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claims | 1. An encapsulated β− particle emitter, the emitter comprising:a. a sol-gel derived core that comprises a β−-emitting radioisotope; andb. an encapsulant enclosing the core through which at least some of the β− emissions from the β−-emitting radioisotope pass, wherein the encapsulant comprises a substrate and a cover and at least a portion of the encapsulant is electrically conductive. 2. The encapsulated β− particle emitter of claim 1, wherein substantially all of the substrate and cover are electrically conductive. 3. The encapsulated β− particle emitter of claim 1, wherein the cover is an electrically conductive sheet and the substrate is an electrically conductive sheet that is thicker than the cover and is able to support the core and cover without substantial deformation. 4. The encapsulated β− particle emitter of claim 3, wherein the β−-emitting radioisotope is 147Pm. 5. The encapsulated β− particle emitter of claim 4, wherein the core has a mass thickness no greater than about 2 mg/cm2. 6. The encapsulated β− particle emitter of claim 5, wherein the substrate has a mass thickness that is no greater than about 2.5 mg/cm2 and the cover has a mass thickness that is no greater than about 0.6 mg/cm2. 7. The encapsulated β− particle emitter of claim 6 having a β− particle emission efficiency of at least about 50%, wherein the substrate and the cover consist essentially of aluminum and the substrate has a thickness that is no more than about 8 μm and the cover has a thickness that is no more than about 2 μm. 8. The encapsulated β− particle emitter of claim 1, wherein the β−-emitting radioisotope is at a concentration that is substantially uniformly throughout the sol-gel derived core. 9. The encapsulated β− particle emitter of claim 1, wherein the β−-emitting radioisotope is selected from the group consisting of 3H, 10Be, 14C, 36Cl, 59Fe, 60Fe, 60Co, 63Ni, 79Se, 87Rb, 90Sr, 93Zr, 94Nb, 95Tc, 99Mo, 99Tc, 106Ru, 107Pd, 110Ag, 111Ag, 121Sn, 124Sb, 125Sb, 129I, 134Cs, 135Cs, 137Cs, 144Ce, 146Pm, 147Pm, 151Sm, 150Eu, 152Eu, 154Eu, 160Tb, 166Ho, 170Tm, 171Tm, 182Ta, 185W, 188W, 194Os, 204Tl, 227Ac, 228Ra, 241Pu, and combinations thereof. 10. The encapsulated β− particle emitter of claim 1, wherein the β−-emitting radioisotope is selected from the group consisting of 3H, 63Ni, 90Sr, and 147Pm. 11. The encapsulated β− particle emitter of claim 1, wherein the encapsulant has a density that is no greater than about 9 g/cm3. 12. The encapsulated β− particle emitter of claim 11, wherein the encapsulant comprises one or more elements selected from the group consisting of Be, Al, and Ti. 13. The encapsulated β− particle emitter of claim 11, wherein the encapsulant consists essentially of aluminum or a low-density aluminum-based alloy. 14. The encapsulated β− particle emitter of claim 1, wherein the sol-gel derived core, in addition to the β−-emitting radioisotope, comprises oxides of elements selected from the group consisting of silicon, boron, zirconium, titanium, aluminum, and combinations thereof. 15. The encapsulated β− particle emitter of claim 1, wherein the sol-gel derived core, in addition to the β−-emitting radioisotope, comprises oxides of silicon. 16. The encapsulated β− particle emitter of claim 15, wherein the sol-gel derived core further comprises oxides of titanium in amount of up to 40 percent by weight of the sol-gel derived core. 17. A method for making an encapsulated β− particle emitter, the method comprising:a. depositing a β−-emitting radioisotope-containing sol-gel on a surface of a substrate;b. curing the deposited β−-emitting radioisotope-containing sol-gel to form a solid radioactive oxide coating comprising the β−-emitting radioisotope and an oxide; andc. placing a cover, at least a portion of which is an electrically conductive sheet, on the deposited β−-emitting radioisotope-containing sol-gel so that cover in combination with the substrate encapsulate the cured deposited β−-emitting radioisotope-containing sol-gel. 18. The method of claim 17, wherein the cover is placed on the deposited β−-emitting radioisotope-containing sol-gel before the curing is complete. 19. The method of claim 18 further comprising heat treating the encapsulated β− particle emitter in order to condense the cured β−-emitting radioisotope-containing sol-gel. 20. The method of claim 19, wherein the heat treating comprises heating the encapsulated β− particle emitter to a temperature within the range of about 60° C. to about 80° C. for a duration of about 12 hours. 21. The method of claim 17, wherein the surface of the substrate is contacted with a coupling agent before the β−-emitting radioisotope-containing sol-gel is deposited on the surface of the substrate, wherein the β−-emitting radioisotope-containing sol-gel further comprises a coupling agent, or a combination thereof in order to enhance the adhesion between the cured β−-emitting radioisotope-containing sol-gel and the surface of the substrate. 22. The method of claim 21, wherein the coupling agent is an alkoxy silane. 23. The method of claim 22, wherein the coupling agent is glycidoxypropyltrimethoxysilane. 24. The method of claim 17, wherein the cover is an electrically conductive sheet that has a mass thickness that is no greater than about 0.6 mg/cm2 and the substrate is an electrically conductive sheet that has mass thickness that is no greater than about 2.5 mg/cm2 and is able to support the core and cover without substantial deformation. 25. The method of claim 24, wherein the substrate and cover each consist essentially of aluminum, a low-density aluminum-based alloy, titanium, a low-density titanium-based alloy, or combinations thereof. 26. The method of claim 17, wherein the β−-emitting radioisotope is at a concentration that is substantially uniformly throughout the β−-emitting radioisotope-containing sol-gel. 27. The method of claim 17, wherein the β−-emitting radioisotope is selected from the group consisting of 10Be, 59Fe, 60Fe, 60Co, 63Ni, 79Se, 87Rb, 90Sr, 93Zr, 94Nb, 98Tc, 99Mo, 99Tc, 106Ru, 107Pd, 110Ag, 111Ag, 121Sn, 124Sb, 125Sb, 134Cs, 135Cs, 137Cs, 144Ce, 146Pm, 147Pm, 151Sm, 150Eu, 152Eu, 154Eu, 160Tb, 166Ho, 170Tm, 171Tm, 182Ta, 185W, 188W, 194Os, 204Tl, 227Ac, 228Ra, 241Pu, and combinations thereof. 28. The method of claim 17, wherein the β−-emitting radioisotope is selected from the group consisting of 63Ni, 90Sr, and 147Pm. 29. The method of claim 17, wherein the β−-emitting radioisotope is 147Pm. 30. The method of claim 17, wherein the cured β−-emitting radioisotope-containing sol-gel has a mass thickness no greater than about 2 mg/cm2. 31. The method of claim 17, wherein the β−-emitting radioisotope-containing sol-gel, in addition to the β−-emitting radioisotope, comprises alkoxides of oxides of elements selected from the group consisting of silicon, boron, zirconium, titanium, aluminum, and combinations thereof. 32. The method of claim 17, wherein the β−-emitting radioisotope-containing sol-gel, in addition to the β−-emitting radioisotope, comprises alkoxides of silicon. 33. The method of claim 32, wherein the β−-emitting radioisotope-containing sol-gel further comprises alkoxides of titanium in amount of up to 40 percent by weight of the β−-emitting radioisotope-containing sol-gel. 34. A directly charged beta (negatron) nuclear decay capacitor comprising:a. an encapsulated β− particle emitter that comprises:i. a sol-gel derived core that comprises a β−-emitting radioisotope; andii. an encapsulant enclosing the core through which at least some of the β− emissions from the β−-emitting radioisotope pass, wherein the encapsulant comprises a substrate and a cover and at least a portion of the encapsulant is electrically conductive;b. an electrically conductive collector for collecting β− particles from the encapsulated β− particle emitter; andc. a dielectric between the encapsulated β− particle emitter and the electrically conductive collector. 35. The directly charged beta (negatron) nuclear decay capacitor of claim 34, wherein the dielectric has a dielectric strength of at least about 200V/micron and a density that is no greater than about 2.5 g/cm3. 36. The directly charge beta (negatron) nuclear decay capacitor of claim 35, wherein the dielectric is an electrical insulating material or a vacuum. 37. The directly charge beta (negatron) nuclear decay capacitor of claim 35, wherein the dielectric comprises polyimides. 38. The directly charged beta (negatron) nuclear decay capacitor of claim 35, wherein at least the portion of the collector for which β− particles from the emitter will be incident is a metal and wherein: (a) the dielectric suppresses the emission of secondary electrons from said metallic portion of the collector, (b) the directly charged beta (negatron) nuclear decay capacitor further comprises a secondary suppression coating on said metallic portion of the collector, or (c) both (a) and (b). 39. The directly charged beta (negatron) nuclear decay capacitor of claim 38, wherein dielectric comprises one or more radiation-resistant polymers and the secondary suppression coating comprises one or more radiation-resistant polymers, graphite, or a combination thereof. 40. The directly charged beta (negatron) nuclear decay capacitor of claim 39, wherein the one or more radiation-resistant polymers are selected from the group consisting of polyimides, polyetherimdes, polyamideimides, polyphenylene sulfides, polyetheretherketones, polystyrenes, polyarylates, polyarylamides, polyethersulfides, polysulfones, polyamides, polyphenyloxides, and combinations thereof. 41. The directly charged beta (negatron) nuclear decay capacitor of claim 34 further comprising a multiplicity of encapsulated β− particle emitters, a multiplicity of electrically conductive collectors, or a multiplicity of encapsulated β− particle emitters and a multiplicity of electrically conductive collectors. 42. The directly charged beta (negatron) nuclear decay capacitor of claim 34, the cover is an electrically conductive sheet and the substrate is an electrically conductive sheet that is thicker than the cover and is able to support the core and the cover without substantial deformation. 43. The directly charged beta (negatron) nuclear decay capacitor of claim 34, wherein the β−-emitting radioisotope is selected from the group consisting of 63Ni, 90Sr, and 147Pm. 44. The directly charged beta (negatron) nuclear decay capacitor of claim 34, wherein the encapsulated β− particle emitter has a β− particle emission efficiency of at least about 50%, the substrate and the cover consist essentially of aluminum, and the substrate has a thickness that is no more than about 8 μm and the cover has a thickness that is no more than about 2 μm. 45. The directly charged beta (negatron) nuclear decay capacitor of claim 34, wherein the sol-gel derived core, in addition to the β−-emitting radioisotope, comprises oxides of elements selected from the group consisting of silicon, boron, zirconium, titanium, aluminum, and combinations thereof. 46. A method of performing work, the method comprising delivering the electrical energy of a directly charged beta (negatron) nuclear decay capacitor through a circuit, wherein the directly charged beta (negatron) nuclear decay capacitor comprises:a. an encapsulated β− particle emitter that comprises:i. a sol-gel derived core that comprises a β−-emitting radioisotope; andii. an encapsulant enclosing the core through which at least some of the β− emissions from the β−-emitting radioisotope pass, wherein the encapsulant comprises a substrate and a cover and at least a portion of the encapsulant is electrically conductive;b. an electrically conductive collector for collecting β− particles from the encapsulated β− particle emitter; andc. a dielectric between the encapsulated β− particle emitter and the electrically conductive collector. 47. A directly charged beta (negatron) nuclear decay capacitor comprising a β− particle emitter, an electrically conductive collector for collecting β− particles from the β− particle emitter, and a dielectric between the encapsulated β− particle emitter and the electrically conductive collector, wherein at least the portion of the collector for which β− particles from the emitter will be incident is a metal and is contact with a volume of one or more radiation-resistant polymers that suppress the emission of secondary electrons from said metallic portion of the collector. 48. The directly charged beta (negatron) nuclear decay capacitor of claim 47, wherein the one or more radiation-resistant polymers are selected from the group consisting of polyimides, polyetherimdes, polyamideimides, polyphenylene sulfides, polyetheretherketones, polystyrenes, polyarylates, polyarylamides, polyethersulfides, polysulfones, polyamides, polyphenyloxides, and combinations thereof. 49. The directly charge beta (negatron) nuclear decay capacitor of claim 48, wherein the one or more radiation-resistant polymers in the form of a film. |
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055307299 | summary | TECHNICAL FIELD The present invention relates to a fuel assembly and a spacer for a boiling reactor. The fuel assembly comprises a bundle of elongated fuel rods retained and fixed by a plurality of spacers arranged in a certain spaced relationship to each other along the bundle. The spacers comprise a plurality of cells to mutually fix the fuel rods and are surrounded by an external spacer frame. A coolant, for example water, is adapted to flow from below and up through the normally vertically arranged fuel assembly and, during a nuclear reaction, to cool the fuel rods arranged in the assembly. The object of the invention is to increase the efficiency in this cooling of the fuel rods, in particular the fuel rods which are arranged at the corners of the spacer. BACKGROUND ART, PROBLEMS A fuel assembly in a nuclear reactor consists of an elongated tubular container, often with a rectangular or square cross section, which is open at both ends forming a continuous flow passage, through which the coolant of the reactor is able to flow. The fuel assembly comprises a larger number of also elongated tubular fuel rods, arranged in parallel in a certain definite, normally symmetrical pattern. At the top, the fuel rods are retained by a top tie plate and at the bottom by a bottom tie plate. To allow coolant in the desired manner to flow past the fuel rods, it is important that these be kept at a distance from each other and prevented from bending or vibrating when the reactor is in operation. For this purpose, a plurality of spacers are used, distributed along the fuel assembly in the longitudinal direction. Known spacers often comprise an external spacer frame and, inside this spacer frame, plate bands arranged crosswise and standing on end, these plate bands forming substantially square cells. It is also common for the cells to be formed from sleeves. Inside the cells there are arranged fixed and resilient supports, respectively, for the fuel rods extending through the cells. Since the coolant in a nuclear reactor of boiling-water type (BWR) boils, a ratio of water to steam is formed which varies axially in the core. The coolant flows from the bottom and upwards in the core. At the bottom of the core, the temperature of the cooling water is lower than the boiling temperature and is thus in single phase, that is, the space between the fuel rods in the lower part of the assembly is, in operation, filled with non-boiling water. Further up, where the coolant has reached the boiling temperature, water is transformed into steam and the coolant is in two phases. The further up in the core, the higher the proportion of steam in relation to the proportion of water. In the upper part of the core, the fuel rods are only covered with a thin film of water, outside of which steam mixed with water droplets flows. If the heat flux from a fuel rod becomes very large in relation to the coolant flow, there may be a risk of dryout occurring, that is, the liquid film becomes so thin that it is not able to hold together. The liquid film is broken up and dry wall portions are formed, which locally leads to a considerably deteriorated thermal transmittance between the fuel rod and the coolant, resulting in a greatly increased wall temperature of the fuel rod. The increased wall temperature may lead to damage with serious consequences arising on the fuel rods. The risk of dryout is greatest in the upper part of the fuel where the percentage of steam is greatest. Also the wall of the fuel assembly, that is, the inside of that fuel channel which surrounds four identical bundles of fuel rods retained by spacers, is coated by a water film. However, this film is not entirely necessary since the wall of the fuel channel is considerably more insensitive to superheating than the fuel rods. The spacers influence the flow of the coolant and hence the cooling of the fuel. It is known that, in a region just below the spacer where the coolant has not yet passed the spacer, a deterioration of the water film on the fuel rods takes place, whereas in region above the spacer, where the coolant has just passed the spacer, a reinforcement of the water film instead occurs. The reinforcement of the water film is due to the turbulence which arises in the coolant when it passes a spacer. The greatest risk of dryout exists in the upper part of the fuel just below the spacers. A limiting factor with respect to the dryout power, that is, the total power that can be obtained from the fuel assembly without the risk of dryout existing, is usually the power that is obtainable from the fuel rods arranged in the corners of the spacer. These fuel rods, in the following referred to as corner rods, are sensitive since they are surrounded by only a small quantity of coolant, which limits the load possibility while at the same time non-boiling water with a good moderating capacity is present outside the corners of the fuel channel, whereby the power in the corner rods tends to become too high. A lower power output from the corner rod can be achieved with a lower enrichment thereof. However, it is not desirable to lower the enrichment level too much since, at the same time, a uniform enrichment design in the fuel assembly and as high a power output as possible are aimed at. One way of improving the cooling is to reduce the distance between the spacers, such that the distance becomes small in the upper half of the fuel bundle where the sensitivity is greatest. However, this requires that the pressure drop in the coolant does not increase too much across the spacers such that the cooling capacity decreases. Normally, the positive cooling capacity of a spacer does not reach all the way up to the next spacer. Dryout occurs, as described above, exactly below the nearest downstream spacer. When an extra spacer level is introduced in the bundle, the total pressure drop should not increase in the fuel bundle, which means that the pressure drop of the individual spacer in such a case must be reduced. One object of the invention is to improve the cooling of the fuel rods, in particular of the fuel rods which are arranged at the corners of the spacers, and to improve the cooling of at least the upper part of the fuel rods so as to reduce the risk of dryout. A reduced risk of dryout means that the fuel can be utilized more efficiently, which entails economical advantages. SUMMARY OF THE INVENTION, ADVANTAGES The present invention relates to a fuel assembly and a spacer for a boiling water reactor in which the cooling of at least its upper part is improved and in particular of the corner rods of the spacers such that the risk of dryout is reduced. The improved cooling is achieved by designing at least some of the spacer frames of the fuel assembly as will be hereinafter described. The spacer frame according to the invention comprises a first portion arranged at a distance from the inner surface of the fuel channel in the fuel assembly, and a second portion which, compared with the first portion, is arranged at a shorter distance from the inner surface of the fuel channel. The spacer frame normally consists of four rectangular frame parts which are joined together at their respective short sides with a pitch angle of 90.degree., forming a spacer frame for surrounding the spacer cells. The second portion is, at the corners of the spacer frame, that is, at the short side of each frame part, adapted to conduct coolant into the inside of the frame part whereupon the coolant encounters an edge which is obliquely positioned in relation to the longitudinal direction of the fuel assembly and which is formed between the first and second portions and adapted such that the coolant is caused to be deflected in a direction towards the corner rod in that the obliquely positioned edge extends in an inclined manner in a direction downstream of the spacer and towards the immediately adjacent corner of the spacer. This deflection of the coolant towards the corner rod means that more coolant reaches the corner rods, which in turn means that the average power output from the fuel assembly can be increased. Further, the spacer frame is provided at its corners with recesses, extending along the direction of flow, which are limited by an upper and a lower projecting part to connect one frame part to another, possibly via a cell. The reduction of material in the corner portion permits improved cooling of the corner rod through reduced friction, that is, lower flow resistance, between the coolant flowing upwards and the spacer frame and more coolant to the corner rod such that the power output therefrom can be increased without the risk of dryout increasing. The reduction of material also results in a reduced cross-section area in the direction of flow. All the frame parts are advantageously designed essentially identically. The design of the frame part in other respects may be made in many different ways, some of which will be described below in connection with the description of the preferred embodiments. At least the upper part of the fuel assembly is provided with the type of spacer described above, that is, that part of the fuel assembly where the coolant is situated in a high degree of two-phase state. In those cases where more spacer levels are chosen than what the above-mentioned spacers are intended for, in order to reduce the total pressure drop, the lower part of the fuel assembly may be provided with low-pressure drop spacers. This method is possible since the risk of dryout does not exist there since the coolant is essentially in single-phase state. The advantage of the fuel assembly and the spacer according to the invention is that they allow a more efficient cooling of especially the corner rods of the spacers, whereby the power output therefrom, and hence the power output from the entire fuel assembly, can be increased. Further, the cross-section area of the spacer frame in the direction of flow is minimized through, inter alia, the open corners, which allows a low pressure drop across the respective spacer, which in turn provides a possibility of insertion of additional spacer levels. In those cases where the spacer according to the invention in the fuel assembly is combined with any other type of spacer with a very low pressure drop, the pressure drop per spacer can be further reduced and further spacer levels be inserted. |
H00004464 | claims | 1. A method of controlling the reaction rates of fuel nuclei in a fusion reactor having a plasma confining magnetic field, a vacuum vessel and a fuel consisting essentially of a fusion plasma, said method comprising the steps of: (a) polarizing the nuclei of neutral fuel atoms in a particular direction relative to the plasma confining magnetic field, said fuel atoms being polarized such that essentially all of said atoms have the same polarization; (b) injecting said polarized fuel atoms into said vacuum vessels; and (c) forming said fusion plasma from said polarized fuel atoms. (a) polarizing the nuclei of said fuel atoms in a particular direction relative to the plasma confining magnetic field, said fuel atoms being polarized such that essentially all of said atoms have the same polarization; (b) injecting said polarized fuel atoms into said vacuum vessel; and (c) forming said fusion plasma from said polarized fuel atoms. 2. The method of claim 1 wherein said fuel atoms comprise D and T and wherein the nuclei of said D and T are polarized parallel to the plasma confining magnetic field such that said reaction rate is increased. 3. The method of claim 1 wherein said fuel atoms comprise D atoms and said D nuclei are polarized transverse to the plasma confining magnetic field, thereby increasing said reaction rate. 4. The method of claim 1 wherein said fuel atoms comprise D atoms and said D nuclei are polarized parallel to the plasma confining magnetic field, such that said reaction rate is suppressed. 5. The method of claim 1 wherein said fuel atoms comprise D and He.sup.3 and said D nuclei are polarized parallel to said plasma confining magnetic field, such that said reaction rate is increased. 6. A method of controlling the direction of emission of the reaction products of the fuel in a fusion reactor having a plasma confining magnetic field, a vacuum vessel and a fuel consisting essentially of a fusion plasma said reaction products including neutrons and alpha particles, said method comprising the steps of: 7. In a controlled fusion reactor having a vacuum vessel and a plasma confining magnetic field, an improved nuclear fuel which consist essentially of a plasma of fuel atoms with polarized nuclei. 8. The fuel of claim 7 wherein the fuel atoms comprise D and T atoms and said D and T nuclei are polarized parallel to the plasma confining magnetic field. 9. The fuel of claim 7 wherein the fuel atoms comprise D and He.sup.3 atom and said D nuclei are polarized parallel to the plasma confining magnetic field. 10. The fuel of claim 7 wherein the fuel atoms comprise D atoms and said D nuclei are polarized parallel to the plasma confining magnetic field. 11. The fuel of claim 7 wherein the fuel atoms comprise D atoms and said D nuclei are polarized transverse to the plasma confining magnetic field. 12. The method of claim 6 wherein said fusion reactor is a mirror machine, said fuel atoms comprise D and T atoms and said D and T nuclei are polarized parallel to the plasma confining magnetic field, thereby increasing the fraction of alpha particles trapped in the mirror field. 13. The method of claim 6 wherein said fusion reactor is a tokamak, said fuel atoms comprise D and T atoms and said D nuclei are polarized transverse to the plasma confining magnetic field, thereby emitting said alpha particles and said neutrons along the plasma confining magnetic field. |
claims | 1. A method for analyzing a defect of a photolithographic mask for an extreme ultraviolet (EUV) wavelength range (EUV mask), the method comprising:a. generating at least one focus stack relating to the defect using an EUV mask inspection tool, wherein the at least one focus stack comprises an image recorded in a focus plane, at least one image recorded above the focal plane, and at least one image recorded below the focal plane;b. determining a surface configuration of the EUV mask at a position of the defect;c. providing model structures having the determined surface configuration which have different phase errors and generating the respective focus stacks; andd. determining a three dimensional error structure of the EUV mask defect by comparing the at least one generated focus stack of the defect and the generated focus stacks of the model structures. 2. The method of claim 1, further comprising applying different repairing methods to the three dimensional error structure and simulating respective focus stacks in order to determine an optimal repairing method. 3. The method of claim 2, further comprising applying the optimal repairing method to the defective position. 4. The method of claim 2, wherein the repairing method comprises at least partially removing the multilayer structure, in particular drilling at least one hole into the multilayer structure. 5. The method of claim 2, wherein the repairing method comprises locally compacting and/or expanding the multilayer structure and/or a substrate of the EUV mask by locally focusing femtosecond laser pulses into the EUV mask. 6. The method of claim 1, wherein the model structures comprise an absorbing pattern structure on a surface of the EUV mask. 7. The method of claim 6, further comprising providing the absorbing pattern structure from EUV mask design data and/or from a recording of at least one image. 8. The method of claim 1, further comprising using a repairing method correcting the three dimensional error structure, so that a resulting multilayer structure is at least approximately corrected to an ideal multilayer structure. 9. The method of claim 8, further comprising applying the repairing method directly onto the defective position of the EUV mask. 10. An inspection microscope for photolithographic masks in the extreme ultraviolet wavelength range adapted to:a. generate at least one focus stack relating to the defect using an EUV mask inspection tool, wherein the at least one focus stack comprises an image recorded in a focus plane and at least one image recorded above the focal plane and at least one image recorded below the focal plane;b. determine a surface configuration of the EUV mask at a position of the defect;c. provide model structures having the determined surface configuration which have different phase errors and generating the respective focus stacks; andd. determining a three dimensional error structure of the EUV mask defect by comparing the at least one generated focus stack of the defect and the generated focus stacks of the model structures. |
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description | This application claims the benefit of U.S. Provisional Application Ser. No. 60/591,410, filed on Jul. 27, 2004 entitled “Razor Array Shutter for LPP Debris Mitigation” commonly assigned with the present application and incorporated herein by reference in its entirety for all purposes. This disclosure generally relates to laser-produced plasma (LPP) devices, and more particularly to devices and methods for obstructing the passage of debris from an LPP device through the use of a rotating debris shutter during a radiation generating event. Laser-produced plasma (LPP) devices are an attractive source of X-rays or short-wavelength radiation due to their relative small size, high brightness and high spatial stability. Two established applications for LPP are microscopy and lithography. However, conventional LPP devices utilize solid targets that produce debris that may easily contaminate, coat, or destroy sensitive X-ray components, such as optics or zone plates, that are positioned close to the plasma. Unfortunately, increasing the distance or introducing filters in order to protect the components typically reduces the amount of radiation that can be captured or utilized. For convenience, solid targets have often been used for LPP soft X-ray sources. Examples of solid target LPP systems are described in U.S. Pat. Nos. 5,539,764; 6,016,324; 6,307,913; and 6,707,101, all of which are hereby incorporated by reference herein in their entirely for all purposes. In general, targets formed from materials having low molecular weights yield emission spectra that are very narrow, while targets formed from materials having high molecular weights yield emission spectra having continuum radiation due to Brehmsstrahlung emission. Thus, low molecular weight targets are desirable for LPP applications. Unfortunately, with low molecular weight targets, significant amounts of debris, e.g., hot ions and larger particles, are created. In addition, such debris often follows the generated X-rays out of the laser ablation chamber of the LPP device, which can contaminate or damage components outside of the chamber as well. Several methods have been developed to reduce the effect of debris, such as using a small back pressure of helium or other gas, or strategically locating a relay mirror for the protection of sensitive components. Additionally, thin film tape targets, which are becoming more commonplace, help reduce the amount of debris by avoiding shock wave ejection or delayed evaporation. Unfortunately, significant amounts of debris particles are produced, presumably from cooler zones illuminated by the noncentral parts of the laser beam. Gas-phase targets have been another low-debris alternative; however, such low density results in low X-ray intensity. Other approaches to debris reduction have included waterjet devices and liquid droplets used for the laser target. However, even these approaches still result in the creation of some amount of debris when the X-rays are generated, and thus the potential for debris escaping the vacuum chamber and potentially contaminating and/or damaging outside components still exists. Accordingly, since the production of debris within a typical LPP device is difficult to eliminate, devices and methods are needed to prevent the LPP-generated debris from exiting the vacuum chamber and damaging delicate components of the LPP device. Disclosed are devices and methods for mitigating the exit of debris from a laser-produced plasma (LPP) device during a laser ablation process. In one embodiment, an LPP device comprises a laser source for generating a laser used for irradiation of a target, and a radiation source (sometimes called a “point source”) that generates short-wavelength radiation (e.g., X-rays) and debris by irradiating the target with the laser so as to generate a plasma. In these embodiments, the LPP device also includes a shutter assembly for mitigating the damaging effects of the ablated debris, where the shutter assembly includes a rotatable shutter having at least one aperture that provides a line-of-sight between the radiation source and an exit of the device during a first period of rotation of the shutter, and obstructs the line-of-sight between the radiation source and the exit during a second period of rotation. The shutter assembly in this embodiment also includes a motor configured to rotate the shutter to permit passage of the X-rays through the at least one aperture and to the exit during the first period of rotation, and to thereafter rotate the shutter to obstruct the passage of the debris through the at least one aperture during the second period of rotation. In another embodiment, a method for mitigating debris in an LPP device comprises providing a rotatable shutter having at least one aperture, and rotating the shutter a first period of its rotation to provide a line-of-sight between a radiation source and an exit of the device through the at least one aperture. In this embodiment, the method further includes rotating the shutter a second period of its rotation to provide no line-of-sight between the radiation source and the exit through the at least one aperture. Additionally, in such a method, rotating the shutter during the first period of rotation permits passage of radiation generated at the radiation source through the at least one aperture and to the exit, and thereafter rotating the shutter during the second period of rotation obstructs the passage of debris generated at the radiation source through the at least one aperture and to the exit. Referring initially to FIG. 1, illustrated is one embodiment of a shutter assembly 100 constructed according to the disclosed principles for use with a laser-produced plasma (LPP) device. The assembly 100 is included in the vacuum chamber of the LPP device (see FIG. 2) to reduce or eliminate debris produced by the radiation generating process from exiting the vacuum chamber with the generated X-rays. The assembly 100 includes a shutter 105 mounted on a rotating shaft 110, which is connected to a motor 115. As discussed in greater detail below, the motor 115 and shaft 110 are used to rotate the shutter 105 (as indicated by arrow A1) at a precise angular velocity selected to allow X-rays or other short-wavelength radiation to pass through the shutter 105, but block most or all of the unwanted debris from passing through the shutter 105. The shutter 105 includes a base 120 and a plurality of openings or apertures 125 created between multiple vanes or blades. The blades are held together and precisely spaced using spacers 130 placed between the blades and held together using fasteners, such as bolts 135. In some embodiments, the vanes may be constructed of metal for durability; however, in other embodiments the vanes may be constructed of plastic or other material. Moreover, construction techniques for the vanes/shutter can include cutting the component from a solid material, such as with an EDM device; however, even manufacturing technique may be employed. In accordance with the disclosed principles, the shutter 105 reduces or eliminates the amount of debris created through the laser irradiation process used to generate X-rays in the LPP device by timing the alignment of the apertures 125 with the X-rays to be collected at the output of the vacuum chamber. Specifically, when a laser is used to irradiate a target, such as copper tape, X-rays are generated from the plasma created by the irradiation of the target. In addition, debris from the irradiated target in the form of projectile or ballistic particles is also generated at the radiation source. However, since the X-rays travel much faster than the ballistic debris, the rotation of the shutter 105 is timed so that the X-rays will pass through the apertures 125 in the shutter 105 at the desired time. But the rotation of the shutter 105 is also timed so that after the X-rays pass through the apertures 125, the shutter 105 turns to obstruct the ballistic debris traveling in the same or similar direction as the collected X-rays. Thus, this debris impacts the blades of the shutter 105 and most if not all of it cannot reach the output of the chamber where the X-rays were collected. In the illustrated embodiment, to time the rotation of the shutter 105 with the laser ablation process, a synchronization device having a blade 140 is formed on the rotating base 120. In this approach, a photodetector 145 receives a light or laser beam 150, and the blade 140 interrupts the beam 150 at a given point during the rotation of the shutter 105. Thus, the firing of the laser generator that irradiates the target material to create the X-rays (and the resulting debris) can be timed by when the blade 140 interrupts the beam 150. Of course, this timing adjustment also takes into account the speed of the X-rays and the debris, as well as the rotational velocity of the rotating shutter 105 and its distance from the radiation source. A more detailed example having such parameters is discussed with reference to FIG. 2. FIG. 2 illustrates a plan view of a vacuum chamber 200 of an LPP device, which provides an environment for implementing a rotational mechanical shutter as disclosed herein. The embodiment in FIG. 2 also illustrates a different embodiment of a rotational shutter 205 constructed in accordance with the disclosed principles. In this embodiment, the shutter 205 has a square shape and still includes apertures 210 created by the spacing of a plurality of blades. As before, the shutter 205 is configured to rotate (shown by arrow A1) on a shaft in order to align the apertures 210 with the output 215 of the vacuum chamber 200 at only desired times. In operation, as mentioned above, a laser 220 is generated from a source external to the vacuum chamber 200. That laser 220 is then directed and focused to precisely impact a target (not illustrated) to generate a radiation source 225. The radiation source 225 created by the irradiation process forms a plasma that generates X-rays 230, as well as debris 235. The debris 235 typically consists of particles of the target that have been ablated during the irradiation process. As illustrated, the rotation of the shutter 210 is timed with the irradiation process such that the desired X-rays 230 are allowed to pass through the apertures 210 of the shutter 205 to the output 215 of the chamber 200 to be collected and harnessed as needed. Since the generated X-rays 230 travel much faster than the generated debris 235, the rotation of the shutter 205 is also timed so that the apertures 210 no longer provide a line-of-sight between the radiation source 225 and the output 215 of the vacuum chamber 200 by the time that the debris 235 reaches the shutter. As a result, debris 235 with the same or similar trajectory as the X-rays 230 will not be permitted to pass through the shutter 205 to the output 215. Thus, most or all of this debris 235 will be prevented from exiting the chamber 200 at the point where the X-rays 230 are collected. Moreover, as the shutter 205 continues its rotation to allow the next batch of generated X-rays to pass through the apertures, the vanes or blades of the shutter 205 further work to brush or knock away debris 235 that may be lingering near the shutter 205 after its prior rotation obstructed the line-of-sight to the output 215. By obstructing the path of the debris 235, equipment and other components of the LPP device proximate to the output 215 of the chamber 200 will receive much less contamination by the debris 235. Accordingly, cleaning or replacement of these components is reduced or even eliminated. Maintenance time and costs on the LPP device may consequently be reduced by obstructing debris with a shutter constructed and operated according to the disclosed principles. In the embodiment illustrated in FIG. 2, the shutter 205 is again constructed in the shape of a square and, in this example, has dimensions of approximately 2 cm on all sides. Of course, other sizes and shapes for a shutter constructed as disclosed herein may be utilized. Moreover, in the illustrated embodiment of FIG. 2, the shutter 205 is located 200 cm from the radiation source 225. By taking into account these dimensions, as well as other parameters of the X-ray generation process, the precise rotation of the shutter 205 needed to perform as disclosed herein can be easily calculated. For example, if a source laser 220 and target are selected such that X-rays 230 of about 5 mrad are generated, the X-rays 230 are transmitted at the speed of light (3.0×1010 cm/sec). In addition, if the debris 235 from this particular ablation process is determined to be traveling at approximately 105 cm/sec or slower, then the rotation of this embodiment of the shutter 205 (e.g., having apertures 210 that are approximately 1.2 mm wide and lengths of 2 cm in this example) may be calculated to be about 0.06 radians in 2 ms. Through conversion, in order to travel 0.06 radians in 2 ms, it is determined that the shutter 205 should be rotated at about 5 Hz, or 300 rpm. With these parameters, the shutter 205 should be capable of blocking about 90% of debris 235 traveling at this velocity at the outer edges of the shutter 205, while blocking about 100% of such debris 235 at the center of the shutter 205. In other examples, where faster debris is present, the rotational speed of the shutter 205 can be adjusted. For example, for debris traveling at a velocity of 106 cm/sec, it is determined that the rotation of the shutter 205 should be about 3000 rpm, rather than the previous 300 rpm. Of course, as the rotation of the shutter 205 is adjusted, so too can the timing of the firing of the source laser beam 220 used in the ablation process be adjusted to work in tandem with the debris shutter 205. Turning finally to FIGS. 3A and 3B concurrently, illustrated is another embodiment of a shutter assembly 300 constructed according to the disclosed principles. This embodiment provides a “wheel” type shutter 305 that differs from the embodiments discussed above with reference to FIGS. 1 and 2. As before, the shutter 305 is again mounted on a rotating shaft 310 at the center of the shutter 305. In this embodiment, the shaft 310 is coupled to an encoded motor 315 that is configured to rotate the shutter 305 at the precise, needed velocity. More specifically, rather than including the blade and photodetector used in the embodiment of FIG. 2 for synchronizing the laser ablation process with the rotation of the shutter, the encoded motor 315 may be employed to provide such alignment and timing. Once aligned, a laser 320 is fired at a target to generate a radiation source, as discussed above. The generated X-rays 325 travel from the radiation source to the exit or output 335 of the chamber. As seen from the figures, the shutter 305 is rotated so that the X-rays 325 are permitted to travel through rotating openings or apertures 330 in the shutter 305 to the output 335 of the chamber. This embodiment of the shutter 305 includes apertures 330 that are radially arranged within the shutter 305, and extend through its center. With this arrangement, as the shutter 305 rotates about its center, the apertures 330 provide a line-of-sight between the radiation source and the output 335 of the vacuum chamber. Moreover, although only three apertures 330 are illustrated extending through the diameter of the shutter 305, it should be noted that any number of apertures 330 may be included in the shutter 305. The rotation of the shutter 305, and consequently the alignment of the apertures 330 with the path of the X-rays and blocking of debris, may then be adjusted to account for the change in the number apertures 330 provided in the shutter 305. It will be appreciated by those of ordinary skill in the art that the invention can be embodied in other specific forms without departing from the spirit or essential character thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all changes that come within the meaning and ranges of equivalents thereof are intended to be embraced therein. Additionally, the section headings herein are provided for consistency with the suggestions under 37 C.F.R. § 1.77 or otherwise to provide organizational cues. These headings shall not limit or characterize the invention(s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings refer to a “Technical Field,” the claims should not be limited by the language chosen under this heading to describe the so-called technical field. Further, a description of a technology in the “Background” is not to be construed as an admission that technology is prior art to any invention(s) in this disclosure. Neither is the “Summary” to be considered as a characterization of the invention(s) set forth in the claims found herein. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty claimed in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims associated with this disclosure, and the claims accordingly define the invention(s), and their equivalents, that are protected thereby. In all instances, the scope of the claims shall be considered on their own merits in light of the specification, but should not be constrained by the headings set forth herein. |
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description | The present invention relates to a bag house for filtering dust and other particles from a gaseous exhaust from, for example, a combustion system. Specifically, the present invention is related to control and monitoring systems for a bag house. Bag houses filter dust and other gas borne particles from exhaust gas, such as flue gases from combustion systems. A bag house typically has an array of filter bags. The bag house ducts exhaust through the filter bags. As gas passes through the filter bags, dust and other particles are captured on the surfaces of the media of the filter bags. The buildup of dust and particles on the filter bags continues as the bag house filters dust from the exhaust air. The buildup of dust and particles on the filter bags eventually clogs the porous media of the filter bags and obstructs the flow of exhaust gas through the bag house. Mechanisms are employed to remove the buildup from bag filter, such as agitators that shake the bags to cause the dust and particles to fall off the bags. In addition or as an alternative to, the bag filters may be cleaned by pulse jets that pulse air jets to the interior of the bag to apply an impulse to the bag that knocks off the dust and particles. However, these mechanisms do not entirely open the porous openings in the media of the bag filters. Even with periodic cleaning operations, the bag filters become clogged and unsuitable after prolonged use in a bag house. Bag filters are conventionally assigned an operational life by the manufacturer of the bag. The operator of the bag house replaces the filter bags before they reach the end of their operational life. The assigned operational life of a bag filter is conventionally a fixed period. The assigned operational life may be assigned by bag filter manufacturer and is based, in part, on the type of bag house into which the filter is to be used. The assigned operational life is based on assumptions of the operating conditions in the bag house. The operating conditions in a bag house may vary depending on ambient conditions, the composition of the mixture of exhaust gas, dust and other particles passing through the bag house and other factors. These variations in operating conditions affect the actual operational life of the bag filters. The assigned operational life does not vary and thus does not account for variations in the actual operation life of a bag filter. At the expiration of the assigned operational life, the bag filter is typically replaced regardless of whether there is remaining actual operating life of the filter. Bag filters having an expired actual operating life may remain in use in a bag house because the assigned operational life of the filter. Similarly, bag filters having an expired actual operating life may remain in use in a bag house because the assigned operational life of the filter has not expired. A method has been developed for dynamically determining a remaining actual operational period for a filter in a filtration device including: determining an initial remaining operational period based on an installation date of the filter and an initial expected operational period; periodically determining a remaining actual operational period of the filter based on the initial remaining operational period based and an elapsed operational period from the installation date; monitoring at least one operating parameter in the filtration device; adjusting the remaining actual operational period based on the monitored operating parameter, and continuing to periodically determine the remaining actual operational period based on the adjusted remaining actual operational period and the elapsed operational period. A method has been developed for dynamically determining a remaining operational period for a bag filter in a bag house comprising: determining an initial remaining operational period based on an installation date of the bag filter and an initial expected operational period; periodically determining a remaining operational period of the bag filter based on the initial remaining operational period based and an elapsed operational period from the installation date; monitoring at least one operating parameter in the bag house; adjusting the remaining operation period based on the monitored operating parameter, and continuing to periodically determine the remaining operational period based on the adjusted remaining operation period and the elapsed operational period. A method for dynamically determining a remaining operational life a bag filter in a bag house having a controller, the method comprising: entering into the controller bag filter data and an installation date of the bag filter in the bag house; determining an initial bag filter life based on the bag filter data; decrementing the initial bag filter life to determine a remaining bag filter life and periodically decrementing the remaining bag filter life; monitoring a bag house operating condition, wherein the operating condition is at least one of temperature of an inlet gas flow to the bag house, a pressure differential across the bag filter and particulate level in a outlet gas flow from the bag house; adjusting the remaining bag filter life based on the monitored bag house operating condition and periodically decrementing the remaining bag filter life, and replacing the bag filter at a time based on the decremented, adjusted remaining operational period. An apparatus has been developed for dynamically determining a remaining operational life a bag filter in a bag house comprising: electronic storage containing data including an installation date of the bag filter, and data sufficient to determine an initial bag filter life; sensors monitoring a bag house operational condition which is at least one of temperature of an inlet gas flow to the bag house, a pressure differential across the bag filter and a particulate level in a outlet gas flow from the bag house; a computer controller including an executable program which counts down the bag filter life by decrementing the life based an operational period of the bag house to determine a remaining bag filter life and adjusts the remaining bag filter life based on the monitored bag house operational condition, and a user terminal indicating the remaining bag filter life. As an example, a sensor may be an exhaust gas opacity sensor in the outlet gas flow from the device, and the executable program adjusts the remaining filter life to reduce a difference between a sensed level exhaust gas opacity provided by the opacity sensor and expected opacity level. The expected opacity level is determined by the controller based on opacity data, such as a lookup table which correlates various periods of expected remaining life to various opacity levels. The opacity data is stored in the electronic storage correlating the expected opacity level to an operational period of the filter. FIG. 1 is a schematic view of a bag house 10 having internal bag filters 12. Exhaust gas 14 enters an inlet 16 to the bag house and is ducted through the bag filters. The exhaust gas enters a lower portion of the bag house and passes upward to the array of bag filters 12 hanging from the top of an interior chamber 18 of the bag house. Dust and particles collect and buildup on the outer surfaces of the bag filters. A bin 20 at the bottom of the chamber 18 collects the dust and particles that fall from the filter bags. The bags are periodically shaken by agitators 21, e.g., to remove the dust and particles from the filters. Exhaust gas passes into the bag filters and enter an exhaust duct 22 downstream of the filters. The exhaust gas, without the dust and particles, is exhausted from the bag house to the atmosphere or to further pollution control systems. A computer controller 24 monitors the operating conditions of the bag house 10. The computer controller includes a computer system having electronic storage having an executable program for monitoring the bag house and dynamically determining the operational life of the bag filters. A user interface 26 includes an input terminal through which data is entered to the controller by operators of the bag house. The user interface also includes a display or other output device to provide data regarding the operational life of the filter bags to the users. The data input to the terminal by the operator may include installation date of the bag filters 28, the assigned expected operational life of the bag filters 30, the bag material of the bag filters in the bag house 32, and the type 34, e.g., coal combustion particles, or composition of the dust and particles that are deposited on the bag filters. This data is used by the controller 24 and its program in dynamically determining the remaining life of the bag filters in the bag house. Sensors in the bag house collect data regarding the operation condition of the bag house. The sensors preferably includes a temperature sensor 36 determining the temperature of the exhaust gas entering the bag house, a particulate sensor 37, e.g., an opacity sensor, detecting a dust/particulate level in the exhaust of the bag house, and a differential pressure sensor 38 in the bag house, such as the pressure difference between the exhaust gas inlet and outlet of the bag house. The pressure differential indicates the amount of dust and particle buildup on the bag filters. Further, the pressure differential at a time promptly after the bags are agitated or pulsed with air indicates the pressure drop as the exhaust gas flows through the bags after the dust and particle deposits have been shaken off the bas. This pressure differential indicates the continued ability of the bags to filter out dust and particles without excessive pressure losses through the bag house. To remove dust and particles from the bag filters the controller periodically executes a cleaning mode program 40 which determines when to agitate or pulse the bag filters. In addition, the cleaning mode program 40 identifies when the bags have been agitated and thereafter prompts a differential temperature measurement to determine the pressure drop through the bag house attributable to the filter bags with minimal dust and particle buildup on the bags. The pressure differential data (which may be an analog signal from the pressure sensors) is stored in the bag house control system 24. The bag house controller 24 may collect and store data regarding other process conditions in the bag house and, optionally, in the combustion system or other gas generation system to which the bag house is attached. Data regarding the process conditions are provided by a process condition indication system 42. This system may, for example, detect when the gas generation system turns ON and OFF, when the gas generation system changes process conditions, and when the gas generation system inadvertently exhausts combustible materials, such as unburned fuel oil. The bag house controller 24 maintains counters 44 to track the remaining life of the bag filters and determine when to activate the agitators 21 to shake the dust and particles off of the bag filters. The counter for determining when to enter a cleaning mode may be based on cleaning cycle prescribed by the cleaning mode and cycle program 40. The counter for determining when the agitators are to be activated uses a cycle time from the cleaning mode and cycle program 40 and counts down until it is time to activate the cleaning mode. The bag life counter 44 determines when to replace the bag filters by decrementing the remaining actual life of the filters. For example, the bag life counter 44 may initially set the bag life to be equal to the expected bag life 30 input by the operator. The counter counts down the time to replacement of the bag filters based on the operational time of the bag house. The counter 44 counts down the time to when the bag filters should be replaced and thereby tracks the remaining life of the bag filters. The remaining actual life of the filters is determined based on the assigned operational life of the bag filter, the elapsed time, such as operational time, between the filter installation date and the current operational time, and adjustment one or more of filter life adjustments based on Accelerated Life Factors (ALF) that are applicable to the bag filters. The controller determines which of the ALFs are applicable. Based on the applicable ALFs, the controller determines an adjustment(s) to be made to remaining actual filter life. The determination of the applicable ALFs is based on input parameters, such as user inputs and sensor inputs, received by the controller. The controller 24 may adjust the remaining life of the bag filters based on operating conditions, such as the differential pressure (as measured by the pressure sensors 38) promptly after the bag filters are agitated, inlet temperature (as measured by the temperature sensor 38) to the bag house and other process conditions (see process condition indicator 42). The program stored and executed by the controller 24 may include an algorithm 45 to dynamically determine the bag life. An exemplary algorithm is (Eq. 1) below:BL=(Assign BL−Elapsed Operating Time)+Accelerated Life Factors(ALF). Eq. 1: Where, BL is remaining bag life; fabric material in a given process is considered in the base line Bag Life (BL). Temperature, pressure drop and cleaning frequency will drive the Accelerated Life Factors ALF. These factors will be driven based on the period of time that passes and the intensity of each. The ALFs are one or more operating factors that affect, such as by accelerating the aging of the installed filter bags. Temperature exposure, high pressure drop across the filters, frequency of cleaning and the cleaning intensity are examples of ALFs. These exemplary ALFs each independently accelerate the aging of the filters. The ALFs tend to be application and filter media dependent. In other words, the specific effect that each ALF has on the aging of the bag filter depends on the bag house application and the media used to form the filter. An adjustment factor for each of these specific ALFs is stored in the lookup table 46. The adjustment factor may be dependent on the ALF, the bag house application and the media of the bag filter. The controller determines which ALFs affect the bag house based on sensor and user inputs. The controller selects the adjustment factor(s) that correspond to the ALFs that influence the actual operational life of the bag filters. The lookup table 46 correlates input and sensor data to an appropriate adjustment factor for each of the ALFs. To determine the appropriate adjustment factor from the lookup table, the controller would input to the lookup table one or more of the selected ALFs, the bag house application, the filter bag media and data obtained from the sensors. The outputted adjustment factors are applied by the algorithm and controller to determine an adjusted actual operational life of the filters. The controller adjustment factors outputted by the lookup table indicate a period(s) of time to be added or subtracted from the actual operating life of the filters. The above algorithm, i.e., Equation 1, or other algorithm that accounts for the effects on bag life of at least one of bag house inlet temperature, bag house differential pressure or another process condition provides a means for the controller 24 to dynamically adjust the remaining bag life count down. Specifically, the bag life counter 44 is initialized with the installation date of the bag filters and at least one of the assigned operational life of the bag filters, the make and model of the bag filters or the material of the bag filters. The controller may access the electronic lookup table 46 stored in memory to determine the initial expected bag life, e.g., in days or weeks, of the bag filters. The controller initializes the bag life counter 44 based on the initial expected bag life and the installation date of the bag filter 28. The bag life counter begins to count down the remaining life of the bag filters based on the operating time of the bag house. For example, the bag life counter may decrement by one day the remaining life of the bag filters based on each 24-hour operation of the bag house. The remaining bag life may be displayed on the user interface. The bag life counter and controller may adjust the remaining bag life based on operational conditions of the bag house and other parameters, such as ambient conditions and process conditions in the combustion system upstream of the bag house. For example, the controller may apply the algorithm (Eq. 1) to increase or decrease the remaining bag life based on: (i) the inlet temperature to the bag house being above or below (Temp. Delta) an expected or baseline inlet temperature (for example an inlet temperature at least 10 degrees Celsius above a baseline temperature may decrease the remaining bag life by one day for each period of 12 hours that the inlet temperature is the high level). (ii) the pressure differential across the bag house inlet and exhaust being greater or less than an expected or baseline pressure differential (especially if the differential is determined promptly after a bag filter cleaning process. For example, if the pressure differential is greater than 20 percent of a base line pressure value for a period of two hours after a bag cleaning operation, the remaining bag life may be decremented by two weeks). (iii) the particulate level in the bag house exhaust is above or below a base line level (for example, days are added or subtracted from the remaining bag life to minimize a delta between the actual particulate level in the bag house exhaust and a baseline particulate level, where the baseline is a function, e.g., linear function, of remaining bag life). Alternatively, the electronic memory in the computer controller may store a lookup table which correlates various periods of expected remaining bag life to various opacity levels, and the lookup table is used to adjust the remaining bag life based, and (iv) the delta between an actual process condition and a base line condition over a period of time is applied to increase or decrease the remaining bag life (such as an actual moisture level in the inlet gas (see inlet 16) more than 20 percent above a baseline moisture level decreases the bag life by a day for each 24 hour period that the actual moisture level continues at such a high level). These factors (i) to (iv) are applied by the controller to dynamically adjust the remaining bag life as determined by the bag life counter. The counter continues to count down the remaining bag life and display the remaining life on the user interface. The counter may trigger the controller to send messages and alarms to the user interface as the remaining bag life decrements past certain periods, such as two months remaining of life, 2 weeks remaining of life, and bag life expired. The bag filters are preferably replaced at the expiration of the bag life period. The user interface may also report data collected from the operation of the bag house, such as data 50 showing temperature trends in the bag house, shutdowns of the bag house and in cleaning cycles. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. |
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abstract | Example embodiments disclose an apparatus for inspecting welds in a nuclear reactor. The apparatus may include a body, a rotatable pad on the body, a pair of opposing horizontal pads for moving the device in a vertical direction, a pair of opposing vertical pads for moving the device in a horizontal direction, and an inspection device. |
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052372332 | summary | TECHNICAL FIELD The present invention pertains to the field of optoelectronic devices. In particular, this invention pertains to an optoelectronic element comprised of a light source means, an optical control means and a photocell means intimately coupled together so that the optoelectronic element behaves like an active circuit element, such as a transistor or a diode. BACKGROUND ART It is well known that optical energy can be absorbed in a semiconductor material if the photon energy is greater than the band-gap energy of the semiconductor material. This phenomenon, known as the photovoltaic or photoconductive effect, occurs when the photons absorbed by the semiconductor material generate electron-hole pairs that produce a potential difference or increased conductance across the p-n junction of the semiconductor. The phenomenon has been used in the prior art to create a variety of hybrid optical/electrical devices. For a more detailed explanation of this phenomenon and its application, reference is made to J. Wilson and J. Hawkes, Optoelectronics: An Introduction, pgs. 286-327, Prentice Hall (1983). Most well known among the uses of the photovolatic/photoconductive effect is the use of a photodiode for generating electrical power, e.g., solar cells converting sunlight to electricity. Other variations of the basic photodiode include the avalanche photodiode and the phototransistor, both of which internally amplify the current flow across the p-n junction of the photodiode. The photodiode is also used as a photodetector for detecting the presence or absence of optical energy, e.g. the light beam switch in an elevator door or a photochopper wheel. Optoisolators make use of the photodiode and a photoemmissive device (e.g., a light emitting diode or LED) to convert electrical energy to photon energy and back again for the purpose of decoupling a power source or an electrical signal. For example, U.S. Pat. No. 4,695,120 shows the combined use of optoisolators to electrically isolate all of the signals to an integrated circuit and a photodiode to provide the electrical power for the integrated circuit. A detailed description of the various types of optoelectronic devices that are available in the prior art is provided in Optoelectronics Fiber-Optic Applications Manual, Hewlett Packard (1981), and Optoelectronics: Theory and Practice, Texas Instruments (1978). Another phenomenon that has been put to use in optical and hybrid optical/electrical circuit devices is the atomic level relationship between electrical fields and optical transmisivity, sometimes referred to as photorefractivity. Photorefractive substances exhibit a change in their index of refraction in response to the application of an electrical field. The most well known of photorefractive materials is the liquid crystal display or LCD. For a more detailed explanation of this phenomenon and its application, reference is made to Photorefractive Materials and Their Applications, Topics in Applied Physics, Vols. 61 and 62, Gunter, P. and Huignard, J. (eds.) (1989). For purposes of understanding the wide variety of electrical/optical devices that are available in the prior art with respect to the present invention, it is helpful to categorize present hybrid electrical/optical circuit devices based upon the nature of their inputs and outputs. Primary electrical/optical devices convert photon energy (input) to electrical energy (output) or vice-versa. Examples of primary types of hybrid electrical/optical devices include the photodiode (optical input/electrical output), the light emitting diode (electrical input/optical output) and the semiconductor laser (electrical input/optical output). Intermediary or secondary electrical/optical devices have a common input and output, but use either photon energy or electrical energy as part of an intermediary step internal to the device. Examples of intermediary or secondary types of hybrid electrical/optical devices include solid state image intensifiers and electroluminiscient devices (optical input/output, electrical intermediary) and photoisolators and optocouplers (electrical input/output, optical intermediary). Of interest for purposes of the present invention are those secondary or intermediary hybrid electrical/optical devices that utilize photorefractive materials as part of the intermediary step. Prior art application of photorefractive materials to hybrid electrical/optical devices has been limited to secondary devices having optical inputs and outputs with an electrical intermediary. The most prevalent uses of photorefractive materials include optical amplifiers, waveguides and light valves, such as liquid crystal light valves, which are used as part of an optical computing network. For example, U.S. Pat. No. 4,764,889 describes the use of optically nonlinear self electro-optic effect devices as part of an optical logical arrangement. U.S. Pat. No. 4,818,867 describes the use of an optical shutter on the output of an optical logic element. An overview of the various types of hybrid electrical/optical devices used in connection with prior art optical computing networks is provided in Feitelson, D., Optical Computing (1988). Although the use of photorefractive materials is well known as part of the intermediary step for electrical/optical hybrid devices having optical inputs and outputs with an electrical intermediary, photorefractive materials have not been used in connection with other types of electrical/optical hybrid devices having electrical inputs and outputs with an optical intermediary. The optical intermediaries of photoisolators and optocouplers are designed for the optimum transfer of photon energy between the photoemissive device and the photovoltaic/photoconductive element and, hence, there is no need for intermediary optical control in such devices. Accordingly, it would be desirable to provide an optoelectronic device that makes use of photorefractive materials as part of an optical intermediary for electrical/optical hybrid devices having electrical inputs and outputs that could take advantage of a modulated transfer function of the photon energy in such a device. SUMMARY OF THE INVENTION In accordance with the present invention, an optoelectronic active circuit element is comprised of a light source means, a photocell means and an optical control means. The light source means has at least one light emitting surface for emitting light energy in a specified frequency bandwidth and the photocell means also has at least one light collecting surface for absorbing light energy. The optical control means is intimately interposed between the light emitting surface of the light source means and the light collecting surface of the photocell means for controlling the emitted light energy that may be absorbed by the photocell means in response to an input signal. The light optical means is capable of either frequency or amplitude modulation of the emitted light energy as a result of changes in the indices of refraction and/or polarization of a photorefractive material. In the preferred embodiment, the photorefractive material is a liquid crystal display material or a lead lantium zirconium titinate material capable of fast switching speeds in response to small changes in an electrical input signal. In the preferred embodiment of the present invention, the light source means is self-powered by the use of a light emitting polymer as the light source means. The light emitting polymer is comprised of a tritiated organic polymer to which at least one organic phosphor or scintillant is bonded. Because the electrical energy generated by the preferred embodiment is dependent upon the rate of emission of photons from the light emitting polymer (which is in turn dependent upon the rate of beta-emissions from the radioisotope used to activate the light emitting polymer), the amount of photon energy available is essentially constant and determinable and is isolated from any electrical noise in the system. In addition to providing a unique source of electrical energy, as well as electrical signals, for CMOS, NMOS and other low power types of electronic circuitry, the output stability and isolation of the present invention makes it ideally suited for applications that require a voltage or current sources that have high signal to noise ratios. Accordingly, a primary objective of the present invention is to provide an optoelectronic active circuit element that includes an optical control means for controlling the amount of electrical energy generated by a photovoltaic cell by controlling the amount of light that is received by a photovoltaic cell from a light source. Another objective of the present invention is to provide an optoelectronic device that makes use of photorefractive materials as part of an optical intermediary for electrical/optical hybrid devices having electrical inputs and outputs and takes advantage of a modulated transfer function of the photon energy in such a device. A further objective of the present invention is to provide an optoelectronic active circuit element wherein the light source means is selfpowered by the use of a light emitting polymer as the light source means. Still another objective of the present invention is to provide an optoelectronic active circuit element that includes an optical control means capable of both amplitude and frequency modulation of the photon energy transmitted through the optical control means. A still further objective of the present invention is to provide an optoelectronic active circuit element having an optical control means comprised of an interference filter means and a photorefractive material in combination. These and other objectives of the present invention will become apparent with reference to the drawings, the detailed description of the preferred embodiment and the appended claims. |
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050842285 | claims | 1. Sealing device for an instrumentation column penetrating a head of a pressurized-water nuclear reactor vessel, inside a tubular follower fastened in a penetration opening of said head and projecting inwardly and outwardly from said head, having a tubular bearing unit fastened to an end of said follower situated outside said head and in its extension, in which a leaktight bearing area is provided for said instrumentation column traversing a bore of said tubular bearing unit and of said follower, and means for pulling on one end of said instrumentation column projecting outwardly from said bearing unit and resting on an end of said bearing unit, wherein said bearing unit has an end part in which is provided said bearing area of said instrumentation column and on which said pulling means of said instrumentation column rests, consisting of two successive sections in an axial direction, (a) a first section being fastened to an outer end of said follower and having an outer, peripheral annular throat and at least three openings traversing said first section in an axial direction so as to open into said throat; (b) a second section superposed on said first section and having openings in an extension of said openings of said first section and said bearing area of said instrumentation column; (c) a mounting piece consisting of two half-rings being introduced into said throat of said first section and comprising tapped openings in the extension of said openings of said first and second sections in assembled position where screws are introduced into coinciding openings of said first and second sections and screwed into said tapped openings of the mounting piece so as to assemble said first and the second sections, a sealing strip being placed therebetween. 2. Sealing device according to claim 1, wherein said means for pulling on an end of said instrumentation column consists of an annular pressure plate arranged about the upper part of the thermocouple column projecting above the upper surface of the upper section of the bearing unit, a traction ring with two parts which can be engaged laterally into a throat machined in the upper part of said thermocouple column, and at least three compression screws engaged in tapped holes axially traversing the compression plate and bearing with their heads against a bearing surface of the second section opposite the first section. 3. Sealing device according to claim 2, wherein each of said compression screws has, about its head, a washer having a deformable locking part intended to enter a cavity of the upper surface of said second section in order to lock the screw against rotation. 4. Sealing device according to claim 1, wherein the compression plate has through openings enabling access to the heads of the screws for assembling said first and second sections. 5. Sealing device according to claim 1, wherein said pulling means has four screws arranged at 90.degree. about an axis of said thermocouple column and about the penetration of said head of said vessel. 6. Sealing device according to claim 1, comprising four screws for assembling said first section and said second section of the upper part of said bearing unit. 7. Sealing device according to claim 1, wherein said first section is unitary, with a tubular mounting element of said bearing unit at the end of said follower situated outside said head of said vessel. |
041994043 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an enlarged view of a very small portion of a fuel pellet made according to the present invention. Area 10 is a relatively high-density (greater than about 95 percent of theoretical) uranium carbide particle. Fabrication and surface-area consideration dictate that the particle size, on the average, be greater than around 50 microns. This particulate region contains depleted or naturally occurring uranium. According to the invention, any fertile material, such as uranium-238 silicide, uranium-238 nitride, or uranium-238 oxide, can make up the particles. Since carbide fuels are noted both for high density and high swelling rate and are of interest in the American fast-breeder effort, it is thought that the beneficial characteristics of the invention will be exhibited most advantageously in a carbide fuel, so carbide is chosen for the preferred embodiment. In addition to the fertile component, fissionable uranium is also present in the particles because natural, and even depleted, uranium always has some U.sup.235 in it. For that matter, fissionable plutonium or other materials could be included in the particles; according to the invention, as much as 10 percent of the fissile content of the pellet may be contained in the particles. However, the advantages of the present invention are greatest when the fissile component of the particles is kept low, since it is desired that gaseous fission products not be produced in quantity in the high-density regions of the fuel. Uranium carbide in this particulate form makes up between 60 percent and 90 percent of the total volume of the pellet in the preferred embodiment. The remainder of the pellet, between 10 percent and 40 percent by volume, is made of uranium-238-plutonium carbide, a fissile-fertile blend, in the form of a low-density powder 12 having a stable microstructure. The powder is, by methods known to the art, to have a surface area fabricated greater than about 0.5 m.sup.2 /g. This insures an interconnected pore structure that will allow the fission gases to escape. The powder must be fine enough to fill in between the particles in a manner similar to that in which mortar fills in between bricks, because this will allow a relatively homogeneous particle-powder mixture. This is among the reasons why the particle size is specified as being greater than about 50 microns; a smaller particle size could result in too great a surface area to be covered by the powder. According to the invention, the density of the powder is less than 85 percent of theoretical density and contains 90 percent or more of the fissile material. In the preferred embodiment some fertile component is also included in the powder because the melting point of pure plutonium carbide is low and tends to decrease as the fuel is burned up. The addition of uranium both increases the melting point and decreases the effect of burn-up. In order to keep the sintering and temperature-dependent properties of the powder similar to those of a uranium ceramic powder, the fissile-component percentage of the powder should be less than about 40 percent, but to maintain a high enough total-pellet density, the percentage should be above 20 percent. The preferable percentage range is 25 percent to 35 percent. The addition of uranium also increases the amount of powder in the pellet, which is desirable because the powder has a greater tendency than the particles do to give under pressure, so the tendency of pellet chips to damage the clad is reduced. Another advantage of the fertile-fissile blend is that the uranium content, together with the stable microstructure, reduces the amount of diffusion of plutonium into the high-density uranium region and the diffusion of the uranium from the high-density region to the low-density region during use of the fuel. Thus, a fissile-fertile blend is preferred for the powder. It is to be noted that the term blend is used. This is because blend is thought to have no definite chemical meaning, and it can therefore be defined, for present purposes, to refer to a structure having a crystal structure like that of the fertile component (uranium-238 carbide) with some of the fertile atoms (U.sup.238) being replaced by fissile atoms (Pu). Such a structure has been described by several terms, such as alloy, solid solution, and even mixture, but it is thought that each of these terms may be chemically incorrect. The term blend is therefore used for want of a definitely correct term. Since it is necessary for the fission gases to escape, it is a requirement that the powder have a stable microstructure. This means that the pores must remain in the fuel during burnup. Experience in the art of fabricating fuel for conventional reactors has taught methods of producing fuels having stable microstructures, and successful practice of the present invention requires that now-conventional techniques for guaranteeing a stable microstructure be employed in the fabrication of the fuel pellets. The particles are generally made by agglomerating the fertile material, produced as a highly sinterable powder, into particles greater that about 50 microns in diameter. "Burnt" (not highly sinterable) powders of fertile-fissile material are mixed to a high degree of homogenity with the agglomerated fertile particles. This mixture is then pressed into pellets and sintered. The process is arranged to produce a pellet structure containing high-density particles of fertile material dispersed in a low-density powder of fertile-fissile material having a stable microstructure. It is possible for experienced practitioners of this art to arrange the process so that the particulate fertile-material regions have densities greater than about 95 percent of theoretical, while the powder regions have densities below about 85 percent. Through the use of the fuel pellet of the present invention, maximum effect can be given to the density of carbide fuels, and an associated decrease in cladding damage can be effected. |
summary | ||
053430484 | claims | 1. A contour collimator for shaping a radiation beam comprising: a holder; two sets of radiation-impermeable lamellae disposed in said holder, each lamella in each set being individually movable toward and away from a corresponding lamella in the other set; each lamella having a displacement element engager; two spring means, coupled to and respectively acting on said two sets of lamellae, for generating a spring force for normally urging all lamellae in a set toward the lamellae in the other set; two displacement elements respectively engaging said displacement element engagers of said lamellae in said sets of lamellae; and two user-manipulable means, on which said displacement elements are respectively mounted, operable in a first manner for moving said displacement elements so as to collectively displace said sets of lamellae away from each other against said spring force and operable in a second manner for releasing said sets of lamellae so as to permit said spring force to act thereon and urge all lamella in a set toward the lamella in the other set. 2. A contour collimator as claimed in claim 1 wherein each spring means comprises a plurality of springs corresponding in number and uniquely allocated to the lamellae in a respective one of said two sets of lamellae. 3. A contour collimator as claimed in claim 2 wherein said spring means comprises a plurality of thrust rods respectively interacting with each spring and the lamella allocated thereto, each spring forcing a thrust rod against its allocated lamella. 4. A contour collimator as claimed in claim 1 further comprising means for clamping said lamellae in said sets of lamellae in a selected position upon said lamellae being released by said user-manipulable means. 5. A contour collimator as claimed in claim 4 wherein said means for clamping comprises movable lateral walls of said holder, and means for moving said movable lateral walls toward and away from said lamellae in said sets. 6. A contour collimator as claimed in claim 5 wherein said movable lateral walls are movable independently of each other. 7. A contour collimator as claimed in claim 1 wherein each lamella has a slot forming said displacement element engager, and wherein each displacement element consists of a pin extending through the respective slots of all lamellae in a set. 8. A contour collimator as claimed in claim 7 wherein each user-manipulable means includes a lever, on which said pin is mounted, and a rotatable cam interacting with said lever to move said pin to displace and to release said lamellae. 9. A contour collimator as claimed in claim 1 further comprising a form-holding plate including means for securing a form between said two sets of lamellae. 10. A contour collimator as claimed in claim 9 wherein said form-holding plate includes index means for defining alignment of said form-holding plate relative to said holder. 11. A contour collimator as claimed in claim 9 wherein said form-holding plate includes positioning means for defining alignment of a form, when secured in said means for securing, relative to said holder. |
053234405 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing a general structure of an X-ray exposure apparatus of the present invention. Radiation light 101 emanates from a light source device such as a synchrotron, for example, and is diffracted and expanded by a mirror 102 having a large curvature radius. Then, it goes through a window 104 of an exposure chamber 103 and a mask 105, such that a wafer (semiconductor wafer) 106 placed on a wafer stage 107 is exposed. With this exposure, one of the processes for manufacture of semiconductor devices on the wafer 106 proceeds. Accumulated dose detecting means 108 is disposed adjacent to the circumferential portion of the mask 105 so as to detect the accumulated dose of the mask 105. FIG. 2 is a side view of the mask 105 of FIG. 1. Mask supporting film 202 is held by a mask supporting member 203, and a mask pattern provided by a mask absorbing material 201 is formed on the supporting film 202. The mask supporting member 203 is mounted onto a mask reinforcing member 204. The reinforcing member 204 has on its side a record of mask identification (mask ID) 205 representing an identification number of the mask 105, in the form of pattern information such as a bar code, for example. FIG. 3 is a block diagram of the accumulated dose detecting means 108. FIG. 4 is a block diagram of a storing means 305 of FIG. 3. The accumulated dose detecting means 108 comprises a mask ID reader 301 for reading the mask ID 205 recorded on the mask 105; an X-ray detector (detecting means) 303 for detecting the strength of X-rays of the exposure light; exposure apparatus operational unit 304 for calculating the accumulated dose of the mask 105 in accordance with the detection by the X-ray detector 303; a storing device (storing means) 305 for memorizing the accumulated dose of each mask 105; a display means 306 for displaying the accumulated dose of each mask 105; and mask history record controller (control device) 302 for receiving outputs of these components and controlling their operations as well as checking various operations of the exposure apparatus. The detection of the dose of the mask 105 in this embodiment can be carried out in the manner as disclosed in Japanese Laid-Open Patent Application, Laid-Open No. 3-53199. The operation to be made in the exposure process in accordance with this embodiment will now be explained. As a mask 105 is placed in the exposure chamber 103, the mask ID 205 of the mask 105 is read by the mask ID reader 301. In response, the mask history record controller 302 recognizes the mask ID 205 and reads out the accumulated dose memorized in the storing means 305 in relation to the mask ID 205. In response to a start of the exposure operation, the dose in each exposure is detected. The X-ray detector 303 detects the strength of the X-rays not passing through the mask 105, prior to the setting of the mask 105, as well as the strength of the X-rays passed through the mask 105, after the setting of the same. The results are outputted to the exposure operational unit 304. Now, the i-th exposure of the mask 105 will be considered. If the X-ray strength before passing through the mask 105 is Iie0 and the X-ray strength after passing through the mask 105 is Iie1, then the X-ray strength Ii absorbed in this exposure by the mask 105 is Iie0-Iie1. The exposure apparatus operational unit 304 calculates this X-ray strength Ii and outputs the same to the mask history record controller 302. In response and from the X-ray strength Id and the exposure time Ti of the i-th exposure, the mask history record controller 302 calculates the exposure amount Di (=Ii.times.Ti) and adds the same to the accumulated dose accomplished up to the (i-1)-th exposure to thereby determine the accumulated dose Z of the mask 105. Subsequently, it signals to the storing device 305 the mask ID 205 and the accumulated dose Z together with an accumulated dose rewriting command. Also, it signals to the display 306 the mask ID 205 and the accumulated dose Z. In response, in the storing device 305, the accumulated dose memorized in relation to the mask ID 205 therein is rewritten into Z. On the other hand, in the display means 306, the mask ID 205 and the accumulated dose Z are displayed. Referring now to FIG. 4, the writing and reading operation in the storing device 305 will be explained. As shown in FIG. 4, the storing means 305 comprises a magnetic recording head 401, a magnetic recording medium 402, a reproducing magnetic head 403 and a storing means controller 404 for controlling the writing and reading operation. In response to the reception of the accumulated dose reading command and the mask ID 205 as outputted from the mask history record controller 302, the storing means controller 404 causes the reproducing magnetic head 403 to read out the accumulated dose having been recorded in the magnetic recording medium 402 in relation to the mask ID 205, and supplies it to the mask history record controller 302. Also, if the mask ID 205 and the accumulated dose Z are inputted together with an accumulated dose rewriting command as outputted from the mask history record controller 302, the accumulated dose having been recorded in the magnetic recording medium 402 in relation to the mask ID 205 is rewritten into Z through the recording magnetic head 401. Since in the display 306 the accumulated dose Z of the mask 105 is displayed together with the mask ID 205, an operator can easily recognize the timing of replacement of the mask. Such mask replacement may be made automatically in accordance with the accumulated dose. FIG. 5 is a flow chart showing an example wherein the mask replacement can be done automatically. As a mask 105 is set, its mask ID 205 is read (step S1). After this, the exposure operation is effected (step S2). Then, the accumulated dose Z of the mask 105 is calculated (step S3) and the accumulated dose for the mask ID 205 as memorized in the storing means 305 is rewritten (step S4). Then, discrimination is made by the mask history record controller 302 as to whether the accumulated dose Z is greater than a predetermined allowable dose (step S5). If not, the subsequent sequence operation (exposure, stepwise movement, etc.) is carried out (step S7). If so, on the other hand, a mask changing means (not shown) is actuated to replace the mask 105 by a new one (step S6) and, thereafter, the subsequent sequence operation is effected. A second embodiment of the present invention will now be explained. In this embodiment, the X-ray detector 303 shown in the block diagram of FIG. 3 is omitted and only the exposure apparatus operational unit 304, the mask history record controller 302 and the storing means 305 are used. Therefore, explanation will be made by reference to FIGS. 2 and 3, using the same reference numerals. In the first embodiment, the X-ray quantity absorbed by the mask 105 is calculated on the basis of a change in the X-ray strength detected by the X-ray detector 303. In the present embodiment, as compared therewith, the X-ray quantity is calculated on the basis of the wavelength characteristic I(.lambda.) of the X-ray strength of the radiation light 101 as well as the materials of the mask absorbing medium 201 and the mask supporting film 202. Here, the materials of the mask absorbing medium 201 and the mask supporting film 202 are denoted by k1 and k2, respectively. The thickness of the former is denoted by d1 and that of the latter is denoted by d2. Also, the section along a plane A--A' in FIG. 2 is taken as an x-y plane, and such a function S(x,y) which presents "1" if the mask absorbing material 201 is present on the x-y plane and which presents "0" if no mask absorbing material is present on that plane, is determined. If the wavelength characteristics of X-ray absorptivities of the materials k1 and k2 are .mu.k1(.lambda.) and .mu.k2(.lambda.), respectively, and the exposure time is T, then the X-ray strength Ii as absorbed by the mask 105 in the exposure time T can be calculated in accordance with the following equation: ##EQU1## The mask history record controller 302 of this embodiment stores the wavelength characteristic I(.lambda.) of the X-ray strength as above into an inside memory thereof, and the storing means 305 records on the magnetic recording medium 402 (FIG. 4) the data of the materials k1 and k2, thicknesses d1 and d2 and the function S(x,y) as well as the wavelength characteristics .mu.k(.lambda.) of various materials, in the form of a table. The mask history record controller operates to cause the exposure apparatus operational unit 304 to calculate, on the basis of various data as memorized and the exposure time Ti, the exposure amount Di (=Ii.times.Ti). Additionally, it causes the operational unit to calculate .epsilon.Di (n is the number of exposures having been made to the mask 205), whereby the accumulated dose Z is obtained. Subsequently, the mask history record controller 302 applies the accumulated dose Z and the mask ID 205 to the storing means 305 and the display 306, to cause the former to rewrite the memorized data and to cause the latter to display information. As described, the detecting means of this embodiment is constituted by the mask history record controller 302 which also serves as a control means, the storing device 305 which also serves as a storing means, and the exposure apparatus operational unit 304. FIG. 6 is a block diagram showing the general structure of a third embodiment of the present invention. Mask 601 of this embodiment accommodates a static random access memory (SRAM) 702 (FIG. 7) which is used as the storing means 305 of the first embodiment. It is connectable with a mask history record controller 603 through an input/output element 602. The structure and operation of the remaining part of this embodiment, such as an X-ray detector 604, an exposure apparatus operational unit 605 and a display 606, are essentially the same as that of the X-ray detector 303, the exposure apparatus operational unit 304 and the display 306 shown in FIG. 3. Therefore, detailed explanation of them is omitted here. The SRAM 702 accommodated in the mask 601 is power-supplied from a backup voltage source 703 such as a lithium battery, for example, shown in FIG. 7. It can be connected to the input/output element 602 shown in FIG. 6 through a wiring means 701. FIG. 8 is a perspective view showing the general structure of the mask 601, and FIG. 9 is a perspective view showing the structure of the input/output element 602. The SRAM 702 and the voltage source 703 are embedded in a mask reinforcing member 801 which is a constituent element of the mask 601. The reinforcing member 801 has a recess formed in its outer circumferential portion, and a plurality of electrodes 802 to be connected to corresponding terminals of the SRAM 702 through the wiring means 701 are provided on the bottom of the recess. The input/output element 602 has a convex shape suited to engage with the recess of the mask reinforcing member 801, and it can be coupled to the mask reinforcing member 801 by means of a locking mechanism (not shown). Electrodes 901 are provided at the top of the input/output element 602 so as to engage with corresponding electrodes 802, respectively. By means of a wiring means 902 connected to these electrodes 901, they can be connected to the mask history record controller 603. The mask history record controller 603 can be connected to the SRAM 702 through these wirings 701 and 902 as well as the electrodes 802 and 901, for read-out or rewriting of a record memorized in the SRAM 702. The operation of this embodiment will now be explained. The SRAM 702 accommodates four 8-bit addresses and has a 1024-bit memory region. The mask history record controller 603 recognizes the quotient "b" obtained by dividing the allowable accumulated dose P by "1024", as the dose corresponding to one bit. As an exposure is effected, it reads out the bit number B recorded in the SRAM 702. Subsequently, by multiplying the read bit number B by the dose b corresponding to one bit, the mask history record controller calculates the accumulated dose having been accomplished up to the preceding exposures. After this, like the first embodiment, the amount of "current exposure" as obtainable from the X-ray detector 604 and the exposure operational unit 605 is added to the accumulated dose, and the sum is compared with the allowable dose P. If the accumulated dose is less than the allowable level P, the quotient obtained by dividing the accumulated dose by the dose b corresponding to one bit is memorized into the SRAM 702, and this is displayed in the display 606. When, after this, the mask 601 is replaced by another, the content of the memory of the SRAM 702 is cleared. In the present embodiment, as described, a memorizing means is incorporated into a mask 601. Thus, there is no necessity of recording a mask ID or using a reader to read the mask ID. As a result, it is possible to make the structure simple. In the second embodiment, the accumulated dose is displayed. In the third embodiment, the result of a comparison of the accumulated dose with the allowable level is displayed. However, as with the first embodiment, the device may be used in combination with a mask changing means to allow automatic mask replacement. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. |
