were heated to give cylinders that showed a uniform distribution of boron carbide within the cylinders without voids. In effect, this reference discloses the use of conventional glass components for use as a binder, in the formation of an actinide oxide, or other additives, in the formation of fuel elements, or other elements, such as cylindrical fuel shapes, or formation of cylindrical burnable absorber shapes. Since problems exist with the formation and use of fuel elements that incorporate a burnable absorber directly within the pellet or element, it has been proposed to provide the burnable absorber in the form of a coating on the pellet. As disclosed in U.S. Pat. No. 3,427,222, which is assigned to the assignee of the present invention, a sintered nuclear fuel pellet may have a coating of boron carbide, or other burnable absorber, formed thereon by fusion bonding of the burnable absorber, as a coating, on the surface of the fuel pellet. As disclosed therein, the coating may be formed by (1) plasma spraying or flame spraying of the burnable absorber with optional addition of uranium dioxide or other ceramic oxides, (2) dipping the pellets in a slurry of the burnable absorber and a ceramic binder such as zirconium silicate or sodium tetraborate and firing, (3) vapor coating the pellets, or (4) electron beam bombardment of a burnable absorber on the pellets. Coatings formed by application of a mixture of boron carbide with a binder such as zirconium silicate or by application of sodium tetraborate, however, have resultant problems. Where a coating of a mixture of boron carbide and zirconium silicate was formed, the resultant coating was not adequately stable, and peel tests, using Scotch tape, resulted in removal of the coating. If higher temperatures, in excess of 1000.degree. C. were to be used to sinter the material to improve adhesion, the boron carbide will react with both the uranium dioxide of the pellets and possibly with the zirconium silicate resulting in loss of boron as an absorber in the finished pellet. Where a coating of sodium tetraborate was formed, while the resultant coating showed excellent bonding and passed a peel test, the coatings were not moisture resistant and hydrogen pickup was evident indicating significant moisture adsorption. In addition, the coating has a low melting point (.ltoreq.750.degree. C.) and during normal reactor operation, it would be expected to slump and possible adhesion/reaction of the coating with the cladding will occur. The present inventors are also aware of the earlier work disclosed in applications, "Burnable Absorber Coated Nuclear Fuel", Ser. No. 468,788, filed Feb. 22, 1983 in the names of K. C. Radford and B. H. Parks; and "Coating a Uranium Dioxide Nuclear Fuel with a Zirconium Diboride Burnable Poison", Ser. No. 468,743, also filed Feb. 22, 1983 in the name of Walston Chubb, which relate to coated nuclear fuel pellets, both of which applications are assigned to the assignee of the present invention. It is an object of the present invention to provide a glaze coating composition for use in coating of nuclear fuel pellets with a boron-containing burnable absorber which forms a coating having a high melting point and a low propensity for moisture adsorption. It is another object of the present invention to provide a method for forming nuclear fuel pellets having a burnable absorber combined therewith in the form of a coating of a boron-containing burnable absorber encapsulated in a specially developed boron-containing glass composition. SUMMARY OF THE INVENTION Nuclear fuel pellets having a burnable absorber combined therewith are formed by combining discrete particles of a boron-containing burnable absorber and a special boron-containing glass composition to form a coating mixture, applying the coating mixture to the surface of the pellets, heating the pellets having the coating mixture thereon to an elevated temperature, between 900.degree.-1100.degree. C., for 5 to 15 minutes, to melt the boron-containing glass and encapsulate the boron carbide particles, without enabling reaction between the boron carbide with the glass or fuel, and coating the pellets. The resultant coated pellets have a glaze coating of boron carbide particles encapsulated in a boron-containing glass and the coating exhibits excellent adhesion to the pellets and excellent resistance to moisture adsorption. The burnable absorber-containing coating composition used to coat the fuel pellets is composed of discrete particles of 20-80 percent by weight of a boron-containing burnable absorber, such as boron carbide, and 80-20 percent by weight of a specific boron-containing glass composition. Preferably, the discrete boron carbide particles are of a size less than 10 microns in diameter and the boron-containing glass particles are of a size less than 5 microns in diameter, which enables intimate mixing thereof, and after firing, each of the boron carbide particles are coated with a thin film of glass, and encapsulated in a thin glaze coating. These fine particle sizes enable the use of a higher boron carbide content than is usable when the particle size is somewhat larger, but still less than 325 mesh.
	claims	1. A computer-implemented method of compliance testing, said method comprising:inputting data from at least one analytical instrument or controlling software of an analytical instrument to a system;converting said inputted data of said at least one analytical instrument or said controlling software to a technology-neutral format;performing one or more calculations on said inputted data, using a computer-implemented analytical instrument compliance system, to produce one or more outputs;selecting from said one or more outputs to populate a final report; wherein said one or more outputs are standardized and are directly comparable to outputs resultant from said method carried out on another set of one or more other analytical instruments or controlling softwares for analytical instruments, irrespective of manufacturer or model of said other analytical instruments;comparing at least one of said outputs to first and second test limits indicative of said instrument's performance; andreporting compliance status of said at least one output based on said comparing to said first test limit and to said second test limit. 2. The method of claim 1, wherein said data is converted to said technology neutral format prior to said inputting. 3. The method of claim 1, wherein said data is converted to said technology neutral format after said inputting. 4. The method of claim 1, wherein at least one of said first and second test limits is user-settable. 5. The method of claim 1, wherein one of said first and second test limits is automatically preset. 6. The method of claim 1, wherein said performing one or more calculations comprises data reduction, said data reduction being carried out by a data reduction engine, wherein the same data reduction engine may be used for data received from multiple analytical instruments. 7. The method of claim 6, further comprising inputting results of said data reduction to a calculation engine and performing at least one further calculation based upon said inputted results. 8. The method of claim 1, wherein said calculations are performed to answer a series of questions relating to one or more performance tests designed to determine compliance of said analytical instrument or software under consideration with a set of predefined criteria. 9. A computer-implemented method of compliance testing, said method comprising:inputting data from at least one analytical instrument or controlling software of an analytical instrument to a system;performing one or more calculations on the inputted data, using a computer-implemented analytical instrument compliance system, to produce one or more outputs;selecting from said one or more outputs to populate a final report; wherein the one or more outputs are standardized and are directly comparable to outputs resultant from said method carried out on another set of one or more other analytical instruments or controlling software for analytical instruments, irrespective of manufacturer or model of the other analytical instruments;comparing at least one of said outputs to first and second test limits; andreporting compliance status of said at least one output based on said comparing to said first test limit and to said second test limit;wherein said performing one or more calculations are performed according to instructions instantiated as forms. 10. The method of claim 9, wherein said forms contain data generated from at least one of interactive manual input, information detected by a system performing said method, a computerized data system of an instrument from which data is being converted, and calculated, reduced data. 11. The method of claim 9, wherein said forms include launch points for executables that perform functions performed by said method. 12. The method of claim 9, further comprising storing said outputs of performed calculations on the forms. 13. The method of claim 9, further comprising storing said forms in a database as a repository of processed data. 14. The method of claim 13, further comprising identifying an audit trail based upon forms and data stored in the database. 15. A computer-implemented method of compliance testing, said method comprising:inputting data from at least one analytical instrument or controlling software of an analytical instrument to a system;performing one or more calculations on said inputted data, using a computer-implemented analytical instrument compliance system, to produce one or more outputs;selecting from said one or more outputs to populate a final report; wherein said one or more outputs are standardized and are directly comparable to outputs resultant from said method carried out on another set of one or more other analytical instruments or controlling softwares for analytical instruments, irrespective of manufacturer or model of said other analytical instruments;comparing at least one of said outputs to first and second test limits indicative of said instrument's performance, wherein said comparing is performed according to instructions instantiated as forms; andreporting compliance status of said at least one output relative to based on said comparing to said first test limit and to said second test limit. 16. The method of claim 15, wherein at least one of said forms contains said first and second test limits. 17. The method of claim 16, wherein at least one of said first and second test limits is user-specifiable. 18. A computer-implemented method of compliance testing, said method comprising:inputting data from at least one analytical instrument;converting said inputted data to a technology-neutral format if said inputted data is not already in said technology-neutral format;performing one or more calculations on said inputted data in said technology-neutral format, using a computer-implemented analytical instrument compliance system, to produce one or more outputs;comparing at least one of said outputs to first and second test limits indicative of said instrument's performance; andreporting compliance status of said at least one output based on said comparing to said first test limit and to said second test limit. 19. A method of compliance testing at least one of analytical instrumentation and analytical instrumentation software, said method comprising:displaying a test protocol form configured for said compliance testing of said at least one of analytical instrumentation and analytical software on a user interface and prompting a user to input information regarding a test for qualifying a result of the test;prompting at least one analytical instrument or analytical instrument software associated with an analytical instrument to initiate the test protocol, either in response to an input by the user into the test protocol displayed on the user interface, or in response to results from another analytical instrument in response to a test protocol run on the another analytical instrument;automatically calculating results of the test protocol run on the at least one analytical instrument; andoutputting status of the results as determined by comparing said results to at least one set of dual test limits. 20. The method of claim 19, further comprising inputting a first test limit value, by a user, of at least one of said at least one set of dual test limits. 21. The method of claim 20, wherein a second test limit value of said at least one set of dual test limits in which said first test limit was user inputted, is automatically preset. 22. The method of claim 21, wherein said first test limit is more stringent than said second test limit. 23. The method of claim 19, further comprising selecting from said one or more outputs to populate a final report; wherein said one or more outputs are standardized and are directly comparable to outputs resultant from said method carried out on another set of one or more other instruments and/or software, irrespective of manufacturer or model of the other analytical instruments. 24. A system for standardizing characterizations of at least one of analytical hardware and controlling software during compliance testing, said system comprising:a data reduction engine configured to reduce data outputted by an analytical instrument;a calculation engine configured to perform at least one calculation on at least one of said data outputted by an analytical instrument and the reduced data to produce one or more outputs required for a set of predefined criteria; andinteractive forms comprising computer executable format executable by said system to provide instructions executable by said data reduction engine and said calculation engine, said forms providing procedural information including calculation instructions;wherein said interactive forms provide instructions for calculating outputs to answer one or more questions relating to one or more performance tests designed to determine compliance of the at least one of analytical instrument and controlling software. 25. The system of claim 24, wherein said data reduction engine reduces said data to a technology-independent, reduced metadata set. 26. The system of claim 24, wherein at least one of said interactive forms includes dual test limits. 27. The system of claim 24, further comprising algorithms for converting data from a native format as outputted by an analytical instrument to a technology-neutral format. 28. The system of claim 24, further comprising an automatic detection engine configured to determine at least one of instrument and controlling software specific information to automatically characterize said at least one of said instrument and said controlling software. 29. The system of claim 24, wherein said outputs are stored on said forms. 30. The system of claim 29, further comprising means for mining said forms to extract metadata needed to produce a final report. 31. The system of claim 30, further comprising means for compiling the extracted metadata into the final report. 32. The system of claim 24, further comprising a user interface configured to facilitate manual input to at least one of said interactive forms by a user. 33. A non-transitory computer readable medium carrying one or more sequences of instructions for compliance testing, wherein execution of said one or more sequences of instructions by one or more processors causes said one or more processors to perform:inputting data from at least one analytical instrument;converting said inputted data to a technology-neutral format if said inputted data is not already in said technology-neutral format;performing one or more calculations on said inputted data in said technology-neutral format to produce one or more outputs,comparing at least one of said outputs to first and second test limits indicative of said instrument's performance; andreporting compliance status of said at least one output based on said comparing to said first test limit and to said second test limit. 34. A computer-implemented method of compliance testing at least one of instrumentation and software, said method comprising the steps of:inputting data from said at least one analytical instrument or software to a computer-implemented analytical instrument compliance system;performing one or more calculations on the inputted data, using the computer-implemented analytical instrument compliance system, to produce one or more outputs;comparing at least one of said outputs to first and second test limits, wherein said comparing is performed according to instructions instantiated as forms;selecting from said one or more outputs to populate a final report and reporting compliance status of said at least one output based on said comparing to said first test limit and to said second test limit;wherein the at least one output is standardized and are directly comparable to outputs resultant from said method carried out on another set of one or more other analytical instruments, irrespective of manufacturer or model of the other analytical instruments. 35. A system for standardizing characterizations of at least one of analytical hardware and controlling software during compliance testing, said system comprising:a data reduction engine configured to reduce data outputted by an instrument;a calculation engine configured to perform at least one calculation on at least one of said reduced data to produce one or more outputs required for a set of predefined criteria;an automatic detection engine configured to determine at least one of instrument specific information to automatically characterize said instrument; andinteractive forms comprising computer executable format that provides instructions executable by said data reduction engine, said calculation engine and said automatic detection engine, said forms providing procedural information including calculation instructions. 36. A computer-implemented method of compliance testing, said method comprising:inputting data from at least one analytical instrument or controlling software of an analytical instrument to a computer-implemented analytical instrument compliance system;converting said inputted data to a technology-neutral format if said inputted data is not already in said technology-neutral format;performing one or more calculations on said inputted data in said technology-neutral format, using said computer-implemented analytical instrument compliance system, to produce one or more outputs; andselecting from said one or more outputs to populate a final report; wherein said one or more outputs are standardized and are directly comparable to outputs resultant from said method carried out on another set of one or more other analytical instruments or controlling softwares for analytical instruments, irrespective of manufacturer or model of said other analytical instruments,wherein said calculations are performed to answer a series of questions relating to one or more performance tests designed to determine compliance of said analytical instrument or software under consideration with a set of predefined criteria indicative of said instrument's performance. 37. A computer-implemented method of compliance testing, said method comprising:inputting data from at least one analytical instrument or controlling software of an analytical instrument to a system;performing one or more calculations on the inputted data to produce one or more outputs;selecting from said one or more outputs to populate a final report; wherein the one or more outputs are standardized and are directly comparable to outputs resultant from said method carried out on another set of one or more other analytical instruments or controlling softwares for analytical instruments, irrespective of manufacturer or model of the other analytical instruments;comparing at least one of said outputs to first and second test limits; andreporting compliance status of said at least one output based on said comparing to said first test limit and to said second test limit;wherein said performing one or more calculations are performed according to instructions instantiated as forms; andwherein said forms contain data generated from at least one of interactive manual input, information detected by a system performing said method and software of system, a computerized data system of an instrument from which data is being converted, and calculated, reduced data.
