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description | This is a continuation application of Ser. No. 10/381,641 filed on Mar. 26, 2003, now abandoned which was allowed by Notice of allowance dated Nov. 18, 2005. The sole purpose of the present filing is to supply copies of the background publications cited in the specification. The present invention relates to a micro beam collimator for compressing X-ray beams for use in a X-ray diffractometer and a method of carrying out high resolution XRD studies by using the same. Concentrators or condensers producing high intensity X-ray beams in the micrometer size are valuable tools in many industrial and scientific fields. Applications of microfocusing techniques are increasingly reported in metal refining, semiconductor and ceramic industry, as well as in biological and medical sciences [see prior art references 1, 2]. Also, use of micro beams in several types of techniques, such as diffraction, spectroscopy or microscopy, improves their resolution and increases their applicability in many individual cases [see prior art references 1, 2]. Constructively, hard X-ray micro beam formation is overwhelmed by many limitations and technical difficulties. Contrary to visible light, X-ray focusing optics can not be based on conventional lenses, since the refractive index n for the air/solid interface is slightly less than unity. Also, due to this property, an X-ray striking a plane smooth surface will be reflected only if the incident angle remains lower than a critical θc which is calculated in the simplified form to θc=(2δ)1/2 and δ=(Ne2λ2Zρ/(2πmc2A), where N=Avogadro's number, e=electron charge, λ=wave length of radiation, Z=atomic number, ρ=material density, m=electron mass, c=velocity of light and A=atomic mass [see prior art references 3, 4]. Detailed description of these phenomena can be found in many fundamental physics books [see prior art references 5, 6] and so will not be mentioned further in this text. Most approaches for parallel micro beam generation are then based on the multiple total reflection of X-rays, usually inside lead-glass capillaries [see prior art references 1-4, 7, 8]. Directing the source X-rays towards the capillary tube entrance, the incident beam may be compressed, as long as the angle of incidence for each reflection remains below the critical value θc. For lead glass and X-ray photons of 8 KeV, θc does not exceed 3 mrad (0.17°) [see prior art-reference 9]. Practically, this means that a tapered (lead glass) capillary of about 10 cm length will be limited to an entrance opening of about 20-50 μm, if an output beam size of 3-11 μm is required [see prior art references 1, 7]. Hence only an extremely small amount of the incident radiation can be condensed, for which micro-beam experiments of this kind require high input X-ray intensities and are usually performed with high-energy synchrotron radiation sources. Further, an important aspect taken into account is that XRD observations of polycrystalline materials using Bragg-Brentano diffractometers, only the grains oriented parallel to the sample surface and therefore coincident with the zero position of the apparatus contribute to the diffracted intensity. Since in solid materials the grain size is in general in the micrometer range, it is only by chance that favourably oriented grains are illuminated when using cross-sectional micro-beam from capillary tubes, such that in this case, not only the incident but also the diffracted intensity is very low. Therefore, it is the object of the present invention to provide a micro beam collimator for compressing X-ray beams for use in a conventional X-ray diffractometer with the Bragg-Brentano geometry, so as to enable the characterisation of very small sample regions without the need of very large radiation sources (synchrotron). This technical problem is solved by a micro beam collimator having the features of claim 1 and by a method having the features of claim 19. Further features of the present invention are disclosed in the subclaims. A possibility of increasing the amount of radiation that can be condensed is to use reflecting materials with higher θc, such that larger portion of the incident beam is intersected by the collimator. Ideal materials for such a purpose are the heavyweight metals with high electron density=(Z·ρ/A), where Z=atomic number, ρ=material density and A=atomic mass). In addition, metals exhibit higher mechanical strength than glass, allowing more stable and larger capillary-type constructions. Thus, the efficiency of the collimator can be increased, since the longer the capillary and the larger its inlet aperture, the bigger the amount of radiation that can be captured and compressed. These concepts have been considered and successfully applied in the present invention, which deals with a capillary type construction based on opposite polished, oblong reflecting plates made of or coated with a material selected from the group consisting of the heavyweight metals and materials having total reflection properties comparable to those of the heavyweight metals. Preferably, the two plate means are fully made of one of the materials according to the present invention. However, it would be sufficient to only have a coating of the respective material on the surfaces of the two plate means which are facing each other thereby forming a channel for guiding X-ray beams. Preferably, Nickel, Wolfram or Platinum is selected for the plate means. Alternatively, other heavyweight metals or such materials having total reflection properties, in particular critical angles of total reflection, comparable to those of the heavyweight metals may be used. Examples for the latter materials are alloys from heavyweight metals. Each of the two plate means can be made in a one-piece or integral manner. Alternatively, each of the oblong or elongated plates may be made of two or more plate sections which are connected at their end surfaces in an appropriate manner. The micro beam collimator of the present invention produces micro beams having a line- or linear-shaped rectangular cross-section, thin enough in one direction such that fine structure changes can be detected on scanning the sample, but sufficiently long in the other direction such that the largest number of grains is exposed for diffraction. The invention is therefore particularly applicable to diffraction analyses of very thin but long sample regions, as those characteristic of unidirectional interface growth (e.g. oxide layers in tubes or metal plates), requiring a specific sample preparation. The invention applies the total reflection principles preferably on two opposite, flexible, polished, oblong Nickel (Ni)-plates (mirrors) that condense or compress the primary radiation emitted by a 2 kW laboratory X-ray tube with normal focus (Cu-anode). The compression is mono-directional and takes place between the two flexible-Ni-mirrors, which form a narrow channel of variable longitudinal profile (for example convex or tapered). The variability of this profile is assured by the reduced thickness of the Ni plates (chosen as for example 1 mm), so that they are stable but flexible enough, allowing adjustments of the channel profile to be freely done by adequate spacers and screws. Since the critical angle θc for Ni is 0.42°, i.e., 2.5 times higher than for lead glass, a large entrance opening of the channel (about 0.5 mm) is permitted. Nominal dimension of the channel entrance is therefore 0.5 mm×4 mm. At the other extreme, the channel exit portion is provided with a constant cross section of 30 μm×4000 μm along a distance of about 37 mm, such that a quasi-parallel output beam is produced. To further stop oblique radiation, an anti-divergence diaphragm (beam stopper) of 15 μm is placed at the channel exit. The output or compressed beam has therefore final norminal dimensions 15 μm×4000 μm, with measured intensity two orders of magnitude higher than an uncompressed beam with same dimensions. Due to this high brilliance, the micro beam collimator can be operated in combination with common X-ray diffractometers to perform high-resolution structure analysis of very-thin but long solid layers or interfaces. This special kind of sample geometry appears in several technical materials applications, like in the rim region of longitudinally cut nuclear fuel pellets, oxide layers on metal plates, bonding layers in metal sheet-sandwiches, bonding layers in double-wall tubes, etc. To ensure safe handling, according to the present invention, the two plates are contained in a preferably cylindrical housing- or holding means, preferably made of aluminium, mounted in a double-axis micro-positioning stage that is attached to the radiation tube housing. This construction allows easy alignment of the micro beam collimator with respect to the source beam. Summarizing the present invention a micro beam collimator has been developed for condensing hard X-rays, providing very thin but intense low divergent beams. The primary radiation is compressed down to the micrometer size scale by multiple total reflections on the polished inner surfaces of a flat metallic channel of adjustable longitudinal profile. The obtained beam at the exit aperture has nominal dimensions of for example 15 μm×4000 μm (linear-shape cross section) and is two orders of magnitude more intense than the uncompressed radiation going through a slit of the same size. Owing to this high brilliance win, the collimator can be operated even with the conventional radiation tube of a common diffractometer. A prototype, being mounted on a commercial theta-theta diffractometer, has been thoroughly tested for intensity gain, divergence and spatial resolution. Thus, acquisition of accurate XRD patterns on oblong but very thin (only some tens of microns) sample regions has been easily carried out in the laboratory, without need of expensive high energy (sychnchrotron) radiation sources, as demanded in the most approaches of micro beams formation based on glass capillaries. FIG. 1 shows the utilised θ/θ-diffractometer with the micro beam collimator 1 of the present invention attached to an radiation tube 2 and a sample-positioning table or micro-positioner 3 that allows precise movements of the sample S with respect to the micro beam B by means of micro screw 4. Further, FIG. 1 shows a scintillation counter or detector 5, a goniometer head and gimbal means comprising a vertical positioner 7, a tilt stage 8 and an angular frame 9. The whole system shown in FIG. 1 has been used to characterise the beam and to check the technique applicability under realistic operation conditions. Characterisation of the micro beam included intensity gain measurements, as well as beam divergence and spatial resolution tests. Representative XRD observations and lattice parameter measurements were also performed on the longitudinal cut of a nuclear spent fuel pellets and oxidised Zirconium-alloy tubes, demonstrating the capability of the present invention to deliver absolutely resolved (non-overlapping) diffraction spectra of the samples at spatial intervals as low as 30 μm. FIG. 2 shows micro beam collimator 1 more detailed. In particular, vertical positioner 7, tilt stage 8 and angular frame 9 constituting the gimbal means are shown. The two plates, upper plate 10 and lower plate 11, forming the channel for guiding micro beam B can be seen. Oblong plates 10, 11 are received in a holding means which is formed by a cylindrical housing 12 preferably made of aluminium. An outer housing or outer tube 13 is threadably connected at 14 to cylindrical housing 12 and partially encloses plates 10, 11 and housing 12. An inner threaded receiving sleeve 15 supports cylindrical housing 12, plates 10, 11 and outer housing 13 of micro beam collimator 1 for connecting it with the gimbal means. FIG. 3 shows micro beam collimator 1 without outer housing 13. It can be seen that plates 10, 11 project to the right from housing 12. In FIG. 4 micro beam collimator 1 is shown in a top elevational view. FIGS. 5, 6 and 7 are showing upper plate 10, lower plate 11 and the assembly comprising plates 10 and 11. In the shown embodiment plates 10, 11 are made of Nickel (Ni). Plates 10, 11 have identical geometry, namely a length of L=150 mm, a width of b=9 mm and a thickness of t=1 mm. The Ni-Plates 10, 11, one side final-polished with OP-S colloidal silica suspension (grain size 0.04 μm), are positioned with the polished sides to the inside as can be seen in FIG. 7. In the channel exit portion (39), spacer means in the form of two noble metal strip foils 16 of 30 μm thickness are placed between the Ni-plates 10, 11 which are fixed together with a plurality of screws 17 and nuts 18, thereby forming a 37 mm long beam guide of constant cross section of 4 mm×30 μm. Foils 16 of different thickness can be used depending on the required thickness of the generated beam B. As shown in FIG. 6, the length of strip foils 16 amounts to Lf=40 mm leading to a longitudinal extension of the channel exit portion (39) of 37 mm which is defined by the distance between the left most pairs of screws and nuts and the right hand end of plates 10, 11 in FIGS. 5, 6 and 7. Preferably, the channel exit portion (39) having a constant cross section has a length of less than 50%, more preferably of less than 30%, of the total length L of plates 10, 11. The aperture or opening width at the channel entrance arranged on the left hand side of FIG. 7 is variable. Since the Ni-plates 10, 11 are only 1 mm thick and maintain enough flexibility, their separation at this point can be varied as desired by adjustment or spacer screws 19, 20 as shown in FIGS. 2 and 3, such that adjustments of the entrance (critical) angle can be done until the maximum output intensity is obtained. On the external side of Ni-plates 10, 11 small bronze blocks 21, 22 are attached by screws 23, as shown in FIG. 7, to facilitate their mounting in the cylindrical housing- or holder means 12 illustrated in particular in FIGS. 2 and 3. Since blocks 21, 22 are fixed to plates 10, 11 respectively and are interacting with spacer screws 19, 20 they form a part of the adjustment means for adjusting the longitudinal profile of the channel and/or the opening width of the channel entrance. The cylindrical holding means 12 is shown more detailed in FIG. 8 through 12. As shown in FIG. 8, holding means 12 comprises a base part 24 and a cover part 25. The separation plane between base part 24 and cover part 25 is offset from the longitudinal axis of holding means 12, as can be seen in FIGS. 10, 11 and 12. FIG. 9 shows an elevational view of base part 24, wherein the separation plane is identical or parallel with the drawing plane. As best seen in FIGS. 10, 11 and 12 base part 24 has a groove 26 serving as a receiving cavity for receiving Ni-plates 10, 11. After inserting Ni-plates 10, 11 in groove 26 they are held in base part 24 by means of screws 27, 19 and 20 illustrated for example in FIG. 3. Then, base part 24 is closed by cover part 25. Using screws 19, 20 not only the opening width of the beam channel entrance can be varied, but also the longitudinal profile of the formed oblong channel space between Ni-plates 10, 11. By pressing outer or inner screws 19, either a parabolic (convex) or a tapered (concave) profile can be formed. The radiation compression takes place then between the Ni-plates 10, 11 following multiple total reflections. The set of Ni-plates 10, 11 and holding means 12 constitutes the condenser unit of the micro beam collimator 1, which is placed between the radiation tube 2 and the sample S. To adjust the position of this unit with respect to the primary beam a gimbal-system that allows combined vertical and tilting movements of the condenser unit is used. This gimbal-system is composed by three elements; namely the vertical positioner 7, the tilt stage 8 and the angular frame 9 as shown in FIGS. 1, 2 and 3. The mounting sequence is as follows: the condenser unit is inserted in the vertical positioner 7, this last is screwed to the top plate of the tilt stage 8, the last is mounted in the angular frame 9 and finally this frame 9 is attached to the X-ray tube housing 2. The angular frame 9 has already a pre-given angle with respect to the horizontal plane (in the present embodiment −6°), which corresponds to the “take-off” angle of the primary beam according to indications of the X-ray tube provider. The vertical positioner 7 is provided with a micro screw (M-619.00 from PI Physik Instrumente GmbH & Co), which allows vertical displacements of the condenser unit at controllable steps as fine as 10 μm. The tilt stage 8 is a commercial inclinometer of the Type M-041.00, supplied by PI-Physik Instrumente GmbH & Co., Germany. This allows fine variations of the collimator axis orientation around the pre-given take-off angle of the angular frame 9 (−6°), at controllable steps of 0.005°. Once the optimum alignment is achieved, confirmed by collecting the maximum intensity at the collimator exit, both vertical and angular micro-positioners can be locked in their positions by appropriated screws. An outer tube 13 serving as outer housing is partially enclosing the condenser unit, as shown in FIG. 2. Outer tube 13 is illustrated in FIGS. 13, 14 and 15 more detailed. It has a double function, namely to protect Ni-plates 10, 11 from external physical forces and to support a slit diaphragm 28 serving as anti-divergence means at the output of the micro beam path in order to eliminate the oblique radiation. It is well-known from the glass capillaries that small imperfections in the inner reflecting walls or slight misalignments of the entrance opening with respect to the primary beam cause significant intensity variations within the concentrated beams, such as helical or other noncentrosymmetric features [see prior art reference 8] and produce disturbing divergent beams (satellites). In the present invention, to cut the disturbing the oblique radiation and to keep only the central core of the concentrated beam, a 15 μm anti-divergence slit is located in the front of the exit aperture of the condenser unit. The slit diaphragm 28 (beam stopper) comprises two blocks 29 and 30, with polished surfaces (up to 0.04 μm roughness) at the inside of the beam, which are fixed together by screws 31 and are attached to an end cap 32 forming a part of outer housing 13, as shown in FIGS. 13, 16 and 17. The round end cap 32 carrying the slit diaphragm 28 is inserted in the front of a protective tube 33, being possible to lock it by tightening screws 34 after setting the slit-aperture parallel to the Ni-plate aperture. To form the desired slit-aperture, two spacer-rings preferably in the form of foils are laid around screws 31 and thus between blocks 29 and 30. The thickness of the spacer-rings is about 15 μm. Consequently, the slit diaphragm aperture is half of the aperture of the Ni-plates 10, 11 in the channel exit portion 39. To set slit diaphragm 28 at the middle plane of micro beam B, up and down movements of blocks 29 and 30 on two pins 35 can be done by turning screw 36 against the action of springs 37, as is best shown in FIG. 17. Now, experimental data with respect to the present invention will be presented: 1. Instrumentation The apparatus which is shown in FIG. 1 has been employed to characterise and to test the micro beam B of this invention. It consists of a θ/θ mode diffractometer (Seifert XRD-3000) equipped with a standard 2 KW radiation tube with line focus Cu anode and a double collimated (i.e. with anti-scatter and receiving slits) scintillation counter (Seifert SZ 20/SE). A Ni filter placed on the tube housing is utilised to eliminate the Cu—Kβ wavelengths, permitting only Cu—Kα (8.05 keV) to be guided into the collimator. For all experiments the applied power to the radiation tube was 46 KV and 38 mA. The X-ray micro beam collimator 1 is mounted on the radiation tube housing 2. Keeping both the radiation source and detector arms at the goniometer's zero position, the condenser is oriented into the primary beam path, searching for the maximum transmitted intensity by movements of the vertical and tilt micro-positioning systems. The intensity profile of the formed micro beam B is then scanned by oscillating the scintillation counter around the zero-position. For such direct measurements the scintillation-counter must be protected by an intensity-attenuator to avoid its overflow. This is usually achieved by placing several metallic foils in the front of the detector, some tens or hundreds micrometer thick depending on the incoming intensity. During the alignment, also the angular and vertical positions of the anti-divergence slit at the end of the protective tube (33) are optimised. Furthermore, the entrance opening of the Ni-plates and the profile of the channel enclosed by them are adjusted by using the screws (19) and (20), so as to obtain the maximum transmitted intensity. 2. Intensity Gain and Operational Characteristics The brilliance win has been determined by measuring the intensity that is emerged from the collimator with and without having inside the Ni-plates, i.e., with and without beam compression. Both measurements have been done under the same experimental conditions, i.e., maintaining the generator parameters constant and after adjustment of the system for maximum transmitted intensity at the goniometer zero position, with a thickness of 50 μm stainless steel foils as intensity-attenuator in the front of the detector. Under these conditions, the arrangement with Ni-plates gave an intensity of 4×104 counts/s, whereas without the Ni-plates the maximum intensity did not exceed 2×102 counts/s. Doubtless, the 200 times higher intensity attained with the Ni-plates verifies the efficiency of the presented beam-compression system, which is utilisable for hard X-rays in the range 5-30 keV. For comparison, glass mono-capillary concentrators operated with conventional Cu Kα radiation sources reached only a gain of intensity of about 28 [see prior art references 7]. The intensity profile measured at a distance of 205 mm from the exit of the collimator, with 350 μm stainless steel foils in front of the detector, is shown in FIG. 18 as a function of the departure of the detector from the angular zero position. It can be seen that the here presented system provides a very well defined and compact X-ray beam (needle form), without significant disturbing “satellite” peaks or increased background radiation. Due to the narrow and pure beam-profile, not only the instrument centre (zero) position can be defined therefore very precisely (a known handicap of the glass-capillary concentrated beams is the diffuse zero position [see prior art references 8]), but also the obtained Bragg peaks from studied samples are free of deformations and very narrow. This contributes also to obtain very precise lattice parameter measurements. Compared to glass-capillary constructions, the presented concentrator exhibits also some additional advantages. For instance, the intensity of the generated beam during operation is constant, being showed that the system is not sensible to heating effects, which in the case of glass capillaries influence negatively the throughput and disturb the transmitted signal [see prior art references 7]. Also, since our concentrator is made of metal, with a larger absorption coefficient, there is practically no radiation “leakage” through the reflecting walls as in the case of glass-capillaries [see prior art references 2]. Finally, radiation damages in the reflecting Ni-plates have not been detected after several months of continuous operation, different to glass-capillares that show darkening of the walls after a certain time [see prior art references 7], which could affect the efficiency and decrease the reflecting power. 3. Beam Divergence In the arrangement shown in FIG. 1, the distance between the anti-divergence slit at the collimator exit and receiving slit at the detector, when both radiation source and detector are brought to zero position, is fixed at 205 mm. A simple measurement has been therefore conducted to estimate the beam divergence, by placing different receiving slits of increasing apertures (FIG. 19), until a saturating maximum intensity was recorded. Clearly, a saturating maximum value of transmitted intensity is achieved when the width of the receiving slit exceeds the width of the beam at the intersection place, i.e. after the entire beam enters the detector window. The results of the measured intensities as a function of the receiving slit widths are shown in FIG. 20a. In FIG. 20b the same results are represented assuming total symmetry of the beam, i.e. half of the beam intensity is assumed to pass through half of the receiving slit. The 1st derivative of the curve of FIG. 20b is shown in FIG. 20c. Similarly as in references [see prior art references 2,8], a characteristic width is assigned to the micro-beam as the “full width at half maximum” (FWHM) of the peak in FIG. 4c, which implies a width of 120 μm of the beam at a distance of 205 mm from the anti-divergence slit. From simple geometry it can be easily calculated that the corresponding angular divergence is only 0.014°. This value, certainly quite lower than the 0.32° measured for glass monocapillary concentrators under similar conditions [see prior art references 7,8], indicates the high compactness of the here presented micro beam. It should be noted also that the given value of 0.014° is the highest possible angular divergence in our case. This is because any misalignment of the receiving slit position from the ideal plane perpendicular to the beam axis leads to the measurement of higher divergence angles than the real. Since in the measurements described before no optimisation of the receiving slit position was done, the derived angular dependence implies therefore a conservative (high) limit value. The low beam divergence implies another advantage of the presented system with respect to the glass capillaries, since it allows the micro-beam device to be placed at higher distances from the sample surface without sensible loss of spatial resolution. In the following spatial resolution test, certainly confirming the high compactness of the formed beam, the collimator exit is placed at the comfortable distance of 17 mm from the sample, which facilitates the whole experimental handling. As a comparison, conditioned by the larger beam divergence, similar measurements with glass capillaries are done with the exit of the capillary almost in contact with the sample [see prior art reference 8], i.e. at a distance of 2 mm or less from the sample surface. 4. Spatial Resolution The spatial resolution of the micro beam collimator has been determined experimentally under the same operating conditions of routine measurements with the diffractometer of FIG. 1. For this purpose, a specific sample has been prepared, consisting of a junction of two different materials, a stainless steel plate and a CaF2 single crystal which were fixed together forming a well-defined straight interface edge. The examinations were done on the specimen after fine polishing, placing it on the translation stage (M-105.10 PI Physik Instrumente GmbH & Co.) of the sample positioning system. The measuring procedure is described schematically in FIG. 21; the goniometer arms were located at a certain pre-selected angle θ with respect to the sample surface, such that a diffracted peak for the CaF2 single crystal was obtained. The beam spot was then positioned initially on the stainless steel plate and the sample was carefully displaced horizontally at 5 μm steps. The illuminated zone thickness (spot size) was then evaluated from the total sample displacement needed, so that the diffracted intensity varied from the background level to a maximum. (It is only to be remarked that because the prepared sample surface was not perfectly parallel to the growth-plane of the CaF2 crystal used, the measured diffraction angles θ did correspond exactly to be tabulated Bragg-angles for CaF2) A representative result obtained with the micro beam positioned at an incident angle θ=34.540° is given in FIG. 22(a). By differentiation of the curve intensity vs. displacement of FIG. 22(a), the spatial resolution was defined as the displacement interval corresponding to the full width of half maximum (FWHM) of the peak shown in FIG. 22 (b). Such intensity profiles were then obtained for all incident angles θ leading to diffracted peaks of the CaF2 crystal, being the measured spatial resolutions plotted as a function of the incident angle as represented in FIG. 23. The exponential decrease of the spatial resolution follows the expected dependence of the beam width projection on the sample surface with the incident angle, which is equal to the cross-section beam width divided by sin θ. Obviously, at θ=0 the projected width becomes infinite large, while at the extrapolation to θ=90° it approaches the cross-sectional beam width, which in our case is 21.2 μm (FIG. 23). The beam width as a function of distance from the collimator tip can be of course calculated by the known divergence angle (0.014°). Taking into account that the anti-divergence slit aperture is 15 μm and that in the chosen configuration it is positioned 17 mm from the sample surface, the cross-sectional beam width in μm is 15+2·17×103·tan(0.014°)=23.3 μm. The resulted value is in very good agreement with the experimentally obtained (21.2 μm) and confirms once more the high compactness of the created micro beam. 5. High Resolution XRD Investigations The XRD apparatus of FIG. 1 equipped with the micro beam collimator and the sample micro-positioning stage has been used to carry out high resolution crystallographic investigations on the nuclear spent fuel specimen of FIG. 24(a). The sample, a longitudinal cut in the middle of small segment (disk) of a fuel pin, was positioned on the translation stage of the goniometer. By displacing it horizontally, a series of XRD spectra were obtained at several positions on the sample surface. The unit cell constant (parameter) calculated from each individual XRD spectrum is given in FIG. 24 (b) as a function of relative radial position (r/r0) of the beam spot on the sample surface. In the same graph is also shown the average unit cell parameter (a=5.4768 Å) as observed using the conventional collimator, which illuminated the whole sample surface. More about the physical meaning of the structural changes among the radius of the examined sample can be found shortly in ref. [see prior art references 10]. The results of FIG. 24(b) are presented in this section as an example of important high resolution XRD results obtained using the X-ray micro beam concentrator. As is evident from the above description the present invention provides the following advantages: Stable construction against physical external forces. Higher construction lengths allowing larger entrance openings for capturing most radiation available for compression. No radiation leakage through the condenser, walls due to the high density of the Ni-material. No heating effects affecting the transmitted intensity. High stability against radiation damages. Exit flat channel of constant cross-section providing quasi-parallel output beam. Variable nominal output width of the formed beam using different spacer foils between the plates of controllable thickness. Variable cross-section profile of the channel formed between the Ni-plates with tapered or parabolic configurations for maximum transmitted intensity. Variable slit width by using different spacer foils, slightly lower than the output width of the metallic channel in the X-ray condenser. Absorption of most divergent and disturbing radiation and final formation of a low divergent micro beam with narrow-compact intensity profile. Precise definition of the system zero position due to high compactness of the beam. Due to compactness of the incident beam, very thin and well defined diffracted beams (peaks) allowing high precision crystallographic determinations. Due to the low divergence of the formed beam, comfortable distance between the collimator tip and the sample, at least 17 mm, without loss of spatial resolution. Due to the high spatial resolution, possibility of obtaining precise non-overlapping diffraction spectra of the samples at intervals slightly larger than 20 μm. 1. D. Bilderback, S. A. Hoffman and D. Thiel, Science, 263, (1994). 2. Naoki Yamamoto, Rev. Sci. Instrum., 67 (9), (1996). 3. P. Dhez, P. Chevallier, T. B. Lucatorto and C. Tarrio, Rev. Sci. Instrum., 70, (4), (1999). 4. D. H. Bilderback, D. J. Thiel, Rev. Sci. Instrum., 66 (2), 1995). 5. H. Klug and L. Alexander, “X-ray diffraction procedures”, John. Wiley & Sons, Inc., New York (1954). 6. A. H. Compton and S. K. Allison, “X-rays in Theory and Experiment”, D. Van Nostrand Company, Inc., (1935). 7. D. J. Thiel, D. H. Bilderback and A. Lewis, Rev. Sci. Instrum., 64 (10), (1993). 8. I. C. Noyan, P.-C. Wang, S. K. Kaldor, J. L. Jordan-Sweet and E. G. Liniger, Rev. Sci. Instrumen., 71 (5), (2000). 9. C. A. MacDonald, S. M. Owens and W. M. Gibson, J. Appl. Cryst., 32, 160-167, (1999). |
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abstract | Disclosed is an electromagnetic wave-shielding coating material which is superior in both paintability and a electromagnetic wave shielding activity. Also, the coating material is of antistatic activity. The coating material comprises polyaniline (ES) with a solid content of 1-50%, a matrix polymer with a solid content of 1-50%, and additives at a predetermined amount. Also disclosed is an electromagnetic wave-shielding coating material, which is prepared by mixing polyaniline (ES, 100%), an acrylic resin and additives at predetermined amounts and adding the mixture with a hardener and a mixed solvent at predetermined amounts just before use. The electromagnetic-shielding coating material is able to effectively shield electromagnetic waves with a broad band of frequencies and be coated onto cases of various electromagnetic apparatuses, thereby protecting the body from electromagnetic wave pollutions. |
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description | The present application is a continuation of, and claims benefit under 35 USC 120 to, U.S. application Ser. No. 15/405,012, filed Jan. 12, 2017, now U.S. Pat. No. 10,401,540, which is a continuation of, and claims benefit under 35 USC 120 to, international application PCT/EP2015/066340, filed Jul. 16, 2015, which claims benefit under 35 USC 119 of German Application No. 10 2014 216 458.3, filed Aug. 19, 2014. The entire disclosures of U.S. application Ser. No. 15/405,012, international application PCT/EP2015/066340 and German Application No. 10 2014 216 458.3 are incorporated by reference herein. The disclosure relates to an optical element and to an optical arrangement having at least one such optical element. Due to the high absorption of radiation at used wavelengths in the EUV wavelength range between approximately 1 nm and approximately 35 nm, no refractive optics, such as for example lens elements, but rather mirror elements are typically used as optical elements for this wavelength range. Such optical elements which reflect EUV radiation absorb a portion of the EUV radiation, which is incident on the optical surface during operation, and expand in the process. Due to the absorption, or the associated expansion, deformations occur on the optical surface of these mirror elements, which result in undesired optical aberrations. WO 2012/013747 A1 discloses controlling the location-dependent temperature distribution in a substrate of a reflective optical element using a temperature control device in two or three spatial directions to correct aberrations. The temperature control device can have heating elements, for example in the form of resistance heating elements which can be arranged in a grid. It is also possible for radiation sources which act on the substrate or on the reflective optical element by way of thermal radiation (for example IR radiation) so as to thermally influence it to be provided as heating elements. An absorption layer serving for absorption of the IR radiation can here be arranged below a reflective surface of the optical element. In order to produce a temperature distribution in the substrate which is as homogeneous as possible, it is possible for the radiation sources to be configured for supplying thermal radiation onto the front side of the substrate at which the EUV radiation is reflected, or for supplying thermal radiation to the rear side of the substrate. WO 2009/152959 A1 discloses a projection exposure apparatus for semiconductor lithography, having a device for thermally manipulating an optical element which has a front side for reflecting electromagnetic radiation and a rear side. Provided are thermal actuators what act on the optical element from the rear side. The thermal actuators can be LEDs or lasers, the emission spectrum of which can be in the IR wavelength range. Such thermal actuators can emit electromagnetic radiation which at least partially passes through the substrate and which is at least partially absorbed by an absorption layer which is disposed on the front side of the substrate on which a multi-layer coating is also applied. A coating exhibiting high absorption for radiation emitted by the actuators can also be applied on the rear side of a plane mirror. A substrate which is transparent for radiation at the used wavelength can be disposed on the front side of the plane mirror. For the purposes of heat dissipation, optical elements reflecting EUV radiation are typically cooled from the rear side and/or from the peripheral surfaces. Due to issues relating to installation space, the heat sinks used for this purpose frequently cannot be designed in an ideal fashion and generate a non-constant, location-dependently varying temperature distribution on the rear side of such an optical element. In principle, it is possible, with sufficient installation space, for the temperature distribution in a substrate to be appropriately set or thermally homogenized tomographically in all three spatial directions. For example, it is known from WO 2013/044936 A1 to arrange a wavefront correction apparatus having a refractive optical element in a microlithographic projection lens. A first and second partial region of a circumferential peripheral surface of the refractive optical element can be respectively irradiated with first and second thermal radiation which at least partially penetrates the optical element. A refractive index distribution within the optical element, caused by the partial absorption of the thermal radiation, serves for changing, or at least partially correcting, a wavefront error. PCT/EP2013/000728 discloses the arrangement of a wavefront correction apparatus in the form of a mirror having a reflective coating and a mirror substrate in a projection lens. A first and second partial region of a circumferential peripheral surface of the mirror substrate can be respectively irradiated with first and second thermal radiation which at least partially penetrates the mirror substrate. A temperature distribution in the substrate, caused by the partial absorption of the thermal radiation, results in a deformation of the mirror which serves for changing, or at least partially correcting, a wavefront error. In order to neutralize the thermal profile caused by the heat sink or to homogenize the temperature distribution in the substrate, additional heating from the front side of the substrate, for example using a radiation source or using the resistance heating elements which were described further above, can be effected in principle. However, a coating reflecting EUV radiation, which is disposed on the front side of the substrate, could be damaged by the additional introduction of heat and that hysteresis can occur, for example, if the thermal profile on the rear side of the substrate is intended to be set or regulated by the action on the front side of the substrate. The disclosure seeks to provide an optical element and an optical arrangement which allow simplified influencing of the temperature distribution in the optical element. In one general aspect, the disclosure provides an optical element that includes: a substrate, a first coating, which is disposed on a first side of the substrate and is configured for reflecting radiation having a used wavelength in the EUV wavelength range, and a second coating, which is disposed on a second side of the substrate, for influencing heating radiation that is incident on the second side of the substrate. In an optical element according to the disclosure, a second coating is disposed on the second side of the substrate, i.e. the side on which typically a heat sink, which is spaced apart from the substrate, is arranged, which second coating serves for influencing heating radiation that is incident on the second side of the substrate. The second coating can serve in particular for generating a targeted heat introduction of the heating radiation in the proximity of the second side of the substrate, in the proximity of the first side of the substrate, and/or in the volume of the substrate. The coating disposed on the first side typically has an EUV coating or consists of an EUV coating. Such an EUV coating typically has a high reflectance (HR) coating for the used wavelength in the EUV wavelength range. A further coating can be arranged between the HR coating and the substrate in order to protect the substrate against damaging EUV radiation (what is known as an SPL (“substrate protection layer”) coating) and/or in order to prevent undesired deformation of the optical element (what is known as an ASL (“anti stress layer”) coating). Additionally, a cover layer or a cover layer system (what is known as a cap coating) can also be applied on the reflective coating, which cover layer is intended to protect the entire EUV coating against oxidation or corrosion. In one embodiment, the second coating has at least one absorbing layer which absorbs heating radiation at a first heating wavelength which differs from the used wavelength and is greater than the used wavelength. Typical heating wavelengths are generally in a wavelength range above approximately 193 nm, in particular in the visible wavelength range or in the IR wavelength range, for example at more than 1.5 μm, in particular in a wavelength range between 2000 nm and 2100 nm or between 2300 nm and 2500 nm. The heating radiation is received by the absorbing layer and generates a heat introduction within the absorbing layer or within the substrate in the region of the second side, which serves for homogenizing the thermal profile of the substrate. Homogenizing the thermal profile or the temperature gradient in the thickness direction of the substrate can be supported in particular by additional generation of heat introduction in the region of the first side of the substrate. The heat introduction on the first side can be generated, for example, by heating elements, for example by resistance heating elements, which are disposed or positioned on the first side on the substrate, and/or by radiating additional heating radiation onto the first side of the substrate using one or more heating light sources. The heating wavelength of the additional heating radiation can match the first heating wavelength or differ therefrom. In one development, the at least one absorbing layer is disposed between the substrate and at least one anti-reflection layer for suppressing the reflection of the heating radiation at the first heating wavelength. In particular, the at least one absorbing layer can be disposed between the substrate and a plurality of anti-reflection layers which together form an anti-reflection coating. The anti-reflection layer or the anti-reflection coating serves for reducing the reflectance of the heating radiation at the first heating wavelength that is incident on the second side of the substrate or on the absorbing layer and for thus avoiding that a not insignificant portion of the incident heating radiation is reflected. The reflected heating radiation can otherwise be incident directly or indirectly, that is to say via further, strongly reflecting components, for example heat sinks, on other optical elements, for example mirrors or—in the case of a projection exposure apparatus—on the wafer and result here in parasitic undesired heating up. Within the meaning of this application, an anti-reflection layer or an anti-reflection coating is understood to mean a layer or a coating which achieves a decrease in the reflectance by way of destructive interference of the reflected heating radiation. That means that the layer materials and the layer thicknesses of the layers of the anti-reflection coating are selected such that destructive interference occurs for the heating radiation, which is incident on the anti-reflection coating, at the respective heating wavelength. The properties of the layer materials which are relevant for destructive interference are the s (wavelength-dependent) refractive index n and the (wavelength-dependent) extinction coefficient k, which together form the complex refractive index b=n−i k of a respective layer material. In order to produce the destructive interference, the anti-reflection coating can have a multiplicity of individual layers. In this case, the layer construction of the anti-reflection coating is preferably periodic or partially periodic. However, the anti-reflection coating can also have just a single anti-reflection layer, the layer thickness and layer properties of which (complex refractive index) are matched to the properties of the absorbing layer such that the anti-reflection layer has an anti-reflective effect for the heating radiation at the heating wavelength. In one development, an absorptance of the at least one absorbing layer and/or the suppression of the reflection by the at least one anti-reflection layer for heating radiation at the first heating wavelength has a maximum at wavelengths of more than 1500 nm. The layer materials of the at least one absorbing layer and/or of the at least one anti-reflection layer are in this case optimized for heating radiation at a heating wavelength in the above-stated heating wavelength range. In one further embodiment, the at least one layer absorbing the heating radiation at the first heating wavelength is configured for transmitting heating radiation at a second heating wavelength which differs from the first one. The further layers provided in the second coating are also typically transparent for the heating radiation at the second wavelength, with the result that heating radiation having the second heating wavelength that is incident on the second side of the substrate can penetrate the substrate practically without hindrance. The material of the substrate is typically transparent for heating radiation at the second heating wavelength, with the result that the latter passes through the substrate nearly without absorption and is incident on the first coating. The first coating in this case is typically configured to absorb the heating radiation at the second heating wavelength, with the result that the heat introduction is effected in the proximity of the optical surface of the optical element at which the EUV radiation at the used wavelength is reflected. In this way it is possible, if appropriate, to dispense with the irradiation of the first side of the substrate with additional heating radiation. The substrate material can be, for example, quartz glass (SiO2). However, in EUV mirrors typically what are known as zero-expansion materials are used as substrate materials, that is to say materials which have only a very low coefficient of thermal expansion (CTE) in the range of the operating temperatures which are used there. Such a mirror material is synthetic, amorphous quartz glass which has a small proportion of titanium doping. Such a commercially available silicate glass is sold by Corning Inc. under the trade name ULE® (Ultra Low Expansion glass). For heating wavelengths between approximately 193 nm and approximately 2300 nm, the mirror material ULE® exhibits low absorption. As an alternative to the use of a doped quartz glass, specifically a TiO2-doped quartz glass, it is also possible to use a glass ceramic as the zero-crossing material. Such a glass ceramic is, for example, ZERODUR® from SCHOTT. In one further embodiment, a transmittance of the at least one absorbing layer for heating radiation at the second heating wavelength has a maximum at wavelengths of less than 1500 nm. Heating radiation having a second heating wavelength in this wavelength range can pass through the layer almost without loss. The material of the absorbing layer can be, for example, germanium (Ge), which has an absorption edge at a comparatively large wavelength of approximately 1.5 μm. In one alternative embodiment, the second coating has at least one layer which transmits heating radiation at a first heating wavelength and heating radiation at a second heating wavelength which differs from the first one. The heating radiation at the second heating wavelength can be, as described above, within a wavelength range which is transmitted by the substrate to generate heat introduction in the region of the first coating. The first heating wavelength can be selected such that it is strongly absorbed by the substrate material, with the result that the heat introduction of the heating radiation at the first wavelength is effected substantially in the proximity of the second coating. In one development, the substrate is formed from a material which at least partially absorbs heating radiation at the first heating wavelength. By way of example, the substrate material can be ULE®. In this case, the first heating wavelength is typically less than 200 nm or more than approximately 3700 nm. In other substrate materials, for example glass ceramics such as Zerodur®, the wavelength range at which the heating radiation is absorbed deviates from the wavelength range stated above for ULE®. In one development, the at least one transmitting layer is disposed between the substrate and at least one anti-reflection layer for suppressing the reflection of the heating radiation at the first heating wavelength and the second heating wavelength. As described further above, the anti-reflection layer or the anti-reflection coating prevents the reflection of heating radiation which could otherwise result in undesired heat introduction in other components. In one further embodiment, the first coating has at least one reflective layer which is configured to reflect heating radiation at a third heating wavelength. This embodiment can be implemented in combination with the above-described embodiments, that is to say using heating radiation at a first and/or second heating wavelength, wherein in this case, the third heating wavelength typically differs from the first and/or second heating wavelength. However, this embodiment can also be implemented without using heating radiation at the first heating wavelength and the second heating wavelength, that is to say only heating radiation having the third heating wavelength is incident on the second side of the substrate. The reflective layer can be an additional layer which is introduced into the first coating only for the purposes of reflecting the heating radiation. If appropriate, the reflective layer or the plurality of reflective layers which together form a coating that reflects heating radiation can be part of an EUV coating which is applied on the first side of the substrate in any case. The latter may be the case in particular if the EUV coating has an SPL coating or an ASL coating. In this embodiment, the third heating wavelength is typically selected such that it is absorbed weakly or with medium strength by the substrate material. Using ULE® as a substrate material, third heating wavelengths at which the heating radiation is weakly absorbed are between, for example, approximately 400 nm and approximately 2300 nm. Medium-strong absorption of the heating radiation takes place at heating wavelengths of between approximately 3500 nm and approximately 3700 nm in dependence on the thickness of the mirror main body (of the substrate). The preferred wavelength here depends on the absorption capacity of the substrate for the heating radiation and thus on the thickness of the substrate. In one further embodiment, the second coating has at least one anti-reflection layer for suppressing the reflection of heating radiation at the third heating wavelength. As was described further above, if a suitable anti-reflection coating which is optimized for the third heating wavelength is selected, reflection of heating radiation at the second side of the optical element, which could otherwise lead to undesired heat introduction into other components, can be avoided or greatly attenuated. In one development, the reflectance of the heating radiation having the third heating wavelength at the at least one reflective layer and/or the suppression of the reflection of the heating radiation by the at least one anti-reflection layer for the third heating wavelength has a maximum in a wavelength range between 3500 nm and 3700 nm, preferably between 3550 nm and 3650 nm. The at least one reflective layer or the at least one anti-reflection layer are optimized for heating radiation which is in the above-stated wavelength range. If the at least one reflective layer is an SPL coating or an ASL coating, the layer materials or layer thicknesses thereof can also be selected such that they are optimized for the reflection of heating radiation in the above-stated wavelength range. In this embodiment, it is typically advantageous if the heating radiation at the third wavelength is absorbed with medium strength by the substrate material such that the radiation proportion which is reflected at the reflective layer back into the substrate volume is completely absorbed before it can exit the substrate on the second side. In one alternative embodiment, the second coating has a polarization-selective layer which is configured for the transmission of heating radiation at the third wavelength in a first (typically linear) polarization state and for the reflection of heating radiation at the third wavelength in a second (typically linear) polarization state which differs from the first one. In this embodiment, the heating radiation is incident on the second side of the substrate at an angle (different from zero) with respect to the surface normal. The heating radiation is typically linearly polarized heating radiation, as is generated, for example, by heating light sources in the form of lasers or possibly using polarization filters. In this embodiment, the heating radiation generated by the heating light source is typically incident in the first polarization state (i.e. linearly polarized) on the polarization-selective layer and is transmitted thereby, as a result of which only a small proportion of the incident heating radiation is reflected due to the suppression of the reflection or the utilization of the polarization-selective layer as an anti-reflection layer. The transmitted heating radiation passes through the substrate and is reflected at the reflective layer of the first coating in the direction back to the second side of the substrate and is incident again on the polarization-selective layer. In order to ensure that the heating radiation is reflected at the polarization-selective layer back into the substrate volume, the heating radiation is converted from the first polarization state into the second polarization state, which is typically likewise linear, on its way through the substrate volume. In one development, the optical element additionally has at least one polarization-changing layer which is disposed at the first coating between the reflective layer and the substrate or at the second coating between the polarization-selective layer and the substrate. The heating radiation typically passes twice through the polarization-changing layer, which in the process rotates the polarization direction of the heating radiation by 90°, with the result that p-polarized heating radiation is generated from s-polarized heating radiation, or vice versa. If appropriate, a polarization-changing layer can be provided both on the first coating and on the second coating, which both cause a change of the polarization state in each case (retardation), which in sum effects a rotation of the polarization direction by 90°. In one development, the second coating is configured for the transmission of heating radiation at the third heating wavelength, but, if appropriate, only in the first polarization state (see above). The anti-reflection layer, the polarization-selective layer and also the polarization-changing layer, if present, transmit heating radiation at the third heating wavelength which is incident on the substrate from the second side. If the embodiment which was just described is combined with the embodiments which were described further above, in which heating radiation is generated at the first or the second heating wavelength, care is taken that the second coating transmits the heating radiation at the third heating wavelength. In particular, the first, the second and the third heating wavelength should be selected such that they differ. In one embodiment, the substrate is formed from a material which is at least partially transparent for the heating radiation at the second and/or the third wavelength. The substrate material can be, for example, ULE®, which is, as described further above, substantially transparent for wavelengths of between approximately 400 nm and approximately 2300 nm. In particular in the embodiment which is described further above, in which polarized heating radiation is used, the substrate is transparent for the third heating wavelength. In one further embodiment, the optical element is configured in the form of an EUV mirror or in the form of an EUV mask. An EUV mirror serves for reflecting EUV radiation typically over its entire surface. An EUV mask has partial regions which reflect EUV radiation and (typically absorbing) partial regions which do not reflect or only somewhat reflect EUV radiation, which together form a structure which is illuminated with EUV radiation by an illumination unit and is imaged on a wafer using a projection lens. The reflected structures should reflect the highest possible proportion of the EUV radiation and can be formed by an EUV coating or HR coating. One further aspect of the disclosure relates to an optical arrangement, including at least one optical element as described above, and at least one device for thermally influencing the optical element, which device has at least one, preferably a plurality of heating light sources for generating heating radiation at at least one heating wavelength, wherein the device is configured to irradiate the second side of the substrate of the optical element with heating radiation. For this purpose, the heating radiation is typically guided into an intermediate space between a heat sink and the second side of the substrate or is generated in the region of the intermediate space, i.e. the heating light sources are arranged there. The optical arrangement containing the at least one optical element can be, for example, a projection optics for an EUV lithography apparatus, a system for inspecting EUV masks, or an EUV lithography apparatus. In order to effect targeted local heat introduction into the optical element, the device typically has a plurality of heating light sources which direct heating radiation to respectively different locations at the second side of the substrate. In order to influence the local heat introduction in a targeted fashion and to effect in this way homogenization of the thermal profile of the optical element or of the substrate, the device for thermal influencing is configured to set or regulate the radiation output of the heating light sources independently of one another. In one embodiment, the device for thermal influencing has a plurality of heating light sources in a grid-type or matrix-type arrangement. The grid-type arrangement having equidistantly arranged heating light sources allows thermal influencing of the optical element with a desired spatial resolution to be effected. A suitable optics for beam shaping can be connected upstream of each of the light sources. If heating radiation at two or more heating wavelengths is used, two or more arrangements of heating light sources can be provided, if appropriate, in the device, which are configured in each case for generating heating radiation having a respective heating wavelength. For the input coupling of the heating radiation, a plurality of heating light sources, for example in the form of heating diodes, can be mounted typically in a grid-type arrangement at the side of the heat sink which faces the substrate. However, it is also possible to arrange the heating light sources at a distance from the heat sink and for the heating radiation to be guided into the intermediate space between the heat sink and the second side of the optical element using beam guiding devices, for example in the form of fibre-optic cables and to be directed here, for example using deflection elements, for example deflection prisms or mirrors, to the second side of the substrate. In one embodiment, the optical arrangement is configured in the form of an EUV lithography apparatus. The thermally influenceable optical element can be, for example, an EUV mirror which is arranged in an illumination unit or in a projection lens of the EUV lithography apparatus, but can also be an EUV mask. Further features and advantages of the disclosure emerge from the following description of exemplary embodiments of the disclosure, on the basis of the figures in the drawing, which show details of the disclosure, and from the claims. The individual features can be realized respectively on their own or together in any combination in one variant of the disclosure. Identical reference signs are used in the following description of the drawings for components that are the same or functionally the same. FIG. 1 schematically shows an optical element 1 in the form of an EUV mirror which has a substrate 2 made of ULE®, a first coating 3, applied on a first side (upper side) 2a of the substrate 2, in the form of an EUV coating, and a second coating 4, applied on a second side (bottom side) 2b of the substrate 2 which is located opposite the first side. The EUV coating 3 has a coating 3b (what is known as an HR coating) which reflects EUV radiation 5 at a used wavelength λEUV. Applied on the reflective coating 3b is additionally a cover layer or a cover layer system (what is known as a cap coating 3c), which is intended to protect the entire EUV coating 3 against oxidation or corrosion, for example if the EUV mirror 1 is cleaned by way of a hydrogen plasma. The cap coating 3c is arranged adjacently to an optical surface 6 of the EUV mirror 1, which forms the boundary surface of the EUV mirror 1 with the environment. The reflective coating 3b has a plurality of individual layers (not illustrated in FIG. 1), which typically consist of layer pairs of two materials having different refractive indices. If EUV radiation 5 at a used wavelength in the range of λEUV=13.5 nm is used, the individual layers are typically made of molybdenum and silicon. In dependence on the used wavelength λEUV, other material combinations such as for example molybdenum and beryllium, ruthenium and beryllium, or lanthanum and B4C are likewise possible. In addition to the individual layers, the reflective coating 3b typically has intermediate layers to prevent diffusion (what are known as barrier layers). The EUV coating 3 of FIG. 1 has, below the reflective coating 3b, what is known as an SPL (substrate protection layer) coating 3a to protect the substrate 2 against damaging EUV radiation 5. In addition or alternatively to an SPL coating 3a, what is known as an ASL (anti-stress layer) coating can also be provided below the reflective coating 3b on the EUV mirror 1 in order to avoid undesired deformations due to layer stresses. FIG. 1 likewise shows a device 20 for thermally influencing the EUV mirror 1, having a plurality of heating light sources 8, two of which are illustrated by way of example in FIG. 1, which can be attached to a heat sink 21. The heating light sources 8 are configured for generating heating radiation 9 at a first heating wavelength λ1H, with which the second side 2b of the substrate 2, more specifically the second coating 4, is irradiated. The second coating 4 has an absorbing layer 4a, which is applied in the example shown directly to the bottom side 2b of the substrate 2 and which has absorbing properties for the heating radiation 9 at the first heating wavelength λ1H. The material of the absorbing layer 4a can be, for example, a layer of germanium (Ge). Germanium is sufficiently transparent up to a wavelength of approximately 1.5 μm, in particular between 400 nm and 1000 nm. An anti-reflection layer 4b which serves for suppressing the reflection of the heating radiation 9 at the first heating wavelength λ1H is applied onto the absorbing layer 4a. The anti-reflection layer 4b can be, for example, a multilayer coating or a layer stack, for example the following layer stack: (1Si 4.981Si3N4){circumflex over ( )}5. Details relating to this layer stack can be gathered from the patent application DE 102014204171.6, which is incorporated in the content of this application with respect to this aspect. In the shown example, the first heating wavelength λ1H is within the IR range at approximately 2000 nm, with typical values for the first heating wavelength λ1H being between approximately 2000 nm and 2100 nm or between 2300 nm and 2500 nm. The material of the absorbing layer 4a is selected such that the absorptance has a maximum in the above-stated wavelength range of more than 1.5 μm. However, since materials exist which have strongly absorbing properties for electromagnetic radiation over a wide wavelength range, it is not absolutely necessary for the absorbing layer 4a to have a maximum of its absorbance A1H within the above-stated wavelength range. The material of the anti-reflection layer 4b and the layer thickness thereof are selected such that an anti-reflective effect sets in within the above-stated wavelength range, i.e. for the anti-reflection layer 4b, the suppression of the reflection R1H of the heating radiation 9 is at a maximum at the first heating wavelength λ1H. In place of an individual anti-reflection layer 4b, an anti-reflection coating can also be formed on the second coating 4, i.e. a plurality of anti-reflection layers 4b which together have an anti-reflective effect. The heating radiation 9 serves for thermally influencing the EUV mirror 1, more specifically for generating a targeted location-dependent heat introduction into the absorbing layer 4a in order to produce a desired temperature profile in the proximity of the bottom side 2b of the substrate 2 or within the substrate volume which adjoins it. The desired temperature profile typically corresponds to a thermal profile which runs counter to the thermal profile produced in the region of the bottom side 2b of the substrate 2 due to the presence of the heat sink 21, with the result that, in the ideal case, in total, a temperature is established in the substrate 2 which is constant over the entire bottom side 2b. Accordingly, homogenization of the temperature distribution can also be effected at the upper side 2a of the substrate 2 by irradiating the upper side 2a of the substrate 2 with additional heating radiation 14 which is typically generated by a plurality of further heating light sources 15. In the example shown, the heating wavelength λ1H of the further heating light sources 15 corresponds to the first heating wavelength λ1H, although this is not absolutely necessary. During operation, EUV radiation 5 is incident on the EUV mirror 1, the intensity distribution of which varies in a location-dependent manner over the optical surface 6 and is generally not constant over time. The intensity distribution of the EUV radiation 5 which varies in a location-dependent manner results in a locally differing heat introduction at the upper side 2a of the EUV mirror 1, and thus in a temperature distribution which is not spatially or temporally constant. The further heating radiation 14 serves for counter-heating, that is to say those regions in which the substrate 2 or the EUV coating 3 has a comparatively low temperature are additionally heated to homogenize the temperature distribution and to obtain, in the ideal case, a constant temperature on the optical surface 6 overall. In the example illustrated in FIG. 2A, and in contrast with FIG. 1, the upper side 2a of the substrate 2 is heated from the bottom side 2b of the substrate 2, i.e. through the substrate 2. For this purpose, a second heating light source 10 is arranged on the heat sink 21, which generates heating radiation 11 at a second heating wavelength λ2H, which in the illustrated example is approximately 400 nm, with typical values being between approximately 400 nm and approximately 1500 nm. The second coating 4, more specifically the layer 4a which absorbs the heating radiation 9 at the first heating wavelength λ1H, is transparent for the second heating wavelength λ2H. The heating radiation 11 at the second heating wavelength λ2H is transmitted by the substrate 2 and absorbed at the EUV coating 3. If the absorption by the EUV coating 3 is not sufficient, an additional absorbing layer or coating, for example a metallic layer, can be provided, if appropriate, on the side thereof which faces the substrate 2. In the ideal case, the anti-reflection layer 4b is configured such that the suppression of the reflection is maximum both for heating radiation 9 of the first heating wavelength λ1H and for heating radiation 11 of the second heating wavelength λ2H. If appropriate, the layer 4a, which transmits both the heating radiation 11 at the second heating wavelength λ2H, can also serve as an anti-reflection layer for the second heating wavelength λ2H and possibly for the first heating wavelength λ1H, such that the provision of an additional anti-reflection layer can be dispensed with. In one alternative exemplary embodiment illustrated in FIG. 2B, the second coating 4 has a layer 4a′ which transmits both heating radiation 9 at the first heating wavelength λ1H and also heating radiation 11 at the second heating wavelength λ2H. The transmissive layer 4a′ in the example shown is made of germanium (Ge) and has a high transmittance T1H, T2H for both heating wavelengths λ1H, λ2H. The heating radiation 11 at the second heating wavelength λ2H, which is generated by the second heating light source 10, passes through the substrate 2, as in FIG. 2A, and is absorbed at the EUV coating 3, more specifically at the SPL coating 3c, in order to produce heat introduction here. The heating radiation 9 at the first heating wavelength λ1H, which is generated by the first heating light source 8 and is in the IR range, is strongly absorbed within the volume of the substrate 2 made of ULE® and therefore produces a heat introduction in the proximity of the bottom side 2b of the substrate 2. The second coating 4 has an anti-reflection coating or an anti-reflection layer 4b, which serves both for suppressing the reflection of the heating radiation 9 at the first heating wavelength λ1H and for suppressing the reflection of the heating radiation 11 at the second heating wavelength λ2H. If appropriate, it is also possible to dispense with the provision of the transparent layer 4a′. The second heating wavelength λ2H can be selected to be between approximately 2650 nm and approximately 2800 nm, or between approximately 4000 nm and approximately 10 000 nm, in particular between 4500 nm and 5500 nm. According to the preceding example, the first heating wavelength λ1H can be between approximately 2000 nm and approximately 2100 nm, and between approximately 2300 nm and approximately 2500 nm. FIGS. 3A-3C show examples of EUV mirrors 1, in which the EUV coating 3 has an additional, bottommost layer 3d, which is configured for reflecting heating radiation 13 at a third heating wavelength λ3H, which is generated by a third heating light source 12. In place of an additional reflective layer 3d, as is shown in FIGS. 3A-3C, it is also possible, if appropriate, for the SPL coating 3a to serve as the layer which reflects heating radiation 13 at the third heating wavelength λ3H, with the result that the additional reflective layer 3d can be dispensed with. The heating radiation 13 at the third heating wavelength λ3H serves for generating heat introduction within the volume of the substrate 2, which likewise serves for homogenizing the temperature distribution. FIG. 3A shows an example of an EUV mirror 1, in which the heating radiation 9 at the first heating wavelength λ1H and the heating radiation 11 at the second heating wavelength λ2H are supplied analogously to FIG. 2A. In addition, heating radiation 13, which has a third heating wavelength λ3H and is generated by a third heating light source 12, is transmitted by the second coating 4, passes through the substrate 2, is incident on the reflective layer 3d, and is reflected at the latter back into the substrate 2. The absorptance of the ULE® material of the substrate 2 with respect to the heating radiation 13 at the third heating wavelength λ3H in this case is medium strong, such that the heating radiation 13, which is reflected at the reflective layer 3d, does not propagate all the way to the bottom side 2b of the substrate 2 and cannot exit at the bottom side 2b. In the example shown in FIG. 3A, in which the heating radiation 13 is absorbed by the substrate 2 with medium strength, the third heating wavelength λ3H is approximately 3600 nm, with typical values for the third heating wavelength λ3H in this case being, in dependence on the thickness of the substrate 2, between approximately 3500 nm and approximately 3700 nm. With a specified thickness of the substrate 2, it is possible to ascertain the optimum heating wavelength on the basis of a wavelength-dependent transmission curve for the material of the substrate 2, in the present case ULE®. Similar relationships apply to a substrate 2 made of a different material, such as for example Zerodur®. The reflectance R3H of the reflective layer 3d is maximum, or has a maximum, within the above-stated wavelength range. In the example shown in FIG. 3A, the second coating 4 has an anti-reflection layer 4b, which, in addition to suppressing the reflection of the heating radiation 9 at the first heating wavelength λ1H and to suppressing the reflection of the heating radiation 11 at the second heating wavelength λ2H, is also configured for suppressing the reflection of the heating radiation 13 at the third heating wavelength λ3H. The anti-reflection layer 4b typically has a local maximum of the suppression of the reflection or a minimum reflectance at the respective heating wavelength λ1H, λ2H, λ3H. Whereas in the examples shown in FIGS. 2A, 2B and FIG. 3A the heating radiation 9, 11, 13 is aligned substantially perpendicular to the bottom side 2b of the substrate 2, in the example shown in FIG. 3B, the heating radiation 13 at the third heating wavelength λ3H is aligned with an angle a with respect to the surface normal of the bottom side 2b of the substrate 2, which is typically no more than approximately 10°. In order to align the heating radiation 13 under the angle α, the third heating light source 12 can be positioned on the heat sink 21 such that it is, if appropriate, suitably tilted, and/or the emission characteristic thereof can be appropriately set. As is likewise seen in FIG. 3B, the third heating light source 12, which can be configured, for example, as a laser diode, generates linearly polarized heating radiation 13 which, in the example shown in FIG. 3B, has a first polarization state (s-polarization) with respect to an XZ plane, which corresponds to the drawing plane, of an XYZ coordinate system. In the example shown in FIG. 3B, the second coating 4 has a polarization-selective layer 4a″, which transmits the s-polarized heating radiation 13 at the third heating wavelength λ3H, with the result that it passes through the substrate 2 and is reflected back at the layer 3d, which reflects the heating radiation 13, of the first coating 3. Arranged between the upper side 2a of the substrate 2 and the layer 3d, which reflects the heating radiation 13, a polarization-changing layer 3e is arranged in FIG. 3B, through which the heating radiation 13 at the third heating wavelength λ3H passes twice, and which effects a rotation of the polarization direction of the heating radiation 13 by 90° such that the reflected heating radiation 13 is p-polarized. The p-polarized heating radiation 13 is incident on the polarization-selective layer 4a″ of the second coating 4, and is reflected thereby back into the volume of the substrate 2. The EUV mirror 1, shown in FIG. 3C, differs from the EUV mirror 1, shown in FIG. 3B, merely in that the second coating 4 rather than the first coating 3 is provided with a polarization-changing layer 4c. The s-polarized heating radiation 13 passes through the polarization-changing layer 4c and is circularly polarized thereby before the heating radiation 13 enters the substrate 2. The circularly polarized heating radiation 13, which is reflected back at the reflective layer 3d, is again incident on the polarization-changing layer 4c and is converted into p-polarized heating radiation 13. The p-polarized heating radiation 13 is incident on the polarization-selective layer 4a″, and is reflected thereby back into the substrate 2. In the examples shown in FIG. 3B and FIG. 3C, the third heating wavelength λ3H is selected such that it is absorbed only slightly by the substrate 2, i.e. it is typically between approximately 400 nm and approximately 2300 nm. As can be seen in FIGS. 3A-3C, the entire second coating 4 is configured to be transmissive for the heating radiation 13 at the third heating wavelength λ3H and for the heating radiation 11 at the second heating wavelength λ2H. The polarization-selective layer 4a″ is here configured to absorb the heating radiation 9 at the first heating wavelength λ1H in order to heat the substrate 2 in the region of the bottom side 2b thereof. In the devices 20, which are described further above in connection with FIGS. 2A, 2B and FIGS. 3A-3C, in each case only a first, second or third heating light source 8, 10, 12 for generating heating radiation 9, 11, 13 at a respective heating wavelength λ1H, λ2H, λ3H is shown. However, typically a plurality of first, second or third heating light sources 8, 10, 12 are arranged on the heat sink 21 in a grid-type arrangement (matrix) so as to achieve thermal influencing of the EUV mirror with a desired spatial resolution. The heating radiation 8, 10, 12, generated by a heating light source, can be substantially monochromatic, i.e. the radiation intensity is concentrated around the maximum at the heating wavelength, as is the case for example in laser diodes or LEDs. Alternatively, it is also possible to use heating light sources which emit heating radiation in a comparatively broadband wavelength range, wherein the desired heating wavelength or a narrow-band heating wavelength range is selected by suitable wavelength-selective filters. As an alternative to the devices 20, which are shown further above in connection with FIG. 1 to FIGS. 3A-3C, the first, second and/or third heating light sources 8, 10, 12 can be arranged at a distance from the heat sink 21 and be supplied to the EUV mirror 1 by way of beam guide devices, for example in the form of fibre-optic cables. In order to align the heating radiation 9, 11, 13 in this case with the substrate 2, it is possible for deflection devices to be attached to the heat sink 21, for example, which deflect the heating radiation 9, 11, 13, which exits the fibre-optic cables, in the direction of the bottom side 2b of the substrate 2. FIG. 4 shows, in a highly schematic fashion, an optical arrangement in the form of an EUV lithography apparatus 101, in which the EUV mirrors 1 of FIG. 1, FIGS. 2A, 2B or of FIGS. 3A-3C can be integrated. The EUV lithography apparatus 101 has an EUV light source 102 for generating EUV radiation, which has a high energy density in an EUV wavelength range below 50 nm, in particular between about 5 nm and about 15 nm. The EUV light source 102 may for example take the form of a plasma light source for generating a laser-induced plasma or be formed as a synchrotron radiation source. In particular in the former case, a collector mirror 103 may be used, as shown in FIG. 4, in order to focus the EUV radiation of the EUV light source 102 into an illumination beam 104 and in this way increase the energy density further. The illumination beam 104 serves for the illumination of a structured object M via an illumination system 110, which in the present example has five reflective optical elements 112 to 116 (mirrors). The structured object M may be for example a reflective mask, which has reflective and non-reflective, or at least much less reflective, regions for producing at least one structure on the object M. Alternatively, the structured object M may be a plurality of micro-mirrors, which are arranged in a one-dimensional or multi-dimensional arrangement and which are possibly movable about at least one axis, in order to set the angle of incidence of the EUV radiation 104 on the respective mirror. The structured object M reflects part of the illumination beam 104 and forms a projection beam path 105, which carries the information about the structure of the structured object M and is radiated into a projection lens 120, which produces a projected image of the structured object M or of a respective partial region thereof on a substrate W. The substrate W, for example a wafer, includes a semiconductor material, for example silicon, and is arranged on a mounting, which is also referred to as a wafer stage WS. In the present example, the projection lens 120 has six reflective optical elements 121 to 126 (mirrors) in order to produce an image of the structure that is present on the structured object M on the wafer W. The number of mirrors in a projection lens 120 typically lies between four and eight; however, only two mirrors may also possibly be used. In order to achieve a high imaging quality in the imaging of a respective object point OP of the structured object M onto a respective image point IP on the wafer W, highest desired properties are imposed on the surface form of the mirrors 121 to 126; and the position or the alignment of the mirrors 121 to 126 in relation to one another and in relation to the object M and the substrate W also involves precision in the nanometre range. Each of the EUV mirrors 121 to 126 can be configured as described further above in connection with FIG. 1, FIGS. 2A, 2B and FIGS. 3A-3C, and a dedicated device 20 for thermal manipulation, which can be configured as described above, for example, can be assigned thereto. In the projection lens 120, illustrated in FIG. 4, the sixth mirror 126 is configured in the form of a thermally influenceable EUV mirror 1 according to FIG. 3A, and a device 21 for thermal manipulation is assigned thereto, which is configured to individually drive the heating light sources 8, 10, 12 (not shown in FIG. 4) to set a desired, typically homogeneous temperature distribution in the EUV mirror 126 and to thus avoid undesired deformations and resulting undesired aberrations on the optical surface 6 (cf. FIG. 3A) of the sixth EUV mirror 126. It is additionally possible for one or more sensors for capturing the temperature of the EUV mirror 126 or of the optical surface 6 and/or the temperature of the substrate 2 of the EUV mirror 126 to be arranged in the EUV lithography apparatus 101, so that the device 20 for thermal influencing can effect regulation of a location-dependent heat introduction into the EUV mirror 126 in order to produce in a targeted fashion a desired location- and time-dependent heat introduction in the EUV mirror 126, with the result that the temperature distribution of the EUV mirror 126 is homogenized. Additionally or alternatively, it is also possible for the EUV mask 130 to be thermally influenced by way of a device 20, as is illustrated in FIGS. 2A, 2B or in FIGS. 3A-3C. The EUV mask 130 in this case is constructed like the EUV mirrors 1, which are described further above, wherein partial regions in the form of an absorber material, which do not or only slightly reflect the incident EUV radiation 5, are formed additionally on the upper side of the EUV coating 3. The absorbing partial regions together with the reflective partial regions form the structure of the EUV mask 130 to be imaged. It is to be understood that the EUV mirrors 1, described further above, or the devices 20 for thermal influencing, can also be advantageously used in other optical systems for the EUV wavelength range, for example in inspection systems for EUV masks. |
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047626631 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the presently preferred embodiments of the invention, an example of which is illustrated in the accompanying drawings. FIG. 1 shows a functional block diagram of a basic circuit according to the present invention. Numeral 10 designates generally a switch having two pairs of contacts, one of which is normally open (contact pair 20 in FIG. 1), and the other of which is normally closed (contact pair 30 in FIG. 1). Connected across contact pair 20 is first test circuit 40. Similarly, connected across contact pair 30 is a second test circuit 50. First test circuit 40 is adapted to produce a first status signal STAT1 normally indicative of the state of contact pair 20. Similarly, second test circuit 50 is adapted to produce a second status signal STAT2, normally indicative of the state of contact pair 30. Since it is given that when the switch is operating properly, the contact pairs will be in opposite states, the value of STAT1 and STAT2 should never be equal if the switch is operating properly. Logic circuit 60 compares the values of STAT1 and STAT2 and produces a monitoring signal having a first value if STAT1 and STAT2 are not equal, thus indicating normal operation, and a second value if STAT1 equals STAT2, thus indicating that the switch 10 is malfunctioning. The circuit depicted in FIG. 1 also includes a test control circuit 70. Test control circuit 70, in response to a control signal C, is capable of producing a first enable signal EN1 and a first select signal SEL1 for first test circuit 40, and a second enable signal (EN2) and a second select signal (SEL2) for second test circuit 50. Details of the construction of a circuit serving as test control circuit 70 will be readily apparent to one having ordinary skill in the art. When the enable signals have a first logical value (e.g. low) first and second test circuits 40 and 50 operate normally, i.e., the signals STAT1 and STAT2 are indicative of the actual state of contact pair 20 and 30, respectively. When the enable signals assume a second value (e.g., high), the signals STAT1 and STAT2 are no longer reflective of the condition of the contact pairs, but instead assume a value dependent on the value of the SEL1 and SEL2 signals, respectively. Thus, it is possible to "inject" forbidden logical values into the system. When the enable signals enable testing, and the select signals select the same value for STAT1 and STAT2, an error condition is artificially created. If the logic circuit does not produce a malfunction indication in response to the injection of the invalid logic state, then it may be inferred that the logic circuit is malfunctioning or that the test circuits are malfunctioning, and appropriate corrective measures may be undertaken. Switch 10 is intended to represent a form "C" switch, but a form "D" switch, or any other switch which includes two pairs of contacts which normally have different states, may be used. If a form "D" switch is used (make before break), there is naturally a brief instant when both switches are closed. The brief existence of an invalid logic state, however, can be identified and discriminated so that it does not produce an error signal. Also, in the foregoing discussion and the discussion which follows, it is assumed that there are separate enable and select signals generated. It will apparent to one of ordinary skill in the art, however, that the same enable and select signal could be sent to first test circuit 40 and second test circuit 50 and still provide satisfactory operation of the system. Finally, for maximum reliability, it is desirable that each "channel" (defined by a pair of contacts) have an independent power supply. In the circuit shown in FIG. 1, two power supplies are represented by separate numerals for the triangles representing ground. The power supplies are assumed to have their high sides tied together between the pairs of contacts at +V. FIG. 2A shows a preferred circuit to serve the function of first test circuit 401. This can be seen, the circuit comprises a first relay 80 having a first terminal 90, a second terminal 100, and a third terminal 110. The first terminal 90 is connected to the contact of switch 20 which is not directly connected to the other pair of contacts 30. The third contact 110 is selectably connectable to either first terminal 90 or second terminal 100 depending on the position first relay arm 120. The position of first relay arm 120 is controlled according to whether or not a current flows first relay coil 130, a condition which is, in turn, controlled by whether EN1 is high or low (i.e., the presence or absence of EN1). The circuit also includes a second switch or relay 140 having at least fourth terminal 150 and a fifth terminal 160. The second terminal 100 of first relay 80 is connected to fourth terminal 150 of second relay 140. The fifth terminal is connected to +V. Whether the fourth terminal, and thus the second terminal, is connected to +V is controlled by the position of second relay arm 180, which is in turn controlled by second relay coil 190. In other words, the connection between fourth terminal 150 and fifth terminal 160 will be made when current flows through coil 190, which occurs when the select signal SEL1 goes high. Relays 80 and 140 may be any suitable relay, for example, a Teledyne 712M-112. Also, relay 140 may be replaced by a simple electromagnetic switch. The output from third terminal 110 is used as input for optoelectronic isolation circuit 195. When terminal 110 is high (that is, when it connected to +V either through contact pair 20 or through second relay 140 in a manner which will be described below) current flows through the LED internal to optoelectronic isolation circuit 195 so that it emits light. This transmission of light renders the diode in the output side of optoelectronic isolation circuit conductive, thus rendering a low or logical 0 signal for status signal STAT1. Otherwise, the status signal STAT1 remains high. In normal operation, the enable signal would be low, which directly connects switch 20 to the optoelectronic isolation circuit 195, so that the logical value of status signal STAT1 would be reflective of whether contact pair 20 is open or closed. When it is desired to test the circuit, on the other hand, the enable signal EN1 goes high to energize relay coil 130, thus moving relay arm 120 from contact with first terminal 90 to contact with second terminal 100. The logical value of status signal STAT1 will depend upon whether the switch defined by relay arm 180 and fourth contact 150 is open or closed. The state of the switch is controlled by the select signal SEL1. When SEL1 is low, the switch remains open, no current flows through the optoelectronic isolation circuit 195, and the STAT1 signal remains high. When the switch is closed, current flows through the light emitting diode within optoelectronic isolation circuit 195 and so the STAT1 signal becomes low. The optoelectronic isolation circuit may be any suitable circuit, for example, an HCPL-3700. Details of construction and operation of second test circuit 502 are identical to those just described, and will be omitted here for the sake of brevity. Let it suffice to say that second test circuit 50 as shown in FIG. 2B also comprises a pair of relays 85, 145, interconnected in a fashion similar to that described above for relays 80, 140, respectively, and an optoelectronic isolation circuit 197. With a circuit such as that just described, it is expected that periodic testing of each contact input circuit on a 4-6 week interval will be feasible. As mentioned above, a contact arrangement such as a form "C" contact arrangement offers a means in inherent error detection. Of the four possible combinations (00, 01, 10, and 11), only two are valid, and the other two are detectable as invalid. The test circuit in effect forces the inputs to assume the invalid states of 00 and 11 (those having even parity) and verify that the built-in error detection logic is working correctly. Until the next periodic test, the contact closure's input system continuously checks for valid inputs, and if a wire, connection, or switch should fail "shorted" or "open" the logic processor is programmed to take appropriate action such as reporting the fault and reverting to a safer or preferred state. In addition to testing the continous test capability of the contact closure input logic processor, the automatic tester sets up test conditions to check the system logic from input to output. When enabled, for example, by a key switch, the auto tester can force the status of each individual contact closure input (CCI) signal to be either closed or open. It does this by outputting a logic "0" and thus causes the switch to appear to be closed. Thus, all four possible states may be injected into the system, and proper system operation may be ascertained by means of output signals which are monitored by the automatic tester via data links. FIG. 3 shows the testable contact closure input circuit as part of an overall system such as would be used in a safety grade application such as in a nuclear power plant. In the arrangement shown in FIG. 3, surge withstand circuits 200 and 210 have been interposed between the test circuits and their respective pair of contacts. The surge withstand circuits are used to decouple the plant contacts from the test injection circuit during invalidity tests, and they also serve to limit surge withstand circuit test currents to the test circuitry. These test circuits are well known to one of ordinary skill in the art, and typically include choke coils to reject RF signals, appropriate resistor networks, and capacitor networks. Typically, they are designed to withstand up to a 3,000 volt surge. Downstream of first test circuit 40 and second test circuit 50 are debounce circuits 240 and 250. These circuits "debounce" the signals (i.e., prevent erroneous indications of multiple depression of a switch inadvertently caused by "bounce" in the switch) by accepting a change in state only after the signal level has been stable for several consecutive samples. Such debounce circuits are well known in the art, and commercially available. For example, a Motorola MC14490 Hex Contact Bounce Eliminator would suffice in this application. Finally, an additional pair of optoelectronic isolation circuits, 260 and 270 are interposed between the debounce circuits and the logic circuit, respectively, in order to provide an additional degree of electric isolation and to prevent any circulating currents. FIG. 4 shows the self-testing monitoring circuit incorporated into the monitoring system of a nuclear plant. Switch 10 having normally open contacts 20 and normally closed contacts 30 represents any of the multitude of such switches (e.g., form "C" or form "D") normally included in a control system panel of a nuclear reactor. The self-testing monitoring circuit connects across the contacts as previously described, and produces a monitor signal which the monitoring system uses to determine either proper operation or malfunction and response. If will obvious to one of ordinary skill in the art that many modifications of the specific embodiments described above can be made without departing from the spirit of the invention. For example, if desired, the first and second relays may be replaced with optoelectronic isolation circuit for forcing the status outputs STAT1 and STAT2 high or low as desired. Therefore, the invention should not be regarded as being limited to the embodiments specifically described above, but instead should be regarded as being fully commensurate in scope with the following claims. |
abstract | The power monitoring system has: a local power range monitor (LPRM) unit that has a plurality of local power channels to obtain local neutron distribution in a nuclear reactor core; an averaged power range monitor (APRM) unit that receives power output signals from the LPRM unit and obtains average output power signal of the reactor core as a whole; and an oscillation power range monitor (OPRM) unit that receives the power output signals from the LPRM unit and monitors power oscillations of the reactor core. The output signals from the LPRM unit to the APRM unit and the output signals from the LPRM unit to the OPRM unit are independent. |
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050080709 | claims | 1. A fuel assembly comprising a plurality of first fuel rods each of which contains nuclear fuel material but does not contain burnable poison and a plurality of second fuel rods each of which contains nuclear fuel material and burnable poison, characterized in that an amount of the burnable poison in a lower region of said fuel assembly is smaller than that in an upper region of said fuel assembly, and that when each of said second fuel rods is divided into an upper region and a lower region, a region of said divided regions in said second fuel rods containing a maximum burnable poison concentration Gmax and a region of said divided regions in said second fuel rods containing a minimum burnable poison concentration Gmin are located in the lower region of said fuel assembly, the maximum burnable poison concentration Gmax being located only in the lower region of said fuel assembly. 2. The fuel assembly according to claim 1, wherein said minimum burnable poison concentration Gmin is zero. 3. The fuel assembly according to claim 1, wherein said minimum burnable poison concentration Gmin is greater than zero. 4. The fuel assembly according to claim 1, wherein an average enrichment in the lower region of said fuel assembly is smaller than that of the upper region thereof. 5. The fuel assembly according to claim 1, wherein the burnable poison concentration G of the upper region of each of said second fuel rods meet a relationship, Gmin<G<Gmax. 6. The fuel assembly according to claim 1, wherein said fuel assembly further comprising a third fuel rod having an axial length of fuel effective length portion smaller than that of said first fuel rod and smaller than that of said second fuel rod. 7. The fuel assembly according to claim 6, wherein said third fuel rod is a part of said first fuel rod. 8. A fuel assembly comprising a plurality of fuel rods each of which contains nuclear fuel material but does not contain burnable poison, a plurality of fuel rods each of which contains the nuclear fuel material and the burnable poison, and at least one water rod disposed between said fuel rods, characterized in that an amount of said burnable poison in a lower region of said fuel assembly is smaller than that in an upper region thereof, and said plurality of fuel rods containing the nuclear fuel material and the burnable poison include first fuel rods and second fuel rods whose average burnable poison concentration is lower than that of said first fuel rods, and said second fuel rods are arranged close to said water rod, and than when each of said first and said second fuel rods is divided into upper and lower regions, a region of said divided regions containing a maximum burnable poison concentration Gmax and a region of said divided regions containing a minimum burnable poison concentration Gmin are located in the lower region of said fuel assembly, the maximum burnable poison concentration Gmax being located only in the lower region of said fuel assembly. 9. The fuel assembly according to claim 8, wherein the burnable poison concentration of the lower region of said first fuel rods is said maximum burnable poison. concentration Gmax, and the burnable poison concentration of the lower region of said second fuel rods is said minimum poison concentration Gmin. 10. The fuel assembly according to claim 8, wherein said first fuel rods are disposed in a fuel rod arrangement region except for an outermost peripheral fuel rod arrangement region of the fuel assembly and for a fuel rod arrangement region adjacent to said water rod. 11. The fuel assembly according to claim 8, wherein the burnable poison concentration G in the upper regions of said first and said second fuel rods meets a relationship, Gmin<G<Gmax. 12. The fuel assembly according to claim 8, wherein the burnable poison concentration in the lower region of the first fuel rods is higher than that in the upper region thereof, and the burnable poison concentration in the lower region of the second fuel rods is lower than that in the upper region thereof. 13. The fuel assembly according to claim 8, wherein said fuel assembly further comprising a third fuel rod having an axial length of fuel effective length portion smaller than that of said first fuel rod and smaller than that of said second fuel rod. 14. The fuel assembly according to claim 1, wherein both the maximum burnable poison concentration Gmax and the minimum burnable poison concentration Gmin are located only in the lower region of said fuel assembly. 15. The fuel assembly according to claim 1, wherein the upper region and the lower region of said divided regions of said second fuel rods contain enriched uranium, and the regions containing at least one of the maximum burnable poison concentration Gmax and the minimum burnable poison concentration Gmin are located in the lower region which is filled with the enriched uranium. 16. The fuel assembly according to claim 8, wherein both the maximum burnable poison concentration Gmax and the minimum burnable poison concentration Gmin are located only in the lower region of said fuel assembly. 17. The fuel assembly according to claim 8, wherein the upper region and the lower region of said divided regions of said second fuel rods contain enriched uranium, and the regions containing at least one of the maximum burnable poison concentration Gmax and the minimum burnable poison concentration Gmin are located in the lower region which is filled with the enriched uranium. |