description | This invention relates to X-ray diffraction systems. X-ray diffraction is a non-destructive technique for the qualitative and quantitative analysis of crystalline material samples, which are generally provided in the form of crystals or powders. In accordance with this technique, an X-ray beam is generated by an X-ray tube with a stationary anode, by a conventional rotating anode X-ray source or by a synchrotron source and directed toward the material sample under investigation. When the X-rays strike the sample, they are diffracted according to the atomic structure of the sample. A typical laboratory system 100 for performing single crystal diffraction experiments normally consists of five components as shown in FIG. 1. The components include an X-ray source 102 that produces a primary X-ray beam 104 with the required radiation energy, focal spot size and intensity. X-ray optics 106 are provided to condition the primary X-ray beam 104 to a conditioned, or incident, beam 108 with the required wavelength, beam focus size, beam profile and divergence. A goniometer and stage 110 are used to establish and manipulate geometric relationships between the incident X-ray beam 108, the crystal sample 112 and the X-ray detector 114. The incident X-ray beam 108 strikes the crystal sample 112 and produces scattered X-rays 116 which are recorded in the detector 114. A sample alignment and monitor assembly comprises a sample illuminator 118, typically a laser, that illuminates the sample 112 and a sample monitor 120, typically a video camera, which generates a video image of the sample to assist users in positioning the sample in the instrument center and monitoring the sample state and position. In order to increase the X-ray intensity at the crystal sample, focusing optics are routinely used. The X-ray beam path 200 of a typical single crystal diffraction set-up is schematically shown in FIG. 2. In this set-up, a multi-layer focusing X-ray optic 202 is used. Optic 202 has a focusing surface that is part of an ellipse, schematically shown as 204 in FIG. 2. An X-ray source 206 is placed at a first focal point of optic 202. This source generates X-rays 208 that are redirected by optic 202 to form a focused and redirected beam 210, which is focused on an image 212 at the second focal point. The sample is placed at the position of the image 212. The source and image focal points are located at distances f1 and f2 from the middle of the optic 202, respectively. Most applications require an X-ray beam that is large enough to completely illuminate the sample. Single crystal diffraction systems are thus designed to produce an image at the sample location with a size, or diameter, that is comparable in size to the dimension of a typical sample, which is a few tenths of a millimeter. However, some applications require much smaller image sizes. For example, in some applications, diffraction data produced from only a part of the sample must be obtained. Such local analysis could be needed if the sample contains different parts with different properties. To study these parts separately, the sample must be illuminated with a beam image smaller than the sample. In particular, a method to make a beam with an image size smaller than 0.1 mm is thus desired. Traditionally, X-ray image size is made smaller by placing apertures in-between the X-ray optic and image focal point. This is routinely done in commercial diffraction equipment, such as the X8 Proteum X-ray diffraction system manufactured and sold by Bruker AXS Inc., Madison, Wis. In the simplest case, one aperture is placed close to the image focal point, as shown in FIG. 3. In this set-up 300, aperture 214 has been added to the set-up illustrated in FIG. 2. The resulting beam 218 is smaller than the original beam (shown as dotted lines 216). The beam image can be made smaller and smaller by using smaller and smaller apertures, but there is a limit. For an infinitely small aperture the image size of the image 212 is determined by the distance (x) between the aperture 214 and the image focal point times the beam divergence. Ray-tracing illustrates the limitations of an aperture to reduce the image size. The X-ray flux and beam size (at the image focal point) were calculated for a range of aperture diameters and are shown in FIG. 4 for two aperture distances: x=20 mm and x=30 mm. In these calculations, the flux numbers have been normalized. In the calculations, an optic with f1/f2=100 mm/300 mm, a divergence of 4.5 mrad and a source diameter of 0.1 mm were assumed. These parameters are typical for protein single crystal diffraction systems and represent a realistic situation. The results show that an aperture is capable of reducing the image size, but only for large sized beams. For smaller sized beams, the flux quickly reduces and image sizes beyond a minimum size are not practical because the flux is so low. Positioning the aperture closer to the sample extends the range of image sizes, but this range is also limited because of practical reasons. Some space between aperture and sample must be kept clear, for example, to accommodate an additional aperture to block scattered radiation or to allow for handling of the sample. Consequently, the aperture cannot be placed exactly at the sample (x=0). Accordingly, there is a limit on the smallest image size. The image size can be reduced further by the introduction of a second aperture, as illustrated in the arrangement 500 shown in FIG. 5. This aperture 220, placed close to the X-ray optic 202, reduces the divergence and thus the intensity of the beam 210. With a reduced divergence, the aperture 214 close to the image area 212 is much more capable of reducing the image size. FIG. 6 shows ray-tracing results of the arrangement shown in FIG. 5, with two optimized apertures using the same parameters as in FIG. 4. As can be seen in FIG. 6, the introduction of a second aperture does enable the generation of smaller sized beams, but the beam flux quickly diminishes. In the ideal case, a one-aperture system reduces only the size and not the intensity of the beam whereas a two-aperture system reduces both the size and intensity. The end effect of the combined apertures is that the flux in a small sized beam is not reduced by the square of the reduction in the beam diameter (as would be the ideal case shown by the dotted line in FIG. 6), but by the fourth power. This quickly leads to a flux too small to be useful in case of beam images smaller than 0.1 mm. Another conventional method for producing a small image size is to use a small source size. For example, in FIG. 2, the optic 202 magnifies the source 206 with a magnification factor M=f2/f1. If the source 206 has a size S the resulting beam image A at the sample 212 is then M times S (A=MS). Consequently, the beam image size can be made small by reducing the source size, S and using a low magnification, M. In one prior art device, a micro-focus tube is combined with a focusing optic with a magnification of one. The small source of a micro-focus tube produces a small beam, but the X-ray beam brightness at the sample is only slightly larger than a conventional sealed tube using apertures. Consequently, a method to make beams that are both small and intense is thus desired. In accordance with the principles of the invention, a high brightness source, such as a rotating anode generator, is combined with demagnification X-ray optics to produce a beam with small image size and high-intensity. In one embodiment, an elliptical X-ray optic is positioned relative to the source and image focal points so that the magnification of the optic is less than one. In another embodiment, apertures are used either at the entrance or the exit of the optic in order to reduce beam divergence. In yet another embodiment, apertures are used near the sample focal point in order to further limit the beam image size. In still another embodiment, slits and apertures can be located along the beam path in order to remove scattered radiation. In accordance with the principles of the invention, a high brightness source, such as a rotating anode generator, is combined with demagnification X-ray optics to produce a beam with small size and high-intensity. In particular, modern rotating anode X-ray generators (RAGs) are much brighter than micro-focus sources and are thus preferred as a source. However, the source size of a RAG is significantly larger than the source size of a micro-focus source. Consequently, a RAG source must be combined with de-magnifying optics in order to produce a system that has both small beam size and high intensity. Such an arrangement is shown in FIG. 7. In this arrangement, the X-ray optic 202 has been repositioned relative to the source 206 and the image focal point 212 so that the magnification (M) of the X-ray optic 202 is less than one (M<1). With this arrangement, the beam image 212 size is smaller than the source 206 size and can be smaller than the sample 222. FIG. 8 shows ray-tracing results of a source-optic combinations with different optic magnifications. As in FIGS. 4 and 6, two aperture distances: x=20 mm and x=30 mm are illustrated. In the calculations, the flux numbers have been normalized and an optic 202 with f1/f2=300 mm/100 mm, a divergence of 4.5 mrad and a source diameter of 0.1 mm were assumed. As with the arrangements using apertures, the source-optic combination in FIG. 7 provides very small beam images but, as illustrated in FIG. 8, the beam flux is much larger. As shown in FIGS. 4 and 6, apertures are effective in producing beams with images down to typically 0.1 mm, but below this image size the inventive source-optic combinations provide superior beam image sizes. In another embodiment, if the beam image size obtained with the inventive arrangement is still not small enough, apertures placed close to the sample or at the exit of the optic can be used to make the beam image even smaller. In all the proposed situations scatter limiting slits or apertures can be used throughout the beam path. The following is an example in which a specially designed optic is used for local diffraction analyses with a small X-ray beam. The example involves retrieving diffraction data from an area with size A of 50 μm on a protein crystal with a size of 200 μm. The X-ray source used in the illustrative set-up has a size S of 100 μm. The anode is made from copper and produces Cu—Kα photons with energy of 8041 eV. The divergence of the beam must be small enough to resolve d-spacings up to 330 Å, which is reached for a divergence of 3.3 mrad, or less. These specifications are typical for local diffraction analyses of proteins using a modern rotating anode X-ray generator. To generate a beam with a 50 μm beam size at the sample, the X-ray optic must de-magnify the source by a factor of two. The following optic design fulfils the specifications: elliptically shaped optic with f1=200 mm and f2=100 mm, long ellipse axis a 150 mm, short ellipse axis b 3.2 mm and length L 15 mm. This arrangement is illustrated in FIG. 9. Note that this design satisfies the condition A=S f2/f1. The geometry is further chosen such that the resulting divergence is 3.3 mrad, satisfying the resolving power specification. The short ellipse axis is much smaller than the long ellipse axis and the ellipse focal points are therefore almost at the ellipse edges. The sum of the focal lengths therefore approximately equals twice the long ellipse axis: f1+f2≈2a. The actual ellipse is flatter than the ellipse shown in FIG. 9, which for clarity, is drawn with a different vertical scale. Finally, the optic is coated with a multilayer to increase the reflectivity and to monochromize the beam. The specially designed optic provides much more flux than another optic that requires apertures to reduce the beam size. FIG. 10 shows ray tracing results for the specially designed optic shown in FIG. 9 and a commercially available optic. The commercial optic has elliptical surfaces with f1=120 mm, f2=380 mm and produces a beam with a divergence of 3.3 mrad. In a first situation, the beam from the commercial optic is reduced in size with only one aperture positioned close to the crystal. In a second situation, an additional aperture is placed close to the optic exit. Different aperture sizes result in a different flux and beam size, which are shown in the graph as lines. To achieve the 50 μm beam size with the commercial optic, two apertures are required, as one aperture is not sufficient. The specially designed optic does not need any aperture to produce a 50 μm beam. In addition, the flux is five times larger than for the commercial optic. This much larger flux shows the benefit of an optic that is designed according to the described invention. While the invention has been shown and described with reference to a number of embodiments thereof, it will be recognized by those skilled in the art that various changes in form and detail may be made herein without departing from the spirit and scope of the invention as defined by the appended claims. |
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description | This application is a continuation of and claims priority under 35 U.S.C. §120 to application Ser. No. 11/002,677 “ROD ASSEMBLY FOR NUCLEAR REACTORS” filed Dec. 3, 2004, now U.S. Pat. No. 7,526,058, the entirety of which is incorporated by reference. 1. Field of the Invention This invention relates generally to nuclear reactors, and more particularly to a rod assembly for a nuclear reactor. 2. Description of the Related Art A continuing problem during operation of a nuclear reactor is the existence of debris of various sizes. Examples of such debris may include small-sized fasteners, metal clips, welding slag, pieces of wire, etc. The debris may be generated as a result of the original construction of the reactor core, subsequent reactor operation and/or due to repairs made during a planned or unplanned maintenance outage. During the operation of such nuclear reactors, the debris may be carried by the cooling water (reactor coolant) and may become wedged between or within reactor components such as fuel rods of a fuel assembly in a boiling water reactor (BWR) or pressurized water reactor (PWR), or in control rod assemblies in a PWR, etc. The repeated interaction between the entrained debris and component(s) can result in fretting damage to the component(s), such as damage to the fuel rods. Some of the debris may be caught between the fuel rods and other fuel assembly components. The debris vibrates in the moving coolant and interacts with the fuel rods, potentially causing what is known as fretting wear of the fuel rod cladding. This fretting may be recognized as a significant cause of failure of the fuel rod in a BWR or PWR, for example. Conventional solutions have included employing the use of debris filters to filter the debris from the reactor coolant. These are typically positioned in the lower tie plate or nozzle of a fuel assembly and so are replaced when the fuel is discharged. Debris filtering devices have also been introduced into the nuclear plant piping system. However, the debris filter and/or external filter mechanisms do not completely obviate the fretting problem in nuclear reactors. Fretting still may occur and cause fuel failures, which may release fuel, fission products or other rod contents into the coolant, potentially leading to the premature withdrawal from service of the fuel assembly or costly mid-cycle fuel replacement. Exemplary embodiments of the present invention are directed to a rod assembly for a fuel bundle of a nuclear reactor. The rod assembly may include an upper end piece, lower end piece and a plurality of rod segments attached between the upper and lower end pieces and to each other so as to form an axial length of the rod assembly. The rod assembly may include an adaptor subassembly provided at given connection points for connecting adjacent rod segments or a given rod segment with one of the upper and lower end pieces. The connection points along the axial length of the rod assembly may be located where the rod assembly contacts a spacer in the fuel bundle. One (or more) of the rod segments may include an irradiation target therein for producing a desired isotope when a fuel bundle containing one (or more) rod assemblies is irradiated in a core of the reactor. FIG. 1A illustrates an exemplary fuel bundle of a nuclear reactor such as a BWR. Fuel bundle 10 may include an outer channel 12 surrounding an upper tie plate 14 and a lower tie plate 16. A plurality of full length fuel rods 18 and/or part length fuel rods 19 may be arranged in a matrix within the fuel bundle 10 and pass through a plurality of spacers (also known as spacer grids) 20 vertically spaced one from the other maintaining the rods 18, 19 in the given matrix thereof. The fuel rods 18 and 19 with at least a pair of water rods 22 and 24 may be maintained in spaced relation to each other in the fuel bundle 10 by a plurality of spacers 20 provided at different axial locations in the fuel bundle 10 so as to define passages for reactor coolant flow between fuel rods 18, 19 in the fuel bundle 10. There may typically be between five to eight spacers 20 spaced along the entire axial length of the fuel bundle 10 for maintaining the fuel rods 18, 19 in the desired array thereof. Spacer 20 may be embodied as any type of spacer, for example, ferrule-type spacers or spacers of the type described and illustrated in U.S. Pat. No. 5,209,899. In FIG. 1A, the matrix may be a 10×10 array, although the illustrative fuel bundle 10 may have a different matrix array of rods 18, 19 such as a 9×9 array. The bundle 10 may include all full length fuel rods 18 and/or a combination of full 18 and part length 19 fuel rods, as is known. Each of the full length fuel rods 18 and part length fuel rods 19 is cladded, as is known in the art. The water rods 22 and 24 (two are shown, there may be more or less water rods in bundle 10) may be dispersed among the fuel rods 18, 19 in bundle 10, between the lower tie plate 16 and the upper tie plate 14. The water rods 22, 24 serve to transfer fluid from the lower regions of the nuclear fuel bundle 10 to the upper regions, where the water is dispersed through openings located at the top of the water rods, as shown. FIG. 1B illustrates a spacer to rod location in the fuel bundle 10 of FIG. 1A. In particular, FIG. 1B illustrates exemplary debris catching areas 50a-50d between a given fuel rod 18 and spacer 20 to show where debris might be caught or entrained so as to exacerbate the fretting problem. FIG. 1C illustrates a spacer to water rod location in the fuel bundle 10 of FIG. 1A and exemplary debris catching areas 50a-50e between a given water rod 22, 24 and spacer 20 to show where debris might become lodged or entrained so as to potentially causing fretting with an adjacent rod 18, 19. The water rods 22 and 24 are bound by a spacer 20. Spacer 20 is bound by a pair of radial directed flanges or tabs 34 and 36 which lie on opposite sides of the spacer 20, to maintain the spacer at the desired elevation. During reactor power operations, debris may be carried by the reactor coolant and may become lodged in and around the circumference of the water rods 22, 24 and spacer 20 within bundle 10. The repeated interaction between the entrained debris at spacer 20 and the water rods 22, 24 can result in the aforementioned fretting wear and potential damage to the adjacent rods 18, 19 and/or the water rods 22, 24. FIG. 2A illustrates a rod assembly 100 for a fuel bundle 10 in accordance with an exemplary embodiment of the invention. In an effort to provide a fretless rod designed so as to substantially eliminate fretting wear as described in a conventional art, there is described a rod assembly 100 (also occasionally referred to as a multi-segmented rod or multi-part rod) that includes a plurality of parts or cladded rod segments 110. As shown in FIG. 2A, a rod assembly 100 may include a plurality of rod segments 110 (two adjacent rod segments shown as 110a and 110b) between an upper end piece 120 and a lower end piece 130. The upper end piece 120 and lower end piece 130 may include threads to mate with the lower and upper tie plates of the fuel bundle 10 (not shown), as is known. Adjacent rod segments 110a, 110b may be interconnected to each other via at least one adaptor subassembly, shown generally as a subassembly 300 within the dotted line circle of FIG. 2A. Only one rod assembly 100 is shown in FIG. 2A, it being understood that one or more of the rod assemblies 100 shown in FIG. 2A may be inserted into a fuel bundle such as the fuel bundle 10 shown in FIG. 1A. Rod segments 110 may be attached between the upper and lower end pieces 120, 130 and to each other so as to form the entire axial length of the rod assembly 100. In an example, a rod segment 110a, a rod segment 110b and one each of the upper and lower end pieces 120, 130 may be connected by adaptor subassemblies 300 at connections points along the axial length of the rod assembly 100 where the rod assembly contacts spacers 20. Although only three spacers 20 and adaptor subassemblies 300 are shown in FIG. 2A for reasons of brevity, it should be understood that the fuel bundle 10 could include one or more rod assemblies 100, each having at least one rod segment 110a and at least one rod segment 110b connected by adaptor subassemblies 300 at any number of spacer 20 locations. The rod segments 110a, 110b may be fixed length segments to facilitate the manufacturing process. Similarly, the adaptor subassemblies 300 may also be manufactured at a fixed size so as to be of equal lengths. In this exemplary embodiment, the rod segments and adaptor subassemblies are constructed of a material which is corrosion resistant and compatible with the other reactor components. An exemplary material may be a zirconium alloy, for example. Desirably, a portion of each spacer 20 contacts the rod assembly 100 at each of the adaptor subassemblies 300 so as to substantially cover adaptor subassemblies 300 and/or connection points 115 between rod segments 110, or substantially covers an adaptor subassembly 300 or connection point 115 connecting a given rod segment 110 and one of the upper and lower end pieces 120 and 130. Accordingly, the consequences of fretting of the rod assembly 100 at these points 115 and/or adaptor subassemblies 300 within a given spacer 20 may be eliminated. While fretting may still occur, the fretting wear on the rod assembly 100 occurs on the adaptor subassembly 300, instead of on a segment 110a, b. Accordingly, this may eliminate to potential release of contents from within a given rod segment 10 to the reactor coolant. As shown in FIG. 13, which illustrates the multi-segmented fuel rod 100 of FIG. 2A. The multi-segmented fuel rod 100 is broken up into various segments 110A, 110B, 110C, 110D, 110E, 110F and 110G that connect to each other via a corresponding adaptor subassembly 300 at connection points 115 (as previously shown) to form a contiguous multi-segmented fuel rod 100′ (as evident by the dotted connection lines 111 in FIG. 13). FIG. 13 also illustrates enlargements of cross-sectional views I-VII of the target container 600 in each of segments 110A, 110C, 110E, 110F and 110G of the multi-segmented rod 100. Views I and II show a plurality of containment structures 600 within rod 100 that are housing multiple different targets, shown as a liquid, solid and a gas target 620 within a single rod segment 110A. Further, enlargements I and II illustrate indicia 650 that can be placed on the containment structures 600 within a given rod segment 110A, 110C, 110E, etc. As shown, the indicia 650 can indicate whether or not the target is in solid, liquid or gas form, and can also provide the name of the target isotope and/or the name of the isotope to be produced due to irradiation, for example (not shown in FIG. 13 for purposes of clarity). Rod segments 110B and 110D are shown to contain nuclear fuel 660, as shown in enlargements III and IV, for example. Of course in an alternative, multi-segmented rod 100 can be composed of a plurality of rod segments 110 in which no segment 110 includes nuclear fuel, as previously described. Enlargement V of rod segment 110e illustrates a container assembly 600 which includes a target that is in gaseous form. Enlargement VI of rod segment 110F illustrates a container assembly 600 within the rod segment 110f that includes a target 620 in liquid form. Enlargement VII of rod segment 110G illustrates a container assembly 600 which includes a solid target 620, shown as a single column of Co-59 BBs, which can be irradiated to produce the desire isotope, in this case, Co-60. Each of the container assemblies 600 can thus be prepackaged with the target 620 isotope material in solid, liquid or gas form, for insertion into a corresponding rod segment 110 of the multi-segmented rod 100, for example. Further, since each of the container assemblies 600 are sealed by end plugs 630 at one end 612 and by exterior threads 601 and an O-ring 602 at the first end 611 (as previously shown in FIGS. 6A, 6D and 6E), the removal of a particular segment 110 at its connection point 115 (i.e., at the disconnection of the adapter subassembly 300 at connection point 115 between two segments 110) will not cause a breach which would expose the irradiation target 620 to the reactor coolant. Thus, the container assembly 600′ together with the outer cladding of the rod segment 110 provides a double-walled containment for the irradiation target 620. FIG. 2A illustrates an exemplary adaptor subassembly 300 between adjacent rod segments 110a and 100b in transparent detail (i.e., phantom lines illustrate components within rod segments 110 and/or adaptor subassemblies 300) so as to show weld points 155 between an adjacent rod segment 110b and a part of the adaptor subassembly 300. FIG. 2A also illustrates (in phantom) an optional container assembly 600 provided within one or more of the rod segments 110 for applications described in detail hereafter. The rod segments may or may not include a container assembly 600 therein. Additionally, in FIG. 2A, there is illustrated an undercut portion or recessed break line 360. As will be described in further detail below, the recessed break line 360 provides an alternative location to break a particular adaptor subassembly 300/rod segment 110 in order to remove a particular rod segment 110 from the rod assembly 100, which may be desirable to reduce length in transport, etc., for example. FIG. 2B illustrates an exploded view of a portion of FIG. 2A to illustrate the rod assembly in further detail. Portions of FIG. 2B are also shown in phantom (dotted lines) to indicate components within an interior of a rod segment 110a, 110b or subassembly 300. The adaptor subassembly 300 may include a male adaptor plug 330 that is attached to a rod segment 110a via a weld at weld joint 155. Similarly, the adaptor subassembly 300 may include a female adaptor plug 350 which may be attached at one end to a rod segment 110b via a weld at weld joint 155. Both the male and female adaptor plugs 330, 350 may include a plurality of nut-shaped depressions 357 around an outer circumference thereof. In general, the depressions 357 may facilitate removal/disassembly of a given rod segment 110, upper end piece 120 or lower end piece 130 by a suitable tool during a maintenance outage, for example. In FIG. 2B, the depressions 357 may include recessed angled surfaces at opposite ends thereof, such as angle edges 380, to prevent damage to the spacer 20 during insertion or assembly of the rod assembly 100 into the fuel bundle 10 of the reactor. Further, as shown in dotted line form, each of the male and female adaptor plugs 330 and 350 may include weld alignment members 355 to facilitate inserting the corresponding adaptor plug 330, 350 into an end of a given rod segment 10 for welding the plug 330/350 to the segment 10 at the weld joint 155. FIGS. 3A and 3B are perspective and side-view profiles illustrating part of an adaptor subassembly for the rod assembly in accordance with an exemplary embodiment of the invention. As shown in FIGS. 3A and 3B, male adaptor plug 330 may be attached (such as by a weld) to rod segment 10 at a first end 332. A second end 334 of male adaptor plug 330 may be inserted into a corresponding chamber or cavity of the female adaptor plug 350. The male adaptor plug 330 may include the aforementioned weld alignment member 335 as part of a cylindrical section 333, which includes the depressions 357 around the circumference thereof with angled edges 380. An intermediate member 339 connects the cylindrical section 333 to an elongate section 338. The elongate section 338 may be threaded, as shown in FIG. 3A. The elongate section 338 tapers into a generally cone-shaped end 336 at the male adaptor plug second end 334. The cone-shaped end 336 represents a self-alignment aid for connecting the female adaptor plug 350 to the male adaptor plug 330 as a single adaptor subassembly 300. The male adaptor plug 330 may be made of a material that is corrosion resistant and compatible with the other reactor components, such as a zirconium alloy, as is known in the art. FIGS. 4A and 4B are perspective and side-view profiles illustrating another part of the adaptor subassembly in accordance with an exemplary embodiment of the present invention. As shown in FIGS. 4A and 4B, female adaptor plug 350 has a first end 352 for attachment to a given rod segment 110 (not shown) and a second end 354 for receiving the cone-shaped end 336 and elongate member 338 of the male adaptor plug 330 therein. Female adaptor plug 350 may include weld alignment member 355 and a generally cylindrical section 353, which has a plurality of nut-shaped 357 depressions around the circumference with angled edges 380 at the first end 352 to facilitate removal of the female adaptor plug 350 and/or removal of an adjacent rod segment. The female adaptor 350 includes an interior cavity 358. A surface of the cavity 358 may include a plurality of mating threads 356 for receiving corresponding threads (see FIG. 3A) on the elongate section 338 of the male adaptor plug 330. The cavity 358 may have a concave angled portion 359 at an end thereof that is configurable as a self-alignment aid for receiving the cone-shaped end 336 to connect male adaptor plug 330 within the female adaptor plug 350. As shown in FIG. 4B, the cylindrical section 353 of the female adaptor plug 350 may include a recessed break line 360 at second end 354. The recessed break line 360 may also be referred to as an undercut section, for example. Undercutting may be designed into each of the adaptor subassemblies 300 so that a given rod segment 110 may be safely broken down by snapping and/or cutting a section loose without unscrewing the connecting joints 115 of FIG. 2B. This will be illustrated in further detail below. In another aspect, as the threads of the elongate section 338 engage the corresponding mating threads 356 within the cavity 358 of the female adaptor plug 350, the recessed break line 360 aligns with the intermediate member 339 of the male adaptor plug 330. Since the diameter of the intermediate member 339 is less than a diameter of the cylindrical section 333, this represents a ‘weakened area’ that facilitates cutting, snapping or breaking of the adaptor subassembly 300 of FIG. 2B at that location. The recessed break line 360 may thus provide a visual identification as to where to cut an adaptor subassembly 330 of FIG. 3B, in the event of segment 110 of FIG. 2B replacement, adaptor subassembly 300 of FIG. 2B replacement, etc. FIGS. 5A and 5B are perspective and side-view profiles illustrating an exemplary lower end piece of the rod assembly in accordance with an exemplary embodiment of the invention. As shown in FIG. 5A or 5B, one or both of the upper and lower end pieces 120 and 130 of FIG. 2A may be formed as a solid end piece assembly 500. The solid end piece assembly may be made of a solid metal material for example. End piece assembly 500 may include an end plug portion 505 at one end thereof and may have an integral end piece adaptor subassembly 530 at another end thereof for threaded engagement with a corresponding female adaptor segment 350 of FIG. 4B within an adjacent rod segment 110 of FIG. 2B. The end piece assembly 500 may be fabricated of solid Zircaloy and does not necessarily have any nuclear fuel (enriched uranium) or poisons (gadolinium) loaded therein, since axial flux near the top and bottom of a fuel bundle such as fuel bundle 10 of FIG. 1A is generally substantially lower than between the upper and lower end pieces 120 and 130 of FIG. 2A, for example. FIGS. 5A and 5B thus may illustrate a reusable end plug (reusable as either an upper end piece or lower end piece) that can be removed with relative ease from an adjacent segment 110 of FIG. 2B of the rod assembly 100 of FIG. 2A during a scheduled maintenance outage. FIGS. 6A-6E are views illustrating an exemplary container assembly with contents adapted for insertion in a given rod segment 110 of the rod assembly 100 of FIG. 2A, in accordance with an exemplary embodiment of the invention. In an exemplary embodiment of the present invention, various ones of the rod segments 110 may include a container assembly 600 therein, as shown previously in FIG. 2B. In an example, the container assembly 600 may house or contain selected contents. An example of such contents may be one or more irradiation targets that produce one or more desired isotopes when a fuel bundle containing the rod assembly 100 is irradiated in the core of the reactor. One or more rod segments 110 of the rod assembly 100 may each include the same target, different targets or multiple irradiation targets, for example. Referring to FIGS. 2A and 2B, in one exemplary aspect of the invention, at least one of the rod segments 110 of rod assembly 100 includes a container assembly 600 therein, and none of the other rod segments 110 of rod assembly 100 (nor either of the end pieces 120, 130) contain any nuclear fuel/poisons. In another aspect, one or more of the rod segments 110 of rod assembly 100 may include desired enrichments of uranium and/or concentrations of gadolinia. The locations and concentrations may be based on the desired characteristics of the bundle 10 for a planned energy cycle, for example. A rod segment 110 that includes an irradiation target may not also include nuclear fuel, although adjacent rod segments 110 could include nuclear fuel therein. Referring now to FIGS. 6A-6E, the container assembly 600 shown initially in phantom in FIGS. 2A and 2B may include a container 610 that houses an irradiation target 620 therein. The container 610 may be closed at one end 611, open at the other end 612 and may include a seal 613 to close the container by a suitable end cap 630, as shown in FIG. 6D, although end caps 630 may be provided at both ends. Although container 610 is shown as having a generally cylindrical shape, container 610 may be oriented in any geometrical shape so long as the largest diameter of the shape is less than the inner diameter of rod segment 110. Container 610 may be made of a suitable material such as zirconium alloys, for example. Container 610 may house one or more irradiation targets 620. The irradiation target 620 shown in FIG. 6B is illustrated in a generally cylindrical form or shape. However, the irradiation target 620 may be embodied as a solid, liquid and/or gas, and may take any geometry so long as the diameter of the geometry is small enough to fit inside the container 610 (less than an inner diameter of the container 610) within a given rod segment 110. The container 610, coupled with its cladded rod segment 110, therefore provides a double-walled containment for the irradiation target 620 when in place within the rod segment 110. FIG. 6E illustrates a transparent front or side view of container assembly 600, to show the container 610 housing the irradiation target 620 therein and sealed by the end plug 630 at location 613. Optionally, an interior of the container 610 may include a spring 640 to provide a counter force against irradiation target 620 when sealed by end plug 630. The end plug 630 may be attached to the container 610 by suitable attachment means, i.e., weld, threaded engagement, friction connection, etc. In another aspect, the container 600 houses irradiation target 620 therein, having a first end 611 that has a pilot hole 603 for removing the irradiation target 620 after irradiation. The first end 611 may include exterior threads 601 and an O-ring 602 that is used for sealing container 600 when inserted into a piece of equipment. Pilot hole 603 has interior threads to aid in the removal of container 600 from the rod segment 110. The irradiation target 620 may be a target selected from the group of isotopes comprising one or more of cadmium, cobalt, iridium, nickel, thallium, thulium isotope, for example, or any other isotope having an atomic number greater than 3. Desirably, a given segment 110 and/or container assembly 600 may include indicia or indicators thereon to indicate what irradiation target 620 is loaded in that rod segment 110/container 600, for example, and/or what isotope is to be produced from that target. The specific methodology in which one or more of the rod assemblies 100 containing irradiation targets is irradiated within a fuel bundle (such as fuel bundle 10 of FIG. 1A) of a nuclear reactor to generate one or more desired isotopes is described in more detail in the co-pending and commonly assigned application by the inventors entitled “Methods of Producing Isotopes in Power Nuclear Reactors”, Ser. No. 11/002,680. Therefore, a detailed discussion of these processes is omitted herein for purposes of brevity. FIG. 7 illustrates a rod assembly for a fuel bundle in accordance with another exemplary embodiment of the invention. FIG. 7 illustrates a rod assembly 100′ in accordance with another exemplary embodiment of the present invention. In FIG. 7, only a few rod segments 110 of the rod assembly 100′ are shown for purposes of brevity, it being understood that the rod assembly 100′ could include additional rod segments 110 and spacers 20. In an example, the fuel bundle 10 may include eight spacers 20 with various sized (different length) rod segments 110 attached to the upper and lower end pieces 120 and 130 with an expansion spring 125 attached atop the upper end piece 120, as is known in the art. Unlike FIG. 2A, in FIG. 7 various sized adaptor ‘mini-subassemblies’ 300a may be provided at various locations such that connection points between two adjacent rod segments 110 do not occur at the spacer location (i.e., at spacer 20). FIG. 7 also illustrates an undercut section 160 (segmented break line 360 in FIG. 2B) as well as a container assembly 600′ in further detail. As it may be desirable to have additional locations to more easily remove rod segments 110 which include a container assembly 600′ therein (for removal of the container assembly 600′ and shipping to a desired customer), the rod assembly 100′ may include different length adaptor subassemblies 300, such as mini-subassemblies 300a and extended sub-assemblies to use between adjacent rod segments 110 of different lengths, for example. One or more of the rod assemblies 100′ shown in FIG. 7 may be inserted into a fuel bundle such as the fuel bundle 10 shown in FIG. 1A. Additionally, a rod assembly 100 or 100′ could have both adaptor subassemblies 300 at spacer 20 locations as well as one or more mini-subassemblies 300a between spacers 20 for connecting adjacent rod segments 110, and/or for connecting a rod segment 10 to one of an upper or lower end piece 120, 130 (as shown in FIG. 2A) or one of an upper end piece assembly 1000 and a lower end piece assembly 1100 as shown in FIG. 7. As also shown in FIG. 7, a given rod segment 110 may include multiple container assemblies 600′ therein. In FIG. 7, the container assembly 600′ may include a plurality of irradiation targets in “BB” form, which is another alternative form for the irradiation target in accordance with the present invention. Accordingly, as shown in FIG. 7, the rod assembly 100′ may include various sized adaptor mini-subassemblies 300a which may be used in addition to the fixed-size adaptor subassembly 300 described in FIG. 2A. This may produce a single multijoint rod assembly 100′ that has more than one usage. This utilizes varying levels of neutron flux in the reactor for variations in the degree of isotope production in the target. As an example, the rod assembly 100′ may contain a plurality of irradiation targets at various locations within different sized rod segments 110, and still maintain the same length of a standard full length fuel rod 18 or part length rod 19 within a fuel bundle 10 of FIG. 1A, and/or provide a rod assembly 100′ having the same length as a part length rod within fuel bundle 10 of FIG. 1A, for example. Different rod segments 110 of the rod assembly 100′ may be removed and/or reconnected at different connection points along the axially length of the rod assembly 100′. A given rod segment 110 and/or adaptor mini-subassembly 300a may be removed by unscrewing, cutting and/or snapping or breaking a specific section loose at its connecting point or at the undercut section 160, for example. Additionally as shown in FIG. 7, irradiation targets 620 may be placed in prepackaged container assemblies 600′ that may facilitate shipping directly from the reactor site to the receiving customer. Such prepackaged containers 600′ may contain different irradiation target materials, whether the target isotopes are in solid, liquid or gas form and placed inside a rod segment 110. FIGS. 8A-8B are views illustrating an adaptor subassembly for the rod assembly in accordance with another exemplary embodiment of the invention; and FIGS. 9A-9B illustrate the mini-subassembly 300a in further detail. FIG. 8A shows a male adaptor plug 330′ and a direction of insertion into the female adaptor plug 350′. FIG. 8B illustrates the connective engagement between male and female adaptor plugs 330′, 350′ as part of an exemplary adaptor subassembly 300′. FIGS. 8A and 8B illustrate a longer-length adaptor subassembly 300′ than is shown in FIGS. 3A-3B and FIGS. 4A-4B, or in FIGS. 9A-9B. For example, the longer elongate section 338A of the longer male adaptor segment 330′ may provide an adaptor subassembly 300′ which enables connection of a smaller length section of rod segment 110 to be interchangeable with a much longer/heavier rod segment 110, should the need arise. In FIG. 8A, the length of the longer elongate section 338A is indicated as “y*n” so as to distinguish it from the length of the shorter elongate section 338B in the mini-subassembly 300a of FIG. 9A. Similarly, the overall length of the adaptor subassembly 300′ in FIG. 8B may be longer than the corresponding mini-subassembly 300a in FIG. 9B by an integer multiple n, or by an addition of an integer n to the length ‘x’ of mini-subassembly 300a in FIG. 9B. The smaller, two-piece mini-subassembly 300a of FIGS. 9A-B may be used in between spacer 20 locations for producing even smaller subassemblies of rod segments 110. The smaller two piece adaptor mini-subassembly 300a of FIG. 9B may be used in the same rod assembly 100′ as the larger two piece adaptor subassembly 300′ shown in FIG. 8B, for example. FIGS. 10A-B are views illustrating an upper end piece adaptor for the rod assembly in accordance with another exemplary embodiment of the present invention. FIGS. 11A-B are views illustrating a lower end piece adaptor for the rod assembly in accordance with another exemplary embodiment of the present invention. FIGS. 10A-11B illustrate alternative embodiments to the end piece assembly 500 shown in FIGS. 5A and 5B. FIGS. 10A and 10B illustrate an upper end piece assembly 1000. The upper end piece assembly 1000 may include an upper end piece adaptor subassembly 1330 at one end and the upper end piece 1310 connected thereto at another end, which may contain threads. Unlike the integral end piece assembly 500 shown in FIGS. 5A and 5B, in FIGS. 10A and 10B, the upper end piece 1310 is attached to a female adaptor plug 1350 similar to the female adaptor plug 350 as described in FIGS. 4A and 4B. The female adaptor plug 1350 may be engaged to the male adaptor plug 1330 such as previously described above in FIGS. 3A-3B. The upper end piece subassembly 1000 allows a full length rod from its upper end piece 1310 down to its bottom end piece 2310 to be built by mixing and matching different lengths of rod segments 110 to different connection points within the same axial length of the rod assembly 100′. Similarly, in FIGS. 11A and 11B, a lower end piece assembly 1100 may include a lower end piece adaptor subassembly 2300 connected to the lower end piece 2310. In particular, the lower end piece 2310 is attached to the male adaptor plug 2330, which mates with a female adaptor plug 2350 that is attached to an adjacent rod segment 110, for example. In an aspect, the lower end piece may be used after the removal of a lower section of a rod segment 110, so that the remaining axial length of the rod assembly 100′ can remain within the bundle 10 for additional cycles using the detachable lower end piece assembly 1100. Accordingly, the upper end piece assembly 1000 and lower end piece assembly 1100 provide reusable and removable lower and upper end pieces which can facilitate quick repairs or removal of designated rod segments 110 within the rod assembly 100′. FIGS. 12A-C are views illustrating an adaptor subassembly for the rod assembly in accordance with another exemplary embodiment of the invention. In general, adaptor subassembly 300b may be understood as a push-snap locking mechanism having a male connector 330″ engaging a corresponding female connector 350″ to connect two rod segments 110 or a rod segment 110 with one of the upper and lower end pieces 120/130 of FIG. 2A. The male connector 330″ may include an expandable member at an end thereof, and the female connector 350″ may include an interior cavity terminating in a receiver that is adapted to receive the expandable member. FIGS. 12A and 12B illustrates a male connector 330″ and female connector 350″ and direction of connective engagement between the two connectors 330″, 350″. As shown in FIG. 12B, the male connector 330″ may include a weld alignment member 355 (such as shown in FIG. 2B) to assist in aligning the male connector 330″ within the interior of its corresponding rod segment 110. The other end of the male connector 330″ may include a spring plug bayonet 1205 for connective engagement within an interior cavity 358″ to terminate once fully engaged within a corresponding ball and socket joint fit-up 1210 of the female connector 350″. FIG. 12A illustrates a female connector 350″ with the interior cavity 358″ that may be shaped so as to receive the spring plug bayonet 1205 within the corresponding ball and socket joint fit-up 1210, as shown in FIG. 12A. FIG. 12C illustrates the connective engagement between the female 350″ and male 330″ connectors of connector subassembly 300b. Accordingly, the rod segments 110 may be fully assembled into a singular rod assembly 100/100′ once the expandable bayonet plug spring collet 1205 is fixedly secured within the ball and socket joint fit-up 1210 of the female connector 350″. Accordingly, the adaptor subassembly 300b in FIGS. 12A, 12B and 12C illustrate a push-snap mechanism to connect adjacent rod segments 100 of the rod assembly 100/100′ and may reduce the sticking probability that could occur using the threaded engagement as shown in FIGS. 2A, 2B and 7. This may lead to fast assembly and/or disassembly of various rod segments 110, without the need for breaking, snapping, or cutting the segments 110 apart, for example. As previously described, each of the rod segments 110 may have identification marks or indicia thereon that identify the contents that are within that particular rod segment 110. Alternatively, the identification marks can be labeled on the container assemblies 600/600′ within a given rod segment 10, for example. In another aspect, the threaded screw length of the elongate sections 338/338A/338B of FIGS. 8A-B and 9A-B on a given male adaptor plug 330 may be of a sufficient length so that a given rod segment cannot become unscrewed during a reactor operation. As an example, the threaded screw length of the elongate sections 338/338A/338B may be long enough such that it cannot come apart. This may help to ensure that a given rod length would not become unscrewed during reactor operation. In a further aspect, male adaptor plugs 330 and 330′, and/or male connector 330″ may be oriented in the same direction for ease of extraction of a given rod segment 110. For example, segments 110 having male adaptor plugs 330, 330′ and/or 330″ may all be loaded and/or arranged in a given rod assembly 100/100′ so that the male adaptor plugs/connector 330, 330′, 330″ of the segment 110 extend vertically upward toward the top of bundle 10, to facilitate grasping by a suitable tool for removal, installation, for example. In the event the rod segment 110 is dropped, it would land with side having the female adaptor plug 350, 350′ and/or 350″ down, so as to reduce the chance that the male end snaps or breaks. Accordingly, the exemplary rod assembly with multiple rod segments connected thereto may provide a full length or part length rod. The rod assembly 100 may include adaptor subassemblies 300 which connect adjacent rod segments 110 at spacer 20 locations so as to eliminate the consequences of fretting that is currently prevalent in full length and part length rods of conventional fuel assemblies. In an aspect, the use of multiple rod segments 110 in a full length or part length rod assembly 100 or 100′ may allow for multiple irradiation targets to be loaded at different segments and at different axial locations of the rod assembly 100/100′. This may allow for multiple isotopes to be generated in each fuel bundle of a reactor, should the reactor be configured solely for generating isotopes and/or for generating isotopes and providing power generation, and also enables the ability to place irradiation targets at desired flux locations along the axial length of the rod within a given fuel bundle. The exemplary embodiments of the present invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as departure from the spirit and scope of the exemplary embodiments of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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claims | 1. A radiation image storage panel having a phosphor layer which comprises a stimulable cerium activated lutetium borate phosphor represented by the following formula (I):(Lux,Lny)BO3:aCe,bA (I)in which Ln is at least one rare earth element selected from the group consisting of Y, La and Gd; A is at least one element selected from the group consisting of Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Zr; and x, y, a and b are numbers satisfying the conditions of 0.5≦x<1, 0≦y<0.5, 0<a≦0.2, 0≦b≦0.2 and x+y+a+b=1.0. 2. The radiation image storage panel of claim 1, in which A of the formula (I) is Sm or Zr. 3. The radiation image storage panel of claim 1, in which b of the formula (I) is 0. 4. The radiation image storage panel of claim 1, in which y of the formula (I) is 0. 5. The radiation image storage panel of claim 1, which comprises a support, the phosphor layer and a protective layer in order. 6. A method for producing a stimulated emission which comprises the steps of:applying a radiation to a stimulable cerium activated lutetium borate phosphor of the following formula (I):(Lux,Lny)BO3:aCe,bA (I)in which Ln is at least one rare earth element selected from the group consisting of Y, La and Gd; A is at least one element selected from the group consisting of Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Zr; and x, y, a and b are numbers satisfying the conditions of 0.5≦x<1, 0≦y<0.5, 0<a≦0.2, 0≦b≦0.2 and x+y+a+b=1.0, whereby storing an energy of the radiation in the phosphor andstimulating the phosphor in which the energy of the radiation is stored with a stimulating light, whereby giving a stimulated emission off. 7. The method of claim 6, in which A of the formula (I) is Sm or Zr. 8. The method of claim 6, in which b of the formula (I) is 0. 9. The method of claim 6, in which y of the formula (I) is 0. 10. A radiation image recording and reproducing method comprising the steps of:exposing the radiation image storage panel of claim 1 to a radiation having passed through an object or having radiated from an object, whereby a spatial energy distribution of the radiation is recorded as a latent image in the phosphor layer of the storage panel;irradiating the storage panel with a stimulating light to emit a stimulated light from the latent image in the phosphor layer;photoelectrically detecting and converting the stimulated light to image signals; andforming a radiation image from the image signals. |
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046848100 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, there is disclosed a fluorescent light fixture 10 having fluorescent tubes 12 and 14 mounted therein in the usual manner. The marginal ends 16 of tube 12 contain a cathode each of which emits soft X-rays as generally illustrated at numeral 18. A person seated at 20 is injured when the soft X-rays 18 impinge upon his person. The tube 14 is provided with a shield assembly 22, made in accordance with the present invention. The shield assembly is supported by the marginal terminal ends of tube 14 As seen in the embodiment disclosed in FIG. 2, the shield assembly 22 has an adjacent end 24 and an opposed end 26. The shield is generally cylindrical in form and is discontinuous because a longitudinally extending slot has been formed in a side wall thereof, thereby providing longitudinal spaced parallel edges 28 and 30. In FIG. 3, the tube interior is indicated by numeral 32. A fiberous material 34, such as cardboard or heavy self-supporting paper, is covered by a sheet of lead 36. The lead sheet can be attached to the cardboard by any convenient method, as for example gluing the marginal edge portions thereof in proximity of the longitudinal extending edge portions 28 and 30. The exterior of the lead preferably is painted at 38 to provide an attractive finish, and to protect the lead from atmospheric oxidation, or other undesirable chemical reactions. The shield assembly of FIGS. 2 and 3 is affixed to an existing tube 12 by outwardly deforming edges 28 and 30 so that the slot receives the marginal end of the tube therethrough, thereby enabling the shield to be installed in the manner of FIG. 1 without removing the tube from the fixture. The slot upwardly opens towards the light fixtures so that any radiation 18 in an upward direction through the slot is intercepted by the metal light fixture. In any event, the area of the slot can be made insignificant. In FIG. 4, the shield 122 is generally cylindrical in form and has a continuous outer peripheral surface area. The support member 34 and sheet of lead 36 extend 360.degree. about the outer circumferentially extending surface of the cylinder. Numeral 38 indicates the attractive coating of paint or the like. In the embodiment of FIGS. 2 and 4, the thickness of the lead sheet can vary from a thin foil of about 0.004 inches up to a thickness of 0.035 inches. The end of the tube is provided with a conventional cap 40, electrical contacts 42, and a cathode 44 in the usual manner. As seen illustrated by numeral 46, the shield assembly is loosely received in supported relationship about the exterior surface of the marginal ends of the tube. Therefore, the tube must be removed from the fixture in order to slide the cylinder over the marginal ends thereof. The length of the cylinder preferably is twice the diameter of the tube, and in any instance should be at least equal to the diameter of the tube in order to adequately shield radiation emitted from the cathode 44. A length in excess of three times the diameter is considered too long for such a length because it blocks out excess light from the tube. In FIG. 6, the shield 222 is seen to be comprised of a layer 48 of material having particles of metallic lead dispersed in sufficient concentration therewithin to intercept X-rays radiating from the cathode 44. The layer is formed by painting the outer surface. The metal is finely ground and admixed with the paint in sufficient quantity to shield the X-rays emitted by the cathode. In FIG. 7, the shield 322 is comprised of a layer or coating of material 50 applied to the inside peripheral wall surface 32 of the marginal ends of the tube. The shield must be applied during manufacture of the tube. The shield 50 is a layer of lead particles which is applied as in the previous example of FIG. 6, or alternatively, can be deposited by vapor condensation or by ordinary painting. In practicing the present invention, the embodiment of FIG. 2 is affixed in supported relationship respective to the tubes 12 and 14 by springing the edge portions 28 and 30 apart from one another an amount sufficient to enable the marginal terminal end of the tube to be received therewithin, so that the resultant combination eliminates the X-rays 18 from impinging on a person 20 within the illustrated enclosure. The material from which the shield is made preferably is sufficiently resilient to be biased towards its original configuration of FIG. 2 after it has been sprung apart sufficiently to capture the marginal end of the tube therewithin. The shield is therefore supported by the tube, and when the tubes 12 and 14 are changed, the shield can be removed and placed about the new tube. Hence, the material from which the supporting member 34 is fabricated has sufficient memory so that when it is deformed and then released, the member is biased back towards its original configuration. The inside diameter of the shield 22 should therefore be slightly less than the outside diameter of the tube so that when the shield is installed on the tube, the memory of the material 34 causes the shield to slidably capture the tube therewithin. The slot is oriented vertically upward so that any X-rays traveling therethrough are intercepted by the light fixture. In the embodiment of FIG. 4, the cylindrical continuous surface circumferentially surrounds the tube and therefore, the tube must be removed from the fixture in order to install the embodiment 122 thereon. The inside diameter of the shield 122 preferably is one thirty second to one eigth inch greater than the outside diameter of the tube. Therefore, the shield loosely captures the tube therewithin, with the marginal end of the tube supporting the shield in the illustrated manners of FIGS. 4 and 5. The shield gravitates into the illustrated position set forth in FIGS. 4 and 5. In the illustrated embodiment of FIGS. 2-5, the supporting member 34 is made of self supporting cardboard, a rolled sheet of asbestos, heat resistent plastic material such a polypropylene, or a thin sheet of metal such as steel. In the embodiment of FIG. 6, the shield 22 is comprised of a coating of material which has been applied by painting the external surface of the glass tube. The coating of material contains ground up metal particles of lead and is of a sufficient density to form an effective barrier through which the X-rays radiating from the cathode 44 cannot pass. One example of paint suitable for this embodiment is a mixture of 75% lead powder and 0.25% expoxy resin by volume. In the embodiment of FIG. 7, the shield 322 is comprised of a coating of metallic lead 50. The metal is deposited onto the glass interior surface by vaporizing the metal and permitting it to condense onto the interior surface. The metal can also be applied as an adhesive backed lead foil. The embodiments of FIGS. 6 and 7 are shields for one time use whereas the embodiments of FIGS. 2 and 4 can be continually used over and over again, as well as retrofitting existing fluorescent tubes. |
044951450 | claims | 1. A loading probe for loading spherical nuclear fuel of three different diameters into a fuel rod comprising: (a) funnel means for receiving said spherical nuclear fuel, said funnel means maintaining a separation of said spherical fuel of different diameters; (b) tubing means corresponding to each of said spherical nuclear fuel diameters, said tubing means of sufficient length so that said tubing means extends about the length of said fuel rod in the load portion; (c) valve means for releasably containing said fuel spheres within said funnel means, said valve means able to release said fuel spheres to said tubing means; (d) gate means between said valve means and said tubing means for regulating the rate of flow of each said spherical fuel as it passes from said funnel means through said valve means into the end of said tubing means away from said fuel rod; and (e) deflector means attached to said end of said tubing means within said fuel rod for mixing said fuel as it emerges from said tubing means; (a) three tubes aligned longitudinally each one tube corresponding to each of said diameters of nuclear fuel spheres, and (b) a hopper divided into three sections, one end of each of said three tubes connected to a corresponding one of said three sections of said hopper, each section of said hopper adacent to a corresponding gate means. (a) scoop shaped extensions of each of said tube ends toward said fuel rod, (b) a tubular collar aligned along the axis of said three tubes, one end of said collar surrounding scoop shaped extensions on said tube ends so that said fuel emerges within said collar as it leaves said tubes, and (c) a cone axically alligned with the axis of said tubes fixed to the other end of said collar so that a space exists between said cone and the periphery of said other end of said collar, the point of said cone directed along the axis of said collar toward said scoops, said space sufficient to allow said fuel spheres to pass and enter said fuel rod. (a) scoop shaped extensions of each of said tube ends toward said fuel rod, (b) a cone axially aligned with the axis of said tubes, fixed to scoop end of said tubes by two rods, one end of said rods fixed to said tubes and the other end of said rods fixed to said cone, the point of said cone toward said tubes. 2. The probe of claim 1 wherein said valve means are solenoid valves. 3. The probe of claim 1 wherein said tubing means includes: 4. The probe of claim 3 wherein said deflector means includes: 5. The probe of claim 3 wherein said deflector means includes: 6. The probe of claim 1 wherein said gate means includes three V-shaped members releasably attached, one member corresponding to each of said fuel sphere diameters, each of said members including an opening whose dimensions are chosen so as to achieve sufficient density of fuel in said fuel rod to operate in a nuclear reactor. |
claims | 1. A method of creating a virtual confinement barrier between a top portion and a bottom portion of a substantially vertically-disposed substantially closed volume that extends continuously and physically uninterruptedly between the top and bottom portions, each of the top and bottom portions containing a fluid intended to be substantially separately contained in a respective one of the top and bottom portions, said method comprising the steps of: maintaining the fluid in the bottom portion at a first mean temperature; and maintaining the fluid in the top portion at a second mean temperature selectively greater than said first mean temperature to thereby define a temperature differential between the fluids in said top and bottom portions and a temperature gradient in an intermediate mixing zone of constricted width between said top and bottom portions within which said temperature differential and said temperature gradient creates turbulence in said mixing zone sufficient to prevent unintended intermixing fluid flow between said top and bottom portions and thereby define by said temperature differential a virtual confinement barrier substantially confining within each of the top and bottom portions the fluid contained in the respective top and bottom portions of the vertically-disposed volume. 2. The method according to claim 1 , wherein said maintaining of the fluid in the bottom portion at the first mean temperature comprises: claim 1 injecting the fluid at the first mean temperature into the bottom portion in a manner so as to avoid by said fluid injection creation of turbulence in said mixing zone as a result of said fluid injection; and extracting the fluid at a location disposed between a location of said fluid injection in the bottom portion and said mixing zone. 3. The method according to claim 1 , wherein said maintaining of the fluid in the top portion at the second mean temperature comprises: claim 1 injecting the fluid at the second mean temperature into the top portion in a manner so as to avoid by said fluid injection creation of turbulence in said mixing zone as a result of said fluid injection; and extracting the fluid at a location between a location of said fluid injection into the top portion and said mixing zone. 4. The method according to claim 3 , wherein said maintaining of the fluid in the top portion at the second mean temperature comprises: claim 3 injecting the fluid at the second mean temperature into the top portion in a manner so as to avoid by said fluid injection creation of turbulence in said mixing zone as a result of said fluid injection; and extracting the fluid at a location between a location of said fluid injection into the top portion and said mixing zone. 5. The method according to claim 1 , wherein the temperature differential is further selected to create a density difference between the fluids in the top and bottom portions that minimizes a vertical component of a speed of fluid turbulence in the top and bottom portions. claim 1 6. The method according to claim 1 , further comprising the step of: claim 1 recycling at least some of the fluid in the top portion. 7. The method according to claim 1 , wherein the fluid in the top and bottom portions comprises gas. claim 1 8. The method according to claim 7 , wherein the gas comprises air. claim 7 9. The method according to claim 7 , wherein said volume is bounded by an enclosure configured to confine in one of the top and bottom portions a pollutant generated by a pollution source. claim 7 10. The method according to claim 1 , wherein the fluid in the top and bottom portions comprises liquid. claim 1 11. The method according to claim 10 , wherein the liquid comprises water. claim 10 12. An apparatus for creating in a walled enclosure a virtual confinement barrier between a top portion and a bottom portion of a substantially vertically-disposed substantially closed volume of the enclosure that extends continuously and physically uninterruptedly between the top and bottom portions, each of the top and bottom portions containing a fluid intended to be substantially separately contained in a respective one of the top and bottom portions, said apparatus comprising: a first temperature-maintaining means for maintaining the fluid in the bottom portion at a first mean temperature; and a second temperature-maintaining means for maintaining the fluid in the top portion at a second mean temperature selectively greater than said first mean temperature to thereby define a temperature differential between the fluids in said top and bottom portions and a temperature gradient in an intermediate mixing zone of constricted width between said top and bottom portions within which said temperature differential and said temperature gradient creates turbulence in said mixing zone sufficient to prevent unintended intermixing fluid flow between said top and bottom portions and thereby define by said temperature differential a virtual confinement barrier substantially confining within each of the top and bottom portions the fluid contained in the respective top and bottom portions of the vertically-disposed volume. 13. The apparatus in accordance with claim 12 , wherein said first temperature-maintaining means comprises: claim 12 a first fluid injection means for injecting the fluid at the first mean temperature into said bottom portion in a manner so as to avoid by said fluid injection creation of turbulence in said mixing zone as a result of said fluid injection from said first fluid injection means; and a first fluid extraction means disposed at a location between said first fluid injection means and said mixing zone for extracting the injected fluid from said bottom portion. 14. The apparatus in accordance with claim 13 , wherein said second temperature-maintaining means comprises: claim 13 a second fluid injection means for injecting the fluid at the second mean temperature into said top portion in a manner so as to avoid by said fluid injection creation of turbulence in said mixing zone as a result of said fluid injection from said second fluid injection means; and a second fluid extraction apparatus disposed at a location between said second fluid injection apparatus and said mixing zone for extracting the injected fluid from said bottom portion. 15. The apparatus according to claim 14 , wherein the enclosure further comprises means for insulating walls of the enclosure at the top portion of the volume. claim 14 16. The apparatus according to claim 12 wherein said first and second temperature-maintaining means are configured so that the temperature differential creates a density difference between the fluids in said top and bottom portions that minimizes a vertical component of a speed of fluid turbulence in said top and bottom portions. claim 12 17. The apparatus according to claim 14 , wherein said first and second fluid extraction means each comprise a slot disposed at a like vertical level on opposite walls of said enclosure. claim 14 18. The apparatus according to claim 14 , wherein at least one of said first and second fluid injection means is disposed on a substantially horizontal wall surface of the respective bottom and top portion. claim 14 19. The apparatus according to claim 14 , wherein at least one of said first and second fluid injection means comprises at least two slots distributed along a length of a horizontal wall of the enclosure. claim 14 20. The apparatus according to claim 14 , wherein at least one of said first and second fluid injection means comprises two series of slots distributed in a staggered manner along a length of opposite vertically-oriented walls of the enclosure, said slots being proximate to an intersection of a horizontal wall and said vertical walls. claim 14 21. The apparatus according to claim 14 , further comprising a recycling means configured to recycle at least some of the fluid in said top portion. claim 14 22. The apparatus according to claim 14 , said first fluid injection means is fed with one of fluid at ambient temperature and cooled fluid. claim 14 23. The apparatus according to claim 22 , further comprising a heat pump for drawing heat energy from fluid injected into said bottom portion for use in raising the mean temperature of the fluid injected into said top portion. claim 22 24. The apparatus according to claim 12 , wherein the fluid in said top and bottom portions comprises a gas. claim 12 25. The apparatus according to claim 24 , wherein the gas comprises air. claim 24 26. The apparatus according to claim 12 , wherein the fluid in said top and bottom portions comprises a liquid. claim 12 27. The apparatus according to claim 26 , wherein the liquid comprises water. claim 26 |
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description | The present application is a continuation application of U.S. patent application Ser. No. 14/033,950, filed on Sep. 23, 2013, entitled “COMPACT PROTON THERAPY SYSTEM WITH ENERGY SELECTION ONBOARD A ROTATABLE GANTRY,” which claims the priority to and benefit of U.S. Provisional Patent Application No. 61/798,354 filed on Mar. 15, 2013. The present application claims priority to and benefit of PCT application No. PCT/US14/22092, filed on Mar. 7, 2014, entitled “COMPACT PROTON THERAPY SYSTEM WITH ENERGY SELECTION ONBOARD A ROTATABLE GANTRY,” which claims the priority to and benefit of U.S. Provisional Patent Application No. 61/798,354 filed on Mar. 15, 2013. The present application is related to the U.S. patent titled “Irradiation device,” U.S. Pat. No. 8,053,736, filed on Apr. 5, 2007, which claims priority to German patent application No. 202006019307.3, file don Dec. 21, 2006. The foregoing patent applications and patent are hereby incorporated by reference in their entirety for all purposes. Embodiments of the present disclosure relate generally to medical devices, and more particularly, to radiation therapy devices. In a typical proton therapy system used for tumor radiation treatments for example, a proton beam is produced in a cyclotron or a synchrotron in a specific level of energy that can be adjusted to a prescribed energy level by virtue of energy selection then provided to a treatment station via a beam transportation system. Such a therapy system includes a particle accelerator, such as a cyclotron or a synchrotron, for providing the particle beam at a specific energy level. The beam transport system can tune and deliver the particle beam to a radiation station. At the end of the beam transport system, a rotational gantry associated with a radiation nozzle delivers the beam onto an irradiation object, e.g. a tumor of a patient, in a fixed position supported by the irradiation station during operation. Similar systems can be used for other heavy particle radiation treatment, such as neutron, He or C ion beam. Typically a beam output from an accelerator has a fixed energy, e.g. 250 MeV. Depending on the diagnosis of a patient's condition, for example the depth of a tumor to be treated, different patients are prescribed with different depth doses of radiation. An energy selection system (ESS) is usually used to tune the fixed energy to the prescribed energy, e.g. 170 MeV. Conventionally, an ESS comprises an energy degrader for attenuating the beam energy roughly, followed by a set of energy selection dipole magnets dedicated for fine energy selection by filtering the undesired traverse emittances, momentum spread and energy spread resulted from the energy degrader. The transport system also includes a plurality of other magnets for beam focusing and steering purposes. Due to the high cost for purchasing and maintaining such a radiation system, a medical facility usually uses one accelerator for a plurality of treatment stations so the high expenditure for the accelerator facilities is distributed. FIG. 1 illustrates a configuration of a medical facility that accommodates a proton radiation system 100 providing proton beams for multiple treatment stations in accordance with the prior art. The system 100 comprises a single stationary cyclotron 101 located in a dedicated room 110, a carbon wedge energy degrader 102 disposed in a vacuum component of the beam line, a gantry 121 and 122 for each treatment room 131 and 132, and an ESS, several sets of quadrupole magnets for focusing the beam, e.g. 104, and a plurality sets of bending magnets that directs the proton beams from the cyclotron to respective treatment rooms, e.g. 131 and 132. As shown, the ESS of this system is composed of a carbon wedge degrader 102, and two dipole magnets 105 and 106 with an energy slit (not explicitly shown) sitting in between. The dipole magnets 105 and 106 are located proximate to the accelerator 101 and dedicated for selectively passing the particles with the targeted energy. In order to supply the particle beams to different rooms located in various places relative to the accelerator room 110, the system 100 is equipped with long beam lines, e.g. 111 and 112, along different paths in which dipole magnets are used to change beam directions. For example, dipoles 107 and 108 are used to redirect the particle beam into the room 110. The dipole 141 bends the beam by 45° at the entrance of the gantry 121. Another dipole 142 bends the beam by 135° and toward the isocenter. Collectively, the two dipoles 141 and 142 in the gantry bends the beam by 90° from the beam line 111. Although using a multi-station single-cyclotron system is effective to distribute the cost for large medical facilities, the overall cost for such a multi-gantry system may be prohibitively high for smaller facilities that may only need one treatment station. Also, some multi-station systems do not support simultaneous treatment in multiple stations. This contribute to further disadvantage that a delay at one treatment station can cause delay at the other station. Among the costly factors in the conventional proton radiation system, the dipole magnets consume significant expenditure associate with manufacture, installation, control, maintenance, and space that is limited and valuable in the medical facility. Moreover, connecting to the stationary cyclotron and the rotating gantry, the beam line pipe comprises a rotating portion that can rotate along with the gantry and a stationary or non-rotating portion leading to the cyclotron, both portions being maintained under continuous low pressure (vacuum) typically in the 10E-05 mbar range. Conventionally, a rotating vacuum seal is used at the beam line connection between the stationary part of the beam line and the rotating part of the beam line to keep the pipe sealed from outside air during rotation. Thus, it would be advantageous to provide a compact proton radiation system that has reduced cost and dimension and is feasible for single room proton therapy facility. Accordingly, embodiments of the present disclosure advantageously provide a radiation system that utilizes a set of dipole magnets on the gantry for the dual purposes of energy selection and redirecting the particle beam. By integrating the energy selection magnets onto the gantry, rather than in a dedicated section of the beam line, consumption of cost and space can be advantageously decreased, making the system suitable for a compact single-room design. Embodiments of the present disclosure further simplifies a proton radiation system by placing the energy degrader in the atmosphere and by replacing the vacuum seal with an air gap at the joint between the stationary portion and the rotating of the beam line. In one embodiment of the present disclosure, a radiation therapy system for irradiating an irradiation object with particle beam in a predetermined energy comprises a stationary particle accelerator, a beam line assembly, an energy degrader, and a swiveling gantry assembly. The beam line assembly is operable to direct and focalize a particle beam along a first direction. The energy degrader is operable to attenuate the energy of the particle beam and may be exposed to an air pressure. The swiveling gantry assembly comprises a set of dipole magnets as well as additional quadrupole and steerer magnets, all with controllable magnetic fields, and a collimator disposed in between the dipole magnets. The set of dipole magnets are operable to select a portion of the particle beam with a predetermined energy, and redirect the portion of the beam to a second direction. The set of dipole magnets may comprise a 45° and a 135° magnet arranged in sequence. The swiveling gantry may be capable of rotating 360° about the first direction and may comprise a housing that has a first member made of low-Z material and a second member made of high-Z material. The beam line assembly may comprise a rotating segment and a stationary segment couple to respective vacuum apparatuses. The rotating segment and the stationary segment may be separated by an air gap. The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the present invention, as defined solely by the claims, will become apparent in the non-limiting detailed description set forth below. Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of embodiments of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the embodiments of the present invention. Although a method may be depicted as a sequence of numbered steps for clarity, the numbering does not necessarily dictate the order of the steps. It should be understood that some of the steps may be skipped, performed in parallel, or performed without the requirement of maintaining a strict order of sequence. The drawings showing embodiments of the invention are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown exaggerated in the drawing Figures. Similarly, although the views in the drawings for the ease of description generally show similar orientations, this depiction in the Figures is arbitrary for the most part. Generally, the invention can be operated in any orientation. Notation and Nomenclature: It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing terms such as “processing” or “accessing” or “executing” or “storing” or “rendering” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories and other computer readable media into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. When a component appears in several embodiments, the use of the same reference numeral signifies that the component is the same component as illustrated in the original embodiment. FIG. 2 is an exemplary configuration of a medical facility equipped with a single-room proton therapy system 200 in accordance with an embodiment of the present disclosure. The compact radiation system 200 is designed to deliver a proton beam from the stationary cyclotron 201 to an adjacent single treatment room 203. The proton radiation system 200 includes an accelerator 201, e.g. a cyclotron as shown, a short beam line 202 transporting the particle beam from the cyclotron 201 to the single treatment room 203 along a linear axis, an energy degrader 204 disposed in the beam line 202, a single set of dipole magnets 206 and 207, and a swiveling gantry 205 operable to deliver a proton beam to the treatment station through a nozzle in different angles. In the single-room configuration 200, the cyclotron can be placed near the treat room as close as practically possible, and thus the beam line 204 can be short and linear, reducing the need for dipole magnets used for reorienting a particle beam. The system may further comprise a plurality of sets of focusing magnets mounted in the beam path to focus the particle team. In contrast to the multi-station system in FIG. 1, the single-room system 200 has a simplified arrangement of dipole magnets as well as the entire transporting system. Particularly, the dipole magnets 206 and 207 installed on the gantry 205 undertake the dual functions of energy selection as well as deflecting the particle beam from the beam line axis to the isocenter of the treatment station. In the illustrated embodiment, the 45° dipole magnet 206 located at the entry point of the gantry and the 135° dipole magnet 207 downstream can collectively bend the particle beam by 90° from the beam line 202 axis. At the same time, when the current in the coils of the magnets 206 and 207 is controlled to a precise current according to a target energy level, the magnets 206 and 207 in combination with a beam collimator are operable to perform the energy selection function. By integrating the ESS magnets in the gantry assembly, rather than in a dedicated section of the beam line as in the prior art, system consumption of cost and space can be advantageously and remarkably reduced, making the system suitable for a single-room design and more accessible to relatively small clinics. A beam optics simulation on the beam profile along the beam path proves that the simplified magnet system as illustrated in FIG. 2 is feasible to provide substantially identical clinical specification, such as beam size and shape for example, as resulted from a corresponding conventional multi-room radiation system that has separate dedicated ESS magnets and the deflection magnets. The disclosure is not limited by the angles, configurations or locations of the dual-function magnets. For instance, the magnets may comprise three 90° magnets that can collectively bend the beam by 90°. However, using the minimum number (two) of dipole magnets to reorient the magnets furthers the purposes of cost-efficiency and compact design. A set of scanning magnets can be used to control the raster scan of the particle beam. In some embodiment, the scanning magnets 211 can be placed in between the set of dual-function magnets 206 and 207. In the illustrated embodiment, the scanning magnets can be placed downstream after the magnet 207 and near the nozzle, which contributes to yet another design for a smaller gantry. The magnetic fields generated by the deflection/energy selection magnets 206 and 207 can be controlled by software programs to guide the beam as well as select the beam of desire energy. The software program can be implemented by any known computer implemented methods. In some other embodiment, the deflection magnets may comprise two 45° dipole magnets and collectively bend the beam by 90°. In some other embodiments, the deflection magnets may collectively bend the beam by 135° or any other angle. Any other suitable configuration of the deflection magnets can be used to practice the present disclosure. The deflection/energy selection magnets can be controlled by software programs to achieve a specific particle energy dictated by each specific treatment plan. The present disclosure can be implemented with any type of collimator suitable for particle beam energy selection that is disposed downstream after an energy selection magnet. The collimator 212 may comprise energy slits, apertures, and/or orifices disposed in between the two magnets 206 and 207. In some embodiments, the positions and openings of the collimators may be controllable. In some embodiments, the collimator features a compact design, such as an energy selection slit in a slim form, which can advantageously contribute to further reduction in system consumption of cost and space. Still in some other embodiments, the energy selection function can be solely assumed by a combination of suitable magnetic components and one or more energy degraders, which may advantageously eliminate the need for a collimator in an energy selection system. For example, a set of additional magnets may be used to narrow the spatial cross section and/or energy spectrum of the beam that exits from an energy degrader. In the illustrated embodiment, the energy degrader 204 comprises a carbon wedge disposed under a vacuum chamber situated in the beam line 202 and proximate to the accelerator 201. Any other suitable energy degrader can be used to implement the present disclosure. In some other embodiments, the energy degrader material can be integrated in the gantry as well, and disposed proximate to the deflection/energy selection magnets. In still some other embodiments, the degrader may be exposed to ambient pressure, which can advantageously save cost related to material, manufacturing and installation etc. Still in some other embodiments, the degrader, in conjunction with other magnet fields on the system, may be configured such that the beam at its exit point has a narrow spatial cross section and energy spectrum, eliminating the need for a collimator. The gantry assembly 205 may be rotatable while the accelerator remains stationary. The system may be equipped with a swiveling device that renders the rotations of the gantry such that the particle beam can impinges on the isocentrically arranged irradiation station in various directions. In some embodiments, the gantry can swivel 360° about an axis that is substantially parallel to the beam line axis such that the particle beam can impinge on an isocenter in a full circle. The gantry is coupled to a nozzle operable to emit the particle beam onto the radiation object. The nozzle may be coupled to a set of deflection magnets 211 that deflect the beam in mutually orthogonal directions for purposes of traverse scan, e.g. X-Y scan. The nozzle may be coupled to means for monitoring beam position and means for monitoring the radiation dose. The nozzle and the focusing magnets may also be integrated in the gantry. In some embodiments, the nozzle is rotatable and capable of raster scan in two or three dimensions. In some embodiments, the nozzle is capable of pencil-beam scan where the particle beam can be focused on a beam cross-section which lies distinctly below the size of typical irradiation volumes. The peak deposition of the radiation dose along the radiation path corresponds to the Bragg peak location determined by the particle energy. By using a suitable focused pencil beam, many small volumes, so-called voxels, thus can be irradiated, so that the irradiation volumes of any shape, conformal to the specific shape of a tumor, can be raster-scanned. The depth scan can be achieved by varying the particle energy, for example through the ESS. The gantry may comprise a shielding plug 210 which reduces neutron dose risk near the patient. There may be additional shielding around the beam line. The shielding plug may be a cylindrical sphere or any other suitable configurations. The gantry may comprise hybrid materials to balance the cost reduction and protection against undesirable neutron dose risk. In some embodiments, high-Z material shields, such as lead (Pb), are used at places along gantry that would be prevalent to radiation/neutron emission. Cheaper/lighter materials, such as C, can be used in any other places, for example, the part of the gantry that does not face the patient. The present disclosure is not limited to any particular type of accelerator or the associated particle source. In some embodiments, the accelerator may be a cyclotron, for example a superconducting synchrocyclotron in a compact design. In some embodiments, the accelerator may be able to provide protons, neutron, electrons, or heavy ion, such as He2+ or C6+ particles. FIG. 3 is a side view diagram illustrates the mechanical schematics of the compact radiation system equipped with a set of deflection/energy selection magnets 301 and 302 in accordance with an embodiment of present disclosure. In some embodiments of a single-room radiation system in accordance with the present disclosure, the entire beam line, including the rotating portion leading to the gantry and the non-rotating portion leading to the accelerator, is under vacuum. The rotating portion and the non-rotating portion are connected through a vacuum seal. In the illustrated embodiment, the beam is transferred from stationary to rotating parts via a small air gap 303 and two thin kapton (polymide film) windows for example. Thus, each portion has its own vacuum devices and independent of the other portion. This advantageously further simplifies the system, by eliminating the need for a rotating, mechanical vacuum joint, and reduces material cost, simplifies maintenance and less vacuum leaks on the beam pipe. Besides the components described with reference to FIG. 2, FIG. 3 also illustrates the other pertaining components, including storage activated parts and a PV control alcove, and can be appreciated by those with ordinary skills in the art. FIG. 4 is a 3D view diagram illustrating the exterior mechanical schematics of the compact radiation system equipped with a set of deflection/energy selection magnets 401 and 402 in accordance with an embodiment of present disclosure. FIG. 5A and FIG. 5B illustrate a side view and a top view of the beam line in that transport the particle beam from the cyclotron to the gantry in accordance with an embodiment of the present disclosure. Although certain preferred embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. It is intended that the invention shall be limited only to the extent required by the appended claims and the rules and principles of applicable law. |
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description | The present application hereby claims priority under 35 U.S.C. §119 on German patent application number DE 10 2007 058 104.3 filed Dec. 3, 2007, the entire contents of which is hereby incorporated herein by reference. Embodiments of the invention generally relate to a beam admission unit, a beam generation device and/or a tomography device having a beam admission unit. Beam admission devices are used, for example, in x-ray machines such as x-ray computed tomography devices for admitting the x-ray radiation emanating from an x-ray source onto a desired examination or detection region, for example in the form of a fan. By way of the admission unit, inter alia, direct irradiation outside of the desired examination region by the x-ray radiation can be avoided, at least to the greatest extent. The latter in particular decreases the radiation dose applied during the examination of a body. It is known to use a slit screen to admit the x-ray radiation; the former comprises a planar tantalum plate with admission slits provided therein. By using admission slits having different widths, it is possible to admit the x-ray radiation emanating from an x-ray source onto examination or detection regions having different widths, which is desirable in the case of x-ray computed tomography using multirow detectors, for example. It is possible to obtain different admissions by longitudinal displacement of the tantalum plate, that is to say a displacement perpendicular to the longitudinal direction of the admission slits, which positions a respectively suitable admission slit on the beam port of the x-ray source. However, it is disadvantageous in this case that the length of the tantalum plate rapidly increases with an increasing number of desired admission regions and hence increasing number of admission slits. Occasionally, this is due to the fact that, depending on the geometric conditions, a prescribed minimum distance has to be observed between adjacent admission slits. The minimum distance depends on, inter alia, the distance of the tantalum plate from the beam port and the aperture of the beam port. The space available for attaching and to-and-fro displacement of the tantalum plate is substantially limited by housing walls and the like, for example by the housing of the gantry of an x-ray computed tomography scanner, which should be as thin as possible for patient-psychological reasons; hence the number of admission possibilities that can be implemented is limited. In addition, the complexity involved for the mechanical support of the tantalum plate increases with increasing linear dimensions. This is all the more important in x-ray computed tomography since non-negligible acceleration forces act on the tantalum plate during circular or helical scans of the body. Furthermore, conventional drive systems for moving the tantalum plate to-and-fro, which for example comprise a motor-driven threaded spindle for moving the tantalum plate, have a low dynamic range. The latter means that, for example, setting two admission possibilities based on two admission slits which are at a distance from one another requires a relatively long time; this is in contrast to a time-optimized examination of a body, in particular using different recording modes. In addition, a drive system with a threaded spindle is not very stiff and has relatively high wear and tear. However, high wear and tear in turn leads to the play in the drive unit rapidly increasing, which reduces in a non-negligible way the achievable positional accuracy of the admission slits. It is known to design the tantalum plate in an arced shape, in particular in order to decrease its linear extent. However, in this case too, the space available in the cramped spatial conditions is quickly exhausted with increasing numbers of admission slits, in particular with respect to the minimum distance of the admission slits. For example, so-called jaw screens provide a space-saving implementation of a multiplicity of admission possibilities. These screens can for example comprise two jaws which can be moved against one another, or two eccentrically mounted rollers which can be rotated. Moving the jaws or rotating the rollers affords the possibility of realizing many admission slits with different widths. However, a disadvantage of the jaw screen is that two jaws or rollers always have to be synchronously moved in order to set a desired width of an admission slit. This makes the design, and the required control and drive devices for setting the admission slit, more complicated and more expensive. At least one embodiment of the invention reduces or even eliminates at least one of the disadvantages of the prior art. In particular, a beam admission unit of at least one embodiment is intended to be specified which affords the possibility of a multiplicity of admission possibilities by way of a particularly space-saving design. Furthermore, a mechanically robust beam admission unit of at least one embodiment is intended to be specified which affords the possibility of very dynamically interchanging different admission possibilities. Moreover, a beam admission unit of at least one embodiment is intended to be specified which has a compact design and which at the same time affords the possibility of examining a body using a particularly low radiation dose. It is a further goal to specify, in at least one embodiment, a beam generation device and/or a tomography device in an analogous statement of the object. A first aspect of at least one embodiment of the invention relates to a beam admission unit with a plurality of admission segments. Each admission segment has at least one admission slit for admitting radiation emanating from a radiation source onto a predetermined admission region. In particular, the radiation can be x-ray or gamma radiation. The admission slit can be in the form of a thinning of the admission segment, or even a slit-like recess penetrating the admission segment. Deviating from this, within the scope of the invention, the admission slit can also be designed differently depending on, inter alia, the respectively desired admission width and shape, the type of radiation and the latter's energy. The admission segments are arranged one behind the other, interconnected in an articulated fashion and form an admission plate chain in this way. The admission plate chain thus comprises a number of admission segments, interconnected by means of articulated connections. The admission segments can be moved relative to one another by means of these articulated connections, for example about respective rotational axes. This affords the possibility of, for example, rolling up or unrolling the admission segments like a roller blind, as a result of which a particularly space-saving design can be attained, even in the case of a multiplicity of admission segments, that is to say a multiplicity of admission slits and admission possibilities connected to this. In addition to the rolling up and unrolling, any number of other alternatives suitable for space-saving reception and housing of the admission plate chain are feasible, such as curved guide rails or the like. In addition to the space-saving and compact design, a particularly advantageous mechanical stability can moreover be attained. Rolling up and unrolling the admission plate chain onto one or more roller-shaped receptacles is mentioned by way of example without limiting the generality. By rolling up and unrolling the admission plate chain, combined with corresponding guide rails, it is possible to move the admission segments past the beam port and position the respectively suitable admission segment in front of the beam port in order to set a respectively desired admission. A second aspect of at least one embodiment of the invention relates to a beam generation device, comprising a radiation source, in particular an x-ray or gamma radiation source, for generating the respective radiation, and a beam admission unit according to the first aspect of at least one embodiment of the invention arranged downstream of the radiation source in the emission direction. A third aspect of at least one embodiment of the invention relates to a tomography device, in particular an x-ray computed tomography device, comprising a radiation source for generating the radiation; a radiation detector arranged opposite the radiation source in the emission direction of the radiation; and a beam admission unit arranged downstream of the radiation source in the emission direction according to the first aspect of at least one embodiment of the invention. Advantages and advantageous effects of the second and third aspect of at least one embodiment of the invention emerge from the advantages and advantageous effects according to the first aspect of at least one embodiment of the invention. Various example embodiments will now be described more fully with reference to the accompanying drawings in which only some example embodiments are shown. Specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The present invention, however, may be embodied in many alternate forms and should not be construed as limited to only the example embodiments set forth herein. Accordingly, while example embodiments of the invention are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments of the present invention to the particular forms disclosed. On the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of the invention. Like numbers refer to like elements throughout the description of the figures. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments of the present invention. As used herein, the term “and/or,” includes any and all combinations of one or more of the associated listed items. It will be understood that when an element is referred to as being “connected,” or “coupled,” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected, ” or “directly coupled,” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between,” versus “directly between,” “adjacent,” versus “directly adjacent,” etc.). The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention. As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the terms “and/or” and “at least one of” include any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper”, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein are interpreted accordingly. Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the present invention. In the figures, identical, or functionally identical, elements are referred to throughout using the same reference symbols. The illustrations in the figures are schematic and not necessarily true to scale, with the scales possibly varying between the figures. In the following text, the x-ray computed tomography device and the beam generation device are—without limiting the generality—only discussed to the extent considered to be necessary for understanding the invention. FIG. 1 schematically shows an x-ray computed tomography device 1, as an example of a tomography device, according to the third aspect of an embodiment of the invention. The x-ray computed tomography device 1 has a patient couch 2 on which a patient 3 to be examined (also referred to as a body in the following text) is positioned. Provision is made in a gantry 4 for a beam generation device 6 and, arranged opposite it, a detector 7 such that they can rotate about a system axis 5. The beam generation device 6 comprises an x-ray tube 8 for generating x-ray radiation 9. A beam admission unit 10 is arranged downstream of the x-ray tube 8 in the emission direction of the x-ray radiation 9, that is to say in the direction of the detector 7 starting from the x-ray tube 8. In order to examine the body 3 or an area of interest of the latter, it is scanned, e.g. circularly or helically, by the x-ray radiation 9 emanating from the beam generation device 6. In the process, the x-ray radiation 9 passes through the body 3 and is attenuated when passing through the body 3 in accordance with the respective absorption properties of the body 3. The part of the x-ray radiation 9 transmitted through the body 3 is detected by means of the detector 7. A, for example, two- or three-dimensional display of at least the part of the body 3 of interest can be determined based on the measurement data of the detector 7 which reflects the absorption properties of the body 3. The detector 7 is—without limiting the generality—a multirow, pixelated detector. It has a number of detector rows 11, parallel to the system axis 5, which are only shown in FIG. 4. The number of detector rows 11 can differ from the illustration in FIG. 4. Furthermore, within the scope of at least one embodiment of the invention, provision can also be made for detector rows 11 of varying width so that different layers of the body 3 can be scanned. Additionally, housing walls and a gantry opening, through which the body 3 can be moved during an examination, are referred to by reference symbols 12 and 13. Reference is already made here to the fact that the space available for mounting and operating the beam admission unit 10 is significantly limited by the housing walls 12 and the width B of the gantry opening 13 in the direction of the system axis 5 which is occasionally restricted by non-technical, patient-specific circumstances. FIG. 2 shows a cross-sectional illustration of the beam generation device 6 in a plane perpendicular to the system axis 5, with the beam generation device 6 comprising the x-ray tube 8 and the beam admission unit 10, as already mentioned above. The housing walls 12 of the gantry 4, located to the left and right of the beam generation device 6, are indicated by the dashed lines. X-ray radiation is generated in a conventional fashion by means of the x-ray tube 8 by electron bombardment of an anode 14 which in the present case has an annular design. The x-ray beams, emitted in the direction of the gantry opening 13 due to the beveled shape of the anode 14, can escape the housing of the x-ray tube 8 through a beam port 15. A maximum aperture αmax for the x-ray radiation 9 is defined by the beam port 15. In some applications or examination protocols, limiting the maximum aperture αmax is desirable or required. The later is the case, for example, if body layers having differing thicknesses are intended to be scanned. The beam admission unit 10 is provided for limiting the maximum aperture αmax to a respectively required reduced aperture αred, that is to say for admitting the x-ray radiation 9 onto a desired or prescribed admission region E on the detector 7 (see FIG. 4). The beam admission unit 10 comprises an admission plate chain 16, which in turn has a number of interconnected admission segments 17 connected in an articulated fashion. Each admission segment 17 has an admission slit 18 designed to admit the x-ray radiation 9. As can be seen from FIG. 2, the admission segments 17 form individual elements of the admission plate chain 16. The admission segments 17 are arranged one behind the other, with in each case two admission segments 17 lying one behind the other, that is to say a first and a second, adjacent admission segment, being connected to one another by means of an articulated connection 19 so that they can be moved relative to one another. The articulated connection 19 can basically be any type of articulated connection. Without limiting the generality, the following are mentioned as articulated connections 19: hinge joints, ball and socket joints. In the case of a hinge joint, a joint head, for example on the first admission segment, is generally enclosed by a joint recess, for example on the second admission segment, with a rotation of the first admission segment relative to the second admission segment about a common rotational axis 24 (FIG. 2) being possible. In the case of a ball and socket joint, the joint head and joint recess have a spherical design. The admission segments 17 of the admission plate chain 16 can have substantially arbitrary widths in their longitudinal direction, corresponding to the respective demands on the admission of the x-ray radiation 9. In the case illustrated in FIG. 2, the admission segments 17 have the same width and can basically cover the entire width of the beam port 15. This can avoid excessive radiation in the case of a respectively set admission possibility, that is to say undesired radiation can be prevented from passing through the space between two adjacent admission segments 17 or through a neighboring admission slit 18. As can be seen from FIG. 3, the admission segments 17 are arranged one behind the other in such a way that spaces between the admission segments 17 and the first possibility of excessive radiation are avoided. By way of example, this can be achieved by means of a for example step-like overlap of two adjacent admission segments 17 and the like (not shown). By way of an identical structural width of the admission segments 17, the admission segments 17 can be interchanged without any problem and can be arranged one behind the other in an arbitrary sequence without changing the overall length of the admission plate chain 16 and the positioning prescriptions for positioning a particular admission segment 17 at a prescribed location in the admission plate chain 16. Inter alia, this also allows simple adaptation for different detector types which have a different number of detector rows 11 and different widths of the detector rows 11. With regard to simple positioning and avoiding excessive radiation, it is also advantageous if the admission slits 18 of the admission segments 17 are arranged centrally in the longitudinal direction of the admission plate chain 16. As can be seen from the cross-sectional illustration in FIG. 2, the admission slits 18 have, with respect to the longitudinal direction of the admission plate chain 16, different widths in the sectional plane relevant to FIG. 2, which widths reflect the admission possibilities. The admission slits 18 can be rectangular, as can be seen in the plan view in FIG. 3. The shape of the admission slits 18 also depends on, inter alia, the respective section of the body 3 to be scanned or the respective body layer to be scanned. If the admission segments 17 are of planar design, as is illustrated in FIG. 2 and FIG. 3, it is possible that there is barrel-shaped excessive radiation on the admission region E provided on the detector 7. The latter leads to the patient 3 being unnecessarily exposed to radiation. Such excessive radiation can be avoided by suitably shaped admission slits 18. The admission slits 18 can, for example, be tapered toward their center with respect to their longitudinal direction, as is shown in FIG. 4. The tapered shape affords the possibility of only a, for example rectangular, detection region relevant for imaging being admitted onto the detector 7. This affords the possibility of requiring a particularly small amount of space and at the same time significantly reducing the exposure of the patient to radiation. So that a large enough proportion of the x-ray radiation 9 is absorbed by the admission segments 17, these can be produced from, for example, tantalum, tungsten or another radiation absorbing material which can satisfy the respective absorption requirements. The required degree of absorption of the admission segments 17 sometimes depends on the respective application and the respectively desired degree of the reduction in the radiation dose. As can be seen from FIG. 2 and FIG. 3, the beam admission unit 10 furthermore comprises a first cylinder roll receptacle 20 and a second cylinder roll receptacle 21. A first end 22 of the admission plate chain 16 is connected to the first cylinder roll receptacle 20, and a second end 23, at the far end from the first end 22, is connected to the second cylinder roll receptacle 21. Although the cylinder roll receptacles 20 and 21 are in the shape of a barrel, other shapes which are suitable for rolling up or unrolling the admission plate chain onto or from them are also feasible within the scope of the invention. The first 20 and second 21 cylinder roll receptacles are mounted such that they can rotate about the respective rotational axis 24. The first cylinder roll receptacle 20 is connected to a stepper motor 25 for its rotational drive. The second cylinder roll receptacle 21 is pre-stressed against the first cylinder roll receptacle 20 by means of a helical spring so that the admission plate chain 16 is acted on by a tensioning force acting between the first 20 and second 21 cylinder roll receptacles. A play of the admission plate chain 16 detrimental to a positionally-exact setting of an admission possibility can be substantially reduced by the pre-stressing. A guide unit for guiding the admission segments 17 along a prescribed guide path in the longitudinal direction of the admission plate chain 16 is arranged between the first cylinder roll receptacle 20 and the second cylinder roll receptacle 21. In the present case, the guide path is prescribed by two (in general at least one) guide rails 27 such that the admission segments 17 can be led past, and positioned in front of, the beam port 15 in such a fashion that the respectively desired admission can be set. The admission segments 17, connected in an articulated fashion according to the invention, can be rolled up onto or unrolled from the first 20 and second 21 cylinder roll receptacles. This affords the possibility of implementing a multiplicity of admission possibilities, basically given by the number of admission segments 17, while at the same time having a particularly space-saving embodiment of the beam admission unit 10. The number of admission possibilities that can be implemented is limited to a substantially smaller extent by the housing walls 12 (see FIG. 2) and the like compared to known, planar admission plates. Additionally, the beam admission unit 10 is robust and affords the possibility of rapid and precise displacement of the admission segments 17, for example by way of a stepper motor flange-mounted directly, or via a transmission, to the first cylinder roll receptacle 20. This means that different admission possibilities can be set quickly and very precisely. In particular, the displacement can be effected in a time window of the order of milliseconds, which is expedient for x-ray computed tomography. It is possible that in addition to the abovementioned advantages, the radiation exposure of the patient 3 to be examined can be kept particularly low by means of a suitably chosen average width of the admission slits 18. Furthermore, the beam admission unit 10 according to the invention having a multiplicity of admission possibilities can be produced with comparatively small structural complexity and at a low cost. Deviating from the preceding illustration, it is also possible that provision is only made for one cylinder roll receptacle, and the part of the admission plate chain 16 not held therein is held in guide rails and guided in the latter. In the process, it is possible that, in a way similar to the above, the second end 23 is pre-stressed against the first cylinder roll receptacle by way of a pre-stressing unit, e.g. a helical spring. The course of the guide rails can, for example, be adapted to the spatial conditions within the gantry 4. For example, the guide rails can extend linearly in the region of the beam port 15 and have a spiral profile in an adjacent region so that the part of the admission plate chain 16 unrolled from the first cylinder roll receptacle 20 can be held in a space-saving fashion. It is also possible that the admission plate chain 16 is only guided in guide rails, without cylinder roll receptacles being provided. To this extent, the embodiments shown in the figures should not be considered to be limiting. Rather, further beam admission units, modified with respect to the figures, are feasible and possible within the scope of at least one embodiment of the invention. It is clear, in particular from the above description and the above example embodiments, that the beam admission unit according to the invention, the beam generation device and the tomography device achieve objects on which embodiments of the invention are based. Thus, provision can be made especially for a particularly space-saving, robust and reliable beam admission unit. Further, elements and/or features of different example embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. Still further, any one of the above-described and other example features of the present invention may be embodied in the form of an apparatus, method, system, computer program and computer program product. For example, of the aforementioned methods may be embodied in the form of a system or device, including, but not limited to, any of the structure for performing the methodology illustrated in the drawings. Even further, any of the aforementioned methods may be embodied in the form of a program. The program may be stored on a computer readable media and is adapted to perform any one of the aforementioned methods when run on a computer device (a device including a processor). Thus, the storage medium or computer readable medium, is adapted to store information and is adapted to interact with a data processing facility or computer device to perform the method of any of the above mentioned embodiments. The storage medium may be a built-in medium installed inside a computer device main body or a removable medium arranged so that it can be separated from the computer device main body. Examples of the built-in medium include, but are not limited to, rewriteable non-volatile memories, such as ROMs and flash memories, and hard disks. Examples of the removable medium include, but are not limited to, optical storage media such as CD-ROMs and DVDs; magneto-optical storage media, such as MOs; magnetism storage media, including but not limited to floppy disks (trademark), cassette tapes, and removable hard disks; media with a built-in rewriteable non-volatile memory, including but not limited to memory cards; and media with a built-in ROM, including but not limited to ROM cassettes; etc. Furthermore, various information regarding stored images, for example, property information, may be stored in any other form, or it may be provided in other ways. Example embodiments being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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abstract | A method for inspecting a settling time of a deflection amplifier includes setting a settling time, performing shooting a plurality of times alternately to project two patterns of different types which are shaped by making a charged particle beam pass through a first and a second apertures while deflecting the charged particle beam by a deflector controlled by an output of a deflection amplifier which is driven based on the settling time having been set, measuring beam currents of the shooting, calculating an integral current of the beam currents measured, and calculating a difference between the integral current calculated and a reference integral current to output the difference. |
