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	summary
	description	For decades, radiation shielding has been almost synonymous with bulky materials, such as concrete and/or lead, depending on the application. Concrete, often formulated with Boron, is effective as an attenuator of neutron radiation. In many neutron generating applications, including isotope generation for nuclear medical uses, several feet of borated concrete is required to attenuate neutron radiation to safe levels. Lead, although toxic, is an effective attenuator of high energy photonic radiation, such as X-rays and γ-rays. Because of the bulk of concrete and lead as well as the mass of those materials necessary for effective shielding, most radiation-generating activities currently take place at facilities having substantial physical space and structure. Certain trends within nuclear science, for example, Positron Emission Tomography (PET), are leading towards the need to locate wide-spectrum radiation producing sources in facilities not originally designed to accommodate the weight and space requirements of conventional shielding. For example, radioisotopes used for PET often have a relatively short half-life necessitating that they be produced close to a patient. Also, the accelerator production of radioisotopes typically used for PET generates wide spectrum radiation including both photonic radiation and neutron radiation. Accordingly, there is a desire and need to practice wide-spectrum nuclear techniques in small-scale facilities where it is often not cost-effective and/or practical to create the physical structure necessary to support concrete and/or lead shielding. Accordingly, there is a need for radiation shielding that is compact and light relative to conventional concrete or lead shielding. There is also a need for improved radiation shielding that shields wide spectrum radiation including photonic radiation and neutron radiation. According to one aspect of the present disclosure, embodiments of a radiation shield are disclosed. The radiation shield may comprise a first layer, a second layer, and a third layer. The first layer may include a neutron moderating material. The second layer may be adjacent the first layer and may include a neutron absorbing material. The third layer may be adjacent the second layer, and may include a photonic radiation attenuating material. At least one of the first layer and the second layer may be removable from the radiation shield. According to another aspect of the present disclosure, embodiments of a device for attenuating radiation are disclosed. The device for attenuating radiation may comprise at least a first radiation shield panel. The first radiation shield panel may comprise a first layer including a neutron moderating material, and a second layer adjacent the first layer. The second layer may include a neutron absorbing material. The first radiation shield panel may also comprise a third layer adjacent the second layer, wherein the third layer comprises a photonic radiation attenuating material. At least one of the first layer and the second layer may be removable from the first radiation shield panel. According to another aspect of the present disclosure, embodiments of an apparatus are disclosed comprising a radiation-emitting source and a radiation shield positioned adjacent the radiation-emitting source. The radiation shield may comprise a first layer including a neutron moderating material and a second layer adjacent the first layer. The second layer may include a neutron absorbing material. The radiation shield may also comprise a third layer adjacent the second layer. The third layer may include a photonic radiation attenuating material. At least one of the first layer and the second layer may be removable from the radiation shield panel. According to yet another aspect of the present disclosure, methods of shielding an object from a radiation source are disclosed. The methods may comprise the step of placing a radiation shield intermediate the object and the radiation source. The radiation shield may comprise a first layer including a neutron absorbing material, and a second layer including a photonic radiation attenuating material. The methods may also comprise the step of monitoring the neutron transmissivity of the radiation shield and replacing at least a portion of the first layer when the neutron transmissivity of the radiation shield exceeds a predetermined value. According to another aspect of the present disclosure, embodiments of a radiation shield are disclosed. The radiation shield may comprise a first layer including a neutron moderating material and a neutron absorbing material. The radiation shield may also comprise a second layer adjacent the first layer. The second layer may include a photonic radiation attenuating material. The first layer may be removable from the radiation shield. The term “neutron moderating material” refers to any material tending to reduce the energy of incident neutron radiation toward thermal levels. Non-limiting examples of neutron moderating materials include water and hydrogen-rich polymers. The term “neutron absorbing material” refers to any material with a neutron capture cross section making the material suitable for use as a shield for incident neutron radiation. Non-limiting examples of neutron absorbing materials include boron, cadmium, gadolinium and or compounds incorporating boron, cadmium, and gadolinium. The term “photonic radiation attenuating material” refers to any material tending to reduce the intensity of incident photonic radiation. Non-limiting examples of photonic radiation attenuating materials include lead, tungsten and depleted uranium. The term “adjacent,” when used in relation to two or more objects, refers to objects that are in close physical proximity. Adjacent objects may or may not physically touch one another, and may have air, other materials, or objects positioned intermediate them. The term “burn out” refers to a state of a neutron absorbing material, or a portion thereof, resulting from neutron capture, wherein the neutron transmissivity of the material or material portion exceeds a predetermined value. The term “hydrogen-rich polymer” refers to a polymer including hydrogen atoms in a concentration greater than or about equal to the hydrogen concentration of water (˜8×1022 atoms H per cm3). The term “tungsten heavy alloy” refers to an alloy including at least about 50% tungsten by weight and preferably between 88% and 97% tungsten by weight. Certain embodiments of tungsten heavy alloys comprise other elements such as, for example, nickel, iron, copper, cobalt, and/or transition metals. FIG. 1 illustrates a configuration of a radiation shield 100 according to various non-limiting embodiments of the present invention. A radiation source 110 may emit radiation 108, for example, in the direction of the radiation shield 100. The radiation source 110 may be any device, material, or reaction generating radiation. For example, the radiation source 110 may be a cyclotron target or other apparatus for generating radioactive isotopes such as those that may be used for nuclear medical applications. The radiation 108 may include any kind of radiation including, for example, γ-rays, X-rays, α-radiation, β-radiation, and neutron radiation. The radiation shield 100 may include a series of functional layers. A neutron moderating layer 102 may moderate the energy of incoming neutrons, e.g., neutrons emitted by the radiation source 110, to thermal levels, for example, for more efficient capture. A neutron absorbing layer 104 may capture the neutrons. A photonic radiation attenuating layer 106 may attenuate photonic radiation 108 emitted from the radiation source 110 as well as, for example, γ-rays emitted by layers 102, 104. It will be appreciated that materials included in one or more of the neutron moderating layer 102, the neutron absorbing layer 104, and/or the photonic radiation attenuating layer 106 may also attenuate α-radiation and/or β-radiation. It will also be appreciated that layers of additional material, such as, for example, polystyrene or a metallic alloy, may be included between the layers 102, 104, 106. The additional material may, for example, aid in heat dissipation, modify the mechanical properties of the shield 100, and/or facilitate removal of a layer or layers from the shield 100. The layers 102, 104, 106 of the radiation shield 100 may be physically joined together according to any suitable means. In various embodiments, the neutron moderating layer 102 and/or the neutron absorbing layer 104 may be joined to the other layer/layers of the radiation shield 100 in a manner that allows layers 102, 104 to be easily replaced on burn out, or for other reasons. For example, the layers 102, 104, 106 may be joined directly to one another with a light adhesive. When one or more of the layers 102, 104 burn out, then they may be pulled from the layer 106, breaking the adhesive bond. Replacement layers equivalent to layers 102, 104 may be installed by applying additional light adhesive. In other various embodiments, the layers 102, 104, 106 may be slideably installed into a frame structure. The layers 102, 104, 106 may be secured within the frame structure by a latch or other suitable mechanism. On burn out, layers 102 and/or 104 may be slid out of the frame structure and replacement layers may be installed. In yet other embodiments, the layers 102, 104, 106 may be secured to one another by suitable fasteners including, for example, screws and/or bolts. The neutron moderating layer 102, neutron absorbing layer 104, and photonic radiation attenuating layer 106 may include any materials capable of performing the desired function. For example, neutron moderating layer 102 of radiation shield 100 may include any suitable neutron moderating material. In various non-limiting embodiments, the neutron moderating layer 102 may include polyethylene (PE), or any suitable hydrogen-rich polymer or material. Neutrons encountering an embodiment of the neutron moderating layer 102 including PE may collide elastically with one or more hydrogen nuclei present in the PE, reducing the energy of the colliding neutrons to thermal levels. The use of low atomic number elements in layer 102 may also cause the attenuation of β radiation with only minimal Bremsstrahlung X-ray generation. In various embodiments, the neutron moderating properties of neutron moderating layer 102 may degrade over time, for example, due to protium conversion. Thermal degradation of the neutron moderating layer 102 may also occur in cases where high radiation flux deposits a large amount of energy within a relatively small volume of a polymer possessing only limited thermal conductivity. Thus, the PE may suffer reduced mechanical integrity due to both heat related damage and radiation-induced depolymerization. In addition, the performance of embodiments of neutron moderating layer 102 including, for example, PE as a neutron moderator may degrade over time due to protium conversion. In some collisions between a neutron and a hydrogen nucleus within the PE, the hydrogen nucleus may capture the neutron, converting the hydrogen nucleus from protium to deuterium and emitting a γ photon with energy of 2.22 MeV. This may cause the functionality of the neutron moderating layer 102 to further degrade over time as it will be appreciated that the neutron moderating properties of deuterium are inferior to those of protium. Neutron absorbing layer 104 may be made from any suitable material with a high neutron capture cross-section. For example, the neutron absorbing layer 104 may include boron, cadmium, gadolinium, and/or compounds thereof. In various embodiments, the neutron absorbing layer 104 may be made from or include gadolinium or a gadolinium compound, as gadolinium has the highest known neutron cross section of any element. The physical form of the neutron absorbing layer 104 may vary. In certain embodiments, the neutron absorbing layer 104 may include a composite comprising a neutron absorbing material in particulate form, such as a powdered form, disbursed as a discontinuous phase in a polymer binder. The polymeric binder may be in continuous phase, though some embodiments may include a polymeric binder in discontinuous phase. Non-limiting examples of suitable polymeric binders may include polyolefins, polyamides, polyesters, silicones, thermoplastic elastomers, and epoxies as well as blends thereof. The neutron absorbing material may include any suitable material including, for example, gadolinium or a compound of gadolinium, such as, for example, gadolinium oxide, as discussed above. In other various embodiments, the neutron absorbing layer 104 may be in metallic form. In metallic form, neutron absorbing materials may be alloyed with different metals. For example, gadolinium may be alloyed with aluminum, copper, etc. The metallic form of the neutron absorbing layer 104 may have superior thermal characteristics which may help dissipate heat generated in the layer 104 as well as the neutron moderating layer 102. Also, the physical integrity of a metallic form may facilitate fastening the layer 104 to the other layers 102, 106 of the radiation shield 100, for example, by including holes for fasteners, including threaded holes for threaded fasteners such as, for example, screws. Gadolinium, and other neutron absorbing materials, may lose their effectiveness as neutron absorbers, e.g., burn out, over time. Natural gadolinium has a very high neutron capture cross section on average (˜48,700 barns). Much of the average value, however, is due to the exceptionally high neutron capture cross section of a few isotopes. This is demonstrated by Table I, which shows the neutron capture cross sections and crustal abundance of various isotopes of gadolinium. TABLE INeutron Cross Sections of Gadolinium (Gd) IsotopesNeutron Capture CrossIsotopeCrustal Abundance (%)Section (barns)64Gd1520.270064Gd1542.26064Gd15514.861,00064Gd15620.5264Gd15715.6254,00064Gd15824.8264Gd16021.92 As gadolinium atoms that may be present in neutron absorbing layer 104 capture neutrons, they may change from one isotope to another of increasing atomic weight, eventually settling into an isotope with a relatively low neutron capture cross section. As this happens, the functionality of the neutron absorbing layer 104 may slowly degrade. This may eventually lead to burn out when the neutron absorbing properties of these layers drop below the predetermined acceptable level, prompting replacement. The photonic radiation attenuating layer 106 may attenuate radiation components included in the radiation 108, but not completely attenuated by the other layers in the radiation shield. For example, in various embodiments, the radiation 108 may include photonic radiation, such as γ-rays and X-rays that are not effectively attenuated by the other layers of the shield 100. Also, it will be appreciated that neutron capture events in either the neutron moderating layer 102 or the neutron absorbing layer 104 may create a γ-ray with energy of 2.22 MeV. The photonic radiation attenuating layer 106 may be made from any material that attenuates photonic radiation, such as, for example, γ-rays and X-rays. Such materials include, for example, lead (Pb), an alloy or compound of Pb, or preferably a Pb substitute material. For example, in various embodiments, the photonic radiation attenuating layer 106 may include tungsten (W), depleted uranium, or any other Pb substitute material, in pure, alloy, and/or compound form. The photonic radiation attenuating layer 106 may take various physical forms. For example, in various embodiments, the photonic radiation attenuating layer 106 may comprise a polymeric binder and a discontinuous phase of dispersed particulate filler material, for example, tungsten or a compound or alloy of tungsten in particulate form. In one non-limiting embodiment, the dispersed particulate filler material may be powdered ferrotungsten. The polymeric binder may be present as either a continuous or discontinuous phase, and may, for example, include a polyolefin, a polyamide, a polyester, a silicone, a thermoplastic elastomer, and/or an epoxy, as well as blends thereof. In other various embodiments, the photonic radiation attenuating layer 106 may include metallic material, for example, a sheet of sintered or rolled tungsten or tungsten alloy, such as a tungsten heavy alloy. For example, an embodiment of a photonic radiation attenuating layer 106 may include one or more tungsten heavy alloys. Providing layer 106 in a substantially or entirely metallic form may provide advantageous heat dissipation, and may also provide physical integrity, facilitating the fastening together of the various layers in the radiation shield. For example, a metallic layer 106 may include threaded holes for fasteners such as screws and bolts. In various embodiments, the functionality of two or more of the layers of the radiation shield 100 may be combined in a single layer. For example, FIG. 2 shows a radiation shield 200 including mixed-function layer 212 and photonic radiation attenuating layer 206. The mixed-function layer 212 may perform the functions of both the neutron moderating layer 102 and the neutron absorbing layer 104 of the radiation shield 100. The photonic radiation attenuating layer 206 of radiation shield 200 may perform a function equivalent to that of photonic radiation attenuating layer 106 of the radiation shield 100. In one non-limiting embodiment, mixed-function layer 212 of shield 200 may include a composite of a neutron absorbing material disbursed in a polymeric binder. The polymeric binder may include a hydrogen rich polymer such as, for example, PE, which may give the layer 212 neutron moderating properties as discussed above. Accordingly, layer 212 may perform both neutron moderating and neutron absorbing functions. It will be appreciated that neutron moderating and absorbing materials that may be present in mixed-function layer 212 may also degrade and/or burn out as discussed above with respect to neutron moderating layer 102 and neutron absorbing layer 104, ultimately necessitating replacement of the mixed-function layer 212. In other non-limiting embodiments, two or more of the neutron moderating layer 102, neutron absorbing layer 104, and the photonic radiation attenuating layer 104 may be bonded to one another in a permanent manner. For example, FIG. 3 shows a non-limiting embodiment of a radiation shield 300 including neutron moderating layer 302 bonded to neutron absorbing layer 304. On burn out, the layers 302, 304 may be replaced together without the need to separate them. In various non-limiting embodiments, the layers 302 and 304, may be simultaneously extruded in a low temperature, cold forming process and/or in a high temperature extruding process. This may facilitate a bond between polymers that may be included in one or more of layers 302, 304. In other non-limiting embodiments, the layers 302, 304 may be welded and/or joined using an adhesive. Other techniques of joining layers 302, 304 will be readily apparent to those having ordinary skill in the art. The radiation shields 100, 200, 300 may be constructed as a single multi-layered monolithic unit, or as a plurality of joined multi-layered panels. The panels may be of any suitable shape, for example, squares or rectangles. In various non-limiting embodiments, panels may have curvature, for example, allowing the assembly of cylindrical, spherical or other geometric arrays of panels. Multiple multi-layered panels may be joined together to form any of the radiation shields 100, 200, 300 into any desired dimension or shape. For example, several multi-layered panels of any of the radiation shields 100, 200, 300 may be used to completely shield a room, for example, a room containing a radiation source, such as the radiation source 110. Panels of any of the radiation shields 100, 200, 300 may be joined in a manner intended to avoid straight line radiation leakage. FIG. 4 shows an interface 410 between two panels 402, 404 of exemplary radiation shield 400. The panel 402 and the panel 404 may include geometrically interlocking features 406. The interlocking features 406, unlike a typical butt joint, do not form a straight seam from one side of the radiation shield 410 to the other. A straight seam may allow elements of radiation to pass through the radiation shield 100 unattenuated. FIG. 5 shows a process flow 500 for using radiation shield 100 according to various embodiments, though the steps of the process flow 500 may be performed using any of the radiation shields 100, 200, 300, 400 above. At step 502, the radiation shield 100 may be installed. For example, the radiation shield 100 may be installed to completely shield a room or other area containing radiation source 110. At step 504, the neutron transmissivity of the radiation shield 100 may be monitored. The neutron transmissivity of the radiation shield 100 may be compared to a predetermined threshold at step 506. If the neutron transmissivity of the shield 100 is not above the predetermined threshold, then the monitoring may continue at step 504. If the neutron transmissivity of the shield 100 is above the predetermined threshold, then one or more of the neutron moderating layer 102 and the neutron absorbing layer 104 may be replaced at step 508. The same process flow may be applied to the use of radiation shields 200, 300, and 400 although with regard to shield 200, for example, replacement step 508 would involve replacement of combined neutron moderating/absorbing layer 212. It will be appreciated that the radiation shields 100, 200, 300 described herein may be used in any application where radiation shielding is required including as non-limiting examples, PET, other nuclear medical applications, power plant maintenance applications, homeland security applications, etc. Unless otherwise indicated, all numbers expressing quantities of energy level, dimension, and so forth used in the present specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and claims are approximations that may vary depending upon the properties sought to be obtained by the present invention. While several embodiments of the invention have been described, it should be apparent that various modifications, alterations and adaptations to those embodiments may occur to persons skilled in the art with the attainment of some or all of the advantages of the present invention. For example, some steps of the process flow described above may be omitted or performed in a different order. It is therefore intended to cover all such modifications, alterations and adaptations without departing from the scope and spirit of the present invention as defined by the appended claims.
	abstract	Provided is a method of manufacturing a lattice-shaped laminated scintillator panel capable of enlarging the area and increasing the thickness with a means completely different from a conventional technique using a silicon wafer.
	claims	1. A neutron generator comprising:a target electrode;a sealed envelope providing an environment for a gas, said sealed envelope defining an ion source chamber bounded by an extraction electrode, said extraction electrode spaced apart from the target electrode;an RF antenna external to said sealed envelope and disposed in proximity to said ion source chamber, said RF antenna for transmitting time-varying electromagnetic fields within said ion source chamber for producing a plasma in said ion source chamber;insulation disposed between said RF antenna and said ion source chamber for electrically insulating said RF antenna from voltages of said ion source chamber and said extraction electrode, the insulation comprising a different material than the sealed envelope;a voltage coupler, wherein the coupler is mounted to the insulation;wherein said extraction electrode operates at a positive voltage potential less than or equal to a steady state potential of the plasma and said target electrode operates at or near ground potential in order to produce an electric field that accelerates ions of said plasma towards said target electrode to induce collisions of ions with target material, thereby causing fusion reactions that generate neutrons; anda plasma electrode disposed within the ion source chamber to influence the steady state potential of the plasma so as to aid extraction of the ions through the extraction electrode;wherein said RF antenna is axially positioned between said extraction electrode and said plasma electrode in relation to an axis formed by the extraction electrode, the plasma electrode, and the target electrode. 2. The neutron generator according to claim 1, wherein:said RF antenna comprises a coil of tubing with coolant flowing therethrough. 3. The neutron generator according to claim 1, wherein:said insulation comprises solid-form voltage insulation surrounding said ion source. 4. The neutron generator according to claim 3, wherein:said solid-form voltage insulation comprises at least one tubular member realized from perfluoroalkoxy. 5. The neutron generator according to claim 3, wherein:said solid-form voltage insulation comprises two or more concentric tubular members realized from perfluoroalkoxy, each having a wall thickness of at least 0.04 inches. 6. The neutron generator according to claim 3, comprising:a first housing that houses said sealed envelope, said RF antenna and said solid-form voltage insulation. 7. The neutron generator according to claim 6, wherein:said solid-form voltage insulation extends between said sealed envelope and said first housing over at least a portion of the lengthwise dimension of said sealed envelope. 8. The neutron generator according to claim 6, wherein:at least one of liquid-form electrically insulating material and gas-form electrically insulating material fill the space between said sealed envelope and said first housing for electrical insulating purposes. 9. The neutron generator according to claim 6, comprising:an RF generator, electrically coupled to said RF antenna, for driving said RF antenna, said RF generator including an RF signal source and an impedance matching network. 10. The neutron generator according to claim 9, wherein:said RF signal generator operates substantially at ground potential and is disposed outside said first housing near said target electrode. 11. The neutron generator according to claim 10, comprising:voltage supply circuit means, electrically coupled to said extraction electrode, for operating said extraction electrode such that it floats at a positive voltage potential. 12. The neutron generator according to claim 11, wherein:said voltage supply circuit means comprises a Cockcroft-Walton voltage multiplier circuit. 13. The neutron generator according to claim 11, wherein:said voltage supply circuit means is disposed within said first housing adjacent or near an end of said sealed envelope opposite said target electrode. 14. The neutron generator according to claim 13, comprising:solid-form voltage insulation, disposed within said first housing and surrounding said voltage supply circuit means, for electrically insulating said voltage supply circuit means. 15. The neutron generator according to claim 14, wherein:said solid-form voltage insulation comprises at least one tubular member realized from perfluoroalkoxy. 16. The neutron generator according to claim 14, wherein:said solid-form voltage insulation comprises at least two concentric tubular members realized from perfluoroalkoxy, each having a wall thickness of at least 0.04 inches. 17. The neutron generator according to claim 14, wherein:said solid-form voltage insulation is part of a unitary member that surrounds said sealed envelope, said unitary member being part of said insulation. 18. The neutron generator according to claim 6, comprising:gas supply means for supplying gas to said enclosed envelope, said gas supply means operating at or near ground potential, said gas supply means disposed near said target electrode. 19. The neutron generator according to claim 11, comprising:control circuitry that interfaces to said voltage supply circuit means, said control circuitry operating at lower voltages than those output by the voltage supply circuit means and disposed outside said first housing. 20. The neutron generator according to claim 19, wherein:said control circuitry and said RF signal generator provide controlled output of ions in a continuous output mode. 21. The neutron generator according to claim 19, wherein:said control circuitry and said RF signal generator provide controlled output of ions in a pulsed output mode. 22. The neutron generator according to claim 21, wherein:said RF signal generator applies pulsed-mode excitation signals to said RF antenna in order to achieve said pulsed output mode. 23. The neutron generator according to claim 21, wherein:said voltage supply circuit means comprises i) DC power supply circuitry floating at positive voltage potentials and ii) circuitry for generating pulsed output signals from output of said DC power supply circuitry and for outputting said pulsed output signals for supply to said extractor electrode. 24. The neutron generator according to claim 23, comprising:an interface to couple control circuitry located outside voltage environment of said voltage supply circuit means to the circuitry for generating pulsed output signals. 25. The neutron generator according to claim 24, wherein:said interface comprises an optical transmitter located outside the voltage environment of said voltage supply circuit means, a fiber optic cable passing through the voltage environment of said voltage supply circuit means and leading to an optical detector located in the voltage environment of said voltage supply circuit means. 26. The neutron generator according to claim 24, wherein:said interface comprises the voltage coupler, wherein the voltage coupler comprises a voltage capacitive coupler, wherein the voltage capacitive coupler is mounted to the insulation. 27. The neutron generator according to claim 1, wherein:said RF antenna comprises a coil of wire or tubing in a helix geometry that surrounds said ion source chamber. 28. The neutron generator according to claim 1, wherein:said RF antenna comprises a coil of wire or tubing in a pancake geometry that is disposed in the vicinity of said ion source chamber. 29. A neutron generator comprising:a target electrode;a sealed envelope providing a pressure environment for a gas, said sealed envelope including an ion source chamber bounded by an extraction electrode, said extraction electrode spaced apart from the target electrode;an RF antenna external to said envelope and disposed in proximity to said ion source chamber, said RF antenna for transmitting time-varying electromagnetic fields within said ion source chamber for producing a plasma in said ion source chamber; anda plasma electrode disposed within the ion source chamber to influence the steady state potential of the plasma so as to aid extraction of the ions through the extraction electrode;wherein said extraction electrode operates at a positive voltage potential with respect to ground potential and said target electrode operates at negative with respect to ground potential in order to produce an electric field gradient that accelerates ions of said plasma towards said target electrode to induce collisions of ions with target material, thereby causing fusion reactions that generate neutrons;insulation disposed between said RF antenna and both said ion source chamber and said extraction electrode, for electrically insulating said RF antenna from voltages of said ion source chamber and said extraction electrode;a voltage capacitive coupler, wherein the coupler is mounted to the insulation; andwherein the RF antenna is axially positioned between said extraction electrode and said plasma electrode in relation to an axis formed by the extraction electrode, the plasma electrode, and the target electrode. 30. The neutron generator according to claim 29,wherein the voltage coupler comprises a voltage capacitive coupler, wherein the voltage capacitive coupler is mounted to the insulation. 31. The neutron generator according to claim 29, wherein:a portion of said sealed envelope defines said ion source chamber, said insulation comprises said portion of said sealed envelope, and said RF antenna is disposed adjacent said portion of said sealed envelope. 32. The neutron generator according to claim 31, wherein:said insulation comprises solid-form voltage insulation surrounding said portion of said sealed envelope. 33. The neutron generator according to claim 32, wherein:said solid-form voltage insulation comprises at least one tubular member realized from perfluoroalkoxy. 34. The neutron generator according to claim 33, wherein:said solid-form voltage insulation comprises two or more concentric tubular members realized from perfluoroalkoxy, each having a wall thickness of at least 0.04 inches. 35. The neutron generator according to claim 33, comprising:a first housing that houses said sealed envelope, said RF antenna and said solid-form voltage insulation. 36. The neutron generator according to claim 35, wherein:said solid-form voltage insulation extends between said sealed envelope and said first housing over at least a portion of the lengthwise dimension of said sealed envelope. 37. The neutron generator according to claim 35, wherein:at least one of liquid-form electrically insulating material and gas-form electrically insulating material fill the space between said sealed envelope and said first housing for insulating purposes. 38. The neutron generator according to claim 35, comprising:an RF generator, electrically coupled to said RF antenna, for driving said RF antenna, said RF generator including an RF signal source and an impedance matching network. 39. The neutron generator according to claim 38, wherein:said RF signal generator operates substantially at ground potential and is disposed outside said first housing near said target electrode. 40. The neutron generator according to claim 39, comprising:first voltage supply circuit means, electrically coupled to said extraction electrode, for operating said extraction electrode such that it floats at a positive voltage potential; andsecond voltage supply circuit means, electrically coupled to said target electrode, for operating said target electrode such that it floats at a negative voltage potential. 41. The neutron generator according to claim 40, wherein:said first and second voltage supply circuit means each comprise a Cockcroft-Walton voltage multiplier circuit. 42. The neutron generator according to claim 40, wherein:said first voltage supply circuit means is disposed within said first housing adjacent or near an end of said sealed envelope opposite said target electrode, and said second voltage supply circuit means is disposed within said first housing adjacent or near said target electrode. 43. The neutron generator according to claim 42, comprising:solid-form voltage insulation, disposed within said first housing and surrounding said first and second voltage supply circuit means, for electrically insulating said first and second voltage supply circuit means. 44. The neutron generator according to claim 43, wherein:said solid-form voltage insulation comprises at least one tubular member realized from perfluoroalkoxy. 45. The neutron generator according to claim 43, wherein:said solid-form voltage insulation comprises at least two concentric tubular members realized from perfluoroalkoxy, each having a wall thickness of at least 0.04 inches. 46. The neutron generator according to claim 43, wherein:said solid-form voltage insulation is part of a unitary member that surrounds said sealed envelope, said unitary member being part of said insulation. 47. The neutron generator according to claim 40, comprising:gas supply means for supplying gas to said enclosed envelope, said gas supply means operably coupled to said first voltage supply circuit means and operating at a positive voltage potential. 48. The neutron generator according to claim 40, comprising:control circuitry that interfaces to said first and second voltage supply circuit means, said control circuitry disposed outside said first housing. 49. The neutron generator according to claim 48, wherein:said control circuitry and said RF signal generator provide controlled output of ions in a continuous output mode. 50. The neutron generator according to claim 48, wherein:said control circuitry and said RF signal generator provide controlled output of ions in a pulsed output mode. 51. The neutron generator according to claim 50, wherein:said RF signal generator applies pulsed-mode excitation signals to said RF antenna in order to achieve said pulsed output mode. 52. The neutron generator according to claim 50, wherein:said voltage supply circuit means comprises i) DC power supply circuitry floating at positive voltage potentials and ii) circuitry for generating pulsed output signals from output of said DC power supply circuitry and for outputting said pulsed output signals for supply to said extractor electrode. 53. The neutron generator according to claim 29, comprising:an electrode disposed between said extraction electrode and said target electrode and operating at or near ground potential.
	claims	1. An ion beam sample preparation apparatus comprising:(a) an ion beam irradiating means disposed in a vacuum chamber and directing an ion beam toward a shield; said ion beam further characterized as being a broad ion beam;(b) a shield retention stage disposed in the vacuum chamber; said shield retention stage comprising:i. a first datum feature;ii. a second datum feature;iii. a shield retention means having at least a shield releasing position and a shield retaining position;(c) the shield having at least a rigid planar portion, removeably and replaceably held in said shield retention stage, said shield further comprising:i. a proximal sample surface configured to durably adhere the sample to the shield;ii. a first shielding surface disposed in the path of the ion beam and positioned to shield a portion of the ion beam directed at the sample when said shield is held in the shield retaining position of the shield retention means;iii. a third datum feature formed integrally with said shield, wherein said shield retention means in said shield retaining position urges said third datum feature to abut said first datum feature; and,iv. a fourth datum feature formed integrally with said shield, wherein said shield retention means in said shield retaining position urges said fourth datum feature to abut said second datum feature. 2. The apparatus of claim 1 wherein the shield retention stage further comprises a fifth datum feature, and the shield further comprises a sixth datum feature formed integrally with the shield, wherein the shield retention means in said shield retaining position urges said sixth datum feature to abut said fifth datum feature. 3. The apparatus of claim 1 wherein the first shielding surface meets said proximal sample surface at an angle of less than about 90 degrees and more than about 80 degrees. 4. The apparatus of claim 1 wherein the first shielding surface meets said proximal sample surface at an angle of less than about 87 degrees and more than about 83 degrees. 5. The apparatus of claim 1 wherein the first shielding surface is made of non-magnetic material with low sputtering yield. 6. The apparatus of claim 1 wherein at least a portion of the first shielding surface is made of tantalum or titanium. 7. The apparatus of claim 1 wherein the third datum feature is a datum surface and at least a portion of said datum surface is coextensive with at least a portion of said proximal sample surface. 8. The apparatus of claim 1 wherein the proximal sample surface has at least one recessed portion for the flowing of adhesive between the shield and the sample. 9. The apparatus of claim 1 wherein the shield further comprises a sample clamping means coupled to the shield configured to hold the sample against said proximal sample surface. 10. The apparatus of claim 1 wherein the shield further comprises:(a) a second shielding surface having a portion disposed in the path of a portion of the ion beam;(b) a shield edge formed where the first shielding surface meets the proximal sample surface; and,(c) a visible alignment mark on the second shielding surface, configured such that the location of said visible alignment mark is in a predetermined relationship to the region where the ion beam impinges on said shield edge when said shield is held in the shield retaining position of the shield retention means. 11. The apparatus of claim 1 wherein the shield is made of a cladding material joined to a core material such that a portion of the cladding material forms at least a portion of the first shielding surface, and a portion of the core material forms the third and fourth datum features of the shield. 12. An ion beam sample preparation apparatus comprising:(a) an ion beam irradiating means disposed in a vacuum chamber and directing an ion beam toward a shield; said ion beam further characterized as being a broad ion beam;(b) a rotating shield retention stage disposed in the vacuum chamber; said shield retention stage comprising:i. a first datum feature;ii. a second datum feature;iii. a shield retention means having at least a shield releasing position and a shield retaining position;iv. a rotation axis located substantially in the plane of the first datum feature;v. a rotation drive for rotating the shield retention stage around the rotation axis;(c) the shield having at least a rigid planar portion, removeably and replaceably held in said shield retention stage, said shield further comprising:i. a third datum feature formed integrally with the shield, wherein said shield retention means in said shield retaining position urges said third datum feature to abut said first datum feature;ii. a fourth datum feature formed integrally with the shield, wherein said shield retention means in said shield retaining position urges said fourth datum feature to abut said second datum feature;iii. a first shielding surface disposed in the path of the ion beam and positioned to shield a portion of the ion beam directed at the sample when said shield is held in the shield retaining position of the shield retention means;iv. a proximal sample surface configured to durably adhere the sample to the shield;v. a shield edge formed where the first shielding surface meets the proximal sample surface, wherein said shield edge is held substantially perpendicular to said rotation axis when said shield is held in the shield retaining position of the shield retention means. 13. The apparatus of claim 12 wherein the shield retention stage further comprises a fifth datum feature, and the shield further comprises a sixth datum feature formed integrally with the shield, wherein the shield retention means in said shield retaining position urges said sixth datum feature to abut said fifth datum feature. 14. The apparatus of claim 12 wherein the first shielding surface meets said proximal sample surface at an angle of less than about 90 degrees and more than about 80 degrees. 15. The apparatus of claim 12 wherein the first shielding surface meets said proximal sample surface at an angle of less than about 87 degrees and more than about 83 degrees. 16. The apparatus of claim 12 wherein the first shielding surface is made of non-magnetic material with low sputtering yield. 17. The apparatus of claim one wherein at least a portion of the first shielding surface is made of tantalum or titanium. 18. The apparatus of claim 12 wherein the third datum feature is a datum surface and a portion of said datum surface is coextensive with a portion of said proximal sample surface. 19. The apparatus of claim 12 wherein the proximal sample surface has at least one recessed portion for the flowing of adhesive between the shield and the sample. 20. The apparatus of claim 12 wherein the shield further comprises a sample clamping means coupled to the shield configured to hold the sample against said proximal sample surface. 21. The apparatus of claim 12 wherein the shield further comprises:(a) a second shielding surface having a portion disposed in the path of a portion of the ion beam;(b) a visible alignment mark on the second shielding surface, configured such that the location of said visible alignment mark is in a predetermined relationship to the region where the ion beam impinges on said shield edge when said shield is held in the shield retaining position of the shield retention means. 22. The apparatus of claim 12 wherein the shield is made of a cladding material joined to a core material such that a portion of the cladding material forms at least a portion of the first shielding surface, and a portion of the core material forms the third and fourth datum features of the shield. 23. A kit for preparing a sample in an ion beam sample preparation device using a broad ion beam, said kit comprising:(a) a shield retention stage comprising:i. a first datum feature;ii. a second datum feature;iii. a shield retention means having at least a shield releasing position and a shield retaining position;(b) a shield having at least a rigid planar portion, removeably and replaceably held in said shield retention stage, said shield further comprising:i. a third datum feature formed integrally with said shield, wherein said shield retention means in said shield retaining position urges said third datum feature to abut said first datum feature;ii. a fourth datum feature formed integrally with said shield, wherein said shield retention means in said shield retaining position urges said fourth datum feature to abut said second datum feature;iii. a first shielding surface,iv. a proximal sample surface for durably adhering the sample to the shield. 24. The kit of claim 23 wherein the shield retention stage further comprises a fifth datum feature, and the shield further comprises a sixth datum feature formed integrally with the shield, wherein the shield retention means in said shield retaining position urges said sixth datum feature to abut said fifth datum feature. 25. The kit of claim 23 wherein the first shielding surface meets the proximal sample surface at an angle of less than about 90 degrees and more than about 80 degrees. 26. The kit of claim 23 wherein the first shielding surface meets said proximal sample surface at an angle of less than about 87 degrees and more than about 83 degrees. 27. The kit of claim 23 wherein the third datum feature is a datum surface and a portion of said datum surface is coextensive with a portion of said proximal sample surface. 28. The kit of claim 23 wherein the the first shielding surface is made of non-magnetic material with low sputtering yield. 29. The kit of claim 23 wherein at least a portion of the first shielding surface is made of tantalum or titanium. 30. The kit of claim 23 wherein the proximal sample surface has at least one recessed portion for the flowing of adhesive between the shield and the sample. 31. The kit of claim 23 wherein the shield further comprises a sample clamping means coupled to the shield configured to hold the sample against said proximal sample surface. 32. The kit of claim 23 wherein the shield further comprises:(a) a second shielding surface having a portion disposed in the path of a portion of the ion beam;(b) a shield edge formed where the first shielding surface meets the proximal sample surface; and,(c) a visible alignment mark on the second shielding surface configured such that the location of said visible alignment mark is in a predetermined relationship to the region where the ion beam impinges on said shield edge when said shield is held in the shield retaining position of the shield retention means. 33. The kit of claim 23 wherein the shield is made of a cladding material joined to a core material such that a portion of the cladding material forms at least a portion of the first shielding surface, and a portion of the core material forms the third and fourth datum features of the shield. 34. The kit of claim 23 wherein the shield retention stage and the shield are separately packaged. 35. A kit for observing in a microscope a sample prepared in an ion beam sample preparation device using a broad ion beam, said kit comprising:(a) a shield retention stage comprising:i. a first datum feature;ii. a second datum feature;iii. a shield retention means having at least a shield releasing position and a shield retaining position;(b) a shield having at least a rigid planar portion, removeably and replaceably held in said shield retention stage, said shield further comprising:i. a third datum feature formed integrally with the shield, wherein said shield retention means in said shield retaining position urges said third datum feature to abut said first datum feature;ii. a fourth datum feature formed integrally with the shield, wherein said shield retention means in said shield retaining position urges said fourth datum feature to abut said second datum feature;iii. a first shielding surface; and,iv. a proximal sample surface for durably adhering the sample to the shield. 36. The kit of claim 35 wherein the shield retention stage further comprises a fifth datum feature, and the shield further comprises a sixth datum feature formed integrally with the shield, wherein the shield retention means in said shield retaining position urges said sixth datum feature to abut said fifth datum feature. 37. The kit of claim 35 wherein the first shielding surface meets the proximal sample surface at an angle of less than about 90 degrees and more than about 80 degrees. 38. The kit of claim 35 wherein the first shielding surface meets said proximal sample surface at an angle of less than about 87 degrees and more than about 83 degrees. 39. The kit of claim 35 wherein the third datum feature is a datum surface and a portion of said datum surface is coextensive with a portion of said proximal sample surface. 40. The kit of claim 35 wherein the shield is made of non-magnetic material with low sputtering yield. 41. The kit of claim 35 wherein at least a portion of the shield is made of tantalum or titanium. 42. The kit of claim 35 wherein the proximal sample surface has at least one recessed portion for the flowing of adhesive between the shield and the sample. 43. The kit of claim 35 wherein the shield further comprises a sample clamping means coupled to the shield configured to hold the sample against said proximal sample surface. 44. The kit of claim 35 wherein the shield further comprises:(a) a shield edge formed where the first shielding surface meets the proximal sample surface; and,(b) a visible alignment mark configured such that the location of said visible alignment mark is in a predetermined relationship to the region where the sample was prepared by the ion beam sample preparation device. 45. The kit of claim 35 wherein the shield is made of a cladding material joined to a core material such that a portion of the cladding material forms at least a portion of the first shielding surface, and a portion of the core material forms the third and fourth datum features of the shield. 46. The kit of claim 35 wherein the shield retention stage and the shield are separately packaged.
	claims	1. A lithographic projection apparatus comprising: a radiation system to provide a projection beam of radiation; a support structure adapted to support patterning structure which can be used to pattern the projection beam according to a desired pattern; a substrate table to hold a substrate; a projection system to project the patterned beam onto a target portion of the substrate, wherein said projection system includes precisely four imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of 2(xe2x88x92), 6(xe2x88x92), or 9(xe2x88x92), where: a i =1 if an angle of incidence of a chief ray at mirror i is negative, a i =0 if the angle of incidence of the chief ray at mirror i is positive, M is a magnification of the projection system, and the index i numbers the mirrors from object to image. 2. Apparatus according to claim 1 wherein said projection system has a stop on one of a second mirror of the four imaging mirrors and a third mirror of the four imaging mirrors. claim 1 3. Apparatus according to claim 1 wherein said projection system has an intermediate image located at one of between first and second ones of the mirrors, between second and third ones of the mirrors and between third and fourth ones of the mirrors. claim 1 4. A lithographic projection apparatus comprising: a radiation system to provide a projection beam of radiation; a support structure adapted to support patterning structure which can be used to pattern the projection beam according to a desired pattern; a substrate table to hold a substrate; a projection system to project the patterned beam onto a target portion of the substrate, wherein said projection system has precisely six imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of 5(+), 6(xe2x88x92), 9(+), 13(+), 18(xe2x88x92), 21(+), 22(xe2x88x92), 25(+), 29(+), 34(xe2x88x92), 37(+), 38(xe2x88x92), 42(xe2x88x92), or 54(xe2x88x92), where: a i =1 if an angle of incidence of a chief ray at mirror i is negative, a i =0 if the angle of incidence of the chief ray at mirror i is positive, M is a magnification of the projection system, and the index i numbers the mirrors from object to image. 5. Apparatus according to claim 4 , wherein said projection system has a stop located on one of second, third, fourth and fifth ones of the mirrors. claim 4 6. Apparatus according to claim 4 , wherein said projection system has an intermediate image between the second and fifth mirror. claim 4 7. Apparatus according to claim 4 wherein said projection system has the smallest deviation from telecentricity while still enabling obscuration-free illumination of the mask such that, for each point on the object, in a pencil of rays leaving an object, a ray forming the smallest angle with an optical axis forms an angle not larger than 10xc2x0 to the optical axis. claim 4 8. Apparatus according to claim 4 wherein said projection is substantially telecentric on the image side such that for each point on an object, the ray passing through the center of the aperture stop forms in an image space an angle with an optical axis not larger than 1xc2x0. claim 4 9. Apparatus according to claim 4 wherein each mirror in said projection system is substantially rotationally symmetric about an optical axis. claim 4 10. Apparatus according to claim 4 wherein said projection system has a magnification whose absolute value is in the range of from ⅓ to {fraction (1/10)}. claim 4 11. Apparatus according to claim 10 wherein said magnification has an absolute value substantially equal to one of xc2xc and ⅕. claim 10 12. Apparatus according to claim 4 wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 8 to 20 nm. claim 4 13. Apparatus according to claim 12 wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 9 to 16 nm. claim 12 14. An apparatus according to any claim 4 , wherein the support structure comprises a mask table for holding a mask. claim 4 15. An apparatus according to claim 4 , wherein the radiation system comprises a radiation source. claim 4 16. A device manufacturing method comprising: projecting the patterned beam onto a target portion of the substrate, wherein said projection system has precisely six imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of 5(+), 6(xe2x88x92), 9(+), 13(+), 18(xe2x88x92), 21(+), 22(xe2x88x92), 25(+), 29(+), 34(xe2x88x92), 37(+), 38(xe2x88x92), 42(xe2x88x92), or 54(xe2x88x92), where: a i =1 if an angle of incidence of a chief ray at mirror i is negative, a i =0 if the angle of incidence of the chief ray at mirror i is positive, M is a magnification of the projection system, and the index i numbers the mirrors from object to image. 17. A lithographic projection apparatus comprising: a radiation system to provide a projection beam of radiation; a support structure adapted to support patterning structure which can be used to pattern the projection beam according to a desired pattern; a substrate table to hold a substrate; a projection system to project the patterned beam onto a target portion of the substrate, wherein said projection system has precisely eight imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of 2(+), 5(+), 9(+), 12(+), 13(+), 18(+), 18(xe2x88x92), 19(+), 20(+), 21(+), 22(+), 23(+), 25(+), 26(+), 34(xe2x88x92), 36(+), 37(+), 38(xe2x88x92), 45(+), 46(+), 49(+), 52(+), 53(+), 54(+), 54(xe2x88x92), 55(xe2x88x92), 59(xe2x88x92), 68(+), 69(+), 73(+), 74(+), 77(+), 82(+), 82(xe2x88x92), 85(+), 88(+), 89(+), 90(xe2x88x92), 92(+), 93(+), 97(+), 100(xe2x88x92), 101(+), 102(xe2x88x92), 104(+), 105(+), 106(+), 106(xe2x88x92), 107(+), 108(+), 109(+), 109(xe2x88x92), 110(+), 110(xe2x88x92), 111(+), 113(+), 116(+), 117(+), 118(+), 118(xe2x88x92), 120(+), 121(+), 122(xe2x88x92), 123(xe2x88x92), 132(+), 133(+), 134(xe2x88x92), 137(+), 138(+), 141(+), 145(+), 145(xe2x88x92), 146(+), 146(xe2x88x92), 147(+), 148(+), 148(xe2x88x92), 149(+), 150(+), 150(xe2x88x92), 151(+), 151(xe2x88x92), 152(xe2x88x92), 153(+), 154(+), 154(xe2x88x92), 155(+), 155(xe2x88x92), 156(+), 157(+), 159(+), 161(+), 162(xe2x88x92), 163(xe2x88x92), 164(+), 165(+), 166(+), 166(xe2x88x92), 167(+), 168(+), 169(+), 170(+), 170(xe2x88x92), 171(+), 172(+), 173(+), 174(+), 175(+), 176(+), 177(+), 178(xe2x88x92), 179(+), 180(+), 180(xe2x88x92), 181(+), 181(xe2x88x92), 182(+), 182(xe2x88x92), 183(+), 183(xe2x88x92), 184(+), 185(+), 185(xe2x88x92), 186(xe2x88x92), 187(+), 187(xe2x88x92), 188(xe2x88x92), 189(+), 196(+), 197(+), 201(+), 203(+), 205(+), 209(+), 214(xe2x88x92), 216(+), 217(+), 218(+), 218(xe2x88x92), 225(+), 228(+), 229(+), 230(+), 232(+), 233(+), 235(+), 236(+), 237(+), 238(xe2x88x92), 243(+), 246(+), 247(+), 248(+), 250(xe2x88x92), where: a i =1 if an angle of incidence of a chief ray at mirror i is negative, a i =0 if the angle of incidence of the chief ray at mirror i is positive, M is a magnification of the projection system, and the index i numbers the mirrors from object to image. 18. Apparatus according to claim 1 wherein said projection system has the smallest deviation from telecentricity while still enabling obscuration-free illumination of the mask such that, for each point on the object, in a pencil of rays leaving an object, a ray forming the smallest angle with an optical axis forms an angle not larger than 10xc2x0 to the optical axis. claim 1 19. Apparatus according to claim 1 wherein said projection is substantially telecentric on the image side such that for each point on an object, the ray passing through the center of the aperture stop forms in an image space an angle with an optical axis not larger than 1xc2x0. claim 1 20. Apparatus according to claim 1 wherein each mirror in said projection system is substantially rotationally symmetric about an optical axis. claim 1 21. Apparatus according to claim 1 wherein said projection system has a magnification whose absolute value is in the range of from ⅓ to {fraction (1/10)}. claim 1 22. Apparatus according to claim 21 wherein said magnification has an absolute value substantially equal to one of xc2xc and ⅕. claim 21 23. Apparatus according to claim 1 wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 8 to 20 nm. claim 1 24. Apparatus according to claim 23 wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 9 to 16 nm. claim 23 25. An apparatus according to any claim 1 , wherein the support structure comprises a mask table for holding a mask. claim 1 26. An apparatus according to claim 1 , wherein the radiation system comprises a radiation source. claim 1 27. Apparatus according to claim 17 wherein said projection system has the smallest deviation from telecentricity while still enabling obscuration-free illumination of the mask such that, for each point on the object, in a pencil of rays leaving an object, a ray forming the smallest angle with an optical axis forms an angle not larger than 10xc2x0 to the optical axis. claim 17 28. Apparatus according to claim 17 wherein said projection is substantially telecentric on the image side such that for each point on an object, the ray passing through the center of the aperture stop forms in an image space an angle with an optical axis not larger than 1xc2x0. claim 17 29. Apparatus according to claim 17 wherein each mirror in said projection system is substantially rotationally symmetric about an optical axis. claim 17 30. Apparatus according to claim 17 wherein said projection system has a magnification whose absolute value is in the range of from 1/3 to 1/10. claim 17 31. Apparatus according to claim 2 wherein said magnification has an absolute value substantially equal to one of xc2xc and ⅕. claim 2 32. Apparatus according to claim 17 wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 8 to 20 nm. claim 17 33. Apparatus according to claim 32 wherein said projection beam comprises extreme ultraviolet radiation having a wavelength in the range of from 9 to 16 nm. claim 32 34. An apparatus according to any claim 17 , wherein the support structure comprises a mask table for holding a mask. claim 17 35. An apparatus according to claim 17 , wherein the radiation system comprises a radiation source. claim 17 36. A device manufacturing method comprising: projecting a patterned beam of radiation onto a target portion of a layer of radiation-sensitive material on a substrate using an imaging system including precisely four imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of 2(xe2x88x92), 6(xe2x88x92), or 9(xe2x88x92), where: a i =1 if an angle of incidence of a chief ray at mirror i is negative, a i =0 if the angle of incidence of the chief ray at mirror i is positive, M is a magnification of the projection system, and the index i numbers the mirrors from object to image. 37. A device manufactured in accordance with the method of claim 36 . claim 36 38. A device manufacturing method comprising: projecting the patterned beam onto a target portion of the substrate, wherein said projection system has precisely eight imaging mirrors in the optical path of the projection beam and has an incidence angle classification, C, of C, of 2(+), 5(+), 9(+), 12(+), 13(+), 18(+), 18(xe2x88x92), 19(+), 20(+), 21(+), 22(+), 23(+), 25(+), 26(+), 34(xe2x88x92), 36(+), 37(+), 38(xe2x88x92), 45(+), 46(+), 49(+), 52(+), 53(+), 54(+), 54(xe2x88x92), 55(xe2x88x92), 59(xe2x88x92), 68(+), 69(+), 73(+), 74(+), 77(+), 82(+), 82(xe2x88x92), 85(+), 88(+), 89(+), 90(xe2x88x92), 92(+), 93(+), 97(+), 100(xe2x88x92), 101(+), 102(xe2x88x92), 104(+), 105(+), 106(+), 106(xe2x88x92), 107(+), 108(+), 109(+), 109(xe2x88x92), 110(+), 110(xe2x88x92), 111(+), 113(+), 116(+), 117(+), 118(+), 118(xe2x88x92), 120(+), 121(+), 122(xe2x88x92), 123(xe2x88x92), 132(+), 133(+), 134(xe2x88x92), 137(+), 138(+), 141(+), 145(+), 145(xe2x88x92), 146(+), 146(xe2x88x92), 147(+), 148(+), 148(xe2x88x92), 149(+), 150(+), 150(xe2x88x92), 151(+), 151(xe2x88x92), 152(xe2x88x92), 153(+), 154(+), 154(xe2x88x92), 155(+), 155(xe2x88x92), 156(+), 157(+), 159(+), 161(+), 162(xe2x88x92), 163(xe2x88x92), 164(+), 165(+), 166(+), 166(xe2x88x92), 167(+), 168(+), 169(+), 170(+), 170(xe2x88x92), 171(+), 172(+), 173(+), 174(+), 175(+), 176(+), 177(+), 178(xe2x88x92), 179(+), 180(+), 180(xe2x88x92), 181(+), 181(xe2x88x92), 182(+), 182(xe2x88x92), 183(+), 183(xe2x88x92), 184(+), 185(+), 185(xe2x88x92), 186(xe2x88x92), 187(+), 187(xe2x88x92), 188(xe2x88x92), 189(+), 196(+), 197(+), 201(+), 203(+), 205(+), 209(+), 214(xe2x88x92), 216(+), 217(+), 218(+), 218(xe2x88x92), 225(+), 228(+), 229(+), 230(+), 232(+), 233(+), 235(+), 236(+), 237(+), 238(xe2x88x92), 243(+), 246(+), 247(+), 248(+), 250(xe2x88x92), where: a i =1 if an angle of incidence of a chief ray at mirror i is negative, a i =0 if the angle of incidence of the chief ray at mirror i is positive, M is a magnification of the projection system, and the index i numbers the mirrors from object to image.
	claims	1. A ventilated system for storing high level waste emitting heat, the system comprising:an air-intake shell forming a downcomer air-intake cavity;a plurality of storage shells, each storage shell forming a substantially vertical storage cavity, the plurality of storage shells arranged so as to surround the air-intake shell in a side-by side relationship;a hermetically sealed canister for holding high level waste positioned in one or more of the storage cavities so that a gap exists between the storage shell and the canister, the storage cavities having horizontal cross-sections that accommodate no more than one of the canisters;a removable lid positioned atop each of the storage shells so as to form a lid-to-shell interface, each lid containing an outlet vent forming a passageway between an ambient environment and the storage cavity;a network of pipes forming hermetically sealed fluid passageways between a bottom portion of the downcomer air-intake cavity and a bottom portion of each of the storage cavities;the downcomer air-intake cavity forming a passageway from the ambient environment to the network of pipes; andwherein the network of pipes is configured so that the quantity of air drawn by each of the storage shells adjusts to comply with Bernoulli's law. 2. The system of claim 1 wherein the network of pipes is configured so that two different paths exist through the hermetically sealed fluid passageway from the downcomer air-intake cavity to each of the storage cavities without passing through any of the other storage cavities. 3. The system of claim 1 further comprising:a lid positioned atop the air-intake shell and containing an inlet vent forming a passageway between the ambient environment and the air-intake cavity. 4. The system of claim 1 wherein the network of pipes comprises one or more headers that fluidly couple the storage shells to the air-intake shell. 5. The system of claim 1 further comprising a layer of insulating material circumferentially surrounding the storage shells. 6. The system of claim 1 further comprising:means for supporting the canister in the storage cavity so that a first plenum exists between the canister and a floor of the cavity and a second plenum exists between the canister and the lid, the network of pipes forming passageways between the air-intake cavity and the first plenums, and the outlet vents of the lids forming passageways between an ambient environment and the second plenums. 7. The system of claim 6 wherein the support means comprises a plurality of circumferentially spaced support blocks. 8. The system of claim 1 further comprising a radiation shielding body surrounding the storage shells. 9. The system of claim 8 wherein the radiation shielding body is a concrete monolith. 10. The system of claim 1 further comprising:a ground having a grade; andwherein the storage shells are positioned so that at least a major portion of a height of each storage shell is located below the grade, the network of pipes being located below the grade, and the downcomer air-intake cavity forming a passageway between an opening located above the grade and the network of pipes. 11. The system of claim 10 further comprising a radiation absorbing material surrounding each of the storage shells. 12. The system of claim 11 wherein the radiation absorbing material is selected from a group consisting of concrete, an engineered fill, and soil. 13. The system of claim 10 wherein the lids positioned atop the storage shells are located above the grade. 14. The system of claim 10 wherein the storage shells, the air-intake shell, and the network of pipes are hermetically sealed to ingress of below grade liquids. 15. The system of claim 1 wherein all connections between the network of pipes, the storage shells, and the air-intake shell are hermetic. 16. The system of claim 1 wherein the gaps that exist between the storage shells and the canisters are annular gaps. 17. The system of claim 16 further comprising:wherein each storage cavity comprises a first plenum between the canister and a floor of the storage cavity and a second plenum between the canister and the lid, the annular gaps forming passageways between the first and second plenums, the network of pipes forming passageways between the downcomer air-intake cavity and the first plenums, and the outlet vents of the lids forming passageways between the ambient environment and the second plenums. 18. A ventilated system for storing high level waste having a heat load, the system comprising:an array of substantially vertically oriented shells arranged in a side-by-side relation, each shell forming a cavity;at least one hermetically sealed canister for holding high level waste positioned in one of the cavities, the cavities having horizontal cross-sections that accommodate no more than one of the canisters;a network of pipes forming hermetically sealed fluid passageways between bottom portions of all of the cavities;wherein at least one of the cavities is empty so as to allow cool air to enter the network of pipes; andwherein the network of pipes is configured so that at least two different paths exist through the hermetically sealed fluid passageways from the empty cavity to each of the remaining cavities without passing through any of the other cavities. 19. The system of claim 18 wherein the shells are positioned so that at least a major portion of a height of each shell is located below grade, the network of pipes being located below grade, and the lids located above grade. 20. A ventilated system for storing high level waste emitting heat, the system comprising:an air-intake shell forming a downcomer air-intake cavity;a plurality of storage shells, each storage shell forming a substantially vertical storage cavity, the plurality of storage shells arranged so as to surround the air-intake shell in a side-by side relationship;a removable lid positioned atop each of the storage shells so as to form a lid-to-shell interface;an outlet vent forming a passageway between an ambient environment and a top portion of the storage cavity for each storage shell;a network of pipes forming hermetically sealed fluid passageways between a bottom portion of the downcomer air-intake cavity and a bottom portion of each of the storage cavities;the downcomer air-intake cavity forming a passageway from the ambient environment to the network of pipes; andwherein the network of pipes is configured so that two different paths exist through the hermetically sealed fluid passageway from the downcomer air-intake cavity to each of the storage cavities without passing through any of the other storage cavities.
050376047	abstract	A cylindrical coffer dam assembly is described for use in temporary shielding personnel from nuclear reactor stored internals' radiation. The coffer dam is made up of substantially equal segments small enough to pass through the equipment hatch of the reactor containment building. The segments are pre-fabricated at a factory, transported to the plant, introduced individually into the containment building, and assembled together in sealing relation at the operating floor into a complete coffer dam. The coffer dam is moved to the reactor vessel and connected to the reactor vessel upper flange in sealing relation. The coffer dam can be disconnected, disassembled, removed and re-used at other nuclear reactors.
054901855	claims	1. A refueling system for a nuclear power plant having a reactor containment building housing a reactor with a plurality of core support locations, a fuel storage building having a plurality of fuel assembly storage locations, and a plurality of fuel assemblies, said refueling system comprising: a fuel transfer system operable to move fuel assemblies between said containment building and said fuel storage building; a refueling machine operable to move fuel assemblies among said core support locations, as well as between said reactor and said fuel transfer system; a spent fuel handling machine operable to move fuel assemblies among said fuel assembly storage locations, as well as between said fuel assembly storage locations and said fuel transfer system; a means for operator interface; a network comprising a plurality of nodes interconnected by a data link, said network further comprising nodes connected to said fuel transfer system, said refueling machine, said spent fuel handling machine, and said means for operator interface; a means for controlling said refueling system, said means for controlling being connected to a node of said network and being operable to automatically control the operation of said fuel transfer system, said refueling machine, and said spent fuel handling machine so that fuel assembly moves are accomplished between said containment building and said fuel storage building automatically in accordance with a preselected program; and a refueling machine operable to move fuel assemblies among said core support locations, as well as between said reactor and said fuel transfer system; a means for measuring the reactivity of said reactor; a controller means connected to said means for measuring reactivity, said controller means operable to compare the measured rate of reactivity change to a predetermined setpoint, and further operable to interrupt the movement of said refueling machine whenever the measured rate of reactivity change exceeds said setpoint. 2. The refueling system of claim 1, wherein said means for controlling is operable to take action to reduce said reactivity whenever the output of said means for measuring reactivity exceeds a predetermined setpoint. 3. A refueling system for a nuclear power plant having a containment building housing a reactor with a plurality of core support locations, a fuel storage building having a plurality of fuel assembly storage locations, a fuel transfer system connecting said containment building and said fuel storage building, and a plurality of fuel assemblies, said refueling system comprising:
049903039	abstract	A fuel element for a nuclear reactor having a zirconium-tin alloy cladding tube, with a thin coating of particles of enriched boron-containing compound burnable poison particles, deposited from a liquid sol-gel which includes a glass binder material.
060581530	abstract	A preventive maintenance apparatus for structural members inside a nuclear reactor pressure vessel includes a ring-shaped guide rail having a plurality of lugs which is placed on an upper flange of a core shroud provided inside a reactor pressure vessel. At least some of lugs separately engage with a plurality of guide rods provided on an inner surface of the reactor pressure vessel. A turntable is rotated on the guide rail. A first discharging nozzle moving apparatus placed on the turntable moves a first discharging nozzle for adding compressive remaining stress to an outer surface of the core shroud in a radial direction of the core shroud and in an axial direction of the core shroud. A second discharging nozzle moving apparatus placed on the turntable moves a second discharging nozzle for adding compressive remaining stress to an inner surface of the core shroud in a radial direction of the core shroud and in an axial direction of the core shroud.
	description	The present invention relates to a pit gate that seals service water retained in a pit in a watertight manner, pit equipment, a nuclear power facility, and an installation method of the pit gate. Conventionally, there is a known pool gate provided in a canal unit, which is provided between pools constructed inside a nuclear reactor building in a nuclear power generating station or inside a building adjacent to the nuclear reactor building, such that both pools are partitioned by the pool gate (for example, see Patent Literature 1). This pool gate has a U-shaped packing that is in contact with the wall surface of the pool on the canal unit side or in contact with a slot and receives the lateral direction load due to water pressure. At this time, the packing, which is an elastic packing, is pressurized and is thus brought into close contact with the wall surface on the canal unit side or contact with the slot, whereby exhibiting the sealing function. Patent Literature 1: Japanese Laid-open Patent Publication No. 10-332869 However, with the packing used in Patent Literature 1, because the sealing function is not operated unless pressurization is performed by the pressure source, the pressure source is needed to ensure the sealing property due to the pool gate. Accordingly, to enhance the rationality, a pit gate with a simple structure that does not need a pressure source has been proposed. In this case, because pressurization is not performed by the pressure source, in an initial state in which a lateral direction load due to water pressure is not applied to a gate before water in a pit is drained, the contact property between the packing and the wall surface is decreased and thus possibly resulting in a decrease in the sealing property. Accordingly, an object of the present invention is to provide a pit gate that is brought into close contact with a slot even if the pit gate has a simple structure, pit equipment, a nuclear power facility, and an installation method of the pit gate. According to an aspect of the present invention, a pit gate that is accommodated in a slot and that seals service water retained in the pit in a watertight manner, comprising: a gate main body; a sealing member that is provided on a surface opposite to the slot in the gate main body and that seals between the gate main body and the slot in a watertight manner; and a pressing clamp that is provided in the gate main body and that moves the gate main body toward the sealing member side due to a weight of the gate main body itself. According to this configuration, because the gate main body can be moved toward the sealing member side by the pressing clamp, the sealing member can be appropriately brought into close contact with the slot. Consequently, because it is possible to seal between the gate main body and the slot by the sealing member in a watertight manner, the leakage of service water from the pit can be suppressed. Advantageously, in the pit gate, the sealing member is formed so as to protrude toward the slot side in cross section. According to this configuration, the shape of the sealing member can be easily brought into close contact with the slot. Advantageously, in the pit gate, the pressing clamp includes a first gate-side pressing member that is provided on a surface of the gate main body opposite from a surface on which the sealing member is provided, and the first gate-side pressing member is formed in a wedge shape whose thickness becomes thinner from the upper side toward the lower side in the vertical direction, so that a first gate-side inclined surface that is inclined toward the sealing member side from the upper side toward the lower side in the vertical direction is formed. According to this configuration, if the gate main body is accommodated in the slot from the upper side toward the lower side in the vertical direction, the gate main body moves toward the sealing member side due to the first gate-side inclined surface. Consequently, the gate main body can be appropriately moved toward the sealing member side by the pressing clamp. Advantageously, in the pit gate, the pressing clamp includes a second gate-side pressing member that is shaped as a rod and that is provided so as to protrude from the gate main body along the horizontal direction, and a second slot-side pressing member that is in contact with the second gate-side pressing member and that is provided in the slot that faces a surface opposite from a surface on which the sealing member of the gate main body is provided, and the second slot-side pressing member is formed in a wedge shape whose thickness becomes greater from the upper side toward the lower side in the vertical direction, so that a second slot-side inclined surface that is inclined toward the sealing member side from the upper side toward the lower side in the vertical direction is formed, and the second gate-side pressing member comes into contact with the second slot-side inclined surface, so that the second gate-side pressing member moves the gate main body toward the sealing member side. According to this configuration, if the gate main body is accommodated in the slot from the upper side toward the lower side in the vertical direction, because the second gate-side pressing member in the gate main body moves toward the sealing member side along the second slot-side inclined surface of the second slot-side pressing member, the gate main body moves toward the sealing member side. Consequently, the gate main body can be appropriately moved toward the sealing member side by the pressing clamp. Advantageously, in the pit gate, the pressing clamp includes a third gate-side pressing member that is provided so as to protrude from the gate main body toward the lower side in the vertical direction, and a third slot-side pressing member that is in contact with the third gate-side pressing member and that is provided on a bottom portion of the slot, and the third slot-side pressing member is formed in a wedge shape whose thickness becomes greater from the upper side toward the lower side in the vertical direction, so that a third slot-side inclined surface that is inclined toward the sealing member side from the upper side toward the lower side in the vertical direction is formed, and the third gate-side pressing member comes into contact with the third slot-side inclined surface, so that the third gate-side pressing member moves the gate main body toward the sealing member side. According to this configuration, if the gate main body is accommodated in the slot from the upper side toward the lower side in the vertical direction, because the third gate-side pressing member in the gate main body moves toward the sealing member side along the third slot-side inclined surface of the third slot-side pressing member, the gate main body moves toward the sealing member side. Consequently, the gate main body can be appropriately moved toward the sealing member side by the pressing clamp. Advantageously, in the pit gate, a plurality of the pressing clamps is provided at a predetermined distance in the vertical direction of the gate main body, the plurality of the pressing clamps includes a first pressing clamp, a second pressing clamp, and a third pressing clamp, the first pressing clamp includes a first gate-side pressing member that is provided on a surface of the gate main body opposite from a surface on which the sealing member is provided, the first gate-side pressing member is formed in a wedge shape whose thickness becomes thinner from the upper side toward the lower side in the vertical direction, so that a first gate-side inclined surface that is inclined toward the sealing member side from the upper side toward the lower side in the vertical direction is formed, and the second pressing clamp includes a second gate-side pressing member that is shaped as a rod and that is provided so as to protrude from the gate main body along the horizontal direction, and a second slot-side pressing member that is in contact with the second gate-side pressing member and that is provided on the slot that faces a surface opposite from a surface on which the sealing member of the gate main body is provided, and the second slot-side pressing member is formed in a wedge shape whose thickness becomes greater from the upper side toward the lower side in the vertical direction, so that a second slot-side inclined surface that is inclined toward the sealing member side from the upper side toward the lower side in the vertical direction is formed, the second gate-side pressing member comes into contact with the second slot-side inclined surface, so that the second gate-side pressing member moves the gate main body toward the sealing member side, and the third pressing clamp includes a third gate-side pressing member that is provided so as to protrude from the gate main body toward the lower side in the vertical direction, and a third slot-side pressing member that is in contact with the third gate-side pressing member and that is provided on a bottom portion of the slot, and the third slot-side pressing member is formed in a wedge shape whose thickness becomes greater from the upper side toward the lower side in the vertical direction, so that a third slot-side inclined surface that is inclined toward the sealing member side from the upper side toward the lower side in the vertical direction is formed, and the third gate-side pressing member comes into contact with the third slot-side inclined surface, so that the third gate-side pressing member moves the gate main body toward the sealing member side. According to this configuration, if the gate main body is accommodated in the slot from the upper side toward the lower side in the vertical direction, the gate main body moves toward the sealing member side along the first gate-side inclined surface, the second slot-side inclined surface, and the third slot-side inclined surface. Consequently, the gate main body can be appropriately moved toward the sealing member side in the vertical direction by the first pressing clamp, the second pressing clamp, and the third pressing clamp. Advantageously, in the pit gate, the first gate-side inclined surface, the second slot-side inclined surface, and the third slot-side inclined surface have the same inclination angle with respect to the horizontal plane. According to this configuration, by using the same inclination angle of the first gate-side inclined surface, the second slot-side inclined surface, and the third slot-side inclined surface, the amount of movement of the gate main body toward the sealing member side with respect to the amount of movement of the gate main body in the vertical direction can be made equal to the amount of movement of the first pressing clamp, the second pressing clamp, and the third pressing clamp. Consequently, the pressing force of the gate main body applied to the slot side can be made uniform in the vertical direction of the gate main body. Advantageously, in the pit gate, the thickness direction of the gate main body is a direction in which a surface on which the sealing member is provided faces a surface opposite side on which the sealing member is provided, and the second gate-side pressing member is provided closer to the other side on which the sealing member is provided with respect to the center in the thickness direction of the gate main body. According to this configuration, because the second gate-side pressing member can be disposed closer to the second slot-side pressing member side, it is possible to appropriately ensure the amount of movement of the second gate-side pressing member toward the sealing member side. Advantageously, in the pit gate, the second slot-side pressing member and the third slot-side pressing member are provided in the slot that faces a surface opposite from a surface on which the sealing member of the gate main body is provided and are provided in the slot that faces the surface on which the sealing member of the gate main body is provided. According to this configuration, even if the position of the gate main body with respect to the slot is inverted by 180° such that the surface on which the sealing member is provided is replaced with a surface opposite from the surface on which the sealing member is provided, the gate main body can be moved toward the sealing member side by the first pressing clamp, the second pressing clamp, and the third pressing clamp. Consequently, the position of the gate main body can be replaced. Advantageously, in the pit gate, a plurality of the second pressing clamps is provided at a predetermined distance in the vertical direction of the gate main body, the second gate-side pressing member on the upper side in the vertical direction is formed such that the protruding length from the gate main body is greater than that of the second gate-side pressing member on the lower side in the vertical direction, and the second slot-side pressing member on the upper side in the vertical direction is disposed on the outer side in the horizontal direction with respect to the gate main body than the second slot-side pressing member on the lower side in the vertical direction. According to this configuration, even if a plurality of the second pressing clamps is provided in the vertical direction, it is possible to avoid physical interference between the second pressing clamps. Advantageously, in the pit gate, the gate main body includes a waveform member that has a wave shape and in which peak portions and valley portions are alternately formed from the upper side toward the lower side in the vertical direction, and the waveform member is formed such that the pitch between the adjacent peak portions in the vertical direction is narrower toward the lower side in the vertical direction. According to this configuration, because water pressure on the lower side in the vertical direction is higher than that on the upper side, by narrowing the pitch on the lower side in the vertical direction, the gate main body has a structure that can appropriately endure water pressure. According to another aspect of the present invention, a pit equipment comprising: a first pit; a second pit; a channel that connects the first pit and the second pit; a slot provided in the channel; and any one of the above pit gate accommodated in the slot. According to this configuration, the channel can be partitioned in a watertight manner by using the pit gate with a simple structure. Consequently, between the first pit and the second pit, even if service water is drained from one of the pits, the leakage of service water from the other pit can be suppressed. According to still another aspect of the present invention, a nuclear power facility is provided with the above pit equipment. According to this configuration, between the first pit and the second pit, even if service water is drained from one of the pits, in the other pit that is filled with the service water, fuel used in the nuclear power facility can be appropriately treated. According to still another aspect of the present invention, an installation method for installing a pit gate in the slot in the pit equipment above, comprising: installing, in a state in which the first pit, the second pit, and the channel are filled with the service water, by facing a surface on which the sealing member is provided, the pit gate in the slot on the first pit side or the second pit side from which the service water is supposed to be drained. According to this configuration, by setting the position of the pit gate with respect to the slot to the position in accordance with the first pit or the second pit from which the service water is drained and by accommodating the pit gate in the slot, the channel can be easily partitioned. Advantageously, in the installation method, further comprising: forming the first pit and the second pit by being depressed from a floor surface; fixing the pit gate to the floor surface via a spacer; and adjusting the height of the spacer in accordance with the protrusion state of the sealing member toward the slot side. According to this configuration, if the protruding length of the sealing member toward the slot side is small, by reducing the height of the spacer, the amount of movement of the pit gate with respect to the slot in the height direction can be increased, whereby the amount of movement toward the sealing member side can be increased. Consequently, by adjusting the height of the spacer, the contact property to the slot can be adjusted in accordance with the degree of degradation of the sealing member. Preferred embodiment according to the present invention will be described in detail below with reference to the accompanying drawings. The present invention is not limited to the embodiment. Furthermore, for the components described in the embodiment below, components that can be easily substituted by those skilled in the art or components that are substantially the same are included. Furthermore, the components described below may be appropriately used in combination and, furthermore, if several embodiments are present, the embodiments can be used in combination. FIG. 1 is an external perspective view illustrating pit equipment provided in a nuclear power facility according to an embodiment. A nuclear power facility 1 provided with pit equipment 10 according to an embodiment is a facility that stores therein fuel or that replaces fuel and is, for example, a nuclear power plant, a reprocessing facility, or the like. The pit equipment 10 is provided so as to be dipped below a floor surface 5 and is filled with service water. This service water functions as a coolant that cools fuel and also functions as a moderator that decelerates a neutron generated from the fuel. For example, water is used as the service water. In the pit equipment 10, fuel is dipped in the filled service water and, in this state, the fuel is treated. As illustrated in FIG. 1, The pit equipment 10 includes a first pit 11, a second pit 12, a channel (also called a canal) 13, a slot 14, and a pit gate 15. The first pit 11 is formed as a hollow cuboid and one end of the channel 13 is connected to one surface of the first pit 11. The volume of the first pit 11 is greater than that of the second pit 12. The first pit 11 is covered by a lining material having a sealing property such that inside the first pit 11 becomes a watertight state. Similarly to the first pit 11, the second pit 12 is formed as a hollow and the other end of the channel 13 is connected to one surface of the second pit 12. The volume of the second pit 12 is smaller than that of the first pit 11. Similarly to the first pit 11, the second pit 12 is also covered by a lining material having a sealing property such that inside the second pit 12 becomes a watertight state. The shapes of the first pit 11 and the second pit 12 are not limited to the shapes described above and any shape may also be used. For the channel 13, one end of the channel 13 is connected to the first pit 11 and the other end of the channel 13 is connected to the second pit 12. The extending direction of the channel 13, i.e., the direction in which the first pit 11 and the second pit 12 face each other is defined to be the length direction; the vertical direction (the top-to-bottom direction in FIG. 1) is defined to be the height direction; and the direction orthogonal to the length direction and the height direction is defined to be the width direction. The size of the channel 13 is large enough for fuel to move between the first pit 11 and the second pit 12. The channel 13 is formed by a bottom surface 13a, which is formed on the lower side in the height direction, and two side surfaces 13b, which are formed on both sides of the bottom surface 13a in the width direction. Because the channel 13 communicates the first pit 11 and the second pit 12, the service water filled in the first pit 11 and the second pit 12 freely flows; therefore, the water level of the service water filled in the first pit 11 is the same as that filled in the second pit 12. The slot 14 is provided in the channel 13 and has space that can accommodate therein the pit gate 15. The slot 14 is formed so as to be slightly larger than the channel 13 in a cross section perpendicular to the length direction. Namely, the slot 14 has a bottom surface 14a, which is formed by being depressed from the bottom surface 13a of the channel 13 (see FIG. 2), and two side surfaces 14b (see FIG. 2), which is formed on both sides of the bottom surface 14a in the width direction and formed by being depressed from the two side surfaces 13b of the channel 13. Furthermore, because the slot 14 is formed by being depressed from the channel 13, two U-shaped side surfaces are formed on both sides of the bottom surface 13a in the length direction and these U-shaped side surfaces act as sealing surfaces 14c (see FIG. 2) that are brought into close contact with the pit gate 15, which will be described later. Namely, one of the two sealing surfaces 14c corresponds to the surface of the slot 14 on the first pit 11 side and the other one of the sealing surfaces 14c corresponds to the surface of the slot 14 on the second pit 12 side. Furthermore, each of the two sealing surfaces 14c is formed on the flat surface. In the following, the pit gate 15 will be described with reference to FIGS. 2 to 10. FIG. 2 is a front view of a pit gate according to the embodiment and FIG. 3 is a side view of the pit gate according to the embodiment. FIG. 4 is a sectional view of a sealing member. FIG. 5 is a front view of an upper pressing clamp and FIG. 6 is a side view of the upper pressing clamp. FIG. 7 is a front view of an intermediate pressing clamp and FIG. 8 is a side view of the intermediate pressing clamp. FIG. 9 is a front view of a lower pressing clamp and FIG. 10 is a side view of the lower pressing clamp. The pit gate 15 is accommodated in the slot 14 and partitions the channel 13 in a watertight manner by water pressure applied from one of the first pit 11 and the second pit 12 generated due to water in one of the first pit 11 and the second pit 12 being drained. Here, for the pit gate 15, the length direction of the channel 13 corresponds to the thickness direction, the width direction of the channel 13 corresponds to the width direction, and the height direction of the channel 13 corresponds to the longitudinal direction. As illustrated in FIGS. 2 and 3, the pit gate 15 includes a gate main body 21, a sealing member 22, an upper pressing clamp (a first pressing clamp) 23, two intermediate pressing clamps (second pressing clamps) 24, and a lower pressing clamp (a third pressing clamp) 25. At this point, the upper pressing clamp 23, the two intermediate pressing clamps 24, and the lower pressing clamp 25 are provided at a predetermined distance in the longitudinal direction. The gate main body 21 is formed so as to have the length in the longitudinal direction and is accommodated in the slot 14 such that the longitudinal direction of the gate main body 21 corresponds to the height direction. The gate main body 21 constructed by including a gate frame 31 and a waveform member 32 that is provided inside the gate frame 31. The gate frame 31 is formed on four sides, i.e., on the upper side of the longitudinal direction, on the lower side of the longitudinal direction, on the left side of the width direction, and the right side of the width direction, so as to surround the circumference of the waveform member 32. In the state in which the gate frame 31 is accommodated in the slot 14, the three sides, i.e., the lower side of the longitudinal direction, the left side of the width direction, and the right side of the width direction, are formed opposite to the sealing surface 14c of the slot 14. The upper portion of the gate frame 31 is fixed to the floor surface 5 of the pit equipment 10 via a spacer 35. Furthermore, gate-side pressing members 41, 44, and 48 of the upper pressing clamp 23, the intermediate pressing clamp 24, and the lower pressing clamp 25, respectively, which will be described later, are attached to the gate frame 31. The waveform member 32 is a wave-shaped member in which peak portions and valley portions are alternately formed from the upper side toward the lower side in the longitudinal direction. The waveform member 32 is integrally fixed to the gate frame 31. The peak portions and the valley portions of the waveform member 32 are formed so as to extend in the width direction, the pitch between the adjacent peak portions in the height direction, in other words, the pitch between the adjacent valley portions in the longitudinal direction, is formed to be narrower from the upper side toward the lower side in the longitudinal direction. This is because, for the water pressure applied to the waveform member 32 in the pit gate 15, the lower side of the waveform member 32 in the longitudinal direction is greater than that applied to the upper side of the waveform member 32. The sealing member 22 is provided on the gate frame 31 at the position opposite to the sealing surface 14c of the slot 14. Namely, the sealing member 22 is provided on one of the surfaces of the gate main body 21 (the gate frame 31) in the thickness direction. The sealing member 22 is provided along the gate frame 31 and is continuously disposed, in a U-shaped manner, on the lower side in the longitudinal direction and on the left and right sides in the width direction. Accordingly, the sealing member 22 can be brought into close contact with the U-shaped sealing surface 14c of the slot 14 along with the shape of the sealing surface 14c. As illustrated in FIG. 4, the sealing member 22 is solid in which hollow space is not formed inside thereof and is formed in a substantially triangular shape whose cross section protrudes toward the sealing surface 14c side. The sealing member 22 is made by using, for example, silicone rubber. As illustrated in FIGS. 5 and 6, the upper pressing clamp 23 constructed by including a pair of upper gate-side pressing members (first gate-side pressing members) 41 that are provided on the other side of the surface of the gate main body 21 (the gate frame 31) in the thickness direction, i.e., on the surface opposite from the sealing member 22. The pair of the upper gate-side pressing members 41 is provided on both sides of the gate main body 21 in the width direction. Each of the upper gate-side pressing members 41 is formed in a wedge shape whose thickness becomes thinner from the upper side toward the lower side in the longitudinal direction. One of the surfaces of the upper gate-side pressing member 41 in the thickness direction is an attachment surface that is attached to the gate main body 21 and, on the other surface of the attachment surface, a first gate-side inclined surface 42 is formed. The upper gate-side inclined surface (the first gate-side inclined surface) 42 is inclined toward the sealing member 22 side from the upper side toward the lower side in the longitudinal direction. When the pit gate 15 is inserted into the slot 14, the upper gate-side inclined surface 42 comes into contact with the slot 14. Accordingly, if the pit gate 15 is inserted into the slot 14, the upper gate-side inclined surface 42 comes into contact with the slot 14, thereby the upper pressing clamp 23 moves the pit gate 15 toward the sealing member 22 side. As illustrated in FIGS. 7 and 8, the intermediate pressing clamp 24 is provided with a pair of intermediate gate-side pressing members (second gate-side pressing members) 44 that protrude from both sides of the gate main body 21 (the gate frame 31) in the width direction and a pair of intermediate slot-side pressing members (second slot-side pressing members) 45 that are in contact with a pair of the intermediate gate-side pressing members 44. Furthermore, two sets of the pair of the intermediate slot-side pressing members 45 are provided in accordance with the opposing two sealing surfaces 14c. The pair of the intermediate gate-side pressing members 44 is formed in a rod shape with the axial direction thereof corresponding to the horizontal direction. Each of the intermediate gate-side pressing members 44 is formed in the shape of a column or a cylinder and is fixed to the gate frame 31 that is located on the side opposite to the sealing member 22 with the waveform member 32 in the gate main body 21 located therebetween. Furthermore, each of the intermediate gate-side pressing members 44 is disposed such that the axial center thereof is located closer to the other side of the sealing member 22 from the center of the gate frame 31 in the thickness direction. The pair of the intermediate slot-side pressing members 45 are attached to the sealing surfaces 14c of the slot 14 and are disposed on both sides of the pit gate 15 accommodated in the slot 14 in the width direction. Each of the intermediate slot-side pressing members 45 is formed in a wedge shape whose thickness becomes greater from the upper side toward the lower side in the longitudinal direction. Each of the intermediate slot-side pressing members 45 is attached to the sealing surface 14c of the slot 14 and intermediate slot-side inclined surfaces (second slot-side inclined surfaces) 46 are formed on the surface opposite from the surface of the sealing surface 14c. The intermediate slot-side inclined surface 46 is inclined toward the sealing member 22 side (the inner side of the slot 14) from the upper side toward the lower side in the longitudinal direction. When the pit gate 15 is inserted into the slot 14, the intermediate slot-side inclined surface 46 comes into contact with the intermediate gate-side pressing member 44 of the pit gate 15. Furthermore, a set of the pair of the intermediate slot-side pressing members 45 and the other set of the pair of the intermediate slot-side pressing members 45 are provided at the position facing each other in the thickness direction (in the length direction of the slot 14) of the pit gate 15. Namely, the set of the pair of the intermediate slot-side pressing members 45 is provided on the sealing surface 14c of the slot 14 on the first pit 11 side and the other set of the pair of the intermediate slot-side pressing members 45 is provided on the sealing surface 14c of the slot 14 on the second pit 12 side. Accordingly, when the pit gate 15 is inserted into the slot 14, the pair of the intermediate gate-side pressing members 44 comes into contact with the set of the pair of (the intermediate slot-side inclined surfaces 46) the intermediate slot-side pressing members 45, whereby the intermediate pressing clamp 24 moves the pit gate 15 toward the sealing member 22 side. Here, the two intermediate pressing clamps 24 are disposed at a predetermined distance in the longitudinal direction of the gate main body 21. For the two intermediate pressing clamps 24, the shape of the intermediate gate-side pressing members 44 and the placement of the intermediate slot-side pressing member 45 differ so as not to physically interfere with each other when the pit gate 15 is inserted into the slot 14. Specifically, the pair of the intermediate gate-side pressing members 44 of the intermediate pressing clamps 24 on the upper side in the longitudinal direction is formed such that the length in the axial direction is greater than that of the pair of the intermediate gate-side pressing members 44 of the intermediate pressing clamps 24 on the lower side in the longitudinal direction. Namely, the pair of the intermediate gate-side pressing members 44 on the upper side is formed such that the length thereof in the width direction of the gate main body 21 is great, whereas the pair of the intermediate gate-side pressing members 44 on the lower side is formed such that the length thereof in the width direction of the gate main body 21 is small. Furthermore, the pair of the intermediate slot-side pressing members 45 of the intermediate pressing clamps 24 on the upper side in the longitudinal direction is disposed on the outer side in the width direction of the gate main body 21 than the pair of the intermediate slot-side pressing members 45 of the intermediate pressing clamps 24 on the lower side in the longitudinal direction. Namely, for the pair of the intermediate slot-side pressing members 45 on the upper side, the length thereof in the width direction is great, whereas, for the pair of the intermediate slot-side pressing members 45 on the lower side, the length thereof in the width direction is small. Accordingly, when the pit gate 15 is inserted into the slot 14, the pair of the intermediate gate-side pressing members 44 on the lower side avoids the pair of the intermediate slot-side pressing members 45 on the upper side. Thereafter, when the pit gate 15 is further inserted into the slot 14, the pair of the intermediate gate-side pressing members 44 on the lower side comes into contact with the pair of the intermediate slot-side pressing members 45 on the lower side and the pair of the intermediate gate-side pressing members 44 on the upper side comes into contact with the pair of the intermediate slot-side pressing members 45 on the upper side. As illustrated in FIGS. 9 and 10, the lower pressing clamp 25 is provided with lower gate-side pressing member (a third gate-side pressing member) 48 that is provided so as to protrude from the lower side of the gate main body 21 (the gate frame 31) in the longitudinal direction and a pair of lower slot-side pressing members (third slot-side pressing members) 49 that is in contact with the lower gate-side pressing member 48. Furthermore, two sets of the pair of the lower slot-side pressing members 49 are provided in accordance with the opposing two sealing surfaces 14c. The lower gate-side pressing member 48 is provided so as to extend in the width direction of the gate main body 21 and has a curved surface that is convex towards the lower side. The lower gate-side pressing member 48 is disposed closer to the other side of the sealing member 22 with respect to the center in the thickness direction of the gate frame 31. The pair of the lower slot-side pressing members 49 is provided at the corner that is formed by the bottom surface 14a and the sealing surface 14c of the slot 14 and is disposed at a predetermined distance in the width direction of the slot 14. Furthermore, the pair of the lower slot-side pressing members 49 is provided, at the position facing each other, on both sides in the width direction of the lower gate-side pressing member 48. Each of the lower slot-side pressing members 49 is formed in a wedge shape whose thickness becomes greater from the upper side toward the lower side in the longitudinal direction. Each of the lower slot-side pressing members 49 are attached to the bottom surface 14a and the sealing surface 14c of the slot 14 and a lower slot-side inclined surface (a third slot-side inclined surface) 50 is formed on the surface opposite from the sealing surface 14c. The lower slot-side inclined surface 50 is inclined on the sealing member 22 side (the inner side of the slot 14) from the upper side toward the lower side in the longitudinal direction. When the pit gate 15 is inserted into the slot 14, the lower slot-side inclined surface 50 comes into contact with the lower gate-side pressing member 48 of the pit gate 15. Furthermore, a set of the pair of the lower slot-side pressing members 49 and the other set of the pair of the lower slot-side pressing members 49 are provided at the position opposing each other in the thickness direction (in the length direction of the slot 14) of the pit gate 15. Namely, the set of the pair of the lower slot-side pressing members 49 is provided on the sealing surface 14c of the slot 14 on the first pit 11 side and the other set of the pair of the lower slot-side pressing members 49 is provided on the sealing surface 14c of the slot 14 on the second pit 12 side. Accordingly, when the pit gate 15 is inserted into the slot 14, the lower gate-side pressing member 48 comes into contact with the set of the pair of the (lower slot-side inclined surfaces 50) of the lower slot-side pressing members 49, whereby the lower pressing clamp 25 moves the pit gate 15 toward the sealing member 22 side. Here, the intermediate pressing clamp 24 includes two sets of the pair of the intermediate slot-side pressing members 45 and, furthermore, the lower pressing clamp 25 includes two sets of the pair of the lower slot-side pressing members 49. This is because the pit gate 15 is replaced so that its position differs by 180 degrees between a case in which the pit gate 15 is brought into close contact with the sealing surface 14c of the slot 14 on the first pit 11 side and a case in which the pit gate 15 is brought into close contact with the sealing surface 14c of the slot 14 on the second pit 12 side. Namely, when the pit gate 15 is brought into close contact with the sealing surface 14c of the slot 14 on the first pit 11 side, the pair of the intermediate slot-side pressing members 45 on the second pit 12 side is used in the intermediate pressing clamp 24 and the pair of the lower slot-side pressing members 49 on the second pit 12 side is used in the lower pressing clamp 25. In contrast, when the pit gate 15 is brought into close contact with the sealing surface 14c of the slot 14 on the second pit 12 side, the pair of the intermediate slot-side pressing members 45 on the first pit 11 side is used in the intermediate pressing clamp 24 and the pair of the lower slot-side pressing members 49 on the first pit 11 side is used in the lower pressing clamp 25. For the upper pressing clamp 23, the two intermediate pressing clamp 24, and the lower pressing clamp 25 formed in this way, the inclination angles of the upper gate-side inclined surfaces 42, the intermediate slot-side inclined surface 46, and the lower slot-side inclined surfaces 50 are the same. Here, the inclination angle is an inclination angle with respect to the horizontal plane orthogonal to the height direction. If the inclination angles of the upper gate-side inclined surfaces 42, the intermediate slot-side inclined surface 46, and the lower slot-side inclined surface 50 are made the same, the amount of movement of the pit gate 15 that moves toward the sealing member 22 side due to the upper pressing clamps 23, the two intermediate pressing clamps 24, and the lower pressing clamp 25 becomes the same. Namely, the amount of movement of the pit gate 15 toward the sealing member 22 side in accordance with the amount of movement in the height direction becomes equal in the upper pressing clamps 23, the two intermediate pressing clamps 24, and the lower pressing clamp 25. Furthermore, the upper pressing clamps 23, the two intermediate pressing clamps 24, and the lower pressing clamp 25 are disposed at an unequal distance in the longitudinal direction of the pit gate 15. This is because the pitch intervals of the peak portions of the waveform member 32 in the gate main body 21 are unequal. In the following, an installation method of the pit gate 15 that is accommodated in the slot 14 will be described with reference to FIG. 11. FIG. 11 is a diagram related to an installation method of the pit gate. As illustrated in FIG. 11, before the installation of the pit gate 15, the first pit 11 and the second pit 12 in the pit equipment 10 are filled with service water (Step S100). At this time, because the pit gate 15 is not installed, the water level of the first pit 11 is the same as that of the second pit 12. In the state at Step S100, if the service water filled in the second pit 12 in the pit equipment 10 is drained, the pit gate 15 is accommodated in the slot 14 such that the surface on which the sealing member 22 is provided faces toward the second pit 12 side. As a result, the pit gate 15 moves toward the sealing member 22 side due to the upper pressing clamp 23, the two intermediate pressing clamps 24, and the lower pressing clamp 25, thus moving toward the second pit 12 side. Consequently, the sealing member 22 of the pit gate 15 comes into contact with the sealing surface 14c of the slot 14 on the second pit 12 side (Step S101). Thereafter, the pit gate 15 is fixed to the floor surface 5 of the pit equipment 10 via the spacer 35. After the pit gate 15 has been fixed, the intermediate gate-side pressing member 44 of the intermediate pressing clamp 24 is located at an intermediate position with respect to the intermediate slot-side inclined surface 46 of the intermediate slot-side pressing member 45, i.e., at a position between an edge portion on the upper side and the lower side of the intermediate slot-side inclined surface 46. Consequently, the intermediate gate-side pressing member 44 has space for moving, with respect to the intermediate slot-side inclined surface 46, toward the lower side in the height direction. Similarly, the lower gate-side pressing member 48 of the lower pressing clamp 25 is located at an intermediate position with respect to the lower slot-side inclined surface 50 of the lower slot-side pressing member 49, i.e., at a position between an edge portion on the upper side and the lower side of the lower slot-side inclined surface 50. Consequently, the lower gate-side pressing member 48 has space for moving, with respect to the lower slot-side inclined surface 50, toward the lower side in the height direction. In the state at Step S101, by draining the service water filled in the second pit 12, water pressure from the service water filled in the first pit 11 is applied to the pit gate 15, whereby the pit gate 15 is brought into close contact with the sealing surface 14c of the slot 14 (Step S102). In the above, a description has been given of a case in which water is drained from the second pit 12; however, if water is drained from the first pit 11, the pit gate 15 is accommodated in the slot 14 such that the surface on which the sealing member 22 is provided faces toward the first pit 11 side. Furthermore, the pit gate 15 is fixed to the floor surface 5 via the spacer 35; however, the height of the spacer 35 may also be adjusted in accordance with the protrusion state of the sealing member 22 toward the slot 14 side. Namely, if the length of the protrusion of the sealing member 22 on the slot 14 side is small, the amount of insertion (amount of movement) of the pit gate 15 in the height direction with respect to the slot 14 is made to increase by making the height of the spacer 35 be small and, consequently, the amount of movement on the sealing member 22 side can be increased. This is because the intermediate gate-side pressing member 44 and the lower gate-side pressing member 48 leave the space for moving on the lower side in the height direction. In this way, by adjusting the height of the spacer 35, it is possible to adjust the contact property of the slot 14 toward the sealing surface 14c in accordance with the degree of degradation of the sealing member 22. As described above, according to the embodiment, if the pit gate 15 is accommodated in the slot 14 from the upper side toward the lower side in the vertical direction, the pit gate 15 moves toward the sealing member 22 side along the upper gate-side inclined surface 42, the intermediate slot-side inclined surface 46, and the lower slot-side inclined surface 50. Consequently, by using the upper pressing clamp 23, the intermediate pressing clamps 24, and the lower pressing clamp 25, the pit gate 15 can be appropriately moved toward the sealing member 22 side in the vertical direction. Thus, by using the upper pressing clamp 23, the intermediate pressing clamps 24, and the lower pressing clamp 25, because the pit gate 15 with a simple structure can be appropriately moved toward the sealing member 22 side, the sealing member 22 can be appropriately brought into close contact with the slot 14. Consequently, because it is possible to seal between the gate main body 21 and the slot 14 by using the sealing member 22 in a watertight manner, the leakage of service water from the first pit 11 and the second pit 12 can be suppressed. Furthermore, according to the embodiment, by using the same inclination angles for the upper gate-side inclined surfaces 42, the intermediate slot-side inclined surfaces 46, and the lower slot-side inclined surfaces 50, the amount of movement of the pit gate 15 toward the sealing member 22 side with respect to the amount of movement of the pit gate 15 in the vertical direction can be made equal to the amount of movement of the upper pressing clamps 23, the intermediate pressing clamps 24, and the lower pressing clamp 25. Consequently, the pressing force of the pit gate 15 to the slot 14 side can be made uniform in the vertical direction of the pit gate 15. Furthermore, according to the embodiment, by forming the sealing member 22 protruding toward the slot 14 side in cross section, the shape of the sealing member 22 can be easily brought into close contact with the slot 14. Furthermore, according to the embodiment, by disposing the intermediate gate-side pressing member 44 at the opposite side from the sealing member 22 with respect to the center in the thickness direction of the gate main body 21, the intermediate gate-side pressing member 44 can be disposed closer to the intermediate slot-side pressing member 45 side; therefore, it is possible to appropriately ensure the amount of movement of the intermediate gate-side pressing member 44 toward the sealing member 22 side. Furthermore, according to the embodiment, by providing two sets of the pair of the intermediate slot-side pressing members 45 and two sets of the pair of the lower slot-side pressing members 49, the position of the pit gate 15 can be replaced; therefore, it is possible to drain the water in the first pit 11 and the second pit 12. Furthermore, according to the embodiment, even if a plurality of the intermediate pressing clamps 24 is provided in the vertical direction, the lengths of the intermediate gate-side pressing members 44 in the axial direction are made to differ between the upper side and the lower side and the placements of the intermediate slot-side pressing members 45 in the width direction are made to differ between the upper side and the lower side, whereby it is possible to avoid physical interference between the intermediate pressing clamps 24. Furthermore, according to the embodiment, by reducing the pitch between the peak portions of the waveform member 32 toward the lower side, the pit gate 15 has a structure that can appropriately endure water pressure. Furthermore, according to the embodiment, by using the pit gate 15 that has a simple structure, the channel 13 can be partitioned in a watertight manner. Consequently, even if service water in one of the first pit 11 and the second pit 12 is drained, it is possible to suppress the service water from leaking from the other one of the pits that is filled with the service water. Furthermore, in the other one of the pits that is filled with the service water, fuel used in the nuclear power facility can be appropriately treated. Furthermore, according to the embodiment, by setting the position of the pit gate 15 with respect to the slot 14 to the position in accordance with the first pit 11 or the second pit 12 from which the service water is drained and by accommodating the pit gate 15 in the slot 14, the channel 13 can be easily partitioned. Furthermore, in the embodiment, the upper pressing clamp 23, the two intermediate pressing clamps 24, and the lower pressing clamp 25 are used; however, the configuration is not particularly limited thereto and any one of the pressing clamps 23, 24, and 25 may be used. Namely, one of the upper pressing clamp 23, the intermediate pressing clamps 24, and the lower pressing clamp 25 may also be used as a single unit; a plurality of the upper pressing clamp 23, the intermediate pressing clamps 24, and the lower pressing clamp 25 may also be used; or the upper pressing clamp 23, the intermediate pressing clamps 24, and the lower pressing clamp 25 may also be appropriately used in combination. Furthermore, in the embodiment, the cross-sectional shape of the sealing member 22 is substantially triangular; however, the shape is not particularly limited thereto. Any shape may be used as long as the sealing member 22 can be brought into close contact with the sealing surface 14c. 1 nuclear power facility 5 floor surface 10 pit equipment 11 the first pit 12 the second pit 13 channel 14 slot 15 pit gate 21 gate main body 22 sealing member 23 upper pressing clamp 24 intermediate pressing clamp 25 lower pressing clamp 31 gate frame 32 waveform member 35 spacer 41 upper gate-side pressing member 42 upper gate-side inclined surface 44 intermediate gate-side pressing member 45 intermediate slot-side pressing member 46 intermediate slot-side inclined surface 48 lower gate-side pressing member 49 lower slot-side pressing member 50 lower slot-side inclined surface
060569298	abstract	Iodine-125 is produced by neutron irradiation of .sup.124 Xe gas to form .sup.125 Xe and permitting decay of .sup.125 Xe to form .sup.125 I. Irradiation of the xenon-124 is effected in a first chamber within an enclosure and decay is effected in a second chamber within the enclosure and free from neutron flux. The apparatus is submersible in a nuclear reactor pool so as to absorb any radiation escaping the apparatus during the process. Xenon can be caused to move between the chambers remotely, underwater. The second chamber is removable from said enclosure and is transported to a suitable location to recover the .sup.125 I from its interior. Such recovery is effected by admitting an aqueous wash solution into the second chamber, whereupon it is heated, causing water from the wash solution to reflux and cleanse the interior surfaces of the second chamber, thus creating an aqueous solution of .sup.125 I, which then is caused to drain into a suitable container.