039765431	claims	1. A temperature actuated shutdown assembly for a nuclear reactor comprising a neutron absorber, a tube disposed around said absorber and coaxial with the longitudinal axis of the absorber, said tube having a plurality of ports therein spaced around its circumference, a flange welded to the tube concentrically over each port, a bimetallic disk retained movably within each flange in the shape of a spherical cap with its inner, normally convex side composed of a layer of metal and its outer, normally concave side composed of a layer of a different metal of a higher coefficient of thermal expansion, a metal ball retained in the center of the inner layer of each disk by a retainer with the center of said metal ball aligned concentrically with and projecting partially through the port in the side of the tube thereby supporting said absorber, said metal ball being biased inwardly toward said absorber, whereby upon reaching a preset temperature, stresses will be created within at least one of the bimetallic disks; the imbalanced thermal stresses will cause at least one disk to reverse concave and convex sides thus removing the ball from the hole in the wall of the tube allowing the absorber to drop into the reactor core. 2. The combination of claim 1 wherein the outer layer of each bimetallic disk is made of stainless steel, the inner layer is made of molybdenum and the ball is made of cobalt alloy tool material. 3. The combination of claim 1 wherein the outer layer of the bimetallic disk is made of a nickel-chromium-iron alloy, and the inner layer is made of molybdenum-titanium alloy. 4. The assembly of claim 1 including means responsive to reactor power for generating heat disposed in each bimetallic disk whereby said generating means in response to an increase in reactor power will cause at least one disk's temperature to increase to the preset temperature where imbalanced thermal stresses in the disk will cause the disk to reverse conical and convex sides. 5. The heat generation means of claim 4 wherein the means is comprised of a foil of fissionable metal disposed in the bimetallic disk between the two layers thereof. 6. The heat generation means of claim 4 wherein the means is comprised of discrete nodules of an oxide of a fissionable metal dispersed within at least one of the layers of the bimetallic disk. 7. A temperature actuated shutdown assembly for a liquid metal cooled nuclear reactor comprising a hexagonal absorber rod, a hexagonal tube disposed around said absorber rod and coaxial with the longitudinal axis of the absorber rod, said tube having three ports therein located in alternate sides of the hexagonal tube, a round "L" shaped flange welded to the tube side concentrically over each of said ports, a bimetallic disk within each flange shaped as a spherical cap with the normally concave outer side of the disk composed of stainless steel and the normally convex inner side composed of molybdenum, means responsive to reactor power for generation of heat within said bimetallic disk, a helical spring trapped compressively between each flange and each disk and urging said disk toward the tube, a cobalt alloy tool material ball retained in a spherical depression in the center of the inner layer of each said disk by a retainer formed of the material of the inner layer, the bimetallic disks being retained movably against the sides of the hexagonal tube by the circular flanges with the centers of the cobalt alloy tool material balls aligned concentrically with and projecting partially through the ports in the sides of the hexagonal tube supporting a conical bottom of said absorber rod, whereby upon reaching a liquid metal coolant temperature in the range of 550.degree.C. to 770.degree.C., a condition of imbalanced, thermally induced stresses will be created within at least one of the bimetallic disks as a result of the differing thermal coefficients of expansion of the two composite metals; the imbalanced thermal stresses will cause at least one bimetallic disk to reverse concave and convex sides thus removing the ball from the hole in the side of the hexagonal tube allowing the absorber rod to slip towards the removed ball or balls thus clearing the unremoved balls or ball and dropping into the reactor core thus depressing reactor power.
	claims	1. An apparatus for transporting and/or storing high level radioactive waste comprising:an overpack body having an outer surface and an inner surface forming an internal cavity about a longitudinal axis;a base enclosing a bottom end of the cavity;a plurality of inlet ducts in a bottom of the overpack body, each of the inlet ducts extending from an opening in the outer surface of the overpack body to an opening in the inner surface of the overpack body so as to form a passageway from an external atmosphere to a bottom portion of the cavity;a columnar structure located within each of the inlet ducts, the columnar structures dividing each of the passageways of the inlet ducts into first and second channels that converge at the openings in the inner and outer surfaces of the overpack body, wherein for each inlet duct a line of sight does not exist between the opening in the inner surface of the overpack body and the opening in the outer surface of the overpack body;a lid enclosing a top end of the cavity; anda plurality of outlet ducts, each of the outlet ducts forming a passageway from a top portion of the cavity to the external atmosphere. 2. The apparatus of claim 1 wherein the lid comprises the outlet ducts, each of the outlet ducts extending from an opening in the inner surface of the lid to an opening in the outer surface of the lid. 3. The apparatus of claim 1 wherein the columnar structures have a longitudinal axis, wherein the longitudinal axis of the columnar structures are substantially parallel with the longitudinal axis of the overpack body. 4. The apparatus of claim 1 wherein for each inlet duct, the opening in the inner surface of the overpack body is aligned with the opening in the outer surface of the overpack body so that: (i) a first reference plane that is perpendicular to the longitudinal axis of the overpack body intersects both the opening in the inner surface of the overpack body and the opening in the outer surface of the overpack body; and (ii) a second reference plane that is parallel with and includes the longitudinal axis of the overpack body intersects both the opening in the inner surface of the overpack body and the opening in the outer surface of the overpack body. 5. The apparatus of claim 1 wherein the columnar structures have a longitudinal axis, the first and second channels collectively surrounding a circumference of the longitudinal axis of the columnar structures. 6. The apparatus of claim 5 wherein the longitudinal axis of the columnar structures are substantially parallel with the longitudinal axis of the overpack body. 7. The apparatus of claim 1 wherein the first and second channels are curved. 8. The apparatus of claim 1 wherein the overpack body comprises an inner shell and an outer shell concentrically arranged so that a gap exists between the inner and outer shells, the gap filled with a radiation shielding material. 9. The apparatus of claim 1 wherein for each inlet duct, the opening in the inner surface of the overpack body is aligned with the opening in the outer surface of the overpack. body so that a first reference plane that is perpendicular to the longitudinal axis of the overpack body intersects both the opening in the inner surface of the overpack body and the opening in the outer surface of the overpack body. 10. The apparatus of claim 9 further comprising a hermetically sealed canister for containing high level radioactive waste positioned within the cavity so that the first reference plane also intersects the canister. 11. The apparatus of claim 1 further comprising a hermetically sealed canister for containing high level radioactive waste positioned within the cavity so that a bottom surface of the canister is in surface contact with a top surface of the base. 12. The apparatus of claim 11 wherein the cavity has a transverse cross-section that accommodates no more than one of the canisters. 13. The apparatus of claim 1 wherein the inlet ducts have a width and a height that is at least three times the width. 14. The apparatus of claim 1 wherein the base is a baseplate connected to the overpack body. 15. The apparatus of claim 1 wherein the overpack body comprises at least six of the inlet vents arranged in a circumferentially spaced and axi-symmetric manner.
	summary
	summary
063079186	claims	1. An x-ray beam filter assembly for an imaging system, the imaging system including a detector array and an x-ray source for radiating an x-ray beam toward the detector array, said filter assembly comprising: a fixed filter portion; and a z-axis movable filter comprising a plurality of portions, wherein each portion configured to alter the x-ray beam intensity and quality. selecting a scan type; positioning the movable filter; filtering the x-ray beam through the fixed filter portion and the positioned movable filter; and performing an object scan. selecting a scan type; positioning the movable filter so the x-ray beam is filtered by the movable filter first portion; and performing an object scan. determine a scan type; position the movable filter; filter the x-ray beam through the fixed filter portion and the positioned movable filter; and perform an object scan. determine a scan type; position the movable filter so that the x-ray beam is filtered by said first portion; and perform an object scan. 2. A filter assembly in accordance with claim 1 wherein said movable filter comprises a first portion configured to alter the x-ray beam into a first beam and a second portion configured to alter the x-ray beam into a second beam. 3. A filter assembly in accordance with claim 1 further comprising a drive assembly coupled to said movable filter and configured to alter the z-axis position of said movable filter. 4. A filter assembly in accordance with claim 2 wherein said first portion comprises at least one filter material and said second portion comprises at least a first filter material. 5. A filter assembly in accordance with claim 2 wherein said first portion configured to generate a harder x-ray beam quality. 6. A filter assembly in accordance with claim 2 wherein said second portion configured to generate a softer x-ray beam quality. 7. A filter assembly in accordance with claim 4 wherein said first portion comprises a first filter material, a second filter material and a third filter material. 8. A filter assembly in accordance with claim 4 wherein said second portion comprises a first filter material and a second filter material. 9. A filter assembly in accordance with claim 5 wherein said first portion configured to perform a body scan. 10. A filter assembly in accordance with claim 6 wherein said second portion configured to perform a head scan. 11. A filter assembly in accordance with claim 7 wherein said third material is positioned between said first portion first filter material and said first portion second filter material. 12. A filter assembly in accordance with claim 8 wherein said second portion first filter material comprises graphite and said second portion second filter material comprises aluminum. 13. A filter assembly in accordance with claim 11 wherein said first portion first filter material comprises graphite, said first portion second filter material comprises aluminum, and said first portion third material comprises copper. 14. A filter assembly in accordance with claim 13 wherein said first portion third filter material has a thickness of about 75 micrometers. 15. A method for altering an x-ray beam in an imaging system, the imaging system including a detector array; an x-ray source for radiating an x-ray beam toward the detector array; and a filter assembly including a movable filter having a plurality of portions each configured to alter the x-ray beam intensity and quality, and a fixed filter portion; said method comprising the steps of: 16. A method in accordance with claim 15 wherein the movable filter comprises a first portion configured to alter the x-ray beam into a first beam and a second portion configured to alter the x-ray beam into a second beam, and wherein positioning the movable filter comprising the step of positioning the movable filter so that the x-ray beam is filtered by the movable filter first portion. 17. A method in accordance with claim 15 wherein selecting a scan type comprises the step of selecting a body scan. 18. A method in accordance with claim 15 wherein selecting a scan type comprises the step of selecting a head scan. 19. A method in accordance with claim 16 wherein positioning the movable filter further comprises the step of positioning the movable filter so that the x-ray beam is filtered by the movable filter second portion. 20. A method in accordance with claim 16 wherein the filter assembly further includes a drive assembly coupled to the movable filter, and wherein positioning the movable filter so that the x-ray beam is filtered by the movable filter first portion comprises the step of altering the position of the movable filter with the drive assembly. 21. A method in accordance with claim 20 wherein positioning the movable filter so that the x-ray beam is filtered by the movable filter second portion comprises the step of altering the position of the movable filter with the drive assembly. 22. A method for altering an x-ray beam in an imaging system, the imaging system including a detector array, an x-ray source for radiating an x-ray beam toward the detector array and a filter assembly including a movable filter having a plurality of portions, wherein the first portion comprises a first filter material, a second filter material and a third filter material positioned between the first filter material and the second filter material, and the movable filter first portion configured to alter the x-ray beam into a first beam and the second portion configured to alter the x-ray beam into a second beam, said method comprising the steps of: 23. An imaging system including a detector array; an x-ray source for radiating an x-ray beam toward the detector array; and a filter assembly including a movable filter having a plurality of portions each configured to alter the x-ray beam intensity and quality, and a fixed filter portion; said imaging system configured to: 24. A system in accordance with claim 23 wherein said movable filter includes a first portion configured to alter the x-ray beam into a first beam and a second portion configured to alter the x-ray beam into a second beam, and wherein to position said movable filter, said system configured to position the movable filter so that the x-ray beam is filtered by said first portion. 25. A system in accordance with claim 23 wherein to select a scan type, said system is configured to obtain scan type from an operator. 26. A system in accordance with claim 23 wherein said detector array is a multislice detector array. 27. A system in accordance with claim 23 wherein said scan is helical scan. 28. A system in accordance with claim 24 wherein said imaging system further includes a drive assembly coupled to said movable filter and wherein to position the movable filter so that the x-ray beam is filtered by said first portion, said system configured to alter position of said movable filter with said drive assembly. 29. A system in accordance with claim 25 wherein obtained scan type is a body scan. 30. A system in accordance with claim 25 wherein obtained scan type is a head scan. 31. A system in accordance with claim 28 wherein to position said movable filter so that the x-ray beam is filtered by said the second portion, said system configured to alter the position of the movable filter with the drive assembly. 32. An imaging system including a detector array, an x-ray source for radiating an x-ray beam toward the detector array and a filter assembly including a movable filter having a plurality of portions, wherein said first portion comprises a filter first material, a second filter material and a third filter material positioned between said first filter material and said second filter material, and said movable filter first portion configured to alter the x-ray beam into a first beam and said second portion configured to alter the x-ray beam into a second beam, said imaging system configured to: 33. A system in accordance with claim 32 wherein to position said movable filter, said system further configured to position said movable filter so that the x-ray beam is filtered by said second portion. 34. An imaging system in accordance with claim 32 wherein said detector array is a multislice detector array. 35. An imaging system in accordance with claim 32 wherein said scan is a helical scan.