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claims | 1. A system for the storage of a radioactive waste product beneath a ground surface, the system comprising:a bore hole formed through the ground surface, the bore hole having a wall and a bottom;a container storage area defined by the bottom, the wall, and a removable upper cover opposite the bottom;a chain of containers comprising a first container connected to a second container through a flexible link, each of the first container and the second container containing the radioactive waste product and both being positioned within the container storage area; anda cable connected to the first container through which the chain of containers is selectively inserted and retrieved from the bore hole, the cable being further attached to one or both of the bore hole and the removable upper cover. 2. The system of claim 1, wherein cooling water fills at least a portion of the container storage area covering the first container and the second container, an air gap being formed between a water surface of the cooling water and the removable upper cover. 3. The system of claim 1, wherein an inert gas is contained within the container storage area. 4. The system of claim 1, wherein one or more sensors are located in the container storage area positioned near one or both of the first container and the second container. 5. The system of claim 4, wherein the one or more sensors pass through one or more sensor passages in selective communication with the bore hole. 6. The system of claim 1, wherein the first container is constructed of a metal, a plastic, a fiber or a composite. 7. The system of claim 1, wherein the first container is in the shape of a barrel, a tube, a sphere, or a cylinder. 8. The system of claim 1, wherein the radioactive waste product is a vitrified waste or bundles of spent nuclear fuel rods. 9. The system of claim 1, wherein the flexible link permits the suspension of the second container beneath the first container when the chain of containers is suspended from the cable. 10. The system of claim 1, wherein the flexible link comprises one or more of a cable, a chain, a rope, or a flexible tube. 11. The system of claim 1, wherein a lining sheaths the wall of the container storage area. 12. The system of claim 11, wherein the lining is constructed of steel, plastic, a fiber, a composite, or any combination thereof. 13. The system of claim 1, wherein a lower cover is positioned in the bore hole between the bottom and the chain of containers, the lower cover further defining a lower boundary of the container storage area. 14. The system of claim 13, wherein the lower cover forms a seal from the bottom of the bore hole. 15. The system of claim 1, wherein one or more sensors in the container storage area are positioned in a location near the chain of containers to detect a radiation leakage so as to trigger removal of all or part of the chain of containers. 16. A system for the storage of a radioactive waste product beneath a ground surface, the system comprising:a bore hole formed through the ground surface, the bore hole having a wall and a bottom;a container storage area defined by the bottom, the wall, and a removable upper cover opposite the bottom;a chain of containers comprising a first container directly linked to a second container through a flexible link, each of the first container and the second container containing the radioactive waste product and both being positioned within the container storage area; anda cable connected to the first container through which the chain of containers is selectively inserted and retrieved from the bore hole;wherein the flexible link permits the suspension of the second container beneath the first container when the chain of containers is suspended from the cable. 17. The system of claim 16 wherein the cable further is attached to one or both of the bore hole and the removable upper cover. |
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claims | 1. A nuclear fuel composition comprising:a nuclear fissile material; anda neutron-absorption material adjoining the nuclear fissile material, the neutron-absorption material including 25 wt %-75 wt % samarium as a partial substitute for a remainder amount of a rare earth element to limit destroying a negative temperature coefficient of reactivity of the nuclear fissile material by the rare earth element, wherein the neutron-absorption material comprises ≦0.5 wt % of a combined weight of the nuclear fissile material and the neutron-absorption material. 2. The nuclear fuel composition as recited in claim 1, wherein the rare earth element is gadolinium. 3. The nuclear fuel composition as recited in claim 1, wherein the neutron-absorption material includes 30 wt % -40 wt % of the samarium. 4. The nuclear fuel composition as recited in claim 1, wherein the neutron-absorption material includes 35 wt % -38 wt % of the samarium. 5. The nuclear fuel composition as recited in claim 1, wherein the neutron-absorption material comprises ≦0.1 wt % of the combined weight. 6. The nuclear fuel composition as recited in claim 1, wherein the neutron-absorption material comprises ≦0.05 wt % of the combined weight. 7. The nuclear fuel composition as recited in claim 1, wherein the neutron-absorption material is dispersed within the nuclear fissile material. 8. The nuclear fuel composition as recited in claim 1, wherein the neutron-absorption material is a coating disposed on pellets of the nuclear fissile material. 9. The nuclear fuel composition as recited in claim 1, wherein the nuclear fissile material comprises uranium-zirconium-hydride (UZrHx). 10. The nuclear fuel composition as recited in claim 1, wherein the samarium has a neutron-absorption energy peak (cross-section) that at least partially overlaps a thermal energy range of the neutrons from the nuclear fissile material. 11. A nuclear reactor comprising:a nuclear fissile material; anda neutron-absorption material adjoining the nuclear fissile material, the neutron-absorption material including 25 wt % -75 wt % samarium as a partial substitute for a remainder amount of a rare earth element to limit destroying a negative temperature coefficient of reactivity of the nuclear fissile material by the rare earth element, wherein the neutron-absorption material comprises ≦0.5 wt % of a combined weight of the nuclear fissile material and the neutron-absorption material. 12. The nuclear reactor as recited in claim 11, wherein the neutron-absorption material is dispersed within the nuclear fissile material. 13. The nuclear reactor as recited in claim 11, wherein the neutron-absorption material is a coating disposed on pellets of the nuclear fissile material. 14. The nuclear reactor as recited in claim 11, further comprising a hollow cladding containing the nuclear fissile material, and the neutron-absorption material is a coating disposed on an inside surface of the hollow cladding. 15. The nuclear reactor as recited in 11, wherein the rare earth element is gadolinium. 16. The nuclear reactor as recited in claim 11, wherein the neutron-absorption material includes 30 wt % -40 wt % of the samarium. 17. A method of rendering a nuclear fuel inherently subcritical, comprising:forming nuclear fuel from a nuclear fissile material and a neutron-absorption material adjoining the nuclear fissile material, and the neutron-absorption material includes 25 wt % -75 wt % samarium as a partial substitute for a remainder amount of a rare earth element to limit destroying a negative temperature coefficient of reactivity of the nuclear fissile material by the rare earth element, wherein the neutron-absorption material comprises ≦0.5 wt % of a combined weight of the nuclear fissile material and the neutron-absorption material, and the neutron-absorption material has a neutron absorption energy range that overlaps a thermal energy range of neutrons from the nuclear fissile material to thereby render the nuclear fuel inherently subcritical. 18. The method as recited in claim 17, including dispersing the neutron-absorption material within the nuclear fissile material. 19. The method as recited in claim 17, including depositing the neutron-absorption material as a coating. 20. The method as recited in claim 17, wherein the rare earth element is gadolinium. 21. The method as recited in claim 17, wherein the neutron-absorption material includes 30 wt % -40 wt % of the samarium. |
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046474250 | description | DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to the presently preferred embodiment of the invention, with reference to the accompanying Figure. After shutdown of a reactor 100 for maintenance, refueling, or the like the coolant is usually borated to refueling conditions. The RCS is then cooled down using an RHR system 102 which typically comprises a RHR pump 104, a RHR heat exchanger 106 and control valves 108 and 109. The RHR system 102 is connected between a "hot leg" 110 of the RCS which connects the outlet nozzle 112 of the reactor vessel 114 to a steam generator 116. In the Figure, the numeral 118 indicates the reactor vessel head and numeral 120 the reactor vessel flange. The RHR system is an auxiliary cooling system used to cool down the reactor if the main cooling system is isolated as a result of a fault or the like. Since the reactor core 122 continues to generate decay heat for a period of time after shutdown, the RHRS is utilized to take out this residual heat. In accordance with the present invention, selected steam generator(s) 116 and the RHR system are used during degassing. It should be understood that a typical reactor will have on the order of two to four steam generators associated with it, not all of which are necessarily used during the vacuum degassing and refill method described herein. The RCS is drained to the middle of the reactor vessel outlet nozzle 112 which coincides with the middle of the hot leg 110. At the same time, cooling water is set to flow through the shell (secondary side) of selected steam generators 116 via cooling water inlet 122 and cooling water outlet 124. A two-phase pump 126 is used to draindown the RCS to the middle of the hot leg. A two-phase pump 126 is used since, in accordance with the present invention, the RCS is not vented during draindown and will eventually reach saturation conditions resulting in a low available net positive suction head (NPSH). The two-phase pump is required to satisfy the pump suction condition of low pressure. The pump 126 is the only significant structural modification to the existing reactor system necessary in order to practice the present invention. In prior vacuum degassing systems, nitrogen was admitted to the reactor vessel through a nitrogen reservoir via a pressure relief tank. Thus, two-phase pumping was not required and the single, liquid phase reactor coolant would drain by gravity to the reactor coolant drain tank pump 129 to draindown the RCS. As the RCS is drained, the RHR flow is throttled as necessary using valves 108 and 109 to prevent cavitation of the RHR pump 104. The valve 109 is operated by a flow controller FC to bypass the RHR heat exchanger through bypass line 111 whenever the outlet flow rate falls below a predetermined value. Since according to the present invention the RCS is not vented during draindown, steam bubbles will be formed in the reactor coolant due to the low pressure saturation condition existing in the RCS. Essentially, using the present method, the reactor coolant boils during draindown as a result of lowering the pressure at the prevailing temperature. This boiling action enhances degassing the reactor coolant. As alluded to above, in prior art vacuum degassing systems, the draindown operation was performed using a single phase pump 129 and over a slight nitrogen pressure, thus avoiding boiling during the draindown. Because the RHR system is throttled, condensation will occur in the inverted U-tubs 134 of the steam generator 116 whose shell is being cooled by a secondary cooling system 122, 124. This condensed steam will flow back or reflux to the hot leg 110 and be drawn through the RHR system. Thus, the present invention utilizes selected steam generators 116 as reflux condensers to condense steam in the primary side (the side carrying reactor coolant flow) into droplets which form on the inside of the steam generator tubes 134. Thus, using the present invention, both selected steam generators 116 and the RHR heat exchanger 106 are used to cool the reactor coolant and strip away non-condensible gases. As further explained below, the steam generators 116 continue to function as reflux condensers until the vacuum on the RCS is broken thus causing coolant boiling to stop. Radiogas, hydrogen and other gases stripped from the reactor coolant are removed as non-condensibles by the vacuum pump 136 and gas removal system, generally 138, via the pressurizer tank 132. In accordance with a preferred embodiment of the present method, after the reactor coolant level has been drained to the middle of the hot leg 110 and the RHR stabilized, the pressurizer tank 132 is drained and the vacuum pump 136 started. Preferably, the vacuum pump is of the water ring type where water is used as a pump sealant and capable of handling steam. After a vacuum is established in the pressurizer tank 132 due to the draindown, relief valve 142 is opened and the non-condensibles, as well as any steam in the RCS, are drawn by the vacuum pump 126 into a gas removal system which may comprise either the existing waste gas removal system including a gas compressor 140 and evacuated gas delay tanks 141 or a dedicated waste gas removal system specifically designed to accommodate any oxygen present in the gas handling portion of the system. After a suitable storage period the evacuated gases may be vented through a vent 143. Vacuum induced gas flow continues until an RHR system sample indicates acceptable radiogas and hydrogen concentration. In a typical reactor, the vacuum degassing operation, when performed according to the present invention, can be accomplished in approximately two hours or less depending upon the design of the vacuum system. After establishing the proper radiogas and hydrogen concentration in the coolant, the vacuum pump 136 is stopped and isolated from the RCS by means of isolation valve 144. Air is admitted into the vacuum system from the air reservoir 146 via a filter 131 and valve 133. This breaks the vacuum and instantly aerates the circulating reactor coolant. The oxygen in the air dissolves in the reactor coolant thus facilitating the solubilization of radioactive material that may subsequently be removed by ion-exchange in a CVCS demineralizer or the like. Both air and hydrogen perioxide are sources of oxygen and either can be used to oxygenate the coolant. It should be appreciated that hydrogen peroxide is a difficult chemical to handle and the sudden inrush of air caused by the breaking of the vacuum is a preferred way to oxygenate the reactor coolant. Purification for solubilized radioactive material removal may be achieved by using a mixed bed demineralizer 180 via feed and bleed through the low pressure purification system of the CVCS. Since condensing stops in the steam generators 116 when the vacuum is broken, RHR flow is increased to satisfy the additional heat load. When adequate purification is achieved, the pressure vessel head 118 is removed and the reactor vessel and refueling cavity is flooded and refueling or other shutdown operations may commence. At the end of the shutdown operations, such as refueling, and after the reactor vessel head 118 is resecured, the vessel is again drained down to the nozzle midplane and the vacuum system is again used to evacuate the vapor space and refill the RCS. Air is evacuated from the steam generator tubes and the vapor space in the reactor vessel using the vacuum pump 136. The system is then refilled under vacuum. The air suctioned off during this evacuation may be vented through the containment vent 152 since it will contain no radiogas. This eliminates the very time consuming operation of jogging the reactor coolant pumps and venting the system multiple times. Importantly, the amount of oxygen previously required to be removed by addition of hydrazine during this operation is also reduced. Air which was previously trapped in the steam generator tubes during the system refill operation and literally squeezed into solution during the prior art jog-vent-fill cycle of refilling is now removed by the evacuation process and therefore very little free oxygen is dissolved in the coolant for removal by hydrazine. Thus, not only is the hydrazine/oxygen reaction time reduced, but also much less hydrazine is required. In this regard it should be appreciated that the jog-fill-vent cycle of the reactor coolant pumps and the removal of oxygen using the hydrazine/oxygen reaction is a very time consuming operation. When refill is completed, the reactor coolant pumps are started once and remain running. Startup then proceeds as normal and the reactor coolant vacuum degassing and refill system is secured. It is important to appreciate that with the method of the present application, the RCS is not vented as it is being drained down by the two-phase pump 126. In accordance with the present method, no nitrogen gas or the like will be introduced into the RCS. This results in degassing during draindown since as the reactor coolant level is lowered, a vacuum is created in the RCS which results in reactor coolant boiling at the prevailing relatively low temperature. In addition, the present method utilizes selected steam generators as reflux condensers by flowing cooling water through the secondary or shell side of the steam generator causing the steam in the primary or reactor coolant side to condense as liquid droplets and reflux back into the bulk of reactor coolant which is flowing through the RHR system. 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 in order to best explain the principles of the invention and its practical application to 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. |
description | This application claims the benefit of U.S. provisional application Ser. No. 60/481,722, filed Nov. 29, 2003. The present invention relates generally to diagnostic imaging and, more particularly, to a self-aligning scintillator-collimator assembly and method of manufacturing same. Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image. Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator having a plurality of collimator plates for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom. Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction. Image quality can be directly associated with the degree of alignment between the components of the detector. “Cross-talk” between detector cells of a CT detector is common and to some degree is affected by the alignment, or lack thereof, of the detector components. In this regard, cross-talk is typically higher when the components of the CT detector are misaligned. Cross-talk is generally defined as the communication of data between adjacent cells of a CT detector. Generally, cross-talk is sought to be reduced as cross-talk leads to artifact presence in the final reconstructed CT image and contributes to poor spatial resolution. Typically, four different types of cross-talk may result within a single CT detector. Cross-talk can occur as light from one cell is passed to another through a contiguous layer between the photodiode layer and the scintillator. Electrical cross-talk can occur from unwanted communication between photodiodes. Optical cross-talk may occur through the transmission of light through the reflectors that surround the scintillators. X-ray cross-talk may occur due to x-ray scattering between scintillator cells. In order to reduce cross-talk, the plates or layers of a collimator are aligned with the cells of the scintillator arrays to very tight and exacting tolerances. This alignment of the plurality of cells of the scintillator array and the plates of the collimator can be a time consuming a labor intensive process. Further, the physical placement or alignment of the collimator to the scintillator array is particularly susceptible to misalignment stack-up. That is, one of the scintillator-collimator assemblies, if unaligned, can detrimentally effect the alignment of adjacent assemblies. Simply, if one collimator-scintillator array combination is misaligned, all subsequently positioned collimator-scintillator array combinations will be misaligned absent implementation of corrective measures. Further, such assemblies require adjusting several detectors when only one of the detectors is misaligned. Therefore, it would be desirable to design a method and apparatus for the alignment of a collimator and a scintillator module to thereby reduce cross-talk and improve spatial resolution of a final reconstructed image. The present invention is directed to a CT detector and method of manufacturing the same that overcomes the aforementioned drawbacks. The CT detector includes a scintillator module having at least one indexing pin. The indexing pin is constructed to engage a recess between a pair of teeth of a comb designed to align collimating elements of a collimator assembly. Therefore, according to one aspect of the present invention, a CT detector is disclosed which includes a scintillator module having at least one scintillator and at least one indexing pin connected thereto. The at least one scintillator is configured to be impinged with radiographic energy from a radiographic energy source. A collimator assembly includes a plurality of collimator elements and a plurality of teeth configured to define a relative position of the plurality of collimator elements. A portion of the plurality of teeth is configured to engage the at least one indexing pin. According to another aspect of the present invention, a scintillator-collimator combination is disclosed which includes a plurality of collimator elements configured to collimate x-rays projected thereat and a scintillator module. The scintillator module has a scintillator pack formed of a material configured to illuminate upon reception of x-rays. A comb having a first set and a second set of teeth is constructed to align the plurality of collimator elements. Additionally, the second set of teeth is constructed to engage the scintillator module and align the scintillator module relative to the plurality of collimator elements. The first set of teeth extends in a direction generally transverse to the second set of teeth. Such a construction forms a collimator assembly and scintillator module that can be quickly and repeat-ably associated. In accordance with another aspect of the present invention, a CT system is disclosed that includes a rotatable gantry having a bore centrally disposed therein. A table is configured to position a subject for CT data acquisition and is movable fore and aft through the bore. A high frequency electromagnetic energy projection source is positioned within the rotatable gantry and configured to project high frequency electromagnetic energy toward the subject. A detector array is disposed within the rotatable gantry and configured to detect high frequency electromagnetic energy projected by the projection source and impinged by the subject. The detector array includes a plurality of scintillator modules and a collimator assembly. Each scintillator module has a scintillator array and an indexing pin, and the collimator assembly has a plurality of collimator plates. The detector array also includes a detector support having at least one comb of alignment teeth. The alignment teeth are constructed to align the plurality of collimator plates and are constructed to engage an indexing pin to align a scintillator array with a plurality of collimator plates. Such a construction forms a detector array wherein the teeth of the comb align the scintillator module and the collimator, and position the plates relative thereto. According to yet another aspect of the present invention, a method of manufacturing a CT detector is disclosed which includes providing a scintillator array having at least one locator extending beyond the scintillator array, providing a comb having a plurality of teeth constructed to define a spacing between collimating elements of a collimator, and positioning the at least one locator between at least two of the plurality of teeth. Various other features and advantages of the present invention will be made apparent from the following detailed description and the drawings. The operating environment of the present invention is described with respect to a four-slice computed tomography (CT) system. However, it will be appreciated by those skilled in the art that the present invention is equally applicable for use with single-slice or other multi-slice configurations. Moreover, the present invention will be described with respect to the detection and conversion of x-rays. However, one skilled in the art will further appreciate that the present invention is equally applicable for the detection and conversion of other high frequency electromagnetic energy. The present invention will be described with respect to a “third generation” CT scanner, but is equally applicable with other CT systems. Referring to FIGS. 1 and 2, a computed tomography (CT) imaging system 10 is shown as including a gantry 12 representative of a “third generation” CT scanner. Gantry 12 has an x-ray source 14 that projects a beam of x-rays 16 toward a detector array 18 on the opposite side of the gantry 12. Detector array 18 is formed by a plurality of detectors 20 which together sense the projected x-rays that pass through a medical patient 22. Each detector 20 produces an electrical signal that represents the intensity of an impinging x-ray beam and hence the attenuated beam as it passes through the patient 22. During a scan to acquire x-ray projection data, gantry 12 and the components mounted thereon rotate about a center of rotation 24. Rotation of gantry 12 and the operation of x-ray source 14 are governed by a control mechanism 26 of CT system 10. Control mechanism 26 includes an x-ray controller 28 that provides power and timing signals to an x-ray source 14 and a gantry motor controller 30 that controls the rotational speed and position of gantry 12. A data acquisition system (DAS) 32 in control mechanism 26 samples analog data from detectors 20 and converts the data to digital signals for subsequent processing. An image reconstructor 34 receives sampled and digitized x-ray data from DAS 32 and performs high speed reconstruction. The reconstructed image is applied as an input to a computer 36 which stores the image in a mass storage device 38. Computer 36 also receives commands and scanning parameters from an operator via console 40 that has a keyboard. An associated cathode ray tube display 42 allows the operator to observe the reconstructed image and other data from computer 36. The operator supplied commands and parameters are used by computer 36 to provide control signals and information to DAS 32, x-ray controller 28 and gantry motor controller 30. In addition, computer 36 operates a table motor controller 44 which controls a motorized table 46 to position patient 22 and gantry 12. Particularly, table 46 moves portions of patient 22 through a gantry opening 48. As shown in FIGS. 3 and 4, detector array 18 includes a plurality of single scintillator fibers 57 forming a scintillator array 56. In one embodiment, shown in FIG. 3, detector array 18 includes 57 detectors 20, each detector 20 having an array size of 16×16. As a result, array 18 has 16 rows and 912 columns (16×57 detectors) which allows 16 simultaneous slices of data to be collected with each rotation of gantry 12. Switch arrays 80 and 82, as shown in FIG. 4, are multi-dimensional semiconductor arrays coupled between scintillator array 56 and DAS 32. Switch arrays 80 and 82 include a plurality of field effect transistors (FET) (not shown) arranged as multi-dimensional array. The FET array includes a number of electrical leads connected to each of the respective photodiodes 60 and a number of output leads electrically connected to DAS 32 via a flexible electrical interface 84. Particularly, about one-half of photodiode outputs are electrically connected to switch 80 with the other one-half of photodiode outputs electrically connected to switch 82. Additionally, a thin reflector layer (not shown) may be interposed between each scintillator fiber 57 to reduce light scattering from adjacent scintillators. Each detector 20 is secured to a detector frame 77, FIG. 3, by mounting brackets 79. Referring to FIG. 4, switch arrays 80 and 82 further include a decoder (not shown) that enables, disables, or combines photodiode outputs in accordance with a desired number of slices and slice resolutions for each slice. Decoder, in one embodiment, is a decoder chip or a FET controller as known in the art. Decoder includes a plurality of output and control lines coupled to switch arrays 80 and 82 and DAS 32. In one embodiment defined as a 16 slice mode, decoder enables switch arrays 80 and 82 so that all rows of the photodiode array 52 are activated, resulting in 16 simultaneous slices of data for processing by DAS 32. Of course, many other slice combinations are possible. For example, decoder may also select from other slice modes, including one, two, and four-slice modes. Referring to FIG. 5, each detector module 20 is constructed to have a pair of indexing pins 100 that engages a comb 102 integrally formed with or connected to detector frame 77. Comb 102 includes a first set of teeth 106 and a second set of teeth 108. X-rays 16 pass through the plates 104 of collimator assembly 103 and impinge upon scintillators 57. It is understood that comb 102 does not extend over the scintillator array 56 of the detector 20. As such, while comb 102 positions collimator 103 relative to the scintillator array 56, comb 102 does not interfere with the passage of x-rays through the collimator 103 to the scintillator array. First set of teeth 106 of comb 102 extend in a direction, indicated by arrow 110, and second set of teeth 108 of comb 102 extend in another direction, indicated by arrow 112, generally transverse to direction 110. In this regard, the second set of teeth has a height greater than that of the first set of teeth. As such, the second set of teeth defines a recess sized to snuggly receive an indexing pin 100. Moreover, the spacing between the adjacent teeth of the first set of teeth and the second set of teeth is uniform. This opening defines the direction or gap between the collimator plates. That is, when positioning the collimator plate 104, teeth 106, 108 are used to achieve a uniform alignment and spacing. Plates 104 are generally aligned with the scintillators in order to minimize x-ray cross-talk. It is understood that plates 104 could be constructed to substantially match the construction of different scintillator constructions. These constructions include, but are not limited to, scintillators having generally cellular constructions. Moreover, the collimator plates may extend along the x-axis, z-axis, or both. It is noted that the first set of teeth 106, by extending in direction 110, do not obstruct or interfere with the engagement of indexing pin 100 with second set of teeth 108. Collimator 103 is positioned between detector 20 and x-ray source 14 such that plates 104 are aligned with the scintillators 57 of the scintillator array 56. As such, comb 102 not only defines the spacing between adjacent plates 104, but also aligns the collimator and the scintillator. Although shown as a one-dimensional collimator, it is understood that collimator 103 could be constructed to be a two-dimensional collimator and therefore extend across the scintillator module in both the x and z-directions. Also, while only one comb 102 is shown, it is contemplated that a second comb may also be used to align the collimator plate and scintillator array at each respective end thereof. As such, the scintillator pack may include two indexing pins, aligned with one another, but at opposite ends of the module. Scintillators 57 of scintillator array 56, particularly for multi-slice detectors, are commonly oriented in two orthogonal dimensions, generally the x and the z-directions. In order to minimize x-ray cross-talk between adjacent scintillators 57, the plates 104 of the collimator are aligned with the scintillators of the scintillator array. The plates of the collimator must also be precisely oriented relative to one another to ensure uniform spacing between adjacent plates. The teeth 106,108 of comb 102 define a spacing between collimator plates or elements and therefore ensure a precise orientation of each of the plates of collimator 103 relative to each other, and the precise alignment of collimator 103 and scintillator array 56. Each scintillator array 56 is also indexed to the position of its respective collimator 103 and associated plates 104. This construction reduces stack-up error between adjacent scintillator/collimator arrays resulting from the misalignment of one scintillator/collimator alignment. As such, any stack-up error associated with adjacent scintillator-collimator pairs is significantly reduced. Another stack-up error is reduced in the assembly of individual scintillators. The indexing pins are positioned relative to the positioning of the scintillator pixels. By positioning the indexing pins relative to the pixels of the scintillator, any stack-up error associated with the relationship between the indexing pins and the scintillator is reduced. As such, serviceability of a detector according to the present invention is improved as the indexing reference points, i.e. the indexing pins and the teeth of the comb, are integrally formed into the components of the device. Pins 100 are also formed to index the detector 20 to a rail of detector frame 77 as shown in FIG. 5. Such a construction ensures that a plurality of detectors, when attached to the detector frame, will be aligned therewith prior to connection thereto. Such a construction reduces the time required to associate the individual detectors to the frame during the initial assembly and/or during servicing. Referring now to FIG. 6, by transmitting the appropriate decoder instructions, switch arrays 80 and 82 can be configured in the four-slice mode so that the data is collected from four slices of one or more rows of photodiode array 52. Depending upon the specific configuration of switch arrays 80 and 82, various combinations of photodiodes 60 can be enabled, disabled, or combined so that the slice thickness may consist of one, two, three, or four rows of scintillator array elements 57. Additional examples include, a single slice mode including one slice with slices ranging from 1.25 mm thick to 20 mm thick, and a two slice mode including two slices with slices ranging from 1.25 mm thick to 10 mm thick. Additional modes beyond those described are contemplated. Referring now to FIG. 7 package/baggage inspection system 200 includes a rotatable gantry 202 having an opening 204 therein through which packages or pieces of baggage 216 may pass. The rotatable gantry 202 houses a high frequency electromagnetic energy source 206 as well as a detector assembly 208 having scintillator arrays comprised of scintillator cells similar to that shown in FIG. 6. A conveyor system 210 is also provided and includes a conveyor belt 212 supported by structure 214 to automatically and continuously pass packages or baggage pieces through opening to be scanned. Objects are fed through opening by conveyor belt 212, imaging data is then acquired, and the conveyor belt 212 removes the packages 216 from opening 204 in a controlled and continuous manner. As a result, postal inspectors, baggage handlers, and other security personnel may non-invasively inspect the contents of packages 216 for explosives, knives, guns, contraband, etc. Therefore, according to one embodiment of the present invention, a CT detector includes a scintillator module having at least one scintillator and at least one indexing pin connected thereto. The at least one scintillator is configured to be impinged with radiographic energy from a radiographic energy source. A collimator assembly includes a plurality of collimator elements and a plurality of teeth configured to define a relative position of the plurality of collimator elements. A portion of the plurality of teeth is configured to engage the at least one indexing pin. According to another embodiment of the present invention, a scintillator-collimator combination includes a plurality of collimator elements configured to collimate x-rays projected thereat and a scintillator module. The scintillator module has a scintillator pack formed of a material configured to illuminate upon reception of x-rays. A comb having a first set and a second set of teeth is constructed to align the plurality of collimator elements and the second set of teeth is constructed to engage the scintillator module and align the scintillator module relative to the plurality of collimator elements. The first set of teeth extends in a direction generally transverse to the second set of teeth. In accordance with another embodiment of the present invention, a CT system includes a rotatable gantry having a bore centrally disposed therein. A table is configured to position a subject for CT data acquisition and is movable fore and aft through the bore. A high frequency electromagnetic energy projection source is positioned within the rotatable gantry and configured to project high frequency electromagnetic energy toward the subject. A detector array is disposed within the rotatable gantry and configured to detect high frequency electromagnetic energy projected by the projection source and impinged by the subject. The detector array includes a plurality of scintillator modules and a collimator assembly for each scintillator module. Each scintillator module has a scintillator array and an indexing pin and each collimator assembly has a plurality of collimator plates. The detector array also includes a detector support having at least one comb of alignment teeth. The alignment teeth are constructed to align the plurality of collimator plates and is constructed to engage an indexing pin to align a scintillator array with the plurality of collimator plates. According to yet another embodiment of the present invention, a method of manufacturing a scintillator module is disclosed which includes providing a scintillator array having at least one locator extending beyond the scintillator array, providing a comb having a plurality of teeth constructed to define a spacing between collimating elements of a collimator, and positioning the at least one locator between at least two of the plurality of teeth. The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims. |
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description | This application is a Continuation-In-Part of Ser. No. 13/815,070, filed Jan. 28, 2013, which is hereby incorporated herein by reference, and claims the benefit of Provisional Patent Applications Ser. No. 61/744,473 filed Sep. 27, 2012 and Ser. No. 61/855,135 filed Jun. 14, 2013. The present invention relates to radiation-monitoring and measuring equipment and systems and in particular to such systems designed to detect particular sources of radiation in the presence of relatively large background radiation. Radiation can be classified as ionizing or non-ionizing. The word radiation is often colloquially used to refer to ionizing radiation such as x-ray and gamma rays. But the word radiation can also refer to non-ionizing radiation such as radio waves heat radiation and visible light. Radiation can also be classified by its ability to penetrate matter. Examples are alpha, beta and gamma radiation. Alpha particles are stopped by a sheet of paper while beta particles are stopped by an aluminum plate and gamma radiation is merely diminished as it penetrates lead. Neutron beams can be very penetrating. They do not ionize in the same way as charged particle radiation. Neutrons are absorbed, creating unstable nuclei that emit radiation. An important use of radiation monitors is the scanning of cargo especially at ports of entry into a country or other region to prevent entry of dangerous sources of radiation. In the United States, its Department of Homeland Security has the major responsibility to detect special nuclear materials and other dangerous cargo. Special radiation monitors are currently in use for scanning incoming cargo. A significant percentage of incoming cargo is currently being scanned by a variety of radiation monitors. Cargo is typically scanned for gamma radiation or sometime for neutron beams since these types of radiation will penetrate the walls of the shipping containers. Radiation monitors are widely used in the nuclear power industry primarily for control and monitoring sources of radiation. In more than a half-century of nuclear power, there have been several major accidents at commercial nuclear power plants that resulted in releases of significant or substantial radiation, evacuation of surrounding population, and huge financial costs for cleanup and power-generation displacement. On Mar. 28, 1979, a minor malfunction initiated an accident sequence at the Three Mile Island Unit 2 (TMI-2) nuclear generating station near Harrisburg, Pa. During routine maintenance of the secondary coolant side, feedwater to the steam generators was inadvertently interrupted. The water loss caused the primary coolant system to overheat, resulting in an increase in primary-system pressure. A small valve had been opened to relieve pressure in the reactor, but it malfunctioned and failed to close. Lacking direct water-level instrumentation, the operators were not aware that cooling water was draining and events would be initiated that would cause the core to overheat. The instruments that monitored essential conditions inside the nuclear core provided misleading or inadequate information; as a result, plant operators shut down the very emergency water that would have cooled the nuclear core and prevented the subsequent accident. Although the reactor-protective system automatically scrammed the reactor, it was not in sufficient time to prevent a loss-of-coolant accident and core meltdown. This event has been the most serious commercial nuclear accident in U.S. history, causing fundamental changes in the way nuclear power plants were operated and regulated. The accident itself progressed to the point where over 90% of the reactor core was damaged. No reactor personnel or members of the public received excessive doses of radiation or were injured. It was about five years before it was possible to carry out sufficient nuclear-core diagnostics so as to determine the extent and location of reactor fuel-debris re-concentration, and it required altogether about a ten years for the reactor to be decommissioned and defueled. After the 2011 Tohoku earthquake and tsunami in Japan beginning Mar. 11, 2011, three reactors at the Fukushima Dai-ichi Nuclear Power Plant underwent loss-of-coolant accidents and core meltdowns. Evacuation, power-displacement, and related costs have been quite expensive and enduring, but no lives were lost as a result of the nuclear accidents. Because of tsunami-induced flood damage to backup reactor-water-cooling systems, improvised backup and emergency systems were not available in time to supply supplementary water cooling in the three reactors so as to prevent the loss-of-coolant accidents. To this day, the degree of fuel re-concentration is unknown in each of the disabled reactors. A common problem resulting from the loss-of-coolant in the four cited accidents at water-cooled reactors has been the uncertainty and associated potential re-criticality nuclear hazard related to the uncontrolled re-concentration of fuel and debris. In addition, it would have been and remains invaluable to have the capability installed to assess—for the purposes of safe and timely decommissioning—the degree of fuel re-concentration and the level of cooling water maintained inside or outside the reactor pressure vessel, depending on the reactor design. A hodoscope (from the Greek hodos, for way or path, and skopos, for an observer) is an instrument used to optimally detect radiation and to enhance determination of the radiation trajectory. Typical hodoscopes are comprised of multiple detector-collimating segments arranged in a pattern. As the radiation passes through collimating segments, the detectors associated with these segments record the selected radiation, and this information is then used to infer the direction from which the radiation originated. A typical detector segment is a piece of scintillating material, which emits light when the energy of a charge-producing particle is absorbed in the scintillator The emitted scintillation light can be measured by a photomultiplier tube (PMT) or its equivalent. If the PMT measures a significant amount of light, it can be inferred that radiation passed was absorbed in the scintillator. A significant design requirement for nuclear diagnostics using a hodoscope consists of arrangements of the collimating and functional elements in such a manner as to minimize extraneous background radiation that might conflict with the desired source of radiation. Other important design requirements relate to spatial and time resolution. Applicant's U.S. Pat. No. 4,092,542 “High-Resolution Radiography by Means of a Hodoscope,” teaches that both neutron and gamma digitally-reconstructed radiographs of high spatial resolution are obtained from the hodoscope by the scanning operation of a collimator, by storing detector data outputs, and by rendering computer reconstruction of the data so obtained. The apparatus is adapted to detect fast neutrons, gamma rays, or both, and to use various combinations of the information obtained from fast neutrons and gamma rays to determine what was occurring within the field of view. Applicant's U.S. Pat. No. 4,649,015 “Monitoring system for a liquid-cooled nuclear fission reactor”, also referred to above, illustrates a system for detecting changes in water-coolant levels at various elevations of a water-cooled nuclear power reactor operating at full power. A pre-installed vertical array of gamma-radiation detectors was to be mounted at the inside wall of the reactor biological shield, and the detectors were to be collimated so that each received gamma radiation only from predetermined reactor-vessel elevations and axial positions. No known application is known to have followed from that patent. The U.S. Pat. No. 4,649,015 was based on applicant's technical analysis that, during normal nuclear-reactor operation to produce steam and thus electrical power, neutrons released in the fission reaction were often thermalized and/or captured: in the water coolant, or in the steel reactor walls, and/or in nuclear fuel or control structures within the reactor vessel. Nuclear-reactor power production results in many neutrons being absorbed in the steel structure and containment, thereby often being converted to gamma radiation having an energy level of the energy range of 5-12 MeV (million electron volts). Gamma rays are a high-energy form of penetrating electromagnetic radiation. Gamma-ray photons can be counted individually. While most radiation-detection counters determine only the count rate (i.e. the number of gamma rays interacting in the detector, for example, in one second), a gamma-ray spectrometer also determines the energies of the gamma-ray photons emitted from a source. Radioactive nuclei (radionuclides) commonly emit gamma rays in the energy range from a few keV to ˜10 MeV. Such sources typically produce gamma-ray “line spectra” (i.e., many photons emitted at discrete energies). The boundary between gamma rays and X rays is somewhat blurred, as X rays typically refer to the high-energy electromagnetic emission of atoms, which may extend to over 100 keV. Huge numbers of gamma- and x-ray photons are released in the course of fission processes in nuclear-power plants. Scintillation detectors use crystals that emit light when gamma rays interact with the atoms in the crystals. The intensity of the light produced is proportional to the energy deposited in the crystal by the gamma ray. The detectors are joined to photomultipliers (or their solid-state equivalent) that convert the light ultimately into an electrical signal and then amplify the electrical signal. Common scintillators include thallium-doped sodium-iodide (NaI(Tl))—often simplified to sodium-iodide (NaI)—and bismuth-germanate (BGO). Because photomultipliers are also sensitive to ambient light, scintillators are encased in light-tight coverings. NaI(Tl) has two principal advantages: It can be produced in large crystals, yielding good efficiency, and it produces intense bursts of light compared to other spectroscopic scintillators. The Compton-effect, a form of gamma-radiation interaction, is represented by a continuous distribution at the lower pulse-height regions of the gamma-energy spectrum. The distribution arises because of primary gamma rays that undergo Compton-effect scattering within the crystal: Depending on the scattering angle, Compton-effect electrons have different energies and hence produce pulses in different energy channels. If too many gamma rays are present in a spectrum, Compton gamma-ray distributions can present analysis challenges. Sodium-iodide detector systems, as with all scintillator systems, are sensitive to changes in temperature. Changes in the operating temperature caused by changes in environmental temperature will shift the spectrum on the horizontal axis. Semiconductor detectors, also called solid-state detectors, rely on detection of the charge carriers (electrons and holes) generated in semiconductors by energy deposited by gamma-ray photons. The arrival of the electron at the positive contact and the hole at the negative contact produces the electrical signal that is sent to the preamplifier, a multichannel amplifier (MCA), and on through the system for analysis. The movement of electrons and holes in a solid-state detector is very similar to the movement of ions within the sensitive volume of gas-filled detectors such as ionization chambers. Common semiconductor-based detectors include germanium, cadmium telluride and cadmium zinc telluride. Germanium semiconductor detectors provide significantly improved energy resolution in comparison to sodium-iodide scintillation detectors, as explained in the preceding discussion. Germanium semiconductor detectors produce the highest resolution commonly available today, and cryogenic temperatures are vital to their operation. The equipment used in gamma spectroscopy includes an energy-sensitive radiation detector, electronics to collect and process the signals produced by the detector—such as a pulse sorter (i,e. a single channel or multichannel analyzer)—and associated amplifiers and data readout devices to generate, display, and store the spectrum. Other components, such as rate meters and peak-position stabilizers, may also be included. The most common detectors in spectroscopy include sodium-iodide (NaI) scintillation counters and high-purity germanium detectors. Gamma-spectroscopy detectors contain passive materials that are available for a gamma interaction to occur in the detector volume. The most important interaction mechanisms are the photoelectric effect, the Compton effect, and pair production. The photoelectric effect is preferred, as it absorbs all of the energy of the incident gamma ray. Full energy absorption is also possible when a series of these interaction mechanisms take place within the detector volume. The voltage pulse ultimately produced by the detector (or by the photomultiplier in a scintillation detector) is usually shaped by a pre-amplifier and an amplifier. The amplitude of the voltage pulse can be measured and recorded by a single-channel analyzer (SCA) or a multi-channel analyzer (MCA). The analyzers take the very small voltage signal produced from the detector electronic processing system, and convert that analog signal into a digital signal. An analog-to-digital converter (ADC) also sorts pulses by their voltage amplitude. ADCs have specific numbers of “bins” into which the pulses can be sorted; these bins represent the channels in the spectrum, with each channel corresponding to a specific range of gamma-ray photon energy. In a single-channel analyzer, data is recorded for only one channel at a time whereas multi-channel analyzers record data for multiple channels simultaneously. The choice for number of channels for the MCA depends on the resolution of the system and the energy range being studied. The SCA or MCA output is usually sent to a computer, which stores, displays, and analyzes the data. For hodoscope purposes, single channel pulse-amplitude analysis is often sufficient if the detected radiation exceeds a designated energy threshold. Gamma-detection systems are selected to take advantage of several detector-performance characteristics. Two of the most important include detector resolution and detector efficiency. Gamma rays detected in a spectroscopic system produce amplitude peaks in the energy spectrum. The pulse width of the peaks is determined by the resolution of the detector, a very important characteristic of gamma-spectroscopic detectors. High resolution enables energy-separation of two gamma-ray lines that are close to each other in energy. Gamma-spectroscopy systems are designed and adjusted to produce symmetrical peaks of the best possible resolution. The peak shape is usually a Gaussian statistical pulse-energy distribution. For most spectra the horizontal-axis position of the peak is determined by the gamma-ray detection energy, and the area of the peak is determined by the intensity of the gamma ray and the efficiency of the detector. The most common figure-of-merit used to express detector resolution is full-width-at-half-maximum (FWHM). This is the energy bandwidth of the gamma-ray peak at half of the highest point on the peak distribution. Resolution figures are given with reference to specified gamma-ray energies. Resolution can be expressed in absolute (i.e., eV or MeV) or relative terms. For example, a sodium iodide (NaI) detector may have a FWHM of 9.15 keV at 122 keV, and 82.75 keV at 662 keV. These resolution values are expressed in absolute terms. To express the resolution in relative terms, the FWHM pulse shape in eV or MeV is divided by the energy of the gamma ray. Using the preceding example, the resolution of the detector is 7.5% at 122 keV, and 12.5% at 662 keV. A germanium detector may give resolution of 560 eV at 122 keV, yielding a relative resolution of 0.46%. Not all gamma rays emitted by a source and passing through the (collimated) detector will produce a count in the system. The probability that an emitted gamma ray will interact with the detector and produce a count is the efficiency of the detector. In general, larger detectors have higher efficiency than smaller detectors, although the shielding properties of the detector material are also important factors. Detector efficiency is measured by comparing a spectrum from a source of known activity to the count rates in each peak to the count rates expected from the known intensities of each gamma ray. “Efficiency,” like resolution, can be expressed in absolute or relative terms. Absolute efficiency values represent the probability that a gamma ray of a specified energy passing through the detector will interact and be detected. The energy of the gamma rays being detected is an important factor in the efficiency of the detector. Radiation detectors may be operated in a “current” mode, in addition to the aforesaid “pulse” mode. In the current mode, pulses are integrated over a time interval such that the output of the detector is a small measurable electrical current, rather than single pulses. Current mode is usually used in situations that involve very high pulse rates and preferably high signal/background ratios. If a gamma spectrometer is used for identifying samples of unknown composition, its energy scale must be calibrated. Calibration is performed by using the peaks of a known radioactive source, such as cesium-137 or cobalt-60. If the channel number is proportional to energy, the channel scale can then be converted to an energy scale. Because some radioactivity is present everywhere (i.e., background radiation), the gamma spectrum should ideally be analyzed when no source is present. In any event, background radiation must be kept to a minimum and its effects subtracted from the actual measurement. The heavy-element lead and other high-density absorbers can be placed around the measurement apparatus to reduce background radiation. Often there is a need to search for particular sources of radiation in situations where there exist other similar sources of radiation generally referred to a background radiation which may be larger (sometime much larger) than to radiation from the particular sources. Most radiation instruments also will register a relatively small amount of false signals referred to a noise which needs to be accounted for in determining the sought-after radiation from the particular source. One technique is to (if feasible) measure the background radiation and noise when the source is known to not be present. When the source is present, the technique is to measure the total indicated radiation and subtract the background and noise to determine the radiation from the source. What is needed is a technique for determining the intensity of a source of radiation in the presence of relative large background radiation. The present invention in its simplest and most fundamental manifestation utilizes at least one pair of hodoscope radiation monitors arranged to simultaneously monitor a single region that contains a particular suspected source of radiation. The hodoscopes are preferably arranged so that their respective fields of view of the region are as close to orthogonal as feasible. The fields of view (FoV) of the two detectors will converge in an overlap region that contains the suspected source of radiation. Each of the two detectors will record radiation from the overlap region and in addition will record background radiation emanating from other regions within the respective fields of view of the detectors. The present invention provides for the appropriate data recording and use of mathematical correlation techniques to estimate the extent to which a radiation source originates in the overlap region. The present invention also applies to situations where the detectors sense ambient radiation that reaches the detectors from outside the collimated beam of source and background radiation. As a simple example, the radiation detected by the two detectors may be recorded in counts per interval for a series of intervals. The radiation may then be detected as counts per 10-second interval for twenty 10-second intervals and these counts per 10 seconds are compared utilizing a mathematical correlation algorithm technique. A preferred statistical algorithm uses a known analysis of covariance means, called an Ftest, in which the variance for each of the twenty 10-second intervals is determined for each detector for each of the twenty 10-second intervals. Applicant has determined with actual test that radiation originating in an overlap region in the fields of views of two orthogonally arranged radiation detectors will result in substantially higher Ftest values and that radiation originating in non-overlap regions will result in substantially lower Ftest. Therefore, in preferred embodiments, Applicant calculated for each examination the comparative Ftest (and other statistical properties) of the data from the two detectors and found the Ftest to be the best indicator of the source in the presence of background, especially and including when the background rate was contemporaneously large with respect to the source rate. Preferred radiation-monitoring diagnostic hodoscopes are adapted to detect gamma or neutron or gamma and neutron radiation in a limited radiation beam of less than 50 degrees defining a field of view. They should be positioned so that their beams overlap in a region containing all or a part of the target location. The computer processor is programmed with an algorithm adapted examine the data recorded by the at least two hodoscope units so as to determine the correlation of the recorded data so as to estimate the extent to which the radiation source or sources originate in the overlap region. Preferably the fields of view are orthogonal or approximately orthogonal to each other. If not orthogonal, the fields of view of each unit in each pair of units define a center line and the center lines define an angle, originating at a central location in the target region, of less than 30 degrees. A first preferred embodiment of the present invention (which is referred to herein as the hodoscope orthogonal correlation (HOC) method) is described below with reference to the FIGS. 1 through 4. The underlying technical analysis is intended to explain the hodoscope orthogonal positional-correlation detection method, as well as to assist recognition of its inherent benefits compared to the traditional two-step background-subtraction radiation measurement procedure. Fundamentally, the positional-correlation method is a means of significantly improving detection of a radiation source S when a large background B of competing radiation is present. This is a common problem encountered in radiation detection and identification, that is, in radiation diagnostics. The term “hodoscope” represents a radiation-detection system that because of radiation collimation has an effective limited field of view, and because the type of chosen sensing material has a detection capacity that might be deliberately limited to a single type and range of radiation, such as gamma rays. The simplest representation of this concept is through an independent pair of nearly identical collimated detectors, both of which are aimed at the same source. Orthogonality is generally obtained by placing the pair of hodoscope detectors on the same plane, at right angles to each other, with the collimators directed at a radiation source common to their respective fields of view. The positional-correlation method, to be further defined and evaluated, is basically a specific means of collecting, processing, and analyzing data collected from the orthogonal hodoscope detectors. The traditional two-step nuclear-measurement method for background subtraction might make use of a similar or identical pair of orthogonal hodoscope detectors; however, the pair is not ordinarily operated in the correlation mode. For the traditional two-step method, each detector unavoidably measures a combination of source and background, and then the background is subtracted after it is estimated or determined in a separate measurement. The net statistical confidence associated with determining the source strength can thus often be significantly degraded by the statistical impact of the background, especially when the background rate is large with respect to the source signal strength. An isolated radiation source is ordinarily emitting into 4π steradians, as depicted in FIG. 1, which schematically represents a time- and space-varying pincushion-type of random source emanation angles. If we position a pair of collimating detectors Dx and Dy to view the pincushion-type source, we could have the arrangement schematically illustrated in FIG. 2. The hodoscope orthogonal correlation method is further distinguished from the traditional two-step nuclear measurement process by using a sequence of orthogonally-paired collimated-detector measurements, as depicted in FIG. 3, analyzed by correlation analysis. In FIG. 3, the background observed in line of sight of the collimators is divided into two components, the foregrounds fx and fy and the backgrounds bx and by. For initial simplification, these are combined such that Bx=fx+bx and By=fy+by. Also in FIG. 3, the source is represented by a finite included cross-hatched area T. This recognizes that in some situations, the collimator angles might exceed the boundaries of the source area T. The total (collimated+external) count in a HOC detector X or Y can be represented as follows:Xi=εx[ωx(α*δx*Si+Bxi)]+Nxi Yi=εy[ωy(β*δy*Si+Byi)]+Nyi where N represents the intrinsic noise+background of a detector extraneous to that viewed through the collimator. The subscript i represent each independent and sequential—usually contiguous and usually identical—count recording time interval. In any event, it is an interval common to recording data from both X and Y. The symbols δx and δy represent averaged attenuation (and relevant outscattering) effects that influence the transmission and detection of radiation in channels Xi and Yi. These effects are assumed here or postulated for the purposes of simplified relational analysis to be representable by integral terms that are independent of the native intensity for the common source Si. This assumption is a convenient simplified representation of integrals over space and time. The combined quantities αδxSi and βδySi represents the subtended outflow of radiation received from a positionally correlated target source term Si that is common to the respective fields of view in both the X and Y detectors. The coefficients α and β are related to the solid angle subtended by the collimated detectors. Only a fraction of the source emission flows into the respective field of view of the detectors, the remainder directed proportionately elsewhere, although subject to in-scattering from nearby materials. This incoming fraction within the separate collimators necessarily varies from instant to instant, but on average the detectors respectively view the fractions <αδxSi> and <βδySi> of the source average <Si>, assuming S emits isotropically in 4π steradians. Depending on design parameters and manufacturing tolerances, α might equal β, but in any case the multiplication product with ω would represent intercept of a small fraction of the source intensity S. This latter assertion is fundamental to the hodoscope orthogonal correlation method: that is, a typical random radiation source emits isotropically on average into 4π steradians, although the portion flowing into the respective solid angles ωx and ωy varies from instant-to-instant. The intensity and spatial distribution of such a random radiation source is usually parametrically characterized by the mean value of a Poisson or Gaussian distribution in time and space. The coefficient α represents that fraction of the common source i which is subtended within the field of view of detector Xi—while β represents the corresponding fraction of common source i which is subtended within the field of view of detector Yi. If the intrinsic extraneous noise plus background component N is small with respect to all sources that come through the collimator, then:Xi=εx[ωx(α*δx*Si+Bxi)]Yi=εy[ωy(β*δy*Si+Byi)]and, if we set kx=εx*ωx and ky=εy*ωy, thenXi=kx*(α*δx*Si+Bxi)Yi=ky*(β*δy*Si+Byi) We use the simplifying parameters kx=ε(x) ω(x) and ky=ε(y) ω(y), where it is understood that these are energy and rate dependent to the extent recognized above, but are otherwise not correlated with the source and background being measured. We defined kx and ky such that ω takes into account the solid angle that the hodoscope collimator defines for each detector. However, if we have a point source, the collimator fully encompasses the subtended solid angle. If quantitative assessment of the source were sought, by direct detection, these extraneous effects would have to be taken into account: Avoiding the necessity of directly determining these extraneous effects is a major advantage of the present invention covariance method (the first advantage being the qualitative separation of signal from a strong background, this other advantage being its relative independence of the effect of intervening materials. For a special case of a point source of spontaneous emission, we could represent the source term Si by vi Si, for each interval i. As shown in FIG. 4 it is quite possible that the detectors will view overlapping source and background contributions. In that case, we write:Dx=kx*(Bxf+Sxf+Sxy+Sxb+Bxb)Dy=ky*(Byf+Syf+Sxy+Syb+Byb)which can be measured for each ith interval and for a series of N intervals, such that i=1,N. For the purposes of correlation analysis, only Sxy is common to both detectors. The Sxf, Sxb, Syf, Syb do indeed represent a portion of what we call the “source,” as geometrically distinguished from the “background” components Bxf, Bxb, Byf, and Byb. However, the correlation-analysis treatment will only recognize the Sxy commonality, excluding all the remaining components of source and background from the correlation. Note that the source volume (or area subtended by a source that has a spatial extent on the x,y plane for this diagram) is definable by rotating or otherwise scanning the detector pair or complementary pairs of detectors. This process of scanning represents a normal operating and calibration mode for a hodoscope system. For an extended (areal) source S, we could write:X=kx*[Bxf+Sxy (1+cxf+cxb)+Bxb]Y=ky*[Byf+Sxy (1+cyf+cyb)+Byb]where the coefficients cxf, cxb, cyf, and cyb represent overlapping fractions of an extended source. Moreover, for practical purposes, we could simplify further:X=kx*[Bx+(1+cx)*Sxy]=kx*[Bx+(1+cx)*S]Y=ky*[By+(1+cy)*Sxy]=ky*[By+(1+cy)*S]. As a result, the correlation will be modulated by the extent by which each detector subsumes the common source S. If the solid angle of each detector happens to be large enough to subsume the entire source, then cx and cy both approach zero. Of course, realistically, the source will be non-uniform, so the coefficients c represent a simplified rendering of a complex situation. Inasmuch as source non-uniformity will take the form of both density and volumetric variations, the correlation coefficient will have to be interpreted as a single-parameter representation of a likely complicated geometric and qualitiative measure of radiation originating from the “source” region. In such situations where background is likely to provide strong interference with measurement of specific properties, the correlation coefficient is of considerable value. This would be the case expected in determining fuel re-concentration within the now-disabled Fukushima reactors, where linear relationships between measured results and actual “fuel” density would be difficult to quantify, and where a large overwhelming background is present. Fundamentally, certain geometrically-correlated features of the reactor that constitute background (such as the pressure vessel and the biological shield—see FIG. 5) present radiation background sources that are relatively uniform or slowly varying in spatial extent and radiation emission. Thus, the isolated structure and density concentrations found within the pressure vessel or biological containment are more likely correlated with the original core or its redistributed debris. FIG. 5 is included herein simply as a reminder that this HOC concept was originated by the desire to improve signal/background criteria in attempting to measure fuel reconcentration in the impacted Fukushima BWRs. Substantial background is created by and within the structure, including the pressure vessel and the biological shield, such that it would interfere significantly with the desired recognition of clusters of original or reconcentrated fuel within the reactor (and within the biological shield). It appears that the HOC method would offer several orders of magnitude improvement in SB measurements, which are sufficient to differentiate fuel in a large radiation background (that is, determination of the signal rate S is not needed per se). Count rates from radioactive sources can be estimated for specific detection geometries and efficiencies, and these rates and their role in this HOC model can be quantified. For computational purposes, using proprietary GQ GMC hardware and software, the following approximations can be used: A Curie is a unit for quantification of a radioactive source emission rate, such that 1 Ci=3.7×1010 decays per second (1 Bq=1 decay/s), and 1 μCi=3.7×104 disintegrations per second=2.22×106 disintegrations per minute. The following values of efficiencies and solid angles were found to be approximately suitable for a pair of commercially available GQ GMC radiation detectors in which a smaller Geiger Muller tube (purchased from the Ukraine) was substituted:ωx=0.1300 εx=0.01800 ωy=0.0840 εy=0.03300kx=εx*ωx =0.0054 and ky=εy*ωy=0.0028 Typical background rates were found to be 7.3 and 3.1 cpm, respectively. For a simulation that does not involve source attenuation and out-scattering, the corresponding terms δx and δy go to zero, and our previous relevant equations simplify to:Xi=kx*(α*Si+Bxi)Yi=ky*(β*Si+Byi) Furthermore, the coefficients α and β related to the solid angle subtended by the collimated detectors can be considered to be equal to each other, at least depending on the placement of sources. In practical effect, the counts collected in detectors X and Y are proportional to a term involving a common source term Si and an added background term that differs for each detector, resulting in a pair of linear equations of the form a+bS. The efficiency factors k are relatively small, but it matters mostly in terms of the statistical outcome of the relative relationship between source, background, and detectors. This relationship has been found to be adequate for obtaining statistically useful results in practical experiments using radioactive sources and small GM detectors, with data collected in 1-minute intervals, for time periods in the time frame of hours. Spreadsheet tabulation of the data collected has proven to be consistent with Monte Carlo simulations of the input data as transformed according to the indicated HOC model. Computer modeling of radiation sources used in the HOC process must adhere to physical constraints, such as those influenced by the characteristics of the source. As far as radioactive source emanation is concerned, modeling must take into account two separate physical processes. First, a “passive” radioactive source—assuming a point geometry—is spontaneously emitting at a rate characterized by its radiative nature, in particular its half-life. This source term is ordinarily approximated with a gaussian distribution about the instantaneous mean emission rate. Thus, the instantaneous emission rate for any given time interval is the same for all observing detectors. For most measurements and simulations, we normally deal with sources for which the mean value does not change significantly during the measurement interval, even though the instantaneous rate varies with a standard Gaussian distribution. Thus, we characterize the integral source rate at some arbitrary time t with some instantaneous value that is an integral over the measurement interval i. The second feature that should be independently modeled is the instantaneous spatial distribution of the source with a value centered about its mean emission rate. At any given instant, each solid angle will contain radiative emission proportionate to its subtended solid angle, but instantaneously variable in time such that the integral over 4π emission will equal the instantaneous time average for the ith measurement interval. This would be represented by some fraction of the instantaneous mean emission rate as distributed about the 4π distribution. This, in modeling, thus represents a second randomization process within the subtended solid angle (which ordinarily will be a small fraction of 4π). The source strength during a single ith time interval is thereupon represented by the product of its ith mean value and its ith solid angle. The ith mean value is normally a gaussian distribution about its mean value, and the ith solid angle is likewise a gaussian distribution representing a subset of the mean value during the same ith interval. If not a point geometry, suitable approximations might be needed for modeling purposes. Correlation values were computationally simulated using a multi-parameter computer program, such that various parameters were randomized and the assumed source value was simulated with a Gaussian (normal) distribution. Despite wide variations in the operative parameters and the variable source intensity the randomized systematic results confirm that a pair of detectors would provide under stable theoretical conditions a statistically reliable result even with a background/signal ratio of 1000 or more. In contrast to any other detection method, the HOC dual-channel method appears able to detect a very small correlated signal within the field of view of a pair of collimated detectors despite an otherwise overwhelming background of similar radiation in the same field of view. Hodoscopes as described above detect radiation within their field of view which field of view is determined by the design of the hodoscope. The radiation may be passive, active or scatter radiation. This HOC invention applies to each type of radiation source. The first preferred embodiment has been described as if the radiation being monitored (i.e. radiation from the overlap region as well as other radiation originating outside the overlap region but within the field of view of the detectors) is the result of natural decay of radioactive nuclei within the field of view of the detectors. Applicant refers to this type of arrangement as a “passive” arrangement. In some cases especially when an objective is to search for special nuclear material an “active” arrangement may be utilized. In such an arrangement an object suspected of possibly containing special nuclear material could be irradiated, for example, with one or more neutron beams. If the container does hold special nuclear material some of the atoms of the special nuclear material would absorb neutrons and as a consequence would fission releasing gamma rays and additional neutrons each of which could be detected by the orthogonally arranged hodoscopes as shown in FIGS. 1 through 4. Another possible utilization of the present invention is in a radiation-scattering situation. In this case, a container would be irradiated with a source of penetrating radiation, such as gamma radiation or neutron radiation. This penetrating radiation (gamma or neutron) would be absorbed or scattered from the contents of the container and the orthogonally arranged hodoscopes of the present invention could monitor the scattered radiation. The orthogonally arranged hodoscopes could be scanned relative to the container or the container could be scanned relative to the hodoscopes. In either case a reconstructed image of certain contents of the container could be determined from the collected data. Aside from the assumptions made inherent in the use of single parameters to represent effects that should be integrated over various variables, there are a number of identifiable and probably unidentified considerations. One of these relates to limitations of typical detection systems, for example deadtime and multipulsing effects, that are found to be factors particularly in GM tubes and associated electrons. Moreover, these effects differ for each detector. Workarounds include exclusion of anomalous data that are clearly associated with multipulsing, and the observation that these effects are secondary or tend to cancel out when the data from two similar detection systems are being compared in a statistical correlation process. Another refinement would be associated with each specific type of background (e.g. foreground, background, ambient). Each would have its own efficiency for detection, depending very much on its average energy. The role of overlapping coverage of collimators has already been mentioned, and with a good geometric model, the overlap could be unraveled. However, in simply asking for a degree of correlation to be extracted from a series of measurements, this overlap can usually be deduced in part by scanning detectors vertically and horizontally. In connection with real-world situations, there are two extremes in experimental geometry related to the HOC method: collimated and uncollimated. It is possible, on one extreme, to have a pair of uncollimated detectors receiving counts from a point source; and, on the other extreme, to have an extended source and background within the field of view such that it requires narrow and effective collimation. Based on actual (“passive”) radiation measurements taken with a pair of commercial GMC Geiger-Muller detectors, usually arranged orthogonally, with appropriate shielding as needed, certain simplified conclusions can be confirmed. Almost all data conforms to the HOC theoretical model, as presented above. The (only) proven useful statistical metric is the Ftest, which primarily analyzes a ratio of variances. HOC values as presented by the experimental data conform quite closely to expectations: that is, when a common “source” is presented, the Ftest (@Ftest spreadsheet function) values are relatively high, approaching 1, and when there is no common “source,” the Ftest values approach zero. These results have been obtained with rather good consistency for ambient background measurements, for a variety of common sources (Co-60, Cs-137, Ba-133, Na-22, Cd-109, and U-238), and for a variety of HOC source combinations. The detection data has better adherence to the theoretical HOC model summarized in this paper than do the Monte Carlo random-walk computations modeled for the HOC process. The model-generated results fail to show Ftest values approaching zero when there is no common source, even when experimental data replaces artificially-generated Gaussian-distributed input data. The discrepancy noted in this paragraph is the only discrepancy noted in the MC computations. The detection data has been varied in count rate, count ratios, signal/background ratio, and other properties in order to generate a substantial data base. For reasons apparently related with the conditions of derivation, the Pearson's covariance (@correl spreadsheet function) fails to track the changes that take place with the experimental data, and to some extent with the computer-generated data. Moreover, other statistics (such the Dtest, Ttest, and the Ztest) have not proven to yield useful results. In addition, applications of @Ftest and @Correl to autocorrelation have resulted in null values, which is consistent with the assumptions of the model. FIGS. 6A and 6B show some essential features of two versions (13 in FIGS. 6A and 15 in FIG. 6B) of a single-channel hodoscope that could be used in the present invention. The FIG. 6A version includes a thick, long tungsten (lead or steel could be substituted) collimating tube having a 2-cm channel drilled through the center of the tube. At the end of the tube is installed an off-the-shelf gamma scintillation detector, such as Model 943-37 available from Fluke Biomedical with offices in Everett, Wash. This model is 5 cm in diameter and includes a 5-cm long sodium iodide (NaI) crystal 14, a photomultiplier tube assembly 16 and a preamplifier 18. Mounted in front of the detector might be a thin lead and/or cadmium filter, the position of which is shown at 20, used to block low-energy neutrons and/or gamma-ray background. This channel limits the field of view of this specific hodoscope collimator to about 4 degrees. In the unit shown in FIG. 2B, the collimating channel is tapered to provide a field of view of slightly more than 6 degrees. Preferably the field of view of the single-channel hodoscope should be kept within 10 degrees. In some preferred embodiments the field of view could be restricted to less than 4 degrees as shown in FIG. 6A by making the channel longer or tapering the channel in a direction opposite that shown in FIG. 6B. Both Co-60 and Cs-137 radioactive isotopes are expected to contribute significantly to the radiation emitted from a reactor core that has been shut down for about two years. In preferred embodiments it would be important to be able to distinguish the radiation produced by such sources so as to determine where the fission products are located as a strong indication of the location of the reactor core materials. A single-channel hodoscope of the type described above—if used in very high radiation environments—could be utilized as a part of an HOC-paired robotic system. An example from the parent application is shown in FIG. 6C. This system includes the single-channel or multi-channel hodoscope 13 or 15, a two-axis gimbal 17 for pointing the hodoscope 360 degrees in horizontal and about 120 degrees in elevation, a telescoping support 19 to position the gimbal vertically, and the above components are mounted on a robotic base 21. All of these components should be designed to be remotely controlled. In preferred embodiments a camera and a visible light source (not shown) could be bore-mounted on the hodoscope so that visible images of the reactor structures can be recorded simultaneously with the radiation data. For embodiments of the present invention two separate robots could be used to provide the overlapping of fields of view. A large variety of gamma ray detectors are available off-the-shelf that can be utilized in hodoscopes as described above, These include scintillator detectors of various types including the NaI detectors as described in detail. These detectors typically include a photomultiplier tube or a photodiode that absorbs light emitted by the scintillator and reemits in the form of electrons via the photoelectric effect. An alternative to the photomultiplier tube is the relatively new single-photon silicon photomultiplier (SPM) detectors. These devices convert the light from the scintillator to electrical pulses without amplification electronics. One advantage of these devices is that they do not require high voltages. Semiconductor detectors of various types can also be used in the hodoscopes. Many of these detectors are available off-the-shelf. As explained in the Background section, high-purity germanium detectors provide much better resolution than the NaI detectors, but are much more expensive and require cooling (typically with liquid nitrogen). Applications of the present invention as stated above fall into three categories. These are passive, active, and scattering. Passive arrangements provide improved means of non-destructive determination of coolant-water level and core-fuel distribution or redistribution in such reactors, as well as an improved means for detection of any type of self-emissive (passive) radiation source, by the use of the hodoscope orthogonal-correlation (HOC) passive-mode methodology. Active arrangements of this invention is specific to the detection of uncontrolled or illicit substances that endanger public and government security and safety include unauthorized explosives, nuclear materials, hazardous chemicals, illegal contraband, and prohibited drugs, by the use of the HOC active-mode methodology. Scattering-mode arrangements of this invention are specific to the detection of substances similar to the active arrangements, but are based on a scattering-mode methodology. Provided below are additional details of each of these three applications of the present invention: The traumatic events that followed the 2011 earthquakes and tsunamis in Japan have revitalized interest in nuclear-reactor instrumentation which might minimize reactor accidents and their consequence. Three reactors at the Fukushima Dai-ichi nuclear-power station were irreparably damaged and remain under stressful conditions that could yet result in further internal damage or danger to remediation personnel. In any event, those reactors are to be eventually decommissioned, expectedly in a safe, orderly, and timely manner. The parent patent application which has been incorporated by reference herein provides a detailed discussion of the Fukushima reactors and techniques for utilizing hodoscopes for examining the damaged reactor. Described below are preferred techniques for applying the correlation concepts of the present invention to the radiation monitoring situations such as the situation currently being experienced at the Fukushima station and other similar situations as they may arise. The present invention applies specifically not only to the Fukushima Dai-Ichi boiling-water nuclear reactors, but also to other reactors around the world, as well as to other types of water-cooled power reactors. The difficulties and malfunctions experienced at the Fukushima Dai-Ichi nuclear-reactor station as an aftermath of the 2011 earthquake and tsunami illustrated the need for radiation-monitoring diagnostic hodoscope system in order to (1) prevent or minimize further harmful damage to the damaged reactors, (2) assist the safe and economic decommissioning of the damaged reactors, and (3) assist in the orderly restart of the undamaged reactors. The correlation concepts of the present invention could be applied to supplement those specifically described in the parent applicant to significantly improve sensitivity to fuel reconcentration. There are two specific embodiments of this radiation-monitoring multichannel diagnostic hodoscope invention, as referred to in applicant's 2012 Fukushima Hodoscope Provisional Patent Application. The first embodiment is in the form of an array of gamma-ray detectors embedded in the reactor biological shield; this embodiment will be called an embedded hodoscope. The second embodiment is in the form of a movable array of gamma-ray detectors that can be moved into and remotely operated within the reactor containment building; this embodiment will be called a movable hodoscope. Either of these embodiments could be expanded, positioned, and processed in such a manner as to be compliant with the HOC requirement. Because measurements made by a movable hodoscope detector array are made simultaneously by all detector channels, it is possible to create overlapping data results through a horizontal and/or vertical scanning operation that self-calibrates the array, making it possible to achieve spatial resolution much better than the inter-channel spacing between collimated detectors. This principle, observed routinely with apparatus constructed using the principles of the 1978 Hodoscope Patent, is of profound importance in application of this invention for the unusual conditions that exist in a reactor that has been shut down but provides an otherwise hazardous environment for human beings. Operation in this manner is consistent with the requirements and benefit of this present HOC invention. The simplest embodiment of the present invention would consist of at least two hodoscope collimated detectors, similar or not in type or detection mode, that are arranged orthogonally and aimed at a common “source” region, wherein the data-response functions of each detector would overlap at the “source.” The source might consist of a form of radioactive emanation that spontaneously and randomly emits radiation sensed in two or more of the HOC detectors during simultaneous time intervals. A more complex embodiment consists of more than one radiation source, accompanied by one or more forms of radiation-like background that conflicts with quantitative estimation of the emissive strength of the radiation source or sources. An example of the more complex embodiment would be the situation that is presented in applicant's Fukushima Hodoscope Patent application, in which the source of radiation is within the confines of a nuclear reactor, wherein some of that radiation is defined as a “source” term and the undesired remainder is considered the “background.” As in the case of applicant's parent application, there are two separate and complementary embodiments of this present invention depending on the degree of access available in the reactor building. Either of these manifestations enable external diagnostic interpretation simultaneously of both fuel and coolant configuration or reconfiguration resulting from an accident. These embodiments are the embedded and the movable hodoscopes of applicant's Fukushima Hodoscope Patent, but they could be aligned and operated specifically in a mode that provides correlation of orthogonal data. An embedded hodoscope system could be positioned entirely external of the pressure boundaries of the reactor vessel. In an HOC mode, the system should thus also have great durability and be immune from destruction or inoperative condition caused by deliberate or uncontrolled water level changes, reactor-core overheating, or internal reactor-fuel redistribution. It should also be self-actuated and have independent internal electrical-power sources. Calibration and inter-calibration of all HOC embodiments would be accomplished as in the case of applicant's parent application. Resolution and sensitivity is expected to be significantly improved when the HOC embodiment is functional. HOC electronic modules and signal processing for each hodoscope detector should be designed to provide a wide dynamic range, have designed redundancy, be capable of high radiation endurance, and have independent backup power in case of system-wide electrical-supply loss. It is expected that water-level, fuel-reconcentration, and process-variable sensitivity will be improved by the HOC arrangement. In addition, the detectors would be qualified to operate under the harsh conditions that exist within the reactor biological shield. The HOC technology can be installed, adapted, or modified for instrumentation that has been previously installed, or it could still be implemented at Fukushima, as well as in similar water-cooled nuclear-power reactors before they too might suffer similar malfunctions. The present invention makes possible comparative diagnostic analysis of radiation-monitoring hodoscope gamma-detector data is capable of identifying in an operating reactor radical changes from the normal condition. There presently is substantial lingering uncertainty regarding the damaged Fukushima reactors, that is, as to the height, location, and concentration of water coolant in the reactor pressure vessel and in its external containment vessel. At the same time, there is considerable and crucial safety-related uncertainty as to the distribution or redistribution of fuel and structural components in the damaged Fukushima reactor core and pressure vessels. Obtaining detailed actionable knowledge of these factors through the HOC invention could be extremely important to the safety, cost, procedures, and duration of decommissioning the tsunami-affected reactors. Application of the present invention specifically to the detection of fuel and water concentrations in shutdown nuclear reactors represents a significantly sensitivity improvement compared to applicant's parent application. This HOC Patent includes an external radiation-monitoring diagnostic hodoscope system for determining water-coolant levels and reactor-fuel concentrations in various regions of a water-cooled nuclear power reactors after the reactor is shut down. Specifically the present invention can be applied for detecting vertical and horizontal changes in the density of the liquid and fuel within the shutdown reactor. In the simplest embodiment of this invention, a pair of hodoscope correlation detectors is positioned outside the reactor biological shield at orthogonal angles aimed at the central region of the reactor pressure vessel in order to determine the location of either unaffected or redistributed nuclear fuel. These orthogonal hodoscope detector pairs may be deliberately repositioned at different elevations in order to compare respective results and thus determine the water-level transition. Residual radiation from and scattered in or around the fuel, structure, and water provide a means of detecting and distinguishing major changes in distribution of the distinguishable materials. In another manifestation of the invention, a multiplicity of gamma-radiation detectors is installed, arranged vertically and radially inside or outside the secondary concrete shield wall in a fixed-position embedded system, but operated as detectors for the purposes of improved sensitivity after reactor shutdown. Collimation provided for each detector limits the gamma-radiation it receives as emitting primarily from isolated regions within the reactor vessel. Comparative analysis of adjacent HOC detectors senses penetrating-radiation changes from the normal condition to advise of changes in the presence and/or density of reactor fuel and/or coolant at these specific regions. The detectors can also sense the distribution or redistribution of core fuel and some structural constituents with greatly improved sensitivity compared to other radiation-detection methods. Most important is that these detectors operate in the mixed radiation field remaining weeks, months, and years after shutdown. A movable radiation-monitoring diagnostic hodoscope array operating in the HOC mode can be utilized in the crippled boiling-water reactors at Fukushima and at commercial water-cooled reactors after shutdown. A previously-embedded array of HOC detectors can have their signal processing electronics modified for operation in the correlation mode. This would take the form of installed pre-positioned and functional backup instrumentation for determining and monitoring the configuration or reconfiguration of coolant and fuel inside a reactor pressure vessel after accidental or emergency shutdown of a boiling or pressurized water-cooled nuclear reactor. The primary observation to be taken from the HOC methodology is the use of statistical methods to derive information that is otherwise difficult to extract. This invention embodiment is based on the orthogonal physical arrangement of at least two radiation detectors, both focused on a common correlated feature. It therefore because possible to treat the accumulated data stream in such a manner as to derive mutually-correlated properties, in contrast to being overwhelmed with background data that otherwise obscures the desired correlation. Once satisfactory detector operating parameters are determined, using traditional hodoscope diagnostic methods, it might become possible to use pairs or arrays of much smaller detectors for the HOC method. For situations in which radiation detectors would have already been installed in a manner similar to that proposed in applicant's 1987 Water-Monitoring Patent, the output signals from paired or multiplexed detectors could be processed in accordance with the requirements of this HOC invention. Doing so would allow the water-monitoring detectors to be used long after reactor shutdown for the purposes of monitoring fuel and water concentrations, which otherwise would not be feasible in the absence of this modification. Depending on results of scoping experiments and calculations, the requisite signal data processing could proceed according to any of several available optimization choices, such as single-channel or multiple-channel pulse-height data recording. The accumulated data would be in the form of either electronic pulses or ionization current values. To determine the water-lever vertical interface, the HOC detectors of this invention would be mounted or moved so as to act as a vertical-displacement hodoscope with the results of at least two horizontal orthogonal-correlation detectors being compare at one or more vertical levels. At a given elevation, we would have (above or below discontinuities) either the effects of water at one elevation compared to the effects of no water at another elevation. This would be reflected in an abrupt change in foreground and background. The advantage of the HOC method is that it would enable detection of water levels under situations where applicant's Fukushima Hodoscope Patent technology would not have sufficient sensitivity. Uncontrolled or illicit substances that endanger public and government security and safety include unauthorized explosives, nuclear materials, hazardous chemicals, illegal contraband, and prohibited drugs. Detecting and identifying such dangerous or controlled substances has been the objective of many applied technologies, especially sensors based on nuclear radiation, including definitive radiographic methodology. For