050135201	abstract	An apparatus for the insertion of mutually parallel, elongated fuel rods into an elongated can having a rectangular cross section, a longitudinal direction and a lateral transverse slit formed therein, includes a holder for holding a can. A fuel rod positioning arm has an insertion end for insertion through the slit in the can in an insertion direction at right angles to the longitudinal direction of the can. A support structure is attached to the insertion end of the arm for supporting fuel rods. The support structure has a pivot axis at right angles to the insertion direction of the arm and to the longitudinal direction of the can about which the support structure is pivotable back and forth within a given pivot angle. The support structure has a jacket surface with two fuel rod support surfaces being curved outwardly about the pivot axis and offset alongside one another in the direction of the pivot axis. One of the support surfaces merges from a first segment with a relatively shorter radial spacing from the pivot axis than the other of the support surfaces, into a second segment with a relatively greater radial spacing from the pivot axis than the other of the support surfaces. The radial spacings of the two support surfaces from the pivot axis increases in infinite graduations within the given pivot angle, as seen in opposite directions.
	abstract	Nuclear fuel structures and methods for fabricating are disclosed herein. The nuclear fuel structure includes a plurality of fibers arranged in the structure and a multilayer fuel region within at least one fiber of the plurality of fibers. The multilayer fuel region includes an inner layer region made of a nuclear fuel material, and an outer layer region encasing the nuclear fuel material. A plurality of discrete multilayer fuel regions may be formed over a core region along the at least one fiber, the plurality of discrete multilayer fuel regions having a respective inner layer region of nuclear fuel material and a respective outer layer region encasing the nuclear fuel material. The plurality of fibers may be wrapped around an inner rod or tube structure or inside an outer tube structure of the nuclear fuel structure, providing both structural support and the nuclear fuel material of the nuclear fuel structure.
056384149	claims	1. A method for detecting failure of a nuclear reactor fuel comprising the steps of: (a) identifying one or more failed fuel assemblies; and (b) identifying one or more failed fuel elements in each identified failed fuel assembly, including the substeps of (b1) detecting gamma radiation emitted by the identified fuel assembly with a gamma radiation detector and acquiring detector data, while relatively rotating and translating the identified fuel assembly about the gamma radiation detector, (b2) constructing a tomographic image of the radiation intensity distribution over a cross section of the identified fuel assembly based upon the detector data, and (b3) determining said one or more failed fuel elements by variations in the radiation intensity in the tomographic image. 2. A method for detecting failure in fuel for a nuclear reactor according to claim 1, wherein the radiation detector is placed opposite to a gas plenum of the fuel element of the fuel assembly, and radiation emitted from fission product nuclides in the gas plenum is detected.
	claims	1. A method for reviewing defects of patterns in a large number of chips formed on each of semiconductor wafers, the method comprising:a cell comparison step including ofa first acquisition step of acquiring an electron beam defect image of a low magnification with moving a stage on which the wafer is mounted in accordance with position coordinate of a review defect on the wafer obtained from an inspection apparatus, and then imaging the review defect at the low magnification by using an electron beam optical system,a step of selecting a review sequence of either a cell comparison scheme or a die comparison scheme on the basis of a defect detection success ratio or defect detection success map due to at least the cell comparison scheme for each wafer or for each chip formed on the wafer,a step of, if the cell comparison scheme is selected in the sequence selection step, judging whether detection of the review defect is possible by executing the selected cell comparison scheme based on the electron beam defect image acquired from the review defect at the low magnification in the first acquisition step, anda first calculation step of, if judgment result in the detection possibility judgment step indicates that the detection of the review defect is possible, calculating position coordinate of the detected review defect in a coordinate system of a defect-reviewing apparatus;a die comparison step including ofa second acquisition step of, if the judgment result in the detection possibility judgment step indicates that the detection of the review defect is impossible, or if the die comparison scheme is selected in the sequence selection step, acquiring an electron beam reference image at a low magnification for a normal part to perform the selected die comparison scheme by using the electron beam optical system with moving the stage, anda second calculation step of detecting the review defect by performing the selected die comparison scheme between the electron beam defect image of the review defect at the low magnification acquired in the first acquisition step and the electron beam reference image of the low magnification acquired in the second acquisition step, and calculating the position coordinate of the detected review defect in the coordinate system of the defect-reviewing apparatus; anda defect image acquisition step of acquiring electron beam defect images of a high magnification by imaging the review defects at the high magnification by using the electron beam optical system in accordance with the position coordinates of the review defects calculated in the coordinate system of the defect-reviewing apparatus in the first and second calculation steps. 2. The method for reviewing defects of patterns according to claim 1, wherein, in the selection step, the selection of either the cell comparison scheme or the die comparison scheme is performed for each wafer or for each defect that is to be reviewed. 3. The method for reviewing defects of patterns according to claim 1, wherein the cell comparison uses a previously provided electron beam reference image of a low magnification or an electron beam reference image made at a low magnification based on the electron beam defect image imaged the review defect at the low magnification. 4. A method for reviewing defects of patterns in a large number of chips formed on each of semiconductor wafers, the method comprising:a cell comparison step including ofa first acquisition step of acquiring an electron beam defect image of a low magnification by moving a stage on which the wafer is mounted in accordance with position coordinate of a review defect on the wafer obtained from an inspection apparatus, and then imaging the review defect at the low magnification by using an electron beam optical system,a step of previously providing a defect detection success ratio or defect detection success map due to at least the cell comparison scheme for each wafer or for each chip formed on the wafer,a step of selecting a review sequence of either the cell comparison scheme or a die comparison scheme on the basis of the defect detection success ratio or defect detection success map due to at least the cell comparison scheme for each wafer or for each chip formed on the wafer previously provided in the provision step,a step of, if the cell comparison scheme is selected in the sequence selection step, judging whether detection of the review defect is possible by executing the cell comparison scheme based on the electron beam defect image acquired from the review defect at the low magnification in the acquisition step, anda first calculation step of, if judgment result in the detection possibility judgment step indicates that the detection of the review defect is possible, calculating position coordinate of the detected review defect in a coordinate system of a defect-reviewing apparatus;a die comparison step including ofa second acquisition step of, if the judgment result in the detection possibility judgment step indicates that the detection of the review defect is impossible, or if the die comparison scheme is selected in the sequence selection step, acquiring an electron beam reference image at a low magnification for a normal part to perform the die comparison scheme by using the electron beam optical system with moving the stage, anda second calculation step of detecting the review defect by performing the die comparison scheme between the electron beam defect image of the review defect at the low magnification acquired in the first acquisition step and the electron beam reference image of the low magnification acquired in the second acquisition step, and calculating the position coordinate of the detected review defect in the coordinate system of the defect-reviewing apparatus; anda defect image acquisition step of acquiring an electron beam defect images of a high magnification by imaging the review defects at the high magnification by using the electron beam optical system in accordance with the defect position coordinates calculated in the coordinate system of the defect-reviewing apparatus in the first and second calculation steps. 5. The method for reviewing defects of patterns according to claim 4, wherein, in the provision step, the defect detection success ratio or defect detection success map due to at least the cell comparison scheme for each wafer or for each chip formed on the wafer, is calculated by performing the cell comparison scheme based on an electron beam defect image of the low magnification acquired from a sample of a review defect by using the sample of the review defect present on the wafer mounted on the stage. 6. The method for reviewing defects of patterns according to claim 5, wherein, in the provision step, the calculated defect detection success ratio or defect detection success map due to at least the cell comparisons scheme is displayed on a GUI unit. 7. The method for reviewing defects of patterns according to claim 4, wherein, in the provision step, the defect detection success ratio or defect detection success map due to at least the cell comparisons scheme for each wafer or each chip, is calculated based on historical information due to the cell comparison scheme for a wafer of the same kind as that of the wafer mounted on the stage. 8. The method for reviewing defects of patterns according to claim 4, wherein, in the provision step, whether the defect detection due to the cell comparison succeeds or fails is judged based on the electron beam defect image of the low magnification, acquired at the review defect position, and the defect detection success map due to at least the cell comparison scheme for each chip is calculated by summing up the judgment result for the each chip. 9. The method for reviewing defects of patterns according to claim 8, wherein, when the calculation of the defect detection success map due to at least the cell comparison scheme for the each chip, is calculated, regions in which the defect detection due to the cell comparison scheme is possible are integrated on the basis of a distance between the review defects for which the defect detection has been performed by using the cell comparison scheme. 10. The method for reviewing defects of patterns according to claim 4, wherein, in the selection step, the selection of either the cell comparison scheme or the die comparison scheme is performed for each wafer or for each defect that is to be reviewed. 11. The method for reviewing defects of patterns according to claim 4, wherein the cell comparison scheme uses a previously provided electron beam reference image of a low magnification or an electron beam reference image of a low magnification made based on the electron beam defect image imaged the review defect at the low magnification. 12. A SEM-type defect-reviewing apparatus, comprising:a cell comparator including ofa first acquisition unit which acquires an electron beam defect image of a low magnification with moving a stage on which a wafer is mounted in accordance with position coordinate of a review defect on the wafer obtained from an inspection apparatus, and then images the review defect at the low magnification by using an electron beam optical system,a review sequence selector which selects a review sequence of either a cell comparison scheme or a die comparison scheme on the basis of a defect detection success ratio or defect detection success map due to at least the cell comparison scheme for each wafer or for each chip formed on the wafer,a detection possibility judgment unit which, if the cell comparison scheme is selected in the review sequence selector, judges whether detection of the review defect is possible by executing the selected cell comparison scheme based on the electron beam defect image acquired from the review defect at the low magnification in the first acquisition unit, anda first calculator which, if judgment result in the detection possibility judgment unit indicates that the detection of the review defect is possible, calculates position coordinate of the detected review defect in a coordinate system of a defect-reviewing apparatus;a die comparator including ofa second acquisition unit which, if the judgment result in the detection possibility judgment unit indicates that the detection of the review defect is impossible, or if the die comparison scheme is selected in the review sequence selector, acquires an electron beam reference image at a low magnification for a normal part to perform the selected die comparison scheme by using the electron beam optical system with moving the stage, anda second calculator which detects the review defect by performing the selected die comparison scheme between the electron beam defect image of the review defect at the low magnification acquired in the first acquisition unit and the electron beam reference image of the low magnification acquired in the second acquisition unit, and calculates the position coordinate of the detected review defect in the coordinate system of the defect-reviewing apparatus; anda high-magnification defect image acquisition unit which acquires electron beam defect images of a high magnification by imaging the review defects at the high magnification by using the electron beam optical system in accordance with the position coordinates of the review defects calculated in the coordinate system of the defect-reviewing apparatus in the first and second calculators. 13. The SEM-type defect-reviewing apparatus according to claim 12, further comprising a detail analyzer which calculates at least feature quantities of electron beam image by performing detailed analyses with using the electron beam defect image of the high magnification acquired from the defect image acquisition unit. 14. The SEM-type defect-reviewing apparatus according to claim 12, further comprising a provision unit which comprises so as to calculate the defect detection success ratio or defect detection success map due to at least the cell comparison scheme for each wafer or for each chip formed on the wafer by performing the cell comparison scheme based on an electron beam defect image of the low magnification acquired from a sample of a review defect by using the sample of the review defect present on the wafer mounted on the stage. 15. The SEM-type defect-reviewing apparatus according to claim 12, wherein in the selector, the selection of either the cell comparison scheme or the die comparison scheme is performed for each wafer or for each defect that is to be reviewed. 16. A SEM-type defect-reviewing apparatus, comprising:a cell comparator including ofa first acquisition unit which acquires an electron beam defect image of a low magnification with moving a stage on which a wafer is mounted in accordance with position coordinate of a review defect on the wafer obtained from an inspection apparatus, and then images the review defect at the low magnification by using an electron beam optical system,a provision unit which previously provides a defect detection success ratio or defect detection success map due to at least the cell comparison scheme for each wafer or for each chip formed on the wafer,a review sequence selector which selects a review sequence of either the cell comparison scheme or a die comparison scheme on the basis of the defect detection success ratio or defect detection success map due to at least the cell comparison scheme for each wafer or for each chip previously provided in the provision unit,a detection possibility judgment unit which, if the cell comparison scheme is selected in the review sequence selector, judges whether detection of the review defect is possible by executing the cell comparison scheme based on the electron beam defect image acquired from the review defect at the low magnification, anda first calculator which, if judgment result in the detection possibility judgment unit indicates that the detection of the review defect is possible, calculates position coordinate of the detected review defect in a coordinate system of a defect-reviewing apparatus;a die comparator including ofa second acquisition unit which, if the judgment result in the detection possibility judgment unit indicates that the detection of the review defect is impossible, or if the die comparison scheme is selected in the review sequence selector, acquires an electron beam reference image at a low magnification for a normal part to perform the die comparison scheme by using the electron beam optical system with moving the stage, anda second calculator which detects the review defect by performing the die comparison scheme between the electron beam defect image of the defect at the low magnification acquired in the first acquisition unit and the electron beam reference image of the low magnification acquired in the second acquisition unit, and calculates the position coordinate of the detected review defect in the coordinate system of the defect-reviewing apparatus; anda defect image acquisition unit which acquires an electron beam defect image of a high magnification by imaging the review defects at the high magnification by using the electron beam optical system in accordance with the defect position coordinates calculated in the coordinate system of the defect-reviewing apparatus in the first and second calculators. 17. The SEM-type defect-reviewing apparatus according to claim 16, further comprising a detail analyzer which calculates at least feature quantities of electron beam image by performing detailed analyses with using the electron beam defect image of the high magnification acquired from the defect image acquisition unit. 18. The SEM-type defect-reviewing apparatus according to claim 16, wherein the provision unit section comprises so as to calculate the defect detection success ratio or defect detection success map due to at least the cell comparison scheme for each wafer or for each chip formed on the wafer by performing the cell comparison scheme based on an electron beam defect image of the low magnification acquired from a sample of a review defect by using the sample of the review defect present on the wafer mounted on the stage. 19. The SEM-type defect-reviewing apparatus according to claim 16, wherein the provision unit comprises so as to calculate the defect detection success ratio or defect detection success map due to at least the cell comparisons scheme for each wafer or each chip, based on historical information due to the cell comparison scheme for a wafer of the same kind as that of the wafer mounted on the stage. 20. The SEM-type defect-reviewing apparatus according to claim 16, wherein the provision unit comprises so that whether the defect detection due to the cell comparison succeeds or fails is judged based on the electron beam defect image of the low magnification, acquired at the review defect position, and the defect detection success map due to at least the cell comparison scheme for each chip is calculated by summing up the judgment result for the each chip. 21. The SEM-type defect-reviewing apparatus according to claim 16, further comprising a GUI unit; wherein, after being calculated in the provision unit, the defect detection success ratio or defect detection success map due to at least the cell comparison scheme is displayed on the GUI unit.
	description	FIG. 1 shows a first embodiment of a leaf 22 of a multi-leaf collimator 23 configured in accordance with the invention. A displacement detecting element 1 formed as potentiometer comprising electrical functional elements, i.e. measuring resistance 2 or 15, voltage pick-off 4, conductor path 13 and slide contact path 16, is disposed in a region 33, 33xe2x80x2 of a leaf 22 which is not subjected to the main radiation 34 of a radiation source 45 since this region 33, 33xe2x80x2 is located in the shadow of a pre-collimator 36 which delimits the main radiation 34 corresponding to the lines 46 and 46xe2x80x2 or another linexe2x80x94depending on the setting. Another setting of the leaf 22 is shown with dashed lines in which the front edge 44 was adjusted through an adjusting motion 38. To safeguard the shielding region 33xe2x80x2, the pre-collimator 36 must also be displaced corresponding to the adjusting motion 39 (shown with dashed lines). In this embodiment, the housing 9 must be shielded in regions where no electrical functional elements are provided since the shielding material should not be weakened in areas where only the leaves 22 shield the main radiation 34. Of course, a fixed delimitation of the main radiation 36 could be provided instead of the pre-collimator 36. The displacement-detecting element 1 should then be arranged such that no electrical functional element of the displacement-detecting element 1 can move into this main radiation 46. This embodiment also shows that the housing 9 of the displacement-detecting element 1 has a dovetailed outer contour 31, which is inserted into a complementary recess 32 of the leaf 22. The housing 9 of the displacement detecting element 1 is rigidly connected to the leaf 22 by screwing it into a recess 37 and surrounds a tongue 11 which is fixed to the collimator housing by means of a mounting 43 at its bore 27. The housing 9 may e.g. also be glued, soldered, riveted or mounted in a different fashion. In this manner, the tongue 11 can move in the housing 9 when the leaf 22 performs the adjusting motion 38 to produce, as described in detail below, a signal that is converted into displacement information through a means 5 and is processed by the control of a multileaf collimator 23. Clearly, the latter can also effect the displacement information conversion. The illustration also shows the guidance 41 of the leaf 22 and a drive 42, which is indicated by a bar and a double arrow. The leaf 22 has an adjustment path with indicated maximum length 7.7xe2x80x2 thereby shows the position on the adjusting path to be detected. It is thereby advantageous to be able to adjust the leaf 38 past the centerline 40 of the multi-leaf collimator 23 to produce desired shapes. The functional principle of shaping using the multi-leaf collimator 23 is also explained below. The front edge 44 of the leaf 22 is advantageously inclined parallel to the main radiation 34. The corresponding device is, however, not subject matter of this application. FIG. 1a shows the leaf 22 in section Ixe2x80x94I. The leaf 22 is a thin plate (shown in larger scale than in FIG. 1). One sees that the displacement-detecting element 1 must be extremely flat. It preferably has an extremely flat housing 9 to permit insertion of the housing 9 of the displacement-detecting element 1 into a recess 37 laterally disposed in the leaf 22. The housing 9 should not protrude since the next leaf borders at that location although it could also partially extend in a groove in the neighboring leaf. FIG. 1b schematically shows a multi-leaf collimator 23 in plan view, opposite to the direction of irradiation, wherein the delimitation 24 is shown within which the leaves 22 set the opening 25 for the radiation 34. This is effected by the drives 42 of the leaves 22 with precise positioning being obtained by the inventive displacement-detecting element 1. Since the leaves 22 are formed as densely packed lamellas of minimum width, it is important that the displacement detecting elements 1 detect the positions of the leaves 22 while having an extremely flat construction. They can be disposed e.g. in a recess 37 on the side of the leaves 22, above or below the material required for shielding. In this fashion, their positions can be directly detected and they can be protected from the main radiation 34 thereby avoiding error sources and obtaining an inexpensive solution requiring little space. FIG. 1c shows an embodiment with an alternative arrangement of a displacement-detecting element 1 on a leaf 22. In this case, the housing 9 of the displacement detecting element 1 is disposed on the lower side of the leaf 22 so that it is completely shielded by the leaf 22 and therefore positioned in a region 33xe2x80x2 where the main radiation 34 is largely shielded for each position of the leaf 22. FIG. 2 shows an embodiment of the inventive displacement-detecting element 1. This displacement-detecting element 1 comprises a housing 9 and a tongue 11, wherein the housing 9 has a recess 10 extended along the housing 9 in which the tongue 11, formed in correspondence with the recess 10, is displaceably disposed. The housing 9 can be mounted to the structural component 22 being measured via bores 28 and the bore 27 fixes the tongue 11. In this fashion, the housing 9 is displaced relative to the tongue 11 corresponding to the position changes of the leaf 22 to which the housing 9 is mounted. To detect the position changes, the tongue 9 has a measuring resistance 2 formed as resistance strip 6. The irregular edge of the resistance strip 6 constitutes a compensation 8, which is provided by removing part of the material from the resistance strip 6 to serve for precise adjustment of the displacement-detecting element 1. The measuring resistance 2 has a terminal 12 at one end and its other end is connected to a conductor path 13 which extends parallel to the resistance strip 6 to the second terminal 14 of the measuring resistance 2, disposed next to the first terminal 12. The voltage source 3 is connected to these terminals 12 and 14. A second slide contact path 16 is disposed on the tongue 11 which extends parallel to the resistance strip 6 and the conductor path 13 and which has a terminal 17. The resistance strip 6 serves as first slide contact path 15. The voltage pick-off 4 is effected in that the housing 9 has a first wiper 18 and a second wiper 19 which are electrically connected to thereby produce an electrical connection between the measuring resistance 2 and the second slide contact path 16 at the respective position. For this reason, all the terminals 12, 14 and 17 are located on the fixed tongue 11. This avoids cable connections subjected to motion, which could cause cable breakage. To increase the reliability of the contact, the wipers 18, 19 are fork-shaped and have several contact zones. In the position detected herein, the wipers 18, 19 are disposed on the partial length 7xe2x80x2 of the full displacement path 7 of a leaf 22 to be detected. Advantageously, the first and second wiper 18 and 19 pass through a window 21 of the housing 9. The two wipers 18 and 19 can be resiliently disposed without requiring too much height. This embodiment permits flat construction of the displacement-detecting element 1 and mounting to very flat leaves 22. The voltage pick-off 4 permits measurement between the terminal 17 and one of the terminals 12 or 14 by means of which the length of the respective displacement 7xe2x80x2 and therefore the position of a leaf 22 can be determined. The measurement can be effected by disposing a resistance 20 between the terminals 17 and 12 or 14 where the voltage is picked off using a means for converting the signal into displacement information 5. This may be a voltage meter calibrated to the displacement. The resistance 20, the means 5 for converting a signal into displacement information and the voltage source 3 are symbolically drawn here. This or a corresponding function is generally integrated in the overall electronics of the device. The signals of the displacement detecting elements of all leaves are advantageously passed on to the control device of the multi-leaf collimator to thereby form the desired contours in a rapid and exact fashion. FIG. 2 shows a conducting layer 26, which is mounted on the housing 9 for shielding. A further conducting layer 26xe2x80x2 serves for soldering on the wipers 18 and 19. This layer 26xe2x80x2 is very thin. FIG. 3 shows a housing 9 of the inventive displacement-detecting element 1 which must be sufficiently long to permit a pushing motion of the tongue 11 relative to the housing 9, which corresponds, to the length of maximum displacement 7 of the leaf 22 to be detected. The other structural components correspond to those already described in FIG. 2. FIG. 4 shows a tongue 11 of the embodiment shown in FIG. 2 wherein the measuring resistance 2 must have the above-mentioned length of displacement 7. Compensation 8 of the measuring resistance 2 was effected within this region. The figure also shows the connection between the end of the resistance strip 6 opposite to the terminal 12 and the conductor path 13, which leads to the other terminal 14. The second slide contact path 16 must also have the same length 7. FIG. 5 shows advantageous embodiments of the displacement-detecting element 1. In one embodiment, electrical functional elements such as the measuring resistance 2, the conductor path 13 and the second slide contact path 16 are disposed in a gap 29 between the housing 9 and the tongue 11 to protect them from wear and soiling. Such a gap 29 can be realized e.g. by two steps 30 in the recess 10. A further advantageous embodiment has the above-mentioned dovetailed outer contour 31 of the housing 9 to be able to insert the housing 9 into the leaf 22 to be detected. In this manner, a very flat displacement-detecting element 1 can be mounted to very flat leaves 22 of multi-leaf collimators 23. This embodiment is of course only one possible realization of the invention. Depending on the design of the leaves 22, it is also possible to dispose the electrically insulated measuring resistance 2 directly on a leaf 22 and make the voltage pick-off 4 stationary. The housing 9 and tongue 11 can also have other designs. The functional elements 2 and 4 may also be disposed vice versa. Other shapes are also feasible. One leaf can have several displacement detecting elements 1 to increase the operating safety through a checking measurement and/or via increased precision of displacement detection. LIST OF REFERENCE NUMERALS 1 displacement-detecting element (potentiometer) 2 measuring resistance (functional element) 3 voltage source 4 voltage pick-off (functional element) 5 means for converting the signal into displacement information 6 resistance strip 7 maximum length 7xe2x80x2 part of the displacement (displacement to be detected) 8 balance 9 housing 10 recess 11 tongue 12 terminal of the measuring resistance 13 conductor path 14 connection of the measuring resistance (via conductor path) 15 first slide contact path (measuring resistance) 16 second slide contact path 17 terminal of the second slide contact path 18 first wiper (at the measuring resistance) 19 second wiper (at the second slide contact path) 20 resistance 21 window 22 leaf 23 multi-leaf collimator 24 delimitation 25 opening for radiation 26, 26xe2x80x2 conducting layers 27 bore for mounting the tongue 28 bore for mounting the housing 29 gap 30 steps 31 dovetailed outer contour 32 complementary recess for dovetailed outer contour 33, 33xe2x80x2, 33xe2x80x3 region of the leaves, which is not subjected to main radiation 33 region shielded by the pre-collimator 33xe2x80x2 region of shielding in a different position of the pre-collimator 33xe2x80x3 region shielded by the leaves 34 main radiation 35 side of the leaves facing away from radiation 36 pre-collimator 37 recess on the leaves for insertion of the housing 9 38 double arrow: adjusting motion of the leaf 39 double arrow: adjusting motion of the pre-collimator 40 center line of the multi-leaf collimator 41 guidance of the leaf 42 drive of the leaf 43 mounting of the tongue 44 front edge of the leaves 45 radiation source 46, 46xe2x80x2 delimitation of the main radiation
	abstract	An apparatus having a nuclear reactor comprising a pressure vessel containing primary coolant water and further containing a nuclear reactor core comprising fissile material, a mounting/electrical distribution plate secured entirely within the pressure vessel and configured to be submerged in the primary coolant, a set of control rod drive mechanism (CRDM) units mounted directly on the mounting/electrical distribution plate, and a plurality of cable modules mounted in receptacles of the mounting/electrical distribution plate wherein each cable module includes mineral insulated (MI) cables connected with one or more of the CRDM units, the cable module including its MI cables being removable as a unit from the receptacle of the mounting/electrical distribution plate.
	summary
	abstract	The present disclosure provides a neutron capture therapy system including a beam shaping assembly. The beam shaping assembly includes a beam inlet; a neutron generator arranged into the beam shaping assembly, the neutron generator has nuclear reaction with an incident proton beam from the beam inlet to produce neutrons; a moderator adjacent to the neutron generator, the neutrons are moderated by the moderator to epithermal neutron energies; a reflector surrounding the neutron generator and the moderator, the reflector leads the deflected neutrons back to enhance epithermal neutron beam intensity; a beam outlet; and at least a movable member moving away from or close to the neutron generator, the movable member moves between a first position where the neutron generator is replaceable, and a second position where the neutron generator is irreplaceable. The neutron capture therapy system has a simple structure, and the neutron generator is easy to be replaced.
	description	1. Field of the Invention The present invention relates to a radiation imaging apparatus using a portable solid-state imaging device configured to allow a grid to be mounted outside the housing. 2. Description of the Related Art Conventionally, apparatuses which obtain radiographic images of objects by irradiating the objects with radiation and detecting the intensity distributions of radiation transmitted through the objects have been widely and generally used in the fields of industrial nondestructive testing and medical diagnosis. As a general method for such radiography, a film/screen method using radiation is available. This is the method of performing radiography by using a combination of a photosensitive film and a fluorescent having sensitivity to radiation. In this method, rare-earth fluorescent sheets which emit light upon application of radiation are held in tight contact with the two surfaces of a photosensitive film. The fluorescent converts radiation transmitted through an object into visible light. The method then develops, by chemical treatment, the latent image formed on the photosensitive film by making it capture this visible light, thereby visualizing the image. The recent advances in digital technology have popularized the scheme of obtaining high-quality radiographic images by converting radiographic images into electrical signals, performing image processing for the obtained electrical signals, and then reproducing the resultant information as visible images on a CRT or the like. As such a method, there has been proposed a radiographic image recording/reproduction system which temporarily stores a transmission image of radiation as a latent image in a fluorescent, photoelectrically reads out the latent image by irradiating the fluorescent with exciting light such as a laser beam, and then outputs the readout image as a visible image. In addition, with the recent advances in semiconductor process technology, there has been developed an apparatus for capturing a radiographic image in the same manner as described above by using a semiconductor sensor. These systems have very wide dynamic ranges as compared with conventional radiographic systems using photosensitive films, and can obtain radiographic images which are robust against the influences of variations in the amount of radiation exposure. At the same time, unlike the conventional photosensitive film scheme, this method need not perform any chemical treatment and can instantly obtain an output image. FIG. 7 is a view showing the arrangement of a radiation imaging system using the above semiconductor sensor. A radiation imaging apparatus 103 mounted on a radiographic stand 106 includes a solid-state imaging device 104 having a detection surface on which a plurality of photoelectric conversion elements are two-dimensionally arranged. A radiation generator (X-ray tube) 101 emits radiation to irradiate an object 102. The solid-state imaging device 104 then images the radiation transmitted through the object 102, and converts it into visible light through the fluorescent. A control unit 107 reads out the electrical signal output from the solid-state imaging device 104, performs digital image processing for the signal, and then displays the resultant information as a radiographic image of the object 102 on a monitor 108. The radiation imaging apparatus 103 as an imaging unit incorporates an anti-scatter grid (to be referred to as a grid hereinafter) 105. The grid is designed to remove scattered X-rays generated inside the object (e.g., a human body) 102 upon X-ray irradiation, and is used to improve the contrast of an X-ray image. This apparatus performs radiography with the grid 105 being disposed between the X-ray tube 101 and a detector such as a film. Such grids are defined as JIS Z 4910 anti-scatter grids, which will be briefly described below. FIG. 8 is a schematic sectional view of the grid described above. X-rays are applied from a direction A on the left side of FIG. 8. The grid is formed by alternately stacking foils 201 made of a material having a high X-ray absorptance and intermediate materials 202 having a low X-ray absorptance. In general, lead is used for the foils 201 having a high absorptance, and aluminum, paper, wood, synthetic resin, carbon fiber reinforced resin, or the like is used for the intermediate materials 202 having a low X-ray absorptance. The outer surface of this multilayered structure is covered by, for example, an aluminum or carbon fiber reinforced resin cover. In many cases, the above grid is a focused grid including a foil represented by a foil 201a which is located at a central portion immediately below the X-ray source and is perpendicular to the cover and foils 201b which gradually tilt in the direction of the light source toward the fringes. When a focused grid is to be used, it is necessary to perform radiography upon adjusting the distance between the grid and the light source and their centers. A grid without any tilting of foils is also available, which is called a parallel grid. Such grids differ in the property of attenuating transmitted X-rays depending on the density or geometrical shape of foils. A grid with optimal specifications is selected in accordance with radiography. In particular, the solid-state imaging device 104 described above is generally selected so as to prevent the pixel size from interfering with the intervals between grid foils in terms of frequency. An imaging apparatus of this type has been installed and used in a radiation room. Recently, a portable imaging apparatus (also called an electronic cassette) has also been provided to allow quicker radiography of regions in a wider range. Such an electronic cassette is required to be low in profile and lightweight and have high mechanical strength. In cassette radiography, a person as an object may be rested on the cassette. In addition, since the electronic cassette is portable, a shock may act on the cassette if it is dropped or collides with something. As compared with conventional stationary imaging units, therefore, it is necessary to greatly improve the resistance of such electronic cassettes in terms of mechanical strength. A cassette can be applied to various regions, and hence the grid is preferably configured to be easily attached/detached depending on a region to be radiographed. Therefore, a grid which can be mounted outside an imaging unit has been proposed as disclosed in Japanese Patent Laid-Open No. 2004-177251. This grid is mounted on a metal frame component to secure its mechanical strength. As a grid mounted outside an imaging unit like that described above, a grid having the following characteristics has been provided. The first characteristic is that a metal frame member is mounted on the grid body to protect it in terms of mechanical strength. The second characteristic is associated with the pixel array of the imaging unit and the relative angle of the grid lattice. Unlike film radiography, digital imaging has the merit of reducing, by image processing, streaks appearing on an image when the foils of the grid are captured on it. For this reason, the relative angle preferably falls within the computational tolerance of image processing. Therefore, in order to make the relative angle fall within the tolerance range, the grid is mounted on the imaging unit with a side wall being provided on a frame member for positional restriction for the imaging unit. In addition, some grids have a buffer member mounted on a side wall to prevent the operator from being injured if the grid is accidentally dropped or to prevent the grid from being damaged during transport. Consider a case in which a portable X-ray imaging apparatus 111 is used to radiograph a side surface of a head portion 110 on a table 114, as shown in FIG. 9. In this case, since a distance L from the outer shape of a grid fixing frame 113 to an effective imaging area 112 of the imaging unit 111 is large, it is necessary to use a tool for applying some correction for an offset relative to an object. That is, such radiography accompanies cumbersome operation. Studies have been focused on the imaging unit to meet the requirement for a reduction in weight. In practice, however, it is necessary to implement weight reduction, including a reduction in the weight of the grid. The present invention provides a radiation imaging apparatus including a grid unit which makes improvements in the distance to an effective imaging area and the mass, which contradict the implementation of required relative angle restriction, the securement of mechanical strength, and protection against a shock. According to one aspect of embodiments, the present invention relates to a radiation imaging apparatus comprising a detection unit for detecting a radiation distribution transmitted through an object, an imaging unit which includes the detection unit, and a grid for suppressing scattered light which is detachably mounted on an outside of the imaging unit, wherein the imaging unit includes a buffer member on a side surface facing a surface side which radiation strikes, the grid includes a grid body placed on the surface side which the radiation strikes, and a fixing unit for fixing the grid body to the imaging unit, and sides constituting the fixing unit include a side which does not protrude from an outer shape of the imaging unit when viewed from the surface side which the radiation strikes. Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). The embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIGS. 1 to 4 show an X-ray imaging apparatus according to an embodiment of the present invention. FIG. 1 is a front view showing an imaging unit alone when viewed from the X-ray incident surface. FIG. 2 is a front view showing the imaging unit when a grid unit is mounted on it. Referring to FIG. 2, reference numeral 1 denotes an imaging unit; and 10, an anti-scatter grid unit. FIG. 3 is a side sectional view taken along a line A-A in FIG. 2. FIG. 4 is a side sectional view taken along a line B-B in FIG. 2. FIG. 1 is a front view showing the radiation imaging unit 1 alone when viewed from the X-ray incident surface side. An X-ray detection unit which receives X-rays and detects a radiation distribution is rectangular. A housing lid 2b is placed on the X-ray incident surface side so as to cover an image-receiving area. The housing lid 2b is made of a material having a high X-ray transmittance. The housing lid 2b is combined with a housing body 2a to form a closed type housing 2 having a rectangular shape (almost a quadrangle). The radiation imaging unit 1 described above is used singly as a cassette or used in combination with various gantries. Requirements for transportation in changing the state of use are that the imaging unit 1 is lightweight, and has mechanical strength sufficient to maintain functionality even if it is dropped. In addition, when the imaging unit 1 is to be used as a cassette, the unit must be made low in profile to prevent a person as an object from feeling pain even if the unit is placed under him/her, and needs to have mechanical strength high enough to allow him/her to directly rest upon it. For this purpose, a material such as aluminum or magnesium is used for the housing body 2a to achieve a reduction in weight. In addition, to prevent accidents during transportation like those described above, the imaging unit 1 has a handle and a buffer function. The imaging unit 1 has a hole 9 as a handle which extends through part of the housing. This allows stable gripping of the imaging unit 1 during transportation. A buffer member 8 is placed around the side surfaces of the imaging unit 1 when viewed from the X-ray irradiation surface side. The buffer member 8 is placed on the imaging unit 1 as shown in FIG. 1 because the three sides other than one side (near the handle) where the handle is formed tend to sustain damage due to collisions with other objects or due to dropping when the operator carries the unit while gripping the handle. The buffer member 8 is made of a shock absorbing material such as rubber or an elastomer, and is aimed at protecting an operator as well as other people from injury to themselves as well as at reducing the shock absorbed by the imaging unit 1. The imaging unit 1 described above is used in combination with a detachable grid for suppressing scattered light to improve the contrast of an X-ray image by removing scattered X-rays generated inside an object (e.g., a human body) upon X-ray irradiation. Since grids having different X-ray shielding characteristics are selectively used in accordance with the region to be radiographed, the grid unit is designed to be externally attached/detached to/from the housing 2 so as to be easily attached/detached to/from the imaging unit, as shown in FIG. 2. Referring to the side sectional view shown in FIG. 3, a metal base 4 is fixed in the housing 2 through a support portion 3, and an X-ray image detection panel 5 formed by stacking a substrate 5a, photoelectric conversion elements 5b, and a fluorescent plate 5c is placed on the base 4. As the substrate 5a, a glass plate is often used because, for example, it must not have any chemical action with a semiconductor element and needs to endure the semiconductor process temperature and have dimensional stability. The photoelectric conversion elements 5b are formed on the substrate 5a in a two-dimensional array by a semiconductor process. The fluorescent plate 5c used is one that is formed by coating a resin plate with a metal compound fluorescent. They are integrated with each other with an adhesive. In addition, the photoelectric conversion elements 5b are connected, through a flexible circuit board 6 connected to their side surfaces, to a circuit board 7 which is placed on the lower surface of the base 4 and on which electronic parts for processing electrical signals having undergone photoelectric conversion are mounted. The circuit board 7 is connected to an external control unit (not shown) to, for example, supply power and transfer signals. The radiation imaging unit 1 described above can perform radiography by being used in combination with an X-ray tube which emits X-rays. When the X-rays emitted by the X-ray tube positioned above the imaging unit 1 are transmitted through an object and strike the radiation imaging unit 1, the fluorescent plate 5c of the X-ray image detection panel 5 emits light. The two-dimensionally arrayed photoelectric conversion elements 5b convert the light into electrical signals, thereby obtaining a digital image. This digital image is further transferred to the external control unit. This allows the operator to observe the image on a monitor (not shown) in real time. The grid unit 10 includes a grid body 11 and a metal frame 12. As described above, the grid body 11 has a layer structure constituted by an X-ray shield member and an intermediate material having small X-ray absorption, and hence is low in mechanical strength. The grid body 11 is therefore attached with the frame 12 as a reinforced frame which has an X-ray transmission opening portion 12a. The grid body 11 is held on the surface of the imaging unit 1 on the incident surface side in tight contact with it. The frame 12 shown in FIG. 3 has a cross-section in a direction parallel to the side having the handle. This frame has two side portions 12b which are bent by the thickness of the grid. This shape can make the edge of the frame end portion difficult to come into contact with an object and can increase the mechanical strength of the frame 12, as compared with the simple planar shape like that denoted by reference symbol E in FIG. 3. In addition, this frame can achieve a great reduction in weight as compared with a conventional frame covering the entire side surfaces. Furthermore, the distal ends of the bent portions 12b do not protrude outside the buffer member 8 on the side surfaces of the imaging unit. This shape allows the buffer member 8 of the imaging unit 1, which is placed outside, to receive a shock first, thus reducing the shock directly acting on the grid frame 12. Even if the grid unit 10 is attached to the imaging unit 1, the distance from the outermost shape to the effective imaging area does not change. This makes it possible to perform positioning in the same manner and eliminate the necessity to use any tool to newly correct an offset relative to an object. A means for attaching the grid unit 10 to the imaging unit 1 will be described with reference to FIG. 4. The frame 12 is bent in an almost U shape to have bent portions 12c and 12d so as to hold, between them, the side having the handle and its opposite side. A stepped portion 2c is formed on the housing 2 so as to lock a bent portion 12e of the frame. The frame 12 is mounted on the housing 2 while a side surface wall 2d of the stepped portion 2c restricts the movement of the frame 12 in the horizontal direction (the vertical direction in FIG. 4). On the other hand, a stepped portion is also provided on the side on the handle side so as to lock a hook 13d of a slide member 13 provided on the bent portion 12c of the frame 12. A guide member 13c is mounted on the slide member 13 so as to be slidable on guide grooves 12f formed in the bent portion 12c. Simple operation can detachably mount the grid unit 10 on the imaging unit 1. This lock mechanism allows to safely carry the imaging unit 1 even while the grid unit 10 is mounted on it. The bent portion 12d of the frame 12 and the slide member 13 hold the imaging unit 1 between them. This structure therefore restricts the rotation of the grid unit 10 so as to make the relative angle of the grid unit 10 with respect to the imaging unit 1 fall within a predetermined angle. FIG. 5 shows an X-ray imaging apparatus according to another embodiment of the present invention, which is a modification of the above embodiment. According to the above embodiment, the frame of the grid unit is formed to expose the buffer member provided on the side surfaces of the imaging unit on the two sides perpendicular to the side where the handle is formed, and the grip unit defines the outermost shape on the side on which the handle is formed and its opposite side. If an imaging area is rectangular, it is necessary to select the portrait orientation or the landscape orientation as the suitable posture of the imaging unit. If radiography is performed with the long side being the bottom, the distance from the outermost shape to the effective imaging area undesirably increases. In order to cope with this problem, in this embodiment, a buffer member is partly notched to be divided into parts 22, 23, and 24. Bent portions 32a and 32b for locking which are provided on a frame member 32 on which a grid 31 is to be mounted are placed in the gaps between the respective parts. With this arrangement, the buffer members 22, 23, and 24 of an imaging unit 21 on the sides other than the side where a handle 29 is formed each define the outermost shape. That is, the three sides have the same effect as that described in the first embodiment. Setting the width of the bent portions 32a and 32b to reduce backlash in the gaps between the respective parts of the buffer member can manage the relative position accuracy of the grid 31 with respect to the imaging unit 21 within a predetermined range. FIG. 6 shows an X-ray imaging apparatus according to still another embodiment of the present invention, which is a modification of the embodiment shown in FIG. 5. In the embodiment shown in FIG. 5, the outer shape of the imaging unit defines the outermost shape at the three sides. In this embodiment, however, a grid unit is formed such that the outer shape of an imaging unit at the four sides including the side where a handle is formed defines the outermost shape. Buffer members 42 and 43 are placed on the entire side surfaces of an imaging unit 41. This arrangement allows the effect of reducing shock even when the imaging unit 41 is accidentally dropped as well as when a shock acts on the imaging unit 41 while the operator is gripping the handle and transporting the imaging unit 41. A grid unit 50 includes a lock portion 53 which is locked in a through hole 49 formed as a handle. The grid unit 50 is mounted on the imaging unit 41 by holding it with bent portions 52a and 52b and the lock portion 53. As described above, a grid frame 52 does not completely protrude from the outer shape of the imaging unit 41 when viewed from the incident surface side. This makes it possible to maintain the same effect against a shock from the side surface direction as that obtained when the imaging unit is used singly, even in a state in which the grid unit 50 is mounted on the imaging unit. The embodiments of the present invention have been described above. Obviously, however, the present invention is not limited to these embodiments. Various modifications and changes of the embodiments can be made within the spirit and scope of the present invention. Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiment(s), and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiment(s). For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (e.g., computer-readable medium). While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. This application claims the benefit of Japanese Patent Application No. 2009-090486, filed Apr. 2, 2009, which is hereby incorporated by reference herein in its entirety.
061838179	abstract	A method and apparatus to fabricate nano-device and semiconductor device structures and features by controlling a coherent or near coherent particle beam to directly deposit, or direct write, onto a preselected deposition site of a substrate and into a predetermined shape is provided. Evanescent wave plates are optionally included to increase the order of the particle beam prior to interaction with a photonic lens. The photonic lens is holographically generated by means of a source laser and an optical lens to focus the atomic beam onto the deposition site by means of Lorenz force interaction between light fields of the photonic lens and dipole moments of the atoms of the atomic beam. The diffraction pattern of the optical lens is computer calculated to precisely form the desired photonic lens in accordance with the shape and size of the desired feature or structure to be built on the substrate and the characteristics of the atomic beam, the source laser, the shape and position of the substrate and the location of the deposition site.
051732505	summary	FIELD OF THE INVENTION The present invention relates to an apparatus for demolishing a biological shield wall of a nuclear reactor after its life and a method of demolishing the same. PRIOR ART Conventionally, as a method of demolishing a biological shield wall of a nuclear reactor after its life, a method of mechanical cutting using a combined wall saw and a core boring machine, or a method of demolishing of fluid cutting dynamics using an abrasive water jet are proposed. This cutting method, however, applies a cutter device with its tripod legs fixed on the inside surface of a bell-shaped biological shield wall of a nuclear reactor, and its travelling operations with along the progressing of the operation are very troublesome, and the wall being a heavy structure, the fixing device therefor with the supporting legs assembled become comparatively larger, and by the fact that the device suffers radioactive contamination during the demolishing operation, there results a problem that mass of radioactive matters to be disposed of as the wastes increases after the operation. Then, in view of the above-mentioned current state, the present invention was made to eliminate the disadvantage of the prior art, and the object of which is to present a novel apparatus and a method of demolishing a biological shield wall of a nuclear rector without requiring a large scale for the apparatus even for the larger biological shield wall, and accordingly never resulting in the increasing of mass of active wastes, and with along the progressing of the cutting operation, easy movement and also improvement of the efficiency of the operation can be accomplished. DISCLOSURE OF THE INVENTION The feature of the present invention lies in that, in a demolishing apparatus for a biological shield wall of a nuclear reactor using a concrete cutter device working on a wire saw, said apparatus comprises a concrete cutter device consisting of a driving part for a wire saw and a concrete cutting part attached to the engaging receiver of the driving part, a core boring machine to be attached interchangeably on the engaging receiver in the place of the cutting part and a carrier truck to carry the wire saw driving part of said cutter device. Further, the concrete cutting part has a pair of vertical rods supported on a table movable vertically and adjustable in a distance from each other rods, and the table is pivoted to swing horizontally, and at the bottom end of the rods, supporting pulleys and guide rollers for arranging the wire saw are provided. The other feature of the present invention lies in that, in a method of demolishing a biological shield wall of a nuclear reactor using the demolishing apparatus described above, a method comprising a step of setting the carrier truck on the operating floor of the reactor building, with a core boring machine attached on the reciever and with the carrier moving on, a step of boring holes downward from top of the shield wall at a predetermined distance, then with the concrete cutting part attached in the place of the boring machine, a step of inserting a pair of vertical rods in the bored hole through adjusting of the table to circurate the wire saw between the supporting pulleys, while with the carrier moved along and the vertical rods controlled and adjusted to enable the cutting of wire saw to cut a concrete block from the shield wall to dispose finally. According to the present invention, by setting the carrier truck carrying the wire saw driving part attached by the wire saw cutting part on the operating floor of the reactor building, the biological shield wall is cut and demolished by the core boring machine and the wire saw cutting part, and then, with along the progressing of the cutting operation, easy movement and also improvement of the efficiency of the operation can be accomplished, without requiring a large scale for the apparatus even when the biological shield wall gets larger, and accordingly never resulting in the increasing of mass of active wastes. The other features of the present invention are understood by the following non-limiting embodiments shown in the following drawings.
	abstract	The invention provides a framework for collecting, storing, and analyzing system metrics concerning a computing system or a computer component. A configuration module is provided to configure settings specific to a metric. A data collection module is provided to collect metric data according to the settings in the configuration module and in one or more component specific plug-ins that extend and customize the framework according to specific needs of the component. The data collection module collects metrics at specified time intervals and periodically updates metric data stored in a central metrics storage module. An analysis module is provided to analyze metric data stored in the central metrics storage module online or offline. The analysis module may analyze a metric statistically or graphically, individually or combined with other metrics.
	abstract	Syringe shield (2) includes a barrel housing (4), which includes: a barrel housing (6) with a radiation-shielding material, a first open end (8), and a second open end (10); and a removable cover (12) which is slidably connectable to the barrel housing (6). The removable cover (12) includes an end cap (14) which covers the second open end (10) when the removable cover (12) is slidably connected to the barrel housing (6). The barrel housing (4) also includes a plunger housing (16) with a radiation-shielding material. A first end (18) of the plunger housing (16) is open and is connectable to the first open end (8) of the barrel housing (4), and a second end (20) of the plunger housing (16) includes a top cap (22).
	abstract	A fuel assembly for a pressure-tube nuclear reactor includes a fuel channel assembly. The fuel channel assembly has an outer conduit and an inner conduit received within the outer conduit. The conduits define an annular fuel bundle chamber for receiving a flow of a coolant in one direction. The inner conduit includes a central flow passage for receiving a flow of the coolant in an opposite direction. A fuel bundle positioned within the fuel bundle chamber consists of fuel elements arranged to form an inner ring surrounding the inner conduit, and an outer ring surrounding the inner ring. The coolant may be light water, and geometries of the fuel assembly may be selected so moderation by the volume of coolant promotes generally uniform power distribution in the fuel elements.
054266866	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention concerns the generation of x-rays, and particularly time-resolved x-rays having nanosecond and shorter duration. The present invention particularly concerns x-ray sources for lithography, and especially sources providing an energetic flux of hard x-ray radiation over a spatially extended area. 2. Background of the Invention The present invention generally relates to the production of x-ray radiation, particularly time-resolved pulses of x-ray radiation, and particularly relates to the production of x-ray radiation over a spatially extended area. 2.1 Time-Resolved X-ray Sources The earliest attempts to produce time-resolved x-rays employed mechanical shutters that moved in front of x-ray sources. For example, transmission of x-rays through x-ray transparent apertures within a rotating apertured disk that was otherwise opaque to x-rays permitted the generation of millisecond x-ray pulses. These millisecond x-ray pulses were too slow to permit the study by x-ray diffraction of any type of molecular phenomena such as reaction, melding, dissociation, or vibration. Millisecond x-ray pulses were, however, sometimes sufficient to permit observation of certain biological phenomena, although not normally at the biomolecular level. Davanloo et al., Rev. Sci. Instrum. 58:2103-2109 (1987) reported constructing an x-ray source capable of producing x-ray pulses of nanosecond (ns) duration. That x-ray source utilized (i) a low impedance x-ray tube, (ii) a Blumlein power source, and (iii) a commutation system for periodically applying power from the Blumlein power source to the x-ray tube. The system yielded 140-mW average power in 15 ns pulses of radiation near 1 .ANG.. That device, and others based on Blumlein-generators, suffers from (i) low repetition rates in the range of 100 hertz, (ii) prospective inability to produce pulses shorter than about 15 nsec, and (iii) low energy efficiency on the order of 25%. The durability in operational use of Blumlein-based sources of x-ray flashes is also uncertain. More recently, Science News, Vol. 134, No. 2: pp. 20 (1989) reported that scientists at Cornell University and the Argonne National Laboratory have developed a device, called an undulator, capable of producing x-ray pulses one-tenth of a billionth of a second (100 picoseconds) in duration. The undulator utilized synchrotron radiation from fast-moving charged particles in an electron storage ring. Because electron storage rings are typically large and expensive, the ring used at Cornell being one half-mile in diameter, the production of bright x-ray flashes by such means is distinctly not adaptable to the scale and budget of a typical materials or biological laboratory. X-rays have been produced using plasma sources that are energized by lasers. In laser plasma x-ray sources, either a pulsed-infrared (IR) laser or a ultraviolet (UV) excimer laser is used with pulse widths varying from less than 10 picoseconds to 10 nanoseconds. The laser beam is focused on a target where it creates a plasma having a sufficiently high temperature to produce continuous and characteristic x-ray radiation. Major disadvantages of laser plasma x-ray sources include (i) a diffuse, non-point, area of x-ray emission (ii) low efficiency (iii) low repetition rate. 2.2 X-ray Sources for Lithography Since the seminal paper by Henry Smith appeared in 1972, the achievement of economical x-ray lithography has been rather elusive. During the intervening years, however, considerable progress in many areas has been made, including development of masks, resists and registration capabilities. Three main classes of x-ray sources are considered as a possible choice for lithography. Those are electron impact tubes, laser-based plasmas, and synchrotrons. Progress has been made in each of these sources, particularly in laser-driven plasma x-ray sources. Efforts in Japan have been devoted to the development of compact, high density synchrotrons. Even today, each of these sources has its limitations for a practical system. The most intense sources are the synchrotrons, but so far their price, size and complexity make them prohibitive for use in a production line. Electron impact tubes are the simplest and cheapest sources. However, their effectiveness is best only in the hard x-ray region. For high current output electron impact tubes must be pulsed because of the extreme heat generated on the anode by electron impact on the anode. Laser driven x-ray sources have started to appear and show promise. The requirements for a practical x-ray source for lithography are dependent on development of the other two critical components of the lithographic process--mask and resist. Most of the research and development for x-ray sources is centered in the 0.4-5 nm wavelength range where suitable resists are available. Use of still harder x-rays, 0.1-1.0 nm, would bring additional benefits, such as the possibility of ultrasensitive microsensors for medical and technological applications and, of course, higher resolution lithography permitting a denser layout of semiconductor components. The present invention will be seen to be concerned with the generation of x-ray pulses for lithography in a manner that is believed to provide several distinct advantages over previous x-ray sources. 2.3 Photoemissive Sources of Electrons By way of background to the present invention, Lee, et al., in Rev. Sci. Instrum., 56:560-562 (1985) described a laser-activated photoemissive source of electrons. In the laser-activated photoemissive electron source a photocathode is illuminated with high intensity laser light as a means of generating numerous electrons by the photoelectric effect. The electrons emitted from the photocathode are focused in an electrical field, typically produced by electrodes in an electron-gun configuration, in order to produce a high intensity electron beam. 2.4 Rectification of Ultrashort Optical Pulses to Produce Electrical Pulses By way of further background to the present invention, the rectification of ultrashort optical pulses in order to generate electrical pulses having durations and amplitudes that are unobtainable by conventional electronic techniques is described by Auston, et al, in the Annl. Phys. Lett., 20:398-399 (1972). Electrical pulses on the order of 4 amperes in 10 picoseconds are generated by rectification of 1.06 micrometer optical pulses in a LiTaO.sub.3 crystal doped with approximately 2.24% Cu (LiTaO.sub.3 :Cu.sup.++). A doped transmission line, having an absorption coefficient of 60 cm.sup.-1 and a thickness of 0.2 mm, is bonded with a thin epoxy layer to an undoped crystal in the form of a TEM electro-optic transmission line of 0.5.times.0.5-mm cross-sectional area. Current pulses are generated by absorption in this transducer of single 1.06 micrometer mode-locked Nd: glass laser pulses, typically of duration 3-15 psec and with an energy of approximately 1 mJ. The electro-optic transmission line, or switch, operates to conduct current during the presence of laser excitation by action of the macroscopic polarization resulting from the difference in dipole moment between the ground and excited states of absorbing Cu.sup.++ impurities. Effectively, the electric-optic transmission line, or switch, has a very great number of charge carriers, and is a very good conductor, during the presence of laser excitation. During other times it is a semiconductor and does not conduct appreciable current. The excited-state dipole effect of the transmission line, or switch, is exceptionally fast, on the order of 1 or 2 psec or less. SUMMARY OF THE INVENTION The present invention contemplates a compact, high-intensity, inexpensive, reliable, tunable, high-intensity pulsed x-ray (PXR) light source where copious electrons are efficiently produced at a photocathode by the photoelectric effect and then, having been efficiently produced, effectively accelerated and focused in a strong electric field to impinge upon a desired area of an anode, thereby to produce bright x-ray light by bremstrahlung. In various embodiments an x-ray source in accordance with the present invention can produce pulsed x-ray radiation that is any one or ones of (i) very short (typically 20 ps), (ii) very bright (typically 6.2.times.10.sup.6 cm.sup.-2 sr.sup.-1 at the Ka wavelength (1.54 .ANG.), and/or (iii) very hard (typically 0.1-1 micrometer wavelength). X-ray source in accordance with the present invention are effectively applied in the areas of crystallography, spectrography, and especially lithography. Particularly for lithography applications, a compact wide-area x-ray source can produce from 1 to 40 mW/cm.sup.2 x-ray radiation flux (depending upon the duration and repetition rate of the laser pulses) uniformly over an area (typically circular in shape) that is as large as 20 cm.sup.2. Such an energetic high-intensity pulsed hard x-ray flux over such a large area is manifestly suitable for the masked exposure of photoresists in the production of semiconductors: the x-ray source, mask, resist and semiconductor substrate are placed tight together in simple close contact--obviating any need for focusing. An x-ray source in accordance with the present invention has (i) a laser for producing a laser beam (a beam of laser light), and (ii) an electron source means, preferably photoemissive, that is capable of producing electrons in response to illumination by the laser beam and which is positioned for illumination by the laser beam. The x-ray source also includes (iii) a high voltage means energized to generate an electric field for accelerating, as an electron beam, the electrons produced by the impinging of the laser beam on the electron source means, and (iv) an electron beam target means positioned to intercept the accelerated electrons.(electron beam) in order to produce x-rays in response thereto. Preferably, the x-ray source further includes a high voltage switching means selectively operable to energize the high voltage means for a selected period of time for accelerating the electron beam during the selected time period to produce an x-ray pulse. Preferably, the high voltage switching means comprises an electrical switch selectively operable to selectively energize the high voltage means in response to, and in synchronism with, the laser beam pulses. In another preferred embodiment, the x-ray source further includes a means for producing the laser beam as pulses in substantial temporal synchronization with the energization of the high voltage means. In still another preferred embodiment, the x-ray source includes a field electrode means disposed between the electron source means and the electron beam target means for substantially suppressing the electron beam in response to deenergization of the high voltage means. Preferably, the field electrode means comprises an electrode positioned closer to the electron source means than to the electron beam target means. In embodiments containing an electrode, it is preferred that the x-ray source further include a means for negatively voltage biasing the electrode relative to the electron source means for substantially maintaining the electrons produced by the electron source means in a region between the electrode and the electron source means in response to deenergization of the high voltage means. A still further preferred embodiment of the x-ray source of this invention includes a means for directing the laser beam pulses onto a scattering sample (a sample for scattering the x-ray radiation) for energizing the scattering sample substantially simultaneously with illumination of the sample by the x-ray radiation. Still another preferred embodiment of the x-ray source of this invention includes an x-ray switch means for switching x-rays received from the electron beam target means to produce an x-ray pulse. Preferably, the x-ray switch means comprises an apertured plate, such as a rotating plate, movable to selectively and alternately occlude and to pass the x-rays through an aperture for producing an x-ray pulse. In one preferred x-ray source in accordance with the present invention, the electron source means comprises a photocathode, the electron beam target means comprises an anode, and the high voltage power supply is connected between the photocathode and the anode for generating the electric field used for accelerating the electrons produced by the photocathode as an electron beam that impinges the anode to produce the x-rays. In another embodiment, the present invention contemplates a source of x-ray radiation comprising a laser source of laser light, a chamber evacuated to a high vacuum, a photocathode within the chamber for emitting electrons in response to illumination thereof by the laser light, an anode within the chamber spaced apart from the photocathode, and a high voltage source for electrically biasing the anode to a high voltage relative to the cathode for accelerating electrons emitted from the cathode as an electron beam to impinge upon the anode and to produce x-ray radiation. Preferably, a high voltage switch is connected to the high voltage source, the photocathode and the anode, for selectively biasing the anode with high voltage relative to the cathode in synchronization with the illumination of the photocathode by the pulses of laser light. Preferably, the high voltage switch is selectively operable for switching the biasing of the anode in response to and in synchronization with the pulses of laser light. Preferably, the high voltage switch comprises a semiconductor switch responsive to the pulses of laser light. Preferably, the source of x-ray radiation of this invention further includes (i) a grid electrode within the chamber between the anode and the photocathode, and (ii) a voltage source for electrically biasing the grid electrode with a voltage, lower than the high voltage, for jointly limiting the drift of the emitted electrons under the space charge effect to a region of the chamber proximate the anode when the anode is not electrically biased with the high voltage, and (iii) a high voltage switch connected to the high voltage source and the photocathode for selectively applying the high voltage between the anode and the photocathode to produce pulses of emitted electrons accelerated from the photocathode through the grid electrode to impinge the anode, producing pulses of x-ray radiation. The present invention still further contemplates an improvement to the photocathode element of the laser-activated, photoemissive, electron source. A metal, is preferably deposited on, or is alternatively mixed in bulk with, a semiconductor. The metal is preferably tantalum (Ta), copper (Cu), silver (Ag), aluminum (Al) or gold (Au) or oxides or halides of these metals, and is more preferably tantalum. The depositing is preferably by sputtering or annealing, and is preferably by annealing. The semiconductor is preferably cesium (Cs) or cesium antimonide (Cs.sub.3 Sb) or gallium arsenide (GaAs), and is more preferably cesium antimonide. A photocathode so formed exhibits efficient electron emission by the photoelectric effect and improved longevity. In another embodiment, the present invention contemplates a method of producing x-ray radiation comprising illuminating a photocathode in a high vacuum with laser light, preferably at intermittent intervals, in order to produce electrons therefrom by the photoelectric effect and accelerating the produced electrons in a high voltage electric field to impinge on an anode in the high vacuum to produce x-ray radiation. In an embodiment particularly suited for use in x-ray lithography the x-ray source of the present invention includes a laser light generator for producing laser light illumination over a spatially extended area and a spatially extended photoemitter means intercepting the laser light illumination over the spatially extended area in order to produce electrons by the photoelectric effect over the same spatially extended area. A high voltage source generates an electric field for accelerating the produced electrons as a wavefront of electrons, the wavefront again occurring over the spatially extended area. A spatially extended metal foil is positioned to intercept the wavefront of electrons over the spatially extended area of such wavefront, and, responsively to this interception, for producing x-rays. The x-rays so produced over a spatially extended area are particularly useful for lithography, including in the masked exposure of photoresist upon a semiconductor substrate where the substrate, photoresist, and mask are tight against (i.e., at a separation that is typically .ltoreq.5 micrometers) the metal foil. These and other aspects and attributes of the present invention will become increasingly clear by reference to the following drawings and accompanying specification.
	abstract	An X-ray and gamma-ray shielding glass, including the following components in weight-%: 10-35% SiO2; 60-70% PbO; 0-8% B2O3; 0-10% Al2O3; 0-10% Na2O; 0-10% K2O; 0-0.3% As2O3; 0-2% Sb2O3; 0-6% BaO; and 0.05-2% ZrO2.
	description	This application is a Continuation of U.S. application Ser. No. 13/551,452 filed on Jul. 17, 2012, which is a Continuation of U.S. application Ser. No. 12/385,612 filed on Apr. 14, 2009. Priority is claimed based on U.S. application Ser. No. 13/551,452 filed on Jul. 17, 2012, which claims the priority of U.S. application Ser. No. 12/385,612 filed on Apr. 14, 2009, which claims priority from Japanese patent application JP 2008-104232 filed on Apr. 14, 2008, the content of which is hereby incorporated by reference into this application. 1. Field of the Invention The present invention relates to a charged particle beam application apparatus, or more particularly, to a charged particle beam application apparatus that is used to observe, inspect, and analyze a wafer sample, which has a minute circuit pattern, with a high resolution using a low-acceleration electron beam. 2. Description of the Related Art Various techniques have been employed in detecting a defect which occurs in fabrication of a microscopic circuit such as an LSI, measuring the length of the defect, or assessing the shape of the defect. For example, an optical inspection apparatus produces an optical image of the microscopic circuit and inspects the image to detect an abnormality. However, the resolution of the optical image is not high enough to identify a very small shape-related feature, and is not high enough to discriminate a harmful defect from a harmless defect in terms of fabrication of a circuit. A sample to be handled by such a measurement/inspection apparatus has become more and more microscopic along with advancement of technologies. For example, in a recent DRAM manufacturing process, the width of a metal wire is 90 nm or less. For a logic IC, a gate dimension has reached 45 nm. A defect inspection technique using an electron beam provides a resolution that is high enough to image a microscopic shape-related feature of a contact hole, a gate, or a wire and a shape-related feature of a microscopic defect, and can therefore be used to classify or detect a grave defect on the basis of a contrast of a shaded image of a detective shape. Therefore, for measurement/inspection of a microscopic circuit, a measurement/inspection technique employing a charged particle beam has an advantage over the optical inspection technique. A scanning electron microscope (SEM) that is a type of charged particle beam apparatus focuses a charged particle beam emitted from an electron source of a heating type or a field emission type so as to form a thin beam (probe-like beam), and sweeps the probe-like beam over a sample. Secondary charged particles (secondary electrons or reflected electrons) are emitted from the sample due to the sweep. Synchronously with the sweep of the primary charged particle beam, a scan image is acquired by using the secondary charged particles as a luminance signal of image data. A typical scanning electron microscope accelerates electrons emitted from the electron source using an extracting electrode interposed between the electron source, at which a negative potential is developed, and a ground at which a ground potential is developed, and irradiates the resultant electrons to the sample. The resolution offered by a scanning charged particle microscope such as an SEM and the energy of a charged particle beam have a close relationship. When a primary charged particle beam of high energy reaches a sample (that is, when the landing energy of a primary charged particle beam is large), since primary charged particles deeply invade into the sample, an emissive range on the sample from which secondary electrons and reflected electrons are emitted expands. As a result, the emissive range becomes wider than the probe diameter of the charged particle beam, and an observational resolution is markedly degraded. When the energy of a primary charged particle beam is excessively reduced in order to lower the landing energy, the probe diameter of the charged particle beam greatly increases due to aberrations. Eventually, the observational resolution is degraded. Further, a contrast of an SEM image is affected by the value of a current carried by a primary charged particle beam to be irradiated to a sample. When the beam current decreases, the ratio of a secondary signal to a noise (signal-to-noise ratio) is greatly lowered and a contrast of a scan image is degraded. Preferably, the beam current value should be controlled to be as large as possible. When the energy of the primary charged particle beam is reduced, formation of a thinner probe-like beam becomes hard to do due to the Coulomb's law. When the energy of the primary charged particle beam is excessively controlled to become small, a beam current required for producing the scan image becomes insufficient. This makes it hard to acquire the scan image with a high magnification and a high resolution. For observation with a high resolution, the energy of a primary charged particle beam, or especially, landing energy has to be appropriately controlled according to an object of observation. As a control technology for landing energy, a retarding method is widely adopted. In the retarding method, a potential causing a primary charged particle beam to decelerate is developed at a sample in order to decrease the energy of the charged particle beam to a desired level of energy immediately before the charged particle beam reaches the sample. For example, in JP-A-6-139985, an invention that controls the timing, at which a negative potential for retarding is developed at a sample, responsively to mounting or replacement of a sample has been disclosed. An invention disclosed in JP-A-2001-185066 is such that: when the slope of a sample is observed according to the retarding method, the magnetic poles of an objective lens are separated into upper and lower ones, and a potential identical to the one at the sample is developed at the lower magnetic pole in efforts to minimize the adverse effect of an asymmetric retarding electric field derived from the slope of the sample (to minimize occurrence of astigmatism or reduction in efficiency in detecting secondary electrons). In JP-A-6-260127, an invention of a potential measurement apparatus employing an electron beam has been disclosed. In the potential measurement apparatus described in JP-A-6-260127, an objective lens is divided into a yoke part for excitation and a magnetic-pole part, and is formed with two magnetic circuits. An electric field for pulling up secondary electrons is applied to the magnetic-pole part. According to JP-A-6-260127, since the objective lens is divided into two parts, the magnetic circuits can be readily designed according to the working distance between a sample and the objective lens. The diameter of the spot of an electron beam can be appropriately controlled irrespective of the working distance. A contrast of a charged particle beam image is affected by an amount of current carried by a charged particle beam. In order to acquire a high-contrast scan image, the amount of beam current has to be increased. However, if the amount of beam current increases, a probe diameter expands due to the Coulomb's law. In order to focus a spread beam on a sample, an objective lens whose lens action is intense is needed. In the case of a magnetic-field type objective lens that narrows a beam by causing a magnetic field to leak out to the ray axis of a primary charged particle beam, a magnitude of excitation has to be increased in order to intensify the lens action. However, as long as a magnetic field type objective lens has the conventional structure, even if a magnitude of excitation is increased, an expected lens action cannot be exerted. A magnitude of a magnetic flux occurring in a magnetic path in the objective lens is restricted by magnetic saturation. The saturated magnetic flux density in the magnetic path is determined with a magnetic material made into the magnetic path. Therefore, even if the magnitude of the magnetic flux occurring in the magnetic path increases, a magnetic flux unacceptable by the magnetic path leaks out from any part of the magnetic path. As a result, the lens action is not so intensified as the increase in the magnitude of excitation. In particular, when an accelerating voltage for a charged particle beam is increased, if a probe-like beam of high energy is produced, an incident that the beam cannot be focused may take place. Further, when a magnetic flux leaks out to the trajectory of secondary charged particles, the number of secondary charged particles reaching a detector decreases. Eventually, the quality of an acquired scan image deteriorates. When a magnitude of a magnetic flux is distributed along the axis of a beam, a lens action is exerted. Therefore, in order to approach a site of action of the lens to a sample, when a magnitude of a magnetic flux is increased, a magnetic flux distribution is developed near the desired site of action at the same time. Thus, the magnetic flux distribution has to be prevented from spreading to an axial position away from the site of action. A resolution offered by a charged particle beam apparatus is determined with the probe diameter of a beam. When the energy of a charged particle beam decreases, the probe diameter increases due to chromatic aberration and the resolution is degraded. What is referred to as the chromatic aberration is an aberration attributable to a velocity distribution of a charged particle beam emitted from an electron source. In the retarding method, if a position at which the charged particle beam is decelerated is approached to the sample, the adverse effect of aberrations can be lessened. Therefore, when an apparatus is designed, the working distance of an objective lens is designed to be as short as possible. However, since an objective lens and a sample into must not be physically brought into contact with each other, a technique for lessening the adverse effect of aberrations by decreasing the working distance of the objective lens has its limitations. In the case of the retarding method, since there is a large potential difference between the sample (or a sample stage) and objective lens, if the working distance is made too short, there is a risk that the sample may be destroyed with electric discharge. The inventions described in JP-A-6-139985, JP-A-2001-185066, and JP-A-6-260127 are intended to provide an electron microscope that acquires a high-contrast and high-resolution observation image. For measurement or inspection of a microscopic circuit for which the ongoing apparatuses are designed, even when an apparatus is produced using the conventional technology described in any of JP-A-6-139985, JP-A-2001-185066, and JP-A-6-260127, basic performance such as a contrast or a resolution is insufficient. In particular, when it comes to semiconductor devices fabricated using a micro-machining technology, a signal generated from a concave part such as a contact hole or a line pattern is so feeble that observation of a microscopic object or measurement of a length is terribly hindered. The present invention provides a charged particle beam apparatus that adopts a retarding method and a magnetic field type objective lens for a charged particle optical system. In the charged particle beam apparatus, a lower magnetic pole member of an objective lens is divided into upper and lower stages. The potential at a magnetic pole member on a sample side of the divided lower magnetic pole member is controlled into an intermediate potential between the potential at a magnetic pole member on a side far away from a sample and the potential at the sample. Thus, the charged particle beam apparatus can detect a high-contrast and high-resolution secondary-charged particle signal. Preferably, the potential at the magnetic pole member on the sample side is controlled to be equal to the potential at the sample. Since the lower magnetic pole member is divided into the upper and lower stages, an induced magnetic flux is concentrated on the distal part of an upper magnetic pole member (upper pole piece) and the distal part of the lower magnetic pole member (lower pole piece). This is attributable to the fact that when the lower pole piece is placed adjacently to the sample, the magnetic flux extending from the upper pole piece to the lower pole piece can be concentrated on the sample. The division of the magnetic pole member makes it possible to form an objective lens that exerts a greater lens action than a conventional objective lens does. The magnetic pole member on the sample side alleviates a potential gradient between the bottom of the objective lens and the sample, and acts as means for suppressing electric discharge of the sample. Owing to the present invention, an objective lens that exerts a satisfactory lens action on a primary charged particle beam having a large amount of beam current and requiring a high accelerating voltage can be manufactured. Eventually, a charged particle beam apparatus offering a high contrast and a high resolution can be realized. Since the charged particle beam apparatus offering a high contrast and a high resolution can be realized, a charged particle beam application apparatus permitting observation of a microscopic defect, measurement of a length, and assessment of a shape can be provided. For brevity's sake, in relation to embodiments to be described below, examples in which the present invention is applied to an apparatus using a scanning electron microscope will be mainly described. An electromagnetic superposition type objective lens in each of the embodiments can be generally adapted to charged particle beam apparatuses including an electron beam apparatus and an ion beam apparatus. In the embodiments to be described below, apparatuses that deal with a semiconductor wafer as a sample will be described. As for samples to be dealt with by various types of charged particle beam apparatuses, in addition to the semiconductor wafer, various samples including a semiconductor substrate, a fragment of a wafer having a pattern formed therein, a chip cut out from the wafer, a hard disk, and a liquid crystal panel can be regarded as objects of inspection or measurement. Embodiment 1 In relation to an embodiment 1, an example in which the present invention is applied to a scanning electron microscope will be described below. FIG. 1A is an illustrative diagram showing an overall constitution of a scanning electron microscope. The scanning electron microscope of the present embodiment includes: an electron optical system 102 formed in a vacuum housing 101; an electron optical system control device 103 disposed on the perimeter of the electron optical system; a host computer 104 that controls control units included in respective control power supplies, and controls the whole of the apparatus on a centralized basis; an operator console 105 connected to the control device; and display means 106 including a monitor on which an acquired image is displayed. The electron optical system control device 103 includes a power supply unit that feeds a current or a voltage to each of the components of the electron optical system 102, and signal control lines over which control signals are transmitted to the components. The electron optical system 102 includes: an electron source 111 that produces an electron beam (primary charged particle beam) 110; a deflector 112 that deflects the primary electron beam; an electromagnetic superposition type objective lens 123 that focuses the electron beam; a booster magnetic path member 116 that focuses or diffuses secondary particles 115 emitted from a sample 114 held on a stage; a reflecting member 118 with which the secondary particles collide; and a central detector 122 that detects collateral (tertiary) particles reemitted due to the collision. The reflecting member 118 is formed with a disk-shaped metallic member having a passage opening for a primary beam formed therein. The bottom of the reflecting member 118 realizes a secondary-particle reflecting surface 126. An electron beam 110 emitted from the electron source 111 is accelerated due to a potential difference developed between a extracting electrode 130 and an accelerating electrode 131, and routed to the electromagnetic superposition type objective lens 123. The objective lens 123 focuses an incident primary electron beam on the sample 114. Referring to FIG. 1B, the internal structure of the electromagnetic superposition type objective lens 123 included in the present embodiment will be detailed below. In FIG. 1B, in addition to the internal structure of the electromagnetic superposition type objective lens 123, the sample 114 to be measured or inspected is shown. The electromagnetic superposition type objective lens 123 in the present embodiment includes at least: three members, that is, a yoke member 132 disposed around the ray axis of a primary electron beam (or the center axis of the electron optical system 102), the booster magnetic path member 116 disposed in a space between the yoke member 132 and the ray axis of the primary electron beam, and a control magnetic path member 133 disposed in a closed space defined between the bottom of the yoke member 132 and the sample 114; and a coil 134. The ray axis of the primary electron beam or the center axis of the electron optical system 102 is often aligned with the center axis of the electromagnetic superposition type objective lens 123 or vacuum housing 101. The yoke member 132 in FIG. 1B is formed with a hollowed annular member, and the section of the yoke member 132 is shaped like a trapezoid having the side thereof, which is opposed to the ray axis of the primary electron beam, inclined. In the electromagnetic superposition type objective lens in the present embodiment, the yoke member is disposed so that the ray axis of the primary electron beam will pass through the center of the annular member. The coil 134 is sustained inside the yoke member 132 that is the annular member. A magnetic flux to be used to focus the primary electron beam is excited by the coil. A space is formed on the internal surface side of the bottom of the trapezoidal shape (the side opposed to the primary electron beam). Owing to the space, the excited magnetic flux does not form a closed magnetic path in the yoke member 132 but extends to the booster magnetic path member 116 and control magnetic path member 133. An opening through which the primary electron beam passes is formed in the top of the yoke member 132 (a falling direction of the primary electron beam) and in the bottom thereof (an emitting direction of the primary electron beam). A soft magnetic material is adopted as the material of the yoke member. Although the yoke member 132 shown in FIG. 1B is realized with the annular member having a trapezoidal section, as long as the capability to transfer the excited magnetic flux to the booster magnetic path member 116 and control magnetic path member 133 is exerted, the shape of the yoke member 132 is not limited to any specific one. For example, the section of the yoke member may be shaped like a bracket. The booster magnetic path member 116 is a cylindrical (or conical) member formed along the internal surface (area opposed to a primary electron beam) of the annular member realizing the yoke member 132. The booster magnetic path member 116 is disposed in the electromagnetic superposition type objective lens so that the center axis of the cylinder will be aligned with the ray axis of the primary electron beam (or the center axis of the vacuum housing 101). As the material, a soft magnetic material is adopted as it is for the yoke member 132. The lower distal end of the cylinder (the distal part of the side thereof opposed to the sample) acts as a magnetic pole (pole piece) on which a magnetic flux excited by the coil is concentrated. The control magnetic path member 133 is disposed on the side of the bottom of the yoke member 132. The control magnetic path member 133 is a disk-like or conical soft magnetic plate having an opening, through which the booster magnetic path is extended, in the center thereof. The yoke member 132 is disposed to have the axis thereof aligned with the ray axis of a primary electron beam in the electromagnetic superposition type objective lens. The opening edge of the control magnetic path member 133 realizes a magnetic pole on which a magnetic flux is concentrated. If a magnetic flux is concentrated on a gap between the magnetic pole of the control magnetic path member 133 and the magnetic pole of the booster magnetic path member 116, a lens effect that is greater than a conventional one can be exerted on a primary electron beam. A pole piece belonging to the booster magnetic path member may be called an upper magnetic pole, and a pole piece belonging to the booster magnetic path member may be called a lower magnetic pole. Not only the control magnetic path member 133 and booster magnetic path member 116 but also the yoke member 132 and control magnetic path member 133 and the yoke member 132 and booster magnetic path member 116 are spatially separated from each other with a predetermined gap between them. However, the yoke member 132, control magnetic path member 133, and booster magnetic path member 116 are magnetically intensively coupled to one another. A magnetic flux excited by the coil 134 penetrates through the magnetic path members. The distal part of the objective lens in which the booster magnetic path member 116 and control magnetic path member 133 adjoin is formed to be so thin as to have a thickness of 3 mm or less in order to concentrate the magnetic flux adjacently to the sample. The proximal part of the objective lens in which the booster magnetic path member 116 adjoins the yoke member 132 is formed to have a thickness of 1 cm or more in order to avoid magnetic saturation. Next, potentials to be developed at the booster magnetic path member 116, yoke member 132, and control magnetic path member 133 will be described below. The yoke member 132, control magnetic path member 133, and booster magnetic path member 116 are electrically isolated from one another with an insulating material between each pair of them. A voltage that causes the potential at the booster magnetic path member 116 relative to the potential at the yoke member 132 to be positive and that causes a potential difference from the potential at the accelerating electrode 131 to be positive is applied to the booster magnetic path member 116. The voltage is fed from a booster power supply 135. The yoke member 132 is retained at a ground potential. Therefore, the electron beam 110 passes through the booster magnetic path member 116 while being most greatly accelerated on the trajectory thereof due to the potential difference between the accelerating electrode 131 and booster magnetic path member 116. Even in the charged particle beam apparatus of the present embodiment, the retarding method is adopted. Therefore, a decelerating electric field has to be induced between the objective lens and sample. A voltage causing the potential at the control magnetic path member 133 relative to the potential at the yoke magnetic field member 132 to be negative is applied to the control magnetic path member 133. The voltage is fed from a control magnetic path power supply 136. A voltage causing a potential difference from the potential at the booster magnetic path member 116 to be negative is applied from a stage power supply 141 to the stage 140. Therefore, the electron beam 110 having passed through the booster magnetic path member 116 is rapidly decelerated to reach the surface of the sample. Since the landing energy of a primary beam is determined solely with the potential difference between the electron source 111 and stage 140, if voltages to be applied to the electron source 111 and stage 140 respectively are controlled into predetermined values, the landing energy can be controlled into a desired value irrespective of the voltages to be applied to the booster magnetic path member 116 and accelerating electrode 131. For a better understanding, if the relationships among the control voltage values for the foregoing components are expressed with equations, the equations are described as follows:Electron source<sample<control magnetic path member<yoke member whose potential is approximately equal to 0 V<booster magnetic path member (1)Electron source<accelerating electrode whose potential is approximately equal to 0 V<booster magnetic path member (2) Therefore, when the voltages to be applied to the accelerating electrode 131 and booster magnetic path member 116 respectively are set to values that are positive relative to the potential at the electron source 111, the electron beam 110 can rapidly pass through the electron optical system 102. The probe diameter of the electron beam 110 on the sample can be decreased. However, a decelerating action on the electron beam 110 exerted between the electromagnetic superposition type objective lens 123 and sample hinders a focusing action of the lens. Therefore, the electromagnetic superposition type objective lens 123 is requested to exert an intense beam focusing action. By approaching the electromagnetic superposition type objective lens 123 to the sample, the electron beam 110 can be focused more thinly. The electromagnetic superposition type objective lens 123 is therefore requested to exert the intense focusing action at a distance immediately above the sample. FIG. 2 shows axial magnetic field distributions on an objective lens with the control magnetic path member and an objective lens without it, and also shows the positional relationship among the magnetic pole members in the electromagnetic superposition type objective lens in the present embodiment. In the left part of FIG. 2, the curvature of each of curves, which are drawn with a solid line and a dashed line respectively, in the direction of the axis of abscissas expresses a magnetic flux density distribution on the axis (nearly aligned with the ray axis of a primary electron beam). The axis of ordinates indicates heights in the objective lens. The curve drawn with the solid line is concerned with the objective lens with a third magnetic pole, and the curve drawn with the dashed line is concerned with the objective lens without the third magnetic pole. Since the intensity of a lens action is nearly proportional to the degree and sharpness of the magnetic flux density distribution, the lens action of the electromagnetic superposition type objective lens can be thought to be exerted at a position associated with the peak of the curve shown in FIG. 2. In the right part of FIG. 2, a solid line depicting an electron beam schematically expresses a section of a primary electron beam that undergoes the lens action of the objective lens with the third magnetic pole, and a dashed line depicting an electron beam schematically expresses a section of a primary electron beam that undergoes the lens action of the objective lens without the third magnetic pole. In the schematic diagram of the right part of FIG. 2, the booster magnetic path member, yoke member, and control magnetic path member are shown as a first magnetic pole, a second magnetic pole, and a third magnetic pole respectively. In the arrangement of the magnetic poles in the objective lens shown in the schematic diagram of the right part of FIG. 2, the third magnetic pole can be disposed at a position closer to a sample than a position in the related art. Therefore, the lens action exerted position of the objective lens can be more greatly approached to the sample than that can in the related art. In the case of a charged particle beam apparatus adopting the retarding method, a negative high voltage is conventionally applied to a sample in order to induce a retarding electric field, and a voltage (typically, a ground potential) higher than the voltage applied to the sample is applied to the second magnetic pole. Therefore, the distance between the second magnetic pole and sample cannot help being set to a long distance that does not bring about electrical discharge. Therefore, the conventional second magnetic pole cannot be approached to the sample as close to the sample as the third magnetic pole in the present embodiment is. In the electromagnetic superposition type objective lens of the present embodiment, since a voltage nearly identical to a retarding voltage is applied to the third magnetic pole, the objective lens is devoid of a drawback of electric discharge between a sample and an electrode. The gap between the third magnetic pole and sample can be narrowed. Therefore, a position at which an intense lens action is exerted can be more closely approached to the sample than it is conventionally. Since a negative high voltage equivalent to the retarding voltage is applied to the control magnetic path member 133, the control magnetic path member 133 has to have a structure, which can withstand a high voltage, in relation to the yoke member 132. The third magnetic pole is functionally equivalent to a separated magnetic path on the side of the bottom of the conventional second magnetic pole. As mentioned previously, when a magnetic path is separated, a degree of concentration of a magnetic flux on each of upper and lower magnetic poles rises. An objective lens that exerts an intense focusing action on the electron beam 110 can be realized. As a result, the electron beam 110 can be focused more thinly. Eventually, high-resolution microscopic observation is enabled. For the foregoing reason, the electromagnetic superposition type objective lens of the present embodiment can balance a short focal length of a lens and a focusing action. Even in the electromagnetic superposition type objective lens of the present embodiment, there is a limitation in decreasing the working distance. The limitation is determined with the upper limit of the intensity of a lens action. The intensity of a lens action becomes larger along with an increase in an amount of current to be fed to the coil 134. However, since the yoke member 132, control magnetic path member 133, and booster magnetic path member 116 are magnetically saturated, if the amount of exciting current is increased, the peak of an axial magnetic field becomes obtuse. If the peak disappears, the focusing action of the electromagnetic superposition type objective lens 123 deteriorates. High-resolution microscopic observation is disabled. The shortest distance between the electromagnetic superposition type objective lens 123 and sample making it possible to avoid the deterioration of the focusing action is the lower limit of the working distance, and shall be called the shortest focal length in the present embodiment. For adjustment of the electron optical system 102, an exciting current for the objective lens may have to be adjusted according to various control parameters for the optical system. For example, when the landing energy of the electron beam 110 is changed, the magnitude of excitation has to be adjusted based on a degree of adjustment to which the landing energy is adjusted. In FIG. 3, the dependency of the shortest focal length on the landing energy of an electron beam is shown by comparing the objective lens in the present embodiment with the conventional objective lens. A solid line indicates the dependency of the shortest focal length of the objective lens with a third magnetic pole, and a dashed line indicates the dependency of the shortest focal length of the objective lens without the third magnetic pole. Domains on the upper sides of the solid line and dashed line correspond to domains of in-focus points. As seen from FIG. 3, as long as the landing energy remains unchanged, the shortest focal length of the objective lens of the present embodiment including the third magnetic pole can be more greatly shortened than that of the conventional objective lens without the third magnetic pole. This is because when the focusing action on the electron beam 110 is intensified by approaching the peak of a sharp axial magnetic field to a position immediately above a sample, the magnetic saturation of the first magnetic pole can be avoided. Owing to the constitution of the electromagnetic superposition type objective lens of the present embodiment, an electron beam whose landing energy ranges from 50 eV to 10 keV can be focused by the electromagnetic superposition type objective lens having the ability to focus a beam. The secondary particles 115 derived from irradiation of a primary beam have a negative polarity, and are therefore accelerated due to a potential difference between the sample 114 and booster magnetic path member 116. The resultant secondary particles reach the top of the electromagnetic superposition type objective lens 123. The secondary particles 115 having passed through the booster magnetic path member 116 to which a high voltage is applied are rapidly decelerated. Thereafter, the secondary particles 115 reach the upper reflective member 118 and collide with the secondary-particle collision surface 126. This results in tertiary particles 147. In a main body of the central detector 122 disposed by the side of the upper reflecting member, an attracting electric field is induced by a central fetching power supply 148. The reemitted tertiary particles are fetched into the detector with the strong electric field. Thus, a top-view image can be obtained. An axial detector (a multi-channel plate, axial scintillator, or semiconductor detector) may be substituted for the upper reflecting member 118 and central detector 122. A primary electron beam focused using the foregoing electromagnetic superposition type objective lens is swept over a sample. Secondary charged particles derived from the sweep are detected and imaged by the host computer 104. Thus, microscopic observation with a higher resolution than the conventional one is enabled. Embodiment 2 In relation to the present embodiment, an example in which the present invention is applied to a review SEM will be described below. FIG. 4 is an overall constitution diagram of the review SEM of the present embodiment. An iterative description of components whose operations and capabilities are identical to those of the components shown in FIG. 1 will be omitted in order to avoid a complication. The review SEM shown in FIG. 4 broadly includes: an electron optical system 102 formed in a vacuum housing 101; an electron optical system control device 103 disposed on the perimeter of the electron optical system; a host computer 104 that controls the control units included in respective control power supplies and controls the whole of the apparatus on a centralized basis; an operator console 105 connected to the control device; and display means 106 including a monitor on which an acquired image is displayed. The electron optical system control device 103 includes a power unit that feeds a current or a voltage to each of the components of the electron optical system 102, and signal control lines over which control signals are transmitted to the respective components. The components of the electron optical system 102 are nearly identical to those of the electron optical system described in conjunction with FIG. 1. A difference lies in that the electron optical system 102 includes a detecting capability for a shaded image. What is referred to as the shaded image is an image that has shades thereof enhanced and that is obtained by discriminating or detecting the azimuth angles and elevation angles of secondary electrons and reflected electrons that are generated from a sample to be inspected (a sample image having lights and darks associated with concave and convex parts of the surface of a sample). Using the shaded image, a defect can be efficiently detected. The electron optical system 102 of the review SEM of the present embodiment includes as discriminating means, which discriminates the azimuth angles and elevation angles of secondary particles, two reflecting members of a lower reflecting member 117 and an upper reflecting member 118, and a left detector 120, a right detector 121, and a central detector 122 that detect collateral (tertiary) particles 119 reemitted due to collision of secondary particles with the reflecting members. The lower reflecting member 117 is disposed between an electromagnetic superposition type objective lens 123 and a deflector 112. The lower reflecting member 117 is formed with a conical metal member and has a left collision surface 124 and a right collision surface 125, with which the secondary particle collide, formed on the flank thereof. The upper reflecting member 118 is formed with a disk-like metal member having a passage opening, through which a primary beam passes, formed therein. The bottom of the upper reflecting member 118 realizes a secondary-particle reflecting surface 126. The disposed positions of the left detector 120, right detector 121, and central detector 122 are not limited to those shown in FIG. 4 but may be altered. For example, if an axial detector is disposed on the secondary-particle reflecting surface of the upper reflecting member 118, the same capability as the capability of the central detector 122 can be realized. If an axial detector is disposed on each of the left collision surface 124 and right collision surface, nearly the same capabilities as those of the left detector 120 and right detector 121 can be realized. If an electromagnetic superposition type deflector (E×B deflector) is disposed on the ray axis of a primary electron beam, the primary electron beam 110 is not deflected but tertiary particles emitted from the secondary-particle reflecting surface can be guided to the central detector 122. The secondary particles 115 derived from irradiation of a primary beam have a negative polarity and are therefore accelerated due to a potential difference between the sample 114 and booster magnetic path member 116. The secondary particles then reach the top of the electromagnetic superposition type objective lens 123. The secondary particles 115 having passed through the booster magnetic path member 116 to which a high voltage is applied are rapidly decelerated. High-velocity components (reflected electrons) contained in the secondary particles have the trajectory thereof separated from the trajectory of low-velocity components, and collide with the left collision surface 124 and right collision surface 125 of the lower reflecting member 117. Using the electromagnetic superposition type objective lens of the present embodiment, the trajectory separation can be realized and both a contrast and a resolution of a shaped image can be improved. A voltage for electric-field formation to be used to guide the tertiary particles 119, which are derived from collision of the high-velocity components of the secondary particles 115, into the left detector 120 and right detector 121 is fed from a left power supply 142 or right power supply 143 to the left collision surface 124 or right collision surface 125. At this time, the number of reflected electrons to be fetched into each of the left detector 120 and right detector 121 can be controlled. The left power supply 142 and right power supply 143 may be integrated into one unit in order to bring the left collision surface 124 and right collision surface 125 to the same potential. However, this makes it impossible to control the number of reflected electrons. Further, a voltage for electric-field formation to be used to fetch the guided reflected electrons into the detector is fed from a left fetching power supply 144 or a right fetching power supply 145 to the left detector 120 or right detector 121. Reflected electrons advance from the sample 114 toward the lower reflecting member 117 while being rotated by a magnetic field induced by the electromagnetic superposition type objective lens 123. In consideration of the rotation caused by the magnetic field, coordinates representing each of positions on the lower reflecting member 117 with which the reflected electrons collide are associated with azimuth angles at which the respective reflected electrons are emitted from the sample. Therefore, when the left collision surface 124 and right collision surface 125 are disposed in consideration of a magnitude of rotation caused by the magnetic field, the coordinates may be associated with each of concave and convex parts of the surface of the sample. The secondary particles 146 having the reflected electrons (strictly speaking, the high-velocity components of secondary particles) separated therefrom reach the upper reflecting member 118 located on the side of the electron source 111 at a shorter distance than the distance in which it is located away from the lower reflecting member 117. The secondary particles collide with the secondary-particle collision surface 126, whereby tertiary particles 147 are generated. In the main body of the central detector 122 disposed by the side of the upper reflecting member, an attracting electric field is induced by the central fetching power supply 148. The reemitted tertiary particles are fetched into the detector with the strong electric field. Thus, a top-view image can be acquired concurrently with an irregularities image of the surface of a sample. The electron optical system of the review SEM of the present embodiment includes an assistant electrode for secondary-electron focusing on the side of the electron source 111 away from the electromagnetic superposition type objective lens 123. The assistant electrode is formed with a conductor plate having an opening through which the electron beam 110 passes. The magnitudes of a retarding voltage and an accelerating voltage are controlled so that a majority of secondary electrons emitted from a sample will pass through the opening. Since diffusion of the secondary electrons is suppressed by the assistant electrode, a high-contrast sample image having different lights and darks associated with the concave and convex parts of the surface of the sample can be acquired. However, when a resist film or an insulating film is inspected in the process of forming an LSI, electrification or damage occurs due to irradiation of a charged particle beam for image formation. Due to the electrification, the trajectory of secondary electrons may change and luminous flecks (shading) may appear in an observation image. In the constitution of the apparatus of the present embodiment, a secondary-particle detector is located at a position, at which the detector is axially symmetrical to the ray axis of a primary electron beam, in order to discriminate azimuth angles of secondary particles. If a sample is electrified, the ray axis of the trajectory of the secondary particles is shifted relatively from the center axis of the detector. Shading occurs on such an occasion. If a shaded image is enhanced in order to improve the sensitivity in detecting a defect, an adverse effect of the shift of the trajectory of secondary electrons on the observation image is intensified. The shading is likely to occur readily. At this time, when only higher-velocity components are separated from the secondary particles through focusing control by the assistant electrode so that the higher-velocity components will collide with the left collision surface 124 and right collision surface 125, the shading can be suppressed. In other words, when high-resolution and high-contrast SEM observation is implemented in a state devoid of the shading and damage, an inspection method that is superior in detection sensitivity and a detection speed can be provided. In addition to beam landing, an amount of beam current carried by the primary electron beam has to be appropriately determined in line with an object of observation. The scanning electron microscope of the present embodiment can implement automatic control in two operating modes, that is, an operating mode (review mode) in which a defect image is rapidly acquired and an operating mode (length measurement mode) in which the length of a fabricated pattern is measured or the fabricated pattern is inspected. Two selection buttons Review Mode and Length Measurement Mode and a button Electrification Cancel are always displayed on the display screen of the display means 106. A user of the apparatus can select any of the buttons using the operator console 105. Further, an image processing unit is incorporated in the host computer 104. If a surface potentiometer is included, a degree-of-electrification distribution on a wafer can be measured and a degree-of-electrification distribution function can be stored in the host computer 104. If a Z sensor is included, the distance between the sample 114 such as the wafer and the electromagnetic superposition type objective lens 123 can be measured all the time. Pieces of information on parameters that should be specified in the electron optical system control device, a stage control device, and the image processing unit in association with the operating modes are stored in the host computer 104. If necessary, the information is transmitted to the electron optical system control device 103. When shading occurs, if the operation of the apparatus is switched to the electrification cancel mode, the shading can be removed. When the user of the apparatus depresses the Electrification Cancel button, voltages to be applied to the assistant electrode interposed between the yoke member 132 and lower reflecting member 117 and to the lower reflecting member 117 are changed. Thus, the conditions for secondary-particle detection dependent on the electrified state of a sample are satisfied. Eventually, an image having shading removed therefrom can be produced. The foregoing constitution is the minimum constitution of the review SEM for implementing the present embodiment. For example, a condenser lens that helps focus an electron beam or a Faraday cup that measures a beam current may be included in order to accomplish the capabilities of the present embodiment. For example, when the condenser lens is interposed between the accelerating electrode 131 and upper reflecting member 118, the condenser lens can help focus the electron beam. Further, when a current limiting diaphragm is interposed between two stages of condenser lenses, the beam current and the spread of a beam in the objective lens can be mutually independently controlled. Thus, the condenser lenses can help focus the electron beam. The deflector 112 generally falls into an electrostatic type and an electromagnetic type. In the review mode, a defect image is acquired according to a procedure described below. (1) A desired wafer is loaded into the apparatus. (2) The wafer is aligned. (3) The electron optical system is moved to a defective point represented by coordinates and an in-focus point is located. (4) A defect observation image is acquired. For acquiring the defect observation images of multiple points on the wafer, the steps (3) and (4) are repeated. The procedure is effective means for collecting a large number of defect observation images quickly. If the precision in coordinates representing a defective point is found to be insufficient at the step (3), the apparatus executes the flow from step (5) to step (8) described below so as to detect accurate coordinates representing a defective point. Eventually, a defect image is acquired. (5) The optical magnification of the electron optical system is made lower that that in the state established at the step (3). (6) An in-focus point is located at the same position. If necessary, an electron-beam irradiation area is finely adjusted by adjusting the position of the stage or shifting an image. (7) A low-magnification observation image is acquired, and is subjected to image processing in order to identify the defective point. (8) The optical magnification of the electron optical system is made higher than that designated at the step (5). (9) A defect observation image is acquired. For acquiring defect observation images of multiple points on the wafer, the steps (3) to (9) are repeated. If a defective point cannot be identified merely by performing image processing at the step (7), a defect observation image is acquired according to a procedure described below. (10) The electron optical system is moved to the position of a die adjoining a defective point which is represented by coordinates, and an in-focus point is located. (11) A low-magnification observation image is acquired. (12) The electron optical system is moved to the defective point represented by coordinates, and an in-focus point is located. (13) A low-magnification observation image is acquired, and compared with the observation image acquired at the step (11) in order to identify the defective point. (14) The optical magnification of the electron optical system is raised in order to acquire an image of the identified defective point. For acquiring defect observation images of multiple points on the wafer, the steps (10) to (14) are repeated. When the apparatus executes the steps (10) to (14), the apparatus can collect defect observation images while flexibly coping with the precision in coordinates representing a defective point or the size of the defect. In the length measurement mode, an observation image of a fabricated pattern is acquired according to a procedure described below. (1) A desired wafer is loaded in the apparatus. (2) The wafer is aligned. (3) The electron optical system is moved to an observation point represented by coordinates, and an in-focus point is located. (4) An observation image of a fabricated pattern is acquired. For acquiring observation images of fabricated patterns at multiple points on the wafer, the steps (3) and (4) are repeated. The procedure is effective means for quickly collecting a large number of observation images of fabricated patterns. If the precision in coordinates representing an observation point is found to be insufficient at the step (3), an observation image is acquired according to a procedure described below. (5) The wafer is aligned again. (6) The electron optical system is moved to the alignment point represented by coordinates, and an in-focus point is located. (7) An alignment observation image is acquired, and an observation point represented by coordinates is aligned through image processing. (8) The electron optical system is moved to the observation point represented by coordinates, and an in-focus point is located. (9) An observation image of a fabricated pattern is acquired. For acquiring observation images of multiple points on the wafer, the steps (6) to (9) are repeated. For assessing the shape of a fabricated pattern, an observation image of the fabricated pattern is acquired according to a procedure described below. (10) The electron optical system is moved to an observation point, which is represented by coordinates, in a die adjoining a position at which an image is acquired at the step (9), and an in-focus point is located. (11) A reference observation image is acquired. (12) The electron optical system is moved to an observation point represented by coordinates, and an in-focus point is located. (13) An observation image is acquired and compared with the reference observation image acquired at the step (11). If the precision in coordinates representing an observation point is found to be insufficient at the step (10) or (12), an observation image is acquired according to a procedure described below. (14) The wafer is aligned again. (15) The electron optical system is moved to an alignment point on the adjoining die which is represented by coordinates, and an in-focus point is located. (16) An alignment observation image is acquired, and an observation point represented by coordinates is aligned through image processing. (17) The electron optical system is moved to a reference observation point, which is represented by coordinates, in the adjoining die, and an in-focus point is located. (18) A reference observation image of a fabricated pattern is acquired. (19) The electron optical system is moved to an alignment point which is represented by coordinates, and an in-focus point is located. (20) An alignment observation image is acquired, and an observation point represented by coordinates is aligned through image processing. (21) The electron optical system is moved to the observation point represented by coordinates, and an in-focus point is found. (22) An observation image of a fabricated pattern is acquired and compared with the reference observation image acquired at the step (18). For acquiring observation images of fabricated patterns at multiple points on the wafer, the steps (15) to (22) are repeated. The procedure is means capable of collecting observation images while flexibly coping with the precision in coordinates representing an observation point or the fabricated pattern. Next, a control method for the electromagnetic superposition type objective lens included in the review SEM of the present embodiment will be described below. In either the review mode or length measurement mode, the focal point of an electron beam has to be controlled using the electromagnetic superposition type objective lens in order to locate an in-focus point. However, the scanning electron microscope of the present embodiment cannot largely change the focal position due to such restrictions as limitations in the focal length of the electromagnetic superposition type objective lens or limitations imposed on a detector according to a change in a position on a reflecting member with which secondary particles collide. The factors causing the focal position to largely change are two of electrification of a sample and the height of the sample. When the sample electrification causes the large change in the focal position, if a retarding voltage is finely adjusted, an in-focus point can be detected without the restrictions of the limitations in the focal position of the electromagnetic superposition type objective lens and the limitation imposed on a detector. When the sample height causes the large change in the focal position, an in-focus position can be detected according to, for example, a technique described below. (1) An electrostatic chuck is used to reduce a warp in the surface of a wafer at the time of immobilizing the wafer on the stage. (2) The height of the stage is controlled in line with the thickness of the sample. (3) An exciting current for the coil included in the electromagnetic superposition type objective lens is changed. (4) A voltage to be applied to the booster magnetic path member is changed. Owing to the foregoing constitution, reflected electrons can be discriminated and detected, and an image having a shade contrast thereof enhanced can be acquired. Eventually, a microscopic foreign matter having shallow irregularities can be highly sensitively detected. Embodiment 3 In relation to the present embodiment, an example of a constitution of a review SEM including an electrostatic adsorption device will be described below. FIG. 5 is an overall constitution diagram of the review SEM of the present embodiment. As for the components other than an electrostatic chuck, since the operations and capabilities thereof are identical to those of the components shown in FIG. 4, an iterative description of the components other than the electrostatic chuck will be omitted. The review SEM of the present embodiment has a sample stage thereof provided with an electrostatic chuck mechanism. In addition to signal control lines and a power unit for the electron optical system 102, a stage control device is incorporated in the electron optical system control device 103. The stage control device includes a power unit that feeds a current or a voltage to the components of the electrostatic chuck, and signal control lines over which control signals are transmitted to the respective components. The electrostatic chuck mechanism includes a dielectric layer 200 and an internal electrode 201, which are incorporated in the stage 140, and an internal electrode power supply 203 that applies a voltage across the internal electrode 201 and wafer 114. Along with application of a voltage, electrostatic adsorption force is generated between the internal electrode 201 and wafer 114, and the wafer 114 is adsorbed by the generated force. Depending on an adsorption method, the electrostatic chuck generally falls into a Coulomb force type and a Johnson-Rabeck force type. The Coulomb force type can reduce a current flowing across the internal electrode 201 and wafer, and the Johnson-Rabeck force type can reduce a potential difference between the internal electrode 201 and wafer. In general, the electrostatic chuck falls into a mono-polar method and a bipolar method according to the internal electrode 201 located below the dielectric layer 200. The bipolar method can keep charges, which are accumulated on the dielectric layer 200 and wafer 114, neutral. The stage 140 is provided with a contact electrode 202 to be used to bring the stage into contact with a wafer. A potential causing a potential difference from the potential at the booster magnetic path to be negative is developed at the contact electrode 202. When the potential difference between the control magnetic path member 133 and contact electrode 202 falls within ±100 V, the potential difference between the wafer and control magnetic path can be controlled. Owing to the control of the potential difference, the efficiency in focusing a primary beam or collecting and discriminating secondary particles can be controlled. Eventually, a high-resolution top-view image and a high-resolution shaded image can be obtained. When an object of observation is a large flat-plate sample such as a wafer, if the electrostatic chuck is adopted as the sample stage, a warp of the sample is suppressed, and an observation area including an electron-beam irradiation area is flattened. Since a variance in the gap between the wafer and control magnetic path is suppressed, the magnetic poles in the objective lens can be approached to the sample accordingly. The electromagnetic superposition type objective lens of the present invention capable of balancing a short focal length of a lens and a focusing action thereof is highly compatible with the electrostatic chuck. When the electromagnetic superposition type objective lens and electrostatic chuck are used in combination, an irradiation optical system whose working distance is shorter than that of the charged particle optical system described in relation to the embodiments 1 and 2 can be realized. Thus, a primary beam can be more thinly focused, the beam diameter can be reduced, and the efficiency in collecting and discriminating secondary particles can be improved. Eventually, a high-resolution top-view image and a high-resolution shaded image can be obtained. FIG. 6A and FIG. 6B show a variant of the review SEM including the electrostatic adsorption device. FIG. 6A is an overall constitution diagram of the review SEM, and FIG. 6B is an illustrative diagram showing the structure of an electromagnetic superposition type objective lens including a temperature control mechanism for a control magnetic path member. The electrostatic chuck dissipates heat when adsorbing the wafer 114. In particular, the Johnson-Rabeck force type electrostatic chuck dissipates much heat. Therefore, after the wafer is adsorbed by the electrostatic chuck, the wafer 114 is thermally expanded until the temperature is stabilized. When the wafer is thermally expanded, the drift of a beam landing position occurs, and a blur appears in an observation image. In addition, the alignment of the wafer is broken. The electron optical system cannot be moved to a desired point on the wafer represented by coordinates, and automatic control in the review mode or length measurement mode cannot be implemented. In order to suppress the drift, it is necessary to manage the temperature of the wafer. In general, the electrostatic chuck mechanism includes a temperature control mechanism. The temperature of the stage 140 can be controlled by pouring an air or liquid into a pipe 300 in the electrostatic chuck. However, measurement of the temperatures of the wafer 114 and electrostatic chuck has revealed that a temperature difference is observed between the wafer and electrostatic chuck. This is attributable to the inflow of radiant heat into the wafer. The electromagnetic superposition type objective lens 123 acts as a heating source because the electromagnetic superposition type objective lens causes a large current to flow into the coil 134 due to the necessity of exciting a strong magnetic field. In particular, since the control magnetic path in the electromagnetic superposition type objective lens is opposed to the wafer with a narrow gap between them, the control magnetic path is largely involved with the inflow of radiant heat to the wafer. Therefore, a mechanism for controlling the temperature of the control magnetic path member is included in the control magnetic path member. A cooling pipe 301 through which a coolant flows is embedded in the control magnetic path member 133. In the present embodiment, water is adopted as the coolant. When the control magnetic path member is cooled, the control magnetic path member has the capability to shield the radiation of heat dissipated from the electromagnetic superposition type objective lens to the wafer. Thus, the temperature difference between the wafer and electrostatic chuck can be suppressed. As a result, the drift of a beam landing position and misalignment of the wafer can be suppressed. In the review SEM of the present embodiment, the control magnetic path member 133 and stage 104 are provided with thermometers 302 and 303 respectively. Temperature information measured by the thermometer 302 is transmitted to the host computer 104 over a signal transmission line that is not shown. A coolant feeding pipe 304 and a pump 306 serving as coolant circulation means are connected to the cooling pipe 300 for the electrostatic chuck. A mass-flow controller 305 is disposed as flow rate adjustment means on the path of the coolant feeding pipe 304. When receiving the temperature information measured by the thermometer 302 or 303, the host computer 104 controls the mass-flow controller 305 so as to appropriately control the flow rate of the coolant flowing through the cooling pipes 300 and 301. Thus, the temperatures of the control magnetic path member 133 and stage 104 are controlled. By including the above mechanism, the temperatures of the control magnetic member 133 and stage 104 can be highly precisely controlled, and the thermal expansion of the wafer can be managed. The precision in alignment of the wafer is upgraded to 500 nm or less. The throughput of automatic control in the review mode or length measurement mode is markedly improved. Incidentally, as the coolant, aside from a liquid such as water, an air whose heat capacity is large, such as, helium (He) may be adopted. Nevertheless, the same advantage as the advantage of water can be provided. However, the liquid is preferred because of the high cooling effect. Owing to the review SEM of the present embodiment, the gap between the control magnetic path member and the booster magnetic path or wafer can be set to a value smaller than the conventionally adopted value. Further, the performance of the electromagnetic superposition type objective lens is improved. Eventually, a higher-resolution top-view image and a higher-resolution shaded image can be acquired. Embodiment 4 In relation to the present embodiment, an example in which the present invention is applied to a scanning electron microscope including a stage tilting mechanism will be described below. FIG. 7A is an overall constitution diagram of the scanning electron microscope, and FIG. 7B is an enlarged view of an electromagnetic superposition type objective lens capable of coping with stage tilting. The scanning electron microscope of the present embodiment includes an electron optical system 102 formed in a vacuum housing 101, an electron optical system control device 103 disposed on the perimeter of the electron optical system, a host computer 104 that controls control units included in respective control power supplies and controls the whole of the apparatus on a centralized basis, an operator console 105 connected to the control device, and display means 106 including a monitor on which an acquired image is displayed. The electron optical system control device 103 includes a power supply unit that feeds a current or a voltage to each of the components of the electron optical system 102, and signal control lines over which control signals are transmitted to the respective components. The capabilities and operations of a primary electron beam irradiation system and a secondary-particle detection system are nearly identical to the capabilities and operations described in conjunction with FIG. 1A. An iterative description will be omitted. The scanning electron microscope of the present embodiment has a stage tilting capability. The stage 104 includes a stage tilting mechanism and a motor that drives the tilting mechanism. A tilt angle of the stage is controlled by the host computer 104 via the electron optical system control device 103. Since the scanning electron microscope has the stage tilting capability, the objective lens has a shape like the one shown in FIG. 7B. The electromagnetic superposition type objective lens shown in FIG. 7B includes, similarly to the objective lens shown in FIG. 1B, a yoke member 132, a booster magnetic path member 116, a control magnetic path member 133, and a coil 134. However, the bottom of the yoke member 132 is different from that of the yoke member shown in FIG. 1B, and is conical. This is intended to prevent the bottom of the objective lens from colliding with the sample placement surface of the stage or a sample during stage tilting. The control magnetic path member 133 is disposed along the conical surface of the bottom of the yoke member 132. The control magnetic path member 133 is supported by an insulating supporting member so that the distance between the bottom of the yoke member 132 and the control magnetic path member 133 will remain constant, though the supporting member is not shown. The slope of the conical surface of the bottom of the yoke member 132 (apex angle) is designed in line with the maximum tilt angle of the stage. Since the electromagnetic superposition type objective lens of the present embodiment applies a voltage, which is nearly equal to the potential at a sample, to the control magnetic path member 133, the potential difference between the stage 140 and control magnetic path member 133 is smaller than the conventional one. Therefore, even when the distance from a wafer to the bottom of the objective lens varies depending on a position on the wafer, a potential distribution between the wafer and the bottom of the objective lens will not take on an abnormal shape (will not be asymmetric). Further, since the potential difference is smaller than the conventional one, electric discharge between the sample 114 and control magnetic path member 133 can be suppressed. Therefore, oblique observation of a sample with a higher resolution than a conventional one can be realized. When the booster magnetic path member 116 is shielded with the control magnetic path member 133, an electric field that efficiently attracts secondary particles can be induced in a detector disposed in a sample chamber by the side of the electron optical system 102. Eventually, a high-contrast observation image can be acquired. In the electromagnetic superposition type objective lens of the present embodiment, the booster magnetic path member 116 has a conical shape having the sample surface side thereof sharpened. When the electromagnetic superposition type objective lens is approached to the surface of a sample with the distal part thereof thinned, a magnitude of the action of a tilted electric field in the sample chamber, which is derived from tilting of the stage, on an electron beam can be reduced, and the tendency of the spot of the probe-like electron beam toward a non-point shape can be suppressed. Further, even when the stage is tilted, the booster magnetic path member 116 sucks secondary particles so that the secondary particles will collide with the left collision surface and right collision surface of the lower reflecting member and the upper reflecting member. As a result, a high-contrast top-view image and a high-contrast shaded image can be acquired. Since the shortest distance between the stage and booster magnetic path member 116 is shortened due to tilting of the stage, a voltage to be applied to the booster magnetic path member 116 has to be approached to the potential at the control magnetic path member along with an increase in the tilt angle. Using the scanning electron microscope of the present embodiment, a high-performance scanning electron microscope capable of balancing high-resolution and high-contrast observation performance and a stage tilting capability can be realized. The present invention can be applied to an electron microscope or ion microscope application apparatus requested to permit high-resolution and high-contrast observation.