claims | 1. A near-field scanning optical microscope system, composing:an NSOM probe; andhigh precision translational stages for moving one of the NSOM probe and a substrate such that the NSOM probe traverses, in continuous motion, over the entire substrate. 2. The near-field scanning optical microscope system of claim 1, wherein one or more of the translational stages comprise granite air bearing stages. 3. The NSOM system of claim 2, wherein at least one of the translational stages is capable of continuous motion of at least 300 mm. 4. The NSOM system of claim 2, wherein at least one of the translational stages is capable of 2 nm step sizes. 5. The NSOM system of claim 3, wherein at least one of the translational stages is capable of 2 nm step sizes. 6. The near-field scanning optical microscope system of claim 1, further comprising a rotational stage mounted with the translational stages, for aligning axes of the substrate to axes of the translational stages. 7. The near-field scanning optical microscope system of claim 1, further comprising means for generating NSOM image data. 8. The near-field scanning optical microscope system of claim 7, wherein NSOM image data is used to calculate registration correction factors for subsequent photoresist exposure. 9. The near-field scanning optical microscope system of claim 7, further comprising a light source operable to alternate between a first wavelength of light, to generate the NSOM image data, and a second wavelength of light, to expose photoresist. 10. The near-field scanning optical microscope system of claim 1, further comprising a photodiode integrated with a substrate holder. 11. The near-field scanning optical microscope system of claim 1, wherein the NSOM probe traverses the substrate in one of a vector scan and a raster scan. 12. The NSOM system of claim 11, wherein the NSOM probe traverses the substrate in a vector scan. 13. A near-field scanning optical microscope system, comprising:an array of NSOM probes; andhigh precision translational stages for moving one of the array of NSOM probes and the substrate such that the array of NSOM probes traverses, in continuous motion, over the entire substrate. 14. The near-field scanning optical microscope system of claim 13, wherein one or more of the translational stages comprise granite air bearing stages. 15. The NSOM system of claim 13, wherein at least one of the translational stages is capable of continuous motion of at least 300 mm. 16. The near-field scanning optical microscope system of claim 13, further comprising a rotational stage mounted with the translational stages, for aligning axes of the substrate to axes of the translational stages. 17. The near-field scanning optical microscope system of claim 13, further comprising means for generating NSOM image data. 18. The near-field scanning optical microscope system of claim 17, wherein NSOM image data is used to calculate registration correction factors for subsequent photoresist exposure. 19. The near-field scanning optical microscope system of claim 17, further comprising a light source operable to alternate between a first wavelength of light, to generate the NSOM image data, and a second wavelength of light, to expose photoresist. 20. The near-field scanning optical microscope system of claim 13, further comprising a photodiode integrated with a substrate holder. 21. The near-field scanning optical microscope system of claim 13, wherein the array of NSOM probes traverses the substrate in one of a vector scan and a raster scan. 22. A method for exposing photoresist on a substrate, comprising:translating a surface of the substrate across an NSOM probe in continuous motion, translating comprising utilizing a high precision translational stages; andselectively exposing the photoresist through the NSOM probe during the continuous motion. 23. The method of claim 22, the step of translating comprising adjusting a speed of the substrate relative to the NSOM probe, to adjust exposure of the photoresist. 24. The method of claim 22, further comprising a step of selectively exposing the photoresist through a photomask, before the step of translating. 25. The method of claim 24, the step of translating comprising utilizing image data from a latent image of the photoresist to align the NSOM probe. 26. The method of claim 24, further comprising the step of developing the photoresist, after the step of selectively exposing the photoresist through a photomask, before the step of translating. 27. The method of claim 26, the step of translating comprising utilizing image data from a developed photoresist image to align the NSOM probe. 28. A method for exposing photoresist on a substrate, comprising:translating a surface of the substrate across an array of NSOM probes in continuous motion, translating comprising utilizing a high precision translational stages; andselectively exposing the photoresist through the array of NSOM probes during the continuous motion. 29. A software product comprising instructions, stored on computer-readable media, wherein the instructions, when executed by a computer,perform steps forgenerating control signals for high precision translational stages to translate a surface of a substrate across an NSOM probe in continuous motion, andselectively exposing photoresist through the NSOM probe during the continuous motion. 30. The software product of claim 29, wherein the Step of generating control signals comprises utilizing design database information to adjust a translational speed produced by the control signals, to adjust exposure of the photoresist. 31. The software product of claim 29, further comprising instructions, stored on computer-readable media, wherein the instructions, when executed by a computer, perform steps forgenerating NSOM image data,calculating at least one of pattern registration data and scaling data from the NSOM image data, andutilizing the at least one of pattern registration data and scaling data to generate corrections for the control signals, to align the NSOM probe to features of the substrate. 32. The software product of claim 31, wherein the step of generating NSOM image data comprises utilizing a first light source, andthe step of selectively exposing photoresist comprises utilizing a second light source. |
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053295641 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is generally related to open cycle reactors and more particularly to passive cooling of open cycle reactors. 2. General Background Open cycle reactors intended for use in outer space have generally been focused on their use in nuclear rockets. Core fission power from delayed neutrons and gamma heating from fission products will continue to produce power after the reactor is shutdown. Information obtained from the NERVA program indicates that, because of this continued heating, the rocket engine turbopump would have to provide coolant to the reactor after reactor shutdown to prevent core melting. This turbopump was powered by coolant heated in the reactor core by decay heat. However, the turbopump could not operate efficiently at the low coolant flows and reactor powers produced by decay heat. This led to an operating scheme where the turbopump would be operated in a pulsed mode. In this mode, the engine is allowed to heat up to the designed operating temperature before providing a burst of coolant flow which would cool the reactor down to a lower temperature. The problem with this mode of operation is that it cycles much of the engine equipment and increases the potential for failure. One approach is to have the coolant pump continue to pump coolant to the reactor at a reduced rate. Pump failure or premature emptying of the coolant tank can result in reactor damage by melting. Over cooling of the reactor can also cause damage if the flow rate of the coolant pump is too high. This leaves a need for a means of removing decay heat from the reactor that does not require constant cycling of the engine equipment and is not dependent on the coolant pump. SUMMARY OF THE INVENTION The present invention addresses the above need in a straightforward manner. What is provided is a passive cooling system. Coolant tanks are connected to the normal coolant flow line between the coolant pump and the reactor. The coolant tanks are filled with pressurized coolant through check valves until they equal the pump discharge pressure. The pressure in the tanks remains constant while the coolant pump is operating. When the reactor and coolant pump are shut down, coolant escapes from the coolant tanks through lines in communication with the normal coolant line and flow to the reactor for removal of decay heat. Orifices of selected sizes control the coolant flow rate to match the decay heat rate of the reactor to provide the proper cooling required. |
abstract | A system for providing radiation protection is provided that includes a garment that contours to an operator's body. The garment protects the operator from radiation. The garment is supported by a suspension component that reduces a portion of weight of the garment for the operator, the garment including a belt, which includes a release mechanism that offers an entry into the garment. In more specific embodiments, the release mechanism is a quick release that allows the operator to disengage from the garment using a single hand movement. The belt can include at least one flexible joint. The belt opens to allow the operator to enter the garment, and the operator, in entering and exiting the garment, is able to limit his contact to components on or near a front of the garment such that the operator can operate the release mechanism for the garment without losing sterility. |
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summary | ||
040452883 | claims | 1. A nuclear fuel element comprising (a) a central core of a body of nuclear fuel material selected from the group consisting of compounds of uraniun, plutonium, thorium and mixtures thereof and (b) an elongated composite cladding container including an outer portion formed of a material selected from the group of zirconium and zirconium alloys and forming a substrate, an undeformed metal barrier of constant thickness formed of a material selected from the group of niobium, aluminum, copper, nickel, stainless steel and iron metallurgically bonded on the inside surface of the substrate, said metal barrier comprising from about 1 to about 4 percent of the thickness of the cladding container and an undeformed inner layer of constant thickness formed of zirconium metallurgically bonded on the inside surface of the metal barrier, said inner layer comprising from about 5 to about 15 percent of the thickness of the cladding container, said cladding container enclosing said core so as to leave a gap between said core and said cladding during use in a nuclear reactor. 2. The nuclear fuel element of claim 1 which has in addition a cavity inside the fuel element and a nuclear fuel material retaining means comprising a helical member positioned in the cavity. 3. A nuclear fuel element of claim 1 in which the metal barrier is aluminum. 4. A nuclear fuel element of claim 1 in which the metal barrier is copper. 5. A nuclear fuel element of claim 1 in which the metal barrier is niobium. 6. A nuclear fuel element of claim 1 in which the metal barrier is nickel. 7. A nuclear fuel element of claim 1 in which the metal barrier is stainless steel. 8. A nuclear fuel element of claim 1 in which the metal barrier is iron. 9. A nuclear fuel element of claim 1 in which the nuclear fuel material is selected from the group consisting of uranium compounds, plutonium compounds and mixtures thereof. 10. A nuclear fuel element of claim 1 in which the nuclear fuel material is comprised of uranium dioxide. 11. A nuclear fuel element of claim 1 in which the nuclear fuel material is a mixture comprising uranium dioxide and plutonium dioxide. 12. A composite cladding container for nuclear reactors comprising an outer portion forming a substrate and formed of a zirconium alloy, an undeformed metal barrier of constant thickness formed of a material selected from the group of niobium, aluminum, copper, nickel, stainless steel and iron mettallurgically bonded on the inside surface of the substrate, said metal barrier comprising from about 1 to about 4 percent of the thickness of the cladding container and an undeformed inner layer of constant thickness formed of zirconium metallurgically bonded on the inside surface of the metal barrier, said inner layer comprising from about 5 to 15 percent of the thickness of the cladding container metallurgically bonded on the inside surface of the metal barrier. 13. A composite cladding container according to claim 12 in which the metal barrier is aluminum. 14. A composite cladding container according to claim 12 in which the metal barrier is niobium. 15. A composite cladding container according to claim 12 in which the metal barrier is copper. 16. A composite cladding container according to claim 12 in which the metal barrier is nickel. 17. A composite cladding container according to claim 12 in which the metal barrier is stainless steel. 18. A composite cladding container according to claim 12 in which the metal barrier is iron. 19. A nuclear fuel element which comprises an elongated composite cladding container including an outer portion formed of a material selected from the group of zirconium and zirconium alloys forming a substrate, an undeformed metal barrier of constant thickness formed of a material selected from the group of niobium, aluminum, copper, nickel, stainless steel and iron metallurgically bonded on the inside surface of the substrate, said metal barrier comprising from about 1 to about 4 percent of the thickness of the cladding container, and an undeformed inner layer of constant thickness formed of zirconium metallurgically bonded on the inside surface of the metal barrier, said inner layer comprising from about 5 to about 15 percent of the thickness of the cladding container, a central core of a body of nuclear fuel material selected from the group consisting of compounds of uranium, plutonium, thorium and mixtures thereof disposed in and partially filling said container and forming an internal cavity in the container, an enclosure integrally secured and sealed at each end of said container, and a nuclear fuel material retaining means positioned in the cavity, said cladding container enclosing said core so as to leave a gap between said core and said cladding during use in a nuclear reactor. |
description | The present application hereby claims priority under 35 U.S.C. §119 on German patent application number DE 10 2008 063 323.2 filed Dec. 30, 2008, the entire contents of which are hereby incorporated herein by reference. At least one embodiment of the present invention generally relates to a radiation detector. In at least one embodiment, it relates to a detector comprising a plurality of radiation detector modules arranged adjacent to one another with in each case one scintillation element with a radiation inlet surface aligned transversely with respect to a main direction of a radiation, and light detector arrangements arranged transversely with respect to the radiation inlet surfaces of the scintillation elements. Furthermore, at least one embodiment generally relates to a light detector arrangement for such a radiation detector, a method for producing such a radiation detector and/or an imaging system, preferably a computed tomography scanner. Radiation detectors for computed tomography scanners generally comprises rows or matrices of so-called pixels arranged adjacent to one another, that is to say of individual radiation detector modules which directly or indirectly convert incident (X-ray) radiation into electrical signals which can subsequently be used to derive projection images therefrom, which images can be processed further for reconstructing an image of an examination object to be imaged. In the case of indirect conversion of the incent radiation, so-called scintillation elements are used, which first of all convert the radiation into light (usually in the visible wavelength band). The scintillation elements are separated from one another by so-called septa which have light-reflecting materials inserted into them in order to prevent light pulses generated in the individual elements from passing into adjacent pixels. Likewise, the radiation inlet surface toward the interior of the scintillation elements is designed to reflect. A light detector arrangement, for example in the form of a photodiode, then converts the light into electrical signals. Until now, the light detector arrangements were attached below the scintillation elements, i.e. the light inlet surfaces thereof used to be parallel to the radiation inlet surface of the scintillation elements. The electronic system used for further signal processing, preferably converter elements for the electrical signals, was then attached to the side of the light detector arrangements opposite to the radiation inlet surface. For quite some time now, the tendency has been to reduce the size of the pixels in the z- and φ-directions, that is to say in the directions which approximately form a plane which is basically aligned perpendicularly with respect to the main direction of the radiation to be detected. In the following text, the main direction of the radiation to be detected is considered to be the direction of propagation of the radiation in which the substantial portion of the radiation to be detected is incident on the radiation detector and which can for example be defined by a collimator or the like arranged upstream of the detector. In the process, it is usually ensured that the radiation to be detected is basically incident on the radiation inlet surface in a perpendicular fashion, that is to say that the main direction is perpendicular with respect to the radiation inlet surface. Basically perpendicular should in this case respectively be understood to mean that the respective directions are perpendicular with respect to one another within certain tolerances. The reduction of pixel size can achieve both higher time and spatial resolutions in radiation detectors. However, in the arrangement of radiation detector modules with scintillation elements and light detector arrangements attached to the underside described above, this also automatically reduces the size of the detection surface of the light detector arrangements and leads to the undesired effect that increasing the miniaturization reduces the number of light quanta generated and the light collection becomes less and less efficient. In the end, the strength of the measurement signals is reduced and so interference effects such as more noticeable noise become more emphasized. WO 2006/114715 A2 and WO 2006/114716 A2 point toward a solution to this problem. Therein, the light detector arrangements are in each case not on the underside of the scintillation elements, but are on the side between the scintillation elements. Since the pixel heights can, in contrast to the extents parallel to the detector surface, only be varied slightly, a sufficient size of the light detector arrangements is maintained for the light collection efficiency when there is such a lateral readout of the light signals, even when the pixels are reduced in size. However, a further problem during the miniaturization of the scintillator pixels consists of the fact that the number of pixels per unit area or per detector length unit attained thereby, that is to say the so-called pixel density, makes the signal processing more complicated. The technical limits of producible printed circuit board densities are already being reached these days. If anything, this problem is further increased in the case of a lateral arrangement of the light detector arrangements, because now the electronic system which used to have space on the underside of the light detector arrangements now no longer has sufficient space. In at least one embodiment of the invention, an option is provided for improved utilization of space within a detector design with light detector arrangements attached between scintillation elements. Accordingly, in a radiation detector of at least one embodiment, one light detector arrangement is arranged between two scintillation elements and has two light inlet surfaces which point away from one another, of which one is associated with a first scintillation element and one is associated with a second scintillation element. Thus, in at least one embodiment, a common light detector arrangement is situated between respectively a first and a second scintillation element, the light inlet surfaces of which detector arrangement respectively point in the direction of one of the two scintillation elements, and so the latter are aligned in opposite directions. The light detector arrangement is situated in a septum between the scintillation elements. This leads to a significant simplification in the design of the radiation detector, because now a light detector arrangement is only inserted into every second septum, which detector arrangement converts light signals from both the first and the second scintillation element into voltage pulses. Thus, there is no light detector arrangement in the respective other septum which delimits a scintillation element in the same arrangement direction as the septum filled by the light detector arrangement. In addition to saving material, this mainly results in a simplification of the design in respect of the spatial requirement of the light detector arrangements and the continuative lines connected thereto which now likewise only lead away from every second septum. Accordingly, a light detector arrangement according to at least one embodiment of the invention has two light inlet surfaces which point away from one another, one of which can be associated with a first scintillation element and one can be associated with a second scintillation element of the radiation detector. Thus, the light detector arrangement can be provided as a separate component. Such a component can be used in a method according to at least one embodiment of the invention for producing a radiation detector which comprises at least the following steps: a) providing a detector blank with a number of scintillation elements arranged adjacent to one another with a radiation inlet surface aligned transversely with respect to a main direction of a radiation, b) providing light detector arrangements which have two light inlet surfaces which point away from one another, c) applying the light detector arrangements between the scintillation elements such that one light inlet surface is associated with a first scintillation element and another light inlet surface is associated with a second scintillation element, wherein the light inlet surfaces of the light detector arrangements are arranged transversely with respect to the radiation inlet surfaces of the scintillation elements. Thus, use is made of a light detector arrangement according to at least one embodiment of the invention which is inserted into the interspaces, i.e. the septa of a detector blank. Here, a detector blank is defined as a radiation detector which has not yet been assembled completely, but which already has scintillation elements which have been separated from one another and between which the light detector arrangement can be inserted. The production method according to at least one embodiment of the invention is also significantly simplified compared to the abovementioned prior art, because a light detector arrangement now only has to be inserted into every second septum. Finally, at least one embodiment of the invention comprises an imaging system with a radiation detector according to at least one embodiment of the invention and/or a light detector arrangement according to at least one embodiment of the invention. Further particularly advantageous refinements and developments of at least one embodiment of the invention also result from the dependent claims and the following description. In the process, the radiation detector and the light detector arrangement, as well as the production method and the imaging system, can in each case be developed in accordance with the dependent claims of the other claim categories. The light detector arrangement of at least one embodiment can be designed as a component which converts light pulses from the two scintillation elements into voltage pulses in one and the same functional region. However, the light detector arrangement of at least one embodiment preferably comprises two light detector units which can be operated independently of one another and which respectively form one of the light inlet surfaces. These light detector units then particularly preferably each have their own connection contacts, and so they act as completely self-sufficient units which are only connected to one another as a result of their common assembly within the light detector arrangement. A light detector unit can in turn have a plurality of partial units which are independent of one another. A particularly advantageous embodiment then includes the light detector arrangement comprising two back-to-back conjoined light detector units which have preferably been adhesively bonded or polymer- or fusion bonded. Thus, the light detector units which can be operated independently of one another are firstly produced as individual components and are then conjoined back-to-back using methods which are as sparing as possible. In the process, conjoining is also possible by a first light detector unit being provided on a substrate, with the second light detector unit being built on the rear side thereof, for example by coating with a light-sensitive material. The above-cited documents regarding the prior art provide for a design of the radiation detector modules made of two scintillation elements arranged above one another in the main direction of the radiation. In other words, the corresponding radiation detector module comprises a double-layer scintillation element. Such a refinement is also possible within the scope of at least one embodiment of the present invention. However, by contrast, it is particularly advantageous for the scintillation elements to be formed from an inherently homogeneous scintillation layer because, for example, the design is much simpler. In particular, this can save signal lines and possibly circuits. Moreover, in accordance with a particularly advantageous embodiment of the invention, the light detector arrangement and/or the light detector units are arranged on a (common) support. The support can be flexible but it is preferably made of a stiff material—for example in the form of a common printed circuit board—because as a result of this it is easier to insert said support into the septa between the individual scintillation elements. A particularly advantageous development includes the light detector arrangement being arranged on the support together with at least one converter device. The converter device is preferably at least one analog/digital converter, possibly also connected to further signal conversion elements and/or signal circuit elements such as multiplexers. By arranging the light detector arrangement and the converter device on a common support, more space can, in particular, be saved on the underside (i.e. on the side opposite to the radiation inlet surface) of the radiation detector. In particular, line guides which are complicated and prone to error both mechanically and in terms of signaling become superfluous. Thus, on the one hand, the solution is particularly space-saving and moreover offers the advantage of affording the possibility of directly coupling to one another electronic elements which are assigned to one another. In particular, this affords the possibility of providing an electrical connection at a defined distance (preferably equaling zero) between the individual elements without additional cable connections. This possibility of completely avoiding cable lines moreover leads to a significant reduction in the input capacitance of the analog/digital converters and thus the noise properties are also significantly improved during the measurement. The support particularly preferably basically extends in a plane aligned parallel to the main direction of the radiation to be detected. In other words, the support is a basically planar component, the alignment of which is defined by the radiation main direction or by the septa which are arranged between the scintillation elements and which are preferably arranged parallel to the radiation main direction. The advantage of the planar alignment is that every support is situated in, and possibly in the continuation of, a septum and therefore basically sticks out perpendicularly with respect to the rear side of the scintillation elements (i.e. with respect to the side opposite to the radiation inlet surface). It can thus easily be recognized and contacted; its structuring can clearly be seen even from the rear side of the radiation detector, and individual elements—for example the individual supports—are easily accessible and, if need be, can be replaced. Furthermore, a particular advantage results from the converter device being arranged on a side of the scintillation element pointing away from the radiation inlet surface. Thus, the converter device is attached to the rear-side region of the radiation detector and spatially constitutes a continuation of the light detector arrangement. In the process, the converter device on the support protrudes beyond the rear limit of the scintillation element, as a result of which it can easily be connected to continuative lines and simultaneously uses a space which is no longer used for other purposes due to the installation of the light detector arrangement between the scintillation elements. An imaging system according to at least one embodiment of the invention is preferably designed such that the radiation detector extends along a circular or arced path running around an axis of rotational symmetry. Here, this preferably is a computed tomography scanner or a PET (positron emission tomography) or SPECT (single photon emission computed tomography) system. In the process, a row of light detector arrangements of the radiation detector is preferably arranged on a light detector bar structured in a direction parallel to the axis of rotational symmetry. This direction, which is generally referred to as the z-direction or the insertion direction of examination objects into the imaging system, defines the so-called detector width, that is to say the extent to which an examination object is covered by the detector during a circulation with a position of the examination object remaining constant in relation to the rotational plane of the detector. A light detector bar can be structured along this width such that a plurality of light detector arrangements are formed therefrom and cover individual pixels, i.e. individual radiation detector modules. The light detector bar preferably extends over the entire detector width. Accordingly, the planes of preferably all light detector arrangements of the radiation detector are preferably aligned in precisely the direction of the detector width, i.e. parallel to the axis of rotational symmetry. An imaging system according to at least one embodiment of the invention is preferably distinguished by the fact that a light detector arrangement is arranged between every second scintillation element in the direction parallel to the axis of rotational symmetry and/or in the angular direction of the radiation detector. It thus uses the saving potential realized by at least one embodiment of the invention to the fullest. It is particularly advantageous for the outermost scintillation elements in an arrangement direction of the light detector arrangements to complete a row of scintillation elements and light detector arrangements. This means that the radiation detector respectively terminates with a scintillation element at its lateral outer borders in the direction parallel to the axis of rotational symmetry and in the direction of rotation, while the light detector arrangement associated with this scintillation element lies between this and another scintillation element. This exploits the saving effect in terms of space and material in an optimal fashion within the scope of the invention and, moreover, the light detector arrangements are all protected from external effects on both sides by scintillation elements. Various example embodiments will now be described more fully with reference to the accompanying drawings in which only some example embodiments are shown. Specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The present invention, however, may be embodied in many alternate forms and should not be construed as limited to only the example embodiments set forth herein. Accordingly, while example embodiments of the invention are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments of the present invention to the particular forms disclosed. On the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of the invention. Like numbers refer to like elements throughout the description of the figures. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments of the present invention. As used herein, the term “and/or,” includes any and all combinations of one or more of the associated listed items. It will be understood that when an element is referred to as being “connected,” or “coupled,” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected,” or “directly coupled,” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between,” versus “directly between,” “adjacent,” versus “directly adjacent,” etc.). The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention. As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the terms “and/or” and “at least one of” include any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper”, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein are interpreted accordingly. Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the present invention. FIG. 1 shows part of a radiation detector 1 for detecting X-ray radiation within the scope of a computed tomography scanner. It has a plurality of radiation detector modules 3 with scintillation elements 7a, 7b and light detector arrangements 9. On their upper side which points against the main direction H of the X-ray radiation, the radiation detector modules 3 have radiation inlet surfaces 5 through which the X-ray radiation impinges into the scintillation elements 7a, 7b. The scintillation elements 7a, 7b are respectively separated from one another by septa 10. In the angular direction φ of the radiation detector in the computed tomography scanner, the light detector arrangements 9 are in this case only assigned to every second septum 10. This is because they have two light inlet surfaces A, B which point away from one another and are respectively associated with one scintillation element 7a or 7b. This figure does not show collimator sheets for filtering scattered radiation, which usually protrude perpendicularly from the radiation inlet surfaces 5 on the septa 10 in such detectors, that is to say which are aligned against the main direction H of the X-ray radiation. The X-ray radiation impinging into the scintillation elements 7a, 7b in the main direction H of the X-ray radiation is converted into light radiation L—usually in the visible wavelength band—at said location. As a result of reflection on the septa, the radiation inlet surfaces 5 and the undersides of the scintillation elements 7a, 7b lying opposite the radiation inlet surfaces, the light radiation is respectively guided in the direction of the light inlet surfaces A, B of the light detector arrangements 9, where voltage signals are derived from the light pulses. These signals are passed on to further processing units via lines on a support 11. FIG. 2 shows the same part of the radiation detector 1 in a perspective view. It shows that said radiation detector also extends over a plurality of radiation detector modules 3 in the z direction. In the computed tomography scanner, this z direction is the insertion direction of an examination object, and so the number of radiation detector modules 3 arranged in this direction defines the detector width. FIG. 2 shows in particular that the support 11 extends over the entire detector width. Compared to the prior art, the use of the design illustrated here in an example fashion now affords the possibility of only providing every second septum with a light detector arrangement 9 in the angular direction φ, i.e. in the arrangement direction of such light detector arrangements 9, with the septa situated in between in each case no longer having to have a light detector arrangement 9. Thus, half of the light detector arrangements required in the prior art, and in particular the space required for this, can be saved. The illustration in FIGS. 1 and 2 should be understood in a purely schematic fashion. It is neither drawn to scale (nor are the following figures), nor is the fact taken into account that the radiation detector 1 generally has a curved design in the angular direction φ. This illustrative form is used to simplify the illustration of the circumstances. An example embodiment of a light detector arrangement 9 is illustrated in FIG. 3. It has two contacts 19 by which the signals generated by said detector arrangement can be picked up. This light detector arrangement 9 is designed in the form of a single-arrangement, i.e. it is not part of a larger overall combination and, in particular, it is not inherently structured. It is particularly suitable for application in radiation detectors in rows, which only have a single radiation detector module in the z direction and consist of radiation detector modules which are arranged next to one another in the φ direction. FIGS. 4 and 5 both show a light detector bar 17 which, as a result of structuring, is subdivided into individual segments 13 in the z direction (indicated here by dashed lines), which form the one side of a light detector arrangement 9. The light detector bar 17 has a contact region 15 for each segment 13 formed by the structuring, where the signals of this segment 13 can be picked up. The structuring of the light detector bar 17 into segments 13 is particularly advantageous in that only one whole unit has to be inserted into the septa over the entire detector width of the radiation detector 1. In FIG. 4, the light detector bar 17 is contacted on its contact regions 15 by conductor tracks 23 which are fixed on a flexible support 11, for example printed thereon or etched out of a printed circuit board made of flexible foil. These conductor tracks all lead to a connection element 25 which can, for example, be designed as a plug, but can also be formed as a soldering connection or a connection with the aid of an electrically conductive adhesive. Since the signals are passed on from the contact regions 15 via the conductor tracks 23 arranged on the common support 11, these conductor tracks 23 are spatially assigned to a certain region and as a result of this the arrangement of the wiring is significantly simplified. Moreover, the support 11 can simultaneously serve as a support for the light arrangements 9, which support is passed on further only on the underside of the radiation detector 1. FIG. 5 shows the same arrangement as in FIG. 4, but in this case there is a component 27 which is attached to the support 11. This can already carry out a first signal processing operation in the immediate vicinity of the light detector arrangements 9, particularly analog/digital conversion of the received signals. The component 27 therefore preferably comprises an analog/digital converter. In respect of the illustrations of FIGS. 3 to 5, reference should be made to the fact that the illustrated light detector bar 17 and the individual light detector arrangement 9 from FIG. 3 only show one of the two light inlet surfaces A or B in a planar view. This means that there is a second light inlet surface with an analog design on the side of the light detector bar 17 or individual light detector arrangement 9 which faces away from the observer. Finally, reference is again made to the fact that the method described in detail above and the illustrated apparatus are merely exemplary embodiments which a person skilled in the art can modify in various ways without departing from the scope of the invention. Furthermore, the use of the indefinite article “a” or “an” does not preclude the relevant features from being present a number of times. The patent claims filed with the application are formulation proposals without prejudice for obtaining more extensive patent protection. The applicant reserves the right to claim even further combinations of features previously disclosed only in the description and/or drawings. The example embodiment or each example embodiment should not be understood as a restriction of the invention. Rather, numerous variations and modifications are possible in the context of the present disclosure, in particular those variants and combinations which can be inferred by the person skilled in the art with regard to achieving the object for example by combination or modification of individual features or elements or method steps that are described in connection with the general or specific part of the description and are contained in the claims and/or the drawings, and, by way of combinable features, lead to a new subject matter or to new method steps or sequences of method steps, including insofar as they concern production, testing and operating methods. References back that are used in dependent claims indicate the further embodiment of the subject matter of the main claim by way of the features of the respective dependent claim; they should not be understood as dispensing with obtaining independent protection of the subject matter for the combinations of features in the referred-back dependent claims. Furthermore, with regard to interpreting the claims, where a feature is concretized in more specific detail in a subordinate claim, it should be assumed that such a restriction is not present in the respective preceding claims. Since the subject matter of the dependent claims in relation to the prior art on the priority date may form separate and independent inventions, the applicant reserves the right to make them the subject matter of independent claims or divisional declarations. They may furthermore also contain independent inventions which have a configuration that is independent of the subject matters of the preceding dependent claims. Further, elements and/or features of different example embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. Still further, any one of the above-described and other example features of the present invention may be embodied in the form of an apparatus, method, system, computer program, computer readable medium and computer program product. For example, of the aforementioned methods may be embodied in the form of a system or device, including, but not limited to, any of the structure for performing the methodology illustrated in the drawings. Even further, any of the aforementioned methods may be embodied in the form of a program. The program may be stored on a computer readable medium and is adapted to perform any one of the aforementioned methods when run on a computer device (a device including a processor). Thus, the storage medium or computer readable medium, is adapted to store information and is adapted to interact with a data processing facility or computer device to execute the program of any of the above mentioned embodiments and/or to perform the method of any of the above mentioned embodiments. The computer readable medium or storage medium may be a built-in medium installed inside a computer device main body or a removable medium arranged so that it can be separated from the computer device main body. Examples of the built-in medium include, but are not limited to, rewriteable non-volatile memories, such as ROMs and flash memories, and hard disks. Examples of the removable medium include, but are not limited to, optical storage media such as CD-ROMs and DVDs; magneto-optical storage media, such as MOs; magnetism storage media, including but not limited to floppy disks (trademark), cassette tapes, and removable hard disks; media with a built-in rewriteable non-volatile memory, including but not limited to memory cards; and media with a built-in ROM, including but not limited to ROM cassettes; etc. Furthermore, various information regarding stored images, for example, property information, may be stored in any other form, or it may be provided in other ways. Example embodiments being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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051480409 | summary | BACKGROUND OF THE INVENTION This invention relates generally to detecting radiation in a living being for medical applications, and more particularly to detecting, localizing, and imaging or mapping of radiation in a portion of the body of a being by means of a radiation detecting probe and an associated radiation blocking shield. The use of radioactive materials to tag tissue within a patient for effecting its localization and demarcation by radiation detecting devices has been disclosed in the medical literature for at least forty years. Significant developments in the localization and demarcation of tissue bearing radioactive isotope tags for diagnostic and/or therapeutic purposes have occurred since that time. Thus, it is now becoming an established modality in the diagnosis and/or treatment of certain diseases, e.g., cancer, to introduce monoclonal antibodies tagged with a radioactive isotope (e.g., Indium 111, Technetium 99m, Iodine 123, and Iodine 125) into the body of the patient. Such monoclonal antibodies tend to seek out particular tissue, such as the cancerous tissue, so that the gamma radiation emitted by the isotope can be detected by a hand-held radiation detecting probe. Such a probe is disposed or held adjacent portion of the patient's body where the cancerous tissue is suspected to be in order to detect if any radiation is emanating from that site, thereby indicating that cancerous tissue is likely to be found there. Prior art, hand-held, radiation detecting probes are commercially a available from the assignee of this invention, Care Wise Medical Products, Inc. under the trademark OncoProbe. In copending U.S. patent applications Ser. Nos. 07/363,243 and 07/491,390, filed on Jun. 8, 1989 and Mar. 9, 1990, respectively, and assigned to the same assignee as this invention there are disclosed hand-held radiation detecting probes having collimating means to establish the field of view of the probe. In U.S. Pat. No. 4,801,803 (Denen et al) there is also disclosed a hand-held radiation detecting probe. In some cases background activity (i.e., radiation emanating from portions of the body other than the portion being investigated) may interfere with sensitive and accurate surgical radiation detecting probe localization of radiolabeled tissues within body cavities. OBJECTS OF THE INVENTION It is a general object of this invention to provide simple means and a method of use for minimizing the problem of background activity interference with sensitive and accurate localization of radiolabeled tissues within body cavities. It is a further object of this invention to provide a means for use with a radiation detecting probe to block background radiation emanating from sources other than the tissue being examined by the probe within the probe's field of view. It is still a further object of this invention to provide means which may be readily inserted into the body of a being interposed between the tissues being examined by a radiation detecting probe and the remainder of the body cavity in the field of view of the probe. It is yet a further object of this invention to provide a radiation blocking shield which is simple in construction and easy to use. SUMMARY OF THE INVENTION These and other objects of this invention are achieved by providing a shield for use with a radiation detecting probe to effect the detection, localization, imaging or mapping of radiation in a first, internal, portion of the body of a living being by use of the probe. The shield comprises a sheet formed of a radiation blocking material which is sized to be readily located within a space within the body of the being so that the first portion of the body of the being is interposed between it and the probe, whereupon the shield fills up a substantial portion of the field of view of the probe, thereby blocking radiation from sources behind the shield. In one embodiment the shield is mounted on the probe by an adjustable yoke assembly. In another embodiment the shield is separate from the probe. |
abstract | A hybrid indirect-drive/direct drive for inertial confinement fusion utilizing laser beams from a first direction and laser beams from a second direction including a central fusion fuel component; a first portion of a shell surrounding said central fusion fuel component, said first portion of a shell having a first thickness; a second portion of a shell surrounding said fusion fuel component, said second portion of a shell having a second thickness that is greater than said thickness of said first portion of a shell; and a hohlraum containing at least a portion of said fusion fuel component and at least a portion of said first portion of a shell; wherein said hohlraum is in a position relative to said first laser beam and to receive said first laser beam and produce X-rays that are directed to said first portion of a shell and said fusion fuel component; and wherein said fusion fuel component and said second portion of a shell are in a position relative to said second laser beam such that said second portion of a shell and said fusion fuel component receive said second laser beam. |
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051788233 | claims | 1. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material, including a pressurized cleaning liquid heating system for supplying a continuous flow of pressurized heated cleaning liquid to a remote cleaning tool which dispenses the pressurized cleaning liquid onto the surface to be decontaminated, wherein the improvement comprises; a) a first recovery unit comprising a single vacuum creating means and a final contaminated material disposal tank, b) a second recovery unit providing a moisture laden contaminated material filter means for separating air borne contaminates from recovered cleaning liquids and for delivering said air borne contaminates to said disposal tank of said first recovery unit, c) a collectable volume control provided by said second recovery unit for controlling the vacuum created by said first recovery unit when a critical mass of cleaning liquids is recovered by said second recovery unit, d) a third recovery unit providing a vacuum activated contaminate collector interposed between said second recovery unit and a remote cleaning tool, e) means within said collector providing a restricted area for collecting a predetermined volume of critical radioactive material, f) means within said collector providing a critical mass control of the collected radioactive contaminated material with said means controlling the vacuum created by said first recovery unit when a critical mass of radioactive contaminates are recovered by said third recovery unit, and, g) means providing vacuum induced communication between said collector and said second recovery unit. 2. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 1 wherein said collector of said third recovery unit includes a conically shaped hopper. 3. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 1 wherein said means within said collector is a reduced core member spaced from said collector so as to provide an internal restricted area within said collector for a predetermined volume of critical radioactive material. 4. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 1 wherein said means within said collector providing a critical mass control of the collected radioactive material comprises a vacuum cut- off ball member for disrupting the vacuum induced communication between said collector of said third recovery unit and said second recovery unit. 5. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 1 wherein said means providing vacuum induced communication with said collector and said second recovery unit is a hose. 6. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 2 wherein said means within said hopper is a reduced core member internally spaced from said hopper so as to provide a restricted area within said hopper for collecting a predetermined volume of critical radioactive material. 7. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 6 wherein said means within said hopper providing a critical mass control of the collected radioactive material comprises a vacuum cut- off ball member for disrupting the vacuum induced communication between said hopper of said third recovery unit and said second recovery unit. 8. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 6 wherein said means providing vacuum induced communication with said hopper and said second recovery unit is a hose. 9. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 1 wherein said collectable volume control provided by said second recovery unit is a float switch responsive to the volume of recovered cleaning liquids by said second recovery unit, with said float switch connected to and controlling the operation of said vacuum creating means of said first recovery unit. 10. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 9 wherein said collector of said third recovery unit is a conically shaped hopper. 11. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 9 wherein said means within said collector is a reduced core member spaced from said collector so as to provide an internal restricted area within said collector for a predetermined volume of critical radioactive material. 12. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 9 wherein said means within said collector providing a critical mass control of the collected radioactive material comprises a vacuum cut- off ball member for disrupting the vacuum induced communication between said collector of said third recovery unit and said second recovery unit. 13. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 10 wherein said means within said hopper is a reduced core member internally spaced from said hopper so as to provide a restricted area within said hopper for collecting a predetermined volume of critical radioactive material. 14. A decontaminating apparatus for cleaning radioactive contaminated surfaces and recovering for disposal the contaminated material as defined by claim 13 wherein said means within said hopper providing a critical mass control of the collected radioactive material comprises a vacuum cut- off ball member for disrupting the vacuum induced communication between said hopper of said third recovery unit and said second recovery unit. |
claims | 1. An x-ray attenuating filter comprising:an envelope containing x-ray attenuating fluid;a fluid displacement device disposed within the envelope and configured to displace the x-ray attenuating fluid, the fluid displacement device having a shell having one of foam or air sealing disposed therein;an actuator; andwherein the shell is operable connected to the actuator at one end and connected to a fixed point at another end and wherein the actuator is configured to rotate the one end relative to the fixed point to re-shape the shell. 2. The filter of claim 1 wherein the shell is operable connected to the actuator at one end and connected to a fixed point at another end, and wherein the actuator is configured to translate the one end at least one of toward or away from the fixed point to re-shape the shell. 3. The filter of claim 1 wherein the fluid displacement device has a frustoconical shape. 4. The filter of claim 1 wherein the fluid displacement device has a complex, noncylindrical shape being non-uniformed around a three dimensional axis. 5. The filter of claim 1 wherein the fluid displacement device has a shape of geometric proportions similar to the object to be scanned. 6. The filter of claim 1 wherein the x-ray attenuating fluid includes of one liquid metal or high-density powder suspended in a non-settling colloidal suspension. 7. The x-ray filter of claim 6 wherein high-density powder suspended in a non-settling colloidal suspension includes Na2WO4 in a solution of water, oil, organic liquid, or non-organic liquid. 8. The filter of claim 1 wherein the envelope has a general bowtie shape. 9. The filter of claim 1 wherein the fluid displacement device is configured to be at least one rotated or translated during an active radiographic scan. 10. The x-ray filter, of claim 1 wherein the x-ray attenuating fluid is at least one of:liquid metal;nanoparticles suspended in a non-settling solution; ora compound with pH control buffer dissolved in a liquid. 11. The x-ray filter of claim 10 wherein the liquid metal includes liquid mercury, wherein nanoparticles include high density powder, wherein the non-settling solution is a colloidal suspension, and wherein the compound includes salt. 12. The x-ray filter of claim 10 wherein the nanoparticles include tungsten oxide. 13. The filter of claim 1 wherein the shell is formed of pliable material. 14. The filter of claim 13 wherein the pliable material includes a viscoelastic material. 15. A CT system comprising an x-ray source, an x-ray detector, and an x-ray filter assembly disposed between the x-ray detector and the x-ray source along a path of irradiation, the x-ray filter assembly having:a bowtie filter having a body with an x-ray attenuating fluid disposed therein;an x-ray attenuating fluid displacement device sealingly enclosed within the body of the bowtie filter; anda mechanized actuator connected to the x-ray attenuating fluid displacement device to dynamically position the attenuating fluid displacement device within the body of the bowtie filter to define a desired filtering profile for the bowtie filter. 16. The system of claim 15 wherein the mechanized actuator includes a motor connected to the x-ray attenuating fluid displacement device by a rotatable shaft, the rotatable shaft configured to rotate the attenuating displacement device. 17. The system of claim 15 wherein the mechanized actuator includes a motion controller connected to the x-ray attenuating fluid device by a first rotor shaft disposed concentrically within a second rotor shaft, the first rotor shaft designed to contort the attenuating fluid displacement device and the second rotor shaft designed to rotate the attenuating fluid displacement device. 18. The system of claim 15 wherein the mechanized actuator is designed to at least one of compress, stretch, or twist the x-ray attenuating fluid displacement device to a desired 3D shape. 19. The system of claim 15 wherein the x-ray attenuating fluid displacement device has an elastomeric shell with one of air or foam disposed therein. 20. The system of claim 15 wherein the x-ray attenuating fluid includes alkali halide salts in water. |
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054250714 | claims | 1. Apparatus for inserting an end plug into a fuel pin cladding tube after loading nuclear fuel pellets into said cladding tube, the apparatus comprising a sleeve removably mounted on one end of the cladding tube, said sleeve being slidably locatable in a resilient seal, a carrier having a closed reces for locating therein an end plug for closing said one end of the cladding tube, the carrier being slidable in the sleeve so that on moving the carrier through the sleeve the end plug is inserted into the end of the cladding tube, whereby withdrawal of the cladding tube with the end plug therein leaves the sleeve and the carrier trapped in the seal. 2. Apparatus according to claim 1, in which the sleeve has an internal seating surface comprising a reduced diameter portion extending from one end of the sleeve, wherein the seating surface is adapted to fit on the said one end of the cladding tube. 3. Apparatus according to claim 2, in which the seating surface extends from said one end of the sleeve to an internal end surface which is coincident with an end surface of the cladding tube. 4. Apparatus according to claim 2, wherein te seating surface is a press fit on the cladding tube. 5. Apparatus according to claim 1, which the end plug has a head portion having an end surface and a peripheral surface, wherein the said recess has a depth sufficient to surround the end surface and the peripheral surface. 6. Apparatus according to claim 1, wherein stop means are provided to retain the sleeve and the carrier in the resilient seal upon withdrawal of the cladding tube. 7. Apparatus according to claim 1, wherein the resilient seal comprises a sphincter seal of the type having a plurality of resilient rings adapted so as to press against the sleeve. 8. A method of inserting an end plug into a fuel pin cladding tube after loading nuclear fuel pellets into the cladding tube, wherein the said method comprises the steps of mounting a sleeve on one end of the cladding tube, inserting the sleeve in a resilient seal, introducing a carrier into said sleeve said carrier containing therein an end plug which is inserted into said one end of the cladding tube upon introduction of the carrier into the sleeve, and withdrawing said cladding tube with the end plug inserted therein while leaving the sleeve and the carrier located in the seal. 9. A method according to claim 8, comprising the further step of displacing the sleeve and the carrier from the sea by a sleeve mounted on a fresh fuel pin cladding tube during a subsequent pellet loading sequence. |
claims | 1. A method for removing contaminant particles produced by a radiation source during generation of short-wave radiation having a wavelength of up to approximately 20 nm for illuminating an object, the method comprising the act of:guiding between the radiation source and the particle trap a first gas at a first side of a particle trap arranged across an opening in a wall of a chamber;introducing a second gas into the chamber at a second side of the particle trap, wherein the first side is different from the second side and the object receives the short-wave radiation from the second side; andadjusting a pressure of the second gas to be at least as high as a pressure of the first gas so that the second gas flows from the second side to the first side, wherein the second gas is different from the first gas and the second side does not include the first gas. 2. The method according to claim 1, wherein the adjusting act adjusts the pressure of the second gas to be higher than the pressure of the first gas. 3. The method according to claim 1, wherein the guiding act guides the first gas transversely to a propagation direction of the radiation in a channel that is located at the first side and is at least partially laterally bounded for transporting the contaminant particles to a one side of the channel, and wherein the adjusting act causes the second gas to enter the channel and flow with the first gas for transporting the contaminant particles to the one side of the channel. 4. The method according to claim 1, wherein the first gas comprises a noble gas having an atomic weight of at least 39 g/mol. 5. The method according to claim 1, wherein the second gas comprises a substance that is substantially transparent for the radiation, the second gas including helium or hydrogen. 6. The method according to claim 1, further comprising the act of adjusting a flow velocity of the first gas and/or of the second gas. 7. The use of the method according to claim 1, for generating radiation in a wavelength range of approximately 2 nm up to approximately 20 nm for a lithography device. 8. The use of the method according to claim 1, for generating radiation in a wavelength range of approximately 2 nm up to approximately 20 nm for a microscope. 9. The method of claim 1, wherein the act of introducing the second gas prevents the first gas from flowing through the particle trap from the first side to the second side. 10. The method of claim 1, further comprising the act of introducing the first gas from a first source at the first side of the particle trap, wherein the act of introducing the second gas introduces the second gas from a second source at the second side of the particle trap. 11. A device for removing contaminant particles produced by a radiation source during generation of short-wave radiation having a wavelength of up to approximately 20 nm for illuminating an object, comprising:a chamber configured to receive a device to be protected against soiling with the contaminant particles;a particle trap arranged across an opening in a wall of the chamber, wherein a first gas is guidable at a first side of the particle trap between the radiation source and the particle trap; and wherein a second gas is introducible into the chamber at a second side of the particle trap, wherein the first side is different from the second side and the object receives the short-wave radiation from the second side; andan adjustor configured to adjust a pressure of the second gas at the second side of the particle trap to be at least as high as a pressure of the first gas at the first side of the particle trap so that the second gas flows from the second side to the first side, wherein the second gas is different from the first gas and the second side does not include the first gas. 12. The device according to claim 11, wherein the adjustor is further configured to adjust the pressure of the second gas to be higher than the pressure of the first gas. 13. The device according to claim 11, further comprising a channel for guiding the first gas transversely to the propagation direction of the radiation, wherein the channel is at least partially laterally bounded. 14. The device according to claim 13, wherein the channel is located at the first side, wherein the first gas flows in the channel for transporting the contaminant particles to a one side of the channel, and wherein the adjustor is configured to cause the second gas to enter the channel and flow with the first gas for transporting the contaminant particles to the one side of the channel. 15. The device according to claim 11, wherein the first gas comprises a noble gas having an atomic weight of at least 39 g/mol. 16. The device according to claim 11, wherein the second gas comprises a substance that is essentially transparent for the radiation, the second gas including helium or hydrogen. 17. The device according to claim 11, wherein a flow velocity of the first gas and/or of the second gas is adjustable by means of appropriate devices. 18. A lithographic projection apparatus comprising a device according to claim 11. 19. The device of claim 11, wherein the second gas prevents the first gas from flowing through the particle trap from the first side to the second side. 20. The device of claim 11, further comprising:a first source at the first side of the particle trap for introducing the first gas at the first side of the particle trap; anda second source at the second side of the particle trap for introducing the second gas at the second side of the particle trap. |
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047598999 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Very generally, the preferred embodiment of the present invention comprises a nuclear reactor 10 having a core 12 supported within a closed vessel 14 and means for providing flow of primary coolant through the core 12. The core 12 is made up of a plurality of generally vertically oriented, elongated fuel elements 15. The vessel 14 in the illustrated embodiment is an elongated tank of generally circular cross-section comprising a generally cylindrical side wall 16, a closed bottom 18, and a top 20. The top generally has a removable cover plate 22 thereon which provides access to the interior of the vessel 14 for refueling, maintenance, etc. The core 12 is located near the bottom of the vessel 14, and has a plurality of passages extending from its lower end 24 to its upper end 26 to enable flow of coolant therethrough. During normal operation, primary coolant enters the reactor vessel 14 through an inlet port 28 and travels therefrom through an inlet conduit system 30 to the core 12. The inlet conduit system 30 herein comprises an inlet chamber 32 providing a plenum 34 beneath the core 12 and an inlet pipe 36 extending from the inlet port 28 to the inlet chamber 32. A flow distribution shroud 38 is provided in the inlet chamber 32 to distribute flow approximately evenly over the area of the lower end 24 of the core 12. The coolant flows upwardly through the core 12 from the inlet plenum 34 to an outlet conduit system 40 which includes an outlet chamber 42 defining an outlet plenum 43 located above the core 12 and an outlet pipe 44 extending therefrom to an outlet port 46 near the upper end of the side wall 16 of the vessel 14. The outlet port 46 typically communicates with exterior piping 48 which carries the primary coolant to a heat exchanger 50 (FIG. 5) for extracting heat therefrom. A pump 52 (FIG. 5) is typically employed to maintain circulation of the fluid through the core 12. Due to the possibility of failure of the pump 52, or some other occurrence which might interrupt supply of primary coolant to the inlet port 28, it is desirable for the reactor 10 to have a secondary system for providing coolant flow through the core 12 to prevent the core from overheating. To this end, the core 12 is located beneath the surface of a pool 54 of relatively cool liquid which functions as a secondary coolant, and means are provided to enable circulation of the secondary coolant from the pool 54 through the core 12 to remove heat therefrom by natural convection in the absence of forced primary coolant circulation. To provide a path for flow of secondary coolant from the pool 54, the inlet conduit system 30 has one or more openings 56 therein communicating with the pool 54, and the outlet conduit system 40 has one or more openings 58 therein also communicating with the pool 54 so that, upon cessation of forced coolant circulation, the difference in density between the hot coolant in the core 12 and the relatively cold coolant in the pool 54 causes coolant within the core 12 to rise, drawing secondary coolant from the pool 54 into the inlet conduit system 30 through the openings 56 therein, and establishing circulation of secondary coolant upwardly through the core 12 into the outlet chamber 42 and thence through the openings 58 in the outlet conduit system 40 back to the pool 54. During normal operation, it is desirable that little or no flow occur between the secondary coolant in the pool 54 and the coolant in the primary cooling circuit, i.e., the primary coolant flowing through the inlet and outlet conduit systems 30, 40. More particularly, it is desirable that means be provided to prevent flow either out of or into the openings 56 in the inlet conduit system 30 and either into or out of the opening 58 in the outlet conduit system 40 through the pool 54, bypassing the core 12. However, it is desirable to accomplish this without the use of components which might prevent flow of secondary coolant through the core after failure of the primary cooling system. As noted above, past attempts to solve this problems have involved reactors wherein the flow rate of the primary coolant is determined by the core reactivity. In accordance with the present invention, means are provided to enable forced flow of primary coolant at a rate selected independently of core reactivity without permitting substantial flow through the openings 56 and 58. This is accomplished in the preferred embodiment by increasing the coolant velocity within the inlet conduit system 30 adjacent the openings 56 therein so as to reduce pressure locally by an amount approximately equal to the pressure drop across the core at any given flow rate. This enables a desired pressure differential to be maintained across the core so as to provide adequate coolant flow therethrough, with little or no flow through the openings 56, 58 in the respective conduit systems 30, 40. The means to increase the coolant velocity preferably comprises one or more venturi throats 60 for restricting the interior cross-sectional area of the inlet conduit system 30 adjacent the openings 56 therein. In the illustrated embodiment, the openings 56 in the inlet conduit system take the form of transverse annular gaps in the venturi throats 60. Turning to a more detailed description of the illustrated inlet conduit system 30, the inlet port 28 is located near the top of the side wall 16 of the reactor vessel 14, and the pipe 36 connecting the inlet port to the inlet chamber beneath the core has a 90.degree. elbow 62 at its upper end to enable it to carry fluid from a horizontal exterior pipe 63 (FIG. 5) vertically downwardly along the interior 64 of the side wall 16. At an elevation near the lower end of the vessel, the inlet pipe 36 is bifurcated into a pair of nozzles 66. Located beneath each nozzle 66 and separated therefrom by a narrow annular gap 56 is a diffuser 68 for receiving flow from its associated nozzle 66. Each diffuser 68 extends downwardly to the inlet chamber 32 beneath the core 12. The nozzles 66 and diffusers 68 provide a pair of parallel venturi throats 60 which lower pressure within the inlet conduit system 30 adjacent the openings 56. Use of a pair of venturi throats 60 improves reliability in that obstruction of one would not disable the secondary cooling system, since flow could proceed through the second. As noted above, it is desirable to have little or no flow through the openings 56, 58 during normal operation. To achieve this, the venturi throats 60 are configured so that the difference between the pressure increase from the venturi throats 60 to the inlet plenum 34 and the pressure drop from the inlet plenum 34 to the outlet pleunum 43 is equal to the difference in static pressure in the pool 54 between the openings 56 in the inlet conduit system 30 and the openings 58 in the outlet conduit system 40. This balancing may be expressed by the equation EQU (p.sub.2 -p.sub.1)-(p.sub.2 -p.sub.3)=P.sub.3a -P.sub.1a where p.sub.1 is the static pressure of the relatively high velocity coolant between the nozzles 66 and the diffusers 68; p.sub.2 is the static pressure in the inlet plenum 34; p.sub.3 is the static pressure in the outlet plenum 43; p.sub.1a is the static pressure in the pool 54 adjacent the nozzles 66; and p.sub.3a is the static pressure in the pool 54 adjacent the outlet plenum 43. In the illustrated system, the gaps 56 between the nozzles 66 and diffusers 68 are located at the same elevation as the outlet plenum 43. Accordingly, p.sub.3a is equal to p.sub.1a and the above equation reduces to the following: EQU p.sub.2 -p.sub.1 =p.sub.2 -p.sub.3. The quantity (p.sub.2 -p.sub.1) represents the increase in pressure between the venturi throat 60 and the inlet plenum 34, and (p.sub.2 -p.sub.3) represents the pressure drop due to flow resistance within the core 12. Generally, the pressure drop due to flow resistance within the core 12 is approximately proportional to the square of the flow rate. Although heating of coolant within the core 12 tends to drive coolant upward therethrough by natural convective flow, the flow rate of primary coolant under normal operating conditions is generally so high that this effect is negligible for purposes of the present analysis. A major advantage provided by the venturi throats 60 of the present invention is that the pressure increase between the venturi throats 60 and the inlet plenum 34 is also approximately proportional to the square of the flow rate. Accordingly, for a given core configuration and a given inlet conduit system configuration, variation of the flow rate will cause only minor variations in the static pressure difference between the venturi throats 60 and the outlet plenum 43. To compensate for such minor variations, means are provided to enable adjustment of the pressure within the venturi throats 60 independently of the flow rate therethrough. Herein, the means to enable adjustment of the pressure within the venturi throats 60 comprises a pair of adjustable obstructions 70, one provided in each venturi throat 60. The obstructions 70 herein are generally conical, each mounted at the lower end of a vertically oriented, vertically movable rod 72 which is movably supported at its upper end. Adjustments of pressure within the venturi throats 60 can be made by adjusting the vertical positions of the respective obstructions 70 by vertical adjustments of the rods 72. The rods 72 preferably operate in unison. The venturi throats 60 and obstructions 70 are preferably configured so that the spools 70 may be used to provide flow in either direction between the interior of the venturi throats 60 and the surrounding pool 54. The inlet chamber 32 is defined by the bottom 18 of the reactor vessel 14 and the support structure 76 for the core. The support structure 76 for the core 12 herein comprises a generally cylindrical vertical wall 78 extending upwardly from the bottom 18 of the vessel, a generally frustoconical wall 80 extending upwardly and radially inwardly therefrom, and a circular grid plate 82 which extends generally horizontally over the top of the frustoconical wall 80 and which supports the fuel elements 15. The grid plate 82 has a number of openings therein communicating with vertical passages in the fuel elements 15 for coolant flow. It is generally desirable that the flow of coolant be distributed relatively evenly among the various fuel elements 15. To this end, a generally cylindrical skirt or shroud 84 extends downwardly from the periphery of the grip plate 82 into the inlet plenum 34. The shroud 84 extends almost to the bottom 18 of the vessel 14 adjacent the inlet pipe 36 so as to deflect coolant entering the inlet chamber 32. The lower edge 86 of the shroud 84 increases in elevation toward the opposite side of the inlet chamber 32, providing a variable width gap 90 for coolant flow between the lower edge 86 and the bottom 18 of the vessel 14. The upper ends 92 of the fuel elements 15 are constrained by a hold-down grid 94 which prevents upward movement of the fuel elements 15. During normal operation, the magnitude of the upward force on the fuel elements 15 due to coolant flow is much smaller than their weight. However, provision of the hold-down grid 94 reduces the possibility that one or more elements 15 might be dislodged by a coolant surge or some other unusual occurence. The core is enclosed by a generally cylindrical vertical wall 95 which extends between the outlet chamber and the inlet chamber. A plurality of control rod assemblies 96 are provided for insertion into the core 12. A typical control rod assembly 96 is illustrated in FIG. 1. The control rod assemblies 96 are supported at the upper end of the vessel 14. Water flowing upwardly through the core 12 is received by the outlet chamber 42. The outlet chamber 42 is generally ovoid in shape as viewed in plan, and includes a substantially vertical side wall 98 which encloses the area above the core 12 and extends radially outward about the lower end of the outlet pipe 44. The outlet pipe 44 extends substantailly vertically upward from the outlet chamber 42 along the interior 64 of the side wall 16 of the vessel at a location diametrically opposite that of the inlet pipe 36. Like the inlet pipe 36, the outlet pipe 44 has a 90.degree. elbow 100 at its upper end connecting it to a horizontal exterior pipe 48. A shroud 102 extends upwardly about the periphery of the core 12 into the outlet chamber 42 to aid in distribution of coolant as it emerges from the upper ends of the fuel elements 15 so as to maintain approximately evenly distributed pressure at the outlet ends of the fuel elements 15. The shroud 102 is similar in shape to the shroud 84 extending into the inlet chamber 32, having its upper edge 104 varying in elevation to distribute pressure approximately evenly over the upper end 26 of the core 12. The liquid in the pool 54 is typically maintained at a relatively low temperature, such as 140.degree. F. The coolant in the primary fluid circuit enters the vessel 14 at a higher temperature, such as 200.degree. F., and is heated to a still higher temperature by the core 12 as it flows therethrough. It is desirable to limit heat transfer from the coolant to the pool liquid, because such heat transfer decreases the efficiency of the system. The above-described venturi throats 60 limit intermixing of the two fluids during normal opeation, which aids in limiting heat transfer therebetween. In addition, thermal insulation 105 is provided along the inlet conduit system 30, outlet conduit system 40, and cylindrical wall 95 about the core 12 to limit conductive heat transfer therethrough. Turning to a more detailed description of the function of the secondary cooling circuit, to enable communication between the interior of the outlet chamber 42 and the pool 54 in the event of failure of the primary circulation system, one or more openings 58 are provided in the top of the outlet chamber 42 to enable upward flow of coolant therethrough. Preferably, two such openings 58 are provided, one on each side of the outlet chamber 42. Extending upwardly from each opening 58 is a T-shaped pipe assembly 106 composed of a vertical riser 108 and a horizontal sparger 110. Each sparger 110 has openings 112 at its opposite ends so that coolant may flow upward through the riser 108 and out both ends of the sparger 110 into the pool 54. During natural convection through the secondary cooling system, coolant enters the gaps 56 in the venturi throats 60, flows downwardly through the diffusers 68 into the inlet chamber 32, flows upwardly through the core 12 into the outlet chamber 42, flows upwardly through the risers 108, and flows horizontally through the openings 112 at the ends of the spargers 110 into the pool 54. The driving force for the secondary cooling system is provided by expansion of the fluid therein as it is heated by the core 12. This expansion lowers the density of the fluid in the core 12 relative to the lower temperature coolant in the difusers 68 so that a convection current results. It will be appreciated that the effectiveness of the secondary cooling system of the present invention requires that the fluid in the pool 54 be maintained at a relatively low temperature. To this end, one or more tank coolers 114 are provided for removing heat from the pool 54. As illustrated in FIGS. 3 and 4, two tank coolers 114 are preferably provided. The tank coolers 114 are preferably located on opposite sides of the vessel 14, one beneath each of the spargers 110. Each tank cooler 114 comprises a system of piping containing a tank coolant such as water which flows through the coolers 114 and circulates through an external heat sink such as a pond 116 (FIG. 5) or other large mass of water at substantially ambient temperature. The tank coolant in the coolers 114 is preferably circulated by natural convection so that no reliance on external power is necessary for its circulation. To this end, the external heat sink 116 is preferably located at a higher elevation than the tank coolers 114 so that high temperature tank coolant will naturally flow upwardly to the heat sink after being heated in the tank coolers 114 as lower temperature tank coolant flows downwardly from the heat sink 116 to the tank coolers 114. Referring particularly to FIGS. 3 and 4, each cooler includes an inlet header 118 and an outlet header 120 connected by a plurality of serpentine aluminum tubes (not shown) for flow of the coolant from the lower pipe to the upper pipe. To aid in maintaining natural convective flow through the aluminum tubes, the inlet header 118 is located beneath the outlet header 120 so that tank coolant flows upward through the tubes as it is heated by the surrounding pool liquid. Tank coolant is supplied to each tank cooler 114 by a vertical inlet pipe 122 which is connected to the inlet header, and the tank coolant is carried from each cooler 114 to the heat sink by a vertical outlet pipe 124 which is conneced to the outlet header 120. The tank coolers 114 are preferably independent of one another so that failure of one does not impede the functioning of the other. The tank coolers 114 preferably have sufficient cooling capcities that either one alone is capable of providing adequate cooling in the event of failure of the primary system. The tank coolers 114 preferably have no valves or other components which might tend to restrict flow therethrough under any circumstances. Accordingly, during normal operation, the tank coolers 114 function to maintain the temperature of the pool 54 at a desired temperature. During normal operation, relatively little heat is transferred to the pool 54, and accordingly, the flow rate through the tank coolers 114 is relatively low. During operation of the secondary cooling system, greater heat transfer to the tank coolant within the coolers 114 will increase the convective flow rate therethrough, thus increasing the amount of heat removed from the pool 54, and eventually establishing a temperature equilibrium in the pool 54. The fact that the tank coolant is isolated from the primary coolant which flows through the core 12 during normal operation enables the tank coolant to be circulated to an outdoor pond 116 without significant radioactive contamination of the pond 116. During operation of the secondary cooling system, irradiation of the tank coolant is still relatively low as there is no intermixing of the tank coolant with the secondary coolant, and the reactivity of the core has presumably been minimized, as by insertion of control rods. As set forth above, the reactor 10 employs three different fluids: a primary coolant which flows through the primary cooling circuit under normal operating conditions; a secondary coolant, the pool liquid, which intermixes with primary coolant and flows through the core during emergency conditions; and a tertiary coolant, the tank coolant, which flows through the tank coolers and does not intermix with either the primary coolant or the pool liquid. Preferably, all three coolants are liquid water. In some embodiments, it may be desirable to employ a secondary coolant which decreases reactivity in the core upon entry into the core 12. For example, borated water may be used as the secondary coolant. An important advantage of the above-described reactor lies in the ability of the venturi throats 60 to maintain the desired pressure balance between the primary coolant and the secondary coolant during start-up of the reactor. Because the pressure recovery in the venturi throats is approximately equal to the pressure drop across the core at any flow rate, maintenance of the desired pressure balance does not require addition of heat to coolant within the core 12, nor does it require any particular coolant flow rate. Accordingly, during start-up, coolant flow may be commenced with relatively little intermixing occurring between the primary coolant and the secondary coolant. From the foregoing, it will be appreciated that the present invention provides a nuclear reactor with a novel cooling system. While a preferred embodiment has been illustrated and described herein, there is no intent to limit the scope of the invention to this or any other particular embodiment. |
claims | 1. Nuclear fuel element comprising a first plate, a first network having a plurality of walls integral with the first plate for forming a plurality of individual cells separated from one another and defined by said walls, and at least one nuclear fuel pellet having opposite sides confined within a corresponding cell such that a circumferential gap is formed between said opposite sides of said pellet and the walls of the cell, with the nuclear fuel pellet extending along an axis aligned in a direction approximately parallel to the walls of the cell; a second plate disposed in parallel alignment with said first plate on a side of said network opposite to the first plate in order to close the cells; said second plate is integral with a second network, substantially the same as the first network; and an axial gap formed between the at least one fuel pellet and the first and second plates. 2. Element according to claim 1, wherein the walls of the networks have the same thickness, taken in a direction parallel to the first and second plates. 3. Element according to claim 1, wherein the first and second networks are manufactured in a unitary manner with the first and second plates, respectively. 4. Element according to claim 1, wherein each closed cell is filled with helium. 5. Element according to claim 4, wherein the fissile phase of the fuel pellets accounts for more than 20% of the volume of the element. 6. Element according to claim 1, wherein the gaps formed in the cell create a residual volume in such cell, which accounts for at least 40% of the volume of the pellet located in such cell. 7. Element according to claim 1, wherein at least one of the opposite sides of the pellet is curved outwards to minimize comparative stress levels in the plate facing said opposite side of the pellet. 8. Element according to claim 1, wherein the first and second networks are a honeycomb structure of hexagonal cells. 9. Element according to claim 1, wherein the plates and the networks are made from the same refractory material, metal or ceramic. 10. Element according to claim 9, wherein the plates and the networks are composed of a ceramic. 11. Element according to claim 10, wherein said ceramic is SiC. 12. Element according to claim 11, wherein each pellet is cylindrical in geometry. 13. Element according to claim 10, wherein said ceramic is fibrous. 14. Element according to claim 10, further comprising a metallic layer plated on to the walls of each cell. |
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048517020 | description | STRUCTURE Referring to FIG. 1, radiopaque sleeve 14, containing microtube 12, containing radioactive solution 19, has a flange 24 for suspending it from a top shelf 16 of a rack 10, and a lower tapered portion 26 which extends through a lower shelf 18 of rack 10. Sleeve 10 is inserted within two concentrically aligned holes 20, 22 in rack 10. The bottom of sleeve 14 is slightly elevated from the lowest level 15 of the rack. Sleeve 14 is made of radiopaque plastic, such as Plexiglass.TM., (acrylic) or Lexan.TM. (polycarbonate) and is approximately 1/4 inch thick. This thickness is sufficient to block high energy .beta.-particles. The inner diameter of sleeve 14 is approximately equal to the outer diameter of microtube (about 1.0 cm) 12 so that when microtube 12 is inserted into sleeve 14, they are in close proximity. When microtube 12 is placed within sleeve 14, it extends only a portion of the way through sleeve 14. This prevents radiation from emanating from solution 19 in a horizontal direction. Both the outer surface and the inner surface of the sleeve are substantially optically transparent to allow visual inspection of solution 19. Lid 28 of microtube 12 is elevated from flange 24 by a circular ridge 30 (or alternatively dimples) to facilitate access to lid 28. The base 31 of sleeve 14 is substantially flat, which allows it to rest in a free standing position so that sampling of the contents of microtube 12 is readily performed. Placed on rack 10, the geometry of sleeve 14 (open at the top and bottom) permits liquid in any incubator bath to directly enter sleeve 14 through bottom opening 33 and surround that portion of the microtube enclosing solution 19 contained in microtube 12. OTHER EMBODIMENTS Other embodiments are within the following claims. For example, referring to FIG. 2, an incubation rack 32 is designed for suspending several microtubes 34, 36 (only two are shown) from a single radiopaque shelf 38. A plastic skirt 40 surrounds the perimeter of shelf 38 and encloses microtubes 34, 36 suspended from shelf 38 (for clarity the front of skirt 40 is not shown). To prevent lateral radiation, skirt 40 extends just above and below the suspended microtubes 34, 36. Skirt 40 is elevated by two handles 44, 46 to permit incubation rack 32 to be placed in any water bath and allow incubation water (not shown) to circulate around the lower portion of microtubes 34, 36. A plastic lid 42 is hinged to skirt 40 and serves to block radiation emanating upward. Skirt 40 and lid 42 are made of transparent plastic at least 1/4 inch thick for blocking .beta.-emmitting particles. Identifying marks for suspended microtubes can be made on top of lid 42. Referring to FIG. 3, a block of transparent, radiopaque material 48 is provided with a plurality of bores 50 which extend through block 48. Preferably block 48 is made of plastic such as Plexiglass.TM. and has a minimum thickness T of 1/4 inch between bores 50 along the perimeter of block 48. Radioactive emission from the solution contained in microtubes 34, 36 is therefore limited to the top and bottom openings of bore 50. Handles 52 elevate block 48 and permit incubation water to circulate around microtubes 34, 36 suspended from the top of block 48. |
claims | 1. A method for measuring a property of material penetrated by a borehole comprising the steps of:(a) irradiating said material with a source of radiation generating a plurality pulses of neutrons of about five microseconds per pulse and at a periodic pulse repetition rate of about 10,000 to 20,000 pulses per second thereby inducing gamma radiation within said material;(b) measuring said induced radiation with a single radiation detector comprising a YAP scintillator crystal, a light responsive means coupled to said scintillator crystal, and circuitry connected to said light responsive means for processing output from said scintillator crystal, wherein said detector is operated during each of said pulses, and(c) determining said property from said measure of said induced radiation, wherein(d) said radiation detector processes and resolves up to three detected scintillations without scintillation pulse pile-up during each said neutron pulse. 2. The method of claim 1 comprising the additional step of generating said pulses at said pulse repetition rate at about 20,000 pulses per second. 3. The method of claim 2 comprising the additional step of operating said detector to measure energy of said gamma radiation during said pulses. 4. The method of claim 1 wherein said gamma radiation results from neutron inelastic scatter. 5. The method of claim 1 comprising the additional steps of:(a) disposing said source and said radiation detector in a housing; and(b) conveying said housing along a borehole by means of a wireline. 6. The method of claim 1 comprising the additional steps of:(a) disposing said source and said radiation detector in a housing; and(b) conveying said housing along a borehole by means of a drill string. 7. The method of claim 4 comprising the additional step of measuring said gamma radiation in at least one energy window. 8. The method of claim 4 comprising the additional step of measuring said gamma radiation in a plurality of energy windows representing inelastic scatter of neutrons from oxygen, carbon, calcium and silicon. 9. A method for measuring a property of material penetrated by a borehole comprising the steps of:(a) irradiating said material with a source of radiation generating a plurality of pulses of neutrons at a periodic repetition rate thereby inducing gamma radiation within said material;(b) measuring said induced radiation with a single radiation detector comprising a YAP scintillator crystal, a light responsive means coupled to said scintillator crystal, and circuitry connected to said light responsive means for processing output from said scintillator crystal, and(c) determining said property from said measure of said induced radiation, wherein(d) said radiation detector processes and resolves a plurality of detected scintillations measured without scintillation pulse pile-up during a time interval of about 5 microseconds,(e) energy of each said gamma ray inducing each said detected scintillation is determined, and(f) at least one energy window is obtained by integrating said gamma rays over a predetermined energy range. 10. The method of claim 9 wherein said detector is operated during each of said pulses. 11. The method of claim 9 comprising the additional step of pulsing said neutron source at a pulse repetition rate greater than 10,000 pulses per second. 12. The method of claim 9 comprising the additional step of operating said radiation detector coincident with each said pulse from said neutron source. 13. The method of claim 9 comprising the additional step of operating said radiation detector during quiescent periods between pulses from said pulsing neutron source. 14. The method of claim 9 wherein said gamma radiation results from neutron inelastic scattering. 15. The method of claim 9 comprising the additional steps of:(a) disposing said source of radiation and said radiation detector in a housing; and(b) conveying said housing along a borehole by means of a wireline. 16. The method of claim 9 comprising the additional steps of:(a) disposing said source of radiation and said radiation detector in a housing; and(b) conveying said housing along a borehole by means of a drill string. |