homeland security, particular emphasis has been on the detection of explosives at checkpoints, including airport portals and cargo transfer stations. For national security, high priority has been given to sensing unexploded ordnance, latent landmines, and chemical weapons. These hazardous materials and objects can be broadly categorized as substances of concern. The concepts described in this section provides a new, more efficient and definitive means of detecting and identifying substances of concern, as well as potentially reducing unnecessary radiation exposures in nuclear diagnostics. The embodiments described herein is explicitly distinguished from prior art that is similar in methodology, as well as prior art that uses other means to achieve similar purposes. Only this invention provides a broad functional and efficient capability of specific-materials detection and identification of substances that have dangerous, forbidden, commercial, or other aspects that gain deliberate attention. The external detection and identification of specified substances by the selective and novel use of nuclear technology is the general purpose of this invention. More explicitly, nuclear detection and identification of various dangerous and important substances are greatly enhanced by the means offered in this patent, namely HOC for active sources. The technology can be implemented by non-intrusive and non-invasive means consisting of two external specialized radiation detectors and one external radiation-generating source. The public- and commercial-interest justification for application and originality of this invention is based on recognized public value for technologies to improve or ensure public security, safety, and health. This universal mandate embraces military operations, public transportation, energy production, and the general welfare and security. Uncontrolled or illicit substances that endanger public and government security and safety include unauthorized explosives, nuclear materials, hazardous chemicals, illegal contraband, and prohibited drugs. Detecting and identifying such dangerous or controlled substances has been the objective of many applied technologies, especially sensors based on nuclear radiation, including definitive radiographic methodology. For homeland security, particular emphasis has been on the detection of explosives at checkpoints, including airport portals and cargo transfer stations. For national security, high priority has been given to sensing unexploded ordnance, latent landmines, and chemical weapons. These hazardous materials and objects can be broadly categorized as substances of public concern. The concepts described herein provides a new, more efficient and definitive means of detecting substances of concern, as well as potentially reducing unnecessary radiation exposures in nuclear diagnostics. This invention can be explicitly distinguished from prior art that is similar in methodology, as well as prior art that uses other means to achieve similar purposes. Only this invention provides a broad functional capability of specific-materials detection and identification of substances that have dangerous, forbidden, commercial, or otherwise interesting aspects. Specific substances of high public and government interest include chemical explosives and nuclear materials, as well as various forms of contraband and other illicit substances. For military applications, buried-mine detection, chemical weapons, and unexploded ordnance are important. For humanitarian purposes, unexploded mine and ordnance warrant a high level of attention. In terms of nuclear security, fissionable, fertile, and radioactive materials—especially if coupled with conventional explosives—are of prime concern for efficacious detection. Although substantial sums of money (billions of dollars) have been spent on improving substance detection and identification, prevailing or competing technology is either too time consuming, intrusive, complex, or has other fundamental limitations. The detection hardware in this invention combines hodoscope collimation and detection techniques with a radiation source, while the data processing hardware in this invention makes use of classic data-correlation techniques. When the specified target is irradiated by a highly-penetrating neutron source (not necessarily pulsed), characteristic radiation is unavoidably emitted from the target. This approach makes use of substance identification by means of composition templates associated with specific chemical elements. This method can make use of, or be used in connection with, essentially all forms of induced, transmissive, or scattered penetrating radiation (not just fast neutrons as an interrogation source, but also lower-energy neutrons, gamma rays, ultrasonic pulses, radar reflections, and other means of probing that might provide specific correlated identifying characteristics from the target zone). Preferably a pair of detectors is arranged externally and orthogonally on a plane that is itself orthogonal to the active source. The active-source HOC method enhances nuclear inelastic-scattering detection of chemical explosives that are rich in nitrogen compared to other elements. Because of its enhanced efficiency for characterizing radiation, it is possible to use comparatively weak-intensity neutron radiation sources. This method would allow efficient determination of the relative quantities of nitrogen, oxygen, and hydrogen by distinguishing inelastic fast-neutron scattering reactions that are specific to explosives. National-security application of interrogation techniques such as the active-source HOC method are of considerable value for detecting special nuclear material, for enhancing domestic and international nuclear safeguards, for reinforcing nuclear nonproliferation, and for improving homeland security. In active interrogation systems, external neutron or gamma ray sources are often used to induce fission or other nuclear reactions in the threat substance, and appropriate radiation detectors are used to measure characteristic emissions. The data derived from these detectors are subsequently analyzed to identify unique features that can be used to detect, identify, and characterize the threat material. Passive detection techniques can sometimes unveil illicit trafficking of radioactive material. The HOC method in either the active or passive mode includes appropriate data processing and mathematical algorithms aimed at improving both the sensitivity of the systems and their effectiveness in discriminating false positives and nuisance alarms. The implementation of an active-source HOC is based on a combination of theoretical and experimental results, as well as new analysis capabilities in the form of improved algorithms, so as to provide more efficient and accurate determinations of substance composition. Because detection and localization of radiation is improved in active-source HOC, this method can be applied to medical radiography and other related fields of radiography where radiation sources are normally used. This method should reduce the radiation dose absorbed, and as well as incidental doses involved in handling radiation sources. Because dose localization can be improved, reduced doses could result from diagnostic testing, imaging, and treatment with medical radiation beams. According to the present invention no less than two hodoscope collimated detectors are operated as mutually independent by observing an overlapping target area from different angles, even if not at right angles from each other on any given plane. The one-or-more-collimated-radiation-detectors would preferably be oriented at 90-degrees to each other on a single spatial plane. Correlation refers to a broad class of statistical relationships that involve functional dependence. A correlation coefficient commonly refers to the Pearson product-moment correlation coefficient, a measure of the strength and tendency of the linear relationship between two variables that is defined in terms of the (sample) covariance of the variables divided by their (sample) standard deviations. Pearson's correlation coefficient, the most familiar measure of dependence between two quantities, is obtained by dividing the covariance of the two variables by the product of their standard deviations. In practice, the Ftest measure of statistical correlation has been found to be systematically more useful as an indicator of HOC values. In practice, the one-or-more-collimated-radiation-detectors for an orthogonal hodoscope system, as defined, produce data that is subject to statistical-correlation analysis for any of several possible functional dependencies, including spatial, temporal, and energy relationships. If there are more than one pair of said-one-or-more-collimated-radiation-detectors, such correlations can be computed between each and every detector as long as the data is collected in time-stamped or time-connected intervals that are amenable to cross-correlation and auto-correlation analysis. In at least one preferred embodiment the “source” is a neutron source arriving along a z axis, which means there is a vertical as well as horizontal flux profile. The “target” region is the region common to the intersection of detection zones for the two orthogonal hodoscope collimated detectors. The radiation stimulated by an external neutron source (of unspecified energy) will consist of scattered and thermalized neutrons, thermal and high-energy capture gamma rays, inelastic gamma rays, and possibly fission gamma rays (which are in time coincidence as well as delayed coincidence) and fission neutrons (in time coincidence as well as delayed coincidence). For most active-source HOC applications, we are probably dealing with penetrating 14-Mev neutrons from the (D,T) accelerator. We might have just one pair of HOC gamma detectors with an active neutron-generating source that produces gamma rays mostly in the target zone. Although orthogonal orientation is preferred, the detectors need not be perpendicular (e.g., at right angles), but could be at some other mutually exclusive angles so that their fields of view overlap only with exclusivity as represented schematically but not exactly. The detection energies E on which we want to concentrate would be chosen from those that are associated with prominent reactions for substances of interest (e.g., explosives, drugs, fissile materials, other contraband). Particular attention would be given to the elements N, H, C, and O. So, our initiating source term S is the active radiation source impinging on correlated zone of interest, while the foreground and background are composed of either similar or dissimilar radiative events that are not associated with the source/target zone. For the purposes of these computer-calculated simulations, we would need to estimate specific interactions (and rates) in each zone as a result of the external neutron source effects. Hodoscope collimation is one controlling factor to reduce background. Another background controlling factor would have to come from the HOC approach in order to improve the signal/background ratio so that it is sufficient for specific substance detection and identification. Presumably we can include the direct uncorrelated source effect on the detector from within the consolidated background terms, but it really amounts to a third “background” effect, which might have to be taken into consideration separately. It might be possible to fold it into the “foreground” and “background” although it is a factor that is directly proportional to the source term, as will be the most if not essentially all of the foreground and background in this application too. For this situation with an active source that induces background outside the correlation overlap zone, foreground and background need to be modeled such that they too are accordingly proportional to the strength of the external source. Using a term proportional to the external source and the target of interest that is itself independent of the source, the effect is manifested in accordance with its material properties that are chemical and density related within the target. The internal properties of the target are of interest because those properties, in aggregate, help characterize substances of interest. For example, the target energy might represent a definitive inelastic neutron scattering gamma ray from nitrogen at a defining energy, such as at 5.11 MeV, or a prompt capture gamma at 10.8 MeV. Other energy bands of interest for the target energy might be set for prominent H, O, and C peaks. Although background from structural materials, would usually be present, such background as that from steel can be separated by energy windows at 7.6 and 9.3 MeV from iron. In some cases, these correlations will lag if they are the result of radiative activation. The originating source term will probably include radiation from the active neutron source which impinges directly on each respective detector by penetration or scattering that is entirely independent of the target. Let us suppose we are detecting gamma rays directly correlated to neutrons from the neutron source S, which might also inject some gamma rays into the target region. So in this case source energy represents what is a gamma background effect that depends on the intensity of the neutron source. Also each detector might have some inherent “noise” that is unrelated to the target zone, but occurs without any source or target. Some of it would be electronic noise and some cosmic-ray or other radiation background that is uncorrelated with the source or target. For validation purposes, it really doesn't matter whether the radiation source in a target zone is internally or externally induced, that is, whether it is a “passive” or “active” source. What matters is that the target zone radiates with its own characteristic (integrated over the zone) intensity. So one doesn't really need to compute how much radiation is needed to be generated in the target zone, as long as integration takes place over the non-uniform distributions emanating from each zone (e.g., foreground, background, and target [e.g., passive source]). A very logical question—that goes to the question of obviousness—arises when it is necessary to justify the correlation approach used in this patent. Why should the basic HOC arrangement of equipment, its operation, data recording, and data analysis be preferred over the traditional arrangements of a pair of independent detectors that are positioned orthogonally? The answer is partly a matter of more efficient statistics, which also differentiates this method from traditional methods. The necessity for more efficient statistics is based on existence of experimental situations whereby the signal from background is greater, or much greater, than the signal from the target. The present invention, by means of its HOC equipment arrangement explicitly allows data to be accumulated in such a manner as to have considerably improved statistics compared to the traditional means of independent detectors separately collecting sequential data that can be averaged by taking the sum of all data over all count intervals and dividing by the total counting time. This fundamental arrangement makes enables the use of established algorithms which advise that accumulating data in the form of the sum of products, differences, and ratios is a much more “efficient” statistical method of data treatment than using products, differences, and ratios of their sums. In the HOC method, each of these parameters and associated statistics can be separately computed for each ith interval, whereas in the traditional method of two independent detectors, only the computed sums integrated over all time intervals are available for analysis of their relationship to the source term. The HOC method also can and does of course compute sums over all time intervals in order to use those data values retroactively for determining variances as needed in orthogonal-correlation analysis. The method of least squares is a standard and statistically efficient approach to the approximate solution of over-determined algebraic relationships, i.e., sets of equations in which there are more equations than unknowns. This situation applies here in making use of the two measured and four parametric relationships of the orthogonal-correlation method. In mathematics, the idea of least-squares can be applied to approximating a given function by a weighted sum of other functions. The best approximation can be defined as that which minimizes the difference between the original function and the approximation. For the least-squares approach, the quality of the approximation is measured in terms of the squared differences of values and its average. Balance and symmetry are ways of insuring that the hodoscope correlation method will be orthogonal. Such orthogonal effects are independently estimable. When the data-collection design is orthogonal, there is less interference form possible masking or interference from other variables when assessing the importance of one particular variable, or of possible interactions among variables. Thus, in essence, the HOC for active sources method is distinguished from traditional methods by its defining properties of (1) hodoscope hardware collimation, (2) positional orthogonality, and (3) data-processing capability for—and employment of—the correlation analysis for every data-collection interval in the entire data stream. If the total path length of all the neutrons in a cubic centimeter in a second is known, (neutron flux (φ)), and if the probability of having an interaction per centimeter path length is also known (macroscopic cross section (Σ)), multiply them together to get the number of interactions taking place in that cubic centimeter in one second. This value is known as the reaction rate and is denoted by the symbol R. The reaction rate can be calculated by the equation shown below.R=φΣwhere: R=reaction rate (reactions/sec) φ=neutron flux (neutrons/cm-sec) Σ=macroscopic cross section (cm) Substituting the fact that Σ=Nσ into Equation (2-6) yields the equation below.R=φNσ,where σ=microscopic cross section (cm) N=atom density (atoms/cm) One important property of a material is the atom density. The atom density is the number of atoms of a given type per unit volume of the material. To calculate the atom density of a substance, in atoms/cm3: ρ=density (g/cm3) N=Avogadro's number (6.022×1023 atoms/mole) M=gram atomic weight Example: A block of aluminum has a density of 2.699 g/cm3. If the gram atomic weight of aluminum is 26.9815 g, the atom density of aluminum isN=ρNa/M=2.699 (6.022×1023)/26.9815=6.024×1022 atoms/cm3 If a neutron has a certain probability of undergoing a particular interaction in one centimeter of travel, then the inverse of this value describes how far the neutron will travel (in the average case) before undergoing an interaction. This average distance traveled by a neutron before interaction is known as the mean free path for that interaction and is represented by the symbol λ. The relationship between the mean free path and the macroscopic cross section is shown below:λ=1/Σ. Targets of interest or concern for HOC detection fall primarily in a number of general categories, depending on the intended area of application (e.g., national security, homeland security, medicine, military, research, dangerous substances, drugs, etc.). The category term itself is a rather coy effort to generalize without being judgmental. In the military field, materials of interest fall largely into four operational categories: de-mining, explosives detection, special nuclear materials, and chemical warfare agents. Civilian contraband, in general, includes drugs and other banned substances, including duty-payable items being smuggled. For aviation and other security purposes, explosives and concentrated chemicals are substances of particular interest. Firearms and other weapons also fall into a broad category of interest in Homeland Security. The external configuration of substance carriers might consist of postal parcels, luggage, cargo containers, trucks, and rail cars. Neutron-based inspection techniques, the elemental densities of hydrogen, chlorine, and nitrogen can be measured thermal-neutron capture. Chlorine is the basis for the detection of hydrochlorinated cocaine and heroin. Nitrogen detection underlies detection of nitrogen-rich explosives. More specific detection of these forms of contraband is achieved by measuring their elemental constituents, namely oxygen, carbon, nitrogen, chlorine and hydrogen. The first four elements are detected by the characteristic gamma rays emitted when fast neutrons are inelastically scattered by the nuclei of the elements. Indeed, oxygen can only be detected by this process, while carbon is detected more efficiently by the same process. Nitrogen and chlorine can also be detected through the fast neutron inelastic scattering process, but with lower energy characteristic gamma rays. Fissionable materials are detected, obviously, by the products of the fission process. The elemental densities in minerals is determined mainly by the characteristic gamma rays emitted following the radiative capture of thermal neutrons. More specifically, explosives are identified on the basis of high elemental density for O, N, but low C and H. Four defining and usable inelastic-scattering gamma-emitting nuclear reactions are 6.13 MeV for O; 10.8, 5.11, 2.31, and 1.64 for N; and 4.43 for C. Low-energy capture gammas of interest would be from N and H (at 2.22 MeV). Drugs such as cocaine and heroin have relatively high C, H, low O, and medium-low Cl, which has several strong lines. Cement and sand, which often constitute background, have thermal-neutron captures in Ca and Si. Nuclear materials, besides producing fission and capture reactions, have a high atomic density. With the HOC technique, thermal-neutron capture and other types of reactions that are delayed with respect to the initiating event (such as radiative activation) can be detected and analyzed because a continuous stream of data is recorded in the binary intervals. The data can be analyzed for delayed correlations that correspond to radiative activation because it is all recorded in the case of pulsed radiation sources. When pulsed-neutron radiation is available as a source, the pulse-time event can be recorded in a separate time bin that is synchronously recorded in parallel with the correlation data from the detectors. Thus, with no additional field equipment outlay, all three forms of reactions—thermal capture, activation, and inelastic scattering—are recorded and can be analyzed, depending on the requirements of the measurement. A similar situation applies to the APSTNG source method of neutron-emission marker by associated alpha-particle detection. The data stream can be analyzed according to prompt and delayed radiation correlated with the neutron initiation. The analysis of delayed-correlation events provides an important additional means of ensuring the most efficient means of detecting all substances of interest. Modern computer data storage and algorithm calculations enable the contemporaneous on-site treatment of large data bases. In other words, instantaneous and delayed correlations with one or more detection channels can be analyzed with and without using the initialization trigger timing of neutron pulsing. The extent to which the HOC configuration and analysis can be augmented by the initiated-pulse time depends on the field situation, which depends in part on the required rate of initiating pulses. Neutron issuance rates (from radioactive or accelerator sources) could be in the range of 103 to 109 per second, which would affect required timing and data storage requirements. Conversely, some useful activation events would not be consummated before delays in the millisecond to second time span. Inasmuch as binned data can be deliberately aggregated for optimal analysis, this should not be a problem because of large data-storage (and analysis) capacity now available. Real-time detection of explosives is a major challenge in military de-mining. Detection of nitrogen-enriched chemical compositions is a major example of what would be required of an active-source HOC system. For simplicity, we note that N/H ratios for explosives are typically ˜9; so simultaneous detection of N and H would be significant. Typical weight percent portions of N would be 20%-30% and for H would be ˜2-4%. Explosives usually have an even larger weight fraction of O, but not many innocuous materials would have N/H or N/C ratios as large as do explosives. Thus, as a surrogate for proof-of-principle, detection of N is sufficient. The 5.11 MeV inelastic gamma is a good indicator of N while the 2.33 MeV capture gamma from H. Notably, C has a prominent inelastic gamma at 4.43 MeV, and O at 6.13 MeV. The inelastic-scattering cross-section for 14 MeV neutrons is about 0.4 b (See Table: Nitrogen Cross Sections). Generalized concept for alternative orientations of source and detectors for various conceivable accessible geometries, the basic equipment involved consists of (1) a source of radiation, usually neutron-induced gamma rays, (2) at least a pair of collimated detectors of the induced radiation, arranged orthogonally in such a matter as permitted by the circumstances to minimize conflicting radiation background effects, and (3) an electronic processing system for the collected data, arranged in such a manner as to continuously measure and evaluate correlation effects between the detectors. In addition, decision-making software might also be included so as to carry out pre-determined actions resulting from the data collected. National security applications involve, for the most part, detection of weapons that are detonated with the aid of conventional explosives, including—but not limited to—improvised explosive devices (IEDs), landmines, chemical weapons, and nuclear explosives. One application of particular interest to military forces is an improvised explosives device (IED and landmine) detector, such as applications to unexploded-ordnance or improvised-explosive detection in national-security applications. Multiple source-detector combinations can be mounted laterally to broaden the sweep. Whether the system can be reduced in size for open-field use by non-mobilized personnel would depend on field-test results. In addition to the conventional-explosive content, distinct signatures of chemical weapons can be detected by virtue of their unique combination of certain elements, such a Cl, S, and P. In order to carry out checked-luggage inspection for banned substances, the apparatus could be located within internal checked-luggage-transport facilities. Any or all of the HOC concepts could be applied to luggage inspection in homeland-security applications. The unique signature of nuclear weapons, and fissionable materials of any type, is the creation of fission events as a result of neutron interrogation. The HOC method is particularly sensitive to small quantities of fissile or fertile materials, even if shielded. This specific concept for applies to nuclear-materials detection inspection in national-security and homeland-security applications. Homeland security has a broad range of interest in banned substances, including explosives, chemicals, nuclear materials, drugs, and other contraband. All such substances are subject to distinct detection and identification by the HOC method. In those situations which involve high radiation levels for medical diagnostic or therapeutic purposes, more efficient and/or definitive means of detecting the radiation or specifying its location in a body reduces the dose that must be ingested, injected, or otherwise applied to human beings and animals. The HOC methods lends itself to reducing necessary exposures for both passive (internal) and active (external) radiation sources needed to obtain the same medical benefits as stronger sources that depend on present-day technology for detection and localization in a body. Based on receiving a pre-amplified linear signal from a detection device, such as a sodium-iodide crystal mounted on photomultiplier tube, computer-controlled equipment would be used to process and collect data in uniform count intervals, recording designated multiplicity of pulse amplitudes depending on the application. While the data is being recorded, the digital-data processing software would be analyzing correlations on a continuous basis, providing readouts that are manually or automatically interpreted and acted upon, according the established respective protocols. No especially complex or extraordinary equipment is needed for processing HOC data. In general, preset algorithms will be invoked to distribute warnings, alerts, or information to equipment operators, system managers, or responsible officials. For fielded equipment, many of these functions will be consolidated in order to minimize operator decision-making, and the potential for erroneous interpretation. Embodiments described in this section relate to all types of scattered radiation sources, whether radioactive or by accelerator production, although it does not preclude that the substance of interest might itself have inherent radiation that is constructively helpful or that is an unavoidable source of radiation background in this application. Underlying these embodiments, as well as the referenced specific prior art, is the aforesaid hodoscope-diagnostic technology which optimizes the detection of selected types and origins of nuclear radiation. In general, as compared to most other radiation-detection technology, hodoscope radiation-detection systems are designed in a modular manner so as to offer specificity, durability, and reliability in designated functions. Operated either in single or multiple modules, with designed ability to be calibrated and to change its field of view, hodoscope detectors have a proven high degree of utility in a variety of unique applications. Various types, intensities, and durations of radiation can be accommodated by design. For the purposes of these related patents, this feature specifically includes pre-selected sensitivities to neutrons of specific energy ranges and to gamma rays of various energy levels. In addition, functional neutron/gamma diagnostic hodoscopes have accumulated decades of relevant experience operating at nuclear reactors. Based on the established foundation and applicability of hodoscope technical and operational experience in nuclear reactors, the present invention has been proven to operate immediately external to or within severe and complex radiation environments. Not only has a substantial experimental base been established, but detailed determinative and stochastic computations have been performed for applications extended to new environments and geometries. Many radiation-detection technologies utilize scattered radiation, that is, radiation that is incident upon but deflected from an object. Such radiation-detection technologies differ fundamentally from radiation-detection technologies that utilize passive or active radiation sources. Passive sources spontaneously emit detectable radiation, and active sources emit detectable radiation when stimulated by external means. Radiation is a physical process in which energetic particles or waves travel through a vacuum or through matter. Energetic types of radiation are differentiated by the way in which they interact with normal chemical matter: whether they ionize or do not ionizing the material with which they interact. This patent chooses not to differentiate between ionizing radiation (e.g., neutrons, gamma rays, electrons, or x-rays) or non-ionizing radiation (e.g., radio waves, heat, or visible light), inasmuch as all such forms might benefit from this patent application. As explained generally in the Background section of this application, specific particles or waves that are the subject of this patent radiate (i.e., travel outward in all directions) from a source of emission, usually following an inverse-square law of radiated power with regard to distance from the source. Radiation with sufficiently high energy can ionize atoms, which often leads to one of several means for practical detection of such radiation. Typically, photons and particles with energies above about a 10-electron volt (eV) threshold are ionizing forms of radiation. Alpha particles, beta particles, cosmic rays, gamma rays, and x-ray radiation all carry energy high enough above the threshold to ionize atoms. In addition, neutron radiation can also be ionizing in effect, since the result of neutron interactions in matter is inevitably more energetic than this threshold. Ionizing radiation comes from radioactive materials, x-ray tubes, particle accelerators, and is present in the environment on Earth and from cosmic-radiation sources. Nuclear instruments such as Geiger counters are usually required to detect the presence of ionizing radiation. In some cases, it may lead to secondary emission of visible light upon interaction with matter, as in Cherenkov radiation and radioluminescence. The ability of an electromagnetic wave (of photons) to ionize an atom or molecule depends on its wavelength (or corresponding radiative frequency), which characterizes the energy of a photon of the radiation. Light, or visible light, consists of a very narrow range of electromagnetic radiation at a wavelength visible to the human eye (about 400-700 nm), or up to 380-750 nm. More broadly, physicists refer to light as electromagnetic radiation of all wavelengths, whether visible or not. Visible and other wavelengths of light, such as infrared, are subject to detection by suitable devices. Alpha particles are helium-4 nuclei that interact with matter with a high degree of ionization, such that its range of penetration in matter is quite short. Beta-minus (β−) radiation consists of an energetic electron. Beta radiation from radioactive decay can be stopped with a few centimeters of plastic or a few millimeters of metal. Beta radiation from linac accelerators is far more energetic and penetrating than natural beta radiation. Beta-plus (β+) radiation is the emission of positrons, which are antimatter electrons. When a positron slows down to speeds similar to those of electrons in the material, the positron will annihilate an electron, releasing two gamma photons in the process. Those two gamma photons will be traveling in (approximately) opposite directions. Neutrons are often categorized according to their speed. Neutron radiation consists of free neutrons, which might be emitted during either spontaneous or induced nuclear fission, nuclear fusion processes, or from other nuclear reactions. Neutrons can make other objects, or material, radioactive. This process, called neutron activation, is the primary method used to produce radioactive sources for use in medical, academic, and industrial applications. Even comparatively low speed thermal neutrons, which do not carry enough kinetic energy individually to be ionizing, will cause neutron activation. Both slow and fast neutrons react with the atomic nuclei of many elements upon collision with those nuclei, often creating unstable isotopes and therefore inducing radioactivity in a previously non-radioactive material. This is called neutron activation. High-energy neutrons have the ability to directly ionize atoms. High-energy neutrons are very penetrating and can travel great distances in air (hundreds or even thousands of meters) and moderate distances (several meters) in common solids. They typically require hydrogen-rich shielding materials, such as concrete or water, to block them within distances of less than a meter. Neutron scattering for 1 MeV incident neutrons is generally two orders-of-magnitude greater than neutron absorption for most elements. However, the angle of deflection of the neutron is smaller as the mass of the target nucleus becomes larger. Neutrons with energy of 1 MeV have a scattering mean-free-path (1/Σs) of about 1.9 cm in the oxide of uranium. It implies, for example, that a 1-MeV neutron will have a high initial reaction rate in uranium oxide, but that rate will be subsequently and rapidly altered because the neutron energy will decrease in each collision and the cross-section will also be changing as the neutron energy decreases. Some neutron scattering will result in energy lost through inelastic scattering, which will create a gamma-ray at the point of interaction. Neutron absorption (usually at lower energies), in contrast to neutron scattering, could result in any one of several processes in which various other forms of detectable radiation are emitted. For the purposes of the present patent application, it is important to note that the predominant interaction of 1-MeV incident neutrons with materials of various densities is outscattering from the target zone, although the angle of outscattering for high-density materials is small compared to the angle of outscattering for water. In general, neutrons of energies greater than 1 keV (or thereabouts) incident on a target will undergo scattering reactions (with the exception of certain resonant reactions) in preference to any kind of absorption reaction. This phenomenon preferentially favors the HOC method for radiation-scattering detection. X-rays are electromagnetic waves with a wavelength smaller than about 10 nanometers. A smaller wavelength corresponds to a higher energy. A “packet” of electromagnetic waves is called a photon. When an x-ray photon collides with an atom, the atom may absorb the energy of the photon and boost an electron to a higher orbital level or if the photon is very energetic, it may knock an electron from the atom altogether, causing the atom to ionize. Generally, a larger atom is more likely to absorb an x-ray photon, since larger atoms have greater energy differences between orbital electrons. Soft tissue in the human body is composed of smaller atoms than the calcium atoms that make up bone, hence there is a contrast in the absorption of x-rays. X-ray machines are specifically designed to take advantage of the absorption difference between bone and soft tissue, allowing physicians to examine structure in the human body. Radiation and radioactive substances of many types are frequently used for medical diagnosis, treatment, and research. For example, x-rays pass through muscles and other soft tissue but are stopped by dense materials. This property of x-rays enables medical practitioners to identify broken bones and to locate cancers that might be growing in the body. Doctors also find certain diseases by injecting a radioactive substance and monitoring the radiation given off as the substance moves through the body. Radiation used for cancer treatment is called ionizing because it forms ions in the cells of the tissues it passes through as it dislodges electrons from atoms. This ionization process is deliberately used to kill cells or change genes so the cells cannot grow. Most other common forms of radiation found in the environment such as radio waves, microwaves, and light waves don't have as much energy and are not able to ionize cells. In general, neutron scattering cross-sections tend to be large both for water on one extreme, moderate for medium elements, and become gradually larger for heavy metals. However, x-ray (and gamma-ray) scattering cross-sections are small for water and increase substantially as the target density increases. Gamma (γ) radiation consists of photons with a frequency nominally greater than 1019 Hz. Gamma radiation is composed of photons, which have neither mass nor electric charge. Gamma radiation penetrates much further through matter than either alpha or beta radiation, which have an electric charge and mass, and thus are far more likely to quickly interact with other atoms in their path. Gamma rays, which are highly energetic photons, penetrate substances deeply and are difficult to stop. They can be absorbed by a sufficiently thick layer of material, where stopping power of the material per given area depends mostly (but not entirely) on its total mass, whether the material is of high or low density. However, as is the case with x-rays, materials with high atomic number such as lead or depleted uranium add a modest (typically 20% to 30%) amount of stopping power over an equal mass of less-dense and lower atomic weight materials (such as water or concrete). This proportional effect can be useful in selectively detecting materials of high density. The so-called Compton effect is the predominant interaction mechanism for gamma-ray energies that are typical of radioisotope sources, while pair-production would be the dominant effect for accelerator-produced high-energy gamma sources (above several MeV). At high values of incident gamma-ray energy there is a strong forward-scattering tendency, which increases monotonically with increased atomic number. Radiation might derive either from spontaneous natural origin or from some source artificially assembled, manufactured, or created. If from natural inception, it is usually diffuse in spatial extent, emanating from soil, nearby objects, or through the atmosphere from outer space. A spontaneous radiation source is one that exudes radiation without external stimulation, although that emission might be stimulated by conversion of one form of spontaneous radiation to another, as in neutron sources caused by alpha radiation impinging directly on the element beryllium. Another commonly used source of spontaneous radiation is produced by the decay of the transuranium element Cf-252. A natural spontaneous radiation source could be assembled on a simple metal foil or other medium so as to be concentrated at a single point—considered to be a point source—or it could be dispersed in a larger volume—considered a distributed source—or derived from a beam of radiation, typically from an accelerator. Spontaneous radiation sources could consist of a single form of radiation of a single energy, considered monoenergetic, or consist of a mixture of radiation with one or more emission energies. Artificially created radiation is produced typically in devices that accelerate electrons or protons so as to create nuclear reactions of the type that result in the contrived emission of neutrons and/or gamma rays. These accelerator-created radiation sources are, for the most part, focused at a target point or directed in a beam: some might be emitted isotropically, and some might be emitted in a forward-based direction along the path of acceleration. The primary objective with artificially created radiation is to irradiate a target in its FoV. Radiation “background” consists of any external effect that is not associated with, but competes with identification and quantification of the intended radiation “source.” Generally background is present as an external, unwanted form of radiative emanation that competes with the deliberate and specific detection of a source. In various contexts, radiation background may simply be any extraneous radiation that is pervasive and detectable, whether ionizing or not. A particular example of this is the cosmic microwave radiation background, a nearly uniform glow that fills the sky in the microwave part of the electromagnetic spectrum. Light and other radiation from discrete stars, galaxies and other objects of interest in radioastronomy stand out prominently against this form of generalized radiation background. Some radiation that is considered background might, in fact, be directly related to the designated source of interest, but that form of background radiation might arrive at the detector by undesired means or direction. Collimation is the primary technical method by which incoming radiation is limited or confined to the designated source and to minimize radiation background; collimation is a feature fundamental to the HOC method. In a laboratory or experimental environment, background radiation refers to any competing sources that affect an instrument measurement when a radiation source sample is absent. This pervasive radiation background rate is ordinarily subtracted from the sample measurement; however, such radiation background must be determined by multiple measurements, usually before and after sample measurement, provided the source and background are sufficiently stable and mensurable. The process of subtracting radiation background based on one or more separate disparate measurements will affect the statistical quality assignable to the source radiation intensity, as parameterized above. This effect on statistical confidence is often a major limitation in attempting to determine the strength of the source based on the process of making measurements of total intensity separate from radiation background. While radiation background measurements can be attempted when the source is not present, it is often not feasible in actual circumstances in the field. The ubiquitous ionizing radiation to which the general human population is exposed, including natural and artificial sources, is one form of background. (Both natural and artificial background radiation vary by location.) However, specific instantaneous background radiation at a given location (or altitude) is unavoidably associated with uncontrollable circumstances that often affects the statistical quality of a measurement made for a given radiation source. For the purposes of this invention, scattered radiation consists of all effects that result from the dispersion or spreading out of radiation as a result of radiation-source interaction with any material medium in its path (including air). Radiation of all forms and energies are subject to sometimes-unavoidable scattering processes. Radiation deflection might involve back scattering, out scattering, or forward scattering at any angle with respect to the incident direction of the source radiation. Most scattering processes result in energy being lost by the incident radiation when it suffers any kind of interaction. Considered a significant and ongoing technical problem in national and international security is the possibility that transshipped cargo containers conceal dangerous or clandestine items. In order to detect such contraband, many technical methods can be and are applied: Some of the most non-invasive means reduced to practice use external radiation sources to interrogate (or to “scan”) contents without requiring that the cargo container be opened for inspection. Cargo is shipped by a variety of transport: waterborne ships, highway trucks, rail trains, aircraft, and other conveyance. Cargo is often crated into containers that are often officially and functionally sealed and logistically controlled by appropriate shippers, authorities, and manifest documentation. Publically shipped cargo has sometimes been used to transport clandestine materials—including illicit drugs, explosives, money, chemicals, heritage items, as well as other banned substances and equipment. Transport of illegal cargo across national or state boundaries has been a particular focus of law-enforcement and customs authorities, especially because of post-9/11 threat perceptions. A variety of means—aside from intrusive ad-hoc physical inspection by human beings—have been used to detect banned materials. The technical means of inspection are needed because of a huge quantity of cargo crosses state and national boundaries. Some of the most effective technical means of inspection involve the use of external radiation sources that are capable of penetrating through and identifying hidden banned substances. A variety of inspection applications of penetrating radiation have been employed. For cargo, cargo containers, and cargo vehicles, often used have been radioactive gamma-ray sources, such as Co-60 or Cs-137. Such radiation sources are relatively easy to utilize in technical-inspection practice, but they have fundamental limitations when applied, for example, to large containers filled with dense objects. Linear accelerators (LINACs) can also be used to produce gamma rays that scan larger cargo items. X-ray radiography using LINACs is similar to gamma-ray radiography, but instead of employing a radioactive source, it utilizes a high-energy bremsstrahlung spectrum with energy in the 5-10 MeV range created by a linear accelerator. Such high-energy x-ray systems can penetrate up to 30-40 cm of steel: High-energy x-rays are usually more suitable than radioactive gamma-ray systems for the detection of bulk special high-density nuclear materials. Some cargo-scanning concepts combine fast-neutron and x-ray/gamma radiography. Multiple-radiation scans can be processed to produce high-resolution radiographic images that sense and depict areal density and material composition. Determination of such properties increases the likelihood that clandestine materials will be detected; if not, the risk of detection acts as a deterrent. However, one problem is that the range of clandestine materials is too extensive for a “one-size-fits-all” detection and identification strategy. Moreover, radiation scanning of large cargo is usually limited to interrogation of certain technically detectable parameters of an object, such as materials density, rather than chemical composition of the object (which might be more definitive). Another constraint, especially for application in cargo inspection, is the intensity and amount of radiation that can be applied in the vicinity of personnel, such as drivers, operators, inspectors, bystanders, and stowaways. Intermodal cargo containers are typically 2.5 meters in height and width, 6 or 12 meters in length, and carry up to 27 metric tons of freight. Thus, the task of finding a small amount (less than 1 kilogram) of hidden fissile material within intermodal cargo containers is technically and procedurally difficult. It is the intent of this HOC “scattering” patent to minimize some of these contraband-inspection difficulties, causing such inspections to be more fruitful and definitive, while requiring less time and requiring less extraneous radiation. An essential aspect of this HOC “Scattering” patent for detection of radiation scattering is the inclusion of means to concurrently record data collected for different variants and features of radiation incident on the HOC detectors. Examples of concurrent-detection data requirements are (1) having in place the means for recording data from both neutron and gamma detectors simultaneously and (2) recording such data in separate data-recording channels. Another example of concurrent detection, is the sorting of simultaneously recorded data for any given detector into separate corresponding energy bins, such that cross-correlations can be mathematically analyzed for one or more different recorded energy combinations, as well as between one or more types of radiation detected. A more specific example would be a pair of neutron and gamma detectors assembled in tandem for each HOC detector, wherein the quantity and range of data available will consist of pulse-height spectra for each neutron detector and each gamma-ray detector, such data simultaneously and electronically registered for each time interval being recorded. A similar, but less comprehensive physical layout and data recording arrangement was enabled for the TREAT hodoscope, as detailed in applicant's expired 1978 patent “High-Resolution Radiography by Means of a Hodoscope,” in which neutron detectors preceded gamma detectors in chosen collimated hodoscope channels. While data was collected during simultaneous intervals from all detectors in application of that aforesaid expired patent, no positionally orthogonal relationship existed between detectors (partly because of physical-access limitations), and no subsequent correlation data analysis was carried out for the collected data (although data was recorded for simultaneous intervals), and no phenomenological comparison was made between recorded neutron and gamma data (lacking a specific requirement). In practice, data collected from neutron channels was simply intercompared after each experiment with data from like adjacent neutron channels, and data collected from gamma channels was intercompared with data from like adjacent gamma channels. Concurrent radiation detection in the forms described is, however, an essential embodiment of this present invention for scattered-source HOC function. Prior existing technical means for detecting scattered radiation has often been the same as or similar to that used for detecting unscattered radiation. Radiation-detection technology usually ignores or makes use of the fact that scattered radiation loses some energy and suffers some changes its direction, whereas unscattered radiation (or that radiation which undergoes very slight change in direction upon being scattered) is transmitted and/or detected. This difference in transmittance is normally a feature observed and utilized in traditional radiation-transmission measurements. Transmission radiography generally depends on significant variations in object density compared to adjacent materials—thus on total mass or density of the object under inspection and thus on the degree of attenuation or outscattering of the transmitted radiation beam. Embodiments described in this section apply specifically to scattered radiation for which the type of radiation that is available after scatter is the same type as that which existed before the scattering event. In general, this scattered radiation would consist of the same incoming radiation form, but scattered in a direction different from the incoming beam, and probably losing energy in the one or more scattering processes that take place. Nothing precludes the occurrence of multiple-scattering events, nor is there any requirement that multiple-scattered radiation propagate in its original form. Ordinarily, x-ray images are reconstructed from the relative intensity of transmitted radiation. For example, soft tissue compared to bony tissue in a biological object would result in more x-ray transmission—and, thus, detected x-rays. The result of this phenomenon is a contrast-enhanced image of x-ray transmission, scattering, and absorption. X-rays incident on a target might be transmitted, absorbed, or scattered out of the incoming x-ray beam. Those x-rays that are transmitted, when compared to those that are incident, provide a contrast-defined image when absorbed in a recording medium, such as photographic film or an array of solid-state x-ray detectors. Consider, for example, a collimated beam of x-rays directed at a specific artificial target, as in X-rays scattered out of the incident beam would be deliberately subject to detection by the HOC system, and thus would provide additional information associated with whatever target zone is common to the FoV of the HOC detectors. If that common FoV has unique density-variation characteristics, the HOC method covariance analysis will thus provide an indication of target-material density; however, it will not by itself provide an indication that is linearly proportional to target density. Usually, incorporation of the HOC method in the measurement process for traditional medical and dental applications of x-rays would not expected produce substantial added information. However, the outcome of the HOC method might be more positive for high-energy gamma-ray and/or neutron transmission and scattering because so few gamma rays and fast neutrons might be absorbed compared to the number that are scattered. The typical gamma-ray scattering cross-section σs is large compared to its corresponding absorption cross section. Moreover, the cross-section dependence on target density might be such that transmission is less of a meaningful indicator than scattering, for example in the detection of high-density materials such as uranium. A similar observation might be made of fast-neutron scattering from a target, wherein the elastic scattering cross-section is often much larger than the combined neutron inelastic and absorption cross-sections. When interrogating an object using fast neutrons, many neutrons do not become of value to the inspection object-differentiation process if the detection requirement is limited to neutron transmission, capture, or inelastic scattering. Unique features of embodiments described in this section include: (1) detection hardware in this invention that combines well-defined prior-art hodoscope collimation and detection techniques for scatter radiation, coupled with a radiation source, and (2) data processing hardware and software in this invention that makes use of classic data-correlation techniques. When the specified target of interest is irradiated by highly-penetrating radiation, usually neutrons or gamma-rays (not necessarily pulsed), the incident radiation is unavoidably scattered by the target and its immediate environment. The approach of this invention complements and supplements the “active” and “passive” modes of substance identification for which separate provisional patents had been previously filed. This method can make use of, or be used in connection with or simultaneously with, essentially all forms of induced, transmitted, or scattered penetrating radiation (not only fast neutrons as an interrogation source, but also lower-energy neutrons, as well as high-energy x-rays, gamma rays, ultrasonic pulses, radar reflections, and other means of probing that might provide specific correlated identifying characteristics from the target zone). Typically, in implementation of this HOC invention, a pair of gamma and/or neutron detectors is arranged externally and orthogonally on a plane that is itself orthogonal to the active source. The HOC for radiation scattering method of this patent enhances nuclear detection of heavy elements, such as uranium or lead, compared to lighter elements. Because of its enhanced efficiency, it is possible to use comparatively weak-intensity neutron or gamma radiation sources. This method would allow efficient determination of the relative densities elements by distinguishing scattering reactions that typify specific elements or components. The HOC method for radiation scattering of this patent includes appropriate data processing and mathematical algorithms aimed at improving both the sensitivity of the systems and their effectiveness in discriminating false positives and nuisance alarms. The implementation of the HOC for scattered radiation sources of these embodiments is based on a combination of theoretical and experimental results, as well as new analysis capabilities in the form of improved algorithms. These methods can be applied to medical and other related fields of radiography where radiation sources are normally used. This method should reduce the radiation dose absorbed, and as well as incidental doses involved in handling radiation sources. Because dose localization can be improved, reduced doses could result from diagnostic testing, imaging, and treatment with medical radiation beams. If the external radiation source is in the form of neutrons, some radiation from the external radiation source (of unspecified energy) will consist of scattered and thermalized neutrons, thermal and high-energy capture gamma rays, inelastic gamma rays, and possibly fission gamma rays (which are in time coincidence as well as delayed coincidence) and fission neutrons (in time coincidence as well as delayed coincidence). In addition, and of defining importance to this patent application, is that the neutrons introduced by the external neutron source will also be scattered by the various components within the target zone, as well as by its immediate surroundings. If the external radiation source is in the form of x-rays or gamma-rays, some radiation from the external radiation source (of unspecified energy) will consist of scattered and collision-product x- or gamma-rays. In addition, and of defining importance to this patent application, is that the radiation introduced by the external radiation source will also be scattered by the various components within the target zone, as well as by its immediate surroundings. For most applications, we are probably dealing with “active” penetrating radiation generated by an nuclear accelerator, although “passive” radiation sources might be used as well in certain situations. Detector pairs might be for either or both of neutron and/or gamma rays, as appropriate. If we just have one pair of HOC radiation detectors with an active radiation-generating source which produces radiation that is scattered within in the target-beam radiation cone, but especially in the overlapping zone, the following applies: Each radiation detector will be operated in a pulse- or current-collection mode, and energy spectra, if appropriate, will be stored by a pulse-height analyzer in energy bins. To be considered truly orthogonal, the detectors should be perpendicular (e.g., at right angles) to each other, but in practice their orientation could be at some other mutually exclusive angles such that their FoVs overlap only with the exclusivity as represented schematically but not exactly. The radiation-detection energies on which these embodiments concentrate would be chosen from those that are associated with prominent reactions for substances of interest (e.g., radiation from high-density materials). Particular attention would be given to fissionable materials that might be enclosed in radiation-shielded surroundings; such materials have higher density than most other materials usually to be found in drums or cargo containers. Thus, in this typical or representative arrangement, our initiating source term is an active radiation source impinging on the central positionally-correlated zone of interest, while the intervening foreground and external radiation background cause either similar or dissimilar radiation scattering effects aside from that occurring in the source/target zone. For the purposes of computerized numerical simulations, specific scattering interactions (and rates) would be estimated in each zone as a result of the external radiation source effects. From target and radiation background rates or ratios would be recorded counts derived from a single detector, with more definitive results expected from the orthogonal pair. Without collimation, each detector would receive a larger fraction of the radiation background. In addition, the source would directly affect the detectors and their shielding. While the originating source of radiation might eventually result in an energy-dependent flux through and around the target zone, the source energy term is included in the discrete energy intervals for which correlated data will be recorded. Hodoscope collimation is one controlling factor to reduce detector radiation background. Another radiation background controlling factor would have to come from the correlation-analysis approach used to improve the signal/background ratio in order to obtain specific indication of an object that has a different interaction cross-section. Presumably we can include the direct uncorrelated source effect on the detector within the consolidated radiation background terms, but it mathematically amounts to a third “background” effect, which might have to be taken into consideration separately. It might be possible to fold it into the “foreground” and “background” although it is a factor that is directly proportional to the source term, as will be most if not essentially all of the foreground and background in this application. For an application wherein an active source that induces radiation background outside the HOC overlap zone, foreground and background need to be modeled such that they too are accordingly proportional to the strength of the external source. As previously described in the Background section, a fundamental underlying concept has been the author's invention of the hodoscope, which has extensively proven itself to provide durable, reliable, and definitive means of detecting and imaging a radiation field in a complex environment that included stray radiation which constituted non-informative background. The hodoscope was able to function at a wide range of reactor-source power levels. The hodoscope system was designed in one of its embodiments so that it could operate as a stationary detection system while the reactor was at high or transient power levels, or immediately after shutdown. The hodoscope was also designed in another embodiment so as to be movable in order to scan the source of residual radiation at the center of the reactor long after the reactor had been shut down. The hodoscope invention relied on detection of either or both of neutrons or gamma rays of selected energies. However, the hodoscope as previously patented did not operate in an orthogonal mode, nor was its data analyze in the correlation mode. This HOC method for “scattered” sources is based on the continuous recording of collected data in equal time intervals for at least one pair of detectors that are chronologically synched. It is not necessary that the detector angles be perpendicular on any plane; they must, however, be able to collect data independently of each other that is recorded in identical time intervals, and all data in the identical intervals must be tagged and stored according to corresponding detector identification and time interval. The target of interest for this invention is the object subject to substance detection and/or identification. It usually is, but need not be, enclosed within a large container which is likely to be filled with an unknown surrounding material of unknown and possibly variable density. The external source of active stimulation, typically an artificial-radiation generator, is to be located close to the target container, but as far away as possible from the collimated detectors. The source must generate detectable reactions in the target. However, the external source might also cause radiation background events, some of which are necessarily included in the detector count during any interval. In fact, this invention is of most value compared to traditional methods when there is an unavoidably large proportion of radiation background compared to signal from the source. The FoV of view of both HOC detectors should intersect within the container and be focused at a common nexus within the target container, usually an object of interest for substance identification. In addition, it is assumed that the all identical intervals for the collection of data are free of data deadtime and data overlap. However, it is possible to operate and use the HOC mode invention in an ionization-current mode as well as a pulse-amplitude mode. Current mode might be important if source and background signals might overwhelm the pulse-data processing equipment (as might be the case if the source or background are generated by pre-existing radiation background of the same type as, or sufficiently similar to, that which is sought to be detected from the source). It is important to keep in mind that almost all of the applications for the HOC equipment and operation deal with situations for which detection, rather than quantification, is a necessary and sufficient primary goal. In other words, determining the presence of a substance is more important than determining how much of the substance is present. For example, determining that nuclear material is present in the target zone is usually far more important than determining how much is present. More quantitative detection can be obtained either by maneuvering the detectors in such a way as to obtain more data, or by using complementary or alternative means. If the geometry of the substance in question is at issue, the HOC detectors could be mechanically scanned vertically and/or laterally to further define the region for which a positive correlation is obtained. Again, this is not a matter that requires statistically accurate determination, but it is a matter that benefits from adequate precision to determine the general shape of the object under inspection. In order to enable estimation of the intensity required for a scatter gamma source that impinges on an assumed target, some ad-hoc approximations are needed. For detection we could use a pair of large (2″ or 4″) NaI or BGO crystals. Two types of neutron sources would be useful to simulate: Cf-252 and 14 MeV(D,T). From an external 4π-emitting source, induced gamma production in the target and its surroundings is likely to be some type of continuous distribution as a function of distance into the target, starting at the origin, peaking at some distance inside, and tailing off to a low value at the most distant point. If the object of inspection is larger than the FoV of the orthogonal detectors, we need to consider the correlation associated with portions of the target that are in the foreground and background zones of each detector. As far as the detectors are concerned, they are not correlated, but as far as the target is concerned, they are an extension of the target source term. Both neutron and gamma/x-ray sources need to be estimated. In order to evaluate comparative effectiveness and statistical confidence, it is necessary to evaluate the expected rates of useful nuclear reactions. If the total path length of all the radiation in a cubic centimeter in a second is known, flux, and if the probability of having an interaction per centimeter path length is also known (macroscopic cross section), multiply them together to get the number of interactions taking place in that cubic centimeter in one second. This value is known as the reaction rate. The reaction rate can be calculated. If a neutron has a certain probability of undergoing a particular interaction in one centimeter of travel, then the inverse of this value describes how far the neutron will travel (in the average case) before undergoing an interaction. This average distance traveled by a neutron before interaction is known as the mean free path for that interaction and is represented by the symbol λ. The relationship between the mean free path and the macroscopic cross section Σ is shown below:λ=1/Σ The main point to take from the table above is that transmission radiography that employs high-energy neutrons will have a difficult time distinguishing heavy metals from other substances in a container. However, neutron-scattering as proposed in this invention would have a better opportunity to gain a significant count rate. More promising for better detection of heavy metals would be gamma-transmission radiography. Targets of interest or concern fall primarily in a number of general categories, depending on the intended area of application (e.g., national security, homeland security, medicine, military, research, dangerous substances, drugs, etc.). These targets for scattering techniques are basically the same as for active techniques discussed above. Some parameters will be outlined that need to be taken into account in making sensitivity estimates for HOC gamma-ray scattering estimates will be provided. The actual physical situation will need to be taken into account for numerical estimates to be made. Gamma-ray radiography systems capable of scanning trucks usually use cobalt-60 or caesium-137 as a radioactive source and a vertical tower of gamma detectors. In this invention, there would be two vertical towers to detect scattering from any type of radiation source, neutron and/or gamma. The horizontal dimension of the image may be produced by moving either the truck, the scanning hardware, or a underlying platform. “Passive” radiation sources, such as cobalt-60 use gamma photons with a mean energy 1.25 MeV, which can penetrate up to 15-18 cm of steel. Such systems provide good quality transmission-attenuation contrast images which can be used for identifying cargo and comparing it with the manifest, in an attempt to detect anomalies. It can also identify high-density regions too thick to penetrate, which would be the most likely to hide nuclear threats. The HOC detector vertical tower of this patent would not be in direct line of sight of the source, but would rely on scattered radiation, although it could be used as well for gamma-rays produced by neutron interactions in the target, as presented in the “Active” version 2013 Active HOC Provisional Patent Application. The primary difference between that patent application and the present application is that the latter relies primarily on neutron-produced induced radiation as the measured parameter, while this present application relies on scattered radiation as the measured parameter. In practice, similar HOC detection-array tower pairs could be implemented with a dual function of detecting both scattered and induced radiation. Of the interactions that can occur in any object are photoelectric absorption (mostly at low energies, Compton scattering (at intermediate energies), and pair production (at higher energies). The three interaction processes contribute to the total mass-attenuation coefficient. The relative importance of the three interactions depends on gamma-ray energy and the atomic number of the absorber. All elements except hydrogen show a sharp rise at low energies, where photoelectric absorption is the dominant interaction. The energy-related position of the rise is very dependent on atomic number. Above the low-energy rise, the value of the mass-attenuation coefficient decreases gradually, indicating the region where Compton scattering becomes the dominant interaction. The mass attenuation coefficients for all elements with atomic number less than 25 (iron) are nearly identical in the energy range 200 to 2000 keV. The attenuation curves converge for all elements in the range 1 to 2 MeV. The shape of the mass attenuation curve of hydrogen shows that it interacts with gamma rays with energy greater than 10 keV almost exclusively by Compton scattering. Above 2 MeV, the pair-production interaction becomes important for high-Z elements and the mass attenuation coefficient begins to rise again. For the purposes of this patent, pair production can be considered a form of out-scattering whereupon the radiation initially incident on the target is converted to a form of radiation that is well-suited for detection by orthogonal radiation-scattering detectors. For gamma rays introduced with energies between 1 and 10 MeV, the mass-attenuation coefficient for low Z materials is roughly linear, whereas elements such as iron begin to have a constant coefficient, and heavy metals tend to have a larger and increasing coefficient with increasing gamma energy. Whereas the differentiation between the heavy elements and the medium elements is roughly similar around 2 MeV, it becomes more pronounced above 5 MeV. With the exception of total photoelectric absorption, which occurs primarily at low energies, most of the gamma interactions result in what amounts to effective outscattering of the incoming gamma beam. The primary method advocated in this patent for determination of measurement objectives is the detection of radiation scattered from the incident beam. Thus, all gamma-ray incident-beam interaction processes that result in outscattering are significant for HOC detection in this invention; accordingly, it is useful to be aware of those processes which improve detection of gamma rays from scattered radiation, in contrast to radiation from the incoming beam which is transmitted or fully absorbed. Interactions that result in backscatter, which peaks at approximately 0.25 MeV, might be especially useful because its frequency of occurrence as an indicator of outscattering from the target. The energy-specific response density and linearity of the HOC gamma detector is fundamentally unimportant, although some degree of specificity might be achievable by recording and analyzing linear (or roughly linear) energy responses in separate concurrent data channels. The specific type of gamma-ray detector is relatively unimportant; more important are generalized properties of efficiency, cost, and reliability. Usually traditional sodium-iodide (NaI-Tl) and bismuth-germanate (BGO) scintillation detectors will suffice, especially because they are commercially available in large sizes. Total absorption efficiency of a 10 cm×10 cm cylindrical NaI detector would be better than 70% (as much as 90% at 1 Mev). (BGO would be closer to 90%.) Peak-to-total detection-ratio for a 4″ NaI detector at 10 MeV is no less than 0.4 and is close to 0.8 at 1 MeV. If one were to choose an approximate a single detector efficiency, the value of ε=0.5 could be used for peak detection efficiency in the representative range. For our 10-cm target diameter at 30 cm distance and 10 cm detector diameter, the solid angle Ω would be ˜0.08. The collimation and shielding inherent in hodoscope design is important in reducing cross-detection of radiation that is not directly associated with out-scattering from the incoming gamma-ray beam. Some direct detection of radiation from the incoming beam can be tolerated as background that is not directly associated with the target of the beam. The HOC method of correlation analysis circumvents the limitations of subtracting large radiation backgrounds from comparatively small signals. This is an cardinal outcome of the HOC methodology. The traditional two-step nuclear-measurement method could make use of a similar or identical pair of orthogonal hodoscope detectors; however, the traditional pair is not ordinarily operated in the correlation mode. For the traditional two-step method, each detector unavoidably measures a combination of source and background, and then the background is subtracted after it is determined by making a separate measurement—if that is possible. The net statistical confidence associated with determining the source strength can thus often be significantly degraded by the statistical impact of the background. Only when the background B is small compared to the signal S, that is, S<<B—in the traditional two-step process of separate estimation of B and the total measured value—does the result for S gain good statistical quality. In most realistic situations, B>>S, which means that the statistical quality of the desired property D is dominated by the statistics inherent in measurement of B. Often the background B is much larger than the signal S and cannot be determined without a separate measurement. Ignoring statistical variations in kx and ky, the respective standard deviations associated with estimating the value S would be:σ2S=σ2D+σ2B If σ2D is large compared to σ2S, then σ2S will be comparably large and thus be correspondingly imprecise. Moreover, if it were possible to reduce σ2B by a separate measurement of the backgrounds, then potential systematic errors have to be taken into account in addition to the random statistical errors. Detectors Each detector may be formed of a radiation-sensitive scintillation element to be stimulated by the gamma or neutron radiation and a photomultiplier tube to receive the output from the scintillator element. Several such elements may be placed in each detector assembly. Also, a lead radiation filter may be placed ahead of the detector in the collimator, and other lead filters may be placed in front of each subsequent scintillation element, respectively. Many gamma detectors are available which may be substituted for the sodium-iodide detector described in detail above. The detection element can be a small sodium-iodide (thallium-activated) scintillation crystal, for example, or other gamma detector with energy discrimination capability. A photomultiplier tube or photodiode associated with each scintillator generates an electric signal that is proportional to the intensity of gamma radiation imposed on the scintillator. The signal from the photomultiplier or photodiode may be transmitted via conductor from the detector to the electronic analysis components and circuitry located outside of the biological shield. Also, with respect to preferred thermal-operation environment, the ambient temperature limit for scintillator detector and photomultiplier assemblies should be considered. Other Electromagnetic Radiation The present invention may be applied to electromagnetic radiation other than gamma radiation. For example, X-ray sources may be used in the scatter mode of practicing the present invention in the same manner as gamma radiation. Also there are situations where visible light radiation could be examined by a pair or pairs of visible light detectors having overlapping fields of view. For example, a flame within a target region could be monitored by a pair of visible light detectors with fields of view both of which overlap the target region. If the intensity of the visible light from the flame is small compared to background visible light (such as bright sunlight); the correlation techniques of the present invention may be utilized to distinguish radiation from the flame and the background radiation. The various types of electromagnetic radiation that could be examined utilizing the correlation concepts of the present invention include: gamma radiation, X-radiation, ultraviolet radiation, visible light radiation, infrared radiation and millimeter wave radiation. Muons and Neutrinos For those object-detection systems that make use of muons and neutrinos generated from cosmic-ray interactions, and/or neutrinos generated from Earth-origin sources such as nuclear reactors, the HOC method can significantly improve object discrimination. For example, both muon and neutrino detection systems have been considered for detecting fuel reconcentration as an object in the disabled Fukushima reactors. The muon-detection systems, for the most part, rely either on differential scattering or absorption of cosmic-ray induced muons in the heavy metals compared to other less-dense materials in the object. The neutrino-detecton systems, for the most part, rely on a flux of neutrinos originating from the reconcentrated reactor fuel, which is the object of interest. Muon-detection systems also provide a potential means of preferentially detecting concentrations of heavy metals in large commercial cargo containers. An object of interest might be a concentration of banned substance, such as uranium. Aside from their inherently very low differential interaction fractions and rates, both muon and neutrino systems are also severely limited because of substantial background of indistinguishable detected radiation of the same type. The HOC method can be effectively applied to improve specificity in neutrino or muon detection of heavy metals compared to background effects. The HOC modification to current neutrino and muon detection practice would be similar to that asserted for neutron and gamma detection, namely the addition of a comparable hodoscope orthogonal detector for said neutrinos or muons, operated in the said correlation mode, and—importantly—the analysis of pixelated data from sequential time intervals. Muon detectors sometimes use hodoscope-collimating principles for their detection and definition of muons. This present invention would incorporate such detectors as modified to operate in the said HOC mode. In such applications, because of the very low usable rate of muon or neutrino radiation, the usable interaction rates would be very low, necessitating long recording time intervals, such as hours, days, or months. If photographic film or equivalent active-matrix detectors are used, pixel images collected for equal periods of time could be individually and collectively analyzed, in order to obtain spatial resolution in accordance with the HOC method. For example, passive photographic images—or their active electronic recording equivalent—could be obtained on a daily basis, and the array of pixels would be deciphered and compared on a day-to-day and pixel-by-pixel basis so as to be analyzed with their orthogonal equivalents by the covariance methods taught in this patent application. The most likely manifestation of this application for muons would be in the use of active radiographic imaging, as taught—for example—in applications of the original patented multi-channel hodoscope array, such that data collected in each active pixel is electronically collected and analyzed as part of an overall mathematically-reconstructed image. In the case of this present patent application the recording medium would necessarily take the form of at least one pair of such orthogonal arrays of detectors. Classical radiographic recordings—whether active or passive—are amenable to the same approach. That is, orthogonal data set from photographs/radiographs—or their electronic equivalent—could be imaged in sequential time increments (hours or days), and each such orthogonal-pair pixel rendition can be compared pixel-by-pixel using correlation methods. Therefore the scope of the present invention should be determined by the appended claims and not by the examples that have been given. |
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claims | 1. A hohlraum for an indirect drive inertial confinement fusion power plant in which the hohlraum surrounds a capsule at a central location containing fusion fuel, with the hohlraum comprising:an exterior surface having two end regions and a mid-region between the two end regions, the mid-region having a generally symmetrical cylindrical configuration of first diameter about a central axis and characterized by a center plane perpendicular to the central axis of the hohlraum and disposed at the central location, each of the end regions tapering from the first diameter to a second smaller diameter at ends of the hohlraum;a laser beam entrance hole at each of the end regions of the hohlraum;a covering at each of the end regions of the hohlraum to enclose a gas therein; anda hollow interior defined by an interior wall having a continuously curved oval shape, wherein normals to the interior wall are only perpendicular to the central axis of the hohlraum in the center plane. 2. A hohlraum as in claim 1 wherein each of the end regions comprises a truncated cone shaped protrusion extending between the mid-region and the laser beam entrance holes. 3. A hohlraum as in claim 2 wherein the covering over each of the laser entrance holes is substantially transparent. 4. A hohlraum as in claim 2 wherein the hollow interior contains an inert gas confined between the covering at each end of the hohlraum. 5. A hohlraum as in claim 4 wherein the inert gas comprises helium. 6. A hohlraum as in claim 1 further comprising a lining material disposed on the interior wall. 7. A hohlraum as in claim 6 wherein the lining material comprises a material of higher density than the interior wall. 8. A hohlraum as in claim 6 further comprising two infrared reflectors, one disposed between the covering at one end of the hohlraum and a mid-point along the central axis of the hohlraum and the other disposed between the covering at an opposite end of the hohlraum and the mid-point along the central axis of the hohlraum. 9. A hohlraum as in claim 8 further comprising a shield disposed on each of the two infrared reflectors. 10. A hohlraum as in claim 9 wherein each of the shields comprises material which is the same as the lining material. 11. A hohlraum as in claim 9 wherein each of the shields comprises a reflective disk having a center aligned to the central axis of the hohlraum. 12. A hohlraum as in claim 1 further comprising a membrane disposed perpendicular to the central axis to support the capsule along the central axis near a central point along the central axis. 13. A hohlraum as in claim 12 wherein the membrane comprises a carbon-based material. 14. A hohlraum as in claim 13 wherein the carbon-based material comprises at least one of polyimide, graphene, graphene-reinforced polymer, diamond-like-carbon, or diamond. 15. A hohlraum as in claim 1 further comprising a membrane disposed along the central axis to support the capsule along the central axis. 16. A hohlraum as in claim 6 wherein the lining material comprises a high-Z material such as lead. 17. A hohlraum as in claim 1 wherein the covering at each of the end regions comprises a carbon-based material. 18. A hohlraum as in claim 17 wherein the carbon-based material comprises at least one of polyimide, graphene, graphene-reinforced polymer, diamond-like-carbon, or diamond. 19. A hohlraum as in claim 1 wherein the tapering of the end regions comprises a linear taper from the first diameter to the second smaller diameter. 20. A hohlraum as in claim 2 wherein the truncated cone shaped protrusions are characterized by the first diameter near the mid-region and the second smaller diameter near the laser beam entrance holes. |
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description | This application claims the benefit to, and priority to, U.S. provisional application Ser. No. 62/432,396, filed on Dec. 9, 2016. The subject matter of this earlier filed application is incorporated herein in its entirety. The United States government has rights in this invention pursuant to Contract No. DE-AC52-06NA25396 between the United States Department of Energy and Los Alamos National Security, LLC for the operation of Los Alamos National Laboratory. The present invention generally relates to a heat pipe reactor core and the formation and deployment of heat exchangers. A heat pipe nuclear reactor core may include discrete heat pipe modules. A heat pipe module may include a single heat pipe with an evaporator bonded to several tubes. These tubes may hold nuclear fuel. Heat pipe modules are generally bundled together to form a critical assembly when neutron reflectors are placed on the perimeter of the assembly. The bundled heat pipe modules and fuel tubes are mechanically connected at the heat pipe module level and not at the reactor core level. The array of heat pipe modules spans the reactor core (including the heat pipe evaporator) and through the heat exchanger (including the heat pipe condenser). The heat pipe expands thermally during start up, and if bonded to the heat exchanger, stress may be generated due to the differential thermal expansion. However, an alternative configuration may be desirable. Certain embodiments of the present invention may provide solutions to the problems and needs in the art that have not yet been fully identified, appreciated, or solved by conventional heat pipe reactors. For example, some embodiments of the present invention pertain to a heat pipe reactor core and the formation and deployment of heat exchangers. In an embodiment, a heat pipe reactor may include a reactor core and one or more heat exchangers positioned on one or both sides of the reactor core. The heat pipe reactor may also include a plurality of heat pipes extending from the reactor core and out through the one or more heat exchangers. The reactor core may be composed of a plurality of monolithic blocks. Some embodiments of the present invention pertain to a method of producing a heat pipe reactor. The heat pipe reactor, including the reactor core and heat exchangers, may be part of a chemical or nuclear reactor, depending on the configuration of the heat pipe reactor. For purposes of explanation, the embodiments may be related to a nuclear reactor. The reactor core may include a monolithic block. The monolithic block may be composed of one or more plates. In embodiments that include several plates, these plates may be hot isostatically pressed (“hipped”) or cold pressed and diffusion bonded, for example. An array of heat pipes (hereinafter “the heat pipes”) may span the cross section of the monolithic block, eliminating the shifting of the heat pipes and the nuclear fuel as the reactor core heats and cools. The monolithic block provides a predictable reactivity feedback as the reactor core heats and cools. The reactor may also include one or more heat exchangers. In some embodiments, rather than two walls separating the working fluid of the heat pipe from the working fluid of the energy converter, a single wall may exist to separate the working fluid of the heat pipe from the working fluid of the energy converter. This may allow the heat pipes to freely expand and contract axially within the heat exchangers, which minimizes stress due to differential thermal expansion. The heat pipes may also be positioned inside the heat exchangers at room temperature to permit the heat pipes to grow within the channel of the heat exchangers as the reactor core expands radially relative to the heat exchangers. FIGS. 1A-1F perspective views illustrating a reactor 100, according to an embodiment of the present invention. In some embodiments, reactor 100 includes a reactor core 102, a first transition section 104, a first heat exchanger 106, a second transition section 108, a first manifold 110, a second heat exchanger 112, a second manifold 114, and an end cap 116. In some embodiments, first and second transition sections 104 and 108 may be any type of lens shaped element. For purposes of explanation, first and second transition sections 104 and 108 will be referred to as “first transition lens 104” and “second transition lens 108”. First heat exchanger 106 may be used to remove decay heat, and may be referred to as “decay heat exchanger 106” in one or more of the embodiments described herein. Second heat exchanger may be referred to as “primary heat exchanger 112”. As shown in FIGS. 1B and 1C, heat pipes 128 may project from one end reactor 100 to the other end of reactor 100. Reactor 100 may be composed of metal in some embodiments. In other embodiments, reactor 100 may be composed of stainless steel, super alloy, or refractory metal such as molybdenum. Reactor 100 may use any elemental working fluid, molecular working fluid, or a mixture of the same. For example, an alkali metal heat pipe working fluid, such as cesium, potassium, sodium, lithium, may be used. In some embodiments, tubes for heat pipes 128 may be expanded by processes, such as swaging, into holes of reactor core 102 or of lens 104. See, for example, FIG. 1F. These expanded tubes may be welded into or reactor core 102 or lens 104, and faced to mate with reactor core 102 by processes such as hipping, for example. It should be appreciated that these embodiments are not limited to welding and hipping. Heat pipes 128 may span from reactor core 102, first heat exchanger 106, and second heat exchanger 112 and out into end cap 116. Heat pipes 128 may project from either end of reactor core 102 in either the horizontal or the vertical orientations or any other orientation. Reactor core 102 may support heat pipes 128 in a fixed manner. Heat pipes 128 in first heat exchanger 106 and second heat exchanger 112 are supported simply to allow heat pipes 128 to move freely, minimizing stress concentrations due to temperature gradient induced differential expansion. Heat pipes 128 may be filled by direct transfer of working fluid, or vacuum distillation of working fluid, into the condenser or evaporator ends of individual heat pipes 128. Heat pipe 128 may be sealed by pinch and welding of the fill tube, for example. Referring to FIGS. 1B and 2B, heat pipes 128 or 228 may be bonded to an inner surface of reactor core 102 or 202. FIG. 1B will be used for the purposes of explanation. This may be accomplished by insertion of a dissolvable mandrel tube inside each heat pipe 128 along the length of reactor core 102. The ends of the dissolvable mandrel tube are closed on either end of reactor core 102. Hydraulic fluid may then be introduced into the mandrel tubes through one or more capillary fluid lines that can pass axially inside heat pipes 128 from either or both ends of heat pipes 128. The hydraulic fluid inside the dissolvable mandrels may be pressurized, allowing the mandrel tube to press the tubes within heat pipe 128 against the block heat pipe holes at reactor core 102. Once expanded, the hydraulic fluid may be removed from the assembly (e.g., mandrel, reactor core 102, heat pipes 128). The assembly is then heated to diffusion bond the tubes within heat pipe 128 to reactor core 102. The mandrel tubes are then removed from the assembly by chemical dissolution. Reactor Core Reactor core 102 may include an assembly of one or more monolithic blocks. See, for example, FIG. 1D, which shows an assembly of six monolithic blocks 1301, 1302, 1303, 1304, 1305, and 1306 with a trapezoid cross section, according to an embodiment of the present invention. It should be appreciated that the embodiments should not be limited to six monolithic blocks nor a trapezoid cross section. For instance, cross sectional arrangements may include pentagonal, heptagonal, or octagonal cross sections as well as spherical and nested annular cross sections. Other non-trapezoidal segment arrangements may include triangular or a monolithic segment shapes. Each monolithic block 1301, 1302, 1303, 1304, 1305, and 1306 may include regularly spaced through holes 1321, 1322, 1323, 1324, 1325, and 1326 oriented axially along the length of reactor core 102. Holes 1321, 1322, 1323, 1324, 1325, and 1326 may include a combination of nuclear reactor fuel rods or other heating elements such as electrical heater (e.g., cartridge heater, graphite heater, etc.), moderator, nuclear control rods, and heat pipes. As shown in FIG. 1B, heat pipes 128 may project from one end of reactor core 102 and out through first and second heat exchangers 106, 112. In other embodiments, and more specifically as shown in FIG. 2B, heat pipes 228 project from both sides of reactor core 202 of dual-ended reactor 200. Continuing with the discussion of monolithic blocks 1301, 1302, 1303, 1304, 1305, and 1306, each monolithic block 1301, 1302, 1303, 1304, 1305, and 1306 includes several plates. FIG. 1E, for example, illustrates a plate 136 with a pattern of holes 1321 with heat pipes arranged along the perimeter of plate 136, as well as fuel tubes 1341 arranged within the interior of plate 136. This may avoid heat pipe core cascade failure. It should be appreciated that monolithic blocks 1301, 1302, 1303, 1304, 1305, and 1306 may be formed with a series of axially bonded perforated (or drilled) plates. See, for example, FIG. 3, which illustrates a monolithic block 300, which may be part of a reactor core, according to an embodiment of the present invention. Monolithic block 300 may include multiple plates that are machined together. A pattern of holes may be drilled into the plates, and these plates may be hipped together or diffusion bonded, for example. It should be appreciated that the plates may be joined using one or more of the following techniques—diffusion bonding, brazing, welding, vacuum hot pressing, additive manufacture, or hot isostatic pressing. It should be appreciated, however, that the embodiments described herein are not limited to these techniques, and are provided for purposes of explanation. It should also be appreciated that these joining techniques may be used to join any component of reactor 100. Returning to FIG. 1A, reactor core 102, first and second transition lenses 104, 108, and heat exchangers 106, 112 may be joined using one or more of the above-mentioned joining techniques. As mentioned above, reactor core 102 may be formed from several monolithic plates, each of the monolithic plates composed of plates. See, for example, FIG. 3, which shows a monolithic block 300 composed of several plates. As shown in FIG. 1B, an array of seamless or welded tubes (or heat pipes) 128, which are inserted through the holes of the plates, string the plates together for aligning or sealing before bonding. Once bonded, these pipes 128 may remain at their initial thickness or have their interior diameter increased by line boring, for example. As discussed above, the monolithic blocks may be manufactured from a series of pre-machined perforated plates. See, for example, FIG. 1E. In this example, plates 136 may be arranged axially or radially, irrespective of the bonding technique. In some embodiments, upon forming of the monolithic block, line boring further opens holes 1321, which was briefly discussed above. Honing or chemical vapor deposition of the inner surface of holes 1321 may provide final finish to diminish the number and size of potential boiling nucleation sites thereon. Embedding thermodynamically stable materials, such as titanium, zirconium, and hafnium, into the wall of heat pipe 128 at or below the inner surface of heat pipe 128 getters oxygen and other non-metallic impurities from sources. These sources may be both external and internal to heat pipe 128 in some embodiments. These materials may be embedded using techniques such as hydroformed foils, thin walled tubes, or chemical vapor deposition. Placing thermodynamically stable materials, such as titanium, zirconium, and hafnium, into the inner spaces of heat pipe 128 getters oxygen and other non-metallic impurities from sources that are both external and internal to heat pipe 128. These materials may include coatings, wires, and foils. Heat Exchangers Returning to FIGS. 1A and 1B, heat pipes 128 project from reactor core 102 to one or more heat exchangers 106, 112. In other embodiments, heat pipes may project from reactor core to heat exchangers, which may be on one or both sides of the reactor core. See, for example, FIGS. 2A and 2B, which show a dual ended reactor 200, according to an embodiment of the present invention. In this embodiment, heat pipes 228 may project from reactor core 202 to heat exchangers 206A, 206B, 212A, 212B. Referring to FIG. 2B, for illustrative purposes of showing heat exchanger detail in reactor 200, the array of heat pipes 228 may extend into heat exchangers 206A and 212A, but not into heat exchangers 206B and 212B. Returning to FIGS. 1A and 1B, first heat exchanger 106, for example, may span azimuthally across the entire face of reactor core 102, allowing heat pipes 128 to project from reactor core 102 to pass through. This may simply the assembly process for reactor 100. Alternatively, first and second heat exchangers 106, 112 may azimuthally cover only each monolithic block of reactor core 102 allowing only the heat pipes projecting from each segment to project through them. First and/or second heat exchangers 106, 112 may be manufactured from a series of pre-machined plates arranged axially or radially, irrespective of bonding technique. First heat exchanger 106 may include ports 124 and 126. For example, as shown by the dashed-line arrow 140 in FIG. 1C, gas may enter port 124, and move up through heat pipes 128, and moves axially across first heat exchanger, and down through heat pipes 128, and finally exit out from port 126. In other embodiments, port 124 and port 126 may perform the same functions or the opposition functions as the other. First heat exchanger 106 may remove radioactive decay heat generated from nuclear reactor core fission products following shutdown. First heat exchanger 106 may reject decay heat to any suitable end use or place with any suitable heat transfer working fluid in any state. The ends of the decay-heat removal heat exchanger may have convex shape to minimize stress on the heat exchanger walls from internal pressure of a pressured working fluid. See, for example, FIG. 1F. Second heat exchanger 112 may remove fission heat generated during reactor operation. In some embodiments, one or more heat exchangers may be attached to reactor core 102. Heat pipes may link reactor core 102 to first heat exchanger 106. First heat exchanger 106 may reject fission heat via the working fluid through gas manifolds and working fluid ports 120, 122 to any suitable end use or place with any suitable heat transfer working fluid. For example, as shown in FIG. 1C, gas may enter through port 120, traverses across heat pipes 128 and flows through an annular region between heat pipe 128 and second heat exchanger 112, and out through port 122. Manifolds 110, 114 may be placed on either end of second heat exchanger 112, and may have convex shape to minimize stress on the walls of second heat exchanger 112 from the internal pressure of gas or the heat exchange medium. See, for example, FIG. 1F. The body of second heat exchanger 112 may be produced from a series of pre-machined perforated plates arranged axially or radially, irrespective of the bonding technique. Manifolds 110, 114 may be produced by a combination of hydroforming (or additive manufacture) of a series perforated curved sections that match the projected heat pipe hole pattern. Manifolds 110, 114 may then be attached to the body of second heat exchanger 112 by one or more techniques. These techniques may include welding, hot isostatic pressing, additive manufacture, diffusion bonding, vacuum hot pressing, or brazing. End cap 116 may be a cover or a solid plate, with a hemispherical cross-section. End cap 116 may include sockets for heat pipes 128 to expand into and move radially and axially within end cap 116. This may form a pressure boundary by sealing the medium of second heat exchanger 112 from the environment external to reactor 100. Transition Lens Reactor core 102 and first heat exchanger 106 are connected using a first transition lens 104. A second transition lens 108 may connect reactor core 102 to second heat exchanger 112. Second transition lens 108 may also connect first heat exchanger 106 to second heat exchanger 112. Although not shown, first and second transition lens 104, 108 may also connect a first heat exchanger to another first heat exchanger, second heat exchanger to another secondary heat exchanger, or any combination thereof. First and second transition lens 104, 108 may span the entire core cross section or be segmented azimuthally as reactor core 102. Transition lens 104, 108 may have a perimeter that largely conforms to the shape of the heat pipe pattern projecting from reactor core 102. Transition lens 104, 108 may have a flat shape, a convex shape, a concave shape, or any combination thereof, to minimize stress concentrations in reactor core 102, first heat exchanger 106, or second heat exchanger 112. Simply put, transition lens 104, 108 form lens shaped elements with through holes reflecting the pattern of heat pipes projecting from reactor core 102. In certain embodiments, transition lens 104, 108 may be formed by a combination of hydroforming a series perforated curved sections that may then be attached together. Techniques used for attachment may be similar to the joining technique discussed above. A hole (or tunnel) 118 may be placed along the center axis of the central cross sections of heat exchangers 106, 112, transition lens 104, 108, and reactor core 102. Hole 118 may serve as a cylindrical passage for neutron absorption material to control core criticality. This way, hole 118 is hermitically sealed, preventing gas from ports 120, 122, 124, or 126 to exit from hole 118. FIG. 4 illustrates an operation 400 of heat pipe centering cam 406, according to an embodiment of the present invention. In some embodiments, heat pipe condenser 402 may be supported by a simple support 408, which is in contact heat pipe centering cam 406 to accommodate differential thermal expansion of the heat pipe and reactor core 404 during start up, operation, and shutdown. A heat pipe centering cam 406 on the heat-pipe surface centers the heat pipe in the heat exchanger channel 410 as reactor core 404 expands radially and the heat pipe expands axially during start up. FIG. 5 is a flow diagram illustrating a process 500 for assembling the monolithic blocks, according to an embodiment of the present invention. In some embodiments, process 500 may begin at 502 with cutting a series of plates with holes drilled according to the heat pipe and fuel rod pattern. At 504, stacking the series of plates, and at 506, introduce a series of tubes into the heat pipe and fuel rod holes. At 508, the ends of the tubes are then swaged to the inside diameter of the top and bottom plates in the series of plates. At 510, the tube ends are then welded to the end plates, hermetically sealing the tubes to the monolithic block. At 512, sheets are welded to the side walls of the stack of plates. At 514, a vacuum port may be placed on one or more of the sheet faces, allowing the evacuation of the hermetically welded plate assembly. The assembly may then be introduced at 516 into a furnace where the assembly is brought to sufficient temperature and external pressure to metallurgically bond all parts (e.g., hot isostatic pressing). A similar process may be applied for forming the secondary heat exchanger. The sealing of the heat pipe tubes results in a hermetically sealed tube. However, one of ordinary skill in the art would understand that the heat pipe tubes are not limited to being continuous. In certain embodiments, the heat pipe tubes may be segmented in a hermetic fashion by way of hipping or other processes that achieve a similar result. For example, the heat pipe tubes are initially segmented, and by hipping or welding, become a continuous tube. FIG. 6 is a flow diagram illustrating a process 600 of assembling the reactor, according to an embodiment of the present invention. For example, process 600 may begin at 602 with forming several monolithic blocks from a series of plates. At 604, transitional sections (or lenses) are formed. This may include the first and second lenses, as well as the heat exchangers depending on the selected embodiment. At 606, once the reactor core, the lenses, and the heat exchangers are formed, heat pipes may be inserted within the holes of the monolithic blocks of the reactor core. In another embodiment, the monolithic block holes may also serve as heat pipe walls. At 608, in certain embodiments, the heat pipes may be expanded into the monolithic block using hydraulic pressure. At 510, the condenser ends of the heat pipes may be joined using one or more of the above-mentioned techniques. In some embodiments, augmented heat exchange surfaces may be manufactured on the perimeter of the heat pipe condenser, enhancing convective heat transfer coefficient. These augmented surfaces include circumferential, axial, or helical ribs, fins, swirl promotion, or similar heat transfer enhancement devices. These heat transfer enhancement devices may be formed while manufacturing the heat pipe wall. For example, machining, drawing, additive manufacture or similar technique may increase radial heat transfer from the heat pipe condenser. Once the elements bond together, the overall assembly is chemically cleaned, and vacuum fired to remove non-metallic impurities from the inner heat pipe surface to prevent impurity-induced corrosion. During operation, the reactor is heated and cooled at finite rates to control differential thermal expansion between the hot core and heat pipes and the cooler heat exchanger parts. Heat exchanger surface temperature may be controlled by trace heat from electrical elements, such as nichrome, to minimize thermal stresses and cycle fatigue. Temperature gradient minimization may be realized across the reactor and heat exchangers by controlling heat exchanger coupling to the working fluid and/or by operating the reactor core at a low power. This may be accomplished using fission or decay heat in a standby operating mode. In some embodiments, remote repair of contaminated or non-working but filled heat pipes may be performed by cutting into one or both ends of the heat pipes, cleaning with steam, rewelding at one end of the heat pipe, chemically cleaning, vacuum firing with a localized heater rod, reintroduction of a new wick, heat pipe closure welding, and filled by direct transfer or vacuum distillation of working fluid. It will be readily understood that the components of various embodiments of the present invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the detailed description of the embodiments of the present invention, as represented in the attached figures, is not intended to limit the scope of the invention, but is merely representative of selected embodiments of the invention. The features, structures, or characteristics of the invention described throughout this specification may be combined in any suitable manner in one or more embodiments. For example, reference throughout this specification to “certain embodiments,” “some embodiments,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in certain embodiments,” “in some embodiment,” “in other embodiments,” or similar language throughout this specification do not necessarily all refer to the same group of embodiments and the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be noted that reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment. Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention. In order to determine the metes and bounds of the invention, therefore, reference should be made to the appended claims. |