	description	Hereinafter, explanation will be given on embodiments of a high-resolution optical system, a defect examining apparatus and a method thereof, with using such the optical system therein, according to the present invention, by referring to the attached FIGS. 1 to 20. First, explanation will be given on a first embodiment of the defect examining apparatus according to the present invention. According to the present invention, for the purpose of obtaining high-brightness illumination in DUV (Deep Ultraviolet) region, a device for emitting an ultraviolet laser ray therefrom is applied as a light source (i.e., a source of ultraviolet laser ray) 3. A stage 2 has freedom in the directions of X, Y, Z and xcex8, on which as a sample 1 is mounted a semiconductor wafer (an object to be tested: test object), for an example, on which is formed patterns to be tested (test patterns). The ultraviolet laser ray (DUV laser ray) L2, which is emitted from the source 3 of ultraviolet laser ray, through a beam expander 6, an optical system 7 provided for the purpose of coherence reduction, a lens 8, a polarization light splitter 9, and a group 10 of polarizer elements, is incident upon an objective lens 11, to be irradiated upon the object to be tested (for example, the semiconductor wafer: test object) 1, on which is formed the test pattern. The beam expander 6 is provided for expanding the ultraviolet laser ray up to a certain size thereof, and it is in a form of so-called the Koehler illumination, i.e., it is irradiated upon the sample 1 after being condensed in the vicinity of the pupil 11a of the objective lens 11 by means of the lens 8. The reflection light, or an optical image obtained from the sample 1 is detected, through the objective lens 11, the group 10 of polarizer elements, the polarization light splitter 9 and further an image-forming lens 12, by a image sensor 13, from the upper direction of the sample 1. For the image sensor 13, it is necessary to detect the DUV light and it may be constructed by, such as, a TDI (Time Delayed Image) sensor. In case of applying the TDI sensor as such the image sensor 13, as shown in FIG. 20, it is preferable to construct the lens 8 to include a cylindrical lens 8 therein, so as to bring the luminous flux for illumination upon a slit form 140 fitting to the light receiving surface 130 of the TDI sensor, from a view point of an efficiency of the illumination. The polarization light splitter 9 has a function of reflecting the laser ray when the polarization direction thereof is in parallel with the reflection surface, while penetrating it when that is perpendicular thereto. The ultraviolet laser ray generated by the ultraviolet laser ray source 3 is inherently a polarization laser ray, and the polarization light splitter 9 is so positioned that the ultraviolet laser ray L2 emitted from the coherence reduction optical system 7 is reflected by the total reflection thereon. The test patterns formed on the test object 1, such as the wafer, in process, show various shapes or configurations, therefore the reflection light from the patterns has various polarization directions. The group 10 of polarizer elements, controlling the laser illumination ray and the reflection light, has a function of adjusting the rate of polarization in the illumination light, so that the reflection light does not reach upon the image sensor 13 accompanying with unevenness in brightness due to the shapes of the patterns and the difference in density thereof. For example, there are installed a xc2xd wavelength plate 10a and xc2xc wavelength plate 10b for shifting the phase of the illumination light by 45 degree to 90 degree. Therefore, the light irradiating from the group 10 of polarizer elements upon the test object 1 for illumination comes to be the light that is polarized circularly, and thereafter, all the lights reflected (or scattered) upon the test object 1, once polarized by the group 10 of polarizer elements, are further polarized by 90 degree thereby in the direction of the polarization thereof on the reflection surface, then they penetrate through the polarization beam splitter 9. In this manner, since the resolution of the optical system 70 can be changed depending upon the condition on the illumination, or the condition on polarization of the detection light. Therefore, it is possible to improve the performance (i.e., the resolution) of the optical system 70 through detecting the reflection light, changing depending upon the density of the circuit patterns formed on the test object 1, by means of the image sensor 13, while controlling the polarization condition thereof, by controlling the polarization elements 10a and 10b to rotate around the optical axes thereof, relatively, upon basis of a spatial image of a plane of pupil of the objective lens 11, which is detected by a mirror 86, a lens 87 and a detector 88, as shown in FIG. 11 which will be explained later, for example. And, the image sensor 13 is formed by a sensor of, such as an accumulation type, which can detect the ultraviolet lays (i.e., the TDI sensor), for example, thereby outputting an image signal of light and shade corresponding to the brightness (i.e., the light and shade) of reflection light from the test patterns which are formed on the test object 1. Namely, scanning the stage 2 while moving the test object 1 at a constant speed, the image sensor 13 detects information of the brightness (the light and shade image signal) of the test patterns that are formed on the test object 1. And the light and shade image signal 13a obtained from the image sensor 13 is inputted into a signal processing circuit 60, in which the inspection on defects is conducted, including the foreign matters in/on the test object. The signal processing circuit 60 may be constructed with an A/D converter 14, a gradation converter 15, a delay memory 16, a comparator 17, a CPU 19, etc. Further, the A/D converter 14 converts the light and shade image signal 13a obtained from the image sensor 13 into a digital image signal. An optical system 71 for focus detection detects the deviation of the stage 2 in the Z direction. And, a circuit 72 for focus detection, processing the deviation of the stage 2 in the Z direction detected by the focus detection system 71, controls driving of deviation of the stage 2 in the Z direction, for example, upon the basis of a drive control instruction from a driver circuit 73 which corresponds to that processing. Due to this, it is possible for the image sensor 13 to detect the brightness information of the test patterns formed on the test object 1 under the condition of focusing thereupon, with high accuracy. The gradation converter 15 may be constructed with, for example, an eight (8) bit gradation converter, and it treats the gradation conversion, as shown in Japanese Patent Laying-Open No. Hei 8-320294 (1996), upon the digital image signal that is outputted from the A/D converter 14. Namely, the gradation converter 15 performs conversion into a logarithm, an exponent, a polynomial, etc., so as to make compensation for a thin film that is formed on the test object 1, such as the semiconductor wafer, etc., in process, as well as for the unevenness in brightness of the image produced by interference of the laser light. The delay memory 16 is provided for delaying an output of image signal from the gradation converter 15 by the scanning a width of the image sensor 13, through memorizing it in an amount for one (1) cell, one (1) chip or one (1) shot, which construct the test object 1, such as the semiconductor wafer, etc. The comparator 17 is for comparing the image signal outputted from the gradation converter 15 and the image signal obtained from the delay memory 16, so as to detect a portion(s) being inconsistent with, as the defect(s). Namely, the comparator 17 compares, in more details, the image delayed by the amount corresponding to a cell pitch, etc., which is outputted from the delay memory 16, and the detected image. Accordingly, inputting the coordinates, for example, arranged data on the test object 1, such as the semiconductor wafer, obtainable upon the basis of design information, with using an input means 18 which may be constructed with a keyboard, a recording medium, a network, etc., the CPU 19 produces defect inspection data upon basis of the comparison result in the compartor 17, so as to store it into a memory device 20. This defect inspection data can be displayed on a display means 21, such as a display, etc., or may be outputted to an output means 22, thereby enabling observation of a spot(s) of defects through other review device, etc. Further, the details of the comparator 17 may be constructed with, as shown in Japanese Patent Laying-Open No. Sho 61-212708 (1986), for example, a circuit for adjusting positions on images, a circuit for detecting difference between the adjusted images, an inconsistency detector circuit for binary-coding the difference of image, and a character extraction circuit for extracting an area, a length, coordinates, etc., from the binary-coded output. Next, explanation will be explained on an embodiment of the source of ultraviolet laser ray (i.e., the ultraviolet laser-generating device). For obtaining high resolution, there is a necessity of shortening the wavelength of light, and for improving the test speed, the illumination of high brightness. Conventionally, a discharge lamp of mercury-xenon is used, and it is used widely in the visible region of the light emission spectrums (i.e., the emission line spectrums) that the lamp generates. However, separating from those light intensities, the emission line spectrums in the ultraviolet and the deep ultraviolet regions come up only around several %, comparing to that of the visible light (i.e., that in the visible light regions), a large-scaled light source is necessary for obtaining a desired brightness with certainty. In case of such the large-scaled light source, there is a limit to separate it from the optical system for protection from the ill influence of heat generation thereof. From this viewpoint, according to the present invention, the ultraviolet laser beam (DUV (Deep Ultraviolet) ray) is generated by means of the light source 3. The ultraviolet laser ray indicates the laser ray from 100 nm to 400 nm in wavelength, and the DUV laser ray is the laser ray from 100 nm to 314 in wavelength. The ultraviolet laser ray source (the ultraviolet laser-generating device) 3 is constructed with, as shown in FIG. 2, a solid-state laser device (a laser excitation light source) 4 for emitting a basic wave of laser ray of 532 nm in wavelength, and a wavelength converter device 5, for example. The solid-state laser device 4, penetrating Nd:YAG laser ray of 1064 nm in wavelength through a non-linear optical crystal thereof, so as to obtain a wave doubled in frequency (xc2xd in wavelength), is so controlled that it emits the laser ray of 532 nm in wavelength at a constant intensity. Namely, the solid-state laser device 4 for outputting the doubled wave of the Nd:YAG laser ray is so constructed that it controls current of a laser power source depending upon a monitor output, thereby to emit an output of the laser ray L1 having a constant intensity. The laser ray L1 of wavelength 532 nm emitted from the solid-state laser device 4 is in the single mode oscillation, and is incident upon the wavelength converter device 5. Also, it does not matter whether the oscillation of the solid-state laser device 4 as the ultraviolet laser ray source 3 is in a continuous oscillation mode or in a pulse oscillation mode, however in particular, in case of detecting the image from the test object 1 while continuously scanning the stage 2, that continuous oscillation is preferable. Also, the ultraviolet laser ray source 3 may be constructed so that it converts the laser ray of the solid-state YAG laser (1064 nm) by the non-linear optical crystal, etc., thereby to generate the third (3rd) high harmonic (355 nm) or the fourth (4th) high harmonic (266 nm) of the basic wave thereof. Further, the ultraviolet laser ray source 3 may be constructed with a laser device of generating the laser ray having wavelength equal or less than 100 nm. Next, explanation will be given on the wavelength converter device 5 as an element of the present invention. FIG. 2 is the view of the ultraviolet laser ray source 3 in the FIG. 1, seeing from the Z direction, for showing the outline structure (cross-section) of the wavelength converter device 5. Inside a container of the wavelength converter device 5, there are positioned mirrors M1 to M4. Being emitted from the solid-state laser-generating device 4 and incident upon a transparent window 35 at an entrance 39 provided on the container 41, the laser ray L1 passes through the mirror M1 and reaches the mirror M2. The mirror M2 penetrates through a part of the incident light, while it reflects the remaining thereof. The laser ray reflected upon the mirror M2 reaches to the mirror M3. Anon-linear optical crystal 30 is disposed on an optical path between the mirror M3 and the mirror M4, and then the laser ray, being reflected upon the mirror M3 by the total reflection, passes though the non-linear optical crystal 30 to reaches the mirror M4. And, an optic resonator is constructed with such the optical members, each having high reflectivity, including those mirrors M1 to M4 therein. Further, the non-linear optical crystal 30 is disposed at a suitable location that can be calculated optically, therefore by means of this crystal 30, the incident light is converted into the second (2nd) high harmonic of wavelength having wavelength of 266 nm. Upon the mirror M4, only the ultraviolet laser ray L2 of the second (2nd) high harmonic passes through, therefore it is emitted outside the wavelength converter device 5, via the transparent window 35 at an exit 40, which is provided on the container 41. Namely, upon the mirror M4 is treated a coating, which penetrates through the second (2nd) high harmonic but reflects other wavelengths. The laser ray L3 that is not converted by the non-linear optical crystal 30 is reflected upon the mirror M4 to reach the mirror M1, and it follows the same optical path for the laser ray L1, again. Herein, a portion of the incident light passing through the mirror M2 is detected by a detector means which is not shown in the figure, to detect the error between the frequency of the incident light and the resonance frequency of the wavelength converter, thereby bringing both into synchronism with (in a resonating condition), always. In more details, by means of a servo-mechanism not shown in the figure (for example, a piezoelectric element, etc.), the mirror M3 is moved minutely or finely, so that the length of the optic resonator is controlled with high accuracy. With controlling the length thereof in this manner, the optical resonator is constructed with the optical members, each having the high reflectivity, such as the mirrors M1 to M4. And, with the above-mentioned optic resonator and the non-linear optical crystal 30, which are provided inside the container 41, the wavelength converter 50 is constructed. On a while, the ultraviolet laser ray L2 of wavelength 266 nm, which is emitted from the wavelength converter device 5, has coherence therewith, and it comes to be a cause of generating so-called speckles when illuminating the circuit patterns on the test object 1 with using such the laser ray. Accordingly, in the illumination with using such the ultraviolet laser ray L2, it is necessary to reduce the coherence. For reduction of the coherence, it is sufficient to reduce down either one of the time and spatial coherences thereof. Then, according to the present invention, only the special coherence is reduced down by means of an optical system 7 for reduction of the coherence. FIG. 3 is a block diagram for showing an embodiment of an illumination optical system, including the coherence reduction optical system 7 according to the present invention, therein. The laser ray L2 emitted from the transparent window 35 at the exit 40 of the wavelength converter device 5 is expanded in the beam expander 6 to a parallel luminous flux of a certain size, to be