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abstract | A method and apparatus for controlling deflection, deceleration, and focus of an ion beam are disclosed. The apparatus may include a graded deflection/deceleration lens including a plurality of upper and lower electrodes disposed on opposite sides of an ion beam, as well as a control system for adjusting the voltages applied to the electrodes. The difference in potential between pairs of upper and lower electrodes are varied using a set of “virtual knobs” that are operable to independently control deflection and deceleration of the ion beam. The virtual knobs include control of beam focus and residual energy contamination, control of upstream electron suppression, control of beam deflection, and fine tuning of the final deflection angle of the beam while constraining the beam's position at the exit of the lens. In one embodiment, this is done by fine tuning beam deflection while constraining the beam position at the exit of the VEEF. In another embodiment, this is done by fine tuning beam deflection while measuring the beam position and angle at the wafer plane. In a further embodiment, this is done by tuning a deflection factor to achieve a centered beam at the wafer plane. |
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abstract | A method for preparing low level radioactive hazardous wastes (LLHZ) for disposal in a landfill. The method includes providing a softsided transportable container at a hazardous debris collection site, where the softsided container has at least three layers of materials, an outer, middle and an inner layer, where the middle layer is a water impervious material. Each layer has a closable opening located on the top of the softsided layer. Hardsided closed containers containing LLHZ located in the interior of the hard container are loaded into the interior of the softsided container. Each layer of the softsided container is then closed, and the package transported and shipped to a disposal site for burial. |
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061887498 | claims | 1. An X-ray examination apparatus comprising: an X-ray source, an X-ray detector, and an X-ray filter which is arranged between the X-ray source and the X-ray detector, wherein the X-ray filter comprises a plurality of filter elements having an X-ray absorptivity which can be adjusted by controlling a quantity of X-ray absorbing liquid within the individual filter elements in a matrix arrangement of rows and columns, which filter elements communicate with the X-ray absorbing liquid by way of a first end an X-ray transparent liquid by way of a second end; and wherein 2. An X-ray examination apparatus as claimed in claim 1, wherein individual filter elements are formed by cylinders having a cross-section of a diameter smaller than 5 mm. 3. An X-ray examination apparatus as claimed in claim 1, wherein individual row ducts and individual column ducts are provided with respective valves, and the pressure control system is arranged to control the valves. 4. An X-ray examination apparatus as claimed in claim 1, wherein individual filter elements are provided with a piston for separating the X-ray absorbing liquid from the X-ray transparent liquid. 5. An examination apparatus as claimed in claim 4, wherein the piston is provided with a coating layer. 6. An X-ray examination apparatus as claimed in claim 1, wherein the X-ray absorbing liquid and the X-ray transparent liquid are not miscible. 7. The apparatus of claim 6 wherein the X-ray absorbing liquid comprises an aqueous solution and the X-ray transparent liquid comprises an oil. |
summary | ||
abstract | Systems, devices, and methods are described for providing, among other things, an intra-oral x-ray imaging system configured to reduce patient exposure to x-rays, reduce amount of scatter, transmission, or re-radiation during imaging, or improve x-ray image quality. In an embodiment, an intra-oral x-ray imaging system includes an intra-oral x-ray sensor configured to communicate intra-oral x-ray sensor position information or intra-oral x-ray sensor orientation information to a remote x-ray source. |
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042631637 | abstract | This invention is directed to a method and an apparatus to heat certain particles. These certain particles are heated to make them more desirable. In the heating of these particles, it is often desirable to expand the particles to make a light-weight aggregate. The light-weight aggregate may be used in making a building material or the like. In carrying out the process of heating these particles, there is used air for combustion of the combustible fuel and only a minimum of air for carrying of the particles or expansion of the particles. |
description | This invention relates generally to imaging systems and more particularly to systems and methods for reducing radiation dosage incident on a subject. A third generation computed tomography (CT) scanner includes an x-ray source and a detector that are rotated together around a patient. An x-ray beam is passed through the patient and intensity of the x-ray beam is measured on the detector. In some CT imaging systems, an x-ray tube is used to create the x-rays. X-rays are produced when electrons are accelerated against a focal spot or an anode by a high voltage difference between the anode and a cathode of the x-ray tube. These x-rays typically diverge conically from the focal spot, and the diverging x-ray beam is typically passed through a pre-patient collimator to define an x-ray beam profile on the detector. Some CT imaging systems include detector cells arranged on an arc of constant radius from the source. If the collimator is linear, or rectangular, an x-ray beam profile on the detector will become curved along a fan of the detector as an aperture of the collimator is opened along a z-axis. The curvature can result in both unused x-ray dose and degradation in a CT image formed from the curved x-ray beam profile. In one aspect, an imaging system is provided. The imaging system includes a radiation source configured to generate a beam, a collimator configured to collimate the beam to generate a collimated beam, and a detector configured to detect the collimated beam. The collimator is one of a first collimator with a curved contour proportional to a contour of the detector, a second collimator with blades, where slopes of two oppositely-facing surfaces of at least one of the blades are different from each other, and a third collimator having at least two sets of plates, where the plates in a set pivot with respect to each other. In another aspect, a computed tomography imaging system is provided. The computed tomography imaging system includes an x-ray source configured to generate a beam, a collimator configured to collimate the x-ray beam to generate a collimated x-ray beam, and a detector configured to detect the collimated x-ray beam. The collimator is one of a first collimator with a curved contour proportional to a contour of the detector, a second collimator with blades, where slopes of two oppositely-facing surfaces of at least one of the blades are different from each other, and a third collimator having at least two sets of plates, where the plates in a set pivot with respect to each other. In yet another aspect, a method for reducing dosage of radiation incident on a subject is provided. The method includes transmitting a beam of radiation toward the subject, collimating the beam of radiation before the beam reaches the subject, and detecting the collimated beam of radiation. The collimating is performed by one of a first collimator with a curved contour proportional to a contour of a detector that detects the collimated beam, a second collimator with blades, where slopes of two oppositely-facing surfaces of at least one of the blades are different from each other, and a third collimator having at least two sets of plates, where the plates in a set pivot with respect to each other. In some known CT imaging system configurations, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as an “imaging plane”. The x-ray beam passes through an object, such as a patient, being imaged. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated radiation beam received at the detector array is dependent upon the attenuation of an x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile. In third generation CT imaging systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged such that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a “view”. A “scan” of the object comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source and detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered back projection technique. This process converts the attenuation measurements from a scan into integers called “CT numbers” or “Hounsfield units”, which are used to control the brightness of a corresponding pixel on a cathode ray tube display. To reduce the total scan time, a “helical” scan may be performed. To perform a “helical” scan, the object is moved while the data for the prescribed number of slices is acquired. Such a system generates a single helix from a one fan beam helical scan. The helix mapped out by the fan beam yields projection data from which images in each prescribed slice may be reconstructed. Reconstruction algorithms for helical scanning typically use helical weighing algorithms that weight the collected data as a function of view angle and detector channel index. Specifically, prior to a filtered backprojection process, the data is weighted according to a helical weighing factor, which is a function of both the gantry angle and detector angle. The helical weighting algorithms also scale the data according to a scaling factor, which is a function of the distance between the x-ray source and the object. The weighted and scaled data is then processed to generate CT numbers and to construct an image that corresponds to a two dimensional slice taken through the object. As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Also as used herein, the phrase “reconstructing an image” is not intended to exclude embodiments of the present invention in which data representing an image is generated but a viewable image is not. However, many embodiments generate (or are configured to generate) at least one viewable image. Referring to FIGS. 1 and 2, a multi-slice scanning imaging system, for example, a computed tomography (CT) imaging system 10, is shown as including a gantry 12 representative of a “third generation” CT imaging system. Gantry 12 has an x-ray source 14 that projects a beam of x-rays 16 toward a detector array 18 on the opposite side of gantry 12. Detector array 18 is formed by a plurality of detector rows (not shown) including a plurality of detector elements or cells 20 which together sense the projected x-rays that pass through an object 22, such as a medical patient. As an example, width of each detector element 20 along a z-axis is greater than 40 millimeters (mm) as scaled to an isocenter of x-ray beam 16. Each detector element 20 produces an electrical signal that represents the intensity of an impinging x-ray and hence the attenuation of the x-ray as it passes through object 22. During a scan to acquire x-ray projection data, gantry 12 and the components mounted thereon rotate about a center of rotation 24. FIG. 2 shows only a single row of detector elements 20 (i.e., a detector row). However, multislice detector array 18 includes a plurality of parallel detector rows of detector elements 20 such that projection data corresponding to a plurality of quasi-parallel or parallel slices can be acquired simultaneously during a scan. Rotation of gantry 12 and the operation of x-ray source 14 are governed by a control mechanism 26 of CT imaging 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 object 22 in gantry 12. Particularly, table 46 moves portions of object 22 through gantry opening 48. In one embodiment, computer 36 includes a device 50, for example, a floppy disk drive, CD-ROM drive, DVD drive, magnetic optical disk (MOD) device, or any other digital device including a network connecting device such as an Ethernet device for reading instructions and/or data from a computer-readable medium 52, such as a floppy disk, a CD-ROM, a DVD or an other digital source such as a network or the Internet, as well as yet to be developed digital means. In another embodiment, computer 36 executes instructions stored in firmware (not shown). Computer 36 is programmed to perform functions described herein, and as used herein, the term computer is not limited to just those integrated circuits referred to in the art as computers, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein. FIG. 3 is a diagram of an embodiment of a pre-patient collimator 62 and a portion of gantry 12 of CT imaging system 10. X-ray beam 16 emanates from a focal point 60 at which x-ray source 14 is located. X-ray beam 16 is collimated by collimator 62, and a collimated fan beam 64 is projected via an object 66 toward detector array 18 along a fan beam axis centered within collimated beam 64. Detector array 18 is curved at a fixed radius from focal point 60. FIG. 4 shows an embodiment of a system 120 for reducing radiation dosage. System 120 includes x-ray source 14 at a focal point 60, a collimator 122, and detector array 18. An isometric view of an embodiment of collimator 122 is shown in FIG. 5. Collimator 122 is contoured in a direction along a y-axis. Collimator 122 includes a plurality of cams 123 that are driven linearly along the z-axis to produce apertures of various sizes, such as widths. Referring back to FIG. 4, aperture 124 is an example of an aperture formed by the cams 123 of collimator 122. Prior to scanning, the cams 123 are driven to a pre-set position by a linear drive mechanism 125 (FIG. 5), such as a screw, to form a pre-set aperture between the cams. To change a size of the pre-set aperture during a scan, a piezo-electric drive mechanism 127 (FIG. 5) is used to position the cams 123. X-ray source 14 transmits x-ray beam 16 towards collimator 122. Collimator 122 collimates or restricts x-ray beam 16 to generate a collimated beam 126. Collimated beam 126 falls on detector elements 20 and generates an x-ray beam profile 128. X-ray beam profile 128 is a projection of collimated beam 126. Curvature of x-ray beam profile 128 is minimal for all sizes, such as widths, of apertures formed by the cams 123 of collimator 122. A radius of curvature of collimator 122 is proportional to a radius of curvature of detector array 18. As an example, a radius of curvature of detector array 18 at a point 130 is x+y centimeters (cm), where x is a radius of curvature of collimator 122 at a distance 132 from focal point 60, and where x and y are real numbers greater than zero. In this example, a radius of curvature of detector array 18 at a point 134 is m+y cm, where m is a radius of curvature of collimator 122 at a distance 136 from focal point 60, and where m is a real number greater than zero. A radius of curvature of collimator 122 and detector array 18 is measured from focal point 60. Distance 132 is approximately equal to distance 136 because a contour of collimator 122 matches a contour of detector array 18. FIG. 6 shows an embodiment of a collimator 150 that is used in systems and methods for radiation dosage. Collimator 150 includes blades or plates 152 and 154. Blades 152 and 154 can be of shapes such as square, rectangular, polygonal, circular, and oval. Each blade 152 and 154 has a respective outer surface 156 and 158 and a respective inner surface 160 and 162. Inner surface 160 of blade 152 has different taper or slope than outer surface 156 and inner surface 162 of blade 154 has a different taper than outer surface 158. In an alternative embodiment, any one of surfaces 156, 158, 160, and 162 has a different taper than remaining surfaces. Blades 152 and 154 may be of the same or different sizes. A pivot arm 163 supports blade 152 and a pivot arm 165 supports blade 154. Blades 152 and 154 are partially closed but do not overlap each other, as shown in an isometric view 164, to form an aperture with a large width between inner surfaces 160 and 162 of blades 152 and 154. An example of an aperture with a large width is an aperture whose x-ray beam profile has a width greater than 30 mm on detector array 18. When blades 152 and 154 are partially closed to obtain the aperture with the large width, distance between outer surfaces 156 and 158 is greater than distance between inner surfaces 160 and 162. Tapers of inner surfaces 160 and 162 can be optimized for apertures of large widths. Alternatively, blades 152 and 154 are partially closed but do not overlap each other to form an aperture with a medium width between outer surfaces 156 and 158 of the blades. If blades 152 and 154 are in a position shown in isometric view 164, the blades are overlapped with each other and cross-over each other so that an aperture with a medium width is formed between outer surfaces 156 and 158 of the blades. An example of an aperture with a medium width is an aperture whose x-ray beam profile has a width from 1 mm to 30 mm on detector array 18. When blades 152 and 154 are partially closed to obtain the aperture with the medium width, distance between inner surfaces 160 and 162 is greater than distance between outer surfaces 156 and 158. Tapers of outer surfaces 156 and 158 can be optimized for apertures of medium widths. In yet another alternative embodiment, blade 154 includes a slit 166 or an aperture having a small width through which x-ray beam 16 passes to form an x-ray beam profile on detector array 18. An example of an aperture with a small width is an aperture whose x-ray beam profile has a width of approximately 1 mm on detector array 18. Alternatively, blade 152 includes slit 166. Each blade 152 and 154 is coupled to a respective shaft 168 and 170 that is coupled to a respective motor 172 and 174. Motors 172 and 174 provide rotational motion to blades 152 and 154 so that the blades can overlap and cross-over each other. Alternatively, a linear drive mechanism is used to operate blades 152 and 154. However, motors 172 and 174 have less susceptibility to wear and tear as compared to the linear drive mechanism. FIG. 7 shows another alternative embodiment of a collimator 180 that is used in systems and methods for reducing radiation dosage. Collimator 180 includes a first set 182 of plates or blades 184 and 186 and a second set 188 of plates or blades 190 and 192. Plates 184 and 186 can be of shapes such as square, rectangular, polygonal, circular, and oval. Plates 184 and 186 are coupled to each other by a hinge 194 so that plates 184 and 186 move with respect to each other. Plates 190 and 192 are coupled in a similar manner to that of plates 184 and 186. Inner drives, which are shown as arrows 196 and 198, and rectangles 200 and 202, control a nominal width, for instance, a width at ends, of an aperture formed between set 182 and set 188. Outer drives, which are shown as arrows 204, 206, 208, and 210, and rectangles 212, 214, 216, and 218, adjust a taper or a slope, for instance, along the z-axis, of the aperture formed between set 182 and set 188. An optimal x-ray beam profile can be generated on detector array 18 for all nominal apertures formed between set 182 and set 188. Technical effects of the herein described systems and methods include reducing a curvature of an x-ray beam profile formed on detector array 18 while simultaneously supporting a wide range of apertures. For instance, collimator 150 provides apertures of large, medium, and small widths while simultaneously reducing curvature of x-ray beam profiles. It is noted that although CT imaging system 10 described herein is a “third generation” system in which both the x-ray source 14 and detector array 18 rotate with gantry 12, many other CT imaging systems including “fourth generation” systems where a detector is a full-ring stationary detector and an x-ray source rotates with the gantry, may be used. It is also noted that although a curved detector array is shown in FIGS. 1, 2, 3, 4, and 5, a linear or a straight detector array can be used instead. For instance, collimator 150 collimates x-ray beam 16 to project an x-ray beam profile on the linear detector array. As another instance, collimator 180 collimates x-ray beam 16 to project an x-ray beam profile on the linear detector array. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. |
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claims | 1. A decontamination system, comprising:a chamber adapted to house an object to be decontaminated;a first x-ray radiation source arranged to radiate the chamber with x-ray radiation and operable to emit x-ray radiation having a diffused radiation angle and a first photon energy level; anda second x-ray radiation source arranged to radiate the chamber x-ray radiation and operable to emit x-ray radiation having a diffused radiation angle and a second photon energy level that is different than the first photon energy level. 2. The decontamination system of claim 1 wherein the x-ray radiation from the first x-ray radiation source is tailored to penetrate an exterior surface of the object and the x-ray radiation of the second x-ray radiation source is tailored to decontaminate the exterior surface of the object. 3. The decontamination system in claim 1 wherein the first x-ray radiation source includes:a power supply;a cathode electrically connected to the power supply and operable to emit electrons when energized by the power supply; andan anode disposed proximate to the cathode and operable to emit x-ray radiation when electrons from the cathode impinge upon an emitting surface thereof, where the emitting surface of the anode is shaped to disperse the x-ray radiation emitting therefrom. 4. The decontamination system of claim 3 wherein the x-ray radiation source includes:a power supply;a cathode electrically connected to the power supply and operable to emit electrons when energized by the power supply; andan anode disposed proximate to the cathode and operable to emit x-ray radiation when electrons from the cathode impinge upon an emitting surface thereof, where the emitting surface of the anode is shaped to disperse the x-ray radiation emitting therefrom. 5. The decontamination system of claim 1 wherein the first x-ray radiation source operable to emit x-ray radiation having a photon energy of approximately 8 keV and the second x-ray radiation source operable to emit x-ray radiation having a phonon energy of approximately 22 keV. 6. The decontamination system of claim 1 wherein the first x-ray radiation source having an anode comprised of a first material and the second x-ray radiation source having an anode comprised of a second material different than the first material. 7. The decontamination system of claim 1 wherein the first x-ray radiation source having an anode comprised of molybdenum and the second x-ray radiation having an anode comprised of silver. 8. A decontamination system, comprising:a chamber adapted to house an electronic device to be decontaminated;an x-ray radiation source arranged to radiate the chamber with x-ray radiation and operable to emit x-ray radiation having a diffused radiation angle by accelerating electrons from a cathode towards a concave surface of an anode, wherein the x-ray radiation is tailored to penetrate an exterior surface of the electronic device. 9. The decontamination system of claim 3 further comprises a second x-ray radiation source arranged to radiate the chamber with x-ray radiation tailored to contaminate the exterior surface of the electronic device. 10. The decontamination system of claim 8 wherein the first x-ray radiation source operable to emit x-ray radiation at a first photon energy and the second x-ray radiation source operable to emit x-ray radiation at a second photon energy that is different than the first photon energy. 11. The decontamination system of claim 10 wherein the first x-ray radiation source having an anode comprised of a first material and the second x-ray radiation source having an anode comprised of a second material different than the first material. 12. A decontamination system, comprising:a chamber adapted to house an object to be decontaminated;a first x-ray radiation source having an anode comprised of a first material and arranged to radiate the chamber with x-ray radiation that is tailored to penetrate an exterior surface of the object; anda second x-ray radiation source having an anode comprised of a second material and arranged to radiate the chamber x-ray radiation that is tailored to decontaminate the exterior surface of the object, wherein the second material is different than the first material. 13. The decontamination system of claim 12 wherein the first and second x-ray radiation sources are orientated at different angles within the chamber. 14. The decontamination system of claim 12 wherein the first and second x-ray radiation sources are configured to generate x-ray radiation at different photon energy levels. 15. The decontamination system of claim 12 further comprises ultraviolet radiation source arrange to radiate the chamber with ultraviolet radiation. 16. The decontamination system of claim 12 wherein the first x-ray radiation source includes:a power supply;a cathode electrically connected to the power supply and operable to emit electrons when energized by the power supply; andan anode disposed proximate to the cathode and operable to emit x-ray radiation when electrons from the cathode impinge upon an emitting surface thereof, where the emitting surface of the anode is shaped to disperse the x-ray radiation emitting therefrom. 17. The decontamination system of claim 12 wherein the first x-ray radiation source operable to emit radiation at a first photon energy level and the second x-ray radiation source operable to emit radiation at a second photon energy level that is different than the first photon energy level. 18. The decontamination system of claim 17 wherein the first x-ray radiation source operable to emit x-ray radiation having a photon energy of approximately 8 keV and the second x-ray radiation source operable to emit x-ray radiation having a photon energy of approximately 22 keV. 19. The decontamination system of claim 12 wherein the first x-ray radiation source having an anode comprised of molybdenum and the second x-ray radiation having an anode comprised of silver. |
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abstract | A reactor pressure vessel with an upper support plate, in which an equalization opening is provided as a bypass is described. A process for temperature equalization between an upper dome chamber above a support plate and a lower chamber below it is described. It is proposed that the cross section of the equalization opening be variable as a function of the temperature, so that the flow of medium between the upper dome chamber and the lower chamber is varied as a function of the temperature. |
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053708270 | summary | BACKGROUND OF THE INVENTION This invention relates generally to precipitation methods for decontaminating various types of solutions which are contaminated with a variety of contaminants such as heavy metals and radioactive compounds, using a novel combination of treatment steps. More particularly, this invention relates to methods for remediating water contaminated with uranium, thorium, mercury and/or copper, using sodium silicate, ammonium hydroxide and hydrochloric acid, to precipitate the contaminants and ultimately separate them from solution. There is increasing concern over the hazards posed by the rising levels of inorganic contaminants within the world's water supplies due to accidental spills, leaks, mining practices and poor disposal practices. Most heavy metal contaminants are toxic to some degree to all life-forms. In humans, toxic heavy metal poisoning can lead to severe nervous system disorders and can cause death. It has been suggested that various inorganic contaminants in solution can be removed via precipitation solution using, for example, carbonates, hydroxides, sulfides, and/or silicates. Such techniques are described in Canter, L. W., and Knox, R. C., Ground Water Pollution Control, Lewis Publishers, Inc., 1985, pp. 110-120; and Willey, B. R., Finding Treatment Options for Inorganics, in WATER/Engineering & Management, October, 1987, pp. 28-31. In particular, the use of sodium silicate (also referred to as water glass or Na.sub.2 SiO.sub.3) to remove uranium and/or thorium from waste streams has been suggested. For example, in U.S. Pat. No. 4,501,691, issued in the name of Tanaka et al., on Feb. 26, 1985, there is described a process for treating radioactive liquid waste in which the liquid waste is treated with sodium silicate to form a uranium containing silica precipitate. The precipitate subsequently is treated in a step-wise fashion with acid to recover the uranium, and then alkali metal hydroxide solution to regenerate the water glass. Silicate precipitation processes for uranium and thorium recovery also are described in U.S. Pat. Nos. 4,349,513, issued Sep. 14, 1982, in the name of Ishiwata et al.; U.S. Pat. No. 5,077,020, issued Dec. 31, 1991, in the name of Lahoda et al; and U.S. Pat. No. 4,338,286, issued Jul. 6, 1982, in the name of Nakai et al. In Ishiwata, the liquid waste is treated with sodium silicate in the presence of aqueous fluorine and ammonia to make a uranium/thorium-containing silicate precipitate which is filtered out of the process stream find sent to a holding tank. In Lahoda et al., the contaminated stream is treated with sodium silicate in the presence of ammonia, fluoride, and nitrate in water. Nakai et al. generally describe a precipitation process for treating liquids contaminated with uranium/thorium wherein sodium silicate is added to the solution in the presence of ammonia water and chlorine to cause a contaminant-containing silica precipitate to form. There are significant disadvantages associated with the application of each of these methods. For example, carbonate systems, while relatively easy to operate, are difficult to control and often result in processing problems such as premature plugging of equipment. Sulfide systems are difficult to handle, complex to operate, and frequently produce a high waste volume and harmful residual levels of precipitating agent. Hydroxide systems are widely used to remove inorganics because they are the most reliable, and have the added advantages of ease in chemical handling and low volume of sludge. However, the resulting sludge often is gelatinous and difficult to dewater, making treatment, separation, and storage of the contaminated material difficult. In addition, pH must be precisely controlled. Otherwise, contaminant-containing precipitate can readily go back into solution. The above mentioned silicate precipitation methods suffer from at least two critical drawbacks. First, typically such methods produce a contaminant-containing, slime or sludge which is not readily treatable, separable, or easily stored. For example, the slime/sludge is not easily dewatered, making further treatment with filtration devices either impossible (due to plugging) or impractical (due to excessively slow filtration rates). Second, silicate precipitation generally is not effective on other inorganic contaminants; for example, silicates do not readily precipitate other heavy metals like mercury. Consequently, silicate precipitation methods are slow, inefficient, and ineffective in reducing the level of uranium, thorium and other heavy metals to environmentally acceptable levels. What is needed is a simplified, easy-to-operate method of treating large volumes of solutions containing heavy metals and radioactive contaminants, singly or in combination, which effectively segregates the contaminates from the clean solution and concentrates the contaminated material in a manageable, low volume, concentrated waste stream. There is a further need for a system that can effectively and economically remove metals from contaminated solutions, whereby the contaminated material is readily separable from the cleansed solution, especially by filtration methods. There is also a need for a process which can effectively remove various metal contaminants like uranium, thorium, mercury, and copper from solution. SUMMARY OF THE INVENTION These and other needs are satisfied by the invention which is characterized by treating process streams such as groundwater, drinking water, soil extracting solutions, leaching solutions, and the like, which are contaminated with various inorganic contaminates, either singly or in combination, with a unique combination of treatment steps. In the process of the invention, the contaminated process stream is treated with a unique combination of precipitating/gelling/polymerization agents comprising silicate, ammonium hydroxide, and acid. The acid is added to the process stream after the addition of silicate and ammonium hydroxide, in an amount sufficient to lower the pH of the stream to between about 5 to about 9.5. Next, the stream is allowed to age for a time sufficient to allow the contaminant-containing silica matrix to gel, polymerize and/or precipitate to a filterable "solid". The resulting solid is readily dewatered and can be quickly separated from the clean stream. In practicing the precipitation method of the invention, it is important that the precipitating agents are added in the proper sequence and at the required amounts, that the proper pH of the stream is maintained, and that the stream is permitted to age for the requisite length of time. It has been found that the controlled addition of the sequence of precipitating agents, the maintenance of pH, and proper aging of the stream minimizes the consumption of precipitating agent and the generation of waste volume, and results in a contaminated solid which is readily filterable in minutes, as opposed to hours or even days. Consequently, a smaller amount of precipitant is used, a manageable volume of waste is generated, and a lower disposable/clean-up cost is incurred. Moreover, the inventors experimentally have determined that it is the combination of sodium silicate with ammonium hydroxide which renders the present process more effective at removing a wider variety of contaminants. For example, as indicated in Table 1, the use of sodium silicate alone, sodium silicate with ammonium chloride, or sodium silicate with sodium hydroxide, was not effective at removing mercury from a contaminated stream to desirable levels. It was only when both sodium silicate and ammonium hydroxide precipitants were added that levels of +99% mercury removal were obtained. Similarly, +99% copper removal was achieved only through the combined use of sodium silicate and ammonium hydroxide precipitants. TABLE 1 ______________________________________ Effectiveness of Ammonium Hydroxide Addition on Heavy Metal Removal Using Sodium Silicate % Contaminant Additive* Contaminant Removed ______________________________________ None Mercury 0% 0.25 g/L Mercury +99% Ammonium Hydroxide 0.25 g/L Mercury 71.4% Ammonium Chloride 0.25 g/L Mercury 3.5% Sodium Hydroxide None Copper 99% 0.25 g/L Copper +99% Ammonium Hydroxide ______________________________________ *Added with 5 g/L sodium silicate to contaminated water stream The inventors also have found that after the addition of silicate and ammonium hydroxide, the pH of the stream must be adjusted to between about 5 to about 9.5 with mineral acid. As FIG. 1 indicates, contaminant removal is optimized at a pH above about 7, while less than about 10% of contaminant is removed at a pH below about 5. Accordingly, if the pH of the stream is permitted to go below about 5, unsatisfactory amounts of contaminants are likely to remain in the process stream. With respect to one preferred embodiment of the invention, the method for removing metals from a contaminated stream comprises the steps of: a. treating the process stream with sodium silicate in an amount of from about 5 to about 25 g/L of stream to be treated, and ammonium hydroxide in an amount of from about 0.1 to about 1 g/L of stream to be treated to precipitate said contaminants; PA1 b. adding a mineral acid to the process stream in an amount sufficient to lower the pH of the stream to between about 7 to about 7.5; PA1 c. allowing said stream to age for about 1 to about 5 hours; and PA1 d. separating the clean stream from the precipitate. Accordingly, it is an object of this invention to provide a precipitation method for the decontamination of solutions which produces a clean solution having environmentally acceptable levels of contamination, and readily manageable waste having a relatively low volume. It is a further object of this invention to provide a precipitation method for the decontamination of solutions wherein the contaminant containing waste is easy to handle, and simple to treat, separate and store. It is yet another object of this invention to provide a precipitation method which can be utilized to remove a variety of heavy metals. |
047939648 | summary | BACKGROUND OF THE INVENTION The present invention relates to a small natural circulation pressurized water nuclear reactor of the calogenic or electrogenic type intended for local use. Such a reactor can be installed on an ocean drilling platform, or on a river or sheet of water, in an isolated region not having the electric power necessary for the operation of an industrial installation. In view of these uses of a very particular type, such a reactor must be completely autonomous and transportable in a safe manner between a loading site, where its core is installed and its place of use. This reactor must also fulfil long term intrinsic safety conditions, preferably including the hypothesis of capsizing, because it has to be installed and transported at sea or on a river. Finally, the very local use of such a reactor makes it necessary for it to be constructed in a particularly simple manner, so as to reduce costs, increase reliability and simplify use thereof. In the particular case of the nuclear propulsion of ships, small pressurized water nuclear reactors are already used. These reactors are generally derived by homothetic transformation from large pressurized water reactors. In particular, they still have pumps for circulating water from the primary circuit, as well as auxiliary circuits ensuring the extraction of the residual power on shut down and in the case of the ship capsizing. Thus, these reactors are too complex and costly to be used for the local production of electricity or heat according to the invention. The present invention specifically relates to a pressurized water nuclear reactor of an original design and which is particularly simple, fulfilling all the imposed safety conditions, particularly in the case of capsizing, without having recourse to any auxiliary standby cooling circuit, whereby said reactor is also autopressurized and operates on a natural circulation basis, which makes it possible to eliminate the heating members of the pressurizer and the primary pumps indispensable in existing reactors. SUMMARY OF THE INVENTION The present invention therefore specifically relates to a pressurized nuclear reactor with circulation by natural convection, comprising a main vessel filled with water surmounted by a pressurized steam layer, said vessel containing in the lower part the reactor core and in the upper part a steam generator, internal structures channelling the circulation of water between the core and the steam generator, a confinement enclosure externally duplicating the main vessel and defining with the latter an intermediate space, wherein the main vessel is not thermally insulated, the intermediate space having an upper zone filled with pressurized neutral gas, an intermediate zone filled with water and communicating with the upper zone and defined between the enclosure and a thin ferrule sealingly connecting the confinement enclosure to the vessel, above the reactor core and a lower zone filled with water and defined between the thin ferrule, the vessel and the enclosure, the confinement enclosure being immersed in an external cooling liquid such as water and internally equipped with thermal insulation in the lower zone of the intermediate space, except in a lower part of the confinement enclosure located at a level below the reactor core. This special design of the main vessel, confinement enclosure and intermediate space defined between these two components makes it possible to limit thermal leaks to a minimum value during the normal operation of the reactor and to bring about a short term evacuation of the residual power dissipated in the reactor core, no matter what the slope of the latter, when power extraction by the secondary circuit of the steam generator is stopped. Thus, a nuclear reactor is obtained without any auxiliary circuit, requiring no continuous monitoring, able to function without intervention during the use period of the core and usable in an intrinsically safe manner in all cases where it is possible to ensure that the confinement enclosure remains immersed in the external cooling liquid. In a preferred embodiment of the invention, the upper zone of the intermediate space is formed in a spherical upper part of the confinement enclosure. This particular shape aids the condensation of the steam formed by the boiling of the water in the intermediate zone during low power operation of the reactor, the extraction of power by the secondary circuit being stopped. In this preferred embodiment, outside the spherical upper part of the confinement enclosure, the main vessel and the confinement enclosure have a cylindrical configuration centered on a common vertical axis, the thin ferrule also having a cylindrical configuration centred on said axis and being fixed by its upper end to the confinement enclosure, at the bottom of the spherical upper part and by its lower end to the main vessel. Preferably, pressure balancing means are provided between the lower zone and the upper and intermediate zones of the intermediate space. These means can be constituted by a swanneck tube projecting upwards into the intermediate zone from the thin ferrule. According to another interesting aspect of the invention, the main vessel also contains an annular reflector surrounding the reactor core, said reflector being formed from several separate sectors, normally positioned level with the core, each sector being able to move upwards with the aid of elastic means during an inclination of the reactor exceeding a given angle, e.g. approximately 60.degree.. If the ship capsizes, this feature makes it possible to ensure the smothering of the power dissipated by the reactor by introducing antireactivity into the latter. Thus, it is possible to compensate the fact that under these conditions that it is not possible for absorbing elements to drop or dropping cannot be completed. According to another feature of the invention, the main vessel contains at least one system of absorbing elements able to move in guide tubes provided in the reactor core during the actuation of the control means outside the vessel, said control means creating a rotary movement transmitted to a threaded rod located in the vessel and on which is mounted a nut carrying said system, via a mechanism comprising a magnetic coupler ensuring the transmission of the rotary movement through the vessel. These control means can also be outside the confinement enclosure. In this case, a second magnetic coupler is disposed on the confinement enclosure to ensure the transmission of the rotary movement through the latter. Means within the vessel are provided in this case to automatically disconnect said system of absorbing elements from the nut when the pressure in the vessel exceeds a given pressure and when the level of the water in the vessel drops below a given level. It is also possible to consider a manual dropping of the system of absorbing elements by means of a tube connecting the upper part of the vessel to the outside of the enclosure and permitting the pressure in the vessel to rise by injecting gases. This tube can also be used for injecting boron or any other soluble nuclear poison. This tube, equipped with a burster disk, is normally closed by sealing means. As the reactor core has an active part of given height, the guides preferably project beyond said active parts downwards by half said height and upwards by the equivalent of said height. The absorbing elements then have a length equal to one and a half times the height of the active part of the core, one half of the elements being absorbing over their entire length and the other half being absorbing over the upper two thirds of their length. |
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abstract | A nuclear reactor having a penetration seal ring interposed between the reactor vessel flange and a mating flange on the reactor vessel head. Radial ports through the flange provide passage into the interior of the reactor vessel for utility conduits that can be used to convey signal cables, power cables or hydraulic lines to the components within the interior of the pressure vessel. A double o-ring seal is provided on both sides of the penetration flange and partial J-welds on the inside diameter of the flange between the flange and the utility conduits secure the pressure boundary. |
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050846256 | abstract | An apparatus and method are provided for selectively receiving, transporting, and releasing one or more radioactive or other hazardous samples for analysis on a differential thermal analysis (DTA) apparatus. The apparatus includes a portable sample transporting apparatus for storing and transporting the samples and includes a support assembly for supporting the transporting apparatus when a sample is transferred to the DTA apparatus. The transporting apparatus includes a storage member which includes a plurality of storage chambers arrayed circumferentially with respect to a central axis. An adjustable top door is located on the top side of the storage member, and the top door includes a channel capable of being selectively placed in registration with the respective storage chambers thereby permitting the samples to selectively enter the respective storage chambers. The top door, when closed, isolates the respective samples within the storage chambers. A plurality of spring-biased bottom doors are located on the bottom sides of the respective storage chambers. The bottom doors isolate the samples in the respective storage chambers when the bottom doors are in the closed position. The bottom doors permit the samples to leave the respective storage chambers from the bottom side when the respective bottom doors are in respective open positions. The bottom doors permit the samples to be loaded into the respective storage chambers after the analysis for storage and transport to a permanent storage location. |
claims | 1. A storage basket for radioactive materials, the basket configured to be arranged into a containment enclosure of a packaging for transporting and/or warehousing radioactive materials, the basket defining a plurality of housings each for receiving radioactive materials, the housings being parallel to each other and each extending along a housing axis parallel to a longitudinal central axis of the basket, the latter including:a transverse plate or a plurality of transverse plates distributed along the longitudinal central axis of the basket and arranged orthogonally to the longitudinal central axis, each plate having a plurality of holes passing therethrough;a plurality of housing tubes arranged parallel to the longitudinal central axis of the basket,wherein the housing tubes are arranged alternately with the transverse plate(s) along the longitudinal central axis, so that an inner side surface of each housing is defined, successively along the longitudinal central axis, at least by an inner surface of a first housing tube, an inner surface of one of the holes of a first transverse plate, and an inner surface of a second housing tube, andwherein the respective inner surfaces of the first and second housing tubes are flush with the inner surface of said one of the holes of the first transverse plate such that a cross-sectional shape of the inner side surface of each said housing remains constant along the housing axis. 2. The basket according to claim 1, wherein the cross-sectional shape of the inner side surface of each said housing is a circle, square, rectangle, or hexagon. 3. The basket according to claim 1, wherein the transverse plate(s) each have a disc shape. 4. The basket according to claim 1, wherein the transverse plate(s) are made of steel. 5. The basket according to claim 1, wherein each housing is defined using a number N of transverse plate(s), number N being between 1 and 20. 6. The basket according to claim 1, wherein a ratio of a length (L) of any of the housing tubes to a thickness (E) of the transverse plate or one of the plurality of transverse plates is between 3 and 15. 7. The basket according to claim 1, wherein a length of the housing tubes is between 20 and 70 cm. 8. A packaging for transporting and/or warehousing radioactive materials, the packaging comprising a containment enclosure delimited by a side body, a bottom and a lid, the packaging being fitted with a storage basket according to claim 1, arranged into the containment enclosure. 9. The basket according to claim 1, wherein the transverse plate(s) each comprise, at both opposite faces whose normal is directed along the longitudinal axis, means for holding the housing tubes. 10. The basket according to claim 9, wherein the holding means take the shape of sockets into which the ends of the housing tubes are inserted. 11. The basket according to claim 1, wherein each housing tube is made of a steel, and in that each housing tube forms an internal tube surrounded by an external tube made of an aluminium alloy. 12. The basket according to claim 11, wherein each internal tube axially projects from each of both opposite ends of the external tube. 13. The basket according to claim 11, wherein the steel is devoid of neutron absorbing elements, and wherein the aluminium alloy comprises neutron absorbing elements. 14. The basket according to claim 13, wherein the neutron absorbing elements are boron. 15. The basket according to claim 1, also including a top plate and a bottom plate sandwiching between each other the alternating transverse plate(s) and housing tubes. 16. The basket according to claim 15, also including tie rods each passing through the top plate, the bottom plate, as well as the transverse plate(s). 17. A storage basket for radioactive materials, the basket configured to be arranged into a containment enclosure of a packaging for transporting and/or warehousing radioactive materials, the basket defining a plurality of housings each for receiving radioactive materials, the housings being parallel to each other and each extending along a housing axis parallel to a longitudinal central axis of the basket, the latter including:a transverse plate or a plurality of transverse plates distributed along the longitudinal central axis of the basket and arranged orthogonally to the longitudinal central axis, each plate having a plurality of holes passing therethrough;a plurality of housing tubes arranged parallel to the longitudinal central axis of the basket,wherein the housing tubes are arranged alternately with the transverse plate(s) along the longitudinal central axis, so that an inner side surface of each housing is defined, successively along the longitudinal central axis, at least by an inner surface of a first housing tube, an inner surface of one of the holes of a first transverse plate, and an inner surface of a second housing tube,and wherein the transverse plate(s) each comprise, at both opposite faces whose normal is directed along the longitudinal axis, sockets into which corresponding ends of the housing tubes are inserted. |
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040101088 | abstract | A method of disposing of wet radioactive waste materials such as those generated in the water used to cool atomic reactors, comprising combining the waste material with a hydrophilic resin in proportions sufficient to provide a solid mass of the resin with the radioactive waste component distributed within. In its preferred form, the waste material is concentrated by separating water from the radioactive portions thereof by methods such as evaporation, taking up the waste components with an ion exchange resin and separating the resin from the bulk of the water, or by the addition of flocculating agents or the like and filtering. The preferred hydrophilic resinous material is a conventional urea-formaldehyde dispersion, which is partially polymerized and capable of taking up water and fully polymerizing upon the addition of an acidic curing agent. The method also contemplates adding a substantially waterproof resinous material to the surface of the solid block, or enclosing it in a waterproof container, or both. |
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description | This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/331,718 filed May 4, 2016, which is incorporated herein by reference. The present invention relates to doped semiconductor materials, and more particularly relates to semiconductor materials such as silicon with dopants such as phosphorous that are formed by isotope transmutation processes. Conventional semiconductor materials such as Si are doped with various elements to change their charge carrier properties. For example, N-type doped silicon materials may be coupled with P-typed doped silicon materials to form P—N junctions in devices such as solar cells. However, the types of elemental dopants that can be added to semiconductor materials are limited due to factors such as insolubility. For example, as demonstrated by a conventional Si—P phase diagram, P is only slightly soluble in Si at very high temperatures, e.g., 2.2 atomic percent solubility at 1,131° C., and P is considered insoluble in Si at lower temperatures such as room temperature. The present invention provides methods for modifying the basic material lattice structure of semiconductor materials at the atomic level. One embodiment of the process involves modifying the distribution and number density of holes in these materials. The number density of holes is related to the efficiency of semiconducting properties such as electrical conductivity. Thus, the present processes may be used to modify properties of semiconductor materials. In accordance with embodiments of the invention, the structure of a base semiconductor material such as Si may be modified by the use of isotope transmutation alloying. In this process, a radioisotope is added as an alloying solute into the molten base solvent material. The radioisotope may be selected such that solvent material properties are improved as a result of the transformation of the radioisotope into its transmuted form after the base semiconductor material has solidified. This property improvement results from the production of metastable thermodynamic state due to the result of the transmutation process. An aspect of the present invention is to provide a method of making a silicon-based semiconductor material comprising introducing Si31 radioisotope into molten Si, solidifying the Si and Si31 radioisotope to form a transition material comprising atoms of the Si31 radioisotope within a Si crystal lattice structure, and P31 atoms retained in the Si crystal lattice structure to thereby form a metastable silicon-based semiconductor material doped with P31. Another aspect of the present invention is to provide a master alloy for use in making a silicon-based material doped with P31, the master alloy comprising Si and Si31 radioisotope wherein the Si31 radioisotope is present in the master alloy in a greater amount than an amount of the P31 contained in the silicon-based material. A further aspect of the present invention is to provide a metastable silicon-based semiconductor material doped with P31 transmuted from Si31. These and other aspects of the present invention will be more apparent from the following description. FIG. 1 is a schematic diagram illustrating the production of metastable Si doped with P in accordance with embodiments of the present invention. As shown in FIG. 1, the radioisotope Si31 is introduced into a molten semiconductor base material comprising Si. As used herein, “Si” means silicon in its standard isotope form, which predominantly comprises the Si28 isotope. However, minor amounts of Si29 and Si30 isotopes may also be present in the Si. The Si31 radioisotope may be introduced in solid form into the molten Si. Alternatively, solid Si31 may be mixed with solid Si, followed by melting of the mixture to thereby allow the Si31 radioisotope atoms to diffuse in the molten Si material. As further shown in FIG. 1, the Si31 radioisotope atoms easily diffuse into the molten Si base semiconductor material at a self diffusion rate that is the same for both Si31 and Si. The relative amounts of Si and Si31 may be selected such that essentially all of the Si31 radioisotope atoms are soluble within the Si base semiconductor material at elevated temperatures and upon solidifying Si transforms to P and is frozen in the lattice at room temperature both the elevated temperature of the molten Si and upon solidification and cooling, e.g., to room temperature. As shown in FIG. 1, upon solidification, the Si31 atoms form a solid solution in the crystal lattice structure of the Si base semiconductor material. As the Si31 radioisotope atoms transmute, they form P31 atoms within the Si crystal structure. The Si31 thus transmutes to P31. A solid material comprising Si and P31 is thereby formed in a metastable state. As used herein, the terms “metastable” and “metastable state” mean a material containing both stable Si and Si31 radioisotope that is subsequently aged to transmute the Si31 to P31. FIG. 1 also illustrates an alternative embodiment in which the Si and Si31 are initially solidified to form a master alloy. The Si/Si31 master alloy may be added to an additional amount of molten Si to thereby diffuse the Si and Si31 atoms of the master alloy into the additional amount of molten Si. Upon solidification, the cooled material comprises Si31 radioisotope atoms from the master alloy, Si atoms from the master alloy, and Si atoms from the additional amount of molten Si. The Si31 radioisotope atoms then transmute into P31 atoms to form a metastable solid material comprising P31 atoms within the Si crystal lattice. In the embodiments shown in FIG. 1, the final semiconductor material comprises Si having a face centered cubic crystal lattice structure in which P31 atoms are substituted for Si atoms within the crystal lattice structure. The semiconductor material thus comprises phosphorous-substituted silicon within a face centered cubic crystal structure. In certain embodiments, the material may be provided in single crystal form, while in other embodiments the material may be polycrystalline. In certain embodiments, most or essentially all of the P31 atoms occupy sites within the Si crystal structure, rather than forming as Si—P precipitates separate from the crystal structure. Thus, the majority of the P31 atoms are substituted into the Si crystal structure rather than forming as precipitates. Typically, less than 10 atomic percent of the P31 atoms form precipitates, for example, less than 5 atomic percent, less than 2 atomic percent, less than 1 atomic percent, or less than 0.1 atomic percent, or less than 0.01 percent, or less than 0.001 percent. The metastable Si and P31 semiconductor materials produced in the embodiments shown in FIG. 1 may include controlled amounts of P31. In certain embodiments, the P31 may comprise from 0.001% to 10% atomic percent of the Si/P31 material. For example, the P31 may comprise from 0.0001% to 20% atomic percent, or from 0.001% to 2.2% atomic percent, or from 0.01% to 1.5% atomic percent. In a particular embodiment, when the metastable Si/P31 semiconductor material is used for solar cell applications, the amount of P31 may comprise from 0.01% to 1% atomic percent. Table 1 below lists the ranges above. TABLE 1Amount of P31 in Si Semiconductor Material (atomic percent)RangesP31SiA0.00001%-20% balanceB0.001%-2.2%balanceC 0.01%-1.5%balanceD0.01%-1% balance To produce Si/P31 semiconductor materials as described above, the amount of Si31 radioisotope used to make such materials may correspond to the amounts of transmuted P31 described above. Thus, the amounts of Si31 added to the molten Si base material may be within the same ranges as the P31 amounts listed in Table 1 above. When master alloys are formed, the P31 may comprise from 0.001% to 10% atomic percent of the Si/P31 material. For example, the P31 may comprise from 0.0001% to 20% atomic percent, or from 0.001% to 2.2% atomic percent, or from 0.01% to 1.5% atomic percent. Table 2 below lists ranges of Si31 radioisotope that may be used in Si/Si31 master alloys in accordance with embodiments of the present invention. In certain embodiments, the amount of Si31 in a master alloy may be up to 50%, for example, from 1 to 47%, or from 2 to 30%. TABLE 2Amount of Si31 in Si Master Alloy (atomic percent)RangesSi31SiA0.005%-20% balanceB0.01%-10%balanceC0.05%-5% balanceE0.05%-2% balance In addition to Si and P31, the metastable Si-based semiconductor materials produced in accordance with embodiments of the present invention may further include minor amounts of other elements such as Ge, Ga, As, B, Al, Se and the like. The Si31 radioisotope material may be produced by bombarding Si with high energy neutrons to create in-situ Si31, for example, at room temperature or by bringing the Si up to a temperature close to the melting point of Si, e.g., either above or below the Si melting point. The neutron flux used during bombardment of the Si may typically range from 1010 to 1016 neutrons/cm·sec, or from 1011 to 1015 neutrons/cm2·sec, or from 1012 to 1014 neutrons/cm2·sec. The neutron bombardment may be carried out for a suitable period of time, for example, ranging from 1 second to 72 hours, or from 30 seconds to 48 hours, or from 1 minute to 24 hours, or from 30 minutes to 12 hours. Radioisotope Si31 material produced as described above may be added to the base Si semiconductor by adding the isotope Si31 directly into molten Si, or by using a seed Si31 material or master alloy, e.g., to grow single crystal Si in floating zone equipment. These methods may be set up in solid form before melting. When an Si/Si31 master alloy is used, it may be made in a similar manner as described above, except higher concentrations of Si31 may be present in the master alloys, e.g., as described in Table 2 above. Solidification of the molten Si/Si31 material may be performed at slow cooling rates, e.g., 50° C./min to room temperature. Transmutation of the Si31 to P31 within the solid Si material occurs in situ by aging the material for an appropriate amount of time. During aging, conversion of Si31 to P31 occurs within the Si lattice, which is retained in the same crystal structure. Once the metastable Si and P31 material has been formed, it may be fabricated into any suitable type of semiconductor device. For example, the metastable Si/P31 material may be used as N-type materials in P—N junctions of semiconductor devices such as solar panels. Although the Si31 radioisotope is primarily described herein, it is to be understood that other types of radioisotopes may be generated and used in accordance with embodiments of the invention. In accordance with embodiments of the present invention, radioisotopes such as Si31 described above may be selected based on specific criteria: the radioisotope should have solubility in the base material; the transmuted element derived from the radioisotope is insoluble or has limited solubility in the base semiconductor material; the radioisotope has a higher diffusion rate in the base semiconductor material than the transmuted element; the transmuted element derived from the radioisotope has a low diffusion rate in the base material; the radioisotope is selected based on the atom size of the transmuted element such that it induces atomic size mismatch stresses in the crystal lattice; the radioisotope is selected based on the position it takes in the crystal lattice before transmutation, e.g., a substitutional site or an interstitial site (octahedral or tetrahedral); the radioisotope is selected based on its cost, ease of manufacture and abundance; the radioisotope is selected based on its half-life; the radioisotope is selected based on energy imparted into the base material on decay; and the radioisotope is selected based on the need of the end point application. Examples of radioisotopes selected for various types of base semiconductor materials in accordance with embodiments of the invention are listed in Table 3. TABLE 3Radioisotopes and Transmuted ElementsSemiconductorIsotopeHalf LifeTransmuted ElementSiSi312.62hoursP31Ge—GaGe7111daysGa71Si—GeGe7111daysGa71Ge—SeSe73120daysAs75 While the present invention may include additional combinations of base semiconductor materials, radioisotopes and transmuted elements, the present description is primarily directed to a silicon-based semiconductor material comprising Si doped with P31 transmuted from S31 radioisotope. However, it is to be understood that other combinations are within the scope of the present invention. For example, the method can be extended to add any other isotope that will give as donor or as acceptor element to Si. Consider a pure semiconductor like Si. The element P when added gives a donor impurity. Phase diagrams for Si—P indicate that P is soluble at about 2.2 atomic percent at 1,131° C., and is insoluble at room temperature. With this limited solubility, only limited numbers of holes can be produced. However, if the Si31 radioisotope is doped into Si, it is possible to adjust to higher/lower number densities of holes. The effect of adding radioisotope of Si31 (solute) to the non-radioactive pure Si (solvent). Si31 has a half-life of 2.62 hours and will decay to a transmutation product P31 emitting β−radiation. If such an element Si31 is added to a molten pure Si and the resulting alloy is cooled to room temperature the atoms will randomly distribute in the lattice of Si. These atoms will transmute in-situ into the atoms of the transmuted product P31. Thus the transmuted product will be frozen in the lattice of Si. This method of forming a metastable solid solution of P in Si can exceed the equilibrium solubility of the alloy dictated by Si—P phase diagrams. It is possible to estimate the charge carrier concentration and conductivity of Si doped with P (same as P31) 0.1% at (P-concentration CP=10−3) amount at room temperature. For this calculation we define the following parameters: For solvent Si: density ρ=2330 kg/m3; at.wt.=28; lattice parameter a=5.43×10−10 m; atomic volume of a unit Si cell=a3=1.6×10−28 m3; electron mobility μe=0.15 m2/V−s; hole mobility μh=0.05 m2V−s; energy gap Eg=1.2 eV; Proton charge e=1.6×10−19 C, Avagadro's # A=6.02×1023 NP=charge carrier concentration; NSi=# of Si atoms per unit volume; nc=concentration electron charge in conduction band; nv=concentration of holes in valance band. NSi=(8 atom in unit cell)/(cell volume)=8/1.6×10−28=5×1028/m3 NP=NSi×CP=5×1028×10−3=5×1025/m3=charge carrier concentration nc, neglecting very small nv.For intrinsic semiconductors like Si, nc=nv.With complete ionization of P in Si, the charge carrier concentrationnc=NP=5×1025/m3 for P=10−3 concentration as an example. We now calculate the conductivity (a) of Si/P semiconductor:σ(Si/P)=NPeμe=(5×1025/m3)×(1.6×10−19C)×(0.15 m2/V−s)=1.2×105/ohm·m The intrinsic carrier concentration (ni) in pure Si refers to electron (or hole) concentration. Commonly accepted values of ni for Si is about 1.4×1015/m3. This value is significantly smaller than for Si/P nc=5×1025/m3 for P=0.1 at % concentration, by about 1010. Intrinsic Si conductivity σSi=ni·e[μe+μh], since nc=nv for pure Si; hence:σSi=1.4×1015×1.6×10−18×0.2=0.448×10−3=4.5×10−4/ohm·mThis number is fixed for Si. This conductivity of Si is significantly smaller by about 109 compared to Si/P alloy at a P=10−3 concentration. Thus the carrier concentration and its conductivity can be estimated, with the assumption of complete ionization of P in Si. The calculation suggests that isotope alloying of a semiconductor Si can be significantly improved with very small concentration of doping impurities like P. Deliberate additions of impurities to a solvent material in a controlled manner can allow charge concentrations to be tailored in order to improve conductivity to desired values needed for specific applications. In accordance with certain embodiments, metastable silicon-based semiconductor material may typically have a conductivity of from 105 to 1017 per ohms-m, for example, from 107 to 1015, or from 109 to 1013, or from 109 to 1012. In accordance with certain embodiments, metastable silicon-based semiconductor material may typically have a carrier concentration of from 1020 to 1040/m3, for example, from 1027 to 1033, or from 1029 to 1034, or from 1028 to 1034. Various methods can be used to add the alloying radioisotope into the base metal solvent. These include: directly add the isotope into to molten base material, solidify and fabricate; surface coating of the isotope onto the base material and diffusing it into the base material at a desired temperature; thermal spray on the surface of the base material and diffuse it in; add the isotope to the seed crystal to grow the single crystals; powder blends of isotope with the desired base material, compact, sinter into a final wrought product; and mechanically alloy via ball milling method both the isotope and the base material. The following example is intended to illustrate various aspects of the present invention, and are not intended to limit the scope of the invention. An amount of Si is bombarded by a neutron flux at an energy level of from 1012 to 1014 neutrons cm2·sec for a sufficient amount of time within 1 to 12 hours to change a desired percentage of the Si atoms to Si31 radioisotope atoms, e.g., up to 50% conversion of the Si to Si31. Bombardment with the neutron flux is conducted at any suitable temperature, including room temperature, or close to the melting point of Si, to form a master alloy. The resultant master alloy, in either solid or molten form, is added to base Si material, e.g., in a molten state. Upon cooling, a metastable material is formed comprising a standard Si crystal lattice containing P31 atoms that have been transmitted from the S31 radioisotope atoms. In one embodiment of the invention, radioisotopes are added to semiconductor materials used to make photovoltaic cells. The radioisotope is selected based on its solubility and diffusivity in the semiconductor and based on the doping effectiveness of its transmutated product. Semiconductor materials may be N-type materials used to make up P—N junctions used in solar cells. For example, transmutation of Si31 to P31 over time results in increased efficiency of the photovoltaic cells (or other semiconductor devices). In one example of the embodiment, a uniform distribution of phosphorous is formed in the lattice of silicon which may be used to make the N-type material in a P-N junction in a solar cell. Prior work showed that techniques such as diffusion do not provide a uniform distribution of dopant in silicon. More uniform distribution of dopants could be achieved using techniques such as neutron transmutation doping (NTD) but this technique requires that the material be exposed to a neutron flux which induces extensive damage to the silicon lattice. In this example of the embodiment, the radioisotope Si31 is mixed in a predetermined ratio with the Si in the molten bath used to grow the N-type silicon material. The Si radioisotope is totally soluble and will self-diffuse within the silicon lattice. Thus on solidification the Si31 will be randomly distributed in the lattice. The Si31 in the lattice decays to form P31. Thus, N-type silicon material with random-uniform distributions of phosphorous present in the lattice at predetermined concentrations can fabricated. Very little segregation of phosphorous is observed on grain boundaries if polycrystalline silicon is grown. Phosphorous concentrations of 1013 to 1018 atoms/cm3 may be achieved using the approach. Thermal annealing treatments may not be required due to the uniform distribution of the dopant and the relative lack of damage induced by the process. The N-type silicon fabricated as per this example may be coupled with a P-type silicon material to form a P-N junction in a solar cell device. The disclosed process can be used to improve performance of semiconductor materials used in various applications. For example the efficiency of the following components can be improved: solar cells to improve its efficiency; metal oxide semiconductor chemical sensors; silicon crystals used in CPU; and high power electronic device components Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims. |
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abstract | A fuel assembly mechanical flow restriction apparatus for detecting failure in situ of nuclear fuel rods in a fuel assembly during reactor shutdown. |
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052672786 | claims | 1. A console for the control room of a nuclear power plant, wherein the console is constructed from a plurality of panels and each panel comprises: a substantially flat vertically oriented upper portion for mounting plant monitoring and display devices and a transversely extending, substantially flat lower portion for mounting plant control interfaces; a relatively large, first display interface device located substantially centrally in the upper portion, for displaying integrated images and textual information concerning monitoring and control of the plant; a plurality of a second type of uniformly sized, relatively smaller display interface devices located on both sides of the first large interface device, at least one of the second type adapted for displaying images of alarm tiles and at least another of the second type adapted for displaying images of process variable indicators; an alarm processor including means for generating images of alarm tiles on one of the second type of interface devices and programmable alarm logic means for activating an alarm upon the occurrence of a predetermined relationship of alarm input signals; an indication processor including means for generating images of process indicator instrumentation on the other of the second type of interface device and programmable indicator logic means for computing process parameter values in response to input signals from process sensors. |
061907251 | summary | BACKGROUND OF THE INVENTION The present invention relates to a coating method for the preparation of coated nuclear fuel. Particularly, the present invention relates to the coating method of nuclear fuel surface with more than two coated layers of carbides, borides or nitrides, comprising steps of depositing or permeating i) elements or compounds that can form carbides, borides or nitrides by reacting with pyrolytic carbon, boron or nitrogen and ii) a layer of pyrolytic carbon or boron prepared by chemical vapor deposition(CVD) or sputtering in sequence or in reverse sequence, or nitrogen prepared by gas permeation in sequence, on the nuclear fuel surface. The coated layers are formed with carbides, borides, nitrides or their mixtures at high temperature and pressure by combustion synthesis. Various types of nuclear power plants have been developed in different concepts such as High Temperature Gas-cooled Reactor (HTGR), Pressurized Light Water Reactor (PLWR) and Pressurized Heavy Water Reactor (PHWR). Nuclear fuels used in the nuclear power plants depend on such reactor types. For example, spherical shape nuclear fuels are used for High Temperature Gas-cooled Reactor (HTGR) and cylindrical pellet type nuclear fuels are normally used in Water-cooled Reactors which are the most popular nuclear power plants in operation worldwide. In order to secure the safety of high temperature gas-cooled reactor, deposition of graphite and carbide on the nuclear fuel kernel was applied to avoid fission gas release. The coated layers were prepared on the surface of spherical nuclear fuel kernel with a thickness of hundreds micron(.mu.m). For this preparation, the coating on spherical nuclear fuels(UCO, ThO.sub.2) was carried out with a mixture of methylchlorosilane and ethylene gases in a fluidized bed type chamber by a chemical vapor deposition method (FBT CVD): pyrolytic carbon and silicon carbide layers are formed at high temperatures of about 1200.degree. C. and 1600.degree. C., respectively. The problems of these methods are the occurrence of microstructural defects due to relatively high temperature employed and the formation of hazardous by-products such as hydrochloric acid and chlorine gas due to the thermal decomposition of silane compounds such as methylchlorosilane, dimethylchlorosilane and triethylchlorosilane. Meanwhile, in water-cooled reactors, used is relatively large-sized pellet type nuclear fuel in cylindrical shape, whose dimension varies from 7 to 12 mm in diameter and from 10 to 15 mm in height with dish-shaped grooves in its upper and lower faces. Coating of carbides, borides or nitrides on this pellet type nuclear fuel can be thought to effectively reduce the fission gas release, particularly in high-burnup fuel. Coated pellet type nuclear fuel has never been used and the coating method for this type fuel has not been yet envisaged. Furthermore, conventional FBT CVD method can not be applied to pellet type nuclear fuel which has anisotropic shape and is relatively larger and heavier than spherical type nuclear fuel. The present inventors have found a coating method for nuclear fuel surface with more than two coated layers of carbides, borides, nitrides or their mixture comprising deposition or permeation steps of i) elements or compounds that can form carbides, borides or nitrides by reacting with pyrolytic carbon, boron or nitrogen and ii) a layer of pyrolytic carbon or boron prepared by chemical vapor deposition(CVD) or sputtering in sequence or in reverse sequence, or nitrogen prepared by gas permeation in sequence, on the nuclear fuel surface. The coated layers are formed with carbides, borides, nitrides or their mixture at high temperature and pressure by combustion synthesis. SUMMARY OF THE INVENTION The objective of the present invention is to provide a coating method for the preparation of a coated nuclear fuel with multi-coated layers of pyrolytic carbon or boron; and carbides, borides, nitrides or their mixture in sequence or in reverse sequence. |
050769944 | claims | 1. A lock assembly for selectively locking and unlocking a shaft for a control rod drive comprising: a stationary housing surrounding said shaft; a gear fixedly joined to said shaft in said housing and having a plurality of circumferentially spaced teeth; a key assembly including: and means for selectively moving said cam roller against said cam finger for translating said key in said guide hole for positioning said key and locking tooth in an engaged position in abutting contact with one of said gear teeth for preventing rotation of said gear and shaft in a first direction, and in a disengaged position spaced outwardly from said gear teeth for allowing unrestricted rotation of said gear and shaft in said first direction and in a second, opposite, direction. a plunger having a distal end rotatably joined to said cam roller, an intermediate portion, and a proximal end; an actuator housing surrounding said plunger intermediate portion and proximal end; an electrical solenoid disposed in said actuator housing and surrounding said plunger intermediate portion; a second spring disposed between said solenoid and said plunger proximal end for retracting said plunger away from said cam surface; and said solenoid being selectively energizable for magnetically drawing said plunger toward said cam surface and loading said second spring and in turn translating said key away from said gear and loading said first spring for moving said key to said disengaged position, and being deenergizable for allowing said second spring to draw said plunger away from said cam surface and in turn allowing said first spring to urge said key toward said gear for moving said key to said engaged position. said locking tooth has a straight locking surface and an inclined cam surface; each of said gear teeth has a straight locking surface and an inclined cam surface; and said locking surfaces of said locking tooth and said gear tooth are disposed generally parallel with said key longitudinal axis in said engaged position for preventing rotation of said gear in said first direction. 2. A lock assembly according to claim 1 wherein said key assembly further includes a first spring disposed in said guide hole in abutting contact with a proximal end of said key for generating a force for translating said key in said guide hole toward said gear. 3. A lock assembly according to claim 2 wherein said cam finger includes a base fixedly joined to said key and extending through an access hole in said key support, and a cam surface inclined relative to a longitudinal axis of said key and disposed adjacent to said cam roller for being moved by said roller for positioning said locking tooth in said disengaged position. 4. A lock assembly according to claim 3 wherein said cam finger base has a first diameter, and said access hole has a second diameter greater than said first diameter for limiting travel of said key between said engaged and disengaged positions. 5. A lock assembly according to claim 3 wherein said cam roller moving means include: 6. A lock assembly according to claim 5 wherein: 7. A lock assembly according to claim 6 wherein said cam surfaces of said locking tooth and said gear tooth are inclined relative to said key longitudinal axis in said engaged position so that rotation of said gear in said second direction causes said gear tooth cam surface to slide against and translate said locking tooth cam surface away from said gear tooth for intermittently freeing successive gear teeth as said gear rotates in said second direction while allowing said locking surfaces of said locking tooth and said gear tooth to abut for preventing rotation of said gear in said first direction. |
claims | 1. An operation stage system for edge and backside substrate inspection and review, comprising:a supporting frame to sustain the weight of the system;a stage to adjust variation of a focus of an e-beam image in z (vertical) direction;a station to adjust variation of a focus of the e-beam image in X and Y (horizontal) direction;an electrostatic chuck to hold the substrate by electrostatic force;a pendulum stage to mount the electrostatic chuck, the pendulum stage can swing from 0° to 180° while performing top bevel, apex and bottom bevel inspection or review; anda rotation track for the pendulum stage, which provides support and stabilizes the pendulum stage during the edge inspection and review. 2. The operation stage system of claim 1, wherein the electrostatic chuck has ability to rotate to a desired angle with respect to a substrate notch for edge inspection and review. 3. The operation stage system of claim 1, wherein the electrostatic chuck holds the substrate in such a way that the rotation axis of the pendulum stage consists of the tangent of upper edge of the substrate. 4. The operation stage system of claim 1, wherein the electrostatic chuck is mounted on the pendulum stage. 5. The operation stage system of claim 1, wherein the diameter of the electrostatic chuck is smaller than that of the substrate. 6. A method for edge and side substrate inspection and review comprising:adjusting for variation of a focus of an e-beam image in a vertical direction;holding the substrate by electrostatic force;adjusting the variation of the focus of the e-beam image in a horizontal direction; andswinging the substrate from 0° to 180° while performing top bevel, apex and bottom bevel inspection and review. 7. The method of claim 6, wherein an electrostatic chuck has ability to rotate to a desired angle with respect to a substrate notch for edge inspection and review. 8. The method of claim 6, wherein an electrostatic chuck holds the substrate in such a way that the rotation axis of a pendulum stage consists of the tangent of upper edge of the substrate. 9. The method of claim 6, wherein an electrostatic chuck is mounted on a pendulum stage. 10. The method of claim 6, wherein the diameter of an electrostatic chuck is smaller than that of the substrate. |
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abstract | A method and structure for preventing damage to an electronic device. The structure includes a sensor outputting signals indicating environmental conditions experienced by the electronic device, a non-volatile memory storing ones of the signals that exceed a limit, and an output device outputting signals stored in the non-volatile memory, thereby providing a history of the environmental conditions experienced by the electronic device that exceed the limit. |
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description | This application claims priority from U.S. Provisional Application Ser. No. 62/365,518 filed Jul. 22, 2016 and incorporated herein by reference. This invention was made with government support under Contract No. DE-NE0008222 awarded by the Department of Energy. The U.S. Government has certain rights in this invention. The invention relates to coatings for nuclear fuel rod cladding, and more particularly to the use of cold spray methods for depositing chromium on a zirconium alloy flat, cylindrical, or tubular substrate. Zirconium alloys rapidly react with steam at temperatures of 1100° C. and above to form zirconium oxide and hydrogen. In the environment of a nuclear reactor, the hydrogen produced from that reaction would dramatically pressurize the reactor and would eventually leak into the containment or reactor building leading to potentially explosive atmospheres and to potential hydrogen detonations, which could lead to fission product dispersion outside of the containment building. Maintaining the fission product boundary is of critical importance. U.S. Patent Application US 2014/0254740 discloses efforts to apply metal oxides, ceramic materials, or metallic alloys that contain chromium to a zirconium alloy cladding tube using a thermal spray, such as a cold spray technique wherein powderized coating materials are deposited with substantial velocity on a substrate in order to plastically deform the particles into a flattened, interlocking material that forms a coating. See U.S. Pat. No. 5,302,414. The suitability of materials for cold spray application depends mainly on their deformation properties. Materials with relatively low melting points and low mechanical strength such as Zn and Cu have been shown to be ideal materials for cold spray application as they have a low yield strength and exhibit significant softening at elevated temperatures. Al is also shown to be a good candidate but is more difficult to apply than other soft materials. Materials with higher strength such as Fe and Ni based materials do not provide successful deposition. A. Moridi et al., Cold spray coating: review of material systems and future perspectives, Surface Engineering, vol. 36, No. 6, pp. 369-395 (2014). Metallic chromium is known to provide excellent corrosion resistance. It is a hard and brittle metal, and has not been considered to be a good candidate for deposition by cold spray because of its lack of ductility and high melting point. There is a need for dramatically reducing the rate of reaction of steam with zirconium cladding to avoid generation of large quantities of hydrogen. There is a need for dramatically reducing the rate of reaction of steam with zirconium cladding to contain fission products. The method described herein addresses the problem associated with the potential reaction of steam with zirconium in a nuclear reactor. The method described herein provides a corrosion resistant coating that forms a barrier on the zirconium substrate. In various aspects, a method of coating a substrate of a component for use in a water cooled nuclear reactor is provided. The method includes heating a pressurized carrier gas to a temperature between 200° C. and 1200° C., adding particles having an average diameter of 20 microns or less to the heated carrier gas, and spraying the carrier gas with entrained particles onto a substrate at a velocity of 800 to 4000 ft./sec. (about 243.84 to 1219.20 meters/sec) to form a coating on the substrate to a desired thickness, for example, up to 100 or more microns. The particles are selected from pure chromium particles, chromium-based alloys and combinations thereof. When the particles are chromium-based alloys, they may comprise 80 to 99 atom % of chromium. In various aspects, the chromium-based alloy may include at least one element selected from the group consisting of silicon, yttrium, aluminum, titanium, niobium, zirconium, and transition metal elements, at a combined content of 0.1 to 20 atomic %. The carrier gas may be heated at a pressure up to 5.0 MPa. The carrier gas and particles are preferably sprayed continuously at very high rates until the desired coating thickness is reached. The coating thickness may, for example, be between 5 and 100 microns, but greater thicknesses of, for example, several hundred microns, may be deposited. Following formation of the coating, the method may further include annealing the coating. Annealing may impart ductility and may create sub-micron sized grains that, it is believed, will be beneficial for isotropy in properties and resistance to radiation damage. The substrate is preferably a zirconium alloy and the component, in various aspects, may be a cladding tube for a nuclear fuel rod. The substrate may be any shape associated with the component to be coated. For example, the substrate may be cylindrical in shape, curved, or may be flat. The carrier gas is advantageously selected from inert and unreactive gases. In various aspects, the carrier gas may be selected from the group consisting of nitrogen, hydrogen, argon, carbon dioxide, helium, and combinations thereof. The method described herein also provides a cladding tube formed from a zirconium alloy and having a coating deposited thereon. The coating is selected from pure chromium, chromium-based alloys and combinations thereof. The coating may be of a desired thickness, but typically would be about 5 to 100 microns or more. Cold spray coatings can be built up to several hundred microns thick. The coating acts as a corrosion barrier for the substrate. When the substrate is a zirconium alloy cladding, the chromium coating provides a barrier against corrosion at normal operating conditions, for example, between 270° C. and 350° C. in pressurized water reactors and between 200° C. and 300° C. in boiling water reactors. The coating reduces the steam zirconium and air zirconium reactions and hydrogen generation at high temperatures, i.e., those greater than 1100° C. As used herein, the singular form of “a”, “an”, and “the” include the plural references unless the context clearly dictates otherwise. Thus, the articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element. Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, lower, upper, front, back, and variations thereof, shall relate to the orientation of the elements shown in the accompanying drawing and are not limiting upon the claims unless otherwise expressly stated. In the present application, including the claims, other than where otherwise indicated, all numbers expressing quantities, values or characteristics are to be understood as being modified in all instances by the term “about.” Thus, numbers may be read as if preceded by the word “about” even though the term “about” may not expressly appear with the number. Accordingly, unless indicated to the contrary, any numerical parameters set forth in the following description may vary depending on the desired properties one seeks to obtain in the compositions and methods according to the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter described in the present description should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Further, any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. An improved cold spray method has been developed that deposits chromium (Cr) or chromium-based alloys onto the surface of a substrate, including tubular surfaces. Of particular interest, are substrates used as components in nuclear reactors, and more specifically, zirconium alloy substrates, such as fuel rod cladding tubes used in water cooled nuclear reactors. “Pure Cr”, or “pure chromium”, as used herein, means 100% metallic chromium that may include trace amounts of unintended impurities that do not serve any metallurgical function. For example, pure Cr may contain a few ppm of oxygen. “Cr-alloy,” “chromium alloy,” “Cr-based alloy,” or chromium-based alloy” as used herein refer to alloys with Cr as the dominant or majority element together with small but reasonable amounts of other elements that serve a specific function. The Cr alloy may comprise 80% to 99 atom % of chromium. Other element in the Cr alloy may include at least one chemical element selected from silicon, yttrium, aluminum, titanium, niobium, zirconium, and other transition metal elements. Such elements may be present for example at a content of 0.1 atomic % to 20 atomic %. “Cr-containing alloys” or “chromium-containing alloys” are those where Cr is added in smaller quantities than the majority element or elements. For example, 316 stainless steel, which is an iron-based alloy that contains 16 to 18% Cr and 10 to 14% Ni, would be classified as Cr-containing, but not Cr-based. The improved coating method improves the integrity of the cladding tube coating under high temperature accident conditions and equally as important, under normal operating conditions. Even under normal operating conditions hydrogen may form due to Zr oxidation or may be present in water. This hydrogen diffuses into the Zr-cladding (called hydriding) and causes brittleness in the cladding. The improved Cr coated cladding tube will be less susceptible to hydriding of Zr-cladding which would contribute to increased cycle length, and thus, improve the economics of operating the reactor. The Cr coated cladding tube is also expected to resist delayed hydride cracking, so it would perform better in subsequent dry cask storage. The Cr or Cr-based alloy coating provided by the method described herein will reduce hydriding by way of reduced oxidation and by acting as a diffusion barrier to hydrogen in the water from entering the cladding. There are important benefits to having such a Cr coating even under normal conditions, but the role of the Cr or Cr-based coating becomes indispensable during higher temperature accident conditions. Cr exhibits negligible thermal diffusion into the underlying Zr under normal operating conditions and even at temperatures up to 650° C. Despite the intimate contact between the coating and the substrate induced by cold spray there is only very limited inter-diffusion between the pure Cr coating and the substrate at 1200° C. It is believed that in fact, the slight thermal diffusion that occurs under accident temperatures may be beneficial in keeping the coating anchored to the substrate. The method proceeds by delivering a carrier gas to a heater where the carrier gas is heated to a temperature sufficient to maintain the gas at a reasonable temperature (e.g., 100° C. to 500° C.) after expansion in the nozzle. The expansion of the gas propels the particles. In various aspects, the carrier gas may be heated to a temperature between 200° C. and 1200° C., with a pressure, for example, of 5.0 MPa. In certain aspects, the carrier gas may be heated to a temperature between 200° C. and 800° C. In certain aspects, the carrier gas may be heated to between 300° C. and 800° C. and in other aspects, may be heated to a temperature between 500° C. and 800° C. The temperature to which the gas is preheated depends on the gas used as the carrier and on the Joule-Thomson cooling coefficient of the particular gas. Whether or not a gas cools upon expansion or compression when subjected to pressure changes depends on the value of its Joule-Thomson coefficient. For positive Joule-Thomson coefficients, the carrier gas cools and must be preheated to prevent excessive cooling which can affect the performance of the cold spray process. Those skilled in the art can determine the degree of heating using well known calculations to prevent excessive cooling. See, for example, for N2 as a carrier gas, if the inlet temperature is 130° C., the Joule-Thomson coefficient is 0.1° C./bar. For the gas to impact the tube at 130° C. if its initial pressure is 10 bar (˜146.9 psia) and the final pressure is 1 bar (˜14.69 psia), then the gas needs to be preheated to about 9 bar*0.1° C./bar or about 0.9 C to about 130.9° C. For example, the temperature for helium gas as the carrier is preferably 450° C. at a pressure of 3.0 to 4.0 MPa, and the temperature for nitrogen as the carrier may be 1100° C. at a pressure of 5.0 MPa, but may also be 600° C.-800° C. at a pressure of 3.0 to 4.0 MPa. Those skilled in the art will recognize that the temperature and pressure variables may change depending on the type of the equipment used and that equipment can be modified to adjust the temperature, pressure and volume parameters. Suitable carrier gases are those that are inert or are not reactive, and those that particularly will not react with the Cr or Cr-based alloy particles or the substrate. Exemplary carrier gases include nitrogen (N2), hydrogen (H2), argon (Ar), carbon dioxide (CO2), and helium (He). There is considerable flexibility in regard to the selected carrier gases. Mixtures of gases may be used. Selection is driven by both physics and economics. For example, lower molecular weight gases provide higher velocities, but the highest velocities should be avoided as they could lead to a rebound of particles and therefore diminish the number of deposited particles. Referring to FIG. 1, a cold spray assembly 10 is shown. Assembly 10 includes a heater 12, a powder or particle hopper 14, a gun 16, nozzle 18 and delivery conduits 34, 26, 32 and 28. High pressure gas enters conduit 24 for delivery to heater 12, where heating occurs quickly; substantially instantaneously. When heated to the desired temperature, the gas is directed through conduit 26 to gun 16. Particles held in hopper 14 are released and directed to gun 16 through conduit 28 where they are forced through nozzle 18 towards the substrate 22 by the pressurized gas jet 20. The sprayed particles 36 are deposited onto substrate 22 to form a coating 30 comprised of particles 24. The cold spray process relies on the controlled expansion of the heated carrier gas to propel the particles onto the substrate. The particles impact the substrate or a previous deposited layer and undergo plastic deformation through adiabatic shear. Subsequent particle impacts build up to form the coating. The particles may also be warmed to temperatures one-third to one-half the melting point of powder expressed in degrees Kelvin before entering the flowing carrier gas in order to promote deformation. The nozzle is rastered (i.e., sprayed in a pattern in which an area is sprayed from side to side in lines from top to bottom) across the area to be coated or where material buildup is needed. Coating tubular geometries, rather than just flat surfaces, has heretofore been challenging. Whereas flat surfaces can readily be coated, tubular and other curved surfaces have been economically challenging. Coating a tubular or cylindrical geometry requires the tube be rotated as the nozzle moves lengthwise across the tube or cylinder. The nozzle traverse speed and tube rotation are in synchronized motion so that uniform coverage is achieved. The rate of rotation and speed of traverse can vary substantially as long as the movement is synchronized for uniform coverage. The tube may require some surface preparation such as grinding or chemical cleaning to remove surface contamination to improve adherence and distribution of the coating. In various aspects of the method, the particles are pure metallic chromium particles that have an average diameter of less than 20 microns. By “average diameter,” as used herein, those skilled in the art will recognize that the particles may be both spherical and non-spherical so that the “diameter” will be the longest dimension of the regularly or irregularly shaped particles, and the average diameter means that there will be some variation in the largest dimension of any given particle above or below 20 microns, but the average of the longest dimension of all particles used in the coating are together, 20 microns or less. The chromium or chromium-based alloy particles are solid particles. The chromium particles become entrained in the carrier gas when brought together in gun 16. The nozzle 18 narrows to force the particles and gas together and to increase the velocity of the gas jet 20 exiting nozzle 18. The particles are sprayed at a velocity sufficient to provide a compact, impervious, or substantially impervious, Cr and/or Cr-based alloy layers. In various aspects the velocity of the jet spray may be from 800 to 4000 ft./sec. (about 243.84 to 1219.20 meters/sec.). The particles 24 are deposited onto the surface of the substrate at a rate sufficient to provide the desired production rate of coated tubing, at a commercial or research level. The rate of particle deposition depends on the powder apparent density (i.e., the amount of powder vs. the air or empty space in a specific volume) and the mechanical powder feeder or hopper used to inject the powder particles into the gas stream. Those skilled in the art can readily calculate the rate of deposition based on the equipment used in the process, and can adjust the rate of deposition by altering the components that factor into the rate. In certain aspects of the method, the rate of particle deposition may be up to 1000 kg/hour. An acceptable rate is between 1 and 100 kg/hour, and in various aspects, between 10 and 100 kg/hour, but higher and lower rates, such as 1.5 kg/hour, have been successfully used. The rate of deposition is important from the standpoint of economics when more tubes can be sprayed per unit of time at higher deposition rates. The repetitive hammering of particles one after the other has a beneficial effect on improving interparticle bonding (and particle-substrate bonding) because of the longer duration of transient heating. Transient heating occurs over micro- or even nano-second time scale and over nanometer length scales. It can also result in the fragmentation and removal of nanometer thickness oxide layers that are inherently present on all powder and substrate surfaces. The spray continues until a desired thickness of the coating on the substrate surface is reached. In various aspects, a desired thickness may be several hundred microns, for example, from 100 to 300 microns, or may be thinner, for example, from 5 to 100 microns. The coating should be thick enough to form a barrier against corrosion. The coating barrier reduces, and in various aspects may eliminate, any steam zirconium and air zirconium reactions, and reduces, and in various aspects eliminates, zirconium hydride formation at temperatures of about 1000° C. and above. Referring to FIGS. 2a and 2b, a Zr-alloy (Zircaloy-4) tube was coated on the outer side with Cr by the cold spray method described herein. The tube was not coated on the inner side, which therefore remains a Zircaloy-4 surface. After air oxidation at 1200° C. for 20 minutes, an image of the cross section of the coated tube was made. This low magnification photomicrograph shows the entire tube cross-section from outer surface to the inner surface of the tube. Note that the inner uncoated Zr-alloy surface is highly oxidized but the outer surface that was Cr coated shows very little oxidation. Cr loss due to oxidation is about 5 microns, but Zircaloy-4 loss is 400 microns. Although air oxidation does not simulate steam oxidation, this test nevertheless shows the potential for Cr cold spray coating to act as a barrier against corrosion and provide qualitative testimony to the adhesion of the coating under thermal shock conditions. Tests in steam environment have also shown promising results. The average weight gain ate for Cr coated ZIRLO (a Zr alloy) samples is about 0.03 mg/dm2 day. The cold spray method of depositing Cr or Cr based alloy coating onto Zr-alloy tube provides notable benefits over other coating techniques. For example, certain coating methods may not be feasible because of the presence of a native oxide layer on the Zr-alloy surface which interferes with deposition. Other coating methods have to be performed in vacuum chambers and result in low deposition rates which may not be economical. Yet other coating methods involve high temperatures or intense heat which may alter the microstructure of the Zr-alloy. Moreover, the Cr or Cr-based alloy coating does not thermally diffuse into the underlying Zr-alloy substrate under normal operating conditions, but it has been found that some thermal diffusion will occur under accident conditions, which is useful to better anchor the coating to the substrate exactly when it is needed most. Following the deposition of the chromium coating 30 onto the substrate, the method may further include annealing the coating. Annealing modifies mechanical properties and microstructure of the coated tube. Annealing involves heating the coating in the temperature range of 200° C. to 800° C., and preferably between 350° C. to 550° C. It relieves the stresses in the coating and imparts ductility to the coating which is necessary to sustain internal pressure in the cladding. As the tube bulges, the coating should also be able to bulge. Another important effect of annealing is the deformed grains formed during cold spray process get recrystallized to form fine sub-micron sized equiaxed grains which may be beneficial for isotropic properties and radiation damage resistance. FIG. 3 shows high magnification images of the cold spray Cr coating in the as-deposited condition. FIG. 3a shows a deformed grain structure and after annealing at 450° C. for 8 hours (FIG. 3b) shows a fine grained recrystallized structure. The high strain rate plastic deformation or flattening of particles leads to adiabatic shear (i.e, heat stays within the system) which causes transient heating at the interfaces (again at nanometer length scales and nanosecond time scales). The adiabatic shear also fragments nanometer oxide layer that is inevitably present on powders and leads to metal-to-metal contact. Solid state diffusion (on nanometer length scales) between particles and particle and substrate lead to bonding. Annealing following the deposition of the Cr or Cr-based alloy coating results in structures that are rather unique to cold spray coatings. This is very beneficial to achieving higher ductility, to better sustain tube bursts, as shown in testing, and is believed to be beneficial for radiation damage resistance. The coatings provided by the method described herein create the initial structure for giving rise to fine equiaxed grains. The coated substrate may also be ground, buffed, polished, or treated by other known techniques to achieve a smoother surface finish. The method described herein produces a cladding tube comprised of a zirconium alloy tube having a chromium coating of a desired thickness, for example, about 100 to 300 microns or more. Thinner coatings from about 50 to 100 microns thick may also be applied. All patents, patent applications, publications, or other disclosure material mentioned herein, are hereby incorporated by reference in their entirety, except that all references, and any material, or portion thereof, that are said to be incorporated by reference herein are incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material expressly set forth in this disclosure. As such, and to the extent necessary, the disclosure as set forth herein supersedes any conflicting material incorporated herein by reference and the disclosure expressly set forth in the present application controls. The present invention has been described with reference to various exemplary and illustrative embodiments. The embodiments described herein are understood as providing illustrative features of varying detail of various embodiments of the disclosed invention; and therefore, unless otherwise specified, it is to be understood that, to the extent possible, one or more features, elements, components, constituents, ingredients, structures, modules, and/or aspects of the disclosed embodiments may be combined, separated, interchanged, and/or rearranged with or relative to one or more other features, elements, components, constituents, ingredients, structures, modules, and/or aspects of the disclosed embodiments without departing from the scope of the disclosed invention. Accordingly, it will be recognized by persons having ordinary skill in the art that various substitutions, modifications or combinations of any of the exemplary embodiments may be made without departing from the scope of the invention. In addition, persons skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the various embodiments of the invention described herein upon review of this specification. Thus, the invention is not limited by the description of the various embodiments, but rather by the claims. |