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050230476 | summary | BACKGROUND OF THE INVENTION This invention relates to a nuclear reactor operating method and a nuclear reactor, and more particularly to a nuclear reactor operating method and a nuclear reactor which are suitably applicable to boiling-water reactors for reducing consumption of nuclear fuel. In conventional boiling-water reactors, a reactor core is installed inside a pressure vessel and is loaded with a large number of fuel assemblies, between which control rods operated by control rod drivers are inserted. The heat generation in the reactor is maintained by a self-sustaining fission chain reaction of fissile material (for example uranium-235) present in fuel rods. That is, in the reactor core, neutrons strike uranium atoms, resulting in the fission of the uranium atoms. The energy produced by the fission reaction is converted to thermal energy. Of the uranium, a uranium-235 is the fissionable material that is bombarded with neutrons to cause fission reactions. The uranium-235 accounts for only 0.7% of the naturally occurring uranium, with the remainder being unfissionable uranium-238. The uranium-235 is enriched to about several percent for use as a nuclear fuel. In the conventional nuclear reactors, the chain reaction is maintained by operating the control rod and controlling the flow rate of coolant supplied to the core (hereinafter referred to as a core flow rate). The control rods absorb excess neutrons released by nuclear fission to control the chain reaction; and the core flow rate is adjusted to change the volume factor of water lacking part (a void fraction) by changing the amount of vapor bubbles in the core for controlling the chain reaction. In boiling-water reactors using fuel assemblies (burnup: 0 GWd/T), as the core flow rate is increased, the void fraction generally decreases, promoting deceleration of neutrons, which is turn increases the neutron multiplication factor and therefore the reactivity. Now, the method of controlling the reactivity through absorption of excess neutrons and regulation of the void fraction will be described. We will explain the state of the reactor after a certain point in one fuel cycle (a fuel cycle is the period after the fuel assemblies have been loaded into the core and the reactor operation started until the reactor is stopped to replace spent fuel assemblies in the core), that is, after the reactor power has reached the rated output. At the initial period of the fuel cycle, the reactivity is potentially high, which requires the reactor operation to be performed in such a way as to raise the void fraction to reduce neutron deceleration, keeping reactivity at a desired level. As the burnup of fissile material proceeds and the reactivity lowers, the core flow rate is gradually increased to reduce the void fraction in the core, compensating for the reduction in reactivity. However, since the range in which the void fraction can be changed is small, a lower limit of void fraction is soon reached, making it impossible to continue compensating for the reduction in reactivity. To avoid this problem, a common practice is that the control rods are withdrawn to the exert corresponding to the amount of reactivity compensation obtained by the void fraction adjustment. Then, the core flow rate is again increased gradually to lower the void fraction and thereby compensate for the reduction of reactivity which accompanies the burnup of fissionable material. For effective utilization of fuel, a reactor operation method is being considered which involves making the void fraction large at the initial stage of the fuel cycle to positively accumulate plutonium in the core and at the end of the fuel cycle burning the accumulated plutonium. The void fraction may be changed by the foregoing described in the U.S. Pat. No. 4,716,007, or a method which adjusts the subcooling (the difference between the amount of energy per unit of mass of the cooling water at the saturated temperature and that of the cooling water entering the core). The U.S. Pat. No. 4,716,007 describes the method of changing the void fraction in which slow-neutron absorbing water purge rods and neutron absorbing water purge rods made of stainless steel, which has a greater reactivity worth than the former, are provided and in which the amount of insertion into the core of the water purge rods is controlled to regulate the amount of cooling water in the core. The water purge rods constitute a means to change the void fraction in the core. The advantages of progressively changing the number of hydrogen atoms in the core according to the burnup of nuclear fuel are explained below. In the boiling-water reactors, a higher burnup is obtained when the reactor is operated with the void fraction set at high value (50%) at first and then lowered (to 30%) than when the void fraction is kept constant (at 30%) throughout the operation. This is because the larger the void fraction, the smaller the number of hydrogen atoms in the core and the less the neutrons will be decelerated. And the energy of neutrons remains higher, so that uranium-238 is converted into plutonium-239 at higher rates, retarding the reduction in the total amount of uranium-235 and plutonium-239. However, since the absolute value of the reactivity is small, the reactivity when the void fraction is high will reach the minimum level of reactivity to maintain criticality in a shorter period of time than when the void fraction is low. Thus when the minimum level of criticality is reached, the void fraction is lowered to cause neutron deceleration, which is turn increases reactivity. This enables the nuclear fuel to burn for a longer period than it does with the void fraction kept constant. The above reactor operating technique which makes use of void fraction changes for effective utilization of fuel is called a spectral shift operation. The above spectral shift operation in which the water purge rods are manipulated requires the water purge rods and a device for driving these rods, making the reactor construction and its operation complicated. An example of the fuel assembly to which the spectrum shift operation is applicable is disclosed in the Japanese Patent Application Laid-Open No. 38589/1986. The fuel assembly has a heater in a water rod. However, since the heater is formed of a low-enriched fuel rod, the structure of the fuel assembly is complex and its manufacture is not easy. In this respect, the spectrum shift operation that regulates the core flow rate can eliminate such problems. The spectrum shift operation, however, has the following problems The lower limit of the core flow rate is restricted by thermal limitations, and the upper limit is constrained by the performance of a circulation pump and a heat exchanger as well as by flow vibrations. Thus, with the boiling-water reactor operating at the rated power, the void fraction can only be changed in a narrow range with its center at a void fraction which corresponds to the core flow rate for the 100% output rating. For example, suppose the range in which the core flow rate can be varied is 80 to 120%. Then the range in which the void fraction is varied is about 9%. With such a small variation range for the void fraction, the spectrum shift operation will not be effective. This also applies to the reactor operation using the fuel assembly described in the Japanese Patent Application Laid-Open No. 38589/1986. SUMMARY OF THE INVENTION A primary object of this invention is to provide a nuclear reactor operating method and a nuclear reactor which can increase the range of variation of void fraction in the core and which can reduce the number of times that the control rods need to be replaced. A second object is to provide a nuclear reactor operating method which can prevent too fast increase in reactivity by restricting a sharp rise of water level in the water rod. A third object is to provide a nuclear reactor operating method which can simplify the control operation to hold the reactor power at a specified level. A fourth object is to provide a nuclear reactor operating method which can raise the reactor power in a short time at the start of the reactor. A first feature which achieves the first objective lies in that after the reactor power control by the control rod withdrawal operation is completed, the reactor power control is performed not by the control rod operation, but by regulating the level of coolant in the water rods arranged in the core. According to the first feature of this invention, as the flow of coolant passing through the core is reduced, vapor fills the coolant ascending and descending paths in the water rods. As the coolant flow increases, the amount of vapor in the coolant ascending paths significantly reduces. Since the void fraction in the water rods can be changed greatly in this way, there is no need to manipulate the control rods for regulating the reactor power. The second feature which achieves the second objective of this invention involves regulating the coolant level in such a way that the rate of increase of the reactor power does not exceed a specified value. With the second feature, it is possible to prevent a sharp increase in the liquid level in the water rods that would result from a rapid increase in the coolant flow. The third objective of this invention is achieved by holding the reactor power at a target value by regulating the coolant level in the water rods until the end of the fuel cycle, without operating the control rods, once the reactor power has reached the target value. This feature eliminates the necessity for changing the pattern of control rods and allows the reactor power to be maintained at a target value by a simplified control operation involving only the coolant level regulation. A feature of this invention that achieves the fourth objective lies in the fact that, after having been raised by the pull-out operation of the control rods, the reactor power is further raised to a target value not by the control rod operation, but by regulating the coolant level in the water rods installed in the core. These features eliminate the need for the control rod withdrawal operation, which has been performed at the start of conventional reactors by taking advantage of the buildup of xenon caused by an increase in the coolant flow rate. It is therefore possible to raise the reactor power in a short period of time at the startup. SUMMARY OF THE INVENTION A first object of this invention is to provide a nuclear reactor operating method and a nuclear reactor which can increase the range of variation of the void fraction in the core and which can reduce the number of times that the control rods are replaced. A second object is to provide a nuclear reactor operating method which can simplify the control operation to hold the reactor power at a specified level. A first feature which achieves the first objective is that after the reactor power control by the control rod pull-out operation is completed, the reactor power control is performed not by the control rod operation, but by regulating the level of coolant in the water rods installed in the core. According to the first feature of this invention, as the flow of coolant passing through the core is reduced, vapor fills the coolant ascending and descending paths in the water rods. As the coolant flow increases, the amount of vapor in the coolant ascending paths significantly reduces. Since the void fraction in the water rods can be changed greatly in this way, there is no need to manipulate the control rods for regulating the reactor power. The second objective of this invention is achieved by holding the reactor power at a target value by regulating the coolant level in the water rods until the end of the fuel cycle, without operating the control rods, once the reactor power has reached the target value. This feature eliminates the need for changing the pattern of control rods and allows the reactor power to be maintained at a target value by a simplified control operation involving only the coolant level regulation. |
claims | 1. An electron microscope for observing a surface or inside of a semiconductor wafer or a mask for exposing a semiconductor pattern for faults and/or foreign objects, comprising:a function of loading measurement data of coordinates of said faults and/or foreign objects which were observed by another wafer or mask inspecting apparatus, moving a field of view of the electron microscope to an area of coordinates of said fault and/or foreign object, and simultaneously displaying said coordinates of said faults and/or objects which were obtained by observing said semiconductor wafer or said mask with said another wafer or mask inspecting apparatus, an electron microscope image of said field of view of the electron microscope, a vicinity area of said field of view of the electron microscope, showing said fault positions and sizes according to the coordinates and the sizes of said fault and/or foreign object observed by said another wafer or mask inspecting apparatus,a function of moving said field of view of the electron microscope when the fault is not found to a position which is pointed by a pointer on a display, anda function of magnifying said vicinity area after moving said field of view of the electron microscope,wherein said field of view and the magnification of said vicinity area are automatically shrunk when said field of view of the electron microscope is not found in the vicinity area after the movement of the field of view of the electron microscope or said field of view and the magnification of the vicinity area are automatically enlarged when said field of view of the electron microscope is in the vicinity area after the movement of the field of view of the electron microscope. 2. An electron microscope in accordance with claim 1, further comprising a function which moves and displays the center coordinates of the field of view and its vicinity area as said field of view moves. 3. An electron microscope in accordance with claim 1, wherein said loaded measurement data further includes sizes of said faults and/or foreign objects and said display displays shapes of faults and/or foreign objects on a screen. 4. An electron microscope in accordance with claim 1, further comprising a function which displays coordinates of faults or objects obtained by said another wafer or mask inspecting apparatus and distances of the field of view of the electron microscope, a function which stores said distance values, and a function which relatively moves the field of view of the electron microscope by said stored distances. 5. An electron microscope in accordance with claim 1, further comprising a function which displays an observed area and a non-observed area separately on a screen displaying said field of view and its vicinity area, and a function which changes said display as the observing conditions of the electron microscope change. 6. An electron microscope for observing a surface or inside of a semiconductor wafer or a mask for exposing a semiconductor pattern for faults and/or foreign objects, comprising:a memory device for storing coordinate information of sizes of said faults or foreign objects which were obtained by another wafer or mask inspecting apparatus,a control computer for controlling so as to move a field of view of said the electron microscope to an area where a fault of foreign object exists based on said coordinate information, anda display for simultaneously displaying said coordinates of said faults or objects which were obtained by observing said semiconductor wafer or said mask with said another wafer or mask inspecting apparatus, said field of view of said electron microscope moved according to the coordinates of said faults or objects which were obtained by another wafer or mask inspecting apparatus, and a vicinity area of said field of view of the electron microscope showing fault positions and sizes according to said coordinate information or sizes of said faults or foreign objects stored in said memory device,a pointing device which moves said area indicating said field of view of said electron microscope to a position on said vicinity area which is pointed by the pointing device, whereinsaid control computer controls said electron microscope so as to move said field of view of said electron microscope to said position on said vicinity area which is pointed to by said pointing device and calculates a magnification of displaying size of said field of view of said electron microscope and said vicinity area, andsaid display displays said semiconductor wafer or a mask observed in said field of view to said position on said vicinity area which is pointed to by the said pointing device and with the calculated magnification by the control computer, andwherein said field of view and the magnification of said vicinity area are automatically shrunk when said field of view of the electron microscope is not found in the vicinity area after the movement of the field of view of the electron microscope or said field of view and the magnification of the vicinity area are automatically enlarged when said field of view of the electron microscope is in the vicinity area after the movement of the field of view of the electron microscope. 7. An electron microscope in accordance with claim 6, wherein said display further displays a step value on a display to change an actual size of said vicinity area. |
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abstract | An electrical penetration assembly for a nuclear reactor vessel, mountable in an aperture of a nuclear reactor vessel, includes a penetration body including first and second ends to be positioned, respectively, inside and outside the vessel; a sealed electrical connector providing a first seal for the electrical penetration assembly, the sealed connector insulating the penetration body at the first end; a feed-through carrier flange having a plurality of unitary electrical feed-throughs, each unitary feed-through allowing a single electrical conductor to pass therethrough, thereby ensuring continuity of the electrical connections, each unitary feed-through being individually insulated by an individual insulator providing a second seal, the unitary feed-throughs insulating the penetration body at the second end; and an anti-ejection device formed by the engagement between a narrowed portion provided at each unitary feed-through and a shoulder that is larger than the narrowed portion and provided on each of the electrical conductors. |
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description | The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2010-277193, filed Dec. 13, 2010, which is incorporated herein by reference. (1) Field of the Invention This invention relates to a method of removing foil shadows of a synchronous grid which removes scattered radiation of a radiographic apparatus, and a radiographic apparatus using the same. (2) Description of the Related Art Conventionally, an X-ray apparatus includes an X-ray tube, and an X-ray detector opposed to the X-ray tube. The X-ray detector has a grid disposed adjacent an X-ray incident plane thereof. The grid reduces image quality degradation due to scattered X-rays, but on the other hand, grid foil shadows are superimposed on radiographic images. An FPD (Flat Panel Detector) has come to be used widely as the X-ray detector in recent years. The FPD can improve the spatial resolution and X-ray sensitivity of radiographic images, and for this and other reasons its use is spreading at a rapid rate. However, as improvement is made in the spatial resolution and X-ray sensitivity of the X-ray detector, the grid foil shadows appear clearly on radiographic images, which are obstructive to interpretation of the radiographic images. In order to remove these grid foil shadows from the radiographic images, it is known to remove the shadows by image processing using frequency conversion. See Patent Document 1 (Japanese Unexamined Patent Publication No. 2000-83951 (paragraphs “0033”-“0036”)), for example. Patent Document 1 describes what is called a fixed grid which is fixedly attached to the X-ray detector although changeable to one different in grid intervals. Besides the above fixed grid, there is a moving grid. The moving grid is moved in a direction perpendicular to grid stripes synchronously with X-ray irradiation to prevent a fixed pattern of the grid from appearing on radiographic images. Although the fixed pattern of the grid does not appear on radiographic images, the moving grid has problems of requiring a complicated moving mechanism and lowering detection efficiency. Such grids are constructed of an alternate arrangement of metal foil strips consisting of an X-ray absorbing material such as lead, and interspacers consisting of aluminum or carbon fiber which does not easily absorb X-rays. However, these interspacers absorb a certain quantity of X-rays, which leads to a sensitivity lowering of desired X-ray images. So, a synchronous grid has been proposed as a solution to these problems. See Patent Document 2 (Japanese Unexamined Patent Publication No. 2002-257939 (paragraphs “0018” and “0019”, and FIG. 1)). This synchronous grid has grid foil strips arranged so that grid foil shadows fall in middles of detecting pixels of the FPD. More particularly, the grid foil strips are arranged as inclined such that each has flat surfaces thereof aligned to a straight line extending between a focus of the X-ray tube and an X-ray detecting plane of the FPD. Patent Document 3 (Japanese Unexamined Patent Publication No. 2008-232731 (paragraphs “0001”-“0003” and “0007”)), for example, describes a specific method of manufacturing a synchronous grid. This method excludes the interspacers members to provide layers of air, thereby to obtain X-ray images of improved sensitivity. However, the conventional example with such construction has the following problems. For reasons of manufacture of the grid foil strips and construction for aligning the grid foil strips, the synchronous grid has a certain distortion of the linear grid foil strips and a minute shift in their positions of arrangement. Further, since the grid foil strips of the synchronous grid are higher than those of the other type grids, the foil shadows of the synchronous grid are susceptible to influences of the distortion and shifting of the grid foil strips. Distortion and shifting occur also with the grid foil shadows, which are caused by the distortion and shifting of the grid foil strips. As a result, variations in measurements of the foil shadows will occur to different lines of the grid foil shadows, and density variations will occur to the grid foil shadows. There is a drawback that, even if frequency conversion is used for removing the grid foil shadows, the grid foil shadows in a longitudinal pattern cannot fully be removed. The grid foil shadows failing to be removed will become artifacts on radiographic images after the grid foil shadows are removed therefrom. In an X-ray apparatus having a C-arm, the heavy X-ray tube and FPD are mounted at opposite ends of the C-arm. Thus, subtle bending of the C-arm will occur with movement such as rotation of the C-arm, thereby causing a shift between the FPD and the focus of the X-ray tube. This shift is in the order of 2 mm, for example, but the grid foil shadows on the FPD will also move, and hence a problem that the grid foil shadows cannot fully be removed. In order to solve the above problems, Applicant has proposed the following technique (International Application PCT/JP2010/003221). According to this technique, pixels free from influences of grid foil shadows are first extracted from a fluoroscopic image, and an interpolation process is carried out based on detection signal values of these pixels, to obtain an approximate fluoroscopic image without influences of the grid foil shadows. Next, a grid foil shadow image which is an image of only the grid foil shadows is obtained based on a difference between the fluoroscopic image and the approximate fluoroscopic image. Further, the grid foil shadow image is averaged to obtain a foil shadow standard image inhibiting variations in the grid foil shadows due to random errors such as quantum noise. Then, based on the foil shadow standard image and the fluoroscopic image, the grid foil shadows are removed from the fluoroscopic image. This is a technique intended to obtain, through such processes, a fluoroscopic image with no grid foil shadows appearing thereon. It is important for the above proposed technique how the pixels free from influences of the grid foil shadows should be extracted. However, under the influence of random quantum noise occurring with X-rays, pixels influenced by the grid foil shadows can be extracted in error. Then, since the approximate fluoroscopic image has low accuracy, accuracy of the grid foil shadow image also becomes low. There arises a problem that it is impossible to remove the grid foil shadows from the fluoroscopic image ultimately with high accuracy, with artifacts remaining to impart influence. This invention has been made having regard to the state of the art noted above, and its object is to provide a method of removing foil shadows of a synchronous grid and a radiographic apparatus using the same, which are capable of removing artifacts due to distortion of the synchronous grid while inhibiting adverse influences of random quantum noise. The above object is fulfilled, according to this invention, by a grid foil shadow removing method for a radiographic apparatus for obtaining fluoroscopic images and having a synchronous grid with grid foil strips arranged at regular intervals so that grid foil shadows fall on middles of pixels which detect radiation, the method comprising an extracting step including a grouping step for dividing pixels forming a fluoroscopic image into groups each having a predetermined number of pixels within each row in a direction of row, a most influenced pixel selecting step for selecting a pixel most influenced by one of the grid foil shadows in each group as most influenced pixel, a voting step for casting, with the most influenced pixel in each group serving as a reference, a predetermined number of votes for other pixels spaced apart forward and backward in the direction of row, and an electing step for electing a pixel given a maximum number of votes within each group as an uninfluenced pixel which is free from influences of a foil shadow of the grid; an approximate fluoroscopic image calculating step for obtaining an approximate fluoroscopic image by carrying out an interpolation process based on detection signal values of the uninfluenced pixels; a grid foil shadow image calculating step for obtaining a grid foil shadow image based on a difference between the fluoroscopic image and the approximate fluoroscopic image; a foil shadow standard image calculating step for obtaining a foil shadow standard image by averaging the grid foil shadow image in a longitudinal direction of the grid foil shadows; and a foil shadow removing step for removing the grid foil shadows from the fluoroscopic image based on a difference between the fluoroscopic image and the foil shadow standard image, thereby to obtain a foil shadow removed image. According to this invention, the pixels arranged in the direction of row are grouped in the grouping step, and the most influenced pixel within each group is selected in the most influenced pixel selecting step. The most influenced pixel is a pixel most influenced by a grid foil shadow, which can be selected relatively easily and relatively reliably compared with selection of pixels not influenced by the grid foil shadows. Next, in the voting step, votes are cast for other pixels spaced forward and backward in the direction of row from the most influenced pixel in each group, and in the electing step, a pixel given a maximum number of votes within each group is elected as an uninfluenced pixel which is free from influences of a grid foil shadow. By executing the extracting step including the above steps, pixels not influenced by the grid foil shadows can be extracted with a relatively high degree of certainty from among pixels with varied detection signal values due to random quantum noise of the radiation. Then, in the approximate fluoroscopic image calculating step, an interpolating process is carried out based on the detection signal values of the uninfluenced pixels, to calculate an approximate fluoroscopic image with the grid foil shadows substantially removed from the fluoroscopic image. Further, the grid foil shadow image calculating step calculates a grid foil shadow image as an image of only the grid foil shadows based on a difference between the fluoroscopic image and the approximate fluoroscopic image. Since this grid foil shadow image has nonuniformity of the grid foil shadows due to influences of the random errors due to quantum noise and the like, the foil shadow standard image calculating step calculates a grid foil shadow standard image without influences of distortions due to noise, for example, by averaging the grid foil shadow image piecewise by units of several tens of pixels in the longitudinal direction. This averaging also can remove some errors in interpolating process. Next, the foil shadow removing step is executed to obtain a foil shadow removed image excluding the grid foil shadows from the fluoroscopic image based on a difference between the fluoroscopic image and the foil shadow standard image. As described above, the extracting step extracts uninfluenced pixels with a relatively high degree of certainty, while avoiding influences of random quantum noise as much as possible. An approximate fluoroscopic image is obtained based on such uninfluenced pixels. Thus, accuracy of the approximate fluoroscopic image can be improved over that of the prior art. Therefore, the grid foil shadow image and foil shadow standard image calculated successively based on the approximate fluoroscopic image have improved accuracy over the prior art. As a result, while inhibiting influence of random quantum noise, the foil shadow removed image is made free from artifacts due to distortion of the synchronous grid. In this invention, it is preferred that, when the predetermined number of pixels constituting each group is four, and the predetermined number of votes is 1; the voting step casts 1 vote for each of a pixel located next but one forward and a pixel located next but one backward in the direction of row; and the electing step elects a pixel having obtained 2 votes as the uninfluenced pixel; the voting step and the electing step having, interposed therebetween, adjusting steps including a first adjusting step for adjusting the number of votes obtained to 2 for a pixel whose number of votes obtained is 1 when pixels located next but three to such pixel forward and backward in the direction of row have 2 votes, respectively; a second adjusting step for adjusting the number of votes obtained to 0 for a pixel whose number of votes obtained is 1 when a pixel located next to such pixel in the direction of row has 2 votes; a third adjusting step for comparing detection signal values of a pixel whose number of votes obtained is 1 and an adjoining pixel, adjusting the number of votes from 1 to 2 for the pixel having the larger detection signal value, and adjusting the number of votes to 0 for the pixel having the smaller detection signal value; and a fourth adjusting step for adjusting the number of votes obtained from 1 to 0 for a pixel whose number of votes obtained is 1 when one of pixels located next but one to such pixel forward and backward in the direction of row has 2 votes. When the number of pixels constituting each group is four and the number of votes is 1, the voting step first casts 1 vote for each of a pixel located next but one forward and a pixel located next but one backward in the direction of row. Then, the electing step elects a pixel having obtained 2 votes at this point of time as the uninfluenced pixel. Further, at this point of time, there exist pixels with the number of votes obtained=1, for which it is unknown whether they are influenced by the foil shadows or not. Then, the adjusting steps including the first to fourth adjusting steps are executed for all pixels whose number of votes obtained is 1. First, the first adjusting step adjusts the number of votes obtained from 1 to 2 for a pixel when pixels located next but three to this pixel forward and backward in the direction of row have 2 votes, respectively. This is because, when four pixels form each group, a pixel next but three to a pixel having 2 votes has a high probability of not being influenced by a foil shadow. Next, the second adjusting step adjusts the number of votes obtained from 1 to 0 for a pixel when a pixel located next to this pixel in the direction of row has 2 votes. This is because the probability of two adjoining pixels not being influenced by a foil shadow or shadows is low. Next, the third adjusting step compares detection signal values of adjoining pixels, adjusts the number of votes to 2 for the pixel having the larger detection signal value, and adjusts the number of votes to 0 for the pixel having the smaller detection signal value. This is because, where pixels with 1 vote adjoin each other, the pixel with the larger detection signal value is more likely not to be influenced by a foil shadow. Next, the fourth adjusting step adjusts the number of votes obtained to 0 for a pixel when one of pixels located forward and backward next but one to this pixel has 2 votes. This is because, when a pixel not influenced by a foil shadow is present close by, the pixel in question has a high probability of being influenced by the foil shadow. These adjusting steps adjust many pixels with the number of votes 1 to have the number of votes=0 or the number of votes=2, which enables uninfluenced pixels to be extracted within the respective groups. In this invention, it is preferred that the method further comprises a fifth adjusting step executed, when there remains a pixel whose number of votes obtained is 1 after the fourth adjusting step, for adjusting the number of votes obtained by such pixel to 2. For a group located in an end portion, the votes are cast only from the group at one side, and there exists a pixel with the number of votes 1 remaining unchanged. So, this remaining pixel is adjusted to have 2 votes. This enables an uninfluenced pixel to be extracted from the end portion for use in the interpolation process. Therefore, the interpolation process for end portions can also be carried out with high accuracy. In this invention, it is preferred that the method comprises a forcible changing step executed after the extracting step, when a predetermined range includes an uninfluenced pixel skipping four pixels, and an uninfluenced pixel skipping two pixels, for forcibly changing the uninfluenced pixels so that each have three pixels at both sides. Even though uninfluenced pixels are extracted through the adjusting steps, there is a possibility of erroneous extraction since, after all, pixels only with a stochastically high degree of certainty are extracted. So, the forcible changing step assumes a high probability of erroneous extraction when a predetermined range includes an uninfluenced pixel skipping four pixels and an uninfluenced pixel skipping two pixels. Then, the uninfluenced pixels are forcibly changed so that each have three pixels at both sides. This can inhibit lowering of the accuracy of an approximate fluoroscopic image due to the erroneous extraction. In another aspect of the invention, a radiographic apparatus for obtaining radiographs comprises a radiation emitting device for emitting radiation to a patient; a radiation detector having pixels arranged in a two-dimensional array for detecting radiation transmitted through the patient; a synchronous grid with foil strips arranged at regular intervals so that grid foil shadows fall on middles of the pixels of the radiation detector; an extracting unit including a grouping unit for dividing pixels forming a fluoroscopic image into groups each having a predetermined number of pixels within each row in a direction of row, a most influenced pixel selecting unit for selecting a pixel most influenced by one of the grid foil shadows in each group as most influenced pixel, a voting unit for casting, with the most influenced pixel in each group serving as a reference, a predetermined number of votes for other pixels spaced apart forward and backward in the direction of row, and an electing unit for electing a pixel given a maximum number of votes within each group as an uninfluenced pixel which is free from influences of a foil shadow of the grid; an approximate fluoroscopic image calculating unit for obtaining an approximate fluoroscopic image by carrying out an interpolation process based on detection signal values of the uninfluenced pixels; a grid foil shadow image calculating unit for obtaining a grid foil shadow image based on a difference between the fluoroscopic image and the approximate fluoroscopic image; a foil shadow standard image calculating unit for obtaining a foil shadow standard image by averaging the grid foil shadow image in a longitudinal direction of the grid foil shadows; and a foil shadow removing unit for removing the grid foil shadows from the fluoroscopic image based on a difference between the fluoroscopic image and the foil shadow standard image, thereby to obtain a foil shadow removed image. According to this invention, the radiation emitting device emits radiation to a patient, and the radiation detector detects radiation transmitted through the patient. The resulting fluoroscopic image has grid foil shadows of the synchronous grid appearing thereon. So, the grouping unit divides the pixels arranged in the direction of row into groups, and the most influenced pixel selecting unit selects the most influenced pixel within each group. The most influenced pixel is a pixel most influenced by a grid foil shadow, which can be selected relatively easily and relatively reliably compared with selection of pixels not influenced by the grid foil shadows. Next, the voting unit casts votes for other pixels spaced forward and backward in the direction of row from the most influenced pixel in each group, and the electing unit elects a pixel given a maximum number of votes within each group as an uninfluenced pixel which is free from influences of a grid foil shadow. With the extracting unit carrying out such processes, pixels not influenced by the grid foil shadows can be extracted with a relatively high degree of certainty from among pixels with varied detection signal values due to random quantum noise of the radiation. Then, the approximate fluoroscopic image calculating unit carries out an interpolating process based on the detection signal values of the uninfluenced pixels, to calculate an approximate fluoroscopic image with the grid foil shadows substantially removed from the fluoroscopic image. Further, the grid foil shadow image calculating unit calculates a grid foil shadow image as an image of only the grid foil shadows based on a difference between the fluoroscopic image and the approximate fluoroscopic image. Since this grid foil shadow image has nonuniformity of the grid foil shadows due to the random errors due to quantum noise and the like, the foil shadow standard image calculating unit calculates a grid foil shadow standard image without influences of distortions, for example, by averaging the grid foil shadow image piecewise by units of several tens of pixels in the longitudinal direction. Next, the foil shadow removing unit obtains a foil shadow removed image excluding the grid foil shadows from the fluoroscopic image based on a difference between the fluoroscopic image and the foil shadow standard image. As described above, the extracting unit extracts uninfluenced pixels with a relatively high degree of certainty, while avoiding influences of random quantum noise as much as possible. An approximate fluoroscopic image is obtained based on such uninfluenced pixels. Thus, accuracy of the approximate fluoroscopic image can be improved over that of the prior art. Therefore, the grid foil shadow image and foil shadow standard image calculated successively based on the approximate fluoroscopic image have improved accuracy over the prior art. As a result, while inhibiting influence of random quantum noise, the foil shadow removed image is made free from artifacts due to distortion of the synchronous grid. An embodiment of this invention will be described hereinafter with reference to the drawings. In this embodiment, an X-ray fluoroscopic apparatus will be described as an example of radiographic apparatus. FIG. 1 is an overall view showing an outline of an X-ray fluoroscopic apparatus according to the embodiment. FIG. 2 is a view in vertical section of a grid. FIG. 3 is a perspective view of grid foil strips. An X-ray fluoroscopic apparatus 1 includes an X-ray tube 3, a synchronous grid 5 and a flat panel detector 7 (hereinafter called FPD). The X-ray tube 3 emits X-rays to a patient M. The synchronous grid 5 is attached to an X-ray incident side of the FPD 7 for removing scattered X-rays. The FPD 7 detects transmission X-rays emitted from the X-ray tube 3. The X-ray tube 3 and the synchronous grid 5/FPD 7 are mounted at opposite ends of a C-arm 9 to be opposed to each other. The C-arm 9 is supported by an arm support 11, and is moved by a C-arm moving mechanism 13. The C-arm moving mechanism 13 is controlled by a C-arm movement controller 15. The above X-ray tube 3 corresponds to the “radiation emitting device” in this invention. The FPD 7 corresponds to the “radiation detecting device” in this invention. The C-arm 9 is constructed movable up and down in vertical directions R1 relative to a top board 17 on which the patient M is placed. The arm support 11 is constructed rotatable about an axis R2 extending vertically. The C-arm 9 is also rotatable about a horizontal axis R3 and movable in arcuate rocking directions R4 relative to the arm support 11. In order to adjust an SID (Source Image Distance) which is a distance between the X-ray tube 3 and FPD 7, the synchronous grid 5 and FPD 7 are movable in vertical directions R5 by the C-arm moving mechanism 13. The X-ray fluoroscopic apparatus 1 further includes an X-ray tube controller 19, an analog-to-digital converter 21, an image processor 23, a main controller 25, an input unit 27, a monitor 29 and a storage unit 31. The X-ray tube controller 19 controls a tube current and tube voltage outputted to the X-ray tube 3. The analog-to-digital converter 21 converts X-ray detection signals outputted from the FPD 7, from analog to digital. The image processor 23 carries out various image processes on the digital X-ray detection signals. The main controller 25 has a CPU and so on for performing overall control of the X-ray tube controller 19 and other components. The input unit 27 has input devices such as a mouse used by the radiographer in making varied settings. The monitor 29 is used to give various displays such as control screens for X-ray diagnosis and X-ray fluoroscopic images picked up. The storage unit 31 is formed of a storage device such as hard disk or semiconductor memory for storing the X-ray fluoroscopic images and various data. The synchronous grid 5 will be described with reference to FIGS. 2 and 3. The synchronous grid 5 is disposed to cover an X-ray detecting plane of the FPD 7. The synchronous grid 5 has grid foil strips 5a stretched to extend in a longitudinal (Y) direction. The grid foil strips 5a are formed of a material for absorbing X-rays. The grid foil strips 5a are arranged as inclined such that each has a flat surface thereof aligned to a straight line extending between a focus F of the X-ray tube 3 and the X-ray detecting plane of the FPD 7. In other words, the synchronous grid 5 has the grid foil strips 5a arranged so that grid foil shadows (hereinafter called simply foil shadows) may fall on middles of X-ray detecting pixels DU of the FPD 7. The grid foil strips 5a will be described with reference to FIGS. 3 and 4. FIG. 4 is a view in vertical section showing a relationship between the grid and FPD. The grid foil strips 5a are arranged at predetermined intervals in a transverse (X) direction. The arrangement pitch Gp is 400 μm, for example. This arrangement pitch Gp is designed as appropriate to synchronize with the width WDU of the X-ray detecting pixels DU of the FPD 7. That is, the grid foil strips 5a are arranged so that, in a C-arm standard position at a reference SID, the foil shadows thereof may fall at predetermined pixel intervals on the X-ray detecting pixels DU. Since the width WDU of the X-ray detecting pixels DU is 100 μm in this embodiment, for example, the foil shadows will be cast in a ratio of one to four of the X-ray detecting pixels DU in the transverse direction. The above grid foil strips 5a are formed of a simple substance such as molybdenum, tungsten, lead or tantalum, or an alloy having one or more of these as main component. These metals, preferably, are materials having large atomic numbers and high X-ray absorptivity. The grid foil strips 5a usually have a thickness of 20-50 μm. The grid foil strips 5a are manufactured by rolling, cutting and so on, but because of being a heavy metal or an alloy thereof, it is very difficult to secure uniformity in shapes such as in the thickness and width of the grid foil strips 5a. This shape nonuniformity of the grid foil strips 5a is a cause of the foil shadows producing variations in detection values. The FPD 7 has X-ray detecting pixels DU arranged in a two-dimensional array for converting X-rays into charge signals. Specifically, for example, 1440×1440 X-ray detecting pixels DU are arranged. The SID will be described now. The SID is a perpendicular distance between the focus of an X-ray source in the X-ray tube 3 and the FPD 7. When the SID is shortened, an enlarged fluoroscopic image of the patient M can be obtained. On the other hand, when the SID is elongated, a wide-field fluoroscopic image of the patient M can be obtained. That is, a zoom adjustment of fluoroscopic images can be made by adjusting the SID. It is assumed in this embodiment that the SID at 1000 mm is set as “reference SID”. The grid foil strips 5a and FPD 7 are positionally adjusted to have one foil shadow falling on every four X-ray detecting pixels DU in the transverse direction of the FPD 7 when in the C-arm standard position at the reference SID. This is because, in the C-arm standard position, the C-arm 9 is considered free from bending due to its rigidity. The C-arm standard position is a position in which, as shown in FIG. 1, the C-arm 9 is in a positional relationship set three-dimensionally relative to the top board 17 or an examination room, and to which the C-arm 9 is initialized for every examination. Reference is now made to FIG. 5. FIG. 5 is an explanatory view of SIDs. When the SID is changed, the foil shadows on the X-ray detecting plane will move. At an elongated SID which is longer than the reference SID, for example, although the foil shadows on a middle portion of the FPD 7 are little influenced, the foil shadows away from the middle portion toward side ends of the FPD 7 move inward of the FPD 7. Conversely, when the SID is made shorter than the reference SID, the foil shadows move outward of the FPD 7. The above movements of the foil shadows will occur also when the C-arm 9 is rotated, for example. Here, reference is made to FIGS. 6 through 9. FIG. 6 is a view showing the C-arm having been moved. FIGS. 7 and 8 are schematic views illustrating movement of the X-ray focus. FIG. 9 is a schematic view illustrating movement of a foil shadow on pixels of the FPD. When the C-arm 9 is rotated to assume a position as shown in FIG. 6, a “bending” will occur to the C-arm 9 due to its rigidity. Then, the X-ray focus in the X-ray tube 3 will also move with this bending, and therefore the foil shadows will move, though minutely, also at the reference SID. This movement is, for example, about 2 mm at most. When the X-ray focus F in the X-ray tube 3 moves minutely as shown in FIG. 7, for example, the straight lines extending between the X-ray focus F and the detecting plane of the FPD 7 will become misaligned with the inclination angles of the flat surfaces of the grid foil strips 5a. Consequently, the foil shadows will move minutely on the X-ray detecting plane. As shown in FIG. 8, when the reference SID is 1000 mm and the distance between the synchronous grid 5 and the FPD 7 is 20 mm, the ratio between the distance from the focus F of the X-ray tube 3 to the synchronous grid 5 and the distance from the synchronous grid 5 to the FPD 7 is about 50:1. Therefore, when the focus F of the X-ray tube 3 moves 2 mm, the foil shadows of the grid foil strips 5a will move about 40 μm on the detecting plane of the FPD 7. Assume that the thickness of the grid foil strips 5a is 30 μm and the width of the foil shadows also 30 μm, since a setting is made such that the foil shadows are located at the middles of the pixels when at the reference SID, there is an allowance of 35 μm from the foil shadows to adjoining pixels. On the other hand, when the above movement of the focus F of the X-ray tube 3 moves the foil shadows 40 μm, the foil shadows will, as shown in FIG. 9, protrude into the adjoining pixels from the pixels arranged beforehand to have the foil shadows cast thereon. When an approximate fluoroscopic image is obtained by fixing pixels not influenced by the grid foil shadows, the accuracy of the approximate fluoroscopic image lowers due to such a phenomenon occurring to the foil shadow. This gives rise to a problem of lowering the accuracy of a fluoroscopic image with no grid foil shadows appearing thereon. It is characteristic of this invention to inhibit such an adverse influence. Next, reference is made to FIG. 10. FIG. 10 is a block diagram of the image processor. The image processor 23 receives the digital X-ray detection signals converted by the analog-to-digital converter 21. The image processor 23 includes a LOG-transforming unit 41, an image memory unit 43, an extracting unit 45, an approximate fluoroscopic image calculating unit 47, a foil shadow image calculating unit 49, a foil shadow standard image calculating unit 51 and a subtracting unit 53. The LOG-transforming unit 41 has a function to LOG-transform the digital X-ray detection signals. This LOG transformation allows arithmetic operations to be carried out by linear sum, which can lighten the load of subsequent arithmetic operations. The image memory unit 43 stores fluoroscopic images based the LOG-transformed X-ray detection signals, and functions also as a buffer. The extracting unit 45 has a function, details of which will be described hereinafter, to extract pixels not influenced by the foil shadows as uninfluenced pixels, based on a fluoroscopic image stored in the image memory unit 43. The approximate fluoroscopic image calculating unit 47 carries out an interpolating process based on the uninfluenced pixels extracted by the extracting unit 45, and calculates an approximate fluoroscopic image having the foil shadows removed from the fluoroscopic image read from the image memory unit 43. The foil shadow image calculating unit 49 calculating a grid foil shadow image which is an image of the grid foil strips 5a by determining a difference between the fluoroscopic image and approximate fluoroscopic image. The foil shadow standard image calculating unit 51 calculates a grid foil shadow standard image by averaging the grid foil shadow image in the longitudinal direction of the grid foil strips 5a. The subtracting unit 53 calculates a foil shadow removed image having the foil shadows removed from the fluoroscopic image by determining a difference between the fluoroscopic image and the grid foil shadow standard image. The above foil shadow image calculating unit 49 corresponds to the “grid foil shadow image calculating unit” in this invention. The subtracting unit 53 corresponds to the “foil shadow removing unit” in this invention. Reference is now made to FIGS. 11 and 12. FIG. 11 is a schematic view illustrating a positional relationship between the FPD and grid foil shadows at a time of reference SID. FIG. 12 is a schematic view illustrating a positional relationship between the FPD and grid foil shadows at a time of deviation from the reference SID. According to the design adopted here, at the reference SID the foil shadows fall on the X-ray detecting pixels DU of the FPD 7 as shown in FIG. 11, for example. That is, assuming that the X-ray detecting pixels DU of the FPD 7 are set to P4n+1 (where n is an integer 0 or more) in the direction of row (transverse direction), the foil shadows fall on the pixels indicated by P4n+1 and arranged at intervals of four pixels (or at intervals of three pixels when the three pixels are seen as being skipped). The shape of the grid foil strips 5a is not strictly uniform, and minute shifts will occur with the arrangement of the grid foil strips 3a also. These result in variations in the width (in the direction of row) of the foil shadows as seen in a foil shadow 55 and a foil shadow 57. However, of a group consisting of four pixels (P4n+1, P4n+2, P4n+3 and P4n+4), the pixels P4n+2, P4n+3 and P4n+4 forming a group excluding the pixel P4n+1 are uninfluenced pixels which are not influenced by the foil shadow 55. Therefore, the foil shadow image calculating unit 49 may carry out an interpolation process using any one of these pixels. However, random quantum noise exists in X-rays, and when uninfluenced pixels are selected based only on the pixel values (X-ray detection signal values), inappropriate pixels can be selected as the uninfluenced pixels. In the case of a deviation from the reference SID or the C-arm 9 moved as described above, for example, the positions of the foil shadows move from the positions of the foil shadows according to the design value of the reference SID as shown in FIG. 12. For example, a foil shadow 59 appears as straddling the pixel P4n+1 and adjoining pixel P4n+2 in the group of four pixels (P4n+1, P4n+2, P4n+3 and P4n+4). In a different condition, a foil shadow 61 may move completely from pixel P4(n+1)+1 onto pixel P4n+4. In this way, the pixels not influenced by the foil shadows are changeable also with the position of the C-arm 9, and therefore a contrivance is needed for extracting uninfluenced pixels. Reference is now made to FIGS. 13 and 14. FIG. 13 is a schematic view showing a relationship between the grid foil shadows and detection values of the pixels in the absence of a patient. FIG. 14 is a schematic view showing a relationship between the grid foil shadows and detection values of the pixels in the presence of a patient. When X-raying is carried out without the patient M placed on the top board 17 as shown in FIG. 13A, X-ray detection signal values will be as follows. As shown in FIG. 13B, the pixels P4n+1 with the foil shadows of the grid foil strips 3a falling thereon have X-ray detection signal values (● (black circle) mark) which are reduced about 20% from X-ray detection signal values (Δ (triangle) mark and (□ (square) mark) of the other pixels. Next, when X-raying is carried out with the patient M placed on the top board 17 as shown in FIG. 14A, X-ray detection signal values will be as follows. As shown in FIG. 14B, the pixels P4n+1 with the foil shadows of the grid foil strips 3a falling thereon have X-ray detection signal values (● (black circle) mark) which are lower than X-ray detection signal values (Δ (triangle) mark and □ (square) mark) of the other pixels. Reference is now made to FIG. 15 showing actual measurements in graphs. FIG. 15 shows an example of detection values of the pixels within one row of the FPD, in which FIG. 15A shows detection values of the entire row, FIG. 15B shows detection values of a middle portion A, and FIG. 15C shows detection values of an end portion B. The FPD 7 used here is 9 inch size with 1440×1440 pixels, the tube voltage is 60 keV, and the elongated SID deviating from the reference SID is 1150 mm. As shown in FIG. 15A, in pixel numbers 1 to 1440 of the X-ray detecting pixels DU in one row of the FPD 7, there are four locations of turnover in the magnitude relation of the X-ray detection signal values. These locations represent instances of foil shadows straddling the pixels as described hereinbefore. FIG. 15B shows an enlarged graph of the middle portion A of FIG. 15A, in which the foil shadows fall on every fourth pixels, i.e. at regular intervals skipping three pixels. FIG. 15 C shows an enlarged graph of the end portion B of FIG. 15A, which includes an instance of a foil shadow straddling the pixels. It will be seen that the X-ray detection signal values assume a complicated pattern in this graph. Such a complicated pattern formed also indicates a difficulty in extracting uninfluenced pixels. Reference is made to FIGS. 10 and 16. FIG. 16 is a schematic view showing a voting process. In FIG. 16, the ● (black circle) mark indicates pixels most influenced by the foil shadows, the ◯ (white circle) mark indicates pixels not influenced by the foil shadows, and hatched ◯ (white circle) mark indicates pixels which are neither of the above two types. The extraction of uninfluenced pixels noted above is carried out by the extracting unit 45. The extracting unit 45 has a grouping unit 71, a most influenced pixel selecting unit 73, a voting unit 75, an adjusting unit 77, an electing unit 79 and a forcible change unit 81. The above adjusting unit 77 corresponds to the “first adjusting unit to the fifth adjusting unit” in this invention. The grouping unit 71 carries out a process of dividing a plurality of pixels i (where i=1 to N) arranged in the direction of row (transverse direction) of the FPD 7 as shown in FIG. 16A, into groups each consisting of a predetermined number of pixels (FIG. 16B). Assume here, for example, that four pixels constitute each group. That is, the grouping unit 71 divides the pixels into a plurality of groups each including four consecutive pixels. In FIG. 16B, the pixels are divided into a group of pixel i, pixel i+1, pixel i+2 and pixel i+3, a group of pixel i+4, pixel i+5, pixel i+6 and pixel i+7, a group of pixel i+8, pixel i+9, pixel i+10 and pixel i+11, a group of pixel i+12 . . . , and so on. The most influenced pixel selecting unit 73 processes each of the groups formed by the grouping unit 71. Specifically, one pixel most influenced by a grid foil shadow 5a in each group is selected as the “most influenced pixel”. This is done only by selecting what has an extremely low detection signal value, and is easy compared with finding uninfluenced pixels. Specifically, pixels i+2, i+6 and i+10 in the respective groups will be selected as the most influenced pixels. The voting unit 75, based on the positions of the most influenced pixels i+2, i+6 and i+10 in the respective groups selected by the most influenced pixel selecting unit 73, casts a predetermined number votes for pixels i, i+4, i+8 and i+12 which are located next but one to the respective most influenced pixels i+2, i+6 and i+10 forward and backward in the direction of row (FIG. 16C). Here, the predetermined number of votes is set to “1”. The electing unit 79, based on the result of voting by the voting unit 75, elects pixels least influenced by the foil shadows as “uninfluenced pixels”. Since the number of votes is set to one vote, the votes are cast for pixels next but one forward and backward, and the number of pixels in each group is four, the number of votes G(i) obtained by each pixel i at this time is 0, 1 or 2. The pixels with G(i)=0 are those influenced by the foil shadows, while the pixels of G(i)=2 are those least influenced by the foil shadows. Therefore, the electing unit 79 elects the pixels having obtained the number of votes G(i)=2 as uninfluenced pixels. Thus, it is so designed that the foil shadows fall on every four pixels, each group is set to every four pixels, and votes are cast for positions spaced from the most influenced pixel in each group by two pixels which are the half of the number of pixels constituting each group, thereby forming peaks of the number of votes at certain places. Moreover, the peaks correspond with a high degree of certainty to positions of the pixels unlikely to be influenced by the foil shadows, and thus the uninfluenced pixels can be elected with a high degree of certainty. The pixels with G(i)=1 are those for which it is unknown whether they are influenced by the foil shadows or not. So, the adjusting unit 77 carries out the following adjustment for the pixels with G(i)=1. First, when the number of votes G(i)=2 is obtained by each of pixels next but three to a given pixel forward and backward in the direction of row (i.e. G(i−4)=2 or G(i+4)=2), the number of votes G(i) obtained by this given pixel is adjusted from 1 to 2. This is because four pixels form each group, and so a pixel next but three to a pixel having obtained the number of votes G(i)=2 has a high probability of not being influenced by a foil shadow. Next, when the number of votes G(i)=2 is obtained by a pixel next to a given pixel in the direction of row (i.e. G(i−1)=2 or G(i+1)=2), the number of votes G(i) obtained by this given pixel is adjusted from 1 to 0. This is because the probability of two adjoining pixels not being influenced by a foil shadow or shadows is low. Next, the detection signal values of adjoining pixels among the pixels of G(i)=1 are compared. The number of votes of the pixel with the larger detection signal value is adjusted to 2, and the number of votes of the pixel with the smaller value to 0. This is because, where pixels of G(i)=1 adjoin each other, the pixel with the larger detection signal value is more likely not to be influenced by a foil shadow. Next, when one of pixels next but one to a given pixel forward and backward has two votes (i.e. G(i−2)=2 or G(i+2)=2), the number of votes of this given pixel is adjusted to 0. This is because, when a pixel not influenced by a foil shadow is present close by, the given pixel has a high probability of being influenced by the foil shadow. These operations adjust many pixels with the number of votes G(i)=1 to have the number of votes G(i)=0 or the number of votes G(i)=2, which enables uninfluenced pixels to be extracted within the respective groups. When there still remain pixels having the number of votes G(i)=1 after the above process, the adjusting unit 77 changes the number of votes of these pixels to G(i)=2. For a group located in an end portion of the FPD 7, the votes are cast only from the group at one side, and there exists a pixel with the number of votes G(i)=1 remaining unchanged. So, this remaining pixel is adjusted to have the number of votes G(i)=2, thereby to extract an uninfluenced pixel from the end portion for use in the interpolation process. Therefore, the interpolation process for the end portions of the FPD 7 can also be carried out with high accuracy. After the above adjustments are carried out and the uninfluenced pixels are elected by the electing unit 79, the forcible change unit 81 checks whether a forcible changing condition is fulfilled or not, and carries out the following forcible change when the condition is fulfilled. Even though uninfluenced pixels are extracted through the adjustment described above, there is a possibility of erroneous extraction since, after all, pixels only with a stochastically high degree of certainty are extracted. Under ideal conditions in which no random noise exists, and when an SID used is longer than the reference SID, most of the uninfluenced pixels occurring within one row skip three pixels each. The uninfluenced pixels, skipping two pixels each, occur in only several locations within one row. The uninfluenced pixels, skipping two pixels each, occur substantially equidistantly. Conversely, when the SID used is shorter than the reference SID, most of the uninfluenced pixels occurring within one row skip three pixels each, the uninfluenced pixels, skipping four pixels each, occur in only several locations within one row, and the uninfluenced pixels, skipping four pixels each, occur substantially equidistantly. That is, with whatever SID, the uninfluenced pixels, skipping two pixels each, and the uninfluenced pixels, skipping four pixels each, never occur at the same time. So, a high probability of erroneous extraction is assumed when the forcible change unit 81 finds fulfillment of a “forcible changing condition” that a predetermined range (e.g. a range of five uninfluenced pixels) includes an uninfluenced pixel skipping four pixels, and an uninfluenced pixel skipping two pixels. Then, the uninfluenced pixels are forcibly changed so that each have three pixels at both sides. This can inhibit lowering of the accuracy of an approximate fluoroscopic image due to the erroneous extraction. Next, a process of X-ray fluoroscopic imaging carried out by the above X-ray apparatus 1 will be described with reference to FIGS. 17 and 18. FIG. 17 is a flow chart showing operation of the image processor. FIG. 18 is a flow chart showing a process of extracting uninfluenced pixels. First, X-ray fluoroscopic imaging carried out before the processes in the flow chart will be described. The radiographer sets an amount of the SID, an amount of movement of the C-arm 9, a tube voltage and a tube current to the input unit 27. The main controller 25 outputs the set amount of the SID and amount of movement of the C-arm 9 to the C-arm movement controller 15. The C-arm movement controller 15 controls the C-arm moving mechanism 13 to move the C-arm 9. The main controller 25 also outputs instructions to the X-ray tube controller 19 to control the X-ray tube 3 with the set tube voltage and tube current. Next, when the radiographer instructs a start of X-raying from the input unit 27, the main controller 25 controls the X-ray tube controller 19 and FPD 7. The X-ray tube controller 19 applies the tube voltage and tube current to the X-ray tube 3 based on the instructions from the main controller 25. Then, X-rays are emitted from the X-ray tube 3 to the patient M. X-rays transmitted through the patient M, while scattered X-rays are inhibited by the synchronous grid 5, fall on the FPD 5 to be detected by the X-ray detecting pixels DU. X-ray detection signals generated by the X-ray detecting pixels DU are outputted to the image processor 23 to be LOG-transformed by the LOG-transforming unit 41. The LOG-transformed X-ray detection signals are stored as a fluoroscopic image in the image memory unit 43. Step S1 The extracting unit 45 carries out a process of extracting uninfluenced pixels. Specifically, this process follows the flow chart shown in FIG. 18. Step T1 The grouping unit 71 divides all the pixels in one row into groups as described above. This grouping is carried out for all the rows of the FPD 7. Step T2 The most influenced pixel selecting unit 73 selects a pixel most influenced by the foil shadows in each group as described above. Step T3 The voting unit 75 casts votes in the procedure described above for fore and aft pixels spaced from the most influenced pixels. Step T4 The adjusting unit 77 adjusts the number of votes obtained by the pixels whose vote is one, as described above. Step T5 Based on the result of voting for each pixel, the electing unit 79 elects uninfluenced pixels as described above. Steps T6 and T7 The forcible change unit 81 checks whether the forcible changing condition which may take place rarely is fulfilled, and forcibly changes the numbers of votes according to a result. Reference is made to FIG. 19 for a specific example. FIG. 19 includes schematic views showing uninfluenced pixels after the extracting process, in which FIG. 19A shows a case of selecting inappropriate uninfluenced pixels, and FIG. 19B shows a state after a forceful changing process. In these figures, the white lines represent the uninfluenced pixels elected in step T5, and the black lines represent pixels other than the uninfluenced pixels and including the most influenced pixels. FIG. 19A shows a case of the above forcible changing condition being fulfilled. Specifically, in two locations near the right end as indicated by an arrow in FIG. 19A, an uninfluenced pixel is elected skipping four pixels and an uninfluenced pixel is elected skipping two pixels. When such elections are made, a forcible change is carried out in steps T6 and T7. The result is shown in FIG. 19B. In this figure, the forcible change has been carried out to show that pixels skipping three pixels are elected as uninfluenced pixels. Step T1 described above corresponds to the “grouping step” in this invention. Step T2 corresponds to the “most influenced pixel selecting step”. Step T3 corresponds to the “voting step”. Step T4 corresponds to the “adjusting step”. Step T5 corresponds to the “electing step”. Step T4 corresponds also to the “first to fifth adjusting steps”. Steps T6 and T7 correspond to the “forcible changing step”. Reference is made to the flow chart of FIG. 17 again. Step S2 The approximate fluoroscopic image calculating unit 47 calculates, by interpolation process, detection signal values corresponding to positions of the most influenced pixels, based on the uninfluenced pixels outputted from the extracting unit 45. Then, an approximate fluoroscopic image is calculated based on the fluoroscopic image from the image memory unit 4 and results of the interpolation. The interpolation process may employ cubic interpolation such as cubic spline method, for example. Step S3 The foil shadow image calculating unit 49 calculates a grid foil shadow image showing only the foil shadows, by determining a difference between the fluoroscopic image from the image memory unit 43 and the approximate fluoroscopic image from the approximate fluoroscopic image calculating unit 47. Step S4 The foil shadow standard image calculating unit 51 calculates a grid foil shadow standard image by averaging the grid foil shadow image from the foil shadow image calculating unit 49, piecewise by units of several tens of pixels in the longitudinal direction corresponding to the direction of length of the grid foil strips 5a. That is, correction is made by averaging variations in the foil shadows due to random errors such as quantum noise and the like as shown in FIGS. 11 and 12. The entire length of each grid foil strip 5a corresponds to 1000 to 2000 pixels. By averaging these piecewise, interpolation errors included in the grid foil shadow image are removed therefrom, while leaving distortions of the foil itself in the image. Step S5 The subtracting unit 53 calculates a foil shadow removed fluoroscopic image by determining a difference between the fluoroscopic image from the image memory unit 43 and the grid foil shadow standard image from the foil shadow standard image calculating unit 51. By removing the standardized foil shadows from the fluoroscopic image, an X-ray fluoroscopic image of the patient from which the interpolation errors have been removed can be obtained. The X-ray fluoroscopic image of the patient obtained in this way is displayed on the monitor 29 or stored in the storage unit 31 through the main controller 25. Step S1 described above corresponds to the “extracting step” in this invention. Step S2 corresponds to the “approximate fluoroscopic image calculating step”. Step S3 corresponds to the “grid foil shadow image calculating step”. Step S4 corresponds to the “foil shadow standard image calculating step”. Step S5 corresponds to the “foil shadow removing step”. Next, reference is made to FIGS. 20 and 21. FIG. 20 includes views showing a process according to this invention, in which FIG. 20A shows a foil shadow removed image, and FIG. 20B shows selected uninfluenced pixels. FIG. 21 includes views showing a process according to a proposed example, in which FIG. 21A shows a foil shadow removed image, and FIG. 21B shows selected uninfluenced pixels. In this invention, as shown in FIG. 20B, uninfluenced pixels are extracted at substantially equal intervals. As a result, as shown in FIG. 20A, an X-ray fluoroscopic image which is a foil shadow removed image is free from artifacts. On the other hand, in the proposed example, as shown in FIG. 21B, uninfluenced pixels are extracted at irregular intervals. As a result, as shown in FIG. 21A, an X-ray fluoroscopic image obtained has artifacts remaining thereon (encircled area in the figure) under the influence of foil shadows. This invention is not limited to the foregoing embodiment, but may be modified as follows: (1) In the foregoing embodiment, the construction provides one grid foil strip 5a for every four pixels, but this invention is not limited to this. For example, one grid foil strip 5a may be provided for every eight pixels. In this case, the grouping described hereinbefore may be carried out for every eight pixels, with votes cast for fourth pixels forward and backward. (2) In the foregoing embodiment, for the pixels given one vote and remaining to the last, the number of votes obtained is changed to 2. Such process may be omitted when peripheral portions of the X-ray fluoroscopic image are not processed. This can lighten the load on the process. (3) In the foregoing embodiment, checking is made whether the forcible changing condition is fulfilled. When the frequency of occurrence is low, such checking process may be omitted. This can lighten processing load, and increase processing speed. (4) In the foregoing embodiment, the X-ray detection signals are LOG-transformed by the LOG-transforming unit 41. It is not necessary to provide the LOG-transforming unit 41 where the arithmetic capability has leeway. This can simplify the construction, and reduce apparatus cost. This invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention. |
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053496159 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT The reactor plant 1 in FIG. 1 with the reactor pressure vessel 2 and the containment 3 contains a core melt-through retention device 4. The containment 3 is connected to a device 10 for filtered pressure relief, the connection line comprising a controllable shut-off device 11. If necessary water can be introduced into the containment with the pump 12. The reactor pressure vessel 2 with the reactor core 5 is cooled by the primary water 20 and 20' respectively. In the foundation plate 31 of the containment 3 is located the cooling basin 32 of the retention device 4 according to the invention constructed as a cavity. The cooling basin 32 forms the lowest part of the containment sump; it is connected to the remaining part of the sump by ducts 33. The device 4 is composed of a crucible 40, which consists of a vat 41 and a plurality of tubular protuberances 42, and a lid 43. The cooling tubes 42 are connected to the concrete foundation 31 by means of a connecting structure 44, which consists of brackets, for example. The connecting structure 44 enables firstly the cooling of the cooling tubes 42 on its underside; secondly its purpose is to permit an unimpeded extension of the retention device 4 in order to keep thermal stresses small. Between the reactor pressure vessel 2 and retention device 4 is shown a collecting structure 6, and function of which has already been explained above. The level 34 indicates the water level of the cooling basin 32 in the state of readiness; the dot-dash line 35 signifies the water level if the requirements are met. The section of a retention device 4 according to the invention shown in FIG. 3 shows four cooling tubes 42, two of these tubes 42 being shown longitudinal section. The walls of the vat 41 and of the tubes 42, which form the crucible 40, are formed by a steel wall 40a and a ceramic lining 40b made of HIP-NB, for example. The vat base is covered by a guard plate 40c. The crucible lid 43 consists of a cover plate 43a and a honeycomb-like reinforcing structure 43b. The lid 43 is tightly connected to the crucible 40. The curve T in the diagram of FIG. 4 shows the radial distribution of the calculated temperature T' in a cooling tube 42. The dot-dash line M corresponds to the axis of the cooling tube. The zones W, A, B and C correspond to the cooling water of the cooling basin 32, the steel wall 40a, the ceramic lining 40b (made of HIP-BN) and the interior of the cooling tube 42 respectively. The following parameters govern the calculation of the curve T: afterheat production=1 MW/m.sup.3, internal diameter of the cooling tube=30 cm, wall thickness of the steel tube=8 mm, wall thickness of the boron nitride tube=10 mm; between the two tubes is assumed a gap having a resistance of 0.55 W/cm.sup.2 .multidot.K. The three temperatures given in FIG. 4 are rounded values; the distribution of curve T has only been roughly reproduced. For a reactor having a thermal output of 3000 MW (afterheat of roughly 20 MW, three hours after subjection to the nuclear fission) is to be provided a core melt-through retention device as specified by the invention, which comprises a height of roughly 2.5 m and a diameter of roughly 7 m. The number of cooling tubes having an internal diameter of 30 cm and a length of 1.8 m is roughly 170 with this device. |
claims | 1. A scanning electron microscope system comprising:a scanning electron microscope including a sampling stage capable of mounting the specimen for observation and moving to change the observation position of the specimen;an image input device to obtain the signals measured by the scanning electron microscope as images;a storage device to store the images that were input;an arithmetic logic unit (ALU) to process the image and make various types of corrections;an input device to enter the conditions for making corrections; andan output device to output the corrected image,wherein the scanning electron microscope system measures a correction reference image in a shorter time than the observation image: anddetects distortion in the observation image caused by drift of the sampling stage that occurred during specimen observation in line units on the applicable observation image by comparing the observation image with the correction reference image, and corrects the detected distortion in line units, and outputs an image with lower distortion. 2. The scanning electron microscope system according to claim 1,wherein one correction reference image is acquired in order to correct distortion in one observation image. 3. The scanning electron microscope system according to claim 1,wherein distortion in the observation image is corrected by detecting the distortion in the lateral direction in the observation image as the drift amount on the line in the lateral direction the observation image by comparing the observation image with the correction reference image. 4. The scanning electron microscope system according to claim 1,wherein distortion in the observation image is corrected by detecting the distortion in the vertical direction in the observation image as the drift amount on the line in the vertical direction in the observation image by comparing the observation image with the correction reference image. 5. The scanning microscope system according to claim 1,wherein in the lateral and vertical drift amount in the observation image, an approximate curve is found from the applicable drift amount, and the distortion in the observation image is corrected by utilizing the drift amount found from the applicable approximate curve as the correction amount. 6. The scanning electron microscope system according to claim 1,wherein the presence or absence of drift in the observation image is displayed on the operating screen. |
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claims | 1. A lithographic apparatus provided with a measurement apparatus constructed and arranged to use surface plasmon resonance to detect a thickness of contamination of a measurement surface within the lithographic apparatus, wherein the measurement surface is positioned such that the detected thickness of contamination of the measurement surface allows the thickness of contamination of an optical surface of the lithographic apparatus to be inferred. 2. The lithographic apparatus of claim 1, wherein the measurement apparatus is a surface plasmon resonance spectrometer. 3. The lithographic apparatus of claim 1, wherein the measurement apparatus is a surface enhanced Raman spectrometer. 4. The lithographic apparatus of claim 1, wherein the measurement apparatus is a surface enhanced resonance Raman spectrometer. 5. The lithographic apparatus of claim 1, wherein the measurement surface is provided on or adjacent to a prism. 6. The lithographic apparatus of claim 1, wherein a waveguide is provided at the measurement surface. 7. The lithographic apparatus of claim 2, wherein the measurement apparatus comprises a detector constructed and arranged to detect contamination of the measurement surface, and the measurement surface being one of a plurality of layers provided on a substrate, the plurality of layers including at least two metal layers and being capable of supporting a waveguide mode. 8. The lithographic apparatus of claim 7, wherein the measurement apparatus further comprises a polarization controller arranged to control the polarization of a radiation beam incident upon the measurement surface, and the plurality of layers are arranged such that s-polarized radiation couples to the waveguide mode and p-polarized radiation excites plasmons which have a resonance that is influenced by contamination on the measurement surface. 9. The lithographic apparatus of claim 8, wherein the polarization controller is a photo-electric modulator which is arranged to modulate the polarization, and the detector is connected to a discrimination apparatus which discriminates between the modulated polarizations. 10. The lithographic apparatus of claim 4, wherein the measurement apparatus comprises radiation sources arranged to emit radiation at first and second wavelengths, the difference between the wavelengths being selected to correspond to a peak of a Raman spectrum of the contamination, and a detector arranged to detect Raman scattered radiation. 11. The lithographic apparatus of claim 1, wherein the apparatus includes a radiation source comprising one of a broadband source or a single wavelength source or a tuneable source. 12. The lithographic apparatus of claim 11, wherein the radiation source includes a Fourier transform spectrometer. 13. The lithographic apparatus of claim 1, wherein the measurement surface forms part of the optical surface. 14. A method of detecting contamination within a lithographic apparatus, the method comprising:measuring a thickness of contamination of a measurement surface within the lithographic apparatus using surface plasmon resonance; anddetermining a thickness of contamination of an optical surface of the lithographic apparatus based on the measured thickness of contamination of the measurement surface. 15. The method of claim 14, wherein said measuring comprises monitoring a radiation wavelength or angle that resonantly excites surface plasmons, and wherein a shift in the wavelength or angle is indicative of contamination on the surface. 16. The method of claim 14, wherein said measuring comprises monitoring a spectrum of Raman scattered radiation from the surface to determine the presence or nature of contamination on the surface. 17. The method of claim 16, wherein the amount of Raman scattered radiation is enhanced by exciting transitions in the contamination, the transitions being excited by directing radiation at first and second wavelengths at the measurement surface, the difference between the wavelengths being selected to correspond to a peak of a Raman spectrum of the contamination. 18. The method of claim 14, wherein the surface being measured forms part of an optical surface. 19. The method of claim 18, wherein the surface being measured is provided on or adjacent to a prism. 20. A lithographic apparatus provided with a measurement apparatus constructed and arranged to use tunneling of photons through a metal layer to detect contamination of a surface within the lithographic apparatus. 21. The lithographic apparatus of claim 20, wherein the measurement apparatus is arranged to measure coupling of incident radiation into a guided mode. 22. The lithographic apparatus of claim 21, wherein the measurement apparatus is arranged such that the guided mode is on an opposite side of the metal layer from the location at which the incident radiation is incident on the metal layer. 23. The lithographic apparatus of claim 21, wherein the guided mode is centered on a waveguide, and wherein the waveguide is arranged such that during propagation of radiation along the waveguide, some of the radiation overlaps with the contaminated surface. 24. A method of detecting contamination on a contaminated surface within a lithographic apparatus, the method comprising:directing incident radiation at a metal layer; anddetecting coupling of the incident radiation into a guided mode through the metal layer. 25. The method of claim 24, wherein the guided mode is centered on a waveguide, and wherein the waveguide is arranged such that during propagation of radiation along the waveguide, some of the radiation overlaps with the contaminated surface. 26. A lithographic apparatus comprising:a pattern device constructed and arranged to pattern radiation; a projection system constructed and arranged to project the patterned radiation onto a substrate; anda contamination detection system constructed and arranged to detect a thickness of contamination of a measurement surface using surface plasmon resonance,wherein the contamination detection system determines a thickness of contamination of an optical surface within the lithographic apparatus using the detected thickness of contamination of the measurement surface. 27. The lithographic apparatus of claim 26, wherein the contamination detection system comprises a surface plasmon resonance spectrometer. 28. The lithographic apparatus of claim 26, wherein the contamination detection system comprises a surface enhanced Raman spectrometer. 29. The lithographic apparatus of claim 26, wherein the contamination detection system comprises a surface enhanced resonance Raman spectrometer. 30. A method for manufacturing a device with a lithographic apparatus, the method comprising:patterning radiation with a patterning device;projecting the patterned radiation onto a substrate with a projection system;detecting a thickness of contamination of a measurement surface using surface plasmon resonance; anddetermining a thickness of contamination of an optical surface within the lithographic apparatus using the detected thickness of contamination of the measurement surface. |
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claims | 1. A particle attachment preventing method in a substrate processing apparatus including an accommodation chamber configured to accommodate a substrate therein and generate a plasma therein, a mounting table configured to mount the accommodated substrate thereon, a first power supply configured to supply a bias power for attracting the plasma to the mounting table, and a second power supply configured to supply an electron density control power for controlling an electron density above the substrate, the method comprising:adjusting the electron density control power supplied from the second power supply such that the electron density above the substrate gets lower than during a plasma processing, for a preset short period of time after the plasma processing is ended; andmaintaining the bias power supplied from the first power for the preset short period of time,wherein the preset short period of time is about 0.5 to 1.0 second. 2. The method of claim 1, wherein the second power supply is a high frequency power supply for supplying a high frequency power having a frequency that is higher than that of the bias power, andin said adjusting of the electron density control power, the high frequency power supplied from the second power supply is lowered as compared with that during the plasma processing. 3. The method of claim 1, wherein the substrate processing apparatus further includes an opposite electrode facing the mounting table,the second power supply serves as a DC power supply for supplying a DC power to the opposite electrode, andin said adjusting of the electron density control power, the DC power supplied from the second power supply is lowered as compared with that during the plasma processing. 4. The method of claim 1, wherein the substrate processing apparatus further includes an opposite electrode facing the mounting table,the second power supply serves as a high frequency power supply for supplying a high frequency power having a frequency that is higher than that of the bias power and a DC power supply for supplying a DC power to the opposite electrode, andin said adjusting of the electron density control power, the DC power supplied from the second power supply is lowered as compared with that during the plasma processing and the high frequency power supplied from the second power supply is lowered as compared with that during the plasma processing. 5. The method of claim 2, wherein, in said adjusting of the electron density control power, the high frequency power supplied from the second power supply is lowered to about 40% or less of the high frequency power during the plasma processing. 6. The method of claim 4, wherein, in said adjusting of the electron density control power, the high frequency power supplied from the second power supply is lowered to about 40% or less of the high frequency power during the plasma processing. 7. A substrate processing apparatus comprising:an accommodation chamber configured to accommodate a substrate therein and generate a plasma therein;a mounting table configured to mount the accommodated substrate thereon;a first power supply configured to supply a bias power for attracting the plasma to the mounting table; anda second power supply configured to supply an electron density control power for controlling an electron density above the substrate,wherein the electron density control power supplied from the second power supply is adjusted such that the electron density above the substrate gets lower than during a plasma processing, for a preset short period of time after the plasma processing is ended, andthe bias power supplied from the first power supply is maintained for the preset short period of time, andwherein the preset short period of time is about 0.5 to 1.0 second. 8. The apparatus of claim 7, wherein the electron density control power is a power for generating the plasma, anda first region in which the electron density control power is supplied to generate the plasma and a second region in which the substrate is subjected to the plasma processing are identical or adjacent to each other. |
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053708270 | abstract | Solutions such as for example drinking water, ground water and extracting solutions contaminated with heavy metals and radioactive species, singly or in combination, are treated by first treating the contaminated solution with silicate and ammonium hydroxide solution precipitants. Then the contaminated solution is separately treated with an acid which gels, polymerizes and/or precipitates the contaminant-containing silica matrix to form an easily dewaterable and separable solid. The solid contaminants are readily removed from the cleansed solution by filtration means. The process utilizes a novel combination of steps which maximizes contaminant removal, minimizes waste volume, and produces a treatable waste solid. The preferred precipitants are sodium silicate, and ammonium hydroxide. The preferred mineral acid is hydrochloric acid. |
042773105 | summary | BACKGROUND OF THE INVENTION The pressure vessel containing the core of water-cooled nuclear reactors in general, requires a continuous supply of water coolant to continuously carry heat away from the core. Even a momentary interruption in the coolant supply can result in serious damage to the core even though the core is thereafter promptly supplied with emergency core cooling water. For example, a pressurized-water reactor normally comprises a pressure vessel containing a core barrel, in which the core is mounted, the core barrel being cylindrical and spaced from the inside of the cylindrical pressure vessel to form an annular space. At its top the barrel has a support flange which rests on a flange formed on the inside of the pressure vessel, the arrangement being such that the annular space is closed by the flanges from the balance of the area inside of the pressure vessel. For core cooling, a coolant inlet nozzle opens through the pressure vessel wall into the upper portion of the above annular space, and a coolant outlet nozzle opens from the inside of the upper portion of the core barrel. The top and bottom of the core barrel are open. The reactor coolant system forms a pipe loop comprising a hot leg pipe welded to the pressure vessel's outlet nozzle and connecting with a steam generator, a cold pipe leg coming from the steam generator, via a coolant circulating pump, and back to the pressure vessel's inlet nozzle to which the pipe is welded. For a power reactor, the reactor coolant system normally includes a multiplicity of such coolant loops, the pressure vessel having coolant inlet and outlet nozzles for each loop. A pressurizer connected to the loop or loops keeps water coolant in the loops and in the pressure vessel under a pressure preventing the water from boiling, although operating at temperatures much above the boiling point of water at atmospheric pressure. The pressurized-water fed through the inlet nozzle, in the case of each loop, flows downwardly in the annular space between the core barrel and the pressure vessel inside, to the bottom of the vessel where the pressurized-water coolant rises up the core within the core barrel and flows outwardly through the coolant nozzle outlet, this circulation via the coolant loop being continuous. In the event such a pressurized-water main coolant loop ruptures at any point, the loop pressure drops with a consequent drop in the pressure in the water on the pressure vessel, and the water in the pressure vessel rather immediately vaporizes and discharges in the direction of the leak, assuming the leak to be of major proportions. In such an event, the reactor protection system normally scrams the core while the emergency core cooling system forces emergency cooling water into the vessel, all this occurring as rapidly as possible. Even so, there is the chance that the vessel might become emptied of water coolant before such systems can become fully effective, and there is always the remote hypothetical possibility that one or another of the systems might not operate. German Offenlegungsschrift No. 1,564,654 suggests that a check valve be positioned in one of the coolant pipes of such a pressurized-water reactor main coolant loop. Apparently the idea is that in the event of a break in the pipe line on the side of the check valve away from the pressure vessel, the check valve will be closed by the reversely flowing coolant discharging from the pressure vessel, thus preventing emptying of the pressure vessel, at least immediately. There are objections to the above proposal. A check valve of the size required necessarily involves a large movable valve plate which because of the size involved, does not provide positive assurance of operation, and the fabrication cost of such a valve is very high. Provision of a safety redundancy by using two such valves in series, is an extremely expensive expedient. Furthermore, any break in the pipe line or connection between such a check valve and the pressure vessel nozzle, makes the check valve useless for its intended purpose. SUMMARY OF THE INVENTION According to the present invention, each cold leg coolant inlet nozzle of the reactor pressure vessel, is internally provided with a check valve assembly inside of the pressure vessel. Each assembly comprises a multiplicity of individually swinging flap valves and means for mounting the flap valves so that they operate in parallel and are interposed in the coolant flow as it enters the vessel. The flap valves are mounted so that they are swung open by the incoming coolant flow, but will flap closed by a reverse coolant flow such as can occur in the event of a leak causing a pressure reduction at the inlet nozzle. Each flap valve may be formed by a relatively small rectangular plate which is pivotally mounted, so the fabrication cost of the assembly is relatively low. The simplicity of flap valves provides a large assurance that each will operate, but if one or more fails to operate when required to block the accidental discharge of coolant from the pressure vessel, the balance of the flap valves are certain to operate so as to greatly retard the loss of coolant from the vessel. Flap valve operation is not only very certain, but it is substantially immediate. The flap valves can be mounted by an annular frame surrounding the inner end of the vessel's cold leg or inlet nozzle, the annular frame being formed with the cylindrical contour of the core barrel and preferably mounted by the latter, the annular frame having a radial extent substantially filling the annular space between the barrel and vessel. In another form, the annular frame can surround the core barrel below each of a number of cold leg inlet nozzles, in which case the frame can perform the function of bracing the core barrel by means of the pressure vessel inside, and of serving all of the cold leg inlet nozzles of the pressure vessel. In this way only a single valve assembly is required for a multiplicity of pipe loop cold legs. When the assembly surrounds the inlet nozzle, the flow through the assembly is radial, with the flap valves appropriately oriented, and when the assembly surrounds the core barrel as just described above, the flow is axial to the frame, again with the flap valves appropriately oriented for this flow direction. In either case the annular check valve assemblies can be fastened to the core barrel so that, during reactor core servicing, the core barrel can be removed, carrying the check valve assembly or assemblies with it, permitting check valve inspection if desired. By making each check valve assembly an integrated unit subsequently fixed to the core barrel during assembly of the reactor, the manufacturing costs involved by the present invention can be kept low. |