condensed at the focal position of the lens 24, and thereafter it is condensed upon the pupil 11a of the objective lens 11 through the lenses 25 and 8, and the polarization beam splitter 9, as well. However, the focal position 28 of the lens 24 is also that of the lens 25 at the same time, therefore the focal position 28 is in conjugated relation with the position of the pupil 11a of the objective lens 11. In the coherence reduction optical system 7, as is shown in FIG. 4, for example, a scattering plate 26 of disc form is positioned at the focal point 28 on the optical path, and is rotated at high speed by a motor 27. Namely, as is shown in FIG. 5, the scattering plate 26, on the surface of which is machined with appropriate roughness, is positioned at the focal position of the lens 24 (and the lens 25), and the laser spot condensed upon the pupil 11a of the objective lens 11 is scanned by means of rotation of the motor 27, thereby reducing the coherence, in particular the spatial coherence thereof. The laser ray is expanded by the scattering plate 26 to a certain degree, however the lens 25 is selected to have numerical aperture to cover it, and the detailed specifications of that scattering plate 26 are determined by experiments. Further, with the coherence reduction optical system 7, the manner for constructing thereof should not be restricted only to the above-mentioned, but it is also possible to apply a polyhedron rotation mirror, a vibrating rotation mirror, etc. By the way, in the laser ray source 3 used for illumination, the ultraviolet ray of wavelength 266 nm is obtained by doubling the frequency of the excitation light L1 of wavelength 532 nm obtained from the solid-state laser, with using the mirrors M1 to M4 disposed within the container of the wavelength converter device 5 and the non-linear optical crystal 30 as well, thereby obtaining the ultraviolet light of wavelength 266 nm. However, as was mentioned previously, the interior of the container of the wavelength converter device 5 is very delicate, due to the fact, for example, that the optical system must be synchronized with so that the frequency of the incident light is always in the resonating condition with the resonance frequency of the wavelength converter 50, etc. Among those, the non-linear optical crystal 30 has deliquescence therewith and is apt to be easily damaged from moisture. Accordingly, for obtaining the ultraviolet laser ray with stability, the surfaces of the mirrors M1 to M4 and the non-linear optical crystal, which are provided within the optical resonator, must be always kept in a clean condition. Also, for obtaining a constant ultraviolet laser ray from the wavelength converter 50 provided within the container of the wavelength converter device 5, a thermostatic device (not shown in the figure) is provided within a slight movement mechanism 45 for supporting the non-linear optical crystal 30. Herein, in case where it is impossible to maintain the interior of the container of the wavelength converter device 5 in such the clean condition, the irradiation of the ultraviolet laser ray causes chemical reactions and the reactant adheres and harden upon the surfaces of the optical elements, in the inside thereof, thereby bringing about the decrease of intensity in an output of the ultraviolet laser ray. Then, it is possible to manage by shifting the irradiation position of the laser ray upon the crystal 30, little by little, when the output intensity of the ultraviolet laser ray is decreased down, however it takes a large amount of labor and times. Then, first of all, explanation will be given on a first embodiment of the wavelength converter device 5. In this first embodiment, as shown in FIGS. 6 and 7, the wavelength converter 50, which is constructed with the optic resonator made with the optical members M1 to M4 and the non-linear optical crystal 30, is shut off or insulated from the air outside, by means of the container 41, i.e., within the construction of sealed condition. FIG. 7 shows the condition of removing a cover 31 there from. Namely, the transparent windows 35 are hermetically provided with using, such as an O ring 36, etc., at the inlet 39 and the outlet 40 for the laser ray, which are formed on the container 41. Further, on the container 41 are provided a supply valve 32, being provided with a filter 37 at an tip thereof, for supplying a gas for use of cleaning, such as an inert gas, from a gas reservoir (not shown in the figure) into the container 41, a discharge valve 33 connected to a discharge pump (not shown in the figure) for discharging residual gas within the container 41, and a detector 34 for observing the condition of the gas within the container 41, especially fulfillment of the inert gas therein. In this manner, the cleaning means for cleaning up the inside of the container 41 is constructed with, for example, the supply valve 32, connected to the inert gas reservoir (not shown in the figure) and provided the filter 37 at the tip thereof, the discharge valve 33 connected to the discharge pump, and the detector 34 for observing the fulfillment of the inert gas therein. Being constructed in this manner, as shown in the FIG. 6, after completion of the optical system therein, the container 41 of the wavelength converter device 5 is attached with the cover 31 thereon, and the discharge valve 33 thereof is connected to the discharge pump not shown in the figure, thereby discharging the residual gas in the container 41. Next, the inert gas is supplied from the supply valve 32 thereinto. The detector 34 may be a barometer, for example, for monitoring an atmospheric pressure within the container 41. The inert gas is preferably a gas that shows no chemical reaction with the laser ray within the wavelength converter 50, such as, nitrogen gas, argon gas, etc. Also, the filter 37 is provided at the tip of the supply valve 32, and this achieves functions of controlling the flow amount of the gas and preventing mixture of impurities therein, when supplying the inert gas through it. In particular, under the condition where the residual gas in the container 41 is discharged by connecting the discharge valve (not shown in the figure) to the discharge pump 33, and next the inert gas is supplied from the supply valve 32 into the container 41, to be filled up therein at around one (1) atmospheric pressure, it is possible to close up the supply valve 32 and the discharge valve 33, thereby to bring the container 41 into a sealing up condition. And, after filling the inert gas from the supply valve 32 into the container 41 at around the one (1) atmospheric pressure, it is also possible to continue to run the inert gas at a very small amount, so that no fluctuation occurs in the laser ray. According to the first embodiment mentioned in the above, it is possible to prevent the mixture of new foreign matters from coming into the container 41, and as a result, it is possible to maintain the surfaces of the mirrors M1 to M4 and the crystal 30, which are provided inside the optic resonator, always clean, thereby to prevent them from bringing about decrease of the ultraviolet laser ray in the output intensity thereof. Next, explanation will be given on the second embodiment of the wavelength converter device 5 according to the present invention. In this second embodiment, as shown in FIG. 9, the wavelength converter 50 is shut off from the air outside, by means of dual structure, including the container 42 and a casing (container) 44, i.e., it has the structure in hermetically sealing condition. In the case of this second embodiment, it is possible to prevent the mechanical stress from being applied onto the wavelength converter 50 when closing the cover 31. Namely, on the outer casing 44, the transparent windows 35 are hermetically provided at the inlet 39 and the exit 40 with using, such as the O-rings 36, etc., and there are provided the valves 32 and 33 for supplying and discharging the gas and the detector 34 for observing the gas condition within the container. And, the container 42 building up the wave length converter 50 there in is supported within the casing 44 by means of supporting members 43, thereby constructing the dual structure. And, on the inner container 42, there are formed an inlet 46 for entering the incident laser ray through the transparent window 35 at the inlet 39, and an outlet 47 for emitting the ultraviolet laser ray L2 to the transparent window 35 at the outlet 40, and further are formed air suction openings 48 and air discharge openings 49 communicating between the inside and the outside of the container 42, as well as pressure openings 51. In particular, with provision of a large number of such the air suction openings 48 and the air discharge openings 49, being small in the size, they function as a buffer between the outside of the container 42 and the inside of the casing 44 even when continuing to run the very small amount of the inert gas, therefore it is possible to remove almost of flow of the inert gas within the container 42, i.e., remove fluctuation of the laser ray. Of course, under the condition where the residual gas in the container 45, including the container 42, is discharged therefrom by connecting the discharge valve (not shown in the figure) to the discharge pump 33, and next the inert gas is supplied from the supply valve 32 into the container 45, to be filled up with therein at around one (1) atmospheric pressure, it is possible to close up the discharge valve 33 and the supply valve 32, thereby to bring the container 45 into the sealing condition. In this manner, according to the second embodiment of the wavelength converter device 50, it is possible to prevent the stress from generating onto the wavelength converter 50, and also to prevent the container 42 from mixture of the new foreign matters, by supplying the inert gas of causing no chemical reaction with the laser ray, such as the nitrogen gas or argon gas, etc., to be filled up with therein. As a result of this, it is possible to keep the surfaces of the mirrors M1 to M4 and the crystal 30, which are provided inside the optic resonator, always in the clean condition, therefore it is possible to prevent them from bringing about the decrease in the output intensity of ultraviolet laser ray. However, according to the second embodiment, the wavelength converter 50 is shut off from the air outside by means of the dual structure of the container 42 and the casing (container) 44, the container may be constructed with triple structure, although it comes to be complicated a little bit in the structure thereof. With such the triple structure of the container, since an aperture can be defined between the containers as the buffer, it is possible to remove the fluctuation of the laser ray, much more. Next, explanation will be given on a third embodiment of the wavelength converter device 5 according to the present invention. This third embodiment, as shown in FIG. 8, is constructed by applying an adhesive or sticky material 38 (a trap means) on an inner wall of the container 41 of the first embodiment. Of course, the third embodiment may be constructed by applying the adhesive material 38 on an inner wall of the container 42 of the second one. According to this third embodiment, it is possible to prevent the foreign matter(s) 39, which stays within the container 42, from being blown up by wind pressure when supplying the inert gas therein, to adhere or attach upon the optical members inside. Further, according to this, it is also possible to catch the floating foreign matter(s) 39 touching on the adhesive material, when discharging the gas within the containers 41 (or 42) outside, thereby to hold it semi-permanently. Next, explanation will be given on a fourth embodiment of the wavelength converter device 5, according to the present invention. In this fourth embodiment, as shown in FIG. 10, further a plural number of optic sensors S1 to S6 are positioned within the container of the wavelength converter device 5, in the third embodiment, and scattering light from the contaminant occurring within the container 41 (or 42) is detected by means of the plural number of the optic sensors S1 to S6, thereby detecting the degree of contamination, or the condition of contamination within the containers, in order to observe the contamination condition on the optical members M1 to M4, and on the non-linear optical crystal 30 as well. Namely, the plural number of those optic sensors S1 to S6 construct an optical contaminant detecting means for detecting the scattering light from the contaminant occurring within the container 41 (or 42). Since, ordinarily the contaminant is made of an organic matter, the optic sensors S1 to S6 detect the fluorescence scattering light generated by such the organic matter. And, each of the plural number of the optic sensors S1 to S6 is made from a light condensing lens and a photoelectric conversion element, and detects the contamination condition upon the surface of the mirror of M1 to M4 or the surface of the non-linear optical crystal 30, for example. Since the photoelectric conversion element generates electromotive force depending upon an amount of the receiving light thereon, a threshold value is provided for it, and then it can be decided that the surface(s) of the mirror(s) M1 to M4 and/or the surface of the non-linear optical crystal 30 is/are contaminated when it exceeds the threshold value. For example, it can be decided that the contaminant 40 adheres upon the surface of the mirror M2 if, there is an output signal from the optic sensor S2. Since the wavelength of the laser ray is already known, it is possible to protect it from an ill influence of an external disturbed light, by applying the sensors having high sensitivity only a specific wavelength band as those sensors S1 to S6, and it is also possible to set the threshold value for detection to be low. Accordingly, even a very little contaminant can be detected upon the surfaces of the mirror M1 to M4 and the crystal 30, with high sensitivity. Monitoring the output of the ultraviolet laser ray L2 emitted from the wavelength converter device 5 by a detector means 100, which is constructed with the photoelectric conversion elements, etc., and which is provided separate from the optic path of the illumination light, an alarm can be given, for example, when decrease is found in the intensity thereof (for example, when it comes down to around 50% of an initial value), then the sensors S1 to S6 are determined by each, whether the output signal of which exceeds a threshold value predetermined for it or not. With this, a portion(s) which is/are contaminated with the contaminant(s) upon the surface(s) thereof can be specified or identified among the optical members, i.e., the mirrors M1 to M4 and the crystal 30. Then, the optical member(s), being determined contaminated, will be treated with cleaning upon the surface thereof, or will be replaced with a new or other optic member that in not contaminated. However, as another method for monitoring the ultraviolet laser ray L2 emitted from the wavelength converter device 5, an output of the beam expander 6 or the coherence reduction optical system 7 may be monitored. Of course, when monitoring the output of the beam expander 6 or the coherence reduction optical system 7, the decrease in the output intensity due to the contamination of the optical system 6 or 7 is included into the output to be monitored. Also, in a case where no output signal is produced from the optic sensors S1 to S6, and where the output intensity is reduced in the ultraviolet laser ray L2, which is emitted from the wavelength converter device 5, when monitoring it by the detection means as was mentioned in the above, the cause may be considered to lie in the non-linear optical crystal 30. In this case, a possibility is high that the inside of crystal 30 burns out upon the irradiation of the laser ray, therefore the non-linear optical crystal 30 may be adjusted to be shifted in the Y and Z directions by means of the slight movement mechanism 45, so that the ultraviolet laser ray L2 can be increased in the output intensity. Of course, the present fourth embodiment can be applied to