	claims	1. A hood for confinement and handling of at least two nuclear material sample tubes comprising:an external first enclosure extending along a longitudinal axis X′, comprising a cover, a bottom provided with an opening and a valve for blocking the opening and thereby sealing the external enclosure;a second enclosure forming a barrel, extending along the axis X′ and guided in rotation about the axis X′ inside the external enclosure; andat least one internal third enclosure and one internal fourth enclosure each extending along a longitudinal axis X1, X2 parallel to the axis X′ and each adapted to accommodate a nuclear material sample tube, the at least two internal enclosures being fastened to each other and guided in translation in the barrel over a stroke A0;each internal enclosure comprising within it:a holding member adapted to pick up a nuclear material sample tube;a screw-nut mechanism comprising a lead screw guided in rotation about the axis X1, X2 and a nut around the screw and to which the holding member is fastened, the mechanism being adapted to guide the latter in translation in the internal enclosure over a stroke A greater than the stroke A0; anda bottom comprising an opening opposite the holding member to allow one of the nuclear material sample tubes picked up thereby to pass through;the hood further comprising:at least one motor fixed above at least one of the said internal enclosures and inside the barrel, the at least one motor being adapted to rotate the screw of the screw-nut mechanism of each internal enclosure and therefore the nut over the stroke A;a mechanical control arranged in part above the cover of the external enclosure for manually guiding the internal enclosures in translation over the stroke A0; anda mechanical control arranged in part above the cover of the external enclosure for manually pivoting the barrel in order to bring a holding member of one of the internal enclosures opposite the opening in the bottom of the external enclosure. 2. The confinement and handling hood of claim 1, further comprising an internal fifth enclosure also extending along a longitudinal axis X3 parallel to the axis X′ and adapted to accommodate a nuclear material sample tube, the three internal enclosures fastened to one another being distributed at 120° to one another inside the barrel. 3. The confinement and handling hood of claim 1, wherein the valve for blocking the opening in the bottom of the external enclosure is further defined as a guillotine valve. 4. The confinement and handling hood of claim 1, further comprising a metal bellows fixed under each opening of an internal enclosure to provide a seal between the latter and the opening of the external enclosure on translation of the internal enclosures in the barrel. 5. The confinement and handling hood of claim 1, further comprising at least two O-rings, each accommodated at least partly in a respective peripheral groove at the top and at the bottom of an external wall of the barrel to provide a seal between the latter and the external enclosure. 6. The confinement and handling hood of claim 1, further comprising a motor fixed above each of the internal enclosures and inside the barrel being adapted to rotate the screw of the screw-nut mechanism of said internal enclosure and therefore the nut over the stroke A. 7. The confinement and handling hood of claim 1, wherein the at least one motor is further defined as an electric motor. 8. The confinement and handling hood of claim 1, wherein the holding member is mounted on the nut of the screw-nut mechanism by means of a plate guided against an internal wall of the internal enclosure by at least two lugs projecting from the plate and forming centering devices. 9. The confinement and handling hood of claim 1, wherein the mechanical control for manually guiding the internal enclosures in translation over the stroke A0 is further defined as comprising a screw-nut mechanism comprising a lead screw on a portion of a rod guided in rotation about the axis X and passing through the cover and a nut around the screw and to which the internal enclosures are fastened. 10. The confinement and handling hood of claim 1, wherein the mechanical control for manually pivoting the barrel comprises a gear mechanism consisting of a gear on a portion of a rod guided in rotation parallel to the axis X′ and passing through the cover and a toothed ring meshing internally with the gear and to which the barrel is fastened. 11. The confinement and handling hood of claim 1, wherein the holding member comprises a holding head adapted to be accommodated in an interior tube constituting a nuclear material sample tube to be picked up, the interior tube itself being adapted to be inserted in an exterior tube which cannot be held by the holding head. 12. The confinement and handling hood of claim 11, wherein the exterior tube is a measuring instrument holder tube. 13. The confinement and handling hood of claim 12, wherein the measurement instrument holder tube is adapted to accommodate at least one measurement sensor and/or a cooling system.
	claims	1. A unitary storage structure for storing spent nuclear fuel, the structure comprising:a metal shell forming a cavity configured to store a spent nuclear fuel canister, the shell having an open top end, a closed metal bottom plate seal welded to a bottom end of the shell to prevent the ingress of water and other fluids, a height, and an opening in a side wall of the shell;an elongated metal inlet ventilation duct disposed externally to the shell, the inlet ventilation duct having an inlet and an outlet in fluid communication with the cavity of the canister, the outlet being seal welded to the opening of the shell forming a sealed passageway from the inlet to the opening of the shell;the outlet of the inlet ventilation duct being positioned at a first vertical height above the bottom end of the shell and the inlet being positioned at a second vertical height above the bottom end of the shell, wherein the second vertical height is greater than the first vertical height;wherein the metal bottom plate has an extension portion that extends outwards beyond the shell, the inlet ventilation duct being seal welded to a top of the extension portion to prevent the ingress of water and other fluids;wherein the shell, metal bottom plate, and inlet ventilation duct form a self-supporting unitary storage structure. 2. The unitary storage structure of claim 1, wherein the inlet ventilation duct includes a vertical section that is spaced apart from the shell. 3. The unitary storage structure of claim 2, wherein the inlet ventilation duct includes a horizontal section fluidly coupled to the vertical section and to the opening of the shell. 4. The unitary storage structure of claim 1, wherein the second vertical height of the inlet of the inlet ventilation duct is higher than the top end of the shell. 5. The unitary storage structure of claim 1, wherein the shell has a cylindrical shape. 6. The unitary storage structure of claim 1, further comprising:a lid positioned atop the shell so as to substantially enclose the open top end of the shell, the lid being non-unitary with respect to the shell;the lid comprising an outlet ventilation duct forming a passageway from a top of the cavity to ambient atmosphere. 7. The unitary storage structure of claim 1, further comprising an outlet ventilation duct forming a passageway from a top of the cavity to ambient atmosphere. 8. A unitary storage structure for storing spent nuclear fuel, the structure comprising:a metal shell forming a cavity configured to store a spent nuclear fuel canister, the shell having an open top end, a closed metal bottom plate seal welded to a bottom end of the shell, a height, and an opening in a side wall of the shell;an elongated metal inlet ventilation duct disposed externally to the shell, the inlet ventilation duct having an inlet in fluid communication with ambient atmosphere and an outlet in fluid communication with the cavity of the canister, the outlet being seal welded to the opening of the shell forming a sealed passageway from the inlet to the opening of the shell;the outlet of the inlet ventilation duct being positioned at a first vertical height above the bottom end of the shell and the inlet being positioned at a second vertical height above the bottom end of the shell, wherein the second vertical height is greater than the first vertical height;wherein the inlet ventilation duct is seal welded to the bottom plate of the shell, the shell, bottom plate, and inlet ventilation duct forming a self-supporting unitary storage structure. 9. The unitary storage structure of claim 8, wherein the inlet ventilation duct is welded to the opening of the shell and bottom plate of the shell. 10. The unitary storage structure of claim 8, wherein the bottom plate has an extension portion that extends outwards beyond the shell, the inlet ventilation duct being welded to the extension portion. 11. The unitary storage structure of claim 8, wherein the inlet ventilation duct includes a vertical section that is spaced apart from the shell. 12. The unitary storage structure of claim 8, wherein the inlet ventilation duct includes a horizontal section fluidly coupled to the vertical second and to the opening of the shell. 13. A unitary storage structure for storing spent nuclear fuel, the structure comprising:a metal shell forming a cavity configured to store a spent nuclear fuel canister, the shell having an open top end, a closed metal bottom plate seal welded to a bottom end of the shell, a height, and an opening in a side wall of the shell;an elongated metal inlet ventilation duct disposed externally to the shell, the inlet ventilation duct having an inlet in fluid communication with ambient atmosphere and an outlet in fluid communication with the cavity of the canister, the outlet being seal welded to the opening of the shell forming a sealed passageway from the inlet to the opening of the shell;wherein the inlet ventilation duct includes a vertical section that is spaced apart from the shell and a horizontal section fluidly coupled to the vertical section and to the opening of the shell;wherein the horizontal section of the inlet ventilation duct is seal welded to the bottom plate of the shell and the shell forming a self-supporting unitary storage structure comprised of the inlet ventilation duct, bottom plate, and shell. 14. The unitary storage structure of claim 13, wherein the outlet of the inlet ventilation duct being positioned at a first vertical height above the bottom end of the shell and the inlet being positioned at a second vertical height above the bottom end of the shell, wherein the second vertical height is greater than the first vertical height. 15. The unitary storage structure of claim 13, wherein the inlet ventilation duct is welded to the opening of the shell and bottom plate of the shell. 16. The unitary storage structure of claim 13, wherein the bottom plate has an extension portion that extends outwards beyond the shell, the inlet ventilation duct being welded to the extension portion.
	summary
	abstract	Provided, in parallel to an electromagnetic pump in a power supply system, is an electromagnetic pump compensation power supply mechanism (10) that will perform a power-factor improving function as a synchronous machine during normal operation of a plant. The electromagnetic pump compensation power supply mechanism (10) is provided with an exciter stator permanent magnetic apparatus (45) that can switch an exciter between a non-excited state and an excited state. The exciter stator permanent magnet apparatus (45) comprises exciter stator permanent magnets (15a), springs (16) that apply force to the exciter stator permanent magnets (15a) towards positions facing an exciter rotor winding (15b), and electromagnetic solenoids (20) that make the exciter stator permanent magnets (15a) move to positions not facing the exciter rotor winding (15b) in resistance to the force applied by the springs (16).
	summary
054232198	description	PREFERRED EMBODIMENT The first embodiment will be explained below with reference to FIGS. 1 to 13. In these drawings, the reference numeral 1 refers to a base, on which is disposed a transport device 10. The transport device 10 includes a transport motor 101 attached to the base 1 via an attachment member 100, and a ball screw shaft 103 attached to the rotation shaft of the transport motor 101 through a coupling 102, the ball screw shaft 103 is freely rotatably supported by the shaft support member 104, and is threaded to a nut member 105 fixed to the transport container 20. By rotating the rotation axis of the transport motor 101, the transport container 20 moves along the ball screw shaft 103 (e.g. 3 mm) through the actions of the coupling 102, ball screw shaft 103 and the nut member 105. The transport container 20 is configured as a box having a lower plate 200, an upper plate 201 and a pair of side plates 202, an end plate 203 with a through hole and a middle section plate 204 with a through hole. Inside the through hole of the end plate 203 of the transport container 20, there is attached a stainless steel support tube 300 which is provided with a cylinder-shaped seal member 301 made of porous silicone and a retainer ring 302 to retain the seal member 301. As shown in FIG. 2, the support tube 300 is narrow tipped, and the tip end is provided with a ring shaped rubber member 303, and a ring shaped contact member 304 (immobile or non-rotating lid member) made of plastic. The elastic force of the ring shaped rubber member 303 forces the contact member 304 towards the tip end of the support tube 300. Also at the tip end of the support tube 300, there is an lid member 306 engaged with a lid support frame 305 so as to be freely openable by swinging upwards. Opposing the contact member 304, a ring-shaped rotating lid member 400 made of stainless steel is freely slidably disposed, and the sliding surface of the rotating lid member 400 against the contact member 304 is coated with Teflon (tetrafluoride resin). The rotating lid member 400 is attached to the opening section of a funnel-shaped inspection section 403 formed on a main body 402 of the rotating member 401. The rotating member 401 includes a cylinder member 404 disposed around the main body 402, and the main body 402 is attached to the hollow rotation section 308 of the air bearing 307 fixed to the through hole of the mid section plate 204. The rotating lid member 400 has a plurality of flow passages 405 around its periphery, and opposite to the flow passages 405 at the upper and the lower sections of the contact member 304, there are formed a supply passage 309 to supply water to the inspection section 403 of the rotating member 401, and an collection passage 310 for collecting the water flowing out of the inspection section 403. The flow passage 405 side of the supply passage 309 is shaped so that the diameter of the passage expands towards the end, and the diameter of the expanded end section of the supply passage 309 is made larger than the inside diameter of the flow passage 405. Furthermore, the inside diameters of the supply passage 309 and the collection passage 310 are chosen to be larger than the distance between the two adjacent flow passages 405. The supply passage 309 is connected to a supply pipe 311, and the water supplied via the supply pipe 311 fills the inspection section 403 via the supply passage 309 and the flow passage 405, and the water from the inspection section 403 of the rotating member 401 flows downstream via the flow passage 405 and is collected via the collection passage 310. There is an interference plate 406 provided on the main body 402 of the rotating member 401, and opposing the interference plate 406, there is an interference plate 312 provided on the transport container 20. The numeral 313 refers to a drain receptor disposed on the end plate 203. On the rotation section 308 of the air bearing 307, there is attached a pulley 315 via a hollow attachment member 314, and the pulley 315 is connected with a pulley 317 via a belt 316. The pulley 317 is attached to the rotation shaft of the motor 318 disposed on the lower surface of the lower plate 200 via a bracket 319. By rotating the rotation shaft of the motor 318, the pulley 317, the belt 316 and the pulley 315 are rotated and thereby rotating the rotating member 401 around its axis. As shown in FIG. 3, on the main body 402 of the rotating member 401, there are formed four probe holes 407, 408, 409 and 410 which passes through to the inspection section 403 from the outer periphery. In each of the four probe holes 407-410, there is disposed a probe 411 for detecting melting deficiency, a probe 412 for detecting defects in the seal section, a high frequency probe 413 for detecting porosity undercut and a probe 411 for detecting defects in the shallow section. The melt deficiency probe 411 is used to detect insufficient melting between the end plug and the edge of the fuel pipe 3 of the fuel rod 2. As shown in FIGS. 11 and 12 (a), the probe 411 is disposed so that the axial line of the probe 411 lies in a plane which includes the rotational axis of the rotating member 401 (i.e the axis of the fuel rod 2), and is inclined at an angle to the rotational axis. The probe 412 for detecting defects in the seal section is used to search for the welding condition of the gas seal hole 5 formed in the center section of the end plug 4. This probe is also disposed so that the axis of the probe 412 crosses the rotational axis of the rotating member 401 as shown in FIGS. 11 and 12 (b). The high frequency probe 413 for detecting defects in the porosity undercut is used to search for porosity defects and undercut defects in the welds. As shown in FIGS. 11 and 13 (a), the probe 413 is disposed opposite to the axis of the probe 412, and is spaced a specific distance away from the probe 412 along the rotational axis. The probe 413 is connected electrically to the preamplifier 415 disposed in the rotating member 401 as shown in FIG. 3. The probe 414 for detecting porosities in the shallow section supplements the probe 413, and is used to search for defects in the surface section of the weld periphery. The probe 414 is disposed as shown in FIGS. 11 and 13 (b) so that its axis lies in the plane perpendicular to the rotation axis of the rotating member 401 (axis of the fuel rod), and is directed towards the outer periphery of the fuel rod 2 away from the center of the rotating member 401. The lead wires for each of the probes 411-414 and the preamplifier 415 are passed through a groove section 416 formed in the main body 402, as shown in FIG. 6, and are led to the rotary connector 417 attached to the hollow attachment section 314 via the rotation section 308 of the air bearing 307 and the interior of the hollow attachment section 314. The electrical signals from the probes 411-414 are sent through the rotary connectors 417 to the outside analyzer. As illustrated in FIG. 1, the rotary connector 417 is fixed to the lower plate 200 by means of wire 320 for preventing the rotation. As shown in FIG. 1, there is a chuck device 6 disposed on the support member 8 erected on the base 1 on the outside of the end plate 203, for fixing in place the fuel rod 2 after it is transported along its axis. Above the fuel rod 2 held in the chuck device 6, there is a laser operated feed meter 7 for detecting the travel distance along the axial direction of the fuel rod 2. Next, the operation of the ultrasonic detection device of the above-described configuration will be presented. First, by rotating the rotation shaft of the motor 318, the rotating member 401 is rotated around its axis (e.g. at 10 rotations per second) via the pulley 317, the belt 316, the pulley 315, the hollow attachment section 314 and the rotation section 308 of the air bearing 307. At the same time, the inspection section 403 is filled with water through the supply pipe 311, the supply passage 309 of the contact member 304 and the flow passage 405 of the rotating lid member 400. With the chuck device 6 in the open state, the fuel rod to be examined is transported along its axis, and is inserted inside the seal member 301 of the support tube 300 so as to push open the lid member 306 until the welded section of the fuel rod 2 is housed in the inspection section 403. In this case, until the fuel rod 2 is inserted into the inspection section 403, the lid member 306 closes the tip end of the support tube 300. After the fuel rod 2 is inserted in the inspection section 403, the fuel rod 2 is enveloped tightly with a seal member 301 made of porous silicone, and the elastic force of the ring shaped rubber member 303 forces the contact member 304 against the rotating lid member 400. The configuration described above is effective in preventing leaking of the water from anywhere except from the collection passage 310, and the water in the inspection section 403 flows out through the flow passage 405 of the rotating lid member 400 and is collected from the collection passage 310 of the contact member 304 to be returned to the pump to be recirculated. The water supply to the inspection section 403 is assured by having the configuration as follows. The supply passage 309 on the flow passage 405 side is made so that the diameter expands towards the end, and the expanded section of the supply passage 309 is made larger than the inside diameter of the flow passage 405, and the inside diameter of the supply passage 309 is made larger than the distance between the two adjacent flow passages 405. Therefore, regardless of the positions of the rotating member 401 and the rotating lid member 400, the water is supplied reliably to the inspection section 403 of the rotating member 401 through the supply passage 309 of the contact member 304. Further, because the inside radius of the collection passage 310 is made to be larger than the distance between the two adjacent flow passages 405, even while the rotating lid member 400 is rotating, the water flowing out of the inspection section 403 of the rotating member 401 through the flow passage 405 is always collected from the collection passage 310 of the contact member 304, thereby smoothly removing the air bubbles mixed in with the water filling the inspection section 403. While the fuel rod 2 is being inserted into the inspection section 403, the analyzer is used to monitor the reflecting surface waves to detect the tip of the fuel rod 2. After the tip of the fuel rod 2 is detected, the fuel rod 2 is moved forward a specific distance which is measured by the laser operated feed meter 7, and is fixed in the inspection position by means of the chuck device 6. Next, the entire periphery of the welded section of the fuel rod 2 is examined with the rotating probes 411-414, to perform the detection of melting deficiency, seal section defects, high frequency search of porosity and undercut and the shallow section. During the inspection process, the position of the transport container 20 is adjusted suitably by operating the transport motor 101 to move the coupling 102, ball screw shaft 103 and the nut section 105. By moving the components in the transport container 20, such as the rotating member 401, rotating lid member 400 and the contact member 304, seal member 301 and the support tube 300 a specific distance (e.g. 1 mm) with respect to the fuel rod 2, it becomes possible to inspect a corresponding specific distance in the welded section of the fuel rod 2 rapidly and with high resolution. The detection signals from the probes 411-414 are led through the groove section 416 in the main body 402 of the rotating body 401, rotation section 308 of the air bearing 307 and the hollow attachment section 314, and are led to the rotary connector 417 to be forwarded outside to the analyzer. When an ultrasonic inspection of one fuel rod 2 is thus completed, the chuck device 6 is released, and the fuel rod 2 is pulled out of the inspection section 403, and a next fuel rod 2 is inserted therein. The inspection process presented above enables to load and discharge the fuel rod 2 to and from the inspection section 403 through the seal member 301 of the support tube 300 and lid member 306 supported by the lid support frame 305 while rotating the probes 411-414 continuously. Therefore the inspection process has been greatly simplified, and even during the inspection process, the fuel rod 2 is firmly gripped and fixed in place by the chuck device 6 as well as supported firmly by the seal member 301, thus avoiding contact with the rotating member 401 or the rotating lid member 400 and assuring that there will be no damage inflicted on the surface of the fuel rod 2.
046648755	description	DETAILED DESCRITPION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings. Also, in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like, are words of convenience and are not to be construed as limiting terms. In General Referring now to the drawings, and particularly to FIG. 1, there is shown an upper end of a reconstitutable fuel assembly, being generally designated by the numberal 10, on which a fixture of the present invention, generally indicated 12, and a tool (not shown) forming the invention of the second cross-referenced patent application are employed in removing and replacing a top nozzle 14 from and onto the fuel assembly 10. Basically, the fuel assembly 10, being of conventional construction, includes an array of fuel rods 16 held in spaced relationship to one another by a number of grids 18 (only one being shown) spaced along the fuel assembly length. Each fuel rod 16 includes nuclear fuel pellets (not shown) and is sealed at its opposite ends. The fuel pellets composed of fissible material are responsible for creating the reactive power of the nuclear reactor core in which the assembly 10 is placed. A liquid moderator/coolant such as water, or water containing boron, is pumped upwardly through the fuel assemblies of the core in order to extract heat generated therein for the production of useful work. The reconstitutable fuel assembly 10 also includes a number of longitudinally extending guide tubes or thimbles 20 along which the grids 18 are spaced and to which they are attached. The opposite ends of the guide thimbles 20 extend a short distance past the opposite ends of the fuel rods 16 and are attached respectively to a bottom nozzle (not shown) and the top nozzle 14. To control the fission process, a number of control rods (not shown) are reciprocally movable in the guide thimbles 20 located at predetermined positions in the fuel assembly 10. Specifically, the top nozzle 14 includes a rod cluster control mechanism (not shown) interconnected to the control rods and operable to move the control rods vertically in the guide thimbles 20 to thereby control the fission process in the fuel assembly 10, all in a well-known manner. As illustrated in FIG. 1, and also in FIGS. 3 and 8-11, the top nozzle 14 comprises a housing 22 having a lower adapter plate 24 surrounded by four interconnected, upstanding side walls 26 with raised sets of pads 28,30 (only one pad in each set being shown) located respectively at pairs of diagonal corners 32,34 formed by the side walls 26. The control rod guide thimbles 20 have their uppermost end portions 36 coaxially positioned within control rod passageways 38 formed through the adapter plate 24 of the top nozzle 14. For gaining access to the fuel rods 16, the adapter plate 24 of the top nozzle 14 is removably connected to the upper end portions 36 of the guide thimbles 20 by an attaching structure, generally designated 40. The attaching structure 40 will be described herein to the extent necessary to facilitate an understanding of the structure and operation of the fixture 12 comprising the present invention. However, a more thorough understanding of the attaching structure 40 can be gained from the first patent application cross-referenced above, the disclosure of which is incorporated herein by reference. Top Nozzle Attaching Structure As best seen in FIGS. 8-11, the attaching structure 40 of the reconstitutable fuel assembly 10 includes a plurality of outer sockets 42 defined in the top nozzle adapter plate 24 by the plurality of passageways 38 which each contain an annular circumferential groove 44, a plurality of inner sockets 46 defined on the upper end portions 36 of the guide thimbles 20, and a plurality of removable locking tubes (not shown) inserted in the inner sockets 46 to maintain them in locking engagement with the outer sockets 42. The locking tubes are illustrated in either one of the above two cross-referenced patent applications. Each inner socket 46 is defined by an annular circumferential bulge 48 on the hollow upper end portion 36 of one guide thimble 20. A plurality of elongated axial slots 50 are formed in the upper end portion 36 of each guide thimble 20 to permit inward elastic collapse of the slotted end portion to a compressed position so as to allow the circumferential bulge 48 thereon to be inserted within and removed from the annular groove 44 via the adapter plate passageway 38. The annular bulge 48 seats in the annular groove 44 when the guide thimble end portion 36 is inserted in the adapter plate passageway 38 and has assumed an expanded position. In such manner, the inner socket 46 of each guide thimble 20 is inserted into and withdrawn from locking engagement with one of the outer sockets 42 of the adapter plate 24. The locking tubes (not shown) of the attaching structure 40 are inserted from above the top nozzle 14 into their respective locking positions in the hollow upper end portions 36 of the guide thimbles 20 forming the inner sockets 46. When each locking tube is inserted in its locking position, it retains the bulge 48 of the inner socket 46 in the latter's expanded locking engagement with the annular groove 44 and prevents the inner socket 46 from being moved to its compressed releasing position in which it could be withdrawn from the outer socket 42. In such manner, the locking tubes maintain the inner sockets 46 in locking engagement with the outer sockets 42, and thereby the attachment of the top nozzle 14 on the upper end portions 36 of the guide thimbles 20. Fixture for Removing and Replacing the Top Nozzle For effectuating inspection, removal, replacement and/or rearrangement of fuel rods 16 contained in the reconstitutable fuel assembly 10, the irradiated assembly must be removed from the reactor core and lowered into a work station 52 by means of a standard fuel assembly handling tool (not shown). In FIGS. 1 and 3, there is illustrated various features in the work station 52 that are used in conjunction with the fixture 12 of the present invention to guide the top nozzle 14 and fixture 12 for proper removal and replacement of the top nozzle. These features include a pair of elongated, bullet-nose guide members 54 which are mounted on, and project upwardly from, a pair of diagonal corners 56 of a top flange 58 of the work station 52. Also, included in the work station 52 are four movable pads 60 that are mounted on and project through the side walls 62 of the work station at the elevation of the uppermost grid 18 of the fuel assembly 10. The pads 60 are advanced inwardly by cylinders 64, also mounted on the side walls 62, to bear against each side of the grid 18 and take up the clearance between the station 52 and the assembly 10, and thus maintain it in a fixed relation to the work station. As will become clear below, maintaining the fixed position of the assembly 10 is particularly important while the top nozzle 14 is off the fuel assembly and from the standpoint of guidance during replacement of the top nozzle. Finally, the work station 52 includes four pneumatic-operated moon-shaped brackets 66 mounted on the top flange 58 which are used in conjunction with the fixture 12 during remounting or replacement of the top nozzle 14. In the work station 52, the fuel assembly 10 is submerged in coolant and thus maintenance operations are performed by manipulation of remotely-controlled submersible equipment. One component of such equipment is the tool (not shown) for removing the locking tubes which forms the invention illustrated and described in the second patent application cross-referenced above. Removal of the locking tubes represents the first step in removing the top nozzle 14 from the reconstitutable fuel assembly 10. Another component of such equipment is the fixture 12 of the present invention which, after the locking tubes have been removed, is used for removing and subsequently replacing the top nozzle 14 from and on the guide thimbles 20 of the reconstitutable fuel assembly 10. Referring again to FIG. 1 and now also to FIGS. 2 and 4, there is shown various features mounted on a base 68 of the fixture 12 which, when used in conjunction with the work station 52, are useful in both removing and replacing the top nozzle 14 from and back onto the guide thimbles 20 of the fuel assembly 10. Basically, these features on the base 68 of the fixture 12 include guiding means 70, aligning means 72, locking means 74, moving means 76 and reference establishing means 78. The guiding means 70 preferably takes the form of a pair of holes 80 formed through one pair of diagonal corners 82 of the fixture base 68. The holes 80 are sized to receive the guide members 54 of the work station 52 which project upwardly from the top flange 58 of the station. Thus, when the fixture 12 is engaged by a long-handled tool (not shown), having an internally-threaded bottom end which threads onto the upper threaded end 84 of a central stud 86, and lowered toward the fuel assembly 10 located in the work station 52, as the fixture 12 approaches the station (as seen in FIG. 1) the two holes 80 in diagonally opposite corners 82 of the fixture base 68 will be guided over the two upstanding guide members 54 of the work station. Soon after the fixture base 68 via its corner holes 80 movably mates with the guide members 54 on the work station top flange 58 and moves downwardly therealong, the aligning means 72 of the fixture 12, which preferably takes the form of two elongated rods 88 positioned along a diagonal of the base 68 on either side of the central stud 86 and having lower conically-tapered heads 90, insert through two of the passageways 38 in the top nozzle adapter plate 24 and into the upper end portions 36 of two guide thimbles 20. Downward movement of the fixture 12 continues until the base 68 and aligning rods 88 reach the position shown in FIG. 8 (only one rod 88 being illustrated for purposes of clarity). In such manner, the fixture 12 also becomes aligned with the top nozzle 14 of the fuel assembly 10 as well as with the top flange 58 of the work station 52 as the fixture base 68 is movably mounted on the work station. Once the fixture base 68 has lowered to the position shown in FIG. 8, it is properly positioned on the top nozzle 14 for top nozzle removal. Such lowering places the locking means 74 on the fixture base 68 into matable relation with complementary means on the top nozzle 14. The locking means 74 preferably takes the form of a pair of releasable expansion members. Referring to FIG. 6 in addition to FIGS. 1 and 2, each expansion member 74 includes a hollow expandable split sleeve 92 and a wedge pin 94 inserted into the sleeve 92 from the lower end. The sleeve 92 is attached at an upper end to the fixture base 68 in diagonal alignment with the alignment rods 88 but radially outward therefrom with respect to the central stud 86 of the fixture 12. The lower end portion of the sleeve 92 contains several axially extending slots 96 which are expandable circumferentially outward (as seen in broken line form in FIG. 6) when a wedge-shaped head 98 on the lower end of the wedge pin 94 is drawn in an upward direction by tightening nut 100 on the threaded upper end 102 of the pin 94. A dowel 101 is inserted through the base 68 into a cutout 103 provided in the pin 94 to prevent the pin 94 from rotating while allowing it to move vertically as the nut 100 is turned. Expansion of the sleeve 92 creates a tight friction fit between its outer surface 104 and the internal surface 106 of a bore 107 defined in one diagonal corner pad of pair 28 at each diagonal corner of pair 32 of the top nozzle housing side walls 26. The tight friction fit attaches the fixture 12 to the top nozzle 20. On the other hand, loosening the nut 100 moves the wedge pin 94 in an opposite direction, allowing the sleeve 92 to contract and release the frictional engagement with the internal surface 106 of the bore 107 and thus frees the base 68 from the top nozzle 14. Consequently, once the fixture 12 is resting on the top nozzle 14 as seen in FIG. 8, wherein the lower edges 108 of outer sleeves 109 which are attached to the underside of the base 68 and surround the upper portions of the split sleeves 92 abut upon the corner pads 28 and the lower edges 111 of a pair of corresponding stub shafts 113 which are also attached to the underside of the base 68, but at opposite diagonal corners 34, abut the corner pads 30, the long-handled tool (not shown) is now unthreaded from the upper end 84 of central stud 86 and a similar tool (not shown) with a socket end is used to turn the nut 100 on the upper end 102 of each wedge pin 94. By turning each nut 100 in a clockwise direction, the wedge-shaped head 98 on the lower end of the pin 94 is raised inside the split sleeve 92 which, in turn, expands and thereby locks into the bore 107 with, for example, an applied torque of 20 ft-lbs. Prior to initiating actual removal of the top nozzle 14 from the guide thimbles 20 of the fuel assembly 10, steps must be taken to ensure that the fixture 12 can be effectively used to remount or replace the top nozzle 14 later back on the fuel assembly 10 at exactly the same axially position thereon. The reference esstablishing means 78 is provided on the fixture base 68 for this purpose. It takes the form of a pair of stop devices 110 mounted on the fixture base 68 adjacent the other pair of diagonal corners 112 of the base. As depicted in FIG. 7 as well as FIGS. 1, 2 and 4, each stop device 110 includes a spring-loaded, vertically oriented stop pin 114 and a stop pin lock assembly 116. The stop pin 114 projects through an opening 117 in the base 68 and is loaded or biased downwardly by coil spring 118. The spring 118 encircles the pin 114 below the base 68 and is positioned in a state of compression between the base and a lower washer 120 attached to the pin. The stop pin assembly 116 takes the form of a threaded rod 122 and an actuating arm 124 attached to one end of the rod. The rod 122 is movable through a elongated hole 126 horizontally tapped into the base 68 from its peripheral edge 128 adjacent each diagonal corner 112 so as to intersect the vertically-extending opening 117 in the base through which the stop pin 114 is inserted. By rotating the actuating arm 124, the threaded rod 122 is rotated within the threaded hole 126 which causes the rod to move through the hole, clockwise rotation to advance the rod toward the pin 114 and counterclockwise rotation to retract the rod away from the pin. The inner terminal end 130 of the rod 122 extends into a vertical groove 132 formed in a side of the stop pin 114 which faces the hole 126. Left and right hand limit lugs 134,136 extend radially outward from the peripheral edge 128 of the base 68 on either side of the location of attachment of the actuating arm 124 to the outer end of the rod 122 for defining the extremes of the rotational stroke of the arm 124. Prior to placing the fixture 12 on the top nozzle 14 in preparation for nozzle removal, the stop devices 110 must be preset so as to function to establish a reference representing the displacement between the fixture base 68 and the top flange 58 of the work station 52 so that the top nozzle 14 can be replaced later at the same axial position on the fuel assembly as it was prior to removal. For facilitating the establishment of such a reference, a ring 138 on the end of each actuating arm 124 is engaged with a long-handled "hook end" tool (not shown) and, with a lifting motion, the actuating arm is pivoted in a counterclockwise direction against the left hand limit lug 134, as seen in FIG. 1. This action causes the threaded rod 122 to rotate in the tapped hole 126 and to move away from the groove 132 in the stop pin 114 to an unlocked position. As the fixture 12 is subsequently lowered onto the top nozzle 14 to the position of FIG. 8, each spring-loaded stop pin 114, regardless of the specific length of the assembly 10, maintains contact with the top flange 58 of the work station 52. Thus, when the fixture 12 is resting in its desired place on the top nozzle 14, the extent of each pin 114 establishes a reference representing the vertical dimension from the work station flange 58 to the fixture base 68. After the fixture 12 has been locked to the top nozzle 14, the stop pins 114 are immobilized by again using the aforementioned long-handled hook-end tool. The ring 138 on each actuating arm 124 is engaged, lifted and pivoted against the right hand limit lug 136 (from the solid line position to the broken line position in FIG. 8) which rotates the stop pin lock rod 122 in a clockwise direction and advances it to a locked position into contact with the side of the pin 114 within the groove 132. The pressure of the inner terminal end 130 of the threaded rod 122 against the stop pin 114 prevents vertical movement of the stop pin during subsequent top nozzle removal and remounting operations, thus preserving the reference dimension between the work station top flange 58 and the fixture base 68. The location of the right hand limit lug 136 allows adequate rod pressure to hold the stop pin 14, while preventing an excessive degree of rotation that could damage the stop devices 110. During the period while the top nozzle 14 is removed, held in temporary storage, and then remounted to the fuel assembly 10, the stop devices 110 remain in the locked positions. This ensures that the remounted top nozzle 14 is axially in an identical position to that prior to removal as established by the reference dimension from the work station top flange 58 to the fixture base 68. Finally, after the axial height reference has been established, the moving means 76 is operated to remove the top nozzle 14 locked to the fixture base 68 from the fuel assembly. Specifically, the moving means 76 on the base 68 engages the top flange 58 of the work station 52 and lifts the base 68 and top nozzle 14 locked thereto away from the top flange. Such action causes release of the attaching structures 40 mating the top nozzle adapter plate 24 to the upper end portions 36 of the guide thimbles 20. Preferably, as seen in FIGS. 1, 2, 4 and 5, the moving means 76 includes a plurality of elongated reaction pins 140 and drive means 142 for moving the pins. The reaction pins 140 extend from the base 68 downwardly toward the top flange 58 when the base is movably mounted on the work station. Each of the reaction pins 140 is threadably coupled through an internally threaded hub 144 fixed to the underside of the base 68 such that upon rotation the pins also move vertically relative to the base. The drive means 142 includes a centrally-located drive gear 146 keyed to a central shaft 148 which is mounted for rotation about a vertical axis by bushings 150,152 respectively supported on the base 68 and on an inverted U-shaped bracket 154 which, in turn, is mounted on the base 68. A nut 156 providing a tool surface for turning the shaft 148 is integrally connected with the upper end of the shaft as is the eariler-mentioned central stud 86 used for lifting the fixture 12. The drive means 142 also includes a plurality of driven gears 158, preferably four in number corresponding to the four reaction pins 140 which are used on the fixture 12. Each driven gear 158 is mounted in intermeshed relationship with the drive gear 146 and at a position circumferentially displaced about the drive gear approximately ninety degrees from one another, as most clearly seen in FIGS. 2 and 4. Furthermore, each driven gear 158 is affixed to a shaft 160 which is mounted for rotation about a vertical axis by bushings 162,164 respectively supported on the base 68 and on an inverted U-shaped bracket 166 which, in turn, is mounted on the base. The reaction pins 140 are each integrally connected at its upper end to the lower end of one of the driven gear shafts 160 so as to rotate therewith. The arrangement of the drive means 142 with the reaction pins 140 must provide for translation of rotational motion of the drive gear 146 into movement of the reaction pins 140 along linear paths due to the threaded mounting of the pins in the hubs 144. To accommodate such requirement, the teeth of the respective driven gears 158 intermesh with the teeth of drive gear 146 so as to allow the driven gears to slidably move vertically in linear fashion with respect to the drive gear concurrently as the driven gears are rotated by the drive gear. Such vertically sliding capability of the driven gears 158 relative to the drive gear 146 can be seen by comparing FIG. 8 to FIG. 9 and FIG. 10 to FIG. 11. For removing the top nozzle 14 from the fuel assembly 10 after the nozzle is locked to the fixture 12, a long-handled socket end tool (not shown) is engaged with the hex nut 156 on the upper end of the central shaft 148 and is turned in counterclockwise direction. This action turns the drive gear 146 and simultaneously rotates the driven gears 158 and drives the reaction pins 140 rotatably and linearly downward against the top flange 58 of the work station 52. There the drive force is reacted, raising the top nozzle 14 with the fixture 12 in a contolled, stepless manner and causing the upper end portions 36 of the guide thimbles to collapse inwardly and release the locking engagement of their annular bulges 48 in the annular grooves 44 within the respective passageways 38 of the top nozzle adapter plate 24. A noticeable reduction in torque (from 5 ft-lbs to less than 1 ft-lb) occurs when the adapter plate 24 is free of the guide thimbles 14, as seen in FIG. 9. The turning action of the tool is continued until the limit of the gear arrangement mechanical travel is reached. The fixture 12 with the attached top nozzle 14 is then carefully removed from the work station 52 and transferred to temporary storage by means of the earlier-mentioned, long-handled, threaded-end tool engaged with the upper threaded end 84 of the central stud 86. Remounting of the top nozzle 14 is substantially the reverse of the removal procedure and uses the same features. However, one additional component is needed--some means to hold the lower ends of the reaction pins 140 so that the adapter plate 24 of the top nozzle 14 can be driven down upon the upper end portions 36 of the guide thimbles 20. As seen in FIG. 3, such means is provided in the form of a plurality of actuators 168, preferably four in number corresponding to the number of reaction pins 140 and being pneumatic cylinders, having moon-shaped brackets 66 attached to their piston rod extensions and movable between the solid line and dashed line positions. When the fixture 12 and top nozzle 14 are lowered to the positions seen in FIG. 10, operation of the actuators 168 advances the brackets 66 against reduced diameter sections 172 on the respective reaction pins 140. The brackets 66 take the reactions transmitted through the pins 140 as the top nozzle adapter plate 24 is forced over the upper end portions 36 of the guide thimbles 20 by turning the drive gear 146 in a clockwise direction. The top nozzle 14 has been lowered to its final assembly elevation when the lower ends of the stop pins 114 contact the top flange 58 of the work station 52. At such elevation the annular bulges 48 on the guide thimbles 20 are seated in the annular grooves 44 in the adapter plate passageways 38. Once such seating relationship has been reached, the actuators 168 are operated to retract the brackets 66. The fixture 12 is then unlocked from the top nozzle 14, and the fixture 12 is lifted off the nozzle and transferred to temporary storage. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof.
	summary
051475979	description	A DETAILED DESCRIPTION OF THE INVENTION The present invention is concerned with coating the internal surfaces of steel members, generally pipes, which are used in the water system of light water nuclear reactors, with a chromium film of at least 500 .ANG. to reduce the amount of Cobalt 59 active corrosion products retained by the piping during normal use. The presently understood source of this cobalt isotope is the corrosion of the underlying steel pipe. Once cobalt from the underlying pipe enters the water coolant system through normal corrosion, it is subjected to conditions which lead to the formation of a radioactive isotope, Cobalt 59. In order to provide a film on the steel (or stainless) surfaces, the steel should first be prepared to receive the chromium film. The preparation steps typically include degreasing step followed by a brief residence time in the chromium plating bath for approximately 60 seconds prior to the application of current through the plating bath. Another preparation step involves anodic dissolution in the plating bath for approximately 90 seconds with a current density of approximately 40 amps per dm.sup.2. The plating step takes place in a common and well-known plating bath which uses chromic acid (CrO.sub.3) and sulfate (SO.sub.4), as sulfuric acid. The plating temperature is 50.degree. C. (122.degree. F.) and the current density applied to the plating bath is 40 A/dm.sup.2. Under these operating conditions, the current efficiency is claimed to be approximately 15%, which gives a plating speed of approximately 35 .mu.m per hour, that is, 97 .ANG. per second. Depending on local parameters, a deviation of up to 30% should be considered as normal. The thickness of an electrolytically plated layer is proportional to the time when the current density remains constant. However, some delay can be observed at the beginning of the deposition process due to phenomena in the cathodic layer. This delay has no importance in normal deposition where at least a few microns must be plated, but cannot be ignored in the present case. In order to evaluate this effect, it was decided to perform several tests with plating times ranging from 10 to 60 seconds and to measure the resulting thickness. These measurements were performed using the Auger Electron Spectroscopy technique. The sputtering time required for as thickness of 1,000 .ANG. of chromium was determined on a calibrated sample at the beginning and at the end of each series of measurements. It varied between 15 and 25 minutes from series to series but did not show differences larger than 5% from the beginning and the end of the measurement of samples from the same series. The results are presented in Table 1. TABLE 1 ______________________________________ Plating Time and Film Thickness Plating Time (in s) Thickness (in angstroms) ______________________________________ 10 900 20 1,900 30 2,850 60 not measured ______________________________________ Table 1 shows that in the present case, the initial delay is negligible and the deposition rate is 95 .ANG./second as shown in FIG. 1. The measurements described in Table 1 were taken at the center of the respective samples. At the periphery, a darker area was observed on the samples plated for 10 and 20 seconds. Beginning in approximately 5 mm from the edge, the thickness of the chromium layer on the first sample was 3200 .ANG., whereas there was 900 .ANG. thickness at the center. This is a consequence of the edge effect which is especially pronounced for chromium plating. To decrease the effect of this edge phenomena, several tests were performed using different types of metallic frames surrounding the sample. The best result was obtained with a cylindrical frame, 5 mm in diameter at a distance of 5 mm from the edges. In this case, the darkened area was much less pronounced coming closer to the edges than extended over a 5 mm maximum of smaller chromium thickness was expected on the test piece. As the total current remained the same as for a sample without the frame, a smaller chromium thickness was expected on the test piece. On a 316 steel specimen, the following thicknesses were measured using the Auger Electron Spectroscopy technique for a plating time of 10 seconds on samples at different places. See Table 2. TABLE 2 ______________________________________ Variation in Chromium Plate Thickness SAMPLE Thickness No. Side Position (in angstrom) ______________________________________ 1 Front 1/4 of the length 600 half of the width 2 Front 3/4 of the length 570 half of the width 3 Front corner, at 7 mm 1,300 from the edges 4 Rear center 620 ______________________________________ FIG. 2 shows the location of the sample site for each of the measurements reported in Table 2. The constancy of the thickness seems acceptable for the present application. If necessary, the periphery could be removed after exposure of the samples to the primary water. The chromium plating method of the present invention may be combined with the passivation techniques described in U.S. Pat. No. 4,636,266. Following coating of the surface with chromium, the chromium surface to be passivated is exposed to a gaseous oxygen source. The oxygen source may be oxygen itself, mixtures of oxygen with other gases, e.g., steam air, inert diluents and mixtures of these. It is essential that the oxygen source be in the gas phase and that the exposing step be carried out in the gas phase. The exposing must take place at a temperature which falls in the range from about 150.degree. C. to 450.degree. C. Preferably, the exposing step will take place at a temperature substantially equal to that of the water temperature within the light water reactor, namely temperatures between 250.degree. C. and 320.degree. C. The time of exposure is not critical but should be at least five hours. Generally, an exposure time from about 50 hours to about 3000 hours is preferred, although longer times can be used. The present invention can be used to provide a chromium coating on carbon steels and stainless steels, e.g., 304 stainless, 316 stainless and 347 stainless. In order to better illustrate the effectiveness of the chromium coating, the following examples are presented. WORKING EXAMPLES In June 1989, new and previous fuel cycle test coupons were installed in the steam generator at Doel-2 for activity buildup measurements. The test coupons were placed on the manway seal plates. Table 3 gives the coupon description and position in the steam generator channel head (i.e., hot leg and cold leg). The plant resumed operation in July, 1989, but an unscheduled shutdown was encountered in November, 1989. Since this was to be an extended shutdown for turbine work, the utility decided to perform a "COMBAT" type decontamination of the primary system. The decontamination consists of recirculating primary coolant with 2500 ppm boron concentration for seven days at a temperature of 120.degree.-140.degree. C. The utility agreed to drain the steam generator so that the coupons could be analyzed both before and after the decontamination. The specimens had been exposed for approximately 2500 hours upon plant shutdown. The pre-contamination measurements were made in January, 1990 with the date decay corrected to time of plant shutdown. After the first measurement, all but one of the specimens were re-installed to undergo the "COMBAT" treatment. Table 4 and 5 give the results of the gamma spectrographic analyses for the pre and post-"COMBAT" treatment, respectively. These tables do not show that the palladium coupon also had levels of Sb-124 and AG-110m of the same order of magnitude as the Cobalt 60 values. TABLE 3 ______________________________________ COUPON SPECIMEN LOADING AT DOEL-2, JUNE, 1989 ID* POSITION STATUS ______________________________________ 309L AR Hot Leg Second cycle exposure 309L EP/PV Hot Leg Second cycle exposure 309L Cr/PV Hot Leg New, first cycle exposure CF8M AR Hot Leg Second cycle exposure CF8M EP/PV Hot Leg Second cycle exposure CF8M Cr/PV Hot Leg New, first cycle exposure 316L Cr/PV Hot Leg New, first cycle exposure 4PP1 Hot Leg Second cycle exposure 309L AR Cold Leg Second cycle exposure 309L EP/PV Cold Leg Second cycle exposure 309L Cr/PV Cold Leg New, first cycle exposure CF8M AR Cold Leg Second cycle exposure CF8M EP/PV Cold Leg Second cycle exposure CF8M Cr/PV Cold Leg New, first cycle exposure 316L Cr/PV Cold Leg New, first cycle exposure PD A-304 Cold Leg Second cycle exposure ______________________________________ AR = As received, EP = electropolished, P/V = RCT Passivation, Cr = Chromium deposition layer applied, PP and PD = Palladium coated. TABLE 4 __________________________________________________________________________ DOEL-2 COUPON ANALYSIS, PRE-DECONTAMINATION, APPROXIMATELY 2500 HOURS EXPOSURE, JAN 1990. MEASURED ACTIVATION CONTACT PRODUCTS DOSERATE (DECAY CORRECTED) IDENTIFICATION (mR/hr) Co-58 Co-60 Mn-54 __________________________________________________________________________ HOT LEG 309L AR 180 5.11E + 5 6.43E + 4 1.27E + 4 309L EP/PV 120 3.89E + 5 4.59E + 4 9.42E + 3 309L Cr/PV 30 4.62E + 4 5.23E + 3 1.24E + 3 CF8M AR 310 9.87E + 5 1.26E + 5 2.47E + 4 CF8M EP/PV 160 5.29E + 5 6.64E + 4 1.49E + 4 CF8M Cr/PV 26 5.11E + 4 5.71E + 3 1.24E + 3 316L Cr/PV 34 5.41E + 4 5.32E + 3 9.99E + 2 4PP 1 210 1.78E + 5 2.60E + 4 5.46E + 3 COLD LEG 309L AR 200 5.12E + 5 8.59E + 4 1.05E + 4 309L EP/PV 135 4.25E + 5 5.02E + 4 7.72E + 3 309L Cr/PV 24 5.21E + 4 5.08E + 3 6.68E + 2 CF8M AR 300 6.36E + 5 1.07E + 5 1.18E + 4 CF8M EP/PV 200 5.20E + 5 6.94E + 4 7.86E + 3 CF8M Cr/PV 180 3.94E + 4 7.19E + 3 1.80E + 3 316L Cr/PV 28 2.74E + 4 3.68E + 3 4.04E + 2 PD A - 304 240 2.65E + 5 5.51E + 4 6.25E + 4 __________________________________________________________________________ APPARENTLY MISREADING, SHOULD BE 18 mR/hr TABLE 5 __________________________________________________________________________ DOEL-2 COUPON ANALYSIS, PRE-DECONTAMINATION, APPROXIMATELY 2500 HOURS EXPOSURE, FEB 1990. MEASURED ACTIVATION CONTACT PRODUCTS DOSERATE (DECAY CORRECTED) IDENTIFICATION (mR/hr) Co-58 Co-60 Mn-54 __________________________________________________________________________ HOT LEG 309L AR 140 2.77E + 5 6.27E + 4 1.23E + 4 309L EP/PV 90 1.95E + 5 4.47E + 4 6.78E + 3 309L Cr/PV 17 1.76E + 4 3.71E + 3 6.43E + 2 CF8M AR 210 5.43E + 5 1.22E + 5 1.86E + 4 CF8M EP/PV 110 2.07E + 5 4.77E + 4 8.36E + 3 CF8M Cr/PV 15 1.85E + 4 3.97E + 3 6.39E + 2 316L Cr/PV 14 2.28E + 4 4.27E + 3 9.58E + 2 4PP 1 210 9.70E + 4 2.49E + 4 3.14E + 3 COLD LEG 309L AR 200 2.99E + 5 8.05E + 4 8.50E + 3 309L EP/PV 90 2.00E + 5 4.42E + 4 5.33E + 3 309L Cr/PV 15 3.11E + 4 4.44E + 3 6.77E + 2 CF8M AR 180 3.25E + 5 1.02E + 5 8.46E + 3 CF8M EP/PV 140 2.70E + 5 6.28E + 4 6.32E + 3 CF8M Cr/PV 15 2.51E + 4 3.91E + 3 5.47E + 2 316L Cr/PV 10 1.47E + 4 2.72E + 3 4.27E + 2 PD A - 304 220 1.39E + 5 4.53E + 4 3.90E + 3 __________________________________________________________________________ Table 4 shows the pre-decontamination data normalized to the appropriate material. It should be noted that in this table, that the 316L stainless steel and palladium coated coupons were normalized to the 309L coupon data. Table 5 shows the effectiveness of the decontamination. All coupons were re-installed for further exposure in the plant. TABLE 6 __________________________________________________________________________ DOEL-2 COUPON ANALYSIS, PRE-DECONTAMINATION, JANUARY 1990 DATA-NORMALIZED. CONTACT NORMALIZED ACTIVATION PRODUCTS COUPON DOSERATE (TO AR FOR SPECIFIC MATERIAL) IDENTIFICATION (mR/hr) Co-58 Co-60 Mn-54 __________________________________________________________________________ HOT LEG 309L EP/PV 0.67 0.76 0.71 0.74 309L Cr/PV 0.17 0.09 0.08 0.10 F8M EP/PV 0.54 0.53 0.60 CF8M Cr/PV 0.08 0.05 0.05 0.05 316L Cr/PV 0.19 0.11 0.08 0.08 4PP 1* 1.17 0.35 0.40 0.43 COLD LEG 309L EP/PV 0.68 0.83 0.58 0.74 309L Cr/PV 0.12 0.10 0.06 0.07 CF8M EP/PV 0.67 0.82 0.65 0.67 CF8M Cr/PV 0.60 0.06 0.07 0.15 316L Cr/PV* 0.14 0.05 0.05 0.04 PD A - 304* 1.20 0.52 0.64 5.95 __________________________________________________________________________ 316L & Pd DATA NORMALIZED TO 309L TABLE 7 __________________________________________________________________________ DOEL-2 COUPON ANALYSIS, PRE-DECONTAMINATION, JANUARY 1990 DATA-NORMALIZED. CONTACT MEASURED ACTIVATION PRODUCTS COUPON DOSERATE (TO AR FOR SPECIFIC MATERIAL) IDENTIFICATION (mR/hr) Co-58 Co-60 Mn-54 __________________________________________________________________________ HOT LEG 309L EP/PV 1.3 2.0 1.0 1.4 309L Cr/PV 1.8 2.6 1.4 1.9 CF8M AR 1.5 1.8 1.0 1.3 CF8M EP/PV 1.5 2.5 1.4 1.8 CF8M Cr/PV 1.7 2.8 1.4 1.9 316L Cr/PV* 2.4 2.4 1.2 1.0 4PP 1* 1.0 1.8 1.0 1.7 COLD LEG 309L AR 1.0 1.7 1.1 1.2 309L EP/PV 1.5 2.1 1.1 1.4 309L Cr/PV 1.6 1.7 1.1 1.0 CF8M AR 1.7 2.0 1.1 1.4 CF8M EP/PV 1.4 1.9 1.1 1.2 CF8M Cr/PV 1.2 1.6 1.8 3.3 316L Cr/PV 2.8 0.2 1.4 0.9 PD A - 304 1.1 1.9 1.2 16.0 AVERAGE, HOT LEG 1.6 2.3 1.2 1.6 AVERAGE, COLD LEG 1.5 1.6 1.2 3.3 __________________________________________________________________________ As shown graphically in FIGS. 3 and 4, the coupons coated with a chromium film and then passivated show very low activity deposition after a few months of exposure. The combination of electropolishing and RCT passivation show a 25 to 50% benefit in activity buildup over the long term. The palladium coated specimen have high doserates and more radionuclides observed than any of the other coupons. The 9300 hour data show that chromium coating followed by passivation represents a four to five times increase in effectiveness over steel passivation without chromium based upon corrosion product deposition. This effectiveness is reduced to two to three times when based on doserate.
	claims	1. A system comprising:at least one coolant pump configured to pump coolant water into or out of an associated nuclear reactor vessel;at least one external coolant conduit that is external to the nuclear reactor vessel connecting said at least one coolant pump with the associated nuclear reactor vessel; anda vessel isolation valve having a mounting flange configured to connect with a mating flange of a vessel penetration through an outer wall of the associated nuclear reactor vessel, the vessel isolation valve fluidly connecting with the at least one external coolant conduit, the vessel isolation valve configured to block outward flow from the pressure vessel when a pressure differential across the valve exceeds prescribed criteria;wherein the vessel isolation valve further includes:a valve seat defined in the mounting flange,a moveable valve member movable between an open position permitting flow through the vessel isolation valve and a closed position seating against the valve seat to block flow through the vessel isolation valve,a biasing member that biases the valve member towards the open position, andan actuator operatively coupled to the movable valve member for maintaining the valve member in the closed position. 2. The system of claim 1, wherein the valve member of the vessel isolation valve includes a piston adapted to seal against the valve seat. 3. The system of claim 2, wherein the vessel isolation valve further comprises:a rod connected to the piston and protruding axially away from the mounting flange along a longitudinal center axis of the biasing member, and wherein the biasing member comprises a spring operatively engaged with the rod. 4. The system of claim 3, wherein the spring is at least partially surrounded by a spring cover removably secured to the vessel isolation valve. 5. The system of claim 1, wherein the movable valve member is entirely contained in one or more of (i) the associated nuclear reactor vessel, (ii) the outer wall of the associated nuclear reactor vessel, and (iii) a flange assembly including the mating flange welded to the outer wall and the mounting flange of the vessel isolation valve. 6. A system comprising:at least one coolant pump configured to pump coolant water into or out of an associated nuclear reactor vessel;at least one external coolant conduit that is external to the nuclear reactor vessel connecting said at least one coolant pump with the associated nuclear reactor vessel; anda vessel isolation valve having a mounting flange configured to connect with a mating flange of a vessel penetration through an outer wall of the associated nuclear reactor vessel, the vessel isolation valve fluidly connecting with the at least one external coolant conduit, the vessel isolation valve configured to block outward flow from the pressure vessel when a pressure differential across the valve exceeds prescribed criteria;wherein the vessel isolation valve further includes:a valve body defining a central bore,a valve seat formed in the central bore of the valve body,a moveable valve member movable between an open position permitting flow through the vessel isolation valve and a closed position seating against the valve seat to block flow through the vessel isolation valve, andwherein the valve seat is coaxially aligned with the mounting flange so as to be disposed within a vessel penetration valve assembly formed by the mounting flange and the mating flange. 7. The system of claim 6, wherein the vessel isolation valve further includes a biasing member that biases the valve member towards the open position. 8. The system of claim 7, wherein the valve member of the vessel isolation valve includes a piston adapted to seal against the valve seat. 9. The system of claim 8, wherein the vessel isolation valve further comprises:a rod connected to the piston and protruding axially away from the mounting flange along a longitudinal counter axis of the biasing member, and wherein the biasing member comprises a spring operatively engaged with the rod. 10. The system of claim 9, wherein the spring is at least partially surrounded by a spring cover removably secured to the vessel isolation valve. 11. The system of claim 6, wherein the movable valve member is entirely contained in one or more of (i) the associated nuclear reactor vessel, (ii) the outer wall of the associated nuclear reactor vessel, and (iii) the vessel penetration valve assembly. 12. The system of claim 6, wherein the vessel isolation valve further includes an actuator operatively coupled to the movable valve member for maintaining the valve member in the closed position.
	abstract	In an irradiation system with an ion beam/charged particle beam, an ion beam/charged particle beam is deflected by an energy filter for the energy analysis and then a wafer irradiated with the beam. The energy filter controls the spread of magnetic field distribution caused by a deflection magnet, cancels a leakage magnetic field in the longitudinal direction, and bends the ion beam/charged particle beam at a uniform angle at any positions overall in scanning-deflection area.
	claims	1. A boiling water reactor comprising:a reactor building including,a top wall defining a penetration therein,a bottom wall, andat least one side wall, the top wall, the bottom wall, and the at least one side wall defining a chamber in the reactor building;a reactor cavity pool adjacent the reactor building;a primary containment vessel, at least a portion of the primary containment vessel is in the chamber of the reactor building; anda passive containment cooling system configured to receive water and expel hot water, the passive containment cooling system including,at least one thermal exchange pipe including,an outer pipe having a first outer pipe end and a second outer pipe end, the first outer pipe end being closed and the second outer pipe end being open, the first outer pipe end being within the primary containment vessel, and the second outer pipe end extending through the penetration in the top wall of the reactor building and into the reactor cavity pool such that the outer pipe is in fluid communication with the reactor cavity pool, the outer pipe including,a side pipe wall defining an opening therein, andan inner pipe at least partially within the outer pipe, the inner pipe having a first inner pipe end and a second inner pipe end, the first inner pipe end and the second inner pipe end being open, and the second inner pipe end extending out of the outer pipe and into the reactor cavity pool such that the second inner pipe end is in fluid communication with the reactor cavity pool, the inner pipe including,a curved portion between the first inner pipe end and the second inner pipe end, the curved portion extending through and past the opening in the side pipe wall and into the reactor cavity pool. 2. The boiling water reactor of claim 1, wherein the outer pipe has a diameter of 200 mm to 520 mm. 3. The boiling water reactor of claim 1, wherein the inner pipe has a diameter of 50 mm to 200 mm. 4. The boiling water reactor of claim 1, wherein the inner pipe and the outer pipe comprise stainless steel. 5. The boiling water reactor of claim 1, further comprising:at least one seal around the outer pipe and adjacent the penetration in the top wall of the reactor building. 6. The boiling water reactor of claim 1, wherein the passive containment cooling system includes a plurality of thermal exchange pipes. 7. The boiling water reactor of claim 6, wherein the passive containment cooling system includes two to twenty thermal exchange pipes. 8. The boiling water reactor of claim 1, further comprising:at least one support within the primary containment vessel, the support configured to support the first outer pipe end of the thermal exchange pipe. 9. The boiling water reactor of claim 8, wherein the support comprises a spring support, the spring support configured to allow vertical movement of the thermal exchange pipe caused by expansion due to absorption of heat. 10. The boiling water reactor of claim 1, wherein the passive containment cooling system is valve-free, pump-free, or both valve-free, and pump-free. 11. A passive containment cooling system comprising:a thermal exchange pipe including,an outer pipe having a first outer pipe end and a second outer pipe end, the first outer pipe end being closed and the second outer pipe end being open, the first outer pipe end being within a primary containment vessel of a boiling water reactor, the second outer pipe end extending into a reactor cavity pool such that the outer pipe is in fluid communication with the reactor cavity pool, the outer pipe including,a side pipe wall defining an opening therein, andan inner pipe at least partially within the outer pipe, the inner pipe having a first inner pipe end and a second inner pipe end, the first inner pipe end and the second inner pipe end being open, and the second inner pipe end extending out of the outer pipe and into the reactor cavity pool such that the second inner pipe end is in fluid communication with the reactor cavity pool, the inner pipe including,a curved portion between the first inner pipe end and the second inner pipe end, the curved portion extending through and past the opening in the side pipe wall and into the reactor cavity pool. 12. The passive containment cooling system of claim 11, wherein the outer pipe has a diameter of 200 mm to 520 mm. 13. The passive containment cooling system of claim 11, wherein the inner pipe has a diameter of 50 mm to 200 mm. 14. The passive containment cooling system of claim 11, wherein the inner pipe and the outer pipe comprise stainless steel. 15. A method of installing the passive containment cooling system of claim 11 comprising:placing the thermal exchange pipe at least partially in the primary containment vessel, such that a portion of the thermal exchange pipe extends into the reactor cavity pool.
	abstract	A weakly ionized plasma of ions and neutrals is generated from a first reactant in a confinement region. Orthogonal electric and magnetic fields induce azimuthal rotation of the ions around a longitudinal axis of the confinement region, the azimuthal rotation of the ions imparting azimuthal rotation to the neutrals of the first reactant, and promoting repeated collisions between one or both of the ions and the neutrals with a second reactant. The repeated collisions produce an interaction between the neutrals and the second reactant that produces a product having a nuclear mass that is different from a nuclear mass of any of the nuclei of the neutrals and the second reactant.
	description	This application is a continuation of U.S. patent application Ser. No. 11/646,155 entitled “Active Particle Trapping for Process Control,” filed Dec. 27, 2006, the disclosure of which is hereby incorporated by reference. This invention relates to semiconductor manufacturing equipment and, more particularly, to a particle isolation system within semiconductor manufacturing equipment. Ion implantation is a standard technique for introducing conductivity-altering impurities into semiconductor wafers. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the wafer. The energetic ions in the beam penetrate into the bulk of the semiconductor material and are embedded into the crystalline lattice of the semiconductor material to form a region of desired conductivity. An ion implanter includes an ion source for converting a gas or a solid material into a well-defined ion beam. The ion beam typically is mass analyzed to eliminate undesired ion species, accelerated to a desired energy, and implanted into a target. The ion beam may be distributed over the target area by electrostatic or magnetic beam scanning, by target movement, or by a combination of beam scanning and target movement. The ion beam may be a spot beam or a ribbon beam having a long dimension and a short dimension. The long dimension usually is at least as wide as the wafer. Examples of ion implanters may be found in, for example, U.S. Pat. No. 4,922,106 issued to Berrian et al. (assigned to Varian Semiconductor Equipment Associates, Inc. of Gloucester, Mass.) and U.S. Pat. No. 5,350,926 White et al., both of which are hereby incorporated by reference. In a plasma doping system, a semiconductor wafer is placed on a conductive platen which functions as a cathode. The desired dopant material is introduced into the chamber, and a voltage pulse is applied between the platen and an anode or the chamber walls, causing formation of a plasma having a plasma sheath in the vicinity of the wafer. The applied voltage causes ions in the plasma to cross the plasma sheath and to be implanted into the wafer. The depth of implantation is related to the voltage applied between the wafer and the anode. An example of a plasma doping system may be found in, for example, U.S. Pat. No. 4,764,394 issued to Conrad, which is hereby incorporated by reference. In other types of plasma systems, known as plasma immersion systems, a continuous RF voltage is applied between the platen and the anode, thus producing a continuous plasma. At intervals, a voltage pulse is applied between the platen and the anode, causing ions in the plasma to be accelerated toward the wafer. An example of a plasma immersion system may be found in, for example, U.S. Pat. No. 5,354,381 issued to Sheng, which is hereby incorporated by reference. Other types of deposition methods, such as chemical vapor deposition or physical vapor deposition also may be used in wafer or workpiece processing. Other semiconductor manufacturing methods, such as lithography, may likewise be used on a wafer or workpiece. Workpiece processing equipment used for semiconductor manufacturing typically is under vacuum in a process chamber. During typical system operation for ion implantation, undesired particles may be formed or generated. These particles may be residual beam or plasma particles, photoresist, particles from a workpiece, or other particles that exist in regions of the process chamber and that may settle on a surface, base, or floor within a process chamber. Particles may, for example, break off a film formed on a surface within an analyzer magnet and settle to the base of that analyzer magnet process chamber. During periodic maintenance, various process chambers used for semiconductor manufacturing may be open to the atmosphere or a process gas. The venting of such process chambers often leads to turbulent fluids being introduced to a process chamber. Particles that have settled on the floor, base, or other surfaces in a process chamber may then be disturbed or agitated and redistributed throughout the process chamber's interior. Due to additional cleaning required to remove these particles, re-qualifying the process chamber becomes more difficult and time consuming. Prior particle isolation technology includes, for example, charged process chamber walls or charged plates or electrodes. This technology also may include mechanical means such as channels or fixed louvers. This technology also may include adhesive material or particle capturing material. However, these types of particle isolation technology may release trapped particles when a process chamber is vented and the particles are disturbed by turbulent fluids entering the process chamber. This may distribute the particles throughout the process chamber and may require additional cleaning to re-qualify the process chamber. These types of particle isolation technology also lack particle isolation devices that may be quickly removed. Accordingly, there is a need in the art for a new and improved apparatus and method of particle isolation within semiconductor manufacturing process chambers. A particle isolation system that substantially retains particles in an isolation compartment and prevents or inhibits movement of particles between the isolation compartment and a semiconductor process chamber is provided. In one embodiment, the particle isolation system includes a semiconductor process chamber; at least one member within the semiconductor process chamber wherein the member has at least a first position and a second position; and at least one isolation compartment having a plurality of walls, the isolation compartment defined by the plurality of walls, at least one of the plurality of walls of the isolation compartment defining at least one opening, wherein the member in the first position permits particles to enter the isolation compartment from the semiconductor process chamber through the opening, and wherein the member in the second position substantially encloses the isolation compartment thereby substantially retaining the particles in the isolation compartment and substantially limiting movement of the particles between the semiconductor process chamber and the isolation compartment through the opening. In another embodiment, an ion implant system is provided. The ion implant system includes an ion source that directs ions toward a workpiece; a semiconductor process chamber; at least one member within the semiconductor process chamber wherein the member has at least a first position and a second position; and at least one isolation compartment having a plurality of walls, the isolation compartment defined by the plurality of walls, at least one of the plurality of walls of the isolation compartment defining at least one opening, wherein the member in the first position permits particles to enter the isolation compartment from the semiconductor process chamber through the opening, and wherein the member in the second position substantially encloses the isolation compartment thereby substantially retaining the particles in the isolation compartment and substantially limiting movement of the particles between the semiconductor process chamber and the isolation compartment through the opening. The invention is described herein in connection with an ion beam implantation apparatus. However, the invention can be used with other systems and processes involved in semiconductor manufacturing such as, for example, plasma doping or immersion, physical vapor deposition, chemical vapor deposition, or lithography. Thus, the invention is not limited to the specific embodiments described below. FIG. 1 is a diagram of a typical ion implanter suitable for implementing a particle isolation system of the present invention. Those skilled in the art will recognize other ion implanter designs or semiconductor manufacturing technology that also may incorporate the present invention. In general, ion implanter 10 includes ion source 80 to generate ions that form ion beam 81. Ion source 80 may include an ion chamber and a gas box containing a gas to be ionized. The gas is supplied to the ion chamber where it is ionized. The ions thus formed are extracted from the ion chamber to form ion. beam 81. Ion beam 81 is directed between the poles of resolving magnet 82. A first power supply 83 is connected to an extraction electrode of ion source 80 and provides a positive first voltage V0. First voltage V0 may be adjustable, for example, from about 0.2 to about 80 kV in a high current ion implanter. Thus, ions from ion source 80 are accelerated to energies of about 0.2 to 80 keV by the first voltage V0. Ion beam 81 passes through suppression electrode 84 and ground electrode 85 to mass analyzer 86. Mass analyzer 86 includes resolving magnet 82 and masking electrode 88 having resolving aperture 89. Resolving magnet 82 deflects ions in ion beam 81 such that ions of a desired ion species pass through resolving aperture 89. Undesired ion species do not pass through resolving aperture 89, but are blocked by masking electrode 88. In one embodiment, resolving magnet 82 deflects ions of the desired species by about 90°. Ions of the desired ion species pass through resolving aperture 89 to angle corrector magnet 94. Angle corrector magnet 94 deflects ions of the desired ion species and converts the ion beam from a diverging ion beam to ribbon ion beam 12, which has substantially parallel ion trajectories. In one embodiment, angle corrector magnet 94 deflects ions of the desired ion species by about 70°. In another embodiment, ions of the desired ion species may pass through a deceleration stage. End station 11 supports one or more workpieces, such as wafer 13, in the path of ribbon ion beam 12 such that ions of the desired species are implanted into wafer 13. End station 11 may include platen 95 to support wafer 13. End station 11 also may include a scanner (not shown) for moving wafer 13 perpendicular to the long dimension of the ribbon ion beam 12 cross-section, thereby distributing ions over the entire surface of wafer 13. Ribbon ion beam 12 preferably is at least as wide as wafer 13. Although ribbon ion beam 12 is illustrated, other ion implanter embodiments may provide a scanned ion beam (scanned in one or two dimensions) or may provide a fixed or spot ion beam. The ion implanter may further include a second deceleration stage in some embodiments. The ion implanter may include additional components known to those skilled in the art. For example, end station 11 typically includes automated workpiece handling equipment for introducing workpieces into the ion implanter and for removing workpieces after ion implantation. End station 11 also may include a dose measuring system, an electron flood gun, or other known components. It will be understood to those skilled in the art that the entire path traversed by the ion beam is evacuated during ion implantation. A process chamber, such as, for example, a semiconductor process chamber, may be any enclosed space in a piece of semiconductor manufacturing equipment. Embodiments of the current particle isolation system may be used in various process chambers in an ion implanter, such as one illustrated in FIG. 1. These may include, for example, ion beam generator chamber 19, beam line chamber 18, mass analyzer 86, angle corrector magnet 94, end station 11, load lock chamber 17, or other devices used in on implantation requiring particle isolation. It is understood to those skilled in the art that many process chambers typically are operated at a vacuum. However, the current particle isolation system in accordance with the present invention may be used in non-vacuum process chambers. FIG. 2 is a view of an embodiment of a member in a chamber having a particle isolation system in a first, or open, position. Particles 22 are found within chamber 21 and on walls 20 of process chamber 15, and enter isolation compartment 24 through opening 27. Isolation compartment 24 has a plurality of walls and may be of any shape that accommodates particles 22. Process chamber 15 includes at least one surface 23 that defines at least one opening 27. In this embodiment, isolation compartment 24 is separated from chamber 21 by surface 23. Surface 23 has, in this particular embodiment, one opening 27. Disposed on surface 23 is hinge 26, upon which member 25 is mounted. Hinge 26 may be capable of full 360° rotation, or may be limited to a certain angle of rotation between a first position, open, and second position, closed. Member 25 is not limited to being disposed on hinge 26 and also may be positioned in, or be translated between a first and second position to substantially retain particles 22 in isolation compartment 24 using other means such as, for example, tracks, slides, pins, rods, or other means or methods known to those skilled in the art. In some embodiments, member 25 may be composed of materials that resist particles 22 from attaching to member 25. In this particular embodiment, member 25 is a flat panel configured to be received by opening 27 in order to prevent movement by particles 22 between chamber 21 and isolation compartment 24. Member 25 may, of course, have other curvatures or shapes. Member 25 is shown in a first position in FIG. 2, but need not be at a 90° angle to surface 23 in its first position. The first position of member 25 may be any angle that permits particles 22 to enter isolation compartment 24. In moving from the illustrated first position to the second position, member 25 may move along the path illustrated by the arrow in FIG. 2. Member 25 may have positions other than a first and second position relative to obtaining or substantially retaining particles 22 in isolation compartment 24. These positions may be within isolation compartment 24, as seen in FIG. 2, or opposite or outside of isolation compartment 24. When member 25 is in its second, or closed, position, which is substantially parallel with surface 23 in this particular embodiment, movement of particles 22 through opening 27 between isolation compartment 24 and chamber 21 is prevented. In this particular embodiment, member 25 is configured to be received by opening 27 and member 25 fills opening 27. A perfect seal between member 25 and surface 23 within opening 27 may be present, or member 25 may fit tightly enough within opening 27 to prevent significant movement of particles 22 through opening 27 between isolation compartment 24 and chamber 21. In another embodiment, member 25 is configured to cover opening 27 and may be substantially parallel with surface 23 in its second position. Member 25 may have a larger surface area than the area of opening 27. Member 25 may have larger dimensions on all non-hinge sides than the corresponding dimensions of opening 27, or just on the side of opening 27 opposite of hinge 26. A perfect seal between member 25 and surface 23 may be present, or member 25 may fit tightly enough around opening 27 to prevent significant movement of particles 22 between isolation compartment 24 and chamber 21 through opening 27. In yet another embodiment, a plurality of members 25 is used in a single opening 27. This plurality of members 25 may be disposed opposite of one another across opening 27. A plurality of members 25 may be used due to the size of opening 27, or other reasons. FIG. 3 illustrates a view of another embodiment of a member in a chamber having a particle isolation system in a first position. Particles 22 are found within chamber 21 and on walls 20 of process chamber 15, and enter isolation compartment 24 through opening 27. In this embodiment, isolation compartment 24 is separated from chamber 21 by surface 23 of process chamber 15. Surface 23 has, in this particular embodiment, one opening 27. In this particular embodiment, member 25 is disposed on surface 23 and is configured to move. Member 25 may use a track or channel to translate between at least a first position and second position, a pin or rod to rotate around, or other actuated means known to those skilled in the art to translate between at least a first position to a second position. Member 25 may be disposed on surface 23, but also may be disposed under surface 23 nearer to isolation compartment 24, or may be disposed within surface 23. Member 23 moves from a first position to a second position in the direction of the arrow illustrated in FIG. 3. The first position may be any position that allows particles 22 to substantially move through opening 27. Multiple positions may be used and member 22 is not limited solely to a first and second position in this embodiment. When member 25 is in its second position, movement of particles 22 through opening 27 between isolation compartment 24 and chamber 21 is substantially prevented or inhibited. Isolation compartment 24 may be substantially enclosed when member 25 is in its second position. In this particular embodiment, member 25 is configured to be cover opening 27 and may be substantially parallel with surface 23 in its second position. Member 25 may have a larger surface area than the area of opening 27. A perfect seal between member 25 and surface 23 may be present, or member 25 may fit tightly enough around opening 27 to prevent or inhibit significant movement of particles 22 between isolation compartment 24 and chamber 21 through opening 27. FIG. 4 is a view of another embodiment of a member in a chamber having a particle isolation system in a first position. Particles 22 are found within chamber 21 and on walls 20 of process chamber 15, and enter isolation compartment 24 through opening 27. In this embodiment, isolation compartment 24 is separated from chamber 21 by surface 23 of process chamber 15. Surface 23 has, in this particular embodiment, one opening 27. Member 25 is mounted upon hinge 26. Member 25 in this embodiment comprises a flat slat, however, member 25 also may comprise a curved slat, a plurality of slats, or a propeller shape with a plurality of arms, as examples, and is not limited to merely being a single flat slat. Hinge 26 is mounted on the center of member 25 in this embodiment, allowing member 25 to pivot about an axis in a rotational manner indicated by the arrows in FIG. 4, rather than pivoting as a lever as seen in FIG. 2. Member 25 is illustrated in a first position in FIG. 4. However, member 25 may rotate about hinge 26 and is not limited to having at first position as illustrated in FIG. 4 or a first position substantially perpendicular to opening 27. The first position in this embodiment may be any angle that allows the movement of particles 22 through opening 27 between chamber 21 and isolation compartment 24. Member 25 may rotate clockwise as indicated by the arrows in FIG. 4, or may rotate counterclockwise. Member 25 may be able to rotate 360° or may be limited to rotating less than 360°. In another embodiment, hinge 26 also may be mounted substantially off-center from the center of member 25, allowing member 25 to pivot about an axis in a rotational manner. Substantially off-center means that hinge 26 is not centered as seen in FIG. 4 and that hinge 26 is spaced substantially not equidistant between the two ends of member 25. Thus, if member 25 were bifurcated by hinge 26, the surface areas of the two bifurcated sides of member 25 would be different. In another embodiment, member 25 also may be longer in width than the width of opening 27. In this particular embodiment, member 25 in its second position may block movement of particles 22 through opening 27 between isolation compartment 24 and chamber 21 while as substantially parallel with surface 23 as is mechanically feasible to fill or cover opening 27. A perfect seal between member 25 and surface 23 may be present, or member 25 may fit tightly enough within opening 27 to prevent or inhibit significant movement of particles 22 between isolation compartment 24 and chamber 21 through opening 27. FIG. 5 shows another view of the embodiment of FIG. 4. FIG. 5 is a view of member 25 of FIG. 4 from a different perspective. Hinge 26 is disposed on surface 23. Member 25 has hinge 26 mounted in its center, allowing rotational movement about hinge 26. Hinge 26 is not limited to bifurcation of the entire length of member 25, but may instead be disposed on only the ends of member 25. FIG. 6 is another view of the embodiment of the member of FIG. 4 in a second position. FIG. 6 corresponds to FIG. 4. Member 25 is now in its second position and movement of particles 22 through opening 27 between isolation compartment 24 and chamber 21 is substantially prevented or inhibited. Isolation compartment 24 may be substantially enclosed when member 25 is in its second position. In this particular embodiment, member 25 is configured to be received by opening 27. When in its second position, which may be substantially parallel with surface 23, member 25 fills opening 27. A perfect seal between member 25 and surface 23 may be present, or member 25 may fit tightly enough within opening 27 to prevent or inhibit significant movement of particles 22 between isolation compartment 24 and chamber 21 through opening 27. FIG. 7 is a view of a chamber incorporating a particle isolation system in a first position. Process chamber 15 has walls 20 and surface 23 defining chamber 21. Surface 23 may be part of process chamber 15, or may be a separate surface disposed within process chamber 15. Process chamber 15 also has particles 22 within chamber 21. Particles 22 may be may be residual beam particles, photoresist, or other particles that exist in various parts of process chamber 15 and which may fall or deposit onto surfaces in process chamber 15. For example, ions from an ion beam that do not strike a workpiece may instead strike walls 20 of process chamber 15 and form a film. Portions of this film may break off and form particles 22. Furthermore, an ion beam may deposit ions on walls 20 of process chamber 15 or within isolation compartment 24 through opening 27 if process chamber 15 is located near or around an analyzer magnet or similar device. Particles 22 also may be formed from the plasma during plasma doping, be introduced to process chamber 15 with an unclean workpiece, be formed from the components of process chamber 15 during operation, be introduced through venting process chamber 15 with a fluid, be introduced by opening process chamber 15 to atmosphere, or be introduced or generated by other means or sources. Some particles 22 within process chamber 15 may eventually settle toward the base of process chamber 15, in this embodiment surface 23. Some particles 22 may have velocity and bounce off walls 20 of process chamber 15. Lastly, some particles 22, such as those from an ion beam, for example, may have a charge and be subjected to electrostatic forces during their movement and settling in process chamber 15. When member 25 is in a first, or open, position, particles 22 may settle or move through opening 27 into isolation compartment 24. Within chamber 21, isolation compartment 24 is provided to substantially retain particles 22. The openings 27 of process chamber 15 may be spaced, for example, equally around a surface of process chamber 15, or in specific regions of process chamber 15 to substantially retain particles 22. Process chamber 15 is not limited to this particular embodiment with multiple openings 27 and may instead only have a single opening 27, as seen in FIG. 2. Member 25 may be in, on, or around surface 23, and may be configured to be received by opening 27, to block opening 27, to cover opening 27, or to occlude opening 27. Process chamber 15 may include just one member, as illustrated in FIG. 2, or may include a plurality of members as illustrated in 7. Having a plurality of members may lower efficiency of isolation compartment 24, but may be desired to accommodate an opening 27 in a small area of process chamber 15 or to place an opening 27 near a particle source within process chamber 15, as examples. FIG. 8 illustrates a view of the particle isolation system of FIG. 7 in a second position. While leaving member 25 predominantly in the first, or open, position of FIG. 7 may allow a maximum amount of particles 22 to enter or settle into isolation compartment 24, each member 25 may be moved from a first position, open, to a second position, closed. Member 25 may wholly or partially fill, occlude, block, or cover opening 27 in this second position provided particles 22 are substantially retained in isolation compartment 24. In FIG. 8, member 25 substantially retains particles 22 by moving to a second position substantially parallel with opening 27 and surface 23. However, member 25 may have second positions not substantially parallel with opening 27 and surface 23 that still substantially retain particles 22 in isolation compartment 24, and member 25 is thus not limited to being solely parallel with opening 27 and surface 23 when in a second position. When substantially all of member 25 are moved to a second position, as illustrated by FIG. 8, particles 22 are substantially retained within isolation compartment 24. Most particles 22 may no longer move to chamber 21 of process chamber 15 from isolation compartment 24. However, member 22 also may move to a second position different from that illustrated in this embodiment to substantially retain particles 22 in isolation compartment 24. Each member 25 may be moved to a second position, for example, while process chamber 15 is vented. This venting may be done by opening process chamber 15 to atmosphere or inserting a fluid into process chamber 15. If process chamber 15 is vented, particles 22 may no longer remain settled on wall 20 or in isolation compartment 24, but rather may be stirred up within chamber 21. This increases the difficulty in cleaning process chamber 15. Thus, moving member 25 to a second position will substantially retain particles 22 in isolation compartment 24 and substantially prevent particles 22 from being stirred up within chamber 21. Once particles 22 settle or fall into and are substantially retained in isolation compartment 24, particles 22 may remain there until removed or cleaned out. This may be during preventative maintenance, which may occur, for example, weekly, monthly, or at other times. A user may clean isolation compartment 24 using, for example, a wet clean or abrasive clean. Other methods of removal known in the art during operation, such as using a vent and rough, or autoclean, routine, also may be used. This example of a removal method is illustrated in FIG. 16. FIG. 9 shows a view of an embodiment of a chamber incorporating a particle isolation system in a first position. Process chamber 15 includes particles 22 in chamber 21. Process chamber 15 further includes at least one surface 23 and at least one hinge 26 on which at least one member 25 is disposed. Process chamber 15 in this particular embodiment also includes a second surface 28. Second surface 28 may be found anywhere within process chamber 15, but here is illustrated on a side of process chamber 15. Second surface 28 may be part of process chamber 15, or may be a separate surface disposed within process chamber 15. Second surface 28 includes at least one second surface opening 30 in which at least one second surface member 29 operates. In this embodiment, one isolation compartment 24 is utilized, however member 25 and second surface member 29 may have two or more separate isolation compartment 24, as illustrated in FIG. 10. Process chamber 15 also may have more than one second surface 28. Adding a second surface opening 30 and second surface member 29 assists in collecting particles 22 that come from a known particle producing source. Second surface opening 30 and second surface member 29 also may assist in collecting particles 22 when positioned where particles 22 will break off from a film formed from an ion beam striking a process chamber surface, among other reasons. FIG. 10 is a view of another embodiment of a chamber incorporating a particle isolation system in a first position. Process chamber 15 includes particles 22 in chamber 21. Process chamber 15 further includes surface 23, at least one hinge 26 on which at least one member 25 is disposed. Process chamber 15 also includes sectional isolation compartments 31. Sectional isolation compartments 31 may correspond to each member 25, but also may include multiple members 25 per sectional isolation compartment 31. Sectional isolation compartments 31 may be found at the base of chamber 21, but also may be found in other regions of process chamber 15. Sectional isolation compartments 31 may be of different sizes to fit underneath specific process equipment or to be accommodated within different regions of process chamber 15, but also may be of uniform size. If process chamber 15 has multiple small members 25 coupled with sectional isolation compartments 31, efficiency may be reduced, but this may he desired due to shape, contents, or particle sources of process chamber 15, as examples. FIG. 11 is a view of an embodiment of the particle isolation system using an electro-mechanical actuator. Electro-mechanical actuator 44 has a motor that powers a gear train. Electro-mechanical actuator 44 also has an electrical feed. Electro-mechanical actuator 44 may provide the motion to member 25 through hinge 26 in response to a signal. Electro-mechanical actuator 44 may provide motion to member 25 through other means than hinge 26. Thus, member 25 moves between first and second positions due to electro-mechanical actuator 44. FIG. 12 is a view of the particle isolation system using a pneumatic actuator. Pneumatic actuator 45 may be a pneumatic actuator, or some other pneumatically-powered drive that converts energy in the form of a fluid into motion. Motion in pneumatic actuator 45 may be rotary, linear, or a combination of both rotary and linear. Pneumatic actuator 45 may power and provide the motion to member 25 through hinge 26. Pneumatic actuator 45 may provide motion to member 25 through other means than hinge 26. Thus, member 25 moves between first and second positions due to pneumatic actuator 45. Pneumatic actuator 45 may have pneumatic source 47 providing gas or liquid to power pneumatic actuator 45. FIG. 13 is a view of an embodiment of the particle isolation system using a controller. Controller 32 is the control system for a piece of semiconductor manufacturing equipment, such as an ion implanter. Controller 32 includes a general-purpose computer or network of general-purpose computers that may be programmed to perform the desired input/output functions. Controller 32 may include processor 33 and machine readable medium 34. Processor 33 may include one or more processors known in the art such as, for example, those commercially available from Intel Corporation. Machine readable medium 34 may include one or more machine readable storage media, such as random-access memory (RAM), dynamic RAM (DRAM), magnetic disk (e.g., floppy disk and hard drive), optical disk (e.g., CD-ROM), and/or any other device that can store instructions for execution. Controller 32 can also include other electronic circuitry or components, such as, but not limited to, application specific integrated circuits, other hardwired or programmable electronic devices, or discrete element circuits. Controller 32 also may include communication devices. Controller 32 may receive input data and instructions from any variety of systems and components of a piece of semiconductor manufacturing equipment and may provide output signals to control the components of that piece of semiconductor manufacturing equipment. Controller 32 may be able to communicate with drive 46, whether drive 46 is a pneumatic actuator, electro-mechanical actuator, piezo actuator, or other form of actuator that can move member 25 between at least a first and second position. Controller 32 may be aware when an ion implanter is going to vent, for example, and may communicate with drive 46 to move member 25 to a second position, substantially retaining particles 22 at that time. Controller 32 also may communicate with drive 46 to move member 25 to a second position for other reasons, such as, for example, user command or the occurrence of preventative maintenance. If there is a plurality of members 25, then controller 32 may move only sonic of members 25 between a first and second position. The particle isolation system also may include a user interface system 35. User interface system 35 may include, but not be limited to, devices such as touch screens, keyboards, user pointing devices, displays, or printers to allow a user to input commands, data, or to monitor the semiconductor manufacturing equipment. User interface system 35 may be located on-site with the ion implanter or may be done remotely via local computer networks. FIG. 14 is a view of another embodiment of the particle isolation system using a particle monitor. Controller 32 may be able to communicate with drive 46. Controller 32 also may be able to communicate with particle monitor 36. Particle monitor 36 may be an in-situ particle monitor or another type of device known to those skilled in the art that measures particle count or particle levels within isolation compartment 24. Particle monitor 36 also may measure the particle count in other parts of a process chamber and is not limited to measuring particle count only in isolation compartment 24. Particle monitor 36 may not only measure particles 22, but may instead measure other particles or fluids in a process chamber. Controller 32 may communicate with particle monitor 36 in real-time, intermittently, or based on some event. These events may be, as examples, the input of new workpieces into a process chamber, the number of workpieces processed, or the set-up of an ion beam or plasma. Particle monitor 36 also may communicate with controller 32 that the number of particles 22 in isolation compartment 24 has exceeded a threshold. This threshold may vary based on the application or process used in the ion implanter. When particle monitor 36 communicates with controller 32 that the threshold for particles 22 has been exceeded, in this embodiment controller 32 communicates with drive 46 to move member 25 from a first position to a second position. Drive 46 may move member 25 from a first position to a second position as illustrated by the arrow in FIG. 14, thereby substantially isolating and substantially retaining particles 22 in isolation compartment 24. Particles 22 will remain substantially retained in isolation compartment 24 until particles 22 are removed during preventative maintenance or some other cleaning occurs. This process substantially prevents or inhibits particles 22 in isolation compartment 24 from escaping if isolation compartment 24 is substantially full or beyond the set threshold, but also may prevent leaving member 25 in a first position when no more particles 22 could enter isolation compartment 24 because isolation compartment 24 is full or beyond the set threshold. FIG. 15 shows a view of another embodiment of a chamber incorporating a particle isolation system in a first position and particle isolators. Process chamber 15 includes particles 22 in chamber 21. Process chamber 15 further includes surface 23 and at least one hinge 26 on which at least one member 25 is disposed. Process chamber 15 also includes at least one particle isolator 40 in this embodiment. Some of particles 22 may be moving about process chamber 15 and may not settle into isolation compartment 24. Particle isolator 40 may catch or attract particles 22, even if particles 22 are moving. Particle isolator 40 may be, for example, an electrostatic sheet or a polymer sheet. Other forms of particle isolator 40 known to those skilled in the art that substantially retain particles 22 may be used and particle isolator 40 is not limited to those listed. Process chamber 15 may include just one particle isolator 40, but also may include a plurality of particle isolators 40 as seen in FIG. 15. If process chamber 15 contains a plurality of particle isolators 40, then these may be either all of one type of particle isolator, or may be a combination of different types of particle isolators. Each particle isolator 40 is found on particle isolator surface 41 at the base of isolation compartment 24. However, as seen in this embodiment, isolation compartment 24 also may include side particle isolator 42 or top particle isolator 43. Top particle isolator may be disposed on surface 23, opposite of particle isolator surface 41. Particle isolator 40 also may be disposed on surface 23 within chamber 21, member 25, walls 20, or other parts of process chamber 15. Particle isolator surface 41 may be, for example, surface 23, walls 20 in chamber 21 or isolation compartment 24, a surface in an isolation compartment 24, a surface on member 25, or other surfaces in process chamber 15, and is not limited solely to the base of process chamber 15 as illustrated in FIG. 15. Particle isolator 40 may be recessed into particle isolator surface 41, as seen in particle isolator 40. Particle isolator 40 also may be disposed on particle isolator surface 41 without being recessed, as seen in side particle isolator 42. Particle isolator 40 also may be raised above particle isolator surface 41 (not illustrated). In one embodiment, an electrostatic sheet may be used as a particle isolator 40. An electrostatic sheet is, in one embodiment, a polymer sheet with a charged conductive layer. This may be either a positive or negative charge, but is negative in this particular embodiment. This electrostatic sheet is insulated from particle isolator surface 41 or walls 20 by a polymer base material. Electrostatic sheets are not limited solely to polymer sheets with conductive layers and may be other materials capable of holding an electric charge. Electrostatic sheets in this embodiment typically require low current to be applied to them. Electrostatic sheets may also use high voltage power. Some of particles 22 may be charged, especially if particles 22 originated in an ion beam or plasma. Opposite charges may exist between particles 22 and an electrostatic sheet. Thus, an attractive force may exist between particles 22 and an electrostatic sheet. Particles 22 may be drawn toward an electrostatic sheet due to electrostatic forces, or other forces. Particles 22 also may be distributed onto an electrostatic sheet due to their own movement or the fluid currents within the process chamber. Particles 22 also may be distributed onto an electrostatic sheet due to particles 22 settling into isolation compartment 24. Particles 22 may become disposed or substantially retained on an electrostatic sheet for other reasons not listed in this embodiment. Particles 22, thus substantially retained, may not be removed from an electrostatic sheet and are not be stirred up during venting. Electrostatic sheets may be cleaned during preventative maintenance, as an example, or at other times. During cleaning, the electrostatic sheet is removed from isolation compartment 24 and replaced with a new electrostatic sheet. Because electrostatic sheets may be disposable, cleaning time may be reduced. In another embodiment, a polymer sheet may be used as particle isolator 40. This polymer sheet comprises a silicon rubber or silicon elastomer layer, as examples. Other elastomers, polymers, or rubbers with a high particle sticking coefficient and low outgas in vacuum also may be used. A polymer sheet will remain sticky in vacuum. Particles 22 may be distributed onto a polymer sheet due to their own movement or the gas currents within the process chamber. Particles 22 also may be distributed onto a polymer sheet due to particles 22 settling down into isolation compartment 24. Particles 22 may become disposed or substantially retained on a polymer sheet for other reasons not listed in this embodiment. Particles 22, thus substantially retained, may not be removed from a polymer sheet and will not be stirred up during venting, Polymer sheets may be cleaned during preventative maintenance, as an example, or at other times. A used polymer sheet may be removed from particle isolator surface 41 and replaced with a new polymer sheet. A polymer sheet also may be replaced at other times than just during preventative maintenance. Because polymer sheets may be disposable, cleaning time may be reduced. FIG. 16 is a view of an embodiment of the particle isolation system using an evacuation system. This evacuation system is an example of removing particles 22 from isolation compartment 24 and may be known as a vent and rough, or autoclean, routine. Member 25 is in a second position. Particles 22 are substantially blocked from moving from isolation compartment 24 to chamber 21 through opening 27. Process chamber 15 further includes a vent 71 connected with a fluid source 70. Fluid 74 enters isolation compartment 24 through vent 71. Fluid 74 may be a process gas, such as nitrogen, or may be atmosphere. Fluid 74 also may be any fluid that removes particles 22 from isolation compartment 24 and that may be removed by pump 73. Vent 71 introduces fluid 74 to isolation compartment 24 by moving vent 71 from a closed position to an open position. The degree vent 71 is opened may vary. Opening of vent 71 need not be substantial, but may be range from slight opening of vent 71 to total opening of vent 71. Fluid 74 is then introduced to isolation compartment 24 in a single burst or in multiple bursts that introduce a series of shockwaves. The amount of fluid 74 introduced may vary based on, for example, the amount of particles 22 in isolation compartment 24. The introduction of fluid 74 creates a pressure burst which causes particles 22 to move toward evacuation outlet 72. Particles 22 move because particles 22 are large enough for pumping by pump 73 and because of the shockwave caused by the addition of fluid 74 through vent 71 to isolation compartment 24. Particles 22 and fluid 74 are then removed from isolation compartment 24 through evacuation outlet 72. Pump 73 may further remove particles 22 without introduction of fluid 74 due to its evacuation action. The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described (or portions thereof), and it is recognized that various modifications are possible within the scope of the claims. Other modifications, variations, and alternatives are also possible. Accordingly, the foregoing description is by way of example only and is not intended as limiting.