044877382 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the preferred embodiment of the method of the present invention, a target is prepared by pressing approximately 90 grams of powdered zinc oxide into a solid disc contained inside a high purity aluminum ring. High purity aluminum is used to avoid the presence of copper contaminants in the aluminum, which would migrate into the target during irradiation and contaminate the spallogenic copper formed from the ZnO. The target is placed in an aluminum target enclosure for introduction into the target region of the linear accelerator. The ZnO target is irradiated with a proton beam having an energy of approximately 800 MeV and a beam current on the order of 300 microamperes, for a period on the order of 60-70 hours. The spallation cross section of the ZnO target for .sup.67 Cu is approximately 5.35 millibarns. Under such conditions, an amount of .sup.67 Cu on the order of 1.0 curie (approximately 1.3 micrograms) is formed, together with approximately 34 other identifiable nuclides, which are presented in FIG. 1. The only other isotopes of copper which are produced in measurable quantities are the short-lived isotopes .sup.64 Cu and .sup.61 Cu. In accordance with the preferred method of chemical separation, which is illustrated schematically in FIG. 2, the irradiated ZnO target is removed from the aluminum ring and dissolved in a concentrated HCl solution. To this acid solution is added approximately 20 milligrams of Pd.sup.+2 (added as 2.5 cc of palladium chloride solution containing 8.5 mg Pd.sup.+2 /cc). Approximately one-half to two grams of finely powdered metallic zinc are then added to the acid solution. The zinc is oxidized to Zn.sup.+2, which reduces the Pd.sup.+2 to metallic palladium and also reduces the spallogenic Cu.sup.+2 in solution to metallic copper. The metallic palladium precipitates as a finely divided solid and quantitatively scavenges from solution the spallogenic copper. The metal precipitate is then redissolved in an acid solution and the palladium and copper are once again precipitated, this time by sparging the acid solution with gaseous hydrogen sulfide. The sulfide precipitate is then dissolved once again in an acid solution, and the palladium and copper in solution are separated by chromatography on an anion exchange column. In an alternative variation of the chemical separation step of the method, the palladium is precipitated by the introduction of powdered zinc as above, and the precipitated palladium/copper mixture is subsequently passed through a series of three ion exchange columns, as illustrated in FIG. 3. In accordance with the latter alternative method, the mixture of metallic palladium and copper, which also contains traces of spallogenic cobalt, manganese and vanadium, is collected by filtration and dissolved in an acid solution consisting of approximately 9 ml concentrated HCl and 1 ml concentrated HNO.sub.3. This solution is passed through a cation exchange resin column, preferably consisting of purified Dowex AG (Analytical Grade) 50.times.4 (sulfonic acid resin type column), which is commercially available from Bio-Rad, Inc. of Richmond, Calif. This column operates to capture any gallium that may be present with the spallogenic copper. In this regard, it is noted that .sup.67 Ga, which is a spallogenic reaction product, has a gamma emission spectrum which is nearly identical to that of .sup.67 Cu, thus making it difficult to detect in the initial stages of chemical separation. The cation column also collects .sup.51 Cr, which is also present in trace amounts in the reaction products. The eluate solution, which contains Cu as well as Pd in essentially concentrated HCl, is introduced untreated into a second column which is an anion exchange column, and which preferably consists of purified Dowex AG 1.times.8 quaternary amine resin, a strong base anion resin. The Cu.sup.+2, together with the Pd.sup.+2, is initially bound to the anion exchange resin. The Cu.sup.+2 is then selectively eluted from the column with 2M HCl, leaving behind the Pd.sup.+2 as a palladium chloro complex. The eluted solution, containing Cu.sup.+2 and having a volume on the order of 15 ml, is evaporated to dryness and the residue subsequently dissolved in a solution consisting of 80% (by volume) acetone and 20% water, acidified to 0.1 molar HCl. This solution is then passed through a third column containing a Bio-Rad Dowex AG 50.times.8 cation exchange resin. The Cu is absorbed on this column initially, together with any Co.sup.+2 or Mn.sup.+2 that may be present. The Cu.sup.+2 is then selectively eluted with an acetone/water solution acidified to 0.5M HCl. The use of this third column to remove traces of Mn and Co is not mandatory to the practice of the method, but is preferred when the .sup.67 Cu is to be used over a period longer than several half-lives, since in such circumstances the activities of trace amounts of spallogenic radioactive Co and Mn isotopes become large relative to the activity of the .sup.67 Cu and thereby interfere with measurement of .sup.67 Cu gamma ray emissions. The 0.5M HCl/acetone/water solution containing the spallogenic .sup.67 Cu is sufficiently pure for use in medical applications. However, if desired, this solution may be evaporated to dryness and the residue redissolved in 0.1M HCl, which renders the solution more desirable for some medical applications. The yield of .sup.67 Cu by this version of the method is on the order of 50% of the spallogenic .sup.67 Cu originally produced. The only impurities that have been detected are trace amounts of inactive Zn and inactive Cu. The spallogenic Cu includes some .sup.64 Cu, which has a half-life of 12.7 hours and which largely decays by the time the .sup.67 Cu-bearing solution is shipped and prepared for use. Also present in the spallogenic Cu is .sup.61 Cu, which decays even faster with its half-life of 3.3 hours. EXAMPLE 1 In an actual demonstration of the method, a spallation target consisting of 79.2 grams of powdered zinc oxide was bombarded with 800 MeV protons for a period of 93.4 hours in the linear accelerator of the Los Alamos Meson Physics Facility. The beam current averaged 423 microamps and resulted in a total integrated irradiation of 39,531 microamp-hours. A yield of 3.11 curies of .sup.67 Cu was obtained, using the alternative separation process described above. Also obtained were 10.0 curies of .sup.64 Cu and an undetermined amount of .sup.61 Cu. Additionally, it was determined that 3.4 curies of .sup.62 Zn and 0.96 curie of .sup.48 V were produced, as well as other unidentified nuclides. EXAMPLE 2 In another demonstration of the method, also using the alternative 3-column separation process, a target consisting of 75.7 grams of zinc oxide was irradiated with 800 MeV protons for a period of 23.9 hours. The beam current was approximately 386 microamps and provided an integrated irradiation of 9,219 microamp-hours. A yield of 1.0 curie of .sup.67 Cu was obtained. Also obtained were 9.4 curies of .sup.64 Cu, 11.9 curies of .sup.61 Cu, 2.5 curies of .sup.62 Zn and 0.22 curie of .sup.48 V. EXAMPLE 3 In another demonstration, a target consisting of 73.2 grams of zinc oxide was irradiated with a total irradiation of 15,643 microamp-hours. The target was then dissolved in 160 cc of concentrated HCl. To this solution was added 2.5 cc of a PdCl.sub.2 solution containing 8.5 mg/cc Pd. 0.5 gm of zinc dust was added to effect reduction of the Pd and spallogenic Cu in solution. The reduced metal was collected by filtration and dissolved in a solution consisting of 10 cc concentrated HCl and 1 cc concentrated HNO.sub.3. The resulting solution was heated and stirred and sparged with hydrogen sulfide for several minutes. The resulting precipitate was collected by filtration and dissolved in a HCl/HNO.sub.3 solution as described above. This solution was diluted with 9M HCl, which was used to rinse the filter, to obtain a solution approximately 9M in HCl. The Cu-bearing 9M HCl solution was added to an AG 1.times.8 anion exchange column. The column was washed with 2 to 3 column volumes of 9M HCl. The copper was then eluted from the column with 2M HCl, leaving the Pd behind on the column. The resulting solution was determined to contain 201 millicuries of .sup.67 Cu. The foregoing descriptions of alternative preferred embodiments of the method of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The particular embodiment described and illustrated were selected in order to best explain the principles of the invention and its practical application to 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. |
abstract | An IGRT apparatus comprising a medical imaging device (1) integrated with a linear accelerator (3, 4), the linear accelerator (3, 4) configured for emitting a radiation beam which is shaped by a beam shaper (8, 17), wherein the position of the beam shaper (8, 17) is adjustable between a first position and a second position, wherein the first position is a treatment position and the second position is a non-treatment position and wherein the IGRT apparatus comprises a gantry (2) and wherein the first position is within the gantry (2) and the second position is removed from the gantry (2). |
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050330748 | claims | 1. An improved microfocus projection radiography system comprising: a body defining an opening through which primary radiation may pass from a focal spot x-ray source toward a sample, wherein said passing primary radiation generally defines a path having a centerline, and said opening has a near end and a distal end relative to said x-ray source; a window covering said opening at said distal end, wherein said window is penetrable by said passing primary radiation with negligible generation of secondary radiation; x-ray detection means disposed in said path beyond said sample and generally normal to said centerline so that portions of said passing primary radiation reach both said sample and said detection means to form a projected x-ray image of said sample at said detection means, wherein said sample is spaced from said window and from said detection means to permit magnification of said image; and a collimator defining an aperture and disposed along said path between said focal spot and said window so as to attenuate any of said passing primary radiation not directly striking said window, wherein said collimator is formed from a material having a low vapor pressure at temperatures and pressures at which said system is operated, and portions of said collimator exposed to said passing primary radiation are formed from a material selected to attenuate any of said passing primary radiation not directly striking said window and which generates negligible secondary radiation on exposure to said primary radiation. a collimator defining an aperture and positionable along said path between said focal spot and said window so as to attenuate any of said passing primary radiation not directly striking said window, wherein said collimator is formed from a material having a low vapor pressure at temperatures and pressures at which said system is operated, and portions of said collimator exposed in use to said passing primary radiation are formed from e material selected to attenuate any of said passing primary radiation not directly striking said window end which generates negligible secondary radiation or exposure to said primary radiation. positioning a collimator defining an aperture along said path between said focal spot and said window so as to attenuate any of said passing primary radiation not directly striking said window, wherein said collimator is formed from a material having a low vapor pressure at temperatures and pressures at which said system is operated, and portions of said collimator exposed in use to said passing primary radiation are formed from a material selected to attenuate any of said passing primary radiation not directly striking said window and which generates negligible secondary radiation on exposure to said primary radiation. 2. An x-ray collimating device in accordance with claim 1 wherein said collimator is disposed at least partially within said opening. 3. An x-ray collimating device in accordance with claim 1 wherein said collimator extends within said opening from said near end to said distal end. 4. An x-ray collimating device for use in a microfocus projection radiography system to eliminate shadow anomalies caused by secondary radiation generated upon exposure to primary radiation of materials along a path of said primary radiation, said microfocus projection radiography system comprising: a body defining an opening through which said primary radiation may pass from a focal spot x-ray source toward a sample along said path having a centerline, wherein said opening has a near end and a distal end relative to said x-ray source; a window covering said opening at said distal end, wherein said window is penetrable by said passing primary radiation with negligible generation of secondary radiation; and x-ray detection means disposed in said path beyond said sample and generally normal to said centerline so that portions of said passing primary radiation reach both said sample and said detection means to form a projected x-ray image of said sample at said detection means, wherein said sample is spaced from said window and from said detection means to permit magnification of said image; and said collimating device comprising: 5. An x-ray collimating device in accordance with claim 4 wherein said collimator material consists essentially of tungsten. 6. An x-ray collimating device in accordance with claim 4 wherein said collimator material has an atomic number greater than 15. 7. An x-ray collimating device in accordance with claim 4 wherein said aperture is tapered outwardly away from said x-ray source. 8. An x-ray collimating device in accordance with claim 7 wherein said aperture is tapered at about a 15.degree. angle. 9. An x-ray collimating device in accordance with claim 4 wherein said vapor pressure is below that of lead at said temperatures and pressures at which said system is operated. 10. An x-ray collimating device in accordance with claim 4 wherein said aperture of said collimator at any point along its length is circular and is of a diameter equal to or less than a maximum cross-sectional diameter at that point of a portion of said passing primary radiation which will directly strike said window. 11. An x-ray collimating device in accordance with claim 10 wherein said aperture of said collimator at any point along its length is circular and is of a diameter equal to or less than a maximum cross-sectional diameter at that point of a portion of said passing primary radiation which will directly strike said window. 12. A method for eliminating the shadow anomaly from microfocus projection radiographs caused by secondary radiation generated upon exposure to primary radiation of materials along a path of said primary radiation through a microfocus projection radiography system, wherein said system comprises: a body defining an opening through which said primary radiation may pass from a focal spot x-ray source toward a sample along said path having a centerline, wherein said opening has a near end and a distal end relative to said x-ray source; a window covering said opening at said distal end, wherein said window is penetrable by said passing primary radiation with negligible generation of secondary radiation; and x-ray detection means disposed in said path beyond said sample and generally normal to said centerline so that portions of said passing primary radiation reach both said sample and said detection means to form a projected x-ray image of said sample at said detection means, wherein said sample is spaced from said window and from said detection means to permit magnification of said image; said method comprising the step of: |
047160160 | summary | CROSS REFERENCE TO RELATED APPLICATIONS Reference is hereby made to the following copending U.S. patent applications dealing with related subject matter and assigned to the same assignee of the present invention: 1. "Fuel Rod Cluster Interchange System And Method For Nuclear Fuel Assemblies" by E. E. DeMario et al, assigned U.S. Ser. No. 716,282 and filed Mar. 26, 1985. 2. "Apparatus And Method For Loading Fuel Rods Into Grids Of A Fuel Assembly" by E. E. DeMario et al, assigned U.S. Ser. No. 717,263 and filed Mar. 28, 1985, now U.S. Pat. No. 4,651,403. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to nuclear reactors and, more particularly, is concerned with a universal construction for a fuel assembly which allows greater flexibility in tailoring the fuel content thereof to the particular location of the assembly in the core of the reactor and provides for substantially total repairability of its component parts. 2. Description of the Prior Art A typical pressurized water nuclear reactor contains a large number of fuel assemblies in its core. Each fuel assembly is substantially identical to the next except for the fuel enrichment of the individual assembly. In order to optimize the fuel burnup and smooth the radial neutron flux profile across the reactor core, historically a zoned enrichment pattern has been used. Particularly, fuel contained in assemblies located in regions nearer to the periphery of the core is somewhat more enriched than fuel contained in assemblies located in regions nearer to the center of the core. After a given core cycle, such as a year, fuel assemblies in a higher enrichment core region are shuffled into a lower enrichment region, while new fuel assemblies are added to the highest enrichment region and depleted or burned out assemblies are removed from the lowest enrichment region. Notwithstanding their variation in fuel enrichment, all of the fuel assemblies in the reactor core have the same construction. Basically, each fuel assembly is composed of a bottom nozzle, a top nozzle, an instrumentation tube and pluralities of guide thimbles, fuel rods and grids. For instance, in one exemplary fuel assembly, the fuel rods are arranged in a square 17 by 17 array with 17 rod locations per side. Of the total possible 289 rod locations per assembly, 264 locations contain fuel rods. In addition to the single bottom nozzle, top nozzle and instrumentation tube, there are 24 guide thimbles and 8 grids. The structural skeleton of the fuel assembly is composed of the bottom and top nozzles and the plurality of guide thimbles which extend vertically between the bottom and top nozzles and rigidly interconnect them. In addition to their shared function of providing the fuel assembly with a rigid skeleton, each one serves other functions. The bottom nozzle directs the distribution of upward coolant flow to the fuel assembly. The guide thimbles provide channels through the fuel assembly for insertion of control-type rods therein. The top nozzle provides a partial support platform for the spider assembly mounting the respective control rods. The top nozzle also has openings which permit upward flow of coolant through it. Also, the bottom and top nozzles respectively act to prevent either downward or upward ejection of a fuel rod from the fuel assembly. The grids and fuel rods are not structural parts of the fuel assembly but instead are respectively supported directly and indirectly by the guide thimbles. The grids are attached in axially spaced positions along the guide thimbles such that the multiplicity of cells defined by interleaved straps of the respective grids are disposed in vertical alignment. The fuel rods are supported in an organized and transversely spaced array in the vertically aligned cells of the transverse grids by springs and dimples on the straps which extend into the cells. Each fuel rod contains nuclear fuel pellets and the opposite ends of the rod being closed by upper and lower end plugs are spaced below the top nozzle and above the bottom nozzle. The fuel pellets composed of fissile material are responsible for creating the reactive power of the reactor which is transferred in the form of heat energy to coolant flowing upwardly throughthe fuel assembly. The guide thimbles are larger in diameter than the fuel rods and, as mentioned above, provide channels adapted to accommodate various types of control rods used in controlling the reactivity of the nuclear fuel. A more detailed description of this typical fuel assembly and the types of rods insertable in the guide thimbles thereof may be gained from U.S. Pat. No. 4,432,934 to Robert K. Gjertsen et al, which patent is assigned to the assignee of the present invention. While the guide thimbles accommodate various types of control rods, fuel rods cannot be placed in them when they are not being otherwise used since the fuel rods would overheat due to lack of enough remaining space within the guide thimble to accommodate sufficient coolant to carry the heat away. Thus, the conventional fuel assembly has a significant number of its rod locations, approaching ten percent in the example above, dedicated to nonfuel use. Even more, since not all fuel assemblies in the reactor core require control rods (about two-thirds of the fuel assemblies in a typical core do not), nonfuel rod locations in many regions of the core go unused which results in reduced power output, increased fuel cycle costs, reduced fuel assembly life and a suboptimum fuel loading configuration. Also, while the interconnections provided by the guide thimbles provide a rigid skeleton of high structural integrity, the large number of thimbles increases the difficulty of top nozzle removal and remounting in carrying out fuel assembly reconstitution. Consequently, a need exists for a fresh approach to fuel assembly design which would avoid or reduce some of the limitations and shortcomings inherent in the conventional fuel assembly construction described above and enhance its adaptability without sacrificing its structural integrity. SUMMARY OF THE INVENTION The preferred embodiment of the fuel assembly, as described herein, includes several improved features which meet the aforementioned needs. While the improved features are particularly suited for working together to provide a more universal fuel assembly construction adapted to be tailored to various operating conditions found in different regions of the reactor core, it is readily apparent that some of such features may be incorporated either singly or together in this or other fuel assembly constructions. Some of the several improved features comprise inventions claimed in other copending applications, cross-referenced above; however, all of the improved features are illustrated and described herein for facilitating a complete and thorough understanding of those of the features comprising the present invention. The present invention relates to those features incorporated into the fuel assembly for facilitating the total repairability of the fuel assembly. The skeletal structure of the fuel assembly is composed of parts which can be disassembled easily. Specifically, the main structural support of the fuel assembly is provided by four corner posts which are detachable from the top and bottom nozzle. This capability ensures that damaged fuel rods and grids can be replaced so that no fuel assemblies need be discarded prematurely. When the fuel of the assembly is finally spent, complete disassembly of the fuel assembly allows compact storage in a spent fuel pit. Also, since the guide thimbles are no longer structural members, the present invention facilitates their attachment to a removable plate which provide the ability to replace unoccupied guide thimbles with fuel rods and alternative devices, also being attached to a removable plate, when the fuel assembly is not at a control rod location in the reactor core. Such replacement can be used to reduce heat flux and Kw/ft in the core, reduce fule cycle costs, extend the life of burned fuel assemblies, optimize loading patterns giving peaking factor reduction, adjust the cycle length late in analysis and increase the capability for longer cycles. Accordingly, the present invention is directed to an universal fuel assembly, comprising: (a) an upper end structure; (b) a lower end structure; (c) a plurality of elongated members extending longitudinally between and rigidly interconnecting the upper and lower end structures, the upper and lower end structures and elongated members together forming a rigid structural skeleton of the fuel assembly; (d) a plurality of transverse grids being supported on the elongated members at axially spaced locations therealong between the upper and lower end structures; (e) a plurality of fuel rods extending through and being supported by the grids between the upper and lower end structures so as to extend in generally side-by-side spaced relation to one another and to the elongated members, certain groups of the fuel rods in the plurality thereof being spaced apart laterally from one another by a greater distance than the rest of the fuel rods so as to define a number of elongated channels extending between the upper and lower end structures; and (f) a cluster assembly having a plurality of elongated rods; (g) the upper end structure being adapted to removably support the cluster assembly such that its plurality of elongated rods extend from the upper end structure through the elongated channels toward the lower end structure. More particularly, the lower end structure is adapted to removably support the elongated rods of the cluster assembly at lower ends thereof. Further, the upper end structure includes a transverse plate having a plurality of openings therein in a pattern matched with that of the plurality of elongated channels. The cluster assembly includes a cluster plate which mounts the plurality of elongated rods at upper ends thereof with the cluster plate being supported upon the transverse plate in an installed position and the plurality of elongated rods of the cluster assembly extending through the openings of the transverse plate. Still further, the elongated members are posts, preferably four in number, with upper and lower ends respectively releasably connecting the upper and lower end structures at corresponding corner regions thereof. The posts at their upper ends are releasably fastened to the transverse plate of the upper end structure at spaced apart corner locations thereon between which the cluster plate rests in its installed position on the transverse plate. Furthermore, at least some of the elongated rods of said cluster assembly are guide thimbles, while one of the elongated rods is an instrumentation tube. In another cluster assembly, at least some of the elongated rods are fuel rods which are larger in size than the other fuel rods ordinarily found in the fuel assembly. |
claims | 1. An X-ray mask structure detachably mountable in an X-ray exposure apparatus, said X-ray mask structure comprising: an X-ray absorptive material pattern; a supporting film for supporting the pattern; a holding frame for holding the supporting film; and a suction port arranged in said X-ray mask structure, and operable to perform gas drawing from a workpiece side to an opposite side thereto. 2. An X-ray mask structure according to claim 1 , further comprising a second suction port operable to perform gas drawing at a side of the supporting film remote from the workpiece side. claim 1 3. An X-ray mask structure according to claim 1 , wherein the suction port is provided in the holding frame. claim 1 4. An X-ray mask structure according to claim 1 , further comprising a reinforcing member provided on the holding frame. claim 1 5. An X-ray mask structure according to claim 4 , wherein the suction port is formed in the reinforcing member. claim 4 6. An X-ray mask structure according to claim 1 , further comprising a pellicle and a pellicle frame for supporting the pellicle. claim 1 7. An X-ray mask structure detachably mountable in an X-ray exposure apparatus, said X-ray mask structure comprising: an X-ray absorptive material pattern; a supporting film for supporting the pattern; a holding frame for holding the supporting film; a suction port arranged in said X-ray mask structure, and arranged to be communicated with external gas drawing means; and a supply port through which a gas can be supplied. 8. An X-ray mask structure according to claim 7 , wherein the suction port and the supply port are formed in the holding frame. claim 7 9. An X-ray mask structure according to claim 7 , further comprising a reinforcing member provided on the holding frame. claim 7 10. An X-ray mask structure according to claim 9 , wherein the suction port and the supply port are formed in the reinforcing member. claim 9 11. An X-ray exposure apparatus, comprising: a supporting member for supporting an X-ray mask structure; and a suction port formed in the supporting member and having a function for drawing an exposure ambient gas under a condition that said supporting member supports the X-ray mask structure. 12. An apparatus according to claim 11 , wherein the suction port is provided in a portion of the supporting member surrounding an X-ray mask structure as held by the supporting member, which portion is at a position other than an upstream position with respect to a gravity direction. claim 11 13. An apparatus according to claim 11 , further comprising a mask cassette for accommodating an X-ray mask structure, wherein the mask cassette has a suction port formed therein. claim 11 14. An apparatus according to claim 11 , wherein, when a step-and-repeat exposure process with X-rays is performed to a workpiece by use of an X-ray mask structure as held by the supporting member, the exposure process is executed in an order from a downstream side of the workpiece with respect to the gravity direction. claim 11 15. An X-ray exposure apparatus, comprising: a supporting member for supporting an X-ray mask structure; a suction port formed in the supporting member and being effective to perform discharging of an exposure ambience gas; and a supply port formed in the supporting member and having a function for drawing an exposure ambient gas under a condition that said supporting member supports the X-ray mask structure. 16. An apparatus according to claim 15 , wherein, when the X-ray mask structure is supported by the supporting member, the suction port and the supply port are operable to perform gas discharging and gas supply through a bore formed in the X-ray mask structure. claim 15 17. An apparatus according to claim 15 , further comprising a mask cassette for accommodating an X-ray mask structure and having a suction port and a supply port formed therein. claim 15 18. An X-ray exposure method, comprising the steps of: holding an X-ray mask structure, wherein X-ray exposure of a workpiece can be performed by using the X-ray mask structure; and performing exposure ambient gas drawing through a suction port formed in one of the X-ray mask structure and a supporting member for holding the X-ray mask structure, the suction port having a function for drawing an exposure ambient gas under a condition that the X-ray mask is held in said holding step. 19. A method according to claim 18 , further comprising supplying a gas through a supply port formed in one of the X-ray mask structure or the supporting member for holding the X-ray mask structure. claim 18 20. A method according to claim 18 , wherein the gas drawing step is executed after X-ray exposure and after separating the X-ray mask structure and a workpiece by a sufficient distance. claim 18 21. A method according to claim 18 , wherein a chemical amplification type resist is used on a workpiece for X-ray exposure. claim 18 22. A device manufacturing method, comprising the steps of: holding an X-ray mask structure, wherein X-ray exposure of a workpiece can be performed by using the X-ray mask structure; performing exposure ambient gas drawing through a suction port formed in one of the X-ray mask structure and a supporting member for holding the X-ray mask structure; and developing the workpiece for which the X-ray exposure has been accomplished by use of the X-ray mask structure, for production of devices. 23. A device produced in accordance with a method as recited in claim 22 . claim 22 24. An X-ray exposure apparatus, comprising: a supporting member for supporting an X-ray mask structure; a suction port effective to perform gas drawing; and a supply port formed in the supporting member and being effective to perform introduction of a gas therethrough containing one of oxygen and ozone, for ozone cleaning with the gas. 25. An apparatus according to claim 24 , further comprising ultraviolet ray projecting means for irradiating oxygen, introduced through the supply port, with ultraviolet rays to perform ozone cleaning to the X-ray mask structure. claim 24 26. An apparatus according to claim 25 , wherein the supply port, the suction port and the ultraviolet ray projecting means are disposed adjacent to an exposure position of said exposure apparatus. claim 25 27. An apparatus according to claim 25 , wherein the supply port, the suction port and the ultraviolet ray projecting means are provided in a mask accommodating member. claim 25 28. An apparatus according to claim 25 , wherein the supply port, the suction port and the ultraviolet ray projecting means are provided in a separate cleaning unit. claim 25 29. An apparatus according to claim 25 , wherein the ultraviolet ray projecting means projects ultraviolet rays of a wavelength not greater than 185 nm. claim 25 30. An X-ray exposure apparatus, comprising: a supporting member for supporting an X-ray mask structure; a suction port effective to perform gas drawing; and a supply port formed in the supporting member and being effective to perform introduction of a gas therethrough containing at least oxygen, for plasma cleaning of the X-ray mask structure with the gas. 31. An apparatus according to claim 30 , wherein the supply port and the suction port are provided in a mask accommodating member. claim 30 32. An apparatus according to claim 30 , wherein the supply port and the suction port are provided in a separate cleaning unit. claim 30 33. An X-ray exposure method, comprising the steps of: performing X-ray exposure with use of an X-ray mask structure; and introducing one of oxygen and ozone for performing ozone cleaning of the X-ray mask structure. 34. A device manufacturing method, comprising the steps of: performing X-ray exposure of a workpiece with use of an X-ray mask structure, whereby a pattern is transferred to the workpiece: introducing one of oxygen and ozone for performing ozone cleaning to the X-ray mask structure: and developing the workpiece having the pattern transferred thereto through the X-ray exposure, for production of devices. 35. An X-ray exposure method, comprising the steps of: performing X-ray exposure by use of an X-ray mask structure: and introducing oxygen for oxygen plasma cleaning of the X-ray mask structure. 36. A device manufacturing method, comprising the steps of: performing X-ray exposure of a workpiece by use of an X-ray mask structure, whereby a pattern is transferred to the workpiece; introducing oxygen for oxygen plasma cleaning of the X-ray mask structure; and developing the workpiece having the pattern transferred thereto, for production of devices. |
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description | This application claims the benefit of DE 10 2012 213 876.5, filed on Aug. 6, 2012, which is hereby incorporated by reference. The present embodiments relate to an arrangement and a method for inverse x-ray phase contrast imaging with a multibeam x-ray tube and a photon-counting x-ray detector. X-ray phase contrast imaging is an x-ray method that, unlike conventional x-ray devices, exclusively uses the absorption by an object as an information source. X-ray phase contrast imaging combines the absorption with the shift in phase of the x-rays when passing through the object. The information content is disproportionately higher, since the absorption provides accurate images of the significantly absorbing bones, and the phase contrast also produces sharp images of the structures of the soft tissue. This provides the possibility of being able to identify pathological changes, such as the appearance of tumors, vascular restrictions or pathological changes to the cartilage substantially earlier than before. The passage of x-rays through matter is described by a complex refraction index. The imaginary part of the refraction index specifies the strength of the absorption. By contrast, the real part of the refraction index specifies the phase shift in the x-ray wave passing through a material. In phase contrast imaging, the phase information of the local phase or of the local gradient of the phase of the wavefront passing through an object are determined. Similar to x-ray tomography, tomographic representations of the phase shift may also be reconstructed on the basis of a plurality of images. A number of possibilities exist in order to realize x-ray phase contrast imaging. The known solutions involve rendering the phase shift in the x-rays during passage through an object visible as an intensity fluctuation using special arrangements and methods. A method is grating-based phase contrast imaging (e.g., Talbot-Lau interferometry), such as is described many times in literature (e.g., in the European patent application EP 1 879 020 A1). Aspects of the Talbot-Lau interferometer are three x-ray gratings that are arranged between an x-ray tube and an x-ray detector. In addition to the classical absorption image, interferometers of this type may present two additional measurement parameters in the form of further images: the phase contrast image and the darkfield image. The phase of the x-ray wave is determined in this process by interference with a reference wave using the interferometric grating arrangement. EP 1 879 020 A1 discloses an arrangement according to FIG. 1 having an x-ray tube 1 and a pixelated x-ray detector 2, between which an object 3 to be irradiated is arranged. A source grating G0 (e.g., coherence grating) is arranged between the focal point of the x-ray tube 1 and the object 3. The source grating G0 is used to simulate a number of line sources with spatial partial coherence of the x-rays, thereby forming a precondition for interferometric imaging. A defraction grating G1, also known as phase grating or Talbot grating, is arranged between the object 3 and the x-ray detector 2. The defraction grating G1 impresses a phase shift by Pi on the phase of the wavefront. An absorption grating G2 between the defraction grating G1 and the x-ray detector 2 is used to measure the phase shift generated by the object 3. The wavefront upstream of the object 3 is designated W0. The wavefront “distorted” by the object 3 is designated W1. The gratings G0, G1 and G2 must be arranged in parallel and at precise distances from one another. The x-ray detector 2 is used as locally-dependent proof of x-ray quanta. Since the pixelization of the x-ray detector 2 is generally not sufficient to resolve the interference strips of the Talbot pattern, the intensity pattern is scanned by shifting one of the gratings G0, G1, G2 (“phase-stepping”). The scanning takes place gradually or continuously at right angles to the direction of the x-ray and at right angles to the slot direction of the absorption grating G2. Three different types of x-ray images are recorded and/or reconstructed: the absorption image, the phase contrast image and the darkfield image. The geometric ratios of the grating arrangement according to EP 1 879 020 A1 are shown schematically in FIG. 2. The gratings G0, G1 and G2 are arranged between the x-ray tube 1 and the planar x-ray detector 2. The source grating G0 has the smallest surface, since it is positioned close to the x-ray tube 1. The absorption grating G2 has the largest surface, since it is positioned directly upstream of the x-ray detector 2. The scope of the present invention is defined solely by the appended claims and is not affected to any degree by the statements within this summary. The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, a further arrangement and an associated method for x-ray phase contrast imaging are provided. In contrast to known x-ray phase contrast imagings, an extended multifocus x-ray source is used instead of an individual x-ray source. Rays of the multifocus x-ray source are collimated on a relatively small photon-counting x-ray detector. As a result, proportions of the gratings in the radiation path may be reversed. A source grating is as large as the x-ray source. A defraction grating is smaller, and an absorption grating is as large as the active detector surface. Multifocus x-ray tubes (e.g., multibeam x-ray tubes) are described by way of example in the patent application DE 10 2010 011 661 A1. In one embodiment, an arrangement for inverse x-ray phase contrast imaging includes a photon-counting x-ray detector and a multibeam x-ray tube. Focal points of the multibeam x-ray tube are collimated such that a narrow x-ray that is directed toward an optical axis of the arrangement and toward the x-ray detector may be generated in each instance. The active surface of the x-ray detector is at least as large as the cross-sectional surface of the narrow x-ray beam. The arrangement further includes a source grating arranged between the x-ray tube and the x-ray detector. The dimensions of the source grating are such that the source grating may be irradiated by all narrow x-rays of the multibeam x-ray tube. A defraction grating is arranged between the source grating and the x-ray detector. The dimensions of the defraction grating are such that the defraction grating be irradiated by all narrow x-rays that penetrate the source grating. An absorption grating is arranged between the defraction grating and the x-ray detector. The dimensions of the absorption grating are such that the absorption grating is irradiated by all narrow x-rays that penetrate the defraction grating. One or more of the present embodiments are advantageous in that the technically demanding absorption grating has the smallest grating surface. With the conventional arrangement, the absorption grating has the largest surface. In accordance with the prior art, large gratings, which are used for the conventional geometry (e.g., extended detector with a used image field), may not be manufactured or may only be manufactured with a significant technical outlay. The source grating has the largest surface but is, however, technically easier to produce on account of the large grating periods. Source gratings and collimators may also be combined. In a further development, the irradiated surface of the absorption grating may be larger than or equal to the photon-receiving active surface of the x-ray detector. In a further embodiment, the irradiateable surface of the absorption grating may be smaller than the irradiateable surface of the defraction grating, and the irradiateable surface of the defraction grating may be smaller than the irradiateable surface of the source grating. In a further embodiment, the source grating, the defraction grating and the absorption grating may be arranged in parallel to one another and at right angles to the optical axis of the arrangement. The width and the length of the active surface of the x-ray detector may, for example, be larger than 1 cm and smaller than 10 cm. The focal points may be actuated sequentially. As a result, the “phase-stepping” is omitted (e.g., no movement of the absorption grating is required). As a result, a fixed attachment of the absorption grating may be provided, and no mechanism for shifting is required. The phase shift may be determined more accurately, since no uncertainties occur in the positioning caused by mechanical shifting. A method for inverse x-ray phase contrast imaging includes generating a number of narrow x-rays with a multibeam x-ray tube. Focal points of the x-ray tube are collimated such that the narrow x-rays are directed at the optical axis of the arrangement and at a photon-counting x-ray detector. The method includes irradiating a source grating arranged between the x-ray tube and the x-ray detector, irradiating a defraction grating arranged between the source grating and the x-ray detector, and, irradiating an absorption grating arranged between the defraction grating and the x-ray detector. In a further development of the method, the focal points may be actuated sequentially. FIG. 3 shows one embodiment of an arrangement with a multibeam x-ray tube 4 including a plurality of focal points 8. Each focal point 8 is collimated by a narrow x-ray beam 7 that is directed at an x-ray detector 5 with a small, active surface. The focal points 8 of the x-ray tube 4 may be actuated individually, in a defined sequence or sequentially. With an arrangement for inverse x-ray imaging, an extended multibeam x-ray tube 4 is used, whereas the x-ray detector 5 only has a small active surface. The focal points 8 are arranged in a 2-dimensional manner and/or in rows. The x-ray detector 5 counts photons and has a very quick read-out rate, since the x-ray detector 5 is to be read out for each active focal point 8 immediately after exposure and/or irradiation. Photon-counting x-ray detectors 5 advantageously have an improved quanta efficient compared with integrating detectors. The narrow x-rays 7 are collimated in the direction of the optical axis 6 of the arrangement. On the way, the x-rays 7 firstly penetrate a source grating G0 that simulates a number of line sources with spatial partial coherence of the x-rays. After irradiating an object 3, the x-ray 7 penetrates a defraction grating G1 and then an absorption grating G2, before the x-ray 7 strikes the x-ray detector 5. With an inverse arrangement of this type, the source grating G0 has the largest surface. The source grating G0 may have the largest period length and thus may have the smallest technical outlay. The source grating G0 may be integrated in a collimator (not shown). The technically most complicated grating with the smallest period length and the largest aspect ratio is the absorption grating G2. With inverse geometry, the absorption grating G2 has the smallest surface and is therefore easier and more cost-effective to manufacture. The defraction grating G1 is arranged downstream of the object 3 and upstream of the absorption grating G2 and is smaller than the source grating G0. The distances between the used gratings G0, G1, G2 in the direction of an optical axis may be determined, for example, with the aid of the published publication T. Donath et al., “Inverse geometry for grating-based x-ray phase-contrast imaging,” J. Appl. phys. 106, 054703 (2009).” The size of the multibeam x-ray tube 4 conforms with the size of the object 3 to be examined. The size of the x-ray detector 5 is dependent on the size of the collimated x-ray 7, the required read-out rate, and the radiation intensity of the individual focal points 8. Dimensions of, for example, 1 to 10 cm may be used. The active surface of the x-ray detector 5 does not have to be square. A sequential actuation of the individual focal points 8 allows for the “phase-stepping” of the conventional x-ray phase contrast imaging to be omitted. The intensity pattern and/or the phase shift generated by the object 3 may be reconstructed with the inverse phase contrast imaging directly via the detector response. The inverse geometry for imaging is also advantageous in that the average skin dose on the radiation entry side may be reduced by a larger surface on the entry side. A lower scatter radiation in the detector allows for the radiation dose to be reduced. In addition, a digital tomosynthesis using reconstruction methods enables additional layer representations of the object. It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present invention. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims can, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification. While the present invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description. |
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041636899 | summary | This invention relates to nuclear reactors and in particular to fuel for, and fission gas venting of a thermionic or similar fuel element. In thermionic nuclear reactors, the generation of gases upon the fission of the fissile fuel presents at least a two-fold problem; first, particular fission product gases such as xenon and krypton have such large neutron absorption cross sections so that if they remain in the reactor core in the neutron flux an appreciable number of neutrons are lost from the fission process effectively reducing the reactor efficiency and possibly reducing reactivity to below critical; and second, fission product gases or other volatile products may be sufficient in amount to create excessive pressure to cause the fuel container to bulge and deform. Since, in a thermionic reactor or any other high temperature reactor the fuel container forms the emitter portion of the thermionic cell, and since the spacing between the emitter and collector portions of the cell are very small, being of the order of hundredths to thousandths of an inch and very critical, any bulging or changing of shape of the emitter may be highly detrimetal to reactor operation and/or thermionic performance of the fuel cell or element. The device of the present invention eliminates these problems by taking advantage of phenomena associated with high temperature operation of nuclear fuels to remove and conduct away from the fuel cell or rod the various gases and volatile products generated during the fission process. Where other venting methods merely permit the gaseous and volatile products permeate the fissile fuel, the present invention provides an arrangement promoting gas and vapor migration to form an accumulated pocket of gas and to remove it from the fuel soon after it is generated. It is, therefore, an object of this invention to provide a venting device for a thermionic nuclear fuel cell or a high temperature fuel element whereby deformation of the cell cladding caused by fission gas pressure is eliminated. It is a further object of this invention to provide a venting device for a nuclear reactor fuel element whereby fission product gases having a high neutron absorption cross section are readily removed from the fuel element. It is another object of this invention to provide a venting device for a nuclear fuel element providing for the directional migration of fission product gases to be accumulated and removed from the reactor. |
040653501 | claims | 1. In the method of confining and stabilizing a plasma current carrying toroidal plasma column in a tokamak having toroidal and poloidal coil means for producing toroidal magnetic surfaces along an equilibrium axis around an axis of rotation, the improvement, comprising the steps of: a. producing a toroidal plasma column in the magnetic surfaces; and b. distributing over the plasma region a non-helical octupole magnetic field around the outside of the plasma column and in the space between the equilibrium axis and the axis of rotation for producing poloidal separatrices external to the plasma column having stagnation points and magnetic field lines that define in cross-section an elongated magnetic surface having a D-shaped poloidal divertor cross-section, said toroidal plasma column having external shell currents computed to make the edge of the plasma region the .PSI. = 0 magnetic surface. a. producing a toroidal plasma column in concentric, circular cross-section, toroidal magnetic surfaces having a poloidal separatrix along an equilibrium axis and plasma particles that diffuse outwardly away from the equilibrium axis toward the sepatrix; and b. imposing on the outside of the toroidal plasma column a magnetic field having spaced apart non-helical poloidal currents that are co-axial with the equilibrium axis for effecting the changing of the outer magnetic surface into an elongated, cross-section having an external separatrix forming a D-shaped poloidal divertor cross-section to bend the plasma particles away from the equilibrium axis and into the poloidal divertor in accordance with their diffusion away from the equilibrium axis toward the separatrix. 2. The method of claim 1 in which said external shell currents and plasma currents produce an elongated plasma column in said magnetic field. 3. The method of claim 2 in which the major radius at the center of the plasma column is at least 1.275 meters, the area of the plasma column cross-section is 0.98 square meters, and the semi-axis ratio is between 1.6 and 3.2. 4. The method of claim 3 in which the external shell currents and plasma currents produce an external magnetic limiter around the plasma outside diameter and four, non-helical, co-axial poloidal divertors having a D-shape in cross-section centered on four co-axial circles at the edges of a rectangle for removing impurities. 5. In the method of confining and stabilizing a plasma current carrying toroidal plasma column in a tokamak having toroidal and poloidal coil means for producing toroidal magnetic surfaces along an equilibrium axis around an axis of rotation, the improvement comprising the steps of: |
046831169 | description | DETAILED DESCRIPTION OF EMBODIMENTS The apparatus shown in the drawings includes a reactor 11 (FIG. 1) having a pressure vessel including a generally cylindrical body 13 having a semi-spherical base and a dome-shaped head 15. The body 13 and the head 15 have flanges 17 and 19 which are engaged and sealed pressure tight by bolts 21. The body 13 has inlet nozzles 23 and outlet nozzles 25 for the coolant. In the lower part of the body 13 there is a core 27. The core 27 is encircled by a core barrel 29 having a flange 31 by which the core barrel 29 is suspended from a ledge 33 on the flange 17 of the body 13. The core 27 has a plurality of fuel assemblies 35. These fuel assemblies are conventional. Typically, such assemblies are shown in U.S. Pat. No. 4,522,780 granted June 11, 1985 to Shallenberger et al. for Removal and Replacement of Nuclear Reactor Fuel Assemblies, assigned to Westinghouse Electric Corporation. Each fuel assembly 35 includes a plurality of fuel rods 37 interposed between a top nozzle 39 and a bottom nozzle 41. Each fuel assembly 35 also has a plurality of thimbles 43. The thimbles are secured to the top nozzle 39 and the bottom nozzle 41 and bind the fuel assembly into an integrated unit. The manner in which the thimbles 43 is secured to the top and bottom nozzles is conventional. Typical structure is shown in Shallenberger et al. (supra). Each fuel assembly 35 has grids (not shown, but see Andrews supra) for holding the fuel rods 37 together. The fuel assemblies 35 are mounted between upper and lower core plates 45 and 47 which are supported by core barrel 29. Control rods (not shown) are moveable into and out of the thimbles 41 of each fuel assembly 35. The control rods associated with each assembly 35 are suspended in a cluster from a spider 49. The control rods are moveable in guides 51 above the upper core plate 45. The assembly of guides 51 is referred to as the upper internals of the reactor. The guides are supported in a generally cup-shaped member 53 having a flange 55 by which it is suspended above the barrel flange 31. The member 53 is also supported by columns 57 which extend between the upper core plate 45 and the member. The control rod clusters are each movable upwardly or downwardly by drive rods 59, which are operated by a mechanism (not shown) above the head 15. The core 27 also includes fuel assemblies 61 (FIGS. 1, 3) with which control rods are not associated. Each of the assemblies 61 includes a top nozzle 63, a bottom nozzle 65, fuel rods 67 interposed between the nozzles 63 and 65 and structural members or tie rods 69 (FIG. 4) secured to the top and bottom nozzles. Typically, each structural member may be threaded onto a screw 77 (FIG. 5) extending from the lower nozzle 65 and secured by a nut 70 to the top nozzle as shown in FIG. 3. The tie rods 69 bind the assembly 61 into an integrated unit. There is also a central tube 71 for instrument secured to the top and bottom nozzles. Such a central tube (not shown) is also included in each of the conventional fuel assemblies 35. The fuel rods 67 and structural members 69 are held together by grids 73 as disclosed in Andrews (supra). The grids 73 are prevented from being displaced longitudinally of the assembly 61 by the force of the sed in Andrews (supra). The grids 73 are prevented from being displaced longitudinally of the assembly 61 by the force of the sed in Andrews (supra). The grids 73 are prevented from being displaced longitudinally of the assembly 61 by the force of the coolant by bulges 75 (FIG. 8) in the structural members on both sides of each grid 73. The coolant flows at a high velocity, typically 50 ft./sec., and is under high pressure, typically 2000 lb./sq. inch. Typically, the structural members 69 have a substantially greater thickness than the thimbles 43 of the conventional fuel assemblies 35 and there are substbers 69 have a substantially greater thickness than the thimbles 43 of the conventional fuel assemblies 35 and there are substantially fewer structural members 69 in each assembly 61 than thimbles in each assembly 35. The remaining locations in each assembly 61 which correspond to those occupied by thimbles in each conventional fuel assembly 35 are occupied by fuel rods in the fixed assembly 61. For example, there are typically 24 thimbles in an assembly 35; in an assembly 61 there are only 8 structural members and 16 additional fuel rods in the remaining locations. The lower nozzle 65 is generally similar to the lower nozzle of the conventional fuel assemblies 35 except that it has fewer mechanisms, specifically screws 77 (FIG. 5) for securing the structural members at their lower ends. Thimbles 43 may be secured as shown in Shallenberger (supra). The top nozzle 63 is of smaller vertical height (or length) than the top nozzle 39 of a conventional fuel assembly 35 because it need not include a groove for receiving the spider 49 (FIG. 1) of the control rod cluster during scram. The structural member 69 (FIG. 4) includes a tube or shell or cladding 81 sealed by end plugs 83 and 85 at the top and bottom. The shell 81 has an extension 86 (FIG. 8) at the top to receive the end plug 83. The end plug 83 at the top has a threaded tip 87 to be engaged by the nut 70 (FIG. 3). The end plug 85 at the bottom has a tapped central hole 89 into which the screw 77 (FIG. 5) from the lower nozzle 65 is threaded. Burnable neutron-absorber pellets 91 are stacked in the tubes 81 of at least certain of the structural members. The others may be empty. Above the stack of pellets 91 there is a space in which there is a spring 93. The spring 93 is compressed between the plug 83 and a cylindrical member 95 which engages the upper pellet 91 of the stack thus maintaining the pellet stack rigid. The burnable neutron absorber burns out to a small residual absorption capability during the early part of a fuel cycle. In fabricating the fuel assembly 61, a skeleton 101 (FIGS. 5, 6) is first formed. The skeleton includes the tubes 81 of the structural members 69. Each tube is empty and is closed by the plug 85 at the bottom and is open at the top. The open tubes 81 are secured to the bottom nozzle 65. The skeleton also includes the instrument tube 71 which is also secured to bottom nozzle 65. The grids 73 are mounted spaced along the tubes 81. Each tube 81 passes through an array of coaxial cells 103 of the grids 73. Each cell 103 is of rectangular transverse cross-section but is lined by an annular sleeve 105 (FIGS. 7, 8) which extends a short distance above and below its associated cell. Each tube 81 engages the coaxial sleeves 105 along which it extends and is a sliding fit in these sleeves. Each tube 81 and the sleeve 105 through which it passes are bulged out to produce bulges 75 above and below each grid 73 by a bulge tool. Once the skeleton 101 is assembled, the burnable neutron-absorber pellets 91 are inserted in each tube 81. The spring 93 and the block 95 for transmitting the pressure of the spring to the stack is then inserted. The tubes 81 are then evacuated and back-filled with an inert gas, and plug 83 is welded to the top of each tube. The fuel rods 67 are then inserted in coaxial cells 103 in the skeleton 101 and the top nozzle 63 is secured to the structural members 69. The assembly 61 is now complete and may be inserted in the appropriate locations in the core 17. FIG. 2 shows the distribution of assemblies 35 and 61 in the core 17. The assemblies 35 are disposed in the cells 107 which are lettered. The assemblies 109 are disposed in the cells which are not lettered. While preferred embodiments of this invention have been disclosed herein, many modifications thereof are feasible. This invention is not to be restricted except insofar as is necessitated by the spirit of the prior art. |
047626658 | description | Referring to FIG. 1, pellets are off-loaded from trays onto a moving belt 10 by an off-loader mechanism generally depicted by reference numeral 12. The belt 10 travels in the direction of arrow A and, initially, the pellets travel in spaced relation within the confines of a guide lane 14 and with their axes parallel to the direction of belt movement. The pellets move through a measurement station 16 in which the lengths are measured preferably by a non-contacting method and while the pellets are in motion. The measuring device may be a laser scanning arrangement such as that manufactured under the brand name "Laser Mike" by Techmat Company of 6060 Executive Boulevard, Dayton, Ohio, 45424, USA. The individual measurements are fed to a microprocessor-based control unit 18 which is preprogrammed with data relating to the required overall length of the stack and also the target length of the stack at one or more intermediate points during its assembly. Depending upon the result of the measurement, each pellet is channelled, under the control of control unit 18, by a diverter mechanism 22 into one of three lanes 24, 26, 28, herein called the oversize, intermediate-size and undersize lanes respectively. The criteria for segregation of the pellets into these lanes will in general be governed by the fact that the stack will be assembled primarily from intermediate-size pellets and the oversize and undersize pellets are principally intended to be used for corrective action in the event that the partially completed stack drifts away from the target length. Thus, the classification of the pellets by the control unit 18 is governed by the need to maintain an adequate supply of intermediate size pellets and the control unit is therefore programmed to update the size ranges corresponding to undersize, oversize and intermediate-size to meet this need. For example, the control unit 18 may be arranged to ensure that say 50% of pellets are channelled to the intermediate-size lane 26 and the remaining 50% are shared between the oversize and undersize lanes 24, 28. For this purpose, the control unit 18 may be arranged to keep an inventory of the pellet distribution between the lanes 24, 26, 28, the size criteria being automatically adjusted when necessary to ensure an adequate supply of pellets in each lane. Alternatively, as illustrated in FIG. 2, instead of an inventory being kept by the control unit 18, the lanes 24, 26, 28 may be provided with sensor means, eg. photoelectric detectors 30, for providing signals to unit 18 indicating the extent to which each lane is occupied by pellets enabling control unit 18 to divert more or less pellets to each lane automatically by adjusting target lengths. The lanes 24, 26, 28 direct the respective pellets to a selector mechanism 32 which is controlled by the unit 18 and serves to hold up pellets in the lanes 24, 26, 28 and release them selectively into a single lane 34 constituting the stacking zone of the apparatus. The pellets thus released collect end-to-end in a stack which can be constrained against movement with the belt 10 at various points during formation of the stack by a series of stops 36-39 which are extendable into and retractable from the stacking lane 34 under the control of unit 18. Associated with the stacking lane 34, there is a stack-length measuring system 40 for detecting the position of the trailing end of the growing stack when the latter makes successive contact with each of the stops 36, 37, 38 and 39. The system 40 may, like device 16, be a laser-scanning device having a well-defined scanning field upon which the trailing end of the growing stack eventually encroaches after the stack initially contacts stop 36 and subsequently, in succession, stops 37, 38 and 39. The microprocessor-based control unit 18 is programmed to co-ordinate the positions of the stops 36-39 with detection of the trailing end of the stack within the field of view of the scanning system 40 and thereby derive length measurements for the partly-completed stack at each of the stop positions 36-39. In this way, length measurements for the stack are obtained at different points in its assembly, eg. halfway (stop 36), three-quarters completed (stop 37), four pellets from completion (stop 38) and one pellet short of being fully completed (stop 39). Each of these measurements is compared by the unit 18 with corresponding target values so that any drift away from the target length can be detected at various points during assembly of the stack. If any deviation occurs at stops 36-38, the control unit 18 computes the combination of oversize or undersize and/or intermediate size pellets to be supplied to the stack to correct for such drift as the stack continues to grow towards the size at which the next length measurement is taken. The required combination of pellets is released into the stacking lane 34 by appropriate operation of the selector mechanism 32 under the control of unit 18. After the stack has advanced to the stop 39 and any corrective action has been taken in selecting the apropriate pellet size for completion of the stack, pellet supply into lane 34 is terminated, stop 39 is retracted and the completed stack is transferred to a tray in loading mechanism 42. The completed stack length can be subsequently checked and if it lies outside the acceptable tolerance range the stack may be rejected and the pellets recycled or it may be transferred to a reject tray for corrective action by manual means, using a glove box if the nature of the fuel material demands this. After transfer of the completed stack from lane 34, stop 36 is extended into lane 34 and pellet supply via the selector mechanism is resumed to build-up a fresh stack in the same manner as described above. One embodiment of the diverter mechanism 22 is illustrated in FIGS. 3, 4 and 5 to which reference is now made. As mentioned previously, the diverter mechanism 22 is operable to divert pellets in lane 14 (defined by rails 46) to one of the lanes 24, 26 or 28 depending on the result of the measurement made at the device 16. In this embodiment, the diverter mechanism is constructed as a three-position actuator having three well-defined settings in which the guide section 47 of its diverting gate 48 is in registry with lanes 24, 26, 28 respectively. The mechanism comprises a pair of elements 50, 52 having a well-defined stroke length, one (50) of which is fixed and the other (52) of which is slidable transversely of direction A along a slide 54 and carries the diverting gate 48. The two elements 50, 52 are coupled together in such a way that when both are at their minimum stroke settings, the guide section 47 is in registry with the lane 24; when one is at its full stroke setting and the other at its minimum, the section 47 is in registry with the lane 26; and when both are at the full stroke settings, the section 47 is in registry with the lane 28. The elements 50, 52 may for example comprise fluid powered piston and cylinder devices arranged with their piston rods coupled together or they may comprise solenoids arranged with their armatures coupled together. The diverter mechanism 22 operates under the control of unit 18, the arrangement being such that the guide section 47 defined by rails 56 is normally in registry with lane 14. When a pellet passes through the measuring device 16 it is allowed to continue into the guide section 47 until the pellet is entirely within the section 47 (as registered for example by a suitable sensor 58 connected to the control unit 18) whereupon the gate 48 is shifted (if necessary) to align the section 47 with the appropriate lane 24, 26, 28 so that the pellet can continue without interruption through the section 47 and into the selected lane. After the pellet has cleared the section 47 (as registered by sensors 60 connected to the control unit 18), the gate 48 is restored (if necessary) into alignment with the lane 14 in preparation for receiving the next pellet. The foregoing description relates to the fabrication of pellet stack in circumstances where all of the pellets are of the same type. However, in some circumstances, it may be necessary to assemble a stack from two or more different types of pellet in such a way that certain types of pellet occupy specific positions along the length of the stack. Thus, fuel for a known form of gas cooled graphite moderated nuclear reactor comprises plain pellets and pellets formed with a circumferential groove into which the sheath of the fuel pin is subsequently deformed to lock the pellet stack axially to the pin. To enable corrective action to be taken to ensure the stack length is within an acceptable tolerance range about the target length, the practice has been to manufacture the plain pellets in two sizes, long and short, so that stack adjustment can be effected by substituting long for short pellets or vice versa. An embodiment of the invention for use in handling pellets in such circumstances is illustrated in FIG. 6. This embodiment is similar to that of FIGS. 1 and 2 in many respects and like reference numerals are therefore used to indicate like components and structures. The control unit 18 and its connections to various parts of the apparatus have been omitted in FIG. 6 for the sake of clarity. The short and long plain pellets are supplied to apparatus via off-loading mechanisms 70, 72 respectively which feed pellets from trays, such as that indicated by reference 74, onto the belt 10 downstream of the diverter mechanism 22 via curved guides 76, 78 which lead into guide lanes 80, 82 running alongside lanes 24, 26, 28 to the selector mechanism 32. The long and short plain pellets are not measured by measuring device 16 since they have already been classified into specific size ranges. The grooved pellets are fed by the off-loading mechanism 12 and follow the route previously described in relation to FIGS. 1 and 2 and consequently lanes 24, 26 and 28 serve to accumulate oversize, undersize and intermediate size grooved pellets, the classification into these size ranges being effected in the manner described previously so as to ensure that an adequate supply of the different grooved pellet sizes is always available. The stack of pellets formed in stacking lane is assembled by operation of the selector mechanism 34 under the control of unit 18 in accordance with a preprogrammed sequence of long, short and grooved pellets so that the grooved pellets will occupy the desired positions along the length of the fuel pin after insertion of the stack into the sheath. The unit 18 may store a range of different pellet sequences since the sequence may be required to differ from one pin to another and, in this event, the required sequence may be preselected by entry of command data via an operator console of the unit 18. As the stack grows in lane 34, its length is periodically checked as before by means of the stops 36-39 and the measuring system 40 to detect any drift away from the target length. In this embodiment, the necessary corrective action can be taken by selecting a suitable combination of pellet sizes from the lanes 24, 26, 28, 80, 82 taking into account also the need to secure the correct number and positioning of the grooved pellets along the stack. In practice, the corrective action may only involve the use of the long and short plain pellets following the first and second measurements at stops 36 and 37 and the different grooved pellet sizes may be employed either alone or in combination with long and short plain pellets after the measurement at stop 38 has been made. One form of selector mechanism for use in the apparatus of FIG. 6 (or in FIG. 1 with modification involving a three lane input instead of five lanes) is shown in FIGS. 7, 8, 9 and 10 to which reference is now made. As shown, the mechanism comprises a base 90 on which a housing structure 92 is pivoted by pivots 94 so that the housing 92 can be pivoted by means of knob 86 between the in-use position shown and a raised position for maintenance purposes. Beneath the housing 92, the base 90 is divided by a set of parallel rails 98 into lanes which, at the right hand side, register with and form continuations of the lanes 24, 26, 28, 80, 82 (not shown). To the left of the housing 92 the lanes are merged by guides 100, 102 into a single lane 104 which registers with the stacking lane 34. For each lane defined by rails 98, the housing 92 mounts a pellet gate 106 and at least one pellet stop 108, the pellet gates 106 being downstream of the pellet stops 108 in the direction A of pellet travel. As shown in FIG. 10, each pellet gate 106 comprises a bifurcated vertically displaceable gate plate 110 whose legs project through openings 112 in a support 114 of the housing 92 and slide in grooves 115 in the rails 98 which, in turn, are secured to the underside of the support 114. The plates 110 are each movable under the control of unit 18 by an actuator 118, such as a pneumatic piston and cylinder, between the lowered position shown in which it impedes pellet motion along the respective lane (see pellet 120 in FIG. 10) and a raised position in which it is clear of the pellet and allows passage of the pellets into the converging section 122. The pellet stops 108 are constructed and operate in a similar fashion to the pellet gates 106 except that the bifurcated stop plates 124 have legs shaped to embrace the pellets so that, when lowered, the stop plates 124 do not impede pellet motion but, when raised, they lift the pellets upwardly and into contact with the underside of the support 114. In this way, raising of a pellet against the support 114 halts its movement and, because the distance it is raised is only a fraction of the pellet diameter, all of the pellets following the raised pellet are also blocked. In use, the pellet gates 106 are used to accumulate pellets in the lanes 24, 26, 28, 80 and 82 and release them under the control of the unit 18. The pellet stops 108 are used under the control of unit 18 to determine the number of pellets released each time the associated pellet gate 106 is opened. Thus, for example, where a lane has two pellet stops 108, the downstream stop 108 may be used to stop the first pellet following the leading pellet so that only the latter is released when the pellet gate 106 is opened. The upstream stop may be used to stop the second pellet following the leading pellet so that if desired the leading and next following pellet may be released by appropriate operation of the pellet gate 106 and the downstream pellet stop 108 while the remaining pellets in that lane are held up by the upstream stop. After the leading two pellets have been released, the gate 106 may be closed and the upstream stop 108 operated to allow the remaining pellets to move up to the gate 106 in readiness for the next pellet-releasing operation which may involve the release of one or two pellets. |
042016908 | abstract | Irradiated nuclear fuel is dissolved in nitric acid under a carbon dioxide atmosphere which is treated to remove iodine, krypton and xenon and recycled. |
abstract | Fuel rods of fuel assemblies of a boiling water reactor are tested for leaks. A plurality of fuel assemblies are each arranged adjacent to one another in a cell of the upper core grid of the boiling water reactor. A hood is placed above a plurality of cells A water sample is taken from each of the cells, and the water samples from a plurality of cells forming a group are combined and tested for the presence of radioactive fission products A plurality of groups are analyzed simultaneously in a number, which number corresponds to the number of groups, of measurement channels. Where a result of a group is positive, the cells of the group are tested separately by the measurement channels. Those fuel assemblies of a cell that is found positive are tested individually outside the hood. |
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description | This application is a continuation of U.S. application Ser. No. 12/685,764, filed Jan. 12, 2010, the contents of which are incorporated herein by reference. The present application claims priority from Japanese Patent application serial no. 2009-011479, filed on Jan. 22, 2009, the content of which is hereby incorporated by reference into this application. 1. Technical Field The present invention relates to jet pump and reactor and, in particular, to a jet pump and a reactor suitable for applying to a boiling water reactor. 2. Background Art A conventional boiling water reactor (BWR) has a jet pump in a reactor pressure vessel (hereinafter referred to as an RPV) to which a recirculation pipe is connected. The jet pump has a nozzle, a bell mouth, a throat, and a diffuser. Cooling water in a downcomer, where the jet pump is disposed, formed in the RPV is pressurized by operation of a recirculation pump, pumped through the recirculation pipe as a driving flow, and ejected from the nozzle into the throat. The nozzle increases the speed of the driving flow. The cooling water around the nozzle in the downcomer is sucked into the bell mouth as a suction flow due to the working of the ejected driving flow, passes the throat, and flows into the diffuser. The cooling water discharged from the diffuser is supplied to a core through a lower plenum in the RPV (see, for example, U.S. Pat. No. 3,625,820, Japanese Patent Laid-open No. Sho 59(1984)-188100, Japanese Patent Laid-open No. Hei 7(1995)-119700, and Japanese Patent Laid-open No. 2007-285165). Jet pumps disclosed in Japanese Patent Laid-open No. Sho 59(1984)-188100, Japanese Patent Laid-open No. Hei 7(1995)-119700, and Japanese Patent Laid-open No. 2007-285165 each have a plurality of nozzles. When the total area of each ejection opening formed in the plurality of nozzles remains constant, an increase in the number of nozzles increases the contact area between driving flows and suction flows, and thus mixing of the driving flows and the suction flows is promoted. Consequently, a mixing loss is decreased, increasing efficiency of the jet pump. A jet pump installed in a reactor has a nozzle connected to a raiser pipe that is installed in the RPV. In this jet pump, an elbow pipe, the nozzle, a bell mouth and a throat are unified into one body, which structure allows the elbow to the throat to be removed for inspection and maintenance. A connection portion between the throat and the diffuser has a joint structure in which a lower end portion of the throat is inserted into an upper end portion of the diffuser. This joint structure is a slip joint. The slip joint, where the throat and the diffuser are connected, has a structure which allows the upper end portion of the diffuser and the lower end portion of the throat to slide up and down, so that no stress is generated due to the difference between the thermal expansions of the raiser pipe and the diffuser. For this reason, a gap is formed between an inner surface of the diffuser's upper end portion and an outer surface of the throat's lower end portion. Part of the cooling water that flows into the diffuser from the throat leaks out to the downcomer through the gap. This leakage flow prevents a foreign object from being caught in the gap or deposited on the surfaces. However, when the flow rate of the leakage flow exceeds a limit, the jet pump may start to vibrate. Thus, in order to suppress the vibration of the jet pump, the leakage flow from the gap in the slip joint should be limited below the limit. Although it is not a jet pump, Japanese Examined Utility Model Application Publication No. Sho 52(1977)-5301 discloses a fluid sealing joint used for pipes for introducing high-temperature and high-pressure gas (or steam). In this fluid sealing joint, a tubular inlet-side joint portion is inserted into a tubular outlet-side joint portion; and an end portion of the inlet joint portion has a narrowing portion whose flow passage cross-sectional area decreases and an expanding portion whose cross-sectional area increases toward the end. A communication hole is formed in the place where the narrowing portion and the expanding portion are connected, the flow passage cross-sectional area of which the place is the smallest in the inlet-side joint portion. This communication hole communicates with an annular space portion formed between the inlet-side joint portion and the outlet-side joint portion. Static pressure inside is reduced at the seam between the narrowing portion and the expanding portion so that a fluid in the annular space portion is sucked inside the narrowing portion through the communication hole. This effectively prevents a fluid from leaking out of the fluid sealing joint through a gap between the inlet-side joint portion and the outlet-side joint portion. Japanese Patent Laid-open No. Sho 59(1984)-159489 discloses a jet pump for suppressing vibration. In this jet pump, a lower end portion of a throat, which is inserted into an upper end portion of a diffuser, has a flow passage cross-sectional area that diminishes toward the end. Other than that, for the purpose of reducing the amount of cooling water leaking from a slip joint of a jet pump, a way of forming a labyrinth seal on an outer surface of a lower end portion of a throat in the slip joint is known (see, for example, Japanese Examined Patent Application Publication No. Sho 59(1984)-48360). A jet pump illustrated in FIG. 3 of Japanese Patent Laid-open No. 2001-90700 has a venturi tube and a nozzle that ejects a driving flow into the venturi tube a driving flow. This nozzle has an inner cylinder and an outer cylinder that surrounds the inner cylinder. A driving flow passage formed between the inner cylinder and the outer cylinder is an annular passage whose cross-sectional area gradually decreases towards the discharge side of the driving flow. The driving flow supplied to the driving flow passage is ejected from one end (a discharge opening) of the driving flow passage into the venturi tube. Cleaning water around the nozzle is sucked into the venturi tube due to the driving flow ejected from the nozzle. To be more specific, this cleaning water flows into the venturi tube through each of a first cooling water suction passage formed between the nozzle and the venturi tube and a second cooling water suction passage formed inside the inner cylinder. From the nozzle, the annular driving flow is ejected. Cross sections of the annular driving flow are similar to continuous rings. Japanese Patent Laid-open No. 2008-82752 discloses a jet pump applicable to a BWR. This jet pump has a ring header for supplying a driving flow surrounding a suction flow suction passage formed in the center of the jet pump; and a nozzle portion installed to a lower end of the ring header, surrounding the suction flow suction passage, having a plurality of ejection openings in an annular arrangement, where the ejection openings eject a driving flow fed to the ring header. Patent Literature 1: U.S. Pat. No. 3,625,820 Patent Literature 2: Japanese Patent Laid-open No. Sho 59(1984)-188100 Patent Literature 3: Japanese Patent Laid-open No. Hei 7(1995)-119700 Patent Literature 4: Japanese Patent Laid-open No. 2007-285165 Patent Literature 5: Japanese Examined Utility Model Application Publication No. Sho 52(1977)-5301 Patent Literature 6: Japanese Patent Laid-open No. Sho 59(1984)-159489 Patent Literature 7: Japanese Examined Patent Application Publication No. Sho 59(1984)-48360 Patent Literature 8: Japanese Patent Laid-open No. 2001-90700 Patent Literature 9: Japanese Patent Laid-open No. 2008-82752 For the soundness of a jet pump, excessive vibration of the jet pump is undesirable. Each slip joint disclosed in Japanese Examined Utility Model Application Publication No. Sho 52(1977)-5301 and Japanese Patent Laid-open No. Sho 59(1984)-159489 can suppress a leakage flow from a slip joint and reduce vibration caused by the leakage flow. However, each slip joint has a flow passage cross-sectional area that changes, or decreases, where the structure somewhat increases a pressure loss in the slip joint. For this reason, when these slip joints are applied to a jet pump, the efficiency of the jet pump is reduced for the increased amount of pressure loss. In Japanese Examined Patent Application Publication No. Sho 59(1984)-48360, a labyrinth seal is provided to a slip joint. When a labyrinth seal is fabricated on the outer surface of a throat, its fabrication range is limited to the thickness of the throat and the length of insertion. For this reason, when the fabrication range is insufficient, a desired effect in leakage flow reduction may not be achieved. An object of the present invention is to provide a jet pump and a reactor, which can suppress the vibration of the jet pump and improve the efficiency of the jet pump. The present invention for achieving the above object is characterized in that a nozzle apparatus has a nozzle base member, and a plurality of nozzles installed to the nozzle base member and forming a plurality of narrowing portions in which a fluid passage cross-sectional area of a driving fluid passage formed in the nozzle is reduced; and in a lower end portion of a throat inserted into a diffuser, a cross-sectional area of a fluid passage formed in the throat diminishes toward a downstream end of the throat. Since, in the lower end portion of the throat inserted into the diffuser, the cross-sectional area of the fluid passage formed in the throat diminishes toward the downstream end of the throat, the amount of a fluid leaking from a space between the throat and the diffuser can be reduced and the vibration of the jet pump can be suppressed. Since the nozzle apparatus has the nozzle base member and the plurality of nozzles installed to the nozzle base member and forming the plurality of narrowing portions, in which the fluid passage cross-sectional area of the driving flow passage is reduced, inside itself, the efficiency of the jet pump can be increased after compensating for a loss in jet pump efficiency caused by the diminishment of the fluid passage cross-sectional area in the throat. The above object can also be achieved by a jet pump comprising a nozzle apparatus having a header portion disposing a first pipe member forming a suction fluid passage for introducing a suction fluid, inside the head portion, and including an annular passage, which surrounds the first pipe member, for introducing a driving fluid, and a nozzle portion installed to the header portion, surrounding the first pipe member, and forming an ejection outlet, which is communicated with the annular passage formed in the header portion, for ejecting the driving fluid; and a second pipe member, one end of which is connected to the nozzle apparatus, forming a driving fluid passage for introducing the driving fluid to annular passage in the header portion, wherein the first pipe member is disposed inside the driving fluid passage formed in the second pipe member through the one end of the second pipe member, and an opening for the suction flow passage is formed on an outer surface of the second pipe member and opened toward outside of the second pipe member; the driving flow passage is formed in a way that the driving fluid flowing toward the one end of the second pipe member hits the first pipe member diagonally in the axial direction of the first pipe member; and, in the lower end portion of a throat inserted into a diffuser, a cross-sectional area of a fluid passage formed in the throat diminishes toward a downstream end of the throat. Since, in the lower end portion of the throat inserted into the diffuser, the cross-sectional area of the fluid passage formed in the throat diminishes toward the downstream end of the throat, the amount of a fluid leaking from a space between the throat and the diffuser can be reduced and the vibration of the jet pump can be suppressed. Since the driving fluid passage formed inside the second pipe member is formed so that the driving fluid flowing toward the one end of the second pipe member hits the first pipe member diagonally to the axial direction of the first pipe member, pressure loss inside the driving fluid passage is decreased. Since the speed of the driving fluid ejected from the annular ejection outlet of the nozzle portion becomes faster, the flow rate of the suction fluid sucked inside the jet pump body is increased. From above, efficiency of the jet pump is improved. Part of this increase in the jet pump efficiency can compensate for a decrease in the jet pump efficiency caused by the diminishment of the flow passage cross-sectional area in the throat. The above object can also be achieved by a jet pump comprising a nozzle apparatus having a first tubular member; a second tubular member disposed in the first tubular member, apart from the first tubular member; a fluid passage forming-member disposed in the first tubular member, and installed to an upper end portion of the second tubular member; a plurality of passage members fixing both ends to the first and the second tubular members and disposed in the circumferential direction of the nozzle apparatus; and an annular ejection outlet is formed between a lower portion of the first tubular member and a lower portion of the second tubular member; Wherein a suction passage formed in each of the passage members, for introducing a suction fluid from the outside to the inside, communicates with an inner region formed in the second tubular member, an annular driving fluid passage for introducing the driving fluid, across which each of the passage members is disposed, is formed between the first tubular member, and the second tubular member and the flow passage forming member, and communicated with the annular ejection outlet, the ejection outlet-side portion of the driving fluid passage slopes inward toward a lower end of the nozzle apparatus, and, in a lower end portion of a throat inserted into a diffuser, a cross-sectional area of a fluid passage formed in the throat diminishes toward a downstream end of the throat. Since, in the lower end portion of the throat inserted into the diffuser, the cross-sectional area of the fluid passage formed in the throat diminishes toward the downstream end of the throat, the amount of fluid leaking from a space between the throat and the diffuser can be reduced and the vibration of the jet pump can be suppressed. Since the ejection outlet-side portion of the driving fluid passage slopes inward toward the lower end of the nozzle apparatus, degree of negative pressure in the inner region is increased, increasing the flow rate of the suction fluid flowing into the inner region through the suction passage. Furthermore, since the ejection outlet-side portion of the driving fluid passage slopes inward toward the lower end of the nozzle apparatus, the width of a gap between the lower end of the outer circumference portion of the nozzle apparatus and the upper end of a jet pump body is increased. This increases the flow rate of a suction fluid flowing into the jet pump body through the gap. From these increases in the flow rates, the efficiency of the jet pump is further increased. Part of this increase in the jet pump efficiency can compensate for a decrease in jet pump efficiency caused by the diminishment of the fluid passage cross-sectional area in the throat. According to the present invention, the vibration of a jet pump can be suppressed and the efficiency of the jet pump can be improved. Various embodiments of the present invention are described below. A jet pump installed to a boiling water reactor, according to an embodiment of the present invention is described below with reference to FIGS. 1, 2, and 3. Before explaining a structure of the jet pump of the present embodiment, an overall structure of a boiling water reactor to which this jet pump is applied is described below with reference to FIGS. 1 and 4. The boiling water reactor (BWR) has a reactor pressure vessel (reactor vessel) 1 and a core shroud 3 installed in the reactor pressure vessel. Hereinafter, the reactor pressure vessel is referred to as an RPV. A core 2 loaded with a plurality of fuel assemblies (not shown) is disposed in the core shroud 3. A steam separator 4 and a steam dryer 5 are disposed above the core 2 in the RPV 1. A plurality of jet pumps 11 is disposed in an annular downcomer 6 formed between the RPV 1 and the core shroud 3. A recirculation system provided to the RPV 1 includes a recirculation pipe 7 and a recirculation pump 8 installed to the recirculation pipe 7. One end of the recirculation pipe 7 communicates with the downcomer 6. Another end of the recirculation pipe 7 is connected to a lower end of a raiser pipe 9 disposed in the downcomer 6. An upper end of the raiser pipe 9 is connected to a branching pipe 60. An elbow pipe (a curved pipe) 10 attached to the branching pipe 60 is connected to a nozzle apparatus 12 of the jet pump 11. A main steam pipe 39 and a feed water pipe 28 are connected to the RPV 1. The nozzle apparatus 12 is fixed to a bell mouth 21 using a plurality of supporting plates 33, and makes up one body with the bell mouth 21. Cooling water (suction fluid, coolant), which is suction flow existing in an upper portion of the RPV 1, is mixed with feed water supplied from the feed water pipe 28 to the RPV 1, and descends in the downcomer 6. This cooling water is sucked into the recirculation pipe 7 by operation of the recirculation pump 8, and pressurized by the recirculation pump 8. This pressurized cooling water is called a driving flow (a driving fluid) 30 for descriptive purposes. The driving flow 30 flows through the recirculation pipe 7, the raiser pipe 9, the branching pipe 60, and the elbow pipe 10, and reaches the nozzle apparatus 12 of the jet pump 11 to be ejected from the nozzle apparatus 12. The cooling water 32, which is a suction flow around the nozzle apparatus 12 (see FIG. 3), is sucked into a throat 22 from the bell mouth 21 due to the working of a jet flow 31 of the driving flow 30 (see FIG. 3). The cooling water 32 descends with the driving flow 30 in the throat 22, and discharged from a lower end of a diffuser 25. The cooling water discharged from the diffuser 25 (including the suction flow 32 and the driving flow 30) is called cooling water 34 for descriptive purposes. The cooling water 34 passes through a lower plenum 29 and is supplied to the core 2. The cooling water 34 is heated while passing the core 2 and becomes a two-phase flow including water and steam. The steam separator 4 separates the gas-liquid two-phase flow into steam and water. The steam dryer 5 removes further moisture from the separated steam, and the steam from which the moisture is removed is exhausted to the main steam pipe 39. This steam is introduced to a steam turbine (not shown) and turns the steam turbine. A power generator (not shown) coupled to the stream turbine rotates to generate power. The steam exhausted from the steam turbine becomes water through condensation in a condenser (not shown). This condensed water is supplied into the RPV 1 as feed water through the feed water pipe 28. The water separated by the separator 4 and the dryer 5 descends and reaches the downcomer 6 as cooling water. The jet pump 11 of the present embodiment, which has the nozzle apparatus 12, the bell mouth 21, the throat 22, and the diffuser 25 as its main components, can supply more cooling water 34 to the core with less driving flow 30 by sucking the cooling water around the nozzle apparatus 12 in the downcomer 6. When the kinetic energy of the driving flow 30 given by the recirculation pump 8 effectively acts on the cooling water 32, more cooling water 32 is sucked into the jet pump 11 and the flow rate of the cooling water 34 is increased more. The jet pump 11 reduces static pressure in the throat 22 by ejecting the driving flow 30 (the jet flow 31) at high speed from the nozzle apparatus 12 into the throat 22. This makes the throat 22 suck in the cooling water 32, and allows the necessary core flow rate to be obtained with a small amount of power. The diffuser 25 has a flow passage cross-sectional area which gradually increases toward the downstream direction within a degree that prevents detachment of cooling water flow. This diffuser 25 changes the kinetic energy of the cooling water into pressure. In the diffuser 25, the pressure of the suction flow 32 is raised higher than the pressure at the position where the suction flow is sucked into the bell mouth 21. A flow passage cross-sectional area of the bell mouth 21 increases toward the upstream direction. The bell mouth 21, the throat 22, and the diffuser 25 are disposed in this order from the upper position to the lower position. A jet pump body comprises the bell mouth 21, the throat 22, and the diffuser 25. The nozzle apparatus 12 is disposed above the bell mouth 21. A structure of a slip joint 26 in the jet pump 11 of the present embodiment is described with reference to FIG. 2. This slip joint 26 has, in a lower end portion (a downstream end portion) of the throat 22, a flow passage reduction portion 23 whose flow passage cross-sectional area gradually diminishes toward a lower end of the throat 22. An inner diameter D6 of a downstream end (the lower end) of the flow passage reduction portion 23 is smaller than an inner diameter D5 of an upstream end (an upper end) of the flow passage reduction portion 23. Part of this flow passage reduction portion 23 is inserted into an upper end portion (an upstream end portion) of the diffuser 25. The flow passage reduction portion 23 has a thick-wall portion 24 on the outer surface. Formation of this thick-wall portion 24 reduces the width of a gap 27 in the radial direction of the throat 22, which gap is formed between the flow passage reduction portion 23 and the diffuser 25. A detailed structure of the nozzle apparatus 12 in the jet pump 11 is described below with reference to FIGS. 3, 5, and 6. The nozzle apparatus 12 has a nozzle base (a nozzle base member) 13 and six nozzles 14. The nozzle base 13 of the nozzle apparatus 12 is fixed to the bell mouth 21 by using the supporting plates 33 to make up one body, and connected to the elbow pipe 10. The nozzle apparatus 12 is disposed above the bell mouth 21. The nozzle base 13 has a protrusion 36 protruding downward, in the center of the nozzle apparatus. The six nozzles 14 are fixed to the nozzle base 13 in an annular arrangement, disposed around the protrusion 36. These nozzles 14 extend toward the bell mouth 21 from the nozzle base 13. A detailed structure of the six nozzles 14 provided to the nozzle apparatus 12 is described with reference to FIG. 6. In the nozzle 14, when the inner diameters, that is, the passage diameters of a jet passage 35 formed inside the nozzle 14, are sequentially defined as D1, D2, and D3 from the upstream end to the downstream end of the nozzle 14, these inner diameters have a relationship which is D1>D2>D3. In the nozzle apparatus 12, the nozzle 14 has a nozzle straight-tube portion 15, a nozzle narrowing portion 16, a nozzle straight-tube portion 17, a nozzle narrowing portion 18, and a nozzle lower end portion 19. The nozzle straight-tube portion 15 positioned in an uppermost position has a uniform inner diameter of D1. In the nozzle narrowing portion 16, which is the first stage of narrowing, connected to a downstream end of the nozzle straight-tube portion 15, a flow passage cross-sectional area in the narrowing portion 16 decreases toward a lower end of the nozzle 14, an inner diameter at an upper end is D1, the inner diameter at a lower end is D2, and the length is L1. The nozzle straight-tube portion 17 connected to the downstream end of the nozzle narrowing portion 16 has a uniform inner diameter of D2. In the nozzle narrowing portion 18, which is the second stage of narrowing, connected to a downstream end of the nozzle straight-tube portion 17, a flow passage cross-sectional area in the narrowing portion 18 decreases toward the lower end of the nozzle 14, an inner diameter at an upper end is D2, the inner diameter at a lower end is D3, and the length is L2. The nozzle lower end portion 19 located in a lowest position of the nozzle 14, connected to the lower end of the nozzle narrowing portion 18 has an inner diameter of D3 and forms an ejection outlet 20 in the end portion. Unlike the nozzle in Japanese Patent Laid-open No. Sho 59(1984)-188100, in which a nozzle narrowing portion is formed only in one place in its end portion, the nozzle 14 narrows the jet passage 35 in two places in the nozzle narrowing portions 16 and 18. A narrowing angle θ1 of the nozzle narrowing portion 16 and a narrowing angle θ2 of the nozzle narrowing portion 18 can be calculated by the following Equation (1) and Equation (2) respectively.