the second embodiment shown in the FIG. 9, too. As was explained in the above, with monitoring the contamination condition within the wavelength converter device, it is possible to make the determination upon the necessity of maintenance in the wavelength converter device, with ease and appropriateness, and as a result, it is possible to remove consumption of unnecessary or needless time paid for adjusting the optical system within the wavelength converter device without reasons. According to the embodiments of the present invention mentioned in the above, it is possible to obtain a source of laser ray of a long life-time, without decrease of output intensity in the ultraviolet laser ray, i.e., stable oscillation of the ultraviolet laser ray for a long time period, by elongating the life-time of the wavelength converter. As a result of this, it is also possible to detect the microscopic patterns formed on the test object 1 with high resolution, thereby to examine those defects occurring in the microscopic patters with high reliability. Next, a second embodiment of the detect examination apparatus, according to the present invention, will be explained by referring to FIGS. 11, 18 and 19. In this second embodiment, the difference from the first embodiment shown in the FIG. 1 lies in that, at first, as shown in FIGS. 19(a) and (b), the ultraviolet laser ray source (the ultraviolet laser-generating device) 3, each comprising the solid-state laser device (the laser exciting light source) 4 and the wavelength converter device 5, is provided in a plural number thereof so that the ultraviolet laser rays emitted from those ultraviolet laser ray sources 3 are on the same axle, and therefore as shown in the FIG. 19(b), they can be used by oscillating only one of them for exchanging it by the other(s) when the one is in trouble, or as shown in the FIG. 19(a), all of them are oscillated while operating each at the low output. Namely, in the second embodiment, the plural number of the ultraviolet laser ray sources 3a, 3b and 3c, each comprising the solid-state laser device 4 and the wavelength converter device 5 therein, are provided, and mirrors 81a, 81b and 81c are so constructed that the ultraviolet laser rays emitted from those ultraviolet laser ray sources 3a, 3b and 3c are reflected upon them on the same axle in a direction, such as of Z, so as to be inputted into the beam expander 6. In particular, as shown in the FIG. 19(b), selecting each of the mirrors 81a to 81c (a selection optical system) by exchanging (or shifting) thereof, it is possible to select the output(s)of the ultraviolet laser ray sources 3a to 3c. With this, it is possible to make the ultraviolet laser ray sources provided for spares emit the normal ultraviolet laser rays always, so as to irradiate upon the test object 1, to detect the microscopic patterns formed on that test object 1 with high resolution, and to detect the defects occurring in those microscopic patterns with high reliability. In this manner, even during a period when they are operating normally as the laser ray sources, it is possible to make adjustment on the wavelength converter device(s) 5 among them, being abnormal as the ultraviolet laser ray source, being broken or deteriorated therein, or to replace it/them by a normal wavelength converter device(s) 5 in place thereof. However, as was shown in the FIG. 19(a), in a case where the ultraviolet laser rays emitted from the plural number of the ultraviolet laser ray sources 3a to 3c are applied upon a combining optical system of 81a to 81c to be combined with, it is possible to adjust an output automatically, by monitoring the output as a whole by, such as a TV camera 85, so that the current value is adjusted, for example, to be supplied to the solid-state laser device 4, which is included in the normal ultraviolet laser ray source(s) other than the deteriorated one, to increase the output thereof, thereby obtaining the monitored output as a whole at a predetermined value. And, for the wavelength converter device 5 of the deteriorated ultraviolet laser ray source, it is also possible to adjust the output intensity of the ultraviolet laser ray L2 so as to increase, through shifting the non-linear optical crystal 30 in the Y and Z directions by means of the slight movement mechanism 45. Further, as shown in the FIG. 18, with positioning the ultraviolet laser ray source 3 comprising plural light sources 3a and 3b separate from the optical system 70, it is so constructed that propagation of mechanical vibration generated by the stage, etc., and transmission of heat can be shut off from the ultraviolet laser ray source 3 to the optical system 7. Further, according to the present embodiment shown in the FIG. 18, the ultraviolet laser ray source 3 is provided under a base 80 for removing vibration. In this case, it is constructed to make exhaustion of the air locally, so that, not shown in the figure, the heat generated by the ultraviolet laser ray source 3 will not transmitted up to the upper portion of the base 80. The laser rays L2, each being emitted from the respective ultraviolet laser ray sources 3a to 3c, are reflected into the direction Z upon the mirrors 81a to 81c, respectively, and reach to the optical system 70 through a mirror 90 and the beam expander 6. In the pattern inspection thereof, the examination is conducted upon the whole surface of the semiconductor wafer 1 by scanning the stage 2, on which the wafer 1 is mounted, into the X and Y directions, however since the position of center of gravity of the stage is shifted accompanying with the movement thereof, the base 80 is inclined. In this case, the base 80 is turned back to the horizontal condition by means of an air turbo, etc., however since the ultraviolet laser ray L2 emitted from the ultraviolet laser ray source 3 is equal or less than 1 mm in a beam diameter, it can be expected that the optical axis of the optical system 70 comes out of that of the ultraviolet laser ray L2, temporally. Because of this, according to the present invention, the mirror 90, the lens 91, and a position detector 90 as well, are provided on the base 80, thereby detecting a shift amount of the ultraviolet laser ray L2, so as to shift the mirror 81 by an actuator, such as a piezoelectric element, etc., and to correct the optical path of the ultraviolet laser ray L2 being out of the axis thereof, at high speed. Herein, on the mirror 90 is coated a reflection film so as to reflect a little amount of light of the ultraviolet laser ray L2, and the lens 91 is provided for extensively projecting this reflection light upon the position detector 92. The position detector 92 is constructed by, for example, positioning a light receiving element to be dividing into the X and Y directions, thereby to detect the shift amount of the laser ray through calculation of detection signals of those light receiving elements, by means of an electric circuit not shown in the figure. With this, it is possible to make the ultraviolet laser ray emitted from each of the ultraviolet laser ray source 3a and 3b to be incident upon the optical system 70, with stability. As was explained in the above, with provision of the plural number of the ultraviolet laser ray sources 3, each comprising the solid-state laser device 4 and the wavelength converter device 5 therein, it is possible to selectively change the output of the ultraviolet laser ray, and as a result of this, it is possible to obtain the normal ultraviolet laser ray source, always with certainty, and to perform the inspection of the microscopic patterns by using the ultraviolet laser ray, with continuity and high reliability. Next, explanation will be given on another embodiment of the coherence reduction optical system 7. In this embodiment, as shown in FIG. 12, the laser ray is scanned in two-dimensional manner by means of a pupil scanning mechanism, which is constructed with two (2) pieces of orthogonal scanning mirrors 61 and 64, thereby being reduced in the coherence thereof, spatially. FIG. 13 is a diagram of the illumination system. The ultraviolet laser ray L2, being emitted from the ultraviolet laser ray source 3 and expanded to a certain size by the beam expander 6, comes to be a parallel luminous flux to be reflected upon the mirror 61 and to be condensed by the lens 62, and thereafter it comes to be a parallel luminous flux, again, through the lens 63 to be condensed upon the pupil 11a of the objective lens 11 by the lens 8. Reference numerals 67 and 69 indicate the reflection positions of the laser light upon the scanning mirrors 61 and 64, and they are in the conjugated relationship with the surface of the test object 1 in the positions thereof. Also, a reference numeral 68 is a surface of a first pupil, being in the conjugated relationship with the pupil 11a of the objective lens 11. Accordingly, through rotational or wobbling control of the scanning mirrors 61 and 64 by means of electric signals, it is possible to scan the ultraviolet laser ray L2 upon the pupil 11a of the objective lens 11, in the two-dimensional manner. The electric signal to be inputted to the scanning mirror 61 or 64 may be a triangle signal or a rectangular signal, etc., for example, and the scanning of the ultraviolet laser ray can be conducted in various shapes, by changing the frequency and/or amplitude of that electric signal. In particular, scanning the ultraviolet laser spot upon the pupil 11a of the objective lens 11 in a zonal (or ring-belt like) manner, as shown in FIGS. 14(a) and (b), by controlling the scanning of the scanning mirrors 61 and 64, respectively, it is possible to perform a zonal illumination through the objective lens 11 upon the test object 1, while reducing the coherence thereof. Further, as will be mentioned later, even in a case that the illumination light is an ultraviolet multi-slit spot beam corresponding to the TDI sensor, it is also possible to remove the optical interference, completely, by positioning the scattering plate after the pupil scanning mechanism which is constructed with the scanning mirrors 61 and 64 mentioned above. By the way, on the optical path of the illumination light, a mirror 82 is positioned for dividing an amount of illumination light so that it does not impedes the illumination of the test object 1, and it is constructed so that a portion of the illumination laser ray divided by the mirror 82 mentioned above can be observed by means of the TV camera 85. Namely, the light divided by the mirror 82 mentioned above is the ultraviolet laser ray, therefore a screen 83, which emits fluorescence light when that ultraviolet laser ray is incident thereupon, is provided at the position in the conjugated relationship with the pupil 11a of the objective lens 11. As a result of this, expanding the fluorescence light image 92 occurring upon the screen 83 (in the case where the ultraviolet laser ray is scanned in the zonal manner, two-dimensionally) through a lens 84, it is possible to observe such the image 91, as shown in FIG. 14(a), through the TV camera 85. Further, a numeral reference 93 indicates an outer diameter of the pupil 11a of the objective lens 11. And, processing the image 91 outputted from the TV camera 85 in a signal processing circuit 60 shown in the FIG. 18, it is possible to obtain an amount of shifting of the illumination light 92 from the center of the pupil 11a, for example, and this shift amount is fed back to a controller circuit 95, thereby enabling control of the scanning by means of the scanning mirrors 61 and 64 of the coherence reducing optical system 7. Also, the signal processing circuit 60, encoding the image received by the TV camera 85 into binary values, obtains an area of the illumination by adding up pixels being brighter than a certain value thereof, thereby enabling optimization of an illumination condition (i.e., the illumination xc3x3). Further, it is needless to say that the scanning of the ultraviolet laser ray by means of the scanning mirrors 61 and 64 is conducted during the storage time of the image sensor 13. Next, explanation will be given on another embodiment in relation to the condition of illumination. Namely, in this embodiment, the ultraviolet laser ray is irradiated upon the pupil 11a of the objective lens 11, for multi-spot illumination. Since the illumination xc3x3 can be gained by conducting the multi-spot illumination in this manner, it is possible to delay the scanning time by means of the scanning mirrors 61 and 64. FIG. 15 is a three-dimensional view of the coherence reducing optical system 7, in which a multi-lens array 65 and a lens 66 are disposed, and FIG. 16 is a diagram of an illumination system using it therein. Namely, the multi-lens array 65 and a lens 66 are added in relation to the incident ultraviolet laser ray L2, thereby making up imaginary multiple sources of the ultraviolet laser rays, and they are condensed upon the pupil 11a of the objective lens 11. Further, a reference numeral 110 shown in FIG. 16(a) indicates a mask for forming the multi-spotlights, in more preferable manner. Also, a reference numeral 110a shown in FIG. 16(b) is a front view of an example of the mask for forming the multi-spotlights, and a reference numeral 110b shown in FIG. 16(c) a front view of another example of the mask for forming the multi-spotlights. Reference numerals 112a and 112b indicate portions for penetrating the light therethrough, while 111a and 111b portions of shutting off the light. As for the means (i.e., the multi-lens array) 65 for making up the imaginary multiple sources of the ultraviolet laser rays, it can be obtained by lens arrays, in which two (2) cylindrical (or renticular) lens arrays 113 are positioned with crossing at right angle, for example, as shown in FIG. 17(a), or by positioning a rod-lens array 115 of disposing small-sized convex lenses two-dimensionally thereon, as shown in FIG. 17(b). However, in a case where the storage type TDI sensor is used as the image sensor, it is necessary to make the multi-spotlights into multi-slit spotlights 140, corresponding to the light receiving surface of the TDI sensor (for example, as was shown in the FIG. 20). For that purpose, as such the means 65 mentioned above, a long and narrow rod-lens array 116, shown in FIG. 17(c), for example, might be used therefor. And, FIG. 14(b) shows the scanning condition by the multi-spotlights, which comes to be the zonal illumination upon the pupil 11a of the objective lens 11. In the same manner, the scanning is conducted upon the pupil 11a of the objective lens 11, by the multi-slit spotlights corresponding to the TDI sensor. A pitch 120 between the points of condensing the laser rays upon the pupil 11a of the objective lens 11 can be changed freely, by changing the focal distance of the lens 66, as well as the focal distance(s) of the other lens(es). According to the present invention, it is possible to achieve an effect of providing the ultraviolet laser-generating device; wherein the wavelength converter device does not receives the ill influence largely, from the heat generated by the non-linear optical elements, and the contaminants can be prevented from adhering upon the optic resonator, as a whole, including the non-linear optical elements therein, with such the simple construction, thereby converting the incident laser ray in the wavelength with high efficiency, and obtaining the long life-time thereof, without reducing the output intensity of the ultraviolet laser ray, as well. Also, according to the present invention, it is possible to achieve an effect that, when the decrease of output intensity in the ultraviolet laser ray occurs in the wavelength converter device, the investigation of the cause thereof, and the maintenances, including the determination of the necessity thereof, can be performed, easily. Further, according to the present invention, it is also possible to achieve an effect that the detection and/or the inspection of defects in the microscopic test patterns, which are formed on the test object, such as the semiconductor wafer, etc., can be achieved, with high resolution and high reliability, through the illumination of the ultraviolet laser ray with stable intensity thereof.