	claims	1. An X-ray beam device for X-ray analytical applications, comprising:an X-ray source designed such as to emit a divergent beam of X-rays; andan optical assembly designed such as to focus said beam onto a focal spot,wherein said optical assembly comprises a first reflecting optical element, a monochromator device and a second reflecting optical element sequentially arranged between said source and said focal spot, wherein said first optical element is designed such as to collimate said beam in two dimensions towards said monochromator device, and wherein said second optical element is designed such as to focus the beam coming from said monochromator device in two dimensions onto said focal spot;wherein the X-ray source has a source size S of 100 microns or less; andwherein the said first optical element has a focal length F1 given by ΔθM≦S/F1≦5*ΔθM in order to produce a focal spot size which is only slightly asymmetric, wherein F1 is also the distance between said X-ray source and said first optical element, and wherein ΔθM is the angular acceptance of said monochromator device. 2. An X-ray beam device according to claim 1, characterized in that said monochromator device comprises at least one crystal monochromator. 3. An X-ray beam device according to claim 1, characterized in that at least one of said first optical element and said second optical element comprises a multilayer. 4. An X-ray beam device according to claim 1, characterized in that at least one of said first optical element and said second optical element has a reflecting surface shaped as a surface of revolution. 5. An X-ray beam device according to claim 4, characterized in that the reflecting surfaces of said first optical element and of said second optical element have the same radius of curvature. 6. An X-ray beam device according to claim 1, characterized in that said distance F1 is equal to a distance F2 between said second optical element and said focal spot. 7. An X-ray beam device according to claim 1, characterized in that it furthermore comprises a plurality of slits, which are positioned between said second optical element and said focal spot and/or in front of said second optical element. 8. An X-ray beam device according to claim 7, characterized in that said slits are designed such as to cause an asymmetric convergence of said beam, wherein the smallest convergence is at least two times the angular acceptance ΔθM of the monochromator, and the largest convergence is larger than 0.25°. 9. An X-ray beam device according to claim 7, characterized in that said slits are adjustable in such a way as to select one among two modes of operation, one mode where the X-ray beam device is adapted for high-resolution X-ray diffraction measurements and the other mode where the X-ray beam device is adapted for refiectometry measurements or low resolution x-ray diffraction measurements. 10. An X-ray beam device according to claim 1 characterized in that at least one of said first optical element and said second optical element has an opening angle in a range between 40° and 180°. 11. An X-ray beam device according to claim 1, characterized in that a distance between said X-ray source and said focal spot is in a range between 50 cm and 1.50 m. 12. An X-ray beam device according to claim 1, characterized in that at least one of said first optical element and said second optical element comprises a plurality of reflecting mirrors positioned in a VVolter arrangement. 13. An X-ray beam device according to claim 1, characterized in that the monochromator device is made removable in such a way that it can be moved out of the X-ray beam. 14. An X-ray beam device according to claim 1, characterized in that the optical assembly comprises a monolithic holding support wherein the reflective surface of each optical element is directly disposed on the holding support and the monochromator device is fixed directly on the holding support on a goniometer stage located on an intermediate zone between the upstream and downstream optical elements. 15. An X-ray beam device according to claim 1, characterized in that the optical assembly comprises a monolithic holding support wherein the reflective surface of each optical element is directly disposed on the holding support and the monochromator device is fixed on a goniometer stage on a cover of the optical assembly which is disposed on top of the optical assembly and attached to the holding support.
061047724	description	DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to the single FIGURE of the drawing, there is seen a pipeline 140 in a primary loop of a nuclear power plant with a pressurized water reactor, which leads from a stub 142 in a dome of a steam generator 144 to a non-illustrated pump. The stub 142 forms an opening which can be reached only through a relatively narrow manhole 146 of the steam generator 144. A self-propelled in-pipe manipulator 2 must be driven in through this opening. To that end, the in-pipe manipulator 2 is introduced into a tubular hollow-cylindrical hollow body 150 that is open on both ends. The in-pipe manipulator 2 is positioned together with the hollow body 150 above the stub 142 with the aid of a boom or crosspiece 152 which is part of a positioning device and protrudes through the manhole 146 into the steam generator 144. To that end, the hollow body 150 is provided with a shell-like support frame 154, which is pivotably supported about a pivot axis extending perpendicular to the boom 152, in a pivot bearing 156 on the boom 152. This pivoting motion is executed with a hydraulic cylinder 158, which is supported between the hollow body 150 and the boom 152. The boom 152 is mounted on a support stand 160, which is positionable outside the steam generator 144, and the boom is oriented in such a way that a pivot axis of its pivot bearing 156 is oriented perpendicular to a plane defined by center axes of the stub 142 and the manhole 146. Through the use of a linear displacement of the boom 152, as represented by an arrow 162 in the drawing, the pivot bearing 156 is positioned virtually at an angle bisector between these center axes, so that a simple pivoting motion, indicated by an arrow 164, enables an adequately exact positioning of the hollow body 150 oriented coaxially to the center axis of the stub 142. A deflection roller 166 which is also disposed on the support frame 154 is provided both for a cable required for supplying the in-pipe manipulator 2 and for a recovery rope, with which the in-pipe manipulator 2 can be retrieved from the pipeline 140 if it fails. The in-pipe manipulator 2 which is shown as an example in the drawing includes a pivot arm 200 disposed on its end surface, with two pivotable intermediate members 282 and 284 and a pivotable terminal member 320 that can be retracted nearly all the way into the interior of the chassis. The in-pipe manipulator 2 is also provided with a plurality, for example six or eight, rollers 206 which are supported extensibly on the base body of the in-pipe manipulator 2. With such an in-pipe manipulator 2, poorly accessible pipelines 140 can be reached even under spatially tight conditions, since the in-pipe manipulator has relatively small dimensions in an initial state. Moreover, since the rollers 206 can be extended relatively far, the demands for precision in positioning the hollow body 150 above the opening are less stringent, because the in-pipe manipulator can be driven into the pipeline 140 even if its center axis and the center axis of the opening are not exactly aligned with one another. In the drawing, the in-pipe manipulator 2 is shown in various working positions. It can be seen that the hollow body 150 performs not only the function of positioning the in-pipe manipulator 2 at a location suitable for introduction into the pipeline 140, but moreover also makes it possible to inspect weld seams positioned directly at the beginning of the pipeline, in this example weld seams 168, 169 on the stub 142 of the steam generator 144, with the aid of the in-pipe manipulator 2, without requiring that the in-pipe manipulator 2 be driven back into the pipeline 140 again in reverse orientation, after inspecting the weld seams located farther into the pipeline 140. Once the pivot arm 200 has been extended, the in-pipe manipulator 2 can already begin its inspection when the chassis is still completely inside the hollow body 150 or is still partly inside the hollow body 150, as explicitly shown in the drawing. This enables inspection of all of the weld seams of the pipeline 140 without requiring the in-pipe manipulator 2 to be turned around. In principle, however, other in-pipe manipulators, for instance of the kind known from the references cited at the outset, may also be introduced into a pipe with the aid of the apparatus of the invention. Depending on the structural layout of the in-pipe manipulator, it may be necessary in an individual case to use a hollow body which is adapted in its dimensions to the dimensions of the opening of the pipeline and which must be positioned at the opening in relatively exact alignment with the pipeline.
	description	This present application is a Continuation of International Application No. PCT/CN2019/094006 filed on Jun. 29, 2019, which claims priority of Chinese Application No. 201810701031.8, filed on Jun. 29, 2018, the contents of each of which are hereby incorporated by reference in its entirety. The present disclosure generally relates to X-ray imaging, and more specifically relates to methods and systems for calibrating an X-ray apparatus. An X-ray imaging system generally allows X-rays emitted by an X-ray source to irradiate an object, and detects X-rays that have transmitted through the object by an X-ray detector. The X-ray imaging systems can easily identify internal structure of the object based on an image generated by the X-ray detector, and diagnose a disease of the object. The X-ray imaging system generally has a collimator for shielding a portion of the X-rays and defining an irradiation region on the object. The collimator is disposed on the X-ray source. In some cases, the X-ray source and the collimator are not fixedly connected with the X-ray detector. The X-ray detector may need to to aligned with the collimator to ensure the X-ray detector detects the X-rays transmitted through the object. However, for an decubitus imaging system, it is required to move a bed board of a scanning table outside the scanning table, to align the collimator and X-ray detector installed on the scanning table. The alignment process is cumbersome and inefficient. Thus, it is desirable to provides convenient systems and methods for effectively calibrating the X-ray detector and the collimator. In one aspect of the present disclosure, a method for calibrating an X-ray apparatus is provided. The X-ray apparatus may include an X-ray detector and a collimator. The method may include moving the X-ray detector from a first position to a second position along a first axis of a coordinate system. The first position may be under a scanning table, and the second position may be outside the scanning table. The method may also include moving the collimator to align the collimator with the X-ray detector at the second position. The method may include determining one or more parameters. The one or more parameters may include at least one of a distance between the first position and the second position, or a first value of a first encoder of the collimator when the collimator is aligned with the X-ray detector at the second position. The first encoder may detect a movement of the collimator along the first axis of the coordinate system. The method may further include determining a second value of the first encoder when the collimator is aligned with the X-ray detector at the first position based on the distance between the first position and the second position and the first value of the first encoder. In some embodiments, the moving the collimator to align the collimator with the X-ray detector may include moving the collimator to align a center of a beam field of the collimator with a center of an imaging region of the X-ray detector at the second position. In some embodiments, the first position may have a first reference coordinate along the first axis and/or a second reference coordinate along a second axis. In some embodiments, the method may further include moving the X-ray detector back to the first positon; and moving the collimator based on the second value of the first encoder so that the collimator is aligned with the X-ray detector at the first position. In some embodiments, the collimator may further include a second encoder and a third encoder. The second encoder may detect a movement of the collimator along a second axis of the coordinate system, and the third encoder may detect a movement of the collimator along a third axis of the coordinate system. In some embodiments, the one or more parameters may further include a value of the second encoder and a value of the third encoder when the collimator is aligned with the X-ray detector at the second position. The moving the collimator so that the collimator is aligned with the X-ray detector at the first position may further include moving the collimator based on the second value of the first encoder, the value of the second encoder, and the value of the third encoder. In some embodiments, the X-ray detector may include a fourth encoder and a fifth encoder. The fourth encoder may detect a movement of the X-ray detector along a second axis of the coordinate system, and the fifth encoder may detect a movement of the X-ray detector along a third axis of the coordinate system. In some embodiments, the one or more parameters may further include a value of the fourth encoder and a value of the fifth encoder when the X-ray detector at the second position. The value of the fourth encoder may correspond to a second reference coordinate of the X-ray detector along the second axis, and the value of the fifth encoder may correspond to a third reference coordinate of the X-ray detector along the third axis. In some embodiments, the X-ray detector further includes a sixth encoder, wherein the sixth encoder detects a movement of the X-ray detector along the first axis of the coordinate system and detects a coordinate of the second position of the X-ray detector along the first axis. In some embodiments, the determining a second value of the first encoder may include determining the second value of the first encoder based on the first value of the first encoder, a coefficient of the first encoder, and the distance between the first position and the second position. In some embodiments, the collimator and the X-ray detector may be aligned periodically. In another aspect of the present disclosure, a system for calibrating an X-ray apparatus is provided. The X-ray apparatus may include an X-ray detector and a collimator. The system may include at least one storage device including a set of instructions; and at least one processor in communication with the at least one storage device. When executing the set of instructions, the at least one processor may be configured to cause the system to move the X-ray detector from a first position to a second position along a first axis of a coordinate system. The first position may be under a scanning table, and the second position may be outside the scanning table. The at least one processor may also be configured to move the collimator to align the collimator with the X-ray detector at the second position; and determine one or more parameters. The one or more parameters may include at least one of a distance between the first position and the second position, or a first value of a first encoder of the collimator when the collimator is aligned with the X-ray detector at the second position. The first encoder may detect a movement of the collimator along the first axis of the coordinate system. The at least one processor may further be configured to determine a second value of the first encoder when the collimator is aligned with the X-ray detector at the first position based on the distance between the first position and the second position and the first value of the first encoder. In yet another aspect of the present disclosure, a non-transitory computer-readable medium is provided. The non-transitory computer-readable medium may include at least one set of instructions. When executed by at least one processor of a computing device, the at least one set of instructions may cause the at least one processor to effectuate a method including moving the X-ray detector from a first position to a second position along a first axis of a coordinate system, wherein the first position is under a scanning table, and the second position is outside the scanning table; moving the collimator to align the collimator with the X-ray detector at the second position; determining one or more parameters, wherein the one or more parameters include at least one of a distance between the first position and the second position, or a first value of a first encoder of the collimator when the collimator is aligned with the X-ray detector at the second position, wherein the first encoder detects a movement of the collimator along the first axis of the coordinate system; and determining a second value of the first encoder when the collimator is aligned with the X-ray detector at the first position based on the distance between the first position and the second position and the first value of the first encoder. In yet another aspect of the present disclosure, an X-ray imaging system is provided. The X-ray imaging system may include an X-ray apparatus and a computing device. The computing device may include a processor, and a storage medium storing computer programs. When executing the computer programs, the processor may be configured to perform the method for calibrating an X-ray apparatus of any one of claims 1-9. Additional features will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of the examples. The features of the present disclosure may be realized and attained by practice or use of various aspects of the methodologies, instrumentalities and combinations set forth in the detailed examples discussed below. In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant disclosure. However, it should be apparent to those skilled in the art that the present disclosure may be practiced without such details. In other instances, well known methods, procedures, systems, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present disclosure. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present disclosure is not limited to the embodiments shown, but to be accorded the widest scope consistent with the claims. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise,” “comprises,” and/or “comprising,” “include,” “includes,” and/or “including,” when used in this specification, 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 will be understood that the term “system,” “unit,” “module,” and/or “block” used herein are one method to distinguish different components, elements, parts, section or assembly of different level in ascending order. However, the terms may be displaced by another expression if they achieve the same purpose. Generally, the word “module,” “unit,” or “block,” as used herein, unless otherwise defined, refers to logic embodied in hardware or firmware, or to a collection of software instructions. A module, a unit, or a block described herein may be implemented as software and/or hardware and may be stored in any type of non-transitory computer-readable medium or another storage device. In some embodiments, a software module/unit/block may be compiled and linked into an executable program. It will be appreciated that software modules can be callable from other modules/units/blocks or from themselves, and/or may be invoked in response to detected events or interrupts. Software modules/units/blocks configured for execution on computing devices (e.g., processor 210 as illustrated in FIG. 2) may be provided on a computer readable medium, such as a compact disc, a digital video disc, a flash drive, a magnetic disc, or any other tangible medium, or as a digital download (and can be originally stored in a compressed or installable format that needs installation, decompression, or decryption prior to execution). Such software code may be stored, partially or fully, on a storage device of the executing computing device, for execution by the computing device. Software instructions may be embedded in firmware, such as an EPROM. It will be further appreciated that hardware modules/units/blocks may be included of connected logic components, such as gates and flip-flops, and/or can be included of programmable units, such as programmable gate arrays or processors. The modules/units/blocks or computing device functionality described herein may be implemented as software modules/units/blocks, but may be represented in hardware or firmware. In general, the modules/units/blocks described herein refer to logical modules/units/blocks that may be combined with other modules/units/blocks or divided into sub-modules/sub-units/sub-blocks despite their physical organization or storage. It will be understood that when a unit, engine, module or block is referred to as being “on,” “connected to,” or “coupled to,” another unit, engine, module, or block, it may be directly on, connected or coupled to, or communicate with the other unit, engine, module, or block, or an intervening unit, engine, module, or block may be present, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. These and other features, and characteristics of the present disclosure, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, may become more apparent upon consideration of the following description with reference to the accompanying drawings, all of which form a part of this disclosure. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended to limit the scope of the present disclosure. It is understood that the drawings are not to scale. An aspect of the present disclosure relates to systems and methods for calibrating an X-ray apparatus. The X-ray apparatus may include an X-ray detector and a collimator. The systems and methods may be configured to calibrate and/or align the X-ray detector and the collimator. Specifically, the systems and methods may move the X-ray detector from a first position to a second position along a first axis of a coordinate system. The first position may be under a scanning table, and the second position may be outside the scanning table. The systems and methods may move the collimator to align the collimator with the X-ray detector at the second position. For example, the systems and methods may move the collimator to align a center of a beam field of the collimator with a center of an imaging region of the X-ray detector at the second position. When the collimator is aligned with the X-ray detector at the second position, the systems and methods may determine one or more parameters. The one or more parameters may include a distance between the first position and the second position, a first value of a first encoder of the collimator, or the like. The systems and methods may further determine a second value of the first encoder when the collimator is aligned with the X-ray detector at the first position based on the distance between the first position and the second position and the first value of the first encoder. FIG. 1 is a schematic diagram illustrating an exemplary X-ray imaging system according to some embodiments of the present disclosure. The X-ray imaging system 100 may include an X-ray apparatus 110, a network 120, one or more terminals 130, a processing device 140, and a storage device 150. The components of the X-ray imaging system 100 may be connected in various ways. Merely by way of example, the X-ray apparatus 110 may be connected to the processing device 140 through the network 120. As another example, the X-ray apparatus 110 may be connected to the processing device 140 directly as indicated by the bi-directional arrow in dotted lines linking the X-ray apparatus 110 and the processing device 140. As a further example, the storage device 150 may be connected to the processing device 140 directly or through the network 120. As still a further example, the terminal 130 may be connected to the processing device 140 directly (as indicated by the bi-directional arrow in dotted lines linking the terminal 130 and the processing device 140) or through the network 120. In some embodiments, the X-ray apparatus 100 may be a decubitus imaging apparatus. As shown in FIG. 1, the X-ray apparatus 110 may include an X-ray source 111, a collimator 112, an X-ray detector 113, and a scanning table 115. The X-ray source 111 may be configured to emit X-rays toward an object (e.g., the object 114). The object may be a biological object (e.g., a patient, an animal) or a non-biological object (e.g., a human-made object). In the present disclosure, “object” and “subject” are used interchangeably. The X-ray detector 113 may be disposed opposite to the X-ray source 111 for detecting X-rays transmitted through the object and generating X-ray images. In some embodiments, the X-ray detector 113 may include a plurality of detector units. The detector units may include a scintillation detector (e.g., a cesium iodide detector) or a gas detector. The detector units may be arranged in a single row or multiple rows. The collimator 112 may be disposed on an X-ray emitting side of the X-ray source 111. The collimator 112 may be configured to guide a path of the X-rays emitted from the X-ray source 111 and adjust an irradiation region irradiated by the X-rays. Merely by way of example, the collimator 112 may have four leaves (not shown in FIG. 1). These four leaves may be arranged to shield a portion of the X-rays emitted from the X-ray source 111 and restrict the X-rays to irradiate a rectangular area of arbitrary size (e.g., 1010, 1015, 2020, 3040, 4343). For illustration purposes, a coordinate system as shown in FIG. 1 is introduced. The coordinate system may include an X-axis, a Y-axis, and a Z-axis. The Z-axis may refer to a direction perpendicular to the scanning table (e.g., perpendicular to a horizontal plane). The X-axis may refer to a long axis of the scanning table. The Y-axis may refer to a short axis of the scanning table. The collimator 112 may be connected to the X-ray source, and thus, the collimator 112 may move to accompany the X-ray source 111. That is, the collimator 113 may be movable with the X-ray source 111 collectively. In some embodiments, the X-ray source 111 and the collimator 112 may be disposed on a support component (e.g., the support component 710 as illustrated in FIG. 7). In some embodiments, the X-ray detector 113 may be disposed under the scanning table 115 via a tray (e.g., the tray 620 as illustrated in FIG. 6). Since the X-ray source 111 (or the collimator 112) is not fixedly connected with the X-ray detector 113, the X-ray detector 113 and the X-ray source 111 (or the collimator 112) may need to be aligned with each other to ensure the X-ray detector 113 detects X-rays transmitted through the object. During an X-ray imaging process, the X-ray detector 113 may move along at least one of the X-axis, the Y-axis, or the Z-axis. For example, the X-ray detector 113 may move along the X-axis. The X-ray source 111 (or the collimator 112) may move along at least one of the X-axis, the Y-axis, or the Z-axis independently of the X-ray detector 113. However, to ensure the X-ray detector 113 is aligned with the X-ray source 111 (or the collimator 112), the X-ray source 111 (or the collimator 112) and the X-ray detector 113 may need to move simultaneously or synchronously. The network 120 may facilitate the exchange of information and/or data. In some embodiments, one or more components of the X-ray imaging system 100 (e.g., the X-ray apparatus 110, the terminal 130, the processing device 140, or the storage device 150) may send information and/or data to another component(s) in the X-ray imaging system 100 via the network 120. In some embodiments, the network 120 may be any type of wired or wireless network, or combination thereof. The network 120 may be and/or include a public network (e.g., the Internet), a private network (e.g., a local area network (LAN), a wide area network (WAN)), etc.), a wired network (e.g., an Ethernet network), a wireless network (e.g., an 802.11 network, a Wi-Fi network), a cellular network (e.g., a Long Term Evolution (LTE) network), a frame relay network, a virtual private network (“VPN”), a satellite network, a telephone network, routers, hubs, switches, server computers, and/or any combination thereof. Merely by way of example, the network 120 may include a cable network, a wireline network, an optical fiber network, a telecommunications network, an intranet, an Internet, a local area network (LAN), a wide area network (WAN), a wireless local area network (WLAN), a metropolitan area network (MAN), a public telephone switched network (PSTN), a Bluetooth™ network, a ZigBee™ network, a near field communication (NFC) network, or the like, or any combination thereof. In some embodiments, the network 120 may include one or more network access points. For example, the network 120 may include wired or wireless network access points such as base stations and/or internet exchange points through which one or more components of the radiation system 100 may be connected to the network 120 to exchange data and/or information. The terminal 130 include a mobile device 130-1, a tablet computer 130-2, a laptop computer 130-3, or the like, or any combination thereof. In some embodiments, the mobile device 130-1 may include a smart home device, a wearable device, a smart mobile device, a virtual reality device, an augmented reality device, or the like, or any combination thereof. In some embodiments, the smart home device may include a smart lighting device, a control device of an intelligent electrical apparatus, a smart monitoring device, a smart television, a smart video camera, an interphone, or the like, or any combination thereof. In some embodiments, the wearable device may include a bracelet, footgear, eyeglasses, a helmet, a watch, clothing, a backpack, an accessory, or the like, or any combination thereof. In some embodiments, the smart mobile device may include a smartphone, a personal digital assistant (PDA), a gaming device, a navigation device, a point of sale (POS) device, or the like, or any combination thereof. In some embodiments, the virtual reality device and/or the augmented reality device may include a virtual reality helmet, a virtual reality glass, a virtual reality patch, an augmented reality helmet, an augmented reality glass, an augmented reality patch, or the like, or any combination thereof. For example, the virtual reality device and/or the augmented reality device may include a Google Glass, an Oculus Rift, a HoloLens, a Gear VR, etc. In some embodiments, the terminal 130 may remotely operate the X-ray apparatus 110. In some embodiments, the terminal 130 may operate the X-ray apparatus 110 via a wireless connection. In some embodiments, the terminal 130 may receive information and/or instructions inputted by a user, and send the received information and/or instructions to the X-ray apparatus 110 or to the processing device 140 via the network 120. In some embodiments, the terminal 130 may receive data and/or information from the processing device 140. In some embodiments, the terminal 130 may be part of the processing device 140. In some embodiments, the terminal 130 may be omitted. In some embodiments, the processing device 140 may process data obtained from the X-ray apparatus 110, the terminal 130, or the storage device 150. For example, the processing device 140 may move a collimator to align the collimator with an X-ray detector at the second position. The processing device 140 may be a central processing unit (CPU), a digital signal processor (DSP), a system on a chip (SoC), a microcontroller unit (MCU), or the like, or any combination thereof. In some embodiments, the processing device 140 may be a single server or a server group. The server group may be centralized or distributed. In some embodiments, the processing device 140 may be local or remote. For example, the processing device 140 may access information and/or data stored in the X-ray apparatus 110, the terminal 130, and/or the storage device 150 via the network 120. As another example, the processing device 140 may be directly connected to the X-ray apparatus 110 (as illustrated by the dashed bidirectional arrow linking the X-ray apparatus 110 and the processing device 140 in FIG. 1), the terminal 130 (as illustrated by the dashed bidirectional arrow linking the terminal 130 and the processing device 140 in FIG. 1), and/or the storage device 150, to access information and/or data. In some embodiments, the processing device 140 may be implemented on a cloud platform. Merely by way of example, the cloud platform may include a private cloud, a public cloud, a hybrid cloud, a community cloud, a distributed cloud, an inter-cloud, a multi-cloud, or the like, or any combination thereof. In some embodiments, the processing device 140 may be implemented on a computing device 200 having one or more components illustrated in FIG. 2 in the present disclosure. The storage device 150 may store data and/or instructions. In some embodiments, the storage device 150 may store data obtained from the terminal 130 and/or the processing device 140. In some embodiments, the storage device 150 may store data and/or instructions that the processing device 140 may execute or use to perform exemplary methods described in the present disclosure. In some embodiments, the storage device 150 may include a mass storage, removable storage, a volatile read-and-write memory, a read-only memory (ROM), or the like, or any combination thereof. Exemplary mass storage may include a magnetic disk, an optical disk, a solid-state drive, etc. Exemplary removable storage may include a flash drive, a floppy disk, an optical disk, a memory card, a zip disk, a magnetic tape, etc. Exemplary volatile read-and-write memory may include a random-access memory (RAM). Exemplary RAM may include a dynamic RAM (DRAM), a double date rate synchronous dynamic RAM (DDR SDRAM), a static RAM (SRAM), a thyristor RAM (T-RAM), and a zero-capacitor RAM (Z-RAM), etc. Exemplary ROM may include a mask ROM (MROM), a programmable ROM (PROM), an erasable programmable ROM (PEROM), an electrically erasable programmable ROM (EEPROM), a compact disk ROM (CD-ROM), and a digital versatile disk ROM, etc. In some embodiments, the storage device 150 may be implemented on a cloud platform. Merely by way of example, the cloud platform may include a private cloud, a public cloud, a hybrid cloud, a community cloud, a distributed cloud, an inter-cloud, a multi-cloud, or the like, or any combination thereof. In some embodiments, the storage device 150 may be connected to the network 120 to communicate with one or more components of the radiation system 100 (e.g., the terminal 130, the processing device 140). One or more components of the radiation system 100 may access the data or instructions stored in the storage device 150 via the network 120. In some embodiments, the storage device 150 may be directly connected to or communicate with one or more components of the radiation system 100 (e.g., the terminal 130, the processing device 140). In some embodiments, the storage device 150 may be part of the processing device 140. FIG. 2 is a schematic diagram illustrating exemplary hardware and/or software components of a computing device 200 on which the processing device 140 may be implemented according to some embodiments of the present disclosure. As illustrated in FIG. 2, the computing device 200 may include a processor 210, a storage 220, an input/output (I/O) 230, and a communication port 240. The processor 210 may execute computer instructions (program code) and, when executing the instructions, cause the processing device 140 to perform functions of the processing device 140 in accordance with techniques described herein. The computer instructions may include, for example, routines, programs, objects, components, signals, data structures, procedures, modules, and functions, which perform particular functions described herein. In some embodiments, the processor 210 may process data and/or images obtained from the X-ray apparatus 110, the terminal 130, the storage device 150, and/or any other component of the radiation system 100. For example, the processor 210 may move a collimator to align the collimator with the X-ray detector at the second position. In some embodiments, the processor 210 may include one or more hardware processors, such as a microcontroller, a microprocessor, a reduced instruction set computer (RISC), an application specific integrated circuits (ASICs), an application-specific instruction-set processor (ASIP), a central processing unit (CPU), a graphics processing unit (GPU), a physics processing unit (PP U), a microcontroller unit, a digital signal processor (DSP), a field programmable gate array (FPGA), an advanced RISC machine (ARM), a programmable logic device (PLD), any circuit or processor capable of executing one or more functions, or the like, or any combinations thereof. Merely for illustration, only one processor is described in the computing device 200. However, it should be noted that the computing device 200 in the present disclosure may also include multiple processors. Thus operations and/or method steps that are performed by one processor as described in the present disclosure may also be jointly or separately performed by the multiple processors. For example, if in the present disclosure the processor of the computing device 200 executes both process A and process B, it should be understood that process A and process B may also be performed by two or more different processors jointly or separately in the computing device 200 (e.g., a first processor executes process A and a second processor executes process B, or the first and second processors jointly execute processes A and B). The storage 220 may store data/information obtained from the X-ray apparatus 110, the terminal 130, the storage device 150, or any other component of the radiation system 100. In some embodiments, the storage 220 may include a mass storage device, removable storage device, a volatile read-and-write memory, a read-only memory (ROM), or the like, or any combination thereof. For example, the mass storage may include a magnetic disk, an optical disk, a solid-state drive, etc. The removable storage may include a flash drive, a floppy disk, an optical disk, a memory card, a zip disk, a magnetic tape, etc. The volatile read-and-write memory may include a random access memory (RAM). The RAM may include a dynamic RAM (DRAM), a double date rate synchronous dynamic RAM (DDR SDRAM), a static RAM (SRAM), a thyristor RAM (T-RAM), and a zero-capacitor RAM (Z-RAM), etc. The ROM may include a mask ROM (MROM), a programmable ROM (PROM), an erasable programmable ROM (PEROM), an electrically erasable programmable ROM (EEPROM), a compact disk ROM (CD-ROM), and a digital versatile disk ROM, etc. In some embodiments, the storage 220 may store one or more programs and/or instructions to perform exemplary methods described in the present disclosure. The I/O 230 may input or output signals, data, and/or information. In some embodiments, the I/O 230 may enable a user interaction with the processing device 140. In some embodiments, the I/O 230 may include an input device and an output device. Exemplary input devices may include a keyboard, a mouse, a touch screen, a microphone, or the like, or a combination thereof. Exemplary output devices may include a display device, a loudspeaker, a printer, a projector, or the like, or a combination thereof. Exemplary display devices may include a liquid crystal display (LCD), a light-emitting diode (LED)-based display, a flat panel display, a curved screen, a television device, a cathode ray tube (CRT), or the like, or a combination thereof. The communication port 240 may be connected to a network (e.g., the network 120) to facilitate data communications. The communication port 240 may establish connections between the processing device 140 and the X-ray apparatus 110, the terminal 130, or the storage device 150. The connection may be a wired connection, a wireless connection, or a combination of both that enables data transmission and reception. The wired connection may include an electrical cable, an optical cable, a telephone wire, or the like, or any combination thereof. The wireless connection may include Bluetooth, Wi-Fi, WiMAX, WLAN, ZigBee, mobile network (e.g., 3G, 4G, 5G, etc.), or the like, or a combination thereof. In some embodiments, the communication port 240 may be a standardized communication port, such as RS232, RS485, etc. In some embodiments, the communication port 240 may be a specially designed communication port. For example, the communication port 240 may be designed in accordance with the digital imaging and communications in medicine (DICOM) protocol. FIG. 3 is a schematic diagram illustrating exemplary hardware and/or software components of a mobile device 300 according to some embodiments of the present disclosure. As illustrated in FIG. 3, the mobile device 300 may include a communication platform 310, a display 320, a graphics processing unit (GPU) 330, a central processing unit (CPU) 340, an I/O 350, a memory 360, and a storage 390. In some embodiments, any other suitable component, including but not limited to a system bus or a controller (not shown), may also be included in the mobile device 300. In some embodiments, a mobile operating system 370 (e.g., iOS, Android, Windows Phone, etc.) and one or more applications 380 may be loaded into the memory 360 from the storage 390 in order to be executed by the CPU 340. The applications 380 may include a browser or any other suitable mobile apps for receiving and rendering information relating to image processing or other information from the processing device 140. User interactions with the information stream may be achieved via the I/O 350 and provided to the processing device 140 and/or other components of the X-ray imaging system 100 via the network 120. To implement various modules, units, and their functionalities described in the present disclosure, computer hardware platforms may be used as the hardware platform(s) for one or more of the elements described herein. The hardware elements, operating systems and programming languages of such computers are conventional in nature, and it is presumed that those skilled in the art are adequately familiar therewith to adapt those technologies to align a collimator with an X-ray detector as described herein. A computer with user interface elements may be used to implement a personal computer (PC) or another type of work station or terminal device, although a computer may also act as a server if appropriately programmed. It is believed that those skilled in the art are familiar with the structure, programming and general operation of such computer equipment and as a result, the drawings should be self-explanatory. FIG. 4 is a block diagram illustrating an exemplary processing device 140 according to some embodiments of the present disclosure. The processing device 140 may be implemented on the computing device 200 (e.g., the processor 210) as illustrated in FIG. 2 or the CPU 340 as illustrated in FIG. 3. The processing device 140 may include a control module 410, a parameter determination module 420, and a value determination module 430. The control module 410 may be configured to control the movement of one or more components of the X-ray imaging system 100. In some embodiments, the control module 140 may move the X-ray detector from a first position to a second position along a first axis of a coordinate system (e.g., the Y-axis of the coordinate system as illustrated in FIG. 1). The first position may be under a scanning table, and the second position may be outside the scanning table. The control module 410 may also move a collimator to align the collimator with the X-ray detector at the second position. Specifically, the control module 410 may move the collimator to align a center of a beam field of the collimator with a center of an imaging region of the X-ray detector at the second position. When the collimator is aligned with the X-ray detector, the control module 410 may move the X-ray detector back to the first position. The control module 410 may also move the collimator so that the collimator is aligned with the X-ray detector at the first position. In some embodiments, the X-ray detector may be moved from the first position to the second position manually. For example, the X-ray detector may be moved from the first position to the second position by manually pulling the tray out of the scanning table by a user. Correspondingly, the X-ray detector may be moved back to the first position manually. For example, the X-ray detector may be moved from the second position back to the first position by manually pushing the tray in the scanning table by the user. The parameter determination module 420 may be configured to determine one or more parameters. The one or more parameters may include a distance between the first position and the second position, a first value of a first encoder of the collimator when the collimator is aligned with the X-ray detector at the second position, or the like. In some embodiments, the one or more parameters may further include a value of a second encoder, a value of a third encoder when the collimator is aligned with the X-ray detector at the second position. The first encoder may be used to detect a movement of the collimator along the first axis. The second encoder may be used to detect a movement of the collimator along a second axis of the coordinate system (e.g., the X-axis of the coordinate system as illustrated in FIG. 1). The third encoder may be used to detect a movement of the collimator along a third axis of the coordinate system (e.g., the Z-axis of the coordinate system as illustrated in FIG. 1). The value determination module 430 may be configured to determine a second value of the first encoder when the collimator is aligned with the X-ray detector at the first position based on the one or more parameters. Merely by way of example, the value determination module 430 may determine the second value of the first encoder based on the first value of the first encoder, a coefficient of the first encoder, and the distance between the first position and the second position. The modules in the processing device 140 may be connected to or communicate with each other via a wired connection or a wireless connection. The wired connection may include a metal cable, an optical cable, a hybrid cable, or the like, or any combination thereof. The wireless connection may include a Local Area Network (LAN), a Wide Area Network (WAN), a Bluetooth, a ZigBee, a Near Field Communication (NFC), or the like, or any combination thereof. It should be noted that the above description is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. In some embodiments, any one of the modules may be divided into two or more units. For example, the control 410 may be divided into a first control unit and a second control unit. The first control unit may be configured to control the movement of the X-ray detector, and the second control unit may be configured to control the movement of the collimator. In some embodiments, the processing device 140 may include one or more additional modules. For example, the processing device 140 may include a storage module (not shown). The storage module may be configured to store data generated during any process performed by any component of the processing device 140. FIG. 5 is a flowchart illustrating an exemplary process 500 for calibrating an X-ray apparatus according to some embodiments of the present disclosure. In some embodiments, the X-ray apparatus may be a decubitus imaging apparatus. In some embodiments, the X-ray apparatus may include an X-ray detector and a collimator. The process 500 may be used to calibrate and/or align the X-ray detector and the collimator. The process 500 may be implemented in the X-ray imaging system 100 illustrated in FIG. 1. For example, the process 500 may be stored in the storage device 150 and/or the storage 220 in the form of instructions (e.g., an application), and invoked and/or executed by the processing device 140 (e.g., the processor 210 illustrated in FIG. 2, the CPU 340 as illustrated in FIG. 3, or one or more modules in the processing device 140 illustrated in FIG. 10). The operations of the illustrated process presented below are intended to be illustrative. In some embodiments, the process 500 may be accomplished with one or more additional operations not described, and/or without one or more of the operations discussed. Additionally, the order in which the operations of the process 500 as illustrated in FIG. 5 and described below is not intended to be limiting. In 510, the processing device 140 (e.g., the control module 410) may move the X-ray detector (e.g., the X-ray detector 113) from a first position to a second position along a first axis of a coordinate system (e.g., the Y-axis of the coordinate system as illustrated in FIG. 1). In some embodiments, the first position may be under the scanning table (e.g., the scanning table 115), and the second position may be outside the scanning table. In some embodiments, the first position and/or the second position may indicate position(s) at which a center of an imaging region of the X-ray detector locates. In some embodiments, the first position may also be referred to as a reference position. In some embodiments, the reference position may be a position on the scanning table. Preferably, the reference position may be a center of a bed board of the scanning table. The reference position may be generally regarded as a reference point to determine the first position of the X-ray detector. When the X-ray detector is located at the second position, the center of the imaging region of the X-ray detector may not be shielded by the scanning table. The second position may be determined when the scanning table is fabricated. For example, the X-ray detector is disposed on a tray under the scanning table. The tray may move out of the scanning table along the first axis. The second position may be determined based on a distance that the tray can move along the first axis. Alternatively, the second position may be a position having a first predetermined distance from the first position along the first axis. The first predetermined distance may be a default value or an empirical value related to the X-ray imaging system 100. The first predetermined distance may be any value as long as the center of the imaging region of the X-ray detector is not shielded by the scanning table at the second position. In some embodiments, the second position may also be referred to as a correction position. In some embodiments, the X-ray detector may be moved from the first position to the second position by the processing device 140 (e.g., the control module 410). Alternatively, the X-ray detector may be moved from the first position to the second position manually. For example, the X-ray detector may be moved by pulling the tray out of the scanning table by a user. In some embodiments, the first position may be regarded as a reference position of the X-ray apparatus that is used to align the X-ray detector and the collimator. The reference position may be selected as a center of the bed board of the scanning table. Generally, the reference position may be designated as a coordinate origin of the coordinate system (e.g., the coordinate system as illustrated in FIG. 1). The reference position (or the coordinate origin) may be used to as a point of reference for space changes of the positions of the X-ray detector and/or the collimator in subsequent use (e.g., performing an X-ray scanning). In prior art, when the X-ray detector and the collimator are calibrated, the X-ray detector may need to move to the coordinate origin (i.e., the reference position). The collimator and the X-ray detector are calibrated at the coordinate origin to obtain one or more parameters related to the X-ray detector and/or the collimator. In the present disclosure, it is not necessary to move the X-ray detector to the reference position, and the X-ray detector may be moved out of the center of the scanning table for calibration. After the one or more parameters at the correction position (i.e., the second position) are determined, the parameters at the reference position (i.e., the first position) may be determined accordingly. Then any component of the X-ray apparatus (e.g., the X-ray detector, the collimator) may be moved to any specified position during the X-ray imaging. In some embodiments, before operation 501, the processing device 140 may move the X-ray detector to the first position. The X-ray detector may be disposed under the scanning table. In some embodiments, the X-ray detector may be connected with the scanning table directly or indirectly. For example, the X-ray detector may be connected with the scanning table via a tray (e.g., the tray 620 as illustrated in FIG. 6). In some embodiments, the X-ray detector may be movable with respect to the scanning table along at least one of the first axis, a second axis (e.g., the X-axis of the coordinate system as illustrated in FIG. 1), or a third axis (e.g., the Z-axis of the coordinate system as illustrated in FIG. 1). In some embodiments, the X-ray detector may be fixed to the scanning table along the third axis. The first position may have a first reference coordinate along the first axis and/or a second reference coordinate along the second axis. Before operation 501, the processing device 140 may move the X-ray detector to the first position. Specifically, the processing device 140 may move the X-ray detector along the first axis to the first reference coordinate, and then move the X-ray detector along the second axis to the second reference coordinate. Alternatively, the processing device 140 may move the X-ray detector along the second axis to the second reference coordinate, and then move the X-ray detector along the first axis to the first reference coordinate. Alternatively, the processing device 140 may move the X-ray detector along the first axis and the second axis simultaneously to the first position (e.g., the first reference coordinate and the second reference coordinate). It should be noted that, for the purposes of convenience, the first reference coordinate along the first axis and the the second reference coordinate along the second axis may coincide at a horizontal plane that has a predetermined height from the ground, for example, at a center of the bed board of the scanning table. Since the X-ray detector is fixed with respect to the scanning table along the third axis, the X-ray detector may move along the third axis as the scanning table moves up and down. That is, the X-ray detector may move to a predetermined height (also referred to as a third reference coordinate) relative to the ground by controlling the movement of the scanning table. In some embodiments, the predetermined height may be a default value or an empirical value related to the X-ray imaging system 100. The predetermined height may be set according to a default setting of the X-ray imaging system 100, or preset or adjusted by a user. For example, the predetermined height may be a fixed height such as 50 cm, 60 cm, 70 cm, which is convenient for a patient to lie on the scanning table. It should be noted that the X-ray detector may be movable with respect to the scanning table along the third axis, and the X-ray detector may move to the predetermined height by controlling, e.g., by the processing device 140, the movement of the X-ray detector. In 520, the processing device 140 (e.g., the control module 420) may move the collimator (e.g., the collimator 112) to align the collimator with the X-ray detector at the second position. In some embodiments, the processing device 140 may move the collimator to align a center of a beam field of the collimator with a center of an imaging region of the X-ray detector at the second position. When the collimator is aligned with the X-ray detector, the position of the collimator may be referred to as a correction position of the collimator, which may be recorded by one or more encoders. In some embodiments, the collimator may include a first encoder, a second encoder, and a third encoder. The first encoder may be used to detect a movement of the collimator along the first axis. The second encoder may be used to detect a movement of the collimator along the second axis. The third encoder may be used to detect a movement of the collimator along the third axis. Correspondingly, the X-ray detector may include a fourth encoder and a fifth encoder. The fourth encoder may be used to detect a movement of the X-ray detector along the second axis. The fifth encoder may be used to detect a movement of the X-ray detector along the third axis. In some embodiments, the encoders may be absolute encoders configured to determine absolute positions of the X-ray detector or the collimator. It should be noted that the encoders may be relative encoders configured to determine relative positions (e.g., changes of position) of the X-ray detector or the collimator. In some embodiments, the positions of the X-ray detector or the collimator may be detected by other position sensor, such as a Hall sensor. In some embodiments, the encoders may be the same. Alternatively, at least two of the encoders may be different. For example, the first encoder may be an absolute encoder, while the third encoder may be a relative encoder. In some embodiments, when performing X-ray imaging, the collimator and the X-ray detector may have a second predetermined distance along the third axis (i.e., the vertical direction). The second predetermined distance may be a default value or an empirical value related to the X-ray imaging system 100. The second predetermined distance may be set according to a default setting of the X-ray imaging system 100, or preset or adjusted by a user. In some embodiments, the second predetermined distance may be a distance value, such as 50 cm, 80 cm, 100 cm, 120 cm, 150 cm, or the like. Preferably, the second predetermined distance may be 100 cm. Alternatively, the second predetermined distance may be a distance range, such as 50-70 cm, 80-120 cm, 100-150 cm, or the like. Preferably, the second predetermined distance may be 80-120 cm. As described in connection with operation 510, the X-ray detector may be located at the predetermined height (e.g., 60 cm relative to the ground). Thus, before the alignment, the collimator may move to a certain coordinate (or a certain height) along the third axis based on the second predetermined distance and the predetermined height. For example, the collimator may move along the third axis to the height of 160 cm relative to the ground. The beam field of the collimator may have a first crosshair, and the imaging region of the X-ray detector may include a second crosshair. When performing the alignment of the collimator and the X-ray detector, a light source (e.g., a laser light) within the collimator may emit a beam of light. The beam of light may pass through the first crosshair of the beam field to reach the X-ray detector. The first crosshair may have a projection on the X-ray detector. The processing device 140 may move the collimator to align the projection of the first crosshair on the X-ray detector and the second crosshair of the X-ray detector. When the projection of the first crosshair on the X-ray detector is aligned with the second crosshair of the X-ray detector, the collimator and the X-ray detector are aligned. In 530, the processing device 140 (e.g., the parameter determination module 420) may determine one or more parameters. The one or more parameters may include a distance between the first position and the second position, a first value of the first encoder of the collimator when the collimator is aligned with the X-ray detector at the second position. In some embodiments, the one or more parameters may further include a value of the second encoder and a value of the third encoder when the collimator is aligned with the X-ray detector at the second position. When the collimator and the X-ray detector are aligned, the first value of the first encoder, the value of the second encoder, and/or the value of the third encoder may be directly read. The first value of the first encoder at the second position may correspond to a coordinate of the collimator along the first axis at the second position. The value of the second encoder at the second position may correspond to a coordinate of the collimator along the second axis at the second position. The value of the third encoder at the second position may correspond to a coordinate of the collimator along the second axis at the second position. In some embodiments, the distance between the first position and the second position may be known. For example, the distance between the first position and the second position may be a distance that the tray (e.g., the tray 620) can move along the first axis, which is determined when the scanning table is fabricated. Alternatively, the X-ray detector may include a sixth encoder, which is used to detect the movement of the X-ray detector along the first axis. For example, the sixth encoder may detect the first reference coordinate of the first position of the X-ray detector along the first axis, and detect a first correction coordinate of the second position of the X-ray detector along the first axis. The value of the sixth encoder at the first position may correspond to the first reference coordinate, and the value of the sixth encoder at the second position may correspond to the first correction coordinate. Then, the distance between the first position and the second position may be determined based on first reference coordinate and the first correction coordinate. The changes of the coordinates of the X-ray detector along the first axis may be represented by the changes of the values of the sixth encoder. Merely by way of example, the distance may be determined according to Equation (1) as below: y = E 6 ′ - E 6 k 6 , ( 1 ) wherein y refers to the distance between the first position and the second position; E′6 refers to the value of the sixth encoder at the second position; E6 refers to the value of the sixth encoder at the first position; k6 refers to a coefficient of the sixth encoder. The one or more parameters may also include a value of the fourth encoder and a value of the fifth encoder when the X-ray detector at the second position. When the processing device 140 moves the X-ray detector from the first position to the second position or from the second position to the first position, the coordinates of the X-ray detector along the second axis and the third axis may be unchanged. That is, the value of the fourth encoder and/or the value of the fifth encoder may be unchanged. The value of the fourth encoder and/or the value of the fifth encoder may be directly read. The value of the fourth encoder may correspond to the second reference coordinate of the X-ray detector along the second axis. Merely by way of example, the first position may be a center of the scanning table, the value of the fourth encoder may be denoted as 0. It should be noted that the fourth encoder may have other values, e.g., a positive value, a negative value. The value of the fifth encoder may correspond to the third reference coordinate of the X-ray detector along the third axis. It should be noted that the value of the encoder (e.g., the fourth encoder, the fifth encoder) may be different from the corresponding coordinate of the X-ray detector. For example, when the height of the X-ray detector is 60 cm, the coordinate along the third axis may be denoted as 600, while the value of the fifth encoder may be denoted as 300. In some embodiments, the X-ray detector may move along the second axis (e.g., the X-axis). Therefore, it is necessary to calibrate the X-ray detector along the second axis (e.g., the X-axis) of the X-ray detector. In some embodiments, the scanning table may have a marker line along a longitudinal direction of the scanning table (e.g., the X-axis). In some embodiments, the marker line may be a center line along the longitudinal direction of the scanning table. The first position and the second position of the X-ray detector may be configured to align with the marker line. Thus, when the X-ray detector at the second position, the value of the fourth encoder of the X-ray detector may be determined as a reference value. For example, the reference value may correspond to the value of the fourth encoder when the coordinate of the second axis (e.g., the X-axis) is 0. It should be noted that the marker line may not be the center line along the longitudinal direction of the scanning table. In 540, the processing device 140 (e.g., the value determination module 430) may determine a second value of the first encoder when the collimator is aligned with the X-ray detector at the first position based on the one or more parameters. In some embodiments, the processing device 140 may determine the second value of the first encoder based on the first value of the first encoder, a coefficient of the first encoder, and the distance between the first position and the second position. In some embodiments, the values of the first encoder and a movement distance of the collimator along the first axis may satisfy Equation (2) as below:E1=E′1+K×y, (2)wherein E1 refers to the value of the first encoder after the movement; E′1 refers to the value of the first encoder before the movement; K refers to the coefficient of the first encoder; and y refers to the movement distance of the collimator along the first axis. Thus, the movement distance of the collimator along the first axis and the value difference may satisfy Equation (3) as below:ΔE=K×y, (3)wherein ΔE refers to the value difference of the first encoder after the movement and beform the movement. In some embodiments, the processing device 140 may determine the second value of the first encoder according to Equation (4) as below:Ey1=E′y1+K×S, (4)wherein Ey1 refers to the second value of the first encoder at the first position; E′y1 refers to the first value of the first encoder at the second position; and S refers to the distance between the first position and the second position at which the X-ray detector moves along the Y-axis. In 550, the processing device 140 (e.g., the control module 410) may move the X-ray detector back to the first position. When the processing device 140 moves the X-ray detector back to the first position, the coordinates of the X-ray detector along the second axis and the third axis may be unchanged. That is, the value of the fourth encoder and/or the value of the fifth encoder may be unchanged. The processing device 140 may also move the collimator based on the second value of the first encoder so that the collimator is aligned with the X-ray detector at the first position. In some embodiments, the processing device 140 may move the collimator based on the second value of the first encoder, the value of the second encoder, and the value of the third encoder. The coordinates of the collimator along the second axis and the third axis may be unchanged, and thus, the value of the second encoder and/or the value of the third encoder may be unchanged. That is, the processing device 140 may move the collimator along the Y-axis. The changes of the coordinates of the collimator along the first axis may be represented by the changes of the values of the sixth encoder. The processing device 140 may move the collimator based on the second value of the first encoder. At the first position, the coordinates of the collimator along the first axis and the second axis may be the same as the coordinates of the X-ray detector along the first axis and the second axis. The coordinate of the collimator along the third axis may be different from the coordinate of the X-ray detector along the third axis. In some embodiments, the height of the collimator may be 160 cm from the ground, and the height of the X-ray detector may be 60 cm from the ground. In some embodiments, when the collimator moves on the plane 160 cm above the ground, i.e., 100 cm above the X-ray detector, the value of the second and third encoders, associated with the X-axis and the Z-axis, of the collimator are designated as the value of these encoders for the collimator aligned with the X-ray detector at the first position. For example, the value of the second encoder may correspond to the coordinate value 0 of the second axis. The value of the third encoder may correspond to the coordinate value 160 of the third axis. The value of the first encoder, associated with the Y-axis, of the collimator when the collimator is aligned with the X-ray detector at the first position may be determined according to Equation (4), which is not repeated herein. When the collimator is aligned with the X-ray detector at the first position, the X-ray apparatus can be used to perform X-ray imaging. Before performing the X-ray imaging, an imaging protocol may be generated by a doctor. The imaging protocol may include an acquisition protocol and/or a reconstruction protocol. The acquisition protocol may include information relating to a voltage of a tube of an X-ray source (e.g., the X-ray source 111), a current of the tube of the X-ray source, the type of a focal spot of the X-ray source, a size of the focal spot of the X-ray source, a shot number of the X-ray source, a collimation width of the collimator (e.g., the collimator 112), a view number of the X-ray detector (e.g., the X-ray detector 113), one or more body parts to be scanned, a movement direction of the scanning table (e.g., the scanning table 115), position information of the object (e.g., a supine position, a prone position, a decubitus right position, a decubitus left position, etc.), a scanning mode, or the like, or any combination thereof. The reconstruction protocol may include information relating to a reconstruction center, a reconstruction field of view, an intensity viewing window level, an intensity viewing window width, an image thickness, an image increment, an image resolution, a noise level of the image, or the like, or any combination thereof. One or more parameters may be generated based on the imaging protocol. The one or more parameters may include coordinates of the X-ray detector and/or the collimator along the first axis, the second axis, and the third axis at a target position. The coordinates of the X-ray detector at the target position may be represented by the values of the encoders (e.g., the fourth encoder, the fifth encoder, the sixth encoder). Since the encoders are absolute encoders, the processing device 140 may determine the values of the fourth encoder, the fifth encoder, and the sixth encoder at the target position based on the coordinates of the X-ray detector. Similarly, the processing device 140 may determine the values of the first encoder, the second encoder, and third encoder at the target position based on the coordinates of the collimator. In some embodiments, the beam field of the collimator may be relatively large (e.g., 4343), and X-ray detector may have enough imaging region along the Y-axis, which can cover the transverse of the object (e.g., the patient). The X-ray detector and/or the collimator may not need to move along the first axis (e.g., the Y-axis) during the X-ray imaging. Thus, the X-ray detector may not need to have the sixth encoder to detect the movement of the X-ray detector along the first axis. However, it should be noted that the X-ray detector can move along the first axis (i.g., the Y-axis) during the X-ray imaging. The sixth encoder of the X-ray detector may also need to be determined according to Equation (4). For example, the value of the sixth encoder at the first position may be determined based on the value of the sixth encoder at the second position and the distance between the first position and the second position. In some embodiments, the value of the sixth encoder at the first position may correspond to the coordinate value 0 of the Y-axis. In some embodiments of the present disclosure, when calibrating the X-ray detector and the collimator, the processing device 140 may move the X-ray detector from the first position to the second position (a position outside the scanning table), and align the X-ray detector and the collimator at the second position without removing the bed board of the scanning table. Compared with the prior art which needs to remove the bed board of the scanning table, the calibration process may be simpler and have higher calibration efficiency. It should be noted that the above description of the process 500 is provided for the purposes of illustration, and is not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. In some embodiments, the collimator and the X-ray detector may be aligned periodically. For example, the processing device 140 may calibrate the collimator and the X-ray detector at fixed periods. The fixed periods may be a default value or an empirical value related to the X-ray imaging system 100. The fixed periods may be a week, a month, three month, half a year, a year, two years, or the like. In some embodiments, the processing device 140 may determine whether the collimator and the X-ray detector are aligned based on images generated by the X-ray imaging system 100. For example, if the images generated by the X-ray imaging system 100 have poor quality (e.g., artifacts), the processing device 140 may determine that the collimator and the X-ray detector are unaligned. Then, the processing device 140 may perform one or more operations of the process 500 to calibrate the collimator and X-ray detector. FIG. 6 is a schematic diagram illustrating a portion of an exemplary X-ray apparatus 600 according to some embodiments of the present disclosure. The X-ray apparatus 600 may be a decubitus imaging apparatus. The X-ray apparatus 600 may include a scanning table 610, a tray 620, and an X-ray detector 630. As shown in FIG. 6, the X-ray detector 630 is disposed on the tray 620, and the tray 620 is under the scanning table 610 and is connected to the scanning table 610. In some embodiments, the tray 620 may be connected to the scanning table 610 via a mechanical structure along a first axis (a short axis of the scanning table 610, i.e., the Y-axis of a coordinate system as shown in FIG. 6). The tray 620 may be slidably connected to the scanning table 610 along a second axis (a long axis of the scanning table 610, i.e., the X-axis of the coordinate system as shown in FIG. 6). During a calibration process, the state of the mechanical structure may be unlocked, and the connection between the tray 620 and the scanning table 610 may be loose along the first axis. Then the tray 620 may be pulled out of the scanning table 610 so that a center of an imaging region of the X-ray detector 630 may not be shielded by the scanning table 610. In some embodiments, the calibration process may be performed according to process 500 as described in FIG. 5, and the descriptions thereof are not repeated herein. During an X-ray imaging process, the state of the mechanical structure may be locked, and the tray 620 may be fixed to the scanning table 610 along the first axis. That is, the X-ray detector 630 may not move along the first axis during the X-ray imaging process. The X-ray detector 630 may move along the second axis (i.e., the X-axis) and/or the third axis (i.e., the Z-axis) during the X-ray imaging process. The coordinate of the X-ray detector 630 along the second axis may be represented by the value of a fourth encoder. The coordinate of the X-ray detector 630 along the third axis may be represented by the value of a fifth encoder. It should be noted that, in some embodiments, the tray 620 may be slidably connected to the scanning table 610 along the first axis. The X-ray detector 630 may be movable along the first axis (i.e., the Y-axis) during the X-ray imaging process. The coordinate of the X-ray detector 630 along the first axis may be represented by the value of a sixth encoder. The three encoders may be absolute encoders configured to detect the absolute coordinates of the collimator. As shown in FIG. 6, the scanning table 610 may move along at least one of the first axis (the Y-axis), the second axis (the X-axis), or a third axis (the Z-axis). For example, before the X-ray imaging process, the scanning table 610 may need to move to a predetermined height so that the object (e.g., a patient) can conveniently lie on the scanning table 610. As another example, during the X-ray imaging process, the scanning table 610 may move along the first axis and/or the second axis to obtain the imaging of different body parts of object (e.g., the patient). It should be noted that the above description of the X-ray apparatus 600 is provided for the purposes of illustration, and is not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. In some embodiments, the tray 620 may be omitted, and the X-ray detector 630 may be directly connected to the scanning table 610. FIG. 7 is a schematic diagram illustrating a portion of an exemplary X-ray apparatus according to some embodiments of the present disclosure. As shown in FIG. 7, the X-ray apparatus 700 may include a support component 710, an X-ray source 720, and a collimator 730. The support component 710 may include a first guide rail 712, a second guide rail 714, and a lifting frame 716. The first guide rail 712 may extend along a first axis (e.g., the Y-axis of a coordinate system as illustrated in FIG. 7, a short axis of the scanning table). The second guide rail 714 may extend along a second axis (e.g., the X-axis of the coordinate system as illustrated in FIG. 7, a long axis of the scanning table). The lifting frame 716 may have a length that is adjustable along a third axis (e.g., the Z-axis of the coordinate system as illustrated in FIG. 7, a vertical direction). The X-ray source 720 may be disposed at the lifting frame 714, and the collimator 730 may be connected with the X-ray source. Thus, the movement of the collimator 730 (or the X-ray source 720) may be achieved by the support component 710. Specifically, the movement of the collimator 730 along the first axis (e.g., the Y-axis) may be achieved by moving the lifting frame 716 along the first guide rail 712. The movement of the collimator 730 along the second axis (e.g., the X-axis) may be achieved by moving the lifting frame 716 along the second guide rail 714. The movement of the collimator 730 along the third axis (e.g., the Z-axis) may be achieved by increasing or decreasing the length of the lifting frame 716. In some embodiments, the coordinate of the collimator 730 along the first axis may be represented by the value of a first encoder. The coordinate of the collimator 730 along the second axis may be represented by the value of a second encoder. The coordinate of the collimator 730 along the third axis may be represented by the value of a third encoder. The three encoders may be absolute encoders configured to detect the absolute coordinates of the collimator 730. It should be noted that the above description of the X-ray apparatus 700 is provided for the purposes of illustration, and is not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. In some embodiments, a rotating joint 740 may be disposed between the X-ray source 720 and the lifting frame 716. The X-ray source 720 and the collimator 730 may rotate on a plane that is perpendicular to the third axis (e.g., the Z-axis) via the rotating joint 740. The rotation may be detected by a first rotating encoder. The X-ray source 720 and the collimator 730 may also rotate on a plane that is perpendicular to the first axis (e.g., the Y-axis) via the rotating joint 740. The rotation may be detected by a second rotating encoder. The X-ray source 720 and the collimator 730 may also rotate on a plane that is perpendicular to the second axis (e.g., the X-axis) via the rotating joint 740. The rotation may be detected by a third rotating encoder. In some embodiments, the rotating encoders may absolute encoders configured to detect the absolute angles of the collimator 730. Alternatively, the rotating encoders may be relative encoders configured to detect angular variations of the collimator 730. Having thus described the basic concepts, it may be rather apparent to those skilled in the art after reading this detailed disclosure that the foregoing detailed disclosure is intended to be presented by way of example only and is not limiting. Various alterations, improvements, and modifications may occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested by this disclosure, and are within the spirit and scope of the exemplary embodiments of this disclosure. Moreover, certain terminology has been used to describe embodiments of the present disclosure. For example, the terms “one embodiment,” “an embodiment,” and/or “some embodiments” mean that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Therefore, it is emphasized and should be appreciated that two or more references to “an embodiment” or “one embodiment” or “an alternative embodiment” in various portions of this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the present disclosure. Further, it will be appreciated by one skilled in the art, aspects of the present disclosure may be illustrated and described herein in any of a number of patentable classes or context including any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof. Accordingly, aspects of the present disclosure may be implemented entirely hardware, entirely software (including firmware, resident software, micro-code, etc.) or combining software and hardware implementation that may all generally be referred to herein as a “unit,” “module,” or “system.” Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable media having computer readable program code embodied thereon. A non-transitory computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including electro-magnetic, optical, or the like, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that may communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer readable signal medium may be transmitted using any appropriate medium, including wireless, wireline, optical fiber cable, RF, or the like, or any suitable combination of the foregoing. Computer program code for carrying out operations for aspects of the present disclosure may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C #, VB. NET, Python or the like, conventional procedural programming languages, such as the “C” programming language, Visual Basic, Fortran 2003, Perl, COBOL 2002, PHP, ABAP, dynamic programming languages such as Python, Ruby and Groovy, or other programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider) or in a cloud computing environment or offered as a service such as a Software as a Service (SaaS). Furthermore, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed processes and methods to any order except as may be specified in the claims. Although the above disclosure discusses through various examples what is currently considered to be a variety of useful embodiments of the disclosure, it is to be understood that such detail is solely for that purpose, and that the appended claims are not limited to the disclosed embodiments, but, on the contrary, are intended to cover modifications and equivalent arrangements that are within the spirit and scope of the disclosed embodiments. For example, although the implementation of various components described above may be embodied in a hardware device, it may also be implemented as a software only solution, e.g., an installation on an existing server or mobile device. Similarly, it should be appreciated that in the foregoing description of embodiments of the present disclosure, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the various inventive embodiments. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed object matter requires more features than are expressly recited in each claim. Rather, inventive embodiments lie in less than all features of a single foregoing disclosed embodiment. In some embodiments, the numbers expressing quantities, properties, and so forth, used to describe and claim certain embodiments of the application are to be understood as being modified in some instances by the term “about,” “approximate,” or “substantially.” For example, “about,” “approximate,” or “substantially” may indicate ±20% variation of the value it describes, unless otherwise stated. Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. Each of the patents, patent applications, publications of patent applications, and other material, such as articles, books, specifications, publications, documents, things, and/or the like, referenced herein is hereby incorporated herein by this reference in its entirety for all purposes, excepting any prosecution file history associated with same, any of same that is inconsistent with or in conflict with the present document, or any of same that may have a limiting affect as to the broadest scope of the claims now or later associated with the present document. By way of example, should there be any inconsistency or conflict between the description, definition, and/or the use of a term associated with any of the incorporated material and that associated with the present document, the description, definition, and/or the use of the term in the present document shall prevail. In closing, it is to be understood that the embodiments of the application disclosed herein are illustrative of the principles of the embodiments of the application. Other modifications that may be employed may be within the scope of the application. Thus, by way of example, but not of limitation, alternative configurations of the embodiments of the application may be utilized in accordance with the teachings herein. Accordingly, embodiments of the present application are not limited to that precisely as shown and described.
	description	The invention relates to a gas discharge source. Preferred application area are those requiring extreme ultraviolet and/or soft X-radiation in the wavelength range from approximately 1 nm to 20 nm, such as, in particular, semiconductor lithography. A device of the same generic type is disclosed in WO 99/29145. FIG. 1 originating from this shows an electrode arrangement in which a gas-filled intermediate electrode space is located between two electrodes. The two electrodes are each equipped with an opening, by which an axis of symmetry is defined. The device operates in an environment of constant gas pressure. If a high voltage is applied to the electrodes, there is a gas breakdown, which depends on the pressure and the electrode spacing. The pressure of the gas and the electrode spacing are selected such that the system operates on the left branch of the Paschen curve and, as a result, no electrical breakdown occurs between the electrodes. The gas discharge cannot propagate between the electrodes because, in this case, the mean free path length of the charge carriers is greater than the electrode spacing. Instead, the gas discharge seeks a longer path, since a sufficiently great number of ionizing collisions to trigger the discharge is possible only with a sufficiently large discharge gap. This longer path can be predetermined by means of the electrode openings via which the axis of symmetry is defined. A current-carrying plasma channel, axially symmetric in shape, develops in line with the electrode openings. The extremely high discharge current creates a magnetic field around the current path. The resultant Lorentz force constricts the plasma and the plasma is thereby heated to very high temperatures, wherein it emits very short wavelength radiation, in particular in the EUV and soft X-radiation wavelength range. The extraction of the radiation takes place in the axial direction, along the axis of symmetry, through the opening of one of the electrodes. For application in EUV lithography, plasmas should exhibit an axial expansion of 1 to 2 mm and a diameter again of 1 to 2 mm, and be visually accessible at an observation angle of 45 to 60 degrees. It is generally known that plasmas of this kind, for this application, are optimally generated in electrical discharges with pulse energies in the range of a few joules, a current pulse duration of around 100 ns and current amplitudes between 10 and 30 kA. The optimum neutral gas pressure typically lies in the range of a few Pa to some 10 Pa. The starting radius for compression of the plasma, which is essentially determined by the openings in the electrode system, lies in the range of a few mm. The spacing between the electrodes is between 3 and 10 mm. WO 01/01736 A1 discloses a device of the same generic type, in which, in addition, an auxiliary electrode exhibiting an opening on the axis of symmetry is present between the main electrodes as a means of increasing the conversion efficiency. DE 101 34 033 A1 discloses a device of the same generic type, in which the gas pressure of the gas filling is higher close to an electrode taking the form of a cathode than in an area of the discharge vessel at a distance from it. The devices described as part of the prior art are, however, not capable of supplying the high outputs required for many applications, in particular for semiconductor lithography. Improvements are therefore necessary in order to achieve the highest possible radiation intensity. It should, however, also be noted that, for the necessarily high current amplitudes and current densities, the current transfer via the cathode is inevitably associated with vaporization of cathode material. Electrode erosion of this kind leads to a geometrical change in the cathode, which ultimately has a negative effect on the emission properties of the plasma. This is the case all the more rapidly the nearer to the cathode surface the pinch plasma is oriented. For the usefulness of devices of this kind, however, a sufficiently long service life is essential. It is therefore an object of the invention to provide a device for generating a radiation-emitting plasma, with which a high radiation intensity in the wavelength range between λ=1 to 20 nm, i.e. in the EUV range and the soft X-radiation wavelength range, can be achieved and extracted as effectively as possible, and which exhibits a service life that is as long as possible. The invention recognizes that the above-described technical problem is solved by means of a gas discharge source, in particular for generating extreme ultraviolet and/or soft X-radiation, in which a gas-filled intermediate electrode space (3) is located between two electrodes (1, 2), in which devices for the admission and evacuation of gas are present, in which one electrode (1) exhibits an opening (5) that defines an axis of symmetry (4) and is provided for the discharge of radiation, and in which a diaphragm (6), which exhibits at least one opening (7) on the axis of symmetry (4) and operates as a differential pump stage, is present between the two electrodes (1, 2). The invention is based on the recognition that, as a result of introducing a diaphragm (6) exhibiting an opening (7) on the axis of symmetry (4) and of using this diaphragm as a differential pump stage, certain desired pressure conditions can, in a simple manner, be set in the intermediate electrode space (3). In addition to the resultant advantages, a larger surface over which heat can be dissipated is present in the intermediate electrode space (3) as a result of the incorporation of a diaphragm (6) of this kind. In this manner, the thermal loading on the electrodes (1, 2) can be reduced, their service life increased and the mean output or pulse energy that can be injected into the system can be increased, along with the achievable radiation power. The intermediate electrode space (3) is intended to designate the entire space between the two electrodes (1, 2). It is divided by the diaphragm (6) into two part-areas, each of which is defined by one of the electrodes (including its opening) and the diaphragm (including its opening). There exists, in particular, the option of providing a greater gas pressure in the part-area of the gas-filled intermediate electrode space (3) defined by the diaphragm (6) and the electrode (2) that faces away from the discharge side of the radiation than in the part-area of the gas-filled intermediate electrode space (3) defined by the diaphragm (6) and the electrode (1) that faces towards the discharge side of the radiation. This measure ensures that the compression, or the injection of energy into the current-carrying plasma and, in association with this, the localization of the area of high impedance, takes place at the desired point close to the electrode (1) facing towards the discharge side of the radiation. This has the advantage that there is optimum usability of the radiation from the point of view of accessibility at large angles of observation. The current transfer from the cathode to this point hereby takes place in a diffuse, low-impedance plasma. As compared with the prior art, in which a plasma channel that is shorter overall arises, this leads to virtually no losses. For this reason also, an increase in radiation power is achievable. The gas pressure in the intermediate electrode space (3) and the space between the two electrodes are selected such that the ignition of the plasma takes place on the left-hand branch of the Paschen curve, i.e. the ionization processes start along the long electrical field lines, which preferably occur in the area of the openings of the anode and cathode. The ignition therefore takes place in the gas volume and thereby occasions an especially low rate of wear. In addition, in the case of operation on the left branch of the Paschen curve, switching elements between the radiation generator and the power supply are not necessary, making possible a low-induction—and therefore extremely efficient—energy injection. It is possible to use as the cathode either the electrode (2) facing away from the discharge side of the radiation or the electrode (1) facing towards the discharge side of the radiation. The first alternative has the advantage that the compressed plasma, which may, in this case, owing to the device in accordance with the invention, arise close to the anode (1), is comparatively far away from the cathode (2). As a result, there is less erosion of the cathode. Above all, however, the generation of the pinch plasma also depends less strongly on geometrical changes in the cathode. A higher degree of erosion can thereby be tolerated. Overall, this leads to a considerably longer service life for the electrode system and offers the opportunity of introducing a higher electrical power and thereby achieving a greater radiation power. Neither is the thermal loading on the electrode (1) facing towards the discharge side of the radiation, e.g. the anode, too excessive, since the diaphragm (6) is capable of dissipating a considerable proportion of the energy. Therefore, owing to the presence of the diaphragm (6), only the proportion of the energy that is injected into the area of the pinch plasma, which emits short-wave radiation, need be taken into account. Since this proportion is equal to only one fifth to one quarter of the total energy, the introducable power and also the pulse energy can thereby be increased accordingly by a factor of 4 to 5. It is especially advantageous to design the electrode (2) facing away from the discharge side of the radiation as a hollow electrode, especially a hollow cathode, equipped with a cavity (8). Within this, in a first phase of the discharge, a pre-ionization of the gas takes place, followed by the development of a dense hollow-cathode plasma. A plasma of this kind is especially suitable for supplying the necessary charge carriers (electrons) to create a low-impedance channel in the intermediate electrode space (3). The hollow electrode (2) may exhibit one or more openings (9) to the intermediate electrode space (3). Since, as a result of the latter alternative, the entire current is distributed over multiple electrode openings (9), the local loading on the electrode (2) can be reduced in this manner, and the service life of the electrode system, and the introducable electrical power, can thereby be increased. In the cavity (8) of the electrode (2) designed as a hollow cathode, additional triggering devices may be present. In this manner, the ignition of the discharge can be triggered precisely as required. This is advantageous, in particular, in the case of a hollow cathode with multiple openings. The triggering device may be designed as, for example, an auxiliary electrode in the hollow cathode, with which the discharge can be triggered in that the auxiliary electrode is switched from a potential that is positive relative to the cathode to a lower potential, e.g. cathode potential. Further triggering options consist in the injection or generation of charge carriers in the hollow cathode via a glow-discharge trigger, a high-dielectric trigger or the triggering of photoelectrons or metal vapor via light pulses or laser pulses. It is favorable if the diaphragm (6) is designed in such a way that it contributes to the current transfer to only a small extent at the most. Instead, the entire, or at least the major, proportion of the current transfer from the cathode to the anode takes place largely only via the plasma channel. In this manner, the current can be used as completely and effectively as possible for generation of the pinch plasma. In addition, the generation of cathode spots on the diaphragm, and the erosion thereby arising there, can be largely avoided. For the manufacture of the diaphragm (6), it is advantageous if the diaphragm (6), or at least a portion of the diaphragm (6), comprises a material that responds well to machining. It is also advantageous if the material of at least a portion of the diaphragm (6) exhibits a high degree of thermal conductivity. This enables effective cooling or heat dissipation. An example of a material that can be used for at least a portion of the diaphragm (6) is ceramics, in particular aluminum oxide or lanthanum hexaboride. For the portion of the diaphragm (6) located close to the opening (7), for which portion, owing to its proximity to the plasma channel, the risk of erosion of the diaphragm (6) is greatest, it is favorable to produce this portion from an especially discharge-resistant material, e.g., in particular, molybdenum, tungsten, titanium nitride or lanthanum hexaboride. As a result, the occurrence of erosion on the diaphragm (6) is greatly reduced, and the service life of the device is thereby increased. It is also possible to introduce multiple diaphragms, each exhibiting an opening (7) on the axis of symmetry (4), into the intermediate electrode space (3). In a particularly advantageous embodiment, these take the form of metallic diaphragms (6, 6′, 6″), separated from one another by isolators (11). In this manner, the multi-stage ignition of cathode hot spots, and thereby the current transfer, are effectively suppressed. This provides the same advantage as the use of a single isolator. In addition, a desired low-inductance structure of the electrode system as compared with a purely ceramic body is possible as a result of the incorporation of metal. Moreover, the deposition of metallic vapor on the diaphragm, which could lead to problems in the case of a ceramic diaphragm, plays virtually no role. The thickness of the diaphragm (6) may lie within a range between approximately 1 and 20 mm. From the point of view of cooling, diaphragms that are as thick as possible should be provided. The diameter of the diaphragm (6) should be roughly between 4 and 20 mm. It is possible to arrange gas inlets (12) in such a way that their openings face towards the part-area of the gas-filled intermediate electrode space (3) defined by the diaphragm (6) and by the electrode (2) facing away from the discharge side of the radiation. The gas pressure in this part-area can thereby be set specifically. In interaction with the diaphragm (6), a higher gas pressure, in particular, may hereby be provided there than in the part-area of the intermediate electrode space (3) defined by the diaphragm (6) and the electrode (1) facing towards the discharge side of the radiation, or a specific desired pressure difference can be set. In addition, gas inlets (12′) may be present that are equipped with openings towards the part-area of the gas-filled intermediate electrode space (3) defined by the diaphragm (6) and by the electrode (1) facing towards the discharge side of the radiation. With the incorporation of gas inlets (12, 12′) in both part-areas of the intermediate electrode space (3), an especially large tolerance is obtained for regulating the gas-pressure distribution in the intermediate electrode space (3). In addition, in conjunction with the presence of the diaphragm (6), the opportunity of generating an inhomogeneous distribution of the gas composition within the intermediate electrode space (3) is provided as a result. In particular, in an especially advantageous embodiment of the invention, additionally introduced into the part-area of the intermediate electrode space (3) defined by the diaphragm (6) and by the electrode (2) facing away from the discharge side of the radiation, via the gas inlets (12) present there, is a filler gas, such as helium or hydrogen, which, by comparison with the working gas, exhibits very low radiation losses under the pulsed currents used. In this manner, the impedance of the plasma is maintained at a low level here in comparison with the EUV-emitting area, and the energy injection is more effective. Introduced into the part-area of the intermediate electrode space (3) defined by the diaphragm (6) and by the electrode (1) facing towards the discharge side of the radiation, via the gas inlets (12′) present there, is the working gas, such as xenon or neon, which is provided for generating the pinch plasma and the resultant emission of EUV radiation. The evacuation of the gas may take place especially easily by means of an evacuation device located outside the intermediate electrode space, through the opening of the electrode (1) facing towards the discharge side of the radiation. However, it is also possible to provide an evacuation device directly in the intermediate electrode space (3), in particular in the part-area of the intermediate electrode space (3) defined by the diaphragm (6) and by the electrode (1) facing towards the discharge side of the radiation. This is especially advantageous if, as described above, different gas compositions are present in the two part-areas of the intermediate electrode space (3), since a comparatively low blending of the two gas mixtures can then be achieved during the evacuation. FIG. 2 shows one embodiment of the electrode system of the device in accordance with the invention. One electrode (2) hereby takes the form of a hollow electrode equipped with a cavity (8), and is used as the cathode. The other electrode (1) acts as the anode. The extraction of the radiation discharged from the pinch plasma (13) generated within the gas-filled intermediate electrode space (3) takes place through the opening (5) in the anode (1). In order to make the highest possible proportion of the emitted radiation usable, the anode opening (5) widens out in the extraction direction. Between the electrodes (1, 2) is arranged a diaphragm (6), which exhibits a through-opening (7) on the axis of symmetry (4) defined by the anode opening (5). In this embodiment, the hollow cathode exhibits an opening (9) to the intermediate electrode space (3), which is also located on the axis of symmetry (4). Gas inlets (12) are present, with openings to the part-area of the gas-filled intermediate electrode space (3) defined by the diaphragm (6) and by the cathode (2). In this embodiment, the feed lines for these gas inlets run through the body of the hollow cathode. Further gas inlets (12′) are present, with openings to the part-area of the gas-filled intermediate electrode space (3) defined by the diaphragm (6) and by the anode (1). FIG. 3 shows an embodiment of the device in accordance with the invention, in which the diaphragm (6) comprises a discharge-resistant material, e.g. molybdenum, tungsten, titanium nitride or lanthanum hexaboride, in an area (10) close to its opening (7). The remaining portion of the diaphragm (6) comprises a material that is amenable to machining and/or a material with a high thermal conductivity. FIG. 4 shows an embodiment of the device in accordance with the invention, in which multiple metallic diaphragms (6, 6′, 6″) are arranged between the electrodes (1, 2), separated by isolators (11) in each case. FIG. 5 shows a further embodiment in which the cathode (2) exhibits three openings (9, 9′, 9″). The opening (9) located centrally on the axis of symmetry hereby takes the form of a blind hole. The other two openings (9′, 9″) are through-openings between the cavity (8) of the cathode (2) and the intermediate electrode space (3). 1 Electrode facing towards the discharge side of the radiation 2 Electrode facing away from the discharge side of the radiation 3 (Gas-filled) intermediate electrode space 4 Axis of symmetry 5 Opening in the electrode (1) facing towards the discharge side of the radiation 6 Diaphragm 7 Opening in the diaphragm 8 Cavity in the hollow electrode (2) 9, 9′, 9″, Opening in the electrode facing away from the discharge side of the radiation 10 Part-area of the diaphragm comprising discharge-resistant material 11 Isolators 12, 12′ Gas inlets 13 Pinch plasma
052573052	summary	The invention relates to a slit radiography device, comprising an X-ray source which is capable, when in operation, of scanning a body under examination, via a slit of a slit diaphragm, with a fan-shaped X-ray beam in a direction transverse to the longitudinal direction of the slit, an absorption device comprising a number of movable absorption elements placed next to each other being provided, which absorption elements can be moved into the fan-shaped X-ray beam to a greater or lesser extent under the influence of suitable control signals in order to influence, when in operation, the X-ray radiation incident on the body per sector of the X-ray beam. A device of the type described above is, for example, known from U.S. Pat. No. 4,715,056. U.S. Pat. No. 4,715,056 shows and describes diverse types of absorption elements which can be moved up and down in order to influence a fan-shaped X-ray beam, transmitted or to be transmitted through the slit of a slit diaphragm, per sector thereof. The absorption elements may be composed of small plates, situated next to each other, of material which attenuates or even completely absorbs X-ray radiation, which small plates are placed on the free ends of cantilever-mounted tongue-shaped devices. The tongue-shaped devices may advantageously be piezoelectric tongues, it being possible to control the position of the free ends, and consequently of the absorption elements, directly by electrical signals. Tongue-shaped devices controlled in a different manner may also be used, however, as can, for example, diverse types of means which are able to cause the absorption elements to perform a rectilinear to-and-fro sliding movement. In all cases it is important that the absorption elements can be moved independently of each other in a direction transverse to the longitudinal direction of the slit of the slit diaphragm. Furthermore, adjacent absorption elements should adjoin each other in a manner such that the X-ray radiation cannot pass freely between two elements. The absorption elements with rectangular cross section shown in U.S. Pat. No. 4,715,056 are only able to satisfy this last requirement if adjacent elements are situated so as to fit tightly against each other. However, this adversely affects the free movement capability. The trapezoidal elements and the elements provided with tongue and groove also shown in U.S. Pat. No. 4,715,056 can indeed be fitted with a small gap without X-ray radiation being able to pass freely between two adjacent elements. However, the radiation is then not absorbed to the same extent in the region of the edge parts of the elements which overlap each other as it is by the central part of the elements. This may produce strip-like artefacts in a radiograph to be made, which is undesirable. The applicant has carried out an investigation into a slit radiography apparatus provided with an absorption device which is constructed with tongue-shaped elements which are provided at the free end with small plates of material, which absorbs X-ray radiation, placed transversely to the longitudinal direction of the tongues. In this case, the tongues were alternately relatively short and relatively long and the small plates of absorbing material were chosen so wide that adjacent small plates, which are consequently situated at different distances from the X-ray source, overlap each other to some extent. A drawback of this arrangement is, however, that the overlapping parts of the small plates give rise to strip-like artefacts in the radiographs to be made. The varying distances of the small plates from the X-ray source also result in a varying influencing of the X-ray beam with positions of the small plates which are otherwise identical. The object of the invention is to eliminate the drawbacks outlined and to provide, in general, a slit radiography apparatus having an advantageous absorption device. For this purpose, an apparatus of the type described is characterized, according to the invention, in that at least the edge sections facing each other of adjacent absorption elements are of matching construction and, viewed from the X-ray source, overlap each other, the edge section of an absorption element which, seen from the X-ray source, overlaps an edge section of an adjacent absorption element always being a small distance nearer the X-ray source than the matchingly constructed edge section of the other absorption element and the total material thickness at the site of the overlapping edge sections being equal to the material thickness between the edge sections. A procedure for producing absorption elements for an absorption device of a slit radiography apparatus is characterized according to the invention in that the shape of the absorption elements is constructed by defining, between two equidistant lines which have a mutual spacing which is equal to the desired absorption thickness of the material to be used for the elements, at least two cut lines extending, at least not over the entire length, transversely to the equidistant lines; by defining, on either side of each cut line, two edge regions, which are each bounded by the cut line, a boundary line extending transversely to the equidistant lines and a part of at least one of the equidistant lines; by moving the edge regions thus determined on either side of each cut line over a small distance in opposite directions along the boundary lines, with the result that a gap is produced at the position of each cut line; and by using the shape situated between two gaps thus obtained as a template for the cross section of the absorption elements.
	description	Referring to the drawings, it is seen in FIG. 1 that the invention is generally indicated by the numeral 10. Thermal solar rocket 10 is generally comprised of a solar energy receiver 12 that is formed from a thermal energy storage section 14 and a direct gain section 16, a solar concentrator 18, means 20 for selectively directing solar energy to either the thermal energy storage section 12 or the direct gain section 14, and a propulsion nozzle 22. Thermal energy storage sections are generally known but will be described for the sake of clarity. Thermal energy storage section 14 is a container with insulation material 24 provided in the walls. The walls define a cavity in the container. Thermal energy storage material 26 provided in the cavity is typically formed from graphite rods clad in rhenium. The thermal energy storage section is in fluid communication with the direct gain section 16 via piping 34. The direct gain section 16 is comprised of refractory metal tubes (typically rhenium) and is positioned adjacent means 20. The metal tubes are provided with channels through which the gaseous propellant flows. The gaseous propellant is heated as it flows through the channels. Insulation material 24 is also provided around the direct gain section 16. The direct gain section is in fluid communication with the propulsion nozzle 22 via piping 28. As seen in the drawings, a gap is left in the insulation material 24 around the direct gain section 16 to allow the solar energy from the solar concentrator into the direct gain section 16 and the thermal energy storage section 14. The solar concentrator 18 collects and focuses solar rays into the solar energy receiver 12. Solar concentrators are generally known and may have a parabolic shape or may be formed from a refractive or fresnel lens. A secondary solar concentrator 38 may be provided in the insulation gap on the direct gain section to further focus the solar rays. The secondary solar concentrator would result in a reduction of the accuracy requirements of the solar concentrator 18. In the preferred embodiment of FIGS. 1 and 2, means 20 for selectively directing solar energy to either the thermal energy storage section 14 or the direct gain section 16 is provided in the form of a movable wall of insulation material 24. In the first open position seen in FIG. 1, the solar rays from the concentrator 18 are directed into the thermal energy storage section 14 for heating the storage material 26. In the second closed position seen in FIG. 2, the solar rays from the concentrator 18 are blocked by the insulation and thus heat the direct gain section 16. A propellant supply tank 30 contains a suitable gaseous propellant such as hydrogen. The tank is in fluid communication with the thermal energy storage section via piping 32 for selectively supplying propellant to the solar energy receiver during the propulsion phase by means of a valve 36 in piping 32. Operation is generally as follows. In the thermal energy collection and storage phase of the orbital period, means 20 is held in the first open position seen in FIG. 1. Solar rays are indicated by the lines striking the solar concentrator 18. The arrows indicate the reflected solar rays. This allows the solar rays from the concentrator to heat the thermal energy storage section 14 to a temperature of approximately two thousand four hundred degrees Kelvin (for a rhenium/graphite cavity). Once the maximum temperature is achieved, means 20 is moved to the second closed position seen in FIG. 2. In this position, the solar rays from the concentrator 18 heat the direct gain section to at least three thousand degrees Kelvin. During the propulsion phase, propellant is released into the thermal energy storage section 14 where it is heated to approximately the temperature of this section. The heated propellant then flows into the direct gain section via piping 34 where it is further heated to approximately the temperature of this section. The heated propellant then flows through piping 28 to the propulsion nozzle where it produces thrust. FIGS. 3 and 4 illustrate an alternate embodiment of the invention where the means for selectively directing solar energy to either the thermal energy storage section 12 or the direct gain section 14 is provided in the form of relative rotation between the solar concentrator and the solar energy receiver. In this embodiment, the thermal energy storage section is provided with one or more apertures in the wall for receiving the solar rays. As indicated above, a secondary solar concentrator 38 may be provided in the aperture to reduce the aperture size. Also, the direct gain section 16 is not positioned around the aperture in the walls of the thermal energy storage section 14. The relative rotation may be in the form of rotating either the solar energy receiver 12 or the solar concentrator 18. In the first position seen in FIG. 3 the solar rays and energy are directed into the thermal energy storage section 14 for solar energy collection and storage. In the second position seen in FIG. 4 the solar rays are directed to the direct gain section 16 for heating thereof during the propulsion phase. Propellant is supplied from propellant supply 30 to the thermal energy storage section 14 via piping 32 where the propellant is pre-heated. The propellant then flows to the direct gain section 16 via piping 34 where it is heated to the propulsion temperature and then to the propellant nozzle 22 via piping 28 for producing thrust. Although means 20 is illustrated as a rotating or butterfly valve in FIGS. 1 and 2, other types of mechanical switches might be used. The insulation could slide in and out, or a rotating design with windows could be used. Another option would be to use a radiative gap insulation (multi-foil insulation) and fill the gap with gas to xe2x80x9copenxe2x80x9d the heat flow and pump out the gas to xe2x80x9cclosexe2x80x9d the heat flow. The thermal energy storage and direct gain sections could be made from a variety of materials. The thermal energy storage material must have a high specific heat and must be compatible with hydrogen. Two material combinations are typically used in these designs, graphite with a rhenium coating/cladding or boron nitride with a tungsten coating/cladding. However, other material combinations are possible. The direct gain section is preferably made of rhenium. However other refractory metals are possible. Highly conductive composite materials may also be used if they can be made compatible with hydrogen and can contain the pressure loads of the propellant. The invention provides the advantage of achieving the high performance of a direct gain rocket (i.e., high propellant temperatures) using small collectors/concentrators like a thermal energy storage rocket. This enables the rocket to use existing collector technology to achieve performance that otherwise would be decades away. The specific impulse of such a system is two to four times that of a conventional chemical rocket and thus can deliver significantly greater payloads to orbit from any launch vehicle. Because many varying and differing embodiments may be made within the scope of the inventive concept herein taught and because many modifications may be made in the embodiment herein detailed in accordance with the descriptive requirement of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.