θ1=tan−1((D1−D2)/2/L1) (1)θ2=tan−1((D2−D3)/2/L2) (2) The narrowing angle θ2 of the nozzle narrowing portion 18 near the ejection outlet 20 is larger than the narrowing angle θ1 of the nozzle narrowing portion 16 (θ2>θ1). The nozzle straight-tube portion 15 having a larger flow passage cross-sectional area is disposed upstream from the nozzle narrowing portion 16, and the nozzle straight-tube portion 17 having a smaller flow passage cross-sectional area is disposed downstream from the nozzle narrowing portion 16 respectively. The nozzle lower end portion 19, which is a straight tube having an inner diameter of D3 and the ejection outlet 20 in its end, is preferably disposed at an outlet portion of the nozzle 14, that is, the lower end portion of the nozzle 14. However, in order to improve the flow speed of the jet flow 31 ejected from the ejection outlet 20, a nozzle narrowing portion having a flow passage cross-sectional area which gradually decreases toward the downstream end may be used in place of the nozzle lower end portion 19 being the straight-tube. When the nozzle narrowing portion having a flow passage cross-sectional area which gradually decreases toward the downstream end is used as the nozzle lower end portion 19, it is preferable to reduce the narrowing angle θ of the nozzle narrowing portion 18 of this nozzle to approximately less than 2 degrees in order to keep the spreading of the jet flow 31 from the ejection outlet 20 of the nozzle lower end portion 19, within a desirable range. The driving flow 30 discharged from the recirculation pump 8 during the operation of the boiling water reactor is introduced through the raiser pipe 9 and the elbow pipe 10 and supplied into the nozzle base 13 of the nozzle apparatus 12. This driving flow 30 is introduced to the jet passage 35 of each nozzle 14. A flow passage cross-sectional area of the jet passage 35 varies according to the inner diameters of the nozzle straight-tube portion 15, the nozzle narrowing portion 16, the nozzle straight-tube portion 17, the nozzle narrowing portion 18, and the nozzle lower end portion 19 disposed from the upper position to the lower position. The driving flow 30 flowing into the jet passage 35 flows through the nozzle straight-tube portion 15, the nozzle narrowing portion 16, the nozzle straight-tube portion 17, and the nozzle narrowing portion 18, and reaches the nozzle lower end portion 19. The driving flow 30 descends in the jet passage 35 gradually gains speed in the nozzle narrowing portion 16, and gains speed even faster in the nozzle narrowing portion 18 than in the nozzle narrowing portion 16. The accelerated driving flow 30 is ejected from the ejection outlet 20 into the throat 22. In the nozzle narrowing portion 18, a velocity component toward the central axis of the nozzle 14 is given to the driving flow 30. However, since a fluid has a characteristic to flow along a wall surface, the jet flow 31 ejected from the ejection outlet 20 formed at the lower end of the nozzle lower end portion 19 has a diameter of D3. Since the larger the narrowing angle θ2 of the nozzle narrowing portion 18, the more the momentum flows toward the central axis of the nozzle, the spreading of the jet flow 31 ejected from the ejection outlet 20 can be suppressed. As a consequence, and the diameter D4 of the jet flow 31, which is a distance L3 away from the ejection outlet 20 in the downstream direction, can be small within a desirable range. The diameter D4 of the jet flow 31 is a width of the jet flow 31. The smaller the diameter D4 of the jet flow 31, the faster the speed of this jet flow. When the jet flow 31 is ejected from the nozzle 14 into the throat 22 while the spreading of the jet flow 31 is suppressed and its speed maintained, the static pressure inside the throat 22 is reduced, making more suction flow 32 around the nozzle apparatus 12 in the downcomer 6 to be sucked into the bell mouth 21. Assume that no nozzle lower end portion 19 is disposed downstream from the nozzle narrowing portion 18. In this case, a diameter of the jet flow 31 keeps decreasing even after being ejected because of the momentum of the driving flow 30 toward the central axis of the nozzle 14, given in the nozzle narrowing portion 18. That is, since no straight-tube portion of the nozzle lower end portion 19 is provided, the jet flow 31 ejected from the ejection outlet 20 formed in the lower end of the nozzle 14 is affected by the nozzle narrowing portion 18. This makes the diameter D4 of the jet flow 31 at the distance L3 away from the ejection outlet 20 in the downstream direction, smaller than the inner diameter D3 of the ejection outlet 20. Thus, the jet speed is raised and the acceleration loss is increased, reducing the flow rate of the driving flow 30. For this reason, the nozzle lower end portion 19 being the straight-tube portion is installed in the downstream side of the nozzle narrowing portion 18 to keep the diameter of the jet flow 31 ejected from the ejection outlet 20 to be no smaller than the inner diameter D3 of the nozzle lower end portion 19 being the straight-tube portion. The installation of the nozzle lower end portion 19 prevents the reduction in the flow rate of the driving flow 30 caused by the increase in the acceleration loss. In addition, the nozzle narrowing portions are provided to the nozzle 14 in two or more locations to reduce the pressure loss in the nozzle 14 as well as to widen the flow passage for the suction flow 32, formed between the nozzles 14. Next, the following case is considered where the inner diameter of the ejection outlet 20 is fixed to D3, the nozzle narrowing portion 16 is made straight, each inner diameter of the nozzle straight-tube portion 15 and the nozzle narrowing portion 16, which is now a straight tube, is set to D2, and a nozzle narrowing portion formed in the nozzle 14 is only in one place in the nozzle narrowing portion 18. When the length L2 of the nozzle narrowing portion 18 is unchanged, the flow passage cross-sectional areas of the nozzle straight-tube portion 15 and the nozzle narrowing portion 16, which is now straight, become smaller, increasing the flow speed of the driving flow 30 flowing inside. Consequently, a loss in friction is increased and the flow rate of the driving flow 30 is reduced. When the length L2 of the nozzle narrowing portion 18 is extended to enlarge the flow passage cross-sectional area of the nozzle narrowing portion 18 in the upstream side, the outer diameter of the nozzle 14 becomes larger and a flow passage cross-sectional area of the suction flow 32 formed among the plurality of nozzles 14 becomes smaller, reducing the suction amount of the suction flow 32 into the bell mouth 21. Therefore, in the present embodiment that two or more nozzle narrowing portions are provided to the nozzle 14, a flow passage cross-sectional area of the jet passage 35 in the nozzle 14 becomes smaller toward the ejection outlet 20, and the flow speed of the driving flow 30 flowing in the jet passage 35 is increased. Because of this, the area where the loss in friction is increased in the jet passage 35 can be reduced. In addition, since the outer diameter of the nozzle 14 can be made smaller below the nozzle narrowing portion 16, a space 37 (see FIG. 5) formed among the nozzles 14 can be larger, and the flow rate of the suction flow 32 sucked into a region 38 (see FIG. 3) inside the six nozzles 14 can be increased. As a result, the flow rate of the suction flow 32 sucked into the throat 21 is increased. As described above, the driving flow 30 flowing into the jet passage 35 is accelerated in the jet passage 35 by the nozzle narrowing portions 16 and 18, and ejected from the ejection outlet 20 into the throat 22 as the jet flow 31. In the present embodiment, the spreading of the jet flow 31 is kept small so that the speed of the jet flow 31 reached inside the throat 22 is higher, reducing the static pressure inside the throat 22. As a result, more suction flow 32 can be sucked into the throat 22. The present embodiment provides the nozzle 14 having two nozzle narrowing portions 16 and 18 so that the flow rate of the suction flow 32 sucked into the throat 22 can be increased, by the above-described working of the nozzle 14, more than the conventional jet pump disclosed in Japanese Patent Laid-open No. Sho 59(1984)-188100 which provides five nozzles, each having one stage of a narrowing portion and a straight-tube portion. For this reason, the flow rate of the cooling water 34 discharged from the jet pump 11 is increased, and the efficiency of the jet pump 11 in a high-M ratio range can be improved more than that of the conventional jet pump. An example of a change in the differential pressure between the inside of the jet pump and the downcomer 6 in the axial direction of the jet pump from the inlet of the throat to the outlet of the diffuser is shown in FIG. 7. In FIG. 7, the broken line shows a characteristic of a conventional jet pump having five nozzles, which has been used in a boiling water reactor of a million kW class. As shown here, the high-speed ejection of a driving flow from the nozzle causes the static pressure in the throat to be lower than the static pressure in the downcomer 6, making the differential pressure between the inside and the outside of the throat inlet portion negative. The differential pressure between the inside of the jet pump and the downcomer 6 becomes positive at a position of a slip joint, and a magnitude of this positive pressure increases toward the diffuser outlet. In the conventional jet pump, in the lower portion of the throat, the static pressure in the throat is recovered by gradually increasing the flow passage cross-sectional area toward the downstream end of the throat. When the static pressure in the jet pump at the position of the slip joint is larger than the static pressure in the downcomer 6 at the same location, cooling water starts to leak from the inside of the jet pump to the downcomer 6 through a gap in the slip joint. When the amount of this leakage flow is excessive, the jet pump may vibrate undesirably. In the slip joint 26 of the jet pump 11 of the present embodiment, as described above, the flow passage reduction portion 23 formed in the downstream end portion of the throat 22 is inserted into the upstream end portion of the diffuser 25 so that the flow speed of the cooling water flowing into the diffuser 25 from the flow passage reduction portion 23 is increased, reducing the static pressure in the diffuser 25 in the vicinity of the downstream end of the flow passage reduction portion 23. This reduces the difference between the static pressure in the jet pump 11, that is, the static pressure in the diffuser 25, and the static pressure in the downcomer 6 at the installation position of the slip joint 26. By using the method that can reduce the difference between these static pressures, the amount of the cooling water leaking to the downcomer 6 through the gap 27 in the slip joint 26 can be reduced more surely than by using the method such as in Japanese Examined Patent Application Publication Sho 59(1984)-48360 which provides a labyrinth seal whose effect in reducing the leakage flow is limited by an available range of fabrication. Consequently, in the present embodiment, the vibration of the jet pump 11 can be controlled. The solid line in FIG. 7 shows a change in the differential pressure between the inside of the jet pump 11 and the downcomer 6, when the jet pump 11 in the present embodiment is used, in which jet pump 11, the inner diameter of the downstream end of the throat 22 is made, by forming the flow passage reduction portion 23, 6% smaller than the inner diameter of the downstream end of the throat in the conventional jet pump having no flow passage reduction portion 23. In the present embodiment, the static pressure starts to decrease at the starting point of the flow passage reduction portion 23, and the differential pressure between the inside of the jet pump 11 and the downcomer 6 at the position of the slip joint 26 drops to about a half of that in the conventional example shown in the broken line. After that, the velocity energy of the cooling water is changed to pressure as the flow passage cross-sectional area in the diffuser 25 is increased, recovering the pressure in the diffuser 25. The drop in the differential pressure between the inside of the jet pump 11 and the downcomer 6 at the position of the slip joint 26 reduces the vibration of the jet pump 11 as described above. However, the present embodiment increases a pressure loss more than the conventional jet pump because of the formation of the flow passage reduction portion 23. As a result, in the present embodiment shown in the solid line, the pressure at the outlet of the diffuser 25 is lower than that in the conventional example shown in the broken line (see FIG. 7). This reduces the flow rate of the cooling water 34 supplied to the core 2 from the jet pump. In other words, the formation of the flow passage reduction portion 23 reduces the efficiency of the jet pump. The jet pump 11 of the present embodiment, as described above, tries to improve the efficiency of the jet pump by installing the nozzle apparatus 12 having six nozzles 14 with two stages of nozzle narrowing portions. In the jet pump 11, the reduction in the jet pump efficiency due to the formation of the flow passage reduction portion 23 can be compensated by part of the improvement in the jet pump efficiency achieved by using the nozzle apparatus 12. Thus, the jet pump 11 can prevent the vibration of the jet pump and at the same time, can improve the efficiency of the jet pump more than the conventional jet pump. The improvement in the efficiency of the jet pump of the present embodiment is explained in detail with reference to FIG. 8. In FIG. 8, the broken line shows the efficiency of the conventional jet pump (the conventional jet pump having the characteristic shown by the broken line in FIG. 7) having a nozzle apparatus with five nozzles. In this conventional jet pump, a flow passage cross-sectional area of the downstream end of the throat is set to a conventional ratio of 100%, and each nozzle has one stage of narrowing portion as in the jet pump disclosed in Japanese Patent Laid-open No. Sho 59(1984)-188100. The alternate long and short dash line in FIG. 8 shows the efficiency of a jet pump of a comparative example, in which the throat in the conventional jet pump having the characteristic shown in the broken line is replaced with a throat having the same flow passage reduction portion 23 as in the present embodiment, in the lower end portion. In the jet pump of the comparative example, a flow passage cross-sectional area of the downstream end of the flow passage reduction portion 23 is 90% of a flow passage cross-sectional area of the corresponding position in the conventional jet pump having the characteristic shown in the broken line. For this jet pump, since the pressure loss is increased by forming the flow passage reduction portion 23 in the throat, the efficiency of the jet pump is lower than that shown in the broken line. The efficiency of the conventional jet pump having the flow passage reduction portion in the throat is reduced by approximately 0.7%. In FIG. 8, the solid line shows the jet pump efficiency of the jet pump 11 of the present embodiment. In the jet pump 11, a flow passage cross-sectional area of the downstream end of the flow passage reduction portion 23 in the throat 22 is also 90%. In the jet pump 11, the reduction in the jet pump efficiency caused by the formation of the flow passage reduction portion 23 in the throat 22 is covered by the increase in the jet pump efficiency achieved by using the nozzle apparatus 12. As a result, the jet pump efficiency is improved more than the jet pump efficiency of the jet pump of the conventional example shown in the broken line. In the present embodiment, the efficiency of the jet pump is improved by approximately 3% more at the peak compared to that of the conventional jet pump without the flow passage reduction portion in the throat. In the jet pump 11 of the present embodiment, the number of the nozzles 14 is increased to six. By using two stages of the nozzle narrowing portions 16 and 18, the spreading of the jet flow 31 ejected from the ejection outlet 20 can be kept small, suppressing the reduction in the speed of the jet flow 31 that has reached the inlet of the throat 22 as well as the decrease in the suction area for the suction flow 32 in the throat 22. This allows more suction flow 32 to be sucked into the throat 22 at the same ejecting speed of the jet flow 31. In addition, in the present embodiment, the total flow passage cross-sectional area of the ejection outlets 20 of the six nozzles 14 is made the same as that of the conventional five nozzles, while making the total length of wetted perimeter of the six nozzles 14 approximately 9% more than that of the conventional five nozzles. This increases the contact area between the suction flow 32 and the jet flow 31 of the driving flow 30 ejected from the ejection outlet 20, making both fluids to be mixed faster, which reduces a loss during the mixing. The jet pump 11 of the present embodiment can improve the jet pump efficiency compared to the conventional jet pump disclosed in Japanese Patent Laid-open No. Sho 59(1984)-188100 which provides five nozzles, each having one stage of a narrowing portion and a straight-tube portion. In the present embodiment, since the narrowing angle θ2 of the nozzle narrowing portion 18 is made larger than the narrowing angle θ1 of the nozzle narrowing portion 16, the spread of the jet flow 31 is suppressed and which prevents the reduction in the speed of the driving flow 30 at the inlet of the throat 22 is also suppressed. At the same time, since the nozzle lower end portion 19 forming the ejection outlet 20 is provided, it can be prevented to accelerate excessively the driving flow 30 by the narrowing portion and to increase the pressure loss in the nozzle 14. Since the speed of the driving flow 30 in the throat 22 is not much slower than the speed at the ejection outlet 20, the static pressure in the throat 22 is reduced and the suction amount of the suction flow 32 into the throat 22 is increased. Consequently, the M ratio and the efficiency of the jet pump can be improved. In a boiling water reactor, a rotational speed of the recirculation pump 8 is controlled to adjust a flow rate of cooling water supplied to the core 2 (a core flow rate). The improvement in the M ratio and the jet pump efficiency allows the core flow rate to be increased using less power from the recirculation pump. Thus, power consumption for driving the recirculation pump 8 can be reduced. In addition, when a power upgrade of a reactor in the U.S. is to be implemented, the core flow rate can be further increased without increasing the capacity of the recirculation pump 8 by employing, for the existing reactor, the jet pump 11 of the present embodiment which can increase the M ratio and the jet pump efficiency. For this reason, the power upgrade of the boiling water reactor can be easily achieved. A jet pump according to embodiment 2, which is another embodiment of the present invention, is described below. The jet pump is also applied to a boiling water reactor. A jet pump 11A of the present embodiment has a structure in which the nozzle apparatus 12 in the jet pump 11 of the embodiment 1 is replaced with a nozzle apparatus 12A. Other components of the jet pump 11A are the same as the jet pump 11. The nozzle apparatus 12A is explained below with reference to FIGS. 9 and 10. In the jet pump 11A, minimizing the loss in pressure and making the most of the suction power induced by a driving flow are both important to increase the M ratio and the N ratio and to raise the efficiency of the jet pump. The jet pump 11A of the present embodiment has an inner cooling water suction passage 50 in and through the nozzle apparatus 12A in the axial direction. The inner cooling water suction passage 50 has, in its upper end, an opening 51 which communicates with the downcomer 6. Furthermore, in the jet pump 11A, the inner cooling water suction passage 50 extends upward inside the elbow pipe 10, and the opening 51 is formed on the outer surface of the elbow pipe 10 at a position lower than a top point TP of the elbow pipe 10. The nozzle apparatus 12A, as shown in FIG. 9, has a nozzle portion 40 and a nozzle header portion 46. The nozzle header portion 46 has an outer cylinder member 47 and an inner cylinder member 48 disposed inside the outer cylinder member 47. An annular header portion 49 is formed between the outer cylinder member 47 and the inner cylinder member 48, both of which are disposed in a concentric manner. The nozzle portion 40 is disposed below the nozzle header portion 46, and fixed to a lower end portion of the nozzle header portion 46. The nozzle portion 40 has an outer cylinder member 41, an inner cylinder member 42, an outer funnel member 43, and an inner funnel member 44. The outer cylinder member 41 surrounds the inner cylinder member 42, and the outer cylinder member 41 and the inner cylinder member 42 are concentrically disposed. The outer funnel member 43 surrounds the inner funnel member 44, and the outer funnel member 43 and the inner funnel member 44 are concentrically disposed. The outer funnel member 43 and the inner funnel member 44 each have a cross-sectional area that decreases downward. The outer funnel member 43 is fixed to an upper end of the outer cylinder member 41, and the inner funnel member 44 is fixed to an upper end of the inner cylinder member 42. The outer funnel member 43 is attached to a lower end of the outer cylinder member 47. The inner funnel member 44 is attached to a lower end of the inner cylinder member 48. An annular ejection outlet 20A is formed between the outer cylinder member 41 and the inner cylinder member 42. An outlet end 53 of the elbow pipe 10 is fixed to the nozzle header portion 46, that is, an upper end of the outer cylinder member 47. An inlet end 52 of the elbow pipe 10 is placed on an upper end of the branching pipe 60. The elbow pipe 10 and the branching pipe 60 are detachably coupled with a fixture. The center of the outlet end 53 of the elbow pipe 10 matches an axis of the nozzle header portion 46, that is, the outer cylinder member 47. The nozzle portion 40, the nozzle header portion 46, and the elbow pipe 10 are joined into one body by welding. The inner cylinder member 48 is inserted into the elbow pipe 10 through the outlet end 53, and extends upward. The opening 51 located in the upper end portion of the inner cylinder member 48 is formed on the outer surface of the elbow pipe 10 and communicates with the downcomer 6. The upper end of the inner cylinder member 48 is welded to the elbow pipe 10. A joint (a fixed position) 57 which is the highest position in a joint portion (a fixed portion) between the inner cylinder member 48 and the elbow pipe 10 is disposed lower than the top point TP which is the highest position on the outer surface of the elbow pipe 10. A flow-adjusting plate (a flow-adjusting member) 54 having the same curvature as the elbow pipe 10 is installed inside the elbow pipe 10, and disposed from the inlet end 52 of the elbow pipe 10 to the inner cylinder member 48 along the axis of the elbow pipe 10. The flow-adjusting plate 54 is disposed upstream from the inner cylinder member 48. An upper passage 55 and a lower passage 56 that are separated into the top and the bottom, are formed in the elbow pipe 10 by the installation of the flow-adjusting plate 54. Since the joint 57 is located lower than the top point TP, the upper flow passage 55 and the lower passage 56 in the elbow pipe 10 extending toward the outlet end 53 are formed diagonally to the axis of the inner cylinder member 48. In other words, the upper passage 55 and the lower passage 56 are formed so that the driving flows in the flow passages flowing toward the outlet end 53, hitting the inner cylinder member 48 diagonally in relation to the axial direction of the inner cylinder member 48. The inner cooling water suction passage 50 communicating with the downcomer 6 through the opening 51 is formed inside the joined inner cylinder member 48, inner funnel member 44, and inner cylinder member 42. The joined inner cylinder member 48, inner funnel member 44, and inner cylinder member 42 are a first pipe member. The inner cooling water suction passage 50 has a flow passage cross-sectional area which gradually decreases downward in the inner funnel member 44, and its lower end opens toward the bell mouth 21. An annular passage 45 formed between the outer funnel member 43 and the inner funnel member 44, communicating with the annular header portion (an annular passage) 49 and the annular ejection outlet 20A, has a flow passage cross-sectional area which gradually decreases downward. The driving flow pressurized by the recirculation pump 8 during the operation of the boiling water reactor reaches the raiser pipe 9 and is introduced into the annular header portion 49 through the elbow pipe 10. The flow-adjusting plate 54 disposed in the elbow pipe 10 reduces the pressure loss in the elbow pipe 10. Part of the driving flow flowing in each of the upper passage 55 and the lower passage 56 in the elbow pipe 10 toward the outlet end 53 hits the outer surface of the inner cylinder member 48 diagonally in relation to the axial direction of the first pipe member (the inner cylinder member 48 in particular). The driving flow introduced into the annular header portion 49 flows through the annular passage 45 and is ejected at high speed into the bell mouth 21 from the annular ejection outlet 20A. The cross-sectional area of the jet flow of the driving flow ejected from the annular ejection outlet 20A is annular. The high-speed supplying of the jet flow of the driving flow into the throat 22 reduces the static pressure in the throat 22, making the cooling water around the nozzle apparatus 12A in the downcomer 6 to be sucked into the bell mouth 21. There are two patterns for the cooling water being the suction flow around the nozzle apparatus 12A to be sucked into the bell mouth 21 due to the reduction in the static pressure in the throat 22. The first pattern is that the cooling water above the elbow pipe 10 flows into the inner cooling water suction passage 50 from the opening 51, and reaches the bell mouth 21 through the inner cooling water suction passage 50. In this pattern, the cooling water sucked through the inner cooling water suction passage 50 flows into the inside of the annular jet flow ejected from the annular ejection outlet 20A. The second pattern is that the cooling water in the downcomer 6 passes through an outer cooling water suction passage 58 formed between the nozzle portion 40 and the bell mouth 21, and reaches the bell mouth 21 at the outside of the annular jet flow. The driving flow ejected from the annular ejection outlet 20A and the cooling water (the suction flow) sucked into the bell mouth 21 by the working of the driving flow are mixed in the throat 22 by exchanging their momentum, and introduced to the diffuser 25 located below the throat 22. The cooling water 34 discharged from the diffuser 25 is introduced to the core 2 through the lower plenum 29. In the present embodiment, since the joint portion 57 is positioned lower than the top point TP, the upper passage 55 and the lower passage 565 in the elbow pipe 10 are formed toward the outlet end 53, diagonally to the inner cylinder member 48 forming the inner cooling water suction passage 50 in the axial direction of the inner cylinder member 48. For this reason, the pressure loss in the elbow pipe 10 where the inner cylinder member 48 exists is reduced, and the flow speed of the cooling water ejected from the annular ejection outlet 20A is increased. The reduction amount of the static pressure in the throat 22 is increased, increasing the flow rate of the cooling water sucked into the bell mouth 21 through the inner cooling water suction passage 50 and the outer cooling water suction passage 58. This increase in the flow rate of the cooling water improves the efficiency of the jet pump 11A. This improvement in the efficiency of the jet pump 11A is explained. FIG. 11 shows a relationship between the M ratio and the jet pump efficiency of a jet pump having the nozzle apparatus 12A with no flow passage reduction portion in the throat, and that of a jet pump of a comparative example. In FIG. 11, the solid line shows a characteristic of the jet pump having the nozzle apparatus 12A with no flow passage reduction portion in the throat, and the broken line shows a characteristic of the comparative jet pump. The jet pump of the comparative example uses the nozzle apparatus shown in FIG. 3 of Japanese Patent Laid-open No. 2001-90700 as a nozzle for the jet pump in a BWR, disclosed in U.S. Pat. No. 3,625,820. While in the comparative example, a pressurized driving flow hits an inner cylinder of the nozzle apparatus at a right angle, in the jet pump having the nozzle apparatus 12A with no flow passage reduction portion in the throat, a driving flow flowing through a cooling water passage in the elbow pipe 10 hits the inner cylinder member 48 diagonally as described above. Because of such a difference in the driving flows, the pressure loss of the jet pump having the nozzle apparatus 12A with no flow passage reduction portion in the throat is less than that of the comparative example. Consequently, in the jet pump having the nozzle apparatus 12A with no flow passage reduction portion in the throat, the efficiency of the jet pump is increased by more than that of the comparative example for the amount of the reduced pressure loss in the nozzle. Since the jet pump 11A of the present embodiment has the flow passage reduction portion 23 in the lower end portion of the throat 22 in the same manner as the jet pump 11 of the embodiment 1, in the jet pump 11A, the flow passage reduction portion 23 causes the efficiency of the jet pump to decrease. However, this reduction in the efficiency can be compensated for by part of the increase in the efficiency achieved by the nozzle apparatus 12A. From the contribution of the remaining increase in the efficiency achieved by the nozzle apparatus 12A, the jet pump 11A, thus, can improve the efficiency of the jet pump more than that of the comparative example. In the present embodiment, a leakage flow from the gap 27 in the slip joint 26 can be reduced because the flow passage reduction portion 23 is formed in the lower end portion of the throat 22. For this reason, the vibration of the jet pump 11A can be suppressed. In the present embodiment, since the flow-adjusting plate 54 is installed in the elbow pipe 10, the pressure loss in the elbow pipe 10 can be further reduced. The reduction in the pressure loss further increases the efficiency of the jet pump 11A. Since the flow-adjusting plate 54 is disposed upstream from the inner cylinder member 48, separation of the flow and uneven distribution of speed in the elbow pipe 10 are improved, and the pressure loss in the elbow pipe 10 is reduced. Since the cooling water passages (the upper passage 55 and the lower passage 56) formed in the elbow pipe 10 are diagonal to the inner cylinder member 48 as described above, the driving flow flowing in the cooling water passages hits the outer surface of the inner cylinder member 48 diagonally to the axial direction of the inner cylinder member 48. This causes the stress generated at the contact portion between the inner cylinder member 48 and the elbow pipe 10 to be small. Thus, when the nozzle apparatus 12A is applied to a current BWR, it is not necessary to reinforce the joint portion by making the member particularly thick, or to modify the raiser pipe 9 and the fixture. In the present embodiment, Since the inner cooling water suction passage 50 is formed in the nozzle apparatus 12A, the effect of the pressure reduction in the area inside the ejected annular jet flow can be effectively used. This generates the flow of the cooling water reaching into the bell mouth 21 through the inner cooling water suction passage 50. Thus, since cooling water can flow into the bell mouth 21 through each of the inner cooling water suction passage 50 and the outer cooling water suction passage 58, the flow rate of the cooling water flowing into the bell mouth 21 is increased. The inner cooling water suction passage 50 is disposed in the axial direction of the RPV 1, and the opening 51 opens upward, so that the flow power of the cooling water descending in the downcomer 6, supplied to the inner cooling water suction passage 50, can be effectively utilized to increase the suction power of the jet pump 11A. This increases the rate of the cooling water sucked into the throat 22. In addition, since the nozzle portion 40 has the outer funnel member 43 whose outer diameter decreases downward, the nozzle apparatus 12A has a structure that allows the cooling water descending in the downcomer 6 to be easily sucked into the bell mouth 21 through the outer cooling water suction passage 58. This also increases the flow rate of the cooling water flowing into the bell mouth 21, increasing the efficiency of the jet pump 11A. In the boiling water reactor installed with the jet pump 11A, the core flow rate can be further increased without increasing the capacity of the recirculation pump 8 in the same manner as in the embodiment 1. For this reason, a power upgrade of the boiling water reactor can be easily achieved. Furthermore, in the present embodiment, the inverted U-shaped elbow pipe 10 is connected to the nozzle apparatus 12A so that a single raiser pipe 9 disposed in the downcomer 6 can be connected to two jet pumps 11A adjacent to the raiser pipe 9, with the elbow pipes 10 each connected to the nozzle apparatus 12A of each of the two jet pumps 11A. For this reason, a space between the jet pumps 11A can be made equal to the corresponding space in the existing boiling water reactor. A jet pump according to embodiment 3, which is another embodiment of the present invention, is described below. A jet pump 11B of the present embodiment has a structure in which the nozzle apparatus 12 in the jet pump 11 in the embodiment 1 is replaced with a nozzle apparatus 12B. Other components of the jet pump 11B are the same as the jet pump 11. The nozzle apparatus 12B is explained below with reference to FIG. 12. The nozzle apparatus 12B, as shown in FIG. 12, has a nozzle portion 61, a suction passage portion 65, and a nozzle holder 78. The suction passage portion 65 is disposed above the nozzle portion 61, and installed on the upper end of the nozzle portion 61. The nozzle holder 78 is disposed above the suction passage portion 65 and installed on an upper end of the suction passage portion 65. The suction passage portion 65 has a cylinder member (a third tubular member) 66, a flow passage forming member 67, and a passage member 72. The flow passage forming member 67 is disposed inside the cylinder member 66 in the center of the cylinder member 66. Six passage members 72 are disposed radially around the central axis of the cylinder member 66, 60 degrees apart from each other in the circumferential direction (see FIG. 13). The outer end portion of the passage member 72 is welded to the cylinder member 66, and the inner end portion of the passage member 72 is welded to the flow passage forming member 67. Each passage member 72 slopes downward and inward (toward the flow passage forming member 67), and has an oval cross-sectional area (see FIG. 15). An opening 74 is formed in the outer end portion of the passage member 72. An annular driving flow passage 76 is formed between the cylinder member 66 and the flow passage forming member 67. Each passage member 72 is placed across this driving flow passage 76. A suction passage 73 communicating with the downcomer 6 through the opening 74 is formed in each passage member 72. The inner surfaces of each passage member 72 at the inlet and the outlet of each suction passage 73 are curved surfaces. The total flow passage cross-sectional area of all the suction passages 73 is larger than the cross-sectional area of a decompression chamber (an inner region) 77 at the lower end of the nozzle portion 61. Each passage member 72 is provided with a streamline member 75 (see FIG. 15) having a cross-sectional area that decreases toward the upper course to reduce the pressure loss in the driving flow passage 76. The flow passage forming member 67 has a circular cross section at any point in the axial direction, and includes an upper region 68, a center region 69, and a lower region 70, each having a different cross-sectional area in the axial direction. The upper region 68 is cylindrical, and the center region 69 connected to a lower end of the upper region 68 is a truncated cone. The lower region 70 connected to a lower end of the center region 69 is an inverted cone. The center region 69 has a cross-sectional area that increases downward. This reduces a cross-sectional area of the driving flow passage 76 downward between the cylinder member 66 and the outer surface of the center region 69. The lower region 70 has a cross-sectional area that decreases downward, and has a curved surface 71 whose outer surface comes together in the axial direction. The nozzle portion 61 has an outer cylinder member (a first tubular member) 62 and an inner cylinder member (a second tubular member) 63 disposed in the outer cylinder member 62. The outer cylinder member 62 is welded to a lower end of the cylinder member 66, and an upper end of the inner cylinder member 63 is welded to the flow passage forming member 67. The outer cylinder member 62 has an outer diameter that is smaller in the lower end than in the upper end, and slopes inward. The inner cylinder member 63 has an outer diameter that becomes the largest in a center portion and smaller in the upper and a lower ends. An inner end portion of the passage member 72 is welded to the upper portion rather than the center portion of the inner cylinder member 63. Therefore, the inner cylinder member 63 exists between the adjacent passage members 72 in the circumferential direction of the inner cylinder member 63. An annular jet passage 64 is formed between the outer cylinder member 62 and the inner cylinder member 63. The annular jet passage 64 slopes inward, and has a flow passage cross-sectional area that becomes smaller downward. The jet passage 64 communicates with the driving flow passage 76. The jet passage 64 is also a part of the driving flow passage. An annular ejection outlet 20B is formed at the end of the jet passage 64. The decompression chamber 77 is formed in the inner cylinder member 63, and the suction passage 73 communicates with the decompression chamber 77. The curved surface 71 of the lower region 70 of the flow passage forming member 67 faces the decompression chamber 77. The inner cylinder member 63 separates the driving flow passage 76 and the decompression chamber 77. The nozzle holder 78 has a cylinder member 81, a reinforcing streamline plate 79, and a cone member 80. The cylinder member 81 is fixed to the upper end of the cylinder member 66 of the suction passage portion 65. The cone member 80 has a cross-sectional area that decreases upward, and disposed in the center of the cylinder member 81. Six reinforcing streamline plates (see FIG. 14) 79 are radially disposed around the central axis of the cylinder member 81, 60 degrees apart from each other in the circumferential direction, and disposed in the positions above the passage members 72 (see FIG. 13). The both ends of each reinforcing streamline plate 79 are fixed to the cylinder member 81 and the cone member 80. A lower end portion of the cone member 80 is fitted to the upper end portion of the flow passage forming member 67. An upper end of the cylinder member 81 is connected to the elbow pipe 10. It can be said that when the nozzle portion 61 and the suction passage portion 65 are unified, the outer cylinder member 62 and the cylinder member 66 make up the first tubular member and the inner cylinder member 63 is the second tubular member. Between these first and second tubular members, the driving flow passage including the jet passage 64 is formed. The driving flow 30 pressurized by the recirculation pump 8 during the operation of the boiling water reactor flows into the cylinder member 81 through the elbow pipe 10, and further reach the jet passage 64 through the driving flow passage 76. This driving flow 30 is ejected as a jet flow 31A into the bell mouth 21 from the ejection outlet 20B located at the end of the jet passage 64. The working of the jet flow 31A makes the suction flow 32, which is part of the cooling water around the nozzle apparatus 12B in the downcomer 6, to flow into the bell mouth 21 through the cooling water suction passage 58. This suction flow 32 is introduced into the throat 22 through the space between the bell mouth 21 and the jet flow 31A. Since the jet passage 64 is sloped, the jet flow 31A is ejected diagonally toward the central axis of the throat 22 from the ejection outlet 20B. Consequently, the working of the jet flow 31A makes the pressure in the decompression chamber 77 negative, so that the suction flow 32A, which is part of the cooling water descending in the downcomer 6, flows into the suction passage 73 to reach the decompression chamber 77. This suction flow 32A further flows into a decompression region 82 formed inside the jet flow 31A in the bell mouth 21. The suction flows 32 and 32A and the driving flow 30 flowing into the bell mouth 21 are mixed in the throat 22 and discharged from the diffuser 25 (see FIGS. 1 and 4). These flows, that is, the cooling water 34, discharged from the diffuser 25 is supplied to the core 2. The jet pump 11B in the present embodiment as described above has the following unique structures (a) to (c). (a) The jet passage 64 in the nozzle portion 61 slopes inward. (b) The suction passage 73 slopes inward. (c) A cross section of the passage member 72 forming the suction passage 73 is oval. Various effects obtained by the unique structures (a) to (c) are explained in detail. First of all, various effects obtained by the unique structure (a) are described. The jet passage 64 in the nozzle portion 61 slopes inward. That is, the jet passage 64 slopes inward and downward toward the central axis of the throat 22. As a consequence, the jet flow 31A ejected from the ejection outlet 20B is ejected downward toward the central axis of the throat 22. Such jet flow 31A reduces the volume of the inverted cone-shaped decompression region 82 formed inside the jet flow 31A below the flow passage forming member 67. The reduction in the volume of the decompression region 82 relatively increases the degree of the pressure reduction, increasing the degree of negative pressure in the decompression chamber 77. As a result, a flow rate Qb2 of the suction flow 32A sucked into the bell mouth 21 through the suction passage 73 is increased. In addition, in the present embodiment, since the jet passage 64 in the nozzle portion 61 slopes inward, a distance L4 between the bell mouth 21 and the end of the outer cylinder member 62 of the nozzle portion 61 can be larger. As a result, a distance L5 between the inner surface of the throat 22 and the jet flow 31A is increased, increasing a flow rate Qb1 of the suction flow 32 flowing into the space between the bell mouth 21 and the jet flow 31A through the cooling water suction passage 58. An increase in the flow rate Qb1 of the suction flow 32 and the flow rate Qb2 of the suction flow 32A increases the flow rate of the cooling water 34 discharged from the diffuser 25. That is, the efficiency of the jet pump 11B is further improved. Various effects obtained by the unique structure (b) are described. Since the suction passage 73 slopes inward, the cooling water descending in the downcomer 6 can flow into the suction passage 73 by only slightly changing its flow direction. This makes the suction flow 32A to be easily sucked into the suction passage 73. In addition, since the suction passage 73 slopes inward, the downward flow force (a flow speed of approximately 2 m/s) of the cooling water in the downcomer 6 can be effectively used, allowing the suction flow 32A to be easily sucked into the suction passage 73. These workings further increase the flow rate Qb2 of the suction flow 32A, further increasing the flow rate of the cooling water 34 as well. Various effects obtained by the unique structure (c) are described. Since a cross section of the passage member 72 forming the suction passage 73 is oval, the cross-sectional area of the suction passage 73 can be enlarged. Consequently, the pressure loss in the suction passage 73 can be reduced and the flow rate Qb2 of the suction flow 32A can be increased. In particular, since the passage members 72 are disposed in such a way that their major axes follow the axial direction of the nozzle apparatus 12B and their minor axes follow the circumferential direction of the nozzle apparatus 12B, the pressure loss in the suction flow passage 76 can be reduced and the cross-sectional area of the suction passage 73 can be enlarged. In addition, such an arrangement with respect to the major and minor axes allows the number of the passage members 72 disposed in the circumferential direction of the nozzle apparatus 12B to be increased. Consequently, the total flow passage cross-sectional area of all the suction passages 73 can be enlarged. This greatly contributes to the increase in the flow rate Qb2 of the suction flow 32A. Besides the unique structures (a) to (c), the nozzle apparatus 12B has some other structures that allow the yielding of new effects. These effects are described. In order to reduce the pressure loss in a flow passage for the driving flow 30, the nozzle apparatus 12B adapts some ideas. A structure for reducing the pressure loss, other than the structure in which the cross section of the passage member 72 is oval, is explained. Each passage member 72 forms, in the upstream side, a streamline member 75 having a cross section that decreases toward the upper course (see FIG. 15). The formation of this streamline member 75 reduces turbulence in the driving flow 30 flowing in the driving flow passage 76, reducing the pressure loss in the driving flow passage 76. The reinforcing streamline plate 79 also has a streamline shape whose cross section decreases toward the upper course (see FIG. 14). This structure reduces the pressure loss in the driving flow passage 76. Furthermore, since each reinforcing streamline plate 79 is disposed to the same position above the passage member 72 located downstream in the circumferential direction of the nozzle apparatus 12B, the pressure loss in the driving flow passage 76 is reduced. Since the flow passage cross-sectional area of the jet passage 64 gradually decreases from the upper course to the ejection outlet 20B, the pressure loss in the jet passage 64 is also reduced. The cone member 80 having a cross-sectional area that increases from the upper course to the lower course, is disposed on the upper end of the flow passage forming member 67, so that the driving flow 30 flowing in the elbow pipe 10 can be smoothly introduced to the annular driving flow passage 76. This reduces the pressure loss in the flow passage for the driving flow 30 in the nozzle apparatus 12B. Furthermore, in the present embodiment, the pressure loss in the nozzle apparatus 12B can be further reduced because the nozzle apparatus 12B forms no flow passage such as the one in the nozzle apparatus shown in FIG. 1 of Japanese Patent Laid-open No. 2008-82752, in which the flow passage turns the driving flow at a right angle. The nozzle apparatus 12B employs some ideas for reducing the pressure loss in the flow passage for the suction flow 32A. This reduction in the pressure loss is obtained by forming curved surfaces on the inlet and the outlet of the passage member 72 as described above. Since the total flow passage cross-sectional area of all the suction passages 73 is larger than the cross-sectional area of the decompression chamber 77 at the lower end of the nozzle portion 61, the pressure loss in the flow passage for the suction flow 32A formed in the nozzle apparatus 12B is reduced. Since the cross section of the passage member 72 is oval and this passage member 72 is disposed in such a way that it slopes downward toward the axial direction of the nozzle apparatus 12B, the opening area of the inlet of the suction passage 73 can be enlarged. This also decreases the pressure loss in the suction passage 73. Since the surface of the lower region 70 of the flow passage forming member 67, facing the decompression chamber 77, is the curved surface 71, the driving flow 32A discharged from the suction passage 73 can smoothly change the direction downward along the curved surface 71 in the decompression chamber 77. By forming the curved surface 71 functioning in this way, the pressure loss in the flow passage for the suction flow 32A, formed in the nozzle apparatus 12B, can be reduced as well. The lower region 70 of the flow passage forming member 67 protrudes below an upper end of the outlet side of the passage member 72. Adapting such a shape allows the negative pressure in the decompression chamber 77, which is increased by the unique structure of (a), to effectively act on the suction passage 73, and allows the flow rate Qb2 of the suction flow 32A flowing into the suction passage 72 to be increased. In other words, the lower region 70 prevents the formation of a decompression dead water region in the decompression chamber 77 by the suction flow 32A discharged from the suction passage 73. The lower region 70 is disposed in the area where the decompression dead water region is to be formed in the decompression chamber 77 when no lower region 70 is provided. For this reason, cavitation induced in the decompression dead water region is prevented from occurring, and the flow rate Qb2 of the suction flow 32A can be increased. In the present embodiment, the ejection outlet 20B is annular, making the jet flow 31A ejected from the ejection outlet 20B also annular. Thus, since a vortex generated by the jet flow 31A is evenly distributed in the circumferential direction, a random vortex formation that causes flow-induced vibration is prevented and consequently, the vibration of structures in the boiling water reactor can be prevented. Since the nozzle apparatus 12B has an annular flow passage for the driving flow 30, the ejection outlet 20B, and the suction passages 73 crossing the flow passage for the driving flow 30, for introducing the suction flow 32A, the nozzle apparatus 12B can be made compact. Therefore, by replacing a nozzle in a conventional jet pump to the nozzle apparatus 12B, the jet pump can be quickly and easily converted into the jet pump 11B having a higher nozzle efficiency. A characteristic of the jet pump having the nozzle apparatus 12B with no flow passage reduction portion in the throat is compared with the characteristics of the conventional jet pumps in FIG. 16. In this comparison, the conventional jet pumps are the jet pumps having five nozzles as shown in FIG. 2 of Japanese Patent Laid-open No. Hei 7(1995)-119700 and the jet pumps having the nozzle apparatus provided with a ring header and a cooling water suction passage in the axis as shown in FIG. 1 of Japanese Patent Laid-open No. 2008-82752. In each jet pump in Japanese Patent Laid-open No. Hei 7(1995)-119700 and Japanese Patent Laid-open No. 2008-82752, each ejection outlet is disposed parallel to the axis of the jet pump, facing downward. FIG. 16 shows a change in the jet pump efficiency to the M ratio for the jet pump having the nozzle apparatus 12B with no flow passage reduction portion in the throat and for the above-described jet pumps in the conventional examples. In the jet pump having the nozzle apparatus 12B with no flow passage reduction portion in the throat, as described above, the efficiency increases more than the conventional examples due to the reduction in the pressure loss in the nozzle apparatus 12B, and the increase in the flow rates Qb1 and Qb2 of the suction flows 32 and 32A. When the M ratio is increased for the power upgrade of the reactors, the efficiency of the jet pump having the nozzle apparatus 12B with no flow passage reduction portion in the throat is higher than the others as shown in FIG. 16. Since the jet pump 11B of the present embodiment has the flow passage reduction portion 23 in the lower end portion of the throat 22 in the same manner as the jet pump 11 of the embodiment 1, by the influence of this flow passage reduction portion 23, the efficiency of the jet pump is reduced. However, this reduction in the efficiency can be compensated for by part of the increase in the efficiency achieved by the nozzle apparatus 12B. From the contribution of the remaining increase in the efficiency achieved by the nozzle apparatus 12B, the jet pump 11B, thus, can improve the efficiency of the jet pump more than those of the conventional examples. The jet pump 11B of the present embodiment has the flow passage reduction portion 23 in the lower end portion of the throat 22 so that vibration can be suppressed. The present embodiment can increase the efficiency of the jet pump as well as the flow rate of the cooling water 34 supplied to the core 2. The boiling water reactor having the jet pump 11B of the present embodiment, including the nozzle apparatus 12B, can easily handle a power upgrade which requires a large increase in the core flow rate. By using the nozzle apparatus 12B, a nozzle in a jet pump in an existing boiling water reactor can be quickly replaced. In addition, the vibration of the jet pump can be kept low. A jet pump according to embodiment 4, which is another embodiment of the present invention, is described below. The jet pump of the present embodiment is a jet pump in which a leakage flow from the gap 27 in the slip joint 26 to the downcomer 6 is completely eliminated from the jet pump 11 of the embodiment 1. To completely eliminate the leakage flow from the gap 27, the differential pressure between the inside of the slip joint 26 and the downcomer 6 should be zero. When the water head of a jet pump is H (Pa), the density of the fluid is ρ (kg/m3), and its speed is v (m/s), a static pressure Pi (Pa) of the slip joint 26 is represented in Equation (3) based on the static pressure in the downcomer 6.Pi=H−0.5ρV2 (3) When Pi=0, the differential pressure between the inside of the slip joint 26 and the downcomer 6 becomes zero. The speed v is represented in Equation (4) using a jet pump flow rate Q (m3/s) and the inner diameter D6 of the outlet of the throat 22.v=Q/(πD62/4) (4) From Equation (3) and Equation (4), a value of the inner diameter D6 that makes Pi=0 is as in Equation (5).D6=(8ρQ2/πH)0.25 (5) Therefore, when the inner diameter D6 is within a range of (8ρQ2/πH)0.25≦D6<D5, the differential pressure between the inside of the slip joint 26 and the downcomer 6 can be reduced. A change in the static pressure in the axial direction of the jet pump when D6=(8ρQ2/πH)0.25 in the present embodiment is shown as the alternate long and short dash line in FIG. 7. The differential pressure between the inside of the slip joint 26 and the downcomer 6 becomes zero at the position of the slip joint 26, eliminating the leakage flow from the gap 27 in the slip joint 26. In the present embodiment, each effect achieved in the embodiment 1 can be obtained. The vibration of the jet pump can be reduced more than in the embodiment 1. A jet pump according to embodiment 5, which is another embodiment of the present invention, is described below. A jet pump 11C of the present embodiment has a structure in which the throat 22 in the jet pump 11 of the embodiment 1 is replaced with a throat 22 having a labyrinth seal 85 on the outer surface of a thick-wall portion 24A of the flow passage reduction portion 23 shown in FIG. 17. Other components of the jet pump 11C are the same as the jet pump 11 of the embodiment 1. Since the jet pump 11C is provided with the labyrinth seal 85 on the outer surface of the thick-wall portion 24A of the flow passage reduction portion 23, the resistance of the flow passage of the gap 27 is increased and thus a leakage flow from the inside of the slip joint 26 to the downcomer 6 can be reduced even more than the jet pumps in the embodiments 1 to 3. Consequently, the vibration of the jet pump 11C can be reduced. The jet pump 11C has the nozzle apparatus 12 so that each effect achieved by the jet pump 11 can be obtained. The throat 22 provided with the labyrinth seal 85 on the outer surface of the thick-wall portion 24A of the flow passage reduction portion 23 may be applied to the jet pumps 11A and 11B. The present invention can be applied to a boiling water reactor. 1: reactor pressure vessel, 2: core, 3: core shroud, 6: downcomer, 7: recirculation pipe, 8: recirculation pump, 10: elbow pipe, 11, 11A, 11B, 11C: jet pump, 12, 12A, 12B: nozzle apparatus, 13: nozzle base, 14: nozzle, 15, 17: nozzle straight-tube portion, 16, 18: nozzle narrowing portion, 19: nozzle lower end portion, 20, 20B: ejection outlet, 20A: annular ejection outlet, 21: bell mouth, 22: throat, 23: flow passage reduction portion, 25: diffuser, 26: slip joint, 30: driving flow (driving fluid), 31, 31A: jet flow, 32, 32A: suction flow (suction fluid), 40, 61: nozzle portion, 41: outer cylinder member, 42: inner cylinder member, 43: outer funnel member, 44: inner funnel member, 45: annular passage, 46: nozzle header portion, 47, 62: outer cylinder member, 48, 63: inner cylinder member, 49: annular header portion, 50: inner cooling water suction passage, 54: flow-adjusting plate, 57: joint portion, 64: jet passage, 65: suction passage portion, 66, 81: cylinder member, 67: flow passage forming member, 70: lower region, 71: curved surface, 72: passage member, 73: suction passage, 74: opening, 77: decompression chamber, 78: nozzle holder, 79: reinforcing streamline plate, 80: cone member. |
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042347980 | abstract | A transport and storage receptacle for radioactive waste, capable of shielding the environment from radiation, comprises a vessel shell, bottom and cover. The shell and bottom are cast in one piece from cast iron (especially spherolytic cast iron) or cast steel and the cover is a shielding cover which can be recessed in the shell. The wall of the vessel is formed unitarily with at least one passage which communicates with the bottom of the chamber receiving the waste and terminates in an end wall along the upper face of the receptacle which can be provided with a separate closure for this passage. |
description | The present invention provides an apparatus for insuring dose uniformity for a product, article or material that receives X-ray beam radiation from X-ray tubes. For purpose of description of a preferred embodiment the invention discloses a system or product for irradiating blood contained in a transfusion bags wherein the bags are all irradiated from opposite sides. It should be understood that the invention may be used to irradiate other materials or products and also that a single X-ray tube may be utilized. However, the two tube configuration described herein has been found practical and efficient. The described configuration further uses a single power source for the two X-ray tubes; a separate power source for each X-ray tube is feasible. Referring to FIGS. 1, 2, 3 and 4, the inventive X-ray system 11 comprises a suitably shielded apparatus or machine 12, which may be portable. The machine 12 includes a first X-ray tube 15 which is oriented to provide a beam of X-rays downwardly (indicated by the line 16) within a chamber 19 which is adapted to receive a cannister or container 18 for blood product bags 22. The system includes suitable known radiation security switches, not shown, so that X-ray irradiation can be initiated only when all the irradiation doors have been closed, as is well known. The cannister 18 (see FIG. 4) has an circular shaped interior for receiving transfusion bags indicated generally as 22, and includes a cover or top 21. The cannister 18 is dimensioned and positioned to receive up to three standard blood product transfusion bags 22. In the embodiment shown the cannister is 10 cm deep and has a diameter of 12 cm. Referring to FIGS. 1 and 3, X-ray tube 15 has an output of 160 kV; the X-ray beam output port 23 of tube 15 is designed to provide a relatively wide X-ray beam directed downwardly and of a sufficiently large diameter, i.e., a maximum angle beam, to fully cover the cannister 18 and the included bags 22, as will be discussed. In one embodiment, X-ray tube 15 provides a 45+ degree beam. The output window of the X-ray tube 15 is positioned relatively close, about 1 cm from outer upper (cover or lid 21) surface of cannister 18 to assure that maximum energy is delivered to the bags 22. As is known, the closer an X-ray source is to the object to be irradiated, the higher the energy delivered to the object; that is, the level of the energy delivered to the object is dependent on the distance between the two components. As is also known, the object can be irradiated faster when more energy is delivered to the object. It is of particular importance that the irradiation received by the blood product in bags 22 be uniform. The blood in all bags must be fully irradiated; that is, irradiation energy within a specified range must be provided to the blood for the same period of time to meet Federal regulations. For this purpose of providing an efficient and uniform irradiation of the blood product bags, a second X-ray tube 17 is mounted to provide X-ray irradiation to the opposite end of the cannister 18. The X-ray tube 17 is essentially identical to X-ray tube 15, and mounted in a position to direct its X-ray beam upwardly toward the cannister 18. Tube 17 is positioned approximately the same relative distance from the cannister as is tube 15. Hence, the bags 22 are concurrently irradiated with the same energy from two opposite sides. Importantly, a collar 30 of low Z (atomic number), high density material such as boron carbide, boron, or carbon (graphite) is mounted around the cannister 18 within chamber 19, see FIGS. 2 and 3. As is disclosed in U.S. Pat. No. 6,389,099, it has been found that X-rays are usefully reflected from the aforementioned low Z high density material. As shown in FIG. 2, the irradiation energy from X-ray tube 17 complements the irradiation energy from X-ray tube 15. Since the energy level varies as the beam penetrates the bags of blood; the energy provided changes with the depth or thickness of the blood in bags 22. The energy from tube 15 is maximum at the top surface of cannister 18 and decreases as it penetrates the bags 22, and is effectively at a minimum level at the lower surface of bags 22. Conversely, the radiation energy from X-ray tube 17 is maximum at the lower surface of cannister 18 and decreases to a minimum at the top surface of bags 22. The relation of the irradiation energy at any level or depth of bags 22 is a sum of the energy developed by the two tubes. Further, the collar 30 reflects the X-rays (those X-ray on the outer portions of the beams 16 from tube 15 and beams 20 from tube 17) that impinge on the inner surface of the collar to thereby utilize essentially the entire X-ray beams from both X-ray tubes. The X-ray energies, that is the X-rays from tube 15, the X-rays of tube 15 reflected by collar 30, the X-rays from tube 17, and the X-rays of tube 17 reflected by collar 30 are effectively combined and concentrated on the bags 22 in cannister 18. Further, as described in the aforesaid Patent No. 6,389,099 some of the X-rays which penetrate the product are reflected back from the collar to re-irradiate the product. In practice, it has been found that irradiation of a single blood product bag 22 for about six minutes with the apparatus disclosed in prior art U.S. Pat. No. 6,212,255 cited above complies with Federal regulations. In contrast, in the present invention, and by utilizing the reflector collar and utilizing a maximum angle X-ray beam, as indicted in FIG. 4, three bags can be irradiated in seven minutes and still comply with the same Federal regulations. That is, there is an approximately a three times improvement in throughput over the prior art. FIG. 5, labeled prior art, shows (in simplified form)a useful type of switching power supply or power generator wherein a single source of power 31 is connected through a switching control 33 that provides power for the two X-ray tubes 15 and 17. As can be appreciated from the circuit, in operation the filaments labeled F15 and F17 in FIG. 5 are continually On and the anodes labeled A15 and A17 of tubes 15 and 17, respectively, are alternately turned On and Off. The 160 kV tubes used in one embodiment of the invention are commercially available tubes with known characteristics and are manufactured by various commercial sources. It should, of course, be understood that the invention is not limited to any specific output of the X-ray tubes. While the invention has been particularly shown and described with reference to a particular embodiment thereof it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention. |
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abstract | Apparatuses for reducing or eliminating Type 1 LOCAs in a nuclear reactor vessel. A nuclear reactor including a nuclear reactor core comprising a fissile material, a pressure vessel containing the nuclear reactor core immersed in primary coolant disposed in the pressure vessel, and an isolation valve assembly including, an isolation valve vessel having a single open end with a flange, a spool piece having a first flange secured to a wall of the pressure vessel and a second flange secured to the flange of the isolation valve vessel, a fluid flow line passing through the spool piece to conduct fluid flow into or out of the first flange wherein a portion of the fluid flow line is disposed in the isolation valve vessel, and at least one valve disposed in the isolation valve vessel and operatively connected with the fluid flow line. |
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claims | 1. A beam data processing apparatus that performs calculation processing of a state of a charged particle beam that has been accelerated by an accelerator and has been scanned by a scanning electromagnet in a particle beam therapy system for irradiating a diseased site, the beam data processing apparatus comprising:a plurality of channel data conversion units that perform A/D conversion processing in which each of a plurality of analogue signals, outputted from a position monitor that detects the passing position of the charged particle beam within the position monitor, is converted into a digital signal;an integrated control unit that controls the plurality of channel data conversion units;wherein each of the channel data conversion units includes (i) a plurality of A/D converters that sequentially operate while the charged particle beam remains stationary to irradiate an irradiation spot of the diseased site, as controlled by the integrated control unit, such that one A/D converter begins A/D conversion processing prior to another A/D converter completing A/D conversion processing, (ii) a demultiplexer that distributes the respective analogue signals to the A/D converters at different timings while the charged particle beam remains stationary, and (iii) a multiplexer that switches the respective digital signals processed by the A/D converters at different timings, andwherein said position monitor (i) is located at a downstream position with respect to said scanning electromagnet and (ii) includes a plurality of detection channels therein for detecting the passing position of the charged particle beam at the downstream location after having been scanned by said scanning electromagnet;a position size processing unit that receives the digital signals output from the multiplexer and calculates a beam position, which is the passing position of the charged particle beam within the position monitor, based on voltage information items obtained through processing by the plurality of channel data conversion units; andan abnormality determination processing unit (i) that determines whether or not the beam position within the position monitor is within a tolerance range, based on a desired position of the charged particle beam and a position allowable value, and (ii) that generates a position abnormality signal when determining that the beam position is not within the tolerance range. 2. The beam data processing apparatus according to claim 1, wherein the position size processing unit calculates a beam size of the charged particle beam that passes through the position monitor, based on voltage information items obtained through processing by the plurality of channel data conversion units; and the abnormality determination processing unit determines whether or not the beam size is within a tolerance range, based on a desired beam size of the charged particle beam and a size allowable value, and that generates a size abnormality signal when determining that the beam size is not within the tolerance range. 3. The beam data processing apparatus according to claim 1, wherein each time receiving an inter-spot travel completion signal indicating that setting of a command to the scanning electromagnet that scans the charged particle beam on the desired position has been completed and a proportion dose completion signal indicating that the dose of the charged particle beam at an irradiation spot where the charged particle beam is stationary has become a predetermined proportion of a desired dose, the integrated control unit outputs respective ADC processing starting commands to the different A/D converters so that the A/D conversion processing is started. 4. The beam data processing apparatus according to claim 1, wherein each time receiving an ADC processing starting signal indicating that one of the plurality of A/D converters has started the A/D conversion processing, the integrated control unit switches the transmission paths of the demultiplexer so that the analogue signal is transmitted to another one of the A/D converters that have not started the A/D conversion processing. 5. The beam data processing apparatus according to claim 1, wherein each time receiving an ADC processing ending signal indicating that one of the plurality of A/D converters has completed the A/D conversion processing, the integrated control unit switches the transmission paths of the multiplexer so that data from the A/D converter that is subsequently to end the A/D conversion processing is transmitted to the position size processing unit. 6. A particle beam therapy system comprising:a beam generation apparatus that generates a charged particle beam and accelerates the charged particle beam by means of an accelerator;a beam transport system that transports the charged particle beam accelerated by the accelerator; anda particle beam irradiation apparatus that irradiates the charged particle beam transported by the beam transport system onto an irradiation subject, wherein the particle beam irradiation apparatus includes a scanning electromagnet that scans a charged particle beam to be irradiated onto the irradiation subject and a beam data processing apparatus that applies calculation processing to the state of a charged particle beam that has been scanned by the scanning electromagnet; and the beam data processing apparatus is the beam data processing apparatus according to claim 1. |
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description | FIG. 1 is a high level schematic illustration of a SEM system 100 according to one aspect of the present invention. SEM system 100 includes scanning electron microscope 130, sample stage 150, calibration standard 140, controller 110, and memory 120. SEM system 100 is calibrated by placing calibration standard 140 on sample stage 150 and scanning calibration standard 140 with scanning electron microscope 130. Controller 110 stores the calibration data in memory 120 and uses the data to interpret data obtained by scanning sample 170 of which an accurate measurement is sought. Calibration standard 140 includes a pattern suitable for use in calibrating a SEM system. A suitable pattern may include features, such as raised lines, trenches, or holes, of predetermined size, width, and/or spacing. The pattern may include periodic or non-periodic features. For example, the pattern may include a series of raised lines with predetermined pitch, or a series of lines with predetermined but varying spacing. In one aspect of the invention, the calibration standard has periodic features with a pitch less than about 1 micron. In another aspect of the invention, the calibration standard has periodic features with a pitch less than about 200 nm. In a further aspect of the invention, the calibration standard has periodic features with a pitch less than about 50 nm. Calibration standard 140 has a coating that includes a transition metal oxide. Examples of transition metal oxides include Group IVa metal oxides, Group Va metal oxides, Group VIa metal oxides, Group VIIa metal oxides, Group VIII metal oxides, Group Ib metal oxides, and Group IIb metal oxides. Specific examples of transition metal oxides include TiO2, Cr2O3, CrO3, MoO2, MoO3, WO2, WO3, MnO2, MnO3, Fe2O3, Co3O4, NiO, CuO, ZnO, In2O3, SnO, and SnO2. The coating may be conductive or non-conductive. The coating may include dopants that increase conductivity. Examples of such dopants include halogen compounds, such as fluorides and chlorides, alumina, cobalt, gallium, titanium, indium, tin, and germanium. While not wishing to be bound by any theory, it is believed that the transition metal oxide containing coating mitigates carbon deposition by promoting oxidation of deposited carbon and/or preventing carbon deposition from taking place. Where the coating is conductive, the mechanism of carbon deposition mitigation usually involves either applying a positive electrical potential to the coating to electrochemically promote oxidation or flowing a current through the coating to promote oxidation through the application of heat. Alternatively, the transition metal oxide may act as an oxidation catalyst. In one aspect of the invention, the transition metal oxide is a photocatalyst. In general, the oxidation rate of carbon increases with increasing temperature. Resistive heating of a conductive transition metal oxide contain coating thereby induces oxidation of deposited carbon. Calibration standard 140 may be provided with two electrical contacts adapted to attach leads from a power source to calibration standard 140, whereby a current, generally a DC current, may be passed through the transition metal oxide containing coating. Alternatively, induction may be used to produce resistive heating within a conductive coating. The calibration standard may promote oxidation of carbon electrochemically. Setting the coating to a suitable positive electrical potential promotes the oxidation reaction. A single electrical contact may be provided to facilitate setting the coating to a positive electrical potential. Generally, a counter electrode is provided for electrochemical oxidation of carbon, however, an electron beam may function as a counter electrode. The transition metal oxide may also, or alternatively, act as an oxidation catalyst. Particularly well suited are low temperature oxidation catalyst. Examples of low temperature oxidation catalysts include TiO2 doped with Pd, SnO2 doped with Pt, and Fe2O3, Co3O4, TiO2, NiO or MnOx doped with Au. The transition metal oxide may specifically be a photocatalyst, such as TiO2, particularly TiO2 in the anatase or rutile form. A photocatalyst promotes oxidation after irradiation with ultraviolet light with an energy above the band gap energy. The transition metal oxide photocatalyst may be irradiated either before or after electron beam scanning. Features of the calibration standard may be formed in the transition metal oxide containing coating or features formed of another material may be coated with the transition metal oxide containing coating. Where the transition metal oxide containing coating coats a calibration pattern formed in another material, the transition metal oxide coating is thin. In one aspect of the invention, the thickness of the transition metal oxide coating is from about 1 nm to about 1000 nm. In another aspect of the invention, the thickness of the transition metal oxide coating is from about 1 nm to about 100 nm. In a further aspect of the invention, the thickness of the transition metal oxide coating is from about 10 nm to about 50 nm. Features of the calibration standard are generally formed over a substrate. The substrate may be of any type, conductor, semi-conductor, or insulator. Where the transition metal oxide containing coating is non-conducting, it is desirable for the substrate to be conducting or semi-conducting and for the features of calibration standard 140 to be grounded to the substrate to prevent accumulation of charges during electron beam scanning. The substrate itself may be grounded to sample stage 150. Where the coating is conductive, the coating itself may be grounded to sample stage 150. The substrate may be of any shape that fits within a sample chamber of electron microscope 130. For example, the substrate may be a silicon wafer that conveniently fits in the sample holder of a CD-SEM adapted for use in measuring critical dimensions on silicon wafers. Where the features of the substrate are not formed of the transition metal oxide containing material, the feature may be formed of any convenient material, such as amorphous silicon or polysilicon. Amorphous silicon or polysilicon features can be bound to a silicon wafer substrate through an intermediate layer of material, such as silicon dioxide. Where the intermediate layer contains an insulating material, such as silicon dioxide, the intermediate layer may be patterned with gaps to provide for electrical communication between the calibration features and the silicon wafer. Electrostatic charges imparted to the calibration features during electron beam scanning may thereby drain to the silicon wafer rather than accumulating to a level where they may distort the electron beam. Alternatively, where the transition metal oxide containing coating is conductive, charges may be drained through the transition metal oxide containing coating. The transition metal oxide containing coating may be formed by any suitable method, including, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), spray pyrolysis, sol gel technique, spin coating a solution containing the corresponding metal salt, or sintering. Alternatively, a coating of the corresponding metal may be formed by one of the forgoing methods and at least the outer surface of the metal oxidized to form the transition metal oxide. Generally, it is desirable to avoid forming large crystallites in the transition metal oxide containing coating. Large crystallites may increase the roughness of feature edges and reduce the accuracy of the calibration standard. Rtm, a measure of surface roughness, is the mean of the maximum peak-to-valley vertical measurement from each of five consecutive sampling measurements, and can be measured using known techniques including using one of an atomic force microscope and a scanning electron microscope. A rough surface is characterized by xe2x80x9cmountainousxe2x80x9d features (numerous peaks and valleys) and/or dendritic features. In one aspect of the invention, the transition metal oxide containing coating has an Rtm of about 100 xc3x85 or less. In another aspect of the invention, the transition metal oxide containing coating has an Rtm of about 50 xc3x85 or less. The features of calibration standard 140 may be patterned in the transition metal oxide containing coating using lithography. FIG. 2 provides a cross-sectional illustration of such a calibration standard. Calibration standard 200 has transition metal oxide containing coating 220, which has been patterned to form a series of raised lines over substrate 210. Either transition metal oxide containing coating 220 or substrate 210 is conducting or semi-conducting and may be grounded to the sample stage during SEM system operation. The transition metal oxide containing coating may be bound directly to the substrate, as illustrated by calibration standard 200. Alternatively, transition metal oxide containing coating can be bound to the substrate through an intermediate layer. For example, a transition metal oxide containing coating can be formed over a silicon wafer substrate and bound thereto through an intermediate layer of material, such as silicon dioxide. Where the intermediate layer contains an insulating material, such as silicon dioxide, the intermediate layer may be patterned with gaps to provide for electrical communication between the transition metal oxide containing coating and the substrate. Electrostatic charges imparted to the transition metal oxide containing coating and during electron beam scanning may thereby drain through the substrate. The features of calibration standard 140 may be patterned in a material other than the transition metal oxide containing coating. FIG. 3 provides a cross-sectional illustration of such a calibration standard. Calibration standard 300 has transition metal oxide containing coating 320 formed over first patterned coating 330. First patterned coating 330 includes a series of raised lines formed over substrate 310. First patterned coating 330 may be formed, for example, by lithographic patterning of a coating that contains silicon dioxide or polysilicon. FIG. 4 provides a cross-sectional illustration of an alternative form for calibration standard 140 in which the transition metal oxide containing coating covers a portion of a surface of a substrate. Calibration standard 400 has transition metal oxide containing coating 420 formed over a primary coating 430. Primary coating 430 and transition metal oxide containing coating 420 have been patterned together through lithography. Transition metal oxide containing coating 420 cover the upper surfaces of raised lines of the patterned coating, but is not found in the trenches between raised lines. Over the course of SEM system calibration, carbon may build up in the trenches. However, the upper dimensions of the raised lines still remains fixed, particularly where lithography has provided the raised lines with reentrant profiles. Returning to FIG. 1, the calibration standard 140 is used in system 100 with scanning electron microscope 130. Scanning electron microscope 130 may detect backscattered electrons, interference of backscattered electrons, secondary electrons, auger electrons, X-rays or cathodoluminescence. In operation of system 100, an electron beam is scanned across calibration standard 140 or sample 170 and a response that varies with position over the course of a scan is measured. Scanning is generally effectuated by varying the angle of the electron beam, although scanning may also be effectuated by moving sample stage 150. In either case, calibration provides a relationship between the measured relative movement of the electron beam and the sample and their actual relative movement. Calibration may also be used to take into account such factors as the effect of electron beam cross-sectional dimensions in measuring sample critical dimensions. Scanning, calibration, and cleaning of carbon from calibration standard 140, or a combination of the foregoing, may take place under the direction of controller 110. Controller 110 receives data from scanning electron microscope 130 and, in some cases, sample stage 150. Where the data includes measurements from sample 170, controller 110 may transmit the data, store the data in memory 120, and/or interpret the data in view of calibration measurements. Where the data concerns calibration standard 140, controller 110 may transmit the data, store the data in memory 120, and/or interpret the data to calibrate scanning electron microscope 130. Controller 110 typically includes a microprocessor, but may be any device that is capable of applying calibration data to scale or interpret measurements from the nano-scale measuring device 130. Controller 110 may be analog or digital. If controller 110 is digital, its instructions may be implemented in either hardware or software. Controller 110 may be configured to calibrate scanning electron microscope 130 in response to an instruction, which may be provided by a user or may be generated automatically based on the passage of time, whether the system has recently been powered on, or any other circumstance that may indicate the need for calibration. As part of the calibration, controller 110 may accept as an input dimensional data regarding features of calibration standard 140. The calibration process involves scanning calibration standard 140 and storing or interpreting the calibration data to adjust scanning electron microscope 130 or interpret measurements of sample 170. The scan, or sequence of scans, of the calibration standard my be directed by controller 110 as part of the calibration process. Controller 110 may also direct the loading of calibration standard 140 onto sample stage 150. The direction may be sent to a user or implemented through an automatic sample loading system, where system 100 is provided with such a sub-system. Controller 110 may also be configured to direct cleaning of calibration standard 140. Such directions may involve flowing a current through the transition metal oxide containing coating, setting the transition metal oxide containing coating to a positive potential, or exposing the transition metal oxide containing coating to ultraviolet light. Alternatively, an operator may be directed to perform one of the forgoing operations based on data regarding usage of calibration standard 140. FIG. 5 is a flow diagram of a process 500 of calibrating a scanning electron microscope according to one aspect of the present invention. In step 510, a calibration standard having a coating containing a transition metal oxide is scanned to obtain calibration data related to the scanning electron microscope. In step 540, which may take place during step 510, carbon that has deposited on the calibration standard is oxidized. In step 520, which may take place before or after step 510, a sample is scanned to obtain sample feature size data. The feature size data may be, for example, data relating to the size of a topographic feature, such as the width of a raised line or the width of a trench. The data could also relate to a non-topographic feature, such as the width of a conductive region. In step 530, the calibration data and a known dimension of the calibration standard are used to relate the measured sample feature size data to the sample feature""s actual size. There are several options for carrying out step 530. In the simplest case, a feature that gives a measured size the same as that of the calibration standard is determined to have the same size as the calibration standard. Generally, however, the size measured for the sample is not the same as the size measured for the calibration standard. Therefore, an interpolation or extrapolation takes place. For example, the calibration data may be used to compute a proportionality factor, a, between measured values VM and actual values VA, such that: VA=aVM Alternatively, the calibration may be used to compute an offset factor, b, such that: VA=VM+b Or, using two or more calibration measurements, a two factor linear relationship may be developed: VA=aVM+b Other relationships, including relationships with greater numbers of parameters, may also be used. The relationship may take into account, for example, variations in the calibration measurement that depend on the positioning of the measured feature in the scanning electron microscope. Rather than expressing the calibration relationship as a function, the calibration data may be stored in a table, for example, and measurements looked up against the table, interpolating where measurements fall between table entries. The application of calibration data to interpretation of feature size measurements may take the form of a model, such as a model of electron beam dimensions (diameter, major and minor elliptical axis, etc.). In this regard, the calibration may be broken down into several elements. For example, one calibration may be used to relate measured relative movement of the electron beam and sample to actual relative movement, while another calibration may be used to characterize the electron beam cross-sectional shape and correct feature size measurements for beam shape effects. The calibration may be applied by adjusting the SEM system or the calibration may be applied in processing data from the SEM system. There are also several options for carrying out step 540, the step of oxidizing carbon that deposits on the calibration standard. In one aspect of the invention, step 540 involves flowing a current through the transition metal oxide coating. In another aspect of the invention, step 540 involves setting the transition metal oxide coating to a positive potential. In a further aspect of the invention, step 540 involves providing conditions under which the transition metal oxide coating acts as a catalyst for the oxidation of deposited carbon. For example, step 540 may include the application of heat or placing the calibration standard in air. In a still further aspect of the invention, step 540 involves irradiating the transition metal oxide containing coating with ultraviolet light. Step 540 may take place inside or outside the scanning electron microscope. In one aspect of the invention, step 540 takes place in the scanning electron microscope. In another aspect of the invention, step 540 takes place during calibration scanning. In a further aspect of the invention, step 540 takes place with the calibration standard outside the scanning electron microscope. Where step 540 takes place during calibration scanning, carbon may never actually accumulate on the calibration standard. Nonetheless, carbon depositing on the calibration standard is still being oxidizedxe2x80x94it is being oxidized as quickly as it deposits. Flowing a current through the transition metal oxide containing coating or setting the transition metal oxide coating to a positive potential during calibration scanning may affect the calibration measurement. To determine whether such an affect is present for a particular calibration standard in a particular SEM system in a particular mode of operation, the calibration scan may be run with and without the flowing current or the positive potential. If the calibration measurement is significantly affected, the step of remove deposited carbon may be postponed until after the calibration measurement has been completed. Catalytic removal of deposited carbon may take place in the electron beam chamber and in some cases during electron beam scanning. Where the transition metal oxide is a photocatalyst, the SEM system may be provided with an ultraviolet light. However, this is not necessary as photocatalytic activity generally continues for a period of time after a photocatalyst has been exposed to ultraviolet light with an energy above the band gap energy. Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (systems, devices, etc.), the terms used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more other features of the other embodiments as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the term xe2x80x9cincludesxe2x80x9d is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term xe2x80x9ccomprising.xe2x80x9d |
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description | The present invention relates to methods for adjusting an interval or gap between two parallel arranged, plate-shaped objects and exposure methods using the same, and gap adjusting apparatuses and exposure apparatuses. More specifically, it relates to a method for detecting a proper gap between a mask and a wafer in a proximity exposure apparatus which exposes a desired pattern by radiating light onto the wafer through the mask arranged in close proximity to the wafer, an exposure method for exposing while using the above to arrange the mask and wafer such that they have a predetermined gap, a gap determination apparatus, and an exposure apparatus. One example of apparatus that needs to keep two plate-shaped objects located in parallel at a predetermined gap is a proximity semiconductor exposure apparatus that locates a mask in a close proximity to a wafer, radiates light through this mask, and exposes a pattern created on the mask onto the wafer. For a semiconductor integrated circuit fabricated by using such a semiconductor exposure apparatus, higher density and higher throughput has been promoted, and along with this, it has been demanded to form an integrated circuit with a narrow line width and a fine pattern. Accordingly, a semiconductor exposure apparatus is required to have high throughput as well as high resolution. It is also demanded for multiple exposure operations in which multiple circuit patterns are overlaid above one wafer to put multiple exposure positions in place with high precision. Further, use of a shorter wavelength of exposure light has been promoted for higher resolution, and thus an exposure apparatus using an X-ray light source has been developed. FIG. 16 shows a typical plan view of an example of such a conventional X-ray exposure apparatus. This X-ray exposure apparatus includes a wafer chuck 94 that holds a wafer 93, and a mask chuck 91 that holds a mask 92 in parallel to and close to the wafer 93. The wafer chuck 94 is supported on a fine adjustment stage 95 that adjusts its position in XYZ-directions finely, and the fine adjustment stage 95 is further supported on a rough adjustment stage 96 that adjusts its position in XY-directions roughly. The mask chuck 91 is supported on a bottom surface of the mask chuck base 97 that is located opposite to the wafer chuck 94. An X-ray light source (not shown) is installed above the mask chuck base 97, and an opening is provided on the mask chuck base 97, through which an X-ray is radiated from top to bottom almost vertically. An X-ray emitted from the X-ray light source is radiated, through the mask 92, onto the wafer 93 to which resist has been applied, thus exposing the resist. In exposing the wafer 93 using a specified pattern formed on the mask 92, the resist is exposed and this pattern is transferred. By removing exposed or unexposed part of the resist that has been exposed by the specified pattern, a semiconductor circuit of the specified pattern is created. In order to expose a specified pattern at a specified position on the wafer 93, the above described exposure apparatus uses the rough adjustment stage 96 and fine adjustment stage 95 for locating the wafer 93 at a specified position relative to the mask 92 and performing an exposure operation there. At this time, a gap between the mask 92 and wafer 93 needs to be correctly adjusted. This is because a radiated X-ray, which is irradiated in an almost vertical direction but not completely as shown in FIG. 17, has divergent and convergent angles to some extent, thus being directed to a direction slightly away from the vertical direction. In other words, since the X-ray propagating direction shifts from the vertical direction, the pattern on the mask 92 is exposed onto the wafer 93 at a position slightly away from vertically right under the pattern. This shift becomes larger as the gap between the mask 92 and the wafer 93 becomes wider. Therefore, if the gap fluctuates, there arises a change in exposure position (i.e., run-out error). This exposure-position shift is problematic especially when different exposure apparatuses are used to overlay and form multiple semiconductor circuit patterns onto one wafer 93. For example, as shown in FIG. 17, when two exposure apparatuses, such as exposure apparatuses A and B which have different gaps between the masks 92 and wafers 93, are used to expose two circuit patterns, there arises a shift amount shown by RE between the two circuit-pattern exposure positions. As a result, two circuit patterns do not match well, possibly causing a defective semiconductor device. One known, conventional method for setting a gap to be a predetermined amount between the mask 92 and wafer 93 to contact the mask 92 and wafer 93 once, making the gap in that state to be 0, and then moving the wafer 93 in a direction z by a predetermined amount. However, this method is likely to damage the mask 92 and wafer 93, cause foreign particles to be stuck between them after contacting them, and negatively affect the fine adjustment stage 95 by causing an unnecessary force to be applied to it by the contact. Accordingly, it is an object of the present invention to provide a method and apparatus for measuring a gap between two objects and confirming that a gap between two parallel arranged, plate-shaped objects is a predetermined absolute value, and an exposure method and apparatus for exposing while using the above method and apparatus to maintain a gap between a mask and wafer at a specified absolute value. A method of one aspect of the present invention for determining an arrangement of first and second objects such that a gap between the first and second objects becomes a predetermined gap includes the steps of forming a light transmitting entry window on the first object, forming a light transmitting exit window on the first object at such a position that light would enter through the entry window the second object, reflect off the second object or off the first and second objects, and then enter the exit window of the first object if the first and second objects are arranged in parallel at the predetermined gap, introducing light to the entry window to provide the second object with the light, detecting an intensity of light from the exit window, and determining the arrangement for the predetermined gap based on the detected light intensity. An apparatus of another aspect of the present invention for determining an arrangement of first and second objects such that a gap between the first and second objects becomes a predetermined gap includes a light transmitting entry window formed in the first object, a light transmitting exit window formed in the first object at such a position that light would enter through the entry window of the first object at a specified angle of incidence, reflect off the second object or off the first and second objects, and then enter the exit window of the first object if the first and second objects are arranged in parallel at the predetermined gap, a light source that introduces light through the entry window to provide the second object with the light at the specified angle of incidence, a light intensity measuring sensor for detecting an intensity of light from the exit window, and a mechanism for moving the second object, in a direction that varies a gap with the first object, wherein the arrangement being determined for the predetermined gap based on the intensity of light detected by the sensor. The sensor may measure an intensity of light exiting from the exit window, while the light source introduces the light to the entry window and the mechanism moves the second object, and the arrangement being determined for the predetermined gap based on an arrangement in which the sensor detects the strongest intensity of light. The apparatus may further include a diffraction grating formed in the entry window, the light source introducing light to the entry window at the specified angle of incidence to generate diffracted light that is guided from the entry window to the second object at the specified angle. Px=λ/sin θ may be met where Px is a pitch of the diffraction grating in a direction parallel to an incident plane of light entering the second object at the specified angle of incidence, λ is a wavelength of light emitted by the light source, and θ is the specified angle of incidence of light entering the second object, and wherein the light source introduces the light with the wavelength of λ to the entry window from a direction perpendicular to the pitch direction of the diffraction grating, and first order diffracted light from the entry window is guided to the second object at the specified angle of incidence of θ. The light source introduces the light to the entry window in such a direction that an incident angle component at an incident plane of light entering the second object at the specified angle is the specified angle of incidence. D=2 nG tan θ may be met where D is a gap between the entry window and the exit window, λ is a wavelength of light emitted by the light source, θ is the incident angle of light entering the second object, G is the predetermined gap between the first and second objects, and n is an arbitrary natural number. The apparatus may further include two sets of the entry windows and exit windows corresponding to the entry windows arranged on the first object and lined up in a straight line, wherein the light source introduces light mutually inclined in opposite directions from the entry windows to the second object at the same specified angle of incidence, an average of arrangements being determined as the arrangement for the predetermined gap, each of the arrangements providing the strongest intensity of the light that has passed through one of the two sets. The apparatus may further include on the entry window a diffraction grating that has a predetermined pitch in a direction parallel to an incident plane of light entering the second object at the specified angle of incidence, wherein the light source introduces light to the entry window from a direction perpendicular to the pitch direction of the diffraction grating, causing plus and minus first order diffracted light from the entry window mutually inclined in opposite directions to the second object at the same specified angle. Py=λ/sin α may be met where Py is a pitch of a diffraction grating formed in the entry window in a direction perpendicular to the incident plane of light entering the second object at the specified angle of incidence, λ is a wavelength of light emitted by the light source, and wherein the light source introduces light to the entry window in such a direction that an incident angle component at a plane perpendicular to an incident plane of light entering the second object at the specified angle of incidence is α. The apparatus may further include a diffraction grating formed in the exit window. An exposure apparatus of another aspect of the present invention for exposing a wafer with a pattern formed on a mask by irradiating light from an exposure light source through the mask includes a stage for moving the wafer, and an arranging apparatus for determining an arrangement of the mask and wafer such that a gap between the mask and wafer becomes a predetermined gap, the arranging apparatus including a light transmitting entry window formed in the mask, a light transmitting exit window formed in the mask at such a position that light would enter through the entry window the wafer at a specified angle of incidence, reflect off the wafer or off the mask and wafer, and then enter the mask if the mask and wafer are arranged in parallel at the predetermined gap, a light source that introduces light through the entry window to provide the wafer with the light at the specified angle of incidence, a light intensity measuring sensor for detecting an intensity of light from the exit window, and the stage for moving the wafer in a direction that varies a gap with the mask, wherein the arrangement is determined for the predetermined gap based on the intensity of light detected by the sensor. The exposure light source may be an X-ray light source. The exposure apparatus may further include a diffraction grating formed in the entry and exit windows, and the light source and the sensor are integrated into one member. A description will now be give of various embodiments according to the present invention with reference to accompanying drawings. FIG. 1 is a typical sectional view for explaining a method of a first embodiment according to the present invention, which adjusts a gap between a first plate-shaped object 2 and a second plate-shaped object 3. The second object 3 is disposed on a Z-stage 5 that can support and move it in a Z-direction. The Z-stage 5 is provided with a Z-position detecting sensor 6 that detects a position of the second object 3 in the Z-direction. The first object 2 is fixed parallel to the second object 3. On the first object 2 are provided a light source and a beam enlarging optical system 10 that reshapes light radiated from it into a beam with a desired diameter, which includes lenses 10a and 10b. This optical system may be a beam reducing optical system. In addition, a sensor 4 is provided that detects light introduced via a condenser lens 11. This embodiment has processed the first object 2 to adjust a gap, i.e., by opening a light transmitting entry window 7 and exit window 8 spaced at a specified distance in X-direction. The entry and exit windows 7 and 8 may be of an equal size. The light source 1 and the beam enlarging optical system 10 are adapted so as to introduce light to the entry window 7 on the first object 2 perpendicularly from above. The entry window 7 has a light transmitting part with a transmitting-type linear diffraction grating arranged at a fixed pitch in X-direction. If it is assumed that a pitch of this diffraction grating is Px, and the wavelength of the light guided vertically from above is λ, Px and λ meet the following equation (1) so that light introduced may be diffracted at 1st order diffracted angle θ, as shown FIG. 2.Px=λ/sin θ (1) As shown in FIG. 2, if it is assumed that a gap between the first and second objects 2 and 3 is a predetermined gap G (a designed gap), a gap D between the entry and exit window 7 and 8 meets the following equation (2) so that 1st order diffracted light produced from light introduced to and diffracted by the entry window 7 may make a regular reflection off the surface of the second object 3 and the reflected light may pass through the exit window 8.G=D/(2 tan θ) (2)The sensor 4 is arranged at such a position that it can detect the reflected light from the exit window 8. The method for adjusting a gap between two objects according to this embodiment is carried out by varying a position of the second object 3 in the Z-direction by use of the Z-stage 5 while introducing light with a wavelength of λ from the light source 1 to the entry window 7 in the first object 2. At this time, the sensor 4 detects a changing intensity of the light from the exit window 8. FIG. 3 shows the changing light intensity measured in this way by assigning a horizontal axis to a Z-position of the second object 3 measured by the Z-position detecting sensor 6. The Z-position of the second object 3 corresponds to a gap between the first and second objects, thus indicating it as a gap in FIG. 3. Since the wavelength λ, the pitch Px, and the distance D are set as described above, when a gap between the first and second objects 2 and 3 is G, the 1st order diffracted light from the entry window 7 makes a regular reflection and its reflected light passes through the exit window 8, thus reaching the sensor 4. If the gap shifts by dG from there, the incident position of the reflected light off of the first object 2 shifts by 2dG tan θ, as shown in FIG. 2, and thus the light will be at least partially shielded by the first object. Accordingly, as shown in FIG. 3, the intensity of the light emitted from the exit window 8 is the maximum when the gap between the first and second objects 2 and 3 is the predetermined gap G, and becomes weaker as the gap shifts from G. The method for adjusting a gap according to the present embodiment determines, as described above, that the arrangement that provides the strongest intensity of light measured by the sensor 4 is the arrangement that the first and second objects 2 and 3 form the predetermined gap G. According to this method, a gap between two objects can be adjusted without contacting the first and second objects, and thus both objects may be positioned with a predetermined gap in between with high precision. This embodiment may determine the arrangement that provides the strongest intensity of the light detected by the sensor 4, by calculating an approximate curve for a graph of changing light intensity shown in FIG. 3, using a quadratic function and the like and based on the peak position of this approximated curve. Thus, it is possible to more precisely determine the arrangement that provides the strongest light intensity. Referring to FIGS. 4 and 5, a description will now be given of the second embodiment. FIG. 4 is a typical sectional view for explaining a method of this embodiment according to the present invention, which adjusts a gap between two plate-shaped objects. An element in these figures, which corresponds to that in the first embodiment, is designated by the same reference numeral, and a description thereof will be partially omitted. A method for adjusting a gap according to this embodiment provides two entry windows 17a and 17b and two corresponding exit windows 18a and 18b in the first object 12. The entry windows 17a and 17b are located near the center of the figure and close to each other, and the exit windows 18a and 18b are provided at one side of the entry windows 17a and 17b. A light source 101 and a beam enlarging optical system 20 are provided around the center of FIG. 4 so that they can introduce light perpendicularly from above to both of the comparatively close entry windows 17a and 17b. Similar to the first embodiment, the entry windows 17a and 17b are formed into a linear diffraction grating with the pitch Px that meets the equation (1) so that incident light with a wavelength of λ may be diffracted by a 1st order diffracted angle of θ. A distance between the entry and exit windows 17a and 18a, and that between the entry and exit windows 17b and 18b are both set to a gap D that satisfies the equation (2). In other words, like the first embodiment, when a gap between the first and second object 12 and 3 is the designed gap, light that has made a 1st order diffraction from the entry windows 17a and 17b, and made a regular reflection off the surface of the second object 3 will pass through the exit windows 18a and 18b, respectively. The sensors 14a and 14b are located to detect the light having passed through the exit windows 18a and 18b in this way. Similar to the first embodiment, the procedure of adjusting the gap is to detect the light intensity by using the sensors 14a and 14b while moving the second object up and down by the Z-stage (not shown). The method for adjusting a gap according to this embodiment has an object to obtain a desired gap between two objects with high precision even if the relative position between the first and second objects 12 and 3 has a slightly shifted tilt component (ωy) around the Y-axis. A description will be given of this below. A description will now be given of a case where there is a little shifted tilt component ωy between the first and second objects 12 and 3. In this case, the light intensities detected by the sensors 14a and 14b both become, similar to the first embodiment, the strongest when the gap between the two objects is the designed gap G, and become weaker as it shifts from the designed gap G. Therefore, the arrangement that provides the strongest light intensity detected by each of the sensors 14a and 14b can be determined as the arrangement that the gap between the first and second objects 12 and 3 is the predetermined gap G. As shown in FIG. 5, the gap Ga that provides the strongest light intensity (signal a) detected by the sensor 14a is different from the gap Gb that provides the light intensity (signal b) detected by the sensor 14b. FIG. 5 shows a detection result where the second object 3 tilts in a clockwise direction of FIG. 4 relative to the first object 12. In this case, as it goes farther to the right in FIG. 4, the gap between the two becomes wider. Further, an angle of incidence of the 1st order diffracted light entering the second object 3 becomes large for the incident light from the entry window 17a, which is guided diagonally to the lower right of FIG. 4, and becomes small for the incident light from the entry window 17b, which is guided diagonally to the lower left of FIG. 4. This means that the arrangement that provides the strongest light intensity detected by the sensor 14a shifts to such a side as decreases the gap between the two objects, and the arrangement that provides the strongest light intensity detected by the sensor 14b shifts to such a side as increases the gap between the two objects. Here, an optical system of this embodiment for adjusting the gap is arranged symmetrically relative to a ZaX-axis as an axis in the Z-direction, in the center of the entry windows 17a and 17b shown in FIG. 4. Accordingly, each shift amount between the gaps Ga/Gb and the designed gap G between the two objects along this ZaX-axis becomes almost equal, i.e., G−Ga=Gb−G. Thus, the arrangement that provides the gap G between two objects along the ZaX-axis results from the gap G calculated by an average between the gaps Ga and Gb where the light intensity detected by the sensor 14a and 14b becomes the strongest:G=(Ga+Gb)/2 (3)By moving the second object 3 by use of the Z-stage so that the position of the second object 3 measured by the Z-position detecting sensor (not shown) becomes the position equivalent to the gap G, a gap between the two objects along the ZaX-axis can be adjusted with high precision. As described, according to this embodiment, even though there is a slightly shifted tilt component around the-Y-axis at relative position between two objects, a gap between the two objects can be adjusted to a desired gap with high precision. Further, in this embodiment, even if there is a slightly shifted tilt component (ωx) around the X-axis at the relative position between two objects, this shift does not influence the gap determination, thus making a gap along the ZaX-axis a desired gap. This is true of the first embodiment. Referring to FIG. 6, a description will now be given of the third embodiment of the present invention. An element in this figure, which corresponds to that in the first and second embodiments, is designated by the same reference numeral, and a description thereof will be partially omitted. A method for adjusting a gap according to this embodiment provides an entry window 27 in the first object 22, and two exit windows 28a and 28b at both its sides. A light source 21 is adapted so as to introduce light to this entry window perpendicularly from above. Similar to the first embodiment, the entry window 27 is formed into a linear diffraction grating with the pitch Px that meets the equation (1) so that incident light with a wavelength of λ may be diffracted by a 1st order diffracted angle of θ. The method for adjusting a gap according to this embodiment makes this entry window 27 serve as the entry windows 17a and 17b in the second embodiment. Namely, when light is introduced into the entry window 27, in addition to the 1st order diffracted light having the 1st order diffracted angle of θ, −1st order diffracted light is produced in an opposite direction by an angle θ. The exit windows 28a and 28b are arranged respectively in place i.e., in opposite directions from the entry window 27 (or right and left directions in FIG. 6) at a distance D that satisfies the equation (2) so that they would receive, if the gap between the first and second objects 22 and 3 is the designed gap G, the plus and minus first order diffracted light through the entry window 27 that has been reflected as a regular reflection off of the surface of the second object 3. The sensors 24a and 24b are arranged in place so that they can detect the light from the exit windows 28a and 28b. Like the second embodiment, even if there is a slightly shifted tilt component (ωy) around the Y-axis at the relative position between two objects, the gap between the two objects can be made a desirable one with high precision. In other words, the center between the two positions, which provides the strongest light intensity detected by the sensors 24a and 24b, can be determined as the position that provides the gap G between two objects along the Z-axis running through the center of the entry window. It is possible to move the second object 3 to this position by using the Z-stage, and to arrange the two objects with high precision such that they have the designed gap G. Referring to FIG. 7, a description will now be given of the fourth embodiment of the present invention. An element in this figure, which corresponds to that in the first to third embodiments, is designated by the same reference numeral, and a description thereof will be partially omitted. A method for adjusting a gap according to this embodiment provides one entry window in the first object 32, and two exit windows 38a and 38b at both its sides. The entry window does not have a diffraction grating, but has an aperture pattern. The method of this embodiment introduces light into the entry window 37 with an angle of incidence θ, instead of diffracting light incident upon the entry window 37. In an illustration in FIG. 7, a light source 31 is arranged such that it introduces light diagonally to the lower left. A beam splitter 41 is provided on the way this light travels, and the light incident upon this is split into two, one of which propagates diagonally to the lower left and the other propagating diagonally to the lower right. There are mirrors 42 and 43 on the way the split respective beams travel. The arranged positions and angles of these mirrors 42 and 43 are adjusted such that the reflected light is guided to the entry window 37 diagonally to the lower right and lower left, respectively with an incident angle θ. Due to this configuration, light incident upon the entry window 37 with an incident angle θ arrives at the second object 3 with the incident angle θ, thus being reflected as a regular reflection. The exit windows 38a and 38b are arranged in place so that the reflected light passes, i.e., away from the entry window 37 in opposite directions at a distance D that satisfies the equation (2). The sensors 34a and 34b are arranged in place so that they can detect the light having passed through the exit windows 38a and 38b. Similar to the second and third embodiments, the method of this embodiment would make a gap between two objects a desirable one with comparatively high precision even if there is a slightly shifted tilt component (ωy) around the Y-axis at the relative position of the two objects. Referring to FIGS. 8–13, a description will now be given of the fifth embodiment of the present invention. FIGS. 8–10 are typical views for explaining a gap determination of this embodiment. FIG. 8 is a sectional view taken in the X-direction. FIG. 9 is a sectional view taken in the Y-direction. FIG. 10 is a plan view. An element in this figure, which corresponds to that in the first to fourth embodiments, is designated by the same reference numeral, and a description thereof will be partially omitted. This embodiment provides two entry windows 57a and 57b in the first object 52 comparatively close to each other, and two exit windows 58a and 58b at both their sides. The entry windows 57a and 57b are transmission type diffraction gratings whose light transmitting parts are formed with a pitch Px1 in the X-direction and a pitch Py1 in the Y-direction. This embodiment introduces, not vertically but at an inclined incident angle a in the Y-direction, light to the entry windows 57a and 57b from a light source 51 through a beam enlarging optical system 60. FIG. 9 exemplarily shows that light from the light source 51 is reflected at a mirror 62, and introduced at an incident angle a. The pitch Px1 in the X-direction of the diffraction gratings formed in the entry windows 57a and 57b satisfies:Px1=λ/sin θ (4)whereby light with a wavelength of λ vertically incident on the X-axis may be diffracted as 1st order diffracted light in the X-direction at an angle θ. In addition, the pitch Py1 in the Y-direction of the diffraction gratings formed at the entry windows 57a and 57b satisfies:Py1=λ/sin α (5)so that light with a wavelength of λ inclined to Y-direction and incident at an incident angle α may be diffracted as 1st order diffracted light in a direction perpendicular to the Y-axis. The exit windows 58a and 58b are arranged in place so that they would receive, if the gap between the two objects is the designed gap G, light that has been diffracted as 1st order diffracted light from the entry windows 57a and 57b, then led to the second object 3 inclined in X-direction at an incident angle θ, and reflected off its surface as a regular reflection, i.e., away from the entry windows 57a and 57b in the X-direction at a distance D that satisfies the equation (2). This embodiment makes each of the exit windows 58a and 58b of a linear diffraction grating with a pitch Px2 in the X-direction and a pitch Py2 in the Y-direction. The pitch Px2 in the X-direction of these exit windows 58a and 58b satisfies:Px2=λ/(sin θ−sin θ) (6)so that 1st order diffracted light of the light inclined in the X-direction and incident at an incident angle θ may exit at an angle of exit β in the X-direction. The pitch Py2 in the Y-direction of the exit windows 58a and 58b satisfies:Py2=λ/sin α′ (7)so that 1st order diffracted light of light vertically incident on the Y-axis may exit at an angle of exit α′ in the Y-direction. FIG. 9 illustrates α=α′. Here, suppose an example using the wavelength λ of 785 nm and the designed gap G of 70 μm. Assuming that Px1=1.3 μm, and Px2=1.5 μm, θ=37.15° from the equation (4), and β=4.61° from the equation (6). Further, assuming α=α′=15°, Py1=Py2=3.03 μm from the equations (5) and (7). The method of this embodiment may adjust an angle of light entering the entry windows 57a and 57b and an angle of light exiting from the exit windows 58a and 58b by making the entry and exit windows 57a, 57b, 58a and 58b of linear diffraction gratings having predetermined pitches in the X- and Y-directions. Such a configuration would enhance the degree of freedom of a light projecting system that introduces light to the entry windows 57a and 57b and a light receiving system that receives light from the exit windows 58a and 58b. In particular, a configuration of this embodiment enables one sensor 54 to detect light from the exit windows 58a and 58b. In other words, as shown in FIG. 12, a light-receiving lens 63 is provided at such a position that it may receive light from the exit windows 58a and 58b, and introduce each light to the sensor 54 through refraction. At this time, as shown in FIG. 11, the signal “A” as the light from the exit window 58a and the signal “B” as the light from the exit window 58b are adapted to enter different spots “A” and “B” on the sensor 54, respectively. This structure would make it possible to separately detect the intensity of light from the exit window 58a based on signal's peak position Pa in the spot “A” and the intensity of the light from the exit window 58b based on signal's peak position Pb in the spot “B”. The first object 52, sensor 54, and the light-receiving lens 63 are arranged, as shown in FIG. 12, such that the sensor 54 and the light-receiving lens 63 are optically conjugate with each other (or in a relationship between an object and image). However, as shown in FIG. 13, it may be so adapted that the sensor 54 is located at a position away from there. Accordingly, since the light-receiving angle can be an exit angle of ±4.61° of emitted diffracted light plus a spreading angle of the diffracted light, the NA of the receiving lens can be made small. Thus, this embodiment would enhance the degree of freedom for the light-projecting and light-receiving systems, and facilitate a fabrication of the apparatus. In addition, the light-projecting and light-receiving systems may be integrated into one member, and the NA of the light-receiving lens may be made small as discussed above, thus realizing a miniaturization of the apparatus. Referring to FIG. 14, a description will now be given of the sixth embodiment. An element in this figure, which corresponds to that in the first to fifth embodiments, is designated by the same reference numeral, and a description thereof will be partially omitted. This embodiment provides, as in the first embodiment, an entry window 67 with a linear diffraction grating with a pitch Px that satisfies the equation (2), and an exit window 68 with an aperture pattern in the first object 62. In this embodiment, a distance 2D between the entry window 67 and the exit window 68 is different from that in the first embodiment, i.e., twice as large as D that satisfies the equation (1). It is assumed that the first and second objects 62 and 3 form the designed gap G in this structure. Light with a wavelength of λ introduced to the entry window 67 vertically from a light source 61 generates light diffracted by a 1st order diffraction angle θ. This diffracted light enters the second object 3 at an incident angle θ, and is reflected as a regular reflection. This reflected light enters the first object 62 at the incident angle θ, and at this time, is reflected as a regular reflection off the first object 62. Again, it enters the second object 3 and its regularly reflected light arrives at a position on the first object 62, where the exit window 68 opens. The sensor 64 is located at such a position that it can detect the light thus passing trough the exit window 68. A gap is adjusted, like the first embodiment, while changing the gap between the first and second objects 62 and 3 by moving the second object 3 up and down using the Z-stage, thus measuring the changing light intensity using the sensor 64. The arrangement that provides the strongest light intensity detected is determined as the arrangement that provides the designed gap G between the first and second objects 62 and 3. Since the light used to adjust the gap is reflected twice off the second object 3 in the structure of this embodiment, a large changing rate of the intensity of the light detected by the sensor 4 is available for a shift dG from the designed gap G. In the first embodiment, if a gap between the first and second objects shifts by dG from the designed gap G, the shift from the exit window 68 at the position of the reflected light incident upon the first object is 2dG tan θ. On the other hand, in the structure of this embodiment, this shift is a doubled 4dG tan θ, and therefore the changing rate of the light intensity grows larger, whereby a gap may be adjusted more precisely. The distance between the entry and exit windows may be n times as much as D (n is a natural number) to reflect light n times off the second object. Then, while the gap between the first and second objects shifts by dG from the designed gap G, a shift, from the exit window, of the position of the reflected light incident upon the first object is 2ndG tan θ, whereby a gap may be adjusted more precisely. Referring to FIG. 15, a description will now be given of the seventh embodiment that exemplarily applies the method for adjusting a gap according to the present invention to an X-ray exposure apparatus. FIG. 15 is a typical sectional view of an X-ray exposure apparatus of this embodiment. This X-ray exposure apparatus includes a wafer chuck 85 for holding a wafer 73 and a mask chuck 84 for holding a mask 72 in parallel near the mask 73. The wafer chuck 84 is supported by a fine adjustment stage 86 that adjusts its position in the XYZ directions finely, which, in turn, is supported by a rough adjustment stage 87 that adjusts its position in the XY directions roughly. The mask chuck 84 is supported below the mask chuck base 83 that is arranged opposed to the wafer chuck 85. An X-ray light source (not shown) is provided above the mask chuck base 83, and an opening is provided in the mask chuck base 83, through which an X-ray is to be radiated from top to down almost vertically. An X-ray emitted from the X-ray light source is radiated through the mask 72 onto the wafer 73 to which resist is applied, thus exposing the resist. In exposing the wafer 73 by a specified pattern on the mask 72, the resist is exposed and the pattern is transferred. By removing the exposed or unexposed part from the resist that has been exposed by the specified pattern, a semiconductor circuit of the specified pattern will be created. The X-ray exposure apparatus of this embodiment further includes an alignment scope 81 used to adjust the relative position between the mask 72 and wafer 73. The alignment scope 81 is supported by an alignment scope stage 82 on the mask chuck base 83 near the edge of the opening for X-ray radiation. The alignment scope 81 is equipped with a light source 71 and a sensor 74 for detecting the light intensity. The alignment scope 81 includes a specified optical system combining lenses and mirrors, which is adapted such that light from the light source is radiated onto the mask 72 at a specified position and at a specified angle of incidence, and the light from the specified position of the mask 72 at a specified angle of exit is guided to the sensor 74. This alignment scope 81 detects alignment marks formed on the mask 72 and wafer 73, and uses them to adjust the positions of the mask 72 and wafer 73 in X-, Y-directions and adjust their relative position in X-, Y-directions. This embodiment makes use of this alignment scope 81 to adjust a gap between the mask 72 and wafer 73. A description will be now given of the method for adjusting the gap between them. An entry window 77 and an exit window 78 of a specified pattern are formed in place in the mask 72. In this embodiment, the pattern, shown in FIG. 10 and described in connection with the fifth embodiment, is formed by EB drawing and used. Light from the light source 71 enters the entry window 77 at a specified angle of incidence, and the sensor 74 detects the intensity of the light from the exit window 78, while a position of the wafer 73 is changed in Z-direction using the fine adjustment stage 86. This may determine the arrangement that provides the gap G between the mask 72 and wafer 73 (in this embodiment, especially as shown in the fifth embodiment, it is 70 μm). This Z-position of the wafer 73 is stored, for example, in a computer and the like for controlling the operations of the X-ray exposure apparatus. In an actual exposure, the wafer 73 is moved to the stored Z-position by using the fine adjustment stage 86, and the exposure follows. As described above, this embodiment forms the predetermined gap between the mask 72 and wafer 73 with high precision without contacting them, and may fabricate high-quality semiconductor devices with high yield. This embodiment has adopted the pattern shown in the fifth embodiment as a pattern for the entry and exit windows 77 and 78 to be formed in the mask 72. It preferably uses the alignment scope 81, which integrates-the light source 71 and sensor 74 and is used to align the mask 72 and wafer 73 in the XY directions, to adjust the gap between the mask 72 and wafer 73. Of course, a gap may be adjusted by providing a light source and a sensor separately, and forming entry and exit windows in the mask, which include other patterns shown in the first to sixth embodiments, or a combination of these embodiments. As described above, use of the present invention would enable one to provide a gap between two plate-shaped objects with a specified absolute value, without contacting them. The method for adjusting a gap according to the present invention, when applied to position a mask and wafer at a predetermined gap in an exposure apparatus, would provide an exposure apparatus that can fabricate devices with high precision and high yield. |