06236698&	summary	FIELD OF THE INVENTION 1. Background of the Invention The present invention generally relates to a reactor power distribution monitor system which computes a core power distribution on the basis of a core present data of a reactor with the use of a physical model. In particular, the present invention relates to a reactor nuclear instrumentation system which can accurately compute a reactor core power distribution with the use of plurality of fixed type neutron detectors and fixed type .gamma.-ray heat detector means which are arranged in a core axial direction and has high reliability, to a reactor power distribution monitor system including such reactor instrumentation system and to a reactor power distribution monitoring method. DISCUSSION OF THE BACKGROUND In a reactor, for example, in a boiling water reactor (BWR), a core performance such as a power distribution and a thermal state of a reactor core are monitored by means of a process control computer included in a reactor power distribution monitor system. In order to monitor the aforesaid reactor power distribution and thermal state, there is a method of computing a core power distribution with the use of reactor core present data measuring means and a physical model (core three-dimensional nuclear hydrothermal computing code) stored in a process control computer on the basis of the measured reactor core present data and confirming whether a maximum linear heat generation ratio (MLHGR) or a minimum critical power ratio (MCPR) satisfies individual predetermined operation limit value. According to such a method, a reactor operation is carried out. FIG. 26 and FIG. 27 show a general reactor power distribution monitor system of a boiling water type reactor. In the boiling water type reactor, a reactor pressure vessel 2 is housed in a reactor container 1, and a reactor core 3 is housed in the reactor pressure vessel 2. The reactor core 3 is constructed in a manner that a plurality of fuel assemblies 4 and control rods 5 and the like are mounted. An incore nuclear instrumented fuel assembly 6 is located on a position surrounded by the fuel assemblies 4 of the reactor core 3. As shown in FIG. 27, a corner gap G formed by four fuel assemblies 4 is provided with an incore nuclear instrumented fuel assembly 6, and a nuclear instrumentation tube 7 is provided with a neutron detector 8 which is dispersively arranged at a plurality of portions in a core axial direction. The neutron detector 8 has a so-called fixed type (stationary or immovable) structure, and in the boiling water reactor, usually, four neutron detectors are dispersively arranged on an effective portion in a fuel axial direction at equal intervals. Further, the nuclear instrumentation tube 7 is provided with a TIP (Traversing In-Core Probe: movable incore instrumentation) guide tube 9. One movable neutron detector (TIP) 10 is located so as to be movable in an axial direction. As shown in FIG. 26, there is provided a movable type neutron flux measuring system which continuously measures a neutron flux and is movable in an axial direction by means of a retrieval device (selector) 11, a TIP drive unit 12, a TIP drive control device and a TIP neutron flux signal processor 13 or the like. A reference numeral 14 denotes a penetration section, 15 denotes a valve mechanism and 16 denotes a shielding container. These neutron detectors 8 and 10 and their control device such as signal processors 13 and 17 (will be described later) are called as a reactor nuclear instrumentation system 24. On the other hand, the fixed type (stationary or immovable) neutron detector (LPRM detector) 8 arranged in the reactor core generates an average signal (APRM signal) for each of some divided groups, and then monitors a power level of a power range of the reactor core 3. Further, the fixed type neutron detector 8 constitutes a reactor safety guard system which rapidly makes a scram-operation with respect to a reactor stop system (not shown) such as a control rod drive mechanism in order to prevent a breakdown of a fuel and a reactor when there occurs an abnormal transient phenomenon or accident such that a neutron flux rapidly increases. By the way, in the fixed type neutron detector 8, a change in sensitivity happens in individual detectors by neutron heat. For this reason, in order to compare and correct the sensitivity of each neutron detector 8 every a predetermined period during operation, the TIP (movable neutron detector) 10 is actuated so as to obtain a continuous power distribution in a core axial direction, and the change in sensitivity of each neutron detector 8 is corrected by a gain adjusting function of a power range detector signal processing unit 17. A neutron flux signal obtained by the TIP 10 is processed as a neutron flux signal corresponding to a core axial direction position by means of a TIP neutron flux signal processing unit 13 constituting a reactor nuclear instrumentation system 24. Further, in a reactor power distribution computing device 18 (which is usually built in one or plural of process control computers for monitoring an operation of an atomic power generation plant as a program), the neutron flux signal is read as a reference power distribution when computing a three-dimensional hydrothermal force. The reactor power distribution computing device 18 includes a power distribution computing module 19, a power distribution learning module 20 and an input-output unit 21. Reading a control rod pattern obtained from a present data measuring device 22 which functions as reactor core present data measuring means, a core flow rate, a reactor doom pressure, a reactor heat power obtained from various core present data, and a process data such as a core inlet coolant temperature or the like, these data are processed by means of a present data processing unit 23, and then, are supplied to the reactor power distribution computing unit 18. The present data measuring device 22 is actually composed of a plurality of monitor equipments and is shown as one example of a measuring device for simplification although it is generally named as a device for collecting process data of various operation parameters in the reactor as shown in FIG. 26. Further, the present data processing unit 23 is composed of a process control computer or a part thereof, and a processed core present process data is supplied to the power distribution computing device 18. The power distribution computing module 19 computes a reactor core power distribution according to the three-dimensional nuclear hydrothermal computing code stored in the process control computer, and then, supplies the computed result to the power distribution learning module 20. The power distribution learning module learns on the basis of the reference power distribution, and then, correct the computed result, and thus, accurately computes a reactor power distribution in a power distribution predictive computation after that. In the conventional incore nuclear instrumented fuel assembly 6, as shown in a perspective view partly in section of FIG. 28, a movable type .gamma.-ray detector 10A may be used in place of the movable neutron detector 10. The movable type .gamma.-ray detector 10A is movable in a core axial direction so as to continuously measure a .gamma.-ray flux in the core axial direction. The .gamma.-ray is generated in proportion to a fission rate in the reactor core 3, and therefore, by measuring a .gamma.-ray flux, it is possible to measure a fission rate in the vicinity of the reactor core. By using the movable type neutron detector 10 and the movable type .gamma.-ray detector 10A, it is possible to compare and correct a dispersion on detection accuracy in each of the plurality of neutron detectors 8 arranged in the core axial direction and to continuously measure a power distribution in the core axial direction. As described above, in the conventional reactor nuclear instrumentation system, continuous measurement of the axial direction power distribution of the reactor core 3 depends on the movable type neutron detector 10 and the movable type .gamma.-ray detector 10A which are a movable type measuring device. Further, there is a conventional reactor nuclear instrumentation system disclosed in Japanese Patent Laid-open Publication No. HEI 6-289182. In the reactor nuclear instrumentation system, a reactor core is provided with an incore nuclear instrumented fuel assembly. The incore nuclear instrumented fuel assembly is constructed in a manner that a fixed type neutron detector assembly and a fixed type gamma thermometer are housed in a nuclear instrumentation tube. The fixed type gamma thermometer is constructed in a manner that many .gamma.-ray heat detectors are dispersively arranged in a core axial direction. These .gamma.-ray heat detectors are arranged at wide intervals in the middle portion of the core axial direction, and are arranged at narrow intervals in an end portion of the core axial direction. The .gamma.-ray heat detector situated on the uppermost end is arranged on a position within 15 cm from the upper end of a fuel effective portion in the core axial direction and measures a .gamma.-ray flux. In the conventional reactor nuclear instrumentation system, in order to accurately monitor a power distribution in the core axial direction, the movable neutron detector 10 or the movable .gamma.-ray detector 10A is required. For this reason, in the case where only movable neutron detector has been used, there is a problem that it is difficult to monitor a power distribution in the core axial direction with a high accuracy. In the movable neutron detector 10 or the movable .gamma.-ray detector 10A, at least one neutron detector 10 or .gamma.-ray detector 10A must be vertically moved over a range from an outside of the reactor pressure vessel 2 housing the reactor core 3 to the whole length (core axial length) of the reactor core 3 in the TIP guide tube 9 so as to monitor the power distribution. For this reason, this is a factor of making large a mechanical drive device for moving the neutron detector 10 and the .gamma.-ray detector 10A, and its structure is made complicated, and as a result, there is a problem that a moving operation and maintenance are troublesome. In particular, there are required maintenance and management for mechanical drive devices such as the detector driving device for moving the neutron detector 10 and the .gamma.-ray detector 10A, the retrieval device 11 for selecting the TIP guide tube 9, the valve mechanism 15, the shield container 16 or the like. Further, the movable type detectors 10 and 10A are activated, and for this reason, their maintenance work is a work having the possibility that an worker is exposed. In view of the above problem, a skilled person is groping a method of monitoring a power distribution in a core axial direction without using a movable measuring device in the reactor nuclear instrumentation system. The incore nuclear instrumented fuel assembly 6 used in the conventional reactor nuclear instrumentation system is usually provided with four movable neutron detectors 8 and one movable type neutron detector (TIP) 10 or the movable .gamma.-ray detector 10A. Nowadays, a study is made such that a fixed type .gamma.-ray detector in place of the TIP is arranged in the same manner as the fixed type neutron detector 8. However, in the case where four fixed type .gamma.-ray detectors are arranged in the core axial direction, it is impossible to measure a power on the upper portion and the lower portion of the reactor core 3. Further, in the case of extrapolating a power on the upper portion and the lower portion of the reactor core 3 from four measured data or in the case of interpolating it from four measured data, a behavior in a change of power distribution is different at each portion of the core axial direction. For this reason, a great measurement error is caused, and as a result, an accuracy becomes worse. Moreover, in the fuel assembly 4 mounted in the reactor core 3 used in a boiling water reactor, in order to keep each interval between fuel rods with a predetermined distance, a plurality of fuel spacers are dispersively located in an axial direction of the fuel assembly 4. In a node where the fuel spacer dispersively exists in the axial direction of the reactor core 3, a neutron flux becomes low due to an elimination effect of a moderator by the fuel spacer, and for this reason, the following matter is anticipated. That is, its power distribution provides a concave power distribution such that a power locally becomes low. However, the three-dimensional nuclear hydrothermal model stored in the conventional process control computer does not deal with the power distribution as described above. For this reason, in the reactor power distribution computing device 18, an error in a power distribution computation in the core axial direction has been corrected by learning a value read by the movable type detector. If the movable detector is replaced with a fixed type detector, an information on correction is not obtained. Thus providing a problem that an error is caused in an evaluation of power on the node where the fuel spacer exists. Accordingly, in the case where the reactor nuclear instrumentation system is provided with only fixed type measuring device, a measurement error becomes great in a power distribution of the core axial direction. For this reason, there is a need of previously having a freedom of restricting conditions on a reactor operation. As a result, a degree of freedom on a reactor operation is decreased, thus also providing problem of giving an influence to an available factor. In order to improve an accuracy of measuring a power distribution of the core axial direction, it is considered that many fixed type .gamma.-ray detectors are arranged in the core axial direction. In this case, a detector signal line is increased, and there is a restriction of the number of detector connecting cables which are capable of passing through the nuclear instrumentation tube 9 of the incore nuclear instrumented fuel assembly 6. For this reason, there is a limit to locate many .gamma.-ray detectors. As disclosed in Japanese Patent Laid-open Publication No. HEI 6-289182, it is considered that the reactor nuclear instrumentation system is provided with many .gamma.-ray heat detectors. However, in the reactor nuclear instrumentation system, there is no knowledge enough to an analysis on a .gamma.-ray heat contributing range and .gamma.-ray heat, and at least one of .gamma.-ray heat detectors located on the upper and lower ends is arranged on a position within a range of 15 cm from the upper and lower ends of a fuel effective portion of the core axial direction. For this reason, it is difficult to accurately detect a .gamma.-ray heat on the upper and lower ends of a fuel effective portion of the core axial direction. SUMMARY OF THE INVENTION The present invention has been made in view of the problems mentioned above and an object of the present invention is to provide a reactor nuclear instrumentation system and a reactor power distribution monitor system, provided with the above instrumentation system, which can accurately and effectively compute and monitor a power distribution in a core axial direction with the use of only fixed type (immovable or stationary) measuring device without using a movable measuring device and also to provide a power distribution monitoring method. Another object of the present invention is to provide a reactor power distribution monitor system which can dispense a movable measuring device and a mechanical drive device so as to achieve a simplification of its structure and dispense and reduce an exposure work by a worker, and to provide a power distribution monitoring method. A further object of the present invention is to provide a reactor power distribution monitor system which can accurately and precisely compute a power distribution of a core axial direction in consideration of a fuel spacer with the use of a .gamma.-ray heat detector which is less than the number of core axial direction nodes and is arranged in a core axial direction as a fixed type measuring device, and has a high reliability, and to provide a power distribution monitoring method. These and other objects can be achieved according to the present invention by providing, in one aspect, a reactor nuclear instrumentation system comprising: a plurality of incore nuclear instrumentation assemblies arranged in a gap between a number of fuel assemblies charged in a reactor core, the incore nuclear instrumentation assemblies including a fixed type neutron detector assembly comprising a plurality of fixed type neutron detectors dispersively arranged in a core axial direction and a fixed type gamma thermometer assembly comprising a plurality of fixed type .gamma.-ray heat detectors arranged at least in a same core axial direction as the fixed type neutron detectors; PA1 a power range detector signal processing device operatively connected to the fixed type neutron detector assemblies through signal cables; and PA1 a gamma thermometer signal processing device operatively connected to the fixed type gamma thermometer assemblies of the incore nuclear instrumentation assembly through signal cables. PA1 a reactor power distribution computing device which computes a core power distribution through a neutron flux distribution computation by means of a three-dimensional nuclear thermal-hydraulics computing code which evaluates an influence on a node power by a fuel spacer on the basis of a core condition (present) data from a reactor core operating (present) status data measuring means; and PA1 a reactor nuclear instrumentation system which measures a core power distribution of a power range on the basis of an actually measured data from a fixed type detector located in the reactor core, PA1 the reactor power distribution computing device having a structure adapted to compute a node power by dividing the fuel in the reactor core into a plurality of nodes in a core axial direction and to carry out a power distribution computation in consideration of an influence by the fuel spacer to a node power with respect to a node having a fuel spacer. PA1 inputting a core condition data from a core operating status data measuring means to a reactor power distribution computing device; PA1 computing a core power distribution through a neutron flux distribution computation by means of a reactor power distribution computing device with a use of a three-dimensional nuclear thermal-hydraulics computing code in an evaluation of an influence of a node power by a fuel spacer; PA1 carrying out a simulation computation of a gamma ray heating value from the computed core power distribution result; PA1 computing a difference between the computed value and a measurement value of gamma ray heating value from the reactor nuclear instrumentation system as a difference correction for each measurement position by means of a power distribution adaption module; PA1 calculating a difference correction of each axial node by interpolating and extrapolating the difference correction to an axial direction; PA1 correcting the computed core power distribution or neutron flux distribution by proportional distribution to each of nodes around a nuclear instrumentation assembly so as to be adapted to the difference correction and computing; and PA1 monitoring the corrected core power distribution. PA1 adding a contribution of .gamma.