051981831	claims	1. An apparatus for close packing of nuclear fuel assemblies, wherein a nuclear fuel assembly has an array of nuclear fuel rods spaced within an envelope with narrow spaces and wider spaces therebetween, said apparatus comprising: (a) said nuclear fuel assembly, and (b) a plate having an effective amount of neutron absorbing material, said plate further having a thickness permitting insertion within said envelope and between said nuclear fuel rods within said narrow spaces, and having a width and length permitting insertion between any grid spacers within said nuclear fuel assembly. (a) a releasable lock on said plate. (a) an elongated member having first and second ends, said first end having a key, said second end rotatably attachable to said plate, (b) a locking disk attached on said elongated member between said key and said second end, and having a thickness less than a shortest distance between said fuel rods and having a width greater than said shortest distance, (c) whereby said thickness of said locking disk permits said disk to be inserted between said nuclear fuel rods then locked between said nuclear fuel rods by rotating said locking disk with said key so that said width of said locking disk prevents removal of said locking disc between said nuclear fuel rods. (a) a retainer attached to an end of said plate near said key and containing said key. (a) making a plate having an effective amount of neutron absorbing material, said plate further having a thickness permitting insertion within said envelope and between said nuclear fuel rods within said narrow spaces, and having a width and length permitting insertion between any grid spacers within said nuclear fuel assembly, and (b) said plate between said nuclear fuel rods within said envelope of said nuclear fuel assembly. (a) releasably locking said plate within said fuel assembly. (a) a plate having an effective amount of neutron absorbing material, (b) a releasable lock having (c) an elongated member having first and second ends, said first end having a key, said second end rotatably attachable to said plate, (d) a locking disk attached on said elongated member between said key and said second end, and having a thickness less than said narrow space between said fuel rods and having a width greater than said narrow space, (e) whereby said plate is placed within said envelope and said thickness of said locking disk permits said disk to be inserted between said nuclear fuel rods then locked between said nuclear fuel rods by rotating said locking disk with said key so that said width of said locking disk prevents removal of said locking disc between said nuclear fuel rods. (a) a retainer attached to an end of said plate near said key and contacting said key. 2. An apparatus as recited in claim 1, further comprising: 3. An apparatus as recited in claim 2, wherein said releasable lock is a rigid lock comprising: 4. An apparatus as recited in claim 3, further comprising: 5. A method for close packing of nuclear fuel assemblies, wherein a nuclear fuel assembly has an array of nuclear fuel rods spaced within an envelope with narrow spaces and wider spaces therebetween, said method comprising the steps of: 6. A method as recited in claim 5, further comprising: 7. An apparatus for close packing of nuclear fuel assemblies, wherein a nuclear fuel assembly has an array of nuclear fuel rods spaced within an envelope with narrow spaces and wider spaces therebetween, said apparatus comprising: 8. An apparatus as recited in claim 7, further comprising:
062636650	abstract	The invention provides a microthruster which includes a housing having a propellant container and a discharge section, means to heat the propellant to drive vapors toward the discharge section, a heating element to heat the vapors and one or more ports to discharge the vapors to provide thrust. Further provided is a method for powering a microthruster by flowing gas in free molecular flow therein so that a plurality of molecules of the gas contact a heating element before discharge from the microthruster.
041860500	description	Illustrated in the drawings is a TRIGA reactor 11 designed to operate at a steady state power level up to about 2 MW with natural-convection core cooling. With forced flow cooling, steady state power levels substantially higher can be achieved. The reactor 11 includes a core assembly 13 which is surrounded by an annular graphite reflector 15. The core assembly 13 is located in a bottom portion of a vertically extending reactor tank 19 which holds a pool 21 of a liquid coolant-moderator, usually water. The reactor tank 19 may be cylindrical. The core assembly 13 is made up of a plurality of vertically extending fuel elements 23 which are located in a predetermined spatial array, as best seen in FIG. 2. Each fuel element 23, as depicted in FIG. 3, includes a fluidtight tubular shell 25 made of a material such as stainless steel or Incoloy. The bottom of each tube 25 is closed with a stainless steel bottom end fixture 27, and its top is similarly closed by a stainless steel top end fixture 29. A representative fuel element 23 for the illustrated reactor employs a stainless steel cladding 25 about 0.02 inch in thickness (about 0.5 mm.) which contains a central fuel body 31 about 15 inches (about 38 cm.) in length having a diameter of about 1.43 inches (36.3 mm.). Although illustrated as a single rod, the fuel body 31 may be made of a plurality of shorter compacts. The fuel body 31 is flanked by upper and lower internal graphite reflectors 33 in the form of short graphite rods about 3.4 inches (8.64 cm.) in length. As illustrated in FIG. 2, the fuel elements 23 extend vertically in a spatial array which is a plurality of uniformly spaced, concentric circles; however, other spatial arrays may also be used. The fuel elements 23 are maintained in the desired spaced relationship from one another within the core by upper and lower grid members 35,37. The lower grid member 37 is made of a suitable material, such as aluminum, and is supported spaced somewhat above the very bottom of the tank section 17 by a lower core assembly support 38. It contains a pattern of openings 41 which receive the depending pin portions of the bottom end fixtures 27. The upper grid member 35 is appropriately secured to the top of the reflector assembly 15 and is preferably spaced slightly above it by spacers 43 to facilitate coolant flow. Openings 47 in the upper grid member 35 are of a diameter approximately equal to the outer diameter of the fuel elements 23 so that the fuel elements can be slideably lowered therethrough. The upper end of each top end fixture 29 is formed with a knob 49 which is designed for engagement by a fuel-element handling device. A flow area is provided in the top end fixture 29 in the region of the upper grid plate 35 to provide passageways for the coolant-moderator which is flowing upward out of the core. Coolant flows downward in the pool outside the reflector portion of the reactor core and then inward through the support assembly 38 via natural convection. In addition to the openings 41 in the lower grid plate 37 which receive the depending pin portions of the bottom end fixtures 27, there are additional openings 53 which permit the upward flow of the coolant-moderator through the lower grid plate and upward into the regions between adjacent fuel elements 23. The coolant-moderator is heated in the core assembly 13 by a heat-exchange with the fuel elements 23, and the lighter liquid rises rapidly into the pool 21 in the main section of the tank 19 above the core assembly. To control the nuclear reaction within the core 13, a plurality of control rods 61 are provided (three are illustrated). The control rods 61 are movable upward and downward, slideably within three tubes 63 in the reactor core which occupy locations in the spatial array that would otherwise be occupied by fuel elements 23. The control rods 61 are vertically movable (as depicted in dotted outline) by mechanisms supported overhead of the tank 19 which are not shown and which do not form a part of the present invention. In a reactor of this general type, the long-life low-enriched fuel elements 23 can be constructed so that the prompt negative temperature coefficient of reactivity may be greater than about 10.times.10.sup.-5 /.degree.C. The fuel bodies 31 in each of the fuel elements 23 are made of a homogeneous mixture of uranium, zirconium hydride and erbium. The zirconium hydride is prepared in accordance with methods known in the art. The hydrogen to zirconium ratio is between about 1.5:1 and about 1.7:1, and preferably is about 1.6:1. As previously indicated, the uranium which is used is low-enriched uranium, i.e., an enrichment of not greater than about 20 percent, and the weight percent of uranium in the fuel body 31 may vary from 20 weight percent to about 50 weight percent. The amount of erbium which is employed will be dependent upon the amount of excess reactivity that is present in the core assembly 13, and thus upon the weight percent of low-enriched uranium which is used. For example, if 20 weight percent of low-enriched uranium is employed, about 0.5 weight percent of erbium is used. If, for example, 30 weight percent low-enriched uranium is employed, about 0.9 weight percent of erbium is employed. The homogeneous mixture of the uranium, zirconium-hydride and erbium is critical to obtaining the prompt negative temperature coefficient of reactivity. One example of such a reactor system contains a core assembly 13 made up of 100 fuel elements of the general type hereinbefore described which are located near the bottom of a pool of light water held by a tank 19 about 6 feet in diameter. The fuel elements 23 are uniformly arranged in an array having a diameter of about 20 inches (51 cm.), which is surrounded by a graphite reflector 15 made up of bricks of dense graphite having a thickness of abone one foot. The annular reflector 15 provides the same thickness of graphite all around the core assembly 13. These dimensions are the dimensions of a standard TRIGA reactor having a power of about 2 MW. In a reactor of this construction, the prompt negative temperature coefficient for a core made up of fuel elements employing 20 weight percent of the low-enriched uranium is about 10.5.times.10.sup.-5 /.degree.C. which is greater than that of the standard TRIGA fuel. Generally, in a core-reflector arrangement such as that illustrated where the region interior of the reflector occupied by the assembly of elements is not greater than about 2 cubic feet for each thousand KW of rated power, the prompt negative temperature coefficient of reactivity will be about 8 to about 11.times.10.sup.-5 /.degree.C. average over the operating temperature range. Thus, by having the U-238 constitute a very large portion (about 80 percent) of the uranium in the fuel element (which themselves contain a high weight percent of uranium, i.e., 20 to 50 weight percent) and by adding a thermal resonance poison, namely erbium, as a part of the homogeneous fuel-moderator mixture, it was unexpectedly found that the total prompt negative temperature coefficient of reactivity of such a reactor core was larger than or at least nearly as large as that of a core assembly utilizing the standard TRIGA fuel, which contains about 8.5 weight percent of low-enriched uranium. In fact, the prompt negative temperature coefficient of a core assembly 13 containing fuel elements with 20 weight percent of the low-enriched uranium is about 10 percent higher than that of a core containing 8.5 weight percent uranium (standard TRIGA fuel). Similarly, the coefficient for a core assembly 13 containing 30 weight percent of the low-enriched uranium is only somewhat lower than the standard TRIGA core. It was found that the loss in prompt negative temperature coefficient, compared to the standard TRIGA fuel core, which is caused by the increased U-235 content and by the reduction in the amount of hydrogen, is unexpectedly able to be more than completely offset, or almost completely offset, by the combination of the use of erbium plus the increase in the amount of U-238, the presence of which causes a significant increase in the Doppler broadening effect. Surprisingly, this is achieved with a significantly lesser amount of erbium than that which was present in the TRIGA-FLIP fuel. As a result, the precise combination of low-enriched uranium, plus ZrH.sub.1.6' plus a minor amount of erbium, usually less than 1 weight percent, surprisingly provides a substitute core for the standard TRIGA reactor which will have both long life, e.g., at least about 1200 MW days, plus a prompt negative temperature coefficient of reactivity which gives it inherent safety. Although the invention has been described with regard to certain preferred embodiments, it should be understood that various modifications and changes as would be obvious to one having the ordinary skill in the art may be made without departing from the scope of the invention which is defined solely by the appended claims. For example, the fuel elements could be in the form of plates instead of being tubular in shape. Moreover, should smaller diameter fuel elements be used, for example one-half inch diameter which include 45 w/o uranium, the core might only have a prompt negative temperature coefficient of about 5.times.10.sup.-5 /.degree.C. which would be acceptable under some circumstances. Various of the features of the invention are emphasized in the claims which follow.
055442056	description	DETAILED DESCRIPTION FIG. 1 shows a part of the cavity 1 of a nuclear reactor in which an inspection stand 3 for the internals 4 of the nuclear reactor is arranged. The upper internals 4 include an upper plate 5 and a lower plate 6 constituting the upper plate of the core of the nuclear reactor, bearing on the upper end of the fuel assemblies when the upper internals 4 are in the service position in the vessel of the reactor. The internals 4 furthermore include a set of guide tubes 8 connected to the upper plate 5 and to the lower plate 6 of the internals and each including a first part interposed between the upper plate 5 and the lower plate 6 and a second part 8a fixed above the upper plate 5. Support columns 7 arranged between the plates 5 and 6, parallel to the tubes 8, make it possible to hold the plates 5 and 6 and ensure rigidity of the internals 4. During a shutdown of the reactor for repair and refuelling, the internals 4 are extracted from the vessel of the reactor and arranged on the storage stand 3, the internals 4 resting via the upper plate 5 on vertical supports of the stand 3. The cavity 1 is filled with water up to its upper level and the intervention is carried out from a bridge arranged above the upper level of the cavity 1. The intervention device according to the invention includes an inspection rod cluster 10 which can be moved by a support carriage 9 over the bottom of the cavity and a long mast 11 which can be manipulated from the bridge of the cavity to be fitted inside any guide tube 8 to engage with the inspection rod cluster 10 and move it in the vertical direction and upwards inside the tube 8. FIG. 2 shows a guide tube 8 for the internals 4 represented in FIG. 1. The guide tube 8 includes the upper part 8a and a lower part 8b which are connected together by assembly means 8c comprising flanges fastened to one another by screws. The upper part 8a of the guide tube 8 is intended to be placed above the upper plate 5 of the upper internals, and the lower part 8b between the upper plate 5 and the lower plate 6. The two parts 8a and 8b of the guide tube include an outer cylindrical casing which is pierced with openings and which contains the guide elements. The lower part 8b, which constitutes the main guide part of the tube 8, itself includes an upper part 13 constituting the discontinuous guide part and a lower part 14 constituting the continuous guide part for the control rods. In the discontinuous guide part 13, the outer casing of the guide tube 8 contains the guide panels 15 as represented in FIG. 3, in successive locations 15a, 15b, 15c, . . . , regularly spaced along the length of the part 13 of the lower section 8b of the tube 8. Continuous guide elements as represented in FIG. 4 are arranged along the entire length of the continuous guide part 14 of the lower section 8b of the guide tube. The discontinuous guide plates or guide panels 15 as represented in FIG. 3 consist of metal plates cut out so as to leave a free space 17 at the central part of the panel 15 and guide openings such as 18, 19, 20 for the absorber rods of the control rod which may be introduced and guided through the guide tube containing the guide panels 15. The openings such as 20 are arranged at the end of a slot 21 passing through the guide panel 15 and emerging in the central free space 17. The openings such as 18 and 19 are aligned along a slot 22 also emerging in the central free space 17. In this manner, all the guide openings 18, 19 and 20 of the guide panel 15 emerge in the central free space 17. The part of the openings 18 communicating with the central free space 17 has circumferential surfaces 23 or 23' and radially directed surfaces 24 and 25. Some of these surfaces may be lined with an anti-wear component or layer. The surfaces such as 23, 23', 24 and 25 which do not undergo significant frictional wear during the use of the control rods can be used as reference surfaces during the checking. FIG. 4 shows in section the continuous guide part 14 of the guide tube 8 which includes, inside the cylindrical casing of the section 8b of the guide tube, a support 26 including a central axially directed bore defining a free space 27 in extension of the free space 17, inside the guide tube, the free spaces 17 of the guide panels and the free space 27 of the continuous guidance constituting the central bore of the guide tube. The continuous guide elements are fixed on the support 26 and consist of guide sleeves 30 and slit tubes 31 arranged in the axial direction of the guide tube 6. Each of the guide sleeves 30 defines two guide bores 28 and 29 which are connected together by a slit 32 and emerge in the free space 27. The tubes 31 include a slit pointing towards the central free space 27. The guide bores 28 and 29 of the sleeves 30 and the slit tubes 31 all communicate with the central free bore of the guide tube. The openings 28, 29 and 30 of the guide panels are arranged so as to reproduce, in cross section, the network of the guide tubes of a core assembly of a nuclear reactor, into which guide tubes the absorber rods of a control rod are introduced. The guide panels 15 are arranged parallel to each other in positions such that the openings of the various successive panels are aligned to constitute axially directed guide channels. The guide bores 28 and 29 of the sleeves 30 and the bores of the tubes 31 are, also arranged so as to reproduce the network of the guide tubes of an assembly of the nuclear reactor. The bores of the continuous guide elements are aligned with the series of openings of the guide panels, along the axial guide directions. FIG. 5 shows, on a larger scale and in more detail, the carriage 9 carrying the inspection rod cluster 10 of the device according to the invention, which can be moved over the bottom 2 of the cavity 1, so as to come into axial extension of any guide tube 8 of the internals 4 in position on their inspection stand 3. The bearing carriage 9, which is of the type currently used in the scope of maintenance operations inside the cavity of a nuclear reactor, includes wheels 33 resting on the bottom 2 of the cavity and drive means (not shown) making it possible to control, remotely and very accurately, the movements of the support carriage 9 over the bottom of the cavity. Two vertical columns 34 and 35 are fixed on the platform 32 of the carriage 9. A support carriage 36 for the inspection rod cluster 10 is mounted movably in the vertical direction on the column 34. The support carriage 36 includes a housing for accommodating the lower part of the inspection rod cluster 10, making it possible to hold it in a vertical position, and drive means for movement along the axial direction of the column 34. The carriage 9 includes a vertical upright 37 on which a pusher-puller 38 is mounted, making it possible to move, in either direction, a set of cables 12 connected to the inspection rod cluster 10, powering the probes and collecting the measurements, during the movements of the inspection rod cluster 10 inside a guide tube, in either direction. Tension is thus continuously exerted on the set of cables 12 during the movements of the inspection rod cluster 10, which makes it possible to prevent the cables from winding up or folding and blocking the movements of the probe support. The set of cables 12 is, in addition, guided by pulleys 39 and 39'. A plate 40 carrying a centering and positioning head 41 for the carriage 9 is slidingly engaged on the column 35. This head is connected to the end of the rod of a jack 42 fixed on the platform of the carriage. The centering head 41 includes openings which can be engaged, by moving the head 41 in the vertical direction, on fuel assembly positioning studs projecting under the lower plate 6 of the upper internals 4. The lower plate 6 of the upper internals 4 actually constitutes the upper plate of the core of the reactor which bears on the upper parts of the fuel assemblies of the core and which includes centering and positioning studs intended to engage in openings of the upper adaptors of the fuel assemblies. When the upper internals 4 are in position on their storage stand, as represented in FIG. 1, the centering studs of the upper plate of the core 6 project at the bottom of the internals, above the bottom 2 of the cavity. The support carriage 9 may be positioned under the upper internals in a position such that the inspection rod cluster 10 is substantially in line with a guide tube in which it is desired to carry out checks. The positioning of the support carriage 9 is carried out using a video camera 43 which makes it possible to supply an image of the bottom 2 of the cavity on which are drawn positioning references in the form of a grid corresponding to the position of the guide tubes of the upper internals on their inspection stand. It is thus possible to stop the support carriage, during its movements under the upper internals, at a location such that the inspection rod cluster 10 is in line with the guide tube in which it is desired to carry out the check. The precise positioning of the support carriage 9 and of the inspection rod cluster 10 under the upper internals of the reactor is completed by engaging the openings of the centering head 41 on guide studs of the core upper plate, such that the position of the carriage 9 is perfectly fixed with respect to the upper internals. A video camera 44 makes it possible to verify that the mast for gripping the inspection rod cluster 10 which is introduced into the guide tube from the upper level of the cavity penetrates correctly into the upper part 10a of the inspection rod cluster 10 constituting a spider assembly similar to the spider assembly of a control rod cluster. The mast for gripping the inspection rod cluster 10 may consist of a rod such as an extender of a control rod cluster, including standard means of assembly with the spider assembly 10a. FIGS. 6 and 7 show a first embodiment of the inspection rod cluster 10 according to the invention. The inspection rod cluster 10 includes a body 45 of tubular shape, one end 45a of which is internally machined in an assembly profile of conventional type to constitute the spider assembly 10a similar to the spider assembly of a rod for controlling the reactivity of the core of the nuclear reactor. The internal profile of the part 45a of the cylindrical body 45 makes it possible to assemble and remotely fasten the end part of a control rod or extender to the inspection rod cluster 10. Four arms 46 are fixed on the outer cylindrical surface of the cylindrical body 45, radially of the cylindrical body 45 and substantially at 90.degree. to one another around its axis. A remote measurement probe 47 is mounted at the end of each of the arms 46, in an arrangement parallel to the axis of the cylindrical body 45. The cylindrical probes 47 are mounted for rotation about their axis parallel to the axis of the body 45 or include only a part which can be rotated about their axis. The set of cables 12 for powering the probes and collecting the measurement signals is engaged axially in the bore of body 45. The inspection rod cluster 10 furthermore includes radially directed arms 46 used as supports for the measurement probes 47, two pairs of radially directed arms 48, longer than the arms 46, at the ends of which are fixed cylindrical bars 49 constituting means for guiding the inspection rod cluster 10 during its movements inside a guide tube for the upper internals. The cylindrical bars 49 have an external diameter identical to the diameter of the absorber rods of a rod cluster for controlling the reactivity of the core of the reactor. As can be seen in FIG. 6, the radially directed arms 48 constitute two sets of two arms 48a and 48b which are arranged and fixed at each of the ends of the body 45, in extension of one another and substantially along a bisector plane of one of the dihedra formed by the support arms 46 of the measurement probes. The length of the cylindrical body 45 of the inspection rod cluster 10 and of the guide bars 49 is greater than the axial length of the space separating two successive panels 15 of a guide tube, so that, during the movements of the inspection rod cluster 10 inside the guide tube, the guide bars 49 are always engaged with at least two successive guide panels. In this way, the inspection rod cluster always remains perfectly centered and guided inside the guide tube. FIG. 8 shows, in more detail, the central part of the inspection rod cluster 10, in a region including the radially directed arms 46 constituting the supports for the probes 47. For greater clarity, only one arm 46 and one probe 47 have been shown in FIG. 8. According to a preferred embodiment, the probe 47 constituting a remote measurement sensor is in the form of a ladar making it possible to measure very small distances which may be much smaller than one millimeter, with very high accuracy. The method of remote optical measurement between a target and a given point, by ladar, consists in sending radiation having periodically variable wavelength towards the target, from a monomode coherent light source supplied with a signal of variable power, placed at the reference point, collecting the radiation backscattered by the target, reinjecting it into the cavity of the light source, and collecting the interference between the backscattered radiation and the radiation output by the source on a photodetector placed at the rear of the source. The interference, whose frequency is proportional to the delay of the backscattered wave, is representative of the distance between the source and the target. In the case of dimensional inspection of the bore of a guide element, this method can be employed by using a probe 47 as represented in FIG. 8, connected to an electronic supply and processing module 63. The probe 47 includes, inside a tubular casing, a diode laser 50 constituting the coherent light source, connected by conductors 51 to the electronic supply and processing module 63 located in the body 45 of the inspection rod cluster, and an optical mirror 52 fixed on a support 53 mounted movably in rotation about an axis parallel to the axis of the tubular support 45 constituting the axis of the probe 47. The rotary support 53 is connected via a flexible cable 54 to a drive gear 55 engaging with a gear 56 fixed on the output shaft of a reducing gear 57. An encoder 58 is combined with the reducing gear 57, so as to provide very accurate indications on the angular position of the support 53 and of the mirror 52 reflecting the radiation towards a region of the internal bore of the guide means, which can thus be determined accurately, at each instant during the measurements. The reducing gear 57 and the encoder 58 are connected to a cable 59 including conductors making it possible to power the reducing gear 57 and return the information from the encoder 58. The electronic module 63 is connected to a cable 60 including conductors making it possible to supply the module with electric current and return the information from the probe 47 coming from a photodetector combined with this probe. The cables 59 and 60 pass inside one and the same sheath to constitute the general power and measurement collection cable 12. During the measurements inside the bore of a guide element of a guide tube, the mirror 52 of the probe is rotated inside the casing of the probe 47, by means of the flexible cable 54 and the reducing gear 57. The diode laser 50 is powered by the electronic module 63, so as to direct radiation of periodically variable wavelength toward the mirror. The casing of the probe 47 includes a window 61, facing the mirror 52 over the entire periphery of the probe. It is thus possible to scan the bore of the guide element into which the probe 47 is introduced over its entire periphery, so as to carry out accurate dimensional inspection of this bore, using the ladar measurement of the distance between the light radiation source and the wall of the bore, making it possible to obtain a measurement of the variations in the distance between the wall of the bore and the axis of the probe, during the rotation of the probe. The measurement signals are processed by the electronic module 63 and sent via the cable 60 to a display and/or recording device located above the level of the cavity of the reactor. It should be noted that, in the case of using a probe 47 as described, only a part of the probe constituted by the mirror is rotationally mounted on the support of the checking device. Instead of a probe using the principle of ladar, it is possible to use a probe of another type, for example a probe consisting of an ultrasonic transducer or an eddy current sensor. In certain cases, it is possible to turn the entire probe about its axis instead of rotating only a part of this probe in order to scan the internal periphery of the bore to be checked. The term "rotationally mounted probe" mentioned above covers both the case of a probe mounted rotationally in its entirety and the case of a probe including an element which can be rotated in order to carry out the scanning. As can be seen in FIG. 8, the inspection rod cluster 10 furthermore includes a retractable stop 62 making it possible to stop the inspection rod cluster 10 in position for checking a guide element, during its movement in the axial direction inside a guide tube. In its extracted position, the stop 62 projects with respect to the outer surface of the body 45 whose outer diameter is slightly less than the diameter of the central free space of the guide panels and of the continuous guide means of a guide tube. During the movements of the inspection rod cluster 10 inside a guide tube, the stop 62 may successively bear on each of the guide panels, so as to stop the inspection rod cluster 10 in position for checking the guide openings of the panel. After the guide openings of a guide panel have been checked, the stop 62 is retracted by remote control, so as to make this stop pass through the central free space of the panel which has just been checked. The retractable stop is then released so as to return to its projecting position and stop the inspection rod cluster at the succeeding guide panel. It is thus possible to check all the guide panels of the discontinuous guide part of the guide tube step by step. In the continuous guide part of the guide tube, the checking is carried out by holding the stop 62 in its retracted position. It is clear that the retractable stop 62 may be replaced by a detector such as an inductive or eddy current sensor or by a microcontactor making it possible either to accurately detect the passage of the measurement probes at the level of the regions to be checked or to automatically stop the inspection rod cluster at each of the measurement regions. FIG. 9 represents a guide panel 15 including four internal guide openings 64 arranged at 90.degree. with respect to one another around the axis of the guide tube, which can be checked simultaneously by using the inspection rod cluster as represented in FIGS. 6 and 7. When the inspection rod cluster 10 is moved axially inside a guide tube including guide panels such as the panel 15, the probes 47 of the inspection rod cluster 10 simultaneously pass through all four guide openings 64 of the guide panel. The guide bars 49 are introduced into two external openings 65 of the guide panel, so as to accurately position the measurement probes 47 in the internal openings 64. The checking of the internal openings such as 64 of the guide panels and of the internal bores of the guide sleeves of the continuous guide part of the guide tube as represented in FIG. 4 is of essential importance, and, in some cases, may be sufficient. FIGS. 9A and 9B represent the elements of an inspection rod cluster of the type described hereinabove with reference to FIGS. 6, 7 and 8, making it possible to calibrate the probe, fitted accurately in the guide elements of the panel 15 and carry out reference measurements on the surfaces of the guide panel which are not subjected to wear in service. A spring 78 is fixed on the cylindrical body 45 of the inspection rod cluster so as to bear on a part 23' of the internal surface of the bore 17 of the guide panel 15 in order to accurately position the probe 47 in the guide opening 64 of the guide panel. The spring 78 includes a central part 78a tangent to the reference part 23' of the guide panel, extended in the direction of the arm 46 of the probe 47 so as to provide a reference face for the measurement probe 47 exactly in the plane of the part 23' of the internal bore of the guide panel 1. In addition, the probe 47 defines a calibration surface 61' pointing inwards, i.e. away from the guide opening 64, at the port 61 of the probe 47. On each revolution of the mirror 52, the calibration surface 61' is scanned by the laser beam, so that a measurement relating to a fixed element can be carried out in order to calibrate the probe. In addition, the faces 24 and 25 of the slit 22 of the guide panel 15 and the end faces 23' of the slit located by the position of the part 78a of the spring 78 make it possible to verify the measurements, because these faces 23', 24 and 25 undergo no wear in the reactor when in use and thus constitute reference surfaces. As can be seen in FIGS. 10 and 11, it is also possible to use an inspection rod cluster making it possible to check all the openings of the guide panels and all the bores of the sleeves and of the tubes of the continuous guide region, by successive passages of the inspection rod cluster through the guide tube, separated by a rotation of the cluster about its axis. As can be seen in FIG. 10, the inspection rod cluster 70 includes a tubular support 66 and eight arms directed radially with respect to the tubular support 66, and having outer end of which carry either a measurement probe 72 or a guide bar 73. The arm 67, which is shorter, carries a probe 72a which can be placed in the checking position inside an internal opening 74 of a guide panel 15, as represented in FIG. 11. The longer arms carry, at their external end opposite the support 66, a measurement probe 72, as regards the arms 68b, 68d and 68e, and a guide bar 73 as regards the arms 68a and 68c. The arm 69, which is slightly shorter than the arms 68a, . . . , 68e, carries a measurement probe 72b. Finally, the arm 71 whose length is intermediate between the length of the arm 67 and the length of the arm 69 carries a measurement probe 72c. As can be seen in FIG. 11, when the inspection rod cluster 70 is in position inside a guide tube, in the discontinuous part of this guide tube, the probe 72a can check an internal opening 74 of the guide panel 15, it being possible for the three probes 72 to check the three external openings 75 of the guide panel, the probe 72b can check one opening 76 and the probe 72c one opening 77. The guide bars 73 are engaged in two external openings 75. The inspection rod cluster 70 therefore makes it possible to simultaneously check six openings (or six bores in the continuous part of the guide tube) situated at different distances from the axis of the guide tube. By turning the inspection rod cluster 70 through 90.degree. around the axis of the support 66, between two passages of the cluster inside the guide tube along its entire length, six new series of openings of the guide panels (or six new bores of the continuous guide part of the guide tube) are checked, because the arrangement of the openings of the guide panels is symmetrical with respect to two diameters of the guide panel extending at an angle of 90.degree. from each other. It is possible to check all the openings of the guide panels (or all the openings of the continuous part) of a guide tube in four passages separated by a 90.degree. rotation of the inspection rod cluster about its axis. The rotation of the inspection rod cluster may be carried out on the support carriage 9 in line with the guide tube which is being checked. An operation of checking a guide tube for the upper internals 4 of a nuclear reactor in position on their inspection stand 3 in the cavity of the reactor will now be described. The bearing carriage 9 equipped with an inspection rod cluster of a type determined as a function of the checking to be carried out is lowered onto the bottom 2 of the cavity 1. The inspection rod cluster may, for example, be of the type represented in FIGS. 6 and 7 or of the type represented in FIG. 10. The probes and the support carriage 9 are connected to a control and command station situated above the upper level of the cavity, by the set of cables 12. The carriage is moved over the bottom of the cavity in a controlled manner, using the video camera 43 which makes it possible to visualize a grid drawn on the bottom of the cavity. The carriage is stopped in a position such that the inspection rod cluster 10 is aligned with a predetermined guide tube 8'. The jack 42 is controlled so as to engage the sentencing head 41 on studs of the upper core plate 6 constituting the lower part of the internals. The bearing carriage 9 and the inspection rod cluster 10 are thus positioned and held in position. A mast or a command rod 11 is introduced into the upper part 8'a of the guide tube 8', from the bridge situated at the upper level of the cavity 1 of the reactor. The mast or command rod 11 is lowered into the central part of the guide tube, so as to project below the upper core plate 6 to engage inside the spider assembly 10a of the inspection rod cluster 10. By simply pushing on the mast or command rod, the inspection rod cluster 10 is fastened to the mast 11. The mast 11 is moved in the vertical direction along the axis of the guide tube 8', such that the lower part of the inspection rod cluster 10 engages in the guide tube 8'. The inspection probes are powered and rotated. The continuous part of the guide tube is checked and each of the guide panels of the discontinuous guide part of the guide tube is then checked in succession. The measurements made by the probes and the angular position of the probe during the measurements are transmitted to the control and command station above the cavity of the reactor, via cables connected to the electronic module 63 and to the probes 47. After the guide tube 8' has been scanned over its entire length by moving the inspection rod cluster 10 upwardly in the axial direction, the inspection rod cluster 10 is again lowered to its starting position on the support 36 of the carriage 9, the cluster 10 still being fixed to the mast 11. In the case of a check carried out by using an inspection rod cluster as represented in FIGS. 6 and 7, the mast is separated from the inspection rod cluster and the carriage 9 and the inspection rod cluster are moved to a new guide tube to be checked, after having separated the centering head 41 from the positioning studs of the upper core plate 6. In the case of an inspection rod cluster such as the inspection rod cluster 70 represented in FIG. 10, the cluster 70 is turned through a quarter turn on the carriage before carrying out a second movement along the entire length of the guide tube. As indicated hereinabove, the checking of all the openings and bores of the guide tube is carried out during four successive displacements of the inspection rod cluster 70 over the entire length of the guide tube, the inspection rod cluster being turned through 90.degree. between two successive movements inside the guide tube. During the movement of the inspection rod cluster downwards inside the guide tube, for returning it to the carriage 9, the pusher-puller 38 continuously tensions the set of cables 12, such that any blockage during the downward movement of the inspection rod cluster is avoided. The device according to the invention therefore makes it possible to very accurately check the openings and bores of the guide tubes of the upper internals of a pressurized water nuclear reactor by using a device which is simple, rigid and perfectly guided inside the guide tube. Furthermore, the check which is carried out from the lower part of the internals does not require any dismantling for passage of the checking means. The inspection rod clusters including measurement probes and guide bars may have different arrangements from those which have been described, and there may be different numbers of them. Although probes allowing remote measurements by the ladar method have significant advantages as regards the accuracy of the measurements, it is possible to use probes functioning on another principle, such as ultrasonic or eddy current probes, to carry out the remote measurements. The invention applies generally to the checking of the guide elements of the upper internals of a nuclear reactor.
	description	The present application hereby claims priority under 35 U.S.C. §119 on German patent application numbers DE 10 2006 004 604.8 filed Feb. 1, 2006, DE 10 2006 004 976.4 filed Feb. 1, 2006, and DE 10 2006 037 281.6 filed Aug. 9, 2006, the entire contents of each of which is hereby incorporated herein by reference. Embodiments of the invention generally relate to an X-ray optical transmission grating of a focus-detector arrangement of an X-ray apparatus for generating projective or tomographic phase contrast recordings of a subject. For example, they may relate to one having a multiplicity of grating bars and grating gaps arranged periodically on at least one surface of at least one wafer. Transmission gratings for generating projective or tomographic phase contrast recordings of a subject are widely known. By way of example, reference is made to the European patent application EP 1 447 046 Al and the German patent applications (not yet published that the priority date of the present application) with the file references 10 2006 017 290.6, 10 2006 015 358.8, 10 2006 017 291.4, 10 2006 015 356.1 and 10 2006 015 355.3. For imaging by ionizing rays, in particular X-rays, principally two effects can be observed which occur when the radiation passes through matter, namely the absorption and the phase shift of the radiation passing through a subject. It is known that in many cases, the phase shift when a ray passes through a subject depends much more strongly on small differences in the thickness and composition of the penetrated matter than the absorption effects do. Structures of a subject, it particular the soft structures of a patient, can thereby be recognized better. For such phase contrast radiography or phase contrast tomography, the phase shift due to the object must be evaluated. Here, similarly as conventional absorption contrast X-radiography or absorption contrast X-ray tomography, both projective images of the phase shift can be compiled or even tomographic representations of the phase shift can be calculated from a multiplicity of projective images. The phase of an X-ray wave cannot be determined directly, rather only by interference with a reference wave. The phase shifts relative to reference waves or neighboring rays can be measured by using interferometric gratings. In respect of interferometric measurement methods, reference is made to the documents cited above. In these methods, coherent X-radiation is passed through a subject, then delivered through a phase grating with a period adapted to the wavelengths of the radiation so as to create an interference pattern, which is phase shifted depends on the phase shift occurring in the object. This interference pattern is measured by a subsequent analysis-detector arrangement, so that the phase shift can be determined with position resolution. The following should essentially be pointed out in this regard: The emission of X-ray photons from laboratory X-ray sources as well as by conventional synchrotron radiation sources of the first to third generations is subject to stochastic processes. The emitted X-radiation therefore has no spatial coherence per se. In phase contrast radiography and tomography or any interference experiment, however, the radiation of X-ray sources behaves as coherent radiation when the observation angle at which the source appears to the observer or the object, the grating or the detector, is sufficiently small. The so-called spatial coherence length Lc can be provided as a measure of the spatial or transverse coherence of an extended X-ray source L c = λ ⁢ a s . ( 1 ) Here, λ is the wavelength, s is the transverse source size and a is the source-observation point distance. Many authors also refer to half the above-defined value as the spatial coherence length. The exact value is incidental; what is important is that the coherence length Lc is large compared to the (transverse) dimension of the spatial region from which rays are intended to interfere with one another. In the context of the patent application, the term coherent radiation is intended to mean radiation which leads to the formation of an interference pattern under the given geometries and given distances of the X-ray optical gratings. It is self evident that the spatial coherence and therefore the spatial coherence length is always determined by the trio of quantities: wavelength, source size and observation distance. With a view to compact formulation, this fact has been abbreviated to terms such as “coherent X-radiation”, “coherent X-radiation source” or “point source for generating coherent X-radiation”. The basis for these abbreviations is that the wavelength or the energy E of the X-radiation in the applications discussed here is limited by the desired penetratability of the subject on the one hand and the spectrum available in laboratory X-ray sources on the other hand. The distance a between the source and the observation point is also subject to certain restrictions in laboratory equipment for nondestructive material testing or medical diagnosis. This usually leaves only the source size s as a single degree of freedom, even though the relationships between source size and tube power set narrow limits here. The requirement for a small or point-like radiation source means that the available intensity is also relatively low. In order to increase the intensity, it has therefore also been proposed to use an X-ray source with a relatively large-area focus and to place an X-ray optical absorption grating, a so-called source grating, in the beam path between the focus and the subject. The large-area focus makes it possible to use larger and therefore more powerful X-ray sources. The narrow slits or gaps of the source grating ensure that all the rays, which have to emerge from the same slit, comply with the requisite spatial coherence. The slit width must satisfy the size requirement given by Equation (1) for the transverse source size s. Correct superposition, at least in terms of intensity, of the maxima and minima of the standing wave field is possible between the photons from slit to slit of the source grating with suitable tuning of the source grating period g0 and the interference pattern period g2 as well as the distance 1 between the source grating G0 and the phase grating G1 and the distance d between the phase grating G1 and the interference pattern, according to:g0/g2=1/d. (2) In the abbreviated formulation of the patent application, the term “quasi-coherent radiation” or “quasi-coherent radiation source” is used in this context. The temporal or longitudinal coherence of the radiation is associated with the monochromaticity of the X-radiation or of the X-radiation source. The X-radiation of intense characteristic lines usually has a sufficient monochromaticity or temporal coherence length for the applications discussed here. Upstream monochromators or selection of the resonant energy via the bar height of the phase grating can also filter out a sufficiently narrow spectral range from a Bremsstrahlung spectrum or synchrotron spectrum, and thus satisfy the requirements for the temporal coherence length in the present arrangements. A problem with these X-ray optical transmission gratings is that the production of such gratings, which require a large aspect ratio (=ratio of the bar height to width of the grating gap), is very elaborate. Furthermore, the precision of the production deteriorates significantly with an increasing aspect ratio. In at least one embodiment of the invention, an X-ray optical transmission grating is provided which allows simpler production. The Inventors, in at least one embodiment, have discovered that without compromising the effect of an X-ray optical transmission grating, it is possible to form this grating from a multiplicity of sub-gratings. A particular X-ray optical grating with a particular function can thus be replaced by a plurality of sub-gratings arranged in direct succession, the sum of the sub-gratings fulfilling the function of the original one grating. In this way, it is possible to reduce the grating bar height according to the number of sub-gratings used, the width of the grating gaps remaining the same, so that the aspect ratio of bar height to width of the grating gaps is drastically reduced. The inventors, in at least one embodiment, therefore propose that an X-ray optical transmission grating of a focus-detector arrangement of an X-ray apparatus for generating projective or tomographic phase contrast recordings of a subject, having a multiplicity of grating bars and grating gaps arranged periodically on at least one surface of at least one wafer, should be refined so that the X-ray optical transmission grating is composed of at least two sub-gratings arranged in direct succession in the beam direction. Advantageously, for example, the transmission grating may be configured so that the grating bars and grating gaps of two sub-gratings are arranged on the two sides of one wafer. A wafer is thus used whose front and rear side is up both designed as gratings. At least with respect to these two sub-gratings, this also obviates the problem of aligning the grating bars and grating gaps during installation in the X-ray apparatus. They are already arranged correspondingly during the production process, and cannot become displaced relative to one another. In order to align the gratings which are applied on the front and rear sides of a wafer, it is conceivable to employ the grating properties of the first grating when the structures for the second grating are being written by lithography. The gratings are partially transparent to X-radiation. With a suitable X-ray energy, transmission takes place essentially only in the grating gaps. The X-radiation passing through could be used to expose a photoresist applied on the rear side. Semiconductor wafers (Si, Ge, GaAs, InP, . . . ) are also transparent to infrared radiation. This infrared radiation could also be employed for exposing the structures on the rear side when using a suitable IR-sensitive photoresist. Thin metallic layers and wafers transparent to ultraviolet light on the far side of a plasma frequency. This could similarly be employed for the lithography on the rear side. Many metals as well as other materials (Al, Si, . . . ) are transparent to neutrons. Neutron-sensitive resists may therefore likewise be used for lithography on the rear side. As an alternative or in addition, however, it is also possible for at least two sub-gratings to be formed by different wafers. It is also proposed that a filler material with a higher, preferably substantially higher, linear attenuation coefficient than the wafer material in the relevant energy range should be arranged in the grating gaps of at least one, precisely one or all the sub-gratings, in which case the filler material may comprise only a part of the height of the grating bars or flush-fill the grating gaps. The Inventors also propose, in at least one embodiment, to align the sub-gratings mutually parallel in respect of their grating bars and grating gaps and are so that each ray passes either only through grating bars or only through grating gaps when crossing the sub-gratings. If the transmission grating is used in a beam geometry which is designed to be fan-shaped or conical, then the sub-gratings arranged successively in the beam direction may comprise different grating periods, in which case the period increases from at least one sub-grating to a subsequent sub-grating, and the sub-gratings are arranged mutually aligned, so that the rays of the ray beam pass either only through grating gaps or only through grating bars. In the transmission gratings according to at least one embodiment of the invention, the sub-gratings may furthermore be designed so that they are flat or curved in at least one plane around the radiation origin of the X-radiation passing through. As an alternative or supplementarily, the sub-gratings may include grating bars and grating gaps which are aligned in the beam direction. If the transmission gratings according to at least one embodiment of the invention are being used not as absorption gratings but as phase gratings, then it may be advantageous that, for the sum of the sub-gratings, the height of the filler material in the gaps is dimensioned so that the X-radiation with the energy used for measuring the phase shift generates a phase shift of λ/2, and after the entire grating, at least in relation to the energy used for measuring the phase shift, the attenuation of the X-radiation is the same after passing through the bars and when passing through the filler material. When phase gratings in grating-based phase contrast radiography are replaced by a plurality of sub-gratings, then it may be advantageous that, for the sum of the sub-gratings, the height of the filler material in the gaps is dimensioned so that between passage through the grating gaps/filler material and passage through the grating bars, (i) the X-radiation experiences a phase shift of π or λ/2 and (ii) the intensity or transmission is the same for the photon energy caused to interfere in the interference pattern. When analyzer gratings in grating-based phase contrast radiography are replaced by a plurality of sub-gratings, then it may be advantageous that, for the sum of the sub-gratings, the height of the filler material in the gaps is dimensioned so that between passage through the grating gaps/filler material and passage through the grating bars, the intensity or transmission is the same for the photon energy caused to interfere in the interference pattern. As an alternative, the sub-gratings could also be designed so that, for each of the sub-gratings individually, the height of the filler material in the gaps is dimensioned so that the X-radiation with the energy used for measuring the phase shift generates a phase shift in the X-radiation of λ/2 and after each sub-grating, at least in relation to the energy used for measuring the phase shift, the attenuation of the X-radiation is the same when passing through the bars and when passing through the filler material. The effect achieved in both variants of a phase grating as mentioned above is that, owing to the equal intensity of the rays which pass through the bars and the rays phase-shifted by π relative thereto, which pass through the gaps and the filler material partially contained there, an optimally image formed interference pattern is generated with maximal intensity modulation and the least possible offset. The image quality of phase contrast images and amplitude contrast depends on how accurately the phase and amplitude can be determined in each pixel. The ratio of the modulation to the offset is crucial in this regard (modulation transfer function of all components of the ray path). The intensity of the direct, undiffracted zeroth order ray also contributes to the offset and therefore to a quality reduction of the image. The aim must therefore be to reduce this component. With respect to the arrangement of the sub-gratings of a transmission grating, according to the invention at least two of the sub-gratings may be aligned in the same direction or counter to one another with respect to the alignment of their grating bars; for sub-gratings without flush filler material in the grating gaps, it may be particularly favorable to place them only with their flat sides against one another so that no damage of the grating bars is possible by engaging in one another. In respect of simpler alignment of the sub-gratings of a transmission grating, the Inventors propose, in at least one embodiment, that at least two sub-gratings arranged on separate wafers should be provided with markings, by which mutual alignment is facilitated. At least one embodiment of the invention also relates to a focus-detector arrangement of an X-ray apparatus for generating projective or tomographic phase contrast recordings of a subject, which includes at least one of the X-ray optical gratings described above as a transmission grating. At least one embodiment of the invention also relates to an X-ray system for generating projective phase contrast recordings, an X-ray C-arc system for generating projective or tomographic phase contrast recordings and an X-ray computer tomography system for generating tomographic phase contrast recordings, respectively equipped with an X-ray optical grating according to at least one embodiment of the invention. It will be understood that if an element or layer is referred to as being “on”, “against”, “connected to”, or “coupled to” another element or layer, then it can be directly on, against, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to”, or “directly coupled to” another element or layer, then there are no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term “and/or”, includes any and all combinations of one or more of the associated listed items. 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. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present 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. It will be further understood that the terms “includes” and/or “including”, when used in this specification, 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. In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner. Referencing the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, example embodiments of the present patent application are hereafter described. For better understanding, the structure of a focus-detector arrangement with X-ray optical gratings according to an embodiment of the invention, which allow phase contrast measurement, will be presented at first. In this regard it should essentially be noted that the figures are not shown true to scale, rather they are intended to highlight the basic structure and the described effects. The transverse axis is expanded relative to the longitudinal axis (=optical axis). The angles are therefore represented with an exaggerated size. For didactic reasons, the interference pattern and the analyzer grating in particular have been shown somewhat spatially separated from one another, even though it is precisely the object of the method to position the analyzer grating at the maximum of the interference pattern, i.e. at the Talbot distance. The dimensions d and r2 therefore refer both to the interference pattern and to the analyzer grating. FIG. 1 shows a schematic 3D representation of a focus-detector system of an X-ray computer tomography system with a sample P lying in the beam path as a subject. The focus F1 on the detector D1 are arranged on a gantry (not represented here) and move circularly around the system axis shown by dots and dashes. If a linear movement of the patient or sample P in the system axis direction is additionally carried out during the rotation of the focus-detector system, then this leads to spirally shaped scanning of the patient or sample P which is known per se. Three X-ray optical gratings G0, G1 and G2 are arranged in the beam path of the focus-detector system, the first grating G0, which is also referred to as a source grating, being applied in the immediate vicinity of the focus F1 and having the X-radiation pass through it. In the propagation direction of the X-radiation, this is followed by the actual subject P. Before the detector D1 lying on the other side of the system axis, there first follows the second grating G1 referred to as a phase grating. This is followed in the radiation direction by the third grating G2, referred to as an analyzer grating, which is advantageously arranged immediately in front of the detector D1. The detector D1 is a position resolving detector. During the scan, the connecting lines between the focus F1 and the individual detector elements respectively represent an X-ray arranged in space, the intensity variation of which is measured by the respective detector element. The grating lines should preferably be oriented perpendicularly to the optical axis, i.e. perpendicularly to the midline between the focus and detector midpoints, and the grating lines of the individual gratings should extend mutually parallel. This applies strictly for plane gratings and at least approximately also for curved gratings. Certain geometrical conditions should be complied with for phase contrast measurement. These are represented in more detail in FIG. 2. This figure shows a focus-detector system according to the invention with a grating set G0 to G2. The focus F1 lies before the first grating G0. The first grating G0 has a grating line period g0 and a grating bar height h0. The gratings G1 and G2 are correspondingly also provided with a height h1 and h2, respectively, and a period g1 and g2, respectively. For the function of the method according to an embodiment of the invention, it is necessary for the distance 1 between the gratings G0 and G1 and the distance d between the gratings G1 and G2 to be in a particular mutual ratio. This ratio has been described above in Equation (2). The distance of the detector D1 with its detector elements E1 to En from the last grating G2 is not essential. The height h1 of the bars of the phase grating should be selected so that a phase shift by one half wavelength compared to the gaps is obtained according to the relevant energy of the X-radiation. It is also essential is that the height h2 of the analyzer grating is sufficient in order to generate effective absorption differences between the bars through which the X-radiation passes and the substantially free positions of the grating, in order to obtain a corresponding interference pattern/standing wave field on the rear side. It should be pointed out that in this embodiment of a focus-detector arrangement, a point-like focus may be replaced by an extended focus if the extended focus is combined with a source grating as described in the introduction, so that the necessary coherence condition for the described phase contrast measurement is fulfilled. In the X-ray optical gratings as presented above, the problem usually arises that they must have grating bars whose height is large relative to the spacing of the bars. The known embodiment of such an example grating is shown in FIG. 3. This grating comprises bars S and gaps L between them, which are impressed into the surface of a wafer, for example by etching processes. According to an embodiment of the invention, this production problem is circumvented by using a combination of a plurality of sub-gratings arranged in direct succession, instead of a single grating with a particular function, these being assembled so that they correspond in their overall effect to the single first grating. A first example of this is represented in FIG. 4. Here, two sub-gratings are generated on the two sides of a common wafer, each individual structure being substantially simpler to produce owing to the now lower depth of the grating gaps. Moreover, the problem of accurate mutual alignment is also resolved here since a common wafer is used. Another variant of an embodiment of an X-ray optical grating according to the invention, by combining a plurality of sub-gratings—here four sub-gratings—is shown in FIG. 5. Here, there are four identical and equally aligned sub-gratings Gx1 to Gx4—the index “x” stands for the index of one of the gratings G0 to G2 of the focus-detector arrangement in FIGS. 1 and 2—with only ¼ of the grating bar height of the grating Gx otherwise to be replaced. With respect to simpler alignment of the sub-gratings, the Inventors propose, in an embodiment, that at least two sub-gratings arranged on separate wafers should be provided with markings, by which mutual alignment is facilitated Fine adjustment of the phase grating and the analyzer grating could also be carried out piecewise. A first phase grating and a first analyzer grating are used. Since the phase grating is too thin for an optimal layout, the resulting standing wave field is only poorly pronounced, but nevertheless present. The grating can thus be aligned with the aid of the standing wave field: 1. Alignment of the grating position along the optical axis of the layout: The periods of the phase grating and of the analyzer grating are interlinked, in the case of a cone beam geometry by: g 2 = 1 2 ⁢ r 1 + d r 1 ⁢ g 1 where d is the distance between the gratings, r1 is the distance between the source and the first grating, g2 is the period of the analyzer grating G2, which is equal to the transverse period of the standing wave field, g1 is the period of the phase grating G1. If this condition is not fulfilled then an interference pattern is not obtained on a detector placed behind the analyzer grating, but instead a so-called division moiré pattern, consisting of shadow lines which are parallel to the grating bars. This is the case, for example, whenever the phase grating is displaced along the optical axis relative to the intended position. The gratings may then be aligned in the position along the beam axis by displacing them so that this pattern vanishes. 2. Parallel Alignment of the Grating Lines: If the grating lines of the analyzer grating are not parallel to the standing wave field (and therefore to the grating lines of the phase grating) then an interference pattern is not obtained on a detector placed behind the analyzer grating, but instead a so-called rotation moiré pattern consisting of shadow lines which are perpendicular to the grating bars. The grating lines may then be aligned parallel by rotating the phase grating so that this pattern vanishes. In practice, a superposition of a rotation and a division moiré pattern can take place. This does not change anything for the principle of aligning the gratings in respect of angle and distance. The grating lines may firstly be aligned parallel by rotating the grating so that a pure division moiré is observed on the detector, i.e. a moiré pattern with shadow lines which are parallel to the grating lines. The spacing of the gratings is then corrected as described above. As an alternative, the grating position may firstly be aligned along the optical axis by displacing the grating until a pure rotation moiré is observed on the detector, i.e. a moiré pattern with shadow lines which are perpendicular to the grating lines. The rotation of the gratings is then corrected as described above. If a further incorrectly aligned grating is added to the correctly aligned gratings, the standing wave field is perturbed. A moiré pattern is then created in the same way as described above. The added phase grating will be aligned in the same way as the first grating. Further gratings are added in the same way. It should be pointed out that it lies within the scope of the embodiments of the invention to configure the orientation of the individual sub-gratings arbitrarily, so long as the grating gaps and the grating bars are respectively arranged successively as seen in the beam direction. This applies for all variants of sub-grating combinations in this document. FIG. 6 shows another variant of a sub-grating combination according to the invention with two different double gratings Gx1, Gx2 and Gx3, Gx4, the lower of the double gratings Gx3, Gx4 additionally comprising a filler material in the gaps L of one grating, which ensures uniform absorption of the X-radiation over the entire grating, the rays which pass through neighboring gaps L and bars S experiencing a phase shift by π. Additionally, but not compulsorily, the lower double grating here is designed in respect of its bar heights so that the filler terminates flush with the grating bars. FIGS. 7 to 9 show alternative embodiments of FIGS. 5 to 6 with a flat sub-gratings, although in this case the alignment of the grating bars and grating gaps is adapted according to the radial alignment of the radiation. The grating of FIG. 7 is furthermore completely filled with filler material in the gaps so that it acts as an absorption grating, i.e. a source grating or analyzer grating. The gratings of FIGS. 8 and 9 are configured as phase gratings with uniform absorption over the entire grating surface, as described with reference to FIG. 6. Lastly, FIGS. 10 to 12 show embodiments corresponding to FIGS. 7 to 9, but in this case the sub-gratings are configured with a curvature around the radiation centre, i.e. the focus. Here again, the grating bars S are respectively aligned radially with the focus so that no shadowing of the individual rays occurs in the edge regions of the grating gaps when passing through the sub-gratings. In addition, platelets or films of small height, which prevent possible mutual damage of the grating structures, may be placed between all the sub-gratings presented here without departing from the scope of the invention. FIG. 13 represents a complete computer tomography system with focus-detector systems according to an embodiment of the invention for carrying out the method according to an embodiment of the invention, by way of example and also generically for other X-ray systems, in particular X-ray systems for generating projective phase contrast recordings and for C-arc equipment. This figure shows the computer tomography system 1 which comprises a first focus-detector system with an X-ray tube 2 and a detector 3 lying opposite, which are arranged on a gantry (not represented in detail) in a gantry housing 6. An X-ray optical grating system according to an embodiment of the invention with gratings composed of sub-gratings is arranged in the beam path of the first focus-detector system 2, 3 so that the patient 7, who lies on a patient support 8 displaceable along the system axis 9, can be displaced into the beam path of the first focus-detector system and scanned there. The computer tomography system is controlled by a computation and control unit 10 in which programs Prg1 to Prgn are stored in a memory 11, which carry out the method according to an embodiment of the invention as described above and reconstruct corresponding tomographic images from the measured ray-dependent phase shifts. Instead of a single focus-detector system, a second focus-detector system may optionally be arranged in the gantry housing. This is indicated in the representation by the X-ray tube 4 shown in dashes and the detector 5 represented in dashes. At least in one focus-detector system, there is a grating according to an embodiment of the invention in which the grating structure, which is required for the detection of phase contrast recordings, is generated in the grating medium by an ultrasound standing wave. Moreover, it should also be pointed out that the focus-detector systems as presented are not only capable of measuring phase shifts of the X-radiation, rather they are furthermore suitable for conventional measurement of the radiation absorption and the reconstruction of corresponding absorption recordings. Optionally, combined absorption and phase contrast recordings may even be generated. It is furthermore to be pointed out that the medical computer tomography systems presented in this patent application are merely intended to be an example representation of an alternative application of the invention. Embodiments of the invention may likewise be used in conjunction with systems for examining biological or inorganic samples, without departing from the scope of this application. In particular, embodiments of the invention are applicable to systems for material analysis. It is to be understood that the features of the invention as mentioned above may be used not only in the combination respectively indicated, but also in other combinations or in isolation, without departing from the scope of the present invention. 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.
062597590	abstract	An incore piping section maintenance system of a reactor comprises a maintenance system main body which is fixed to a maintenance target portion in a reactor pressure vessel or in the vicinity thereof to which a preventive-maintenance operation is executed, a support mechanism provided for the maintenance system main body so as to be movable in a reciprocal manner towards the maintenance target portion, a laser generator for generating a laser beam, a laser de-sensitization treatment apparatus which is rotatably supported around an axis of the support mechanism and which includes a laser irradiation section for irradiating the laser beam to the maintenance target portion, and an optical transmission element which guides the laser beam outputted from the laser generator to the laser de-sensitization treatment mechanism.
	claims	1. A device for artificially weathering or testing the lightfastness of samples comprising:a weathering chamber;an ultraviolet radiation device arranged in the weathering chamber and having at least one ultraviolet light emitting diode; andan ultraviolet light receiving diode, which is constructed on the same material basis as the ultraviolet light emitting diode and is arranged relative to the ultraviolet light emitting diode in such a way that a portion of the radiation emitted by the ultraviolet light emitting diode impinges on the ultraviolet receiving diode during the operation of the device. 2. The device as claimed in claim 1, further comprising:a plurality of classes of ultraviolet light emitting diodes having different emission bands; anda corresponding plurality of ultraviolet light receiving diodes, wherein each of the ultraviolet light receiving diodes is constructed on a same material basis as any ultraviolet light emitting diode in one class. 3. The device as claimed in claim 1, wherein the ultraviolet light emitting diode and the ultraviolet light receiving diode are arranged on a common carrier, in particular a circuit board. 4. The device as claimed in claim 1, wherein the ultraviolet light emitting diode and the ultraviolet receiving diode are oriented in the same way. 5. The device as claimed in claim 1, wherein the ultraviolet light emitting diode and the ultraviolet receiving diode are not oriented in the same way, in particular are tilted relative to one another. 6. The device as claimed in claim 1, wherein a coupling medium is arranged in the beam path of the portion impinging on the ultraviolet light receiving diode, said coupling medium directing the portion onto the ultraviolet light receiving diode. 7. The device as claimed in claim 6, wherein the coupling medium is a plate that is transmissive to ultraviolet radiation. 8. The device as claimed in claim 1, comprising at least one further ultraviolet light emitting diode, wherein a portion of the radiation emitted by the further ultraviolet light emitting diode impinges on the ultraviolet light receiving diode during the operation of the device. 9. The device as claimed in claim 8, wherein the further ultraviolet light emitting diode and the coupling medium are arranged relative to one another in such a way that, during the operation of the device, a portion of the radiation emitted by the further ultraviolet light emitting diode is directed onto the ultraviolet light receiving diode by the coupling medium. 10. The device as claimed in claim 6, wherein the further ultraviolet light emitting diode and the coupling medium are arranged relative to one another in such a way that, during the operation of the device, a portion of the radiation emitted by the further ultraviolet light emitting diode is directed onto the ultraviolet light receiving diode by the coupling medium. 11. An ultraviolet radiation device, comprisinga plurality of ultraviolet light emitting diodes, and an ultraviolet light receiving diode, which is constructed on the same material basis as the ultraviolet light emitting diodes and is arranged relative to the ultraviolet light emitting diodes in such a way that a portion of the radiation emitted by the ultraviolet light emitting diodes impinges on the ultraviolet receiving diode during the operation of the device. 12. A method for operating a device for artificially weathering or testing the lightfastness of samples, comprising:a. providing a weathering chamber;b. providing at least two ultraviolet semiconductor diodes on the same material basis;c. arranging a first of the two ultraviolet semiconductor diodes in the weathering chamber and operating the first ultraviolet semiconductor diode as a ultraviolet light emitting diode; andd. arranging a second of the two ultraviolet semiconductor diodes in the weathering chamber; ande. operating the second semiconductor diode as an ultraviolet light receiving diode, wherein the second ultraviolet semiconductor diode is arranged relative to the first ultraviolet semiconductor diode in such a way that a portion of the radiation emitted by the first ultraviolet semiconductor diode impinges on the second ultraviolet semiconductor diode during the operation of the device. 13. The method as claimed in claim 12, whereinin step b. a plurality of classes of ultraviolet light emitting diodes having different emission bands and a plurality of ultraviolet light receiving diodes are provided, whereineach of the ultraviolet light receiving diodes is constructed on the same material basis as an ultraviolet light emitting diode in one class. 14. The method as claimed in claim 13, wherein in step b. the plurality of classes of ultraviolet light emitting diodes having different emission bands are chosen in such a way that a specific spectral ultraviolet characteristic is approximated. 15. The method as claimed in claim 12, further comprising regulating the operation of the ultraviolet light emitting diode on the basis of an output signal of the ultraviolet light receiving diode. 16. The method as claimed in claim 12, further comprising regulating the operation of the ultraviolet light emitting diodes on the basis of output signals of the ultraviolet light receiving diodes.
	abstract	A method of forming a water resistant boundary on a fissile material for use in a water cooled nuclear reactor is described. The method comprises mixing a powdered fissile material selected from the group consisting of UN and U3Si2 with an additive selected from oxidation resistant materials having a melting or softening point lower than the sintering temperature of the fissile material, pressing the mixed fissile and additive materials into a pellet, sintering the pellet to a temperature greater than the melting point of the additive. Alternatively, if the melting point of the oxidation resistant particles is greater than the sintering temperature of UN or U3Si2, then the oxidation resistant particles can have a particle size distribution less than that of the UN or U3Si2.
	description	This application is a Continuation of PCT International Application No. PCT/JP2019/014810 filed on Apr. 3, 2019, which claims priority under 35 U.S.C § 119 (a) to Japanese Patent Application No. 2018-073484 filed on Apr. 5, 2018. The above application is hereby expressly incorporated by reference, in its entirety, into the present application. The present invention relates to an X-ray tube device. An X-ray tube device is a device that generates X-rays, and incorporates a bulb (so-called X-ray tube) that generates the X-rays. In the X-ray tube device, there are an example where a handle that protrudes to a test object side is provided in an X-ray movable stop (JP2016-047308A), an example where a protection cover is provided on a test object side of an X-ray generator (JP2011-030699A), and an example where a cover (cover unit) is provided around an X-ray source or the like (JP2014-079518A). There is an example where a guide unit that protrudes from an X-ray source to keep a distance between the X-ray source and a test object constant is provided (JP2014-110872A, corresponding to US2014/0133627A1). In addition, in a portable X-ray tube device in which an X-ray tube device is independently movable for round or the like, there is a case where a member for operation, gripping, or keeping an interval from a subject is provided in a front surface (a surface facing the subject) of a collimator. For example, PX-20HF plus manufactured by Kenko Tokina Corporation, or the like has a collimator that is rotatable about an irradiation direction of X-rays, and is provided with a handle (or a guide unit) that protrudes in the irradiation direction of the X-rays in a front surface of the collimator. IPF-21N manufactured by Canon Inc. is provided with a handle (or a guide unit) that protrudes in an irradiation direction of X-rays in a front surface of a housing having a substantially cube shape in which an X-ray tube and a collimator are integrated. In the X-ray tube device, there is a case where a guard unit that sets a distance between the X-ray tube device and the test object to be equal to or longer than a specific distance determined in advance is provided. However, in a case where the X-ray tube device is reduced in size, there is no space for providing the guard unit, and there is a problem in that the guard unit cannot be attached even where necessary. Accordingly, an object of the invention is to provide an X-ray tube device that allows a guard unit to be attached thereto even though the X-ray tube device is reduced in size. An X-ray tube device according to an aspect of the invention comprises a main body that incorporates a bulb, which generates X-rays, a collimator that is provided to protrude from the main body in an irradiation direction of the X-rays in a part of a first surface, which is a surface of the main body, and has an irradiation window for irradiating the X-rays with an adjusted irradiation range, and connectors that are provided for connecting a guard unit for keeping a distance from a test object, between the first surface of the main body and a second surface, which is a surface of the collimator where the irradiation window is provided. It is preferable that the connectors are provided in the collimator. It is preferable that the connectors have a shape in which a length in a direction perpendicular to the irradiation direction of the X-rays is longer than a length in a direction parallel to the irradiation direction of the X-rays. It is preferable that the X-ray tube device comprises the guard unit connected to the connectors. It is preferable that the guard unit comprises a first pillar portion, a second pillar portion, a third pillar portion, and a fourth pillar portion extending in the irradiation direction from the second surface of the collimator, a first beam portion that connects the first pillar portion and the fourth pillar portion on the test object side than the second surface, a second beam portion that connects the second pillar portion and the third pillar portion on the test object side than the second surface, a third beam portion that connects the first pillar portion and the second pillar portion on the first surface side than the second surface, and a fourth beam portion that connects the third pillar portion and the fourth pillar portion on the first surface side than the second surface. It is preferable that the guard unit has a shape in which an interval between the first pillar portion and the second pillar portion and an interval between the third pillar portion and the fourth pillar portion spread in the irradiation direction of the X-rays. It is preferable that the guard unit is configured such that the first pillar portion and the fourth pillar portion are parallel to each other, and the second pillar portion and the third pillar portion are parallel to each other. It is preferable that the guard unit has the connectors in the third beam portion and the fourth beam portion. It is preferable that, in a case where the main body has a rectangular parallelepiped shape, the first beam portion connects the first pillar portion and the fourth pillar portion in a transverse direction of the first surface, the second beam portion connects the second pillar portion and the third pillar portion in the transverse direction of the first surface, the third beam portion connects the first pillar portion and the second pillar portion in a longitudinal direction of the first surface, and the fourth beam portion connects the third pillar portion and the fourth pillar portion in the longitudinal direction of the first surface. It is preferable that, in a case where the main body has a rectangular parallelepiped shape, in comparison in a longitudinal direction of the first surface, the guard unit is longer than the collimator, and the guard unit is shorter than the main body. The X-ray tube device according to the aspect of the invention can provide a small X-ray tube to which the guard unit can be attached. As shown in FIGS. 1 and 2, an X-ray tube device 10 comprises a main body 11, a collimator 21, a gripping portion 31, a switch 41, and the like. The main body 11 incorporates a bulb 17 (see FIG. 3) that generates at least X-rays. In the embodiment, the main body 11 has a substantially rectangular parallelepiped shape. The substantially “rectangular parallelepiped shape” refers to that an appearance is formed by three sets of planes substantially parallel to each other, and the surfaces of the respective sets are substantially connected at 90 degrees. The substantially “rectangular parallelepiped shape” includes a case where connection portions of the surfaces of the respective sets are chamfered or the surfaces of the respective sets are connected with curved surfaces. Hereinafter, an irradiation direction L1 of the X-rays in the X-ray tube device 10 is referred to as a Z direction, a longitudinal direction of the main body 11 that is a direction substantially perpendicular to the Z direction is referred to as an X direction, and a transverse direction of the main body 11 that is a direction substantially perpendicular to the Z direction and the X direction is referred to as a Y direction. The irradiation direction L1 of the X-rays in which a test object (not shown) is disposed is a positive direction of the Z direction, a side on which the gripping portion 31 is provided along the longitudinal direction of the main body 11 is a positive direction of the X direction, and a positive direction of the Y direction is determined such that the X direction, the Y direction, and the Z direction constitute a so-called right-handed system. A surface facing the test object among the surfaces of the main body 11, that is, a surface in which the collimator 21 is provided is a front surface 12 (first surface) of the main body 11. Accordingly, among the surfaces of the main body 11, the front surface 12 is a surface for irradiating the X-rays. Then, among the surfaces of the main body 11, a surface that faces the front surface 12 and is substantially parallel to the front surface 12 is a rear surface 13 of the main body 11. In the rear surface 13, an operating unit 16 that is used for setting, operation, and the like of the X-ray tube device 10 is provided (see FIG. 2). In the embodiment, although the operating unit 16 is a touch panel, the operating unit 16 can be constituted using at least one of buttons, switches, a display, or the like. Among the surfaces of the main body 11, a surface that connects the front surface 12 and the rear surface 13 is a side surface 14 of the main body 11. That is, a surface excluding the front surface 12 and the rear surface 13 among the surfaces of the main body 11 is the side surface 14. In a case where the main body 11 is a substantially rectangular parallelepiped, the side surface 14 has an upper surface 14A and a lower surface 14B that face each other and are substantially parallel to each other, and a right surface 14C and a left surface 14D that face each other and are substantially parallel to each other. The upper surface 14A is a portion in the side surface 14 that is visible in a case where the X-ray tube device 10 is viewed from a positive side in the Y direction. The lower surface 14B is a portion in the side surface 14 that is visible in a case where the X-ray tube device 10 is viewed from a negative side in the Y direction. The right surface 14C is a portion in the side surface 14 that is visible in a case where the X-ray tube device 10 is viewed from a positive side in the X direction. Similarly, the left surface 14D is a portion in the side surface 14 that is visible in a case where the X-ray tube device 10 is viewed from a negative side in the X direction. Accordingly, the upper surface 14A may partially overlap at least one of the right surface 14C or the left surface 14D. Similarly, the lower surface 14B may partially overlap at least one of the right surface 14C or the left surface 14D. The right surface 14C may partially overlap at least one of the upper surface 14A or the lower surface 14B, and the left surface 14D may partially overlap at least one of the upper surface 14A or the lower surface 14B. In the definition of each surface, it is assumed that a portion of the collimator 21 or the like hidden by a portion protruding from the main body 11 is included in the “visible portion”. As shown in FIG. 3, the main body 11 of the embodiment incorporates a battery 18, a control circuit 19, and the like, in addition to the bulb 17 that generates the X-rays. The battery 18 supplies electric power necessary for operation to the bulb 17, the control circuit 19, and the like. The control circuit 19 controls the operation of the main body 11. That is, the control circuit 19 controls a tube voltage, a tube current, an X-ray generation (irradiation) timing, and the like of the bulb 17. The main body 11 can be provided with a plug, a cord, and the like that are connected to a power supply (not shown), which supplies electric power to the respective units of the main body 11, instead of the battery 18 or in addition to mounting of the battery 18. Although the bulb 17 is an X-ray tube that generates the X-rays, the main body 11 can be mounted with a bulb that generates radiation other than X-rays, instead of the bulb 17 that is the X-ray tube. In this case, the X-ray tube device 10 constitutes a so-called radiation generation device according to the kind of radiation generated by the bulb. The collimator 21 is provided to protrude from the main body 11 in the irradiation direction L1 (Z direction) of the X-rays in a part of the front surface 12 (first surface), which is a surface of the main body 11, and has an irradiation window 23 for irradiating the X-rays with an adjusted irradiation range. The reason that the collimator 21 is formed in a shape protruding in “a part” of the front surface 12 of the main body 11 is to reduce the size, such as the appearance and volume of the X-ray tube device 10. In a case where the entire front surface 12 of the main body 11 protrudes and the main body 11 is in a shape in which the collimator 21 is included inside the main body 11, the entire volume of the main body 11, consequently, the X-ray tube device 10 increases. The irradiation range of the X-rays is a shape of the X-rays that reach an X-ray imaging panel or the like, an area of the X-rays, a position of the X-rays with respect to the X-ray tube device 10, and the like. While the X-rays generated by the bulb 17 are cone beams that spread in a conical shape, an imaging surface of the X-ray imaging panel generally has a rectangular shape. For this reason, the collimator 21 adjusts, for example, the cone beams generated by the bulb 17 in a quadrangular pyramid shape in conformity with the imaging surface of the X-ray imaging panel and irradiates the cone beams from the irradiation window 23. As a result, the collimator 21 suppresses wasteful exposure of the test object. The irradiation window 23 is formed of a material that can transmit at least the X-rays without waste. A surface (second surface) where the irradiation window 23 is provided is a front surface 22 of the collimator 21. The collimator 21 incorporates one or a plurality of X-ray shielding members (not shown) and comprises an operating unit (not shown) that adjusts the internal arrangement (an inclination and the like) of the X-ray shielding members in order to adjust the irradiation range of the X-rays. In a case where the portion of the collimator 21 is reduced in size in order to reduce the size of the entire X-ray tube device 10, the collimator 21 has a base end portion 21A having a diameter smaller than a distal end portion. The base end portion 21A of the collimator 21 is a portion on the front surface 12 side of the main body 11, and the distal end portion of the collimator 21 is a portion on the test object side. The reason that the collimator 21 is formed in the above-described shape in a case of reducing the size of the collimator 21 is because the X-rays spread in the irradiation direction L1. The gripping portion 31 is provided to protrude from the main body 11 in the side surface 14, and is a handle that supports the main body 11 (and the entire X-ray tube device 10) by gripping. The gripping portion 31 is provided on the right surface 14C side of the main body 11. The user can support the main body 11 in a posture necessary for imaging, for example, even with one hand and can easily keep the posture by gripping the gripping portion 31. The gripping portion 31 is connected to the main body 11 at one place or two places. In the embodiment, the gripping portion 31 is connected to the main body 11 at two places of a connection point 33A and a connection point 33B. For this reason, the gripping portion 31 and the right surface 14C that is the side surface 14 of the main body 11 form a loop shape. The connection point 33A is a connection point to at least one of the upper surface 14A or the right surface 14C of the main body 11. The connection point 33B is a connection point to at least one of the lower surface 14B or the right surface 14C of the main body 11. In the gripping portion 31, a flat plate portion 32 that is present between the connection point 33A and the connection point 33B is a standard gripping position. Unless there is a need to keep the X-ray tube device 10 in a special posture, normally, the user can easily support the posture of the X-ray tube device 10 in a posture necessary for imaging by gripping the flat plate portion 32. In the embodiment, although the flat plate portion 32 is a flat plate shape, the flat plate portion 32 may be formed in any shape. The flat plate portion 32 can be formed, for example, in a curved or more stereoscopic grip shape. The switch 41 inputs at least one of an irradiation preparation instruction of the X-rays or an irradiation start instruction of the X-rays to the X-ray tube device 10. In the embodiment, the switch 41 is attachably and detachably provided in a corner portion of the main body 11 that is a left end (an end on the negative side in the X direction) of the front surface 12 of the main body 11 and an end of the left surface 14D on the front surface 12 side. The switch 41 is connected to the main body 11 in a wired or wireless manner, and can input the irradiation start instruction or the like and can transmit and receive other control signals even in a state in which the switch 41 is detached from the main body 11 as well as in a state in which the switch 41 is attached to the main body 11. Furthermore, the switch 41 can transmit or receive a synchronization signal to or from the X-ray imaging panel through the main body 11 or directly and can synchronously control the X-ray tube device 10 and the X-ray imaging panel. Synchronization regarding the operation includes a case where the operation is performed with a delay of a specific time. The switch 41 comprises a support 42, and a button 43 that can perform a press operation. In a case where the switch 41 is attached to the main body 11, a surface of the support 42 is smoothly connected to the surface of the main body 11, such as the front surface 12 and the left surface 14D. For this reason, the switch 41 is integrated with the main body 11. On the other hand, in a case where the switch 41 is detached from the main body 11, the support 42 is a gripping portion that is used for gripping the switch 41. The button 43 is pressed in a case of inputting the irradiation start instruction or the like to the main body 11. The button 43 can perform, for example, a two-step press operation of a first step of a press operation to input the irradiation preparation instruction of the X-rays to the main body 11 and a second step of a press operation to input the irradiation start instruction in order to actually irradiates the X-rays after irradiation of the X-rays is enabled. In addition, the X-ray tube device 10 comprises connectors 51A and 51B that are provided for connecting a guard unit 61 (see FIG. 6) for keeping a distance from the test object, between the front surface 12 (first surface) of the main body 11 and the front surface 22 (second surface), which is the surface of the collimator 21 where the irradiation window 23 is provided. In the embodiment, the connector 51A and the connector 51B are provided in the collimator 21. Specifically, as shown in FIGS. 4 and 5, in a range 53 between the front surface 12 of the main body 11 and the front surface 22 of the collimator 21, the connector 51A and the connector 51B are provided at two places of an upper surface (a portion that is visible in a case where the X-ray tube device 10 is viewed from the negative side in the Y direction) and a lower surface (a portion that is visible in a case where the X-ray tube device 10 is viewed from the positive side in the Y direction) of the base end portion 21A of the collimator 21, respectively. The connector 51A and the connector 51B have a shape to be longer in a direction perpendicular to the irradiation direction of the X-rays than in a direction parallel to the irradiation direction L1 of the X-rays. This is because connection strength to the guard unit 61 is kept high compared to other shapes. In a case where the connector 51A and the connector 51B are formed in the above-described shape, even though impact or the like is applied to the connected guard unit 61, the guard unit 61 is hardly detached and the connector 51A and the connector 51B are hardly damaged or the like. The same applies to a case where the connector 51A and the connector 51B are provided in other side surfaces (portions that are visible in a case where the X-ray tube device 10 is viewed from the X direction or the Y direction) of the collimator 21. Not only in a case where the connector 51A and the connector 51B are connected to the guard unit 61 in a form of fitting, engagement, or the like, but also in a case where the connector 51A and the connector 51B are bonded to the guard unit 61 by screwing, welding, adhesion, or the like in a part of the connector 51A and the connector 51B, a similar effect to the above is obtained by forming the connector 51A and the connector 51B in the above-described shape. As described above, the connector 51A and the connector 51B that are connected to the guard unit 61 are provided between the front surface 12 of the main body 11 and the front surface 22 of the collimator 21, whereby the X-ray tube device 10 can solve a problem that the guard unit 61 is hardly attached while achieving reduction in size as a whole. Specifically, in a case where the X-ray tube device 10 is reduced in size, since the area of the front surface 22 of the collimator 21 inevitably decreases, connectors for attaching the guard unit 61 are hardly provided in the front surface 22 of the collimator 21. In a case where the X-ray tube device 10 is reduced in size, even though it seems that there is a space for providing the connector 51A and the connector 51B in the front surface 22 of the collimator 21, the connector 51A and the connector 51B may not be actually provided in the front surface 22 of the collimator 21 according to conditions, such as the arrangement of the X-ray shielding members inside the collimator 21. On the other hand, since the base end portion 21A of the collimator 21 is closer to the bulb 17 than the front surface 22 of the collimator 21, a spread width of the X-rays generated by the bulb 17 is relatively small. For this reason, the X-ray tube device 10 provides the connectors between the front surface 12 of the main body 11 and the front surface 22 of the collimator 21, not in the front surface 22 of the collimator 21, thereby allowing the guard unit 61 to be attached thereto even though the X-ray tube device 10 is reduced in size. In a case where an outer wall of the collimator 21 is made of resin for reduction in weight of the X-ray tube device 10, even though the connector 51A and the connector 51B to the guard unit 61 are provided in the front surface 22 of the collimator 21, the connection strength of the guard unit 61 may be insufficient. This is because the connectors should be subject to the weight of the guard unit 61, impact applied to the guard unit 61, and the like with a very small area. In view of this point, since the X-ray tube device 10 provides the connector 51A and the connector 51B between the front surface 12 of the main body 11 and the front surface 22 of the collimator 21, it is possible to provide the connector 51A and the connector 51B having an area and a shape sufficient capable of sustaining the guard unit 61, impact applied to the guard unit 61, and the like. In addition, in reducing the size of the X-ray tube device 10, in a case where the connector 51A and the connector 51B to the guard unit 61 are provided in the front surface 22 of the collimator 21, the distance between the X-ray tube device 10 and the test object may not be kept at a necessary constant distance even though the guard unit 61 is provided. This is because the guard unit 61 and the irradiation window 23 inevitably become close, causing an amount of the guard unit 61 capable of protruding from the front surface 22 of the collimator 21 to easily overlap the irradiation range of the X-rays. In view of this point, compared to a case where the guard unit is attached to the front surface 22 of the collimator 21, the X-ray tube device 10 can make the guard unit 61 protrude from the side of the collimator 21, that is, from a position relatively far from the irradiation window 23. As a result, even though the X-ray tube device 10 is reduced in size, it is possible to secure a necessary and sufficient protrusion amount of the guard unit 61. For example, as shown in FIG. 6, the guard unit 61 that is connected to the X-ray tube device 10 using the connector 51A and the connector 51B has a first pillar portion 62A, a second pillar portion 62B, a third pillar portion 62C, and a fourth pillar portion 62D. The guard unit 61 has a first beam portion 63A, a second beam portion 63B, a third beam portion 63C, and a fourth beam portion 63D that connect two of the first pillar portion 62A, the second pillar portion 62B, the third pillar portion 62C, and the fourth pillar portion 62D to each other. The first pillar portion 62A, the second pillar portion 62B, the third pillar portion 62C, and the fourth pillar portion 62D are portions in the guard unit 61 extending in the irradiation direction L1 of the X-rays from the front surface 22 (second surface) of the collimator 21. The portions cross at least a position (an XY plane including the front surface 22) of the front surface 22 of the collimator 21 in a case where the X-ray tube device 10 is viewed from the side (the X direction or the Y direction). The first pillar portion 62A is a portion in the guard unit 61 extending substantially in the Z direction on the positive side in the X direction and the positive side in the Y direction of the collimator 21. The second pillar portion 62B is a portion in the guard unit 61 extending substantially in the Z direction on the negative side in the X direction and the positive side in the Y direction of the collimator 21. The third pillar portion 62C is a portion in the guard unit 61 extending substantially in the Z direction on the negative side in the X direction and the negative side in the Y direction of the collimator 21. Similarly, the fourth pillar portion 62D is a portion in the guard unit 61 extending substantially in the Z direction on the positive side in the X direction and the negative side in the Y direction of the collimator 21. The first beam portion 63A, the second beam portion 63B, the third beam portion 63C, and the fourth beam portion 63D connect two of the pillar portions 62A to 62D in the direction (that is, substantially the X direction or the Y direction) perpendicular to the irradiation direction L1 of the X-rays. The first beam portion 63A connects the first pillar portion 62A and the fourth pillar portion 62D on the test object side (the positive side in the Z direction) than the front surface 22 of the collimator 21 substantially in the Y direction. That is, in a case where the main body 11 has a rectangular parallelepiped shape, the first beam portion 63A connects the first pillar portion 62A and the fourth pillar portion 62D substantially in parallel with a transverse direction 72 of the front surface 12 of the main body 11. The first beam portion 63A connects distal end portions of the first pillar portion 62A and the fourth pillar portion 62D on the positive side in the Z direction. For this reason, the first pillar portion 62A and the fourth pillar portion 62D do not protrude to the test object side than the first beam portion 63A. The second beam portion 63B connects the second pillar portion 62B and the third pillar portion 62C substantially in the Y direction on the test object side than the front surface 22 of the collimator 21. That is, in a case where the main body 11 has a rectangular parallelepiped shape, the second beam portion 63B connects the second pillar portion 62B and the third pillar portion 62C substantially in parallel with the transverse direction 72 of the front surface 12 of the main body 11. The second beam portion 63B connects distal end portions of the second pillar portion 62B and the third pillar portion 62C on the positive side in the Z direction. For this reason, the second pillar portion 62B and the third pillar portion 62C do not protrude to the test object side than the second beam portion 63B. The third beam portion 63C connects the first pillar portion 62A and the second pillar portion 62B substantially in the X direction on the front surface 12 (first surface) side of the main body 11 than the front surface 22 of the collimator 21. That is, in a case where the main body 11 has a rectangular parallelepiped shape, the third beam portion 63C connects the first pillar portion 62A and the second pillar portion 62B substantially in parallel with a longitudinal direction 71 of the front surface 12 of the main body 11. The third beam portion 63C connects distal end portions of the first pillar portion 62A and the second pillar portion 62B on the negative side in the Z direction. The third beam portion 63C provides a guard unit-side connector 64, which is connected to the connector 51A, at a predetermined position (a position capable of being bonded to the connector 51A) in an inner surface (a surface on the collimator 21 side). In a case where the guard unit-side connector 64 is provided in the third beam portion 63C, since the entire connector 51A is supported by the third beam portion 63C, and impact or the like can be absorbed by the third beam portion 63C, at least one of connection strength or the impact resistance of the guard unit 61 is excellent. The fourth beam portion 63D connects the third pillar portion 62C and the fourth pillar portion 62D substantially in the X direction on the front surface 12 side of the main body 11 than the front surface 22 of the collimator 21. That is, in a case where the main body 11 has a rectangular parallelepiped shape, the fourth beam portion 63D connects the third pillar portion 62C and the fourth pillar portion 62D substantially in parallel with the longitudinal direction 71 of the front surface 12 of the main body 11. The fourth beam portion 63D connects distal end portions of the third pillar portion 62C and the fourth pillar portion 62D on the negative side in the Z direction. The fourth beam portion 63D has a guard unit-side connector (not shown), which is connected to the connector 51B, at a predetermined position (a position capable of being bonded to the connector 51B) in an inner surface (a surface on the collimator 21 side). In a case where the guard unit-side connector is provided in the fourth beam portion 63D, since the entire connector 51B is supported by the fourth beam portion 63D, and impact or the like can be absorbed by the fourth beam portion 63D, at least one of connection strength or impact resistance of the guard unit 61 is excellent. The guard unit 61 having the above-described shape is relatively excellent in impact resistance (impact absorption) or the like among guard units having various shapes that can be connected to the connector 51A and the connector 51B of the X-ray tube device 10. Furthermore, the guard unit 61, the connector 51A, and the like are hardly deteriorated due to repetitive use. As shown in FIG. 7, the guard unit 61 has a shape in which an interval between the first pillar portion 62A and the second pillar portion 62B spreads in the irradiation direction L1 (to the positive side in the Z direction) of the X-rays. The same applies to an interval between the third pillar portion 62C and the fourth pillar portion 62D. The reason that the guard unit 61 has the shape in which the interval between the first pillar portion 62A and the second pillar portion 62B and the interval between the third pillar portion 62C and the fourth pillar portion 62D spread in the irradiation direction L1 of the X-rays in this way is because the guard unit is relatively excellent in impact resistance (impact absorption) or the like among the guard units having various shapes capable of being connected to the connector 51A and the connector 51B of the X-ray tube device 10. Furthermore, it is possible to reduce impact applied to the test object when the guard unit 61 is brought into contact with the test object. In addition, compared to a case where the interval between the first pillar portion 62A and the second pillar portion 62B and the interval between the third pillar portion 62C and the fourth pillar portion 62D are constant or a case where the interval between the first pillar portion 62A and the second pillar portion 62B and the interval between the third pillar portion 62C and the fourth pillar portion 62D are tapered in the irradiation direction L1 of the X-rays, there is an advantage that the irradiation direction L1 of the X-rays is easily directed toward the test object even though the X-ray tube device 10 is placed on an examination table or the like in a vertical orientation (in an orientation bringing the left surface 14D into contact with the examination table or the like). In a case where the main body 11 has a rectangular parallelepiped shape, in comparison in the longitudinal direction 71 of the front surface 12 of the main body 11, a length (width W2) of the guard unit 61 may be longer than a length (width W1) of the collimator 21, and the length (width W2) of the guard unit 61 may be shorter than a length (width W3) of the main body 11 (see FIG. 7). This is because, in using the X-ray tube device 10, the guard unit 61 is not obstructive, in a case where the guard unit 61 is brought into contact with the test object or the like, a load applied to the connector 51A and the connector 51B is small, and the distance from the test object can be kept at a necessary distance. As shown in FIG. 8, the guard unit 61 is configured such that the interval between the first pillar portion 62A and the fourth pillar portion 62D is substantially constant in the irradiation direction L1 of the X-rays, and the first pillar portion 62A and the fourth pillar portion 62D are substantially parallel to each other. The same applies to the interval between the second pillar portion 62B and the third pillar portion 62C. The reason that the interval between the first pillar portion 62A and the fourth pillar portion 62D and the interval between the second pillar portion 62B and the third pillar portion 62C are substantially constant in this way is because the irradiation direction L1 of the X-rays is easily directed toward the test object in a case where the X-ray tube device 10 is placed on the examination table or the like in a horizontal orientation (in an orientation bringing the lower surface 14B into contact with the examination table or the like). In a case where the main body 11 has a rectangular parallelepiped shape, in comparison in the transverse direction 72 of the front surface 12 of the main body 11, a length (height H2) of the guard unit 61 may be longer than a length (height H1) of the collimator 21, and the length (height H2) of the guard unit 61 may be shorter than a length (height H3) of the main body 11 (see FIG. 8). This is because, in using the X-ray tube device 10, the guard unit 61 is not obstructive, and the distance from the test object can be kept at a necessary distance. In the above-described embodiment, although the connector 51A and the connector 51B are provided in the base end portion 21A of the collimator 21, the connector 51A and the connector 51B can be provided in the main body 11. For example, like an X-ray tube device 81 shown in FIG. 9, in a case where the main body 11 has a convex portion 82 in a portion where the collimator 21 is provided, the convex portion 82 belongs to the range 53 between the front surface 12 of the main body 11 and the front surface 22 of the collimator 21. For this reason, the connector 51A and the connector 51B can be provided in the convex portion 82 that is a part of the main body 11. 10: X-ray tube device 11: main body 12: front surface of main body 13: rear surface 14: side surface 14A: upper surface 14B: lower surface 14C: right surface 14D: left surface 16: operating unit 17: bulb 18: battery 19: control circuit 21: collimator 21A: base end portion 22: front surface of collimator 23: irradiation window 31: gripping portion 32: flat plate portion 33A, 33B: connection point 41: switch 42: support 43: button 51A, 51B: connector 53: range 61: guard unit 62A: first pillar portion 62B: second pillar portion 62C: third pillar portion 62D: fourth pillar portion 63A: first beam portion 63B: second beam portion 63C: third beam portion 63D: fourth beam portion 64: guard unit-side connector 71: longitudinal direction 72: transverse direction 81: X-ray tube device 82: convex portion L1: irradiation direction of X-ray W1, W2, W3: width
	abstract	The present invention is related to a device and a method for producing a radioisotope of interest from a target fluid irradiated with a beam of accelerated charged particles, the device includes in a circulation circuit (17): an irradiation cell (1) having a metallic insert (2) able to form a cavity (8) designed to house the target fluid and closed by an irradiation window (7), the cavity (8) including at least one inlet (4) and at least one outlet (5); a pump (16) for circulating the target fluid inside the circulation circuit (17); an external heat exchanger (15); the pump (16) and the external heat exchanger (15) forming external cooling means of the target fluid; the device means for pressurizing (14) of the circulation circuit (17) and the external cooling means of the target fluid are arranged in such a way that the target fluid remains inside the cavity (8) essentially in the liquid state during the irradiation.
	summary
	claims	1. An electrolytic apparatus for use in an oxide electrowinning method, said apparatus comprising:an annular electrolytic vessel made of a metallic material and having an annular space with a bottom formed therein and an upper portion;a high frequency induction coil for heating a substance to be processed in said electrolytic vessel;an annular anode installed at the bottom of the annular space formed in the annular electrolytic vessel;rod-shaped anodes and rod-shaped cathodes installed in the upper portion along the axial direction in the annular space and arranged in parallel, the rod-shaped anodes and the annular anode being arranged vertically;a first electrolysis controller connected between the rod-shaped cathodes and the annular anode, anda second electrolysis controller connected between the rod-shaped cathodes and the rod-shaped anodes,wherein one of a parallel pair of the rod-shaped anodes and the rod-shaped cathodes arranged in parallel or and a vertical pair of the annular anode and the rod-shaped cathodes arranged vertically is used for main electrolysis and the other of the pairs is used for auxiliary electrolysis. 2. An electrolytic apparatus for use in an oxide electrowinning method according to claim 1, further comprising a rotational driving mechanism, wherein the rod-shaped cathodes are supported rotationally and are rotated by the rotational driving mechanism. 3. A spent nuclear fuel reprocessing method with an oxide electrowinning method by using the electrolytic apparatus according to claim 1, wherein the oxide electrowinning method comprises:a simultaneous electrolytic step, including dissolving uranium oxide contained in spent nuclear fuel into a molten salt in the annular electrolytic vessel due to an anodic oxidation reaction, and simultaneously recovering uranium oxide by depositing uranium oxide on the surface of the cathodes due to cathodic reduction;a dissolution step by chlorination in which the electrolytic step is stopped, including dissolving uranium oxide, plutonium oxide and other elements remaining in the spent nuclear fuel into the molten salt by blowing chlorine gas into the molten salt to convert the uranium oxide, the plutonium oxide and other elements remaining in the spent nuclear fuel to chlorides thereof; anda MOX recovery step, including performing electrolysis between the anodes and the rod-shaped cathodes installed in the upper portion of the annular space, and recovering oxides of uranium and plutonium by deposition of the oxides in a mixed state on the surface of the cathodes, after the entire spent nuclear fuel has been dissolved into the molten salt;wherein in the simultaneous electrolytic step, the vertical pair of the annular anode and the rod-shaped cathodes is used for main electrolysis in which uranium oxide is dissolved and deposited by electrochemical reaction and the parallel pair of the rod-shaped anodes and the rod-shaped cathodes is used for auxiliary electrolysis for suppressing ununiform uranium oxide electrodeposition, andwherein in the MOX recovery step, the parallel pair of the rod-shaped anodes and the rod-shaped cathodes is used for main electrolysis in which the MOX is deposited, and the vertical pair of the annular anode and the rod-shaped cathodes is used for auxiliary electrolysis for dissolving any electrodeposit which has fallen down from the cathodes. 4. A spent nuclear fuel reprocessing method with an oxide electrowinning method by using the electrolytic apparatus according to claim 2, wherein the oxide electrowinning method comprises:a simultaneous electrolytic step, including dissolving uranium oxide contained in spent nuclear fuel into a molten salt in the annular electrolytic vessel due to an anodic oxidation reaction, and simultaneously recovering uranium oxide by depositing uranium oxide on the surface of the cathodes due to cathodic reduction;a dissolution step by chlorination in which the electrolytic step is stopped, including dissolving uranium oxide, plutonium oxide and other elements remaining in the spent nuclear fuel into the molten salt by blowing chlorine gas into the molten salt to convert the uranium oxide, the plutonium oxide and other elements remaining in the spent nuclear fuel to chlorides thereof; anda MOX recovery step, including performing electrolysis between the anodes and the rod-shaped cathodes installed in the upper portion of the annular space, and recovering oxides of uranium and plutonium by deposition of the oxides in a mixed state on the surface of the cathodes, after the entire spent nuclear fuel has been dissolved into the molten salt;wherein in the simultaneous electrolytic step, the vertical pair of the annular anode and the rod-shaped cathodes is used for main electrolysis in which uranium oxide is dissolved and deposited by electrochemical reaction and the parallel pair of the rod-shaped anodes and the rod-shaped cathodes is used for auxiliary electrolysis for suppressing ununiform uranium oxide electrodeposition, andwherein in the MOX recovery step, the parallel pair of the rod-shaped anodes and the rod-shaped cathodes is used for main electrolysis in which the MOX is deposited, and the vertical pair of the annular anode and the rod-shaped cathodes is used for auxiliary electrolysis for dissolving any electrodeposit which has fallen down from the cathodes.