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046541829 | summary | The present invention relates to plasma devices and, more specifically, to a rotatable limiter for protecting the confinement vessel of the device from damage by the plasma. BACKGROUND OF THE INVENTION Vacuum liners for defining a plasma in a high energy plasma device have been constructed using relatively thin wall sections made of stainless steel or Inconel. These sections offer high strength while forming a closed loop having sufficiently high electrical resistance that penetration times are acceptably low for magnetic fields generated by poloidal, toroidal or other associated magnetic systems for containing and energizing the plasma. Unfortunately, the thin sections, when used in a high energy plasma environment, may experience local surface melting upon plasma contact. The melting results in structural weakness and vacuum leaks in the liner. In one attempt to prevent melting of the sections, short pieces of stainless steel rod limiters were installed on the inside surface of the sections. By absorbing the plasma energy, the rods protected the sections. However, contact with the plasma caused the plasma to deteriorate upon the introduction of metal impurities, which radiate and cause loss of power in the plasma. For further information regarding the structure and operation of such limiters, reference may be made to "Experimental and Computational Studies of Reversed-Field Pinch on TPE-IR(M)", by Ogawa et al. in "Proceedings of the 9th International Conference on Plasma Physics and Controlled Nuclear Fashion Research," Baltimore, 1982 (IAEA, Vienna, 1983), Vol. I, p. 575. Metallic limiters are also shown in U.S. Pat. No. 4,073,680. In order to avoid the introduction of metal impurities into the plasma, carbon tiles have been used instead of the metal rods. However, the discrete tiles are not readily reliably fastened to the interior of the sections. In another attempt to protect the sections and avoid contamination of the plasma, rings of carbon tiles were placed at spaced locations in the vacuum chamber in the effort to make the plasma contact only the tiles. However, the expected reduction of the heat level on the sections was not found, and arcing occurred between the liner and the tiles which resulted in damage to the liner. For further information regarding such limiters, reference may be made to "Mushroom Limiter Studies in ZT-40M," Downing et al., Bull. Am. Phy. Soc., 27, 1108 (1982), and "Temperature and Resistivity of the ZT-40M RFP with Poloidal Limiters," Haberstich et al., Bull. Am. Phy. Soc., 28, 1097 (1983). Mirror plasma apparatus has been proposed which utilizes shielding by arc discharge to form a blanket plasma and lithium walls to reduce neutron damage to a solid material wall which rotates to keep a liquid lithium layer against it. For further information regarding the structure and operation of this apparatus, reference may be made to U.S Pat. No. 4,260,455. SUMMARY OF THE INVENTION Among the several aspects and features of the present invention may be noted the provision of improved apparatus for containing plasma in a high energy plasma device. Several armature rings are positioned at spaced locations inside a vacuum liner wall, and each ring has conductors which carry current which interact with the magnetic field inside the liner wall, resulting in rotation of the armature rings. Each ring carries armor tiles facing the plasma and serving as plasma limiters. The tiles transfer heat through the ring and the vacuum liner wall. Rotation of the rings results in more even heating of the tiles to prevent damage to the liner wall due to localized heat concentrations. The coefficient of expansion of the material of the armature rings is greater than the coefficient of expansion of the liner wall material so that with heating, the rings expand into firm engagement with the liner wall. This more efficiently permits heat transfer from the armor tiles to a cooling medium disposed outside the liner wall. Continued expansion occurs after the plasma is turned off due to thermal inertia. After cooling, the rings contract into position for rotation in response to the next plasma pulse. Other aspects and features of the present invention will be, in part, apparent and, in part, pointed out specifically in the following specification and accompanying claims and drawings. Briefly, the apparatus of the present invention includes a vacuum tight liner wall which may be made up of a series of sections each of which has a closed peripheral wall defining an interior with open ends. Adjacent interiors of adjacent sections form a plasma path with each section having an inside surface and an outside surface with the interior being generally circular in cross section. A magnet system has helical conductors disposed outside the liner wall for generating a magnetic field extending inside the liner wall. Armature rings are positioned inside the liner wall with each ring carrying rollers for entering into engagement with the inside surface of the wall. The rings also have current carrying armature conductors extending at an angle to lines of force of the magnetic field. The rings carry armor tiles facing the plasma path which function as plasma limiters (a first wall). The interaction of the magnetic field and the current in the armature conductors results in rotation of the armature rings to prevent damage to the liner wall by localized heat concentration. |
description | The present invention relates to an optical element such as a reflector, and the like making use of reflection by a multilayer film, and more particularly, to the correction of a wavefront phase of rays emerging from a multilayer film reflector. FIG. 1 shows a relationship between the classification of electromagnetic waves and wavelengths thereof. First, extreme ultraviolet rays and X-rays will be described with reference to FIG. 1. Extreme ultraviolet rays (EUV) and vacuum ultraviolet rays (VUV) are electromagnetic waves having a wavelength shorter than that of ultraviolet rays in the classification of the electromagnetic waves shown in FIG. 1(a). As can be seen from the comparison of the classification of the electromagnetic waves of FIG. 1(a) with the wavelengths of electromagnetic waves of FIG. 1(b), X-rays indicate electromagnetic waves having a wavelength of 0.001 to 50 nm, wherein soft X-rays indicate X-rays having a wavelength of 0.5 to 50 nm. While a boundary between extreme ultraviolet rays and vacuum ultraviolet rays and soft X-rays is not clearly determined and they are partly overlapped in the classification, extreme ultraviolet rays, vacuum ultraviolet rays, and soft X-rays are electromagnetic waves having an intermediate wavelength of the wavelengths of ultraviolet rays and hard X-rays. Extreme ultraviolet rays, vacuum ultraviolet rays, and soft X-rays have such a property that they have a small amount of transmittancy and absorbed by an air layer. However, since they have a particularly high photon energy, they exhibit a transmittance force which permits them to penetrate the interior of a material such as metal, semiconductor, insulator, and the like from the surface thereof by several hundreds of nanometers. Further, since soft X-rays have such a degree of a photon energy as to be absorbed in inner shell electrons of atoms constituting a material, they exhibit an apparent difference of absorption depending upon elements constituting various materials. This property of soft X-rays is most suitable to the study of various types of materials together with the high resolution thereof. Thus, soft X-rays contributes to the study and development of an X-ray microscope capable of observing living specimens as they are without drying and dyeing them. Extreme ultraviolet rays (vacuum ultraviolet rays) and X-rays have a high photon energy as compared with that of visible rays and have a high transmittance force to materials. Since extreme ultraviolet rays and X-rays are not refracted in all materials because of the above reason, it is difficult to make a lens. Accordingly, while reflectors are used to converge extreme ultraviolet rays and X-rays and to form images using them, even a metal surface does not always reflect extreme ultraviolet rays and X-rays. However, since the metal surface can reflect extreme ultraviolet rays and X-rays when they are incident on it at an angle close to the metal surface, an optical system making use of oblique incidence cannot be employed. Thereafter, a great deal of attention was paid to a “multilayer film mirror” capable of reflecting extreme ultraviolet rays (vacuum ultraviolet rays) or X-rays including soft X-rays, which opened a way for developing an optical system in which these rays were incident at near normal angle on an extreme ultraviolet ray and X-ray imaging optical system. An X-ray micrometer making use of X-rays employs the above-mentioned multilayer film mirror. The multilayer film mirror will be described with reference to FIGS. 2(a) and (b). FIG. 2(a) shows construction of the multilayer film mirror, and FIG. 2(b) shows construction of a reflective film. In FIG. 2(a), the multilayer film mirror is composed of a multilayer film 20 formed on a substrate 10, and FIG. 2(b) shows an example of construction of a multilayer film used for soft X-rays having a wavelength of about 13 nm (photon energy: 97 eV). In FIG. 2(b), the multilayer film 20 is composed of several tens to several hundreds of layers, each including a pair of molybdenum (Mo) and silicon (Si). The multilayer film 20 is attached to the substrate 10 as shown in FIG. 2(a). A normal incidence reflectance of 60% can be obtained by the multilayer film mirror constructed as described above. FIGS. 3(a) and (b) shows an example of a schematic construction of an X-ray apparatus using the multilayer film reflector shown in FIG. 2(a). In FIGS. 3(a) and (b), the X-ray apparatus is composed of two reflectors, that is, a reflector having the reflective multilayer film 20 attached to the substrate 10 having a concave surface and a hole defined at the center thereof and a reflector having a reflective multilayer film 22 attached to a substrate having a concave surface similarly. Reference symbol L denotes X-rays and the light path thereof. When X-rays are irradiated toward a body 30 from the left side in FIG. 3(a), the X-rays L are reflected by the multilayer film reflectors 20 and 22, and an enlarged image 35 of the body can be obtained. At that time, the apparatus shown in FIG. 3(a) achieves a role as a microscope as shown in (1) of FIG. 3(b). The image is formed by X-rays the wavelength of which is one several hundredth or less those of visual rays and ultraviolet rays, which can improve the accuracy of even a very fine body making the limit of resolution caused by unsharpness due to diffraction to one several hundredth or less in principle. The above technology is further grown to the development and study of an X-ray telescope of high accuracy, which contributes to the investigation of the origin of the Milky Way and structures of supernovas by the observation of soft X-rays generated from ultra-high temperature plasmas. Further, when X-rays are irradiated toward the body 35 from the right side in FIG. 3(a), the X-rays L are reflected by the multilayer film reflectors 22 and 20 so that a reduced image 30 of the body comes out. At that time, the apparatus shown in FIG. 3(a) is constructed as an exposing apparatus for executing micro-focusing and reduction as shown (2) of FIG. 3(b). Competition for developing an X-ray multilayer film mirror for a reduced projection exposure optical system is carried out internationally mainly by United States and Japan to use the X-ray multilayer film mirror as a central component of a next-generation ultra LSI manufacturing apparatus. As described above, the application of the X-ray multilayer film mirror to various fields is expected not only by industrial circles but also by academic circles. These X-ray multilayer film mirrors must be provided with a wavefront accuracy of at least one eighth or less a wavelength to obtain an imaging performance. To achieve this value, however, it is indispensable to finally develop a method of measuring and correcting an wavefront error at a wavelength of X-rays being used, in addition to the developments of a method of measuring and controlling an accuracy of shape of a spherical substrate, a method of forming a multilayer film, which has a high reflectance and applies no distortion to a substrate, on the substrate, a method of holding an imaging mirror without distortion, a method of adjusting the imaging mirror, and the like. In particular, the method of correcting a wavefront aberration which is definitely important to the determination of a final imaging performance is encountered with difficulty because an amount of correction is the order of nanometers. At present, an adaptive optics (compensation optical) system for minutely deforming a substrate at an accuracy of nanometers by driving a piezo element and the like, and a method of applying a thin film to the surface of a substrate or ion etching the substrate are proposed. For example, there is a trial for adaptively correcting a shape of a reflector by an actuator. This trial will be explained by a wavefront aberration correcting apparatus shown in FIG. 4. As shown in FIG. 4, the wavefront aberration correcting apparatus corrects a wavefront by correcting a shape of the multilayer film mirror 20 by applying force to the substrate 10 by an actuator 60 attached to the substrate 10 of a reflector. In the correcting apparatus, soft X-rays L passing through a pinhole 110 are introduced to the reflector by a beam splitter 120 and reflected by the multilayer film mirror 20. In the above construction, when a knife edge 130 is inserted into the light path of the soft X-rays L passing through the beam splitter 120, a shape of a mirror surface can be measured by analyzing an image projected onto a two-dimensional detector 150 with a computer 160. The shape of the reflector is corrected by operating the actuator 60 by a control circuit 170 based on a result of the measurement. However, these methods are encountered with a great deal of difficulty because they are inevitably required to measure and control a very minute amount of 1 nm or less to geometrically and optically control a reflection surface in principle. An object of the present invention is to provide an optical element such as a multilayer film reflector and the like having a structure capable of simply correcting a wavefront phase. To achieve the above object, the present invention is an optical element for controlling a phase and an amplitude of emerging rays by a multilayer film, wherein a wavefront phase of the emerging rays can be adjusted by cutting away the multilayer film in accordance with an amount of adjustment of the wavefront phase. Cutting-away of the multilayer film can be controlled by detecting a difference between a plurality of materials that forms the multilayer film. The formation of a correction film as well as the formation of a multilayer larger than necessary to substantially saturate the reflectance permits the correction of a phase by cutting away also the multilayer film when the phase cannot be corrected only by cutting away the correction film, whereby the phase can be corrected more accurately. The use of the above-mentioned multilayer film reflector in a microscope, an exposing apparatus, a telescope, a microprobe, an analyzer and the like for X-rays and extreme ultraviolet rays (vacuum ultraviolet rays) permits a difference of phase to X-rays and extreme ultraviolet rays (vacuum ultraviolet rays) to be controlled by cutting away the multilayer film and the like, whereby a desired imaging performance can be easily obtained. Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 5 is a graph showing a relationship between the number of cycles as the number of films of a multilayer films (number of repetitions of films constituting the reflective multilayer film, each of the films being composed of a material having a high refractive index and a material composed of a material having a low refractive index) and a reflectance in a reflector using a multilayer film as shown in FIG. 2(a). The films have an optical thickness of one fourth a wavelength, respectively. FIG. 5 shows a relationship between a multilayer film composed of ruthenium (Ru) and silicon (Si), a multilayer film composed of rhodium (Rh) and silicon (Si), a multilayer film composed of molybdenum (Mo) and silicon (Si), a multilayer film composed of ruthenium (Ru) and carbon (C), and a multilayer film composed of rhodium (Rh) and carbon (C) and reflectances. As can be seen from the graph shown in FIG. 5, an increase in the number of cycles of the films constructing the multilayer film causes the reflectance to saturate so that the reflectance is not changed even if the films are repeated. A saturated reflectance does not reach 100% and takes a value of about 15% to 80% in a wavelength region in which film materials that absorb extreme ultraviolet rays, soft X-rays, X-rays, and the like are used as an element of the multilayer film. In this saturated state, a multilayer film formed in the number of cycles larger than that necessary to saturation changes the phase of reflected rays while it does not contribute to an increase in an amplitude. Therefore, a wavefront phase can be corrected by forming a multilayer film the number of cycles of which is larger than that necessary to substantially saturate a reflectance and by cutting away the multilayer film in the range in which the reflectance is saturated because of a reason described below. That is, several tens to several hundreds of layers of lamination is necessary in a multilayer film mirror used for, for example, X-rays, and extreme ultraviolet rays (vacuum ultraviolet rays) because a very minute amount of reflection is caused on respective boundaries. According to a theoretical analysis, reflection is caused on an overall multilayer film physically and optically. Therefore, the surface portion of the multilayer film acts as a transmission film. The present invention corrects the wavefront phase of emerging rays by forming a multilayer film having the number of cycles which is larger than that by which a reflectance is substantially saturated and by cutting away the multilayer film in accordance with an amount of adjustment of the wavefront phase. When the amount of correction is relatively small, the phase can be corrected by cutting away the multilayer film so that the variation of a reflectance can be reduced as compared with a case in which the multilayer film is formed by adding a correction film as described below. FIG. 6 shows an example in which changes of a phase and a reflectance are measured by cutting away a multilayer film formed in the number of cycles larger than necessary to saturate the reflectance. Soft X-rays measured have a wavelength of 12.78 nm, and the multilayer film is composed of Mo/Si, has a thickness one fourth a wavelength and is formed of 121 layers. Complex refractive indices nsi and nMo of silicon (Si) and molybdenum (Mo) that form the multilayer to the soft X-rays having the wavelength of 12.78 nm are as follows.nSi=1.00276−0.0015i nMo=0.9324−0.00598i A reflectance by the multilayer film is 76.4%. FIG. 6 shows a change of a phase (a) and a change of a relative reflectance (b), respectively when the multilayer film is cut away from the upper portion thereof. As can be seen from the graph, even if the multilayer film, which is formed in the number of cycles larger than that necessary to saturate a reflectance, is cut away, the reflectance is not changed, but the phase of reflected rays is changed. A step at which the phase is changed in FIG. 6 is caused by milling (cutting away) one cycle of the multilayer film. That is, the phase is changed in such a manner that it is reduced by milling a Mo film and slightly increased by milling a Si film. Since each layer of the Mo/Si multilayer film shown in FIG. 6 has a film thickness of about 4 nm, milling of one Mo layer corresponds to the reduction of a phase angle of 5°. When this value is shown as an error of shape of a substrate, it corresponds to (13 nm/2)*(5°/360°)=0.09 nm, which shows that the error of shape of the substrate can be digitally controlled by 0.9 A by milling one cycle of the film. In other words, when it is intended to mill a predetermined portion of a surface in a certain amount of correction, a milling thickness can be precisely controlled by stopping milling when a material appearing on the surface is changed from Mo to Si. A change of a material caused by milling can be simply monitored using a method of monitoring a material discharged by milling, an electronic method of utilizing a change of a material in a secondary electron discharge yield, a reflectance measuring method utilizing an optical change of characteristics such as a change of an optical constant of visible rays, ellipsometry, and the like. These methods can be easily used together with a most ordinary method of controlling a milling depth by a cutting-away time by stabilizing an amount to be cut-away in time. These features result from that the phase is corrected by milling at least one cycle of the surface of the multilayer film. It has been described above that when milling is carried out for each one cycle in the example of the Mo/Si multilayer film shown in FIG. 6, an accuracy of 0.1 nm can be achieved to the error of shape of the substrate. However, when the milling of one cycle is examined in detail, the following steps can be found: 1. the phase is not almost changed in the milling of the Si layer (actually, the phase is slightly increased because a refractive index is slightly larger than 1); 2. at the same time, a relative intensity reflectance is in a flat state in which it is not almost changed while the Si layer is being milled (the bottom portion of a change of oscillation due to interference); and 3. in contrast, the phase is reduced and the reflectance is changed while the Mo layer is being milled. Accordingly, when milling is stopped at the portion of each Si film in the above digital milling, only the phase is changed by a predetermined angle (about 6°) each time, and the reflectance is not changed. Specifically, since it is sufficient to stop milling when Si appears by milling a Mo layer, a timing at which milling is stopped has a large amount of allowance. Specifically, when a Si film has a thickness within the range of about 3.5 nm, it has an allowance of at least +1 nm. Further, a change of the reflectance can be easily made within 1% making use of this property. Incidentally, when a complex amplitude reflectance of a multilayer film is taken into consideration on a complex plane, a radius vector is equal to an amplitude and an angle of deviation is represented by the same point. Therefore, cutting-away of the multilayer film causes the complex amplitude reflectance to move on a circumference the center of which substantially coincides with an origin. Theoretically, when a change of an amplitude reflectance is determined in the cutting-away of a multilayer film from the upper surface thereof, a reference of calculation of a phase and an amplitude resides on the uppermost surface of the multilayer film at all times. Thus, it is necessary to use the surface of the multilayer film before it is cut away as the reference surface of the phase to calculate an effect for cutting a certain portion from the surface. To satisfy this object, it is necessary, when a certain thickness d is cut away, to calculate the effect by assuming that a vacuum layer is laminated by the thickness d. This assumption makes it possible to fix the reference surface fixed at a position prior to cutting-away at all times so that the effect of a predetermined phase and a predetermined amplitude obtained by the cutting-away can be precisely calculated. FIG. 7 shows another construction of a reflector of the present invention. In FIG. 7, a correction film 50 is formed on a multilayer film 20 which is formed on a substrate 10 in the number of cycles larger than that necessary to saturation. In a multilayer film mirror used for, for example, X-rays and extreme ultraviolet rays (vacuum ultraviolet rays), several tens to several hundreds of layers of lamination are necessary because a reflection is caused very slightly on respective boundaries. According to a theoretical analysis, reflection is caused on an overall multilayer film physically and optically. Thus, as shown in FIG. 7, the addition of the phase correction film 50 on the uppermost surface of the multilayer film 20 larger than substantial saturation permits the film 50 to act as a transmission phase correction film. However, since no transparent material exists in this wavelength region, a material which can constitute the phase correction film must satisfy the condition of an extinction coefficient k together with a refractive index n. A film material constituting the correction film can provide a larger amount of phase correction when it has a larger difference between refractive indexes (1−n) and a smaller extinction coefficient k. Therefore, an optical reference for selecting a material can be judged by a ratio between an amount of change of a phase caused by a unit thickness and damping of an amplitude caused by absorption, and a suitable material has a lager value of {difference between refractive indexes (1−n)/extinction coefficient k}. When soft X-rays having a wavelength of 13 nm is used as an example, the use of molybdenum (Mo) film, in which a difference (1−n) between a refractive index n of the film and a refractive index 1 of vacuum in a soft X-rays region is about 0.1 or less (difference between refractive indexes: 0.065, extinction coefficient: 0.0065) permits a film thickness to be geometrically controlled at a resolution of about 1/15 because a difference of a phase is physically optically controlled in a difference between refractive indexes (1−n) of about 1/15. That is, an effective wavefront control of 1 nm of an X-ray multilayer film imaging mirror can be achieved by the control of the molybdenum film having a film thickness of 15 nm, and a desired imaging performance can be obtained. Thus, it is sufficient to cut away the correction film at an accuracy of 1.5 nm of a film thickness to correct a phase error at an accuracy of 0.1 nm because the amount of correction is a product of the difference between refractive indexes (1−n) and the amount of change Δd of the film thickness d. Further, a change of reflectance caused by a correction film must be calculated in consideration of a change of film thickness and interference of a multilayer film. However, a reduction rate of reflectance is about 1.2%/nm even if it is simply calculated and it is reduced only by about 0.7% in a mirror having a reflectance of 60%. When sufficient correction cannot be performed by the correction film, correction can be further carried out by cutting away the multilayer film larger than that necessary to substantial saturation. Ruthenium, rhodium, and beryllium are available as the material having a large difference between refractive indexes (1−n) and a small extinction coefficient k. A correction film to soft X-rays can be composed of one of these materials including molybdenum or a combination of these materials. FIGS. 8(a)–(c) explains a method of correction using the correction film and the multilayer film shown in FIG. 7. As shown in FIG. 8(a), the correction film 50 having a sufficient thickness is previously formed on the multilayer film 20 that is formed on the substrate 10, and the correction film 50 is cut away by milling in a necessary amount (refer to FIG. 8(b)). When the correction film 50 cannot be sufficiently cut away, the multilayer film is cut away (refer to FIG. 8(c)). While the uppermost surface of the correction film and the like having been milled by the method is roughened, a transmission wavefront is hardly affected by the roughness because the difference of the refractive index thereof to vacuum is small. FIGS. 9(a) and (b) comprise a graph showing an example that after a multilayer film was formed in the number of cycles which was larger than that necessary to substantial saturation and a correction film was formed thereon, the correction film and the multilayer film were cut away from the upper portions thereof as explained in FIGS. 7 and 8(a)–(c), and a change of wavefront phase was measured. As shown in FIG. 9(a), after 121 cycles of a Mo/Si multilayer film was formed and a molybdenum (Mo) correction film of 300 Å was formed thereon, the Mo correction film was cut away from the upper portion thereof. A complex refractive index of silicon (Si) nsi and a complex refractive index of molybdenum (Mo) nMo that formed the multilayer film to soft X-rays having a wavelength of 12.78 nm were as follows.nSi=1.00276−0.0015i nMo=0.9324−0.00598i Further, a reflectance of the 300 Å correction film and the 121-multilayer film was 56.2%. FIG. 9(b) shows a case in which the correction film and the multilayer film constructed as described above were cut away from the upper portions thereof. FIG. 9(b) shows a relative reflectance to the soft X-rays having the wavelength of 12.78 nm (which is 1 when they are not cut away: shown on a right scale) and a change of wavefront phase (which is 0 when they are not cut away: shown on a left scale). When the correction film is cut away, the phase and the reflectance are not changed linearly and are variably changed by the interference of the Mo film. Further, when the multilayer film is cut away, the cycles of change of the phase and the reflectance coincide with the cycles of the cyclic film. A change of reflectance, when the multilayer film portion is cut away, is small as compared with a change thereof when the correction film is cut away. As can be seen from the graph of FIG. 9(b) showing the correction film having been cut away, the phase can be changed by cutting away also the multilayer film. However, an amount of correction of phase to a cut-away amount, which can be achieved by cutting away the multilayer film, is smaller that achieved by cutting away the correction film. <Example of Use of Reflector> FIG. 10 shows a soft X-ray microscope system using the above-mentioned reflector capable of simply correcting a wavefront error. A light path of soft X-rays is disposed in a vacuum vessel 200 because soft X-rays are absorbed by air. Further, the system is roughly divided into four components of a light source, an imaging optical mirror, a detection subsystem, and a control/measurement subsystem, and can observe a specimen 310 using these components. A laser generator 210, a metal target 300, a spectroscope 220, and a pin hole 230 are used as the soft X-ray source. The imaging optical mirror 240 is composed of a combination of the above-mentioned multilayer film mirror, which has a concave surface and a hole defined at the center thereof, and the above-mentioned multilayer film mirror having a convex surface and disposed just in front of the above multilayer film mirror. The microscope system further includes a two-dimension detector 250 and a computer 260. The two-dimension detector 250 has a photoelectric surface 252 for detecting the soft X-rays irradiated to the specimen 310, and the computer 260 captures detected data and controls a position of the specimen. In this construction, first, when strong infrared pulse laser is converged at the metal target 300 by the pulse laser generator 210 through a lens to generate soft X-rays as a light source, plasma having a high energy is generated. The plasma emits electromagnetic waves having various wavelengths. Thus, soft X-rays are taken out from the electromagnetic waves having the various wavelengths using the spectroscope 220. The soft X-rays emerging from the spectroscope 220 pass through the pin hole 230 and irradiates the specimen 310. The soft X-rays irradiated to the specimen 310 enlarge the image of the specimen 310 by the imaging optical mirror 240 and form it on the photo electric surface 252 of the two-dimension detector 250. Then, the computer 260 captures the data detected by the two-dimension detector 250 and forms it as an image. The computer 260 also controls a position of the above-mentioned specimen 310, in addition to the above. The use of the above-mentioned construction in the reflector used in the microscope system as described above can correct a wavefront aberration of rays at an accuracy and a resolution of 1 nm or less. With this construction, an optimum wavefront accuracy can be obtained in accordance with a state in which the reflector is used by finally correcting an X-ray wavefront using a correction film and the like after a multilayer film is formed even if an error of shape of a substrate does not reach a desired value. In the application of the reflector to an X-ray telescope, a telescope of a directly incident Cassegrainian telescope and the like of light weight and high performance can be constructed in place of a nested-type telescope having an obliquely incident cylindrical mirror as a nest by employing correction executed by the correction film and the like. FIG. 11 shows an example of construction of the telescope. In FIG. 11, a reflective type telescope 400 is mounted on a camera 450. The multilayer film reflector described above is used in each of reflectors 410 and 415 constructing the reflective type telescope 400. After rays incident on an outside cylinder 420 are reflected by the reflector 410, they are reflected by the reflector 415 and incident on the camera 450 from a baffle 430. With this construction, an ultimate resolution as small as an aproximate observing wavelength, which cannot be obtained by a conventional telescope, can be expected in an X-ray telescope of light weight and high performance, which is mounted on, for example, an artificial satellite, by reducing a wavefront aberration of a multilayer film mirror. The above-mentioned multilayer film reflector can also be used in an X-ray microprobe. In the application of the multilayer film reflector to the X-ray microprobe, a special resolution, which is conventionally several tens of micrometers, can be reduced up to the region of 0.01 μm, which can dramatically widen subjects to be inspected by the X-ray microprobe including various types of submicron devices. The above-mentioned multilayer film reflector can be used also in an X-ray analyzer. The X-ray analyzer can improve an angle accuracy as well as can observe a minute specimen because it can collimate beams parallel or converge them. Further, the multilayer film reflector can be applied to the analysis of a two-dimensional image by being combined with an imaging system. Defects made on a reflective wavefront can be repaired in a multilayer film reticle mask and an imaging mirror used in a reduced projection exposure optical system, in addition to the above-mentioned X-ray microscope, X-ray telescope, X-ray microproble, and X-ray analyzer. Since the wavefront of the multilayer film mirror can be easily corrected in the various applications of the X-ray transmission multilayer film in addition to the above, the phase of X-ray transmission and reflection wavefronts can be adjusted to target values and target two-dimensional distributions. While the application of the multilayer film reflector to the equipment using X-rays is described above, it is needless to say that the multilayer film reflector can also be used in equipment using extreme ultraviolet rays (vacuum ultraviolet rays), and the like in the same way. Further, since the principle of the present invention utilizes the physical and optical properties of rays, the present invention is effective to all the electromagnetic waves making use of a multilayer film such as ultraviolet rays, visible rays, infrared rays, and further a microwave region, and the like. For example, in the application for increasing an accuracy of a reflective wavefront, the present invention is very effective to a mirror for a laser oscillator and to a mirror constructing similar Fabry-Perot and ring laser gyro resonators. Further, since it is possible to provide special wavelength dispersion characteristics making use of a diffractive effect, a polarizing element having wavelength dispersion can be made by the utilization of polarizing characteristics accompanying with the special wavelength dispersion characteristics. Thus, the polarizing element can be used in a mirror and a beam splitter. In particular, the polarizing characteristics are effective to a half mirror of a photomagnetic apparatus. It is also possible to make a phase grating using the multilayer film of the present invention. In the formation of the phase grating, a groove structure having a thickness for providing a phase difference of 180° is formed on the surface of a substrate using the multilayer film. The phase grating is a diffraction grating of a new type that acts as a two-dimensional phase grating. In a conventional method, since the surface of a substrate is roughed due to a groove structure formed on the substrate, the characteristics of a multilayer film formed on the surface is deteriorated. Further, a processing accuracy must be kept to at least one-twentieth or less a wavelength to be used. The method of the present invention can achieve an accuracy, which cannot be achieved by a conventional geometrical reflective surface position control, by controlling a difference of light path. The difference of light path is a product of a milling thickness d of a multilayer film and a difference between refractive indexes (n−1). The difference of reflective indexes is a difference between an average refractive index n of a multilayer film and a refractive index 1 of vacuum (medium). A smaller value of (n−1) increases an accuracy of a wavefront which is corrected by milling a thickness d. When visible rays are used in a transparent material such as a glass, improvement in accuracy is doubled (1.5−1=0.5), whereas, in a soft X-ray region, improvement of accuracy of the order of one hundred times is expected because a refractive index is slightly smaller than 1 and (1−n) is the order of 0.01. Further, the multilayer film of the present invention can be used as an amplitude modulation hologram. In this case, the hologram is formed by cutting away the multilayer film by two dimensionally controlling a surface shape in a plane so as to regulate the phase and the amplitude of a wavefront from which rays emerge. An element which can be used to filter a phase and an amplitude can be formed by forming the multilayer film of the present invention. In this case, a novel means for executing various types of filtering in a spatial frequency space is provided by combining the multilayer film with an imaging system. The present invention can provide a new method of realizing a novel image display panel and the like by further modulating an optical length (length of a light path) in time in the above method. Further, the multilayer film can be used as a transmission type multilayer film because it substantially acts as a transmission film with respect to reflection from a lower portion. In addition to the above-mentioned, when such a characteristic that a refractive index is greatly different depending a wavelength is utilized, an element can be made which makes use of a phenomenon that a different surface shape appears depending upon a length of rays. For example, an mirror used for extreme ultraviolet rays (EUV) has an ideal shape (for example, spherical shape) to EUV rays. However, since the spherical surface shape disappears after a wavefront is corrected, the mirror has such characteristics that rays reflected on the surface of the mirror are, for example, diverged apart from the spherical surface. That is, a different refractive index can provide characteristics which are similar to a case in which a surface shape is changed depending upon a wavelength. This permits a mirror to be made which has such a feature, for example, that while rays having a certain wavelength is converged by the mirror, rays having other wavelength are not converged thereby. When this feature is applied to an imaging system, an optical system, in which an image can be formed sharply by rays having a certain wavelength but an image formed by rays of other wavelength is made unsharp. On the contrary, when the rays are stopped at a converging point, an image is formed by rays from which a certain wavelength is removed. This means that a reflector having a very large amount of color aberration can be made in, for example, a transmission optical system. When this feature is developed, an element, which positively makes use of dispersion of a wavelength of a refractive index, such as a mirror having a different focal length depending upon a wavelength, a double focus mirror, and the like can be realized. A refractive index is only slightly dispersed in a conventional transmission optical element because the element makes use of a transparent material, that is, a material in which a refractive index is normally dispersed. Thus, the element is utilized only in a prism type spectrometer, and the like, in which dispersion of refractive index is an obstacle that is rather useless as color aberration. The multilayer film reflector of the present invention is basically constructed as a reflective type reflector, which makes various combinations possible from X-rays to infrared rays and microwaves regardless of the wavelengths thereof. A refractive index is greatly changed in an abnormal dispersion region of various materials or in a region thereof where absorption is caused by molecules, and these materials can be positively utilized. As described above, the present invention can remarkably improve the property of a multilayer film formed for the purpose of controlling the phase and the amplitude of rays and rays emerging from electromagnetic waves. In particular, in an imaging optical system making use of the multilayer film, an imaging performance can be improved up to a limit by improving the controllability of a wavefront phase of reflection and transmission. |
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051820765 | abstract | The fixed structure (10) incorporates an abutment surface (10a) upon which a corresponding abutment surface (8a) of the transportable element (1) comes to bear, with the interposition between the abutment surfaces (8a, 10a) of at least two concentric annular sealing joints (13a, 13b). The pressure in the space (18) between the sealing joints (13a, 13b) and bounded by the abutment surfaces (8a, 10a) is measured during the emplacement of the transportable element (1) to determine whether it is leakproof. The measured maximum pressure and/or the variation of pressure measured over time is compared with predetermined values corresponding to a correct emplacement of the transportable element (1). |
056217765 | summary | FIELD OF THE INVENTION This invention relates generally to protection systems for shutting down a system and maintaining it in a safe condition in the event of a system transient or malfunction. In particular, the invention relates to protection systems for shutting down a nuclear reactor and maintaining it in a safe condition in the event of a system transient or malfunction that could cause damage to the nuclear fuel core, most likely from overheating, or a release of radiation, endangering the public. BACKGROUND OF THE INVENTION Conventional reactor control systems have automatic and manual controls to maintain safe operating conditions as the demand is varied. The several control systems control operation of the reactor in response to given demand signals. Computer programs are used to analyze thermal and hydraulic characteristics of the reactor core for the control thereof. The analysis is based on nuclear data selected from analytical and empirical transient and accident events, and from reactor physics and thermal-hydraulic principles. In the event of an abnormal transient event, the reactor operator is usually able to diagnose the situation and take corrective action based on applicable training, experience and judgment. Whether the manual remedial action is sufficient or rapid enough depends upon the event and upon the operator's knowledge and training. If the event is significant (i.e., challenges any of the reactor safety limits), a reactor trip (also referred to as reactor shutdown, scram, or insertion of all control rods) may be required. Some transient events may occur quickly, i.e., faster than the capability of a human operator to react. In such an event, a reactor trip will be automatically effected. A conventional nuclear reactor protection system comprises a multi-channel electrical alarm and actuating system which monitors operation of the reactor, and upon sensing an abnormal event initiates action to prevent an unsafe or potentially unsafe condition. The conventional protection system provides three functions: (1) reactor trip which shuts down the reactor when certain monitored parameter limits are exceeded; (2) nuclear system isolation which isolates the reactor vessel and all connections penetrating the containment barrier; and (3) engineered safety feature actuation which actuates conventional emergency systems such as cooling systems and residual heat removal systems. An essential requirement of a nuclear reactor protection system is that it must not fail when needed. Therefore, unless the operator promptly and properly identifies the cause of an abnormal transient event in the operation of the reactor, and promptly effects remedial or mitigating action, conventional nuclear reactor protection systems will automatically effect reactor trip. However, it is also essential that reactor trip be avoided when it is not desired or necessary, i.e., when there is an error in the instrumentation or when the malfunction is small enough that reactor trip is unnecessary or when one shutdown function fails, the reactor protection system must not perform the next shutdown function if to do so would be unsafe. SUMMARY OF THE INVENTION The present invention is a reactor protection system (RPS) having four divisions, with quad redundant sensors for each scram parameter providing input to four independent microprocessor-based electronic chassis. Each electronic chassis acquires the scram parameter data from its own sensor, digitizes the information, and then transmits the sensor reading to the other three RPS electronic chassis via optical fibers. To increase system availability and reduce false scrams, the RPS employs two levels of voting on a need for reactor scram. The electronic chassis perform software divisional data processing, vote 2/3 with spare based upon information from all four sensors, and send the divisional scram signals to the hardware logic panel, which performs a 2/4 division vote on whether or not to initiate a reactor scram. Each chassis makes a divisional scram decision based on data from all sensors. Each RPS division performs independently of the others (asynchronous operation). All communications between the divisions are asynchronous. The reactor protection system logic is designed to provide fault tolerance, enhanced reliability, increased availability and improved separation. Features of this system include the ability to have a failed sensor without reducing the level of protection or increasing the likelihood of an inadvertent reactor trip. The design in accordance with the present invention eliminates the need for manual bypasses, virtually eliminates the need for operator action, and achieves fault tolerance without custom design components. The RPS is designed to withstand multiple failures in almost all of its components. Its logic has the following major performance enhancement characteristics: First, the exchange of sensor readings and multiple sensor voting capability within each division provides high scram reliability. This can be seen by considering the case where a scram condition exists in the reactor, which is picked up by any three sensors, assuming all sensors and their data are good and not outside the failed sensor limits. For this case, the RPS would generate scram signals in all four divisions, a highly reliable reactor scram configuration. Most conventional protection systems would only generate a scram signal in three divisions. Scram reliability is also high for scram scenarios involving good sensors that indicate scram, and failed sensors that have even failed low, since for such scenarios the RPS produces scram signals based on good sensors, and is not inhibited by failed low sensors. Second, multiple sensor voting within each division provides discrimination against spurious scrams due to sensor malfunctions. Thus, if a sensor of one scram variable erroneously indicates scram in one division, and a sensor of a second variable erroneously indicates scram in another division, the RPS would vote out the erroneous readings and would not generate a scram signal. Third, automatic detection and discrimination against failed sensors allows the RPS to automatically enter a known state when such failures occur. There is no uncertainty as to whether the sensors have failed high or low, or whether the operator has taken the correct manual bypass action. Fourth, cross communication of sensor readings allows comparison of the four theoretically "identical" values. This permits identification of sensor errors such as drift or malfunction. A diagnostic request for service is issued for errant sensor data. Fifth, automated self test and diagnostic monitoring, sensor input through output relay logic, virtually eliminate the need for manual surveillance testing. This provides an ability for each division to cross-check all divisions and to sense failures of the hardware logic. |
description | The present invention relates to the transportation of irradiated nuclear fuel, in particular between a cooling pond and a storage device. The present invention relates in particular to transportation packaging which allows horizontal or vertical storage of the irradiated fuel contained in a casing. In the context of irradiated fuel management, after being used in the reactor fuel is temporarily stored in a pond in a building, known as the fuel building, next to the reactor building. The irradiated fuel is then removed to a temporary storage device to await its final release destiny, which may be reprocessing or storage. Allowing for the capacity of storage ponds, an intermediate solution must be envisaged. In this context, one could envisage placing the irradiated fuel in a metal casing forming the first containment barrier. Then the casing is placed inside metal packaging which forms a transportation device which provides mechanical protection for the casing and acts as a second confinement barrier during its transportation. The transportation package minimises transfer of contamination during transportation of the casing loaded with nuclear fuel. In order to place the nuclear fuel assemblies inside the casing and in the transportation packaging, one possibility is to use a so-called “hot” radiological shielding enclosure, with remote manipulation of the various components using manipulator arms: it is obvious that personnel cannot be located next to components with no radiological shielding. The drawback to this method is its cumbersomeness, and hence the timescales and the cost, both of the enclosure and of the tools and manipulation arms. Another option is to carry out loading under water. Since water is, in fact, a good radiological shielding medium, and since all plants possess a pond, direct packaging of radioactive material in ponds has been proposed. In this context, the metal confinement casing is immersed in the pond and the fuel is loaded into it. The opening for loading the casing is then closed off using a plug, with this step taking place dry, as described in document FR 2 806 828. When and how this casing is placed in the transportation packaging is not described however. Document U.S. Pat. No. 4,780,269 describes loading a casing in a pond, where the casing has been placed in transportation packaging beforehand. Thus the casing and the transportation packaging are simultaneously immersed. The casing is then closed using a plug in the pond and then the assembly formed by the packaging and the casing is withdrawn from the pond in order to close off the packaging and place it on the platform of a lorry in order to transport it to a storage area. Two storage modes exist: The first storage mode is storage in the vertical position, with the casings being arranged in wells. This storage mode results in significant space being saved, but its construction is very expensive, and is very cumbersome to implement. In effect, wells must be driven, foundations poured etc. Furthermore, legislation requires that it must be possible to recover nuclear fuels at any time. In the event, therefore, of a casing being damaged, the recovery of fuel from the bottom of the well would be very laborious. The second storage mode is horizontal storage, where horizontal concrete housings are placed on a concrete frame, to which there is usually access from both ends. Document U.S. Pat. No. 4,780,269 also describes transportation packaging and a storage device for horizontal storage of nuclear fuel casings. The transfer of the casing between the transportation packaging and the storage device is achieved using a piston. The side of the packaging which can be opened is made to face a first open end of the storage device, the piston then enters through a second open end of the storage device, opposite the first end of the storage device. The casing then leaves through the first end to enter the packaging. The free end of the piston or a winch then takes hold of the casing and exerts a traction force to bring it into the storage device. The transfer of the casing to the storage module requires that the biological shielding plate be removed, so that continuity of biological shielding of the environment in relation to the casing is then broken. Consequently, it is an aim of the present invention to provide a transportation device which is capable of forming a true biological barrier at all times in the transportation of the nuclear fuel. It is also an aim of the present invention to provide a transportation device which allows packaging of irradiated nuclear fuel to take place in a pond. It is also an aim of the present invention to provide a transportation device which allows safe and simple horizontal storage of a casing. It is also an aim of the present invention to provide a transportation device which allows the casing to be recovered in order to store it in another location or reprocess it. The aims stated above are achieved by a transportation package which includes two axially opposite open ends which can be closed off using plugs. A first end allowing the casing to be loaded/unloaded and a second end allowing means to pass through it which are designed to apply a thrust/traction force on the casing, whilst ensuring continuity of biological shielding. The plug which closes off the end opposite that for loading/unloading includes a passage which is equipped with a force transmission component which forms a biological barrier. In other words, a composite plug is constructed whose central part can move with the loading/unloading device by fitting between the loading/unloading device and the casing, whilst maintaining a biological barrier throughout the loading/unloading phase. In the horizontal position the first end can come up against an opening to allow a casing filled with fuel to be loaded/unloaded in a storage device. At the other end, a piston rod for unloading the packaging applies a thrust/traction force on a longitudinal end of the casing through the said force transmission component. Thus continuity of the biological shield is ensured. Furthermore, the design of the transportation device according to the invention renders it especially suitable for loading in ponds, by allowing a casing filled with used fuel to be loaded underwater and allowing the various operations for closing and sealing the casing to be carried out. In effect, an inflatable seal fitted between the compartment and the casing to be loaded into the packaging limits the transfer of contamination due to the casing. Additionally, it is advantageously arranged that the difference between the height of the opening in the packaging and that in the casing is sufficient to allow the operations for closing and sealing the casing to be carried out using an automatic system. A system for draining may also be fitted. The transportation device therefore serves as a biological shield and mechanical protection system and ensures safe transfer of the casing into a storage device. The main subject-matter of the present invention is therefore a device for the transportation of nuclear fuels which comprises a barrel with a longitudinal axis which forms a compartment designed to contain a casing loaded with nuclear fuel, where the said compartment is equipped at a first longitudinal end with a first opening closed off by means of a closure device and designed to allow the casing to pass through, and a second opening closed off by a plug, where the said plug includes a through passage and a component for transmitting force which forms a biological shield fitted so that it slides in the said passage, with the said passage being designed to allow a loading/unloading device to apply a thrust force on the casing along a longitudinal direction in the direction of the first opening in order to unload a casing, or a traction force in the direction of the second opening in order to load the casing into the transportation device. In one example of a construction option, the passage in the plug in the second opening is closed off on the outside by a door and on the inside by the force transmission component, where the said component is designed to slide inside the compartment. The component is, for example, a massive cylindrical component which fits the diameter of the passage and that of the compartment. A sealing system is advantageously fitted between the force transmission component and the passage through the plug. The force transmission component may include a gripper which hooks onto the casing automatically in order to transmit a traction force onto the latter. In one particularly advantageous example, the means of closing off the first opening includes a first plug on the outside and an additional plug on the inside, with the additional plug forming a biological barrier when the first plug is withdrawn. The additional plug may be fitted so that it can rotate around an axis which is orthogonal to the longitudinal axis, and includes a passage with a longitudinal axis whose diameter is such that it allows the casing to pass through and is arranged in such a manner that one rotation of the additional plug around the axis of rotation results in the axis of passage in the additional plug being in alignment with the axis of the compartment, so that the casing may pass through the additional plug. An inflatable seal may be fitted onto an interior wall of the compartment towards the said component, which is designed to come into contact with the casing. Advantageously the transportation device includes shock absorbing caps which cover the longitudinal ends of the said transportation device. A system for checking that the compartment is sealed which includes a means for injecting helium between two concentric seals between the plug and the barrel or between the door and the plug may be fitted, where one of the seals is radially internal and the other seal is an intermediate seal, and a means of detecting the presence of helium in the intermediate seal and a radially external seal. Another subject of the present invention is a loading/unloading device which uses the transportation device according to any of the preceding claims, which includes a piston designed to enter the passage through the plug and to exert a thrust or traction force on the force transmission component. The loading/unloading device may include a sealing system designed to ensure that there is a seal between the piston and the cover. The loading/unloading device may also include means of fastening the piston onto the force transmission component. Another subject of the present invention is a method for the unloading from a transportation device according to the present invention, of a casing loaded with nuclear fuel, where the said method includes a step in which a thrust force is applied from the second opening in the direction of the first opening so that the casing is made to slide in the device towards the first opening causing the casing to emerge from the said transportation device. Another subject of the present invention is a method for the unloading of a transportation device according to the present invention, with a casing loaded with nuclear fuel, where the said method includes a step in which a traction force is applied from the first opening in the direction of the second opening so that the casing is made to slide inside the transportation device. In FIG. 1, one can see an example of a construction option for a device according to the present invention, which includes a chamber 2 with an axis X called the compartment which is designed to receive a casing 18, inside a cylindrical barrel 3. The compartment 2 includes a first longitudinal opening 4 and a second longitudinal opening 6 closed off respectively by a first plug 8 and a second plug 10. The first and second plugs 8 and 10 include openings which are designed to allow the object which will be described below to pass through. The barrel 3 includes, in an advantageous manner, a first internal cylinder 12 made of steel and a second external cylinder 14 made of resin. It could be envisaged that the cylinder be made entirely of steel. The barrel 3 also includes an internal sleeve 16 which covers the internal wall of the internal cylinder 12. Sealing between the internal sleeve 16 and the internal cylinder 12 is achieved using welding during the construction of the packaging. A casing 18 loaded with nuclear fuel, in particular irradiated nuclear fuel, is placed inside the sleeve 16, for example under water in a cooling pond. The first opening 4 is designed to allow the casing 18 to pass through it when it is loaded into the transportation device and when it is being unloaded to a storage module. The first plug 8 closing off the opening 4 includes an external collar 20 fixed to the barrel 3, and a first central plug 22, which is itself fixed to the collar 20. Fastening is achieved, for example, using a threaded fixing. The collar 20 includes a central opening 23 which is closed off by the first plug 22, with this opening 23 allowing the casing 18 to pass through. In a highly advantageous manner, an additional plug 24 is fitted towards the loading/unloading opening, forming a biological barrier once the central plug 22 has been withdrawn. The additional plug 24 has an essentially cylindrical form fitted so as to rotate around its axis Y, where the axis Y is aligned with a diameter of the barrel 3 and is orthogonal to the axis X. The additional plug 24 includes a cylindrical passage 26 with a diameter designed to allow the casing 18 to pass through and whose axis Z is orthogonal to the axis Y. In the closed-off position, as shown in FIG. 1, the axis Z of the passage 26 is orthogonal to the axis X of the compartment 2, preventing passage and forming a biological barrier. In the loading or unloading positions, the axis Z of the passage 26 is aligned with the axis X of the compartment 2, so that passage 26 is an extension of the compartment 2, and allows loading or unloading of the casing which slides inside the passage 26 and inside the compartment 2. The additional plug 24 is operated, for example manually, from the outside of the packaging. According to the present invention the plug 10 which closes off the second opening 6 includes an axial through passage 28 closed off by a door 30, and a force transmission component 32 which is designed to slide in the central passage 28 and inside the compartment 2. This component 32 forms a biological barrier. The passage may also include a plug 29 which forms an additional biological shield between the door 30 and the force transmission component 32. The component 32 can slide inside the passage 28 and emerge into the compartment 2. Thus, by applying a thrust force onto the component 32 in the direction of the first opening 4, the casing 18 can be made to slide inside the compartment 2. The component 32 acts as a push rod during unloading and as a traction device during loading. The force transmission component 32 includes a massive cylindrical component which fits the diameter of the passage 30 and of the compartment 2, and which forms, as stated above, a biological shield. The component 32 advantageously includes, at the end which is designed to come into contact with the casing, a cavity (not shown) which allows it to automatically align with the casing when a thrust force is applied. In one example of a construction option, the component 32 includes a gripper, formed of two or three fingers, designed to connect automatically onto the casing. Thus in the case of loading of the packaging, the component 32 can exert a traction force on the casing. One can envisage the free end of a piston 33 (FIG. 2b) entering the passage 28 when the door 30 is open. It is envisaged that the free end of the piston 33 is fixed onto the component 32, so that when the casing 18 is removed from the compartment 2, the component 32 is brought into its at-rest position when the piston 33 is retracted. The link between the component 32 and the piston rod is achieved, for example, using a nut and bolt system. The link between the piston 33 and the force transmission component 32 is made when the closure door 30 is open. The axial dimension of the piston 33 is therefore designed to allow the casing 18 to slide completely out of the compartment 2. One could envisage the casing 18 being pushed directly using the piston 33, but placing the component 32 between them provides, as described earlier, an additional biological shield for the individuals who are operating the piston 33. It is also advantageous if a sealing system (not shown) is fitted between the body of the piston and the external face of the plug 10, in order to ensure confinement of the piston-packaging assembly in relation to the exterior. When the piston is fitted to the plug 10, the piston rod 33 enters the passage 28 and connects directly onto the component 32. The transportation device according to the invention advantageously includes an inflatable seal 36 placed in a groove 37 made in the internal wall of the compartment 2 towards the second end 6. This comes into contact with the body of the casing 18 and provides confinement of the casing 18 by forming a barrier at a lateral gap between the compartment 2 and the body of the casing 18, so that during loading of the transportation device with a casing in a pond, water does not enter the gap between the casing and the wall of the compartment 2. The persons who operate the piston are completely shielded from any radiation emitted by the fuel contained in the casing and which is not stopped by the casing. It is also envisaged in the example shown that the difference in height between the opening in the packaging and that in the casing is sufficient to allow operations to close and seal the casing in the pond to take place using an automatic system. Means for ensuring a seal are also fitted between the various components which make up the transportation device, in particular between the collar 20 and the barrel 3, between the first plug 22 and the collar 20, between the plug 10 and the barrel 3 and between the component 32 and the plug 10. As an example, three concentric O-ring seals may be fitted between the door 30 and the plug 10, or similarly between the plug 10 and the barrel 3. This arrangement also enables a rapid check on the confinement of the packaging to be carried out. Component 32 includes peripheral seals (not shown), so that for example the risk of transferring contamination during translation movement of the piston is minimised. These seals, for example O-rings and two in number, fitted to the piston, thus ensure that there is a seal between the plug 10 and the component 32. The confinement of the casing is achieved through the various barriers formed by the fuel sheathing, the welding of the casing and the seals made of synthetic materials which ensure that the transportation device is sealed. Also fitted to the transportation device is a system (not shown) for checking that the packaging is sealed. For example, a sampling point equipped with a self-closing rapid connector protected by a sealed door is fitted in the cover 10 and this allows the interior of the packaging to be checked. The sealing of this sample point is provided by a door 50 equipped with two O-rings in series. This system may include: a point for injecting helium located between two seals of the three seals placed between the door 30 and the plug 10 or between the plug 10 and the barrel 3, where one of the seals is the seal which is radially the furthest towards the interior and the other seal being an intermediate seal. A second measurement point to which a helium detector is connected; this point is placed, for example, between the intermediate seal and the third seal which is radially the furthest towards the exterior. Thus if helium is detected between the intermediate seal and the third seal this indicates that the intermediate seal is not leak-tight. In a preferred example, protective caps 38 are fitted which are designed to cover and surround the longitudinal ends of the barrel 3 in order to protect them in the event of an impact. These caps 38 take the form of a cylinder equipped with a central cavity 39 whose internal diameter is effectively equal to the external diameter of the barrel 3. The cavities 39 are fitted onto the longitudinal ends of the barrel 3, and the caps are fixed, for example using bolts, to the plugs 8, 10. These caps protect the sealing systems. These caps are removed during loading or unloading of the casing from the transportation device, in order to allow the door 30 to be removed. This device therefore allows the transportation packaging either to be unloaded by transfer of the casing into the storage device, or allows the casing to be removed from the storage device into the transportation packaging. The set of sealing systems used, in particular between the piston body and the packaging and that of the push-rod 32 fitted with its grips means that the sealing integrity of the packaging as well as biological shielding can be preserved. We will now describe the unloading of a casing contained in a transportation device according to the present invention, based on FIGS. 2A and 2B. The transportation device arrives on the unloading site; it is usually transported in a laid-down position and ready for unloading. The shock absorbing caps 38 are then removed. The first end 4 of the device is aligned with an inlet 44 to a receiving enclosure 40 for horizontal storage of the casing 18. Means 42 are placed between the first end of the transportation device and the inlet 44 to the enclosure 40 in order to withdraw the first plug 22 and to ensure the permanent confinement of the casing 18 (FIG. 2A). The rest of the unloading method is represented in FIG. 2B: the first plug 22 is withdrawn, the additional plug 24 is pivoted around the axis Y so as to align the passage 26 with the compartment 2. the door 30 is opened; if a plug 29 is fitted, then this is removed, the piston is fixed and sealed onto the plug 10 and the free end of the piston 33 is fixed onto the rear face of the push-rod 32. The piston is then operated. The component 32 transmits the thrust force to the casing 18 in the direction of the arrow F, the casing 18 slides in the compartment 2, enters into the passage 26 in the additional plug 24, then into the receiving enclosure 40. The piston is operated until the casing 18 is completely within the enclosure 40. The piston 33 is then retracted, bringing the component 32 to its at-rest position inside the plug 8. When the piston has emerged completely from the device, the door 30 is closed once more. The additional plug 24 pivots to return to its at-rest position in which the axis Z of the passage 26 is orthogonal to that of the compartment 2. The first plug 22 is refitted in place in the collar 20. Loading from the receiving enclosure, is carried out in a similar manner by applying a traction force to the component 32 which pulls on the casing causing it to enter into the compartment 2. The storage device includes an inlet 44 for the casing to pass through and an end 46 for the piston to pass through so that it may apply a thrust force on the casing. The transfer is carried out in a manner which is equivalent to unloading of the device according to the invention described earlier. Throughout the unloading or loading phases, leak-tightness towards the exterior is maintained by means of the sealing systems described above. |
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abstract | Separation devices are disposed in the vent volume above part-length rods and above one or more of the spacers above the upper ends of the part-length rods. The separation devices preferably comprise swirlers located above the lattice openings which would otherwise receive the rods but for the underlying part-length rods. In this manner, flow is directed laterally outwardly onto the surfaces and into the interstices of the full-length fuel rods for improved power performance while simultaneously adverse pressure drops across the spacers are minimized. |
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summary | ||
description | This application is a non-provisional of and claims priority to U.S. Provisional Application No. 61/769,549, filed on Feb. 26, 2013. The contents of Application No. 61/769,549 are incorporated herein by reference. All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. The present invention generally relates to radiation therapy. In various respects, the invention is directed to a highly responsive multileaf collimator, and method of use to provide radiation therapy utilizing beam shaping, intensity modulation and combinations thereof including simultaneous beam shaping and intensity modulation of therapeutic beams. Intensity modulated radiotherapy (commonly referred to as IMRT) is a generic term for a number of radiotherapy techniques that, essentially, vary the beam intensity that is directed at the patient. That variation can be spatial, temporal, or both. In radiation therapy the terms dose, fluence and intensity are sometimes used interchangeably and confusingly. For the purposes of this description and this application these terms are used as follows. Fluence is the number of photons or x-rays that crosses a unit of area perpendicular to a radiation beam. Fluence rate is the fluence per unit time. Intensity is the energy that crosses a unit area per unit time. Fluence and intensity are independent of what occurs in a patient, and more specifically are not dose. Dose is the amount of energy absorbed by tissue by virtue of radiation impacting the tissue. Radiation dose is measured in units of gray (Gy), where each Gy corresponds to a fixed amount of energy absorbed in a unit mass of tissue (e.g., 1 joule/kg). Dose is not the same as fluence, but increases/decreases as fluence increases/decreases. In radiation therapy delivery, the beam aperture is commonly set by a multi-leaf collimator (MLC). One such method of using the MLC is to create one or more patterns that shape the radiation. A single shape that matches a target is commonly referred to as a conformal delivery. For more complicated dose distributions IMRT can be utilized. In IMRT, rather than having the MLC shape the incident radiation to match a certain outline, the MLC is instead used to create an array of beam shapes that create a desired intensity modulation and desired 3D dose distribution. FIG. 1 illustrates an isometric view of a conventional shaping-MLC 31 (such as those used on Varian radiation therapy systems) passing a beam to a target in a patient. Two banks 33, of opposing leaves, where each leaf 37 may be positioned continuously across the radiation field. The two banks of leaves are positioned so as to collimate the beam 30 in the desired shape. Each leaf 37 typically may travel beyond the midpoint of the collimator in order to provide flexibility when achieving the desired collimation. The configuration illustrates fully open (41), partially open (43) and closed (45) leaf states. In an example of radiation therapy, each gantry angle has one beam associated with that particular gantry angle, which beam 30 is then collimated into multiple shapes by an MLC. Treatment beam 30 passes through the shaped aperture 47 formed by the leaves 37. The resulting collimated beam continues onto a target 14 within the patient 38. FIG. 1 also illustrates how the treatment beam may be visualized or conceptualized as many different beamlets 49. Leaves 37 of conventional shaping-MLC 31 are moved into various positions to achieve desired shapes or apertures for specified periods of time to achieve fluence map 51 for that particular beam. Modulation of the conceptualized beamlets occurs by sequentially and monotonically moving the leaves into desired positions to achieve desired shapes or appertures such that the time a conceptualized beamlet is exposed controls the intensity of that beamlet. Monotonic, as used in this application and related to radiation therapy, means an ordered sequence of apertures where the sequence is dictated by a continuum from one aperture to a subsequent aperture or where individual leaves increment in one direction during a given series of apertures. In other words, a sequence of apertures would be dictated by mechanical limitations of the MLC, not so much by what may achieve the more optimal treatment delivery; a sequence would go from aperture 1, then 2 then 3 and so on, and not from 1 to 3 then to 5 then back to 2. Rather than use a single conformal shape, the MLC delivers a sequence of shapes. The net amount of radiation received at any given gantry position is based upon the extent to which the different shapes permit the passage or blockage of radiation. As seen in FIG. 1, the shape of MLC 31 shown does not directly correspond to the beamlet intensities of the fluence map 51. As will be appreciated, the depicted fluence map shows the accumulation of intensities for multiple shapes the MLC has taken for that particular gantry angle. A common limitation of the conventional shaping MLC is that the leaves defining the shapes move relatively slowly. Using large numbers of shapes, or shapes that require large leaf motions, can result in longer patient treatments. Likewise, the speed of the leaves can limit the ability of conventional shaping-MLC's to deliver time-sensitive treatments, such as utilizing synchronized motion of delivery components (e.g., gantry, couch, x-ray energy etc.). A conventional binary MLC 61 is shown in FIG. 2. The binary MLC 61 has a plurality of leaves 63 arranged in two banks 65, 67. Each bank of leaves is used to form a treatment slice by positioning the leaf in a closed position or open position with respect to the beam. As shown in FIG. 2, the leaves may work in concert to be both open (A), both closed (B) or where only one leaf is open/closed (C). Binary MLCs are used in TomoTherapy's Hi-Art® radiation therapy system and the North American Scientific treatment system. In the conventional binary-MLC treatment system the patient is moved past the rotating radiation source to deliver a helical treatment to the patient using the dual bank binary collimator. Alternatively, the patient is indexed for treatment of another subsequent two slices by the dual bank binary collimator, as is done by the North American Scientific system. Leaves of the dual bank binary collimator move with sufficient speed such that leaf sequencing or positioning will not be significantly influenced by any previous or future positions (open or closed for a binary collimator) of any individual leaf. Stated another way, leaf speed is sufficient such that the mechanics of the MLC do not unduly influence the determination of leaf position at any given time for the delivery of a radiation therapy treatment or fraction. Thus, and in contrast to the conventional shaping-MLC, each leaf defines a beamlet that does not require conceptualization by the planning software, i.e., the amount of time a leaf is open directly controls the intensity for that beamlet. For both conventional MLCs (shaping and binary), each beamlet has a fluence and all the fluences combined form a fluence map for the beam. The fluence maps for each gantry angle or for all the beams are combined and optimized into the treatment plan. The example of the conventional shaping MLC has been provided to illustrate the underlying concepts of volumetric intensity modulation using the shaping MLC and that of the binary MLC to illustrate the underlying concepts of direct intensity modulation at discrete gantry angles. More complicated treatment plans and delivery can include gantry motion, couch motion, varying gantry speed, varying MU, etc. in order to provide more sophisticated and theoretically better dose conformation in less time per fraction. It is the treatment plan, via delivery software, that governs the operation of the treatment delivery device. The physical capabilities of the delivery system (gantry, linear accelerator, MLC, couch, etc.) limits or constrains the treatment planning software in the type of plan it can create and optimize for delivery by the delivery system. Treatment planning systems and software (collectively referred to as planning system) are not the focus of this application, but, and as will be appreciated, are integral for treating a patient with radiation. Radiation therapy treatments are governed by a treatment plan, typically generated by a physician or physicist (alone or collectively a “planner”) using the planning system. The planner will typically use a diagnostic 3D image (typically CT, although combinations of any PET, CT, MR maybe used) and define or contour the target structure and any nearby critical structures or organs at risk (OAR). The planner then determines the amounts of radiation for delivery to the target structure and the amount of radiation that will be allowed to the OAR. The treatment planning software, using inverse planning and the physical capabilities of the delivery device will generate a treatment plan. The planner then evaluates the plan to determine if it meets the clinical objectives, and if so will approve the plan for delivery to the patient. Delivery of the plan occurs in multiple treatment sessions or fractions. Conventional MLCs and the treatment paradigms resulting from them have provided steadily advancing and more sophisticated conformal radiation therapy treatments. However, there remains a need for more advanced shaping and modulation of the therapeutic beams, thereby enabling treatment planning software to develop and enable delivery of even more sophisticated plans. As seen by the above summary of radiation therapy techniques, one key component for delivery of radiation therapy is the collimator. While multi-leaf collimators exist, the speed and control of an individual leaf or group of leaves is insufficient to achieve more advanced simultaneous shaping and modulating beam patterns. What is needed are improved multileaf collimator designs, responsive enough to meet the speed and position control requirements of more advanced radiation treatment plans, thereby enabling new treatment paradigms. Embodiments of the present invention provide a multi leaf collimator (MLC). These embodiments have a plurality of leaves having a length of travel. Each leaf has a proximal end, a distal end, a radio opaque distal blocking portion having a length L and width W, a proximal drive portion having a length L′ and width W′, one or more conductive coils fixed to the proximal drive portion and operatively connected to an electrical current source, where electrical current passing through the conductive coils generates a first magnetic field. The MLC of these embodiments also have a leaf guide with a plurality of channels arranged approximately parallel and adjacent to each other where at least a portion of each of the plurality of leaves is slidingly arranged into each of said channels, and a plurality of stationary magnets positioned adjacent to the proximal drive portion, where each stationary magnet has a second magnetic field configured to operate in conjunction with the first magnetic field from the coils to exert a force on the proximal drive portion. In some embodiments the MLC will have dual opposing banks of leaves, and other embodiments will have the stationary magnets on either side of the drive portion. Embodiments of the present invention also include methods for collimating a therapeutic radiation beam with a multi leaf collimator (MLC). These embodiments may include determining a desired state for one or more leaves of the MLC, where the one or more leaves are moved using an electromagnetic drive system, if the one or more leaves are not in the desired state, then a magnetic field is modified to result in a force on the one or more leaves causing them to move, and lastly the leaves are stopped at the desired state or position. If the leaves are not in the desired state further embodiments apply a current to electromagnetic coils residing within a driving portion of the leaves to generate a first magnetic field, where the first magnetic field operates in conjunction with a second magnetic field from stationary magnets on either side of the driving portion, which results in a force on said driving portion causing the leaves to move. In one embodiment, the invention provides a multi leaf collimator (MLC) comprising a plurality of leaves, a leaf guide configured to support the plurality of leaves, and a plurality of stationary magnets. The plurality of leaves have a length of travel, wherein each leaf comprises a blocking portion having a length L and a width W and being radio opaque, a drive portion having a length L′ and a width W′, the drive portion connected to the blocking portion, and a conductive coil operatively connected to an electrical current source, wherein the conductive coil is fixed to the drive portion along at least a portion of length L′, and wherein electrical current passing through the conductive coil generates a first magnetic field. Each of the stationary magnets is positioned adjacent to the drive portion of at least one leaf, wherein each stationary magnet has a second magnetic field configured to operate in conjunction with the first magnetic field to exert a force on the drive portion. In another embodiment, the invention provides a system for collimating a therapeutic radiation beam. The system comprises a multi leaf collimator (MLC), a leaf guide configured to support the plurality of leaves, a plurality of stationary magnets, and a driver component. The MLC comprises a plurality of leaves having a length of travel, wherein each leaf comprises a blocking portion having a length L and a width W and being radio opaque, a drive portion having a length L′ and a width W′, the drive portion connected to the blocking portion, and a conductive coil operatively connected to an electrical current source, wherein the coil is fixed to the drive portion along at least a portion of the length L′, and wherein electrical current passing through the coil generates a first magnetic field. Each of the stationary magnets is positioned adjacent to the drive portion of at least one leaf, wherein each stationary magnet has a second magnetic field configured to operate in conjunction with the first magnetic field to exert a force on the drive portion. The driver component directs electrical current to the coil, thereby causing movement of the plurality of leaves to desired states. In a further embodiment, the invention provides a multi leaf collimator (MLC) comprising a plurality of leaves having a length of travel, wherein each leaf comprises a blocking portion having a length L and a width W, wherein the blocking portion is radio opaque; and a drive portion having a length L′ and a width W′, the drive portion connected to the blocking portion; and wherein at least one of the leaves is capable of moving at a speed of at least 50 cm/s. In a further embodiment, the invention provides a multi leaf collimator (MLC) comprising a plurality of leaves, a leaf guide configured to support the plurality of leaves, and a plurality of conductive coils. The plurality of leaves have a length of travel, wherein each leaf comprises a blocking portion having a length L and a width W and being radio opaque, a drive portion having a length L′ and a width W′, the drive portion connected to the blocking portion, and a permanent magnet positioned in the drive portion. At least one coil is positioned between adjacent leaves and connected to an electrical current source to generate a first magnetic field when current passes through the at least one coil that interacts with a second magnetic field generated by the magnet to exert a force on the drive portion. Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. Although directional references, such as upper, lower, downward, upward, rearward, bottom, front, rear, etc., may be made herein in describing the drawings, these references are made relative to the drawings (as normally viewed) for convenience. These directions are not intended to be taken literally or limit the present invention in any form. In addition, terms such as “first,” “second,” and “third” are used herein for purposes of description and are not intended to indicate or imply relative importance or significance. In addition, it should be understood that embodiments of the invention include both hardware, software, and electronic components or modules that, for purposes of discussion, may be illustrated and described as if the majority of the components were implemented solely in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, would recognize that, in at least one embodiment, the electronic based aspects of the invention may be implemented in software. As such, it should be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components may be utilized to implement the invention. Furthermore, and as described in subsequent paragraphs, the specific mechanical configurations illustrated in the drawings are intended to exemplify embodiments of the invention and that other alternative mechanical configurations are possible. In one embodiment of the present invention, and illustrated in FIG. 3, a radiation modulation device 34 can comprise an electromagnetically actuated MLC 62, which includes a plurality of leaves 66 operable to move from position to position, to provide intensity modulation. Leaves 66 can move to any position between a minimally and maximally-open position, and with sufficient speed such that leaf sequencing or positioning will not be significantly influenced by any previous or future positions (open or closed for binary collimator) of any individual leaf Stated another way, leaf speed is sufficient such that the mechanics of the MLC do not unduly influence the determination of leaf position at any given time for the delivery of a radiation therapy treatment or fraction. Each leaf 66 is independently controlled by an actuator (not shown, but more fully described below), such as a motor, or magnetic drive in order that leaves 66 are controllably moved from fully open, fully closed or to any position between open and closed as described in greater detail below. The actuators can be suitably controlled by computer 74 and/or a controller. FIG. 4 is a block diagram of an exemplary control computer within a radiation modulation system. In this particular embodiment, the control computer would receive a treatment plan and would control delivery of the plan. As will be appreciated, many different configurations can be used to accomplish this purpose, and this is but one example. Radiation modulation system 200 includes control computer 210, beam source 230, multileaf collimator (MLC) 240, gantry 250, and patient support 260. Control computer 210 includes processor 212, memory 214, modulator engine 216, leaf position engine 218, user interface 220, gantry engine 222, and patient support engine 224. In some embodiments, a control computer may be implemented with several processors, separate computing devices, and otherwise be distributed. Processor 212 may load and execute programs stored in memory 214. The programs stored on memory 214 may be executed to perform the functionality described herein, including, gantry control, jaw control, patient support control and other functionality involved in administering a treatment plan. Modulator engine 216 may control all or a portion of the leaf motion and jaw motion, in order to deliver radiation to a patient in accordance with the treatment plan, may process information regarding the position of a leaf and generate a signal to transmit to a driver to move the leaf to a desired position, or control other components in order to ensure a proper delivery of a treatment plan to a patient. To ensure the desired dose is delivered, modulator engine 216 receives gantry position, leaf position and patient support position information from the gantry engine, leaf position engine and patient support engine, respectively. The modulator engine 216 may use the position information and control the required intensity modulation for the necessary dosage for a particular set of treatment parameters (e.g., gantry position and/or speed, leaf position, and patient support position and/or speed), in accordance with the treatment plan. The modulator engine provides control sequences for movement of an individual leaf or group of leaves to form a desired aperture or to modulate a beamlet of a shape in accordance with the treatment plan. In addition or alternatively, one or more jaws may also be opened, closed or repositioned in support of beam shaping, intensity modulation or combinations thereof. In another aspect, the modulator engine provides discrete position information for an individual leaf, a group of leaves, and one or more jaws to maintain, or move independently these components to rapidly create a desired beam shape or collimation, enabling treatments with combined volumetric and direct intensity modulation. The leaf positioning movements and jaw positioning movements may be performed according to desired settings within the treatment plan that correspond to a particular gantry position or speed, patient position or speed or other specific factors for an individual patient's therapy. Modulator engine 216 may be implemented as software stored in memory 214 and executable by processor 212 or a circuit or logic external to processor 212. Leaf position engine 218 may control and monitor the movement and position of one or more leaves within magnetically actuated MLC 240. Leaf position engine 218 may be implemented as logic, a circuit, or software that is stored in memory 214 and loaded and executed by processor 212. User interface 220 may provide text, graphical content, and other content to be provided through an output mechanism for a user. In some embodiments, user interface 220 provides an interactive graphical interface that provides a user with the current status of the radiation modulation system, treatment status and progress, and other information. Gantry engine 222 may control and monitor the position of gantry 250. The gantry position may be provided to modulator engine 216, processor 212 and other portions of control computer 210. Gantry engine 222 may be implemented as logic, a circuit, or software that is stored in memory 214 and loaded and executed by processor 212. Beam source 230 may provide a therapeutic radiation beam used to treat a patient. The beam may be a photon beam generated from a linear accelerator or other particle beam (e.g., proton beam) known in the art to provide treatment to a patient. Magnetically actuated MLC 240 includes leaves 242 and may be controlled by control computer 210 to adjust leaf position and provide leaf motion. Additional details of leaf position control and actuation are described below. Gantry 250 moves about the patient during treatment. The position of gantry 250 may be controlled and monitored by gantry engine 222 of control computer 210. The position of the patient support 260 (and the patient thereon) may be controlled and monitored by the patient support engine 224. Magnetically actuated MLCs in accordance with embodiments of the present invention, unlike conventional MLCs of the past (shaping and binary), enable more control for modulating radiation intensity across a beam field for delivering radiation during discrete gantry positions, during gantry rotation/movement, couch motion, target motion or any combination thereof. Embodiments of the present invention permit moving leaves of a collimator along the continuum of positions between open and closed, such as in conventional shaping MLCs and with a sufficient speed such that leaf sequencing or positioning will not be significantly influenced by any previous or future positions (open or closed for binary collimator) of any individual leaf. Stated another way, leaf speed is sufficient such that the mechanics of the MLC do not unduly influence the determination of leaf position at any given time for the delivery of a radiation therapy treatment or fraction. This capability enables the ability to modify or change apertures non-monotonically, thereby enabling new paradigms of treatment heretofore not enabled by conventional MLCs. As described above, conventional radiation therapy machines have used multileaf collimators with relatively slow moving leaves to shape a beam to specific desired shapes, and in this manner create a volumetric intensity modulation. FIGS. 5A-5D show a leaf in a magnetically actuated collimator, in accordance with embodiments of the present invention, where the leaf is in a fully open (state 1, FIG. 5A) or fully closed position (state 4, FIG. 5D). FIGS. 5B and 5C show a leaf in a magnetically actuated collimator, in accordance with embodiments of the present invention, where the leaf in state 3 (FIG. 5C) permitting 20% radiation transmission (i.e., 20% open position) and the leaf in state 2 (FIG. 5B) permitting 70% transmission or is in a 70% open position. Again, a highly responsive leaf of the discrete-shape binary MLC is one that can achieve a desired position along the continuum of fully opened and fully closed at sufficient speeds such that the mechanics of the MLC do not unduly influence the determination of leaf position at any given time for the delivery of a radiation therapy treatment or fraction. Referring to FIGS. 5A-5D, the leaf can move to any position in maximum amounts of −y and +y from a starting position of x, at sufficient speeds such that the mechanics of the MLC do not unduly influence the determination of leaf position at any given time for the delivery of a radiation therapy treatment or fraction, which may otherwise be referred to herein as the ability of the leaf or leaves to snap from one position or state to another. The limits of conventional shaping MLCs that contribute to the size of +y, −y are leaves driven by rotational motors or leaf screws which limit the speed at which the leaves can be moved. The ability of the discrete-shape binary collimator, in accordance with embodiments of the present invention, to snap from one state to another, in addition to the amount of time the collimator remains in one state versus another enables an increased ability to modulate radiation intensity over the course of a treatment fraction. The proposed MLC systems and methods described herein are able to leverage many of the benefits of each type of intensity modulation, volumetric and direct intensity modulation. Because of the high speeds of the leaves, this technology has the “snap-action” benefit of a binary MLC. Moreover, since individual leaves can be precisely controlled, and can quickly move-to and stop-at intermediate locations, each leaf can be used to create sub-beamlets or multiple intensity levels. This can be applied to a single-row style construction where each leaf covers one set of beamlets, or an opposing dual bank leaf configuration can be built where beamlets are defined by two or more leaves. Thus, this configuration has the volume intensity modulation aspects of traditional MLC's, but with the ability to directly intensity modulate beamlets as with binary collimators. In effect, each leaf can be quickly sent to any of a number of magnetically actuateds, at sufficient speeds such that the mechanics of the MLC do not unduly influence the determination of leaf position at any given time for the delivery of a radiation therapy treatment or fraction. Thus, arbitrary 2D patterns can be created very quickly. The resulting MLC can have the speed and simplicity benefits of a binary MLC, but with the flexibility and 2D beam shaping of a conventional shaping MLC hence the name magnetically actuated MLC. FIG. 6 illustrates exemplary method 500 for delivering radiation therapy utilizing a magnetically actuated MLC, in accordance with an embodiment of the present invention. It is to be understood that method 500 begins following initial patient set up (e.g., registering an on-line image (optionally utilizing MVCT) with a planning image, and adjusting the patient support, if needed, to properly align the patient for radiation delivery). Fluence map(s) are determined or generated according to the plan (step 510), the sum of which make up a treatment fraction. Radiation delivery for a treatment fraction is initiated by receipt of or access to a treatment plan for a patient. Initiating radiation delivery may include determining and setting the initial position of the gantry, the initial leaf position in the multi-leaf collimator, the initial jaws position for primary and secondary collimation (respectively) of the beam, and other initial actions known to those having skill in the art. It will be appreciated by the skilled artisan that this method may be used for other platforms for delivery of radiation therapy, such as a linear accelerator mounted on a six degree of freedom robot (See FIG. 23B for example). In this embodiment the fluence map from the treatment plan determines the collimation sequence, e.g., leaf position and time the leaf is in such position (step 520). The fluence map dictates a series of leaf states necessary to achieve the intensity profile of the fluence map. Thereafter, appropriate control signals are sent by the control computer to leaf actuators to move the leaves in accordance with the treatment plan, i.e., to the desired leaf positions for the desired time to achieve the fluence map. A leaf driver receives the control signals and imparts the commanded leaf movement in accordance with the planned fluence map for that beam, and this process is repeated for each leaf or group of leaves as needed to achieve the fluence map for that beam or gantry angle. The treatment fraction comprises delivery of multiple beams at multiple gantry angles, such that the sum of the delivered fluence maps make up the treatment fraction. It is to be appreciated that other treatment system components may be varied (e.g., dynamic gantry motion, couch motion, variable or servo linac output, etc.) in addition to the apertures of the magnetically actuated MLC. This description isolates the MLC in order to focus the discussion, and not by way of limiting the invention to any one use or aspect of the inventive MLC. At step 520, it is determined if the state of the collimator (i.e., beam or aperture shape) corresponds to or needs to be changed at any particular point within the delivery of a fluence map. This determination, as will be appreciated by the skilled artisan, will be driven by the treatment plan and will be implemented via leaf positioning accomplished as described herein. The position of each leaf is determined and then compared to the position from that collimator state (step 530). If a leaf is not in position, a drive signal is provided (step 535) until the desired position is reached. If the leaf is in the desired position (answer to step 530 is ‘YES’) then next at step 540 determines if the leaf is in the correct position for the correct or desired duration. If the leaf has not been positioned for the desired duration, then do not drive the leaf or alternatively send a hold signal to a leaf actuator (step 545). If the leaf has been in position for the desired duration, then the system may move that leaf to another position according to the fluence map or treatment plan. At step 550, the system looks at the next leaf to determine whether it is in position and for the desired duration (according to steps 530-545). After all leaves for a desired collimator state have been completed (answer to step 550 is ‘NO’) next adjust leaves accordingly to achieve another state (answer to step 555 is ‘YES’). If there is not another state (answer to step 555 is ‘NO’), then delivery of the fluence map or this portion of the treatment plan is completed. If there is another fluence map to deliver at the next gantry angle (answer to step 560 is ‘YES’) the method returns to step 510 to evaluate/adjust leaf positions accordingly to the steps of method 500. If there is not another treatment fluence map (answer to step 560 is ‘NO’) then the treatment/fraction ends (step 565). Over the course of a treatment fraction, a leaf driver receives control signals at various points throughout the treatment plan to set the leaves of a collimator at the appropriate state for the appropriate amounts of time. It is the treatment plan that, in one form or another, controls the leaf driver and the various states of the collimator. The treatment plan, as described and as will be appreciated by the skilled artisan, will have been developed to take advantage of the ability of the magnetically actuated collimator, in accordance with embodiments of the present invention, to snap from one state to an alternate state in order to deliver a better modulated intensity distribution than if the plan was made for conventional MLCs (either binary or shaping MLCs). The treatment plan, as will be appreciated by the skilled artisan, can utilize the snap movements of the collimator as well as delivering during rotation of the gantry and movement of the patient support to achieve increased abilities to modulate the intensity of the delivery. After providing control signals to change the state of the discrete-shape binary MLC or if no state change is required, the method loops back for the next point in the delivery of the treatment plan. The process of determining the position of each leaf in an MLC is described serially. It is to be appreciated that the steps of the method 500 may be conducted serially or in parallel for one or more leaves or where groups of leaves are moved together. The capabilities of techniques with conventional shaping MLCs using a monotonic sequence of shapes is more often a function of limitations of the conventional MLC's responsiveness or leaf speed than to the requirements of an optimized treatment plan. In contrast, leaf, and beamlet control in magnetically actuated MLC embodiments described herein may follow sequential or monotonic movements when called for by the treatment plan, but are not so limited. Individual leaf, leaf pair or beamlet control is controlled to a degree that movements are not limited to monotonic shapes, but rather responsive to the next desired state, and not dependent upon where in the continuum the next desired state may be located. In other words, at any moment in time the MLC controller may position a leaf to any position at sufficient speeds such that the mechanics of the MLC do not unduly influence the determination of leaf position at any given time for the delivery of a radiation therapy treatment or fraction. This contrasts to conventional MLC control schemes and MLC designs where the desired states are sequential or monotonic by necessity because of slower leaf speed. FIG. 7 is an isometric view of an exemplary magnetically actuated MLC having dual leaf banks, one on either side of the area 302 into which radiation is directed for collimation. In this specific embodiment, the leaves are driven by electromagnetic action. The leaves are supported by a pair of leaf guide modules 300 (one for each leaf bank) driven by components of an electromagnetic drive system in a pair of electromagnetic drive modules 400, one on each side of the collimator for each bank of leaves. The present invention can be applied to a single bank collimator, but a dual bank is a preferred embodiment. A two part support frame 97A, 97B (FIG. 8) runs along the length of the magnetically actuated MLC and is attached to each of the leaf guide modules 300 and electromagnetic drive modules 400 to support each of the components and insure proper alignment of each to the other. Additional details of magnetically actuated MLC 240 will become apparent in the figures that follow. Details of the electromagnetic drive module 400 are provided with reference to FIGS. 8-10 and 15-18. Details of the leaf guide modules 300 are provided with reference to FIGS. 12-14. Additional details of an exemplary leaf power system are provided with reference to FIGS. 21A-21C and 22. FIG. 8 is an isometric end view of one end of electromagnetic drive module 400 of magnetically actuated MLC 240 of FIG. 7. This view of the magnetic drive module 400 shows upper and lower openings 415, 425 in end plate 403 for one leaf bank of the preferred dual bank MLC of the present invention. In this view, distal ends 346 of drive portion 341 of leaves 340 protrude from the upper and lower openings 415, 425. Stationary magnets 392 are on either side of drive portion 341 of leaf 340, and serve as part of the leaf power system for moving the leaves, as discussed more thoroughly below. Also shown is upper leaf encoder 330 interacting with upper encoder reader 360 and upper flex circuit 460 (lower leaf encoder, lower encoder reader and lower flex circuit not shown). Referring to FIGS. 16-17, width W of drive portion 341 is smaller than width W′ of blocking portion 342 to facilitate packing a plurality of leaves 340 adjacent to each other while having stationary magnets 392 (FIG. 10) on either side of drive portion 341 for each leaf. Referring to FIG. 10, stationary magnets 392 on either side of drive portion 341 (which protrude from upper opening 415) are horizontally offset by approximately the thickness of one leaf from the stationary magnets 392 on either side of drive portion 341 (FIG. 9). The geometry and placement of leaves 340 in this embodiment facilitates efficient packing of leaves 340 adjacent to each other with magnets 392 on either side of drive portion 341. The skilled artisan will appreciate that other geometries are available to pack the leaves adjacent to one another and remain within the scope of the present invention. Embodiments of the design and operation of the leaf and encoder is discussed in more detail below with regard to FIGS. 15-18 and 20. FIG. 9 is an enlarged view of distal ends 346 of drive portion 341 of leaves 340 protruding from upper opening 415 of the electromagnetic drive module 400 of FIG. 8, also showing a portion of the flex circuit 460 and encoder reader 360. The plurality of leaf drive portions 341 are shown in section view. Additional details of the components of a leaf 340 including drive portion 341 are shown and described more fully below in FIGS. 15-18 and 20. The view of FIG. 9 illustrates the arrangement of the leaf drive section upper and lower portions 341A, 341B alongside stationary magnets 392. The lateral thickness of sections 341A, 341B are used to maintain the leaf coil 350/windings 348 in the desired relationship to magnets 392, as discussed more thoroughly below. Alternatively, the skilled artisan will appreciate that the coils can be in the place of the permanent magnets and remain stationary relative to the leaf, and the permanent magnets may be on board and move with the leaf. FIG. 11 is a top down view of the central portion 302 of the magnetically actuated MLC 240 of FIG. 7 showing inner leaf guides 301, aperture 1050 and 14 leaf pairs (1010-1039) in various positions between leaf guide inner supports 301. While 14 leaf pairs are shown more or fewer leaf pairs may be provided according to the design requirements of a particular system. In one preferred embodiment, there are 64 leaf pairs, in another embodiment there are 96 leaf pairs and in still another embodiment there are 32 leaf pairs. As will be apparent, radiation is collimated through this section 302 of the collimator. In FIG. 11, each leaf is positioned in a particular position to define a particular aperture or shape 1050 through which radiation may pass, also referred to herein as a state. Leaf pairs 1010 and 1011 through 1038 and 1039 are controlled using the control schemes and drivers described herein to enable simultaneous volume and intensity modulation. In alternative aspects one or more controllable jaws are used to provide primary collimation of the beam, defined by the inner edges 301i and the frames 97A, 97B (i.e., the jaws will block the open space between support frame B and leaf pair 1010/1011 and between support frame A and leaf pair 1038/1039). Additionally or alternatively, the one or more pairs of jaws may be adjusted to reduce the size of the primary collimated beam to smaller than the frame size. FIG. 12 is a perspective view of an exemplary leaf guide module 300 of a magnetically actuated MLC 240. The leaf guide module 300 has opening 321 sized to receive a plurality of leaves 340. The size of opening 321 varies based on the number of leaves used in a particular MLC design. A plurality of guide channels 322 is provided on the upper and lower surfaces of the guide about the opening. As best seen in FIGS. 13A and 13B, a portion of the leaf 340 is adapted for sliding arrangement into the plurality of guide channels 322. In this embodiment, primarily blocking portion 342 sits within guide channel 322, though driving portion 341 may also occupy some or all of the length of guide channel 322 as a leaf is moved into and out of a desired position. FIG. 13A is an end on view of leaf guide module 300 in FIG. 12 showing an end on view of the blocking portion 342 of seven leaves 340 within their respective guide channels 322. In a preferred embodiment, the leaves 340 will have a tongue and groove construction (FIG. 13B) to prevent leakage between adjacent leaves, as shown by reference number 341. There are edge portions 342a, 342b of the leaf blocking portion 342 adapted and configured for sliding within the guide channels 322. FIG. 14 is a perspective view of an exemplary curved leaf guide module 300. In this embodiment of leaf guide module 300, opening 321 has an arched shape in contrast to the substantially vertical alignment of the leaf guide embodiment of FIG. 12. A plurality of leaf guide channels 322 is provided in the leaf guide on the upper and lower portions about opening 321. FIG. 15 is a diagram of an exemplary control system 401 for a magnetically actuated MLC 240. In this specific magnetically actuated MLC embodiment, the leaf driver is an electromagnetic drive system 320. This figure presents an exemplary leaf 340 of an electromagnetic multileaf collimator 200. Control system 401 may include control computer 210, driver 320, leaf position encoder 330 and leaf 340. Preferably, additional encoder 360 may also be used to provide two forms of positional feedback, depending upon the specific encoder or positioning system configuration. Leaf 340 has a driving portion 341 and a blocking portion 342. Blocking portion 342 is shaped, adapted and configured for blocking the therapeutic beam, made of radio opaque material, preferably tungsten or tungsten alloy and is about 20-70 mm wide. Leaf driving portion 341, attached to blocking portion 342, provides structural support for blocking portion 342 as well as windings or coil 350 and any additional components needed or desired. As noted previously and shown in FIGS. 15-16, width W of blocking portion 342 is larger than width W′ of driving portion to facilitate efficient packing of the leaves in the MLC. There is a leaf position encoder 330 on driving portion 341. The placement of encoder 330 on driving portion 341 will vary depending on specific leaf design considerations. The number and type of additional components needed to be attached will vary depending upon the specific design of a magnetically actuated MLC. In this specific embodiment, leaf driving portion 341 includes components used for an electromagnetic driver (e.g., coils). The size, number and orientation of coils 350 will vary depending upon other factors such as the size, placement and the strength of stationary magnets 392 used in the embodiment of the magnetically actuated MLC, the dimensions available for the components and other factors. As presently envisioned, the number of coils 350 may vary, but the number of coils 350 exposed to electromagnetic drive module 400 and stationary magnets 392 remain approximately constant in order to apply a uniform force to driving portion 341. Alternatively, the skilled artisan will appreciate that the coils can be in the place of the permanent magnets and remain stationary relative to the leaf, and the permanent magnets may be on board and move with the leaf. It is to be appreciated that individual leaf 340 in a magnetically actuated MLC configuration may be modified depending upon the requirements of electromagnetic driver 320. In this exemplary embodiment of an electromagnetic driver, leaf 340 may include coil 350 made from windings 348 (FIG. 18). Control computer 210 receives signals from encoder 360/330 depending upon the specific position system used. In some embodiments, the signals may indicate position data captured by position encoder 330. Control computer 210 processes the received signals and determines whether leaf 340 is at a desired position. If the position of leaf 340 needs to be changed, control computer 210 signals driver 320 to change the position of the leaf Control computer 210 may also provide control signals to drive a magnetic field generated by coil 350. In some embodiments, control computer 210 may control the strength, activate or deactivate the magnetic field of coil 350 by adjusting current flowing through the coils. Additional details of magnetic drive and control are described herein with regard to FIGS. 20 and 21A-21C. In one alternative embodiment, the position encoder 330 on the leaf and the guide mounted encoder 360 are both fed into the control loop to more precisely control the motion of the leaf position. In one alternative embodiment, the position encoder 330 on the leaf and the guide mounted encoder 360 can be compared against each other as a form of secondary positional verification. In still another alternative embodiment, the controller could use current torque applied as a control input for leaf position control. Referring to FIGS. 15 and 22, driver 320 may receive a signal from control computer 210 to provide a current to coils 350 from electrical drive connector 605 (FIGS. 7 and 15). The current results in a magnetic field generated by coils 350. The magnetic field generated by coils 350 acts in concert with the permanent magnets 392 on either side of driving portion 341 within the magnetic drive module 400 to produce controlled leaf movement. Permanent magnets 392 may be arranged parallel to the coils 350. In some embodiments, permanent magnet 392 in magnetic drive module 400 may be at least twice the length of the coils 350 so that the magnet may apply relatively constant driving force to driving portion 341. Whatever the length of magnetic drive module 400, the number of coils adjacent to permanent magnets 392 preferably remains approximately constant so as to apply an approximately constant force to driving portion 341 for any given current and magnetic strength. Coils 350 may extend at least as long as a leaf so that it is controllable to the full leaf width. The coil length or the number of coils is influenced by the amount of desired leaf travel and desired force to move the leaf. The depicted embodiment shows a preferred nine coils, but the number of coils can be selected based on particular needs, for example three or six coils may be used. The skilled artisan will consider many factors, the power input required to move the leaves, and heat dissipation to name two, when selecting the number of coils and the length of the permanent magnets. For example, if a 6 cm leaf travel is desired, then the stationary magnets should be 6+ cm in length (the extra provided for margin), and the space occupied by the coils would preferably be twice that length, or 12+ cm to insure it always engages with the magnet through the entire leaf motion. The coil height is preferably as high as space will permit to make the motor more powerful or efficient. The magnetic fields from the coils and permanent magnet may result in movement of leaf 340 within a magnet and the leaf guide tracks to change the shape and size of the collimated opening aperture (See FIG. 11). A first magnetic field may be generated by a permanent magnet made of a material such as neodymium or other high density strong permanent magnet. The strength of the magnetic fields from the coils and the permanent magnets may be constant as the leaf is driven through the guides. In the preferred leaf embodiments, the coils are potted to the leaf with a material selected for its thermal, mechanical and environmental properties. Table 1 below provides some estimated specifications for 3, 6 and 9 coil embodiments of a leaf design, where the 9 leaf embodiment is estimated to move at least approximately 1 m/s with an acceleration of approximately 80 m/s2 (a trapezoidal acceleration rate with a peak velocity of approximately 2 m/s in approximately 0.25 ms). TABLE 13 Coil6 Coil9 CoilTotal Moving362.25374.07385.8Mass (gr)Accel Force Req'd28.9829.9330.85(N)Req'd Current5.913.052.10(amps)I{circumflex over ( )}R Heating287153108(watts)(28.7 @10%15.3 (@10%(10.8 @10%Duty)Duty)Duty)Req'd Voltage48.6350.2551.7(cold R) FIG. 16 is a side view of an exemplary leaf. A leaf 340 may include driving portion 341 and blocking portion 342. Driving portion 341 includes proximal end connected to blocking portion 342 and distal portion 346. Driving portion can have any suitable dimensions, but preferably is approximately 135 mm×35 mm. In this illustrative embodiment, driving portion 341 may also include a plurality of windings 348 to form coils 350. When current is applied to these coils, for example by electrical drive connector 605 (FIGS. 7 and 22), the interaction between these coils and the flux density created by the stationary magnets produces a force in the direction of motion desired. Coils 350 may be constructed from a conductive material, such as AWG copper wire. The diameter of the wire and the number of turns may be based on the amount of desired torque among other properties, for example, as will be appreciated by the skilled artisan. Alternatively, the skilled artisan will appreciate that the coils can be in the place of the permanent magnets and remain stationary relative to the leaf, and the permanent magnets may be on board and move with the leaf. Blocking portion 342 is sized and shaped to move within guide structure 300 (see e.g., FIGS. 12 and 13A). In one aspect, blocking portion 342 may be a composite structure made from different materials. In this embodiment, blocking portions 342 include first portion 370 and second portion 380. First portion 370 is preferably made from a radio opaque material such as tungsten or alloy thereof and forms all or nearly all of blocking portion 342. Second portion 380 (the portion not intended to block radiation, but rather move through the leaf guiding structure or motor support areas) is preferably made from a lighter or less dense material to minimize leaf mass (including without limitation aluminum or stainless steel), reduce friction and facilitate ease of leaf acceleration and deceleration. FIG. 17 is a perspective view of an exemplary pair of leaves 340 as would be oriented in the magnetic drive and leaf guide structures of the MLC of FIG. 12. Blocking portion 342 is sized and shaped to move within guide structure 300. Guide rails 342A and 342B on each side of the blocking portion 342 are adapted and configured for sliding cooperation with channels 322 in leaf guide 300. FIG. 18 is a cross-sectional view of leaf 340 having a tapered cross section resulting in varying thicknesses of blocking portion 342 and driving portion 341. In this view one coil 350 made of coil windings 348 is shown within driving section 341. Due to the tapered cross section shape of the leaf, windings 348 have the same number of turns but are arranged to accommodate the available space. FIG. 19 illustrates an exemplary discrete binary MLC leaf arrangement. A collimated field 1040 having a center line 1030 is provided by a pair of jaws or other collimator device (see FIG. 3). In the illustrative embodiment, two leaves form a complementary leaf pair for shaping and modulation of the collimated field 1040. For example, leaves 1010 and 1011 are one leaf pair. Leaves 1018, 1019 are another and leaves 1024, 1025 still another. Each leaf in each pair may be positioned anywhere within field 1040. The inner edges of each leaf within a leaf pair face each other and may create an opening, the collection of openings formed by each leaf pair forms aperture 1050. Aperture 1050 corresponds to an aperture of FIG. 11 previously described and is set according to a treatment plan. Following the method 500 (FIG. 6) an aperture 1050 is determined prior to administering radiation therapy to a patient in the treatment planning process, and occurs at a particular point during delivery of the treatment plan. Aperture 1050 may change according to a number of factors, such as for example, the three dimensional shape of the treatment area, intensity modulation, fluence, and beamlets within a treatment volume as described above. Embodiments of the highly responsive MLCs described herein achieve volume and intensity modulation alone or in simultaneous combination by providing snap state control. FIG. 20 is an exemplary method for using an electromagnetically driven discrete binary MLC (i.e., eMLC). The MLC is controlled as described above in the method 500 of FIG. 6 with appropriate electromagnetic drive signals used to move or hold each leaf in position depending upon the specific implementation of an electromagnetic drive system. The method steps described in FIG. 6 at steps 530, 535, 540 and 545 are thus met by providing drive, control and hold signals as needed to control leaf movement. FIG. 20 illustrates an exemplary method for delivering radiation therapy utilizing an electromagnetic multileaf collimator (eMLC). Radiation treatment for delivering a dose for a current treatment plan is initiated in accordance with a treatment plan. At any particular point in delivery of a treatment plan the state of the eMLC is obtained from the treatment plan. It is determined whether the present state of the eMLC matches the desired state. If yes, the treatment proceeds until the next point within the treatment plan where the same question is asked again. If the present state of the eMLC is not the same as the desired or planned state, then appropriate signals are sent to controller to snap the appropriate leaves to a different position to achieve the desired state. This desired state is maintained until the next point in the treatment plan, where a determination is made whether the present state of the eMLC is the desired state. If the state of an eMLC will be changed, in accordance with the treatment plan, then magnetic field control signals are provided to snap the appropriate leaves to the desired position to achieve the desired state. With reference to FIG. 15, the magnetic field control signals are initially sent by control computer 210 to driver 320. Driver 320 receives the control signals and provides a current to one or more coils to create a magnetic field in the particular coils of the involved leaf. The magnetic field generated by the coils cooperates with a magnetic field of the permanent magnets proximate to the coils and leafs to move the leaves in a desired direction. Optionally, the process repeats for leaves in the MLC. FIG. 20 illustrates an exemplary method 1200 for positioning a leaf using the electromagnetic control system 401 described herein. The steps shown are part of an overall MLC and treatment plan as described above in FIG. 6 and method 500. The method 1200 corresponds to decisions made in method 500 to move a leaf using an electromagnetic MLC control scheme (see FIG. 6). A desired leaf position is determined based on, for example and without limitation, gantry position, patient position, or desired fluence map according to a treatment plan as in steps 510, 520 above. The current leaf position and desired leaf position for field shaping are compared at step 1220. The comparison is used to answer the question “leaf in position?” asked in step 530 of the method 500 (see FIG. 6). The current leaf position for each leaf may be determined by signals provided by a flex circuit and encoder read head to control computer (FIGS. 8 and 15, for example). The desired location for each leaf may be determined as discussed with respect to steps 510, 520 above. A determination is made at step 1230 as to whether a leaf should be moved. A leaf is moved if the current position of the leaf does not satisfy the desired position of the leaf. If the leaf does not need to be moved, the process continues to step 1280 where remaining leaves are moved if needed. If the leaf does need to be moved, a current is applied to the leaf coil at step 1240. The current is applied by driver 320 of FIG. 15 which receives control signals from control computer 210 (see FIGS. 3 and 4). The current applied to the leaf may vary. At first, the current may ramp up to a level required to initiate movement of the leaf and overcome friction between the leaf and any object in contact with the leaf while at rest. A determination is made as to whether the leaf is near the desired position at step 1250. As current is applied to the leaf coil and the leaf changes position, the leaf position may be detected by a flex circuit and encoder read head. A leaf position “near the desired position” may be a position at which a braking current may be applied to slow down movement of the leaf such that it will stop at the desired position, preferably within approximately ±10 microns of the desired position. A braking current may comprise reducing current to the coils thereby reducing the magnetic field of the coils which will reduce the amount of force exerted on the driving portion, and friction will act to reduce the leaf speed. Alternatively, the current to the coils may be reversed in one or more of the coils to create an opposite magnetic field which acting in cooperation with the permanent magnetic field will act as a braking force in combination with friction. Alternatively a physical braking force in addition to normal friction from the guides could be applied. The skilled artisan will appreciate that many different forms of a braking force could be applied without deviating from the scope of the present invention, and that these are but a few examples. The point at which a braking force is applied, as will be appreciated by the skilled artisan, will depend on the system configuration and that of the control system dynamics, and if the detected position is not at the position where braking is to be applied, the method returns to step 1240. If the detected position is near the desired braking position, a braking current may be applied to the leaf coil at step 1260 such that the leaf will stop motion within approximately ±10 microns of the desired position. A determination is made at step 1270 as to whether the leaf is at the desired position. If the leaf is not at the desired position, the method 1200 of FIG. 20 returns to step 1260 where braking current is applied to the coil (alternatively to apply greater or lesser braking force (as applicable)) in the event the leaf has continued motion, or to 1240 to initiate or accelerate leaf motion in the proper direction, if the leaf is not in motion or not moving quickly enough. If the leaf is at the desired position, the position change for the current leaf is complete and the remaining leaf positions are changed if needed (step 1280). It will be appreciated that the method of FIG. 20 may apply to moving leaves in parallel as well as serially. Thereafter, adjusting the state of the eMLC proceeds according to the steps 555 and 560 for additional sequences, fractions of fluence maps according to the method 500. FIGS. 21A, 21B and 21C illustrate representative drive current schemes for various leaf positioning scenarios used in an electromagnetically actuated multi-leaf collimator. FIG. 21A illustrates a current pulse for a high power burst mode. This control mode will be described in conjunction with the leaf movement methods of FIG. 20. In this mode, the leaf control system is driven so as to move a leaf from one position to another as rapidly as possible. In this mode of leaf action, the system may apply maximum drive current in a short pulse based on time rather than position. In one aspect of this scheme, the leaf drive system may operate in an open loop scheme driving current without regard to input from positions sensors. In terms of the leaf positioning method in FIG. 20, if the state of the eMLC collimator needs to be changed these high current pulses may be considered part of either driving, braking or holding a leaf of an eMLC. In other words, in the high pulse rapid movement mode, the drive control signals move a leaf a rapidly as possible. Returning to FIG. 21A, this drive current profile also illustrates how the system is able to provide a peak drive current that is many times greater than the mean drive current (x). In one aspect, the peak drive current in the leaf control system is 50 times, 75 times or even 100 times the mean drive current x. In contrast, conventional systems operate with a peak current that is only about 2 times the mean peak current. FIG. 21B illustrates an exemplary drive control scheme for precise movement during leaf positioning that will be described in conjunction with the leaf movement methods of FIG. 20. This control scheme may be used to achieve the positioning and braking described in FIG. 20. The process of applying a current to a leaf (step 1240) will vary as the position feedback system indicates the leaf is in motion, at the desired movement (e.g., accelerating, steady state velocity, decelerating) or holding a desired position (i.e., no movement). The current demands for a leaf in these different states are different. For example, during the hold phase, the leaf control system provides a hold current to maintain the leaf position. The “hold phase” current level would likely be different from that needed to accelerate or maintain the velocity of a leaf. This process may include many cycles of steps 1230, 1240 and 1250 on a very small scale depending upon the precision of the positioning system and the desired degree of positioning accuracy during the hold step. FIG. 21C illustrates the use of the drive currents as a secondary position sensor. This figure illustrates the phase current drive (lower graph) used as a predictor for position (upper graph). In this way, phase current used to drive a leaf may be checked within the position control system as a secondary positioning indicator to the leaf position indicator (i.e., leaf position encoders or other positioning system used by the system—see FIGS. 13 and 22). FIG. 22 is an isometric view of an exemplary leaf driver circuit positioned between the magnet guide module 400 and the leaf support module 303 of FIG. 7. The power drive module 600 includes a drive connector 605 with a flex connector 610 extending into sliding electrical contact with a power connector or power pick up 615 on a leaf 340. The power pick up 615 provides current to the windings 348 of the one or more coils 350 via electrical connectors on the leaf driving portion 341. Power may be provided to the coils by a brushed type connection or a flexible circuit with either direct wiring from the flex to the coils or with some intermediate connector, which will be appreciated by the skilled artisan. As the specific examples of FIGS. 21A and 21B illustrate, embodiments of the highly responsive leaf control system are adapted and configured to provide individual leaf positioning solutions to provide both IMRT and, if needed, VMRT position solutions alone or in combination on a leaf by leaf basis. As a result, the magnetically actuated MLC, in accordance with embodiments of the present invention (the eMLC being one such embodiment), enables new treatment approaches with improved conformality and speed of delivery. FIG. 23A illustrates a radiation therapy treatment system 10 that can provide radiation therapy to a patient 14 utilizing MLCs in accordance with embodiments of the present invention. The radiation therapy treatment system 10 includes a gantry 18. Gantry 18 can support radiation module 22, which can include radiation source 24 and linear accelerator 26 operable to generate beam 30 of radiation. Though gantry 18 shown in the drawings is a ring gantry, i.e., it extends through a full 360° arc to create a complete ring or circle, other types of mounting arrangements may also be employed. For example, a non-ring-shaped gantry, such as a C-type, partial ring gantry, or robotic arm could be used. Any other framework capable of positioning radiation module 22 at various rotational and/or axial positions relative to patient 14 may also be employed. In addition, radiation source 24 may travel in a path that does not follow the shape of gantry 18. For example, radiation source 24 may travel in a non-circular path even though the illustrated gantry 18 is generally circular-shaped. The radiation therapy treatment can include photon-based radiation therapy, brachytherapy, electron beam therapy, proton, neutron, or particle therapy, or other types of treatment therapy. Radiation module 22 can also include modulation system 200 operable to modify or modulate radiation beam 30. Modulation device 200 provides the modulation of the radiation beam 30 and directs radiation beam 30 toward patient 14. Specifically, radiation beam 30 is directed toward a portion of the patient. The radiation modulation system in accordance with embodiments of the present invention is described in more detail above. Modulation device 34 can include collimation device 42, as illustrated in FIG. 3 and FIGS. 7-19. Collimation device 42 includes a set of jaws 46 that alone or in combination with the primary collimator defines and adjusts the size of aperture 50 through which radiation beam 30 may pass to provide primary collimation. Jaws 46 include upper jaw 54 and lower jaw 58. Upper jaw 54 and lower jaw 58 are moveable to adjust the size of aperture 50. FIG. 23B illustrates an embodiment of a radiation system 700 having a radiation source and modulation device mounted on a robotic arm. The radiation system 700 is similar to the radiation system 10 described herein. FIG. 23B includes a radiation module 720 similar to radiation module 22 including, for example, a linear accelerator and an embodiment of the modulation device is mounted on a robotic arm 746. The robotic arm 746 moves with 6 axes of motion under control of the computer controller 74 to position the radiation source 720 freely and in 6 degrees of freedom about the patient's body, up or down, longitudinally along the patient or laterally along the patient. Also shown are a pair of in room diagnostic imaging devices 730, 732 that direct one or more imaging beams 726, 732 towards the patient 14 and appropriate image receivers 734, 736. Radiation systems similar to those illustrated in FIG. 23B are commercially available from Accuray, Incorporated of Sunnyvale, Calif. under the Cyber Knife® product line. Additional details of this type of radiation treatment system are described in U.S. Pat. No. 5,207,223, issued May 4, 1993, titled “APPARATUS FOR AND METHOD OF PERFORMING STEREOTAXIC SURGERY,” by John R. Adler; U.S. Pat. No. 5,430,308, issued Jul. 4, 1995, titled “3-DIMENSIONAL RADIATION DOSIMETER,” by Feichtner et al.; U.S. Pat. No. 7,046,765 B2, issued May 16, 2006, titled “RADIOSURGERY X-RAY SYSTEM WITH COLLISION AVOIDANCE SUBSYSTEM,” by Wong et al.; U.S. Pat. No. 7,266,176 B2, issued Sep. 4, 2007, titled “WORKSPACE OPTIMIZATION FOR RADIATION TREATMENT DELIVERY SYSTEM,” by Allison et al; and U.S. patent application Ser. No. 11/824,080, filed Jun. 29, 2007, titled “ROBOTIC ARM FOR A RADIATION TREATMENT SYSTEM,” to Kuduvalli et al., now Publication No. US-2009-0003975-A1, published Jan. 1, 2009. In FIGS. 24-25, computer 74 includes an operating system for running various software programs and/or a communications application. In particular, computer 74 can include software program(s) 90 that operates to communicate with radiation therapy treatment system 10. Computer 74 can include typical hardware such as a processor, I/O interfaces, and storage devices or memory, keyboard, mouse, monitor. Computer 74 can be networked with other computers and radiation therapy treatment systems 10. The other computers may include additional and/or different computer programs and software and are not required to be identical to the computer 74, described herein. Computer(s) 74 and radiation therapy treatment system 10 can communicate with network 94 (FIG. 24). Computer(s) 74 and radiation therapy treatment system 10 can also communicate with database(s) 98 and server(s) 102. It is noted that the software program(s) 90 could also reside on the server(s) 102. Communication between the computers and systems shown in FIG. 24 can also occur through the digital imaging and communications in medicine (DICOM) protocol with any version and/or other required protocol. DICOM is an international communications standard developed by NEMA that defines the format used to transfer medical image-related data between different pieces of medical equipment. DICOM RT refers to the standards that are specific to radiation therapy data. FIG. 25 is a schematic illustration of software program 90. Software program 90 includes a plurality of modules that communicate with one another to perform functions of the radiation therapy treatment process. The various modules are adapted to communicate with one another to plan and deliver radiation therapy to patient 14. Software program 90 includes treatment plan module 106 operable to generate a treatment plan for patient 14 based on data input to system 10 by medical personnel, as previously described. The data includes one or more images (e.g., planning images and/or pre-treatment images) of at least a portion of patient 14. Treatment plan module 106 separates the treatment into a plurality of fractions and determines the radiation dose for each fraction or treatment based on the input from medical personnel. Treatment plan module 106 also determines the expected radiation dose for target 38 and surrounding critical structures based on contours drawn by the planner. Multiple targets 38 may be present and included in the same treatment plan. Software program 90 also includes patient positioning module 110 operable to position and align patient 14 with respect to the isocenter of the gantry 18 or other reference for a particular treatment fraction based on a registration of an on-line CT image (preferably an MVCT image) with the planning CT image, commonly referred to as patient setup. It will be appreciated other patient setup procedures are well within common knowledge of the skilled artisan. The image registration provides offsets to the patient positioning module 110, which instructs drive system 86 to move couch 82 to align the patient relative to the treatment delivery system prior to treatment delivery, alternatively patient 14 can be manually moved to a new position or couch 82 can be manually adjusted. Patient positioning module 110 may also control movement of couch 82 during treatment in accordance with the treatment plan. In a robotically mounted system the offsets may be used to direct the robot to deliver radiation to the desired location within the patient, as is well known by the skilled artisan. Software program 90 can also include image module 114 operable to acquire the on-line images of patient 14. Image module 114 can instruct the on-board image device, such as a CT imaging device, to acquire images of patient 14 before treatment commences, during treatment, and after treatment according to desired protocols. Other imaging devices may be used to acquire pre-treatment images of patient 14, such as non-quantitative CT, MRI, PET, SPECT, ultrasound, transmission imaging, fluoroscopy, RF-based localization, and the like. The acquired images can be used for registration of patient 14. Software program 90 can also include treatment plan module 106 and treatment optimization module 118; preferably these two modules are included as a software product, the output of which is an optimized treatment plan for a patient that is ultimately approved by clinical professionals and provides direction to the treatment delivery system for delivering radiation to a patient. Treatment delivery module 122 uses the treatment plan as an input to control and guide delivery of radiation to the patient. As previously described, the treatment plan will include, but is not limited to, providing leaf positions, jaw positions, gantry angles and angular speed, and couch speed. Referring again to FIG. 23A, radiation therapy treatment system 10 can also include detector 78, e.g., a kilovoltage or a megavoltage detector, operable to receive radiation beam 30. Linear accelerator 26 and detector 78 can also operate as a computed tomography (CT) system to generate CT images of patient 14. Linear accelerator 26 emits radiation beam 30 toward target 38 in patient 14. Target 38 and surrounding tissues absorb or attenuate some of the radiation. Detector 78 detects or measures the amount of radiation absorbed from different angles as linear accelerator 26 rotates around, which information is processed or reconstructed to generate images, preferably 3D CT images as is known in the art, of the patient's body tissues and organs. The images can also illustrate bone, soft tissues, and blood vessels. The CT images can be acquired with linear accelerator 26 delivering megavoltage energies or kilovoltage energies. Alternative gantry systems may permit acquisition of cone beam CT images. As will be appreciated by the skilled artisan, other sources of diagnostic x-ray energies (typically Kv energies) can be located on the gantry and be separate from the My therapeutic source. Radiation therapy treatment system 10 can also include a patient support, such as couch 82 (illustrated in FIG. 23A), which supports patient 14. Couch 82 moves along at least one axis 84 in the x, y, or z directions, but may also include the ability to control pitch, roll and yaw. As described previously, the control systems can control couch velocity in accordance with the treatment plan and to achieve the desired intensity modulation. Patient support systems are well known in art and will not be further described here. Various features and advantages of the invention are set forth in the following claims. |
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description | The present invention relates to the field of x-ray generators and more particularly to a shutter-shield system for enhancing the shielding and protection of personnel against stray X-ray radiation in the vicinity of an X-ray product inspection station in a manufacturing environment. In addition to their well-known use for medical examination, X-rays have found increasing use for inspection purposes in manufacturing, e.g. for inspecting food products in containers for impurities that can be detected as having higher density than the substance under test and thus greater attenuation of applied X-rays. In a typical food product inspection station, a shielded head-end unit including an x-ray source and an x-ray sensor scans containers of food or beverages as they are moved sequentially through the head-end unit at a rate that can typically range up to 1000 containers per minute. While the containers are typically closely adjacent, there may be unpredictable periods of time during which the flow of product on a conveyor is interrupted, causing random gaps of substantial distance between adjacent containers. Typically the x-ray source, sensor and conveyor driving mechanism are controlled from a control console which is located nearby in a separate enclosure and which may include a microprocessor along with electronic control and logic circuitry for implementing the inspection program. Despite efforts to collimate the x-rays from the generator, i.e. direct them in parallel straight lines, confined to the product item under test and the sensor, the X-rays tend to diffuse and scatter whenever they collide with matter, and to thus escape through any openings in the shield structure; therefore, in the work environment, tight shielding is required to protect workers from harmful cumulative effects of exposure to extraneous x-ray radiation. In the field of endeavor of the present invention where the product item is typically packaged food and beverage items such as bottled liquids moving along a conveyor, it is customary to surround the generator, product item under test, sensor and the associated portion of the conveyor with an enclosure constructed from high density X-ray shielding material; typically material of ultra high molecular weight is utilized to avoid excessive thickness requirements. Of particular concern are the entry and exit openings that are required for product to flow through the test station: x-ray leakage through such openings may be minimized by providing shield tunnels and/or shield doors, however their shielding effectiveness depends somewhat on full loading and uniform close spacing of product containers within the test station to minimize radiation leakage as the containers move through on the conveyor. A gap in the loading of product moving along the conveyor could result in increased radiation leakage during the corresponding time period as the gap enters and/or exits the test station. Since the health hazard effects of X-ray exposure are cumulative, the degree of risk is proportional to the product of exposure time duration and the level of radiation, so it is important to maximize the margin of safety by minimizing both the time duration and the level of the environmental radiation, and to take special measures to avoid even short periods of increased radiation levels. X-ray generators of known art commonly utilized for inspection purposes generally require a preliminary warmup time in the order of several minutes to recover to normal after being turned off. Furthermore, the life expectancy of the X-ray tube may be seriously impaired by frequently repeated on/off switching, so it is customary to run the X-ray generator continuously, even for periods of time when it is not required for testing. The level of x-ray radiation leakage that occurs during such standby periods is of particular concern with regard to overall environmental x-ray protection of personnel, especially if these periods tend to be lengthy and/or if the environmental radiation level tends to increase significantly in the absence of product in the inspection chamber, U.S. Pat. No. 6,400,795 to Yagi discloses an X-RAY FLUORESCENCE ANALYZER having an x-ray generator and a sensor enclosed in a common shielded enclosure configured with a large aperture providing passageway for both (a) outgoing radiation directed to an externally-located subject being analyzed for fluorescence and (b) reflected radiation returning into the sensor. An exposure-timing shutter opens and closes the aperture for each exposure event. Related U.S. Pat. No. 6,359,962 shows similar structure without a shielding outline. It is a primary object of the present invention, in the production work environment of a test station for X-ray inspection of products in containers moving along a conveyor, to provide improved worker protection against potential harmful cumulative effects of X-ray exposure through enhanced overall containment and suppression of potentially harmful effects of X-ray radiation in the environment around the outside of the test station. More particularly it is an object to minimize any increase x-ray radiation leakage from an x-ray food product inspection test station through entry and exit openings thereof related to the absence or non-uniformity of food containers under inspection. It is a further object to provide implementations of the invention that can be retrofitted onto existing x-ray sources such as those used in food product inspection stations, to enhance worker protection in the testing environment. The abovementioned objects have been met by the present invention of a shutter-shield system applied to a an x-ray generator located in a shielded enclosure of a station for inspecting products such as food or beverages in containers moving through the station on a conveyor. Deployed in a sliding attachment on a collimator housing of the x-ray generator, a shutter plate is made movable by an actuator and is configured with an aperture that, in the absence of power applied to the actuator, is made to align with a fixed aperture of the collimator so as to allow emission of the x-ray beam as required for normal inspection purposes. Whenever an anomaly in the product loading on the conveyer creates a gap at the entry and exit openings in the shielded inspection enclosure that could otherwise cause an increase in environmental radiation levels, powering the actuator moves the shutter plate to an offset location that offsets the apertures to an effectively closed state to initiate a standby condition wherein x-ray radiation is substantially confined to the interior region of the collimator, without having to shut down the x-ray generator itself. FIG. 1 depicts an X-ray collimator 10 configured with a cylindrical opening 10A within a clamping structure for engaging an X-ray tube in a conventional manner. Collimator 10, which may be a pre-existing or custom type, is fitted with a shield-shutter assembly 12 of the present invention in an illustrative embodiment. A front plate 10B is bolted or otherwise firmly attached to the front face of the collimator 10. Attached to the far side of collimator 10 and seen extending to the left is a support bracket 14 which supports a solenoid 16, attached as shown. Plunger 16A of solenoid 16 is coupled to a yoke plate 18 on which is attached a shutter plate 20 configured with an elongate vertical shutter aperture 20A as shown. The front plate 10B, yoke plate 18 and shutter plate 20 are made from materials having lead content and thus high molecular weight for effective x-ray shielding, e.g. brass, moderately leaded steel and highly leaded steel, respectively. Yoke plate 18 is captivated in a sliding manner to the collimator 10 by a pair of ball-bearing slide sets 22 and 22″ at the top and bottom respectively. A pair of coil springs 24′ and 24″ are attached at their left hand ends to yoke plate 18 and at their right hand ends to the collimator 10 via a pair of spring attachment blocks 26′ and 26″ attached to collimator 10 so as to extend slightly beyond its right front corner. In the preferred embodiment, the condition depicted in FIG. 1 is the default condition in which solenoid 16 is not energized. Tension in coil springs 24′ and 24″ holds the yoke plate 18 constrained against a stop block 28 which is attached to front plate 10B, thus the shutter assembly, including plunger 16A, yoke plate 18 and aperture plate 20, is held at the right hand end of its travel range as shown. A fixed aperture 10C similar in size and shape to the shutter aperture 20A is configured in front plate 10B and is located such that in this default state the two apertures are aligned to make this the open-shutter condition that allows the x-ray beam to exit and perform the desired inspection function. FIG. 2 depicts the items of FIG. 1, in the alternate closed-shutter condition with solenoid 16 having been powered so as to move plunger 16A and the shutter assembly including yoke plate 18 and aperture plate 20 to the left hand end of the travel range against the spring tension of coil springs 24′ and 24′ which have become extended as shown. The movement to the left is in a horizontal direction constrained to a linear path by the ball bearing slide assemblies 22′ and 22″. Due to the displacement of aperture 20A to the left, it is no longer aligned with the fixed aperture (10C, FIG. 1) in front plate 10B, thus the shutter is closed and the x-ray radiation is substantially restricted to the interior of collimator 10. The type of control system selected for actuating solenoid 16 depends on particular situation requirements and conditions, and could range from simple on-off control by a human operator to automatic operation in response to signal from sensors arranged to detect the loading of a conveyor and to thus invoke the closed-shutter condition whenever a void, stoppage or other anomalous condition is detected in the product load that might otherwise result in increased x-ray radiation exposure. While in the preferred embodiment, solenoid 16 is implemented as an electrically-powered electro-magnetic solenoid, typically controlled via an electrical relay as part of control system, its function to move the shutter assembly between its two states, open and closed, could alternatively be provided in some other equivalent form such as a pneumatic or hydraulic actuator, with suitable control apparatus. Other forms of energy transducers and couplings such as linear motors, gears and pinions could be utilized to actuate the shutter assembly. As an alternative to the above described embodiment wherein the default condition is made to be the open-shutter condition, the default condition could be made to be the closed-shutter condition by locating the fixed aperture to align with the shutter aperture 20A when the solenoid is not powered (as in FIG. 1). The choice between these two possible locations of the fixed aperture is a matter of design choice with tradeoffs relating to energy-efficiency, depending on the overall duty cycle with which the x-ray is being operated, and considerations in the event of failure of the solenoid or its power source. The choice made for the preferred embodiment was based on the advantages that, under anticipated conditions of near 100% overall duty cycle, the absence of holding power in the solenoid represents an energy saving, and in the event of failure of the solenoid or its power source fail, production could continue without interruption pending corrective action. As an alternative to the spring-loaded system that requires continuous holding power at one of the shutter travel range, it is mechanically possible to utilize a toggled system that requires power only during the period of transition between the two states, i.e. moving the shutter aperture in or out of alignment with the fixed aperture. As an alternative to the linear travel system disclosed, the principle of the invention could be practiced with equivalent alternative mechanical arrangements to move the shutter plate in the desired manner to place the two; for example the shutter plate movement could be rotational to implement the two states. The invention may be embodied and practiced in other specific forms without departing from the spirit and essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description; and all variations, substitutions and changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. |
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abstract | Methods and apparatus for generating an x-ray image. An object is interposed between a detector and an x-ray source. A grid is interposed between the x-ray source and the object. The grid is exposed to primary x-ray energy generated by the x-ray source, thereby exposing the object to a first portion of the primary energy via the interstices of the grid. A second portion of the primary energy is received with first areas of the detector corresponding to the interstices of the grid. Secondary x-ray energy is received with the first areas of the detector and with second areas of the detector corresponding to the elements of the grid. The secondary energy results from scattering of the primary x-ray energy. Image data are generated by altering data from the first areas with reference to data from the second areas. |
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053213270 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGS. 1, 2 and 3 a vortex chamber 1 is formed of a circular, substantially cylindrical wall 2, a hemispheric inward curved fuel inlet end wall 3 and a fuel-air injection arrangement 4 within the hemispheric fuel end wall 3, and an opposite circular exhaust end wall 6 which is also substantially inward curved and has a centrally located exhaust tube 7 with an exhaust inlet 8 located in the central axis of the vortex chamber 1. A shroud 9 composed of a cylindrical part 11 and a hemispheric part 12 encloses the vortex chamber 1, forming between the vortex chamber walls and the shroud 9 an air space composed of a circular hemispheric part 13 and a cylindrical part 14. The air space 13 has an air inlet 16 connected to a compressed air source (not shown) which injects air tangentially into the air space 13, wherein the air is preheated by contact with the hemispheric wall 3 and spirals along a spiral line indicated by arrows A, as also seen in FIG. 2, into a mixing chamber 17, wherein the preheated air is mixed with fuel entering a fuel line 18 and is finely dispersed from a fuel injector nozzle 18. It follows that the injected fuel can be liquid fuel under pressure so that it is finely dispersed, or can be in gaseous or vapor form, or can even, with a suitably adapted injector nozzle 19, be injected as a fine solid fuel dust or powder. A tube 19 can serve to inject a sodium or potassium compound which, if necessary, serves to enhance the ionization of the combustion gases to make them better conductors for electric current as described in more detail below. From the mixing chamber 17 the fuel-air mixture enters a plasma expansion cone 21 wherein the fuel-air mixture is ignited by a spark ignitor 22, and expands rapidly as it burns, and forms an outer vortex as indicated by arrows B, and wherein the hot swirling still expanding gases move in a spiral along the inside of wall 2 of the cylindrical part of the vortex chamber 1 toward the opposite end wall 6, from where the expanding gases are turned inward into an inner vortex indicated by arrow C. The two vortices together form an imploding plasma vortex wherein the gases in the outer circular strata are under high pressure and at high temperatures, while the gases in the inner strata are under lower pressure, even under certain circumstances below atmospheric pressure, and at lower temperatures, but are rotating at very high velocity compared with the plasma in the outer strata. The high rotational velocities in the imploding vortex creates a gravitational gradient in the vortex which, combined with the frictional forces between the strata moving at different velocities cause a separation of the lighter and heavier particles of the plasma, with the heavier particles drifting to the perimeter and the lighter particles to the center. Since the heavier and lighter particles have opposite electrical polarities, the outer wall 6 of the vortex chamber 1 becomes charged to one polarity and the inner structure of the vortex chamber become charged to the opposite polarity. These charges are taken off by means of suitable connected electrodes and voltage converter as described in more detail below. As described above, the particles of the hot plasma rotate in the same direction in the outer and inner strata but are moving axially in opposite directions as shown by arrows B and C in FIG. 1. Part of the hot plasma leaving the expansion cone 21 separates from the main flow at a region 23, indicated by a dashed line circle (FIG. 1) with part of the plasma following arrow D to enter the part 24 of the vortex chamber 1 bounded by the hemispheric end wall 3, wherein the separating plasma forms a secondary imploding vortex, which re-enters the plasma expansion cone 21 via slanted vanes 26 projecting inward or rearward from the expansion cone 21 so as to "catch" part of the plasma of the secondary imploding vortex. The plasma of the secondary vortex re-enters the main vortex, indicated by arrows B and C and insures a high degree of combustion of all parts of the plasma which further insures that the exhaust gases exiting via exhaust tube 7 as indicated by arrows E are almost completely broken down into their basic constituents, composed essentially of nitrogen, carbon dioxide and water vapors. A test analysis of exhaust gases from a supportive prototype using combusted diesel fuel has shown readings of carbon monoxide (CO) of 75 ppm, carbon dioxide (CO2) of 23.5 ppm, sulphur dioxide (SO2) of 0.02 ppm, general hydrocarbons (CHx) of 0.12 ppm, and the remainder of nitrogen (2) and water vapor (H2O) The central structures of the vortex chamber 1 include the above described exhaust tube 8 and magnetic elements that produce a radially extending magnetic field in the cylindrical part of the vortex chamber 1, indicated by arrows E which extend from a conical central magnet 27 and a circular ring shaped peripheral magnet structure 28. The central magnet 27 is an inward tapering conical or cylindrical magnet supported in a circular electrically insulating ceramic body 29 so that it is electrically insulated from the metallic walls of the vortex chamber 1 and the shroud 9. The magnetic elements 27,28 may be permanent magnets or electromagnets and are polarized such that the magnetic field extends radially for example from conical magnet 27 to peripheral magnet 28. The rotation of the ionized plasma in the vortex chamber 1 causes an electromotive force to be formed between the central structures, i.e. the exhaust tube 7, the conical magnet 27 and the peripheral structures, i.e. the cylindrical wall 2 of the vortex chamber. This electromotive force reinforces the electromotive force created by the separation of the electrically charged particles of the rotating gas plasma, described above. The two electromotive forces bridge the gap between the central structures and the peripheral structures of the vortex chamber 1 and can be tapped off at terminal 31 connected to the central exhaust tube 7 and terminal 32 metallically connected via connector 41 to the wall 2 of the vortex chamber 1. Circular electric insulators 45 are placed on each side of connector 41 to insulate it from cylindrical wall 11 and the hemispheric wall 12 of the shroud 9. Similarly, respective circular electric insulators 50 and 50a are placed between the exhaust end wall 6 and the magnetic structures 27 and between magnetic structures 27 and shroud 11 to prevent electric charges on the central magnetic structures from being short-circuited to the end wall 6 and shroud 11. Terminals 31, 32 are connected via conductors 33, 34 to an electric voltage converter 36 that converts the electrical energy tapped off at terminals 31, 32 to a voltage at output leads 37 that is suitable for external use. A heat protective lining 38 of a heat resistant material such as high temperature alloy or graphite or the like is applied to the inside surface of the vortex chamber wall 2. A second air inlet 16' is, like inlet 16, connected to an external source of compressed air which is similarly injected tangentially into the air space 14 where it spirals in direction indicated by arrows F to join the air injected at air inlet 16, while it is preheated by contact with the hot vortex chamber wall 2 and at the same time helps to cool the outer surface of the cylindrical wall 2 and the ring-shaped magnet 28. FIG. 2 shows the interior of the electric generator seen along the line 2--2 of FIG. 1, wherein compressed air enters at air inlet 16 and spirals toward the center as shown by arrows A until it enters the mixing chamber 17 as described above, and from there enters the plasma expansion cone 21. The radially extending slanted vanes 26 are also seen in FIG. 2. FIG. 3 shows the interior of the electric generator seen along the line 3--3 of FIG. 1, wherein the exhaust tube 7 with inlet 8 is seen in the center, surrounded by the conical magnet 27. The magnetic lines of force indicated by arrows E are shown radiating from conical magnet 27 to the ring shaped magnet 28, seen through air openings 39, formed in a circular metal plate 41 also seen in FIG. 1, which in axial direction separates the cylindrical wall 2 and the hemispheric end wall 3 of the vortex chamber 1, and radially serves to separate the walls of the shroud 9 from the walls of the vortex chamber 1. The circular metal plate 41 has an extension 41' which serves as an attachment point for electric terminal 32, also seen in FIG. 1. The spark igniter 22 (FIG. 1) has an insulated center electrode 22' that at one end reaches inside the plasma expansion cone 21 and is at the other end connected to an electric spark generator 42 which starts and/or maintains ignition of the fuel-air mixture entering the plasma expansion cone 21. FIGS. 4 and 5 show an embodiment of the invention having a spherical vortex chamber 51 divided symmetrically into two chamber parts 51 and 51'. Since this embodiment is symmetrical about a symmetry plane 66, except for the second air inlet 57', the following description relates to the right hand part, while the symmetrical left hand part has elements shown with primed reference numerals. A hemispheric chamber wall 52 encloses a plasma expansion cone 63, connected at its narrow end to a conical mixing chamber 54, connected at its wide end to a hemispheric air space 56 receiving air injected at air inlet 57 connected to a source of compressed air, not shown. Compressed air enters air inlet 57 tangentially to the air space 56 and moves in a spiral shaped path indicated by arrows F, while it is preheated by contact with hemispheric wall 52 and enters the mixing chamber 54, wherein it is mixed with fuel entering from a fuel chamber 58 receiving fuel in either vaporized form from a fuel vaporizer 59 or in gaseous form from a gas fuel injector 61, as described in more detail below. Fuel from the fuel chamber 58 flows through apertures 62, enters the mixing chamber 54, from where the fuel-air mixture next enters a plasma expansion cone 63, and is ignited by an ignitor 65 connected to a spark generator not shown but similar to spark generator 42 in FIG. 1. Protective heat linings 60 and 70 are deposited respectively on the inner surface of the hemispherical wall 52 and the plasma expansion cone 63. The heat shields are advantageously made of graphite, alumina or high temperature metallic alloys. The air entering tangentially from air inlet 57 maintains its spiral motion as it travels through air space 56, mixing chamber 54 and as it expands, after ignition, through the expansion cone 63. The expanding burning gases form an imploding vortex as indicated by arrow G that spirals toward the symmetry plane 66, where it meets an oppositely rotating vortex forming in the opposite halfpart of the generator indicated by arrow G', wherein the two oppositely rotating air masses of hot gas plasma cause a separation of the electrical particles in the plasma. Due to the inherent instability of a mass of gas plasma system, electrical particles of opposite polarity drift to opposite sides of the vortex chamber 51. The two hemispheres 52, 52' made of conducting material receive the oppositely charged particles, so that their energy can be tapped off et respective electrical terminals 67, 67', connected to an electric energy converter as shown in FIG. 1. Terminals 67, 67' are electrically insulated by means of insulators 80, 80' from the respective flanges 77 and 77' of the hemispheric walls 52, 52'. It follows that in all cases wherein electric insulators are provided, the connecting bolts, e.g. bolts 79 in FIG. 4, which bridge the insulators must also be mounted in electric bolt insulators so as not to negate the insulating effect of the insulators. These bolt insulators are not shown in the figures in order to maintain clarity. During operation, a sustained imploding vortex is maintained in each halfpart of vortex chamber 51. The imploding vortices indicated by arrows G and G' each move axially toward the symmetry plane 66, and continue rotating while expending to the perimeter of the hemispheric walls 52, 52', from where they return following the contour of the hemispheric walls as they move toward the respective mixing chambers 54, 54', from where part of the gases are drawn into the mixing chambers by the slanted vanes 68, 68', which draw part of the burning and rapidly rotating gases into the mixing chambers 54, 54', from where the gas particles re-enter the imploding vortices in a manner similar to the operation described above for the first embodiment. The exhaust gases leave the vortex chamber 51 through exhaust tubes 64, 64', as indicated by arrows H, H'. An electrically insulating center separator 69 of a heat resistant electrically insulating material such as ceramic or alumina or the like is located at the center plane 66, and serves to electrically insulate the two hemispheres 52, 52' from each other to prevent short-circuiting the electrical power output. A fuel vaporizer 59 also indicated in FIG. 1 serves to preheat and vaporize liquid fuel entering at fuel line 71 via a one-way valve 71a. Various forms of fuel vaporizers are shown and described in more detail below. FIG. 5 is a view of the interior of the electric generator shown in FIG. 4, seen along the line 5--5 of FIG. 4, wherein the exhaust tube 64 is seen in the center, surrounded by apertures 62. The shaded area 63 shows the face of the plasma expansion cone 63. The circle 71 indicates the inner perimeter of a central opening in the center separator 69. The area between dashed line circles 72, 73 indicate the flange 74 by which the two hemispheres 52, 52' are joined by means of bolts or rivets 76 (FIG. 4). Beyond the air space 56 there is shown a flange 77 by which the hemispheric outer walls 78, 78' defining the air space 56, are joined by means of bolts or rivets 79. In a different mode of the invention according to FIG. 13, instead of setting the air masses in the two symmetrical halfparts 52, 52' in opposite rotation, the air masses can be set to rotate in the same direction simply by relocating the air inlet 57' to position 57", where it is located juxtaposed to inlet 57. As a result, the electric charges caused by the parallel rotation of the plasma gas masses will cause oppositely electric charged particles to be deposited respectively on the inner structures formed by the expansion cones 63, 63' which will assume one polarity and the outer structures formed by hemispheric walls 52, 52' which will assume the opposite polarity. It follows that in this embodiment the hemispheric walls 52, 52' are electrically connected together and to the electric terminal 67', while the inner structures composed of the expansion cones 63, 63' and the walls of the conical mixing chambers 54, 54', or other suitable inner structures, form the opposite pole insulated by means of circular electric insulators 116, 116'. Electric take-off means in the form of electric conductors 117 and 117' are connected via terminals 118, 118' to the expansion cones 63, 63' so that an electric potential difference is present between terminal 67' and the two conductors 117, 117'. The two conductors 117 and 117' are threaded through exhaust tubes 64, 64' through insulators 119, 119' in the wall of exhaust tubes 64, 64'. FIGS. 6, 7 and 8 show various forms of fuel vaporizers 59 which can be used in both embodiments of the invention to vaporize liquid fuel. In FIG. 6, liquid fuel entering at fuel pipe 71 traverses a coiled tubular heating element 82, wherein it is vaporized and enters a vapor chamber 83' from where it exits through vapor tube 84. The heating element 82 is heated by current from an electric power source 86, connected thereto via conductor 87, a metallic body 88, the walls 89 of vapor chamber 83 and return path terminal 91. FIG. 7 shows a vaporizer of similar construction as shown in FIG. 6, but having the vapor tube 84 insulated by an electric insulator 92 from the walls 89 of the vapor chamber 83, and having an electrolyzing power source 93 connected via conductors 94, 96 to the vaporizer for applying an electrolyzing potential to the vapor tube 84, so as to electrolyze fuel vapors issuing from vapor tube 84. FIG. 8 shows a vaporizer having a heating element composed of series-connected concentric tubular elements 97, 98 made of resistive electric material heated by electric power source 86 via conductor 99, terminal 101, fuel pipe 71, conducting body 88 and return conductor 102. An outer tubular electrolyzing element 103 is connected to an electrolyzing power source 93 via conductor 103. The electrolyzing power source 93 is connected to electric power source 86 via conductor 104 and terminal 101. FIGS. 9 and 10 show a fuel vaporizer for vaporizing large fuel flows, having a liquid fuel inlet line 106 connected to fuel dispersing spray nozzle 107 which sprays fuel into a reticulated metal heating element 108 having a honey-combed cross-section as shown in FIG. 10, and which is heated by electric current supplied by an electric power source 86 via conductors 109, 111. The fuel is vaporized in heating element 108 and exits at fuel vapor outlet 112. The heating elements 108 and 113 are supported within electrically insulating containing structures indicated by respective reference numerals 100 and 105 so as to avoid short circuiting the heating elements. FIGS. 11 and 12 show a vaporizer of similar construction as in FIGS. 9 and 10, but having a heating element 113 made of porous metal instead of a honey-combed heating body as in FIG. 9. The internal metallic surfaces of the vaporizers shown in FIGS. 6, 7, 8, 9 and 11 may be coated with a catalyzing element, which enhances the catalyzation of the fuel vapors, such as elements platinum, paladium, nickel or the like. |
047822317 | description | DETAILED DESCRIPTION The invention is further described with reference to a number of examples. It will be understood by skilled practitioners that these examples are illustrative, and do not limit the scope of the invention or the appended claims. EXAMPLE 1 With reference to FIG. 1, the main generator column 1 is cylindrical and has a ratio of diameter to height of 1:3-5. The main column 1 is made of zirconium or aluminum, and has an upper flange 2 and a lower flange 3 of the same material. Each flange is affixed to the column as shown, and each is welded shut at the end opposite the column, to form a hermetic seal. Upper flange 2 is provided with a narrower and slightly conical extension tube 22. The lower flange 3 is threaded and has an extension tube 23. The column is filled with a target material 6, such as zirconium molybdate dried at 50.degree. C. and dispersed in particles ranging in size from 50 to 100 .mu.m (270 to 140 mesh). The target material is sealed within the column by sinter 4, of porous aluminum or zirconium oxide, at the lower end of the main column 1 near flange 3; and by a plug 5 of quartz, aluminum composite, or graphite felt an the upper end of column 1 within flange 2. Prior to irradiation, as discussed above, the entire main column assembly is wrapped in aluminum foil to prevent contamination, particularly of the flanges 2 and 3. After irradiation, the foil is removed from the column assembly under sterile conditions, and the welded ends of flanges 2 and 3 are opened by grinding or filing. The threaded lower flange 3 is then connected to a threaded end-piece 8 into which a seat 7 of silicon rubber is inserted. The end-piece 8 is connected to an L-shaped discharge tube 12. A supply tube 11 is affixed to flange 2. EXAMPLE 2 FIG. 2 shows a cylindrical main column 1 made of aluminum or zirconium as in FIG. 1. The column 1 is provided at its lower end with a flange 3. The flange 3 is slightly conical at the interior, where it meets column 1, and contains a discharge tube 24 that terminates with a widened part and a conical internal opening 25. The flange 3 and discharge tube 24 are closed by cap 9 and aluminum foil 21 having no conical recess on the internal side. The column is filled with zirconium molybdate particles 6, which have been dried for several days at room temperature. The particles range in size from 10-150 .mu.m (100-200 mesh). The lower end of column 1 is sealed by a porous sinter 4 of silicon dioxide. The upper end is sealed by plug 5 of graphite felt, beyond which is another cap 9 and foil 21. The column is irradiated according to the invention and is then transferred to a sterile environment. The caps 9 and foil 21 are treated with a disinfecting solution. The column 1 is then connected to sterile supply tube 11 and sterile discharge tube 12 at its opposite ends by piercing the foil 21 at each end, and firmly inserting the respective tube 11 or 12 to achieve a tight fit. EXAMPLE 3 FIG. 3 shows a symmetrically closed embodiment. Main column 1 is aluminum or zirconium and has a diameter to height ratio of 1:2-5. Identical threaded flanges 2 and 3 are welded to column 1, flange 2 at the upper end and flange 3 at the lower end. Within each flange are tubes 27 closed by caps 9 packed internally with aluminum foil 21. Target material 6, such as titanium molybdate dried at 40.degree. C. and having a particle size of 70-150 .mu.m (100-200 mesh), is placed within the column. The target material is sealed within the column by plugs 5. After irradiation, caps 9 are removed in a sterile environment and supply tube 11 and discharge tube 12, each with an end-piece 8, are screwed in place. EXAMPLE 4 FIG. 4 shows an assembled generator of the invention. The main column 1 with supply and discharge tubes 11 and 12, as described in Examples 1-3 and 6 and as shown in FIGS. 1-3, is placed within a primary transport container 13 made of lead or depleted uranium. The tubes 11 and 12 are placed within openings in the container 13 during transport, and their ends are aseptically sealed against bacterial contamination by plugs and/or wrapping. Container 13 has a cover 14 with a spherical handle 28 to facilitate manipulation of cover 14. The cover 14 is held securely in place by at least two screws, or by some other known method, such as rectangular hoops or friction clamps secured around the container 13. For transportation to the end user, these components are placed in a protective sheet container (not shown). Upon arrival at the use-site, the column 1 and container 13 assembly are removed from the protective container and placed in a laboratory container 15. Lab container 15 is a thick-walled vessel made of lead or depleted uranium. The sealed outer end of supply tube 11 is broken and, without loss of sterility, is connected to vessel 16, which contains a sterile apyrogenous physiological solution. The sealed outer end of discharge tube 12 is broken and, without loss of sterility, is connected to protective column 17, which contains a sorbent, such as hydrated zirconium oxide. The protecting column 17 in turn is connected to the piercing head of evacuated, flanged, and sterilized penicillin-type bottles 18. The bottles 18 are situated in a thin-walled lead container 19. The components are placed within a cylindrical enclosure 20 that is provided with cavities to house them. Enclosure 20 itself fits within a circular recess of lab container 15. Each elution is performed by placing an evacuated bottle 18 on the piercing head. In response, a corresponding volume of solution is sucked from vessel 16, passes in through supply tube 11, through main column 1, out through discharge tube 12, into column 17 and finally into bottle 18. The eluate, having passed through the sorption material 6, contains .sup.99m Tc radionuclides when it reaches bottle 18. When elution is complete, the sterile seal is maintained by placing a non-evacuated bottle 18 over the piercing head. EXAMPLE 5 In another embodiment of the invention, the elution generator may be supplied to the user in an assembled version, substantially as shown in FIG. 4. The main column 1 is stored in lab container 15 by the manufacturer and the entire device is shipped to the user. This embodiment requires a stronger connection between enclosure 20 and cover 14, such as a heavy threaded bar. EXAMPLE 6 In its simplest embodiment, not illustrated, the main column can be made of a quartz tube narrowed conically at both extremities, containing target material (ie, zirconium molybdate particles 100-150 .mu.m in size; dried at 60.degree. C.), and fused closed. The target material is packed tightly in the narrow ends of the column by quartz wadding. Prior to irradiation, the sealed column is wrapped in aluminum foil. After irradiation, the narrow ends of the column are cut and broken close to each end by a vidium knife or a file. Bacterial infection is prevented by careful flaming of the ends. Supply and discharge hoses, preferably of silicon rubber, are affixed to the ends of the column. The column is shielded by a simple coiled lead sheet within a laboratorium arrangement and is connected to a vessel, such as a birette or a separating funnel, containing the elution solution. In yet another embodiment, the quartz column can be used in a more complex apparatus as shown in Example 4. In operation, the elution generator of the invention, comprising primarily the main generator column, can produce a standard .sup.99m Tc elution of several GBq for a medium intensity neutron flux of 2 to 5.times.10.sup.17 n/m.sup.2 s. The columns of the invention are manufactured in a nonactivated state, which makes their manufacture much easier and safer. Later activation of the column also permits a single activation and sterilization step. The apparatus as a whole may be manufactured and delivered as components which are readily interconnected for use. In addition, the main column can be supplied separately, and through and independent delivery chain, whereby it may be activated by irradiation in a local reactor. This is a particularly important consideration in developing countries. Activation of the column itself and its contaminants (if any) is not a problem, nor is safe transport after irradiation, because the "extra" activity is always equal to or less than that of .sup.99 Mo. The invention as a whole is advantageous because it permits the use of a reactor with a medium intensity neutron flux which are more readily available than these which provide the high intensity activation required by conventional generators; it benefits from a simple and elegant design in manufacture, delivery and use; it achieves simultaneous sterilization and activation of the main elution column; and it permits independent delivery of activated and nonactivated components. |
039393666 | summary | The present invention relates to a method of converting radioactive energy to electric energy and a device for performing the same method. There is known a method of atomic energy power generation in which nuclear fission energy is converted to thermal energy and thermal energy is further converted to electric energy. With the development of such atomic energy power generation, there has been a rapid increase in the amount of radioactive substance; resulting from the reprocessing of used nuclear reactor fuel and in the radioactive fission products of nuclear reactors. Research is being carried out to find uses for these radioactive substances and, in particular, research is actively being carried out toward the development of a device for converting the radioactive energy emitted from such substances to electric energy. That is to say efforts are being put into the development of an atomic energy battery. Heretofore, there have been known a variety of methods for converting the radioactive energy emitted from radioactive substances into electric energy and, in general, these conventional methods can be classified into the following four systems on the basis of the converting mechanism. A. Direct converting system: Radioactive energy emitted from the radiocative substance is directly converted to electric energy. More particularly, in one example of the system conversion is accomplished by either (i) inserting a radioactive substance (.alpha. radiation source) into a vacuum glass container, the inner wall of which is silverplated and is used as the collector electrode or (ii) surrounding a radioactive substance (.beta. radiation source) disposed in a vacuum container with a solid state dielectric which serves as the collector electrode. However, with this system, the conversion efficiency is low, being less than 0.05%, and thus this system has not been put to practical use. B. Two-step type converting system: This system utilizes two steps for the energy conversion, i.e., radioactive energy emitted from the radioactive substance is used first to induce a certain physical phenomenon and then the phenomenon is caused to produce electric energy. Examples of this system which have been known are (i) to produce electron-hole pairs in a semiconductor by irradiating the semiconductor with a radioactive ray from a radioactive substance and then to derive electric current resulting from an electric field generated at the P-N junction of the semiconductor which causes electrons to move toward the N type region thereof and the holes toward the P type region thereof, (ii) to produce recoil electrons due to Compton scattering by surrounding a radioactive substance (.gamma. radiation source) with an insulating material and then to collect the recoil electrons and (iii) to polarize a gas introduced into the space between a pair of electrodes of metals, whose work functions are different from each other, by irradiating the gas with a radioactive ray from a radioactive substance or by introducing a gaseous radioactive substance etc. into the space and inducing a voltage due to the difference in contact potential difference between the polarized gas and the respective metal electrodes. However, the energy conversion efficiency of this system is less than 0.4%. c. Three-step type converting system: In this system, radioactive energy from a radioactive substance is used to change the physical state of certain substances through two sequential steps and then the resulting state produces electric energy. For example, a mixture of a radioactive substance and a fluorescent material is sandwiched by a pair of photo-electric cells and the fluorescent material is illuminated by the radioactive rays from the radioactive substance. The photo-electric cells detect this luminescence and generate an electromotive force. In general, this system requires a very complex structure but nevertheless provides poor conversion efficiency on the order of less than 0.01%. d. Heat-engine type converting system: This system includes the thermoelectric type converting method, the thermionic type converting method and the heat engine type converting method, and, in some of these methods, there is provided a conversion efficiency as high as 5%. However, the devices used in these converting methods require very complex construction and are not economical. As mentioned above, conventional converters of relatively simple construction generally provide relatively low conversion efficiency. On the other hand, conventional converters of more complex construction generally provide higher efficiency but are not economical. The primary object of the present invention is to provide a two-step type converting system for converting radioactive energy to electric energy and a device for performing the same with a simple construction and with high efficiency. |