-ray heating value from nodes (K-1) and (K+1) vertically adjacent to a core axial node K with a use of a weight correlation function in a case where the axial node for obtaining a .gamma.-ray heating value of the detectors of the fixed type gamma thermometer assembly is set as K; and PA1 computing a .gamma.-ray heating value of each of the .gamma.-ray heat detectors in the core axial position. In preferred embodiments of this aspect, the fixed type fixed type neutron detector assembly of the incore nuclear instrumentation assembly is constructed in a manner that N (number, integer) (N.gtoreq.4) fixed neutron detectors are dispersively arranged in the core axial direction with a predetermined interval and the fixed type gamma thermometer assembly is constructed in a manner that (2N-1) fixed type .gamma.-ray heat detectors are arranged in the core axial direction, N of the (2N-1) fixed type .gamma.-ray heat detectors are arranged at the same core axial position as the fixed type neutron detectors and reminders (N-1) thereof are arranged at an intermediate position in the core axial direction between the fixed type neutron detectors. The fixed type neutron detector assembly of the incore nuclear instrumentation assembly is constructed in a manner that N (number, integer) (N.gtoreq.4) fixed neutron detectors are dispersively arranged in the core axial direction with a predetermined interval and the fixed type gamma thermometer assembly is constructed in a manner that 2N fixed type .gamma.-ray heat detectors are arranged in the core axial direction, N of the 2N fixed type .gamma.-ray heat detectors are arranged at the same core axial position as the fixed type neutron detectors, remainders (N-1) thereof are arranged at an intermediate position in the core axial direction between the fixed type neutron detectors, and further, a further remainder one thereof is arranged below the lowest fixed type neutron detector in a core axial fuel effective portion and at a position separating from a bottom end of the fuel effective portion with a distance of 15 cm or more. The fixed type neutron detector assembly of the incore nuclear instrumentation assembly is constructed in a manner that N (number, integer) (N.gtoreq.4) fixed neutron detectors are dispersively arranged in the core axial direction with a predetermined interval and the fixed type gamma thermometer assembly is constructed in a manner that (2N+1) fixed type .gamma.-ray heat detectors are arranged in the core axial direction, N of the (2N+1) fixed type .gamma.-ray heat detectors are arranged at the same core axial position as the fixed type neutron detectors, remainders (N-1) thereof are arranged at the core axial intermediate position of the fixed type neutron detector and a further remainder one thereof is arranged below the lowest fixed type neutron detector in a core axial fuel effective portion, and furthermore, the remainder thereof is arranged above the lowest fixed type neutron detector in a core axial fuel effective portion at a position separating respectively from a bottom end or top end of the fuel effective portion with a distance 15 cm or more. One of the fixed type .gamma.-ray heat detectors of the fixed type gamma thermometer assembly is arranged on a position L/4 above the lowest fixed type neutron detector in a case where an axial location distance of the neutron detectors is set as L. Furthermore, in a case where the effective fuel portion of the reactor core is divided into several nodes in the core axial direction, each of core axial positions of the fixed type neutron detector and the fixed type .gamma.-ray heat detector are coincident with a center of each of the nodes. The fixed type neutron detectors constituting the fixed type neutron detector assembly is arranged so as to be calibrated respectively by the fixed type .gamma.-ray heat detectors located on the same core axial position and each of the fixed type neutron detectors is calibrated so as to be coincident with a converted .gamma.-ray heating value obtained from the .gamma.-ray heat detector located on the same core axial position. In another aspect, there is provided a reactor power distribution monitor system comprising: In this aspect, the reactor power distribution computing device comprises: a power distribution computing module into which a core condition data is inputted from the operating status data measuring means and which computes as an incore neutron flux distribution, a power distribution, a degree of margin with respect to a thermal operating limit value in according with a three-dimensional nuclear thermal-hydraulics computing code in an evaluation of an influence of a node power by a fuel spacer; a power distribution adaption (learning) module into which a core power distribution computed result is inputted from the power distribution computing module and the adaption module obtains a core power distribution correction reflecting the computed result with reference to the actually measured data from the reactor nuclear instrumentation system; and an input/output device including a display device. A contribution of .gamma.-ray heating value from nodes (K-1) and (K+1) vertically adjacent to a core axial node K is added with a use of a weight correlation function in a case where the axial node for obtaining a .gamma.-ray heating value of the detector of the fixed type gamma thermometer assembly is set as K, and a .gamma.-ray heating value of each of the .gamma.-ray heat detectors in the core axial position is calculated. In a further aspect, there is provided a method of monitoring a reactor power distribution comprising the steps of: In this aspect, in a case of computing the core power distribution with the use of the three-dimensional nuclear thermal-hydraulics computing code, the core power distribution is computed from a node power in consideration of a local distortion of neutron flux by the fuel spacer located at an existing core axial node position. Each of gamma ray heat detectors of the fixed type gamma thermometer assembly is arranged at least on the same core axial position as the fixed type neutron detectors which are dispersively arranged in the core axial direction and an output level adjustment of the fixed type neutron detector is carried out with a gamma ray heating converted from a read value of the gamma ray heat detector. In a still further aspect, there is provided a method of monitoring a reactor power distribution comprising the steps of: According to the present invention in the above various aspect, as is evident from the above description, in the reactor nuclear instrumentation system according to the present invention, the reactor power distribution monitor system including such system and the reactor power distribution monitoring method, it is possible to dispense a movable measuring device such as the movable neutron detector or .gamma.-ray heat detectors, and the axial power distribution can be effectively computed with high precision with the use of only fixed type (stationary or immovable) reactor nuclear instrumentation detector, and thus, it is possible to obtain a reactor core power distribution computing result which reflects an actually measured value with high reliability. Moreover, in the reactor nuclear instrumentation system according to the present invention, the reactor power distribution monitor system including such system and the reactor power distribution monitoring method, the movable measuring device is unnecessary, and it is possible to save a large-sized mechanical drive device such as a tractor device, a drive device or the like. Therefore, a structural simplification can be achieved, and it is possible to reduce or dispense an exposure problem during maintenance work. The incore nuclear instrumentation assembly (reactor power distribution measuring device) is composed of the fixed type (immovable) neutron detector assembly and the fixed type gamma thermometer assembly which are housed in the nuclear instrumentation assembly, i.e. tube. Thus, a movable measuring device such as the movable neutron detector or .gamma.-ray heat detectors is unnecessary, and it is possible to save a large-sized mechanical drive device such as a tractor device, a drive device or the like. Further, it is possible to achieve a simplification of a structure and maintenance work. Furthermore, the reactor power distribution measuring device does not require the movable measuring device and mechanical drive device such as a tractor device, a drive device or the like, and a structural simplification is achieved. The reactor power distribution monitor device and the movable parts are unnecessary. Therefore, maintenance work can be simplified. The fixed type gamma thermometer is employed, and hence, maintenance free can be achieved. The .gamma.-ray heat detector has the same number as the fixed type neutron detector N (number, integer), and is arranged in the same core axial direction, and (N-1) fixed type .gamma.-ray heat (GT) detector is arranged at the intermediate position of the above N fixed type neutron detectors. Thus, it is possible to obtain many GT detector signals in the core axial direction and to further improve a core axial power distribution measurement precision. Furthermore, it is possible to locate the .gamma.-ray heat detector so as to substantially equally cover the fuel effective length and to reduce an extrapolation of the difference between the actually measured value and the computed value. Therefore, it is possible to precisely compute the node power in the vicinity of the lower end higher than the vicinity of the upper end of the fuel effective length from the measured result of the core power distribution. In addition, each of the .gamma.-ray heat detectors is arranged below and above the lowest fixed type neutron detector. Thus, it is possible to locate the .gamma.-ray heat detector so as to substantially equally cover the fuel effective length, and to reduce an extrapolation of the difference between the actually measured value and the computed value. Therefore, it is possible to precisely compute the node power in the vicinity of the lower end higher than the vicinity of the upper end of the fuel effective length from the measured result of the core power distribution. In further addition, the .gamma.-ray heat detector arranged above the lowest fixed type neutron detector at a distance 0.25L. The position where the added fixed type .gamma.-ray heat detector 35 is arranged is a position where the maximum peaking is easy to be generated in the core axial direction in the latest high burnup (combustion) of 8.times.8 fuel or high burnup of 9.times.9 fuel core. Therefore, it is possible to precisely monitor a power distribution at a core position where the maximum linear heat generation ratio is easy to be generated, and to improve a measurement precision. In particular, in the fixed type gamma thermometer assembly, in the case where the locating number of the gamma ray heat detector in the core axial direction is limited in a mechanical design, it is possible to improve a precision in the limited number, thus being optimal. Furthermore, the fixed type neutron detector and the .gamma.-ray heat detector are arranged on the node center divided in the fuel axial direction according to the three-dimensional nuclear thermal-hydraulics computing code used in the reactor power distribution computing device. Thus, it is possible to make same the weight of adjacent nodes with respect to all .gamma.-ray heat detectors, so that the core power distribution computation can be simplified, and also, measurement precision can be improved. In the case where the fixed type neutron detector is not situated at the center of node, a correction is made by interpolating a .gamma.-ray heating value distribution of the reading value of the core axial adjacent node. Moreover, the .gamma.-ray heat detector is a .gamma.-ray source contributing to the detector position, that is, the power distribution advantageously contributes within a range of 15 cm. Thus, even if the .gamma.-ray heat detector is situated on the center of the axial node with a height of 15 cm, the .gamma.-ray heat detector receives the influence of power distribution of the upper and lower (vertical) adjacent nodes. The influence of power distribution from the adjacent nodes is attenuated in series by a function near to an exponential of the locating position z from the .gamma.-ray heat detector. Therefore, in the case where the .gamma.-ray heat detector is not situated at the center of axial node, there is a need of computing a reading value by an axial non-symmetrical weight distribution of the axial power distribution in the node having the .gamma.-ray heat detector and the adjacent nodes. Conversely, in the case of converting the reading value of the .gamma.-ray heat detector into a peripheral power distribution, interpolation or extrapolation is made in the axial direction so as to make the computation easy, and thus, the read value need to be computed. Still furthermore, according to the present invention, a correction of the signal output of the fixed type neutron detector is directly carried out with the use of a .gamma.-ray heating value computed from the .gamma.-ray heat detector signal at the same level of the core axial direction. Thus, it is possible to precisely make a correction on the signal output of the fixed type neutron detector without using the power distribution computing device which includes the three-dimensional nuclear thermal-hydraulics simulation computing code at a high speed with high reliability. A core power distribution computation (calculation) is carried out with the use of the three-dimensional thermal-hydraulics computing code which evaluates an influence on the node power by the fuel spacer, and the core power distribution computed in the core axial direction has a concave and convex from the initial stage. Thus, it is possible to solve the problem of a correction on excessive evaluation of the power peak and on the node power having the fuel spacer, so that the core power distribution can be precisely and accurately learned adapted) and corrected, and a core power distribution having high reliability can be obtained. Still furthermore, according to the present invention, the power distribution computing module of the reactor power distribution computing device computes a core power distribution with the use of the three-dimensional thermal-hydraulics computing code which evaluates an influence on the node power by the fuel spacer. The power distribution adoption (learning) module compares the computed core power distribution result with the actually measured data from the reactor nuclear instrumentation system, and thereby, it is possible to precisely and effectively obtain a core power distribution reflecting the actually measured data. In this aspect, in the case where the power distribution computing device computes a response of the .gamma.-ray heat detector, a consideration is taken such that a range of gamma ray is longer a thermal neutron. Further, by taking not only the axial node having the .gamma.-ray heat detector but also contribution by a .gamma.-ray heating value of upper and lower nodes adjacent to each other into consideration, it is possible to improve a precision of power distribution by the minimum computation. Furthermore, a core power distribution is computed on the basis of the core present data from the core present data measuring means with the use of the three-dimensional thermal-hydraulics computing code which evaluates an influence on the node power by the fuel spacer, and then, a simulation computation value of the .gamma.-ray heating value is obtained from the core power distribution result according to the computing code. The computation value is compared with the measurement value of the .gamma.-ray heating value from each measuring position of the reactor nuclear instrumentation system, and the computed core power distribution or neutron flux distribution is corrected on the basis of proportional distribution to each of nodes. Thus, it is possible to accurately compute a core power distribution which is corresponds to the measurement value and has a high reliability. The three-dimensional thermal-hydraulics computing code evaluates an influence on the node power by the fuel spacer, and has a concave and convex in a core axial power distribution by the fuel spacer at the first stage. Thus, it is possible to solve the problem of a correction on excessive valuation or on underestimation of the node power. Still furthermore, according to the present invention, the output level adjustment of the fixed type neutron detector is carried out with a read value of gamma ray heat detector. Thus, it is possible to simply and easily correct a deterioration in neutron flux measurement sensitivity by the fixed type neutron detector in short time. Still furthermore, in the case where the power distribution computing device computes a response of the .gamma.-ray heat detector, a consideration is taken such that a range of gamma ray is longer a thermal neutron. Further, by taking not only the axial node having the .gamma.-ray heat detector but also contribution by a .gamma.-ray heating value of upper and lower nodes adjacent to each other into consideration, it is possible to improve a precision of power distribution by the minimum computation. The nature and the further characteristic features of the present invention will be made clear from the following descriptions by way of the preferred embodiments with reference to the accompanying drawings.