047633999	summary	BACKGROUND OF THE INVENTION This invention relates to a method of strengthening of a bolt hole and more particularly, but not by way of limitation, to a method of strengthening the bolt hole in a fibrous composite laminate. Heretofore, in the design of fibrous composite parts, ply padups have been required when holes are drilled in laminate sheets. This extra material is required because of reduced allowables due to notch sensitivity of the laminate caused by interlaminar shear stresses around the edges of the bolt holes. These interlaminar shear stresses are a result of edge effects and delamination caused by the relatively low material properties of the "through-the-laminate" direction. Current methods of suppression of edge effects around bolt holes are through the use of stitching of a B-staged laminate and providing quasi-isotropic padups in the area of the bolt holes. A limitation to this stitching method is that the laminate can only be stitched while B-staged. Once cured, the laminate cannot be altered. Providing quasi-isotropic padups in areas to be bolted works fairly well in increasing laminate bearing strength, but the reduced longitudinal stiffness requires a substantial increase in laminate thickness which is directly related to increased weight. Further, highly unidirectional composite laminate sheets exhibit poor bolt hole properties such as thickness strength, bearing strength and galvanic corrosion associated with conventional aircraft fasteners. In the following U.S. Pat. Nos. 2,700,172 to Rohe, 3,158,503 to Young, 3,526,072 to Campbell, 3,895,409 to Kwatonowski, 3,977,146 to Wiley, 4,098,922 to Dinella et al, 4,118,855 to Lequeux, 4,232,496 to Warkentin and 4,296,586 to Heurteux various types of fastening devices and grommet assemblies are shown which are used with different types of airframe structures and composite materials. None of these prior art patents point out the distinguishing features of the subject method of bolt hole strengthening as described herein. SUMMARY OF THE INVENTION The subject method of bolt hole strengthening in a fibrous composite laminate suppresses edge effects by plating the edges of a laminate bolt holes with a metal compatible with the fiber such as titamium, aluminum and similar metals. The metal plating of the bolt hole provides high strength in the "through the laminate" direction and provides increased bearing strength. The increased strength of the bolt hole allows increased allowables and thus a substantial decrease in the overall weight of a composite aircraft. The method of bolt hole strengthening of a fibrous composite laminate includes the steps of drilling a hole through the laminate sheet and applying a metal spray by spraying, soldering or electro-plating the sides of the bolt hole. The liquid metal wicks into delamination and fills voids naturally occuring on the edges of fibrous composite laminate. The plating maybe in the range of a few mils thickness or greater for providing a substantial increase in the "through the laminate" strength. The advantages and objects of the invention will become evident from the following detailed description of the drawings when read in connection with the accompanying drawings which illustrate preferred embodiments of the invention.
	claims	1. An apparatus for shielding an electronic device from light, the apparatus comprising:left and right support assemblies for supporting the apparatus on the electronic device, the left and right support assembly each including:primary support structure;a mounting element positioned near a proximal end of the primary support structure for removably connecting the support assembly to the electronic device; anda lower support member attached to the primary support structure and downwardly extending at an angle to abut a lower portion of the electronic device;an opaque shroud extending between the primary support structures of the left and right support assemblies, the opaque shroud being configured to block light from reaching the electronic device when the mounting elements are connected to the electronic device and the lower support members abut the lower portion of the electronic device. 2. The apparatus of claim 1, wherein the opaque shroud is configured to be urged into a downwardly curving shape. 3. The apparatus of claim 2, wherein the primary support structure of each support assembly includes a sloped surface for urging the opaque shroud into the downwardly curving shape. 4. The apparatus of claim 2, wherein the opaque shroud may be adjusted to have a radius larger than a radius of a scanner bed of the electronic device and smaller than a radius of an end cap of the electronic device. 5. The apparatus of claim 1, wherein the opaque shroud is formed of flexible material. 6. The apparatus of claim 5, wherein the opaque shroud is formed of a canvas material. 7. The apparatus of claim 1, further comprising a plurality of fasteners, the left and right primary support structures each including a fastener hole, the opaque shroud including left and right outwardly extending strips each having at least one fastener hole for receiving one of the fasteners therethrough and removably connecting the opaque shroud to the primary support structures. 8. The apparatus of claim 7, wherein the fastener holes of the left and right primary support structures and/or the fastener holes of the left and right outwardly extending strips are slotted such that the opaque shroud may be adjustably connected to the left and right primary support structures. 9. The apparatus of claim 7, wherein the fasteners are thumbscrews. 10. The apparatus of claim 7, wherein the opaque shroud includes a primary section having an outer side and left and right lower edges, and left and right upturned portions, the left and right outwardly extending strips extending from the left and right upturned portions. 11. The apparatus of claim 10, wherein the upturned portions are attached to the primary section via staples, stitching, glue, or other fastening means so as to reinforce the opaque shroud. 12. The apparatus of claim 1, wherein the mounting elements include one or more hooks for connecting the apparatus onto external mounting features of the electronic device. 13. The apparatus of claim 1, wherein the mounting elements include horizontally extending tabs spaced below the hooks and configured to engage the external mounting features of the electronic device such that the apparatus may be removed from the electronic device by pivoting the apparatus upwards until the horizontally extending tabs clear the external mounting features of the electronic device and then lifting the apparatus until the hooks clear the external mounting features of the electronic device. 14. The apparatus of claim 1, further comprising a cross member for rigidly connecting the left and right primary support structures together. 15. The apparatus of claim 1, wherein the opaque shroud extends past the primary support structures near a proximal end of the apparatus. 16. The apparatus of claim 1, wherein the left and right support assemblies are configured to be spaced closer or further apart from each other for being mounted on electronic devices of different sizes. 17. The apparatus of claim 1, wherein the primary support structures and the support members are formed of rectangular tubing. 18. An apparatus for shielding a phosphor panel of an X-ray device from light, the apparatus comprising:left and right support assemblies for supporting the apparatus on the X-ray device, the left and right support assembly each including:primary support structure;a mounting element positioned near a proximal end of the primary support structure for removably connecting the support assembly to the X-ray device; anda support member depending from the primary support structure and configured to abut a lower portion of the X-ray device;an opaque shroud extending between the primary support structures of the left and right support assemblies, the opaque shroud being configured to block light from reaching the phosphor panel when the apparatus is connected to the X-ray device and the support members abut the lower portion of the X-ray device. 19. The apparatus of claim 13, wherein the opaque shroud is configured to extend over 14″ by 17″ phosphor panels and 14″ by 51″ phosphor panels. 20. An apparatus for shielding a phosphor panel of an X-ray device from light, the apparatus comprising:left and right support assemblies for supporting the apparatus on the X-ray device, the left and right support assembly each including:primary support structure;a mounting element positioned near a proximal end of the primary support structure for removably connecting the support assembly to the X-ray device, the mounting element including:left and right hooks extending outwardly and downwardly from the proximal end of the primary support structure for being inserted into mounting slots of the X-ray device; anda lower tab extending outwardly from the proximal end of the primary support structure for preventing the left and right hooks from being inadvertently dislodged from the slots of the X-ray device; anda support member depending from the primary support structure and configured to abut a lower portion of the X-ray device, the support member including:a downwardly extending section angled towards the proximal end of the support member; anda horizontally extending section continuing from the downwardly extending section towards the proximal end of the primary support member; andan opaque shroud extending between the primary support structures of the left and right support assemblies, the opaque shroud including:a flexible canvas cover configured to take the shape of a cylindrical dome so as to form a central space covered from above;left and right upturned portions depending from the cylindrical dome on an outside of the cover; andleft and right outwardly extending strips depending from the upturned portions and extending away from the cover, the outwardly extending strips having a plurality of slotted fastener holes for adjustably connecting the opaque shroud to the left and right primary support members, the opaque shroud being configured to block light from reaching the phosphor panel when the apparatus is connected to the X-ray device and the support members abut the lower portion of the X-ray device.
	abstract	In an atom probe or other mass spectrometer wherein a specimen is subjected to ionizing pulses (voltage pulses, thermal pulses, etc.) which induce field evaporation of ions from the specimen, the evaporated ions are then subjected to corrective pulses which are synchronized with the ionizing pulses. These corrective pulses have a magnitude and timing sufficient to reduce the velocity distribution of the evaporated ions, thereby resulting in increased mass resolution for the atom probe/mass spectrometer. In a preferred arrangement, ionizing pulses are supplied to the specimen from a first counter electrode adjacent the specimen. The corrective pulses are then supplied from a second counter electrode which is coupled to the first via a passive or active network, with the network controlling the form (timing, amplitude, and shape) of the corrective pulses.
	claims	1. A nuclear fuel comprising:a fuel element comprising a plurality of tristructural-isotropic fuel particles intermixed in a silicon carbide matrix, wherein the silicon carbide matrix separates at least one of the plurality of tristructural-isotropic fuel particles embedded in the silicon carbide matrix from the other tristructural-isotropic fuel particles embedded in the silicon carbide matrix, wherein the silicon carbide matrix has a density substantially equal to the theoretical density of stoichiometric silicon carbide. 2. The nuclear fuel of claim 1, wherein each of the tristructural-isotropic fuel particles comprises a fuel kernel disposed substantially at the center and a ceramic layer surrounding the fuel kernel. 3. The nuclear fuel of claim 1, wherein the fuel element has a shape of a cylindrical pellet. 4. The nuclear fuel of claim 1, further comprising:a tubular enclosure defining an interior space, wherein an outer surface of the tubular enclosure is configured to contact a coolant of a nuclear reactor,wherein the fuel element is disposed in the interior space. 5. The nuclear fuel of claim 4, wherein the tubular enclosure is a metallic cladding tube. 6. The nuclear fuel of claim 1, further comprising a graphite block having one or more holes, wherein the fuel element is disposed inside the one or more holes. 7. The nuclear fuel of claim 1, wherein the plurality of tristructural-isotropic fuel particles comprise transuranic elements extracted from a spent fuel of a light water reactor. 8. The nuclear fuel of claim 1, wherein the plurality of tristructural-isotropic fuel particles comprise transuranic elements extracted from a nuclear weapon. 9. A nuclear fuel comprising:a fuel element comprising a plurality of tristructural-isotropic fuel particles intermixed in a silicon carbide matrix, wherein the silicon carbide matrix separates at least one of the plurality of tristructural-isotropic fuel particles embedded in the silicon carbide matrix from the other tristructural-isotropic fuel particles embedded in the silicon carbide matrix, wherein the silicon carbide matrix is near-stoichiometric and has pockets of porosity of not more than 4%, and wherein the pockets include only rare earth oxides or tramp elements. 10. The nuclear fuel of claim 9, wherein the fuel element has a shape of a cylindrical pellet. 11. The nuclear fuel of claim 9, further comprising:a tubular enclosure defining an interior space, wherein an outer surface of the tubular enclosure is configured to contact a coolant of a nuclear reactor,wherein the fuel element is disposed in the interior space. 12. The nuclear fuel of claim 9, further comprising a graphite block having one or more holes, wherein the fuel element is disposed inside the one or more holes. 13. The nuclear fuel of claim 9, wherein the plurality of tristructural-isotropic fuel particles comprise transuranic elements extracted from a spent fuel of a light water reactor. 14. The nuclear fuel of claim 9, wherein the plurality of tristructural-isotropic fuel particles comprise transuranic elements extracted from a nuclear weapon.
059995831	claims	1. A method for analyzing an electromagnetic drive mechanism for a nuclear control rod while positioning the control rod relative to a core of a reactor for controlling nuclear flux during generation of power by the core, the mechanism having at least one stationary gripper and coil, at least one movable gripper and coil, at least one armature and coil for displacing the movable gripper relative to the stationary gripper, and a timing circuit coupled to a coil current driver operable to provide current to said coils in sequences of operations in which said coils are energized individually and in combinations for advancing and retracting the control rod relative to the core, the method comprising: positioning the control rod relative to the core of the reactor for controlling said nuclear flux by executing said sequences of operations while: 2. The method of claim 1, wherein the current variation comprises a notch occurring upon pull-in of at least one of the stationary gripper and the movable gripper. 3. The method of claim 2, wherein the nominal current amplitudes include occurrence of said notch at a nominal delay and amplitude following application of a current to said at least one of the stationary gripper coil and the movable gripper coil, and further comprising comparing at least one of an actual delay and an actual amplitude of the notch to the nominal delay and amplitude for identifying one of mechanical impairment of the gripper and degradation of a magnetic flux of said at least one of the coils. 4. The method of claim 1, further comprising sensing at least one of current and voltage at a plurality of points between an ac power source and said coils, the points including at least one circuit interrupter, at least one switching device and power regulator, a controller for operating the switching device and the coils, and wherein said current and voltage at the plurality of points are compared to nominal levels for identifying an electrical or mechanical failure point between the power source and the coils, and further comprising indicating said failure point. 5. The method of claim 4, wherein the failure point is determined as at least one of: loss of the ac power source, operation of the circuit interrupter to disengage the ac power source, failure of the switching device, failure of the power regulator and malfunction of the controller. 6. The method of claim 1, wherein the stationary and movable grippers are operable in a grip mode at a higher current amplitude and a hold mode at a lower current amplitude, and further comprising comparing the higher and lower current amplitudes to nominal values. 7. The method of claim 1, further comprising comparing the coil current data of said each later one of the sequences of operations to said nominal amplitudes and timing relationships for the coil current signals.
	claims	1. An electron optical lens column characterized by comprising a column unit and an electrostatic lens disposed inside of said column unit and an inner surface of said column unit having a high-resistance electrical conductivity, that said column unit has an inner column and an outer column, said inner column is disposed on an inside of said outer column, and said electrostatic lens comprises electrodes used to produce an electric field within said column unit, said electrodes are connected to electrical interconnections for apply voltages to said electrodes, and said interconnections are disposed between said inner column and said outer column. 2. The electron optical lens column according to claim 1, characterized in the inner surface of said column unit is formed from a ceramic having high-resistance electrical conductivity. 3. The electron optical lens column according to claim 1, characterized in that said column unit is formed from, essentially, a single material. 4. The electron optical lens column according to claim 3, characterized in that said single material is a ceramic that has high-resistance electrical conductivity. 5. The electron optical lens column according to claim 1, characterized by said high-resistance electrical conductivity has a resistivity in the range of 108 to 1010 Ω-cm. 6. The electron optical lens column according to claim 1 comprises a plurality of said electrodes and is further characterized by said electrodes with identical electric potentials being mutually connected via said electrical interconnections. 7. The electron optical lens column according to claim 1 comprises a plurality of said electrodes and is further characterized by said electrical interconnections connect together via one of resistances and switching element electrodes that have different electric potentials. 8. The electron optical lens column according to claim 1, characterized by said electrostatic lens comprising electrodes for generating electric fields on the inside of said column unit, and that said electrodes are attached to the inner surface of said column unit. 9. The electron optical lens column according to claim 1 further comprises a plurality of said electrostatic lenses, and is further characterized by electrodes for each electrostatic lens comprise multiple electrode parts that are mutually separate, and that the number of electrode parts in each of said electrodes is identical. 10. The electron optical lens column according to claim 1 further comprises a plurality of said electrostatic lenses, and is further characterized by each of said electrostatic lenses comprises electrodes, that said electrodes comprise multiple electrode parts that are mutually separate, and those electrode parts that have identical electric potentials are connected together electrically via common electrical interconnections. 11. The electron optical lens column according to claim 1, comprising a plurality of said electrostatic lenses, and further characterized by grooves formed between said electrostatic lenses. 12. The electron optical lens column according to claim 1, characterized said electrostatic lens comprises a plurality of electrodes, and that grooves are formed between said electrodes. 13. The electron optical lens column according to claim 1, characterized said electrostatic lens comprises an electrode, that said electrode comprises multiple electrode parts, and that grooves are formed between said electrode parts. 14. The electron optical lens column according to claim 1, characterized by an electron gun chamber is provided at one end of said column unit. 15. The electron optical lens column according to claim 14, characterized by a secondary electron detector is provided on another end of said column unit. 16. The electron optical lens column according to claim 1, characterized by a flange for attaching an electron gun chamber is provided on one end of said column unit, and integrated with said column unit. 17. The electron optical lens column according to claim 16, characterized by a sidewall of an electron gun chamber on one end of said column unit is provided integrated with said column unit. 18. A scanning electron microscope comprising a lens column according to claim 1. 19. An ion beam device comprising a lens column according to claim 1. 20. An electron optical lens column characterized by comprising a column unit and an electrostatic lens disposed inside of said column unit and an inner surface of said column unit is given high-resistance electrical conductivity, said column unit has an inner column and an outer column, said inner column is disposed inside said outer column, said column unit comprises a plurality of said electrostatic lenses, said electrostatic lenses comprise electrodes for generating electric fields on the inside of said column unit, said electrodes are attached to the inner surface of said column unit, said electrodes are equipped with a plurality of electrode parts that are mutually separate, said electrode parts that have identical electric potentials are mutually connected electrically via interconnections, and that said electrical interconnection are disposed between said inner column and said outer column, the high-resistance electrical conductivity is within a range of 108 to 1010 Ω-cm. 21. An electron optical lens column characterized by comprising a column unit and an electrostatic lens disposed inside of said column unit and an inner surface of said column unit is given high resistance electrical conductivity, said column unit has an inner column and an outer column, said inner column is disposed inside said outer column, said column unit comprises a plurality of said electrostatic lenses, said electrostatic lenses comprise electrodes for generating electric fields on the inside of said column unit, said electrodes are attached to the inner surface of said column unit, said electrodes are equipped with a plurality of electrode parts that are mutually separate, said electrode parts are connected together via interconnections and resistances in order to apply differing voltages to electrode parts, and said interconnections and resistances are disposed between said inner column and said outer column. 22. An electron optical lens column characterized by comprising a column unit and an electrostatic lens disposed inside of said column unit and an inner surface of said column unit is given high residence electrical conductivity, said column unit comprises a plurality of said electrostatic lenses, said electrostatic lenses comprise electrodes for generating electric fields on the inside of said column unit, said electrodes are attached to the inner surface of said column unit, said electrodes are equipped with a plurality of electrode parts that are mutually separate, said electrode parts are connected together via interconnections and switching elements in order to apply differing voltages to these electrode parts, and said interconnections and switching elements are disposed between said inner column and said outer column. 23. A manufacturing method for an electron optical lens column comprising the following steps:(1) a step that coats an electrically conductive material on the inner surface of a column unit, and(2) a step that forms one set of electrodes for structuring an electrostatic lens through a removal of a portion of the aforementioned electrically conductive material that has been coated on the inner surface of the column unit. 24. A manufacturing method for an electron optical lens column comprising the following steps:(1) a step that coats an electrically conductive material on an inner surface of a column unit,(2) a step that obtains multiple electrodes for structuring one or more electrostatic lenses through of a removal of a potion of the aforementioned electrically conductive material that has been coated, and(3) a step that connects, via interconnections, those aforementioned multiple electrodes that have identical electric potentials. 25. A manufacturing method for an electron optical lens column comprising the following steps:(1) a step that coats an electrically conductive material on an inner surface of a column unit,(2) a step that obtains multiple electrode parts for structuring electrodes for electrostatic lenses through removing a portion of the aforementioned electrically conductive material that has been coated, and(3) a step that connects, via interconnections, those aforementioned multiple electrode parts that have identical electric potentials.
039506517	description	The invention is based on the realization that it is possible to modify the effective cross-section of the radiated beam by means of a device which could be looked upon as a secondary shutter the aperture of which is in a disc- or frame-like member consisting of a composition having special properties. The composition consists of a heavy metal, such as tungsten or lead, in powder form the individual grains of the powder being held together by an adhesive which does not cure with time. The adhesive is of the type known as "pressure-sensitive adhesives" which means that its binding action is dependent of the external pressure to which the cemented product, i.e. in this case the metal powder member, is subjected. The amount of pressure to be applied cannot be specified generally, as it is a function of the particular metal chosen, of its grain size and of the relative amount of adhesive used, etc. However, the skilled worker does not encounter any difficulties in rapidly finding the pressure to be used for certain selected values of the other parameters so that he can produce a composition exhibiting the following two valuable properties. On the one hand, it has in contrast to a solid metal block such a high softness that cuts therein can readily be made by means of an ordinary knife, a cutting wire or the like. On the other hand, although it has that consistency it is stable enough to maintain the shape which has been given to a product made therefrom. The net result is that such a composition can be used for the provision of a beam contour modifying device, or shutter, the cross-section of whose aperture conforms exactly with the contour of the target area, or treatment field. This is in sharp contrast to prior art devices where the field contour can only be simulated approximately in the sense that curved lines have to be composed by a plurality of short straight lines, each defined by one radiation absorption block. In addition thereto, it is generally necessary to arrange such blocks in two or more layers and the result is that the border of the beam is not sharply defined. Instead, penumbras arise. It should also be understood that there is, according to this invention, no need for using either the therapeutic unit or a special, also very expensive, simulator for the construction of the beam cross-section modifying device nor does the patient have to be present when this working step is performed. Also, once such a device has been made and used in the first corresponding treatment of the patient it can be saved and is immediately available for the succeeding treatments thus doing away with the need of having to repeat the time-consuming beam-modifying operation each time a treatment shall be repeated. Moreover, when the patient has received his final treatment so that the device is no more needed as far as he is concerned, the composition contained in his shutter is immediately available for the construction of similar devices for other patients. The manufacture of a composition rendering itself for the use above referred to will now be described. A tungsten powder (available on the market) having a grain size which preferably is in the interval 200-325 mesh according to U.S. standard is mixed with a small amount of a pressure-sensitive adhesive, typically 1-10% by weight. The two ingredients are mixed in a suitable agitating machine until the operator visually establishes that they have formed a homogenous mass. According to a preferred embodiment of the invention the next step is to put an adequate amount of the mass in a box made of a transparent material, such as MACROLON (Registered Trademark). That box is then snugly surrounded by a reinforcing metal frame and placed in a press the piston of which is lowered towards the top surface of the mass. This compaction procedure does only require a few seconds and the resulting product can be described as a disc- or block-shaped member constituting a shutter blank. The next step is to cut out the shutter aperture. This operation can be performed in several different manners. By way of example, the cutting tool can be remote-controlled by a sensor which is manually or automatically caused to track the contour line of the target area as marked on an X-ray photo. While the invention is not limited to the use of any special radiation source in the therapy unit but can be successfully worked with all types of radiation generators, such as betatrons and linear accelerators, it is of special value when the radiation source is constituted by a radioactive sample, usually cobalt 60. Such a sample performs as a point-shaped radiation source and does consequently, in principle, emit a conical beam. By letting the cutting tool pivot around a point at the same distance from the shutter under manufacture as the distance between the focus of the beam and the shutter as installed in the therapy unit, one achieves that the walls of the aperture will be parallel to the radially outermost rays passing through the aperture. As is directly understood, this represents a perfect solution of the penumbra problem. As has already been indicated, upon completion of the cutting operation the final step is to mount the shutter in its desired position. In many applications it is most practical to modify the therapy unit so that its source head supports also the shutter. However, in special cases a member serving as a shutter can also be inserted into the patient's body, orally, rectally, or vaginally. When it forms a portion of the unit proper the latter can conveniently be provided with position-fixing means so that the only adjustment work necessary in preparation of the treatment is correctly to position the patient on the treatment couch, to slide his individual shutter into its position and in the conventional manner, using ordinary light, to check that the beam area projected on the body of the patient coincides with the desired field. In FIG. 1 there has diagrammatically been shown a portion of a patient's body on which a desired treatment area A has been marked. Reference numeral 10 designates a box-like shutter the aperture of which has a cross-sectional area A.sub.1 which is congruent with area A. The aperture has been provided by a cutting operation as above described. It is accordingly surrounded by a, in this case square, disc-like member 11 consisting of a composition comprising the two ingredients also above specified. As is most clearly seen from FIG. 4, the composition is housed in a box 12 made of a transparent material, such as MACROLON. It has a lid 13 and a larger bottom 14 which rests on cross bars 17 and is held in position by guide rails 15, 16. The latter can consequently receive boxes 10 which can be larger or smaller than that shown in FIG. 4 as long as they are mounted on identical bottom plates 14. The arrangement just described is supported by brackets 18 depending from the lower portion of a source head 19. This is carried by a so-called C-arm 20, which can pivot around a horizontal axis 21 as is well-known in the art. The patient is in FIG. 3 shown resting on a treatment couch 22 supported by a base 23 to which there is connected a control box 24 for the operation of the unit. Reference numeral 25 refers to the radiation source, in this case a sample of a radioactive material, e.g. cobalt 60. It is surrounded by a radiation protection cylinder 27 and emits a conical beam 26 the radially outward rays of which first hit a conventional primary shutter 29. The aperture thereof limits the cross-section of the beam so that at the level of the top of box 12 all beams either hit the radiation-protective material 11 or pass through the aperture of shutter 10. FIG. 4 illustrates how, thanks to the above-described way of providing that aperture, the walls 28 thereof are parallel to the border rays thus doing away with the penumbra problem. It is evident that in the practical working of the invention it can be modified in several respects as compared to the embodiment thereof here selected to illustrate the basic inventive concept. This is especially true as far as the relative dimensions of the shutter arrangement are concerned. When the treatment field location is to be checked in the conventional optical way it is convenient to house material 11 in a box having at least its bottom and a lid made of a transparent material. However, in other applications material 11 can be confined in any other suitable way. It should also be understood that other metals than tungsten may be used, especially lead.
	description	The installation described below is of general structure comparable to that disclosed in U.S. Pat. No. 5,317,609 to which reference can be made. Consequently, the description below relates essentially to those elements of the installation which are original. The complete installation can be constituted by apparatuses arranged in a hall provided with handling means, for example winches carried by a monorail. The installation includes means for feeding empty skeleton structures (not shown) and also means for feeding vessels containing rods to be loaded. These vessels are provided with biological protection when the rods they transport are radioactive, as applies in particular for so-called xe2x80x9cMOXxe2x80x9d rods containing pellets of uranium and plutonium oxide. Rods are transferred from a xe2x80x9cwaterfallxe2x80x9d carriage to follow a sinuous path therein, one after another. The waterfall carriage makes it possible to bring rods into rod-receiving magazines in a disposition corresponding to that of the rods in an assembly for loading. The order in which rods are fed to the waterfall carriage can be arranged so that the reception magazine receives rods of different kinds depending on their final locations in the assembly. FIG. 1 shows the position of the waterfall carriage 10 fitted with biological shielding when it is for receiving MOX rods, beside an inlet table 12 which is separated by a cleaning location from an indexing machine 14 of a reception magazine filled with rods coming from the carriage 10. In an advantageous embodiment, the magazine comprises an elongate receptacle in which a plurality of sets of pairs of grooves are formed. Each set is for receiving a particular set of perforated plates corresponding to a determined array of rods in the assembly for loading. An overhead crane that moves in direction 18 serves to bring the magazines 16 into the position shown by chain-dotted lines, on a support 20. The installation also has a rigid structure for receiving each skeleton structure in turn, which structure is constituted by a swingable bench 22 designed to receive biological protection 24 when the installation handles rods containing MOX fuel. The bench can be stationary or it can be mounted on rails enabling it to be brought into alignment with the reception magazine 16 and with a pulling bench 26 which is movable transversely on rails 28 enabling it to be brought into the position shown in dashed lines by being moved along double-headed arrow 30. The skeleton structures for loading can be brought onto the rocking bench 22 by means of a carriage 32. Finally, additional zones enable the usual operations of inspection and cleaning to be performed on complete assemblies, which the crane means can transport in a vertical position in the direction shown by dashed-line arrows 34. The essential apparatuses of the installation are described below in succession. Pulling Bench (FIGS. 2 to 5) The pulling bench 26 is for inserting rods into successive sheets into the skeleton structure of an assembly while the skeleton structure is supported horizontally. The bench can be regarded as comprising a frame 36, a carriage 38 that is movable along the frame, and a removable block 40 for selecting pulling elements. This block is selected from a plurality of blocks corresponding to different distributions of rods in an assembly. The bench 26 can also have removable safety arms 42 whose function is described below. The frame 36 includes a cradle 44 that is movable in the y direction by a motor 48 driving toothed wheels. The pulling bench can thus be taken from the working position in which it is shown in continuous lines in FIG. 1 to the rest position shown in dashed lines. On the cradle, there is mounted a beam 50 carrying the carriage. A motor 52 actuating actuators 54 serves to move the beam 50 vertically (z direction) to adjust the height of the pulling elements 56 (which are constituted by bars) so as to bring them level with each sheet of rods to be loaded. The carriage 38 is mounted on the beam 50 via bearings enabling it to move along the bench (x direction). These movements are driven by rotating a drive screw 58, itself driven by a motor. Pulling elements carried by the carriage are distributed to occupy a complete horizontal sheet. To enable the invention to be implemented, the pulling elements are connected to the carriage 38 by connection means which: in the pulling direction, i.e. when the carriage is tending to pull the rods from the magazine towards a structure, serve to provide a positive connection, via a mechanical abutment; and in the pushing direction, serve to perform resilient locking only, e.g. by means of a spring biased ball engaging into a recess in the pulling element. For safety reasons, a force sensor can be mounted between the pulling elements and the mechanical abutment of the positive connection, so as to measure the pulling force. In addition, the carriage is provided with a mechanism enabling the end clamp of the pulling elements to be opened and closed. FIG. 4 shows only one bell crank 60 of this transmission mechanism, which can be conventional. The clamps can be opened and closed by a mechanism similar to that described in above-mentioned U.S. Pat. No. 5,317,609. The block 40 for selecting pulling elements (FIG. 5) has a row of through holes in the same disposition as the pulling elements. Each hole in the selection block is provided with a retractable cover 61 preventing the corresponding pulling element from advancing when it is placed facing the hole by a pneumatic actuator such as 62. When the carriage moves towards the magazine containing rods in order to take hold of the rods, those elements which are in register with a cover become temporarily separated from the carriage and stop moving. This disposition is simple to implement when all of the assemblies to be loaded have the same rod distribution pitch, even if the rods are replaced by other elements at different locations. If, on the contrary, provision is made for loading assemblies having pitches that are very different, it can be necessary either to provide a plurality of different connection means, at appropriate pitches, or else to ensure that the pulling elements are very flexible. Rocking Bench (FIGS. 6 and 7) The rocking bench 22 holds the skeleton structure of the assembly for loading while the rods are being inserted, and optionally while the bottom and top nozzles are being mounted and guide tubes are fixed in the nozzles. It also serves to swing a loaded assembly from the horizontal position to the vertical position so as to enable it to be taken and transported without deforming by handling means such as an overhead crane. The rocking bench 22 can be regarded as comprising a frame 64 and an upending beam 66. The beam is designed to receive the skeleton structure 68 of the assembly for loading, represented in FIG. 6 by the grids 70 and the virtual envelope or outline 72 of the pull bars of a PWR assembly. The beam also carries an insert magazine 74 and a system 76 for extracting inserts. They can be of relatively conventional structure, and in particular of the structure described in above-mentioned U.S. Pat. No. 5,317,609, and they are designed so as to be easily replaceable depending on the nature of the assembly to be built up, for example by fixing them using eccentric clamping means. The frame 64 is typically rigidly secured to the ground. It is generally built as an all-welded structure. The beam 66 pivots relative to the frame 64 about a horizontal axis 78. To minimize its weight, the beam is advantageously constituted by an all-welded structure or a one-piece machined element whose configuration equalizes stresses and which can be designed by the finite element computation technique. An actuator 80, e.g. an electrical actuator, serves to move the beam 66 from the horizontal position in which it is shown in continuous lines in FIG. 7 to the vertical position shown in chain-dotted lines. When the actuator is extended and the beam is in the horizontal position, the end of the beam rests on a support 82 which is generally fixed to the ground. When the beam is in its vertical position, it enables a winch (not shown) to take hold of the top nozzle of the assembly and move it with minimum stress. To provide biological protection for operators who need to penetrate temporarily into the enclosure, the upending bench 22 is provided with a biological protection hood 24. In order to facilitate handling and upending of the beam, the hood is made up of a plurality of parts capable of sliding relative to one another between the position shown in FIG. 8 where they are placed side by side, and a position in which they overlap. In the embodiment of FIGS. 8 and 9, the hood is made up of a bottom inner part 84, a top inner part 86, and a middle outer part 90. Each of the inner parts carries a closure hatch 92 suspended from a linkage 94 that can be moved vertically by motors 96. These parts can be provided with wheels 98 resting on rails placed on the ground. The component parts of the protection hood can be provided with rings enabling them to be lifted by an overhead crane. The reception magazine 16 can also be covered by a biological protection hood 100 (FIG. 8) that can be closed by means of a hatch 102. The insert magazine 74 (FIG. 10) is similar in structure to that described in document U.S. Pat. No. 5,317,609. However a special type of magazine is provided for each type of assembly to be loaded. It comprises a receptacle 110 having an end wall pierced by passages distributed in the same array as the rods to be loaded and intended for receiving inserts. To enable rapid disassembly, the receptacle 110 can have a stand 111 which engages in a socket fixed to the upending beam 66 by screws. A centering pin 112 fixed to the beam engages in a housing of the receptacle to guarantee accurate assembly, and a pressure screw 112 retains the receptacle. The receptacle 110 and a slideway (not shown) parallel thereto hold a perforated closure plate 114 captive which can be moved by a pneumatic actuator 116 between a position in which it closes the passage and a position in which it opens them. The insert magazine interposed between the pulling bench and the skeleton structure serves to engage inserts on the bars which guide them through the grids of the skeleton structure. The inserts are retained in the magazine by the closure plate while the inserts are being put into place on the pull bars. In one position of the plate, the inserts are locked, and in the other position, the pull bars fitted with the inserts can move freely through the magazine. Clamping Skeleton Structures to the Rocking Bench (FIGS. 11 and 12) To make it possible to switch quickly from loading one type of assembly to another, the upending bench is designed so that different clamping means can be installed and removed quickly. These clamping means hold the skeleton structure in a precise position. FIG. 12 shows one of the clamps 118, out of eight, for example, for locking a PWR assembly skeleton by clamping on its grids simultaneously. The moving elements of the clamps are shown in continuous lines in the positions they occupy when the clamp is closed, and in chain-dotted lines in the positions they occupy when the clamp is open. The clamp can be regarded as comprising a clamp pad 120 fitted with means for installing it quickly on the rocking beam, e.g. constituted by bars 122 engaging beneath a soleplate of the beam and clampable by means of screws. One of the flanks of the pad carries an actuator 124 which actuates a lateral shoe 126 for pressing the grid against the other flank of the pad. The other flank carries a pin 128 on which a lid 130 pivots between a closed position and an open position in which the lid extends the arm of the pad upwards. In this position, a skeleton can be inserted into the pad. Another actuator 134 carried by the lid 130 enables the grid to be pressed down against the bottom of the pad and enables it to be centered exactly in the vertical direction, with horizontal direction centering being performed by the actuator 124. The means for clamping a boiling water reactor assembly skeleton structure can have the structure shown in FIG. 11. To enable each clamp to be placed at a suitable location for assembly, the clamp is mounted on a lockable slide 135 mounted on a slideway 136 which is rigidly mounted on the upending beam. The slide is lockable by means of an eccentric. The clamp can be regarded as having a clamp pad on which two arms 138 and 140 are hinged. A double-acting pneumatic actuator 142 enables the two arms to be pivoted between a position in which they hold the skeleton structure captive and a position (shown in chain-dotted lines in FIG. 11) in which they release it. The arm 138 constitutes one of the side walls of a reception space. The arm 140 constitutes the other side wall and the lid. Each of the arms has shoes, similar to the shoe 126 shown in FIG. 12, serving to lock the skeleton structure in place. Each pivoting arm of each clamp can be provided with means for locking it in closed position, actuated by pneumatic actuators. Sensors make it possible to determine whether or not the clamp is closed. Pins can be provided on the clamp for retaining the skeleton structure in the axial position. Although the actuators of all the clamps can be controlled from a single pneumatic distributor in the example shown in FIG. 12, it is usually necessary for the example shown in FIG. 11 to provide an individual distributor for each clamp. To enable the actuators to be powered electrically and/or pneumatically and to enable the signals delivered by the sensors responsive to the condition of the clamp to be transmitted, the clamp is generally provided with a length of cable terminated by a connector for connection with a general feed cable placed under the beam. The frame 36 can also have a cable path followed by electrical and/or pneumatic connections between the solenoid valves and actuators for moving the pulling or pushing elements, and by a bus line for transferring electrical signals. Further clamps other than those shown in FIGS. 11 and 12 can be provided for assemblies of any other kind, and in particular for assemblies of hexagonal section. The pulling bench 26 can be provided with removable safety arms 42 to ensure that while rods are being pulled they are not pulled too far. FIG. 13 shows two removable arms 42 mounted on the cover block 40. These arms can be placed either in a horizontal working position (in continuous lines in FIG. 13) or in a vertical retracted position. The removable arms carry a photoelectric detector 144 placed on the path of the pulling elements and the rods at a location that is intermediate between the insert magazine 74 and the skeleton structure. During the pulling cycle, the arms are placed in the horizontal position and provide an alarm signal if a rod reaches the line of site of the photoelectric detector during a pulling operation.
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	description	This application is a continuation-in-part application of International Application No. PCT/EP2010/001265, filed Mar. 2, 2010 and published as WO 2011/107111 A1 on Sep. 9, 2011, the content of which is hereby incorporated by reference in its entirety and a continuation-in-part of Application No. PCT/EP2010/001266, filed Mar. 2, 2010 and published as WO/2011/107112 A1 on Sep. 9, 2011, the content of which is hereby incorporated by reference in its entirety. The present invention relates to an improved form of position detection. It is especially (but by no means solely), suitable for the detection of leaf positions in a Multi-Leaf Collimator (“MLC”) for use in radiotherapeutic apparatus. There are a wide range of contexts in which it is necessary to determine the position of a remote object. One particularly difficult context is in tracking the positions of individual leaves of a multi leaf collimator (MLC) in a linear accelerator (Linac). An MLC is used to shape the beam of X-ray (or other) radiation produced by a linac, in order to treat a patient. For the control system to deliver a correctly shaped dose, the position of each leaf must be accurately determined. Current methods that are employed use a combination of a standard CCTV camera and reflectors positioned on each leaf. A source of light illuminates the area in which the reflectors lie, and the CCTV camera receives an image that includes the reflections. The position of each leaf can then be determined from the position of each reflection within the CCTV camera image. The main problem with such systems is that the accuracy and resolution are limited by the number of pixels within the camera. This cannot be easily increased. In addition, most electronics (including CCTV cameras) are susceptible to radiation, and will eventually break down if exposed to significant levels. Radiation hardened cameras can be designed, but these are expensive and are usually bespoke, so are not readily available. Most CCTV cameras also have a limited frame rate of (typically) 30 frames per second at most. Where fast movements are required of the MLC leaves, this frame rate may not be adequate to keep up. Video processing software is also required, which is computationally demanding and therefore increases system complexity and cost. The CCTV camera is bulky, and needs to be fitted into an area where space is at a premium. Electromagnetic noise generated from within the Linac can interfere with the image quality and may interfere with the image processing software, causing a loss of leaf positions. Other contexts exist in which similar problems are encountered, however. Finally, CCTV cameras are responsive to a broad range of optical wavelengths, making them susceptible to sources of interference such as room lasers, fluorescent lights, and the like. The present invention therefore provides apparatus for location-detection of a plurality of objects within a region, comprising a reflective element mountable on each object of the plurality, and a plurality of reflective objects mounted at extremities of the region, a scanning light source adapted to issue a beam of light in a scanning pattern illuminating a point that moves over the region, and a detector for light reflected from the reflective elements or the reflective objects, together with a control unit adapted to report the position of an object based on the point in the scanning pattern at which the detector detects light returned from the reflective element relative to at least one point in the scanning pattern at which the detector detects light returned from a reflective object. The scan can then be repeated, as necessary. It further provides a multi-leaf collimator comprising an array of laterally spaced elongate leaves each having a longitudinal edge on which is mounted a reflective element, a scanning light source adapted to issue a beam of light in a scanning pattern, illuminating a point that moves over the longitudinal edges of a plurality of leaves of the array, and a detector for light reflected from the reflective elements. The scanning light source can comprise a source of light that illuminates a mirror, the mirror being controllably adjustable so as to direct a reflected beam of light in a scan pattern. The mirror is preferably part of a micro-electromechanical (“MEMS”) device, so as to allow swift and accurate control of the mirror position. The reflective objects are preferably fixed, so that the return signal that they produce when illuminated can occur at a fixed point in the scan cycle, making it straightforward to identify a return signal corresponding to a reflective element. At least one other mirror is preferably located (or locatable) in the radiation beam path, to permit the scanning light source to be located out of the beam path thereby protecting it from incident radiation. The scanning pattern can be a raster pattern, or a serpentine pattern, or another form of scanning pattern. It preferably illuminates a point that moves along the longitudinal edges of a plurality of leaves of the array in succession. Other scanning patterns are possible, however. The scanning light source can comprise a laser. The reflective element is preferably retro-reflective. The invention also relates to a radiotherapeutic apparatus comprising such a multi-leaf collimator. Tracking objects using MEMs mirrors and laser light is known, for example from U.S. Pat. No. 7,498,811 or from “Fast and high-precision 3D tracking and position measurement with MEMs micromirrors” Milanovic, V. & Wing, Kin Lo, IEEE/LEOS International Conference on Optical MEMs and Nanophotonics, 2008 (pp 72-73). However, it does not appear to have been applied to the detection of leaf positions in an MLC array. The Milanovic system also needs to interrogate the MEMS driver in order to ascertain the position of the mirror at the instant when the signal is detected or reflected. By placing reflective objects at known locations within the region and/or reflective elements on the moving object, the complexity and the cost of the system is reduced, and the accuracy of the system is improved, and multiple object positions (such as MLC leaves) can be tracked within the laser scanning field of view. In addition, placing so-called “boundary markers” allows the system to determine the object position relative to the boundary markers using simple algorithms based on the signal time measurements, and avoids the need to interrogate the MEMS driver. The reflective objects need not be at the actual boundaries of the region, although that is likely to be particularly straightforward to implement. The invention also provides a corresponding method. The following embodiment of the present invention is a position-detection system for the leaves of a multi-leaf collimator. This faces significant difficulties as set out above, which are alleviated by the present invention. However, the invention is also applicable in other contexts. FIG. 1 shows a known position tracking system for an array of MLC leaves. A radiation source 10 emits a beam of radiation 12 towards a treatment volume, illustrated (by convention) as being in a downward direction. In practice, the source is usually rotated around the treatment volume so as to irradiate the region of interest from a range of different angles, thereby reducing the irradiation of surrounding tissue. The shape of the radiation beam 12 is collimated by an MLC comprising an array of individual leaves 14. These are deep in the beam direction, elongate, and narrow in width. They are arranged side-by-side, and are individually moveable back and forth, into and out of the beam. Thus, a large number of such leaves can shape the beam as required. Typical MLCs include 40, 80 or 160 leaves depending on the desired resolution. The leaves are driven by an electric motor. In order to place the motor out of the beam and protect it from radiation damage, and in order to fit the required number of motors within the available space, the motors are usually spaced some distance from the leaf that they control and the necessary torque is transmitted from the motor to the leaf by a mechanical arrangement. The correct movement of the leaf is therefore subject to correct programming of the motor control unit, correct operation of the motor, and correct operation of whatever mechanical link is employed. It is therefore necessary to verify that the leaf is in fact in the correct position, to allow for failsafe operation of the apparatus. As shown in FIG. 1, this is achieved by providing a light source 16 to one side of the radiation source 10, which illuminates the MLC leaves via a pair of periscopically arranged mylar mirrors 18, 20. A reflector 22 is attached to a known location on an upper (in the orientation shown in FIG. 1) surface of the leaf 14, and reflects light back via the mirrors to a video camera co-located with the light source 16. The camera therefore records an image from which the position of each leaf is obtainable. This can be compared to the intended position of each leaf, and the treatment halted if an error greater than a certain magnitude is detected. FIG. 1 also shows the field lamp 24. This emits a light beam 26 which is incident on the rear of the first mylar mirror 18 through which at least part of the beam is transmitted. That then falls on the second mirror 20 and is reflected toward the treatment volume. Both the source/camera 16 and the field lamp 24 are positioned relative to the radiation source and the mirrors 18, 20 so that they are in a location that is optically identical to that of the radiation source 10. Thus, the camera receives a beam's-eye view of the leaves 14, and the field lamp illuminates the treatment volume in the same manner as the radiation, allowing it to be used for pre-treatment alignment of the patient. This form of camera is however undesirable for the reasons noted above. FIG. 2 shows an embodiment of the present invention. As before, a radiation source 110 emits a beam of radiation 112 towards a treatment volume, and the shape of the radiation beam 112 is collimated by an MLC comprising an array of individual leaves 114. A laser light source 128 is also provided, directed towards a 2D MEMs (Micro-Electra-Mechanical Systems) scanning mirror 130. This is controlled by a driver 132, which is programmed to cause the mirror 130 to oscillate so as to scan the laser light beam across each leaf 114 of the MLC, as described later. To direct the laser light to the leaves 114, mylar mirrors 118, 120 are provided as before. A beam splitter 134 is placed in the path of the laser light, between the oscillating mirror 130 and the first mylar mirror. This directs at least some of the laser light returned from the leaves 114 to a photo sensor 136 capable of detecting the laser light. On top of each leaf 114 is a retro-reflector 138 which reflects the laser light back in the direction from which it came, back towards the photo sensor 136. The time lapse between the laser light being reflected from the reference reflector and from the retro-reflector 138 is then used to determine the location of the retro-reflector 138, and thus the location of the leaf 114. The mirror then scans the laser beam along the length of the next leaf, repeating the process. In practice, the relevant position of the mirror is that which existed a few nanoseconds before receipt of the reflected light, to allow for travel time of up to about a metre in total. However, this small delay is unlikely to make a difference in practice. A means for calibrating the motion of the MEMs within each scan cycle is also included. Additional reference reflectors 140, 142 are affixed just beyond the ends of each leaf 114 at the edges of the scan pattern, such as on the supports 144, 146 that surround the leaves 114. In this way, the position of the sinusoidal or other scanning maxima/minima can be measured during each leaf-pair traversal. This can, in turn, be used to calibrate for amplitude and frequency jitter during each scan cycle. FIG. 3 shows a suitable scan pattern. Viewed from along the radiation beam axis, the array of leaves 114a-114k sit alongside each other and are at varying positions. They are supported in a frame made up of the supports 144, 146 at either end of travel of the leaves 114 and a side member 148. Further leaves (in addition to those depicted in FIG. 3) sit alongside the illustrated leaves but are omitted for clarity; other elements of the frame are likewise omitted. Each leaf 114a-114k has a corresponding reflector 138a-138k located at a known position along the leaf. FIG. 3 illustrates a convenient location, in which the reflector is proximate to, but not at, the end of the leaf. Such a location reduces the risk of damage to the reflector during handling. The oscillating mirror 130 scans the laser light along the serpentine path illustrated by dotted line 150. This takes the light beam along the length of each leaf 114 and will thus prompt a brief return signal as the light passes the respective reflector 138. The path has a maxima/minima that overlaps the supports 144, 146 at either end of travel of the leaves 114, at which points a continuous transverse reflector strip 152, 154 is provided. Thus, there is also a brief return signal at either end of the oscillation. This allows the oscillations to be calibrated, as the time delay between these signals should be constant and predictable, and also provides a frame around the return from the reflector 138 allowing it to be interpreted according to normal principles of pulse position modulation. Alternatively, a raster pattern can be adopted. The system also includes an in-built calibration for each scan cycle, to take into account any effects arising from possible non-linearities due to jitter and the sinusoidal nature of the scanning mirror's motion in the fast scanning axis (along the length of the MLC leaves). These effects are calibrated for by the use of one or more fixed calibration strips 156 upon which are mounted a series of reference reflectors 158 in a known pattern on the calibration strip. In this way, a comparison can be made with the theoretical sinusoidal motion of the MEMs mirror 130, and any deviations can be calibrated for. This also eliminates any drift that may arise from changes in temperature or wear in the scanning mirror mechanism over time. As illustrated in FIG. 3, the calibration strip is placed on the side member 148, but could be located elsewhere within the field of view of the detector 136. More than one such calibration strip could be provided. FIG. 4 illustrates an alternative scan pattern, also serpentine but transverse to the leaves 114 instead of along the leaves 114. Such a pattern would essentially scan through all the possible leaf positions and report which leaf was in that position, rather than scanning along each leaf and reporting the position of that leaf. The following advantages can be gained from such a system; Low cost: none of the active components need to be radiation hard as they can be located away from the direct beam, and are sufficiently small that they can be easily shielded. The mirror device is based upon standard silicon processes and is geared towards mass production. Such a system could easily be 10% of the cost of current camera based systems. High reliability: The scanning mirror devices are fabricated on silicon using standard processes. There is little or no friction to cause wear, therefore the expected lifetime of the scanning mirror is likely to be in excess of the lifetime of the Linac. The remaining components have no moving parts and can expect to have similar lifetimes. Additionally, the system could be made in such a way that it would not be susceptible to radiation, meaning that (potentially) the components may never need replacement. Higher accuracy. The accuracy of the system is limited only by the jitter of the controlling electronics, which can be as low as 0.02%. This offers greater potential accuracy when compared with traditional camera based systems. The resolution of the system can easily exceed that of the current camera based system. Higher scan rate. The achievable scan rate can easily exceed the 30 Hz currently available via a camera based system, allowing faster leaf movements to be tracked safely with improved control. Lower processing requirements. The algorithm used to determine leaf position is a simple one based on interpolation between the calibration points and the known scan pattern (such as sinusoidal), thus eliminating the need for complex image processing and fast processors to cope with the video data (most of which is discarded). Smaller size. The scanning mirror device itself is very small (typically 10 mm2). The laser source and the photo sensor are also similarly small in size, thus reducing space requirements for the system. Reduced interference. The system could be made such that it only responds to one wavelength of light. Filtering this wavelength from entering or leaving the head would be a simple matter, requiring only the necessary optical filters. Additionally, due to the nature of the signals generated (effectively pulse position modulation), the system's susceptibility to electromagnetic interference could be reduced. By using coded pulses of laser light, false pulses from electromagnetic or optical sources could be effectively eliminated. Redundancy. Due to the small size and low cost of the proposed system, an identical backup system could easily be employed to detect failures. As mentioned above, the specific embodiment described herein relates to detecting the positions of individual leaves in a multi-leaf collimator, but the invention is not limited to this context and could be applied in other situations. For example, the invention could be used to measure the shape or position of something by having a bank of leaves in contact with a surface of the item concerned. The leaves will then adopt the shape of the surface, which can then be measured. The surface may be mobile, in which case the moving surface will translate into corresponding motion of the leaves which can be measured by the system. Alternatively, a reflective strip can be affixed directly to a moving object or region, with a stationary reflective strip placed suitably nearby, so that the scanner can scan across both the moving and the stationary markers to determine the distance between them. This could find application in the field of respiration monitors, or in tools for the accurate placement of components in circuit boards, for example. It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention.
	description	This application claims the benefit of Chinese Patent Application No. 200710102914.9 filed May 11, 2007, which is hereby incorporated by reference in its entirety. The subject matter disclosed herein relates to a filter unit for adjusting the energy spectrum of X-ray, as well as an X-ray tube unit and an X-ray imaging system both having the filter unit. Particularly, the embodiments described herein are concerned with a filter unit of low cost permitting replacement of plural filters, as well as an X-ray tube unit and an X-ray imaging system. In an X-ray imaging system, X-ray is radiated to a subject after adjusting its energy spectrum with a filter. The filter is installed within a collimator box attached to an X-ray tube. In the invention of Japanese Unexamined Patent Publication No. 2006-226985, for obtaining a desired spectrum, the filter can be used by switching from one to another among plural filter plates secured to a rotary disc. For radiating X-ray to a standing subject or to a subject who is lying down, it is necessary for an X-ray tube unit to direct its angle in an arbitrary direction. To meet this requirement it is necessary to reduce the size of the X-ray tube unit. An X-ray irradiation unit disclosed in the above-referenced patent publication permits adjustment in multiple stages, but the size of an X-ray tube unit used is large. Besides, if the X-ray tube unit is provided with plural drive devices such as motors, it becomes complicated in structure and gets out of order more frequently, with an increase of the manufacturing cost. Accordingly, it is desirable to provide a filter unit simple in structure and small in size, as well as an X-ray tube unit and an X-ray imaging system both having the filter unit. For solving the above-mentioned problems, a first aspect provides a filter unit comprising a filter plate, the filter plate having a first filter, a second filter disposed in a first direction with respect to the first filter and a third filter disposed in a second direction having a predetermined angle from the first direction with respect to the first filter, a guide plate having a guide frame for movement of the filter plate in the first and second directions, and a drive device for moving the filter plate. According to this configuration, the filter plate having at least three filters can move in both first and second directions along the guide frame. Therefore, the filter unit of simple structure is provided. In a filter unit according to a second aspect, the drive unit comprises a single motor and a rotary disc adapted to rotate by the drive motor. According to this configuration, the filter plate can be moved in both first and second directions by a single drive motor. Since the filter plate can be moved in plural directions by a single drive motor, the filter unit is simple in structure and small-sized. In a filter unit according to a third aspect, the rotary disc and the filter plate are connected with each other through a link member. According to this configuration, since the rotary disc is connected to the filter plate through a link member, a rotational force of the rotary disc is applied to the filter plate. In a filter unit according to a fourth aspect, a bushing is attached to the link member and is adapted to move along the guide frame. According to this configuration, the bushing of the link member moves in the first and second directions along the guide frame. Consequently, a rotational force of the rotary disc is applied to the filter plate as a drive force acting in both first and second directions. In a filter unit according to a fifth aspect, the guide plate is centrally provided with a first aperture, the rotary disc is centrally provided with a second aperture, and the guide plate and the rotary disc are superimposed one on the other. According to this configuration, the filter plate rotates, centered at the first and second apertures. Besides, since the guide plate and the rotary disc are superimposed one on the other, a small space suffices and it is possible to attain the reduction in size of the filter unit. In a filter unit according to a sixth aspect, the filter plate has a square outline and the first direction and the second direction are orthogonal to each other. As can be seen from FIG. 5, if the filter plate has four filters, a square shape thereof is efficient and the filter unit can be constituted while saving space. A seventh aspect of the present invention provides an X-ray tube unit having an X-ray tube, a collimator and a filter unit, the filter unit comprising a filter plate, the filter plate having a first filter, a second filter disposed in a first direction with respect to the first filter and a third filter disposed in a second direction having a predetermined angle from the first direction with respect to the first filter, a guide plate having a guide frame for movement of the filter plate in the first and second directions, and a drive device for moving the filter plate. The filter plate has a first aperture formed centrally of the guide plate and a second aperture formed centrally of a rotary disc, the first aperture and the second aperture being in alignment with an axis joining an X-ray tube and an aperture of a collimator. In an X-ray tube unit according to an eighth aspect, the filter plate has a first aperture formed centrally of the guide plate and a second aperture formed centrally of a rotary disc, the first aperture and the second aperture being in alignment with an axis joining an X-ray tube and an aperture of a collimator. Further, such an X-ray tube unit is employable in an X-ray imaging system. According to such a configuration it is possible to provide an X-ray tube unit simple in structure and small-sized, and an X-ray imaging system using the X-ray tube unit can be reduced in cost. Besides, since the first and second apertures being in alignment with an axis joining the X-ray tube and the collimator aperture, an X-ray beam emitted from the X-ray tube is not obstructed halfway. According to the embodiments described herein, a filter unit having at least three filters can be provided in a simple structure and reduced size. Therefore, it is possible to implement a small-sized X-ray tube unit and an X-ray imaging system having such an X-ray tube unit. The best mode for carrying out the present invention will be described in detail hereinunder with reference to the drawings. The present invention is not limited to the best mode for carrying out the invention. Entire Configuration of X-ray Imaging System. FIG. 1 is a block diagram showing the configuration of an X-ray imaging system (CR: Computed Radiography) 100 for obtaining an X-ray transmitted image of a subject. System 100 includes an X-ray tube 10 for emitting X-ray, a stand 32 for radiographing a subject in a stand-up state, a table 36 on which the subject is to lie down, and an operator console 80. Flat panel detectors 34 for detecting X-ray after passing through the subject are attached to the stand 32 and the table 36 respectively. The operator console 80 has an X-ray data collector 86 for collecting image data transferred from the flat panel detectors 34. The image data collected and stored by the X-ray data collector 86 are subjected to image processing in an image processor 87 and an X-ray radioscopic image resulting from the image processing is displayed on a display 81. The X-ray tube unit 10 is suspended from the ceiling in a diagnostic room through a support post 23 which is extended and contracted with a motor (not shown). The X-ray tube unit 10 and the support post 23 are connected with each other by a ball joint structure and the X-ray tube unit 10 is rotatable in any direction. Therefore, X-ray can be radiated in any direction in accordance with a portion to be radiographed of the subject. The X-ray tube unit 10 may be mounted to a movable stand disposed on a floor. An X-ray power supply unit 84 is provided within the operator console 80 to supply electric power to the X-ray tube unit via an X-ray controller 82. The X-ray tube unit 10 houses therein an X-ray tube 11, a filter unit 12 and a collimator 13. The X-ray tube 11 emits X-ray at voltage and current controlled by the X-ray controller 82. The X-ray emitted from the X-ray tube 11 is adjusted its energy spectrum by the filter unit 12. The collimator 13 has an aperture whose area is changeable and X-ray having been adjusted to an appropriate irradiation area is radiated to a subject through the aperture. The filter unit 12 has plural filters so that the energy spectrum can be changed. In the X-ray tube unit 10 there is provided a drive motor 21 so that the plural filters in the filter unit 12 can be switched from one to another. The drive motor 21 is driven through a motor driver 89 under control by the X-ray controller 82. Configuration of Filter Unit 12. FIG. 2(a) is a perspective view showing the filter unit 12 according to an embodiment of the present invention and FIG. 2(b) is an exploded view thereof FIG. 3 illustrates the X-ray tube 10, including sectional views of the X-ray tube 11, filter unit 12 and collimator 13. The filter unit 12 includes a filter plate 121 having four filters, a guide plate 122 for guiding a moving route of the filter plate 121, and a drive plate 123 for moving the filter plate 121 in a predetermined direction. The filter plate 121 is provided with, for example, a beam attenuating filter F1 of approximately 0.0 millimeters (mm), a beam attenuating filter F2 of approximately 0.1 mm, a beam attenuating filter F3 of approximately 0.2 mm and a beam attenuating filter F4 of approximately 0.3 mm. By the beam attenuating filter F1 of approximately 0.0 mm is meant a filter-free state with only the frame of the filter plate 121 being present. With respect to the beam attenuating filter F1, the beam attenuating filter F2 is disposed in a first direction of the beam attenuating filter F1 and the beam attenuating filter F4 is disposed in a second direction orthogonal to the first direction. The beam attenuating filter F3 is disposed in the second direction with respect to the beam attenuating filter F2. The filters are not limited to beam attenuating filters, but may be any other filters insofar as they change the characteristics of X-ray. One of the filters may be a light shielding filter as a substitute for a light shielding shutter and a metallic sheet having a percentage light shielding of 100% may also be used as one filter. The filter plate 121 is centrally formed with a hole for passing therethrough of a pin 125-a of a link bar 125 which will be described later. The filters F1 to F4 are square in shape and the size of each filter is between approximately 10.0 square centimeters (cm2) and approximately 15.0 cm2. The filters F1 to F4 may be circular. The filter plate 121 is square in shape and its size is between approximately 20.0 cm2 and approximately 35.0 cm2. The material of the filter plate 121 is, for example, light-weight aluminum. The filter plate 121 is provided with, for example, a beam attenuating filter F1 of approximately 0.0 millimeters (mm), a beam attenuating filter F2 of approximately 0.1 mm, a beam attenuating filter F3 of approximately 0.2 mm and a beam attenuating filter F4 of approximately 0.3 mm. By the beam attenuating filter F1 of approximately 0.0 mm is meant a filter-free state with only the frame of the filter plate 121 being present. The filters are not limited to beam attenuating filters, but may be any other filters insofar as they change the characteristics of X-ray. For guiding a moving route of the filter plate 121, the guide plate 122 is formed with a guide groove 122-3 between an outer guide plate 122-1 and an inner guide plate 122-2. A bushing 127 is inserted into the guide groove 122-3. A through hole is formed in the bushing 127 and a pin 125-a of a link bar 125 to be described later passes through the through hole. The bushing 127 is circular or square in shape so as to be movable along the guide groove 122-3. The guide groove 122-3 is formed in conformity with the layout of the filters F1 to F4. One side of the guide groove 122-3 extends in the first direction and the other side thereof extends in the second direction. The bushing 127 is made up of a small-diameter bushing 127-a getting into the guide groove 123-3 and a large-diameter bushing 127-b put in contact with a surface of the outer guide plate 122-1 and that of the inner guide plate 122-2. Consequently, as can be seen from FIG. 3, the bushing 127 can move in a plane in contact with the guide plate 122. To prevent the bushing 127 from falling off the guide groove 122-3, a side face of the outer guide plate 122-1 and that of the inner guide plate 122-2 may be formed in such a structure as sandwiches the bushing 127. The guide plate 122 is fixed to a fixed portion of the X-ray tube unit 10 and is disposed in a fixed positional relation to the X-ray tube 11. That is, the outer guide plate 122-1 is fixed to a housing of the X-ray tube unit 10. Although in FIG. 2 the inner guide plate 122-2 is floating in the air, the inner guide plate 122-2 is connected in at least one position to the outer guide plate 122-1 or to another member. Centrally of the guide plate 122 is formed a first square aperture 122-4 for radiation of an X-ray beam emitted from the X-ray tube 11. Of course, the aperture 122-4 may be a circular aperture. The drive plate 123 is for moving the bushing 127 along the guide groove 122-3. An outer periphery gear is formed on an outer periphery of the drive plate 123 and it is in mesh with a driving gear 124. The driving gear 124 is connected to the drive motor 21. A link bar 125 capable of rotating 360° is secured to a certain position of the drive plate 123. The link bar 125 has a predetermined length and a pin 125-a is provided at one end of the link bar 125. A front end portion of the pin 125-a is threaded and passes through the through hole of the bushing 127, further through the central hole of the filter plate 121, then comes into engagement with a nut 126. Without specially providing the bushing 127, the thickness of the pin 125-a may be made equal to the width of the guide groove 122-3, thereby allowing the pin 125-a to fulfill the same function as the bushing 127. The drive plate 123 is fixed to the fixed portion of the X-ray tube unit 10 via a bearing (not shown) and is disposed in a fixed positional relation to the X-ray tube 11. Centrally of the drive plate 123 is formed a second circular aperture 123-1 for radiation of an X-ray beam emitted from the X-ray tube 11. Of course, the aperture 123-1 may be a square aperture. Although reference has been made above to an example in which the outer periphery gear is formed on the outer periphery of the drive plate 123, the outer periphery gear may be substituted by an inner periphery gear formed on an inner periphery of the drive plate 123. As shown in FIG. 3, the guide plate 122 and the drive plate 123 are disposed in such a manner that the center of the first square aperture 122-4 and that of the second circular aperture 123-1 are coincident with an axis joining the center of the X-ray tube 11 and that of the collimator 13. That is, the X-ray beam emitted from the X-ray tube 11 passes through the filter F in the filter plate 121 and then passes through the first square aperture 122-4. Further, the X-ray beam passes through the second square aperture 123-1, then through the collimator 13 and irradiates a subject (not shown). The filter unit 12 may be reversed right and left in FIG. 3, thereby allowing the X-ray beam to pass through the second circular aperture 123-1, then through the first square aperture 122-4 and thereafter through the filter F in the filer plate 121. Operation of Filter Unit 12. FIG. 4(a) is a plan view of the filter unit 12 and FIG. 4(b) is a drive explaining diagram equivalent to the filter unit 12. In FIG. 4(a), upon rotation of the drive motor 21, the drive gear 124 rotates and so does the drive plate 123. With rotation of the drive plate 123, the link bar 125 moves. The pin 125-a of the link bar 125 is connected to the bushing 127 and the bushing 127 moves along the guide groove 122-3, so that the link bar 125 rotates with respect to the drive plate 123. Since the guide plate 122 is fixed, the filter plate 121 moves along the guide groove 122-3. In the state of FIG. 4(a), an intermediate position between the beam attenuating filters F1 and F2 lies in the central square aperture of the guide plate 122 and the central circular aperture of the drive plate 123. When the drive motor 21 rotates, the filter plate 121 moves along the guide groove 122-3 with respect to the central square aperture of the guide plate 122 and the central circular aperture of the drive plate 123. For briefly explaining the operation of the filter plate 121, reference is here made to the drive explaining diagram of FIG. 4(b) equivalent to the plan view of FIG. 4(a). The guide groove 122-3, the drive plate 123, and the link bar 125, shown in FIG. 4(a), are equivalent to an imaginary guide groove 222-3, an imaginary bar 223, and an imaginary drive member 224, respectively, in FIG. 4(b). Likewise, the link bar 125 and the bushing 127 in FIG. 4(a) are equivalent to an imaginary link bar 225 and an imaginary bushing 227, respectively, in FIG. 4(b). FIG. 5 comprises operation diagrams showing in what manner the beam attenuation filters are switched one after another from F1 to F4 with use of drive explaining diagrams equivalent to the filter unit 12. FIG. 5(a) shows a state in which the beam attenuating filter F1 in the filter plate 121 is disposed in both the central square aperture of the guide plate 122 and the central circular aperture of the drive plate 123. With rotation of the drive motor 21, the filter unit 12 moves and, as shown in FIG. 5(b), the beam attenuating filter F2 is disposed in the central square aperture of the guide plate 122. As the drive motor 21 further rotates, the filter unit 12 moves and a shift is made from the beam attenuating filter F2 to the beam attenuating filter F3. FIG. 5(c) shows this shifting state. FIG. 5(d) shows a state in which a shift has been made to the beam attenuating filter F3 with movement of the filter unit 12. As the drive motor 21 further rotates, a shift is made from the beam attenuating filter F3 to the beam attenuating filter F4. FIG. 5(e) shows this shifting state. As the filter unit 12 further moves, a shift is made to the state of FIG. 5(f) in which the beam attenuating filter F4 is disposed in the central square aperture of the guide plate 122 and the central circular aperture of the drive plate 123. When the drive motor 21 is rotated reverse from its state shown in FIG. 5(f), a shift is made from the beam attenuating filter F4 and through the beam attenuating filters F3 and F2, then the beam attenuating filter F1 returns to the central square aperture of the guide plate 122, as shown in FIG. 5(a). In such an operation of the filter unit 12, the bushing 127 does not pass a hatched portion S of the guide groove 122-3. Therefore, in the hatched portion S it suffices for both outer guide plate 122-1 and inner guide plate 122-2 to be connected with each other. FIG. 6 illustrate filter plates of other shapes with use of explanatory diagrams equivalent to the filter unit 12. FIG. 6(a) illustrates a filter plate 121 of a regular triangle and FIG. 6(b) illustrates a filter plate 121 of a regular hexagon. The filter plate 121 of a regular triangle has three circular beam attenuating filters F1 to F3. The filter plate 121 of a regular hexagon has six circular beam attenuating filters F1 to F6. As shown in FIGS. 6(a) and 6(b), there are formed imaginary guide grooves 222-3 of a regular triangle and a regular hexagon, and as imaginary bushings 227 move along the imaginary guide grooves 222-3, the filter plates 121 of a regular triangle and a regular hexagon move and it is possible to replace beam attenuating filters one after another. Thus, as described above in connection with FIGS. 2 to 5, the shape of the filter plate 121 need not be limited to the square shape. The filter unit 12 may be constructed so as to omit the drive motor 21 and instead permit manual adjustment where required. Although the construction of the present invention has been described above in terms of an X-ray imaging system for obtaining an X-ray radioscopic image of a subject, the present invention is applicable also to an X-ray tube unit used for example in X-ray tomographic imaging apparatus. Moreover, the present invention is applicable to an industrial X-ray inspection apparatus using X-ray radiation. Further, the present invention is applicable not only to digital X-ray apparatus but also to X-ray apparatus for film.
041525850	abstract	An assembly for the transport and storage of nuclear fuel elements comprises a transport flask and a holder for fuel elements which fits within the flask. The assembly has self regulating ullage means which may comprise a plurality of eleongate reservoirs so designed that liquid is maintained in all the reservoirs when the assembly is in either the orientation used to load fuel elements into the assembly or in the orientation used to transport the fuel elements.
	description	This patent application is a continuation-in-part of prior U.S. patent application Ser. No. 11/193,941, filed Jul. 29, 2005 now U.S. Pat. No. 7,175,347 by Andrew P. Tybinkowski et al. for ANATOMICAL IMAGING SYSTEM WITH CENTIPEDE DRIVE, which patent application in turn claims benefit of: (i) prior U.S. Provisional Patent Application Ser. No. 60/670,164, filed Apr. 11, 2005 by Andrew P. Tybinkowski et al. for ANATOMICAL IMAGING SYSTEM WITH CENTIPEDE DRIVE; and (ii) prior U.S. Provisional Patent Application Ser. No. 60/593,001, filed Jul. 30, 2004 by Bernard Gordon et al. for ANATOMICAL SCANNING SYSTEM. The three above-identified patent applications are hereby incorporated herein by reference. This invention relates to anatomical imaging systems in general, and more particularly to Computerized Tomography (CT) imaging systems. Strokes are the third leading cause of death in the United States, causing approximately 177,000 deaths per year, and strokes are the number one cause of long-term disability in the United States, currently affecting nearly 5 million people. Strokes are caused by an abrupt interruption of the blood supply to the brain or spinal cord, thereby depriving the tissue of oxygen and resulting in tissue damage. Strokes typically occur in one of two forms: (i) hemorrhagic stokes, which occur with the rupture of a blood vessel; and (ii) ischemic strokes, which occur with the obstruction of a blood vessel. Rapid diagnosis is a key component of stroke treatment. This is because the treatment for an ischemic stroke may be contra-indicated for the treatment for a hemorrhagic stroke and, furthermore, the effectiveness of a particular treatment may be time-sensitive. More particularly, the current preferred treatment for an acute ischemic stroke, i.e., the administration of tPA to eliminate clots, is contra-indicated for a hemorrhagic stroke. Furthermore, the clinical data suggests that the medication used to treat ischemic strokes (i.e., tPA) is most effective if it is administered within 3 hours of the onset of the stroke. However, current diagnosis times, i.e., the time needed to identify that the patient is suffering from a stroke and to identify the hemorrhagic or ischemic nature of the stroke, frequently exceeds this 3 hour window. As a result, only a fraction of current ischemic stroke victims are timely treated with tPA. Imaging is generally necessary to properly diagnose (and hence properly treat) a stroke. More particularly, imaging is generally necessary to: (i) distinguish strokes from other medical conditions; (ii) distinguish between the different types of strokes (i.e., hemorrhagic or ischemic); and (iii) determine appropriate treatments (e.g., the administration of tPA in the case of an ischemic stroke). Computerized Tomography (CT) has emerged as the key imaging modality in the diagnosis of strokes. CT scanners generally operate by directing X-rays into the body from a variety of positions, detecting the X-rays passing through the body, and then processing the detected X-rays so as to build a computer model of the patient's anatomy. This computer model can then be visualized so as to provide images of the patient's anatomy. It has been found that such CT scanning, including non-enhanced CT scanning, CT angiography scanning and CT perfusion scanning, is able to provide substantially all of the information needed to effectively diagnose (and hence properly treat) a stroke. Unfortunately, in practice, the CT machine is typically located in the hospital's radiology department and the patient is typically received in the hospital's emergency room, and the “round-trip” time between the emergency room and the radiology department can frequently involve substantial delays, even in the best of hospitals. As a result, the time spent in transporting the patient from the emergency room to the radiology department and then back again can consume critical time which can compromise proper treatment of the patient. Thus, there is an urgent need for a new and improved CT machine which is particularly well suited for use in stroke applications. More particularly, there is an urgent need for a small, mobile CT machine which can be pre-positioned in the emergency room and moved to the patient so that the patient can be scanned at their current location, thus effectively eliminating “round-trip” delays and dramatically reducing the time needed to properly diagnose the patient. It is also important that the CT machine be relatively inexpensive, so as to facilitate its rapid proliferation and widespread use, e.g., pre-positioning in substantially all hospital emergency rooms and wide availability in outlying, low-volume settings (e.g., rural hospitals, ships, etc.). In this respect it should also be appreciated that CT scanners utilize X-ray tubes to generate the X-rays that are used to scan the patient. These X-ray tubes typically produce a substantial amount of heat when generating their X-rays, and this heat must generally be dissipated in order to improve image quality and increase component life. However, it can be troublesome to dissipate this heat, particularly inasmuch as the X-ray tube: (i) is encapsulated by the scanner housing, which tends to trap the heat from the X-ray tube; (ii) is generally in close proximity to many other internal scanner components, which can also trap heat; and (iii) must keep at least the emitter portion of the X-ray tube exposed, in order to permit the X-rays to exit the tube and pass into the patient. Such considerations have generally resulted in relatively complex X-ray tube assemblies comprising the X-ray tube and its associated cooling system, which can add to scanner size, weight and cost. This is particularly true inasmuch as the X-ray tubes (and hence their associated cooling systems) are generally mounted on large rotating drums which move the X-ray tubes concentrically about the patient so as to achieve the necessary scanning angles; such rotational mounting generally complicates the delivery of power and/or fluids to the X-ray tube's cooling system. Thus, there is a need for a new and improved approach for cooling the X-ray tube in a CT scanner, so as to help reduce the overall size, weight and cost of the CT scanner. In accordance with the present invention, there is provided a novel system for cooling the X-ray tube in a CT scanner, wherein the novel system facilitates a reduction in the size, weight and cost of the CT scanner. And there is provided a novel X-ray tube assembly for use in a CT scanner, wherein the novel X-ray tube assembly comprises an X-ray tube and its associated cooling system, and further wherein the novel X-ray tube assembly is relatively compact, lightweight and inexpensive. And there is provided a novel CT machine incorporating the novel X-ray tube assembly, wherein the novel CT machine is relatively small, mobile and inexpensive. In one form of the invention, there is provided a system for cooling an X-ray tube in a CT machine, wherein the X-ray tube is of the type comprising a rear cylindrical portion, a front cylindrical portion, an annular face formed at the intersection of the rear cylindrical portion and the front cylindrical portion, and an emitter opening formed in the front cylindrical portion for emitting X-rays from the X-ray tube, the system comprising: a heat sink for drawing heat away from the X-ray tube, the heat sink comprising an annular body having an axial opening, and a window extending radially through the annular body, the heat sink being configured to receive the front cylindrical portion of the X-ray tube within the axial opening of the heat sink, with the emitter opening of the X-ray tube being aligned with the heat sink window; and a collimator connected to the heat sink and adapted to collimate the X-rays emitted by the X-ray tube and “focus” those X-rays on an X-ray detector, the collimator comprising a collimator opening, with the collimator being connected to the heat sink such that the collimator opening is aligned with the heat sink window and the emitter opening of the X-ray tube; the heat sink body being formed out of the same material as the emitter of the X-ray tube, such that the emitter opening of the X-ray tube will remain aligned with both the heat sink window and the collimator opening even when the emitter of the X-ray tube undergoes thermal expansion. In another form of the invention, there is provided an X-ray tube assembly comprising: an X-ray tube comprising: a rear cylindrical portion; a front cylindrical portion; an annular face formed at the intersection of the rear cylindrical portion and the front cylindrical portion; and an emitter opening formed in the front cylindrical portion for emitting X-rays from the X-ray tube; and a system for cooling the X-ray tube in a CT machine, the system comprising: a heat sink for drawing heat away from the X-ray tube, the heat sink comprising an annular body having an axial opening, and a window extending radially through the annular body, the heat sink being configured to receive the front cylindrical portion of the X-ray tube within the axial opening of the heat sink, with the emitter opening of the X-ray tube being aligned with the heat sink window; and a collimator connected to the heat sink and adapted to collimate the X-rays emitted by the X-ray tube and “focus” those X-rays on an X-ray detector, the collimator comprising a collimator opening, with the collimator being connected to the heat sink such that the collimator opening is aligned with the heat sink window and the emitter opening of the X-ray tube; the heat sink body being formed out of the same material as the emitter of the X-ray tube, such that the emitter opening of the X-ray tube will remain aligned with both the heat sink window and the collimator opening even when the emitter of the X-ray tube undergoes thermal expansion. In another form of the invention, there is provided an anatomical imaging system comprising: a CT machine; and a transport mechanism mounted to the base of the CT machine, wherein the transport mechanism comprises a fine movement mechanism for moving the CT machine precisely, relative to the patient, during scanning; wherein the CT machine comprises: an X-ray tube assembly comprising: an X-ray tube comprising: a rear cylindrical portion; a front cylindrical portion; an annular face formed at the intersection of the rear cylindrical portion and the front cylindrical portion; and an emitter opening formed in the front cylindrical portion for emitting X-rays from the X-ray tube; and a system for cooling the X-ray tube in a CT machine, the system comprising: a heat sink for drawing heat away from the X-ray tube, the heat sink comprising an annular body having an axial opening, and a window extending radially through the annular body, the heat sink being configured to receive the front cylindrical portion of the X-ray tube within the axial opening of the heat sink, with the emitter opening of the X-ray tube being aligned with the heat sink window; and a collimator connected to the heat sink and adapted to collimate the X-rays emitted by the X-ray tube and “focus” those X-rays on an X-ray detector, the collimator comprising a collimator opening, with the collimator being connected to the heat sink such that the collimator opening is aligned with the heat sink window and the emitter opening of the X-ray tube; the heat sink body being formed out of the same material as the emitter of the X-ray tube, such that the emitter opening of the X-ray tube will remain aligned with both the heat sink window and the collimator opening even when the emitter of the X-ray tube undergoes thermal expansion. Looking first at FIGS. 1 and 2, there is shown a novel CT machine 5 formed in accordance with the present invention. CT machine 5 generally comprises a torus 10 which is supported by a base 15. A center opening 20 is formed in torus 10. Center opening 20 receives the patient anatomy which is to be scanned, i.e., the head of the patient when CT machine 5 is to be used in stroke applications. Looking next at FIG. 3, torus 10 generally comprises a X-ray tube assembly 25, an X-ray detector assembly 30, and a rotating drum assembly 35. X-ray tube assembly 25 and X-ray detector assembly 30 are mounted to the rotating drum assembly 35 in diametrically-opposing relation, such that the X-ray beam 40 (generated by X-ray tube assembly 25 and detected by X-ray detector assembly 30) is passed through the patient anatomy disposed in center opening 20. Furthermore, since X-ray tube assembly 25 and X-ray detector assembly 30 are mounted on the rotating drum assembly 35 so that they are rotated concentrically about center opening 20, the X-ray beam 40 will be passed through the patient's anatomy along a full range of radial positions, so as to enable the CT machine to create the desired computer model of the scanned anatomy. The various electronic hardware and software for controlling the operation of X-ray tube assembly 25, X-ray detector assembly 30, and rotating drum assembly 35, as well as for processing the acquired scan data so as to generate the desired computer model, may be of the sort well known in the art and may be located in torus 10 and/or base 15. Still looking now at FIG. 3, base 15 comprises a transport assembly 50 for moving the CT machine 5 about relative to the patient. More particularly, as disclosed in the aforementioned U.S. patent application Ser. No. 11/193,941, which patent application is hereby incorporated herein by reference, transport assembly 50 comprises a gross movement mechanism 55 for moving CT machine 5 relatively quickly across room distances, and a fine movement mechanism 60 for moving the CT machine precisely, relative to the patient, during scanning. As discussed in detail in the aforementioned U.S. patent application Ser. No. 11/193,941, gross movement mechanism 55 preferably comprises a plurality of casters, and fine movement mechanism 60 preferably comprises a plurality of centipede belt drives. Hydraulic apparatus 65 permits either gross movement mechanism 55 or fine movement mechanism 60 to be engaged with the floor, whereby to facilitate appropriate movement of the CT machine 5. Base 15 preferably also includes other system components in addition to those discussed above, e.g., batteries 70 for powering the electrical components of CT machine 5, etc. The various components of CT machine 5 are engineered so as to provide a relatively small, mobile and inexpensive CT machine. Among other things, and as will hereinafter be discussed in further detail, X-ray tube assembly 25 is engineered so as to be relatively compact, lightweight and inexpensive. CT machine 5 is particularly well suited for use in stroke applications. More particularly, CT machine 5 is a small, mobile unit which can be pre-positioned in the emergency room and moved to the patient so that the patient can be scanned at their current location, thus eliminating delays due to patient transport and thereby dramatically reducing the time needed to properly diagnose the patient. In addition, the CT machine 5 is relatively inexpensive, so as to facilitate its rapid proliferation and widespread use, e.g., pre-positioning in substantially all hospital emergency rooms and wide availability in outlying, low-volume settings (e.g., rural hospitals, ships, etc.). Thus, the mobile CT machine 5 can be located in the emergency room of a hospital and, when a patient presents stroke symptoms, the patient can be immediately scanned in the emergency room so as to determine if the patient is experiencing a stroke and, if so, to determine the nature of the stroke (i.e., hemorrhagic or ischemic). This may be done quickly and easily by moving the CT machine across the emergency room to the patient's gurney using the casters of gross movement mechanism 55 and then, while the patient remains on their gurney, scanning the patient by precision-advancing the CT machine relative to the patient using the centipede belt drives of fine movement mechanism 60, so that the scanning zone of the CT machine is moved relative to the patient. Thus, with the new CT machine 5, the patient can be scanned in the emergency room while remaining on their gurney, without ever having to be moved from the emergency room to the radiology department and then back again, thereby eliminating the traditional scanning delays associated with conventional CT scanners and thus facilitating proper stroke treatment. As noted above, it is desirable for novel CT machine 5 to be small, mobile and inexpensive in order to enhance its use in stroke applications. To that end, CT machine 5 includes a novel X-ray tube assembly 25 which addresses these goals. More specifically, X-ray tube assembly 25 is engineered so as to be relatively compact, lightweight and inexpensive. Looking now at FIGS. 4 and 5, there is shown the novel X-ray tube assembly 25 and rotating drum assembly 35. Rotating drum assembly 35 comprises an annular drum 75 (FIG. 5). A face plate 80 (FIGS. 4 and 5) is secured to the front side of annular drum 75, so that face plate 80 rotates in conjunction with annular drum 75. X-ray tube assembly 25 is mounted to face plate 80 so that the X-ray tube assembly 25 also rotates in conjunction with the drum. Looking next at FIGS. 4-8, X-ray tube assembly 25 generally comprises a mount 100 for supporting the various components of X-ray tube assembly 25 and securing those components to face plate 80; a power connector 105 for delivering power from a power source to X-ray tube assembly 25; an X-ray tube 110 for emitting X-rays; a heat sink 115 for drawing heat away from X-ray tube 110; a collimator support 120; and a collimator 125 for collimating the X-rays emitted by X-ray tube 110 and “focusing” those X-rays on X-ray detector 30 (FIG. 3). The various components of the novel X-ray tube assembly 25 are designed to interconnect with one another so as to collectively form a relatively compact, lightweight and inexpensive “monoblock” assembly as shown in FIGS. 4-8. More particularly, and looking now at FIGS. 6-8, 9 and 10, mount 100 generally comprises a frame 130 which includes a canister 135 for receiving other components, as will hereinafter be discussed, and a pair of brackets 140 (FIGS. 6 and 7) for securing frame 130 to face plate 80. Additionally, and looking now at FIGS. 6-8 and 11-13, power connector 105 is attached to mount 100 so as to supply power contacts to, and close off, the rear end of canister 135. X-ray tube 110 is shown in FIGS. 14 and 15. X-ray tube 110 is preferably of the sort well known in the art (e.g., it may be a RAD-12™ Rotating Anode X-ray Tube of the sort manufactured by Varian Medical Systems of Palo Alto, Calif.), and is generally characterized by a rear cylindrical portion 141, a front cylindrical portion 142, an annular face 143 formed at the intersection of rear cylindrical portion 141 and front cylindrical portion 142, rear electrical connectors 145 for delivering power to X-ray tube 110, an emitter opening 150 for emitting X-rays from the X-ray tube, and an alignment keyway 155 for use in appropriately aligning X-ray tube 110 in the X-ray tube assembly 25, as will hereinafter be discussed. While not shown in the drawings, it will be appreciated by those skilled in the art that the X-ray tube's anode is disposed in front cylindrical portion 142, adjacent to emitter opening 150. Looking next at FIGS. 16 and 17, heat sink 115 is characterized by a front cylindrical portion 170, a rear cylindrical portion 175 terminating in an end surface 176, an annular face 180 formed at the intersection of front cylindrical portion 170 and rear cylindrical portion 175, an axial opening 183 extending along the length of heat sink 115, a window 185 for passing X-rays through heat sink 115, and a front recess 190 (FIG. 16) for receiving a portion of collimator support 120, whereby to connect collimator 125 to heat sink 115, as will hereinafter be discussed. In order to increase the heat transfer capacity of heat sink 115, it is preferable to have multiple openings formed in the heat sink, whereby to increase its effective surface area. These multiple openings are preferably in the form of a plurality of circumferential slots 195, and a plurality of radial slots 200, formed in both front cylindrical portion 170 and rear cylindrical portion 175. As seen in FIG. 18, heat sink 115 is mounted onto X-ray tube 110 by seating heat sink 115 on the X-ray tube's front cylindrical portion 142, with the rear surface 176 (FIG. 17) of heat sink 115 engaging annular face 143 (FIG. 14) of the X-ray tube, and with window 185 (FIGS. 16 an 17) of heat sink 115 aligned with emitter opening 150 (FIG. 14) of X-ray tube 110. This arrangement positions the heat-conveying mass of heat sink 115 adjacent to the heat-producing anode of X-ray tube 110, and permits X-rays exiting emitter opening 150 to pass through the heat sink via window 185. As seen in FIGS. 19 and 20, X-ray tube 110 and heat sink 115 are positioned, as a subassembly, in canister 135 so that the X-ray tube's electrical connectors 145 electrically connect to power connector 105, whereby to deliver electrical power to X-ray tube 110. As seen in FIGS. 21 and 22, which show the assembly with the heat sink rendered transparent so as to show additional construction details, an alignment pin 156 (FIG. 22) is used to align the alignment keyway 155 in X-ray tube 110 with a corresponding alignment keyway 157 formed in canister 135, whereby to ensure proper orientation of the X-ray tube relative to mount 100. A plurality of clamps 160 (FIGS. 21 and 22), secured by bolts 165, engage annular face 143 of the X-ray tube so as to secure X-ray tube 110 in position within canister 135. Preferably Belleville washers (or other spring washers) are provided to accommodate any thermal expansion of the components. Looking next at FIGS. 6, 8, 19-22 and 23-25, collimator support 120 supports collimator 125 relative to X-ray tube 100 and heat sink 115, with collimator opening 205 (FIG. 25) aligned with window 185 (FIGS. 16 and 17) of heat sink 115 (and hence with emitter opening 150 of X-ray tube 110). More particularly, an arm 210 of collimator support 120 is received in front recess 190 of heat sink 115, with a base 215 (FIGS. 23 and 24) of collimator support 120 being received in a recess 220 (FIGS. 19 and 20) of mount 100. As a result of this construction, collimator opening 205 is kept in alignment with window 185 of heat sink 115 and hence in alignment with emitter opening 150 of X-ray tube 110, so that collimator 125 may “focus” the X-rays emitted by X-ray tube 110 onto X-ray detector 30 (FIG. 3). Heat sink 115 is preferably formed out of the same material as the anode of X-ray tube 110, such that heat sink 115 will thermally expand at the same rate as the anode of X-ray tube 110, thereby ensuring that window 185 of heat sink 115 remains in alignment with the anode of the X-ray tube 110 even if X-ray tube 110 gets hot and undergoes some thermal expansion. Furthermore, since collimator 125 is fixed to heat sink 115 via collimator support 120, collimator opening 205 remains aligned with window 185 of heat sink 115 even if thermal expansion causes some change in the position of window 185 of heat sink 115. Thus, by virtue of the foregoing construction, the emitter of X-ray tube 110 will remain in axial alignment with window 185 of heat sink 115 and opening 205 of collimator 125, regardless of any thermal expansion occurring among the parts. CT machine 5 is preferably used as follows. When a patient arrives at the emergency room presenting stroke-like symptoms, they are quickly scanned in the emergency room, on their gurney, using CT machine 5, which is pre-positioned in the emergency room. More particularly, CT machine 5 is raised on its gross movement mechanism 55, i.e., by actuating hydraulic actuators 65. CT machine 5 is then moved on its casters to the patient, so that the patient (while still lying on their gurney) is positioned within the center opening 20 of CT machine 5. Thereafter, hydraulic apparatus 65 is activated so that CT machine 5 is supported on its fine movement mechanism 60 (i.e., the centipede belt drives). Scanning is then commenced, with fine movement mechanism 60 precision-advancing CT machine 5 relative to the patient during scanning. As this occurs, heat generated by X-ray tube 110 during scanning is quickly and efficiently dissipated by the X-ray tube assembly 25, due to the unique construction of the monoblock assembly. It should be appreciated that the present invention is not limited to use in medical applications or, indeed, to use with CT machines. Thus, for example, the present invention may be used in connection with CT machines used for non-medical applications, e.g., with CT machines which are used to scan inanimate objects. Furthermore, the present invention may be used with non-CT-type scanning systems. In essence, the present invention has application to any X-ray based device which requires simple and effective cooling of the X-ray tube. It will be appreciated that still further embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure. It is to be understood that the present invention is by no means limited to the particular constructions herein disclosed and/or shown in the drawings, but also comprises any modifications or equivalents within the scope of the invention.
	claims	1. A nuclear fuel rod comprising at least two fuel pellets, a cladding tube surrounding the fuel pellets, and at least two burnable absorbers inside the cladding tube,wherein each of the burnable absorbers consists of a burnable absorber material located in a cladding material which surrounds a perimeter edge, a top surface, and a bottom surface of the burnable absorber material,each of the burnable absorbers has a disk shape,the burnable absorber material of at least two burnable absorbers have a different surface area and/or volume,the cladding material is a zirconium-based alloy, each cladding material has a substantially same surface area and/or volume, andeach of the burnable absorbers is located on a respective one of the fuel pellets such that the burnable absorbers and the fuel pellets are stacked along a longitudinal direction of the nuclear fuel rod,and wherein a self-shielding effect is optimized by the different surface area and/or the volume of the burnable absorber material of the at least two burnable absorbers. 2. The nuclear fuel rod of claim 1, wherein in the nuclear fuel rod, each of the at least two burnable absorbers is located between at least two or more fuel pellets. 3. The nuclear fuel rod of claim 1, wherein the burnable absorber material comprises one or more selected from the group consisting of Gadolinium (Gd), gadolinia (Gd2O3), erbium (Er), Er2O3, and boron carbide (B4C). 4. The nuclear fuel rod of claim 1, wherein the diameter of each of the at least two burnable absorbers is equal to the diameter of the at least two fuel pellets. 5. The nuclear fuel rod of claim 1, wherein the thickness of each of the at least two burnable absorbers is approximately 0.1 mm-2.0 mm. 6. The nuclear fuel rod of claim 1, wherein in each of the at least two burnable absorbers, the diameter of the burnable absorber material is approximately 30-95% of the diameter of the at least two fuel pellets. 7. A nuclear reactor comprising the nuclear fuel rod of claim 1. 8. A method for manufacturing a nuclear fuel rod, the method comprising:preparing disk-shaped burnable absorbers, each consisting of a burnable absorber material located in a cladding material which surrounds a perimeter edge, a top surface, and a bottom surface of the burnable absorber material,the burnable absorber material of at least two burnable absorbers have a different surface area and/or volume,the cladding material being a zirconium-based alloy, each cladding material has a substantially same surface area and/or volume; andstacking, in a cladding tube along a longitudinal direction of the nuclear fuel rod, at least two fuel pellets and said at least two burnable absorbers, so that each of the burnable absorbers is located on a respective one of the fuel pellets;and wherein a self-shielding effect is optimized by the different surface area and/or the volume of the burnable absorber material of the at least two burnable absorbers.