claims | 1. A frequency adjusting apparatus comprising:a conveying unit configured to convey, in one direction, a wafer on which a plurality of elements are closely arranged;an ion gun for etching, the ion gun being configured to irradiate the wafer with an ion beam while the wafer is being conveyed;a pattern mask having a plurality of mask holes allowing only target areas of the wafer to be exposed, the pattern mask being disposed upstream of the wafer in a direction in which the ion beam travels; anda plurality of shutters each being configured to adjust an irradiation time during which a target area is irradiated with the ion beam, and thereby adjust a frequency in the target area,wherein each of the plurality of mask holes in the pattern mask corresponds to one area of the wafer;the plurality of mask holes being alternately displaced in a wafer conveying direction in which the wafer is conveyed, and arranged in a plurality of columns perpendicular to the wafer conveying direction;the shutters being arranged to correspond to the respective plurality of mask holes to individually open and close the corresponding plurality of mask holes; andfrequency adjustment, for areas in one column perpendicular to the wafer conveying direction, being performed in multiple steps. 2. The frequency adjusting apparatus according to claim 1, wherein each of the areas of the wafer includes a plurality of elements. 3. The frequency adjusting apparatus according to claim 2, wherein the conveying unit intermittently conveys the wafer at a pitch of one area of the wafer; andthe plurality of mask holes of the pattern mask being alternately displaced in the wafer conveying direction by a distance of one or more elements and arranged in two columns perpendicular to the wafer conveying direction. 4. The frequency adjusting apparatus according to claim 2, wherein the conveying unit intermittently conveys the wafer at a pitch of one area of the wafer; andthe plurality of mask holes of the pattern mask being alternately displaced in the wafer conveying direction by a distance of one or more pitches and arranged in two columns perpendicular to the wafer conveying direction. 5. The frequency adjusting apparatus according to claim 1, wherein the conveying unit intermittently conveys the wafer at a pitch of one area of the wafer; andthe plurality of mask holes of the pattern mask being alternately displaced in the wafer conveying direction by a distance of one or more elements and arranged in two columns perpendicular to the wafer conveying direction. 6. The frequency adjusting apparatus according to claim 5, wherein the shutters are divided into a first shutter group for closing the plurality of mask holes in a first column perpendicular to the wafer conveying direction and a second shutter group for closing the plurality of mask holes in a second column perpendicular to the wafer conveying direction; andfirst actuators configured to drive the first shutter group and second actuators configured to drive the second shutter group are arranged opposite each other on both sides of the pattern mask in the wafer conveying direction. 7. The frequency adjusting apparatus according to claim 1, wherein the conveying unit intermittently conveys the wafer at a pitch of one area of the wafer; andthe plurality of mask holes of the pattern mask being alternately displaced in the wafer conveying direction by a distance of one or more pitches and arranged in two columns perpendicular to the wafer conveying direction. 8. The frequency adjusting apparatus according to claim 7, wherein the shutters are divided into a first shutter group for closing the plurality of mask holes in a first column perpendicular to the wafer conveying direction and a second shutter group for closing the plurality of mask holes in a second column perpendicular to the wafer conveying direction; andfirst actuators configured to drive the first shutter group and second actuators configured to drive the second shutter group being arranged opposite each other on both sides of the pattern mask in the wafer conveying direction. 9. A frequency adjusting apparatus comprising:a conveying unit configured to convey, in one direction, a wafer on which a plurality of elements are closely arranged;a frequency-adjusting-material applying unit configured to apply a frequency adjusting material to the wafer while the wafer is being conveyed;a pattern mask having a plurality of mask holes allowing only target areas of the wafer to be exposed, the pattern mask being disposed upstream of the wafer in a direction in which the frequency adjusting material is applied; anda plurality of shutters, each being configured to adjust an application time during which the frequency adjusting material is applied to a target area, and thereby adjust a frequency in the target area,wherein each of the plurality of mask holes in the pattern mask corresponds to one area of the wafer;the plurality of mask holes being alternately displaced in a wafer conveying direction in which the wafer is conveyed, and being arranged in a plurality of columns perpendicular to the wafer conveying direction;the shutters being arranged to correspond to the respective plurality of mask holes to individually open and close the corresponding plurality of mask holes; andfrequency adjustment, for areas in one column perpendicular to the wafer conveying direction, being performed in multiple steps. 10. The frequency adjusting apparatus according to claim 9, wherein each of the areas of the wafer includes a plurality of elements. 11. The frequency adjusting apparatus according to claim 10, wherein the conveying unit intermittently conveys the wafer at a pitch of one area of the wafer; andthe plurality of mask holes of the pattern mask being alternately displaced in the wafer conveying direction by a distance of one or more elements and arranged in two columns perpendicular to the wafer conveying direction. 12. The frequency adjusting apparatus according to claim 10, wherein the conveying unit intermittently conveys the wafer at a pitch of one area of the wafer; andthe plurality of mask holes of the pattern mask being alternately displaced in the wafer conveying direction by a distance of one or more pitches and arranged in two columns perpendicular to the wafer conveying direction. 13. The frequency adjusting apparatus according to claim 9, wherein the conveying unit intermittently conveys the wafer at a pitch of one area of the wafer; andthe plurality of mask holes of the pattern mask being alternately displaced in the wafer conveying direction by a distance of one or more elements and arranged in two columns perpendicular to the wafer conveying direction. 14. The frequency adjusting apparatus according to claim 13, wherein the shutters are divided into a first shutter group for closing the plurality of mask holes in a first column perpendicular to the wafer conveying direction and a second shutter group for closing the plurality of mask holes in a second column perpendicular to the wafer conveying direction; andfirst actuators configured to drive the first shutter group and second actuators configured to drive the second shutter group being arranged opposite each other on both sides of the pattern mask in the wafer conveying direction. 15. The frequency adjusting apparatus according to claim 9, wherein the conveying unit intermittently conveys the wafer at a pitch of one area of the wafer; andthe plurality of mask holes of the pattern mask being alternately displaced in the wafer conveying direction by a distance of one or more pitches and arranged in two columns perpendicular to the wafer conveying direction. 16. The frequency adjusting apparatus according to claim 15, wherein the shutters are divided into a first shutter group for closing the plurality of mask holes in a first column perpendicular to the wafer conveying direction and a second shutter group for closing the plurality of mask holes in a second column perpendicular to the wafer conveying direction; andfirst actuators configured to drive the first shutter group and second actuators configured to drive the second shutter group being arranged opposite each other on both sides of the pattern mask in the wafer conveying direction. |
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040244202 | abstract | A deep diode atomic battery is made from a bulk semiconductor crystal containing three-dimensional arrays of columnar and lamellar P-N junctions. The battery is powered by gamma rays and x-ray emission from a radioactive source embedded in the interior of the semiconductor crystal. |
description | The invention is directed to a spectral radiation filter for which the selection of an appropriate material of construction, and of an appropriate thickness, are made such that the spectral filter will filter out portions of the x-ray spectra that do not effectively contribute to producing a high-quality image. As used herein, the xe2x80x9cspectral radiation filterxe2x80x9d refers to a filter as described herein that provides attenuation of radiation in selected energy ranges to increase the signal level (CF) or alternatively the contrast-to-noise ratio (CNR) at the x-ray detector in the imaging system, or alternatively a combination thereof. In medical imaging systems, the sought-after spectral filtering must also take into account that the dose of x-rays to which the patient is exposed is preferably minimized. The invention is based upon the determination that, within the spectrum of x-ray energies emitted by the x-ray source and detected by the x-ray detector, certain x-ray energies are more advantageous than others in achieving the higher signal levels and contrast-to-noise ratios, and that by attenuating the less useful x-ray energies, an improved image is obtained and the patient dosage or exposure is kept to a minimum. In an exemplary embodiment of the invention, the x-ray spectral filter is constructed of a material having a high atomic number (Z), e.g., Z=58 or higher when the x-ray spectra exiting the exit port of the x-ray tube is in the range of 50-160 Kvp, typical of high energy medical imaging. In one embodiment, a thickness of the spectral filter would be in the range of between about 40 xcexcm and about 300 xcexcm, and the filter is made of material having Z greater than 64. A spectral filter made of a high-Z material in the prescribed range of thickness can effectively filter out x-rays in spectral ranges determined, in the course of developing the present invention, to be poor contributors to a high-quality image. The use of such a spectral filter results in improvement in the contrast-to-noise ratio (CNR) and an increase in the signal level (CF), for a given unit of exposure to radiation. Thus, a high quality image can be obtained while actually reducing the dose of radiation given to the patient. FIG. 1 illustrates, in substantially schematic form, an x-ray imaging system, generally designated by the numeral 10, for use in examining the condition of an internal structure of an object 16. The object 16 may be, for example, a human patient in a medical diagnosis procedure. The radiation source 12 is preferably an x-ray tube 12 or generator, with the x-ray spectra commonly used in high energy medical imaging being in the range of 50-160 kVp. This range is sometimes narrowed to about 80 kVp to 120 kVp. A spectral radiation filter 14 is positioned between the exit port of x-ray tube 12 and the object 16 to be imaged. The filter is preferably placed in proximity e.g. in a range between about 0xe2x80x3 and 8xe2x80x3 from the exit port of the x-ray tube 12 in order to permit the filter to be constructed in as small a size to intercept substantially all x-ray (e.g. 90% or more) emanating from an exit window of the x-ray tube but having an area that does not present significant issues of increased cost or restructuring of the x-ray apparatus. Additionally, placement of the filter in proximity to the x-ray tube to reduce effects of scatter from these filters in the x-ray image. In one embodiment of the invention, the filter 14 has a surface area of about one square inch (1.0 in2, that is, about 6.5 cm2). Spectral radiation filter 14 comprises at least a primary filter material layer 1 of an x-ray a first attenuating material (e.g., preferably fabricated of a thin layer, such as a sheet or foil, of a metallic material), and in alternative embodiments described below, may comprise a plurality of layers of filter material, e.g., secondary filter material layer 2 and a tertiary filter material layer 3, as shown in FIG. 1. In some x-ray systems, the system 10 also includes a pre-filter 13 disposed as an integral part of x-ray tube assembly 12. This pre-filter, when employed, typically comprises a low Z material (e.g., Beryllium (Z=3)) and performs an initial filtering of the low energy x-rays. The filter 14 is provided to obstruct or attenuate x-rays of certain energy levels that have been determined to be harmful to, or to not contribute significantly to, a higher quality image of the object under examination. The filtered radiation beam passes through the object 16, and may preferably be received by a radiation detector 18 such as an image intensifier or solid state radiation detector. The radiation detector produces an output signal that is further processed to produce the desired image for use by the operator. In one embodiment, the output is processed by an image processor 20 to produce an electronic signal that may be displayed on a video monitor 22. In the course of developing the x-ray imager system 10 of the present invention, spectral filtering of the x-ray exiting the x-ray generator was identified as an aspect of the system that could be changed or modified to improve the performance of the imager. Improved performance can be evidenced by an increase in the signal level on the imager, which increase tends to reduce the effect of electronic noise. In light of the fact that a principal envisioned use of the x-ray imager is to analyze the condition of human patients, any increase in signal level desirably will not come at the expense of increasing the radiation exposure to the patient. The approach for achieving the desired result noted above is to design a spectral filter, based upon the recognition that certain x-ray energies within the complete spectrum of x-ray energies generated by an x-ray source contribute, to a greater extent than other x-ray energies, to improved imaging capabilities. The spectral filter will thus desirably filter out the x-rays of less-than-optimal energies (in terms of contribution to quality imaging), while allowing the x-rays at the more optimal energies to pass through to the scintillator. In one embodiment of the invention, this goal is achieved by constructing a spectral filter from a material having a high atomic number (Z) (as used herein, xe2x80x9chigh atomic numberxe2x80x9d refers to a material having a Z value of at least 58), and desirably an atomic number of Zxe2x89xa765. FIG. 2 presents a graph which illustrates the number of x-rays at various given energies that are needed to generate an exposure of 1.0 xcexcR (micro-Roentgen). This graph establishes the relationship between x-ray flux and exposure of the patient to radiation. FIG. 3 presents a plot of a relative xe2x80x9cconversion factorxe2x80x9d of the x-rays as a function of x-ray energy. The xe2x80x9cconversion factorxe2x80x9d is the signal level produced in a given image detector by a single x-ray for a particular detector (for purposes of this example, a solid state imaging device). The solid line plotted is a measure of the relative conversion factor presented in terms of units of electrons per incident x-ray when a Csl scintillator (420 xcexcm thick) is employed. Also plotted on the same graph, in a broken line, is the relative conversion factor plotted as a function of energy per milli-Roentgen (mR) to the patient. The gap between the solid line and the broken line in FIG. 3 provides an indication of the relative effectiveness of x-rays of the particular energies displayed on the graph at delivering a percentage of the conversion factor (related to signal level in the detector), on a xe2x80x9cper x-rayxe2x80x9d basis (solid line), and on a xe2x80x9cper exposure dosagexe2x80x9d (mR) basis (broken line). Thus, initially, it is seen from FIG. 3 that x-rays having energies from about 40 KeV to about 95 KeV will have the effect of maximizing the signal level in the detector, with respect to patient dose or exposure, in that the values of the conversion factor (CF) on the xe2x80x9cper exposure dosagexe2x80x9d basis lie close to the conversion factor values on a xe2x80x9cper x-rayxe2x80x9d basis. In contrast, for example, it can be seen that, while x-rays having an energy of 27 KeV deliver about 60% of the conversion factor of a 60 KeV x-ray on a xe2x80x9cper x-rayxe2x80x9d basis, those x-rays deliver only about 20% of the conversion factor of a 60 KeV x-ray, on a xe2x80x9cper exposure dosagexe2x80x9d (mR) basis. The ability to see an object of interest in an image is related to the contrast between the object and the noise in the image. Thus, in addition to seeking to obtain increased signal levels at constant or decreased dosages, the contrast produced in a given image and more significantly, the contrast-to-noise ratio, should be maintained as high as is practicable. For the purposes of the development of this invention, a relative contrast-to-noise ratio (rCNR) value was obtained through normalizing a contrast-to-noise ratio of a detector using the Csl scintillator, against an ideal detector. This value provides a figure of merit for comparing the effects of different x-ray spectra, and is preferably expressed as: rCNR = C · S N = C · X TB · QDE xe2x80x83 ; ( 1 ) where C is a value of contrast determined by a background signal level and a signal level of the combined background and the object undergoing imaging, and SN (signal to noise ratio), is the square root of the number of absorbed x-rays. Equation (1) indicates that the number of absorbed x-rays is equal to the product of an incident x-ray flux (XTB) on the detector, and the fractional absorption (QDE) of the scintillator which, in this preferred embodiment, is made of Csl. In order to determine which x-ray energies in the x-ray spectrum produce the best relative contrast-to-noise ratios (rCNR), simulations were conducted with four (4) different objects against three different backgrounds. The objects employed were steel guide wire, iodine contrast fluid, bone, and soft tissue (represented by the curve in the Figure marked xe2x80x9cdensity changexe2x80x9d as this curve was represented by LUCITE(copyright) (generically known as polymethylmethacrylate, or PMMA) material representative of soft tissues of slightly different densities). The backgrounds, chosen to simulate thin, normal, and heavy patients (as these terms are commonly used in the imaging arts), were LUCITE(copyright) panels of 20 cm, 25 cm and 30 cm thickness, respectively. LUCITE(copyright) is a registered trademark of ICI Acrylics, Inc., of Wilmington, Mo. In this simulation, the thicknesses of the four objects were adjusted to provide contrasts of 5% for the bone and soft tissue, and 10% for the steel and the iodine. FIG. 4 illustrates the relative contrast-to-noise ratio (rCNR) as a function of x-ray energy, for the four objects, using the 25 cm background panel. In this simulation, the x-ray flux at each energy level was adjusted so as to give the same incident exposure to the patient. The results presented in FIG. 4 thus represent a comparison of rCNR on a xe2x80x9cper exposure dosagexe2x80x9d (per mR) basis. FIG. 5 illustrates the effect of the background thickness (simulating lighter to heavier patients) on the results. At low x-ray energies, the rCNR is low because fewer incident x-rays reach the object being imaged, and because there are fewer x-rays transmitted through the patient due to absorption. The rCNR is also seen to be low at the higher energies, as the contrast between object and background decreases with the use of higher x-ray energies. The data presented in FIGS. 3-5 lead to the conclusion that maximization of the signal level and minimization of patient exposure is achieved preferably with a monoenergetic beam of about 60 KeV x-rays. In addition, as seen in FIGS. 4 and 5, the contrast-to-noise ratio, on a xe2x80x9cper exposure dosagexe2x80x9d basis, can be maximized by use of x-rays having energies in the range of 40-60 KeV. More specifically, for the simulation objects, the rCNR is maximized for the steel and iodine objects at an x-ray energy of about 40 KeV, at about 50 KeV for bone and at about 60 KeV for the imaging of tissue density changes. Using such simulations, a specific x-ray energy can, in many cases, be identified as the optimal energy for use with a specific object and a specific background. In actual medical imaging, however, it would be impossible, as a practical matter, to provide an imager having the capability of delivering the precise x-ray energy for each different patient and for each different region of interest on each patient. Accordingly, in one embodiment of the present invention, a range of useful or especially advantageous x-ray energies is segregated from x-ray energies which detract from, or do not significantly contribute to, higher signal levels and higher rCNRs in the imaging process. In FIG. 6, the spectrum of energies from 20 KeV to 100 KeV is shown divided into four different regions. Region 1, which includes x-ray energies from 35 to 60 KeV, is selected as being the ideal range of x-ray energies for maximizing rCNR and signal level, while maintaining patient exposure at a reasonable level. A second region, designated as Region 2, with x-ray energies in the range of 60-80 KeV, is seen as providing a good rCNR for a bone specimen and for tissue density fluctuations, and provides a maximum signal level for these objects. In accordance with a preferred embodiment of the present invention, this energy region is seen as being useful especially for heavier patients, due to x-ray tube power limitations. It was determined in developing the present invention that the regions designated as Regions 3 and 4 (above 80 KeV and below 35 KeV, respectively) do not benefit the quality of the image obtained, and that filtering out these x-ray energies will thus enhance the quality of the image obtained. The high x-ray energies of Region 3 (a xe2x80x9chigh endxe2x80x9d of a spectrum of x-rays emitted by the source) provide lower rCNR and signal levels (relative conversion factor, or rCF), and thus are preferably filtered out. The low x-ray energies of Region 4 (the xe2x80x9clow endxe2x80x9d of a spectrum of x-rays emitted by the source) contribute very little to rCNR and rCF, while they greatly increase exposure of the patient to the radiation. The Region 4 x-rays are thus also preferably filtered out. FIG. 7 presents an illustration of a typical x-ray spectrum for a typical imaging system currently in use, which employs an aluminum filter (2.4 mm thick) as an initial filtering medium. The graph shows the same regions of grouped x-ray energies as were developed and illustrated in FIG. 6. It can be seen in FIG. 7 that, despite the use of an initial filtering medium, between 40% and 54% of the x-ray exposure to the patient is from x-ray energies in the regions identified as Regions 3 and 4, the two regions determined to adversely affect, or to be poor contributors to, the quality of the image. The three separate curves in FIG. 7 represent the exposures at three different kVp levels (75 kVp, 90 kVp, 120 kVp) that would commonly be used, for patients of various sizes or builds. The approach used in the present invention for narrowing the x-ray spectrum to the desired Region 1 and Region 2 energies, nominally from about 35 keV to about 80 keV (see FIG. 6), is to provide a spectral filter made of one of a group of specially selected materials. Also, in order to accommodate the broadest range of patient sizes with a manageable number of filters, the thicknesses of the filters are selected to optimize the filtering within practical limits. The x-ray attenuation of a filter is a function of the incident x-ray energy, the thickness of the filter, its density, and the elemental composition of the filter. Prior filtering of incident x-rays focused exclusively on attempting to filter out low energy x-rays, such as those designated in Region 4 in FIG. 6. The behavior of different prospective filter materials for filtering these low x-ray energies has, in the development of the present invention, been determined to be dependent upon filter thickness, and, by varying the thickness of filters of the different materials, the respective x-ray attenuation values of the filters can be matched. This can be seen in FIG. 8, which illustrates the x-ray attenuation of filters made of aluminum (Z=13; 6500 xcexcm thick), copper (Z=29; 196 xcexcm thick), molybdenum (Z=42; 67.7 xcexcm thick) terbium (Z=65; 150 xcexcm thick), tungsten (Z=74; 43.9 xcexcm thick), and lead (Z=82; 56.4 xcexcm thick). It was determined, in the course of developing the filters of the present invention, that the behavior of the materials at the high end of x-ray energies which are desired to be filtered or attenuated, makes a greater difference in terms of which materials will provide the optimal combination of filtering both the low energy (Region 4) x-rays and the high energy (Region 3) x-rays. Specifically, high atomic number (Zxe2x89xa758), and, especially even higher (Z greater than 64) materials were discovered to behave in such optimal fashion. This behavior is due not to the commonly looked-to factors of the thickness and density of the filter, nor the incident x-ray energy, but is instead due to desirable quantum mechanical effects experienced in the high atomic number materials in which increases in x-ray absorption are discontinuous at a few well-defined energies. It can be seen in FIG. 8 that aluminum, which has previously been employed in initially filtering x-rays from an x-ray source, has a relatively weak preferential treatment for x-rays in Region 1 (desirable) versus Region 4 (undesirable). The relative flattening of the curve for the aluminum filter is due to the effects of Compton scattering, which takes place in higher Z materials only at higher energies. Copper is seen in FIG. 8 as providing a greater preferential treatment of x-rays in Regions 1 and 4. Significantly, however, FIG. 8 illustrates that the higher atomic number materials exhibit a discontinuous drop in x-ray transmission (increase in attenuation) at material-specific energies, which leads to increased attenuation in Region 3, as compared with copper or molybdenum. Thus, these materials provide the ability to attain an acceptable relative attenuation of Region 4 x-rays to Region 1 x-rays, and also preferentially attenuate Region 3, and, to an extent, Region 2. The discontinuous increase in absorption experienced with the high Z materials is due to the quantized nature of the electronic orbitals, and the well-defined energies correspond to the L and K shells of the atom of the particular element. K-edge effects can be seen in FIG. 8 for terbium (K-edge=52 KeV), tungsten (K-edge=69.5 KeV) and lead (K-edge=88 KeV). Table I below details the K-edge energies for several high-Z materials of interest, as well as their potential optimal uses. Based solely on the consideration of the desire to deliver the entire x-ray spectrum of Region 1 (FIG. 6, 35-60 KeV), the ideal filter would be made of thulium (Z=69), a rare earth metal having a K-edge at 59.4 KeV. The use of thulium or a higher atomic number material has the additional benefit of performing a weak filtering of Kxcex1 characteristic x-rays (at 58.0 and 59.3 KeV) from a tungsten target (see FIG. 7). Other considerations may weigh in favor of the selection of a different material of construction for the x-ray spectral filter, or alternatively the provision of a small, manageable number of interchangeable spectral filters made of different materials. For example, when thin and moderate-sized patients are to undergo x-ray imaging, the contrast for steel and iodine can be increased by employing terbium (Z=65, K-edge=52.0 KeV) as the material of which the filter is made. In imaging larger patients, the signal level is commonly of greater concern, and x-rays in Region 2 (60-80 KeV) of the spectrum are useful in increasing signal level. Thus a filter material that will not attenuate these x-rays may be preferable. In this situation, gold (Z=79, K-edge=80 KeV), lead (Z=82, K-edge=88 KeV), and bismuth (Z=83, K-edge=90.5 KeV) may be preferred materials from which the filter is constructed. There is a limited degree of flexibility in setting the boundaries for Region 2 and Region 3, shown as 60 KeV and 80 KeV, respectively, in FIG. 6, particularly based upon what imaging parameters are to be maximized. Thus, other high atomic number materials, such as lutetium, tantalum, and tungsten would be alternative preferred materials for use in constructing a spectral filter in accordance with the present invention. In using high atomic number materials as spectral filters, there is a possibility that x-ray fluorescence will occur as x-rays above the K-edge energy of the filter material are absorbed. A secondary x-ray at a slightly lower energy may occur in such instances. Due to the low probability that such a secondary x-ray will strike the imager, the negative effect of such fluorescence is generally thought not to pose a measurable negative impact on the image, particularly for larger patients. The effects of fluorescence can be further minimized by placing additional radiation filters adjacent to primary radiation filter material layer 1 in radiation filter 14. For example, a lead filter (Z=82) will create fluorescent x-rays primarily at 72.8 KeV and 75.0 KeV. By adding at least secondary radiation filter material layer 2 (that is, a layer of a slightly lower Z material disposed next to the lead filter such that it is disposed between the lead filter and the object to be imaged), the secondary filter material layer 2 provides preferential absorption of the x-rays resulting from the fluorescent and thus improves image quality. The material of secondary radiation filter typically has a K-edge right below the energy of the fluorescent x-rays (e.g., tungsten, Z=74, K-edge=69.5 KeV). For the range of primary filter materials discussed, the Z of the secondary radiation filter material has a value that is at least about 6 or 7 less than the Z of the primary filter material. For example, a primary filter material layer 1 material of bismuth (Z=83) should be paired with a secondary radiation filter material layer of a material having a Z less than 76; a primary filter comprising gold (Z=79) should be paired with a secondary filter having a Z less than 72; and a primary filter comprising tungsten (Z=74) should be paired with a secondary filter of a material having a Z less than 68). The thickness of the secondary filter typically has a value that is in the range between about 10% and 50% of the thickness of the primary filter. In another embodiment, additional radiation filter (e.g., a tertiary radiation filter 3) can similarly be coupled to the secondary radiation filter material layer, with the primary, secondary, and tertiary filter material layers being arranged such that the filter comprising the material with the highest Z value is disposed closest to the x-ray source and the filter comprising the material with the lowest Z value disposed farthest from the x-ray source. One example would be a filter arrangement having materials in the order of lead, tungsten, and terbium (with the lead filter being disposed closest to the radiation source). In current x-ray imaging systems employing a 2.4 mm thick aluminum filter, it is not possible, even with heavy patients, to use available x-ray tubes at their maximum rated power (currently 900 W). With x-ray tubes having 1500 W power ratings, aluminum filters will be even more inadequate. Using a high atomic number material in constructing the spectral filter permits, as noted previously, the use of increased power, thus obtaining a better contrast-to-noise ratio and higher signal level, while at the same time keeping the dose to the patient constant. A demonstration of the improved results is presented in Table II below, and the improved results are further evidenced in FIGS. 9-11. Table II sets forth two examples of the use of a thulium filter, for thin and medium patients, and of the use of a gold filter for heavy patients. The results for rCNR and Relative Signal reported in the table are in terms of improvement over the use of a 2.4 mm thick aluminum spectral filter (e.g. a result reported as 1.21 indicates 21% improvement over the value obtained when the 2.4 mm aluminum filter is used). It is noted that, for the thulium and gold filters are employed in these examples, the x-ray tube contained a 1.0 mm thick aluminum pre-filter. In the examples below employing thulium filters, the thickness of the thulium for a medium dose is 194 xcexcm, and, for a low dose, is 298.5 xcexcm. The gold filters for medium and low dose were 39.5 xcexcm and 91 xcexcm, respectively. In the case of the imaging of a thin patient (20 cm thick lucite, 75 kVp), it can be seen that, with a lower dose (0.84), the contrast-to-noise ratio (rCNR) improves by 21-31%, with an increase of about 81% in the signal level. As can be determined from the table, when it is desired to conduct a low dose fluoroimaging, the filters of the present invention make it preferable to retain the same x-ray tube current and power, and to increase the thickness of the filter itself to reduce the patient dose. This may be contrasted with the need, when conventional filter materials are employed, to reduce the x-ray tube current and power. In the case of the thin patient simulation, the rCNR value increased from 24% to 41% over the value obtained with the 2.4 mm aluminum filter, and the signal increased by 215%, while delivering only 84% of the dose delivered when the aluminum filter was used. Similar highly advantageous increases in rCNR and signal level were obtained in the medium and heavy patient simulations. It can be inferred from the results of the simulation reported in Table II and FIGS. 9-11, that the high atomic number spectral filters may be used, instead of to improve image quality at patient dosages currently used, to decrease patient dosages while maintaining image qualities obtained using conventional filters in conventional systems. The spectral filters of the present invention are preferably provided in the form of a thin metal foil made of the desired filter material housed within a frame or support. Alternatively the filter may preferably be provided in the form of a layer of oxide powder of the desired filter material which is encapsulated or encased in a frame structure. The filter 14 may generally has a surface area of about one square inch (1.0 in2), in order to intercept substantially all of the x-rays emanating from the x-ray tube. Copper or other relatively inexpensive, lower Z materials may alternatively be used as a pre-filter 13, in the place of aluminum. The spectral filter 14 is also preferably positioned as close as is practicable to the x-ray window, as this also permits the filter to be as small in size as possible. The imaging system may also be provided with a plurality of radiation spectral filters 14, which are constructed of varying high Z materials and/or thicknesses selected to provide improved imaging capabilities at reduced dosages to a wide variety of patient sizes. As an example, the imaging system 10 may be provided with the set of six filters employed in the demonstration for which the results are presented in Table II above. It should be noted that the invention has been described with reference to particular embodiments, but that the invention is not limited to these embodiments. For example, while examples have been provided with respect to digital radiation images, the invention can similarly be practiced with respect to non-digital imagers. As understood by those skilled in the art, certain of the performance indicators presented herein are independent of the type of detector used (e.g., x-ray emission and absorption information), some relate to the scintillator used (e.g., CNR), and some relate to the particular detector used (such as CF and its role in suppressing electronic noise). Those skilled in the art will understand that other modifications may be made to the embodiments discussed herein that are within the scope of the invention. |
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description | The present invention relates to the field of containers. More specifically, the present invention is directed to a shielded container for a radiopharmaceutical. Radio-pharmaceuticals are typically packaged in a manner that reduces radiation exposure to the end-user of the product. Because most of these pharmaceuticals have short half-lives, radioactive content can be extremely high during manufacturing and handling of these products. Packaging containers consists of several components, with the main component being lead. Lead has a very high density and provides excellent shielding characteristics for both gamma and beta emitting radio-pharmaceuticals. Lead is also very heavy and thus contributes to ergonomically related strains during container assembly and handling. A radio-pharmaceutical container typically consists of an outer shell, an inner shell, and a product container. The outer shell is typically formed from plastic that is bother durable and cleanable. The outer shell is durable to meet the requirements of the Department of Transportation (DOT). The outer shell must contain and protect the inner contents of the package during shipping and use of the product. The outer shell is cleanable so that any radioactive contamination can be washed off of the surface. Radioactive contamination is a possibility due to the nature of the contents and the environment where the containers are used. The outer shell typically has a label containing all of the product information such as; product name, manufacturing date, volume, specific activity, etc. The outer shell is usually and injection molded component that contains sub-parts that are assembled into a lower and upper assembly. The inner shell, also known as the shield, fits within the outer shell. The inner shell is typically manufactured from lead with a small percentage of antimony. The inner shell is designed to provide shielding of the radioactive contents of the container. The inner shell is usually poured from molten lead into a negative void, or form. The inner shell typically includes subparts which correspond to the subparts of the outer shell. The product container is the primary holder of the product. It can be made of plastic or glass and can be sterile or non-sterile. The product container may be kept in the shipping container during use to reduce exposure to the end-user. The container may also include an absorbent material placed inside the inner shell to absorb fluid if the product container is breached during shipment or use. There may also be a cushioning material, such as a sponge, to protect the product container from shock during shipment or use. Additionally, there may also be an inner sleeve that can be positioned between the inner shell and the product container to segregate the product container from the lead. Because the actual dose to be carried by the container may greatly vary from use to use, the lead shield is typically formed to be very thick so as to handle all doses it may encounter. The resulting weight of the container presents greater risks to the assemblers or handlers of the container of ergonomic or repetitive stress injuries. As lead is a non-ferrous metal, the shielding containers of the prior art do not lend themselves to handling machinery which employ magnets for transporting, and handling components. There is therefore a need in the art for a shielded container for a radiopharmaceutical which reduces operator exposure to the radiopharmaceutical and to ergonomic and repetitive stresses relating to the manufacture, assembly, and handling of the container. In view of the needs of the art, the present invention provides a radiation-shielding container for a radiopharmaceutical that may be magnetically picked and placed. One embodiment of the present invention provides a radiation-shielding container for storing and transporting a radiopharmaceutical. The container includes a cap and a base. The container includes a first ferromagnetic plug positioned adjacent to an outer surface of the shield of one of the cap shield and the base shield. The container may also include a second ferromagnetic plug positioned adjacent the other of the cap shield and the base shield. A plug of the present invention may be provided between the outer plastic shell of the container and the lead shield. The plug may be incorporated into the outer plastic shell. Alternatively, the plug may be attached to the outer surface of the outer liner. In this manner, the plug of the present invention may be retrofitted to prior art containers. FIG. 1 shows a shielded container 10 of the present invention for shipping radioactive pharmaceuticals. Container 10 includes a steel plug 12 that is inset into the cap 14 of the plastic outer shell 16. Plug 12 can be made of any ferrous material, or material that can be attracted to a magnetic field. FIG. 2 shows plug 10 as a component that is encapsulated within the cap 14 of the assembled container 10. Plug 12 does not affect the inner shell 18, or lead portion of the container so that the shielding ability of shielded container 10 is ensured. In addition, plug 12 does not affect the outer shell 16, or durable and cleanable, plastic portion of container 10. Outer shell 16 accommodates plug 12, whether plug 12 is to its inside, outside, or incorporated therein. Desirably, plug 12 is incorporated into container 10 during vendor assembly of the container so that an assembled cap 14 and base 20 will be provided to the production department for product filling and final assembly for a product container 22. Product container 22 is desirably a conventional container for a radioactive product such as a vial or a syringe or the like and is typically formed of plastic or glass and includes an elastomeric septum or piston. More fully, container 10 includes a cap 14 and a base 20. Cap 14 includes a lead shield 18 and a plastic outer shell 16. Cap 14 further defines an open cap cavity 24. Base 20 includes a lead shield 26 and an outers shell 28. Base 20 defines an open base cavity 30 in fluid communication with cap cavity 24 when cap 14 is mated to base 20. An elastomeric gasket 32 may be supported at the interface between cap 14 and base 20. It will be appreciated by those of ordinary skill in the art that container 10 may have other configurations for its cap and its base, such as including an inner plastic shell, lead shields fully encased within plastic, or a removable plastic sleeve insertable into cavity 30 and/or 24. The present invention provides a ferromagnetic plug 12 which enables the container to be remotely handled, manipulated and transported. FIG. 2 shows the assembled product container 10 waiting for handling. FIG. 3 shows a magnetic hoist/lift 100 handling container 10. The purpose container 10 is to reduce the ergonomic and repetitive stress associated to the manufacture and handling of a radioactive product. Container 10 can weigh one pound or more, and a typical manufacturing lot may contain several hundred to several thousand product containers. The size of the container is such that single hand manipulation of the product container is common; however, the size may be up to several inches in diameter and/or length and thus ergonomically challenging when handling production volumes. The container 10 will minimize the operator whole body and extremity exposure incurred during manufacturing and handling of the product. In addition, container 10 will reduce the ergonomic and repetitive stress associated with the manufacturing and handling of the product. Finally, container 10 will offer these advantages to the end-user of these products as well as to those lading and assembling container 10. While plug 12 is desirably incorporated into container 10 during the container's manufacture, plug 12 may also be added to an already existing product package. Plug 10 will thus allow for a different set of handling capabilities than shielded containers of the prior art which would forego use of a ferromagnetic material since such material does not provide desirable radiation shielding properties. These handling capabilities can vary in complexity from a remote pick and place mechanical arm to a robotic arm programmed to assemble, pick up, and place the product container into a shipping container. The added weight of the plug is insignificant when compared to the overall weight of the lead portion of the inner shell. It is possible that the plug could provide additional top shielding of the product container, or the dimension of the lead insert may be reduced because of the added shielding by the top plug. As shown in FIG. 4, the present invention further contemplates providing a container 110 having a ferrous plug 13 incorporated in base 20. For this and the remaining embodiments (shown in FIGS. 5 and 6) of the present invention, the identifying nomenclature of container 10 is retained as shown. Container 110 is shown as further providing plug 13 to the components of container 10. Plug 13 allows for a sliding manipulation of either just the base 20 or the entire assembled and filled container 110. As shown in FIG. 5, the present invention alternatively contemplates providing a container 210 having a ferrous cylinder 15 incorporated between the cylindrical walls of base 20 and lower shield 26. Container 210 provides handling capabilities from the sides of container 210. The present invention contemplates that the plugs 12, 13, and 15 of containers 10, 110, and 210, respectively may all be incorporated into a single container. Each of these containers provide a plastic outer surface when the containers are fully assembled, minimizing operator exposure to the lead shields while handling the container and providing an easily cleaned outer surface. While each of the shown containers show that the lead shield components provide an exposed lead surface on the interior, or container-receiving portion of the shields, the present invention is equally applicable to containers having an encapsulated or otherwise interiorly lined shield providing plastic on all of the surfaces to which an operator may be exposed. FIG. 6 depicts a container 310 of the present invention. Container 310 is a conventional shielded container of the prior art which has a ferrous plug 17 attached to the outside of the container. Attachment of plug 17 to container 210 may be accomplished by known adhesives or by other conventional means. While plug 17 is shown attached to cap 14, it is further contemplated that plug 17 may alternatively be attached to the exterior of base 20. The provision of plug 17 provides a simple retrofit of existing lead-shielded containers. Plug 17 itself may further be covered or encapsulated in plastic so as to maintain the general appearance and cleanliness of the original container. The present invention thus provides the ability to use an automated or remote pick and place machine/device with shielded containers for radiopharmaceuticals. Such machines can provide for a reduction in manufacturing time and time spent handling product containers, thereby reducing the ergonomic and repetitive stress risks to human operators. These machines also provide the ability to handle numerous product containers at the same time. The containers may be manufactured and handled in an ergonomically correct way. The present invention thus provides production personnel are provided with the best possible methods and tools for handling radioactive pharmaceuticals While the particular embodiment of the present invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the teachings of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art. |
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046648798 | summary | BACKGROUND OF THE INVENTION The present invention relates to a guide tube flow restrictor for use in conjunction with drive rod assemblies of a pressurized water nuclear reactor. The guide tube flow restrictor serves both to act as a guide for a drive shaft connected to a control rod and as a flow restrictor for primary coolant passing through the reactor. In pressurized water nuclear reactors, the reactor head plenum contains a guide assembly for controlling the movement of various components such as control rods. Such an assembly generally contains a top support plate, having apertures therethrough, through which drive mechanisms for control rods pass. A guide assembly is provided that is disposed in the apertures to both guide the control rod drive shaft and control the upward flow of water through the apertures. Conventionally, such assemblies comprise a grommet-like member secured in the aperture by a plurality of flexure elements aligned in parallel relationship with he drive shaft, which flexure elements are mounted in special fittings supported in the top plate. Such conventional assemblies require machining and welding operations for installation of the flexure members and require time-consuming procedures for their replacement. An improved type of assembly is described in copending application Ser. No. 574,839 filed Jan. 30, 1984 in the names of David E. Boyle and James R. Chrise, entitled "Quick Release Guide Sleeve Assembly", which application is assigned to the assignee of the present invention, the contents of said application incorporated herein by reference. In said application, the assembly comprises an outer sleeve, an inner sleeve, and a locking mechanism movably mounted on the outer sleeve for frictionally engaging the wall surfaces about an aperture in a top support plate of a guide tube rod assembly. The assembly described therein still, however, requires the use of a tool for assembly, as well as disassembly. Also, the construction is such that corrosion or accumulation of deposits about the locking mechanism could develop that would lead to difficulties in removal and replacement of such an assembly. It is an object of the present invention to provide a guide tube flow restrictor that may be assembled without the need for special tools and is readily removable from its position in a support plate. It is another object of the present invention to provide a guide tube flow restrictor that has a design that simplifies manufacture of such an assembly and is more economical. It is a further object of the present invention to provide a guide tube flow restrictor that reduces the possibility of corrosion or collection of deposits between the assembly parts in use, such as would cause difficulties in removal or replacement of the assembly. SUMMARY OF THE INVENTION A guide tube flow restrictor for use in an upper guide tube support plate comprises an outer ring that is seatable on the support plate, with a bore through the ring aligned with an aperture in the support plate, and an inner sleeve coaxially insertable in the outer ring. The outer ring has a flange member that carries a plurality of downwardly extending flexible segments which extend through the bore and the aperture of the support plate. Upon axial insertion of the inner sleeve into the bore of the outer ring, the sleeve contacts deflecting means on the flexible segments and force the segments radially outwardly to frictionally secure the same with the walls of the aperture of the support plate and lock the assembly in place. The flexible segments preferably terminate in an outwardly disposed leg portion which contacts the bottom of the wall of the aperture in the support plate and also carry an inwardly protruding baffle to deflect the upflow of water away from the bottom of the inner sleeve, while the deflecting means preferably comprises an inwardly protruding extension having at least one angular strut extending upwardly therefrom to the flexible segment, with contact of the inner sleeve confined to the angular surface of the strut. Shoulders are provided on the outer ring to prevent accumulation of deposits and corrosive problems, while additional locking means may be provided to positively secure the outer ring and inner sleeve together when assembled. |
summary | ||
048209295 | claims | 1. A device for transforming visible images into infrared images comprising: a photoconductive layer; a first conductive layer integrally affixed to one side of said photoconductive layer, said first conductive layer being transmissive with respect to radiation of known energy, said photoconductive layer being responsive to said radiation of known energy; a second conductive layer integrally affixed to the other side of said photoconductive layer; and an external energy source connected to said first conductive layer and said second conductive layer, said external energy source for passing a current across said layers, said photoconductive layer having a modulated resistivity in relation to said radiation of known energy. enclosure means for maintaining said photoconductive layer, said first conductive layer and said second conductive layer in a darkened environment. a first conductive layer transmissive with respect to radiation of known energy; a dielectric layer affixed to one side of said first conductive layer; a photoconductive layer having one side affixed to said dielectric layer, said photoconductive being responsive to said radiation; a second conductive layer affixed to the other side of said photoconductive layer; and electrical energy means connected to said first conductive layer and said second conductive layer for impressing a voltage across said layers, said photoconductive layer having a modulated resistivity in relation to said radiation of known energy. enclosure means for maintaining said layers in a darkened environment, said enclosure means including optics for the transmission of imaging radiation into said enclosure means and the emission of infrared radiation from said enclosure means. a first conductive layer transmissive with respect to radiation of known energy; a second conductive layer; a plurality of segments of photoconductive material integrally affixed between said first conductive layer and said second conductive layer, each of said segments being individually responsive to said radiation of known energy; and electrical energy means connected to said first conductive layer and said second conductive layer for passing a voltage thorough said segments of photoconductive material. dielectric material disposed between segments of photoconductive material. enclosure means for maintaining said layer in a darkened environment, said enclosure means including optics for the transmission of imaging radiation into said enclosure means and the emission of infrared radiation from said enclosure means. 2. The device of claim 1, said photoconductive layer being a layer of silicon material. 3. The device of claim 1, said photoconductive layer comprising a plurality of segments of photoconductive material. 4. The device of claim 3, said segments of photoconductive material being generally uniformly distributed across said second conductive layer. 5. The device of claim 4, said segments of photoconductive material generally forming the pixels relative to a projected image. 6. The device of claim 3, said photoconductive layer further including insulative material interposed between said segments of photoconductive material. 7. The device of claim 6, said insulative material forming a layer between said first conductive layer and said photoconductive layer. 8. The device of claim 6, said insulative material being a dielectric having high resistivity and high thermal resistance. 9. The device of claim 1, said first conductive material being a transparent layer of gold material. 10. The device of claim 1, said first conductive layer further comprising a conductive band extending about the outer edges of said first conductive layer, said conductive band for transmitting energy from said external energy source to said first conductive layer. 11. The device of claim 1, said second conductive layer including cooling means interactive with said second conductive layer for the removal of heat from said photoconductive layer. 12. The device of claim 11, said cooling means being said second conductive layer comprised of a material having strong heat sink properties. 13. The device of claim 12, said second conductive layer being a layer of aluminum. 14. The device of claim 1, further comprising: 15. The device of claim 2, further comprising a source of imaging radiation directed toward said first conductive layer. 16. The device of claim 15, said source of imaging radiation being a light image directed across the field of said photoconductive layer. 17. The device of claim 15, said source of imaging radiation being a modulated light beam directed to said photoconductive layer in a raster scanning pattern. 18. A device for transforming visible images into infrared images comprising: 19. The device of claim 18, further comprising: 20. The device of claim 18, said photoconductive layer comprising a plurality of segments of photoconductive material, said dielectric layer disposed between said segments. 21. The device of claim 18, said energy means comprising a source of alternating current. 22. The device of claim 18, said first conductive layer being a transparent gold layer, said photoconductive layer being composed of silicon material, and said second conductive layer being a layer of aluminum. 23. A device for transforming visible images into infrared images 24. The device of claim 25, further comprising: 25. The device of claim 24, said dielectric material forming a layer between said first conductive layer and said plurality of segments of photoconductive material. 26. The device of claim 23, further comprising: 27. The device of claim 23, further comprising a source of imaging radiation directed toward said first conductive layer. 28. The device of claim 23, said second conductive layer acting as a heat sink with respect to said photoconductive material. |
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description | The present application claims the benefit of: (1) U.S. Provisional Patent Application Ser. No. 60/944,009, entitled “Non-Intrusive Method To Identify Presence Of Nuclear Materials Using Energetic Prompt Neutrons From Photon Induced Fission” which was filed on Jun. 14, 2007 by Robert J. Ledoux and William Bertozzi, and is hereby incorporated by reference; and (2) U.S. Provisional Patent Application Ser. No. 60/971,638, entitled “Non-Intrusive Method To Identify Presence Of Nuclear Materials Using Energetic Prompt Neutrons From Photon Induced Fission And Neutron-Induced Fission” which was filed on Sep. 12, 2007 by Robert J. Ledoux and William Bertozzi, and is also hereby incorporated by reference. This invention was made with government support under Contract No. N66001-07-D-0025/Delivery Order No. 0001 awarded by the U.S. Navy. The government has certain rights in the invention. This disclosure relates to systems and methods for detecting the presence of fissionable nuclear materials. The systems and methods make use of the distinctive signals provided by the energy and angular distributions of the prompt neutrons produced in photon induced fission of nuclei. They may be used to detect the presence of actinide nuclei (in particular those with Z greater than or equal to 89, that of actinium). Some of these nuclei are classified as Special Nuclear Materials (SNM) and may be used in weapons of mass destruction such as nuclear explosives and in dirty bombs. Illicit clandestine shipment of nuclear explosives, materials that can be employed in the fabrication of nuclear explosives, and materials that can be employed in the fabrication of dirty bombs may constitute a major threat to the peace and security of the world. Such materials may be secreted and smuggled in cargo or other shipments in various containers including ordinary luggage, crates, vehicles, cargo containers, etc. by terrorists, potential terrorists, terrorist supporters, or others. Effective and efficient methods and systems are required for the reliable, non-intrusive, detection of such contraband materials in ports and in other cargo and shipping locations in order to reduce the risk of successful illicit shipments, without unduly impeding the worldwide flow of cargo in a manner that is disruptive of normal commerce. Accordingly, it is especially important that the detection methods not produce large numbers of false positive detection events. Passive detection methods, as for example gamma spectroscopy of natural decay, have not proven universally effective since many of the materials of interest are not highly radioactive and are relatively easily shielded. X-ray techniques do not readily distinguish between fissionable nuclear materials and innocuous high-Z materials like lead or tungsten that may be legitimately present in cargo. In addition to passive detection, several approaches to detection have been employed, attempted, or proposed using active techniques employing probing beams. In one such active technique, an external neutron source has been used to detect fissionable nuclear materials by detecting induced fission events by the neutron multiplication effect of the fission events. However, it has been difficult to discriminate between the probing neutrons and the fission induced prompt neutrons, especially when the energy of the probing neutrons is as high as the energy of the more energetic prompt neutrons from fission or when large containers are involved. Alternative techniques have induced fission events in fissionable nuclear materials with pulsed external neutron sources, then detecting delayed emission of neutrons by fission products, using time delay, as a means of distinguishing the detected signal from the probing neutrons. This delayed neutron signal is a much weaker signal, and is subject to signal-to-noise ratio problems. In other active techniques, gamma ray probe beams have been employed to induce photofission (γ, f) of nuclear materials with detection of neutrons resulting from the fission events. Scattered gamma rays from the probe beam as well as photo-neutrons (direct (γ, n) events resulting from interaction of the gamma probe beam with fissionable and/or non-fissionable nuclei) induced by the probe beam contribute noise to the detection of prompt neutrons from the fission events, contributing to unreliable or ambiguous detection. Photofission also results in delayed neutron production by the fission fragments, but as with neutron-induced fission, the delayed neutron signal is weaker and detection suffers from noise problems. It is therefore an object of this disclosure to provide improved systems and methods for detecting fissionable nuclear material in an article with reduced error and ambiguity. It is a further object of this disclosure to provide improved systems and methods for detecting contraband fissionable nuclear materials by improving discrimination of prompt fission neutrons in the presence of noise-contributing factors. Another object of this disclosure is to provide systems and methods for analyzing the energy or an energy spectrum of prompt fission neutrons to detect the presence of fissionable nuclear materials in an article. A still further object of this disclosure is to provide systems and methods for detecting an angular distribution of prompt fission neutrons to detect the presence of fissionable nuclear materials in an article. Yet another object of this disclosure is to provide systems and methods for using an angular distribution of prompt fission neutrons and an energy distribution of prompt fission neutrons to detect the presence of fissionable nuclear materials in an article. The objects set forth above as well as further and other objects and advantages of the present disclosure are achieved by the embodiments described below. A prompt neutron is a neutron emitted immediately after the fission process; it is characterized by being emitted from a fission fragment generally after the fragment has reached a significant fraction of its final velocity, and thus may be referred to as a fully accelerated fragment. The final velocity is imparted to the fragment by the strong Coulomb repulsion between the fission fragments. Some neutrons arise from photon induced fission at the point of scission (just as the fragments break apart) but these have been shown to be small in number compared to those emitted by the fragments in flight. There are also delayed neutrons that arise following the beta-decay of some of the fragments, but these are not considered herein since they are only a small percentage of the neutrons emitted promptly and thus have a negligible effect on the practice of the methods disclosed herein. One of the advantages of utilizing prompt neutrons from photo-fission as a detection technique is that they are produced with approximately 200 times the yield of delayed neutrons; this allows for higher probabilities of detection, lower false positive rates, and faster scan times. The techniques and methods described herein make use of the boost in velocity (and thus energy) of a neutron that arises because the neutron is emitted from a rapidly moving nuclear fragment which has been produced by the (, f) process. This boost places the neutron in an energy range that will allow for the unambiguous determination of the presence of fissionable nuclei; this energy range is not possible from other processes that could occur with other non-fissionable nuclei such as direct neutron production by photons (γ, n). Additional features of interest are the nucleus-dependent angular distribution of the fragments in the photo-fission process and the prompt neutron energy distributions at various angles. Thus the signature of photon-induced fission is unique. Also, by controlling the incident photon energy used to cause the fission, (γ, n) processes from other nuclei may be reduced in importance or eliminated as a background. Since the process of photon-induced fission is ubiquitous with the actinides, these methods will identify fissionable nuclear materials within a container, in particular those which have Z equal to or greater than 89, that of actinium. This disclosure describes systems and methods for detecting fissile materials by measuring prompt neutron energies and examining prompt neutron energy spectra. The energy spectra of prompt neutrons that originate from photo-fission are readily distinguishable from the energy spectra of neutrons that originate from other processes that may occur in non-fissile materials such as (γ, n). Neutrons at energies greater than E=Eb−Eth, where Eth is the threshold for the (γ, n) process in relevant other heavy non-fissile elements and Eb is the endpoint energy of the incident bremsstrahlung photon beam (or the energy of an incident monochromatic photon beam), indicate with no ambiguity the presence of fissile material in the actinide region. No other photon-induced process can generate neutrons with these energies. Angular distributions of these neutrons reflect the angular distributions of the fission fragments from which they arise: distributions deviating significantly from isotropy indicate the presence of even-even nuclei while almost isotropic distributions indicate the presence of odd-even or even-odd fissile species. (Hereinafter, in the interests of conciseness, “odd-even” shall denote a nucleus with an odd number of nucleons, whether protons or neutrons, and thus the term hereinafter shall encompass both “odd-even” nuclei and “even-odd” nuclei). Comparison of the energy distribution of the prompt neutrons at different angles also provides potentially useful information about the species present. If the energy distributions at different angles are nearly identical, the isotopes undergoing fission are odd-even; if the energy distributions differ significantly at different angles, the isotopes undergoing photo-fission are even-even. Another signature of photo-fission is the fact that the relative yield of prompt neutrons at different neutron energies (i.e., the shape of the yield curve) does not depend upon the incident photon energy. This is in contrast to other processes such as (γ, n) where the relative yield of neutrons at different energies is strongly dependent on incident photon energy, particularly at the highest energies possible. For a better understanding of the present disclosure, together with other and further objects thereof, reference is made to the accompanying drawings and detailed description. Fission is a complex process that has been the subject of many theoretical and experimental studies. (See generally Bohr and Mottelson, “Nuclear Structure”, 1998, World Scientific Publishing Co. Pte. Ltd. Singapore, and references therein). However, common empirically established features imply certain general regularities of the process independent of nucleus or initiating particle. When fission is spontaneous, initiated by low energy neutrons or by the absorption of photons near the threshold for the (γ, f) process, the dominant mode of fission is the breaking apart of the nucleus into two fragments of unequal masses. These unequal masses are in the regions of nucleon numbers 95 and 140 for 235U and in similar regions for other fissionable nuclei. The fragments are accelerated by the strong Coulomb repulsion of their charges (Z1, Z2) and gain kinetic energy ranging approximately from 160 to 180 MeV, depending on the nucleus undergoing fission. Most of this Coulomb energy is gained in approximately 10−22 sec as the fragments separate by several nuclear diameters. The final fragment velocities correspond to kinetic energies of approximately 1 MeV/nucleon for the light fragment and approximately 0.5 MeV/nucleon for the heavy fragment. The rapidly moving fragments are generally excited and emit prompt neutrons, mostly after they have gained most of the kinetic energy available from the Coulomb repulsion. FIGS. 1A and 1B display the analysis by J. Terrell (“Neutron Yields from Individual Fission Fragments”, Physical Review, Vol. 127, Number 3, Aug. 1, 1962, pages 880-904, and references therein) for the neutron induced fission of 235U and 239Pu. These figures (which correspond to FIGS. 8 and 9 in Terrell) display the asymmetric fragment mass distributions from the neutron-induced fission and the average number of neutrons emitted from the heavy and light fragments, as a function of the mass of the fragments, for 235U and 239Pu. (The symbols ν, νL and νH in FIGS. 1A and 1B denote the average total number of neutrons emitted, the average neutrons emitted from the light fragment and the average neutrons emitted from the heavy fragment, respectively, as a function of fragment mass). Similar results have been obtained by Terrell for neutron-induced fission of 233U and the spontaneous fission of 252Cf, showing the generality of the phenomena. Many authors have studied the spontaneous fission of 252Cf, including Harry R. Bowman, Stanley G. Thompson, J. C. D. Milton and J. Swiatecki: “Velocity and Angular Distributions of Prompt Neutrons from Spontaneous Fission of 252Cf”, Phys. Rev., Volume 126, Number 6, Jun. 15, 1962, page 2120-2136 and references therein. These authors were able to demonstrate by direct measurement that: a) “The angular distribution (of the neutrons from the spontaneous fission of 252Cf) is strongly peaked in the direction of the fission fragments. The relative intensities in the direction of the light fragment, in the direction of the heavy fragment and at right angles are about 9, 5 and 1 respectively”: and b) “The broad features of the energy and angular distributions are reproduced by the assumption of isotropic evaporation (in the fragment frame of reference) of the neutrons from fully accelerated fragments.” While not the only important conclusions of the Terrell and Bowman works, those quoted and discussed here sustain the general description of spontaneous fission or fission at low energies that is important to the discussion herein. The work of H. W. Schmitt, J. H. Neiler, and F. J. Walter, “Fragment Energy Correlation Measurements for 252Cf Spontaneous Fission and 235U Thermal-Neutron Fission”, Phys. Rev. Volume 141, Number 3, January 1966, Page 1146-1160, provides additional evidence of the features described above. They find that the average total fragment kinetic energies before neutron emission are 186.5±1.2 MeV for the spontaneous fission of 252Ca and 171.9±1.4 MeV for neutron induced fission of 235U. The fragments have substantially all the kinetic energy available from the mutual Coulomb repulsion of the fragments. Both the energy distribution and the angular distribution of the neutrons from fission fragments created by photon-induced fission are relevant. The case of 232Th reported in C. P. Sargent, W. Bertozzi, P. T. Demos, J. L. Matthews and W. Turchinetz, “Prompt Neutrons from Thorium Photofission”, Physical Review, Volume 137, Number 1B, Jan. 11, 1965, Pages B89-B101 is illustrative. These authors measured the spectra of neutrons from the photo-fission of 232Th at pairs of angles simultaneously, 157 and 77 degrees relative to the photon beam, and 130 and 50 degrees relative to the photon beam. They used bremsstrahlung photons from electrons with kinetic energies of 6.75 and 7.75 MeV. Several subsidiary facts were important in their analysis: 1.) The (γ, n) threshold energy for 232Th is 6.438 MeV. Therefore, the (γ, n) process cannot contribute neutrons of energy greater than 0.31 MeV and 1.31 MeV, respectively at the two energies of the electron beam, 6.75 MeV and 7.75 MeV. Since these neutron energies are achieved only at the end points of the respective bremsstrahlung spectra, there will not be important contributions to the neutron spectra from the (γ, n) process even at neutron energies considerably lower than 0.31 or 1.31 MeV, respectively; and 2.) The fission fragments in photo-fission, (γ, f), are known to have strongly anisotropic angular distributions from 232Th. The distribution is peaked at 90 degrees to the incident photon beam, and the fragment angular distribution is given by I=a+b sin2(θ), where θ is the angle between the incident photon beam direction and the fission fragment direction. The ratio b/a is considerably larger than 1 at the energies discussed herein and remains larger than one even at incident photon energies higher than 9 MeV. (E. J. Winhold, P. T. Demos and I. Halpern, Physical Review, 87, 1139 (1952): and, A. P. Baerg, R. M. Bartholomew, F. Brown, L. Katz and S. B. Kowalski, Canadian Journal of Physics, 37, 1418 (1959)). This fragment directionality provides the correlation between neutron angle and neutron energy that results from the velocity boost if the prompt neutrons are emitted from fragments that have their full kinetic energy. The results of analysis of the neutron energy spectra from 232Th (γ, f) are consistent with the following conclusions of Sargent et al: 1.) The fraction of the prompt neutrons that result from emission from other than the fully accelerated fragments is 0.07±0.09; 2.) The prompt neutron angular distributions and energy distributions are consistent with isotropic neutron evaporation with a thermal-type spectrum in the center of mass frame of reference of the moving fragments, where the fragments are moving with their fully accelerated velocities; and 3.) The energy spectrum of the neutrons in the center of mass frame of reference is characterized by an average energy of 1.14±0.06 MeV. There are no significant components of temperature as high as or higher than this average energy. (That is, the ensuing Maxwellian energy distribution, were it applied to a fragment at rest in the laboratory frame of reference without the kinematic boost from the motion of the photo-fission fragments, would not yield many neutrons at the high energies that result from applying the kinematic boost to neutrons emitted in the fragment frame of reference). FIG. 7 presents angular distributions of prompt neutrons from the fission fragments produced in the (γ, f) process for incident photon energies near the threshold for the (γ, f) process, for 232Th and 238U. It is taken from S. Nair, D. B. Gayther, B. H. Patrick and E. M. Bowey, Journal of Physics, G: Nuclear Physics, Vol 3, No. 7, 1977 (pp 965-978), who corroborate the relevant 232Th results of Sargent et al. and also extend the results to the photo-fission of 238U. These angular distributions are measured by detectors which detect the fragments from neutron induced fission of 238U. Therefore, they are an average over all the energies of the neutrons emitted from the photo-fission fragments convoluted with the (n, f) cross section. This emphasizes neutrons above approximately 1 MeV, where the (n, f) cross section becomes large (See FIG. 10, which presents the (n, f) cross section for 238U. FIG. 10 is reproduced from National Nuclear Data Center, Brookhaven National Laboratory, ENDF, Evaluated Nuclear (reaction) Data File). FIG. 9, also taken from Nair, presents the angular distributions of the fragments from the photo-fission for 232Th and 238U, for the same incident photon energies as FIG. 7. The peaking of the neutrons from the photo-fission fragments in the direction of the motion of the fission fragments is clearly demonstrated by a visual comparison of FIG. 7 with FIG. 9. (The implications of the shape of the neutron angular distribution are discussed below). FIG. 2, which is taken from FIG. 4 of the Sargent et al. reference, displays the time-of-flight (energy) spectrum of prompt neutrons from photo-fission of 232Th at 77 degrees with respect to the direction of an incident 7.75 MeV. photon beam. At the top of FIG. 2 is the prompt neutron energy scale. One outstanding feature of the neutron spectrum in FIG. 2 is the presence of neutrons at very high energy compared to an evaporation (thermal) spectrum with an average energy of approximately 1.14 MeV, as reported by Sargent et. al. from their analysis of the energy and angular distributions of the prompt neutrons from photon induced fission of 232Th. For example, the intensity at 6 MeV is considerable. The presence of a large number of neutrons at high energy results in part from the considerable boost in velocity transferred to the neutrons by the moving fragments. For example, if the velocity of the fragment corresponds to a kinetic energy of 1 MeV/nucleon, then a 1 MeV neutron emitted in the fragment center of mass frame of reference in the direction of fragment motion will have twice the velocity in the laboratory frame of reference and a kinetic energy of 4 MeV. This follows because the neutron velocity in the laboratory frame is the sum of the fragment velocity and the neutron velocity in the fragment frame. Since these are the same for the energies and directions considered in this example, the velocity is doubled. The kinetic energy varies as the square of the velocity. Hence the neutrons with 1 MeV in the fragment frame of reference have 4 MeV in the laboratory frame of reference. More generally, if the fragment velocity is V and the co-directional neutron velocity in the fragment frame is v, then the neutron velocity in the laboratory frame is V+v. The kinetic energy of the neutron in the laboratory frame is E=(m/2)(V2+2Vv+v2) or E=Ef(1+2(En/Ef)0.5+En/Ef) where En is the neutron kinetic energy in the fragment frame and Ef is the kinetic energy of one nucleon of the fragment. Thus, in the above example, a neutron emitted in the fragment direction of motion at 2 MeV in the fragment center of mass frame of reference will have a laboratory kinetic energy of 5.8 MeV. Energy conservation in the direct (γ, n) neutron production process does not allow the production of neutrons with an energy above E=Eb−Eth, where Eb is the bremsstrahlung endpoint energy of the incident photon beam and Eth is the (γ, n) threshold energy for producing neutrons from other relevant heavy elements. Therefore, detecting neutrons with energies above this value is definitive evidence of the presence of fission. Since the (γ,n) threshold of 232Th is 6.438 MeV, a neutron energy of 6 MeV will not be possible from (γ, n) until the bremsstrahlung endpoint reaches 12.438 MeV. Also, even when the bremsstrahlung endpoint reaches that value, neutrons from the (γ, n) process will be very small in number because they can only be produced by the few photons at the bremsstrahlung endpoint energy. These energetic considerations apply in a similar manner for all fissionable nuclear materials, in particular for those with Z≧89, the region of the actinides. In addition, and most importantly, most heavy elements such as Bi, Pb, W, Ta, etc. have isotopes with (γ, n) thresholds at or above 6.5 MeV. Therefore, finding neutrons with energies above E=Eb−Eth where Eth is in the range of 6 MeV constitutes a very definitive test for the presence of fissile material. Another test to verify that the detected neutrons result from photo-fission is the sensitivity of the yield of neutrons at energies above E=Eb−Eth to a modest increase in incident photon energy. In particular, measuring the increase in yield relative to the yield of neutrons below this energy is significant. The increase or relative increase in neutron yield is not substantial when the neutrons are emitted from photo-fission fission fragments because energetic considerations independent of the exact incident photon energy, such as the boost in velocity from fission fragment motion, are most important in determining the yield. FIG. 3 displays spectra of (γ, n) neutrons for gold. (It is FIG. 2 from W. Bertozzi, F. R. Paolini and C. P. Sargent, “Time-of-Flight Measurements of Photoneutron Energy Spectra”, Physical Review, 119, 790 (1958)). FIG. 3 illustrates how the nature of the (γ, n) process causes neutrons produced by that process to be concentrated mostly at low energies. The data in FIG. 3 are normalized to yield the same number of neutrons from the (γ, n) process in a reference target of 2D with neutron energies En>1.4 MeV. Because photon and neutron energy are uniquely related in the (γ, n) process in 2D, this normalization allows the formation of the difference photon spectrum (the difference between the high energy (15.8 MeV) bremsstrahlung spectrum and the low energy (14.3 MeV) bremsstrahlung spectrum), which corresponds to a broad band of photons centered at approximately 14.5 MeV and with approximately a 2 MeV half width. That is, the neutron energy spectrum produced by the difference in the neutron energy spectra at the two energies in FIG. 3 corresponds to photo neutrons produced by photons in the above energy band centered at approximately 14.5 MeV. FIG. 3 confirms that, because neutrons produced by the (γ, n) process are concentrated mostly at low energies, the contamination of a photo-fission spectrum by neutrons from the (γ, n) process is expected to be low at higher neutron energies, even when one looks at neutrons at energies below the E=Eb−Eth cutoff established by the strict application of energy conservation. The spectra in FIG. 3 show the rapid, almost exponential decrease of neutrons from the (γ, n) process with increasing neutron energy, in contrast to the neutron spectrum from the photo-fission (γ, f) of 232Th at 7.75 MeV bremsstrahlung energy as shown in FIG. 2. For gold the neutron spectrum from (γ, n) is nonexistent with if the bremsstrahlung spectrum endpoint is 7.75 MeV, since the (γ, n) threshold, Eth, is above 8 MeV. Even with a 12 MeV bremsstrahlung endpoint, the highest neutron energy from (γ, n) in gold would be less than 4 MeV., and neutrons in this energy range from (γ, n) would not be numerous because they would correspond to photons at the endpoint of the bremsstrahlung spectrum. The neutron yield from (γ, f) in 232Th is very large at 12 MeV bremsstrahlung for neutron energies above 6 MeV. Table 1 gives the (γ, f) and the (γ, n) thresholds (in MeV) for some typical nuclei in the actinide region. The (γ, f) thresholds are from H. W. Koch, “Experimental Photo-Fission Thresholds in 235U, 238U, 233U, 239Pu and 232Th”, Physical Review, 77, 329-336 (1950). The (γ, n) threshold of 207Pb is also listed, as it is a component in natural lead material that may be used as a shield against detection of fissile materials. The table shows the maximum neutron energy available from the (γ, n) process for bremsstrahlung end point energies up to 11 MeV, including for 207Pb. This energy is to be compared to the spectrum in FIG. 3 showing many neutrons with energies in excess of 6 MeV from 232Th photo-fission using bremsstrahlung of only 7.75 MeV. Even with an 11 MeV bremsstrahlung energy there are no neutrons above 5.7 MeV from any nucleus, and no neutrons above 4.26 from 207Pb, and those at or near these energies would be very few in number because they correspond to the photons at or near the end-point energy of the bremsstrahlung spectrum. It should be noted that the (γ, f) process increases in importance as the bremsstrahlung endpoint energy increases from 6 to 11 MeV because of the increasing cross section with energy and because of the increasing number of photons in the bremsstrahlung spectrum at lower photon energies where the (γ, f) cross section is sizable. The (γ, f) thresholds are almost all lower than the (γ, n) thresholds, and are all significantly lower than the (γ, n) threshold for 207Pb. TABLE 1Maximum Neutron Energies from (γ, n) for Selected BremsstrahlungEnergies and Isotopes.Maximum (γ, n) Neutron Energy (MeV)Bremsstrahlung γ Endpoint Energy,(γ, f) Threshold(γ, n) ThresholdEb (MeV)Element(MeV)(MeV)67891011232Th5.40 ± 0.226.438—0.561.562.563.564.56233U5.18 ± 0.275.7590.241.242.243.344.345.34235U5.31 ± 0.275.2980.701.702.703.704.705.70238U5.08 ± 0.156.154—0.851.852.853.854.85239Pu5.31 ± 0.255.6470.351.352.353.354.355.35207Pb—6.738—0.261.262.263.264.26 The data in Table 1 indicates how the yield of neutrons above a specified energy would change as the bremsstrahlung endpoint energy is changed. For 207Pb, Table 1 indicates, there would be no neutron yield above 4 MeV until the electron beam energy exceeded approximately 11 MeV. (For gold, as discussed above in connection with FIG. 3, the electron beam energy would have to exceed 12 MeV to provide a neutron yield above 4 MeV). However, the yield of neutrons above 4 MeV for the actinides would be a strongly increasing function of electron beam energy starting below 6 MeV electron beam energy since the low (γ, f) threshold allows the photo-fission process to grow rapidly as more and more photons are available for photo-fission, all of them producing a neutron spectrum independent of photon energy and strongly populating the selected region of neutron energy (above 4 MeV for example). The (γ, n) process in the actinide examples shown in Table 1 or in other heavy metals such as 207Pb would not be a significant component of the total yield until the electron beam energy is well above 10 MeV since the process involves only the photons near the bremsstrahlung endpoint, Eb. An additional point, which will be discussed further below, is that the photo-fission cross section is larger than the (γ, n) cross section over most photon energies by a considerable amount, as shown in FIGS. 5B and 5D. The neutrons from (γ, f) will dominate (γ, n) in most situations simply on the basis of the cross sections, aside from the other features discussed herein. The data in Table 1 is based upon continuous bremsstrahlung spectra with specific endpoint energies, but a similar discussion applies to monochromatic photon beams. The neutron energy spectra from photo-fission retains the same dependence on neutron energy for different photon energies, but the total yield is modulated for monochromatic photons only by the cross section for (γ, f) at the specific photon energy. In contrast, the total yield for neutron production from a bremsstrahlung beam is modulated by the convolution of the bremsstrahlung spectrum with the (γ, f) cross section. The maximum neutron energy from (γ, n) dictated by energy conservation considerations for monochromatic incident photons follows just as discussed above. Other energies than 4 MeV could be used as the “trigger” or cutoff for defining the presence of fissionable nuclear material. That is, for any specific electron beam energy, a “trigger” energy can be selected such that the presence of neutrons with an energy above that “trigger” energy will be energetically impossible for the (γ, n) process in relevant heavy materials such as 207Pb and therefore any neutrons detected could only originate from the photo-fission process in an actinide. The data in FIG. 2 show that there are many neutrons above 6 MeV from the (γ, f) process, and hence 6 MeV could be selected as a “trigger” energy. Other “trigger” energies are possible also; the choice is dependent on factors such as the speed of detection that is desirable, the false positives that are to be allowed, and the efficiency of detection that is desired. In addition, the choice may be dictated by the specific nature of the cargo in a container; if the cargo is made of materials with high (γ, n) thresholds, such as copper, aluminum, steel or oxygen, then a lower trigger could be selected. Conversely, hydrogenous material that naturally contains a small percentage of deuterium may be of concern because of its low threshold for the (γ, n) process, 2.2 MeV. However, because the energy release is shared almost equally by the neutron and proton, the maximum neutron energy is given by E=(Eb−2.2)/2 MeV and, for the example of an electron beam energy of 10 MeV, the maximum neutron energy is approximately 3.9 MeV and a 9.2 Mev photon results in a neutron energy of 3.5 MeV. Thus, a higher trigger may be appropriate A more important concern may be 9Be. It has a low (γ, n) threshold of only approximately 1.6 MeV and the energy sharing results in a neutron that has most of the available energy, E=(8/9)(Eb−1.6) MeV is the maximum neutron energy available. For the example of Eb=10 MeV, the maximum neutron energy is approximately 7.5 MeV. This high energy could present a serious background. However, one could distinguish neutrons from actinide photo-fission from neutrons from the (γ, n) process in 9Be by taking advantage of the fact that the (γ, n) process follows the strict rule for conservation of energy, so that E=(8/9)(Eb−1.6) defines the maximum neutron energy possible, while the photo-fission process has a neutron energy spectrum largely independent of the photon energy in the energy region under discussion, Eb less than approximately 15 MeV. Therefore, neutrons at an energy greater than E=(8/9)(Eb−1.6), where Eb is the photon beam energy or bremsstrahlung endpoint energy, is proof of a fissile material. At Eb=10 MeV, the presence of neutrons above approximately 7.5 MeV would be proof. At Eb=8 MeV, neutrons above 5.7 MeV would be proof. Also, the prompt neutron energy spectrum is independent of the photon energy while the (γ, n) process in 9Be produces a neutron spectrum that is strongly dependent on photon energy. This difference also permits distinguishing the presence of a fissionable element from the presence of 9Be. However, if there were concern that this measurement could not be reliably made, further steps could be taken. Operating at Eb=10 MeV, the maximum neutron energy from beryllium (γ, n) is approximately 7.5 MeV. By reducing the beam energy to 8 MeV, for example, the maximum energy neutron from beryllium (γ, n) would be reduced to 5.6 MeV but the photo-fission neutron energy distribution would be unchanged. If there are neutrons above 5.6 MeV the process is unquestionably photon induced fission. If there remains any doubt that neutrons are from fission, the photon beam energy can be further reduced. For example at 5 MeV photon or bremsstrahlung beam energy there will be little or no photo-fission. But beryllium (γ, n) will produce neutrons of up to approximately 3 MeV at that photon beam energy. The presence of these neutrons will clearly establish the presence of beryllium. From the yield of these neutrons, the contributions from beryllium to higher neutron energies when higher photon energies are used can be calculated, the neutron energy distribution from beryllium removed, and the remaining spectrum analyzed for the presence of actinide neutrons. Fortunately, 9Be is almost unique in this category. There are a few other nuclei with relatively low (γ, n) thresholds; 6Li, 13C, 17O and 149Sm are notable among these with thresholds of 5.66, 4.95, 4.14 and 5.87 MeV, respectively. The same procedures outlined above can be used to eliminate these sources as contributors masking fissionable nuclei. FIGS. 4A and 4B, from H. W. Koch, “Experimental Photo-Fission Thresholds in 235U, 238U, 233U, 239Pu and 232Th”, Physical Review, 77, 329-336 (1950), FIGS. 4 and 5, display the yield of fission fragments as a function of bremsstrahlung endpoint energy (“Peak Spectrum Energies”) for two isotopes, 235U (FIG. 4A) and 239Pu (FIG. 4B). These illustrate the rapid increase of the fission yield as a function of the energy of the electron beam used to produce bremsstrahlung. FIG. 4A also shows the dominance of the 235U contribution over the impurities of 238U in the enriched uranium sample. These data are based upon the detection of the actual photo-fission fragments. The yield of prompt neutrons follows approximately the same yield curve, since neutron emission in the photo-fission process is not dependent on the photon energy in the regions of interest below the Giant Electric Dipole Resonance at approximately 12 to 13 MeV photon energy. The emission of neutrons from the fragments is determined by the complex dynamics, discussed earlier, of splitting the fissioning nucleus into two fragments. As a result, the shape of the yield curve of prompt neutrons of a given energy as a function of bremsstrahlung energy will be essentially independent of the neutron energy. That is, the yield curve for 6 MeV neutrons will have the same dependence on bremsstrahlung endpoint energy as the yield curve for 2 MeV, 3 MeV, 4 MeV and etc. neutrons. This is in contrast with the yield curves for neutrons from the (γ, n) process, which will start at the endpoint energy given by Eb=Eth+En, where En is the neutron energy that is desired. They are thus displaced from the (γ, n) threshold energy, Eth, by the neutron energy, in contrast to the yield curves for (γ, f). This is a powerful signature that the neutrons detected are from photo-fission rather than from (γ, n). FIGS. 5A through 5D display the photon induced reaction cross sections for 239Pu. They are taken from FIG. 7 of B. L. Berman, J. T. Caldwell, E. J. Dowdy, S. S. Dietrich, P. Meyer, and R. A. Alvarez, “Photofission and photoneutron cross sections and photofission neutron multiplicities for 233U, 234U, 237Np and 239Pu”, Physical Review C Volume 34, Number 6, 2201-2214 (1986). FIG. 5A shows the total photon absorption cross section. FIG. 5B shows the partial cross section for (γ, 1n), single neutron emission. FIG. 5C shows the partial cross section for (γ, 2n), double neutron emission. FIG. 5D shows the partial cross section for (γ, f), photo-fission. The photo-fission cross section (FIG. 5D) is larger than the (γ, n) cross section (FIG. 5B) over most photon energies by a considerable amount. This displays the feature common to the actinides that photo-fission is a strong and often dominant process from the (γ, f) threshold throughout much of the Giant Electric Dipole Resonance. Given that the prompt neutron multiplicities from photo-fission range from approximately 2.5 to more than 3, prompt neutrons from the photo-fission process will dominate the incident photon reaction channel by a large factor at all neutron energies. This feature facilitates identifying the presence of actinide fissionable material despite the potential presence of other heavy elements such as Pb, even without considering the energy-conservation constraints on neutron energy. The photon absorption process in most heavier nuclei is dominated by neutron emission, and the total yield is governed by the giant dipole sum rule that the integrated cross section is proportional to NZ/A, which is a slowly varying function. Since the location of the giant dipole resonance in energy also is a slowly varying function of nuclear mass, a yield of prompt neutrons from the photo-fission process that is 2.5 to 3 times the expected neutron yield from (γ, n) is a signal of photo-fission in that the (γ, f) neutron yield alone will produce a markedly higher photon absorption cross section than would (γ, n) for a given quantity of heavy material. That is, measuring the yield of neutrons per heavy nucleus per photon permits identifying photo-fission as present, if the quantity of heavy material present can be determined by measuring localized density by other methods. The angular distribution of the prompt neutrons and the relationship of the neutron energy to the fragment angular distribution also are signatures of fissile material and the photofission process, and can be used in detection schemes. The fragment angular distributions are not as distinct for odd-even nuclei as for even-even nuclei, in part because of the high population of spin states. Odd-even nuclei angular distributions are almost isotropic as reported by L. P. Geraldo, “Angular Distribution of the Photofission Fragments of 237Np at Threshold Energy”, Journal of Physics G: Nuclear Physics, 12 1423-1431 (1986), which shows angular anisotropy of approximately 10% at 5.6 MeV, 6% at 6.61 MeV and ˜2% at 8.61 MeV. These results are very much in contrast with the large anisotropy for fragments from the photo-fission of even-even nuclei where ground state spins are zero. Thus, once actinide photo-fission is detected, a nearly isotropic neutron angular distribution is an indicator of an odd-even fissile species such as 235U, 237Np and 239Pu. A strongly anisotropic neutron angular distribution would indicate an even-even fissile species such as 232Th and 238U. (See S. Nair, D. B. Gayther, B. H. Patrick and E. M. Bowey, Journal of Physics, G: Nuclear Physics, Vol 3, No. 7, 1977 (pp 1965-1978) and references therein, for example). The energy distributions of the neutrons at various angles are themselves indicators of the fragment anisotropy, and thus of the type of nucleus. This fact was used in the analysis of the work by Sargent et al, discussed above. If the fragments are strongly anisotropic (even-even fissile species), then the energy spectra of the neutrons will show distinct differences at different directions with respect to the photon beam. As an example, if the fragments are strongly peaked at 90 degrees with respect to the photon beam, then the neutron spectrum at 90 degrees will exhibit to a different degree the boost in velocity due to the velocity of the fragments than the neutron spectrum at angles near 180 degrees or 0 degrees to the photon beam. However, if the fragment angular distribution is nearly isotropic (odd-even fissile species), then the energy distribution of the neutrons will be the same at all angles. In both situations, the higher energies reflect the motion of the fragments, but the contrast in the energy distribution of the neutrons at different angles will reflect the fragment anisotropy with angle. The fragment angular distributions dominate the neutron angular distributions and the neutron energy distributions as a function of angle. The results of E. J. Winhold, P. T. Demos and I. Halpern, Physical Review, 87, 1139 (1952); E. J. Winhold and I. Halpern, Physical Review, 103, 990-1000 (1956); and, A. P. Baerg, R. M. Bartholomew, F. Brown, L. Katz and S. B. Kowalski, Canadian Journal of Physics, 37, 1418 (1959) show the fragment angular distributions for various isotopes. The following abstract from Berg et al. is offered as a summary of the data in that paper: Angular distributions of photofission fragments relative to the photon beam have been measured as a function of maximum bremsstrahlung energy in the range 6-20 Mev. The nuclides U-233, U-235, Np-237, Pu-239 and Am-241 give an isotropic distribution at all energies studied. The nuclides Th-232, U-234, U-236, U-238, and Pu-240 give anisotropic distributions which can be described by an equation of the form W(Θ)=1+α sin2 Θ, where Θ is the angle between fragment and beam. The degree of anisotropy is large at low energy and falls rapidly as the energy is increased. At a given energy Th-232 has the greatest degree of anisotropy and Pu-240 the least. The result quoted in the abstract is in basic agreement with that of the other papers referred to herein. In addition, some greater detail about the results from Berg et al. is shown in the two tables taken from that reference: TABLE 2Angular Distributions (from Berg, et al. Table I)Angular distributionsRatio, counts at 90°/counts at 0°*NuclideE0† = 6.0E0 = 6.5E0 = 8.0E0 = 10.0E0 = 20.0U-2331.048 ± 0.071.032 ± 0.040.994 ± 0.03U-2351.084 ± 0.05Np-2371.024 ± 0.10Pu-239‡1.034 ±0.937 ±1.002 ± 0.061.013 ± 0.050.952 ± 0.03Am-2410.260.120.958 ± 0.07*The ratio is the number of counts observed at 90° per unit X-ray dose divided by the number observed at 0° for the same dose.