	description	The application claims priority under 35 U.S.C. §119 from prior provisional application Ser. No. 61/063,623, which was filed Feb. 5, 2008. Fields of the invention include photoneutron and radioisotope generation. Example applications of the invention include production of photoneutrons and radioisotopes for medical, research and industrial uses. There are many medical, industrial, and research applications for neutrons and radioisotopes. Industrial applications include prompt gamma neutron activation analysis (“PGNAA”), neutron radiography and radioactive gas leak testing. Medical applications include brachytherapy, radioactive medicines, radioactive stents, boron neutron capture therapy (“BNCT”) and medical imaging. Production of many useful radioisotopes requires a neutron source that provides a sufficiently high neutron flux (neutrons/cm2-second), measured as the number of neutrons passing through one square centimeter of a target in 1 second. Sufficient sustained neutron flux is generally provided by nuclear reactors. Nuclear reactors are expensive to build and maintain and ill-suited for urban environments clue to safety and regulator concerns. While many useful radioisotopes are produced by nuclear reactors, only a small number of sites around the world can generate medical isotopes in clinically relevant quantities, such as Molybdenum-99 (Mo-99) one of several isotopes in high demand in the medical field. Also, the decay rate of many useful radioisotopes makes remote production of the radioisotopes impossible because the rate of decay does not provide time for processing and transport. Non-reactor neutron sources, such as isotopes that decay by ejecting a neutron are less expensive and more convenient. However, sources such as plutonium-beryllium sources and inertial electrostatic confinement fusion devices are incapable of generating the sustained high neutron fluxes required for many applications. Commonly used medical isotopes are created in light water reactors fueled by critical amounts of fissile material such as uranium-235. Typically, target materials are irradiated within the reactor core for a period of time, then removed and transported to heavily shielded facilities for remote chemical processing. Other reactor types have been proposed for medical isotope production, such as “aqueous homogeneous” reactor designs, also known as “fluid fuel reactors” or “solution reactors.” For example, U.S. Pat. No. 3,050,454 discloses a nuclear reactor system that flows fissile material in a stream through a reaction zone or core via a circulating flow path. U.S. Pat. No. 3,799,883 discloses a method for recovering molybdenum-99 involving irradiation of uranium material, dissolving the uranium material, precipitation of molybdenum by contact with alpha-benzoinoxime, and then contacting the solution with adsorbents. U.S. Pat. No. 3,914,373 discloses a method for isotope separation by the preferential formation of a complex of one isotope with a cyclic polyether and subsequent separation of the cyclic polyether containing the complexed isotope from the feed solution. U.S. Pat. No. 4,158,700 discloses a purification method for producing technetium-99m in a dry, particulate form by eluting an adsorbant chromatographic material containing molybdenum-99 and technetium-99m with a neutral solvent system comprising an organic solvent containing from about 0.1 to less than about 10% water or from about 1 to less than about 70% of a solvent selected from the group consisting of aliphatic alcohols having 1-6 carbon atoms and separating the solvent system from the eluate whereby a dry, particulate residue is obtained containing technetium-99m, the residue being substantially free of molybdenum-99. U.S. Pat. No. 5,596,611 discloses a method of treating the fission products from a nuclear reactor through interaction with inorganic or organic chemicals to extract the medical isotopes. U.S. Pat. No. 5,596,611 attempts to provide a small nuclear reactor dedicated solely to the production of medical isotopes, where the small reactor is of a power level ranging from 100 to 300 kilowatt range, employs 20 liters of uranyl nitrate solution containing approximately 1000 grains of U-235 in a 93% enriched uranium or 100 liters of uranyl nitrate solution containing approximately 1000 grams of uranium enriched to 20% U-235. U.S. Pat. No. 5,910,971 discloses a method for the extraction of Mo-99 from uranyl sulphate nuclear fuel of a homogeneous solution reactor by means of a polymer sorbent. Thus, nuclear reactors remain a key component in the production of useful isotopes. A key medical isotope is technitium-99m, which is a decay product of molybdenum-99. The half life of molybdenum-99 decay into technetium-99m is about 65 hours. Small lead generators are used to ship molybdenum-99 and technetium-99m to medical facilities, where the technetium-99m is added to various pharmaceutical test kits that are designed to test for a variety of illnesses. The four major suppliers of molybdenum-99 are Canada, the Netherlands, Belgium and South Africa. The United States uses about 150,000 doses per week to conduct body scans for cancer, heart disease and bone or kidney illnesses and cardiac stress tests. Because reactors capable of producing technetium-99m (by producing molybdenum-99) only operate in a few countries, production of the important medical isotope depends both upon the export of Uranium and the reliable operation of reactors in other countries. Security and supply concerns are raised by the manufacture, export, and import process. Nuclear reactor facilities have aged and can't be expected to continue reliable production, nor have new facilities been constructed. As an example, a 2007 month long shut down of Canada's NRU reactor in 2007 caused a worldwide shortage of technetium-99m/molybdenum 99). The Netherlands reactor for production of technetium-99m/molybdenum 99 experienced a long shut down in 2008. Other reactor shut downs have occurred in recent years in France. South Africa and other countries. Great benefit can be realized by eliminating the need for a nuclear reactor in the production of radioisotopes, which are typically produced in nuclear reactors because they generate the necessary sustained levels of high neutron flux. Operating reactors have aged, and new reactors have not been built. Many countries, including the United States, lack any facility for the production of medically important isotopes. The invention provides methods for the production of radioisotopes or for the treatment of nuclear waste. In methods of the invention, a solution of heavy water and target material including fissile material is provided in a shielded irradiation vessel. Bremsstrahlung photons are introduced into the solution, and have an energy sufficient to generate photoneutrons by interacting with the nucleus of the deuterons present in the heavy water and the photoneutrons which in turn causes fission of the fissile material. The bremsstrahlung photons can be generated with an electron beam and an x-ray converter. Devices of the invention can be small and generate radioisotopes on site, such as at medical facilities and industrial facilities. Solution can be recycled for continued use after recovery of products. The invention provides methods for the production of radioisotopes. In methods of the invention a solution of heavy water and fissile material is contained in a shielded irradiation vessel. Bremsstrahlung photons are injected into the solution and have an energy sufficient to cause the neutron present in the nucleus of a deuteron to be ejected from the nucleus. The resulting photoneutrons then cause fission of the fissile material. Additional material in the solution can also fission, or can undergo neutron capture. The bremsstrahlung photons can be generated with an electron beam and x-ray converter. Devices of the invention can be small and generate radioisotopes on site, such as at medical facilities and industrial facilities. The heavy water—fissile solution can be recycled for continued use after recovery of products. The invention provides methods for the production of radioisotopes through fission of fissile material and/or neutron capture in target material. In methods of the invention a solution of heavy water (deuterium oxide) and fissile material is contained in a shielded irradiation vessel. Fissile material (typically uranium 235, uranium 233 or plutonium 239) will undergo fission when a neutron of “thermal” energy (˜0.025 MeV) is captured. As fissile material is available with fissionable material (e.g., uranium 235 is available up to a 20/80 ratio of material with uranium 238 after undergoing enrichment) the solution will also include fissionable material, and some of the fissionable material will fission. Fissionable material is material that will undergo fission by capturing a neutron of “epithermal” or “fast” energies. Neutron capture material can also be included in the solution, and is material that can be converted into a useful isotope through the capture of a neutron. In the invention, Bremsstrahlung photons are injected into the heavy water and fissile material solution and have an energy sufficient to interact with the deuterons and cause the neutron in the deuteron nuclei to be ejected. Neutrons generated by photon bombardment of deuterium nuclei are referred to as photo neutrons to differentiate them from neutrons created by the fission process, which are referred to as fission neutrons. The photoneutron field generated in the solution by the interaction of the sufficiently energetic photons and the deuterium then generate useful radioisotopes via fission of the fissile and fissionable material, and/or neutron capture by other target material. The preferred method for generating bremsstrahlung photons is to direct an electron beam onto an x-ray converter. As a small electron accelerator can be used, devices of the invention can be small and generate radioisotopes on site, such as at medical facilities and industrial facilities. The heavy water—fissile solution can be recycled for continued use after recovery of products. Preferred methods and systems of the invention generate radioisotopes from the fission of target material in subcritical amounts via bombardment with photoneutrons (for example, production of molybdenum-99 as a fission product of uranium-235) or through the capture of photoneutrons by other target material included in the fissile-heavy water solution (such as production of yttrium-90 via neutron capture by yttrium-89). Methods of the invention can be carried out without a nuclear reactor, and preferred systems of the invention make use of an electron beam that permits a compact system that can be used on site to generate radioisotopes. Preferred methods and systems of the invention convert an electron beam to bremsstrahlung photons via an x-ray converter and introduce the bremsstrahlung photons into heavy water that includes a subcritical amount of fissile material in a shielded irradiation vessel. The bremsstrahlung photons have sufficient energy to dissociate a neutron from a deuteron (2H) to create photoneutrons. The heavy water both contains the target material and moderates the photoneutron to thermal energies. The invention also provides methods and systems for the treatment of nuclear waste. Used nuclear fuels or other nuclear wastes can be introduced into heavy water and fissile material solution to create the solution of target material and heavy water. Photoneutrons of sufficient energy are generated in the system to cause neutron capture or fission by the target material, allowing for this waste to be converted to more manageable or stable isotopes. To produce a radioisotope that is a fission product, appropriate fissile or fissionable material is included in the solution as additional target material. The bombardment of the target material with photoneutrons then causes a fission reaction of the target material leading to the production of a useful radioisotope as a fission product. To produce a radioisotope that is not a fission product, appropriate material that can capture neutrons to create a radioisotope is included in the solution as additional target material. Thus, methods and systems of the invention can be used to produce radioisotopes that are fission products and radioisotopes that are not available as fission products, e.g. samarium-153 or phosphorus-33. In preferred embodiment methods and systems of the invention, the electron beam has an energy ranging from about 5 to 30 MeV, and most preferably from about 5 to about 15 MeV. In preferred methods and systems of the invention, x-ray convertor material has an atomic number of at least 26, and most preferably at least 71. In preferred embodiments of the invention, radioisotope products are recovered from the irradiation vessel by filtration of the heavy water solution or by interaction with a solvent. The solution with remaining target material can be recycled to perform again as a moderator and medium to contain target material. Recycling can include chemical treatment to adjust pH and addition of heavy water or additional target material. In preferred systems of the invention, the irradiation vessel can be removable from the system, and in other systems of the invention, inlets and outlets can circulate heavy water and target material in and out of the irradiation vessel. A removable irradiation vessel can be moved to a process station to extract the solution of heavy water, radioisotopes and remaining target material for processing. A circulation system can also direct solution to a process station in the case of a fixed irradiation vessel. Systems of the invention can also include a sample station to place target material separate from the heavy water to be irradiated by photoneutrons and fission neutrons in the container. Preferred embodiments of the invention will now be discussed with respect to the drawings. The drawings may include schematic representations, which will be understood by artisans in view of the general knowledge in the art and the description that follows. Features may be exaggerated in the drawings for emphasis, and features may not be to scale. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. FIG. 1 illustrates a preferred method of the invention for producing radioisotopes or for treating nuclear waste. In the method of FIG. 1, a photon environment is created (step 10). The preferred steps for creating photons for the photon environment are creating an electron beam (step 12) and directing the beam onto an x-ray converter (step 12). The photon environment 10 is within an irradiation vessel that contains heavy water and a target material. Bremsstrahlung photons are directed from the x-ray converter into the heavy water within the shielded irradiation vessel that includes a subcritical amount of fissile material, and can also include additional fissionable or neutron capture target material. The photons cause photoneutrons to be ejected from the deuterium present in the heavy water. The heavy water moderates the photoneutrons to thermal energies. The heavy water both contains the target material and moderates the photoneutrons to lower energies which allow for higher rates of fission or neutron capture by the target material. The target material undergoes a fission reaction or neutron capture (step 20). To produce a radioisotope that is a fission product, appropriate fissile or fissionable material is selected as the target material. The bombardment of the target material then causes a fission reaction of the target material leading to a useful radioisotope as fission product. To produce a radioisotope that is not a fission product, additional material that can capture neutrons to create a radioisotope is included in the solution as additional target material. Thus, methods and systems of the invention can be used to produce radioisotopes that are fission products and radioisotopes that are not available as fission products. The additional target material can be nuclear waste in a preferred method for treatment of nuclear waste and undergo fission or neutron capture to convert the nuclear waste to a more acceptable or manageable isotope. Produced radioisotopes are recovered (Step 21). The recovery can be conducted by filtration of the heavy water solution. A subcritical amount of fissile material is utilized in the photon environment. The solution of heavy water, fissile material and any additional target material can be introduced (Step 22) with use of a circulation system or with an irradiation vessel that is removable. A removable irradiation vessel can be moved to a process station to extract the solution of heavy water, radioisotopes and remaining target material for processing. A circulation system can also direct solution to a process station in the case of a fixed irradiation vessel. The solution can be recycled (Step 24) such as by chemical treatment to set a pH level and the addition of heavy water and/or target material. The recycling (Step 24) is conducted after the step of recovering (Step 21) and is readily accomplished with either a circulation system or a removable irradiation vessel. FIG. 2 schematically illustrates events that occur in a preferred device of the invention. An electron beam 30, preferably having an energy ranging from about 5 to 30 MeV, and most preferably from about 5 to 10 MeV, is incident on an x-ray converter 32 (such as tantalum or tungsten) to produce bremsstrahlung photons 34. The bremsstrahlung photons 34 are directed into an irradiation vessel 36 that contains heavy water 38, which provides a source of 2H. Neutrons 40 (referred to as photoneutrons as they originate through the interaction of a deuteron nucleus with a photon), are produced through a photonuclear reaction. A photonuclear reaction occurs when a photon has sufficient energy to overcome the binding energy of the neutron in the nucleus of an atom, where a photon is absorbed by a nucleus and a neutron is emitted. The deuterium 2H has a photonuclear threshold energy of 2.23 MeV. The bremsstrahlung photons have sufficient energy to cause a photonuclear reaction in heavy water. The neutrons 40 are then captured by target material 42, which can trigger a fission reaction of the target material when the target material is fissile or fissionable. During the fission reaction, desired radioisotopes are produced as fission products 44 along with fission neutrons 46. The continuous production of photoneutrons by the photonuclear reaction of heavy water through application of the electron beam 30 to the x-ray converter 32 sustains the fission reaction. While the fission neutrons 46 are also “injected” back to the irradiation vessel and sustain to a certain extent the fission reaction, the fission neutrons alone can not sustain the fission reaction so long as a subcritical amount of target material is used. As discussed previously, target material can also be selected to produce radioisotopes via neutron capture. FIG. 3 shows a cross-section of the irradiation vessel 36 and x-ray converter 32. The x-ray converter 32 receives an electron beam from an electron beam generator 37. A proton beam generator can also be used with an appropriate photon-producing material, but a proton beam and photon-producing material are not as efficient at generating photons. The irradiation vessel 36 is shielded with reflector material 48, which preferably completely surrounds the irradiation vessel 36. A plenum 49 captures gasses released as fission products or due to radiolysis. The irradiation vessel 36 is constructed of material that is resistant to radiation damage and corrosion, such as, but not limited to, various alloys of zirconium or some stainless steels. The reflector 48 is constructed of or contains material that efficiently reflects neutrons back into the irradiation vessel 36, such as, but not limited to, light water, heavy water, beryllium, nickel, or low-density polyethylene. As discussed above, heavy water 50 that contains target material within the irradiation vessel 36 serves both as a source of photoneutrons and as a moderator of photoneutrons and fission neutrons. The irradiation vessel 36 can include or be attached to a mixer or agitator to maintain the solution of heavy water and target material and to inhibit sedimentation of the target material. FIG. 4 illustrates a system for production and extraction of radioisotopes. A circulation loop 52 formed from suitable piping, which should be shielded, defines a loop for the insertion and removal of solution from the irradiation vessel 36. After radioisotope production, solution with its radioisotope product is diverted into a radioisotope recovery station 54 via a valve 56. A sorbent column or filtration system in the station 54 collects the radioisotopes and the solution re-enters the circulation loop 52 via the valve 56. Typically, recovery of the radioisotope at the recovery station can be accomplished after about 12 to 36 hours of filtration or interaction of the solution with the sorbent. A washing and elution station 62 then washes a chemical, such as water, over the sorbent columns or filtration system via a valve 64 to wash elutant carrying purified radioisotopes to an extraction station, thereby rinsing the sorbent 66. Further isotopes of interest may be processed into the radioisotope extraction station where chemical processing suited to the radioisotope of interest is performed. The remaining solution from which radioisotopes have been collected is sent to a recycling station 68 via the circulation loop 52. Recycling can involve chemical treatment, addition of heavy water, and addition of target material. In addition, light water can be introduced into the solution as needed to aid in either chemical processing or to alter the neutronics of the system. While specific embodiments of the present invention have been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the invention, which should be determined from the appended claims. Various features of the invention are set forth in the appended claims.

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