	description	This application is a National Phase Application of PCT International Application No. PCT/FR2012/050548, International Filing Date Mar. 15, 2012, claiming priority of French Patent Application No. 1152101, filed Mar. 15, 2011, both of which are hereby incorporated by reference. The present invention relates to a method for operating a pressurized water nuclear reactor during load follow. FIG. 1 schematically illustrates such a pressurized water nuclear reactor 1, which comprises in a conventional manner: a core 2 divided into an upper area and a lower area and producing power, steam generators 3, a single generator being represented, a turbine 4 coupled to an electric power generator 5, and a condenser 6. The reactor 1 also comprises a primary circuit 8 equipped with pumps 9, a single pump being represented, and in which pressurized water circulates, along the path indicated by the arrows. This water rises particularly to the core 2 to be heated therein while assuring the cooling of the core 2. The water also assures a function of moderation, in other words of slowing down the neutrons produced by the nuclear fuel. The primary circuit 8 further comprises a pressuriser 10 making it possible to regulate the pressure of the water circulating in the primary circuit 8. The water of the primary circuit 8 also supplies the steam generators 3 where it is cooled while assuring the vaporisation of water circulating in a secondary circuit 12. The steam produced by the generators 3 is channelled by the secondary circuit 12 to the turbine 4 then to the condenser 6 where said steam is condensed by indirect heat exchange with the cooling water circulating in the condenser 6. The secondary circuit 12 comprises, downstream of the condenser 6, a pump 13 and a heater 14. The core 2 comprises fuel assemblies 16 which are loaded in a vessel 18. A single assembly 16 is represented in FIG. 1, but the core comprises a plurality of assemblies 16. The fuel assemblies 16 comprise nuclear fuel rods formed, in a conventional manner, of an alloy cladding, based on zirconium, enclosing a stack of nuclear fuel pellets based on uranium oxide or a mixture of uranium oxide and plutonium oxide. The reactor 2 comprises control rods 20, also known as control rod clusters, for controlling the reactivity of the core, which are arranged in the vessel 18, above certain assemblies 16, and which are capable of occupying a plurality of insertion positions in the core. A single rod 20 is represented in FIG. 1, but the core 2 comprises several tens of control rod clusters 20. The control rods 20 can be moved vertically by mechanisms 22 so as to be inserted, in different insertion positions, in the fuel assemblies 16 that they overhang. In a conventional manner, each control rod 20 comprises a plurality of control pencils made of neutron absorbing material. Thus, the vertical movement, or insertion state, of each rod 20 inside the fuel assemblies 16 makes it possible to regulate the reactivity of the core of the reactor 1, thereby authorising variations in the overall power supplied by the core 2, from zero power up to rated power (hereafter noted RP). It may prove to be useful, in fact, particularly in countries such as France where 80% of the electricity is produced by nuclear reactors, that the overall power supplied by the reactors varies in order to adapt to the needs of the grid that they supply; this is then known as grid monitoring or load follow. During load follow, the power produced by the reactor is regulated so as to correspond to a programme pre-established by the service operating the grid. The adjustment of the power supplied by the reactor is achieved by operating means positioning control rods constituted of neutrophage element in different insertion positions in the core so as to absorb more or less the neutrons and/or by optionally adjusting the concentration of a neutron absorbing compound, such as boron, in the primary coolant, as a function of the desired power and/or measurements from the instrumentation of the core of the reactor. For example, the operating means are formed of a set of electronic and electrical equipment which, from measurements from instrumentation chains and by comparing them to limit levels, elaborate orders of movement of control rods 20 and/or modification of the boron concentration in the primary coolant by injection of water (dilution) or boron (boronation). Different modes of operating a pressurized water nuclear reactor are known. Generally speaking, the operation consists in controlling and regulating to the minimum the average temperature of the primary coolant Tav and the distribution of power (thermal and neutronic) and in particular the axial distribution of power DA in order to avoid the formation of a power imbalance between the upper area and the lower area of the core. The methods of regulation of these parameters vary as a function of the different operating modes used. Generally speaking, the average temperature Tav is regulated by the movement of the control rods 20 as a function of different parameters such as the power required at the turbine, the standard value of the temperature of the coolant, and/or optionally by modification of the boron concentration in the primary coolant, which makes it possible indirectly to adapt the positions of the control rods 20 to a desired position, particularly in order to obtain an axial distribution of desired power DA and/or a capacity of rapid rise in the power of the core to the desired power. The choice of the mode for operating a nuclear reactor is determined by taking into consideration the fact that the action of the control rods has immediate effects, whereas the action by injection of boron in solution is comparatively slower. Moreover, the increase in the boron concentration in solution in the primary coolant requires boric acid storage and injection means and thus imposes additional design constraints. Thus, there is a tendency only to use the injection of boron or water in solution to correct the long term effects on the operating reactivity of the reactor, in other words essentially the xenon effect and the ageing of the fuel. In order to meet the needs of the grid, the operation of the reactor is thus preferentially carried out by the movement of the control rods. However, the insertion of the control rods affects, in a prejudicial manner, the axial distribution of power produced in the reactor. This may result in the formation of power peaks in the core as well as the development of oscillations of the xenon concentration in the longer term, favourable to the accentuation of these power peaks, factors intervening in a restrictive manner in the operating procedure and imposing a corrective recourse by modifying the boron concentration in the primary coolant. Yet, in load follow, in other words with a power production level following a daily curve, and even in slave mode, by remote control, the variations in power production multiply the control actions, with the aforementioned unfavourable consequences, engaging in an important manner the control rod mechanisms and leading to considerable volumes of effluents due to repeated operations of dilution and boronation of the coolant. In order to meet these difficulties, methods for operating a pressurized water reactor have been developed determining the positions of the control rods in the core, making it possible to limit perturbations of the axial power distribution and resorting to the use of boron, the concentration of which is adjusted so as to mainly compensate the effects of the release of xenon and the ageing of the fuel rods. However, this operating method is not always optimised and does not always make it possible to minimise the volumes of effluents as well as the movement of the control rod clusters. In addition, the minimisation of the volumes of effluents as well as the engaging of the control rod insertion mechanisms remains a permanent concern of the operator. In this context, the invention aims to resolve the aforementioned problems by making it possible to optimise the reference position of the control clusters in the core of the reactor, minimise the movements of said clusters and thereby optionally minimise the volumes of effluents generated by the operations of dilution/boronation of the primary coolant during power variations of the reactor. To this end, the invention proposes a method for operating a pressurized water reactor, said reactor comprising: a core producing power; a plurality of control rod clusters for controlling the reactivity of said core capable of occupying in the core a plurality of insertion positions staged vertically from a high position; means for acquiring quantities representative of the operating conditions of the core; said method comprising the steps that involve: measuring the effective power of the nuclear reactor; acquiring a reference value for the desired target power of the nuclear reactor; said method being characterised in that it further comprises the steps that involve: acquiring an estimated duration for the increase in power in order to achieve said reference value for the desired target power, said estimated duration corresponding to the time taken for the power to increase from said effective power to said reference value for the target power; determining the reference position of at least one control rod cluster among said plurality of control rods in order to achieve said reference value for said desired target power as a function of said estimated duration, of said measured effective power and of said reference value for said target power; monitoring the position of said at least one control rod cluster so as to position it in its reference position (Z). Thanks to the invention, it is possible to optimise the reference position of the control rods during load follow by taking into account the evolution of the xenon effect, neutrophage element, intervening during said load follow. The optimised reference position is determined by taking into account a time parameter representative of the estimation of the duration for the increase in power to achieve the reference value for the desired target power As an example, the reference position retained could be that giving the best behaviour of the core during the power rise, in other words the position enabling the control rods to find themselves in the optimal position when the target power is achieved. For example, the optimal position of the control rods at 100% rated power, which can be the normal position of the control rods in 100% stabilised operation (i.e. the nominal position of the control rods). Thanks to the method according to the invention, it is also possible to minimise the volumes of effluents in the core of the reactor by suitable management of the dilution and boronation operations while preserving the control rod movement mechanisms by the reduction in the number of steps of the control rods by limiting the movements of the control rods uniquely to movements necessary for the power variation within the desired duration. According to another characteristic, the method comprises a step consisting in acquiring an estimated instant of the start of said power increase, said estimated instant corresponding to the end of the stage of said effective power and being taken into account in the step of determining the reference position of at least one control rod cluster. According to another characteristic, the control step is carried out so that said at least one control rod cluster is positioned in its reference position at the latest at the start of said power increase. According to another characteristic, the method comprises a step of regulation of the concentration of a neutrophage element such as boron in the coolant as a function of said reference position of at least one control rod cluster among said plurality of control rods. Regulation is taken to mean one or more operations of reduction or increase in the concentration of said neutrophage element such as boron (i.e. dilution or boronation) in the primary coolant of the nuclear reactor. According to another characteristic, said step of determining said reference position of said at least one control rod cluster is carried out via software means implementing a neutron code. Neutron code is taken to mean a code resolving periodically the diffusion equation and updating the isotope balance of the core during the burnup of the fuel. According to another characteristic, said step of determining said reference position of said at least one control rod cluster comprises: a sub-step of determining a first position of at least one control rod cluster as a function of said measured effective power and said reference value for the target power; a sub-step of determining the variation in the xenon concentration in said core of said reactor during the future power increase, said variation in xenon concentration being a function of said estimated duration, and/or of said measured effective power and/or of said reference value for the target power; a sub-step of determining a corrective factor of the position of at least one control rod cluster as a function of said variation in the xenon concentration. According to another characteristic, said step of determining said reference position of said at least one control rod cluster comprises: a sub-step of determining a first position of at least one control rod cluster as a function of said effective measured power and of said reference value for the target power; a sub-step of determining the variation in the xenon concentration in said core of said reactor during the future power increase, said variation in xenon concentration being a function of said estimated duration, and/or of said measured effective power and/or of said reference value for the target power, and/or of said estimated instant of start of the increase in power; a sub-step of determining a corrective factor of the position of at least one control rod cluster as a function of said variation in the xenon concentration. FIG. 1 has already been described previously with reference to the general presentation of the invention. FIG. 2 illustrates in a schematic manner the main steps of the optimisation method according to the invention aiming to manage a nuclear reactor and particularly a pressurized water reactor. A pressurized water reactor is represented in a symbolic manner by the reference 100, in FIG. 2 and comprises as indicated previously in FIG. 1: a core 30 comprising nuclear fuel assemblies; a vessel 32 comprising the core 30 of the reactor; steam generators (not represented) able to drive an alternator coupled to the electrical distribution grid; a primary circuit 31 connecting in closed circuit the vessel 32 to a primary side of the steam generator; a secondary circuit (not represented) connecting in closed circuit a secondary side of the steam generators to a turbine. The primary circuit 31 is able to assure the circulation through the core 30 of a pressurized primary coolant along the path indicated by the arrows. The primary coolant is essentially formed of water and dissolved boron. The coolant rises to the core 30, heating up on contact with the fuel assemblies, thereby assuring the cooling of the core 30. The primary coolant also supplies the steam generators, where it is cooled by giving up its heat. The secondary circuit is able to assure the circulation of a secondary coolant, essentially comprising water, said liquid being vaporised in the steam generators by the heat given up by the primary fluid. The steam produced by the generators is channelled to the turbine that it drives, then to a condenser in which the steam is condensed by indirect heat exchange with the cooling water circulating in the condenser. The condensed steam is then sent to the steam generators. The alternator coupled to the turbine supplies to the grid an electric power, variable as a function of grid demand. The reactor 100 is thus operated so as to adapt permanently the power supplied by the core to the electric power required by the grid, by varying the reactivity of the core. In this aim, the reactor 100 further comprises: means for adjusting the boron concentration (not represented) dissolved in the primary coolant, by injection of a solution of concentrated boric acid into the primary liquid in order to vary the concentration of boron upwards, or by injection of pure water in order to vary the concentration of boron downwards; control rods 40 for controlling the reactivity of the core 30, each of the rods 40 being capable of occupying in the core 30 a plurality of insertion positions staged vertically from a high position; means for selectively inserting each control rod cluster into the core 30, from the top down, down to one of the insertion positions determined by the method; means for acquiring quantities representative of the operation of the reactor, such as: the neutron flux, the temperature of the primary liquid in the cold branch TBF of the primary circuit, the temperature of the primary liquid in the hot branch TBC of the primary circuit, the position of the control clusters 40; means for measuring the effective power Pe of the core from quantities representative of the operation of the reactor; means for acquiring operating references set by an operator by means of a human/machine interface (not represented). The operating method according to the invention represented in FIG. 2 makes it possible to minimise the movements of the control rods 40 during load follow by the determination of a reference position Z for the control rods 40 taking into account the variation in the xenon effect during load restoration, the method determining the position of the control rods 40 as a function of the estimated duration of the return power increase. The method according to the invention comprises a first step of acquisition of the effective power Pe, illustrated by block 81. During steps illustrated respectively by blocks 82 and 83, the acquisition means acquire a reference value for the target power Pc, that it is wished to achieve, as well as a duration DURATION corresponding to the estimated time interval of the increase in power of the reactor to achieve the reference value Pc starting from the value of the effective power Pe. These reference values Pc, DURATION are entered by the operator during the programming of the load follow via a human/machine interface (not represented). The operating method further comprises a step of determining the reference position Z of the control rods 40, illustrated by block 84. The position Z of the control rods 40 is determined as a function of the value of the effective power Pe, of the reference power value Pc, of the estimated time interval DURATION of the increase in power of the reactor to achieve the reference value Pc. According to an embodiment variant, the acquisition means also acquire a complementary value corresponding to an estimated instant of the load restoration INST (i.e. the instant of end of the duration of the stage of the effective power). Thus, in this embodiment variant, the determination of the position Z of the control rods 40 will be more precise and a function of the value of the effective power Pe, of the reference power value Pc, of the estimated time interval DURATION of the increase in power of the reactor to achieve the reference value Pc as well as of the estimated instant of load restoration INST. According to a first embodiment of the method according to the invention, the step 84 of determining the reference position Z of the control rods 40 is carried out by software means present in the nuclear reactor 100 implementing a neutron computation code simulating the behaviour of the reactor from data representative of the material, geometric and neutronic characteristics of the core, as well as the operating conditions of the core, continuously, representing the 3D model of the core. As an example, the SMART neutron computation code based on 3D modelling of advanced nodal type may be cited. The principles of core neutron computation are described in more detail in the document “Methods de calcul neutronique de coeur” (Techniques de l'Ingenieur—B 20 3 070—Giovanni B. Bruna and Bernard Guesdon). These software means implementing a neutron computation code make it possible to determine by iterative computation the ideal reference position Z of the control rods from entry data, such as the effective power Pe, the reference value Pc of the target power that it is wished to achieve and the estimated duration DURATION of the increase in power, and optionally the estimated instant of load restoration INST, entered by the operator. As an example, the reference position Z retained by the software means could be that giving the best behaviour of the core during the power rise, in other words the position enabling the control rods 40 to return to the optimal position when the target power is achieved. The optimal position of control rods 40 at 100% rated power which can be the normal position of the control rods in 100% stabilised operation (i.e. the nominal position of the control rods). FIG. 3 illustrates a second mode of implementation of the step 84 of determining the reference position Z of the control rods 40. This second mode of implementation makes it possible to simplify this step of determination in comparison with the previous embodiment and makes it possible to do without the use of a neutron computation code. According to this second mode, comparison means make it possible during a sub-step, illustrated by block 44, to compare the difference ΔP between the effective power Pe and the reference value Pc for the target power that it is wished to achieve. The operating means comprise software means associated with storage means comprising a correlation table dZ=f(ΔP) making it possible to define, during the step illustrated by block 46, a position dZ of control rods as a function of the difference ΔP in the power. The position dZ determined during this step corresponds to the insertion position of the control rods in which it is possible to achieve the reference value Pc for the power without necessity of compensation of the xenon effect. Block 45 illustrates a complementary step in which the software means estimate a variation in the xenon effect ΔX as a function of the difference ΔP in power and of the estimated duration DURATION of the variation in power entered by the operator. According to an advantageous embodiment, this estimation of the variation in xenon ΔX, during the variation in power, is proportional to the duration DURATION of the variation and to the amplitude of the power variation, and may be expressed by the relation:ΔX=Ax(DURATION×ΔP) Where ΔX is the variation in the xenon effect expressed in pcm (for hundred thousand); A is a proportionality coefficient expressed in pcm/(hour x % RP); DURATION is the estimated duration of the variation in power expressed in hours; ΔP is the difference in power expressed in % RP. Nevertheless, the estimation of the variation in xenon is not limited to a linear model and may be carried out by means of a more complex computation model taking into account the inaccuracy of the linearity of the variation in xenon ΔX with the duration DURATION and the power difference ΔP. According to an embodiment variant, the estimation of the variation in xenon can also be a function of the estimated instant INST of load restoration so as to estimate more precisely the variation in xenon. Thus, the variation in xenon ΔX during a rise or a drop in power is all the more important since the duration of this variation is considerable (in so far as the duration of this variation is typically below 7 hours). It is also considered as well as for a variation in power of which the time interval, to achieve the reference power Pc, is greater than one hour, and particularly for a power return, the evolution of xenon in the core of the reactor then becomes significant. As the xenon concentration curve 61 of the diagram represented in FIG. 4A shows, the xenon effect appears as of the start of a drop in load and continues to vary during the lower power stage. This estimated variation in the xenon effect ΔX, during the time interval DURATION assigned to the variation in power, thus makes it possible to compensate the position dZ determined as a function of the power difference ΔP, by the addition of a corrective factor dZc determined, during the step illustrated by block 48, by the relation:dZc=f{ΔX) where f is an increasing function. The reference position Z of the control rods is then determined by the combination of the position dZ and of the corrective factor dZc during the step illustrated by block 47. Thus, in this second embodiment, it is not necessary to have available software means implementing a SMART type neutron code for determining an optimised reference position Z making it possible to minimise the movements of the control clusters. Once the reference position Z of the control rods has been determined, the control and the regulation of the positions of the control rods in their reference positions Z are carried out in a conventional manner by known operating modes, by optionally compensating the movements of the rods by another control means for controlling the reactivity, such as for example the modification of the concentration of a neutron absorbing compound, such as boron, in the primary coolant by dilution/boronation operations. Depending on the operating mode used, injections of boron or water will be used and/or the use of other control rod clusters more or less neutron absorbing that will be positioned in a strategic manner in the core. For example, when it is possible, the return of the control rod clusters to their reference position is favoured by taking advantage of the variations in the xenon concentration rather than by dilution/boronation operations. As an example, if the reference position corresponds to a more extracted position than the position at which the clusters arrive following the load drop, the clusters are left to extract by compensating the increase in the xenon concentration, then the operation of dilution is only started when the clusters have returned to their reference position. The diagrams represented in FIGS. 4B and 4C illustrate the optimisation of the operation of a pressurized water nuclear reactor in load follow in comparison with an operating method not taking into account the xenon effect in the determination of the position Z of the control rods. FIG. 4B illustrates more particularly the evolution of the positions of the control rods (curves 60) as well as the evolution of the rate of dilution and boronation of the primary coolant, according to a method of the prior art, during an example of load follow represented in FIG. 4A. The hatched areas 62 and 63 represent respectively the volume of dilution water and the volume of boronation boron used during the load follow of FIG. 4A. FIG. 4C represents the evolution of the positions of the control rods (curve 50) as well as the evolution of the dilution and boronation rate of the primary coolant, with the operating method according to the invention, during the load follow illustrated in FIG. 4A. FIG. 4C also illustrates the evolution of the positions of the control rods (curves 60) as well as the evolution of the dilution and boronation rate of the primary coolant illustrated in FIG. 4B, by way of comparison. The hatched areas 52, 53a and 53b represent respectively the volume of dilution water and the volume of the boronation boron used during the load follow of FIG. 4A. The load follow, illustrated as an example in FIG. 4A, is a load follow in which a load drop (area B) is carried out from an upper stage at 100% of the rated power RP (area A) down to a lower stage (area C) equivalent to 50% of RP, during a relatively long period, of the order of ten hours, before a load restoration (area D) up to the return to the rated power represented in area E. The power variations, power drop and power rise, are relatively long, of the order of two hours, with a rate of progression of the order of 0.5% of the rated power per minute. Typically, the power variations have a rate of progression less than or equal to 1% of the rated power per minute. In FIG. 4C, the profile 50 in thick solid line shows schematically an example of evolution of the position Z of the control rods positioned in the vessel of the nuclear reactor, determined by the method according to the invention. In comparison, the profile 60 in solid line in FIG. 4B, and also represented in dotted line in FIG. 4C, schematically shows the evolution of the position Z of the control rods determined by an operating mode according to the prior art not taking into account the variation in the xenon effect during load follow. Thus, the growth of the xenon effect (neutrophage element) intervening as of the load drop, illustrated by the curve 61 in FIG. 4A, is compensated by a lesser insertion of the control rods 40 into the core 30 of the reactor 100 during the load drop. The lesser insertion of the control rods 40 determined by the reference position Z allows the operator to reduce the boron dilution rate by reducing the volume of injected water (hatched area 52), or even to do away with the dilution, during the load drop (area B). Thanks to the invention, the lesser insertion of the control rods 40 makes it possible to reduce the volume of dilution water, represented by the hatched area 52, during the load drop compared to the volume of dilution water represented by the hatched area 62, and consequently limits the volumes of effluents. During load restoration (area D), the raising of the control rods being lesser, the variation in xenon during this load restoration is compensated by this lesser insertion of the rods, which makes it possible to stop the boronation flow rate during load restoration, in other words during the power rise from 50% to 100% of RP, as illustrated in FIG. 4C at the level of area D. Thus, during load restoration, the method according to the invention makes it possible to reduce the volume of boron injected into the primary coolant compared to the volume of boron injected with a known operating method (FIG. 4B). In addition, the insertion of the control rods being lesser, the method according to the invention makes it possible to reduce the number of steps necessary during load follow and particularly between an upper stage and a lower stage. The method thus makes it possible to reduce the loads on control rod movement mechanisms. Thus, the method according to the invention makes it possible to optimise the insertion of the control rods into the core in order to reduce the number of steps between different positions making it possible to preserve the means of movement of each control rod cluster during the years of service of the reactor. The insertion of the control rod clusters to the reference position Z determined by the method according to the invention also makes it possible to control the power rise capacity corresponding to the power capable of being produced by said core 30 during the raising of the control rods. This method is directly applicable to the different operating modes known to those skilled in the art, namely the operating modes commonly named mode A, mode G, mode X and mode T. Operating mode G, known to those skilled in the art, takes into account during the determination of the insertion position of the control rods the eventuality of a rapid return to 100% of the rated power by the removal of the control rods. To do this, operating mode G controls two types of control rod clusters having different neutron absorptivities. One of the clusters has its insertion position, which is a function of the level of power and guarantees the possibility of a rapid return to the rated power RP. The term “rapid” is taken to mean a sufficiently rapid load restoration in order for the variation in the xenon concentration to be slight, in other words a load restoration having a rate of progression typically comprised between 3% and 5% RP/min. The other control rod cluster, heavier, is dedicated to the control of the average temperature Tav of the reactor, and indirectly by operations of dilution and boronation to the control of the axial distribution DA. Operating modes X and T are advanced operating modes taking into account, in the positioning of the control rods, the power rise capacity Pmax. Power rise capacity Pmax is taken to mean the possibility of rapidly rising in power, in other words with a rate of progression comprised typically between 2% and 5% RP/min, from a reduced power to a high power (reference Pmax) defined beforehand by the operator during the programming of the load follow. Thus, for power variations, and particularly for a slow power return, typically greater than one hour, the management of the insertion positions of the control rods is not optimal because it does not take into account the evolution of the xenon effect. The method according to the invention makes it possible to take into consideration this evolution of xenon during a rise in power thereby making it possible to optimise the insertion of the control rods into the core of the reactor during “slow” load follow. The method according to the invention, applied to operating modes G, T and X thus makes it possible to improve said modes by a lesser insertion of the different control rod clusters into the core of the reactor, thereby limiting the use of the injection of boron or water into the primary liquid necessary for the compensation of the xenon concentration in the coolant. This method according to the invention is also applicable to the operating mode, called mode A, consisting in controlling and regulating the temperature Tav and the axial distribution of power DA. Operating mode A is the simplest mode used to operate nuclear reactors during load follow. When there is a load drop of the turbine, the control rods are inserted into the core in order to limit the power of the core and thereby avoid an increase in the temperature of the primary cooling circuit. In this operating mode, the control rods are inserted down to a lower limit level defining the acceptable limitation of perturbation of the axial distribution of power DA. When it is wished to further reduce the power, an injection of boron into the primary coolant is then carried out in order to increase its concentration and accompany the drop in the primary power. In the case of a power rise, a reduction in the concentration of boron is carried out by its dilution by injecting water. However, the injection and the dilution of boron have a limited speed of action, which does not enable rapid or large amplitude power variations. The method according to the invention, applied to operating mode A, thereby makes it possible to know the rate of progression at which the load restoration is possible without injection of water (i.e. without dilution). In fact, if the reference position determined by the method according to the invention is within the permitted limits, then the load restoration may be carried out with the rate of progression which is a function of the selected duration of variation in power. If the reference position determined by the method according to the invention is not on the other hand within the permitted limits, then it is possible to deduce the rate of progression associated with a coolant dilution rate, making it possible to remain within the permitted limits. Obviously, the invention is not limited to the embodiments and to the operating modes that have been described. The method according to the invention is applicable to all types of operating mode known to those skilled in the art and not only to the operating modes mentioned in the present application. Depending on the operating mode used, the reference position Z determined by the method according to the invention taking into account the variation in the xenon concentration ΔX may be applied to at least one control rod cluster if the nuclear reactor comprises a plurality of control rod clusters having different neutron absorption characteristics such as in particular in operating modes G, X and T. The method according to the invention is also applicable to an operating mode limiting the volumes of effluents by the use of a control rod cluster inserted beforehand. In this operating mode, the inserted cluster makes it possible to take up the xenon effects (increase in the concentration) by extraction of the inserted cluster during load follow. The method according to the invention applied to this operating mode would make it possible to improve and optimise the placement of the cluster inserted beforehand so as to minimise the movements. The method according to the invention has been particularly described in taking into account as an estimated duration the estimated time interval of the increase in power of the reactor to achieve the reference value starting from the effective value; nevertheless, the method according to the invention is also applicable by taking into account the estimated instant of load restoration, in other words the end of the estimated duration of the stage at the effective power before the increase in power, which makes it possible to further optimise the reference position Z of the control rods. The method according to the invention has been particularly described by taking as estimated duration the estimated time interval of the variation in power of the reactor to achieve the reference value starting from the effective value; nevertheless, the method according to the invention is also applicable by replacing the estimated duration of the time interval of the increase in power by the slope of the increase in power of the reactor to achieve the reference value starting from the effective value, expressed for example in %/min.
	summary
050930702	summary	BACKGROUND OF THE INVENTION The present invention relates to a core loading strategy, and particularly to a core loading strategy which are suitable for use in a boiling water reactor. In each light-water type power reactor, e.g., in each boiling water reactor, many fuel assemblies form a lattice in the core, and control rods are vertically moved among the fuel assemblies. The reactor of such type operates in accordance with the excess reactivity of core which is determined by operating the control rods and by the burnable poisons (for example, gadolinia) contained in the fuel assemblies. When the excess reactivity becomes zero, spent fuel assemblies are discharged from the core and the core is charged with new fuel assemblies so that fuel exchange is performed. The arrangement of the fuel assemblies in the core is changed as occasion demands. In order to increase the core reactivity for improving the economical efficiency of fuel it is preferable that the fuel assemblies having a high degree of reactivity are arranged at the center of the core having a high level of neutron importance. However, in such arrangement, since the output power generated at the radially center of the core is extremely high, the safety margins of fuel rods are reduced. In order to solve these conflicting problems, several methods have been proposed for adjusting the power distribution in the radial direction without producing any loss in reactivity. Examples of methods for flattening the power distribution in the radial direction of a core include the methods disclosed in U.S. Pat. No. 3,986,924 and Japanese Patent Laid-Open (KOKAI) 53-57388. In these methods, the distribution of infinite multiplication factors in the radial direction of a core is changed by adjusting the amount of uranium-235 in the radial direction of the core. That is, the amount of uranium-235 at the center of the core is smaller than that of uranium-235 in the peripheral portion of the core which surrounds the center thereof so that the infinite multiplication factor at the center of the core is lower than that in the peripheral portion thereof. There is a method which employs burnable poison for flattening the power distributions in the radial direction and axial direction of the core. This method is disclosed in U.S. Pat. No. 3,799,839. In the radial direction of the core disclosed in U.S. Pat. No. 3,799,839, the amount of burnable poison at the center of the core is greater than the amount of burnable poison at the peripheral portion thereof, and in the axial direction of the core the amount of burnable poison at the center of the core is greater than the amounts of burnable poison at the upper end and lower end portions of the core. In the core disclosed in Japanese Patent Laid-Open (KOKAI) 53-70489, fuel assemblies, each containing a large amount of burnable poison, are disposed at the center of the core, and the other fuel assemblies, each containing a small amount of burnable poison, are disposed in the peripheral portion of the core. In the radial direction of this core, the amount of burnable poison at the cener of the core is greater than the amount of burnable poison at the peripheral portion thereof. In the core disclosed by U.S. Pat. No. 3,799,839, the concentration of burnable poison of the fuel assemblies disposed at the center of the core is greater than that of the fuel assemblies disposed in the peripheral portion of the core, and the number of the fuel assemblies containing burnable poison and arranged at the center of the core is greater than that of the fuel assemblies containing burnable poison and arranged at the peripheral portion of the core. Japanese Patent Laid-Open No. 57-70489 discloses the concentration of burnable poison and number of fuel assemblies containing burnable poison similarly to U.S. Pat. No. 3,799,839. Japanese Patent Laid-Open No. 57-70489 also discloses an example of a core in which the number of the fuel assemblies containing burnable poison and arranged at the center of the core is equal to that of the fuel assemblies containing burnable poison and arranged at the peripheral portion of the core. Japanese Patent Laid-Open No. 57-70489 discloses that the above-mentioned core can improve the efficiency of fuel utilization without any loss in the shutdown margin. The core disclosed in Japanese Patent Laid-Open No. 57-70489 also can flatten the power distribution in the radial direction of core similarly to the core disclosed in U.S. Pat. No. 3,799,839. SUMMARY OF THE INVENTION It is a first object of the present invention to provide a core loading strategy in which a maximum linear heat generation rate is limited within an allowable range and which improve the efficiency of fuel utilizataion. It is a second object of the present invention to provide a reactor core which improves significantly the efficiency of fuel utilization by utilizing the margin of maximum linear heat generation rate in the end of an operation cycle. It is a third object of the present invention to provide a reactor core which reduces the amount of neutrons absorbed by burnable poison and flattens the power distribution in the radial direction of the core. The first characteristic of the present invention is that in a core, the average infinite multiplication factor in the peripheral region of the core is greater than that in the central region surrounded by the peripheral region in the beginning of an operation cycle, and the average infinite multiplication factor in the central region is greater than that in the peripheral region in the end of the operation cycle. The second characteristic of the present invention is that each of new fuel assemblies is divided into an upper region and a lower region in the axial direction thereof and the average enrichment of the upper region is greater than that of the lower region and the amount of burnable poison contained in the upper region is greater than that contained in the lower region. The third characteristic of the present invention is that in a central region, a plurality of first cells each containing new fuel assemblies and a plurality of second cells are arranged, and an average infinite multiplication factor of second cells is smaller than that of first cells and in each of the second cells a control rod for controlling the power distribution is inserted. According to the first characteristic of the present invention, the infinite multiplication factors of the radially both sides of the core are changed reversely between the beginning and the end of operation cycle so that the reactivity distribution in the radial direction of core is changed reversely between the beginning and the end of the operation cycle. Therefore, the spectral shift effect is increased in the central region of the core and the efficiency of fuel utilization is improved. In particular, since the reactivity in the central region of the core is improved in the end of operation cycle, the spectral shift effect in the central region is significant. However, the maximum linear heat generation rate is limited within a permissible range. According to the second characteristic of the present invention, each of the new fuel assemblies arranged in the central region is divided into an upper region and a lower region in the axial direction thereof, and the average enrichment of the upper region is greater than that of the lower region and the amount of burnable poison contained in the upper region is greater than the amount contained in the lower region so that the above-described change in the reactivity distribution in the radial direction and the change in the reactivity distribution in the axial direction are provided, thereby further increasing the spectral shift effect. Further, since the amount of burnable poison in the upper region is large, the margin of maximum linear heat generation rate is increased in the latter half of the operation cycle, as compared with the former half of the operation cycle, and the reactivity can be increased by utilizing the margin to the maximum. According to the third characteristic of the present invention, since a plurality of second cells are disposed in the central region, an average infinite multiplication factor of the second cells is smaller than that of the first cells and the control rods for controlling the power distriution are inserted in the second cells, the power distribution in the radial direction of core is flattened during the operation of reactor. Thus, the amount of burnable poison is reduced and the amount of neutrons absorbed by the burnable poison is also reduced, whereby production of new fessionable substances is accelerated.
	description	The present disclosure relates to root cause diagnostics. More particularly, it relates to performing root cause diagnostics of machine and/or system faults using temporal data mining for fault data correlation. In a manufacturing or other machine-based environment, faults often occur during normal operation of the machines. In order to maximize productivity and lower costs, it is important to quickly and accurately remedy faults, and return to a normal operating state. As faults occur over a period of time, the sequence of events surrounding each fault can be monitored and recorded in data series, including preconditions that lead to a fault, and post conditions that follow the fault. In many event sequences, individual time-ordered events in the data series are associated with time durations. In many instances, the time durations may carry useful information. For example, in line status logs of manufacturing plants, the durations of various events carry important information. Looking to immediate preconditions before a fault occurs can be helpful to diagnose the cause of the fault, but may not accurately determine the root cause of the fault, as some faults are the result of a series of events. It would be beneficial to develop a process to extract useful information from temporal data in a manufacturing or machine-based environment to assist in fault diagnostics and root cause analysis for a series of faults or events. Accordingly, there is a need in the art for root cause diagnostics of machine and system faults using temporal data mining for fault data correlation. An embodiment of the invention includes a method for fault data correlation in a diagnostic system. The method includes receiving the fault data including a plurality of faults collected over a period of time, and identifying a plurality of episodes within the fault data, where each episode includes a sequence of the faults. The method further includes calculating a frequency of the episodes within the fault data, calculating a correlation confidence of the faults relative to the episodes as a function of the frequency of the episodes, and outputting a report of the faults with the correlation confidence. A further embodiment of the invention includes a system for fault data correlation in a diagnostic system. The system includes a host system and a data storage device, holding fault data, in communication with the host system. A temporal data mining (TDM) diagnostics tool executes on the host system. The TDM diagnostics tool includes computer instructions for receiving the fault data including a plurality of faults collected over a period of time, and identifying a plurality of episodes within the fault data, where each episode includes a sequence of the faults. The TDM diagnostics tool further includes computer instructions for calculating a frequency of the episodes within the fault data, calculating a correlation confidence of the faults relative to the episodes as a function of the frequency of the episodes, and outputting a report of the faults with the correlation confidence. Another embodiment of the invention includes a computer program product for fault data correlation in a diagnostic system. The computer program product includes a storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for implementing a method. The method includes receiving the fault data including a plurality of faults collected over a period of time, and identifying a plurality of episodes within the fault data, where each episode includes a sequence of the faults. The method further includes calculating a frequency of the episodes within the fault data, calculating a correlation confidence of the faults relative to the episodes as a function of the frequency of the episodes, and outputting a report of the faults with the correlation confidence. Other methods, systems, and/or computer program products according to embodiments will be or become apparent to one with skill in the art upon review of the following drawings and detailed description. It is intended that all such additional methods, computer program products, and/or systems be included within the description, be within the scope of the present invention, and be protected by the accompanying claims. Exemplary embodiments, as shown and described by the various figures and the accompanying text, provide systems, methods, and computer program products for performing root cause diagnostics of machine and/or system faults using temporal data mining for fault data correlation. A manufacturing process, or other machine-based process, can be divided into a sequence of controlled events involving multiple machines. Each event has duration, from a start time to an end time, as well as preconditions and post conditions. A sequence of events can vary in length and complexity from one machine to another within a given process. Machines in manufacturing systems may enter a faulted state if one of the events in the sequence exceeds its maximum allowed duration or one of the event's preconditions changes after the start of the event, etc. Thus, machine faults can be viewed as a type of temporal data. In exemplary embodiments, temporal data mining is applied to find hidden sequences, such as episodes of faults, which are noteworthy in identifying likely root causes of machine faults. Turning now to the drawings, it will be seen that in FIG. 1 there is a block diagram of a system 100 upon which performing root cause diagnostics of machine and/or system faults using temporal data mining for fault data correlation is implemented in exemplary embodiments. The system 100 of FIG. 1 includes a host system 102 in communication with user systems 104 over an information technology (IT) network 106. Multiple machine controllers 108 are interfaced to a controller network 107, which may be accessible by the host system 102. In exemplary embodiments, the host system 102 is a high-speed processing device (e.g., a mainframe computer) including at least one processing circuit (e.g., a CPU) capable of reading and executing instructions, and handling large volumes of processing requests from user systems 104. The host system 102 may function as an application server, a database management server, and/or a web server. User systems 104 may comprise desktop or general-purpose computer devices that generate data and processing requests. While only a single host system 102 is shown in FIG. 1, it will be understood that multiple host systems can be implemented, each in communication with one another via direct coupling or via one or more networks. For example, multiple host systems may be interconnected through a distributed network architecture. The single host system 102 may also represent a cluster of hosts collectively performing processes as described in greater detail herein. The IT network 106 and the controller network 107 may be any type of communications networks known in the art. For example, the IT network 106 and/or the controller network 107 may be intranets, extranets, or internetworks, such as the Internet, or a combination thereof. The IT network 106 and/or the controller network 107 can be wireless and/or wired networks. Although the IT network 106 and the controller network 107 are depicted as separate networks, it will be understood that the networks can be combined or further subdivided within the scope of the invention. The machine controllers 108 may be any type of programmable logic controller (PLC), programmable controller (PC), computer numerical control (CNC), or any type of embedded controller hardware that hosts software to control a machine and diagnose machine faults. In exemplary embodiments, each machine controller 108 interfaces with sensors and/or other data collection means (not depicted) to report machine faults and other events to the host system 102. While only two machine controllers 108 are depicted in the system 100 of FIG. 1, it will be understood that any number of machine controllers 108 may be implemented within the scope of the invention. For example, one of the machine controllers 108 may represent a controller for a welding robot, while another machine controller 108 may be a controller for an automated conveyor system. In exemplary embodiments, the host system 102 accesses and stores information to a data storage device 110. The data storage device 110 refers to any type of storage and may comprise a secondary storage element, e.g., hard disk drive, tape, or a storage subsystem that is external to the host system 102. In alternate exemplary embodiments, the data storage device 110 is internal to the host system 102. It will be understood that the data storage device 110 shown in FIG. 1 is provided for purposes of simplification and ease of explanation and is not to be construed as limiting in scope. To the contrary, there may be any number data storage devices 110 accessible by the host system 102. In exemplary embodiments, the data storage device 110 holds fault data 112 that is reported by the machine controllers 108. In exemplary embodiments, the host system 102 executes various applications, such as a temporal data mining (TDM) diagnostics tool 114. The TDM diagnostics tool 114 processes the fault data 112 and outputs one or more reports 116. The reports 116 can be stored on the data storage device 110 for future access and archival purposes. In exemplary embodiments, the TDM diagnostics tool 114 employs temporal data mining on the fault data 112 as detailed herein and described in U.S. patent application Ser. No. 11/068,498, entitled SYSTEM AND METHOD FOR MINING OF TEMPORAL DATA, filed on Feb. 28, 2005, of common assignment herewith and incorporated by reference herein in its entirety. While the TDM diagnostics tool 114 is depicted as a single application executing upon the host system 102, it will be understood that any module, sub-component, or portion of the TDM diagnostics tool 114 may be executed or stored on any combination of the user systems 104, e.g., a distributed application architecture. Other applications, e.g., business applications, a web server, etc., may also be implemented by the host system 102 as dictated by the needs of the enterprise of the host system 102. In exemplary embodiments, the TDM diagnostics tool 114 analyzes the sequence and duration of machine faults in the fault data 112 for episodes. An episode is a sequence of faults or other events that appear as a pattern within the data. The faults or events in an episode may be identified by a single machine controller 108 or across multiple machine controllers 108 in a sequence. For example, as depicted in FIG. 2, the TDM diagnostics tool 114 can identify patterns of temporal data as episodes. The sequence 202 of FIG. 2 represents a time sequence of data captured within the fault data 112, e.g., temporal data. The sequence 202 includes a number of faults, designated as faults A, B, C, and D. Each fault A-D may represent a different fault reported by the same machine controller 108 or different machine controllers 108. While traditional diagnostic approaches typically perform single variable fault analysis, through exemplary embodiments of the present invention, a sequence of faults with multiple variables can be identified as an episode, enabling the true root cause of a fault to be determined. From the sequence 202, the TDM diagnostics tool 114 may discover that an episode 204 frequently occurs (e.g., fault A followed by fault B followed by fault A followed by fault C). By further analysis, the TDM diagnostics tool 114 may reveal that fault A is the root-cause which leads to fault B, another occurrence of fault A, and then finally to fault C. The TDM diagnostics tool 114 is capable of finding the episode 204 in the presence of noise, illustrated as the random presence of a fault D in the episode 204. In other words, even though the fault D appears in different locations within the episode 204, the TDM diagnostics tool 114 can determine that the fault D is not actually a component of the episode 204. The TDM diagnostics tool 114 may also support, categorizing, sorting and filtering of episodes to remove episode types that are known or expected from further analysis. For example, in a typical manufacturing system, machine faults can be classified as well-known episodes, expected episodes, and unexpected episodes. Well-known episodes include fault states that the system 100 or machine controllers 108 are designed to enter in response to a known event. For example, an emergency stop event may trigger machines controllers 108 to place their associated machines in an emergency stop faulted state. Expected episodes include faults within the same component of a machine, and the subsequent faults happen as a result of an incomplete or inappropriate recovery process of the root cause fault. Unexpected episodes include faults that are reported by machine controllers 108 for multiple machines or in different components of the same machine, where correlation between the events or faults may not otherwise be known. As users analyze the reports 116 generated by the TDM diagnostics tool 114, the TDM diagnostics tool 114 can be reconfigured to block reporting of well-known and expected episodes such that only unexpected episodes are reported. Thus, a user's attention can be focused on troubleshooting unexpected episodes and identifying the root cause thereof. In exemplary embodiments, the TDM diagnostics tool 114 correlates faults and calculates a confidence value of the correlations. For example, the TDM diagnostics tool 114 may analyze the fault data 112 and determine the number of times within a sequence, such as the sequence 202 of FIG. 2, that fault A follows fault B (frequency of A->B). The confidence that fault A causes fault B may be calculated as 100frequency of A->B/frequency of A. Similarly the confidence that fault B is caused by fault A may be calculated as 100frequency of A->B/frequency of B. Looking at the confidence calculation in both directions may aid in determining if additional faults contribute to the sequence. For example, fault A may occur before fault B 93% of the time, but 54% of the time fault B may occur without being preceded by fault A, indicating that fault A by itself is not the root cause of fault B. Through extending the analysis to relationships between faults, an episode of multiple faults can be revealed that highlights the true root cause of a given failure. The TDM diagnostics tool 114 may generate multiple reports 116 to assist in diagnosing the root cause of faults collected in the fault data 112. An exemplary report 300 is depicted in FIG. 3 illustrating the top 15 fault correlations for a selected date range. It will be understood that the report 300 merely depicts one example of the type of reports 116 that may be generated by the TDM diagnostics tool 114 of FIG. 1. The report 300 provides a summary of the most frequent faults collected in the fault data 112 of FIG. 1 for a selected period of time, along with the relationships identified between fault pairs. In exemplary embodiments, the report 300 includes a frequency of A->B column 302, a fault-A column 304, a fault-A description column 306, a confidence-A column 308, a fault-B column 310, a fault-B description column 312, a confidence-B column 314. The frequency of A->B column 302 indicates the number of times within the examined data that the sequence of fault A followed by fault B occurred for each row in the report 300, where the specific faults referred to as fault A and fault B are identified in each row of the report 300. For example, in the first row, fault A is “OP281-151-14”, located in the fault-A column 304 and further described in the fault-A description column 306, while in the second row, fault A is “OP281-151-13”. Similarly, fault B, as listed in the fault-B column 310 and further described in the fault-B description column 312, can vary between rows as different relationships between faults are identified. The first two rows of the report 300 illustrate that two different faults “OP281-151-14” and “OP281-151-13”, as identified in the fault-A column 304, both precede the same fault “OP281-151-32”, as identified in the fault-B column 310, with a frequency as defined in frequency of A->B column 302. The confidence-A column 308 and the confidence-B column 314 provide a calculated confidence value for each correlation as previously described. The report 300 may be expanded to include longer correlation chains as episodes. Additional features may include cell highlighting within the report 300 to illustrate correlations between other reports 116 of FIG. 1, such as a single variable analysis report. Highlighting or linking may enable a user to identify high frequency individual faults in relation to other less frequent but related faults that do not otherwise appear in a single variable analysis report. For example, the fault “OP281-151-32” may appear frequently, but the separate preceding faults “OP281-151-14” and “OP281-151-13” may be too individually infrequent to alert a user to an issue when only single variable analysis is performed. Turning now to FIG. 4, a process 400 for fault data correlation in a diagnostic system is depicted in accordance with exemplary embodiments and in reference to the system 100 of FIG. 1. At step 402, the TDM diagnostics tool 114 receives the fault data 112, including a plurality of faults collected over a period of time. While the period of time over which the fault data 112 is collected can vary (e.g., weeks or months), a particular period analyzed by the TDM diagnostics tool 114 can be a user selectable period (e.g., one week of data). Other software (not depicted) may preprocess or otherwise filter the fault data 112 prior to receipt by the TDM diagnostics tool 114. In exemplary embodiments, the fault data 112 includes a temporal data series comprising events with start times and end times, a set of allowed dwelling times, and a threshold frequency. At step 404, the TDM diagnostics tool 114 identifies a plurality of episodes within the fault data 112, where each episode includes a sequence of the faults. The process of identifying episodes is described in greater detail further herein. The TDM diagnostics tool 114 may also identify an initial fault in the sequence of faults in one of the episodes as a root cause, and report the root cause. Furthermore, the TDM diagnostics tool 114 may calculate a downtime as time duration between an initial fault and a final fault in the sequence of faults in one of the episodes, and report the downtime. At step 406, the TDM diagnostics tool 114 calculates a frequency of the episodes within the fault data 112. The frequency of the episodes may be a count of a number of episode instances within the fault data 112. The TDM diagnostics tool 114 may additionally categorize each of the episodes as an episode type, where the episode type is one of a well-known episode, an expected episode, and an unexpected episode. Sorting or filtering based on the episode type may be performed to further enhance reporting options. At step 408, the TDM diagnostics tool 114 calculates a correlation confidence of the faults relative to the episodes as a function of the frequency of the episodes. The correlation confidence may be calculated as a confidence that a first fault caused a second fault. Alternatively or additionally, the correlation confidence may be calculated as a confidence that the second fault was caused by the first fault. At step 410, the TDM diagnostics tool 114 outputs a report of the faults with the correlation confidence, such as the report 300 of FIG. 3. The TDM diagnostics tool 114 may output a number of reports that include information related to the identified root cause of a fault, a downtime, and/or data filtered on one or more episode type (e.g., well-known, expected, and/or unexpected). Additional reports may include or highlight single variable fault frequency to illustrate the most common individual faults. The process used by the TDM diagnostics tool 114 of FIG. 1 to detect frequent or repetitive patterns in the form of sequential episodes in time stamped data series from the fault data 112 to produce the reports 116 is further described herein. An aspect of this technology is the defining of appropriate frequency counts for non-overlapping and non-interleaved episodes. Two frequency measures and embodiments for obtaining frequent episodes are described. The embodiments described herein search through the temporal data series from the fault data 112 to detect non-overlapping and non-interleaved episodes which are frequent (according to these measures) in the temporal data series. The method includes checking whether a frequent episode is principal in the data series. FIG. 5 is a flowchart showing a method for temporal data mining. While the steps are in a particular order and show a particular manner to achieve results, the technology described herein can be implemented in other ways too. The method includes a step 512 for receiving as input a temporal data series including events (e.g., faults) with start times and end times, a set of allowed dwelling times, and a threshold frequency. A set E of event types, an expiry time, and a confidence threshold may also be received as input in step 512. In a step 514, data structures for implementing the method are initialized. In a step 516, all frequent principal episodes of a particular length in the temporal data series having dwelling times within the allowed dwelling times are found. Principal episodes are defined and discussed below. In step 516 also, the particular length is shown as one (1) in FIG. 5, but other values of length may be used. Successive passes are made through the temporal data series to iteratively find all frequent principal episodes. This is shown at steps 518 to 524. In step 518, in the first iteration, all frequent principal episodes of length l are computed; in an iteration, in general, all frequent principal episodes of the particular length are computed at step 518. This is typically done by identifying one or more occurrences of a candidate episode in the temporal data series, incrementing a count for each identified occurrence, and determining frequent episodes from the counts of occurrence in comparison to the threshold frequency. A test for whether a frequent episode is principal is made, and if the episode passes the test it is included in successive steps. Next, at step 520, frequent principal episodes of the particular length are combined in specific ways to produce combined episodes of an increased length. Typically, the increased length may be one more than the particular length. The combined episodes are tested, and those having appropriate subepisodes which are not frequent principal episodes are removed, to leave a set of candidate episodes for the next iteration. The iteration index is incremented at step 522, and may match the value of the increased length. The particular length may be reset to the increased length for the next iterative pass through the temporal data series. If no new candidate episodes are left after removing combined episodes having subepisodes which are not frequent principal episodes, iteration terminates at a step 524. The method continues at step 526 to compute the collection of all frequent principal episodes (i.e. frequent principal episodes of all lengths) by combining all the sets of frequent principal episodes found in the iteration steps 518 to 524. In a step 528, the set of all frequent principal episodes is provided as output of the method. Also shown in FIG. 5 are a rule generation step 530 and a step 532 of producing output of the rules. Depending on details of the embodiment under consideration, the method 500 is capable of recognizing non-overlapping occurrences of episodes or non-interleaved occurrences of episodes. This capability is described in detail below in connection with FIGS. 6-11. To describe mathematical details that are referenced herein, first is a description of some of the terms used. Temporal data series discussed in this disclosure are made up of triplets (Ei, ti, τi), in which an event Ei begins at a start time ti and ends at an end time τi, with τi>ti. Both ti and τi may be integers. Events in the temporal data series are not instantaneous and thus require for their specification both start and end times. Temporal data series discussed in this disclosure are typically ordered so that events are arranged in order of increasing (or at least, nondecreasing) end time value. An example generic temporal data series as described herein may be denoted <(E1, t1, τ1), . . . (En, tn, τn)>. The temporal data series may also be denoted an event sequence (s, Ts, Te) with Ts and Te fixing the lower and upper extremities of the event sequence. For the sake of notational succinctness this triple is denoted by s. The length n of the temporal data series may be denoted \|s\|. The events Ei may be drawn from a set E of possible event types which may be provided as an input at step 512, as described above. The dwelling time or time duration of event Ei is the difference Δi=τi−ti. The events in the temporal data series may have varying dwelling times. Often, in event sequences as discussed herein where the events have associated time durations, the time durations of events can carry useful information. Example events may also be denoted herein by A, B, C, and so on. The associated time/duration value(s) may be suppressed when the order of events is clear from the context, or when the order is not relevant to the discussion. An example event sequence of a temporal data series may be (A, 1, 2), (B, 3, 4), (C, 4, 5), (E, 12, 13), (A, 14, 16), (B, 15, 19), (C, 16, 22). A particular event type may be of interest for frequent episode discovery when its dwelling time lies within a certain range or time interval, e.g., 1 to 10 minutes, or in a set of time intervals. For example, in manufacturing plant data, downtime events of short duration, say, between 10 and 30 minutes, may be of interest. In another example, downtime events of either very short (between 1 and 10 minutes) or very long duration (between 30 and 180 minutes) may be of interest. The set of all allowable dwelling times for events may be a design choice made by the user of a temporal data mining method. This set is denoted herein as B={B1, . . . , BK}. B is a collection of time intervals. That is, B is a discrete set with a finite number of elements, but each element is a time interval. In the instances discussed above of manufacturing plant data. B may be taken as the set containing the single interval [10-30] in the first episode, B={[10-30]}. In the other example above, B may be taken as B={[1-10], [30-180]}. It may be the case that an event in an episode may be of interest for frequent episode discovery only for some, and not all, intervals in B. Thus, an episode includes an associate between a node of the episode and possible durations that are allowed as dwelling times for that node in the episode. An episode therefore includes an ordered set of nodes, each node having an associated event type and an associated set of intervals (in B) that are allowed as durations for that node. The length or size of an episode is the number of nodes in it. For an episode denoted by, e.g., α, its length may be denoted by \|α\|. An ordered sequence of events, e.g., (A→B→C), may be denoted an episode, but this specification is not complete, in the context of this disclosure, without the association between nodes and allowed dwelling times. This association may be specified by providing a map dα which associates with each node of the episode α a collection of intervals in B, that is, a subset of B. For purposes of discussion in this disclosure, the associated subsets of B may also be specified directly in the ordered sequence of events, for short sequences. If, for instance B={[1-2], [30-100]}, a three node episode may be specified as (A([1-2])→B([1-2], [30-100])→C([1-2])). An episode occurs in the temporal data series if the events of the episode occur in the temporal data series in the same order as in the episode, and have durations allowed by the association between nodes of the episode and intervals in B. Returning to discussion of the example seven-event sequence above, consider the three-node episode (A([1-2])→B([1-2], [30-100])→C([1-2])). The sequence of event-time value pairs (A, 1, 2), (B, 3, 4), (C, 4, 5) is an occurrence of the episode. The sequence (A, 14, 16), (B, 3, 4), (C, 4, 5) is not an occurrence of the episode, since A occurs later than B and C. Nor is the sequence (A, 1, 2), (B, 3, 4), (C, 16, 22) an occurrence of the episode, since C has a duration longer than allowed for a dwelling time. There is only one occurrence of the episode (A([1-2])→B([1-2], [30-100])→C([1-2])) in the example event sequence. The specification of B allows the user to direct the search for frequent episodes of the kind that are of interest to the user. Towards this end, it may be preferable to specify event-specific B-sets. The set of all possible time intervals, B, would then be a function of the event type associated with the node under consideration. For example, if an episode α is defined formally as a set of nodes Vα={v1, . . . , vn} on which is defined a total order <α, the association between each node and an event type may be provided by a map gα from the set Vα to the set of event types E. Thus an event specific B-set may be denoted as Bgα(v). Also, as previously discussed, the allowed dwelling times may be provided by a map dα from the set Vα to a subset of B. In the case where event-specific allowable dwelling times are used, then, for each node vεVα, the set of allowed dwelling times may be regarded as a subset of Bgα(v), i.e. dα(v)ε2Bgα(v) (where 2Bgα(v) is the set of all subsets of Bgα(v), the power set of Bgα(v)). Thus, embodiments of the method described herein would be able to handle such event-specific B-sets. However, for the sake of notational convenience, the set of time intervals is denoted herein simply as B. Consider the episode α specified as α=(Vα, <α, gα, da). An episode β specified as β=(Vβ, <β, gβ, dβ), is a subepisode of the episode α, and written β≦α, if there is a 1-to-1 map from the set of nodes of β into the set of nodes of α, ƒβα; Vβ→Vα with the following three properties: First, for each node v in β, the associated event is the same as the event associated with the node in α to which v is mapped by ƒβα, that is, gα(ƒβα(v))=gβ(v). Second, for each node v in β, every allowed dwelling time for the event associated with the node in α to which v is mapped by ƒβα is also an allowed dwelling time for the event associated with the node v, that is, dα(ƒβα(v))⊂dβ(v). Finally, the ordering of nodes is preserved under the mapping between α and β; that is, for each pair of nodes v and w in β, with v<βw under the order relation <β, the nodes in α to which v and w are mapped have the same ordering under the order relation <α, i.e., ƒβα(v)<αƒβα(w). According to the definition of the subepisode, it does not suffice if just the relative ordering of events in the candidate subepisode matches that of the episode. In addition, the dwelling time constraints on the events of the candidate subepisode are to be consistent with those that the episode itself would allow. A strict subepisode β of an episode α is a subepisode for which equality with α does not hold, i.e. β≦α and β≠α. A strict subepisode may be denoted by βα. When β≦α, α may also be denoted a superepisode of β, and written α≧β. Similarly, a strict superepisode may be denoted αβ. An episode α is said to occur in the temporal data series if events of the proper event type occur in the proper order in the temporal data series, with allowed dwelling times, as defined by the set of nodes, ordering, and maps specified by the episode α=(Vα, <α, gα, dα). The occurrence of episode α in the event sequence (s, Ts, Te) is written as αs. An occurrence of an episode in the temporal data series is also an occurrence of each of its subepisodes. That is, if β≦α, then α(s, Ts, Te)=>β(s, Ts, Te). A measure λs(α) of how often α occurs in the event sequence s may be defined. This may be any reasonable notation of frequency, in particular, the frequency measures defined below for non-overlapping and non-interleaved occurrences. One way of defining the frequency of occurrence of an episode in a temporal data series may be by counting the number of occurrences. In the example event sequence (A, 1, 2), (B, 3, 4), (C, 4, 5), (E, 12, 13), (A, 14, 16), (B, 15, 19), (C, 16, 22), the episode (A([1-10])→B([1-10])→C([1-10])), occurring 4 times in the event sequence, results in a frequency 4. Often, the frequency threshold is expressed as a fraction of data length. Thus, if the threshold input is the fraction, th, then, the above episode would become frequent in the given event sequence (which is of length of 7) if 4/7 is greater than th. A non-overlapping occurrence of an episode is one where no event of the episode occurs between two events of another occurrence of the episode. For example, there are two non-overlapping occurrences of the episode (A([1-10])→B([1-10])→C([1-10])) in the event sequence (A, 1, 2), (B, 3, 4), (C, 4, 5), (E, 12, 13), (A, 14, 16), (B, 15, 19), (C, 16, 22). It suffices to track only the innermost occurrence of (A([1-10])→B([1-10])→C([1-10])) in an event sequence like (A, 1, 2), (B, 2, 3), (A, 3, 4), (B, 4, 6), (A, 7, 9), (B, 8, 10), . . . , and this forestalls arbitrarily large memory and processor time consumption. A non-interleaved occurrence of an episode may be defined as follows. Each occurrence of an episode is may be considered as a 1-to-1 map, h, from the nodes of the episode to events in the temporal data series. For an episode α, the number of nodes in α may be denoted by \|α\| and the ordered sequence of nodes of α may be referred to as v1, v2, . . . . The jth node of the episode α may also be denoted herein as α.g[j]. Let h1 and h2 denote two different occurrences of α. Thus, h1(vi) denotes the event in the temporal data series that corresponds to the node vi of the episode α in the occurrence represented by h1. By h1(vi)<h2(vj) is meant that the event (in the temporal data series) corresponding to node vi in occurrence h1 has an earlier occurrence time than that of the event corresponding to node vj in occurrence h2. Two occurrences, h1 and h2 of an episode α are said to be non-interleaved if eitherh2(vj)>h1(vj+1) ∀j, 1≦j<\|α\|orh1(vj)>h2(vj+1) ∀j, 1≦j<\|α\|. As an example, the event sequence (A, 1, 3), (B, 2, 4), (D, 4, 5), (A, 5, 6), (C, 7, 10), (B, 11, 13), (C, 15, 18) contains two non-interleaved occurrences of the episode (A([1-2])→B([2])→C([3])) namely, <(A, 1, 3), (B, 2, 4), (C, 7, 10)> and <(A, 5, 6), (B, 11, 13), (C, 15, 18)>. The A event of the second non-interleaved occurrence occurs in the event sequence after the B event of the first non-interleaved occurrence, and the B event of the second non-interleaved occurrence occurs in the event sequence after the C event of the first non-interleaved occurrence. In the embodiments discussed below, automata are used to identify and recognize occurrences of candidate episodes. In terms of the automata that recognize each occurrence, this definition of non-interleaved means the following. An instance of the automaton for a candidate episode α can transit into the state corresponding to a node, say v2, only if an earlier instance (if any) of the automaton has already transited into state v3 or higher. Non-interleaved occurrences would include some overlapped occurrences though they do not include all occurrences. The definition introduced above for frequency of occurrences of an episode in a temporal data series can be refined by considering an episode to have occurred only if its occurrence meets the criteria for a non-overlapping occurrence, or meets the criteria for a non-interleaved occurrence. Which of these two different criteria are intended is clear from the context in the discussion below. The definitions of non-overlapping occurrences and non-interleaved occurrences thus provide two frequency measures to apply to episode occurrence in a temporal data series. The general procedure for discovering frequent episodes is as follows. First all frequent 1-node episodes in the temporal data series are found. Then these are combined in all possible ways to make candidate 2-node episodes. By calculating the frequencies of these candidates, all frequent 2-node episodes are obtained. These are then used to obtain candidate 3-node episodes and so on. The general method provides a reduced number of passes over the data series. The main computationally intensive step in frequent episode discovery is that of calculating the frequency of sets of candidate episodes. Temporal data mining of frequent episodes described herein can be adapted to detect frequent or repetitive patterns in the form of sequential episodes in time stamped data series. As explained above, an episode or pattern is frequent if its detected occurrences meet or exceed a frequency value specified by a user or from a preprogrammed value. Two episodes are said to be similar if they are identical except for the fact that one allows some more time intervals (for the event dwelling times) than the other, and if their frequencies of occurrence are equal in the given event sequence. Thus, unlike episodes or subepisodes, similar episodes are always defined with respect to a given event sequence and a given frequency count. Formally, two episodes α and β are said to be similar in the event sequence s (written α≡β in s) if all of the following conditions are met. First, either α is a subepisode of β or β is a subepisode of α, α≦β or β≦α. Second, the two episodes have the same length (same number of nodes), \|α\|=\|β\|. Third, α and β occur in s with the same frequency, λs(α)=λs(β). An episode α* is said to be principal in an event sequence s if the following two conditions hold: (1) the episode α* occurs in s, αs, and (2) there is no strict superepisode of it which is similar to it (in the event sequence s), i.e., there is no αα such that α≡α* in s. Given a principal episode, all episodes similar to it can be generated by appending time intervals (that do not contribute to the eventual episode frequency) to the event duration sets of the principal episode. Subepisodes of principal episodes are in general not principal. Indeed, all the non-principal episodes that are similar to a given principal episode are after all subepisodes of the given principal episode. However, all subepisodes generated by dropping nodes (rather than by appending time intervals to the d(·) sets) of a principal episode are most certainly principal. Returning now to FIG. 5, the process of computing the set of all frequent principal episodes is incremental and is done through the steps shown in FIG. 5. In step 512, a temporal data series including events with start times and end times is received as input. The temporal data series may be recorded in a database, such as the fault data 112 of FIG. 1, and the entire data series read into memory at the outset at step 512. That is to say, the processing of the temporal data series may occur offline, and not in real time. In this way, events under consideration may be examined later after identification by the method described here. Also in step 512, a set B of allowed dwelling times, and a threshold frequency λ are received as inputs. An expiry time tx and a confidence threshold ρmin may also be received as inputs. A set E of event types may be provided as well in the input at step 512. Data structures of use in implementing the method may be initialized in a step 514. These data structures may include, but are not limited to, arrays, lists, flags, etc. as appropriate. In particular a variable Fs* to hold frequent principal episodes found in the temporal data series is initialized to be empty. After steps of receiving inputs 512 and initializing data structures 514, the iterative process of scanning through the temporal data series starts with the set C1 of all possible 1-node episodes, at step 516. This may be determined by first finding the set of all distinct event types occurring in the temporal data series. Let F1* be the collection of frequent principal episodes in C1. Once F1* is obtained, the collection C2 of candidate 2-node episodes is generated from it. This incremental process of first obtaining Fk* from the candidates in Ck and then generating Ck+1 from Fk* is repeated till the set of new candidates generated is empty. Generation of frequent principal episodes Fk* from candidates Ck is explained below in connection with FIGS. 6-12, while generation of candidates Ck+1 from Fk* is explained below in connection with FIGS. 13-16. In order to describe episodes with event durations, for each episode α, α.g[i] denotes the event type associated with its ith node and α.d[i] denotes the set of time intervals associated with its ith node. The waits list, which links together all automata that accept a particular event, is indexed by an ordered pair (E,δ) where E is an event type (i.e., element of E) and δ is an allowed duration (i.e., element of B). The set waits(E,δ) stores (α, i) pairs, indicating that an automaton for episode α is waiting in its ith state for the event type E to occur with a duration in the δ time interval so that it can make a transition to the next node of the episode. The temporal data sequence includes a start and end time for each event in the sequence. An event is regarded as completed (and hence is ready for consideration as input to the automata) after its end time, so the iteration loop may be indexed by τ, i.e. the event end time. Now turning to FIG. 6, step 518 of FIG. 5 may include a step of retrieving inputs 602. These inputs may include, but are not be limited to, a temporal data series s including events with associated time values, a set Ck of candidate episodes to be sought in the temporal data series, a threshold value λ for occurrence frequency of an episode in the temporal data series, and an expiry time tX. In step 518, as will be discussed below, the temporal data series is traversed one event at a time. In an embodiment of step 518 as described herein, a single pass of sequentially scanning through the temporal data series may suffice. While this detailed discussion presents certain opportunities to attain the results described herein, other steps in place of those described are possible, without exceeding the scope of this disclosure. Additional data structures of use in implementing the method are initialized in a step 604. In this way a set of automata may be generated and initialized to provide for tracking whether a candidate episode occurs in the temporal data series. In addition, for each candidate episode, a count of occurrences may be initialized to zero. To handle cases in which an event type occurs in consecutive positions in a candidate episode, a variable bag may be initialized to be empty of contents. The variable bag may be a list, an array of pointers, or other appropriate data structure. During practice of an embodiment of the method, the variable bag may hold elements denoted herein by (α, j), denoting an automaton of the episode α is waiting for a particular event type as its jth event. There may be many candidate episodes and for each candidate episode there may be multiple occurrences. Thus, at any time there may be many automata waiting for many event types to occur. In order to traverse and access the automata efficiently, for each event type E in the set Ck the automata that accept E are linked together in the list waits(E,δ). The variable waits(E,δ) is preferably a list, but any other appropriate data structure may be employed. Like the variable bag, the waits(E,δ) list may contain entries of the form (α,j). In the case of waits(E,δ), an entry (α,j) means that an automaton of the episode α is waiting for event type E as its jth event. That is, if the event type E occurs now in the event sequence, this automaton would accept it and transit to the jth state. At any time (including at the start of the counting process) there may be automata waiting for the event types corresponding to first nodes of all the candidate episodes. Accordingly, the waits(·) list is initialized as described below. Further initialization takes place in step 604 by initializing a plurality of automata adapted to detect whether an episode of the set Ck occurs in the temporal data series. Each episode α of Ck may have \|α\| automata initialized, one for each node of the episode. The initialization of the automata includes adding an entry (α,j) to waits(α[1], δ), setting the episode count, α.freq, to zero, and setting the initialization time α.init[j], to zero for each α-automaton. The initialization time is the time at which the first event of the episode occurred, for each instance of the automaton (for a given episode). Further, it may be useful to prescribe an expiry time for episode occurrences, so that very widely spread out events would not be counted as an occurrence of some episode. This condition may be enforced in the method by testing the time taken to reach the new state before permitting a transition into it. This expiry time condition is an added facility in the method and the condition can easily be dropped. It may be noted that the scheme of retaining only the latest initialization time for the automata in a given state is consistent with this expiry time restriction. The expiry time may be provided as an additional input as shown in step 602 above. Identifying occurrences of candidate episodes in the temporal data sequence is accomplished by sequentially searching through the data series with the plurality of automata at 606. This step is discussed in further detail below in connection with FIGS. 7 through 11. In brief, the automata occupy states corresponding to nodes of candidate episodes to track partial occurrences of the candidate episodes, with an automaton entering a final state when an entire occurrence of a candidate episode is detected in the temporal data series by that automaton. When a complete occurrence of a candidate episode has been tracked by an automaton, incrementing of an episode count for that candidate episode takes place. An automaton waiting for an event type makes a transition when that event type occurs, and the waits(·) list is accordingly updated. Multiple automata in the same state would be redundant, as they would only make the same transitions. In an embodiment disclosed herein for counting non-overlapping occurrences, as described below, an automaton that reaches a common state most recently is retained, with other automata reaching the same state being discarded. A variable α.init[j] may be used to store \|α\| initialization times for automata for the episode α. The variable α.init[j] indicates when an automaton for the episode α that is currently in its jth state, becomes initialized, as previously discussed. If multiple instances transit to the same state j, only the most recent initialization time is stored. When a complete occurrence of an episode is identified by an automaton for that episode, all other automata that might have been initialized for that episode are reset, in this embodiment for counting non-overlapping occurrences. Accordingly, a collection of overlapping occurrences increments the frequency for the episode by exactly one. In an embodiment disclosed herein for counting non-interleaved occurrences, as described below, all automaton that reach a common state may be retained, in general. The exception to this is when the state corresponds to the final event of a candidate episode. An automaton reaching that state is reset and the occurrence count for the episode is reset. As is done for counting non-overlapping occurrences, the variable α.init[j] may be used to store \|α\| initialization times for automata for the episode α, with the variable α.init[j] indicating when an automaton for the episode α that is currently in its jth state, becomes initialized. For non-interleaved occurrences, if multiple instances transit to the same state j, multiple initialization times are stored. Also, when a complete occurrence of an episode is identified by an automaton for that episode, other automata that might have been initialized for that episode are retained, in general. The step of producing results is shown in step 608. These results, including a determination of frequent principal episodes found in step 606, are for use in step 520 of FIG. 5. Further detail of step 608 is provided in FIG. 12, discussed below. In brief summary, referring to FIG. 6, there it is shown that step 602 performs retrieving of input (e.g., the fault data 112 of FIG. 1), that step 604 performs initialization of data structures used in an embodiment, and that step 606 performs sequential scanning through the temporal data series so that the results may be produced for episodes identified as frequent as shown in step 608. Continuing with description of FIG. 6, the step of producing an output for candidate episodes whose count of occurrences yields a frequency of occurrence meeting or exceeding the threshold frequency λ provided in step 602, shown at 608, as mentioned above. While FIG. 6 sets forth the details of step 518 in general terms, FIGS. 7-12 provide more detail of the steps in FIG. 6. For example, a more detailed depiction of step 606, identification of episodes occurring in the temporal data series, is shown in FIG. 7. In FIG. 7, at a step 704, the method retrieves the next element (E, t, τ) in the temporal data series. The interval τ−t is then used in a step 705 to get the next element D of B containing that interval. In step 705 also, the variable bag is set to be empty of contents. The event E is then used in retrieval of waits(E, D), which is used in step 706. waits(E, D) contains an entry for each automaton awaiting an occurrence of an event of type E in the temporal data series. In the course of execution of the method, each entry in waits(E, D) is retrieved in turn, beginning with the first one. Retrieval of the entry is identified as step 706, where for the purpose of further discussion, the retrieved entry is identified as (α,j). A variable transition may be cleared, e.g., by setting its value to zero, in preparation for its use later in the method for indicating a state transition has occurred. When all elements of waits(E, D) have been retrieved, the method may branch at 708 to step 705 to retrieve the next element D of B containing the interval τ−t. In the same way, when all elements D of B have been retrieved, the method may branch at 709 to step 704 to retrieve the next element (E, t, τ) in the temporal data series. With (α,j), the method proceeds to a query 710 as to whether the state index j is 1 or not. If j=1, the method executes a step 712 in which the initialization time of the automaton for the episode is set to t. Also in step 712, the flag transition is set to indicate a state transition has occurred. If j is not 1, the method conditionally transits automaton α from state (j−1) (in which it was awaiting an event α.g[j], that is, E) to a state j (in which it awaits an event α.g[j+1]) at 714. Step 714, and the condition for a state transition in step 714, will be discussed more fully in connection with FIGS. 8 and 9. If a state transition has taken place in step 712 or step 714 so that the transition flag is set 715, a query 716 is made as to whether the state index j is less than the number of nodes in the episode or not (if not, then j equals the number of nodes in the episode, by the logic disclosed herein). If j=\|α\|, then an occurrence of episode α is recognized 718. Step 718 is discussed more fully below in connection with FIG. 10. In an embodiment adapted to count non-overlapping occurrences of candidate episodes, a step 720 is executed in which automata in states corresponding to partial occurrences of the episode α are removed. Step 720 is discussed more fully below in connection with FIG. 11. In an embodiment adapted to count non-interleaved occurrences of candidate episodes, execution of step 720 is absent. Thus, in an embodiment in which non-interleaved occurrences are identified, the method does not reset all instances of an episode if one instance of it reaches the final state. This way some overlapping occurrences of a candidate episode may be counted, so long as a previous instance has transited at least one state more than the next instance. Returning to discussion of step 716, if j<\|α\|, then a further query 722 is made as to whether the next event of episode α might also be an event of type E. If not, then as entry (α, j+1) is added to waits(α.g[j+1], δ), ∀δ is α.d[j+1] (which is a distinct waits(·) list, since either α.g[j+1]≠E or D is not in α.d[j+1]). If, on the contrary, the next event of episode α is again an event of type E, that is, α.g[j+1]=E, then an entry (α,j+1) is added to the variable bag. Since the method retrieves entries in waits(E, D) in turn (at step 706), and sets the initialization time (at step 712), sequestering the entry (α,j+1) in bag instead of simply adding it to waits(α.g[j+1], D), which would be waits(E, D) in this case, precludes incorrectly overwriting the initialization time for the episode. In step 726 an entry (α,j+1) is added as well to the variable waits(E, δ) for all δ in α.d[j+1] but not in D. Following 718 (for an embodiment counting non-interleaved occurrences), step 720 (for an embodiment counting non-overlapping occurrences), step 724, or step 726, the system at 728 may branch to step 706 to retrieve the next entry in waits(E, D) if one is available. Returning to step 715 above, if a state transition has not taken place in step 712 or step 714, the method branches to step 728. If a next entry is not available in waits(E, D), the method instead branches to a step 730 in which the contents of the variable bag are transferred into waits(E, D). Note that bag may be empty under some circumstances. Following that, the method returns to step 705. As discussed above, at step 706, the method retrieves the next element D of B containing the interval τ−t. When all elements D of B have been retrieved, the method may branch at 709 to step 704 to retrieve the next element (E, t, τ) in the temporal data series. If the temporal data series is exhausted upon return to step 704, execution of step 606 finishes, and the method may continue with step 608 in FIG. 6. Turning now to FIG. 8, details of step 714 are shown for an embodiment in which non-overlapping occurrences of candidate episodes are tracked and identified. Conditionally, the automaton makes a transit from state j−1 to state j. The condition is that at least some nonzero time has transpired since initialization of the automaton. In an embodiment where an expiry time is input, the condition also includes a test that less than the prescribed expiry time has transpired since the automaton was initialized. In this way the expiry time may provide a criterion for timely occurrence of an episode. The automaton makes a transition from state j−1 to state j by the following actions at a step 802: the initialization time is shifted from α.init[j−1] to α.init[j], and the flag transition is set. At a step 804, the variable α.init[j−1] is reset to zero. The entry (α,j) is removed from waits(E, δ) for all δ in α.d[j] at 806. Steps 804 and 806 occur unconditionally, in contrast to step 802. Although step 806 is shown as following step 804, step 806 may instead occur before step 802, or between step 802 and step 804. The significant order of steps in FIG. 8 is that step 804 follow step 802, if step 802 occurs. Turning now to FIG. 9, details of a step 714′ are shown for an embodiment in which non-interleaved occurrences of candidate episodes are tracked and identified. As in FIG. 8, conditionally the automaton makes a transit from state j−1 to state j. The condition now is that at least some nonzero time has transpired since initialization of the automaton, and that no automaton for that episode is already in state j. This may be determined, for example, by checking that α.init[j] is zero. Thus in an embodiment for identifying non-interleaved occurrences, the method does not permit a transition into a particular state (except for first state) if there is already an instance of the automaton waiting in that state. In other words, while it still uses only one automaton per state, it does not forget an earlier initialization of the automaton until that has transited to the next state. There may be many sets of non-interleaved occurrences of an episode in the event sequence. The embodiment as disclosed herein for counting non-interleaved occurrences counts that set of non-interleaved occurrences, which includes the first occurrence of the episode in the event sequence. In an embodiment where an expiry time is input, the condition may also include a test that less than the prescribed expiry time has transpired since the automaton was initialized, as also shown in FIG. 9. In this way the expiry time may provide a criterion for timely occurrence of an episode. The automaton makes a transition from state j−1 to state j by the actions at step 802′, 804′, and 806′. The initialization time is shifted from α.init[j−1] to α.init[j], and the flag transition is set at 802′. At a step 804′, the variable α.init[j−1] is reset to zero. The entry (α,j) is removed from waits(E,δ) for all δ in α.d[j] at 806′. Steps 804′ and 806′ are conditional, along with step 802′. Although step 806′ is shown as following step 804′, step 806′ may instead occur before step 802′, or between step 802′ and step 804′. The significant order of steps in FIG. 9 is that step 804′ follow step 802′. Turning now to FIG. 10, details of step 718, recognizing an occurrence of episode α, are shown. At 1002 the episode count for episode α is incremented by setting α.freq[j]=α.freq[j]+1. At step 1004, the initialization time is reset to zero, α.init[j]=0. Although shown with step 1002 preceding step 1004, the two steps may occur in the opposite order. Turning now to FIG. 11, details of the step 720 of removing automata in states corresponding to partial occurrences of the episode α are shown. First, an episode traversal index k may be initialized to a value 1 at 1102. Next, if the initialization time α.init[k] is nonzero 1103, then at a step 1104, the initialization time α.init[k] is reset to zero and at a step 1106, the entry (α,k+1) is removed from waits(α.g[k+1], δ), for all δ in α.d[k+1]. Note that steps 1104 and 1106, if they occur, may occur in any order, although FIG. 11 depicts step 1104 occurring first. Next, the episode traversal index k is incremented, k=k+1 at 1108. At 1110 a query is made as to whether k<\|α\|. If so, a branch to step 1103 is made, and execution continues therefrom. Otherwise, at a step 1112, if the variable bag contains an entry (α,k), the entry (α,k) is removed from bag. Following step 1112, step 720 ends at 1114. In brief summary now, discussion of FIGS. 7-11 completes discussion of details of step 606 of FIG. 6. Two embodiments of the method were discussed, one for identification of non-overlapping episodes, and one for identification of non-interleaved episodes. Turning now to further discussion of step 608 of FIG. 6, FIG. 12 depicts a first step 1202 of initializing the variable Fk* to be empty. As described above in connection with step 518 of FIG. 5, Fk* is intended to hold frequent principal episodes of length k. At a step 1204, each frequent k-node episode α is checked to see whether it is principal in the temporal data series. If α is found to be principal, Fk* is updated to contain α. The check for whether α may be principal is made by finding all strict k-node superepisodes β of α that occur in the temporal data series. If no βα is similar in s to α, then α is principal in s. Because the test is restricted to strict k-node superepisodes β that occur in the temporal data series, the test for similarity involves solely a test that the frequencies of occurrence of α and β are identical. If the frequencies differ, then α is principal in s and added to Fk. One arrangement of episodes in Fk is shown in FIG. 13. FIG. 13 displays a set of blocks 1302, 1304, 1306, 1308, and 1310. The actual number of blocks to be used depends on details of the episodes in Fk. Episodes in Fk are sorted in some order. One possible order is lexicographic order. This may be appropriate when event types are considered as symbols and the symbols can be ordered as if listed in a dictionary. Any specific order will suffice, provided where an event is to be positioned in a set of events subject to the order is unambiguous. This definition of order may also include ordering an event according to its allowed duration information, i.e., its interval set. The k-node frequent principal episodes may thus be arranged as a lexicographically sorted collection Fk* of k-length arrays. The ith episode in the collection has two components for its specification—the first is Fk[i].g[j] which refers to the event type association for jth node, and the second is Fk[i].d[j] which stores the collection of intervals (which specify the dwelling times allowed) associated with the jth node. Fk[i].d[j] is a list of intervals and the kth element of this list is denoted by Fk[i].d[j][k]. The episode collection is viewed as constituted in blocks such that within each block in Fk* the first (k−1) nodes are identical, i.e., both the event type as well as the timing information of the first (k−1) nodes are the same for the episodes in a block. Potential (k+1)-node candidates are constructed by combining two episodes within a block as will be discussed below. The newly constructed (k+1)-node episode is declared a candidate only if every subepisode generated by dropping one of its nodes is already known to be principal and frequent (and hence is in Fk). When the episodes are ordered, Fk typically has the structure shown in FIG. 13. Each block, e.g., 1302, will include those episodes whose first k−1 events will be identical, both as to event type and interval set. This is shown in FIG. 14. In the example of FIG. 14, k=4. In FIG. 14, three episodes 1402, 1404, and 1406 are shown as an example, each with four entries. Each of the three episodes has the same event type and interval set for a fist entry, namely event 1 and interval set 1 in FIG. 14. For all three episodes 1402, 1404, and 1406, the second entry is event 2 and interval set 2, as shown. This pattern continues within a block until the last entry of the episodes. In FIG. 14, for example, episode 1402 has a last entry event 4 and interval set 4, while episode 1404 has a last entry event 4′ and interval set 4′. Episode 1406 has a last entry event 4″ and interval set 4″. Adopting episode ordering as the structuring principle for Fk* has a benefit that when a new principal episode α is determined, it readily may be inserted into Fk* in the appropriate block. The block structure of Fk* also facilitates generation of new candidate episodes from frequent principal episodes. FIG. 15 depicts example new candidate episodes 1502 and 1504 generated from episodes 1402, 1404, and 1406 of FIG. 14. Candidate episodes 1502 and 1504 have their first k−1 entries in common. In the example shown, they have their first three entries in common. For their last two entries, one each is drawn from the last entry of 1402, 1404, or 1406. As shown, candidate episode 1502 includes the last entries of episode 1402 and 1406, and candidate episode 1504 includes the last entries of 1406 and 1404. FIG. 16 depicts details of step 520 of FIG. 5. In FIG. 512, the candidate generation is done through the steps shown. First, at 1602, the collection Ck+1 of candidate episodes of length k+1 is initialized to be empty. At 1604, (k+1)-node candidate episodes are built from frequent principal episodes of length k, as discussed above. A newly constructed (k+1)-node episode is declared a candidate only if every subepisode generated by dropping one of its nodes is already known to be principal and frequent (and hence is in Fk). Thus, at step 1606, for each (k+1)-node candidate episode, k+1 k-node subepisodes are constructed by omitting one of the nodes of the (k+1)-node candidate episode. If each of these k+1 k-node subepisodes are in Fk, the (k+1)-node candidate episode is added to Ck+1. At step 1608, the collection Ck+1 is returned as a result or output, and method 500 continues with step 522. Returning now to step 530 of FIG. 5, the rule discovery process in the generalized framework of discovery of frequent episodes with dwelling times can be described in the following form. As above, Fs* denotes the set of all frequent principal episodes in s. The rules take the form β→α, where βα and α, βεFs. To obtain such rules all the frequent principal episodes in the event sequence s are first computed (see step 526). For each such frequent episode-subepisode pair, α, βεFs, with βα, the subepisode is said to imply the episode if the ratio of their frequencies of occurrence in the event sequence exceeds a confidence threshold ρmin. FIG. 17 depicts a modular structure of the TDM diagnostics tool 114 of FIG. 1 in accordance with an exemplary embodiment. In FIG. 17, an input module 1702 provides for accepting input of a temporal data series. The temporal data series may be retrieved by input module 1702 from, e.g., the fault data 112 of FIG. 1. Input module 1702 in addition provides for accepting input of a set B of allowed dwelling times, and for accepting input of a threshold frequency and confidence threshold as well as an expiry time. The TDM diagnostics tool 114 may also include an automata generation and initialization module 1704 to provide a sufficient number of automata, properly initialized, for tracking occurrences of candidate episodes in the temporal data series. As discussed previously, in general, as many as \|α\| automata for a particular episode α may be used to track all partial occurrences of the episode α. A tracking module 1706 manages, in an update module 1708, the automata tracking events of the data series through the transitions they make, and counts detected occurrences of candidate episodes in counting module 1710. Candidate identification module 1711 provides for detection of the occurrences. Tracking module 1706 may branch back to module 1704 for continued generation and/or initialization of automata. An output module 1712 provides for output for candidate episodes whose frequency of occurrence in the data series meets of exceeds the threshold frequency provided to input module 1702. The output module 1712 may also generate the reports 116 of FIG. 1. FIG. 18 depicts an alternate exemplary embodiment of a host system 102′ for performing fault data correlation and root cause diagnostic analysis. In FIG. 18, a processor 1802 processes instructions stored in memory 1804 as input instructions 1806, automata generation and initialization instructions 1808, tracking instructions 1810, update instructions 1812, counting instructions 1814, candidate identification instructions 1815, and output instructions 1816. Processor 1802 executes the instructions to process temporal data retrieved from database 110′ in accordance with input provided through user interface 1820. The database 110′ represents an alternate exemplary embodiment of the data storage device 110 of FIG. 1, and may include fault data as temporal data within the database 110′. Outputs, such as reports, may be sent to the user interface 1820 and/or the database 110′. In summary, the temporal data mining technology as described herein can search for patterns of interest in time series fault data in support of root cause diagnostic analysis. As described in detail above, the TDM diagnostics tool 114 of FIGS. 1 and 17 may perform a method of temporal data mining for fault data correlation. The method may include receiving as input a series of temporal (i.e., time-stamped) data, a set of candidate episodes to be sought in the data series, and a threshold frequency of occurrence for the candidate episodes. The method also includes a step of generating automata adapted to track whether a candidate episode occurs in the temporal data series, and then tracking, with the automata, whether the episode occurs in the temporal data series. The method includes a further step of incrementing a count when an occurrence of the episode has been tracked by the automaton and a step of producing an output for candidate episodes whose count of occurrences results in a frequency exceeding the threshold frequency. A correlation confidence of faults within episodes may be calculated and output as part of the reporting process to assist in determining the root cause of the faults. Technical effects of exemplary embodiments include applying temporal data mining for fault data correlation in a diagnostic system. The fault data correlation may support root cause diagnostics of machine and/or system faults. Further technical effects may include reporting fault episode frequency and confidence levels of correlation between faults. Advantages include elimination of misleading troubleshooting theories through reporting the existence of correlations between faults, as well as the absence of correlations between faults. Further technical effects may include identifying the root cause of an episode of faults and calculating the associated downtime for the episode. Reporting the downtime for an episode can be advantageous, particularly for well-known and expected episodes, as this information can be used to improve planning and reaction strategies for common episodes. As described above, the embodiments of the invention may be embodied in the form of computer-implemented processes and apparatuses for practicing those processes. Embodiments of the invention may also be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. The present invention can also be embodied in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits. While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another.
	abstract	A pressurized water reactor vessel having a flow skirt formed from a perforated cylinder structure supported in the lower reactor vessel head at the outlet of the downcomer annulus, that channels the coolant flow through flow holes in the wall of the cylinder structure. The flow skirt is supported at a plurality of circumferentially spaced locations on the lower reactor vessel head that are not equally spaced or vertically aligned with the core barrel attachment points, and the flow skirt employs a unique arrangement of hole patterns that assure a substantially balanced pressure and flow of the coolant over the entire underside of the lower core support plate.
052456480	abstract	A computerized three-dimensional x-ray tomographic microscopy system is disclosed, comprising:. a) source means for providing a source of parallel x-ray beams, PA1 b) staging means for staging and sequentially rotating a sample to be positioned in the path of the PA1 c) x-ray image magnifier means positioned in the path of the beams downstream from the sample, PA1 d) detecting means for detecting the beams after being passed through and magnified by the image magnifier means, and PA1 e) computing means for analyzing values received from the detecting means, and converting the values into three-dimensional representations. Also disclosed is a process for magnifying an x-ray image, and apparatus therefor.
047327057	summary	BACKGROUND OF THE INVENTION 1. Field of the Invention The current invention concerns a process for the improvement of the stability properties of solidified radioactive ion exchange resin particles, wherein the resin particles are embedded in a mixture containing an inorganic and/or organic binding agent, which is then left to harden. 2. The Prior Art In most nuclear power plants organic ion exchange resins in the form of beads or powder are used for the cleaning of the various water circulation systems. In the following, the beads as well as the powder particles of the ion exchange resins are designated as resin particles. The ion exchange resin particles act to retain general impurities in the water circulation systems, and also radionuclides. In this manner, the activity of the circulation systems can be kept within limits. Active ion exchange resins also accumulate in the reprocessing plants. The use of ion exchange resins almost always is carried out in mixed bed processes, i.e., mixed anion and cation exchange resins. Only fresh resins in the OH' or H' form are used in each case, so that no foreign ions are introduced into the circulation systems. The ion exchange resins have to be replaced each time when their capacity has been exhausted by charging with general impurities when they can no longer accept any activity. The replaced ion exchange resins are to be considered mildly to medium active radioactive waste which has to be disposed of. For a final storage, but even for transport, radioactive waste has to be generally solidified, whereby, for security reasons, varying demands are made with regard to the solidified waste. This includes sufficiently high compressive strength, a good water resistance, sulfate resistance and the lowest possible leach rate. For the solidification of radioactive ion exchange resins, the resin particles are embedded into inorganic and/or organic binding agents, such as cement, bitumen or plastics for the formation of a so-called matrix. It is desired to accommodate the greatest possible amount of waste within a certain matrix volume. The swelling and shrinking behavior of organic ion exchange resins is responsible for the fact that the matrix, after solidification, is possibly not water resistant. For this reason the cement solidification for such resins is often regarded with skepticism. In fact, such a matrix may develop cracks during later storage in water, or even decay, if not special techniques are used during solidification. With regard to the described facts, the amount of resin for the solidification of resin particles has usually been limited to about 20 kg of dry resin particles per 100 liters of matrix, whereby the resulting compressive strength was a little above 20 N/mm.sup.2. In addition, if the solidification of the cement mixture takes place under water, the matrix also becomes water resistant, unless it is not dried between. With a higher share of ion exchange resins in the matrix, the compressive strength decreases below 10 N/mm.sup.2. But even such a matrix can, under certain circumstances, remain stable at water storage, if there is no drying beforehand. However, if test bodies of such cement solidification procedures are conditioned, e.g., in air with 20% relative humidity, whereby drying causes a weight loss of up to 25%, they are no longer stable for water storage. Their compressive strength decreases already considerably during the drying process, whereby shrinkage tears appear. During subsequent water storage, the test pieces decay in most cases within hours or a few days, or at least large tears appear. SUMMARY OF THE INVENTION It is the object of the current invention to create a process by which the stability properties of solidified radioactive ion exchange resin particles is considerably improved and thus also makes it possible to give greater amounts of resin into a matrix volume. The invention is based on the knowledge that by a suitable treatment of the radioactive ion exchange resin particles before or during the solidification process, the swelling and shrinking properties of the resin particles can be improved in such a manner that the resulting solid matrix can, with approximately the same compressive strength, not only contain a considerably increased amount of ion exchange resin, but also have good water resistance and stability after drying. By the treatment according to the invention, the ion exchange resin particles can be brought into a stable state in which they have, compared to untreated resin particles, a reduced swelling capability and possibly also a smaller volume. The invention will be now explained in more detail by way of examples, and compared to the state of the art. Depending on the type of nuclear reactor, two different types of ion exchange resins are used in Switzerland, which are, mainly powder resins such as the Powdex resins from Graver Water Conditioning Co., U.S.A in boiling water reactors, and almost exclusively bead resins such as the Lewatit resins from Bayer/Leverkusen, FRG in pressurized water reactors. The following examples are based on tests with bead resins of the last mentioned type. However, the results with powder resins are almost the same. Used as anion exchange resin was the type Lewatit M-500 and as cation exchange resin the type Lewatit S-100, both from Bayer/Leverkusen, FRG. The radioactive ion exchange resins taken from the water circulation systems of a nuclear power plant were, in addition, charged as follows: anion exchange resin M-500 with approx. 200 g of boric acid (H.sub.3 BO.sub.3) per liter resin; cation exchange resin S-100 with 4 g lithim per liter resin. By treating the anion resin particles with a polysulfide it was surprisingly possible to induce the resin particles to strong shrinkage with simultaneous water expulsion. After drying at room temperature and subsequent washing of the thus treated resin particles, they showed a swelling factor of only 1.5 as compared to 2.0 before the treatment. The swelling factor is here defined as the quotient from the settled volume of the resin particles in water-moistened swollen state and the settled volume of the same resin particles in dry state. When, after the polysulfide treatment, the anion resin particles were treated for about 24 hours at a temperature of 50.degree. C., the swelling factor even dropped to near 1.0, which means that the resin particles then do not swell anymore at all and shrink during washing and drying. If, during the treatment with polysulfide, a vulcanization agent, e.g. a xanthate, was also added to the anion resin particles, the swelling factor dropped to between 1.0 and 1.1, even at room temperature. It was possible, not only by treatment with polysulfides, to greatly reduce the swelling factors of anion resin particles, but also by ion exchange with special organic acids or anion-active organic compounds. Named as such can be mono and polyfunctional carboxylic acids, their salts and their derivatives, such as stearic acid, acrylic acid, natural and modified root resins, sebacic acid, etc.; sulfuric acid mono-esters, such as lauryl sulfate; sulfonates, such as vinyl-sulfonate; phosphoric acid mono and di-esters, such as stearic phosphates, butyl phosphates, nonyl phosphates. These substances block the hydrophilic groups of the anion resins and can, in part, still be cross-linked. For the anion resin, a thermolysis process also proved as suitable as the treatment by addition of polysulfide or of another of the above cited compounds. The splitting off of amines from anion resins at higher temperatures is generally known. The producers of resins issue clear warnings against too high temperatures, as those would endanger the ion exchange properties. However, it has now been discovered that this so far undesirable phenomenon can be used for the improvement of the stability properties of solidified radioactive ion exchange resin particles. If anion resin particles are heated for extended time to 150.degree. C., preferably in an air stream while stirring, amines are split off, primarily trimethylamine. With such a process, the resin particles shrink strongly and lose their swelling and shrinking properties. By adding alkali or earth alkali hydroxides, the decomposition temperature can even be slightly lowered. The duration of the thermal treatment depends on the treatment temperature. The higher the temperature, the shorter the treatment time can be. The temperature for thermolysis can be chosen in the range from between 50.degree. C. and 250.degree. C., preferably between 100.degree. C. and 200.degree. C., whereby the duration of treatment can be, e.g., in the range of between 24 hours and down to 1/2 hour. It is also possible to split off amines from anion resin particles which have previously been treated with sulfides or polysulfides by an additional heat treatment within the limits as described above. Surprisingly, this is already possible successfully at a temperature below 100.degree. C., e.g., between 70.degree. and 80.degree. C. This low decomposition temperature affords essential technical advantages, especially for the gas purification. By a subsequent oxidation with H.sub.2 O.sub.2 it is possible to produce from the original anion resins even cation-active resins, which can disintegrate oxidatively more easily. It was possible to equally strongly reduce the swelling and shrinking properties of cation resin particles with very specific cation or cation active compounds as that of anion resin particles. This was done by the addition of substances from the following groups: primary, secondary, tertiary or quartenary basic amines which have, per molecule, either one, two or more amine groups, whereby the organic groups can be additionally cross-linked; basic organic phosphonium compounds; basic organic sulphonium compounds. A similar effect is shown by Ba.sup.++ and Fe.sup.++ salts. These ionogenic compounds, which sterically fit into the ion exchange resins, are, in part, so tightly bound to the resins that, in the solution of a cement mixture or in highly mineralized ground waters, they no longer exchange these ions and thus the resins remain stable as to volume. This adhesion could often be still improved by a subsequent heat treatment, whereby the swelling factor was still further reduced. In practice, mixtures of anion and cation resin particles are used in most cases. In order to attain, simultaneously, a reduction of the swelling factor for both types of resin particles, one of the described treatments for the anion resin particles as well a one of the described treatments for the cation particles is to be used, or a compoud should be added to the mixture of anion and cation resin particles which contains anion as well as cation active components, and thus effective anions and cations or anion active as well as cation active components. The volume ratios and the swelling factors of the thus treated mixtures of anion and cation resins are composed proportional to the mixture ratio from the data of the individual components, and can thus be precalculted for mixtures when the data of the individual components are known. A series of tests was done with each of the cation resin particles of the type Lewatit S-100 and anion resin particles of the type Lewatit M-500 as well as with a mixture of 50% by weight of Lewatit S-100 and 50% by weight of Lewatit M-500, in order to determine the comparative volumes of the resin particles in water-moistened, swelled state and in dry state, as well as the swelling factor, which was done for resin particles without treatment and for resin particles after one of the treatments described above. The results obtained are displayed in table I. The comparative volumes cited in table I (liter/kg) are, in each case, the specific settled volume in liters of an amount of 1 kg dried ion exchange resin particles in the H or OH form, whereby the specific settled volume is cited once for the wet, swelled resin particles and once for the dry resin particles. The swelling factor is the quotient of wet volume over dry volume. The original state of the resin particles always was the H or OH form. The resin particles were treated with solutions which contained only the substances stated in table I. The amounts of the treatment solution were usually sufficient that a complete charging of the resins according to their maximum capacity was made possible. Where nothing else is stated, the resin particles were treated, in each case, for 1/2 hour at 50.degree. C. with the stated solution, then cooled to 20.degree. C., and stirring continued for another 1/2 hour at 20.degree. C., before filtering and washing the resin particles with distilled water. To determine the specific settled volume of the dried resin particles, the latter were dried in a vacuum at 40.degree. C. until their water content was less than 1% by weight. Where a heat treatment at 160.degree. C. is mentioned in table I, this refers to a drying and subsequent heating to 160.degree. C. for 2 hours. The values cited in table I under nos. 1 to 3 refer to untreated ion exchange resins. The tests no. 4 to 61 were done with cation resin particles and the test no. 62 to 83 with anion resin particles. The information under no. 84 to 103 refer to tests with a mixture of 50% by weight of cation and 50% by weight of anion resin particles. It can be seen from table I that the untreated ion exchange resin particles have a swelling factor between 2.1 and 2.24 at a specific settled volume in a wet, swollen state of 2.5 to 3.23 liter per kg dry substance. Table I shows also that the swelling factor can be substantially reduced to or nearly to 1.0 by a suitable treatment of the resin particles. Of interest in practice are all those types of treatment which result in a swelling factor of less than 1.7. However, also of importance are the statements in table I concerning the wet volume of the treated resin particles. The smaller the wet volume, the greater is the amount of resin particles which can be solidified in a given volume. Thus, a type of treatment should preferably be used which provides an optimum between the lowest possible swelling factor and, simultaneously, the smallest specific wet volume. In order to determine the effect of the reduction of the swelling factor on the stability properties of solidified radioactive ion exchange resin particles, the comparison tests, described below, were executed, on the one hand, on a known standard cement solidification of untreated resin particles and, on the other hand, of a cement solidification for the reduction of the swelling factor of treated resin particles. Used as base was in both cases a mixture of 50% by weight of cation exchange resin of the type Lewatit S-100 and 50% by weight of anion exchange resin of the type Lewatit M-500, as it is obtained, e.g., from the Swiss nuclear power plant Goesgen as radioactive waste.
	claims	1. An optical semiconductor device comprising:a semiconductor film having photoconductive properties, the semiconductor film generating carriers by absorbing light at a light absorption edge of the semiconductor film; anda pair of electrodes for applying an electric field to the semiconductor film causing the carriers to move, the pair of electrodes sandwiching the semiconductor film in a film thickness direction and having a propagating portion extending in a direction opposite the light absorption edge for propagating an electromagnetic wave generated from the semiconductor film by movement of the carriers,wherein the propagating portion is in contact with the semiconductor film and serves as an antenna for radiating into space the electromagnetic wave generated from the semiconductor film, the electromagnetic wave having a frequency in a frequency region of 30 GHz or more and 30 THz or less. 2. An optical semiconductor device according to claim 1, wherein the pair of electrodes are arranged so as to interpose the semiconductor film in the direction perpendicular to the surface of the semiconductor film. 3. An optical semiconductor device according to claim 1, wherein the semiconductor film is a III-V semiconductor film. 4. An optical semiconductor device according to claim 1, wherein overlaid on at least one surface of the semiconductor film is a semiconductor material having a different type of conductivity and a different energy band gap than the semiconductor film. 5. An optical semiconductor device according to claim 1, wherein a transmission path for propagating the electromagnetic wave generated from the semiconductor film is continuously formed, and a metal constituting the transmission path is electrically connected to at least one electrode of the pair of electrodes. 6. An optical semiconductor device according to claim 1, further comprising an optical waveguide for applying light incident on a side surface of the semiconductor film to the region of the semiconductor film to which the electric field is applied. 7. An optical semiconductor device according to claim 2, wherein the electromagnetic wave is generated from the semiconductor film by conducting photoirradiation from above an upper side of the device through spatial propagation to a region of the semiconductor film in a vicinity of an electrode of the pair of electrodes that is arranged toward the upper side of the device relative to a second electrode of the pair of electrodes.