†E0 is the maximum energy in million electron volts of the bremsstrahlung spectrum.‡45°/0° ratio at E0 = 6.5 Mev was 1.09 ± 0.23. TABLE 3Corrected Values of α (from Berg, et al. Table VI)Corrected values of α in W(θ) = 1 + α sin2 θE0Th-232U-238U-236U-234Pu-2406.06.6 ± 2 6.0 ± 2.36.36.7 ± 1.16.5>254.4 ± 1.02.1 ± 0.42.3 ± 0.60.65 ± 0.207.011.0 ± 0.8 2.05 ± 0.241.33 ± 0.170.90 ± 0.160.49 ± 0.127.510.3 ± 1.6 8.04.9 ± 0.61.3 ± 0.10.79 ± 0.090.44 ± 0.080.29 ± 0.079.02.8 ± 0.40.51 ± 0.079.40.44 ± 0.0410.01.61 ± 0.120.41 ± 0.050.32 ± 0.060.17 ± 0.0714.00.46 ± 0.090.09 ± 0.040.04 ± 0.0815.0 0.02 ± 0.04* 0.01 ± 0.03*20.00.14 ± 0.060.05 ± 0.03*These values, which do not differ from zero, have not been corrected for isotopic composition. Table 2 (“Angular Distributions . . . ”) shows that the ratio of events at 90 degrees to those at 0 degrees for the photo-fission of the odd-even isotopes shown is approximately equal to 1 over the energy range of the bremsstrahlung endpoints shown in the table. Thus, the value of b/a discussed earlier is 0 and the angular distribution is isotropic. Table 3 (“Corrected values . . . ”) shows the fit to the normalized form of the angular distribution as exhibited in the table also as a function of bremsstrahlung endpoint. The derived angular distributions are clearly anisotropic. From these data, the quoted abstract, and the theoretical basis referred to in the references herein, the generalization is accurate; the odd-even actinides undergo isotropic photo-fission while the even-even actinides undergo anisotropic photo-fission. In particular, the result is experimentally demonstrated for the isotopes most likely to be used for a nuclear weapon, 235U, 239Pu and 237Np. These will undergo isotropic photo-fission, in contrast to 238U, 232Th and the other even-even isotopes that were measured. FIG. 9, which displays the fission fragment angular distributions from photo-fission of an even-even nucleus, and FIG. 7, which displays the angular distributions of the prompt neutrons emitted from those fragments, demonstrate the general peaking of the fragment and neutron angular distributions at 90 degrees relative to the photon beam. The neutron yield at 150 degrees is approximately 20% less than that at 90 degrees and the shape of the distribution is approximately symmetric about 90 degrees. The fragment angular distributions show a larger anisotropy as expected because the neutron distributions are produced by folding the isotropic angular distributions in the fragment center of mass with the fragment distributions in angle. In contrast to these distributions, the isotopes 235U, 239Pu and 237Np (not shown), which may be used in the manufacture of weapons, display for the most part isotropic angular distributions of the photo-fission fragments as discussed above and the resulting angular distributions of the prompt neutrons also are isotropic. One embodiment of a detector system to carry out the methods described herein requires a source of photons with energy capable of exceeding the (γ, f) threshold and a detector for neutrons. The photons may be monochromatic, may be produced by a source capable of variable energy, or may be distributed over a broad range of energy with a good definition of the highest energy possible, such as an electron-generated bremsstrahlung spectrum in accordance with the discussion above. When an accelerator is used to provide the electrons, the electron accelerator may have the capability to vary the energy of the electron beam from below the fission barrier (threshold) to higher energies in order to exploit all the modalities discussed above. Any neutron detector that is capable of distinguishing neutron energy is appropriate. A detector that takes advantage of energy deposition, such as proton recoil from neutron elastic scattering in a hydrogenous scintillator, is a possible choice. A detector that measures a reaction energy induced by the neutron is another possible choice. A method of measuring neutron energy by time of flight is also an appropriate detection scheme. The energy resolution required for such detection methods will have to be sufficient to eliminate neutrons from the (γ, n) process in materials other than actinides, as discussed above. Because the contamination of non-actinide (γ, n) can be controlled and rendered small by the choice of incident photon energy (or bremsstrahlung endpoint) and neutron energy measured, the resolution required is well within a number of measurement techniques. Specific resolutions required may depend in detail on the particular situation under consideration, but resolutions of approximately 0.5-0.75 MeV at 4 to 6 MeV neutron energy may be adequate. A detection method may be required to operate in a possible flux of photons in some embodiments, these photons being produced by scattering from the material under study in the direction of the detectors. Photons may also be produced by natural radioactivity and cosmic rays. Therefore, the neutron detectors may have to be shielded using passive and active shielding techniques. In addition, as a consequence of the above, a neutron detector may be required to distinguish between photons and neutrons. This can be accommodated by the reaction process used, the time of flight of the photons compared to neutrons and by the ability of the detector to distinguish between the deposition of energy by heavy particles (e.g., neutrons) compared to electrons. Organic and inorganic scintillators that have different decay times according to the density of ionization produced by the passage of a charged particle may be suitable. Separation of photons from neutrons may be achieved in such scintillators utilizing signal processing techniques that exploit these different charged particle responses. FIG. 11 demonstrates the energy separation of prompt neutrons from photon induced fission from neutrons produced from the (, n) reaction, when incident photon energies below 9 MeV are used. That Figure was obtained using 9 MeV bremsstrahlung beams produced at the CW S-DALINAC at the Technical University of Darmstadt. The spectra from Pb and highly enriched uranium (HEU) targets shown in FIG. 11 were obtained using the technique proposed for the CAARS PNPF module. An organic liquid scintillator was used to determine the energy deposited in the detector and to separate photon and neutron events. The lighter data points represent events from Pb (which as discussed above has a (, n) threshold of approximately 6.5 MeV for the 207Pb isotope) and the darker represent events from HEU (which has a photo-fission threshold of 5.5 MeV). The neutron events are grouped in the lower portion of the figure and are clearly differentiated from the photon events above. Within the neutron events, the box shows where the neutrons from prompt photo-fission in HEU appear unambiguously. A neutron signal in this region is an unambiguous signal of an actinide photo-fission event. One exemplary embodiment of a system 600 for detecting fissile materials in a container by analyzing energetic prompt neutrons resulting from photon-induced fission is illustrated in FIG. 6. An electron beam 602 of energy Eb is generated by an electron accelerator 601. The electron beam 602 makes bremsstrahlung radiation photons when it strikes a bremsstrahlung target 603 (also called the radiator). The electron accelerator 601 and radiator 603 optionally may be replaced by a source of monochromatic or nearly monochromatic photons. The optional collimator 604 collimates the bremsstrahlung radiation. A shield 605 may enclose the bremsstrahlung target 603 and electron accelerator 601. The photon beam 607 is directed onto a container 606 which is to be analyzed and which may contain fissile material 608. The distances of the fissile material 608 from (for example) three of the walls of container 606 are designated as x, y and z. A photon detector 609 placed after the container 606 optionally may be used to monitor the transmitted photon flux of photon beam 607. Detectors 610, 611, 612, and 613 may be placed at locations around the container 606 at approximately 90 degrees and at convenient back angles with respect to the collimated photon beam 607. The number and location of the detectors may be varied from that shown in FIG. 6 according to the principles and methods discussed above. In the illustrated embodiment, the detectors 610 and 611 may be placed at known distances L610 and L611 from the container 606 walls. The detectors 610, 611, 612, and 613 optionally may be surrounded by shielding (not shown) and by anti-coincidence counting systems (not shown) if desired. The detectors 610, 611, 612, and 613 themselves may be sensitive to neutron energy or they may be part of a system (such as one utilizing time-of-flight) that will provide a neutron energy for each detected neutron event. A beam dump 614 may be used to absorb the remaining photon flux after the photon beam 607 passes through the container 606 and its contents. The beam dump 614 and optional transmitted flux monitor, detector 609, may be shielded from direct view of the detectors as required. Signals from the detectors 609, 610, 611, 612, and 613 are connected by way of connections 615 to signal processing electronics and/or computer 616, which process the detector signals and optionally may relay them and/or processed information by way of connections 617 to a central control and data analysis and storage system (not shown). Alternatively, the detector signals may be passed directly to the central system for processing and analysis. As an alternative to determining neutron energy directly in the neutron detector, a low duty cycle LINAC (e.g. Varian linatron) or other suitable electron accelerator may be pulsed to permit a time of flight (TOF) technique. Compared to other detection techniques, such as pulse shape discrimination using a continuous incident photon beam, the TOF method is expected to have a higher efficiency for collecting high energy neutrons, reduced environmental background, and a higher likelihood of determining angular distributions. The TOF method may use a shortened pulse structure (10 ns) and gated detectors to reject gamma flash. The advantages inherent in the TOF method, combined with the modified LINAC and detectors, may partially compensate for the reduced duty cycle of commonly deployed pulsed accelerators. In a time-of-flight (TOF) embodiment, the electron accelerator 601 or other source may be pulsed to produce electron beam 602 (pulsed on) for a time period T and turned off for a time long enough to have all the detectable neutrons (resulting from interactions of the photon beam 607 with the container 606 and its contents) pass through the detector(s). Then the electron beam 602 may be pulsed on again for a time period T. This sequence may be repeated until the desired detection data is obtained. The electron accelerator 601 or some subsidiary target (not shown) near the bremsstrahlung target 603 or in the bremsstrahlung or photon beam 607 may provide a fiducial signal that informs the signal processing electronics and/or computer 616 when the photon beam 607 was generated. Neutrons generated by photofission in the fissile sample 608 travel to a detector in the time L/v where L is the distance from the fissile sample 608 to the detector in question and v is the neutron velocity. For detector 611, for example, which is opposite the fissile sample 608 at a right angle to the incident photon beam 607 in the embodiment shown, L=L611+y, the distance from the fissile sample 608 to the corresponding wall of the container 606 nearest detector 611. The velocity of the neutrons is given by v=(2E/m)1/2, where E is the neutron kinetic energy and m is the neutron mass. The signal from detector 611 goes to the signal processing electronics and/or computer 616, which converts the difference between the fiducial signal arrival time and the detector 611 signal arrival time into the time-of-flight (TOF) of the neutron to the detector. Using the relation TOF=(L611+y)/v, the signal processing electronics and/or computer 616 calculates the neutron velocity and therefore its energy (E=mv2/2) and records the data and also transfers it to a central control and analysis system (not shown). The energy resolution of the detection system will depend on the TOF of the neutrons, T, L and the dispersion of the flight distance to different portions of the detectors. Those experienced in the art will recognize that these parameters, including the electron beam pulse width T, and the geometry of the system can be adjusted to achieve energy resolution adequate for the purposes of this disclosure. The (narrow) photon beam 607 may be scanned across the container 606 sequentially to illuminate discrete columns where the fissile sample 608 may be located. This serves to better localize the position of any fissionable material and will reduce backgrounds from other neutron producing materials in a container. Alternatively, the photon beam 607 may be a wide fan-like beam encompassing a greater region of the container 606 with the fan opening out in the direction toward the detectors at 90 degrees, for example. This allows a broad scan region of the container but limited in the narrow direction. Such an embodiment would facilitate scanning the container in shorter times for fissile materials. It would detect fissile materials distributed over the dimensions of the fan beam. In this geometry x and y will not be known but they may be inferred from a comparison of the neutron energy spectra on both sides of the container since they should be very close to identical, especially at the highest energies. Starting with any assumption for “a”, such as ½ the width of the container (x=y), the resulting spectra can be adjusted by varying “a” until the spectra are made to have the same high-energy shape. The technology for short duration electron beam pulses is a well-known art, and pulses of a few nanoseconds are readily generated for high energy electron beams. Time of flight for a 1 MeV neutron over 1 m is 72 nanoseconds. Thus, flight distances of a few meters result in flight times (˜71 nanoseconds for 6 MeV neutrons over a distance of 3 meters, for example) that allow beam pulse duration times of 10 to 20 nanoseconds to separate photo-fission neutrons from those from (γ, n) processes by energy selection. Other specific embodiments are possible and some are mentioned herein as further illustrations of methods to articulate the concepts and methods described earlier. The detectors 610, 611, 612, and 613 in FIG. 6 can be any that are capable of unambiguously detecting a neutron. Rather than measuring the neutron time of flight to determine its energy, it would suffice in some applications to only specify that the event is definitely a neutron and that the energy is greater than a defined amount. This would characterize the neutron energy as above a defined quantity. Several such neutron energies may be involved. Together with control of the electron beam energy or photon energy as discussed above, determining the number of neutrons with energies above certain preset quantities will classify the neutrons as from photo-fission. As discussed above, other processes such as (γ, n) will not be possible at neutron energies greater than E=Eb−Eth, where Eb is the bremsstrahlung endpoint or the photon energy and Eth is the threshold for (γ, n) for relevant non-actinide materials that may be present and need to be distinguished from the suspected actinide. As discussed above, the energy distribution of neutrons from photo-fission is very independent of the energy of the photons used to induce photo-fission in the photon energy regions discussed herein, in or below the Giant Electric Dipole Resonance. Another embodiment uses this fact to determine whether the neutrons originate from photo-fission. Varying the photon energy or the bremsstrahlung endpoint energy will not substantially alter the energy distribution of the neutrons from photo-fission. However, this is not true for other processes such as (γ, n), especially in the higher regions of neutron energy, as a result of energy conservation and the requirement E=Eb−Eth discussed earlier. Therefore, measuring the energy distribution of the neutrons for different photon energies, and comparing the results, can identify actinide photo-fission. Alternatively, measuring and comparing the number of neutrons above a certain energy as the photon energy is changed can achieve the same result. Another embodiment would measure the neutron yield at a given neutron energy, as the photon energy is varied, and would do this for several neutron energies. This would generate yield curves for neutrons of the given energies as a function of photon energy. Because the neutron energy spectra from photon-induced fission is independent of the incident photon energy, the same yield curve as a function of photon energy would result for all neutron energies if the spectrum is dominated by photo-fission. However, if the neutron spectrum originates from (γ, n) for relevant non-actinide materials, each neutron energy has a yield curve as a function of photon energy displaced in photon energy by that explicit neutron separation energy, in particular for the neutrons at the highest energy possible. Once again this follows from energy conservation. Neutron detection can be based on reaction energies between the neutrons and the component materials in the detector. Detectors of such a nature may sometimes but not always be called “threshold detectors” because a reaction will occur only if the neutron energy is greater than a certain amount. Examples of such reactions include but are not limited to (n, n′γ), (n, n′f), (n, n′p), (n, n′d) and (n, n′α). Detection of the event may be based on, but not limited to, the detection of: a scintillation event and measuring the deposited energy; the charge created by ionization in a material and measuring the total charge; and, the detection of radioactive nuclei, wherein the radioactivity would be induced only if the neutron energy (energies) were greater than a certain value (or values). All such methods are included in the embodiments described in this disclosure. As discussed above, some commercially available plastic and liquid scintillators can identify neutrons unambiguously using suitable signal processing techniques. Such detectors also have fast enough time response to qualify for the purposes herein and these will be known to those skilled in the art. Such detectors operate in part as proton recoil detectors, based on the energy imparted to protons by the elastic scattering of neutrons from the protons in the hydrogenous material. Therefore, in part, they can function as “threshold detectors” as discussed above, as well as providing the time for an event in a detector and identifying the event as a neutron. Such detection methods are part of the embodiments described herein. Delayed neutrons following beta decay can also be detected by the methods discussed herein and serve as a method of detecting fissile materials. They will be less abundant than prompt neutrons by a very large factor, as discussed above. In most cases their presence can be used as a further detection method to augment the embodiments discussed herein. They can be distinguished from prompt neutrons by several techniques. Using TOF with a pulsed beam set to measure prompt neutrons, delayed neutrons appear as a uniform distribution in time that builds up with exposure time or the number of pulses in the TOF embodiment discussed above. The time for buildup of the delayed neutron signal is characteristic of beta-decay lifetimes. If the beam is turned off they will diminish in times characteristic of beta-decay lifetimes. The presence of the delayed neutrons may be neglected in many situations as a minor contribution. In some cases they may be used as an aid to the detection of fissile material. In all situations, the presence of delayed neutrons may be accounted for and the results corrected accordingly if the correction is required by these embodiments. The photon beams may be of the pulsed variety described above in discussing TOF embodiments, or they may be of continuous character as from continuous duty radiofrequency accelerators, DC accelerators or similarly functioning photon sources of a monochromatic or nearly monochromatic nature. Another scan embodiment would employ a very broad beam geometry in all directions transverse to the beam direction with collimation so as to limit the beam size to that of the container width in its largest manifestation. This embodiment would be very effective in the detection of fissile materials dispersed in small samples over a large volume, such as thin sheets broadly distributed over a large region of the container or small pellets broadly distributed. Many beam geometries are possible, each with specific advantages for certain situations as will be recognized by those skilled in the art, and they are all included in this disclosure. In order to carry out scanning of containers as rapidly as possible, it may be preferable to carry out an initial scan with a low threshold or trigger neutron detection energy, in order to maximize the signal from photofission, even at the cost of obtaining a signal from (γ, n) processes. If no events are recorded from the container or a portion thereof in an appropriate interval, or no events above an acceptable background, the scan can be continued to a further portion of the container, or the container can be passed on if th entire container has been scanned. If events are detected, the threshold or trigger neutron detection energy can be increased, and the container or portion thereof rescanned, using the higher neutron threshold or trigger detection energy to reduce or eliminate the contamination from the competing (γ, n) processes. Alternatively, of course, other of the methods set forth herein for discriminating between photofission and (γ, n) processes can be employed in the rescan. Because angular distributions may be difficult to measure given the differential absorption and scattering of different cargo loadings, it is important to recognize that, as discussed above, if the energy distribution of the prompt neutrons is independent of angle relative to the photon beam, then the fragments are emitted isotropically and the fissile material is an odd-even isotope: however, if the prompt neutrons have a spectrum with greater population at the higher energies at 90 degrees to the photon beam relative to the prompt neutron spectrum at large angles near 180 degrees, then the fragments have an angular distribution peaking at 90 degrees and the fissile material is an even-even isotope. Therefore, measuring the neutron energy distribution at two angles will enable this determination to be made. Another embodiment removes the uncertainty in the energy distribution and angular dependencies of the prompt neutrons caused by the differential absorption along different paths that neutrons take in traversing a container to the different detectors. This embodiment directs the photon beam into the container in different directions. For example, in one arrangement the photon beam may enter the container from the top and the neutron detectors view the neutrons at 100 degrees to the beam and at 170 degrees from the beam. By altering the photon beam direction to enter from the side of the container the detectors change roles. That one previously at 100 degrees is now at 170 degrees and the one previously at 170 degrees is now at 100 degrees. However, the differential aspects of neutron absorption remain exactly the same. The two measurements now provide a clear indication of the influence on the neutron energy distribution of the angle of emission of the neutron relative to the photon direction as well as the angular distribution of the neutrons relative to the photon beam direction. As one particular feature, if the photo-fission process is isotropic the relative neutron yields in the detectors will not change. A change indicates anisotropy in the original photo-fission process. This process can be generalized for other angles as well. For example, FIGS. 8A and 8B, each show a container 806 with fissile material 808. A first neutron detector 801 is shown in a first location and a second neutron detector 802 is shown in a second location. In FIG. 8A, a photon beam 807A irradiates the container 806 from a first direction (direction 1). In FIG. 8B, a photon beam 807B irradiates the container 806 from a second direction (direction 2) For each of the two photon beam directions, the neutron detectors 801 and 802 interchange angles relative to the photon beam (807A or 807B) direction. For beam direction 1, first neutron detector 801 is at angle θ1 and second neutron detector 802 is at angle θ2. For beam direction 2, first neutron detector 801 is at angle θ2 and second neutron detector 802 is at angle θ1. I1 and I2 are the photon beam intensities at the target 808 (which may be a fissile material) for photon beam directions 1 and 2 respectively. If S(E,θ) is the energy spectrum of neutrons produced in direction θ, the neutrons detected by the two detectors with photon beam direction 1 are described by the measured functions Fi(E, θj):F1(E,θ1)=I1×A1(E)×S(E,θ1) for first neutron detector 801; and,F2(E,θ2)=I1×A2(E)×S(E,θ2) for second neutron detector 802. The neutrons detected by the two detectors with beam in direction 2 are:F1(E,θ2)=I2×A1(E)×S(E,θ2) for first neutron detector 801; and,F2(E,θ1)=I2×A2(E)×S(E,θ1) for second neutron detector 802. The attenuation factors A1 and A2 remain invariant to the beam position and the ratio can be formed to eliminate these factors so that:{S(E,θ1)/S(E,θ2)}2={F1(E,θ1)×F2(E,θ1)}/{F2(E,θ2)×F1(E,θ2)}. (Equation 1) Thus, S(E,θ1) and S(E,θ2) are related via measured quantities and can be compared directly. A person skilled in the art will be able generalize this technique to more than two detectors and this embodiment is intended to contain all these variations. Unless otherwise specified, the illustrative embodiments can be understood as providing exemplary features of varying detail of certain embodiments, and therefore, unless otherwise specified, features, components, modules, and/or aspects of the embodiments can be otherwise combined, specified, interchanged, and/or rearranged without departing from the disclosed devices or methods. Additionally, the shapes and sizes of components are also exemplary, and unless otherwise specified, can be altered without affecting the disclosed devices or methods. Other specific embodiments are possible and some are mentioned herein as further illustrations of methods to articulate the concepts and methods described earlier. Although the terms “nuclear material”, “fissionable nuclear material”, “fissile material”, and “fissionable material” have been variously used in this disclosure, the intent of the inventors is that these terms are used interchangeably and are all intended to designate those materials that can be induced to fission by the effect of a gamma ray or by a thermal neutron or fast neutron. These terms are not intended to mean materials that emit neutrons in response to gamma or neutron irradiation, unless such materials also may be induced to fission by the effect of a gamma ray or by a thermal neutron or a fast neutron. The term “container” as used herein is intended to include any enclosure or partial enclosure that may enclose or partially enclose a fissionable material so as to hide or partly hide it or shield it or partly shield it from conventional detection methods—it includes but is not limited to cargo and shipping containers and vehicles. While the systems and methods disclosed herein have been particularly shown and described with references to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the disclosure. It should be realized this disclosure is also capable of a wide variety of further and other embodiments within the spirit of the disclosure. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, many equivalents to the exemplary embodiments described specifically herein. Such equivalents are intended to be encompassed in the scope of the present disclosure. |
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058959190 | abstract | The invention relates to a gun lens for generating a particle beam with a cathode, an extraction electrode, an anode and a condenser lens, wherein a deceleration field is generated between the extraction electrode and the anode and the condenser lens produces a magnetic field which is superimposed on both the cathode, the extraction electrode and the anode. |
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claims | 1. A heat dissipation structure, comprising:a housing having a bottom surface, a liquid inlet channel, a liquid outlet channel and a protruding portion, wherein the liquid inlet channel and the liquid outlet channel are located at two opposite ends of the housing and above the bottom surface, and the liquid inlet channel and the liquid outlet channel extend along a first direction, the protruding portion is located between the liquid inlet channel and the liquid outlet channel and above the bottom surface, the protruding portion protrudes away from the bottom surface, the protruding portion has a protruding surface facing away from the bottom surface, a highest position of the protruding surface is higher than a highest position of the liquid inlet channel and the liquid outlet channel, the protruding surface has a former half region, a latter half region and a first symmetric line, the first symmetric line extends along a second direction perpendicular to the first direction, the former half region and the latter half region are symmetric with each other relative to the first symmetric line and directly connected with each other at the first symmetric line along the first direction, a first distance between the protruding surface and the bottom surface is continuously increased first throughout the former half region and then continuously decreased throughout the latter half region along the first direction, and the protruding surface is a convex surface curved along the first direction, the housing is configured to support a target, a second distance between the target and the protruding surface along a third direction perpendicular to the target is continuously decreased first throughout the former half region and then continuously increased throughout the latter half region along the first direction. 2. The heat dissipation structure of claim 1, wherein the protruding surface has a second symmetric line extending along the first direction, and the protruding surface is symmetric relative to the second symmetric line. 3. The heat dissipation structure of claim 1, wherein the housing has a pair of buffering grooves respectively located at two opposite ends of the protruding portion and located between the liquid inlet channel and the liquid outlet channel. 4. The heat dissipation structure of claim 1, wherein a lowest position of the protruding surface is higher than the highest position of the liquid inlet channel and the liquid outlet channel. 5. A neutron beam generating device, comprising:the heat dissipation structure of claim 1;a tubular body disposed on the heat dissipation structure and having a channel; andan accelerator connected with the tubular body and configured to emit an ionic beam towards the target disposed between the heat dissipation structure and the tubular body through the channel. 6. A neutron beam generating device, comprising:the heat dissipation structure of claim 2;a tubular body disposed on the heat dissipation structure and having a channel; andan accelerator connected with the tubular body and configured to emit an ionic beam towards the target disposed between the heat dissipation structure and the tubular body through the channel. 7. A neutron beam generating device, comprising:the heat dissipation structure of claim 3;a tubular body disposed on the heat dissipation structure and having a channel; andan accelerator connected with the tubular body and configured to emit an ionic beam towards the target disposed between the heat dissipation structure and the tubular body through the channel. 8. A neutron beam generating device, comprising:the heat dissipation structure of claim 4;a tubular body disposed on the heat dissipation structure and having a channel; andan accelerator connected with the tubular body and configured to emit an ionic beam towards the target disposed between the heat dissipation structure and the tubular body through the channel. |
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claims | 1. A thermal neutron shielding material comprising:a panel containing a resin mixture, said resin mixture including the following constituents: styrene and a polymerization catalyst; andBoron Carbide, said Boron Carbide being nuclear grade Boron Carbide in particle form and comprises 50% of a first coarse particle size and 50% of a second fine particle size,wherein said panel is at least 46% Boron by weight. 2. The thermal neutron shielding material of claim 1 wherein said shielding is in a customizable panel form. 3. A neutron shielding structure comprising:one or more wall elements; andat least one neutron shielding panel element comprised of styrene and Boron Carbide being secured to said one or more wall elements, said Boron Carbide being nuclear grade Boron Carbide in particle form and comprises essentially 50% of a first coarse particle size and essentially 50% of a second fine particle size,wherein said neutron shielding panel element is at least 46% Boron by weight. 4. A method of constructing a neutron shielding material comprising:preparing a mixture including an unsaturated polyester resin in styrene, a curing agent, and nuclear grade Boron Carbide in particle form that comprises essentially 50% of a first coarse particle size and essentially 50% of a second fine particle size;pouring said mixture; andcuring said mixture so as to obtain a finished panel element,wherein said finished panel element is at least 46% Boron by weight. |
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claims | 1. A specimen preparation device comprising:a specimen stage on which a specimen is mounted;an ion beam optical system configured irradiate an ion beam;transfer means for transferring an excising specimen separated from the specimen by means of ion beam irradiation; andan arithmetic unit configured to control the ion beam optical system,wherein the device is structured such that when an ion beam is irradiated on the specimen to separate the excising specimen from the specimen, a mark formed in a region, which makes the excising specimen, on the specimen and a mark formed in another region other than said region are measured and the ion beam irradiation is stopped in the case where a relative position between the marks is put in a predetermined condition. 2. A specimen preparation device comprising:a specimen stage on which a specimen is mounted;an ion beam optical system configured to irradiate an ion beam;transfer means for transferring an excising specimen separated from the specimen by means of ion beam irradiation; andan arithmetic unit configured to control the ion beam optical system,wherein the device is structured such that when an ion beam is irradiated on the specimen to separate the excising specimen from the specimen, a mark formed on the transfer means holding a region, which makes the excising specimen, on the specimen and a mark formed in another region other than said region, which makes the excising specimen, on the specimen are measured and the ion beam irradiation is stopped in the case where a relative position between the marks is put in a predetermined condition. 3. A specimen preparation device comprising:a specimen stage on which a specimen is mounted;an ion beam optical system configured to irradiate an ion beam;transfer means for transferring an excising specimen separated from the specimen by means of ion beam irradiation; andan arithmetic unit configured to control the ion beam optical system,wherein the device is structured such that when the transfer means is moved and brought into contact with the excising specimen, a mark formed on the transfer means and a mark formed in a region, which makes the excising specimen, on the specimen are measured and the transfer means is stopped in the case where a relative position between the marks is put in a predetermined condition. 4. A specimen preparation device comprising:a specimen stage on which a specimen is mounted;an ion beam optical system configured to irradiate an ion beam;transfer means for transferring an excising specimen separated from the specimen by means of ion beam irradiation; andan arithmetic unit configured to control the ion beam optical system,wherein the device is structured such that when the transfer means is moved and brought into contact with the excising specimen, a mark formed on the transfer means and a mark formed in a region other than another region, which makes the excising specimen, on the specimen are measured and the transfer means is stopped in the case where a relative position between the marks is put in a predetermined condition. 5. A specimen preparation device comprising:a specimen stage on which a specimen is mounted;an ion beam optical system configured to irradiate an ion beam;transfer means for transferring an excising specimen separated from the specimen by means of ion beam irradiation;a specimen holder configured to hold the excising specimen; andan arithmetic unit configured to control the ion beam optical system,wherein the device is structured such that when the excising specimen held on the transfer means is transferred to the specimen holder, a mark formed on the excising specimen and a mark formed on the specimen holder are measured and movement of the transfer means is stopped in the case where a relative position between the marks is put in a predetermined condition. 6. A specimen preparation device comprising:a specimen stage on which a specimen is mounted;an ion beam optical system configured to irradiate an ion beam;transfer means for transferring an excising specimen separated from the specimen by means of ion beam irradiation;a specimen holder configured to hold the excising specimen; andan arithmetic unit configured to control the ion beam optical system;wherein the device is structured such that when the excising specimen held on the transfer means is transferred to the specimen holder, a mark formed on the transfer means for transfer of the excising specimen and a mark formed on the specimen holder are measured and movement of the transfer means is stopped in the case where a relative position between the marks is put in a predetermined condition. 7. The specimen preparation device according to claim 1, further comprising an electron beam column configured to irradiate an electron beam, and wherein the marks are measured by the electron beam. 8. The specimen preparation device according to claim 1, wherein an ion beam condition in measuring the marks can be changed to an ion beam condition in processing a specimen. 9. The specimen preparation device according to claim 1, wherein the ion beam comprises a focused ion beam. 10. The specimen preparation device according to claim 1, wherein the ion beam comprises a projection-type ion beam. 11. The specimen preparation device according to claim 1, wherein the transfer means comprises a probe. 12. The specimen preparation device according to claim 11, wherein the probe is provided with a step at a region which comes into contact with the excising specimen. 13. The specimen preparation device according to claim 11, wherein the probe includes at a tip end thereof two or more steps aligned in an axial direction of the probe. 14. The specimen preparation device according to claim 11, wherein the probe includes at a tip end thereof at least two or more steps aligned in a direction substantially perpendicular to an axis of the probe. 15. The specimen preparation device according to claim 1, wherein the transfer means comprises a micro manipulator. 16. The specimen preparation device according to claim 1, wherein the specimen stage and/or the transfer means are/is finely driven so that pressure is generated between the excising specimen and the transfer means. 17. The specimen preparation device according to claim 1, wherein relative parallel movement and/or relative inclined movement of the specimen stage and the transfer means are/is made so that pressure is generated between the excising specimen and the transfer means. 18. The specimen preparation device according to claim 11, wherein the probe is rotated about an axis of the probe so that pressure is generated between the excising specimen and the probe. 19. The specimen preparation device according to claim 1, wherein an ion beam is irradiated on the specimen to prepare a mark formed in a region, which makes the excising specimen, on the specimen and/or a mark formed in another region other than said region, which makes the excising specimen, on the specimen. 20. A control method for a specimen preparation device, the method comprising steps of: mounting a specimen on a specimen stage; irradiating an ion beam by way of an ion beam optical system; transferring by way of transferring means, an excising specimen separated from the specimen by means of ion beam irradiation; and controlling the ion beam optical system with an arithmetic unit,wherein when an ion beam is irradiated on the specimen to separate the excising specimen from the specimen, a mark formed in a region, which makes the excising specimen, on the specimen and a mark formed in another region other than said region are measured and the ion beam irradiation is stopped in the case where a relative position between the marks is put in a predetermined condition. 21. A control method for a specimen preparation device, the method comprising steps of: mounting a specimen on a specimen stage; irradiating an ion beam by way of an ion beam optical system; transferring by way of transferring means, an excising specimen separated from the specimen by means of ion beam irradiation; and controlling the ion beam optical system with an arithmetic unit,wherein when an ion beam is irradiated on the specimen to separate the excising specimen from the specimen, a mark formed on the transfer means holding a region, which makes the excising specimen, on the specimen and a mark formed in another region other than said region, which makes the excising specimen, on the specimen are measured and the ion beam irradiation is stopped in the case where a relative position between the marks is put in a predetermined condition. 22. A control method for a specimen preparation device, the method comprising steps of: mounting a specimen on a specimen stage; irradiating an ion beam by way of an ion beam optical system; transferring by way of transferring means, an excising specimen separated from the specimen by means of ion beam irradiation; and controlling the ion beam optical system with an arithmetic unit,wherein when the transfer means is moved and brought into contact with the excising specimen, a mark formed on the transfer means and a mark formed in a region, which makes the excising specimen, on the specimen are measured and the transfer means is stopped in the case where a relative position between the marks is put in a predetermined condition. 23. A control method for a specimen preparation device, the method comprising steps of: mounting a specimen on a specimen stage; irradiating an ion beam by way of an ion beam optical system; transferring by way of transferring means, an excising specimen separated from the specimen by means of ion beam irradiation; and controlling the ion beam optical system with an arithmetic unit,wherein when the transfer means is moved and brought into contact with the excising specimen, a mark formed on the transfer means and a mark formed in a region other than another region, which makes the excising specimen, on the specimen are measured and the transfer means is stopped in the case where a relative position between the marks is put in a predetermined condition. 24. A control method for a specimen preparation device, the method comprising steps of: mounting a specimen on a specimen stage; irradiating an ion beam by way of an ion beam optical system; transferring by way of transferring means, an excising specimen separated from the specimen by means of ion beam irradiation; holding the excising specimen with a specimen holder; and controlling the ion beam optical system with an arithmetic unit,wherein when the excising specimen held on the transfer means is transferred to the specimen holder, a mark formed on the excising specimen and a mark formed on the specimen holder are measured and movement of the transfer means is stopped in the case where a relative position between the marks is put in a predetermined condition. 25. A control method for a specimen preparation device, the method comprising steps of: mounting a specimen on a specimen stage; irradiating an ion beam by way of an ion beam optical system; transferring by way of transferring means, an excising specimen separated from the specimen by means of ion beam irradiation holding the excising specimen with a specimen holder; and controlling the ion beam optical system with an arithmetic unit,wherein when the excising specimen held on the transfer means is transferred to the specimen holder, a mark formed on the transfer means for transfer of the excising specimen and a mark formed on the specimen holder are measured and movement of the transfer means is stopped in the case where a relative position between the marks is put in a predetermined condition. |
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046438670 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to nuclear reactor facilities, and more particularly to a mounting system for a set of four television cameras upon a nuclear reactor refueling machine outer or stationary mast whereby the television cameras can readily scan reactor core fuel assemblies as the same are being vertically removed from the core by means of the refueling machine during the performance of a refueling operation so as to detect the existence, or determine the extent, of any damage to any one of the fuel assemblies or the fuel assembly grid straps, or alternatively, the television cameras can provide remote viewing of the reactor core so as to facilitate insertion of the fuel assemblies into the core during a refueling operation. 2. Description of the Prior Art As is well known in the nuclear reactor art, fuel, conventionally in the form of pellets, is inserted within suitable cladding material, and the composite assemblage of the fuel pellets and the cladding material or casings define or form the nuclear reactor fuel rods. In turn, a predetermined number of fuel rods, assembled or secured together by means of bands called grid straps, form or define a fuel element or fuel assembly, and a predetermined number of fuel elements or fuel assemblies serve to define or form the nuclear reactor core. As a result of the normal operation of the nuclear reactor facility, the nuclear fuel within the core fuel assemblies naturally becomes depleted, and consequently, the reactor core fuel assemblies must be periodically replaced and refueled. This is achieved by means of conventional refueling operations and techniques. In particular, the fuel within the reactor core fuel assemblies is depleted over a predetermined period of time and at a predetermined consumption rate such that once an initially new reactor facility has attained its steady state fuel consumption activity or operation through means of having undergone, for example, an initial two-year stabilization period of operation, each fuel assembly utilized within the reactor core will have a service life of three years. In lieu of refueling the entire reactor core once every three years by replacing all of the core fuel assemblies with newly fresh fuel assemblies, maintenance requirements and economic considerations have dictated that the reactor core be refueled once per year, during which period the reactor facility is of course shut down. In order to achieve or accommodate such requisite refueling operations, the reactor core is sectionalized, and the fuel supply relatively staggered between the core sections or stages. Specifically, the reactor core fuel assemblies are effectively arranged within three groups, sections, or stages, including a first, central circular section, a second intermediate annular section disposed about the first central section, and a third outermost annular section disposed about the second intermediate annular section. In addition, as a result of the aforenoted initial two-year stabilization period of operation, at the end of any subsequent one-year period of operation, the nuclear fuel disposed within the fuel assemblies of the innermost or first central section of the reactor core, which fuel assemblies have been disposed within the reactor core for an operational period of three years, will have been substantially entirely depleted. Similarly, the nuclear fuel disposed within the fuel assemblies of the second intermediate or middle section of the reactor core, which fuel assemblies have been in operational service within the reactor core for a period of only two years, will be sufficient so as to permit such fuel assemblies to provide service within the reactor core for an additional period of one year. In a like manner, the nuclear fuel disposed within the fuel assemblies of the third outermost section of the reactor core, which fuel assemblies have been in operational service within the reactor core for a period of only one year, will be sufficient so as to permit such fuel assemblies to provide service within the reactor core for an additional period of two years. In accordance with conventional refueling techniques, then, the fuel assemblies from the innermost or central section of the core are removed from the reactor core for actual refueling with fresh or new fuel, while the fuel assemblies disposed within the intermediate or middle section of the core are transferred to the first central section of the core. Continuing further, the fuel assemblies disposed within the outermost third section of the core are transferred to the second intermediate or middle section of the core, while entirely new or fresh fuel assemblies are inserted into the outermost third section of the core, thereby completing the refueling operation of the reactor facility. It is imperative that a complete inspection of the entire external peripheral surface area of each fuel assembly and its grid straps be performed at sometime during the performance of the reactor facility refueling operation in order to detect or determine the existence of any damage to the fuel assemblies and/or the grid straps that may have possibly occurred or developed during the previous cyclic operation of the facility, in view of the obviously desirable objective of replacing damaged fuel assemblies within the reactor core so as not to present any possibility of an operational failure within the reactor facility. It is particularly desirable to be able to accomplish the foregoing fuel assembly inspection procedures during the actual refueling processing or handling sequence without considerably prolonging the refueling operation, and without the requirement of any substantial or large-scale modification of existing reactor facility refueling machine apparatus and equipment. Conventional refueling machines comprise a trolley movable within a horizontal plane along a suitable track system disposed above the reactor core at an elevational height of, for example, thirty-five feet, and a vertically disposed outer or stationary mast is fixedly mounted upon the refueling machine trolley so as to be movable therewith. The lower end of the stationary or outer mast is disposed within the reactor core cavity water, and a vertically movable inner mast or gripper tube is co-axially disposed in a relatively telescopic manner interiorly of the outer stationary mast. A gripper assembly is fixedly secured to the lower end of the inner mast or gripper tube for engaging the fuel assemblies in order to perform the aforenoted refueling operation handling sequences, during which the inner mast, the gripper assembly, and the fuel assembly, are retracted internally within the refueling machine outer mast. Conventional refueling machine apparatus and equipment does not in fact exist so as to therefore permit inspection of the fuel assemblies during the underwater handling modes of the refueling operation, and lowering of the water level within the reactor core cavity is certainly not a viable operational alternative in view of the inordinate amount of time that would be required in performance of such a procedural step, as well as performance of the various operational safety sequences attendant thereto, each time a fuel assembly is being removed from, deposited within, or transferred from one position to another position within, the reactor core. As was noted hereinabove, conventional refueling machines include a trolley movable within a horizontal plane along a suitable track system disposed above the reactor core at an elevational height of, for example, thirty-five feet. The refueling machine operator or personnel control the refueling machine, and perform the refueling operation, from the trolley as a result of observing the reactor core and the various fuel assemblies thereof through means of a suitable viewing aperture or window defined within the refueling machine trolley deck. Consequently, during a refueling operation, when it is desired to insert a particular fuel assembly into a free space of the reactor core, such as, for example, when depositing a fresh or new fuel assembly into the outermost third section of the core or when transferring a fuel assembly from the third or second section of the core to the second or first section of the core, respectively, it may be readily appreciated that considerable difficulty may be encountered by the refueling machine operator or personnel due to the aforenoted distance between the trolley deck and the reactor core. In addition, the reactor core cavity is entirely immersed within water, and consequently, the different light refractive properties of the air environment within which the operator personnel is located and the water environment within which the fuel assemblies are located cause distortion and an apparent erroneous location of the reactor core fuel assembly spacial locations. The refueling operation is therefore considerably impeded, the efficiency of the same accordingly reduced, and the time for completion of the refueling operation correspondingly prolonged. Accordingly, it is an object of the present invention to provide a new and improved nuclear reactor refueling machine. Another object of the present invention is to provide a new and improved nuclear reactor refueling machine which will overcome all of the aforenoted disadvantages and drawbacks of conventional nuclear reactor refueling machines and the refueling operations characteristic thereof. Still another object of the present invention is to provide a new and improved nuclear reactor refueling machine which will readily permit inspection of the entire external surface area of a fuel assembly for the detection and determination of any damage or defects thereof. Yet another object of the present invention is to provide a new and improved nuclear reactor refueling machine which will readily permit inspection of the entire external surface area of a fuel assembly during a refueling handling sequence so as to detect and determine the existence of any damage or defect thereof. Still yet another object of the present invention is to provide a new and improved nuclear reactor refueling machine which will readily permit inspection of the entire external surface area of a fuel assembly during a refueling handling sequence so as to detect and determine the existence of any damage or defect thereof, without prolonging the handling sequence and the refueling operation. Yet still another object of the present invention is to provide a new and improved nuclear reactor refueling machine which will readily permit inspection of the entire exterior surface area of a fuel assembly during a refueling handling sequence so as to detect and determine the existence of any damage or defect thereof, without the necessity of any substantial or large-scale modification of existing refueling machine apparatus or equipment. A further object of the present invention is to provide a new and improved nuclear reactor refueling machine which will in fact readily permit the visual inspection of the entire external surface area of a fuel assembly during a refueling handling sequence so as to detect and determine the existence of any damage or defect thereof, by means of substantially simplified modification of existing, conventional nuclear reactor refueling machines. A yet further object of the present invention is to provide a new and improved nuclear reactor refueling machine which will readily permit the visual inspection of the entire external surface area of a fuel assembly during a refueling handling sequence so as to detect and determine the existence of any damage or defects thereof, as well as the visual monitoring of such inspection procedures by remotely located personnel. A still further object of the present invention is to provide a new and improved nuclear reactor refueling machine which will readily permit the visual inspection of the entire external surface area of a fuel assembly during a refueling handling sequence so as to detect and determine the existence of any damage or defects thereof, as well as the tape recording of such visual inspection so as to provide a permanent record thereof. A yet still further object of the present invention is to provide a new and improved nuclear reactor refueling machine which will greatly facilitate the alignment of the refueling machine and a fuel assembly gripped thereby, and the reactor core spacial location within which the fuel assembly is to be deposited. A still yet further object of the present invention is to provide a new and improved nuclear reactor refueling machine which will provide the refueling machine operator or personnel with a clear and unobstructed view of the particular reactor core spacial location within which a fuel assembly is to be deposited. An additional object of the present invention is to provide a new and improved nuclear reactor refueling machine which will permit the refueling machine operator or personnel, who is positioned at a location within the reactor facility which is remote from the reactor core, to view the particular reactor core spacial location within which a fuel assembly is to be deposited from a vantage point which is effectively within the immediate vicinity of the reactor core and the spacial location. SUMMARY OF THE INVENTION The foregoing and other objectives of the present invention are achieved through the provision of a nuclear reactor refueling machine which, in accordance with a first embodiment of the present invention, comprises a sleeve mounted upon the lower end of the refueling machine stationary or outer mast. Four vertically oriented television cameras are fixedly secured upon the upper end of the outer mast sleeve so as to project vertically downwardly toward the reactor core, the cameras being substantially equiangularly disposed about the refueling machine stationary mast. Four light assemblies, which project light in a substantially horizontal plane or direction transverse or perpendicular to the longitudinal axis of the refueling machine stationary mast, are secured to the lower end of the stationary mast sleeve in a similar, substantially equiangular array about the mast. Each light assembly can illuminate a sector of a fuel assembly, which is being retracted, for example, into the stationary mast by means of the inner, relatively telescopic mast or gripper tube and its associated gripper assembly, the sector being of an angular extent of at least 90.degree.. Four mirror assemblies are also secured to the lower end of the outer mast sleeve in a substantially equiangularly array about the mast, one of the mirror assemblies being disposed directly beneath one of the television cameras, respectively and angularly separated from its respective light assembly in the circumferential direction. The mirrors are angularly oriented relative to a horizontal or vertical plane at an angle of 45.degree., and in this manner, the illuminated sector regions of the fuel assembly may be scanned, and the images thereof transmitted to the television cameras, as the fuel assembly is being removed from the reactor core and retracted internally within the refueling machine outer stationary mast by means of the inner mast and its associated gripper assembly. Television monitors may, in turn, be disposed upon the refueling machine operator trolley for reception of the television signals generated by the television cameras, and consequently, remote scanning of the fuel assemblies may be achieved. Video tape recording apparatus may also be operationally associated with the television monitoring equipment so as to record the scanning operations for permanent record-keeping. In accordance with a second embodiment of the present invention, the cameras, light assemblies, and mirror assemblies are all mounted upon a basket-type structure or framework annularly disposed about the lower end of the outer stationary mast of the refueling machine, and the framework is suspendingly supported from the refueling machine trolley by means of support cables. This embodiment has operational advantages over the first embodiment in that the framework may be readily removed from the lower end of the outer stationary mast by remote control means so as to permit servicing and maintenance of the cameras, light assemblies, and mirror assemblies without necessarily lowering the water level within the reactor core cavity. In connection with both structural arrangements or embodiments of the present invention, it is further noted that all four of the mirror assemblies may be removed from the scanning system, and the light assemblies reoriented so as to project substantially vertically downwardly in order to illuminate the reactor core. In this manner, the television camera and light system may be utilized to aid the refueling machine operator in positioning the refueling machine and a fuel assembly gripper thereby when it is desired, for example, to deposit the fuel assembly within an empty space defined within the reactor core. The camera-light systems facilitate the relative co-axial alignment of the fuel assembly with the core spacial location thereby enhancing the operational efficiency of the refueling operation. |
description | The present invention relates to an assembly intended to be inserted into a liquid-metal-cooled, notably liquid-sodium-cooled fast neutron nuclear reactor known as a liquid sodium FNR or SFR (sodium fast reactor) and which forms part of the family of what are known as fourth generation reactors. The invention seeks first of all to offer a fuel assembly which can be used in the short term in the fourth-generation reactor French technology demonstrator project dubbed ASTRID. The invention seeks more particularly to offer a weldless connection between the assembly hollow body made up of a hexagonal-section tube and the body of the upper neutron shield (UNS) of a fuel assembly for a SFR, which connection can be made with the bundle of fuel pins present in the assembly. The fuel assemblies at which the invention is aimed may be used just as well in a nuclear reactor of the integral type, which means to say in which the primary sodium coolant circuit and pumping means is fully contained within a vessel that also contains the heat exchangers, as it can in a reactor of the circuit type, which means to say in which the intermediate heat exchangers and the primary sodium coolant pumping means are situated outside the vessel. What is meant by an assembly is an assembled unit that is loaded into and/or unloaded from a nuclear reactor. What is meant by a fuel assembly is an assembly comprising fuel elements and that is loaded into and/or unloaded from a nuclear reactor. What is meant by a fuel assembly of the liquid sodium FNR or SFR type, is a fuel assembly designed to be irradiated in a liquid sodium cooled fast neutron nuclear reactor referred to as a liquid sodium FNR or an SFR. Although described with reference to the key intended application, namely a fuel assembly for a nuclear reactor, the invention may be applied to any type of assembly for a nuclear reactor, such as a reflector, a lateral neutron shield (LNS), a control rod, an experimental assembly, an additional safety device, etc. Fuel assemblies intended to be used in sodium fast reactors (SFRs) have a specific mechanical structure in order notably to allow the liquid sodium to pass within them. A fuel assembly 1 already used in the SFR known by the name of “Phénix” has been depicted in FIG. 1. Such an assembly 1 of elongate shape along a longitudinal axis X comprises first of all a tube or casing 10 of hexagonal section, which comprises an upper portion 11 forming the gripping head of the assembly, an upper neutron shield (UNS) device with a body 14, and a central portion 12 constituting the hollow body of the assembly which encloses fuel pins 120. The head 11 of the assembly comprises a central opening 110 opening within it and is generally connected to the UNS or to the central portion 12 by welding. The upper neutron shield device contains blocks 140 of neutron absorbing material such as boron carbide B4C and/or steel. Its role is to lessen the neutron flux and protect the internals and the head of the primary vessel. The body of the UNS 14 is generally connected to the central portion 12 by welding. The assembly 1 also comprises a lower portion 13 forming the foot of the assembly, in the extension of the hexagonal casing 10. The foot 13 of the assembly has a distal end 15 shaped as a cone or rounded so that it can be inserted vertically into the guide sockets of the diagrid (support) of a reactor core. The foot 13 of the assembly comprises at its periphery openings 16 opening into it. Thus, when a fuel assembly is in the installed configuration, which means to say when it is in the position it occupies when loaded into a reactor core, the foot 13 of an assembly 1, which is of a male shape, is inserted into an opening in the diagrid of the reactor thus holding the assembly 1 therein with its longitudinal axis X vertical. The primary coolant sodium may circulate inside the casing 10 of the assembly 1 and thus by thermal conduction carry the heat released by the fuel pins. The sodium is thus introduced via the openings 16 in the foot 13 and emerges via the central opening 110 in the head 11, after having passed along the bundle of fuel pins. The central portion 12 of an assembly comprises a plurality of nuclear fuel pins 120. Each pin takes the form of a sealed cylindrical tube of cladding in which there is stacked a column of fissile (or fertile) fuel pellets within which the nuclear reactions that release heat take place. All of the columns define what is usually referred to as the fissile (or fertile) zone, which is situated approximately midway up the height of an assembly 1. All the assemblies of the one same reactor are arranged vertically on a diagrid to from a core with a compact hexagonal-cells grid. The assemblies in positon on the diagrid are spaced apart from one another at their base (foot), typically by a few mm between facing faces of two adjacent hexagonal section casings. It is necessary for this spacing to be kept substantially constant over the entire height of the assembly while the reactor is in operation. This is because any narrowing of the gap between two adjacent fuel assemblies immediately leads to an increase in reactivity, i.e. a rapid increase in power, which could have serious consequences, such as overheating, blockage, etc. and lead to a core melt accident. In order to guard against that, it is known practice in existing SFRs to add spacer devices 121 in the upper part of the casing of the assemblies, just above the fissile pins. In general, these devices are positioned at a height equivalent to approximately ⅔ of the height of the assembly projecting above the diagrid. These spacer devices, usually referred to as “straps” essentially consist of bosses, namely additional thicknesses, projecting to the outside of the assembly body. Each face of the hexagonal cross section of the casing is provided with a boss (strap). Such spacer straps are found in emergency shutdown rods, more specifically, on the exterior periphery of a ring referred to as a pad ring, substantially at the same longitudinal level as the interior additional thicknesses usually referred to as “pads”. In a fuel assembly, the connection created between the central portion 12 and the UNS body 14, or between the UNS body 14 and the gripper head 11, needs to meet a certain number of requirements. In particular, in an assembly dedicated to a liquid sodium-cooled nuclear assembly, the connection needs to meet the following major requirements: i/ it needs to be compatible with the manufacture and assembly of the assembly, ii/ it needs to withstand the forces during the operation and handling phases, and iii/ it needs not to generate migrating bodies in the primary coolant sodium circuit. In the context of fuel assemblies for SFRs known respectively by the names of “Phénix” and “Superphénix”, this connection was made by welding. Manufacturing feedback on this connection without welding was not completely satisfactory. Not only did the welds prove difficult to achieve, but they were tested using test specimens, leading to a delay between making the test specimen and the time at which the results were available. Furthermore, the bundle of fuel pins is put in place in the hexagonal tube before the welded connection is made between this tube and the mass of components all around, thus requiring welding with protection, and lengthy and costly handlings of assemblies during the welding, inspection or repair operations. Finally, a defective weld made with the bundle of fuel pins in place would lead to complete loss of the assembly. At the present time, in the case of the fuel assemblies envisioned for the ASTRID reactor, the isotopes present in the new fuel generate far more radioactivity and heat than was the case with the Phénix and Superphénix assemblies. Providing operators with radio protection therefore becomes a key issue. Indeed it is out of the question for an operator to weld and inspect welds while the fuel pins are in the assembly, which they are if the hexagonal tube 12 and the UNS body 14 are to be welded together. On the other hand, the welding together of the central portion 12 and the foot of the assembly 13 is performed before the pins are mounted in the assembly. It is thus recommended that any welding be done before the bundle of pins is put in place and that after this placement has been performed only weldless operations which are easier to perform and to inspect be carried out. This recommendation is all the more necessary since, in the context of ASTRID, the use of a central portion made of ferritic steel, of EM10 type, would also entail a high-temperature post-weld stabilization heat treatment operation because the UNS is made from a steel of another type, in this instance austenitic steel. The studies carried out for refueling with Superphénix assemblies proposed, as a solution to this problem, a pressed connection between the UNS 14 and the central portion 12, as detailed in patent FR 2544122. In this type of connection, the hexagonal casing of the central portion is deformed by a spherical punch in the middle of each of its faces and thus pressed into recesses machined in the faces of the UNS. That solution is relatively well suited to the geometry of the Superphénix assemblies given the space available axially (degree to which the UNS and the hexagonal casing are pushed one inside the other) and the great thickness of the steel UNS which make it possible to guarantee good pressing geometry without the risk of deforming the UNS. However, this pressed connection requires there to be in the UNS recesses that are deep enough to provide the pressed connection with sufficient pull-out strength and requires the UNS to be thick enough that any deformation thereof during the pressing phase is excluded. Now, the inventors have analyzed that the thickness of the body of the UNS of the assemblies dedicated to the ASTRID reactor, as planned, is too small for this type of connection to be made reliably. Thus, a pressing operation presents a serious risk of deforming the UNS. Even though pressing might be feasible by adding a retractable counter-punch, the mechanic integrity of the connection would need to be checked via tensile (pull-out) testing simulating handling loads. Given the thickness of the heavy gauge plate that is smaller in comparison with the Superphénix assemblies, and the recess depth that is smaller because of the smaller thickness of UNS, the inventors believe that the mechanical strength of the connection can be expected to be lower. As a result, the inventors believe that it is not technically conceivable to produce a stamped connection between the UNS and the body of the assembly (hexagonal tube) in the case of a fuel assembly dedicated to ASTRID, because the aforementioned major requirements i/ and ii/ would not be met. Another alternative solution to welding envisioned in the context of the Superphénix design studies was to create a pegged connection. This type of connection is achieved by pushing the body of the UNS into the central portion forming the hollow body of the fuel assembly and joining these two elements together by forcibly inserting pegs into orifices in the UNS. Several pegs per face would be needed in order to obtain satisfactory mechanical strength. Nevertheless, the fitting of the pegs carries the risk of deforming the component on the inside when this component is of small thickness, as is the case for the assembly head and the pad ring of the fuel assemblies and shutdown rods dedicated to ASTRID. The close fit of the pegs also requires a great deal of precision vis-à-vis positioning tolerances, which will undoubtedly be incompatible with the clearance required between the components for the purposes of assembly. Therefore compliance with the aforementioned requirement i/ may not be guaranteed. Furthermore, a pegged assembly carries a significant risk of one of the pegs becoming lost or detached, leading to bodies migrating in the primary coolant sodium and therefore possibly having severe consequences regarding the safety and operability of the reactor. In other terms, the aforementioned requirement iii/ may not be met. Patent JPH07260973A refers to an alternative solution to welding for the connection between the central portion and the assembly head which have hexagonal cross sections, in a fuel assembly for a fast neutron reactor. The solution divulged consists in using an attached clamp for the connection between the assembly head and the central portion. These are aligned and brought into abutment via their ends along a planar contact plane. On each face of the head and of the central portion, a cavity with a restriction in cross section is machined into the thickness of the component. A clamp is attached so that it fits into the cavity in the head and in the central portion and is fixed by screwing, thus joining the two elements together. The inventors believe that this clamped connection solution is not conceivable in the context of assemblies for the ASTRID reactor. Specifically, first of all, the butt-joined connection with no interpenetration cannot meet the mechanical strength requirements ii/, notably when the connection is stressed in bending under the lateral loadings of the reactor in operation. In addition, this clamped connection requires an assembly head that is thick enough that a cavity can be machined therein. The inventors estimate that a thickness of the order of 10 mm would be necessary, whereas the thickness available for an assembly head of a fuel assembly dedicated to ASTRID is only of the order of 5 mm. Finally, the screw fixings of the clamp carry the risks that, under mechanical stress loading, they could become unscrewed leading, in addition to the loss of connection and therefore to the impossibility of withdrawing the assembly, to the generation of bodies migrating in the sodium and therefore potentially to serious consequences such as loss of cooling of an assembly caused by a partial blockage. The screwed connection could be made more secure by adding a locking weld, but the inventors estimate that this measure does not offer a sufficient guarantee of dependability. No more dependable mechanical solution for preventing the loss of a screw or of a clamp is disclosed in that patent. Thus, requirements ii/ and iii/ cannot be met with this type of connection using attached clamps secured by screws. Patent application CN104575629A discloses a dismantleable connection between two assembly guide tubes of a control mechanism for a pressurized water reactor, without application to a connection between two parts of an assembly body being envisioned. This connection is intended for performing numerous assembly/dismantling operations blind, under the water of the reactor. One of the two tubes comprises two flexible blades of which the thickened end catches in a cavity inside the second tube. The connection is dismantled by applying pressure along the axis of the tube to the end of the flexible blades. Mechanical locking of the blades in their clipped-together position is achieved by means of a ring internal to the tube. This ring also has the function of centering the two tubes relative to each other. The means of dismantling the connection requires simultaneous axial pressure to be applied to the ends of the blades. The connection requires the use of a return spring between the two tubes in order to eliminate the axial clearance in the connection. The fitting of the ring and of the spring may prove not to be easy. Moreover, in the context of the control rods and, more particularly, of the shutdown rods of the Phénix and Superphénix reactors, the connection between the pad ring and the central portion (assembly body) of the bar is usually performed by welding on two sections of the central portion. Now, the design of the so-called “low void effect core” of ASTRID would lead to an offsetting of the flux toward the top of the assembly, and therefore to a higher dose at the welds between the pad ring and the central portion, if such a welded connection were maintained. That endangers the integrity of the welds under flux, particularly when it is borne in mind that the target lifespan is longer in comparison with Phénix or Superphénix. Thus, requirement ii/ mentioned hereinabove cannot be guaranteed for a shutdown rod with a welded connection. Furthermore, unlike the Superphénix shutdown rod assemblies where the central portion and the ring are made of steels of the same grade, the central portion of a shutdown rod assembly for ASTRID is envisioned to be in ferritic steel, of type EM10, whereas the corresponding pad ring is envisaged to be in austenitic steel, in a grade 316Ti. The weld joining these two components would therefore require an additional high-temperature stabilization treatment. As a result, the manufacture of a shutdown rod dedicated to ASTRID carries with it an additional risk with the lack of a guarantee of conforming to the aforementioned requirement i/. Thus, a welded connection between the central portion and the pad ring is not satisfactory for assemblies (shutdown rods) dedicated to ASTRID. There is therefore still a need to offer an alternative to the existing weldless connections between the UNS and the central portion (assembly body) of a fuel assembly or between a pad ring and the central portion (assembly body) of a control rod, more particularly a shutdown rod, for a fast neutron nuclear reactor of the SFR type, notably in order to meet the aforementioned requirements i/ to iii/ and so that the connection can be made with the bundle of fuel pins present in the fuel assembly, and in instances in which the wall thicknesses of the elements that are to be connected are small. It is an object of the invention to at least partially meet this need. In order to do this, one subject of the invention is an assembly intended to be inserted into a nuclear reactor, notably into a liquid sodium-cooled fast neutron reactor SFR, comprising: an assembly hollow body, of elongate shape along a longitudinal axis X, the wall of the hollow body comprising at least one open-ended opening; an assembly element inserted at least in part into the hollow body, the assembly element comprising at least one flexible blade of which the free end is shaped into a clip-fastening hook collaborating in clip-fastening with the open-ended opening from inside the hollow body, so as to connect the assembly element to the hollow body; at least one removable means for locking the flexible blade clip-fastened into the open-ended opening, the removable locking means making it possible to prevent the flexible blade from flexing and thus lock the connection between the assembly element and the hollow body. Thus, the invention essentially consists in defining a clip-fastened connection, from the inside of the assembly body, of the thickened free end of flexible blades of the assembly element, with a mechanical locking that is removable from the outside of this assembly body. The advantages of the solution according to the invention are many, and include the following. For a fuel assembly dedicated to a reactor of SFR type: simplicity of producing, qualifying and probably also thermomechanically sizing the connection by comparison with the known solutions of welding, stamping and pegging (pinning) as detailed in the preamble. Requirement i/ ought to be met for a fuel assembly with the connection and locking according to the invention; low slippage of the assembly head (housing the UNS) under axial traction by comparison with a stamped solution of the prior art, or in any case slippage limited to the extent of the lateral clearance between the thickened end of a flexible blade and the open-ended opening in the assembly body consisting of the hexagonal-section tube. Requirement ii/ ought to be met for a fuel assembly with the connection and locking according to the invention; possible reversibility of the dismantleable connection after the fuel assembly has become irradiated, unlike the known connections of welding and pressing, which might allow the assembly head to be reused multiple times, the side effect of this being an economic saving, and a reduction in the amount of waste; absence of the risk of generating bodies migrating in the primary coolant circuit of the reactor, unlike the known pegged solution (which carries the risk of loss of pegs). Requirement iii/ ought to be met for a fuel assembly with the connection and locking according to the invention; possibility of applying the connection according to the invention to the solution according to application FR3040234A1 in order to connect the hexagonal strap reinforcing sleeve to the assembly body (hexagonal tube). For a nuclear shutdown rod dedicated to an SNF type nuclear reactor: absence of welded connection between the pad ring and the assembly body (hexagonal tube), thus simplifying manufacture and meeting requirement i/; presence of a single portion of hexagonal tube intact as far as the assembly head, ensuring good mechanical integrity of the assembly body and meeting requirement ii/; possibility of adapting the connection according to the invention to the solution according to application FR3040234A1 for connecting the hexagonal strap reinforcing sleeve to the assembly body (hexagonal tube), the reinforcing sleeve also comprising pads the location of which may be offset with respect to the straps. The clip-fastening hook may advantageously be produced by a thickening of the free end of the flexible blade. According to one advantageous embodiment, the hollow body is of hexagonal cross section and comprising one open-ended opening per face of the hexagon, the assembly element comprising a flexible blade clip-fastened into each of the open-ended openings. The removable locking means advantageously consists of a locking screw which in the position in which it is screwed into the flexible blade, makes it possible to prevent the blade from flexing and from becoming unclipped. According to a first alternative form of embodiment, each flexible blade is produced by cutting into the thickness of the assembly element. According to this first alternative form, the wall of the assembly body comprises at least one open-ended bore designed to allow the locking screw to pass from the outside of the hollow body and the screw head to be housed. According to a second alternative form, each flexible blade is attached and fixed to the assembly element by a fixing screw. According to this second alternative form, each fixing screw is welded to the assembly element and/or to the flexible blade in its screwed-in position. Advantageously, the assembly element comprises at least one cavity in which the clip-fastening hook can become lodged when the blade is in the flexed position, the locking screw being screwed through the hook and housed in the cavity when the blade is clipped in, so as to prevent this blade from flexing. The assembly which has just been described may constitute a nuclear fuel assembly, the hollow body being the central portion forming a casing cladding fuel pins, the assembly element being an upper neutron shield (UNS) device or the upper portion forming the gripper head of the assembly. The assembly may thus constitute a non-fuel assembly chosen notably from among a reflector assembly, a lateral neutron shield (LNS) assembly, a shutdown and/or control rod, an experimental assembly, an additional safety device, a mitigation assembly. When the assembly is a shutdown and/or control rod, the assembly element is the so-called pad ring inserted inside the hollow body forming a casing, the casing comprising on its external periphery at least one spacer plate and at least one pair of open-ended openings on each side of the plate, the pad ring comprising on its internal periphery at least one pad and at least one pair of flexible blades which are arranged in such a way that each clip-fastening hook of the pair of blades collaborates in clip-fastening with one of the open-ended openings. The invention also relates to a method for assembling an assembly described hereinabove, comprising the following steps: a/ inserting the assembly element into the assembly hollow body by a translational movement, so as to achieve simultaneous flexing of the flexible blades toward the inside of the hollow body, lowering of the assembly element down inside the hollow body until the flexible blades return to their position toward the outside of the hollow body with their hooks clip-fastened into the corresponding open-ended openings of the hollow body so as to connect the latter to the assembly element; b/ locking each flexible blade clip-fastened into the open-ended opening using the removable locking means. The invention also relates to a method for dismantling an assembly described hereinabove, comprising the following steps: a1/ unlocking each flexible blade the hook of which is clip-fastened into the open-ended opening, by removing the removable locking means; b1/ applying a radial force to the hook of each flexible blade from the outside of the open-ended opening, so as to cause the flexible blades to flex simultaneously toward the inside of the hollow body, unclipping the hooks, c1/ extracting the assembly element from inside the assembly hollow body via a translational movement. Steps a1/ to c1/ are preferably performed at a temperature above 100° C., so as to prevent the freezing of the residual liquid metal, sodium in the case of an SFR, present in the clearances of the connection. The radial force may advantageously be a force perpendicular to the axis of the hooks. When the assembly element comprises a plurality of flexible blades of which the hooks are individually clip-fastened into an open-ended opening of the hollow body and which are locked, step b1/ is preferably performed by simultaneous actuation of actuators, which are preferably mounted on the one same centering collar, and arranged individually facing one of the open-ended openings. The connection according to the invention could be applied to any type of nuclear reactor requiring there to be a connection between the body of the assembly of tubular cross section, such as the hexagonal-section tube in the ASTRID reactor, and another element, such as the UNS body in the case of a fuel assembly, or the pad ring in the case of a shutdown rod all dedicated to ASTRID. It may cover all fast neutron reactors (sodium, gas, lead, lead-bismuth, etc.). The connection according to the invention would be more generally applicable to any connection between a tubular body that makes up an assembly (assembly body, absorber rod body, UNS body, experimental capsule body, differential pressure device, etc.) and another assembly element (foot, head, pad ring, etc.) that needs to be inserted into or connected to the end of this tubular element, irrespective of the shape of these elements (hexagonal, cylindrical, rectangular, etc.). The present invention is described using as an example a fuel assembly and a shutdown rod, but it is also applicable to all other assemblies (reflectors, LNS, control rods, mitigation assemblies, experimental assemblies, etc.). For the sake of clarity, the same references denoting the same elements of fuel assembly and of strap spacer devices according to the prior art and according to the invention are used throughout FIGS. 1 to 10. Throughout the present application, the terms “vertical”, “lower”, “upper”, “bottom”, “top”, “below” and “above” are to be understood with reference to a fuel assembly such that it is in a vertical configuration inside a nuclear reactor. FIGS. 1 and 2 which relate to the prior art have already been described in detail in the preamble and are therefore not commented upon hereinafter. The weldless connection according to the invention between the assembly hollow body 12 (central portion) and an assembly element 14 which is the UNS of a fuel assembly is depicted in FIGS. 3 to 4B from different angles. The central portion 12 and the UNS 14 are depicted in the assembled position and separately. A thickening 21 is produced at the end of the flexible blade 20 of the UNS and, in the assembled position, namely when the UNS body 14 is inserted into the central portion 12, clips into an open-ended opening 122 of the central portion. For preference, as illustrated, the lower part of the thickening 21 is chamfered to make it easier for the blade 20 to flex as the UNS 1 engages in the end of the hexagonal tube. As shown in FIGS. 5A to 6B, once the thickening 24 has clip-fastened into the opening 122 of the tube 12, the shoulder 22 produced on the upper part of the UNS 14 comes into abutment with the top of the tube 12, whereas the shoulder 24 produced on the upper part of the thickening 21 is in abutment against the upper edge 124 of the opening 122. According to this alternative form illustrated, extraction of the UNS from the hollow component 12 is prevented by the discontinuous profile of the thickening 21 defined by the shoulder 24 at the end of the blade, whereas deeper insertion of the UNS into the hollow component 12 is prevented by the profile defined by the shoulder 22 of the UNS 14, of which the exterior cross section above the head designed for insertion into the hollow component is substantially identical to that of the hollow component. In this way is obtained a weldless connection which allows the manufacture and sizing of a fuel assembly to be simplified considerably as described. Furthermore, the risk of migrating bodies (screws, pegs, etc.) becoming introduced into the primary cooling circuit is avoided. As illustrated in FIGS. 5A and 5B, the flexible blade 20 may be respectively cut into the assembly element 14, if the latter is of small thickness. Alternatively, as shown in FIGS. 6A and 6B the blade 20 may be attached to the element 14 using a fixing screw 40, in cases in which the element 14 is of sufficient thickness. Once the connection has been assembled, the fixing screw 40 is itself secured by the presence of the tube 12. In the assembled position illustrated in FIGS. 5A and 6A, the flexible blade 20 is mechanically locked, by a locking screw 42 which is added after the element 14 has been inserted into the hollow component 12. In the alternative form of FIG. 5A, the locking screw 42 is screwed through a hole 123 provided for this purpose in the tube 12 into a tapping 23 made in the blade 20, this tapping 23 being opposite the tapping 123 when the blade 20 is in the clip-fastened position. In the alternative form of FIG. 6A, the locking of the blade by the screw 42 to prevent the blade from flexing is achieved via its end which comes into abutment against the body of the assembly element 14. If a locking screw 42 is used, a retaining weld needs to be performed in order to prevent it from accidentally loosening and therefore to safeguard its position within the assembly. This screw 42 has no mechanical strength function and therefore the risk of losing this screw is minimal. Furthermore, loss of this screw would not necessarily lead to loss of the connection. Care would be taken to ensure, by design, that the head of the screw 42 is sunk into the thickness of the casing 12 or of the flexible blade 20, so that this head does not extend beyond the volume formed by the casing. As illustrated in FIGS. 5A and 5B, the flexible blade 20 comprises an overhang 25 measuring a few millimeters around the entire periphery of the thickened portion 21. The role of this overhang 25 is to best cover the open-ended opening 122 of the casing and thus form a kind of labyrinth for the liquid metal, thus making it possible to minimize the leakage of metal through this opening. FIGS. 7A to 8A illustrate the weldless connection according to the invention in a shutdown rod between a pad ring 17 and a hollow component 12, the pads 18 being situated in the same plane as the spacer straps 121 of the hollow component 12. The two components are depicted separately and in the assembled positon. In this instance, there are two flexible blades 20 on one same face of the ring 17 facing in two opposite directions so that in the assembled position the thickened portions 21 lock the position of the pad ring both with respect to an upward movement and with respect to a downward movement of the ring within the hollow component. Another advantage of a connection according to the invention is the possibility of dismantling an assembly according to the invention fairly easily, even if it is irradiated. Thus, an assembly head for example, which has received far less radiation than a central portion, could be reused, leading to savings in terms of economy and in terms of waste management. One way of uninserting two elements assembled according to the invention is given in FIGS. 9 and 10. In this example, a collar 3 supporting actuators 30 is inserted around the hollow component 12. The number of actuators 30 is equal to the number of flexible blades 20, 21. Each actuator is positioned facing a thickening 21 of a blade 20. When the assembly is to be dismantled, the actuators 30 are actuated simultaneously and thus apply radial pressure to the thickened portion 21 of each blade, so that the element 14 is no longer connected to the hollow component 12 and can be extracted through an upward translational movement. Other alternative forms and improvements may be made without in any way departing from the scope of the invention. Thus, while in the embodiments illustrated the flexible blades are locked by a locking screw, it is also possible to envision preventing a flexible blade from flexing by using an internal elastic ring housed in a groove provided for this purpose in the flexible blade on the inside. The invention is not restricted to the examples which have just been described. In particular, features of the examples illustrated can notably be combined with one another in alternative forms of embodiment which are not illustrated. The expression “comprising a” is to be understood as meaning “comprising at least one”, unless specified to the contrary. |
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abstract | A collimator control method for an X-ray CT apparatus includes changing an aperture of the collimator according to a position of a helical scan on the body axis of the subject in the progress of the helical scan. |
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claims | 1. A shaper for shaping an ion beam, said shaper comprising:a plate that is placed between an ion beam grid and an ion beam source, said plate for covering holes in said grid, and wherein said plate is shaped and dimensioned such that said plate does not partially cover any holes in said grid that are directly adjacent to said plate;a hole that is configured to mount said shaper at a center of said grid and at least one other hole that is configured to secure said shaper to said grid to prevent said shaper from rotating relative to said grid; anda center mount portion, said center mount portion covering holes in said grid;wherein said shaper has two axes of reflection symmetry. 2. The shaper of claim 1 wherein the width of said plate increases with radius. 3. The shaper of claim 1 having a first arm extending radially in a first direction from said center mount portion and a second arm extending radially from said center mount portion in a second direction opposite said first direction, each of said first and second arms having a first portion that has a first width, a second portion that has a second width greater than said first width, a third portion that has a third width that is greater than said second width, and a fourth portion that has a fourth width that is greater than said third width. 4. The shaper of claim 3 wherein said first portion is rectilinear, wherein said second portion comprises a rectilinear first region and a second region that tapers from said second width, and wherein said third and fourth portions are each chevron-shaped. 5. The shaper of claim 3 wherein said first and second arms cover 53 holes each. 6. The shaper of claim 1 wherein said plate does not partially cover any of said holes. 7. The shaper of claim 1 wherein said plate is usable for both etching and deposition. 8. An ion beam deposition and etching apparatus, said apparatus comprising:an ion beam source for emitting an ion beam toward a specimen;an ion beam grid mounted between said ion beam source and said specimen; anda shaper comprising a plate that is placed between said grid and said ion beam source, said plate covering holes in said grid, a hole that is configured to mount said shaper at a center of said grid and at least one other hole that is configured to secure said shaper to said grid to prevent said shaper from rotating relative to said grid, and a center mount portion, said center mount portion covering holes in said grid, wherein said shaper has a first axis of reflection symmetry and a second axis of reflection symmetry that is perpendicular to said first axis, and wherein said plate is shaped and dimensioned such that said plate does not partially cover any holes in said grid that are directly adjacent to said plate. 9. The apparatus of claim 8 wherein the width of said plate increases with distance along said first axis. 10. The apparatus of claim 8 wherein said shaper comprises a first arm extending radially in a first direction from said center mount portion and a second arm extending radially from said center mount portion in a second direction opposite said first direction, each of said first and second arms having a first portion that has a first width, a second portion that has a second width greater than said first width, a third portion that has a third width that is greater than said second width, and a fourth portion that has a fourth width that is greater than said third width. 11. The apparatus of claim 10 wherein said first portion is rectilinear, wherein said second portion comprises a rectilinear first region and a second region that tapers from said second width, and wherein said third and fourth portions are each V-shaped. 12. The apparatus of claim 10 wherein said first and second arms cover 53 holes each. 13. The apparatus of claim 8 wherein said plate does not partially cover any of said holes. 14. The apparatus of claim 8 wherein said plate is affixed to said grid, and wherein said specimen is rotated relative to said plate and grid. 15. A deposition and etching apparatus, said apparatus comprising:means for emitting an ion beam toward a specimen;means for filtering said ion beam before said ion beam reaches said specimen; andmeans for blocking a portion of said ion beam before said ion beam reaches said specimen, a hole that is configured to mount said means for blocking at a center of said means for filtering and at least one other hole that is configured to secure said means for blocking to said means for filtering to prevent said means for blocking from rotating relative to said means for filtering, and a center mount portion, said center mount portion covering holes in said means for filtering, wherein said means for blocking has a shape that is bilaterally symmetrical along a first axis and bilaterally symmetrical about a second axis that is perpendicular to said first axis and is shaped and dimensioned such that said means for blocking does not partially cover any holes in said means for filtering that are directly adjacent to said means for blocking. 16. The apparatus of claim 15 said means for filtering includes a pattern of holes formed therein, wherein a portion of said holes is blocked by said means for blocking, wherein the number of blocked holes increases with distance along said first axis. 17. The apparatus of claim 16 wherein said means for blocking does not partially cover any of said holes. 18. The apparatus of claim 15 wherein said shape comprises a first portion that has a first width, a second portion that has a second width greater than said first width, a third portion that has a third width that is greater than said second width, and a fourth portion that has a fourth width that is greater than said third width. 19. The apparatus of claim 18 wherein said first portion is rectilinear, wherein said second portion comprises a rectilinear first region and a second region that tapers from said second width, and wherein said third and fourth portions are each chevron-shaped. 20. The apparatus of claim 15 wherein said specimen is rotated relative to said means for filtering and said means for blocking. |
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claims | 1. An apparatus for inspecting material within an annular recess comprising:a track support that may be positioned proximate the annular recess;a generally arcuate track provided on the track support, the track having a radius of curvature substantially identical to that of the annular recess;a carriage arranged and configured to move along the track in a first direction;a sensor support provided on the carriage and configured for movement along an axis substantially perpendicular to the first direction; anda sensor provided on the sensor support, the sensor being configured for insertion into the annual recess, whereby movement of the carriage causes the sensor to move along a portion of the surface of the annular recess. 2. An apparatus for inspecting material within an annular recess according to claim 1, further comprising:a holding mechanism for temporarily fixing the position of the track adjacent and above the annular recess. 3. An apparatus for inspecting material within an annular recess according to claim 2, wherein the holding mechanism includes one or more elements selected from a group consisting of:a stand-off element arranged to contact a surface extending from an outer sidewall of the annular recess for maintaining a predetermined spacing between the track and the surface;first and second actuators arranged proximate opposite ends of the track for positioning fastening elements within the annular recess;a vacuum assembly arranged for attachment to a surface extending from an outer sidewall of the annular recess; anda vacuum assembly arranged for attachment to a surface extending radially from the annular recess. 4. An apparatus for inspecting material within an annular recess according to claim 3, wherein the fastening elements include one or more elements selected from a group consisting of:a substantially wedge-shaped element configured for partial insertion into the annular recess in an insertion direction substantially perpendicular to the first direction for temporarily fixing the position of the inspecting apparatus relative the annular recess;an asymmetric element having a first dimension less than a width of the annular recess and a second dimension at least equal to the width of the annular recess configured for rotation for temporarily fixing the position of the inspecting apparatus relative the annular recess;a resilient element that assumes a compressed configuration as it is inserted into the annular recess; andan element configured for selective transition between an enlarged configuration and a reduced configuration for temporarily fixing the position of the inspecting apparatus relative the annular recess. 5. An apparatus for inspecting material within an annular recess according to claim 1, further comprising:a housing, the housing arranged and configured to contain the track support, the generally arcuate track, the carriage, the sensor support and the sensor in a stored configuration. 6. An apparatus for inspecting material within an annular recess according to claim 5, further comprising:a housing, the housing arranged and configured to contain and protect the track support, the generally arcuate track, the carriage, the sensor support and the sensor when in a stored configuration; anda deployment mechanism arranged for selectively extending the track support, the generally arcuate track, the carriage, the sensor support and the sensor from the housing when in a deployed configuration and returning to the stored configuration. 7. An apparatus for inspecting material within an annular recess according to claim 6, wherein:the deployment mechanism is arranged for the selective rotation of the track between a substantially vertical orientation and a substantially horizontal orientation. 8. An apparatus for inspecting material within an annular recess according to claim 5, wherein:an orientation of the track support is substantially identical in both the stored and deployed configurations. 9. An apparatus for inspecting material within an annular recess according to claim 8, wherein:the deployment mechanism includes a four-bar linkage for maintaining the orientation of the track support as it moves between the stored and deployed configurations. 10. An apparatus for inspecting material within an annular recess according to claim 1, wherein:the sensor support includes an upper connecting portion and a lower sensor supporting portion, the supporting portion having a horizontal extension that exceeds a horizontal extension of the connecting portion. 11. An apparatus for inspecting material within an annular recess according to claim 10, wherein:the horizontal extension of the supporting portion exceeds the horizontal extension of the connecting portion in two directions. 12. An apparatus for inspecting material within an annular recess according to claim 1, wherein:the sensor includes a plurality of ultrasonic transducers. 13. An apparatus for inspecting material within an annular recess according to claim 12, wherein:the plurality of ultrasonic transducers are configured to emit at least two frequencies and focused in at least two directions. 14. An apparatus for inspecting material within an annular recess according to claim 13, wherein:the frequencies include a first frequency of between about 2 and about 2.5 MHz and a second frequency between about 4.5 and about 5.5 MHz. 15. A method for inspecting material within an annular recess using an apparatus configured according to claim 1, the method comprising the steps of:orienting and aligning the generally arcuate track above the annular recess;extending a portion of the sensor support and sensor into the annular recess;activating the sensor for generating data corresponding to a condition of the material; andmoving the carriage along the track, to thereby moving the sensor along an arcuate portion of the material. 16. A method for inspecting material within an annular recess according to claim 15, wherein:the annular recess is formed within a nuclear reactor between an inner surface of a shroud and an outer circumferential surface of a core plate. 17. A method for inspecting material within an annular recess according to claim 16, wherein:the material includes a portion of a weld bead. 18. A method for inspecting material within an annular recess according to claim 17, wherein:the weld bead is the H6A weld bead. 19. An apparatus for inspecting material within an annular recess according to claim 1, further comprising:a holding mechanism for engaging at least one fixed surface adjacent the annular recess to fix a temporary position of the track adjacent and above the annular recess. 20. An apparatus for inspecting material within an annular recess according to claim 1, wherein:the generally arcuate track corresponds to only a minor portion of a circumference of the annular recess. |
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description | This application claims the benefit of a priority under 35 USC 119(a)–(d) to French patent application No. 03 50534 filed Sep. 12, 2003, the entire contents of which are hereby incorporated by reference. An embodiment of the present invention is directed to a radiation emitter and in particular to an emitter of X-ray radiation. An embodiment of the present invention is also directed to a radiology apparatus that may include a radiation emitter and in particular an apparatus that can be used in medical imaging for example, for imaging an object. More particularly, an embodiment of the invention is directed to an apparatus for mammography. The embodiments of the present invention, however, can be applied to any other field in which radiography or a radiological examination is undertaken, to include by way of example, CT, vascular, Rad-R&F. A conventional radiology apparatus comprises means for providing emitted radiation, such as an X-ray tube emitting X-rays. The emitted radiation is directed toward a body to be examined. The body may be any object for which a generally non-destructive investigation by imaging of the internal structure of the object is desired, such as a casting formed by metal and non-metal materials. In medical imaging, the body to be examined may be a patient's body. On another side of this body, relative to the tube, there is a detector. In practice, the detector is typically a radiographic film or an electronic detector, for example of the type with a radiology image intensifier screen. When applied to medical imaging, depending on the nature of the lesions or structures to be revealed, there are known ways of choosing the hardness of the X-rays emitted as well as, for reasons of detection threshold, the emission power. The rays thus emitted cross the body and excite the detector in revealing the attenuation that they undergo at certain places. The problems that disturb this type of detection are of different kinds. In particular, there are known problems of scattering in which certain parts of the body stop the emitted X-rays, without absorbing them, and become the site of Compton scattering. The rays that result from this scattering themselves also go through the rest of the body and excite the detector but, unfortunately, they do so at a place which is not straight ahead of the structure which is the site of their emission. The image is then falsified. To prevent this type of defect, there are known ways of collimating the rays by means of a grid screen which, on the whole, lets through only X-rays having a planned orientation (generally a perpendicular orientation) relative to the detector. However, to prevent traces of the grid screen from being seen in the revealed image, there are known ways of shifting the grid screen during examination. Consequently, the traces of this grid screen are distributed in the image to the point of becoming invisible. Mammography presents a problem that is more difficult than perhaps in other radiological imaging. In mammography (but can be seen in other fields) the difficulty is related to the low level of differentiation of absorption between the healthy tissues of a breast and tissues affected by lesions, especially instances of microcalcification. To resolve this problem, X-ray emission filters that confine the spectrum of the emitted X-rays to the narrowest possible spectrum are used. The spectrum is at a value of hardness such that the rays emitted are highly absorbed by the healthy structures and less absorbed by the unhealthy structures (or vice versa) so that the contrast of the image is increased. The production of the X-rays is obtained by the projection, at very high speeds, of electrons emitted by a cathode on an anode of the tube. Despite the choice of targets of the anode made out of appropriate materials, the spectrum of emission of the X-rays has an excessively great bandwidth. It may happen in this case that the structure to be revealed, which would have blocked rays at a given frequency, lets through rays at another frequency and the reverse would happen for other structures. This results in a loss of contrast. This is why it is desirable to filter the emission produced so as to confine the spectrum to a narrow band. The means for filtering comprises a plate, which is generally a metal plate, interposed between the X-ray tube and the body. Thus, the interposing of a plate made of molybdenum, rhodium, aluminium, copper, gold or silver may, as the case may be, enable the choice of the range of X-rays to be used. However, the interposing of the plate itself poses a problem. This problem is related to defects arising from the manner of manufacture of the plate, which is often obtained by rolling. The defects, which are visible in very precise conditions of examination, especially with a homogeneous interposed body (during the calibration) and with x-radiation confined in a narrow spectrum, take the form of spots or lines. In the latter case especially, the defects often have a pronounced direction that is of the axes of the rollers. Defects of this type are especially present in rhodium type filters. The variations of attenuation of the plate may also have several other possible reasons such as the local liberation of material from the surface, local variations in thickness or variations in density. A way to reveal these defects is a technique of contrast expansion, performed during tests of homogeneity, in a narrow window of brightness of the detected signal. The filter plates generally have a thickness of 25 to 30 micrometers. In X-ray mammography imaging it is sought to obtain very small differences in contrast created by clinical signs such as microcalcification or masses. These biological tissues have a very low difference in coefficient of radiological transmission with the tissues whose place they take. Consequently, the spatial homogeneity of the filter must be very high. For example, it has been recognized that a local variation in attenuation, in the range of 2.5% around the nominal value of 25 to 30 micrometers, makes the images unusable. Ultimately, improved homogeneity must be acquired throughout the surface of the filter plates. An embodiment of the invention seeks to overcome one or more of the above problems by providing a shift in the filter at the time of the exposure, preferably in parallel to its plane, so as to distribute the contribution of the defects that it causes in the image. This contribution is distributed over a wider surface. In this way, the amplitudes of the artefacts thus formed are themselves reduced to the point where they become smaller than the lesion-revealing differences in contrast to be observed. An embodiment of the invention is a radiology apparatus comprising means for emitting radiation, such as an X-ray emitter tube and means for filtering, such as a plate for the filtering of the emitted radiation. The means for filtering can be located in an intermediate position between the means for emitting radiation and a body to be subjected to the emitted radiation. The apparatus comprises means to control a radiation emission for the duration of a radiology exposure and means to move the filter for the duration of the exposure. FIG. 1 presents two views, one to the left and one to the right, of a radiology apparatus respectively before and after the implementation of an embodiment of the invention. The radiology apparatus comprises means for emitting radiation, such as an X-ray tube 1 and means for filtering the emitted radiation, such as a plate 2 for the filtering of the X-rays 3 emitted by the tube 1. The plate 2 is located in an intermediate position between the tube 1 and an object to be imaged, such as body 4, in particular a body of a patient to be examined and which is subjected to radiation from tube 1. On the other side of the body 4 relative to the tube 1, is a means 5 for detecting the radiation after the radiation has passed through the object. The means 5 is surmounted, in a manner that is known in radiography, by a moving anti-scatter grid screen 6 that can shift along arrows showing alternating directions 7. In the prior art, as seen in the left-hand figure, a defect 8 of the means 2 results in a very pronounced spot 9 (of high contrast) which is furthermore of a small size. During exposure or imaging, the means 2 is shifted, for example in the direction of arrow 10 and generally parallel to its plane and perpendicular to the radiation 3. As a result of the movement of means 2, the image of the defect 8 is distributed over a surface 11 that is far greater. As a consequence, the contrast of the spot is far less pronounced. The apparatus comprises means 12 to control the emission from the means 1 for emitting radiation. The means 12 comprises a microprocessor 13 linked by a bus 14 with a program memory 15, a data memory 16, an input/output interface 17 and in an embodiment, means 18 for driving (shown in a schematic view). The means 18 for driving is used to put the means 2 for filtering into motion. The means 18 for driving, may comprise a micromotor interposed between a side of a support of the means 2 and an edge 19 of the means 2 and may furthermore comprise piezoelectric or electromagnetic elements. For example, the edge 19 of the means 2 can be provided with a magnetized tape. This tape is subjected to the influence of an electromagnetic pole delivering a field with an amplitude that varies alternately in time. A program 20 contained in the memory 15 comprises for example means to excite the motor 18 (or the like) at a point in time 24 shortly before the start 21 of the duration 22 of a radiology exposure undertaken with the apparatus. For example, the duration 22 and the instant 21 are dictated by the microprocessor 13 that places one or more voltage square waves, liable to suitably excite the cathode 23 of the tube 1, on the interface 17. Since the speed of shift of the plate 2 is zero at the outset, the placing of the means 2 in motion in the direction 10 of the means 2 is anticipated at a date 24, so that, during the period 22, the speed at which the means 2 is shifted has a perfectly linear shape. By acting in this way, it is ensured that the contribution of the defect 8 will be carried out uniformly throughout the surface 11 and will therefore be reduced in proportion to the size of this spot. FIG. 3 shows different types of defects. The left-hand part of the figure in particular shows traces of rolling 25 presenting an elongated appearance in the plane of the means 2, all these traces being parallel to each other. The defects thus brought about can subsequently be likened to a sine variation whose spatial wavelength is equal to the distance between two contiguous traces. In the right-hand parts of FIG. 3, in a designation square 26, is an indication of an isolated spot having a (very slightly) lighter color. The direction of the motion 10 to which the plate 3 is subjected is, in the case of the rolling traces 25, preferably perpendicular to the direction of elongation of these traces 25. If, as happens sometimes, the plate has been obtained by a crossed double rolling process, then other rolling traces are seen to appear in a direction perpendicular to the direction 25. These traces are elongated in directions perpendicular to the directions 25. In this case, the direction 10 of shift of the plate 2 will be oriented along the direction 27 that is substantially a bisector of the angle formed by the two directions of the rolling alignments such as 25. When the two directions are at 90° to each other, the direction 27 is approximately at 45°. FIGS. 4 to 6 show the length of shift of the plate 2. In FIG. 4, it is shown that for a defect of the type 25 with a density profile that is substantially sinusoidal (in the direction 10), it is possible to make a shift that is equal to a quarter, half or three-quarters of the length of the sine wave thus detected, or equal to the full wavelength thus detected. If the shift is about a quarter of the wavelength, the amplitudes of the artefacts are reduced by only 10%. If the length of the shift is about half the wavelength, the contribution of the artefact is reduced by about 40%. The contribution is reduced by 70% if the length of the shift is about three-quarters of the wavelength. It is reduced by almost 100% when the length of the shift is equal to the wavelength. In FIG. 5, if the contribution of the defects is random in the profile, for defects whose mean wavelength is in the range of 20 to 30 micrometers, their contribution in the image is reduced, in terms of peak value, by 60% when the exploration of the shift is in the same range as this mean wavelength, namely 20 micrometers. This contribution remains still significant, although well attenuated, when the shift is greater than or equal to twice this mean wavelength. However, this contribution is highly attenuated when the shift is greater than or equal to 15 times the mean wavelength of the defects. For shifts in the range of 300 micrometers, the contribution of the defects remains always lower than 10%. FIG. 6 gives a view, under the same conditions, of the spread effect resulting from the shift of the plate 2 for highly accentuated local defects. For random and isolated defects, the shift of about 300 micrometers, for example at least 250 micrometers, and of over 300 micrometer, is sufficient to make the artefacts caused by the manufacture of the plates to disappear significantly (with a remanence of less than 10%). Instead of shifting the plate 2 by means 18, it is possible to use the presence, in a radiology apparatus, of a turntable or carrousel. Such a turntable can used to present either of the chosen plates before the tube 1 in order to carry out an expected radiology examination. Such a turntable comprises a set of cradles such as 28 linked to one another in a continuous circle by a conveyance structure 29. In this case, rather than add as means for driving, such as motor 18, it is sufficient to continue mobilizing the conveyance means 29 and continue to move the turntable during the exposure so as to distribute the defects of the plates. Whatever is the chosen means for driving, the microprocessor 13 implementing the program 20 will drive the means for putting the plate 2 into motion so that the movement remains substantially linear as can be seen in FIG. 2. One skilled in the art may make or propose various modifications in the structure and/or way and/or function and/or result of the disclosed embodiments without departing from the scope and extant of the disclosed embodiments and equivalents thereof. |
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063296624 | summary | FIELD OF THE INVENTION The present invention relates to a radiation image forming system utilizing a combination which comprises a silver halide photographic material and a couple of radiographic intensifying screens. The invention also relates to a method for forming a radiation image or a radiographic image. BACKGROUND OF THE INVENTION In medical radiography such as X-ray photography, a "both-sided emulsion film type" silver halide photographic material (in which a photosensitive silver halide emulsion layer is provided on either side of a transparent support) is used and two radiographic intensifying screens are placed on both of the front and the back sides of the photographic material. A combination of the photographic material and the radiographic intensifying screens are then exposed to X-rays having passed through a patient. Such "both-sided photographic film system" is generally employed to obtain a radiation image of high quality with high sensitivity. However, the sharpness of the resultant image is often lowered by "cross-over light". The term of "cross-over light" means a visible light emitted by the radiographic intensifying screens which are placed on each side of the photographic material and then passes through the support of the photographic material to reach the photosensitive layer provided on the opposite side to deteriorate the sharpness. The deterioration thus caused by the cross-over light is referred to as "cross-over phenomenon". In order to reduce the cross-over light (hereinafter, often referred to as simply "cross-over"), various studies on a silver halide photographic material (herenafter often referred to as "photographic material" or "photosensitive material") and a radiographic intensifying screen (hereinafter often referred to as "intensifying scree" or "screen") have been made. As the studies on the photographic material, for example, Japanese Patent Provisional Publications No. H1-166031 and No. H1-172828 disclose a method using a mordant polymer and a method using a solid fine crystalline dye, respectively. In those methods, however, a considerably large amount of dye should be incorporated into the photographic material so as to satisfactorily reduce the cross-over light. Such large amount of dye is hardly removed rapidly in a development treatment. Therefore, into practically employable photographic materials, such large amount of dye cannot be incorporated. Further, if the dye is used in a large amount, an intensifying screen is liable to be stained with the dye transferred from the photographic material because the dye is insufficiently fixed to the photographic material. Although various dyes have been proposed to solve this problem, a satisfactory dye still has not been reported. A method using an intensifying screen which can intercept the cross-over light is also proposed in, for example, WO 93-01521, EP 650089 and EP 592724. In the method, luminescence of phosphor is shifted to the ultraviolet region so as to reduce the cross-over light. With respect to an intensifying screen containing Gd.sub.2 O.sub.2 S:Tb phosphor, various proposals are reported. Japanese Patent Provisional Publication No. 61-151534 discloses an intensifying screen in which a light-absorbing dye is contained and the phosphor is chosen so that a light emitted by the intensifying screen may comprise a green light component more than a blue light component. Each of Japanese Patent Provisional Publications No. 62-222200 and No. H4-155297 discloses a screen having differently colored phosphor layer to give an image of improved sharpness. RD83-22709 and RD82-218041 suggest that the sharpness of a resultant image can be improved by using a yellow dyesand/or a light-absorbing dye. Japanese Patent Publication No. 58-2640 teaches that the sharpness can be improved by applying a light-absorbing pigment onto the surface of phosphor layer. U.S. Pat. No. 4,362,944 proposes a surface protective layer which absorbs a part of the emitted light. Further, as an intensifying screen giving a low cross-over, an intensifying screen having a yellow-colored phosphor layer is commercially available (Eastman Kodak Co., Lanex Medium [trade name]). However, it appears to be indispensable that the dyes and/or pigments incorporated into an intensifying screen reduce sensitivity. With respect to an intensifying screen containing a fluorescent dye or pigment, EP 0595089 reports that a phosphor which emits a ultraviolet light improves in corporation with fluorescent dyes the sensitivity. Further, DE 2807398 and DE 3143810 disclose intensifying screens using s fluorescent pigment in the form of fine particles. Although various studies such as described above have been reported, it seems that there are no studies reporting that the cross-over of radiographic intensifying screens containing rare earth phosphors is well reduced using fluorescent dyes or pigments. Under the circumstances, a radiation image-forming system giving a radiation image (or radiographic image) of high quality with high sensitivity (i.e., high radiographic speed) is highly desired, and accordingly it is desired to further improve both radiographic intensifying screens and photographic materials. SUMMARY OF THE INVENTION It is an object of the present invention to provide a combination for radiation image formation and a radiation image-forming system giving a radiation image of high sharpness with high sensitivity. The inventors have studied on the radiographic intensifying screen utilizing a rare earth phosphor such as a terbium activated gadolinium oxysulfide phosphor, and have found that not only cross-over can be effectively reduced but also sensitivity (i.e., radiographic speed) can be remarkably enhanced by a combination of an intensifying screen containing a specific fluorescent dye or pigment and a specific photographic material. A typical rare earth phosphor used in the invention emits luminescence having a main peak at approx. 545 nm, and a silver halide photographic material used in combination with the intensifying screen containing said phosphor is beforehand sensitized with a dye so as to become highly sensitive to a light of a wavelength around 545 nm. The fluorescent dye or pigment in the intensifying screen absorbs a portion of luminescence of the phosphor in the wavelength region shorter than 500 nm (light in this wavelength region mainly causes the cross-over phenomenon because the photographic material absorbs almost no light in that wavelength region) and then emits light in the wavelength region near the main peak of the luminescence (i.e., approx. 545 nm). The dye contained in the photographic material selectively absorbs a light in the wavelength region of longer than 500 nm to prevent the light from crossing over the support of photographic material to reach the photographic emulsion layer on the reverse side. Accordingly, the present invention resides in a combination for radiation image formation which comprises a silver halide photographic material having a support and at least one silver halide emulsion layer provided on each side of the support, and two radiographic intensifying screens each having a support and at least one phosphor layer provided thereon, wherein the phosphor layer contains a rare earth phosphor represented by the following formula (I): EQU M.sub.w O.sub.w X:M' (I) PA1 in which M represents at least one rare earth atom selected from the group consisting of Y, La, Gd and Lu; X represents at least one chalcogen atom selected from the group consisting of S, Se and Te, or at least one halogen atom selected from the group consisting of F, Br, Cl and I; M' represents a rare earth atom which activates M; and w is 2 when X is a chalcogen atom or w is 1 when X is a halogen atom, PA1 the radiographic intensifying screen contains a fluorescent dye or pigment which absorbs a portion of luminescence emitted by the rare earth phosphor and then emits light in a visible region, and PA1 the photographic material shows a cross-over of 10% or less when it is exposed to radiation in combination with said intensifying screen. PA1 said photographic material shows a cross-over of 10% or less when it is placed between the two radiographic intensifying screens and exposed to radiation. PA1 the phosphor layer contains a rare earth phosphor represented by the above-mentioned formula (I), PA1 the radiographic intensifying screen contains a fluorescent dye or pigment which absorbs a portion of luminescence emitted by the rare earth phosphor and then emits light in a visible region, and PA1 the photographic material shows a cross-over of 106% or less when it is exposed to radiation in the system. PA1 forming a combination by placing a silver halide photographic material having a support and at least one silver halide emulsion layer provided on each side of the support between two radiographic intensifying screens each having a support and at least one phosphor layer provided thereon, said phosphor layer containing a rare earth phosphor represented by the aforementioned formula (I); PA1 imagewise exposing the combination to X-ray radiation; PA1 separating the exposed photographic material from the intensifying screens; and PA1 developing the exposed photographic material in a developing solution. The invention further resides in a radiation image-forming system comprising two radiographic intensifying screens each having a support and at least one phosphor layer provided thereon and a silver halide photographic material which is interposed between the two intensifying screens and has a support and at least one silver halide emulsion layer provided on each side of the support, wherein The invention furthermore resides in a method for forming a radiation image which comprises the steps of: In the invention, the rare earth phosphor in the radiographic intensifying screen preferably is a terbium activated gadolinium oxysulfide phosphor. The terbium activated gadolinium oxysulfide phosphor preferably contains terbium atom in an amount of 0.001 to 0.02 mol. per 1 mol. of Gd. The fluorescent dye or pigment preferably shows a light absorption peak in a wavelength region of shorter than 500 nm and an emission peak in the wavelength range of 450 to 600 nm under the condition that the wavelength of emission peak is longer than the wavelength of light absorption peak by at least 10 nm, preferably at least 20 nm. Also preferred is that the fluorescent dye or pigment shows a light absorption peak in a wavelength region of 400 to 490 nm and an emission peak in the wavelength range of 500 to 600 nm. The emission peak of the fluorescent dye or pigment preferably has a half-width of 100 nm or less. The fluorescent dye or pigment in the radiographic intensifying screen preferably is a carbocyanine dye, a xanthene dye, a triarylmethane dye, a coumarin dye, a phthalimide compound, a naphthalimide compound, a diketopyrrolopyrrole compound or a perylene compound. The fluorescent dye or pigment in the radiographic intensifying screen is preferably contained in the phosphor layer. In the combination of the invention, the silver halide photographic material preferably contains a dye which shows a light absorption peak in the wavelength region of 500 to 600 nm. The dye in the silver halide photographic material is preferably provided between the support and the silver halide emulsion layer, in the form of a dye layer. Preferably, this dye is decolorizable in a developing process. Also preferred is that the dye shows an absorption coefficient at 550 nm which is twice or more larger than that at 450 nm. The decolorizable dye preferably is in the form of solid fine particles. |
046541721 | abstract | A method of processing radioactive waste resin by pyrolyzing radioactive waste ion exchange resin generated in a nuclear plant such as a nuclear power station. First, the ion exchange resin is pyrolyzed at a low temperature, and the resulting decomposition gas is separated. Second, the ion exchange resin at a high temperature, and the resulting decomposition gas is separated. Finally, the residue of the ion exchange resin is hot-pressed into a molded article. |
summary | ||
055330789 | abstract | A nuclear fuel assembly for a pressurized water reactor having lower and upper tie plates, guide tubes, spacer grids, an instrumentation tube, and extended fuel rods which extend to the lower tie plate and which are spaced radially and supported along the guide tubes by the spacer grids, at least one of the extended fuel rods having at a lower end a fuel rod lower end cap secured by a first spring within an aperture in the lower tie plate and which exerts a lateral force against the lower end cap. The upper tie plate further includes a fuel rod support housing which extends down over the upper end of the at least one of the extended fuel rods and has a second spring positioned in a bore in the fuel rod support housing which exerts a lateral force on the upper end of the extended fuel rod positioned within the bore in the fuel rod support housing. |
description | The present invention relates to a positioning apparatus and a positioning method for an X-ray lens (also called “Kumakhov lens”). The invention further relates to an X-ray device such as an X-ray spectrometer or an X-ray diffractometer comprising an X-ray lens and a positioning apparatus for the X-ray lens. The advent of so-called X-ray lenses over two decades ago has prepared the ground for lightweight, portable X-ray devices with a broad spectrum of applications in areas as different as metallurgy, geology, chemistry, forensic laboratories and customs inspection. In a similar way as conventional optical lenses redirect visible or near-visible photons, X-ray lenses redirect electromagnetic radiation in the X-ray radiation band and may thus be used to collimate or focus a beam of X-rays. An X-ray lens is conventionally formed from a plurality of capillaries. Each capillary guides the X-rays captured at a front end thereof to the opposite end by way of total external reflection. This rule applies so long as the angle of incidence at the front end does not exceed a critical angle. If the critical angle is exceeded, X-rays can no longer be captured within the capillary. In such a case, the capillary becomes transparent to the X-rays. Originally, an X-ray lens was a bulky device with dimensions in the region of up to several meters. These large dimensions were mainly the result of separate support structures that were required to keep the individual capillaries in place. Commercial use of X-ray lenses became feasible when it was recognized that the support structures can be omitted if the X-ray lens is produced out of one or more glass capillary bundles using glass drawing techniques. By fusing the capillary mantles together, separate support structures became obsolete. Today, the commercial application of X-ray lenses includes portable X-ray spectrometers, lightweight X-ray diffractometers and many other small-sized devices. Such devices typically comprise an X-ray source (such as an X-ray tube), an X-ray lens and a detector. X-rays emitted from the X-ray source are focused by the X-ray lens onto a tiny spot on a sample. The detector detects the X-rays emitted back from the sample and generates an output signal that can for example be spectrally analysed to determine the chemical elements included in the sample. To enhance the efficiency of an X-ray device, the X-ray lens must be precisely aligned with respect to an axis of the X-ray device. If the X-ray lens is not correctly aligned, the flux of X-rays captured by the X-ray lens can get drastically reduced as a result of the fact that the angle of incidence exceeds the critical angle for too many X-rays. In the past, the alignment of X-ray lenses was a cumbersome task even for very experienced operators. With conventional positioning mechanisms, the adjustment in one direction often involved a simultaneous (mis-)adjustment in another direction. These dependencies prevented an intuitive alignment of an X-ray lens and required many individual adjustment steps. Accordingly, there is a need for a positioning apparatus and a positioning method that facilitate the adjustment of an X-ray lens. Also, there is a need for an X-ray device including a positioning apparatus for an X-ray lens. According to a first aspect of the invention, a positioning apparatus for aligning an X-ray lens is provided. The positioning apparatus comprises a lens mounting component and a positioning component including at least one goniometer stage, the least one goniometer stage having a centre of rotation that substantially coincides with an X-ray emitting portion of an X-ray source. In a goniometer stage, the centre of rotation is outside the goniometer mechanic. In the present case, the centre of rotation is chosen to essentially coincide with the X-ray emitting portion of the X-ray source. Typically, the goniometer mechanic comprises a curved guidance structure. With the centre point of the curvature being “in the air” and at least close to the X-ray emitting portion, everything mounted on the goniometer stage (such as the X-ray lens) rotates around the X-ray emitting portion. This approach facilitates lens alignment. In one example, the positioning component includes a first goniometer stage for tilting the X-ray lens about a first axis and a second goniometer stage for tilting the X-ray lens about a second axis. The second axis may run perpendicular to the first axis. The first axis and the second axis may be chosen such that they intersect each other at a point that approximately coincides with the X-ray emitting portion of the X-ray source. The two goniometer stages may be arranged one behind the other in relation to the X-ray source. With such an arrangement, the first goniometer stage may have a first distance from the X-ray emitting portion, and the second goniometer stage may have a second distance from the X-ray emitting portion that is different from the first distance. Accordingly, the two goniometer stages may have different radii with respect to the point of intersection between the first tilting axis and the second tilting axis. In one variation, the first goniometer stage is actuable independently from the second goniometer stage. In other words, the first tilting axis may be decoupled from the second tilting axis. To this end, separate actuation mechanisms for the first goniometer stage and the second goniometer stage may be provided. According to a first variant of the invention, the X-rays generated by the X-ray source pass the positioning component outside the at least one goniometer stage. According to a second variant, the at least one goniometer stage has an internal X-ray passage. The internal X-ray passage may extend through the centre of the at least one goniometer stage. Alternatively, the internal X-ray passage may have an eccentric extension in relation to the centre of the at least one goniometer stage. In addition to the at least one goniometer stage, the positioning component may further comprise one, two or more translation stages. In one example, the positioning means comprises a first translation stage having a first axis of translation and a second translation stage having a second axis of translation. The second axis of translation may run obliquely or, preferably, in perpendicular to the first axis of translation. The first translation axis and the second translation axis are preferably arranged in a plane that intersects a longitudinal axis of the X-ray lens at approximately a right angle. In addition to the first and second translation stages, a third translation stage having a third axis of translation may be provided. The third translation axis may extend perpendicularly in relation to the first and second translation axis. Like the goniometer stages, the translation stages may be arranged one behind the other. In the direction of the X-rays emitted from X-ray source, the one or two translation stages may be arranged upstream or downstream of the one or two goniometer stages. The first translation stage and the second translation stage may each be provided with a separate actuation mechanism and may thus be actuable independently from each other (and also independently from the at least one goniometer stage). Accordingly, all the individual positioning axes of the positioning apparatus may be decoupled. In one possible scenario, this decoupling means that a translation along a first axis is independent of the tilting about a second axis perpendicular to the first axis (including all permutated variants). The positioning apparatus may further comprise a first interface member for coupling the positioning apparatus to a housing of the X-ray source. Additionally, or in the alternative, the positioning apparatus may comprise a second interface member for coupling the positioning apparatus to a sample housing. The positioning apparatus may comprise an X-ray shielding component that may be provided at an end of the positioning apparatus to face the X-ray source. The shielding component is preferably configured to define a limited X-ray passage and to block all X-rays outside the X-ray passage. The provision of an X-ray shielding means permits to manufacture the positioning apparatus from a material (such as a aluminum) that is essentially transparent to X-rays. In a variation, the positioning apparatus also comprises an X-ray lens. The X-ray lens may extend centrally through the positioning apparatus and may be aligned with or define the X-ray passages mentioned above. The X-ray lens may have various shapes and configurations. In one embodiment, the X-ray lens comprises one or more bundles of capillaries. The lens mounting component allows for a coupling between the position component and the lens to be positioned. In one example, the less mounting component is configured to generate a clamping force acting on either the lens or any structural member rigidly attached to the lens. According to a further aspect of the invention, an X-ray device is provided. The X-ray device comprises an X-ray source having an X-ray emitting portion, an X-ray lens for redirecting X-rays emitted from the X-ray source, and a positioning apparatus for aligning the X-ray lens, the positioning apparatus comprising at least one goniometer stage having a centre of rotation that substantially coincides with the X-ray emitting portion. The X-ray device may further comprise an X-ray shielding component arranged between the X-ray source and the at least one goniometer stage. The X-ray shielding component preferably restricts the X-ray beam emitted from the X-ray source to an X-ray passage that is defined by or aligned with the X-ray lens. According a still further aspect of the invention, a method of aligning an X-ray lens using a positioning apparatus including at least one translation stage and at least one goniometer stage with a centre of rotation that substantially coincides with an X-ray emitting portion of an X-ray source is provided. The positioning method comprises the steps of positioning an inlet focus of the X-ray lens by actuating the at least one translation stage (preferably by individually actuating the first and second translation stages) to substantially coincide with the X-ray emitting portion, and by actuating the at least one goniometer stage to align the X-ray lens in relation to a predefined axis extending through the X-ray emitting portion (such as an optical axis of any device incorporating the positioning apparatus). In the following, the invention will exemplarily be described with reference to a preferred embodiment in the form of an X-ray spectrometer comprising a positioning apparatus with two goniometer stages and two translation stages. It should be noted that the invention can also be practised in other X-ray devices such as diffractometers and in positioning apparatuses having a different structure (e.g. including no, only one or three translation stages). FIG. 1 shows a cross sectional view of an X-ray spectrometer 10 according to an embodiment of the present invention. The spectrometer 10 includes an X-ray source 12 constituted by an X-ray tube. The spectrometer 10 further comprises a shutter 14, a modular positioning apparatus 16, a sample housing 18 with a sample 20 arranged on a sample positioning platform 22, and a detector 24. An X-ray beam generated within the X-ray source 12 and indicated by reference numeral 26 passes along an optical axis 30 through the shutter 14. An X-ray (or Kumakhov) lens 28 to be aligned by means of the positioning apparatus 16 in relation to the X-ray source 12 and in relation to the optical axis 30 focuses the X-ray beam onto a tiny spot on the sample 20 (note that the size of the sample 20 is exaggerated in the schematic drawing of FIG. 1). The detector 24 collects the X-rays emitted back from the sample 20 and outputs a spectrum signal indicative of the chemical elements included in the sample 20. The spectrometer 10 shown in FIG. 1 has a compact tabletop design and is transportable for in-situ analysis. The samples may be provided in a wide range of physical forms, including solids, powders, pressed pellets, liquids, granules, films and coatings. The typical element detection capabilities of the spectrometer 10 under atmospheric conditions range from aluminum (Al) to uranium (U). The spectrometer 10 allows for a qualitative and quantitative elemental analysis down to very low elemental concentrations and sample sizes of 20 μm. In the view of FIG. 1, the X-ray source 12 and the shutter 14 have been rotated by 90° about the optical axis 30 of the spectrometer 10 to better illustrate their structure. Like conventional X-ray tubes, the X-ray source 12 includes a cathode 32 to emit electrons and an anode 34 to collect the electrons emitted by the cathode 32. Thus, a flow of electrical current is established as the result of a high voltage connected across the cathode 32 and the anode 34. The electron flow within the X-ray source 12 is focused onto a very small spot (the “hot spot”) 36 on the anode 34. The anode 34 is precisely angled at typically 5 to 15 degrees off perpendicular to the electron current so as to allow the escape of some of the X-rays generated at the “hot spot” 36 upon annihilation of the kinetic energy of the electrons colliding with the anode 34. The X-ray beam 26 thus generated is emitted from the “hot spot” 36 essentially perpendicular to the direction of the electron current and essentially along the optical axis 30 at diverging angles. The X-rays emitted from the X-ray source 12 first pass the shutter 14 attached to a housing 38 of the X-ray source 12. The shutter 14 selectively blocks the X-ray beam 26 generated within the X-ray source 12 and thus provides a control mechanism for selectively switching the irradiation of the sample 20 “on” or “off”. The lens positioning apparatus 16 is arranged downstream (in relation to X-ray source 12) of the shutter 14 and is rigidly attached to the shutter 14 by means of an interface member (not shown in FIG. 1). The positioning apparatus 16 includes an X-ray shielding component 40, a positioning component 42 for the X-ray lens 28, and a lens mounting component 44 for rigidly coupling the X-ray lens 28 to the positioning component 42. The individual components 40, 42, 44, which are shown only schematically in FIG. 1, are illustrated in more detail in the various views of FIGS. 2 to 4. As becomes apparent from FIGS. 3 and 4, the X-ray shielding component 40 has an outer flange 46 (not shown in FIG. 2) with two screw holes 48 for rigidly attaching the whole positioning apparatus 16 to the shutter 14 (and thus to the X-ray source 12). The outer flange 46 therefore serves as an interface member of the positioning apparatus 16 in relation to the shutter 14/the X-ray source 12. The X-ray shielding component 40 may comprises further structural elements as required for limiting the X-ray beam essentially to an inlet opening of the X-ray lens 28. The X-ray lens (not shown in FIGS. 2 to 4) is fixedly mounted inside a tube member 50. The tube member 50 in turn is rigidly coupled to the lens mounting component 44. The lens mounting component 44 comprises a base member 52 attached to the positioning component 42. The base member 52 has a central opening for receiving the tube member 50. A plurality of tongues 54 with outer threaded portions 56 extend from the opening of the base member 52 and in the axial direction of the tube member 50. The lens mounting component 44 further comprises a collar member 58 with a central opening through which the tube member 50 extends. The collar member 58 can be screwed onto the tongues 54 and cooperates with their outer threaded portions 56. Be means of an additional screw (not shown) extending in perpendicular to the tube member 50 and through the collar member 58, the free end at least one of the tongues 54 can be moved towards the tubular member 50 as the screw is screwed into the collar member 58. Accordingly, a clamping connection between the tubular member 50 on the one hand and the lens mounting component 44 on the other hand is established. The positioning component 42 is arranged upstream of the lens mounting component 44 and includes two translation stages 60, 62 as well as two goniometer stages 64, 66. As can be seen from FIG. 2, the base member 52 of the lens mounting means 44 is attached to the bottom of the first translation stage 60. The individual positioning stages 60, 62, 64, 66 are arranged one behind the other. Starting with a first translation stage 60 as the most downstream positioning stage, a second translation stage 62, a first goniometer stage 64 and a second goniometer stage 66 as the most upstream positioning stage follow. Each of the positioning stages 60, 62, 64, 68 has a central X-ray passage 68, 70, 72, 74, respectively, through which the tubular member 50 extends. Each of the two translation stages 60, 62 includes a double-dovetail guide (only one, reference numeral 76, is shown in the cross sectional view of FIG. 2). For each of the two translation stages 60, 62, a separate fine-pitch adjustment screw with an associated knob 78, 80 and spring returnment, respectively, is provided. In combination, the first translation stage 60 and the second translation stage 62 form an xy translation stage. Accordingly, the first translation stage 60 has a first axis of translation, namely the x axis which in FIG. 2 runs perpendicular to the axis of the tubular member 50 and in parallel to the drawing plane. The second translation stage 62 has a second axis of translation, namely the y axis which runs perpendicular to the x axis and perpendicular to the axis of the tubular member 50. By means of the respective knobs 78, 80, the first and second translation stage 60, 62 can be actuated independently from each other. In an alternative embodiment not shown in the drawings, a third translation stage having a third axis of translation (z axis) that runs perpendicular to both the first and second axis of translation may be provided. The two goniometer stages 64, 66 are arranged upstream of the two translation stages 60, 62. In their combination, the first goniometer stage 64 and the second goniometer stage 66 form a theta-phi goniometer that provides for two independent rotations about a common centre of rotation. This common centre of rotation is substantially constituted by the “hot spot” 36 shown in FIG. 1, i.e. by the X-ray emitting portion of the X-ray source 12. Each goniometer stage 64, 66 includes a curved dovetail guide 82, 84, respectively, and can be adjusted by associated fine-pitch screws via knobs 86, 88 with spring returnment, respectively. The provision of two separate adjustment knobs 86, 88 allows for a separate actuation of each of the first and second goniometer stage 64, 66. An actuation of the first goniometer stage 64 tilts the tube member 50 (with the X-ray lens) about a first tilting axis that runs through the “hot spot” 36 shown in FIG. 1 and in the drawing plane of FIG. 1 perpendicular to the optical axis 30. An actuation of the second goniometer stage 66 tilts the tube member 50 about a second tilting axis that also runs through the “hot spot” 36 and that is perpendicular to both the first tilting axis and the drawing plane of FIG. 1. Since the first goniometer stage 64 is arranged downstream of the second goniometer stage 66, the distance of a reference point on the first goniometer stage 64 to the “hot spot” 36 is larger than the distance between a corresponding reference point on the second goniometer stage 66 and the “hot spot” 36. The tubular member 50 with the X-ray lens can be positioned in relation to a stack of four decoupled axes (two translation axes running perpendicular to each other and two tilting axes also running perpendicular to each other). Accordingly, a translational movement along any translational axis is independent from a tilting movement about any tilting axis and vice versa. This allows for an easier and more intuitive alignment of the X-ray lens received in the tubular member 50 in relation to the “hot spot” 36 on the anode 34 and in relation to the optical axis 30. The fact that the tubular member 50 with the X-ray lens extends centrally through the positioning module 16 (and centrally through the positioning apparatus 42) further facilitates the alignment procedure. When the X-ray lens 28 shown in FIG. 1 is to be aligned in relation to the “hot spot” 36 of the X-ray source 12 and the optical axis 30, in a first step an inlet focus of the X-ray lens 28 is positioned in the xy plane such that the inlet focus essentially coincides with the “hot spot” 36. This first positioning step therefore only involves an actuation of the first and second translation stages 60, 62. In a second positioning step, the X-ray lens 28 is tilted and turned to align a longitudinal axis of the X-ray lens 28 such that it coincides with the optical axis 30. The second positioning step involves an adjustment of one or both of the first and second goniometer stages 64, 66. While the knobs 78, 80, 86, 88 shown in FIGS. 2 to 4 are intended for manual actuation, an alternative embodiment of the inventions provides for a motor actuation. The X-ray shielding component 40 (only schematically shown in FIG. 1 and only partially shown in FIGS. 2 to 4) is attached at the bottom of the second translation stage 66 via screws extending through openings 92 in the flange portion 46. The shielding component 40 is advantageously configured to block all X-rays outside the circular X-ray passage defined by the upstream opening 90 of the tubular member 50 and thus efficiently shields the positioning component 42 from X-rays. Accordingly, the individual components of the positioning component 42 (such as the translation stages 60, 62 and the goniometer stages 64, 66) can without any X-ray safety problem be manufactured from conventional materials such as aluminium which generally are transparent or nearly transparent to X-rays. While the current invention has been described with respect to a particular embodiment, those skilled in the art will recognize that the current invention is not limited to the specific embodiment described and illustrated herein. Therefore, it is to be understood that the present disclosure is only illustrative. It is intended that the invention be limited only by scope of the claims appended hereto. |
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description | This application claims the priority of Chinese Patent Application 200610116910.1, filed Sep. 30, 2006, the entire disclosure of which is incorporated herein by reference. The invention relates to a method of preparing a sample for transmission electron microscopy (TEM). With the development of Very Large Scale Integration (VLSI), lightly doped drain (LDD) and source/drain regions are employed in deep submicron systems. In order to make the source/drain expansion region shallower so as to control the short channel effect, a large amount of impurities are often used as dopant in an area near the channel of the source/drain PN junction to control the depth of the LDD region and the source/drain expansion region. However, implanting a large amount of impurities into the small region by the ion implantation method will cause defects, resulting in a leakage current in the PN junction and then damaging the semiconductor device. In general, a secondary ion mass spectrometer (SIMS) method is used to perform a failure analysis for semiconductor devices. However, the SIMS method usually is time-consuming due to its low detection speed and therefore is not suitable for analyzing a small region. In addition, the SIMS method can only be used to detect defects in wafers other than semiconductor devices. Thus the detection result cannot faithfully represent defects in the final products. Due to its high resolution, the TEM can be used to observe the patterns and dimensions of very thin films. Therefore, as the dimensions of semiconductor devices become smaller and smaller, especially when the device width is less than 0.13 μm, the TEM has become an important apparatus for observing and analyzing defects and structures in integrated circuits. FIG. 1A-1C are schematic diagrams of TEM samples fabricated by existing methods. As shown in FIG. 1A, a failure region 103 is positioned on the sample 100 by a method of electrical positioning. Two pits 101 and 102 having a larger area than the failure region 103 are dug out at both sides of the failure region 103 in the sample 100 using a focused ion beam (FIB) with a current of 7000 pA. As a result, the cross section of the failure region 103 can be observed during the subsequent process of milling the failure region 103, and the failure region 103 can be taken out from the sample 100 easily. The pits 101 and 102 are 15 μm×8 μm×6 μm (length×width×depth) (the dimension along the X-axis is defined as the length; the dimension along the Y-axis is defined as the width; and the dimension along the Z-axis is defined as the depth; the same below). The failure region 103 between the pits 101 and 102 is 3 μm-12 μm in length and 1 μm-3 μm in width. As shown in FIG. 1B, the current for FIB is adjusted to 300 pA and is used to mill the first surface 104 of the failure region 103, until the cross section of the failure region 103 for the semiconductor device is exposed. The milling depth is 4 μm. The second surface 105 of the observation region 103 is milled by FIB with a current of 300 pA, until the width of the failure region 103 is 80 nm-120 nm. As shown in FIG. 1C, the sample 100 is placed into a TEM observation chamber, and the failure region 103 is irradiated with an electron beam accelerated by a high voltage. The pattern of the failure region 103 for a semiconductor device is magnified and projected onto a screen for analysis. The existing method for preparing TEM samples is disclosed by JP2004245841. FIGS. 2A-2B are schematic diagrams of TEM samples prepared by existing methods. As shown in FIG. 2A, a cross section of the failure region for a semiconductor device is observed by a TEM with an amplifying multiple of 97000. The lightly doped drain 110 and source 112 are ion doped regions, and the silicon substrate 114 is a non-doped region. Since the ion doped regions are in the same thickness as the non-doped region, it is difficult to distinguish the lightly doped drain 110 and source 112 regions from the silicon substrate 114 and to clearly observe the pattern and defects in the lightly doped drain 110 and source 112 regions. As shown in FIG. 2B, the pattern in the lightly doped drain and the source regions is observed by TEM with an amplifying multiple of 97000. The lightly doped drain 116 and drain 118 regions are ion doped regions, and the silicon substrate 120 is a non-doped region. Since the ion doped region are in the same thickness as the non-doped region, it is difficult to distinguish the lightly doped drain 116 and drain 118 regions from the silicon substrate 120 and to clearly observe the pattern and defects in the lightly doped drain 116 and source 118 regions. Since the lightly doped drain, source/drain regions in the TEM sample prepared by FIB according to existing methods are in the same thickness as the silicon substrate, it is difficult to distinguish the lightly doped drain, source/drain regions from the silicon substrate and to clearly observe the pattern and defects in the lightly doped drain, source/drain regions. An object of the present invention is to provides a method for preparing a TEM sample so as to avoid the problem that it is difficult to distinguish the lightly doped drain, source/drain regions from the silicon substrate and to clearly observe the pattern and defects in the lightly doped drain, source/drain regions, since the lightly doped drain, source/drain regions are in the same thickness as the silicon substrate. To solve above this and other problems, a TEM sample preparation method is provided, which comprises the following steps: providing a sample with two pits and a failure region between the two pits, the failure region comprising a semiconductor device; milling the first surface of the failure region until the cross section of the semiconductor device is exposed; etching the first surface of the failure region; cleaning the sample; milling the second surface of the failure region until the failure region can be passed by an electron beam. The first surface of the failure region is etched with a mixed acid solution comprising nitrate acid, hydrofluoric acid, acetic acid, and copper sulfate, wherein the mass percentage of nitrate acid is 45%-60%, the mass percentage of hydrofluoric acid is 4.5%-5%, the nitrate acid is 10 ml-15 ml, the hydrofluoric acid is 5 ml-10 ml, the acetic acid is 80 ml-100 ml, and the copper sulfate is 0.2 g-0.5 g. The time for etching the first surface of the failure region is 7 s-9 s. Next, the first and second surfaces of the failure region are milled by FIB with a current of 300 pA-500 pA. The sample is cleaned by distilled water or deionized water for 60 s-120 s. The second surface of the failure region is milled until the thickness of the failure region which can be passed by the electron beam is 80 nm-120 nm. Because an etching process by acid is added during preparing the TEM sample by FIB, the invention has following advantages over the existing method. Since the lightly doped drain, source/drain regions are ion doped regions, the acid solution will react with the ions in the lightly doped drain, source/drain regions. Since the silicon substrate is a non-doped region, the acid solution will not react with the silicon substrate. Therefore, the etching speed of the ion doped regions by the acid solution is faster than that of the non-doped region. As a result, the lightly doped drain, source/drain regions will be thinner than the silicon substrate after the etching process with acid. When this sample is observed in TEM, it is easy to distinguish the lightly doped drain, source/drain regions from the silicon substrate and to clearly observe the pattern and defects in the lightly doped drain, source/drain regions. Moreover, it is easy to distinguish the boro-phospho-silicate-glass (BPSG) from the non-doped silicon dioxide in the failure regions. There are various test apparatus in the semiconductor manufacturing industry, among which the TEM is an important tool to observe film patterns, dimensions, and properties of devices. The basic principles of TEM are as follows: thinning the sample to be observed by cutting, milling, and ion thinning; placing the sample into the TEM observation chamber; irradiating the sample with the electron beam accelerated by a high voltage; magnifying the pattern of the sample; and projecting it onto a screen; and then analyzing the sample. Due to the fact that the lightly doped drain, source/drain regions in the TEM sample prepared by FIB according to existing methods are in the same thickness as the silicon substrate, it is difficult to distinguish the lightly doped drain, source/drain regions from the silicon substrate and to clearly observe the pattern and defects in the lightly doped drain, source/drain regions. An etching process by acid is added during the preparation of the TEM sample according to the present invention. Since the lightly doped drain, source/drain regions are ion doped regions, the acid solution will react with the ions in the lightly doped drain, source/drain regions. Since the silicon substrate is a non-doped region, the acid solution will not react with the silicon substrate. Therefore, the etching speed of the ion doped regions by the acid solution is faster than that of the non-doped region. As a result, the lightly doped drain, source/drain regions will be thinner than the silicon substrate after the etching process by acid. When this sample is observed in TEM, it is easy to distinguish the lightly doped drain, source/drain regions from the silicon substrate and to clearly observe the pattern and defects in the lightly doped drain, source/drain regions. In addition, it is easy to distinguish the BPSG from the non-doped silicon dioxide in the failure regions. A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. FIG. 3 is a flow chart of the method for preparing TEM samples according to the present invention. At S201, a sample with two pits and a failure region between two pits is provided, the failure region comprising a semiconductor device. At S202, the first surface of the failure region is milled until the cross section of the semiconductor device is exposed. At S203, the first surface of the failure region is etched. At S204, the sample is cleaned. At S205, the second surface of the failure region is milled until the failure region can be passed by the electron beam. FIGS. 4A-4D are schematic diagrams of the procedure for preparing TEM samples according to the present invention. In the first embodiment of the invention, as shown in FIG. 4A, the failure region 201 is first positioned on the sample 200 using an electrical positioning method, i.e., using an emission microscope (EMMI) or an optical beam induced resistance change (OBIRCH) tool. The sample 200 is placed into the FIB apparatus, and positions and dimensions of the pits are defined by a software in the FIB apparatus. The surface of sample 200 is bombarded by FIB with a current of 500 pA-7000 pA to form the pits 202 and 203 having a larger area than the failure region 201 at both sides of the failure region 201, so that the cross section of the failure region 201 can be observed during the subsequent process for milling the failure region 201, and the failure region 201 can be taken out from the sample 200 easily. The pits 202 and 203 are 10 μm-20 μm in length, 5 μm-10 μm in width, and 2 μm-5 μm in depth. The failure region 201 is 3 μm-12 μm in length and 1 μm-3 μm in width. The dimension along the X-axis is defined as the length, the dimension along the Y-axis is defined as the width, and the dimension along the Z-axis is defined as the depth (the same below). As shown in FIG. 4B, the current for FIB is regulated to 300 pA-500 pA and is used to mill the first surface 204 of the failure region 201 until the cross section of the failure region for the semiconductor device is exposed. In this embodiment, the first surface 204 is milled until the lightly doped drain and source/drain regions are exposed, and the first surface 204 of the failure region 201 is near the pit 202, wherein the first surface 204 is milled to 1 μm-4 μm in depth. Next, the sample 200 is taken out from the FIB apparatus, and the first surface 204 of the failure region 201 which has been milled is etched using a mixed acid solution. Then, the sample 200 is cleaned by distilled water or deionized water. Subsequently, the sample 200 is dried by blowing nitrogen on it. As shown in FIG. 4C, the sample 200 is placed into the FIB apparatus again. Next, the second surface 205 of the failure region 201 is milled by FIB with a current of 300 pA-500 pA until the failure region 201 can be passed by electron beam, and the thickness is from 80 nm to 120 nm. The second surface 205 of the failure region 201 is near the pit 203, wherein the second surface 205 is milled to a depth of 1 μm-4 μm. As shown in FIG. 4D, the sample is then placed into the TEM observation chamber, and the failure region 201 is irradiated by electron beam at a high voltage of 100 KV-500 KV; next, the pattern of failure region 201 in the lightly doped drain and source/drain regions of the semiconductor device is magnified and projected onto the screen for analysis. In this embodiment, the mixed acid solution consists of nitrate acid, hydrofluoric acid, acetic acid and copper sulfate. Wherein, the mass percentage of nitrate acid is 45%-60%, specifically 45%, 50%, 55%, or 60%, preferably 45% in this embodiment. The mass percentage of hydrofluoric acid is 4.5%-5%, specifically 4.5%, 4.6%, 4.7%, 4.8%, 4.9% or 5%, preferably 4.9% in this embodiment. The nitrate acid is 10 ml-15 ml, specifically 10 ml, 11 ml, 12 ml, 13 ml, 14 ml or 15 ml; the hydrofluoric acid is 5 ml-10 ml, specifically 5 ml, 6 ml, 7 ml, 8 ml, 9 ml or 10 ml. The acetic acid is 80 ml-100 ml, specifically 80 ml, 85 ml, 90 ml, 95 ml or 100 ml. The copper sulfate is 0.2 g-0.5 g, specifically 0.2 g, 0.3 g, 0.4 g or 0.5 g. The time for etching the sample by the mixed acid solution is 7 s-9 s, specifically 7 s, 8 s, or 9 s. In this embodiment, the surface of the sample 200 is bombarded by FIB with a current of 500 pA-700 pA to form pits 202 and 203 having a larger area than the failure region 201 at both sides of the failure region 201. Specifically, the current for FIB is 500 pA, 5500 pA, 6000 pA, 6500 pA or 7000 pA, preferably 7000 pA in this embodiment. The pits 202 and 203 are 15 μm in length, 8 μm in width and 3 μm in depth; in addition to this embodiment, the pits 202 and 203 can be 10 μm-20 μm in length, specifically 10 μm, 12 μm, 15 μm, 18 μm or 20 μm, preferably 15 μm in this embodiment. The pits 202 and 203 can be 5 μm-10 μm in width, specifically 5 μm, 7 μm, 8 μm or 10 μm, preferably 8 μm in this embodiment. The pits 202 and 203 can be 2 μm-5 μm in depth, specifically 2 μm, 3 μm, 4 μm or 5 μm, preferably 6 μm in this embodiment. The failure region 201 is 3 μm-12 μm in length, specifically 3 μm, 5 μm, 7 μm, 9 μm, 10 μm or 12 μm; and 1 μm-3 μm in width, specifically 1 μm, 2 μm or 3 μm, preferably 1 μm in this embodiment. In this embodiment, the first surface 204 and the second surface 205 of the failure region 201 are bombarded by FIB with a current of 300 pA-500 pA, specifically 300 pA, 350 pA, 400 pA, 450 pA or 500 pA, preferably 300 pA in this embodiment. The first surface 204 and the second surface 205 are milled to a depth of 1 μm-4 μm, specifically 1 μm, 2 μm, 3 μm or 4 μm, preferably 4 μm in this embodiment. The sample 200 is cleaned with distilled water or deionized water for 60 s-120 s, specifically 60 s, 70 s, 80 s, 90 s, 100 s, 110 s or 120 s, preferably 60 s in this embodiment. The sample is dried by blowing nitrogen in this embodiment, or, it can be dried naturally also. In this embodiment, the first surface 204 of the failure region 201 is milled till the cross section of the failure region for the semiconductor device is exposed. The first surface 204 of the failure region 201 is etched. Then the sample 200 is cleaned and dried by blowing. Next, the second surface 205 of the failure region 201 is milled, till the thickness of the failure region 201 which can be passed by the electron beam is 80 nm-120 nm, specifically 80 nm, 90 nm, 100 nm, 110 nm or 120 nm. In addition to this embodiment, the second surface 205 of the failure region 201 can be milled at first, till the cross section of the failure region for the semiconductor device is exposed; then, the second surface 205 of the failure region 201 is etched, and the sample 200 is cleaned and dried by blowing; next, the first surface 204 of the failure region 201 is milled, till the thickness of the failure region 201 which can be passed by the electron beam is 80 nm-120 nm. Next, the second embodiment of the method for preparing TEM samples according to the invention is described referring to FIG. 4A to 4D. As shown in FIG. 4A, firstly, the failure region 201 is positioned on the sample 200 by an electrical positioning method, i.e., by means of EMMI or OBIRCH tool; next, the sample 200 is placed into the FIB apparatus, and the positions and dimensions of the pits are defined by a software in the FIB apparatus; next, the surface of the sample 200 is bombarded by FIB with a current of 5000 pA-7000 pA to form pits 202 and 203 having a larger area than the failure region 201 at both sides of the failure region 201, so that the cross section of the failure region 201 can be observed during the subsequent process for milling the failure region 201 and the failure region 201 can be taken out from the sample 200 easily; the pits 202 and 203 are 15 μm in length, 8 μm in width, and 6 μm in depth; the failure region 201 is 1μm. As shown in FIG. 4B, the current for FIB is regulated to 300 pA-500 pA and is used to mill the first surface 204 of the failure region 201, till the cross section of the failure region for the semiconductor device is exposed. In this embodiment, the first surface 204 is milled till the lightly doped drain and source/drain regions are exposed, and the first surface 204 of the failure region 201 is near the pit 202; wherein, the first surface 204 is milled to a depth of 4 μm; next, the sample 200 is taken out from the FIB apparatus, and the sample which has been milled is etched by a mixed acid solution including nitrate acid, hydrofluoric acid and acetic acid for 7 s; wherein, the nitrate acid is 20 ml and has a mass percentage of 65%; the hydrofluoric acid is 1 ml and has a mass percentage of 49%; and the acetic acid is 100 ml; next, the sample 200 is cleaned with distilled water or deionized water for 60 s-120 s; then, the sample 200 is dried by blowing nitrogen. As shown in FIG. 4C, the sample 200 is placed into the FIB apparatus again; next, the second surface 205 of the failure region 201 is milled by FIB with a current of 300 pA-500 pA, till the thickness of the failure region 201 which can be passed by the electron beam is 80 nm-120 nm; the second surface 205 of the failure region 201 is near the pit 203; wherein, the second surface 205 is milled to 4 μm in depth. As shown in FIG. 4D, the sample is then placed into the TEM observation chamber, and the failure region 201 is irradiated by the electron beam at a high voltage of 100 KV-500 KV. Next, the pattern of failure region 201 in the lightly doped drain and source/drain regions for the semiconductor device is magnified and projected onto the screen for analysis. In this embodiment, the surface of the sample 200 is bombarded by FIB with a current of 5000 pA-7000 pA to form pits 202 and 203 having a larger area than the failure region 201 at both sides of the failure region 201; specifically, the current for FIB is 5000 pA, 5500 pA, 6000 pA, 6500 pA or 7000 pA, preferably 7000 pA in this embodiment. The pits 202 and 203 are 15 μm in length, 8 μm in width and 6 μm in depth. In addition to this embodiment, the pits 202 and 203 can be 10 μm-20 μm in length, specifically 10 μm, 12 μm, 15 μm, 18 μm or 20 μm; the pits 202 and 203 can be 5 μm-10 μm in width, specifically 5 μm, 7 μm, 8 μm or 10 μm; and the pits 202 and 203 can be 2 μm-5 μm in depth, specifically 2 μm, 3 μm, 4 μm or 5 μm. In this embodiment, the first surface 204 and the second surface 205 of the failure region 201 are milled by FIB with a current of 300 pA-500 pA, specifically 300 pA, 350 pA, 400 pA, 450 pA or 500 pA, preferably 300 pA in this embodiment. The sample 200 is cleaned with distilled water or deionized water for 60 s-120 s, specifically 60 s, 70 s, 80 s, 90 s, 100 s, 110 a or 120 s, preferably 60 s in this embodiment. The sample is dried by blowing nitrogen onto it in this embodiment, or, it can also be dried naturally. In this embodiment, the first surface 204 of the failure region 201 is milled until the cross section of the failure region for the semiconductor device is exposed. Then, the first surface 204 of the failure region 201 is etched, and then the sample 200 is cleaned and dried by blowing. Next, the second surface 205 of the failure region 201 is milled until the thickness of the failure region 201 which can be passed by the electron beam is 80 nm-120 nm, specifically 80 nm, 90 nm, 100 nm, 110 nm or 120 nm. In addition to this embodiment, the second surface 205 of the failure region 201 can be milled firstly until the cross section of the failure region for the semiconductor device is exposed. Then, the second surface 205 of the failure region 201 is etched, and the sample 200 is cleaned and dried by blowing. Next, the first surface 204 of the failure region 201 is milled until the thickness of the failure region 201 which can be passed by the electron beam is 80 nm-120 nm. FIGS. 5A-5C are schematic diagrams of TEM samples prepared according to the invention. As shown in FIG. 5A, the TEM samples shown in FIGS. 4A-4D are observed by TEM with an amplifying multiple of 97000. Since the lightly doped drain 210 and source 211 regions are ion doped regions, the acid solution will react with the ions in the lightly doped drain 210 and source 211 regions. Since the silicon substrate 212 is a non-doped region, the acid solution will not react with the silicon substrate 212. Therefore, the etching speed of the lightly doped drain 210 and source 211 regions by the acid solution is higher than that of the silicon substrate 212 region. As a result, the lightly doped drain 210 and source 211 regions are thinner than the silicon substrate 212 region after the etching process, and it is easy to distinguish the lightly doped drain 210 and source 211 regions from the silicon substrate 212 region and to clearly observe the pattern and defects in the lightly doped drain 210 and source 211 regions. As shown in FIG. 5B, the TEM samples shown in FIGS. 4A-4D are observed by TEM with an amplifying multiple of 97000. Since the lightly doped drain 213 and drain 214 regions are ion doped regions, the acid solution will react with the ions in the lightly doped drain 213 and drain 214 regions. Since the silicon substrate 215 is a non-doped region, the acid solution will not react with the silicon substrate 215. Therefore, the etching speed of the lightly doped drain 213 and drain 214 regions by the acid solution is higher than that of the silicon substrate 215 region. As a result, the lightly doped drain 213 and drain 214 regions are thinner than the silicon substrate 215 region after the etching process, and thus it is easy to distinguish the lightly doped drain 213 and drain 214 regions from the silicon substrate 215 region and to clearly observe the pattern and defects in the lightly doped drain 213 and drain 214 regions. As shown in FIG. 5C, the TEM samples shown in FIG. 4A-4D are observed by TEM with an amplifying multiple of 97000. Since the BPSG region is an ion doped region, the acid solution will react with boron and phosphor in the BPSG region. Since the non-doped silicon dioxide 217 is a non-doped region, the acid solution will not react with the non-doped silicon dioxide 217. Therefore, the etching speed of BPSG region by the acid solution is higher than that of the non-doped silicon dioxide 217 region. As a result, the BPSG 216 region is thinner than the non-doped silicon dioxide 217 region after the etching process, and thus it is easy to distinguish the BPSG 216 region from the non-doped silicon dioxide 217 region. While the preferred embodiments of the present invention have been described as above, the scope of the present invention shall not be limited thereto, and those skilled in the art can make various variations and modifications to the embodiments without departing from the scope of the present invention. All these variations and modifications would fall within the scope of the present invention which shall be as defined in the claims thereof. |
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054917310 | abstract | An automated method for maintaining pressure within a nuclear power plant primary loop during either startup or shutdown, the method comprises the steps of partially filling a portion of a pressurizer vessel, in fluid communication with the primary loop, with a liquid for maintaining pressure in the primary loop; circulating a primary coolant through the primary loop; automatically injecting an inert gas by a first automated device, operatively connected to the pressurizer, into the pressurizer vessel when the pressure in the pressurizer vessel is less than a first predetermined pressure; and automatically venting the gas by a second automated device, operatively connected to the pressurizer, from the pressurizer vessel when the pressure in the pressurizer vessel is greater than a second predetermined pressure. |
description | The present invention relates to a method and a system to retrieve absorption, DPC and dark field signals obtained by a grating interferometer. Grating interferometry constitutes a very promising technique for commercial X-ray phase-contrast applications, since it works with traditional X-ray tubes, is mechanically robust and has modest requirements for mono-chromaticity and spatial coherence. In the last few years, several exciting applications of this technique have been reported, ranging from material inspection to medical imaging. To carry out the transition of grating interferometry from the laboratory to the commercial setting, it has to be tailored to cover a large field of view (FOV) and allow reasonable exposure times. To fulfill these requirements, a scanning setup would be an excellent choice, since it requires line instead of 2D detectors and would avoid the fabrication of large-area gratings, which might be laborious and pricey. On the other hand, in order to retrieve different contrast signals, conventional grating interferometry requires a phase-stepping procedure, in which one of the gratings is translated stepwise (in sub-micron scale) and an image is acquired for each step. This procedure is time-consuming in general and demands high system stability and accuracy, so it constitutes a major problem for the implementation of grating interferometry in a commercial setting. A scanning-mode method able to “hard-code” the phase-stepping procedure into a one-dimension scan [1,] can fundamentally solve the problem. In this regard, Kottler et al [2] introduced a scanning-mode grating interferometry setup. They propose a method in which a Moiré fringe parallel to the grating lines is generated by slightly changing the theoretical inter-grating distance. In this arrangement, equidistantly distributed lines of the detector correspond to different relative positions of the phase and absorption gratings, which can be regarded as phase-steps. Therefore, by translating the sample in a direction perpendicular to the fringe orientation, a phase-stepping curve can be retrieved and Fourier-Component Analysis (FCA) can be used to reconstruct the signals. Another possibility to solve this issue is to use a staggered grating, so that the grating is located at a different lateral position for each line detector, and a phase stepping curve can be retrieved by scanning the sample in a direction perpendicular to the grating lines. However, this approach implies the fabrication of gratings with a novel design which will be hard to align, and kept as such, with the line detectors. As mentioned above, to transfer the X-ray grating interferometry technology to a commercial setting, it is necessary to make it suitable to image large field-of-views. To achieve this goal while using the current grating interferometry implementation, large-area gratings would be needed, but they are difficult and pricey to fabricate. Therefore, it would be ideal to avoid the fabrication of this kind of gratings. Managing to integrate the grating interferometer technology into a scanning setup certainly avoids this issue. However, its integration involves the development of a new signal retrieval method, because the conventional retrieval method would be inefficient in this setup. It is therefore the objective of the present invention to provide a system and a method for retrieving absorption, DPC and dark field signals obtained by a grating interferometer. This objective is achieved according to the present invention by a method and a system that use a tilted-grating-based scanning method for grating interferometry as given in the main method claim and the main system claim. The general idea is to generate a Moire fringe perpendicular to the grating lines by tilting one of the gratings, so that each line detector of the detector ends up recording a different phase step as the sample is translated during the scan. Preferred embodiments of the present invention are listed in the dependent claims. A standard grating interferometer is shown in FIG. 1, comprising a source grating G0, a phase grating G1 and an absorption grating G2. The use of source grating G0 is optional, depending on the spatial coherence properties of the X-ray source. During the scanning of a sample, the illumination generated by the X-ray source is recorded by a detector disposed downstream of the absorption grating G2. The scanning approach is achieved by moving one of the gratings stepwise with respect to the recorded images along one period of the analyzer grating G1 in a direction perpendicular to the line of the phase grating G1. The general idea behind the tilted-grating design is illustrated in FIG. 2. FIG. 2(a) schematically shows a sketch of a staggered grating G2, where the grating at a different lateral position covers each detector line. In FIG. 2(b) the same effect is achieved, when the analyzer grating G2 is tilted according to the present invention so that each line detector records a different phase step (red dots on the phase-stepping curve shown on the right). If a staggered grating is used (see FIG. 2a) [3], such that each line detector is covered by the grating at a different position in x direction, the phase-stepping approach is mimicked by scanning the sample along y direction, without the need of moving the analyzer grating G2, and will end up having each line detector record a different phase step for each slice of the sample, as long as the grating lines are subsequently shifted by a distance δx, defined as: δ x = m p 2 n where n is the number of line detectors, so that the whole staggered grating is covering an integer number m of periods p2 of the analyzer grating G2. Since the fabrication of this staggered grating and its successive alignment to the corresponding line detectors might become very challenging, an easier way according to the present invention to achieve the same effect is to tilt of the analyzer grating G2, as shown in FIG. 2b. Assuming the present line detectors are separated by a distance D, the tilting angle θ can be calculated as: θ = arc tan ( δ x D ) To compensate for the beam divergence, the sample-translation step s must be adjusted to: s = D L L + d where L is the source-to-G1 distance and d represents the inter-grating distance. Afterwards, the absorption, DPC and dark-field signals can be retrieved by standard FCA. A reference image (i.e. no sample in the beam) has to be acquired as well in order to subtract the background phase distribution, like in the phase-stepping approach. Recapitulating, the procedure is started by acquiring a reference image and retrieving the background phase-stepping curve. Afterwards, a tilting angle is calculated based on the hardware (i.e. the number of line detectors disposed in the detector and the separation between the line detectors) and the number of periods p2 to be covered. Subsequently, the analyzer grating G2 is tilted and the sample is moved along y direction (see FIG. 2 right side) by successive steps s until the signal corresponding to each slice has been recorded by the number of line detectors used for the calculations, so that a sample phase-stepping curve for each slice can be retrieved. Rearranging the acquired data, the absorption, DPC and dark-field signals can be reconstructed by performing FCA in two dimensions. An example of the Moiré fringe generated with this tilted grating method is shown in FIG. 3 and the corresponding reconstructed absorption, DPC and dark-field images acquired with the tilted-grating method are displayed in FIG. 4. Grating-based X-ray imaging setups like the one shown in FIG. 1 can generate three different signals: the conventional absorption contrast (AC) signal, the differential phase contrast (DPC) signal caused by refraction due to phase shifts, and the small-angle scattering contrast (SC) signal (also named dark-field signal) caused by scattering from inhomogeneities in the sample. Interferometer grating setups with two gratings (G1 and G2) or three gratings (G0, G1, and G2) can be used to record the deflection of the X-rays. In the case of a two-grating setup, the source needs to fulfill certain requirements regarding its spatial coherence. The source grating G0 is required, when the source size is bigger than p2*L/d, where p2 is the period of G2, L is the distance between the source and G1, and d is the distance between G1 and G2. In a three-grating setup no spatial coherence is required. Therefore, the three-grating setup is suited for use with incoherent X-ray sources, in particular with standard X-ray tubes. To separate the conventional attenuation contrast (AC) from the DPC and SC contrast, a phase-stepping approach is carried out. One of the gratings is displaced transversely to the incident beam whilst acquiring multiple images. The intensity signal at each pixel in the detector plane oscillates as a function of the displacement. The average value of the oscillation represents the AC. The phase of the oscillation can be directly linked to the wave-front phase profile and thus to the DPC signal. The amplitude of the oscillation depends on the scattering of X-rays in the object and thus yields the SC signal. For the (two or three) gratings, several variations have been proposed and applied. The source grating G0 (if required) is the one closest to the X-ray source. It usually consists of a transmission grating of absorbing lines with the period p0. It can be replaced by a source that emits radiation only from lines with the same period. The phase grating G1 is placed further downstream of the X-ray source. It consists of lines with a period p1. The analyzer grating G2 is the one most downstream of the setup. It usually consists of a transmission grating of absorbing lines with the period p2. It can be replaced by a detector system that has a grating-like sensitivity with the same period. Two regimes of setups can be distinguished: In the so called “near-field regime” and the “Talbot regime”. In the “near-field regime”, the grating period p, grating distances d and the x-ray wavelength λ are chosen such that diffraction effects are negligible. In this case, all gratings need to consist of absorbing lines. In the “Talbot regime”, diffraction from the grating structures is significant. Here, the phase grating G1 should consist of grating lines that are either absorbing or, preferentially, phase shifting. Several amounts of phase shift are possible, preferentially π/2 or multiples thereof. The grating periods must be matched to the relative distances between the gratings. In the case of setups in the “Talbot regime”, the Talbot effect needs to be taken into account to obtain good contrast. The formulae for the grating periods and distances are described in [4]. It has to be noted that a sharp distinction between the two regimes is not easily given, as the exact criterion depends on the duty cycle of the grating structure, and whether the gratings are absorbing or phase shifting. E.g., for a grating with absorbing lines and a duty cycle of 0.5, the condition for the “near field regime” is d≥p2/2λ. The sample is mostly placed between the source grating G0 and the phase grating G1 (or upstream of the phase grating G1 in the case of a two-grating set-up), however it can be advantageous to place it between the phase grating G1 and the analyzer grating G2 [5]. The presented invention is relevant in all of the aforementioned cases, i.e. in the two- and three-gratings case, in the case of the “near-field regime” and the “Talbot regime”, and for the sample placed upstream or downstream of G1. Intensity curves (with and without sample) are usually obtained with “phase stepping” methods or alternative techniques. Defining for each pixel on the detector the mean, phase and visibility of the intensity curve with sample as Is,Φs,Vs, and without sample as Ib,Φb,Vb, yields: AC = - log ( I s I b ) DPC = Φ s - Φ b SC = - log ( V s V b ) . For both the AC signal and SC signal, the valid data range is [0,+∞], while for the DPC it is [−π,+π]. Images obtained by plotting such signals are all perfectly registered. A similar way to generate these multiple information signals can be found in diffraction enhanced imaging where the equivalent of the intensity curve is named the rocking curve. [1] E. Roessl, H. Daerr, T. Koehler, G. Martens and U. van Stevendaal, “Slit-scanning differential phase-contrast mammography: First experimental results,” Proc. SPIE 9033, 90330C (2014). [2] C. Kottler, F. Pfeiffer, O. Bunk, C. Grünzweig, C. David, “Grating interferometer based scanning setup for hard X-ray phase contrast imaging,” Rev. Sci. Instrum. 78, 043710 (2007). [3] C. David and F. Pfeiffer, “X-ray interferometer for phase contrast imaging,” Patent WO 2008/006470 A1 (17, Jan. 2008). [4] T. Weitkamp, C. David, C. Kottler et al., “Tomography with grating interferometers at low-brilliance sources”, 6318, 6318S (2006). [5] C. David, Optimierte Anordnung von Gittern für die Phasenkontrastbildgebung im Röntgenbereich, Europäische Patentanmeldung EP 2 168 488 A1. |
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