048760730	summary	FIELD OF THE INVENTION There are provided generators for short-lived radionuclides for use in medicine, and especially in diagnostic methods such as angiocardiography. There is also provided a novel process for the production of an osmium complex which is used in one type of such generators. Other objects of the invention and features thereof will become apparent hereinafter. BACKGROUND OF THE INVENTION First pass radionuclide angiography following bolus administration has been used principally for the detection and quantitation of intracardiac shunts, evaluation of right and left ventricular ejection fraction, measurement of cardiac output and various other cardiac parameters. This technique has proved its potential for non-invasive evaluation of a variety of congenital and acquired cardiovascular disorders, especially in children. A radionuclide of short half-life must be used, and the one in use to the largest extent at present is technetium-99m, which is used mainly as sodium pertechnetate with a .gamma. of 140 keV, with a physical half-life of 6 hours. There have also been proposed generator systems of Cd-109.fwdarw.Ag-109m and Os-191.fwdarw.Ir-191m. In the case of the Cd/Ag generator the half life of 1.26 years of Cd poses a problem should breakthrough occur. There has been developed a rubidium-81 krypton-81m generator with Rb half-life of 4.7 hours and Krypton half-life of 13.1 seconds. Krypton-81m is well suited for long studies but is not suitable for angiocardiography as it is readily eliminated by the lungs. Another ultra-short lived generator is Ba-137m with a half-life of 2.55 minutes. However, its photon energy of 662 keV is too high for use with gamm cameras of the Anger type. Yet another generator is the Hg-195.fwdarw.A-195m generator, the daughter having a 30.5 seconds half-life, with the parent having a 40 hour half-life. SUMMARY OF THE INVENTION There is provided a generator for the production of ultra-short lived radionuclides for use in medical diagnostics, and especially for use in angiocardiography in adults and in children. (1) The novel type of radionuclide generator is based on the concept of providing an inorganic support column to which there is applied a suitable ion exchange agent adapted to firmly bind a suitable compound or complex of the parent radioactive element, there being established a steady state between said parent compound and the daughter nuclide of short life time which results from said parent nuclide. The invention is mainly illustrated with reference to a preferred embodiment which is based on .sup.191 Os giving .sup.191m Ir. As pointed out in the following, other generators can be provided based on systems like .sup.178 W .sup.178 Ta, or .sup.195m Hg .sup.195m Au, and the like. The following description describes in detail the embodiment of the generator based on Os/Ir. Thus, the preferred embodiment of a generator for short-lived radionuclides according to the present invention, is based on the use of a column charged with .sup.191 Os which has a half-life of 15.5 days, giving .sup.191m Ir which has a half-life of 4.9 seconds, giving a gamma of 129 keV and X-rays of 65 keV, used advantageously in conjunction with a scavenger minimizing the breakthrough of Os to very low values. There is also provided a novel process for the production of an osmium complex which is used for charging the column, which process is comparatively simple, gives a pure product in a high yield, and which complex has advantageous properties for the intended purposes.
	description	The present invention relates to a reactor water-level measurement system that measures the water level in a reactor. For boiling-water nuclear power plants (BWR power plants), some water-level meters for use to monitor water levels in a reactor have been proposed. For example, a monitoring apparatus for measuring a water level in a reactor core has been proposed (e.g., Patent Document 1). The monitoring apparatus described in Patent Document 1 is configured to use gamma-ray heating in a reactor, insert a sensor structured by combining a thermocouple and stainless steel rod into the reactor, and continuously monitor the reactor water level by detecting an AC component and DC component of output. Patent Document 1: Japanese Patent Application Laid-open Publication No. Heisei 10-39083 The monitoring apparatus described in Patent Document 1 is intended for water-level evaluation when cooling water is located in the reactor core. Therefore, if the water level in the reactor is lower than the reactor core, the monitoring apparatus described in Patent Document 1 cannot monitor the water-level. Further, if the water level in the reactor falls extremely, the water-level meter installed in a neighborhood of the reactor core is heated by fuel and might therefore fail to normally operate. Furthermore, if abnormal heating of the reactor core induces a high-temperature falling object or a situation such as core damage, fuel melting, or penetration of a reactor bottom by molten fuel, a reactor water-level measurement system might be damaged by the falling object, and therefore result in failure to operate normally. The present invention has been made in view of the above circumstances and has an object to provide a reactor water-level measurement system capable of measuring the water level of a reactor regardless of conditions in the reactor. To solve the above problem, the present invention provides a reactor water-level measurement system comprising: a core bottom water-level measuring device that includes a heating element, a heat insulating element installed by surrounding part of the heating element in a height direction of the heating element, and a temperature difference measuring element that measures a temperature difference between an insulated portion of the heating element surrounded by the heat insulating element and a non-insulated portion not surrounded by the heat insulating element; a water-level evaluation device that evaluates a water level of a reactor based on the temperature difference, wherein the core bottom water-level measuring device measures at least a water level from a lower end of a reactor core contained in a reactor pressure vessel to a bottom of the reactor pressure vessel. The reactor water-level measurement system according to the present invention can measure the water level of a reactor regardless of conditions in the reactor. Embodiments of a reactor water-level measurement system according to the present invention will be described with reference to the accompanying drawings. It is noted that the reactor water-level measurement system according to the present invention is applied to a boiling-water reactor (BWR) in each of the embodiments described below. FIG. 1 is a schematic sectional view illustrating a configuration of a reactor water-level measurement system 1 according to a first embodiment. The reactor water-level measurement system (water-level measurement system) 1 includes in-core water-level measuring devices 11 and core bottom water-level measuring devices 12. The in-core water-level measuring device 11 and the core bottom water-level measuring device 12 (which will be merely referred to as “water-level measuring devices 11 and 12” if it is not necessary to distinguish the in-core water-level measuring device 11 from the core bottom water-level measuring device 12) are contained, together with a neutron detector 4, in a protective tube 5 of the neutron detector 4 that monitors neutron fluxes in a reactor core. The protective tube 5 is arranged in the reactor core 3, penetrating a bottom of the reactor pressure vessel (pressure vessel) 2. Since a lower end of the protective tube 5 can be opened, the water-level measuring devices 11 and 12 can be taken in and out of the protective tube 5 as required. The in-core water-level measuring devices 11 are installed within a vertical range of the reactor core 3 to measure a water level in the reactor core 3 along a vertical direction. The core bottom water-level measuring devices 12 are installed running from a lower end of the reactor core 3 to a bottom of the pressure vessel 2 to measure at least the water level in the vertical direction from the lower end of the reactor core 3 to the bottom of the pressure vessel 2. In the first embodiment, the core bottom water-level measuring devices 12 are placed in the vertical direction from the lower end of the reactor core 3 to the outer side below the pressure vessel 2 for the sake of measuring the water level in a range from the lower end of the reactor core 3 to the bottom of the pressure vessel 2 to an outer side below the pressure vessel 2. The water-level measuring devices 11 and 12 are placed in an outer peripheral portion of the reactor core 3 (in the protective tubes 5 placed in the outer peripheral portion of the reactor core 3). Further, the water-level measuring devices 11 and 12 are placed so as to cover two or four different sections (obtained by dividing an area inside the reactor into monitoring zones) of the reactor core 3. FIG. 2 is a plan view illustrating a layout example of the in-core water-level measuring devices 11 and the core bottom water-level measuring devices 12, in the reactor core 3. The water-level measuring devices 11 and 12 are placed along an outer periphery of the reactor core 3 so as to cover, for example, four sections. Consequently, if a single failure occurs in the water-level measurement system 1 (the water-level measuring devices 11 and 12) or a single failure of a power supply system occurs in a same section, water levels can be measured in remaining three sections (or remaining one section if two sections are covered). FIG. 3 is an enlarged view of a measuring unit 15 in region III illustrated in FIG. 1. FIG. 4 is a horizontal sectional view along line IV-IV illustrated in FIG. 3. The water-level measuring devices 11 and 12 include the measuring units 15 that configure a common configuration. As illustrated in FIGS. 3 and 4, the measuring unit 15 includes a heating element 21, a heat insulating element 22, a temperature difference measuring element 23, and a heater 24. The heating element 21 is a rodlike member extending in the vertical direction within a water-level measuring range. The heating element 21 is a member that generates heat when irradiated with gamma rays from the reactor core 3 or when heated by the heater 24, and is formed for example, of stainless steel. The heat insulating element 22 is a cylindrical member in which, for example, argon gas is enclosed and which is installed by surrounding part of the heating element 21 in a height direction of the heating element 21 to keep the heating element 21 from releasing heat to surroundings of the heating element 21. The temperature difference measuring element 23 measures a temperature difference between an insulated portion of the heating element 21 surrounded by the heat insulating element 22 and a non-insulated portion not surrounded by the heat insulating element 22. The temperature difference measuring element 23 is, for example, a pair of thermocouples, a pair of resistance temperature detectors, or a differential thermocouple having a contact point in each of the insulated portion and non-insulated portion. The heater 24 heats the heating element 21 by being installed, for example, inside and along the heating element 21. It is only necessary that the heater 24 can heat the heat insulating element 22 and a neighborhood of the temperature difference measuring element 23. Accordingly, in other portions, the heater 24 may be a conductor other than a heater wire which generates heat. The heating element 21, the heat insulating element 22, the temperature difference measuring element 23, and the heater 24 are contained in a protective tube 26 filled with an insulator (non-conductor) 30. Incidentally, the insulator 30 and the protective tube 26 are omitted (not illustrated) in FIG. 3. A water-level evaluation device 25 illustrated in FIG. 1 is connected to the heater 24 and passes a required current through the heater 24. Further, the water-level evaluation device 25 is connected to the temperature difference measuring element 23 via a signal line 28, and obtains data of temperature difference between the insulated portion and non-insulated portion, measured by the temperature difference measuring element 23. The water-level evaluation device 25 holds temperature difference data taken beforehand when the temperature difference measuring element 23 is surrounded by a coolant (reactor water) and when the temperature difference measuring element 23 is surrounded by air. The water-level evaluation device 25 compares the temperature difference data obtained from the temperature difference measuring element 23 with the temperature difference data which is held in advance, and evaluates whether the temperature difference measuring element 23 is surrounded by a coolant or air. The signal line 28 transmits the temperature difference data obtained from the temperature difference measuring element 23 to outside the pressure vessel 2. Preferably, the signal line 28 is laid at appropriate locations by considering cases in which the bottom of the pressure vessel 2 is damaged by molten fuel or a molten fuel drops into a reactor containment vessel that contains the pressure vessel 2. For example, the signal line 28 is laid so as not to pass a bottom center of the pressure vessel 2. Next, operation of the water-level measurement system 1 according to the first embodiment will be described. Generally, the BWR includes the neutron detector 4 that is used for neutron monitoring of the reactor core 3, and the protective tube 5. Thus, in the water-level measurement system 1, the water-level measuring devices 11 and 12 are installed in the protective tube 5 whereby it is unnecessary to make structural changes to the pressure vessel 2, the reactor core 3, and a shroud surrounding the reactor core 3 even if the water-level measurement system 1 is installed. If gamma rays are emitted from the reactor core 3 during reactor (running) operation, the heating element 21 generates heat. Heat quantity of the heating element 21 is reduced through heat removal by the coolant or air around the heat insulating element 22 (around the protective tube 26). On the other hand, being surrounded by the heat insulating element 22, the insulated portion of the heating element 21 does not undergo heat removal by the coolant or air unlike the non-insulated portion, and thus maintains a hotter state than the non-insulated portion. Heat quantity of the non-insulated portion is gradually heat-transferred upward and downward without undergoing heat removal by the coolant or air. Here, the coolant has higher heat removal capacity (higher thermal conductivity) than air. Consequently, the non-insulated portion is lower in temperature when the temperature difference measuring element 23 is surrounded by the coolant than when the temperature difference measuring element 23 is surrounded by air. Therefore, the temperature difference between the insulated portion and non-insulated portion is larger in the coolant than in air. The water-level evaluation device 25 compares newly obtained temperature difference data with temperature difference data held since before, and evaluates whether the temperature difference measuring element 23 is surrounded by the coolant, i.e., whether the water level of the coolant is higher or lower than the temperature difference measuring element 23. If output from the reactor core 3 is low, there may be a case where a required temperature difference is not obtained by the temperature difference measuring element 23 due to insufficient amount of gamma rays. In this case, the water-level measurement system 1 heats the heating element 21 by the heater 24 instead of gamma rays. The water-level measurement system 1 can measure the water level of the coolant as is the case with a case where the water-level measurement system 1 heats the heating element 21 by using gamma rays. The water-level measurement system 1 according to the first embodiment has the core bottom water-level measuring device 12 to measure the water level below the lower end of the reactor core 3. Therefore, the water-level measurement system 1 can monitor the water level in the vertical direction from the reactor core 3 to the bottom of the pressure vessel 2. For example, as illustrated in FIG. 5, if part of the reactor core is damaged (fuel melting), the in-core water-level measuring device 11 would be melted at the same time, which would result in loss of a monitoring function. In contrast, the core bottom water-level measuring device 12 is installed independently of the in-core water-level measuring device 11, and therefore possible to monitor the water level continuously when the pressure vessel 2 contains the coolant. Since the outer peripheral portion of the reactor core 3 is lower in fuel density and temperature than a central portion, the in-core water-level measuring device 11 is placed in an outermost periphery of the reactor core 3. Consequently, the water-level measurement system 1 would not have the in-core water-level measuring device 11 damaged even if fuel melting in the central portion of the reactor core 3 is partially occurred. The water-level measurement system 1 can continuously measure the water level of the coolant in the pressure vessel 2 using a simple configuration under a condition where the water level in the pressure vessel 2 falls extremely as well as under normal condition. Further, since the water-level measuring devices 11 and 12 are contained in the protective tubes 5 of the existing neutron detector 4 previously provided to the BWR, there is no necessity to additionally install new components in the pressure vessel 2 when the water-level measurement system 1 is installed. Therefore, the water-level measurement system 1 can reduce processes of work for installation and amounts of work for installation. Further, in the water-level measurement system 1, the in-core water-level measuring device 11 and the core bottom water-level measuring device 12 are installed independently of each other. Consequently, even if part of the reactor core 3 is damaged (fuel melting) whereby the in-core water-level measuring device 11 is damaged, the core bottom water-level measuring device 12 can evaluate the water level. Namely, in the example described above, although the in-core water-level measuring devices 11 and the core bottom water-level measuring devices 12 according to the first embodiment are contained in common protective tubes 5, the in-core water-level measuring devices 11 and the core bottom water-level measuring devices 12 may be contained in different protective tubes 5 or may not be contained in protective tubes 5. FIG. 6 is a configuration diagram of a reactor water-level measurement system 41 according to a second embodiment. The reactor water-level measurement system (water-level measurement system) 41 according to the second embodiment differs from the water-level measurement system 1 according to the first embodiment in that plural in-core water-level measuring devices 11 as well as plural core bottom water-level measuring devices 12 are installed with vertical positions of the measuring units 15 differing from one another. Therefore, in the reactor water-level measurement system 41 according to the second embodiment, components or parts corresponding to those of the first embodiment are denoted by the same reference numerals as the corresponding components or parts of the first embodiment or omitted from illustration, and duplicated description thereof will be omitted. Plural in-core water-level measuring devices 11a and 11b are provided (only two of them are illustrated in FIG. 6 for convenience of explanation). The measuring units 15 are installed in the plural in-core water-level measuring devices 11a and 11b at locations differing in the vertical direction between the in-core water-level measuring devices 11a and 11b. That is, measuring units 15a1, 15a2, and 15a3 of the in-core water-level measuring device 11a and measuring units 15b1, 15b2, and 15b3 of the in-core water-level measuring device 11b are provided so as to differ in the water-level measuring range. Incidentally, although illustrations of the core bottom water-level measuring device 12 and neutron detector 4 are omitted in FIG. 6 for convenience of explanation (this omission is also applied in a third embodiment described later), plural core bottom water-level measuring devices 12 are provided as with the in-core water-level measuring devices 11a and 11b and measuring units 15 are installed at locations differing in the vertical direction among the core bottom water-level measuring devices 12. Next, operation of the water-level measurement system 41 according to the second embodiment will be described. FIG. 7 is an explanatory diagram for illustrating a measuring range of the water-level measurement system 41 according to the second embodiment. The number of measuring units 15 which can be installed on a single in-core water-level measuring device 11 is physically limited and a range of identifiable water levels depends on the number of measuring units 15. On the other hand, the water-level measurement system 41 according to the second embodiment can improve water-level detection accuracy by installing plural in-core water-level measuring devices 11a and 11b with vertical positions of the measuring units 15 differing between the in-core water-level measuring devices 11a and 11b. Referring to FIG. 7, specifically, the water-level measurement system 41 measures temperature differences at a height A1, a height A2, and a height A3 in the vertical direction using the measuring units 15a1, 15a2, and 15a3 of the in-core water-level measuring device 11a. Since the reactor water is currently at a water level L, the in-core water-level measuring device 11a detects that the water level L of the reactor water is between the height A2 and the height A3, based on measurement results produced by the measuring units 15a1, 15a2, and 15a3. Further, the water-level measurement system 41 measures temperature differences at a height B1, a height B2, and a height B3 in the vertical direction using the measuring units 15b1, 15b2, and 15b3 of the in-core water-level measuring device 11b. Similarly, the in-core water-level measuring device 11b detects that the water level L of the reactor water is between the height B1 and height B2, based on measurement results measured by the measuring units 15b1, 15b2, and 15b3. Based on results detected by the in-core water-level measuring devices 11a and 11b, the water-level measurement system 41 recognizes that the water level L is in a range between the height A2 and height B2, which is an overlapping range of the in-core water-level measuring devices 11a and 11b. As described above, by superimposing the water levels calculated by the plural in-core water-level measuring devices 11 and the core bottom water-level measuring devices 12, the water-level measurement system 41 according to the second embodiment can improve the water-level detection accuracy without changing structures of the individual water-level measuring devices 11 and 12. FIG. 8 is a configuration diagram of a reactor water-level measurement system 51 according to a third embodiment. FIG. 9 is a plan view illustrating a layout example of the in-core water-level measuring devices 11 according to the third embodiment in the reactor core 3. The reactor water-level measurement system (water-level measurement system) 51 according to the third embodiment differs from the water-level measurement system 1 according to the first embodiment in that the in-core water-level measuring device 11 and the core bottom water-level measuring device 12 further include temperature measuring devices. Therefore, in the water-level measurement system 51 according to the third embodiment, components or parts corresponding to those of the first embodiment are denoted by the same reference numerals as the corresponding components or parts of the first embodiment or omitted from illustration, and duplicated description thereof will be omitted. The in-core water-level measuring device 11 includes a temperature measuring device 52, for example, inside or outside the reactor core 3. The temperature measuring device 52 is configured to being capable of measuring temperatures inside or outside the pressure vessel 2. Plural temperature measuring devices 52 are installed, for example, at positions different from the measuring units 15, running vertically from within a region of the reactor core 3 to lower part of the pressure vessel 2 in the reactor core 3 to the outer side below the pressure vessel 2. As illustrated in FIG. 9, the in-core water-level measuring devices 11 are arranged horizontally in a center of the reactor core 3 and on the outer periphery of the reactor core 3. Because the in-core water-level measuring device 11 includes a temperature measuring device 52, the water-level measurement system 51 according to the third embodiment measures not only the reactor water level, but also the reactor core 3 temperature which indicates a cooled state of fuel. Based on the measured temperature by the temperature measuring device 52, the water-level measurement system 51 can monitor whether the fuel reaches a temperature limit, i.e., the melting point of the fuel. Further, in the water-level measurement system 51, since the in-core water-level measuring devices 11 equipped with the temperature measuring devices 52 are installed in the central portion and outer peripheral portion of the reactor core 3, a three-dimensional temperature distribution of the fuel can be monitored together with signals provided from the measuring units 15. Therefore, the water-level measurement system 51 can estimate a region where the fuel is likely to melt. Furthermore, in the water-level measurement system 51, since plural temperature measuring devices 52 are installed running vertically from within a region of the reactor core 3 to lower part of the pressure vessel 2 in the reactor core 3 to the outer side below the pressure vessel 2, the water-level measurement system 51 can acquire behavior of the high-temperature molten fuel. Specifically, the water-level measurement system 51 can monitor downward movements of the molten fuel to lower part of the pressure vessel 2 by using the temperature measuring devices 52 installed running vertically from within a region of the reactor core 3 to lower part of the pressure vessel 2 in the reactor core 3 to the outer side below the pressure vessel 2, and can therefore estimate position of the moving molten fuel. Further, if molten fuel damages the bottom of the pressure vessel 2 and/or flows out into the reactor containment vessel of the molten fuel, the water-level measurement system 51 can check whether the bottom of the pressure vessel 2 is damaged or not by means of the temperature measuring devices 52 placed in regions outside the pressure vessel 2. Whereas some embodiments of the present invention have been described, these embodiments are merely presented as example, and not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included within the sprit and scope of the invention and are included within the scope of the invention as described in the claims and equivalents thereof. For example, another type of water-level measuring device such as a differential pressure water-level meter may be used for the in-core water-level measuring device 11. Further, the water-level measuring devices 11 and 12 may include temperature measuring devices instead of the temperature difference measuring devices 23 and may measure the water level by measuring temperature differences among the plural temperature measuring devices. 1, 41, 51 - - - reactor water-level measurement system 2 - - - pressure vessel 3 - - - reactor core 4 - - - neutron detector 5 - - - protective tube 11, 11a, 11b - - - in-core water-level measuring device 12 - - - core bottom water-level measuring device 15, 15a1-15a3, 15b1-15b3 - - - measuring unit 52 - - - temperature measuring device
053234405	abstract	An X-ray exposure apparatus using radiation light as exposure light, wherein the apparatus includes: a display device; a detecting device for detecting in each exposure the amount of exposure absorbed by a mask during the exposure; a memory for memorizing an accumulated dose of the mask; and a controller for causing the display device to display a dose of the mask, wherein the dose to be displayed corresponds to the sum of the accumulated dose memorized in the memory and the amount of exposure detected by the detecting device. Also a mask structure suitably usable in such an exposure apparatus.
	description	The present invention relates to a method of manufacturing mirror shells of a nested shells grazing incidence mirror, in particular for extreme ultraviolet radiation (EUV) and/or x-rays. Such a nested shells grazing incidence mirror comprises several mirror shells which are typically arranged concentrically around an optical axis along which the incidence radiation enters the mirror. Nested shells grazing incidence mirrors are used in x-ray, soft x-ray and EUV applications, e.g. in space-based x-ray telescopes or as collector mirrors or collector optics in EUV applications like EUV lithography. Grazing incidence mirrors make use of the physical effect of total reflection of radiation impinging on the surface of a medium under a small angle of incidence. This allows a rather simple realization of mirrors for x-rays or EUV radiation without the need of a high precision multi layer coatings as is the case for near normal incidence mirrors. In contrast to near normal incidence mirrors, the mirror shells of a nested shells grazing incidence mirror have a comparatively small thickness in the direction perpendicular to the reflecting surface in order to minimize the loss of the incoming radiation which also impinges on the side edges of the shells. The small thickness and the required high optical quality of the optical surface of such a mirror shell require a careful manufacturing process. Document EP 2083328 A1 discloses two manners of manufacturing such mirror shells. In one of the methods proposed in EP 2083328 A1 the shells are manufactured by electroforming in which the shell material is galvanically deposited on a mandrel, which carries the negative of the required optical surface with respect to shape and roughness. After thermal break of shell and mandrel, a reflective coating can be applied to the optical surface of the shell if required. The mandrel can be reused for further replications unless it is destroyed during the separation process. The individual shells are then mounted to a mechanical support structure, typically some kind of spider wheel, to form the nested shells grazing incidence mirror. The manufacturing of the mirror shells by galvanic deposition however has a number of disadvantages. The bulk material of the shell must be compatible with the electroforming process. This limits the material choice to a couple of pure metals with only very few exceptions. Consequently, there are restrictions with respect to the material properties desired for the application. The dedicated galvanic deposition of the material is slow and without further measures does not allow a variation in thickness of the shell. Furthermore, the manufactured shells are very fragile and do not allow a refurbishment of the optical surface after degradation which occurs during operation of the mirror, e.g. close to an EUV source. The galvanic deposition furthermore has a significant impact on the costs of the grazing incidence mirror. Due to the fragility of the mirror shells it is also difficult to attach further mechanical structures which are required for mounting the mirror or during operation of the mirror, e.g. cooling structures. There is a high risk of damaging the surface during such later manufacturing steps, in particular when techniques like welding, drilling or milling are necessary. Another method of manufacturing the mirror shells is only very shortly mentioned in EP 2083328 A1. This further method comprises to manufacture the mirror shells by diamond turning in order to achieve shells with a thickness of between 0.5 and 4 mm. The document does not further describe this manufacturing process. Further required mechanical structures for a thermal management system are mounted on the mirror shells, e.g. by micro-machining the rear surface of the mirror shells. Nevertheless, the thickness of the shells mentioned in this document also results in a high fragility so that several of the above mentioned disadvantages still apply. Diamond turning is a well established technique for the manufacturing of reflective optical elements. U.S. Pat. No. 6,634,760 describes an ultra-precision diamond turning technique in which the mechanical process is combined with the deposition of a smoothing layer in order to achieve an optical surface with a high optical quality. It is an object of the present invention to provide a method of manufacturing mirror shells of a nested shells grazing incidence mirror at low costs with high optical quality which may also be refurbished one or several times. The object is achieved with the method of manufacturing the mirror shells according to claim 1. Advantageous embodiments of the method are subject matter of the dependent claims or can be deduced from the subsequent portions of the description of the invention and embodiments. The proposed method comprises the steps of providing and machining a blank of a bulk material to form a mirror body of the shell. During or after the machining of the blank mechanical structures are integrated and/or attached in and/or to the mirror body. These mechanical structures may be required for mounting and/or operating the mirror shells. Examples of such mechanical structures are cooling channels which are required for cooling the mirror shells during operation. Such mechanical structures may also be mounting elements for mounting the mirror shells to a corresponding mechanical support structure which is required to assemble the nested shells grazing incidence mirror. These steps of integrating the mechanical structures or attaching these structures—or both measures in combination—may be performed during the machining of the blank, e.g. by forming appropriate grooves for the cooling channels, or immediately after forming the mirror body. The structures can also be attached for example by appropriate techniques like welding, brazing or screwing. After the integration and/or attachment of the mechanical structures the optical surface is formed on the mirror body by diamond turning. Depending on the material selected for the mirror body the diamond turning may be performed directly on the surface of the mirror body or may also be performed on a coated layer of an appropriate material which may be applied prior to this last step of diamond turning to the corresponding regions of the surface of the body. Since the manufacturing steps for forming the mirror body and integrating and/or attaching all required further mechanical structures are performed prior to the manufacturing step of diamond turning the optical surface, the risk of a deformation or damaging of the optical surface due to rough process steps is avoided. By this, usual manufacturing techniques like brazing, welding, drilling, milling and turning are possible to generate the required mechanical structures for cooling and mounting. Since the optical surface is formed in the latest step, which may also include a further polishing or coating, the imaging quality of the optical system is better than with other techniques in which the mechanical structures are applied after the formation of the optical surface. The proposed method of machining the mirror body from a blank, e.g. by milling, and forming the optical surface by diamond turning allows the selection of a large amount of shell materials. The material of the mirror body can thus be selected to optimally support the needs of the application, e.g. thermo-mechanically and/or chemically. The manufacturing process does not result in any restrictions for the shell thickness and therefore also strong variations of the thickness within a shell are possible, if desired. The mirror body may be formed of an appropriate thickness to allow a refurbishment of the optical surface by a second or further diamond turning run in cases in which the surface is degraded after a certain operation time. In case of the diamond turning being carried out in a coating on the mirror body, also a second diamond turning run is possible in the coating. Alternatively the coating (or its rest) is first removed and a new coating is applied. The diamond turning finishing process is then repeated with this new coating. The coating can be removed for example by another diamond turning step or by chemical treatment. Using such a refurbishment costly manufacturing steps on the blank like forming of the complex cooling structures can be avoided since the mirror shell is simply recycled. In an advantageous embodiment the mirror body is formed to have a varying thickness, the thickness being measured perpendicular to the optical surface. This thickness is smallest at the edges and increases from both edges to provide one or several thicker portions in between. The number, position, shape and maximum thickness of these thicker portions is selected to avoid a blocking of the incoming radiation by the thicker portions when the shells are mounted in the nested shells grazing incidence mirror. With such a design of the mirror body the thicker portions can have up to several centimeters in thickness without blocking the incoming radiation, in particular if the mirror body is formed to have knife edge shaped edges. The mirror body is manufactured with a thickness of ≧5 mm at the thickness maximum of at least one of the thicker portions. With such a thickness, the problems related to a fragility of the shells are substantially reduced resulting in a lower risk of damage during manufacturing and/or later refurbishment. In the proposed method it is also possible to additionally polish the optical surface after the diamond turning process. Furthermore, also one or several additional coatings may be applied to the optical surface, e.g. a coating for increasing the reflectivity of the surface or a coating for increasing the mechanical and/or chemical stability of the surface. In the proposed method of manufacturing mirror shells of a nested shells grazing incidence mirror, first the body of the mirror is made, including e.g. the cooling channels and the fixation points for later mounting. After the body is completely finished, the optical surface is generated by an ultra-precision diamond turning process. For diamond turning, the process described in U.S. Pat. No. 6,634,760 may be used for example. With the process flow of the proposed method it is also possible to refurbish the shells as explained further on. An example for the method steps of the proposed method, some of which being optional steps, is shown in connection with FIG. 1. The figure shows the manufacturing process of a mirror shell in a cross sectional view. Starting point is a block 1 of material with a size that is sufficient for machining the body of the shell. The material is selected to have material properties that fit to the application in a collector shell, for example for EUV applications. First of all, rough production steps like milling the block 1 of material are carried out to form the body 2 of the mirror shell as schematically indicated in FIGS. 1a and 1b. An appropriate material is e.g. aluminum. After the formation of the mirror body cooling channels are milled into the side faces of the mirror body 2 to form the cooling structure as schematically shown in FIG. 1c. The cooling structure is sealed e. g. by welding or brazing in FIG. 1d. FIG. 1e shows the attachment of mounting jigs 4 which may be fixed by welding or screwing. These mounting jigs 4 are necessary for the mounting and connecting the shells to the mounting structure of the nested shells grazing incidence mirror. After these rough manufacturing steps a functional test of these components, e.g. a leak test of the cooling structure or a test of the stiffness of the mirror body may be applied. After the manufacturing of all of the necessary mechanical components or structures the optical surface of the shell is machined. To this end the thickness of the mirror body in the direction perpendicular to the optical surface may be chosen slightly larger than needed. For forming the optical surface different combinations of manufacturing steps may be applied, all of these steps include a diamond turning process for finishing of the optical surface. FIGS. 1f to 1j show these different steps some of which are only optional steps. If the chosen blank material allows the surface finishing of the desired quality, the diamond turning process can be directly applied to generate the optical surface which is shown with the diamond turning finishing process 6 in FIG. 1h. Nevertheless there might be the necessity of more than one turning run. The optical surface 7 will then not be disturbed by other rough manufacturing processes. If the blank material does not support the required surface quality directly, material from the inner surface of the mirror body may be turned away in the diamond turning pre-machining step 5 of FIG. 1f so that the desired surface is slightly outside the blank material. Now a layer 8 of a material which supports the required surface quality is coated on the blank inner surface as schematically indicated in FIG. 1g. This material may be a nickel rich material like nickel-phosphor. The desired surface is now within the layer 8 of the coating material. The optical surface is then generated by one or more diamond turning runs with the diamond turning finishing process 6 of FIG. 1h. If required, the surface roughness of the optical surface can further be reduced by a conventional polishing step 9 (optional) schematically indicated in FIG. 1j. Also a coating of one or more layers 10 may be applied to increase the reflectivity and/or the mechanical or chemical stability, if necessary. This optional step is schematically indicated in FIG. 1j in which, for example, a layer of ruthenium may be applied as a reflective coating. After having manufactured the different mirror shells required for assembling the nested shells grazing incidence mirror, the shells 11 are mounted to a mechanical support structure 12, e.g. some kind of spider wheel as known from existing grazing incidence collectors, to form the nested shells mirror. FIG. 2 schematically shows a cross sectional view of such a nested shells grazing incidence mirror. In this figure only two shells 11 are shown. It is obvious for the skilled person that such a nested shells grazing incidence mirror may have more than two shells 11 concentrically arranged around the optical axis. With the proposed order of manufacturing steps the assembly of the shell modules is easier because a wider choice of e.g. welding and clamping techniques is possible for manufacturing the mechanical structures, since these techniques do not affect the optical surface of the shells. The proposed method also allows manufacturing of shells with non monotone optical surfaces by diamond turning. Additionally, further mechanical structures may be integrated in or attached to the mechanical shells without deteriorating the optical quality due to the order of the proposed method steps, i.e. the generation of the optical surface in the final step. For example, EUV light sources do not only emit photons but also produce undesired material, so called debris, such as droplets or atoms. The debris may condense on the optical components whose performance would deteriorate appropriately. It is known in the art to apply debris mitigation systems by assistance of certain inert gases to reduce this negative impact on system performance. Due to the flexibility and robustness of the diamond turning process, it is possible to realized dedicated layouts of shells resulting in an improved debris mitigation performance of the optical system. This can be achieved by e.g. drilling additional holes or add gas line tubing at certain locations, in particular locations which are shadowed by the mechanical support structure of the shells, to allow for a particular gas distribution which enhances debris mitigation performance. This is impossible with a conventional manufactured nested shell optic but can be integrated in the proposed manufacturing process easily. The proposed manufacturing method allows to realize a grazing incidence collector that is much cheaper to produce, more robust and can be refurbished several times. The mirror body 2 of the mirror shells 11 is preferably formed to have a varying thickness increasing from both edges and forming one or several thicker portions in between. FIG. 3 shows a schematic cross sectional view of a part of such a nested shells grazing incidence mirror. Both edges of the mirror bodies 2 of the inner shells are formed knife edge shaped while still having at least one portion with several centimeters thickness in between without blocking incoming EUV-radiation. The number, position and shape of these thicker portions is selected to avoid the blocking of the radiation. This can be seen from FIG. 3 in which some of the incoming EUV-rays 14 originating from the EUV-source 13 are indicated. With the proposed method it is thus possible to design and manufacture an almost obscuration free collector consisting of very robust (=thick) mirror shells. While the invention has been illustrated and described in detail in the drawings and forgoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. For example, although the figures show a special curved shape of the mirror shells also other shapes are possible. The mechanical structures manufactured prior to the final diamond turning step may also be different from the structures shown in the figures. Other variations of the disclosed embodiments can be understood and affected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures can not be used to advantage. The reference signs in the claims should not be construed as limiting the scope. 1 block of material (blank) 2 mirror body 3 cooling channels 4 mounting jigs 5 diamond turning pre-machining step 6 diamond turning finishing process 7 optical surface 8 layer of material 9 polishing 10 coating 11 mirror shell 12 support structure 13 EUV-source 14 EUV-ray
	claims	1. A string, comprising: a tubing; a sealing element coupled to the tubing; a sand control device positioned below the sealing element; a tool adapted to be run through the tubing to perform at least one of a gravel pack operation, a fracturing operation, a cleaning operation, and a stimulating operation; and a flow control device controllable by a signal that is one of a signal communicated through a control conduit and a wireless signal, the flow control device adapted to control fluid flow from an annulus region outside the sand control device to the tubing. 2. The string of claim 1 , wherein the flow control device is actuatable at least between an open position and a closed position. claim 1 3. The string of claim 2 , wherein the sand control device and the flow control device cooperate to enable a gravel pack squeeze operation in a first state and a circulate operation in a second state. claim 2 4. The string of claim 3 , wherein the sand control device comprises a sand screen and an annular passageway inside the sand screen, the annular passageway in communication with the flow control device. claim 3 5. The string of claim 4 , further comprising a longitudinal bore, wherein the flow control device is adapted to be opened to enable circulation of fluid through the annular passageway and the flow control device into the longitudinal bore of the string. claim 4 6. The string of claim 5 , further comprising a valve actuatable between an open position and a closed position to control fluid flow in the longitudinal bore of the string. claim 5 7. The string of claim 1 , further comprising a closure member adapted to be actuated to an open position to enable fluid flow to the annular region outside the sand control device. claim 1 8. The string of claim 7 , wherein the flow control device is adapted to be closed to perform a squeeze operation. claim 7 9. The string of claim 8 , wherein the flow control device is adapted to be opened to perform a circulate operation. claim 8 10. A string, comprising: a tubing; a sealing element coupled to the tubing; a sand control device positioned below the sealing element; a tool adapted to be run through the tubing to perform at least one of a gravel pack operation, a fracturing operation, a cleaning operation, and a stimulating operation; and an intelligent completions device positioned below the sand control device and a control conduit extending past the sand control device to the intelligent completions device. 11. A string, comprising: a tubing; a sealing element coupled to the tubing; a sand control device positioned below the sealing element; a tool adapted to be run through the tubing to perform at least one of a gravel pack operation, a fracturing operation, a cleaning operation, and a stimulating operation; a flow control device actuatable at least between an open position and a closed position; and a control conduit adapted to carry a signal to operate the flow control device. 12. A string, comprising: a tubing; a sealing element coupled to the tubing; a sand control device positioned below the sealing element; and a fluid communication control device to control flow of fluid between the tubing and a region outside the sand control device; a tool adapted to be run through the tubing and to actuate the fluid communication control device; and a flow control device controllable by a signal that is at least one of a signal communicated through a control conduit and a wireless signal, the flow control device adapted to control fluid flow from the region outside the sand control device to the tubing. 13. The string of claim 12 wherein the tool comprises a service tool adapted to perform at least one of a gravel pack operation, a fracturing operation, a cleaning operation, and a stimulating operation. claim 12 14. The string of claim 12 , wherein the sealing element comprises a packer. claim 12 15. The string of claim 12 , wherein the tubing comprises a production tubing. claim 12 16. The string of claim 12 , wherein the fluid communication control device comprises a closing sleeve. claim 12 17. The string of claim 16 , wherein the tool is adapted to open the closing sleeve to perform a gravel pack operation. claim 16 18. The string of claim 12 , wherein the flow control device is actuatable at least between an open position and a closed position. claim 12 19. The string of claim 18 , wherein the fluid communication control device and the flow control device cooperate to enable a gravel pack squeeze operation in a first state and a circulate operation in a second state. claim 18 20. The string of claim 19 , wherein the sand control device comprises a sand screen and an annular passageway inside the sand screen, the annular passageway in communication with the flow control device. claim 19 21. The string of claim 20 , further comprising a longitudinal bore, wherein the flow control device is adapted to be opened to enable circulation of fluid through the annular passageway and the flow control device into the longitudinal bore of the string. claim 20 22. The string of claim 21 , further comprising a valve actuatable between an open position and a closed position to control fluid flow in the longitudinal bore of the string. claim 21 23. The string of claim 18 , wherein the flow control device is operated by a wireless mechanism. claim 18 24. The string of claim 12 , further comprising at least another sealing element, at least another sand control device, and at least another fluid communication control device, wherein the tool is adapted to be run to another position in the string and to actuate the at least another fluid communication control device. claim 12 25. A string, comprising: a tubing; a sealing element coupled to the tubing; a sand control device positioned below the sealing element; a fluid communication control device to control flow of fluid between the tubing and a region outside the sand control device; a tool adapted to be run through the tubing and to actuate the fluid communication control device; a flow control device actuatable at least between an open position and a closed position; and a control conduit adapted to carry a signal to operate the flow control device. 26. An apparatus for use in a well, comprising: a production tubing; a sand control assembly coupled to the production tubing; an intelligent completions device, the sand control assembly, the intelligent completions device, and the production tubing adapted to be lowered as a string in a single run; and a control conduit extending along the production tubing and to the intelligent completions device, the control conduit adapted to communicate a signal to operate the intelligent completions device. 27. The apparatus of claims 26 , wherein the intelligent completions device is positioned below the sand control assembly. 28. The apparatus of claim 26 , wherein the control conduit comprises at least one of an electrical conduit, a fiber optic conduit, and a hydraulic conduit. claim 26 29. The apparatus of claim 26 , further comprising at least one other sand control assembly comprising an intelligent completions device, the control conduit extending to the intelligent completions device of the at least one other sand control assembly. claim 26 30. An apparatus for use in a wellbore, comprising: a sand control assembly having a screen and defining an annular passageway inside the screen; a sealing element; and a flow control device having one or more radial flow ports to receive fluid from an annular region outside the flow control device, the sealing element being positioned between the sand control assembly and the flow control device, the sealing element having one or more bypass conduits to enable fluid communication between the annular passageway and the annular region outside the flow control device. 31. The apparatus of claim 30 , wherein the sealing element comprises a packer. claim 30 32. The apparatus of claim 30 , wherein the sealing element is adapted to prevent passage of gravel pack material from an annular region outside the screen to the annular region outside the flow control device. claim 30 33. A method of gravel packing a wellbore, comprising: positioning a string having a tubing and sand control assembly; running a service tool through the tubing; using the service tool to perform at least one of a gravel packing operation, a fracturing operation, a stimulating operation, and a cleaning operation; and remotely operating a flow control device to control flow from an annular region outside the sand control assembly using a signal that is one of a signal communicated through a control conduit and a wireless signal. 34. The method of claims 33 , further comprising opening a fluid communication control device using the service tool and flowing a gravel pack slurry through the fluid communication control device to gravel pack the annular region outside the sand control assembly. 35. The method of claim 34 , wherein the service tool is coupled to a conduit that passes through at least a portion of the tubing, and wherein flowing the gravel pack slurry comprises flowing the gravel pack slurry through the conduit. claim 34 36. The method of claim 34 , further comprising maintaining the flow control device closed while gravel packing to enable a squeeze operation. claim 34 37. The method of claim 36 , further comprising opening the flow control device to enable circulation of gravel pack fluid. claim 36 38. The method of claim 37 , further comprising closing the flow control device to perform a squeeze operation. claim 37 39. The method of claim 34 , wherein the string further comprises at least one other sand control assembly and at least one other fluid communication control device, the method further comprising running the service tool proximal the at least one other fluid communication control device to actuate the fluid communication control device. claim 34 40. The method of claim 33 , wherein the wellbore extends through plural zones, the method further comprising running the service tool to the plural zones. claim 33 41. A method of performing sand control in a wellbore, comprising: running, in a single run, a string comprising a production tubing, a sand control assembly, an intelligent completions device positioned below the sand control assembly, and a control conduit extending along the production tubing to the intelligent completions device. 42. The method of claims 41 , further comprising transmitting a signal through the control conduit to activate the intelligent completions device. 43. A method for use in a well, comprising: providing an apparatus having a sand control assembly having a screen and defining an annular passageway inside the screen; providing a sealing element; providing a flow control device to receive fluid from an annular region outside the flow control device; and routing fluid flow from the annular passageway through a bypass flow conduit in the sealing element to the annular region on the other side of the sealing element. 44. The method of claim 43 , further comprising: claim 43 gravel packing in an annular region outside the screen; and preventing passage of gravel pack material from the annular region outside the screen to the annular region outside the flow control device. 45. A well completion disposed within a casing, comprising: a production tubing; a first packer coupled to the production tubing; a first closing sleeve disposed below the first packer; a first sand screen disposed below the first closing sleeve and having a plurality of fluid passageways disposed therethrough; a first internal sleeve member disposed within the first sand screen, the first sand screen and first internal sleeve defining an annular passageway therebetween, the annular passageway being in fluid communication through the fluid passageways in the sand screen with a well annulus formed between the completion and the casing; and a first surface controlled flow control device having at least one remotely openable and closable flow port in fluid communication with the annular passageway, whereby fluid communication between the annular passageway and a longitudinal bore of the completion is established through the at least one flow port when the at least one port is in an open position and restricted when the at least one port is in a closed position, the first surface controlled flow control device actuatable by a signal that is one of a signal communicated through a control conduit and a wireless signal. 46. The well completion of claim 45 , further comprising a first safety shear sub disposed between the first closing sleeve and the first sand screen. claim 45 47. The well completion of claim 46 , further comprising a second packer disposed below the first surface controlled flow control device. claim 46 48. The well completion of claim 47 , further comprising a second safety shear sub disposed between the first surface controlled flow control device and the second packer. claim 47 49. The well completion of claim 45 , wherein the first closing sleeve includes at least one flow port and a remotely shiftable closure member adapted to permit and restrict fluid flow through the at least one flow port. claim 45 50. The well completion of claim 49 , further comprising a service tool adapted for releasable engagement with the closure member to open and close the at least one flow port in the first closing sleeve. claim 49 51. The well completion of claim 45 , further comprising: claim 45 a second packer disposed below the first surface controlled flow control device; a second closing sleeve disposed below the second packer; a second sand screen disposed below the second closing sleeve and having a plurality of fluid passageways disposed therethrough; a second internal sleeve member disposed within the second sand screen, the second sand screen and second internal sleeve defining an annular passageway therebetween, the annular passageway being in fluid communication through the fluid passageways in the sand screen with the well annulus; and a second surface controlled flow control device connected to the control conduit and having at least one remotely openable and closable flow port in fluid communication with the annular passageway, whereby fluid communication between the annular passageway and the longitudinal bore of the completion is established through the at least one flow port when the at least one port is in an open position and restricted when the at least one port is in a closed position, the second surface controlled flow device actuatable by a signal that is one of a signal communicated through a control conduit and a wireless signal. 52. The well completion of claim 45 , further comprising a service tool adapted for being deployed through the production tubing to perform sand control pumping operations in the completion. claim 45 53. The well completion of claim 45 , further comprising a control conduit extending from the earth""s surface and connected to the first surface controlled flow control device. claim 45 54. A method of completing a well having a plurality of production zones, comprising: remotely restricting fluid communication between all but one of the plurality of production zones and a longitudinal bore of a well completion; using a first flow control device and a closure member to remotely establish fluid communication between the one of the plurality of production zones and the longitudinal bore; and remotely controlling the first flow control device using a signal transmitted via a control conduit connected to the first flow control device. 55. The method of claim 54 , further comprising circulating fluid to the one of the plurality of production zones. claim 54 56. The method of claim 55 , wherein the fluid is a gravel pack slurry. claim 55 57. The method of claim 55 , further comprising using a service tool to shift the closure member to permit fluid circulation into a well annulus. claim 55 58. The method of claim 54 , wherein each of the plurality of production zones is selectively isolated by at least one of a closure member and a flow control device. claim 54
051125692	description	DESCRIPTION OF THE PREFERRED EMBODIMENT With specific reference to these figures: FIG. 1 indicates a pressurized metal container inside which the vessel 2 of the nuclear reactor is contained; inside the vessel 2, the reactor has a core 4, a lower input header 5, and an upper output header 6. In the preferred solution illustrated in the figure, the ceiling 8 of the vessel 2 has a cup-shaped structure 7 which defines, inside the vessel 2, a ring-shaped area. This ring-shaped area is split up into two concentric ring-shaped cavities 9 and 10, one acting as an upflow pipe for the hot primary fluid which has crossed through the reactor 4, and one acting as a downflow pipe for the same fluid. At the upper end of the downflow pipe 10 are the circulation pumps 11 which force the hot fluid into the downflow pipe 10, inside which the primary heat exchanger 3 are arranged. The secondary fluid is fed into and extracted from the primary exchanger 3 through insulated pipes 12, which pass through both the vessel 2 and the pressurized metal container 1. The outer wall of the reactor vessel 2 is insulated by means of the coating 13-14, only partly shown. Between the metal container 1 and the reactor vessel 2 there is a tank 15, filled with a neutron-absorbing liquid 16, for instance borated water; in the following description, the term "tank 15" will be used to refer indifferently to this area and to the liquid contained in it. the temperature in the tank 15 is relatively cooler than the temperature of the water contained in reactor vessel 2, thanks to the insulation 13-14 covering the outside wall of the reactor vessel 2; furthermore, the wall of the pressurized container 1 is in contact with the cold water 17 of a non-pressurized pool 18, in which the container is immersed (see FIG. 6). The lower end of the reactor vessel 2 is penetrated by many pipes 20, for free communication between the lower header 5 and the tank 15. These pipes preferably have an elongated shape, so as to maintain a separating interface (I1) between the liquid in the tank 15 and the liquid in the lower header 5, with no widespread mixing of the two liquids. Maintenance of the I1 interface is ensured by the equal pressures, as was already the case for the Canadian patent mentioned above, and as will be explained again below. A second series of passages 21 is arranged between the upper header 6 and the upper part of the tank 15. At the top, these pipes 21 lead into an annular shaped bell 22, and at the bottom into the upper part of the tank 15. The annular shaped bell 22 does not necessarily extend for the whole circumference of the reactor vessel 2. The top part of the bell may contain a gas or steam under pressure, or, as explained below, an interface (I2) may be established by means of pipes 21 between the hot liquid contained in vessel 2 and the cold liquid contained, around the latter, in the tank 15, thanks to the different temperatures of the two fluids. This interface (I2) may be established, together with interface (I1), if the delivery rate of the circulation pumps 11 is such that the pressure drop of the primary fluid in passing through the reactor core is equal to the difference in static head between the column of hot fluid contained in vessel 2 and the column of cold fluid contained in the tank 15, measured in height between interfaces (I1) and (I2). According to the invention, pressurizing of container 1 may be achieved by means of the pressurizer illustrated in FIG. 4. This consists of an elongated shell 30, closed at the ends by convex bottoms 31 and 32. An internal funnel, 33, is extended downwards by vertical pipes 34, dividing the pressurizer into a hot upper area 35 and a cold lower area 36. The hot area may be created in any expedient manner, for example by using a source of heat to generate a steam cushion 37. Since the pressurizer 30 is immersed in the cold water of the pool 18, the wall of the shell surrounding the hot area 35 is equipped with insulation 38. A pipe 39 coming out of the pressurizer 30 immediately below the hot area 35 connects the top part of the cold area with the upper area of the tank 15. A second lower pipe 40 connects the bottom of the pressurizer 30 to the lower area of the tank 15. Pipes 39 and 40 allow the pressurizer to function also as an auxiliary cooler for the reactor vessel, as explained further below. To this end, the cold area 36 may be equipped with a liquid-liquid heat-exchanger 41, submerged in the cold water of the pool 18. The purpose of this exchanger is to increase the heat-exchanging surface of the pressurizer wall. If necessary, liquid-liquid heat-exchangers 43 and liquid gas 44 allow natural cooling of the pool 18, by giving up heat into the surrounding ambient air. Obviously both the various pressurized containers 1 and the pressurizers 30 will be supported by structural elements, schematically illustrated in FIGS. 4 and 6 and indicated as 42. FIG. 5 illustrates a special form of the channels passing through the grid of the core: each pipe has a lower converging portion 51, a neck 52 which creates a Venturi-type effect, and an upper portion with an increasing cross-section. The neck 52 is linked by a pipe 54 to the area 16. In this case the pipes 54 replace the pipes 20 for hydraulic connection between the cold area 16 and the hot area 5, through pipes 51. This configuration, as explained below, allows the pressure drop in the core to be increased for the same difference in static head between the cold column and the hot column. To complete the above description, according to this invention it is possible to distinguish between a normally hot primary circuit and a normally cold fluid, contained in the tank 15, kept cold by the exchange of heat with the fluid contained in the pool 18. As already described, during normal operation of the system there is no appreciable circulation through the natural circulation circuit. This can be achieved by interlocking the circulation pumps 11 with the function of keeping the interface level between the cold water and the hot water in one of the two pipes 20, 21 steady; the choice of the pipe with which the pump is to be interlocked depends on detail technical considerations of a both construction and a control nature. In the following text reference will be made to the upper pipes 21 (represented in FIG. 2 by two hydraulically parallel ducts). The lower pipes 20 are in this case used to compensate the density variations in the primary fluid, as explained below. According to this invention, the container 1 must be kept pressurized by means of a pressurizing system provided for this specific purpose. According to the form of embodiment illustrated, this system is implemented by means of the pressurizer 30, the upper area of which forms a hot water plenum, while the lower area 30 is simply a cold water plenum. Pipes 39 and 40 connected to the pressurized container 1 lead to the cold area 36, so that as a result of density fluctuations in the fluid inside container 1, cold water is transferred between container 1 and the pressurizer 30 (FIG. 4), avoiding thermal shocks on the various structures under pressure. The funnel-shaped device indicated as 33 in FIG. 4 produces cooling of the hot water, and then mixing of the hot water with the cold water below it if the level of the hot water drops, and it is therefore capable of reducing the heat gradient on the outer wall of the pressurizer 30 during transient phenomena. The pipes 34 further cool the hot water during transient phenomena corresponding to drops in the level. In the preferred embodiment of the external pressurizer 30 hydraulically connected to the water of the vessel 15, the flow rate of the water through pipes 39 and 40 must compensate, while the reactor is working, the density variations in the water in the tank 15 and in the water of the primary circuit of the vessel 2. A change in density of the primary circuit water, due for example to a change in the output temperature from the steam generators as a consequence of a different steam demand by the control system, thus entails a change in the level of the hot-cold interface (I1) in the pipes 20. The capacity of the pipes 20 will therefore be suitably sized so as to avoid unwanted entry of borated water into the primary circuit during noormal transient phenomena. Suitable auxiliary systems not part of the plant's safety system will re-establish the correct level of the hot-cold interface (I1) (for example by injecting non-borated water into the primary circuit.) In some accidental transient phenomena, such as if a steam pipe bursts, the rapidity and the extent of the transient heat phenomenon may generate changes in the density of the water in the primary circuit which cannot be compensated by the change in level of the hot-cold front of the connections 20: this benefits safety since any entry of borated water into the primary circuit facilities quenching of the reactor. According to this invention, safety of the reactor is guaranteed in all conditions without intervention of an automatic nature or by an operator. Indeed, according to this invention, safety of the reactor is ensured by the entry of borated water (15) into the primary circuit each time there is a significant imbalance between the power produced and the power extracted, and each time the recirculation pumps stop. Removal of the residual heat takes place by a mixing of the primary circuit water with the water of the tank (15), and thus by transmission of the heat to the pool 18 through the wall of container 1, pipes 39 and 40, and pressurizer 30. Indeed, if the pressurizer has at least two pipes connecting it to the reactor container 1, a naturally circulating flow rate may be established which can transfer heat from the reactor to the cold part of the pressurizer. The thermal capacity of the water in the pool is sufficiently high to absorb the heat produced over several days by all the modules without reaching a temperature of 100.degree. C., and therefore without exerting pressure on the wall 19 surrounding the pool 18. The temperature of the water in the pool will in any case be kept indefinitely at a temperature below 100.degree. C. by cooling with one or more secondary circuits consisting of a circuit of water circulating naturally between the hot source consisting of a water-water exchanger (43) submerged in the pool and the cold source consisting of a water-air exchanger (44) located outside the containment system, on a higher level than the first exchanger. The water-air exchanger, which also operates by natural circulation of air, may be of the type claimed under Italian patent no. 1159163, originally envisaged for exchanges between liquid metals and air. The solution put forward also envisages the possibility of guaranteeing cooling of the core without the intervention of active systems even in the event of breakage of the pressure boundary, whether this occurs at a higher or lower level than the core. During the first emptying phase, the two volumes of cold water located one in the upper part of container 1 and the other in the lower part of the pressurizer 30 work together to depressurize the system and to keep the core flooded with cold water (at least one of the volumes intervenes, depending on the place of the breakage). During the second phase of the transient phenomenon, when the level of the water inside the container tends to stabilize, the steam produced by the boiling of the water of the core condenses on the cold parts of the pressure boundary, allowing progressive filling of the latter with water from the pool through the actual crack, by means of the motive force created by the head of water in the pool. The exchanging surface of the pressure boundary, that is to say of the system 1, 30, 39 and 40, must therefore be sufficient to condense the steam produced at the temperature corresponding to the pressure of the pool water head above the level of the reactor module, if necessary using additional exchangers 41, communicating hydraulically with the water in the tank and in any case immersed in the pool 18. The outflow of hot water and steam during the first stage of emptying (apart from a partial condensation when passing through the cold water head of the pool) may cause initial pressurizing of the ceiling 19 of the pool 18, which is reduced in time, however, due to interruption of the flow of steam and due to condensation of the steam on the cold surfaces and on the free surface of the water in the pool. The suitably shaped cup-type structure 7 serves to limit the quantity of hot water present in the primary circuit. Indeed, this insulated structure allows a sufficient quantity of cold water to be maintained inside it, in communication at the top, with the water in tank 15; convection phenomena ensure that it mixes with the latter and that the heat is removed by dissipation through the insulation 13. The structure 7 may also be used to support the core instruments and possibly control rods for the core. To change the fuel, the structure 7 has to be removed, after removing the lid of the container (1). The loading/unloading machine may then be introduced. Without having to use the gas cushion in the naturally circulating closed circuit, the moving agent consists of the static pressure differential already defined above. During the system heating transient, when the static pressure differential due to the different densities of the hot and cold water is not significant, gas may be introduced into the bell (22), as envisaged in the known solution referred to above; during normal operation, the gas may be removed, leaving the natural circulation path (15, 20, 4, 9, 21, 15) perfectly free. During normal operation, this difference in pressure must equal the pressure drop in the core and in the output header; this relationship must be kept in mind in designing the core. According to a variant of this invention, a Venturi-type narrower cross-section is shaped into the fuel-element feed grid. The main pipe 50 communicates at the bottom with the header 5, while one or more pipes 54 allow the narrower cross-section of the pipe 50 to communicate with the passages 20. With this device a pressure drop in the core which, added to the pressure drop in the header 9, is greater than said static pressure differential pressure is possible without recirculation through the orifice 20. According to the invention, the solution suggested is particularly suitable for modular systems; the modules (1, 2, 30), may be almost completely shop assembled, and fitted on site into a pool 18, the number of modules varying depending on the power output required. The simplicity of the small number of auxiliary systems required drastically reduces the on-site activities required for plants known up to now. Finally, it must be pointed out that unlike the Canadian patent cited above, according to this invention only the limited quantity of cold and borated water in the tank 15 has to be kept under pressure: the heat may be transmitted to a large quantity of cold water contained in the pool 18, with no need for any manual or automatic intervention. This system means that the core may be cooled using only built-in and passive systems. More generally speaking, according to this invention the reactor module may or may not be equipped with a steam generator having spiral, straight or U-shaped pipes and so on. If it is not, the steam may be produced directly by the core (boiling reactor).
062394304	description	DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The beam producer in the form of a thermal field emission source is shown in FIG. 1, denoted overall as (1) and the cathode tip which emits electrons as (1a). Electrons are extracted from the cathode tip (1a) by means of an extraction electrode (2) which is at a positive potential, and are then accelerated to the potential of the anode (3). The anode is electrically connected to a beam guiding tube (4) which passes through the whole apparatus and is of electrically conductive material. The anode potential, and hence the potential of the beam guiding tube (4), is about 10 kV relative to ground. The anode is directly followed by a magnetic condenser lens (5), and the condenser lens (5) is followed by an aperture diaphragm (6). The energy filter (7) is an imaging dispersive electron energy filter which images a so-called input image plane (9) (first input plane) stigmatically and achromatically into an output image plane (10) (first output plane) and simultaneously images an input diffraction plane (second input plane) dispersively and stigmatically into an output diffraction plane (second output plane). The aperture diaphragm (6) is arranged in the input diffraction plane; that is, this plane coincides with the plane of the aperture diaphragm (6). The energy selection diaphragm (8) is arranged in the output diffraction plane, and is constituted as a slit diaphragm. The dispersive filter (7) itself is a purely magnetic filter; the three magnet sectors of the filter are denoted by (7a-7c). The detailed construction of the filter is described in U.S. Pat. No. 4,740,704, which should be consulted for constructional details of the filter. In spite of the construction of the filter (7) which is symmetrical with respect to a plane perpendicular to the plane of the drawing in FIG. 1, the filter (7) has a dispersion, that is, the electrons passing through the filter have beyond the filter a deflection perpendicular to the optical axis and dependent on their energy, so that those electrons are trapped which have an energy deviation from the mean energy which is greater than the energy deviation defined by the dispersion and slit width. In order for high voltage fluctuations to bring about no lateral drift of the successive images of the cathode tip (1a) emitting the electrons, the cathode tip (1a) is imaged by the condenser lens (5) in the input image plane (9) of the filter (7), and in fact is imaged by the filter (7) achromatically in the output image plane (10). A second condenser lens (11) follows the energy selection diaphragm (8), and images the selection diaphragm (8) in the rear focal plane of the objective lens (13). Simultaneously, the condenser lens (11), by imaging the output image plane (10) of the filter (7) produces a further intermediate image of the cathode tip (1a), which is imaged by the succeeding objective lens (13), once again greatly reduced, onto the specimen (15) to be investigated. The objective lens (13) is a combination of a magnetic and electrostatic lens. The specimen (15) and the pole shoes of the objective lens (13) are at ground potential, so that the electrons after leaving the beam guiding tube (4) are substantially braked to the target energy of between 10 eV and 5 keV between the end of the beam guiding tube (4) and the outer pole shoe of the objective lens (13). A further magnetic deflecting system (14) is arranged in the pole shoe gap of the objective lens (13), for scanning a large lateral region of the specimen (15). For the detection of the secondary electrons leaving the specimen (15), a rotationally symmetrical electron detector (12) with a middle bore is arranged between the objective lens (13) and the second condenser lens (11). This detector can be constructed as a scintillation detector, semiconductor detector, or microchannel plate detector. The detailed electron optical beam path is shown in FIG. 2. The cathode tip (1a) which emits electrons is imaged by the first condenser lens (5) into the input image plane (9) of the dispersive filter (7), which is imaged achromatically and stigmatically by the filter into the output image plane (10). The aperture diaphragm (6) is arranged between the first condenser lens (5) and the input image plane (9) of the filter (7), in that plane which is imaged by the filter (7), stigmatically and dispersively, into the output side conjugate plane in which the selection diaphragm (8) is arranged. The imaging of the cathode tip (1a) into the input image plane (9) here takes place with an enlargement of 5-40, and there thus results a corresponding reduction of the effective aperture within the filter (7) and in the plane of the selection diaphragm (8). The energy filtering on the output side of the filter (7) thereby leads to no appreciable cutting down of the aperture of the electron beam bundle. When the energy filter has a dispersion of 10-15 .mu.m/eV at an electron energy of 10 keV, an energy width of 0.1-0.2 eV is set with a selection diaphragm (8) which has a slit width of 2 .mu.m. Since the distance between the input image plane (9) and the input diffraction plane (6) amounts to 40-80 mm in typical dispersive energy filters, an aperture of 1.5.times.10.sup.-5 is transmitted without problems, in spite of the small slit width. With the subsequent two-stage imaging system of the second condenser lens (11) and the objective lens (13), by means of which the probe tip (1a) image present in the output image plane (10) is imaged on the object (15) with a reduction of about 400-700 times, optimum end apertures in the region of 6.times.10.sup.-3 through 1.times.10.sup.-2, and probe sizes between about 1 nm and 3 nm, then result in the specimen plane. The electrons which are back-scattered at the specimen (15) are accelerated back into the beam guiding tube (4) by the deceleration field between the specimen end of the beam guiding tube (4) and the specimen (15), and again have exactly the same energy as the primary electrons and therefore reach the filter system (7) backward. However, because of the opposite direction of motion, these back-scattered electrons are deflected in the opposite direction in the magnet sector (7a) of the filter, and on this path reach a primary electron detector (16). This primary electron detector (16) can be constructed in the usual manner as a scintillation detector, semiconductor detector, or microchannel plate detector. A second slit diaphragm (17) is furthermore arranged between the magnet sector (7a) and the primary electron detector (16), and filters out electrons which have other energies, and which have for example undergone an interaction with the specimen (15) or with the selection diaphragm (8). In the embodiment example of the invention shown in FIGS. 1 and 2, the dispersive filter is constructed according to U.S. Pat. No. 4,740,704. A so-called Omega filter is concerned here, and is also used by the inventors employer in the transmission electron microscope 912 Omega. The filter (7) can also be alternatively constructed as a so-called "alpha filter" corresponding to U.S. Pat. No. 4,760,261 or corresponding to U.S. Pat. No. 5,449,914. In the embodiment example according to FIG. 1, the first condenser lens (5) is constructed as a magnetic lens. In the embodiment example shown in FIG. 3, the condenser lens (24) is an electrostatic lens which is integrated into the beam producer (21) with the cathode tip (21a). This asymmetrical electrostatic immersion lens (24) is arranged between the extraction electrode (21) and the anode (23). It has a considerably greater aperture diameter on the side facing the beam producer (21) than on the side facing the anode (23). The cathode tip (21a) which emits electrons is also directly imaged, magnified by such an electrostatic immersion lens (24), in the input image plane (not further illustrated) of the succeeding dispersive filter. Two alternative objective lenses are shown in FIGS. 4a and 4b, and are preferably used in combination with the invention. The difference between the objective lens (33) in FIG. 4a and the objective lens (13) in FIG. 1 is that in the objective lens (33) the outer pole shoe (33a) is shortened, and ends at the same height as the inner pole shoe (33b). An annular pole shoe gap (33b) results which is aligned perpendicularly to the optical axis (shown dot-dashed). By this construction of the pole shoe gap, the magnet field exits in the direction toward the specimen (35), resulting in a stronger immersion of the specimen (35) and hence a reduction of the aperture aberrations. Electrodes (34) for the superposed electrostatic lens are then constructed as .extensions of the outer pole shoe (33a). The objective lens (36) in FIG. 4b differs from the objective lenses described hereinabove in that the beam guiding tube (4) is extended and ends only at the height of the outer pole shoe (36a) of the magnetic lens (36) or even behind it. The electrostatic lens between the specimen side end of the beam guiding tube (4) and the braking electrode (37) arranged between the specimen,(38) and the objective then first arises beyond the magnetic lens (36). In this embodiment example, the specimen (38) and the braking electrode (37) are at a common potential, which is negative relative to ground. The use of this objective offers advantages particularly at the lowest target energies, since even at the lowest target energies the cathode can be kept at a relatively high potential relative to ground, thus making the negative influence of leakage fields less strongly noticeable.
	summary
048184748	summary	The invention relates to a novel process making it possible to control or manage the core of a pressurized water nuclear reactor, when said core is formed both from uranium dioxide UO.sub.2 assemblies and assemblies of mixed uranium and plutonium oxide UO.sub.2 --PuO.sub.2. In pressurized water nuclear reactors, the reactor core is presently formed from assemblies having rods containing uranium dioxide pellets. A 900 MW reactor has 157 assemblies, each containing 264 rods. The presently most widely adopted solution for ensuring the management or control of the core of such a reactor consists of replacing one third of the assemblies and at the same time rearranging the remaining assemblies at the end of each irradiation cycle, whose duration is e.g. approximately one year. Thus, each of the assemblies undergoes three irradiation cycles before being discharged from the core. Thus, the management of the core takes place as from an elementary quantity which is the assembly containing e.g. 264 rods in the case of a 900 MW reactor. In this presently used solution, each of the assemblies is formed from rods containing uranium dioxide UO.sub.2 pellets which, at the time of manufacture, all have the same uranium 235 content (e.g. 3.25%). Moreover, it is known that nuclear fission reactions occurring in the reactor transform part of the uranium 238 into plutonium. When they are discharged from the core, the assemblies consequently contain a large amount of plutonium, which can in turn be used as nuclear fuel following reprocessing. It is therefore envisaged to recycle the plutonium formed in the irradiated uranium dioxide UO.sub.2 assemblies in pressurized water reactors in order to produce new assemblies, whereof the rods contain a mixed oxide of uranium and plutonium UO.sub.2 --PuO.sub.2. Such mixed oxide UO.sub.2 --PuO.sub.2 assemblies would e.g. constitute approximately one third of the core of a pressurized water reactor, whilst the other two thirds would be formed from conventional uranium dioxide assemblies. For reasons linked with the different physical properties of uranium and plutonium, hot points could occur in the core if the mixed oxide assemblies UO.sub.2 --PuO.sub.2 had a uniform plutonium concentration. This new solution based on the recycling of plutonium consequently presupposes that the mixed uranium and plutonium assemblies are subdivided, from their centre towards their peripherary, into several zones of different Pu concentrations. These assemblies can e.g. be constituted by three concentric zones formed from rods containing mixed oxide UO.sub.2 --PuO.sub.2 pellets, whose plutonium concentration decreases from the central zone towards the peripheral zone. It is therefore envisaged to equip approximately one third of the core of pressurized water nuclear reactors with such assemblies formed from three types of rods containing mixed UO.sub.2 --PuO.sub.2 oxide pellets having a different plutonium concentration. Like the other assemblies, only one third of these assemblies would be replaced during each cycle, so that their total irradiation time would also be three cycles. Thus, as with the present management of the core, the elementary quantity involved is here again the assembly considered as a whole. This novel solution, which has the essential advantage of permitting the recycling of plutonium, however, suffers from disadvantages. Thus, at the end of each irradiation cycle, new mixed oxide UO.sub.2 --PuO.sub.2 assemblies formed from rods of different types (e.g. three) must be introduced into the core. Thus, for each of these new assemblies, this presupposes the manufacture of rods having different plutonium concentrations and consequently the manufacturing costs for such assemblies would be high. Moreover, in order to ensure that a can fracture in one of the rods of an assembly does not require the discharge of said assembly from the reactor core and also to facilitate assembly decanning operations, over the past few years dismantlable assemblies have been developed, in which the rods can be replaced without destroying the assembly structure or framework. Reference is e.g. made to assemblies of the type called AFA (Advanced French Assembly), described on pp 546 to 549 of the article "Les reacteurs nucleaires a eau ordinaire" edited under the direction of Guy DREVON in the Commissariat a l'Energie Atomique collection and published by Eyrolles, 1983. The present invention therefore relates to a novel process for controlling or managing the core of a pressurized water nuclear reactor, partly constituted by mixed oxide UO.sub.2 --PuO.sub.2 assemblies formed from several concentric zones with different enrichments, said process permitting, other than during the first loading of the core, to manufacture a single type of rod containing mixed UO.sub.2 --PuO.sub.2 oxide pellets with a single enrichment, by using dismantlable assemblies. According to the invention this objective is achieved as a result of a process for the control of the core of a pressurized water reactor, formed from dismantlable assemblies, each having a group of rods containing fissile material pellets, characterized in that it comprises initially placing in the core at least one first type of assembly, whereof the rods contain uranium oxide pellets and a second type of assembly. whose rods contain mixed uranium and plutonium oxide pellets, the rods of the assemblies of said second type being distributed in accordance with at least two concentric zones containing mixed oxide pellets having different plutonium concentrations, said concentrations decreasing towards the outside of the assemblies from a central zone towards a peripheral zone, making these assemblies undergo successive irradiation cycles and periodically transferring, following each of these irradiation cycles, the rods of each zone of the assemblies of the second type into the adjacent zone towards the outside of said assemblies, the rods located in the peripheral zone being discharged and new rods containing the mixed oxide pellets with a plutonium concentration equal to the plutonium concentration of the pellets contained in the rods initially placed in the central zone being loaded into said central zone. Obviously, this process is superimposed on the standard control or management process for a pressurized water reactor core. Thus, the internal control of each of the mixed oxide assemblies taking place at the end of each cycle, according to the invention, is accompanied by an overall control of all the core assemblies. More specifically, part of the uranium dioxide assemblies is replaced during each cycle and the other assemblies, no matter whether they are of uranium dioxide or mixed uranium and plutonium oxide, are rearranged in the core in order to obtain an optimum homogenous power distritubion. This overall management of the assemblies is of a conventional nature and does not form part of the invention. The inventive process making it possible to manage the distribution of the rods in the different zones of the mixed oxide assemblies UO.sub.2 --PuO.sub.2 has significant advantages. Firstly, during the life of the reactor, a single type of rods containing mixed UO.sub.2 --PuO.sub.2 oxide pellets with a single enrichment has to be manufactured, so that manufacturing costs are greatly reduced. Moreover, all the rods containing mixed UO.sub.2 --PuO.sub.2 oxide pellets pass successively into different zones of the assemblies which they constitute. Thus, their irradiation is very similar, so that the nuclear material can be better used. The average properties of these assemblies evolve little throughout their life, so that the overall control of the core is improved. In addition, this process makes it possible to independently control the mixed oxide pellets and the skeleton of the corresponding assemblies. Finally, bearing in mind the non-linear character of the evolution of the multiplication factor of the neutrons as a function of the plutonium content (said factor remaining substantially constant beyond a certain concentration), the plutonium quantity present in the reactor is reduced.
	claims	1. An extreme ultraviolet (EUV) radiation source, comprising:a fuel droplet generator configured to provide a plurality of fuel droplets to an EUV source vessel along a first trajectory;a primary laser configured to generate a primary laser beam directed towards the plurality of fuel droplets, wherein the primary laser beam has a sufficient energy to ignite a plasma that emits extreme ultraviolet radiation from the plurality of fuel droplets;a collector mirror that is symmetric about a vertex and that is configured to focus the extreme ultraviolet radiation to an exit aperture of the EUV source vessel located below the collector mirror, wherein the collector mirror is oriented at a first orientation that causes a normal vector extending outward from the vertex of the collector mirror to intersect a vector of a gravitation force by an angle that is less than 90° and further causes a horizontal line extending through the vertex of the collector mirror to overlie an intersection of the first trajectory and the primary laser beam; andwherein the collector mirror has an opening extending through the vertex, and the first orientation of the collector mirror further causes the primary laser beam to extend along the normal vector through the opening from a position overlying the vertex. 2. The EUV radiation source of claim 1, wherein the plurality of fuel droplets are provided to the EUV source vessel along the first trajectory that intersects the normal vector by an angle that is less than 90°. 3. The EUV radiation source of claim 1, further comprising:a pre-pulse laser configured to generate a pre-pulse laser beam, having a lower energy than the primary laser beam, that deforms the plurality of fuel droplets prior to the primary laser beam hitting the plurality of fuel droplets; andwherein the pre-pulse laser beam extends in a first direction that is not parallel to a direction of the primary laser beam, and wherein the direction of the primary laser beam is substantially parallel to an optical axis of the collector mirror. 4. The EUV radiation source of claim 1, further comprising:a fuel droplet collection element located below the fuel droplet generator, wherein the fuel droplet generator and the fuel droplet collection element are aligned along a line that intersects the normal vector by an angle that is less than 90°. 5. The EUV radiation source of claim 4,wherein a topmost point of the collector mirror is arranged above the intersection of the first trajectory and the primary laser beam and is separated from the fuel droplet generator by a first lateral distance, andwherein a bottommost point of the collector mirror is arranged below the intersection of the first trajectory and the primary laser beam and is separated from the fuel droplet collection element by a second lateral distance that is larger than the first lateral distance. 6. The EUV radiation source of claim 1, further comprising:a tin droplet collection element having an angled surface arranged within an interior of the EUV source vessel vertically below the collector mirror, wherein a vertical distance between the angled surface and a bottom of the collector mirror increases as a lateral distance between the angled surface and the bottom of the collector mirror increases. 7. The EUV radiation source of claim 6, further comprising:an intermediate focus unit comprising a cone shaped aperture arranged within the exit aperture between the EUV source vessel and a downstream scanner comprising a plurality of optical elements configured to convey the extreme ultraviolet radiation to a semiconductor workpiece. 8. The EUV radiation source of claim 1, wherein the collector mirror is positioned at a location that is laterally adjacent to and vertically above the intersection of the first trajectory and the primary laser beam. 9. The EUV radiation source of claim 1, wherein the vertex of the collector mirror is arranged vertically above the intersection and a bottommost point of the collector mirror is located vertically below the intersection. 10. The EUV radiation source of claim 1, further comprising:a debris collection element having one or more angled corrugated surfaces extending between the collector mirror and the exit aperture. 11. The EUV radiation source of claim 1, further comprising:a debris collection element having one or more angled corrugated surfaces arranged between the plasma and the EUV source vessel; anda fuel droplet collection element arranged between the debris collection element and the plasma. 12. The EUV radiation source of claim 1, further comprising:a debris collection element having a lower angled surface and an upper angled surface that are configured to collect debris from the plasma, wherein the lower angled surface continuously extends from below the collector mirror to a location that is laterally between the plasma and the exit aperture, and wherein the lower angled surface intersects the vector of the gravitation force by a second angle that is less than 90°. 13. The EUV radiation source of claim 12, wherein the second angle is larger than the angle. 14. A method of generating extreme ultraviolet (EUV) radiation, comprising:providing a plurality of fuel droplets into an EUV source vessel;striking the plurality of fuel droplets with a primary laser beam at an intersection to generate a plasma that emits EUV radiation;focusing the EUV radiation at a focal point using a collector mirror oriented at a first orientation that causes a normal vector extending outward from a vertex of the collector mirror to intersect a vector of a gravitation force by an angle that is less than 90°, wherein the first orientation further causes the vertex to overlie the intersection and the normal vector to further intersect an exit aperture of the EUV source vessel located below the collector mirror; andwherein the collector mirror has an opening extending through the vertex of the collector mirror, and wherein the first orientation of the collector mirror further causes the primary laser beam to extend from a position overlying the vertex and through the opening along the normal vector. 15. The method of claim 14, further comprising:striking the plurality of fuel droplets with a pre-pulse laser beam that deforms the plurality of fuel droplets prior to striking the plurality of fuel droplets with the primary laser beam, wherein the pre-pulse laser beam extends in a direction that is not parallel to a direction of the primary laser beam. 16. The method of claim 14, further comprising:providing the EUV radiation to a semiconductor workpiece via an EUV photomask having a patterned multi-layered reflective surface. 17. An extreme ultraviolet (EUV) radiation source, comprising:a fuel droplet generator configured to provide a plurality of fuel droplets to an EUV source vessel along a first trajectory substantially extending in a same direction as a vector of a gravitation force;a primary laser configured to generate a primary laser beam directed towards the plurality of fuel droplets, wherein the primary laser beam has a sufficient energy to ignite the plurality of fuel droplets to generate a plasma that emits extreme ultraviolet radiation;a collector mirror oriented so that a normal vector extending outward from a vertex of the collector mirror intersects the vector of the gravitation force by an angle that is less than 90°, wherein the normal vector intersects an exit aperture of the EUV source vessel that is located below the collector mirror; andwherein the primary laser beam is configured to intersect the first trajectory at an intersection point that is located vertically below a horizontal line extending through the vertex of the collector mirror and wherein an uppermost point of the exit aperture is located below the intersection point. 18. The EUV radiation source of claim 17,wherein a topmost point of the collector mirror is arranged above the intersection point and is separated from the fuel droplet generator by a first lateral distance, andwherein a bottommost point of the collector mirror is arranged below the intersection point and is separated from a fuel droplet collection element by a second lateral distance that is larger than the first lateral distance. 19. The EUV radiation source of claim 17,wherein the collector mirror has an opening extending through the collector mirror at a location that is offset from the vertex of the collector mirror; andwherein the primary laser beam extends through the opening along a second trajectory that intersects the first trajectory at a substantially perpendicular angle. 20. The EUV radiation source of claim 17, wherein the vertex of the collector mirror is arranged vertically above the intersection point and a bottommost point of the collector mirror is located vertically below the intersection point.
042736706	claims	1. In an apparatus for concentrating low radioactive aqueous waste containing dispersed and dissolved materials including a forced circulation evaporator, a feed tank for holding said low radioactive aqueous waste, and a conduit for supplying low radioactive aqueous waste from the feed tank to the evaporator, the improvement comprising: a drain valve in the evaporator for removing concentrated radioactive bottoms from the evaporator, a drain conduit from the drain valve to a pump, a rinse water conduit, containing a first valve, communicating with the drain conduit, a delivery conduit, from the pump to a bottoms storage tank, containing a second valve, a branch conduit, in communication with the delivery conduit between the pump and the second valve and extending to said feed tank, containing a third valve, means operating the pump, with the drain valve closed and the drain conduit delivery conduit and branch conduit full of rinse water, and opening the drain valve and the third valve to thereby convey the water in the said conduits to the feed tank before bottoms removed from the evaporator reach the third valve, means closing the third valve and opening the second valve to deliver the bottoms removed from the evaporator to the bottoms tank, means opening the first valve in the rinse water conduit, closing the second valve to the bottoms tank and opening the third valve to the feed tank to back flush the drain valve and dilute bottoms in the conduits and deliver the diluted bottoms to the feed tank, means closing the drain valve to discontinue removal of bottoms from the evaporator while flushing the conduits with rinse water by maintaining the first valve open and delivering the rinse water to the feed tank, and means closing the first valve, the third valve and stopping the pump with the conduits and pump full of rinse water. withdrawing concentrated radioactive bottoms from an evaporator through a drain conduit and pumping it to a bottoms storage tank, continuing withdrawal of bottoms from the evaporator and simultaneously feeding an aqueous rinse stream to the drain conduit to dilute the withdrawn bottoms, pumping the diluted withdrawn bottoms to a feed storage tank, discontinuing withdrawal of bottoms from the evaporator, continuing to feed the aqueous rinse stream to the drain conduit until the stream in the drain conduit is very low in radioactivity, pumping the so further diluted stream to the feed storage tank, and discontinuing feeding the rinse stream to the drain conduit and pumping the diluted stream to the feed storage tank but maintaining the drain conduit and pump full of such diluted stream. withdrawing concentrated radioactive bottoms from an evaporator through a drain conduit and pumping it to a bottoms storage tank, continuing withdrawal of bottoms from the evaporator and simultaneously feeding an aqueous rinse stream to the drain conduit to dilute the withdrawn bottoms, pumping the diluted withdrawn bottoms to a feed storage tank, discontinuing withdrawal of bottoms from the evaporator, continuing to feed the aqueous rinse stream to the drain conduit until the stream in the drain conduit is very low in radioactivity, pumping the so further diluted stream to the feed storage tank, discontinuing feeding the rinse stream to the drain conduit and pumping the diluted stream to the feed storage tank but maintaining the drain conduit and pump full of such diluted stream, operating the pump and initiating flow of bottoms to the drain conduit, feeding the dilute stream in the drain conduit and pump to the feed tank until the bottoms nearly occupies the drain conduit, and diverting the bottoms in the drain conduit to the bottoms storage tank. 2. The improvement according to claim 1 in which the drain valve is a ram valve. 3. The improvement according to claim 1 in which a block valve is located on the upstream side of the pump in the drain conduit and a block valve is located on the downstream side of the pump, but upstream of the branch conduit, in the delivery conduit, and means opening the two block valves when the pump is operating and closing the two block valves when the pump is stopped. 4. A method comprising: 5. A method comprising:
052001440	description	DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, there is shown a schematic representation of a simulated nuclear fuel assembly 10 in accordance with the present invention. The assembly 10 includes an experimental reactor vessel top head 12 which is connected to a support plate 14. The support plate 14 is connected to a power lead and heater support tube 16 which extends into a heater assembly 20. Adjacent to the heater support tube 16 are thermocouple guide tubes 18. A sectional view of the simulated nuclear fuel assembly 10 is shown in FIG. 2. It can be seen that the heater assembly 20 includes a plurality of concentric heater tubes. These heater tubes simulate the fuel tubes in a nuclear reactor and include an inner target tube 22, which is unheated, an inner heater tube 24, a middle heater tube 26, and an outer heater tube 28. Surrounding the target tube 22 and the heater tubes 25, 26, and 28 is an outer target tube 30, which is unheated. The outer target tube 30 can also be considered the housing for the heater assembly 20. The power lead and heater support tube 16 is connected to the heater assembly 20 by its connection with the inner target tube 22, and extends into the heater assembly 20 from the top 46 and the entire length thereof. More detailed views of the design of a representative heater tube 24, 26, or 28 is shown by FIGS. 3 and 4. For purposes of this description, the electrical conductor in heater tube 24,26 and 28 are represented by the item number 50, it being understood that the conductor 50 shown in FIG. 3 is typical of any of the conductors in tubes 24, 26 or 28. The concept of the present invention is to split the conductor elements into two halves such as two semicircular halves of a tube or rod. Alternately, and as seen in FIG. 3, the electrical conductor 50 can include elongated slots 52 extending from one end almost substantially the entire length thereof such that each tube is joined at one end and is not joined at the other end. The conductor elements are joined at the top end by welding or brazing. The elongated slots 52 are filled with an electrical insulating ceramic such as alumina. A cross-sectional view of the typical heater tube 50 is shown in FIG. 4, taken from the line 4--4 in FIG. 3. The line "I" represents the heater tube inside surface and the line "O" represents the heater tube outside surface. From the line "I", the tube includes a base tube 56 of aluminum. Adjacent to the base tube 56 is a first ceramic insulating layer 58 deposited by thermal spraying. An electrical conductor element 50 is next to the first insulating layer 56 and is deposited by thermal spraying. The conductor element 50 is preferably a Ni-Al alloy. The thickness of the Ni-Al layer 50 varies, increasing from about 0.005 inches at midplane to about 0.06 inches at both ends. A second ceramic insulating layer 60 is adjacent to the conductor element 50 and is deposited by thermal spraying. The second insulating layer 60 is then covered with an aluminum layer 62 at the heater tube outside surface "O", deposited by thermal spraying. Insulating layers 58 and 60 are preferably a ceramic such as alumina. The ceramic layers 58 and 60 vary in thickness as a function of elevation to offset the variation in the thickness of the conductor element 50. Also shown in FIG. 4 are typical thermocouple notches 64 and 66. The notches 64 and 66 are machined into layers 56 and 62 into which thermocouples 42 are press fitted. Once the thermocouples are fitted into the notches, the notches are filled with an aluminum spray layer 68 identical to the aluminum thermal spray layer 62. Referring again to FIG. 2, a pair of power leads 32 for supplying heat to the assembly 20 are shown. The power leads 32 are copper rods, of about 0.2 inches in diameter and about three feet in length. They are housed at the top of the assembly 10 above the support plate 14 in a housing 34 which is a cylindrical unit having aluminum sides and a nonconductive, machinable ceramic top 36, such as the ceramic sold under the trademark MACOR. An alumina paste 38 fills the housing to provide for electrical insulation. The power leads 32 project outward from the housing 34 to provide for connection to a power source. The power leads 32 then extend downward from the housing 34 through the heater support tube 16 and into the open top of the heater assembly 20 where they are connected to the heater elements 24, 26, and 28 through electrical circuitry, the details of which are shown in FIG. 5. Referring to FIG. 5, there is shown a schematic view of the concentric heater tube assembly 20 taken from the line 5--5 of FIG. 1 through a bottom end cap 15, looking upward from the bottom. This view shows that the conductor layer in each heater tube 24, 26, and 28 is split into two halves. A plurality of ribs, generally denoted 70, are provided in the annular spaces between the tubes. These ribs, preferably of aluminum to match the aluminum of the inner target tube 22 and heater tubes 24, 26, and 28, insure separation of the tubes to prevent them from coming into contact with each other. They are symmetrically arranged and essentially divide each tube into four quadrants. Although FIG. 5 does not show a discernible separation of the ribs from the next outer tubes 24, 26, 28, and 30, it should be understood that this separation provides an extremely small clearance between the ribs and tubes of only about 0.030 inches. There are four ribs provided for each tube, and each rib extends along the full length of the tubes. In the bottom end cap, the ribs and tubes form a single solid construction. Also shown in FIG. 5 are electrical circuit paths between the heater tubes, represented by heavy arrowed lines. This circuit is routed through the end cap 15 at the bottom of the heater assembly 20. Routing of the electrical circuit from the power leads 32 is accomplished through certain of the ribs. More specifically, the electrical circuit is shown routed from the inner target tube 22 to the inner fuel tube 24 through the rib 71. The circuit is also routed from the inner target tube 22 to the inner fuel tube 24 to the middle tube 26 through ribs 71 and 74; and from the middle fuel tube 26 to the outer fuel tube 28 through ribs 74 and 76. The electrical return from the outer fuel tube 28 to the inner target tube 22 is through ribs 75, 73, and 72. The two fuel tubes between the outer fuel tube 28 and the inner target tube 22 (the middle 26 and inner 24 tubes) are not connected to the return circuitry. The conductor elements in heater tubes 24, 26, and 28 are joined at the top of the assembly 20 as shown in FIG. 3 to complete the electrical circuit inside each heater tube. Attached to the power lead and heater support assembly 16 are thermocouple guide tubes 40. These tubes serve to route a multiplicity of thermocouples from thermocouple grids 44 located on the underside of the support plate 14, to various locations on the fuel tubes 24, 26, and 28. Referring to FIG. 6, there is shown a view of the heater tube assembly 20 taken from the line 6--6 of FIG. 1, looking downward from the top. It can be seen in this figure that the ribs contact the next outer tubes; however, in reality there is a separation of about 0.030 inches between the ribs and the next outer tubes. FIG. 6 also shows the radial locations of the various thermocouples 42 on the heater tubes 24, 26, and 28. Each of the heater tubes includes eight thermocouples. As shown, each heater tube has three thermocouples symmetrically located on the outer surface of the tube between two of the ribs 70; one thermocouple on the outer surface of the tube centered between two ribs in each of the other three quadrants; and two thermocouples on the inside surface about one hundred eighty degrees apart. Different numbers and other radial locations of the thermocouples are of course possible, provided that the arrangement provides an accurate measurement of the heat dissipated throughout the assembly. A coolant such as water is provided in the annular spaces between the tubes to remove heat from the tube surfaces. A sufficient number of thermocouples must be installed on all heater surfaces to indicate the onset of sustained dryout. A dryout would occur when the water coolant in the annular spaces between the tubes boils in the regions where the thermocouples are located. This would indicate that too much heat is being transferred such that the coolant reaches the boiling point, and the fuel tubes would go on an uncontrolled heat build-up. This then defines an accident situation corresponding to a critical situation in an actual nuclear reactor. Additionally, the elevational location of these thermocouples can vary depending on the requirements of the guiding experimental program utilizing the heater assembly. For purposes of example, the locations of the thermocouples are at elevations in the range of 11 to 23 inches along the heater tubes with most of the thermocouples located somewhat near the top of the assembly. In this example, the guiding experimental program causes dryout near the top of the heater assembly. In operation, when power is applied, electrical resistance heating occurs. The electrical circuit transmits electrical energy to each successive concentric heater tube through the end piece 15 at the bottom of the assembly 20. This electrical power is related to the amount of nuclear fission produced in a reactor. The split heater concept of the present invention allows full scale geometry and power profile simulation of nuclear fuel assemblies, as well as for simulations where access is available from one direction only. The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiment was chosen and described to best explain the principles of the invention and its practical application and thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
	summary
	abstract	An X-ray imaging apparatus is provided with a multi X-ray source and a collimator in which a plurality of slits for X-rays to pass through are two-dimensionally formed, the size and position of the slits being adjustable. A control unit, as a first control mode, controls the size and position of the slits to move an examination region in parallel, when an X-ray source is changed to a different X-ray source, such that the examination directions are parallel before and after the change. Also, the control unit, as a second control mode, controls the size and position of the slits to rotate the examination direction, when an X-ray source is changed to a different X-ray source, such that the center of the examination regions is the same before and after the change.

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