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description | The instant application is a national phase of PCT International Application No. PCT/RU2015/000100, filed Feb. 17, 2015, and claims priority to Russian Patent Application Serial No. 2014107111, filed Feb. 26, 2014, the entire specifications of both of which are expressly incorporated herein by reference. The invention relates to electrical engineering namely to sealed inputs of electric circuits into the confinement area of multi-layer nuclear power plant containment and can be used in penetrations through external and internal walls subjected to relative mutual displacement due to seismic events or thermal expansion of walls and penetrations. Sealed electric input through a reinforced concrete wall of nuclear power plant containment containing a shell with biological protection system and electrical conductors is disclosed (see USSR Certificate of Authorship No. 1551142 of Apr. 14, 1988 MPK: H01B17/26). This sealed input is designed only for electrical conductors entries in the nuclear power plant containment with one reinforced concrete wall. To improve safety level of nuclear power plant operations, multi-layer containments of at least of two walls came to use. Therefore, it became necessary to create sealed electric inputs that may be passed both through reinforced concrete external and internal walls near the gap. The most appropriate technical solution to the above is a sealed cable input through external and internal walls of the nuclear power plant containment containing an embedded connection pipe installed inside the internal wall with internally and rigidly fixed cable input and a pipe installed inside the external wall in line with the connection pipe with bellows on the external end where cable output is located on supports with a gap relating to the pipe internal surface (see U.S. Pat. No. 4,107,456 C1. G21C13/02 published on Aug. 15, 1978). Cable electrical conductor passing through both internal sealed containment wall and external power containment wall is fixed with a cable input inside the internal sealed wall by means of an embedded connection pipe and is in sliding or rolling joint with cable output towards the external power containment wall. Electrical conductor output connection in the external power wall includes compensation means for relative motion of the electrical conductor and the external wall. Compensation means are made in the form of rollers or their equivalents and shall ensure tight coupling of the conductor with the external wall despite any possible motions of the electrical conductor in the wall or relative motions of both walls or the wall and the conductor relative to each other. Motion of the walls relative to each other or to the conductor may occur during seismic events or due to temperature difference of the external and internal walls or the wall and the conductor, or due to different tension force of cable wires or loosening thereof. Electrical penetration made according to the described invention is designed, first of all, to complete tasks related to prompt and intense motion of the external and internal walls caused by seismic events. In addition, according to the invention design, penetration shall solve problems with slow type of relative motion of the walls and the conductor caused by their thermal expansion. Relative motions either between the walls or between the walls and the conductor may be limited to orthographic motions of the conductor in the pipe with bellows. Horizontal movement is provided by relative motion of the conductor in relation to the external wall. Therefore, tensile load of the conductor or any penetration part is limited due to horizontal movement to the force required to break friction in sliding or rolling sealing providing for compensation means. Movement in a direction orthogonal to the conductor, e.g. vertical movement, is provided by sliding or rolling the conductor in relation to the external wall and slight turning point. Turning point of the conductor output is distributed along the length of the conductor located in the annulus that leads to conductor bending. This design of compensation means is intended only for the conductors capable of bending in the passage area between the external and internal containment walls upon their displacement. If a stiffer conductor of increased diameter that is not capable of bending in the passage area between the external and internal containment walls upon their displacement relative to each other is used, turning point of the conductor output in the compensation means and jamming of the conductor output supports may occur in the pipe and as a result insulating sleeve will be damaged. The purpose of this invention is to improve operating reliability of the sealed cable input if hard-bending high-voltage electrical conductors are used. This purpose is achieved by new development for the known sealed cable input through external and internal walls of the nuclear power plant containment containing an embedded connection pipe installed inside the internal wall with internally and rigidly fixed cable input and a pipe installed inside the external wall in line with the connection pipe with bellows on the external end where cable output is located on supports with a gap relating to the pipe internal surface, its novelty is that this cable input is equipped with the second similar bellows symmetrically installed on the opposite pipe end near internal surface of the external wall while loose ends of both bellows are tapered and the cable output is supported by internal surfaces of tapered bellows ends. In addition, the cable can be located in the space between the external and internal containment walls inside two protective pipes, one of which is cantilever fitted on the internal surface of the internal wall and the other one is cantilever fitted concentrically with the second bellows on the internal surface of the external wall while loose pipe ends are connected with each other using cylinder-shaped bellows. The gap between the cable surface and the pipe internal surface may not be less than the maximum orthographic thermal and seismic planar motion of the internal wall in relation to the external wall and the change of cable coaxial position in the pipe. Tapered ends of the bellows can be located in the pipe and directed towards each other. Twisted conical compression spring may be installed on the bellows crimps. Cable can be suspended in the pipe on springs. Provision of the second similar bellows symmetrically installed on the opposite pipe end near the internal surface of the external wall ensures both cable support in the pipe and additional sealing of the cable input. Loose ends of both bellows are tapered to create supports for the cable output. The supports designed to fix cable output in the ring surface of tapered bellows ends ensure reliable cable coverage both during horizontal and vertical movements of the cable or the external wall or mutual motion of both the wall and the cable. Cable laying in protective pipes connected with each other by cylinder-shaped bellows ensures cable protection from temperature drops caused both by short-term current interruptions and accidental water penetration, and provides continuous temperature mode for the cable and therefore protects it from any additional thermal axial displacements. Cable laying in pipes with the specified gap is calculated on the basis of the maximum displacement of the cable, external and internal walls, the cable and the walls under seismic and thermal impacts on the containment. Direction of tapered bellows ends towards each other and their location in the pipe improves operating reliability of bellows as they are protected from accidental damages. Reinforcement of tapered bellows crimps with twisted conical compression springs allows to increase the load on internal support surfaces of tapered bellows ends. Cable suspension on springs inside the pipe ensures maintenance of the specified gap and redistribution of loads imposed on the internal support surfaces of tapered bellows ends. The following is the description of one of the numerous options of the sealed cable input through the external and internal nuclear power plant containment walls, each option is subject to the single inventive design indicated in the claims given below. The sealed cable input through the external and internal nuclear power plant containment walls contains the first penetration unit consisting of connection pipe 3 fixed with regard to cable 2 and attached to internal reinforced concrete wall 1. Internal wall 1 has a sealed dome-shaped design with average thickness of 1.2 meters and is intended to ensure excess internal pressure containment in case of an accident inside the containment. Ends 4 and 5 of connection pipe 3 overhang beyond the plane of external surface 6 and internal surface 7 of internal wall 1. Counter flange 8 providing for tight and sealed joint of connection pipe 3 in wall 1 is mounted on end 4 of connection pipe 3 on the side of wall 1 internal surface 7. Nozzle 9 connected with cavity 10 of connection pipe 3 is mounted on end 4 of connection pipe 3. Hole 12 is made in line with connection pipe 3 in the opposite external reinforced concrete power dome-shaped wall 11, shell 14 is tightly mounted on walls 13 of this hole where the second penetration unit (moving with regard to cable 2 and including compensation means for relative motion of cable 2 and external wall 11) is mounted. Dome-shaped external wall 11 has average thickness of 0.6 meters and is designed to carry high impact loads from the outside, e.g. aircraft crash. Internal sealed dome-shaped reinforced concrete wall 1 covering the nuclear reactor is enclosed under the power dome of external wall 11. Shell 14 is fixed in wall 11 by external ring 15 and internal ring 16 fastened on external surface 17 of wall 11 and on internal surface 18 of wall 11. Compensation means for relative motion of cable 2 and external wall 11 are located in shell 14. Relative motion compensation means consist of pipe 19 inserted in shell 14 with its ends 20 and 21 fixed in shell 14 by means of external flange 22 and internal flange 23 attached to external ring 15 and internal ring 16 accordingly. Tapered bellows 24 and 25 are mounted on ends 20 and 21 of pipe 19. Both bellows 24 and 25 are made of heat-shrinking non-flammable material with the wider part mounted on ends 20 and 21 of pipe 19. They are mounted by heating with an industrial fan allowing for tight soldering of wider internal surfaces 26 and 27 of bellows 24 and 25 to pipe 19 external end surfaces 20 and 21. Internal support ring-shaped surfaces 28 and 29 of the narrower part of tapered bellows 24 and 25 loose ends 30 and 31 are designed for tight coverage and support of cable 2. For this purpose, twisted conical compression springs 36 and 37 are installed inside cavities 32 and 33 of bellows 24 and 25 for reinforcement on crimps 34 and 35. Protective covers 39 and 40 are located in annulus 38 between internal wall 1 and external wall 11 of the containment in line with embedded connection pipe 3 and pipe 19: protective pipe 40 is cantilever fitted on internal surface 7 of internal wall 1 by means of counter flange 8, and pipe 39 is cantilever fitted on internal surface 18 of external wall 11 concentrically with the second bellows 25 by means of internal flange 23 while loose ends 41 and 42 of protective pipes 39 and 40 are connected to each other using cylinder-shaped bellows 43. For ease of installation, protective pipes 39 and 40 can be made of compound upper and lower parts, gaps for excess heat removal from heated cable 2 can be provided in the lower part. Rigid cables 2 for 10 kV can be used in this electric input design. Cable 2 is located in the penetration as follows: cable 2 input 44 is tightly fixed inside embedded connection pipe 3 of internal wall 1, nitrogen gas 45 is pumped in cavity 10, and cable 2 output 46 is installed in pipe 19 of external wall 11 without restraint by means of bellows 24 and 25. Cable 2 output 46 is located in pipe 19 with annular gap 47 formed between braiding 48 over cable 2 external surface and pipe 19 internal surface 49 and calculated on the basis of at least the maximum orthographic thermal and seismic planar motion of internal wall 1 in relation to external wall 11 and the change of cable 2 coaxial position in pipe 19. Setting of this gap 47 is maintained by means of internal support ring-shaped surfaces 28 and 29 formed on narrower ends 30 and 31 of two tapered bellows 24 and 25. Cable 2 output 46 is fixed in support ring-shaped surfaces 28 and 29 of bellows 24 and 25 by heating with an industrial fan allowing to cover and tightly solder internal support ring-shaped surfaces 28 and 29 of bellows 24 and 25 to cable 2 braiding 48. Support ring-shaped surfaces 28 and 29 are used for centering of cable 2 in pipe 19 and designed to prevent cable 2 output 46 from contact of its braiding 48 with pipe 19 internal surface 49 in case of cable 2 output 46 deviation from the axis of cable 2 input 44. As in normal operation when electrical equipment is switched on the temperature of cable 2 cores reaches 95° C., and in case of short circuit currents the temperature of cable 2 cores may increase up to 300° C., temperature drops during current interruptions and cable 2 cooling up to 20° C. can lead to axial deformation of cable 2, namely to the change of its length up to 13 mm at the highest temperature. Therefore, passage length of cable 2 between internal wall 1 and external wall 11 of the containment reaches two meters in annulus 38, cable 2 is located inside two protective pipes 39 and 40 and cylinder-shaped bellows 43 forming air heat accumulating area 50. Internal dimensions of pipe cavities 39 and 40 and bellows 43 are designed with consideration of formation of an air gap around cable 2 ensuring heat removal on one side and smoothing of temperature drops at cable 2 switching on or off on the other side. By means of this thermostat excess axial deformations of cable 2 are reduced and, therefore, additional operation compensation means for relative motion of cable 2 and external wall 11 are excluded, operating reliability of bellows is improved due to fracture control in crimps 34 and 35 of bellows 24 and 25. Protective pipes 39 and 40 and bellows 43 protect cable 2 from undesirable cooling in case of ingress of condensate that can subside when ventilation system is switched off, or water droplets from the emergency supply system located in annulus 38, etc. Stiffness of cable 2 in the passage area in annulus 38 is additionally increased due to the need to install mounting joint 51 in protective pipe 40. To protect loose narrower ends 30 and 31 of tapered bellows 24 and 25 from damages, as an option, they can be located in pipe 19 and directed towards each other. Depending on cable 2 material, if it is less rigid, cable 2 in pipe 19 is suspended on springs 52 to maintain annular gap 47 between cable 2 braiding 48 and pipe 19 internal surface 49. To ensure control of electric input sealing, pressure gage 53 connected with nozzle 9 with permeation tube 54 is mounted on external flange 22. Permeation tube 54 is located in space 55 formed between shell 14 and pipe 19 and in space 56 formed between cable 2 and internal walls 57, 58 and 59 of protective pipes 39 and 40 and cylinder-shaped bellows 43 accordingly. The sealed cable input through external wall 11 and internal wall 1 of the nuclear power plant containment operates as follows. When current is passing through cable 2, power current heats up its metal cores, cable 2 temperature may reach up to 95° C., and due to thermal stress cable 2 starts to lengthen. During normal operation, connection pipe 3 of the first penetration unit fixed in relation to cable 2 is located in line with pipe 19 of the second penetration unit moving in relation to cable 2. This thermal stress caused by lengthening of cable 2 section covering annulus 38 towards external wall 11 is sufficient to overcome pressure load of crimps 35 in bellows 25 and to overcome stretching force of crimps 34 in bellows 24. Compression and stretching of crimps 35 and 34 in bellows 25 and 24 of the compensation means for relative motion of cable 2 and external wall 11 depend on the temperature drops occurred when cable 2 is switched on and off. When cable 2 is switched off, the latter begins to cool, and its length returns to its initial state, in this case crimps 35 of bellows 25 extend and crimps 34 of bellows 24 contract. In addition, cable 2 penetration located in annulus 38 between walls 1 and 11 may be subject to thermal impacts depending on process pipelines to be located in annulus 38, as well as on air humidity, ventilation flow change rate, etc. As cable 2 passage is enclosed in air heat accumulating area 50 formed by protective pipes 39, 40 and bellows 43 and operates as a thermostat, compensation means for relative motion of cable 2 and external wall 11 are operated in a partial load mode and crimps 34 and 35 will be subject to less wear and tear. However, the following situation may occur. Independent external wall 11 and internal wall 1 of the containment enclosure may start moving. Displacement of walls 1 and 11 or their sections may be independent in relation to each other. For instance in the following cases: when displacements occur due to seismic events, if a polar crane is operated when its supports pass under the first fixed penetration unit, when temperature of walls 1 and 11 or walls 1 and 11 and cable 2 changes, when tension of tensile ropes in internal wall 1 is loosened, etc. Such displacement breaches in-line arrangement of connection pipe 3 and pipe 19. As cable 2 stiffness is sufficient, connection pipe 3 or pipe 19 with internally mounted cable 2 output 46 started to move across the axis of cable 2 output 46 while changing annular gap 47 between its internal surface 49 and cable 2 braiding 48. Crimps 34 and 35 of bellows 24 and 25 start bending thus enabling unconstrained motion of expansion joint pipe 19 in relation to the fixed position of cable 2 output 46 as a response to any motion between walls 1 and 11 or walls 1 and 11 and cable 2 maintaining insulation integrity through the entire thickness of external wall 1. In this case, cylinder-shaped bellows 43 will also be bent, compressed and stretched depending on motion of protective pipes 39 and 40 while maintaining the integrity of cable 2 initial orientation. Technical and economic benefits lie in the fact that reliability of nuclear power plant operation is improved by maintaining insulation integrity of the cable input throughout the nuclear power plant service life with minimum maintenance. |
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description | The present invention relates to an arrangement for x-rays, in particular hard x-rays, for obtaining quantitative x-ray images from a sample. X-ray grating interferometry (GI) can provide simultaneously three complimentary contrasts: absorption, differential phase and small-angle scattering. Each contrast corresponds to a different physical interaction of the incoming x-rays with the sample under examination. The phase signal is highly sensitive to the electron density variations in the sample and can reveal differences between materials with similar absorption properties. The scattering signal is able to access unresolved structure variations of the sample in (sub) micrometer scale, which is beyond the resolution capability of the imaging modality. It has been demonstrated that both differential phase and scattering signals can provide valuable information additional to the traditional absorption contrast in medical imaging, material science and non-destructive testing. Especially, the scattering signal has drawn great attention due to its success in providing quantitative or inaccessible structural information in radiographic applications. In general, the scattering signal exhibits highly directional behavior if the underlying sample contains ordered internal structure. However, up to now imaging with grating interferometers has been mainly performed with linear gratings and the scattering sensitivity is only perpendicular to the grating lines, for instance, one implementation is descripted in Ref. [1] using linear gratings. Therefore, in order to obtain multiple-direction scattering (or differential phase) sensitivity, either the sample or the interferometer needs to be rotated, which is a time-consuming procedure. The usage of 2D gratings can mitigate the issue and provide up to four directions scattering sensitivity, however this approach requires a complicated imaging setup since one of the gratings needs to be scanned in a raster manner. Moreover, the noise performance is not the same in all directions due to different modulation orders of the phase stepping curves. An alternative speckle scanning technique is proposed to sense the scattering signal by scanning a membrane in the direction of interest, but this approach has similar shortcomings as the linear grating interferometric designs since the scattering sensitivity only corresponds to the scan direction. To cope with samples containing unknown directional structures, it would be favorable to design an imaging system with the following characteristics: Omnidirectional scattering sensitivity Differential phase contrast in two directions to allow integration of the phase signal Fast acquisition Straightforward mechanical setup: no need for scanning/rotation of sample or optical elements. Such a system would assure that all micro-structures, highly ordered or not, can be detected with the same sensitivity without taking any demanding precautions of the alignment of the sample with the optical axis. These objectives are achieved according to the present invention by a single-shot imaging arrangement according to the main claim and preferred embodiments according to the dependent claims. The invention discloses an arrangement for x-rays, in particular hard x-rays, for obtaining quantitative x-ray images from a sample, comprising: a) an X-ray source, preferably a standard polychromatic X-ray source (1); b) one phase-shift periodic structure G1 (4); c) a position-sensitive detector (PSD) (5) with spatially modulated detection sensitivity having a number of individual pixels; d) means for recording the images of the detector; e) means for evaluating the intensities in a single shot image in order to obtain the characteristics of the sample including absorption, differential phase contrast and directional (small-angle) scattering contrast, preferably for specified regions of pixels; and f) an optional absorption grating or a mask (G0) in front of, or embedded into the X-ray source (2);wherein the phase-shift periodic structure G1 is:i) a 2D periodic structure composed of unit cells, said unit cells are circular gratings; the period of the unit cells is P and that of the circular gratings is p, wherein the periodic structures in the circular grating generate a considerable X-ray phase shift difference, which is preferably of π/2 or odd multiples thereof, hereinafter referred to as π/2 shift; or π or π+N×2×π, hereinafter referred to as π shift, where N is an integer number; orii) a honeycomb structure composed of unit cells, each unit cell is a circular grating which allows the highest filling factor of circular structures on a 2D plane such periodic structure; the periodic structures in the circular grating generate a considerable X-ray phase shift difference, which is preferably of π/2 or odd multiples thereof, hereinafter referred to as π/2 shift; or π or π+N×2×π, hereinafter referred to as π shift, where N is an integer number. This single-shot imaging arrangement is capable of omnidirectional scattering sensitivity, acquisition of differential phase contrast signals in vertical and horizontal directions and absorption contrast without the rotation or shift of optical elements or the sample under examination. Preferably, the phase-shift periodic structure G1 is made by deep etching into silicon, a polymer or similar material, preferable for low energy X-ray photons; or deposit heavy metal into gaps of low-absorbing structure or grow heavy metal on low-absorbing substrate, in either case the metal is used as the phase shift material, preferably for high energy X-ray photons. A further preferred embodiment of the present invention is achieved, when the phase-shift periodic structure G1 creates a periodic interference pattern with a repetition of each unit cell P′ and the period within each unit cell is p′ at a known distance (Talbot effect) downstream on the PSD; P′ and p′ match the radius of curvature of an incident wavefront by relation p ′ = 1 η p d 1 + l 1 l 1 , P ′ = 1 η P d 1 + l 1 l 1 where l1 is the distance between the X-ray source (or the absorption grating or mask G0 if G0 is used) to the phase-shift periodic structure (G1), d1 is the distance between the phase-shift periodic structure (G1) and the created self-image η=1 for π/2 shift grating while η=2 for π shift grating. Typically, the detector can be a charge integrating detector with single photon sensitivity which has enhanced the spatial resolution using charge sharing effect. For the absorption grating or mask G0 an advantageous design can be achieved when the absorption grating or mask G0 is a 2D chessboard/mesh-type grating with pitch of p 0 = p × l 1 d 1 or integer multiples thereof, or when G0 is not used but the X-ray source comprises 2D array of individual sources that may be mutually incoherent and whose lateral separation p 0 = p × l 1 d 1 or integer multiples thereof. Further, in order to provide a simple arrangement for the sample handling, a mechanism can be comprised to place the sample to be investigated between the X-ray source (or G0 if G0 is used) and the phase-shift periodic structure G1, or between the phase-shift periodic structure G1 and the detector. Suitable analysis means may provide for an analysis procedure being implemented for obtaining the absorption, differential phase contrast and directional scattering contrasts of the sample that comprises the steps of recording two intensity images of the interference pattern (with sample and without sample) on the detector. Further, the analysis means may comprise means to detect the location of individual unit cells on the recorded flat image by using the circular nature of the phase-shift periodic structure G1, that being said, an intensity maximum is observed in the center of a unit cell. Furthermore, the analysis means may comprise means to calculate the shift between the flat and sample images of each unit cell, preferably achieved either with Fourier based methods and/or Hilbert transform methods by calculating the analytical signal or spatial correlation methods. Further, the analysis means may comprise means to evaluate the radial visibility reduction for every angle in order to obtain omnidirectional scattering images, preferably accomplished by Fourier methods from the following formula C ( n , m , θ ) = R k s R 0 f R k f R 0 f . Preferably, the mechanism to handle the sample may also comprise means for rotating the sample relatively to the remaining components to perform data collection for a tomographic scan. Advantageously, the phase-shift periodic structure G1 may be an absorption grating. FIG. 1 schematically shows an experimental arrangement for single-shot X-ray imaging. The arrangement comprises an X-ray source 1. In case of a polychromatic X-ray source a source grating 2 can be used. The source grating 2 can have a checkerboard of a grid design as seen in the figure. A sample 3 is placed downstream the source grating 2. Right after the sample 3 a phase shifting or phase-modulating grating 4 is placed. The phase-shifting grating 4 can have the two shown designs; mosaic and honeycomb. An x-ray detector 5 is placed at Talbot distance from the phase-shifting grating 4. A recorder 6 records the images of the detector 5 and a processors 7 evaluates the intensities in a single shot image in order to obtain the characteristics of the sample. A sample handling mechanism 8 can be comprised to place the sample 3 to be investigated between the X-ray source 1 and the phase-modulating structure 4. Preferably, the mechanism to handle the sample 8 may also comprise means for rotating the sample 9. The single-shot imaging arrangement is capable of omnidirectional scattering sensitivity, acquisition of differential phase contrast signals in vertical and horizontal directions and absorption contrast without the rotation or shift of optical elements or the sample under examination. There are two key components that enable the omnidirectional scattering sensitivity: 1) a dedicated and optimized phase grating design; and 2) a detector with sufficient resolution to resolve the generated interference pattern. These two topics are addressed in FIG. 2 which schematically depicts the experimental setup of FIG. 1 in perspective view (a). FIG. 2(b) shows scanning electron microscopy image of the fabricated phase-shift grating (scale bar 10 μm), having a period of the unit cell of 25 μm and a period of each grating of 5 μm. FIG. 2(c) schematically shows all necessary annotations for analyzing the recorded pattern. The imaging arrangement according to a preferred embodiment of the present invention comprises the following elements: An X-Rays source providing radiation for examining the object of interest (probe). An optional source grating 2 for increasing the coherence of the X-Ray source, the source grating is manufactured from an absorbing material and has a 2D grid or checkerboard design in order to increase coherence of the incoming beam in both horizontal and vertical directions (as shown in FIG. 1). The phase shifting grating 4 that modulates the phase of the incoming X-Rays by π or π/2. Examples for the dedicated design of the phase grating are depicted in FIG. 2(a). An X-Ray sensitive detector that is adapted to detect radiation after passing through the sample 3 and the phase-shifting grating 4 with a resolution sufficient to record the interference pattern at the distance the detector is placed. Particularly new in the proposed grating interferometer arrangement is the design of the phase-shifting grating 4. In conventional grating interferometry with linear gratings the scattering signal is detected from the visibility reduction of the interference fringe. Fine structures of the sample cause a local degradation of the coherence of the beam. Coherence is the main regulator of the local fringe visibility. However, linear grating require coherence only in one direction (the normal to the grating lines) in order to produce interference. In contrary, a circular interference pattern would require coherence in all direction (on the imaging plane) in order to generate a self-image with high visibility. A circular covering the whole field of view would only be capable of providing scattering information for different angles through linear segments passing through the center of the grating. In order to avoid this problem but still exploits the omnidirectional properties of the circular gratings the present invention proposes a design for the phase-shifting grating 4 being composed of a mosaic or a honeycomb repetition of circular gratings as shown in FIGS. 1 and 2(a). In the case of a mosaic repetition the circular gratings (also called unit cell) are repeated with a period of P in horizontal and vertical directions. In the case of the honeycomb arrangement the distance between the centers of neighboring unit cells is again P. The pitch of the circular gratings is p. In order to achieve the maximum filling ratio of the field of view (FOV) p should be a multiple of P, however designs where this condition is not fulfilled are also allowed. The detector is placed at a Talbot distance defined by the design photon energy of the arrangement and the pitch of the circular gratings p. The interference fringe at the selected Talbot distance can be characterized from the following periodicities: P′ and p′, where P′ the repetition rate of the self-images of the individual circular gratings and p′ the period of the self-images of the circular gratings. These periodicities are connected to the design values as following p ′ = 1 η p d 1 + l 1 l 1 , P ′ = 1 η P d 1 + l 1 l 1 where l1 is the distance between the source (or the source grating 2 if the source grating 2 is used) to the phase-shifting grating 4, d1 is the distance between the phase-shifting grating 4 and the generated interference pattern at the detector plane, η=1 for π/2 shift grating while η=2 for it shift grating. The projected period P′ defines the pixel size of the reconstructed images of the sample under investigation. The phase-shifting grating 4 is fabricated in a phase shifting material for the design energy of the imaging arrangement. This means that for low energies the grating can be etched in Si with deep reactive ion etching. For higher energies heavier materials like gold and nickel can be used to reduce the required thickness, at these high energies the required thickness for a phase shift of π or π/2 does not introduce a significant absorption of the incoming X-Rays. The imaging procedure requires the acquisition of two images. Initially, an image is recorded with only the phase-shifting grating 4 (and the source grating 2 if used) being placed in the x-ray beam. This image will be called the flat image (f). As the next step the sample is introduced into the x-ray beam without shifting or removing the phase-shifting grating 4 and a so-called sample image (s) is recorded. The analysis procedure starts by locating the self-images of the individual circular gratings on the pixel matrix of the flat image. Due to the circular nature of the grating a maximum is observed in the center, and this maximum is used as a finding criterion for the centers. Once all the centers have been detected a square area of P′×P′ around each center is selected and will be noted with the spatial coordinate (n, m) as shown in FIG. 2 c). The fringe of each circular grating is approximated by I ( n , m , ρ , θ ) = A ( n , m ) + B ( n , m , θ ) cos ( 2 π ρ ρ ′ ) ,where A(n, m) denotes the average intensity in the defined area, B(n, m, θ) the angular depend scattering coefficient and p, θ are the local coordinates at the unit cell (n, m). The transmission image is calculated as the ratio (sample over flat) of the average values of the recorded interference patterns: T ( n , m ) = Σ θ Σ ρ I s ( n , m , ρ , θ ) Σ θ Σ ρ I f ( n , m , ρ , θ ) The differential phase contrast images in horizontal and vertical directions are calculated by estimating the shift of the individual circular grating self-images. This can be done by a number of methods, for instance, spatial correlation estimation. Here, a method is proposed based on a linear square fit of the local estimated phase difference between the sample and flat fringes with a theoretical model that is valid for a sinusoidal approximation of the fringes. If the sample fringe is shifted by (x0, y0) then the local phase difference for one circular grating is given by Φ ( ρ , θ , x 0 , y 0 ) = 2 π p ′ [ ρ 2 - x 0 2 - y 0 2 - 2 ρ ( x 0 cos θ + y 0 sin θ ) - ρ ] The experimental local phase shift is calculated by a Hilbert phase retrieval in the x or y direction. The theoretical model is then fitted to the experimental phase and the values x0 and y0 are estimated. The directional scattering images are obtained by radial Fourier analysis of the recorded circular fringes. The scattering contrast is calculated by the appropriate Fourier coefficient of the radius of the fringe. The ratio of the Fourier coefficients results in the scatter contrast under that specific angle. Specifically directional scattering images are given by C ( n , m , θ ) = R k s R 0 f R k f R 0 f where Rk is the k-th harmonic of the discrete Fourier transform of the recorded fringe in direction θ and k=P′/p′. The method was experimentally validated at the TOMCAT beam line of the Swiss Light Source at Paul Scherrer Institut, CH-5232 Villigen PSI. A phase shifting grating with a radial period of 5 μm and unit cell period of 25 μm was fabricated by e-beam lithography and deep reactive ion etching (DRIE) of Si in house. The grating was etched to a depth of 11 μm which, at 17 keV illumination, produces a phase shift of pi/2. A scanning electron microscopy (SEM) image of the grating can be seen in FIG. 1 (b). The experimental setup is summarized in FIG. 1 (a). The photon energy was selected by a Si 111 monochromator. A pco. edge 4.2 CCD camera with 10 fold magnification (effective pixel size of 0.65 μm) was placed 17 cm behind the phase-shifting grating 4 which corresponds to the first fractional Talbot order. The directional scattering image of the carbon fiber loop can be seen in FIG. 3. A second sample that was scanned with the same parameters was a butterfly placed on the tip of a steel needle. The resulting transmission, differential phase in horizontal and vertical direction and directional scattering image can be seen in FIG. 4 (a), (b), (c) and (d) respectively. At the moment appropriate optics are used in order to achieve the necessary resolution to resolve the fringe, however current developments in detector research have made possible resolution enhancement beyond the pixel size of charge integrating hybrid detectors with single photon sensitivity. These developments will allow the application of the method for clinical and industrial applications. [1] WO 2011/011014 A1 (US HEALTH [US]; WEN HAN [US]) 27 Jan. 2011 (2011 Jan. 27). |
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description | The instant application claims priority to U.S. provisional application Ser. No. 61/182,288 filed on May 29, 2009, the subject matter of which is incorporated herein by reference in its entirety. 1. Field of the Invention The field of the invention pertains to apparatus and methods used for laser-based speed measurement of moving objects. Non-limiting embodiments of the invention are directed to portable, modularized, and self-contained opto-electronic apparatus for testing and certifying the accurate operation of a laser-based speed measuring device (hereinafter, “laser gun”), and methods associated therewith. 2. Description of Related Art Laser-based speed measuring devices, which are commonly referred to as “laser guns,” are regularly used by law enforcement agencies to monitor vehicle speeds as an aid in enforcing traffic laws. Laser guns incorporate electronic components whose performance can degrade over time. Since they are not intended to be adjusted by the end user, laser guns require periodic certification to correlate the speed values they display to the actual speed of the object being measured. This becomes especially important when the use of a laser gun by law enforcement agencies results in tangible punishment of offenders of vehicle traffic laws. In many such cases, the accuracy of the laser gun used by the officer is called into question in a court of law. Since the accuracy of a laser gun may be called into question, accurate records of each certification performed on each laser gun must be maintained over the service life of the laser gun. These records must also be producible quickly upon demand. In some cases it is also mandatory that a third party conduct the actual laser gun certification. Currently available apparatus and processes used to certify the operation of laser guns suffer from a number of disadvantages including but not limited to: (a) Certifications can be conducted only by using several discrete pieces of highly specialized and relatively costly electronic test equipment. This equipment is generally suitable for use only in a laboratory environment. The cost of this equipment, plus the skills needed to operate and maintain it, precludes most users of laser guns from having their own certification facilities in-house.(b) Each individual piece of test equipment used in laser gun certifications is required to be traceable to the National Institute of Standards and Technology (NIST). Taken as a whole, this requirement results in substantial calibration costs for the owner of the test equipment, and periodically requires the entire complement of equipment to be taken out of service for calibration.(c) Facilities that do have the proper test equipment and personnel are often located some distance from the owners and users of the laser guns. This requires laser guns to be shipped to and from the certification facility. This increases the possibility of the laser guns being damaged or stolen in transit and increases the amount of time the laser guns are out of service, thereby adding additional cost to the process.(d) Certification records typically are produced through manual data entry or recording techniques, based on sequential manual observations of the test equipment used in the certification process. This process is subject to human error and, because testing always proceeds in a known sequence, provides opportunities for deliberate falsification of data.(e) Records of certifications may not necessarily be stored in a secure manner, which provides opportunities for falsification of (or other alterations to) the data after a certification had been conducted and validated.(f) Among the facilities conducting certifications, there is no standard format for certification records and reports, resulting in inconvenience for the users of laser guns and increasing the chance that certification data might be misinterpreted.(g) Certification requirements vary significantly from user to user (e.g., agency-agency; state-state), and sometimes even within the same law enforcement agency. Because these requirements are inconsistent, there is a very real chance that a particular laser gun, although recently certified, still will not produce accurate results under all conditions in which it might reasonably be used. The inventor has appreciated the need for apparatus and methods that address and overcome the foregoing disadvantages with current technology and its use. Embodiments of the invention are directed to apparatus and methods utilizing such apparatus, for testing and/or certifying the operation of a laser gun. An exemplary, non-limiting embodiment of the invention is a modularized, plug-and-play-based apparatus used to test and measure the performance of a laser gun. The apparatus includes a main unit with which various modular, plug-and-play test heads can be interfaced to perform the desired testing and certification of a laser gun speed measuring device. More particularly, the apparatus includes a housing comprising a certification unit, which further includes an integrated programmable display that can provide a visual indicia of instructions or data or both to a user; a programmable control circuit including a plurality of functional blocks that provide control instructions for the apparatus, operationally coupled to the programmable display; a plurality of integrated connectors that each provide a plug-and-play-type interface for a respective modular test head; and at least one modular, plug-and-play-type test head including a programmable test control circuit further including a plurality of functional blocks that provide control operations of the test head. The apparatus has at least one of an optical and an electrical interface that enables a respective operational connection with the laser gun and, further wherein the apparatus (excluding the test heads) is self-contained and has size and weight characteristics that enable hand-held transport by the user. According to various, non-limiting aspects, the at least one modular, plug-and-play-type test head is an optical pulse characterization test head, an optical wavelength measurement test head, a distance measurement test head, an optical power measurement test head, a speed simulation test head, or an internal clock frequency measurement test head. The various test heads enable measurements of optical pulse characteristics, distance calibration characteristics, optical power characteristics, object speed calibration characteristics, internal clock frequency characteristics, and others. These various characteristics include, but are not limited to, pulse width, pulse frequency, a double-pulse condition, pulse wavelength, short-range distance, long-range distance, optical power, and speed simulation. Another exemplary, non-limiting embodiment of the invention is an apparatus used to test and measure the performance of a laser gun, similar to the apparatus embodiment described immediately above, except that the separate, modular test heads have been internalized to the main unit; i.e., all circuitry required to enable the test and measurement of parameters required to provide testing and certification of the speed gun in various jurisdictions are contained within a self-contained apparatus of the invention having size and weight characteristics that enable hand-held transport by the user. Another exemplary, non-limiting embodiment of the invention is directed to a method for making a particular, specified test of a speed gun with the apparatus to determine accuracy of the measurement and, if required, legal certification of the speed gun. In various non-limiting aspects, methods are disclosed for performing ‘pulse width,’ ‘double-pulse,’ ‘pulse frequency,’ ‘wavelength,’ ‘optical power,’ ‘speed simulation,’ internal clock frequency,’ sight alignment,’ horizontal beam width,’ vertical beam width,’ and other tests of a laser-gun-type speed measurement apparatus. These and other embodiments and aspects of the invention are described in detail below with reference to the drawing figures and as defined in the appended claims. An embodiment of the invention is a modularized test and certification apparatus for a laser-based speed measurement device. FIG. 1 shows a global block diagram of a test and certification apparatus 1000 according to a non-limiting, illustrative embodiment of the invention. A laser unit under test 9 (not part of the invention per se) generates an optical output 10a that is directed to a known, variable combination of optics 11 (optical interface stand), which conditions the optical output (i.e., single output 8a and optionally up to three additional outputs 8b, 8c, 8d) in a known manner to allow further processing. The conditioned output(s) 8a (through 8d) is directed at any given time to only one of several possible modular test heads, 7a through 7d, which may, as their function requires, also generate an optical signal 10b that is returned to the laser unit under test 9. Exemplary test head measurements include ‘pulse width,’ ‘double-pulse detection,’ ‘pulse frequency,’ ‘wavelength,’ ‘optical power,’ ‘speed simulation,’ ‘internal clock frequency,’ ‘sight alignment,’ ‘horizontal beam width,’ ‘vertical beam width,’ and others. Although in the non-limiting, illustrative embodiment described herein the apparatus 1000 is capable of interfacing to four test heads (7a-7d) at any given time, any number of test heads may be developed and used. Moreover, the number of interfaces may be expanded to accommodate more than four test heads at the same time. Upon receiving said conditioned data each test head 7a through 7d performs internal processing according to its particular purpose and then communicates the results of said processing to the main certification unit 1 via test head connectors 5a through 5d. The communication 6a through 6d consists of serial data transferred using an “I Squared C” (I2C) interface. It will be appreciated by those skilled in the art that other types of data transfer mechanisms could also be used. Test heads 7a through 7d also receive operating power and a standard clock signal from test head connectors 5a through 5d. Upon receiving data from any test head 7a through 7d, certification unit 1 performs further processing of said data in accordance with its current operating mode and shows the results of said processing on display 20, which may be integrated into the certification unit 1. As such, certification unit 1 is capable of independent operation, in which case display 20 functions to present test results and other information to the user, and user select switches 19 (see FIG. 2) function to accept commands from the user. Certification unit 1 may also convey test results to, and accept commands from, a local computer 2 via attachment 3 as shown in FIG. 1 and described in more detail below. (Line 4 is the variable power, e.g. a nominal 12V DC, being supplied to the laser unit under test by the test apparatus). FIG. 2 shows the face plate of certification unit 1. AC power receptacle 12 accepts a nominal 120 volts 60 Hz AC. DC power receptacle 13 accepts a nominal 12 volts DC. Switch 14 controls the power on/off function of the certification unit 1. Receptacle 15 is a cigar plug socket that may be used to supply a variable voltage to a laser unit under test. Indicator 16 is an LED well known to those skilled in the art, which illuminates when power is available at receptacle 15. Indicator 17 is an LED that illuminates when the certification unit 1 is powered on and operating and also indicates by its color whether or not the output of laser unit under test 9 is being properly directed into the input of the test apparatus. Connector 18 is a “Universal Serial Bus (USB) Type B”. This connector functions to provide communication between the certification unit 1 and an optional local computer 2. Communication methods other than USB as known in the art may be used. Connectors 5a through 5d provide plug-and-play-type interfaces for one or up to a respective plurality of various modular test heads (designated as 7a through 7d in FIG. 1 and described in more detail below), and may be of a “D-Shell” type known in the art. Display 20 is a programmable graphic LCD type known in the art. A typical display found suitable for use is the Crystalfontz CFAG320250CX-YYH; other display technologies could be substituted to suit a particular operating environment. Display 20 conveys instructions and/or data to a user (not shown). Four user select switches 19 provide for setting various operating options described in detail herein below. Each switch is of a pushbutton type. The function of any of the user select switches 19 may vary at any particular time; the operation that will be performed by each switch is indicated by text and/or graphics on display 20 that are positioned adjacent to that particular switch. The four user select switches 21 are reserved for future use and may not be installed in all variations of the embodiment; when installed, they are labeled and operate in the same fashion as the user select switches 19 previously described. FIG. 3a shows a detailed block diagram of the certification unit 1. An electronic circuit board contains the items required to perform the signal processing and control functions of certification unit 1. The various voltages required for the operation of this board are provided by logic power supply 28. A field programmable gate array (FPGA) 25 provides for the majority of the operation of the certification unit 1 via various internal functional blocks that are described below. A device found suitable for use is the Altera EP3C25E144C8NES. The operating configuration for FPGA 25 is stored in an EEPROM 27 and is automatically loaded into the FPGA upon application of power to the system. A 20 MHz oscillator 22 supplies a master clock 23 for the entire system 1000. Upon being applied to FPGA 25, master clock 23 is stepped up to 80 MHz via Phase Locked Loop (PLL) functional block 25a, whereupon it is used to provide an operating clock 25h for NIOS CPU functional block 25b. 20 MHz master clock 23 is also distributed to test head connectors 5a through 5d by a clock distribution buffer 24; a device found suitable for use is the Cypress CY2304. The NIOS CPU 25b performs all processing functions of the certification unit 1. Functional block 25c provides display logic to interface CPU 25b to display 20. Functional block 25d provides a UART to interface CPU 25b to USB-to-Serial converter 29, a Silicon Labs CP2102, which in turn supports USB communication via connector 18. Functional block 25f provides de-bouncing logic to interface CPU 25b to User Select Switches 19 (and 21, if used). Functional block 25e provides a first I2C interface that supports communication 26 with at least one, and up to four, of the modular, external test heads 7a through 7d via test head connectors 5a through 5d. This communication is used to control the test heads and to obtain their result data for further processing. Functional block 25g provides a second I2C interface that supports communication 30 with the Unit-Under-Test Power Supply 31. This communication is used to control the voltage applied to the laser unit under test 9 and also to report the power supply current being drawn by the laser unit under test 9. FIG. 3b shows a detailed block diagram of a modular Optical Pulse Characterization Test Head 1000-2, which interfaces to and operates in conjunction with the certification unit 1. An electronic circuit board contains the items required to perform the signal processing and control functions of the test head. A field programmable gate array (FPGA) 52 provides for the majority of the operation of the Optical Pulse Characterization Test Head via internal functional blocks described below. A device found suitable for use is the Altera EP3C25F256C7N. Test head connector 40 provides a nominal 12 volts DC, 41, to power supply circuit 42, which in turn generates and supplies operating voltages 43 to other parts of the test head as required. Test head connector 40 further provides a 20 MHz master clock 56 that is applied to PLL functional block 52f where it is stepped up to 80 MHz to provide an operating clock 52l for NIOS CPU functional block 52d. Light pulses 10a from the laser unit under test 9 are introduced into the test head via optical fiber interface 44, which comprises a lens system that focuses said light pulses into a fiber optic cable 45, which is in turn connected to optical detector 46. Optical detector 46, a Thor Labs FDS02, converts said light pulses into low-level current pulses 47, which are applied to an amplitude comparator circuit 50 and a high speed amplifier circuit 48. Various optical detectors known in the art could be used to provide this functionality. Amplitude comparator circuit 50 converts low-level current pulses 47 to a corresponding voltage. This voltage is compared to a reference voltage created by a resistor divider network to determine if it is within a usable range. NIOS CPU 52d reads the result 51 of this comparison and communicates, as described below, an “in range” or “out of range” status to NIOS CPU 28 in the certification unit 1, which illuminates indicator 17 green for an “in range” condition or red for an “out of range” condition. High speed amplifier circuit 48 converts low-level current pulses 47 to high-level voltage pulses 49 which are at a level that is suitable for use by sampling circuits 52b and 52c and which directly represent the pulse train being emitted by the laser unit under test 9. Sampling circuit 52b consists of eight parallel sampling paths that operate at phase differences that are successively 45 degrees apart as determined by the inverted and non-inverted states of four separate 400 MHz clocks 52n produced by PLL functional block 52e. Each cycle of eight samples contains a series of “1” or “0” bits that represent whether a pulse from the laser unit under test was present (“1”) or not present (“0”) at the time that sample was taken. This series of “1” and “0” bits results in an 8-bit block of data 52j which is transferred to memory 52a by clock 52i, which occurs at the end of each 8th sample. Said transfers continue until memory 55a has accumulated 512 of said data blocks. NIOS CPU 52d reads the contents of memory 52a and counts the “1” bits in all 512 data blocks. Based on the known 400 MHz sample rate and the use of 8 phase-shifted sampling paths the NIOS CPU 52d multiplies the count of “1” bits by the sample time to calculate the effective ‘pulse width’ of the output of the laser unit under test. NIOS CPU 52d further scans the data in memory 52a for continuity of “1” bits. If one or more “0” bits are found between two “1” bits, the NIOS CPU 52d determines that a “double pulse” event has occurred. After these scans are complete, memory 52a is cleared in preparation for another sampling sequence. Sampling circuit 52c includes a flip-flop function that toggles from a “0” to a “1” state on every other pulse in the pulse train from the laser unit under test 9, as represented by high-level electrical pulses 49. A counter is provided to accumulate the number of 400 MHz clock pulses that occur when the flip-flop is in the “1” state. When the flip-flop returns to the “0” state the value in the counter is transferred to a latch creating the locked value 52k, and the counter is reset in preparation for the next cycle. NIOS CPU 52d uses the locked value 52k to determine the pulse period of the output of the laser unit under test by multiplying said latched value by the period of the 400 MHz clock. Upon being queried by NIOS CPU 25b in certification unit 1, NIOS CPU 52d communicates information 52m about the pulse width and pulse period of the output of the laser unit under test 9 as well as whether or not a ‘double pulse’ event has occurred, to NIOS CPU 25b. Said communication takes place via an I2C pathway consisting of I2C bus logic functional block 52g, I2C low-level data stream 53, I2C buffer-driver 54, and I2C buffered data stream 55. Said information is then used by NIOS CPU 25a in certification unit 1 in determining the outcome of the ‘Pulse Width,’ ‘Pulse Frequency,’ or ‘Double Pulse’ test function that may be active at the particular time. FIG. 3c shows a detailed block diagram of an Optical Wavelength Measurement Test Head 1000-3 that interfaces to and operates in conjunction with the certification unit 1. An electronic circuit board contains the items required to perform the signal processing and control functions of the Test Head 1000-3. A field programmable gate array (FPGA) 68 provides for the majority of the operation of the Optical Wavelength Measurement Test Head 1000-3 via internal functional blocks described below. A device found suitable for use is the Altera EP3C25F256C7N. Test head connector 60 provides a nominal 12 volts DC, 61, to power supply circuit 62, which in turn generates and supplies operating voltages 63 to other parts of the test head as required. Test head connector 60 further provides a 20 MHz master clock 72 that is applied to PLL functional block 68c where it is stepped up to 80 MHz to provide an operating clock 68f for NIOS CPU functional block 68b. Light pulses 10a from the laser unit under test 9 are introduced into the test head 1000-3 via optical fiber interface 65, which comprises a lens system that focuses said light pulses into a fiber optic cable 66, which is in turn connected to spectrometer 64. Spectrometer 64 is an Ocean Optics USB4000 type, which uses an optical grating to separate incoming light into individual wavelengths, which are then focused on elements in a linear detector array in a manner such that each array element is capable of measuring the intensity of a specific wavelength of light. Similar devices known in the art could be used to provide the same functionality. NIOS CPU 68b communicates with spectrometer 64 via UART functional block 68a and serial link 67 to configure spectrometer 64 and to retrieve data from it. The data retrieved is a list of values representing the intensity of the particular wavelength of light that is impacting each linear detector element. NIOS CPU 68b now searches said list of values to find the highest value in the list. Since the map between the elements of the linear detector and the wavelength applied to each is fixed and well known, the overall wavelength of the laser unit under test 9 is determined to be the same as the wavelength associated with the element position that has the highest value in the list. Upon being queried by NIOS CPU 25b in certification unit 1, NIOS CPU 68b communicates information 68g about the wavelength of the output of the laser unit under test 9 to NIOS CPU 25b. Said communication takes place via an I2C pathway consisting of I2C bus logic functional block 68d, low-level I2C data stream 69, I2C buffer-driver 70, and I2C buffered data stream 71. Said information is then used by NIOS CPU 25b in certification unit 1 in determining the outcome of the ‘Wavelength’ test function. FIG. 3d shows a detailed block diagram of a Distance Measurement Test Head 1000-4 that interfaces to and operates in conjunction with the certification unit 1. An electronic circuit board contains the items required to perform the signal processing and control functions of the Test Head 1000-4. FPGA 87 provides for the majority of the operation of the Distance Measurement Test Head 1000-4 via internal functional blocks described below. A device found suitable for use is the Altera EP3C25F256C7N. Test head connector 80 provides a nominal 12 volts DC, 81, to power supply circuit 82, which in turn generates and supplies operating voltages 83 to other parts of the test head as required. Test head connector 80 further provides a 20 MHz master clock 91 that is applied to PLL functional block 87c where it is stepped up to 80 MHz to provide an operating clock 87d for NIOS CPU functional block 87a. Light pulses 10a from the laser unit under test 9 are introduced into the test head 1000-4 via optical fiber interface 84, which comprises a lens system that focuses said light pulses into a coil of bare optical fiber 85, the output of which is in turn connected to optical fiber interface 86. Light pulses 10b exiting coil of bare fiber 85 are returned to the laser unit under test 9 after a delay caused by the time it takes for the light to travel said coil of bare fiber 85. This delay corresponds to a known simulated distance and is the basis for the operation of the Distance Measurement Test Head 1000-4. Various shorter and longer fiber coil lengths may be used for short-range and long-range distance calibrations, respectively. Upon being queried by NIOS CPU 25b in certification unit 1, NIOS CPU 87a communicates the calibrated simulation distance of the coil of bare fiber 85 to NIOS CPU 25b. Said communication takes place via an I2C pathway consisting of I2C bus logic functional block 87b, low-level I2C data stream 88, I2C buffer-driver 89, and I2C buffered data stream 90. Said information is then used by NIOS CPU 25a in certification unit 1 in the operation of the ‘Distance Measurement’ test function. FIG. 3e shows a detailed block diagram of an Optical Power Measurement Test Head 1000-5 that interfaces to and operates in conjunction with the certification unit 1. An electronic circuit board contains the items required to perform the signal processing and control functions of the Test Head. FPGA 113 provides for the majority of the operation of the Optical Power Measurement Test Head 1000-5 via internal functional blocks described below. A device found suitable for use is the Altera EP3C25F256C7N. Test head connector 100 provides a nominal 12 volts DC, 101, to power supply circuit 102, which in turn generates and supplies operating voltages 103 to other parts of the test head as required. Test head connector 100 further provides a 20 MHz master clock 117 that is applied to PLL functional block 113c where it is stepped up to 80 MHz to provide an operating clock 113e for NIOS CPU functional block 113a. Light pulses 10a from the laser unit under test 9 are applied to external optical power probe 104, an Ophir PD200-SH-V2, which is individually calibrated for use with a particular instance of test head 1000-5. Optical power probe 104 utilizes a thermopile effect to convert said light pulses into heat, then converts said heat into an electrical current, 105, which is linearly proportional to the optical power of light pulses 10a. Similar devices as known in the art could be used to provide the same functionality. Electrical current 105 is conveyed via power probe connector 106 and cabling 107 to an amplifier and scaling circuit 108, which converts electrical current 105 to a proportional voltage 109. This conversion is performed using a precision amplifier and collection of four precision resistors with values arranged by factors of 10, which may be switched in and out of the feedback path of the amplifier to change its gain. The switching of the resistors within amplifier and scaling circuit 108 is controlled by NIOS CPU functional block 113b via 4-wire connection 111, each wire being a means by which to select a single one of the four available precision resistors. Voltage 109 is applied to an analog-to-digital converter circuit 112, which provides 16 bits of resolution; a device found suitable for use is the ADS 1110. NIOS CPU 113a interfaces to and queries analog-to-digital converter circuit 110 via I2C functional block 113a and I2C bus connection 112 and utilizes this interface to retrieve a 16-bit value representing the instantaneous amplitude of voltage 109 at the time of said query. The aforementioned calibration between power probe 104 and the individual instance of test head 1000-5 consists of two known data points. The first data point represents a power level of 1 microwatt and the second data point represents a power level of 100 milliwatts. These data points are plotted in an X vs. Y fashion such that current is represented on the X axis and power is represented on the Y axis. An imaginary line is then drawn between these two calibrated points. Utilizing the value obtained from analog-to-digital converter circuit 110 and the known value of the precision resistor, which is currently selected for use within amplifier and scaling circuit 108, NIOS CPU 113b calculates a current that is proportional to the optical power of the light pulses from laser unit under test 9. NIOS CPU 113b then applies the well-known formula “Y=MX+B” to the aforementioned imaginary line to convert the calculated current into its corresponding actual optical power value. In this case Y represents power, X represents current, M is the slope of the aforementioned imaginary line and, B is an imaginary point at which the aforementioned imaginary line crosses the Y axis. Upon being queried by NIOS CPU 25b in certification unit 1, NIOS CPU 113b communicates said calculated optical power to NIOS CPU 25b. Said communication takes place via an I2C pathway consisting of I2C bus logic functional block 113d, low-level I2C data stream 114, I2C buffer-driver 115, and I2C buffered data stream 116. The information is then used by NIOS CPU 25b in certification unit 1 in the operation of the ‘Optical Power’ test function. FIG. 3f shows a detailed block diagram of a Speed Simulation Test Head 1000-6 that interfaces to and operates in conjunction with the certification unit 1. An electronic circuit board contains the items required to perform the signal processing and control functions of the Speed Simulation Test Head. FPGA 132 provides for the majority of the operation of the Speed Simulation Test Head 1000-6 via internal functional blocks described below. A device found suitable for use is the Altera EP3C25F256C7N. Test head connector 120 provides a nominal 12 volts DC, 121, to power supply circuit 122, which in turn generates and supplies operating voltages 123 to other parts of the test head as required. Test head connector 120 further provides a 20 MHz master clock 142 that is applied to PLL functional block 132d where it is stepped up to 80 MHz to provide an operating clock 132i for NIOS CPU functional block 132e. Light pulses 10a from the laser unit under test 9 are introduced into the test head 1000-6 via optical fiber interface 124, which comprises a lens system that focuses the light pulses into a fiber optic cable 125, which is in turn connected to optical detector 126. Optical detector 126 is a Thor Labs FDS02, which converts light into low-level current pulses 127 which are linearly proportional to the optical power of the light pulses. Similar devices as known in the art could be used to provide the same functionality. Amplitude comparator circuit 128 converts low-level current pulses 127 to a corresponding voltage. This voltage is compared to a reference voltage created by a resistor divider network to determine if it is within a usable range. NIOS CPU 132e reads the result 131 of this comparison and communicates an “in range” or “out of range” status to NIOS CPU 25b in the certification unit 1, which illuminates indicator 17 green for an “in range” condition or red for an “out of range” condition. High speed amplifier circuit 129 converts low-level current pulses 127 to logic-level voltage pulses 130, which are at a level that is suitable for use by sampling circuit 132b and, which directly represent the pulse train being emitted by the laser unit under test 9. Sampling circuit 132b consists of eight parallel sampling paths that operate at phase differences that are successively 45 degrees apart as determined by the inverted and non-inverted states of four separate 400 MHz clocks 132h produced by PLL functional block 132c. Logic-level voltage pulses 130 are applied in parallel to all eight sampling paths. Each of the sampling paths consists of a chain of 16 cascaded ‘D’ flip-flops that propagate the logic-level pulses 130 at a rate and phase difference determined by the clock associated with that path. When the output of the last flip-flop in the chain goes to a “1” state, this indicates that a pulse from the laser unit under test 9 has been detected. This indication is used to enable variable delay 132a, driven by the clock associated with that path, to begin counting up from a preloaded value, which is obtained from an 11-bit counter that is common to all 8 sampling paths and, which is continuously incremented by a “0” to “1” transition of the logic-level pulses 130. When variable delay 132a reaches its maximum value its output, 133, goes to a logic “1”. High speed amplifier 134 increases the amplitude of logic-level signal 133 to produce high-level signal 135, which is sufficient to drive the control pin of laser 136. Laser 136 then emits a pulse that is communicated through optical fiber 137 to optics 138, which in turn produce light pulse 10b that is directed to the input of the laser unit under test 9. Light pulse 10b is interpreted by laser unit under test 9 as if it were a return signal from a target object causing laser unit under test 9 to display a speed reading which corresponds to the described delay. Sampling circuit 132b includes a flip-flop function that toggles from a “0” to a “1” state on every other pulse in the pulse train from the laser unit under test 9, as represented by high-level electrical pulses 130. A counter is provided to accumulate the number of 400 MHz clock pulses that occur when the flip-flop is in the “1” state. When the flip-flop returns to the “0” state the value in the counter is transferred to a latch creating the locked value 132b and the counter is reset in preparation for the next cycle. NIOS CPU 132e uses the locked value 132b to determine the pulse period of the output of the laser unit under test 9 by multiplying said latched count by the 2.5 ns period of the 400 MHz clock. By dividing the empirically-derived value of 0.74948 by said pulse period, NIOS CPU 132e calculates the speed that the laser unit under test 9 “should” display. This “expected speed” is typically in the range of 100 miles per hour. Upon being queried by NIOS CPU 25b in certification unit 1, NIOS CPU 132e communicates the “expected speed” 132j to NIOS CPU 25b. Said communication takes place via an I2C pathway consisting of I2C bus logic functional block 132f, low-level I2C data stream 139, I2C buffer-driver 140, and I2C buffered data stream 141. The information is then used by NIOS CPU 25b in certification unit 1 in the operation of the ‘Speed Simulation’ test function. FIG. 3g shows a detailed block diagram of an Internal Clock Frequency Measurement Test Head 1000-7 that interfaces to and operates in conjunction with the certification unit 1. An electronic circuit board contains the items required to perform the signal processing and control functions of the Test Head. FPGA 169 provides for the majority of the operation of the Internal Clock Frequency Test Head via internal functional blocks described below. A device found suitable for use is the Altera EP3C25F256C7N. Test head connector 160 provides a nominal 12 volts DC, 161, to power supply circuit 162, which in turn generates and supplies operating voltages 163 to other parts of the test head 1000-7 as required. Test head connector 160 further provides a 20 MHz master clock 173 that is applied to PLL functional block 169f where it is stepped up to 80 MHz to provide an operating clock 169g for NIOS CPU functional block 169b. 20 MHz master clock 173 is also applied to PLL functional block 169d where it is used to provide an operating clock 169e for sampling circuit 169c. An operating clock signal 164 from the laser unit under test 9 is introduced into the test head 1000-7 via probe interface 165, which comprises an “SMA” style connector that accepts an industry-standard oscilloscope probe. High speed amplifier circuit 167 converts low-level pulses 166 to logic-level voltage pulses 168 that are at a level suitable for use by sampling circuit 132b and, which directly represent the internal operating clock of the laser unit under test 9. Sampling circuit 169c consists of a counter, which is clocked by pulses 168; and a 1-second timer, which causes the count of pulses to be latched once per second to produce latched value 169a. NIOS CPU 169b interprets the latched value 169a as the actual frequency, in Hz, of the internal clock of the laser unit under test 9. Upon being queried by NIOS CPU 25b in certification unit 1, NIOS CPU 169b communicates the measured frequency 169i to NIOS CPU 25b. Said communication takes place via an I2C pathway consisting of I2C bus logic functional block 169h, low-level I2C data stream 170, I2C buffer-driver 171, and I2C buffered data stream 172. The information is then used by NIOS CPU 25b in certification unit 1 in the operation of the ‘Internal Clock Frequency’ test function. FIG. 4 shows a block diagram of an optional computer system 2 that may function to collect and process test result data generated by the embodied apparatus 1000. Programmable computer 2 comprises a main processor 2a, memory 2b, non-volatile storage media 2c, and other I/O resources 2d as required to allow computer system 2 to run a commercial operating system software suited to the requirements of the invention. A large variety of computer hardware exists that can be combined in a variety of suitable fashions to meet the operating requirements of the invention. The operating system 2e is typically Windows XP®, Windows Vista®, or Windows 7®, produced by Microsoft Corporation. Subsequent iterations of these systems as well as other operating systems known in the art offering comparable capabilities could also be used. A display 2f, commonly a video screen, and user input means, commonly a combination of a keyboard 2g and pointing device 2h, allow a user to interact with computer system 2. Other means of user input (touch screen, voice recognition, pen-based, etc.) may also be used in addition to, or in place of, a keyboard and pointing device. Also included in computer system 2 is a communication means 2j, in this case a device driver that emulates a serial port and, a communications port 2i, in this case a USB port, both used in combination to communicate with certification unit 1. Other known means of communication may be used in place of the combination of a serial port emulation device driver and USB connection if conditions require. Programmable computer 2 along with operating system software 2e allows running application software 2k to perform the functions of a client in a data storage and retrieval network and to interact directly with the certification unit 1 as described in more detail below. Operation of the Invention The following paragraphs describe further details of various exemplary test functions within the certification unit 1 and the plurality of modular test heads that may be used in conjunction with the certification unit 1. FIG. 5 shows a flow chart 2000-1 of a “Controls Operational” test that may be applied to the laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) The user is instructed at step 202 to conduct a visual inspection of the laser unit under test 9 to ensure there are no obvious physical defects that would prevent the laser unit under test 9 from being used in normal service. Said instruction may be from prior training of the user, may be displayed on the screen of local computer 2 if connected, or displayed on display 20.(b) If the visual inspection shows any defects (step 204) the laser unit under test 9 fails certification (step 224). The “Controls Operational” test is then concluded at step 224 and no further testing takes place; otherwise,(c) Next, certification unit 1 is placed in an operating mode whose primary purpose is only to vary the power supply voltage to the laser unit under test 9 (step 206). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, certification unit 1 may apply (as necessary, which may not be the case for laser units that are hard-wired into a vehicle) a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 208). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(e) Next, the user is instructed to turn the laser unit under test 9 on if required (step 210) and is then instructed in the same fashion to invoke a typical self test feature of laser unit under test 9 and observe the results in conjunction with the description of said self test as may be contained in the operating manual for the laser unit under test 9 (step 212). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. The certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(f) If the self test of the laser unit under test 9 fails (step 214), the laser unit under test 9 fails certification at step 224. The “Controls Operational” test is then concluded (step 224) and no further testing takes place; otherwise,(g) If the self test of the laser unit under test 9 passes (step 214), the user records this result (step 216). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(h) It is next determined if the “Controls Operational” test is to be repeated at another, different power supply voltage (step 218). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another, different power supply voltage, execution of the test returns to step 208.(i) When the “Controls Operational” test has been successfully concluded at all desired power supply voltages the laser unit under test 9 is considered to have passed the “Controls Operational” test and is eligible to continue the test process (step 220). The “Controls Operational” test is then concluded at step 224. FIG. 6 shows a flow chart 2000-2 of a “Low Voltage Indicator” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) The user is instructed to plug the laser unit under test 9 into receptacle 15 of the certification unit 1 (step 302). Said instruction may be from prior training, may be displayed on the screen of local computer 2 if connected or on display 20. (b) Next, certification unit 1 is placed in an operating mode whose primary purpose is only to vary the power supply voltage to the laser unit under test 9 (step 304). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified starting voltage to receptacle 15 for use by the laser unit under test 9 (step 306). Said starting voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 308). Said instruction may be from prior training of the user, may be displayed on the screen of local computer 2 if connected or on display 20. The certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(e) Next, the supply voltage being applied to laser unit under test 9 is decreased by 0.1 volts (step 310). Said decrease may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(f) If the “Low Voltage” indicator on the laser unit under test 9 is not illuminated (step 312) and the voltage currently being applied to the laser unit under test 9 is greater than the point at which the “Low Voltage” indicator of the laser unit under test 9 is specified to illuminate (step 314), the process continues at step 310 as previously described in paragraph (e).(g) If the “Low Voltage” indicator on the laser unit under test 9 is not illuminated (step 312) and the voltage currently being applied to the laser unit under test 9 is less than the point at which the “Low Voltage” indicator of the laser unit under test 9 is specified to illuminate (step 314), the laser unit under test 9 fails certification (step 322). The “Low Voltage” test is then concluded at step 324 and no further testing takes place; otherwise,(h) If the “Low Voltage” indicator on the laser unit under test 9 is illuminated (step 312) a comparison is made between the supply voltage being applied to laser unit under test 9 and the point at which the “Low Voltage” indicator of the laser unit under test 9 is specified to illuminate (step 316). If said supply voltage is within a specified range of said specified illumination point, the user records this result (step 318). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(i) The laser unit under test 9 is now considered to have passed the “Low Voltage Indicator” test and is eligible to continue the test process (step 320). The “Low Voltage Indicator” test is then concluded at step 324. FIG. 7 shows a flow chart 2000-3 of a “Radio Frequency Interference” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, certification unit 1 is placed in an operating mode whose primary purpose is only to vary the power supply voltage to the laser unit under test 9 (step 402). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(b) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 404). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected. The certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(c) Next, the user is instructed to turn the laser unit under test 9 on if required (step 406). Said instruction may be from prior training of the user, may be displayed on the screen of local computer 2 if connected or on display 20.(d) Next, the user is instructed to place an RF transceiver (not shown) in close proximity to the laser unit under test 9 and then to observe an “RFI” indicator on the laser unit under test 9 (step 408). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(e) If the “RFI” indicator of the laser unit under test 9 fails to illuminate (step 410), the laser unit under test 9 fails certification (step 418). The “Radio Frequency Interference” test is then concluded at step 420 and no further testing takes place; otherwise,(f) If the “RFI” indicator of the laser unit under test 9 illuminates (step 410), the user records this result (step 412). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(g) It is next determined if the “Radio Frequency Interference” test is to be repeated at another, different power supply voltage (step 414). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another, different power supply voltage, execution of the test returns to step 404.(h) When the “Radio Frequency Interference” test has been successfully concluded at all desired power supply voltages the laser unit under test 9 is considered to have passed the “Radio Frequency Interference” test and is eligible to continue the test process (step 416). The “Radio Frequency Interference” test is then concluded at step 420. FIG. 8 shows a flow chart 2000-4 of a “Power Supply Current” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) The user is instructed to plug the laser unit under test 9 into receptacle 15 of the certification unit 1 (step 502). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. (b) Next, certification unit 1 is placed in an operating mode whose primary purpose is to measure the amount of power supply current being drawn by the laser unit under test 9 (step 504). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected. The certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 506). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 508). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(e) Next, the certification unit 1 measures the amount of power supply current being drawn by the laser unit under test 9 and displays this measurement to the user as a peak value and as an instantaneous value (step 510). Said measurements may be shown on the display 20 of the certification unit 1 or on the screen of local computer 2 if connected.(f) Next, a comparison is made between the measured peak power supply current drawn by laser unit under test 9 and the range of power supply current that the laser unit under test 9 is specified to consume (step 512). If said peak current is not within said specified range the laser unit under test 9 fails certification (step 520). The “Power Supply Current” test is then concluded at step 224 and no further testing takes place; otherwise,(g) If said peak current is within said specified range the user records this result along with the peak current measurement (step 514). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(h) It is next determined if the “Power Supply Current” test is to be repeated at another, different power supply voltage (step 516). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another, different power supply voltage, execution of the test returns to step 506.(i) When the “Power Supply Current” test has been successfully concluded at all desired power supply voltages the laser unit under test 9 is considered to have passed the “Power Supply Current” test and is eligible to continue the test process (step 518). The “Power Supply Current” test is then concluded at step 522. FIG. 9 shows a flow chart 2000-5 of a “Distance Measurement” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, certification unit 1 is placed in an operating mode whose primary purpose is to conduct either a Short Range Distance Test or a Long Range Distance Test (step 602). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(b) Next, the user is instructed to connect either the “Short Range Distance Test Head” or the “Long Range Distance Test Head” (not shown) to the certification unit 1 and the test does not proceed until connection of the proper test head is detected (step 604). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. Also as part of step 604, certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 606). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 608). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(e) Next, the “expected distance” for the current test is presented to the user (step 610). Said presentation may be via display 20 of the certification unit 1 or via the screen of local computer 2 if connected.(f) Next, the user is instructed to point the output of the laser unit under test 9 at the optical interface stand 11 (see FIG. 1) interfaced to the test head(s) and to re-orient the laser unit under test 9 in relation to said optics 11 until the laser unit under test 9 displays a valid distance reading (step 612). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(g) Next, the user is instructed to compare the distance displayed by the laser unit under test 9 to the “expected distance” that was presented to the user in step 610. Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. If the result of said comparison is that the distance displayed by the laser unit under test 9 is not within a specified range of the aforementioned “expected distance” the laser unit under test 9 fails certification (step 622). The “Distance Measurement” test is then concluded at step 624 and no further testing takes place; otherwise,(h) If said comparison indicates that the distance displayed by the laser unit under test 9 is within a specified range of the aforementioned “expected distance” the user records this result along with the actual distance displayed by the laser unit under test 9 (step 616). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(i) It is next determined if the “Distance Measurement” test is to be repeated at another, different power supply voltage (step 618). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another, different power supply voltage, execution of the test returns to step 606.(j) When the “Distance Measurement” test has been successfully concluded at all desired power supply voltages the laser unit under test 9 is considered to have passed the “Distance Measurement” test and is eligible to continue the test process (step 620). The “Distance Measurement” test is then concluded at step 522. FIG. 10 shows a flow chart 2000-6 of a “Double Pulse” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, certification unit 1 is placed in an operating mode whose primary purpose is to conduct a Double Pulse Test (step 702). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(b) Next, the user is instructed to connect the “Pulse Characterization Test Head” (not shown) to the certification unit 1 and the test does not proceed until connection of the proper test head is detected (step 704). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. Also as part of step 704, the certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 706). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 708). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(e) Next, the user is instructed to point the output of the laser unit under test 9 at the optical interface stand 11 interfaced to the test head(s) and to re-orient the laser unit under test 9 in relation to said optics 11 until the “Power/Aiming” indicator of the certification unit 1 turns green (step 710). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(f) Next, the Pulse Characterization Test Head samples the pulses in the output 10a of the laser unit under test 9 and performs an analysis, previously described, to determine if a “double pulse” condition exists (step 712).(g) Next, the result of said analysis is presented to the user (step 714). If said analysis indicates that double pulses exist (step 716) the laser unit under test 9 fails certification (step 724). The “Double Pulse” test is then concluded at step 726 and no further testing takes place; otherwise,(h) If no double pulses are indicated the user records this result (step 718). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(i) It is next determined if the “Double Pulse” test is to be repeated at another, different power supply voltage (step 720). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another, different power supply voltage, execution of the test returns to step 706.(j) When the “Double Pulse” test has been successfully concluded at all desired power supply voltages the laser unit under test 9 is considered to have passed the “Double Pulse” test and is eligible to continue the test process (step 722). The “Double Pulse” test is then concluded at step 726. FIG. 11 shows a flow chart 2000-7 of a “Pulse Frequency” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, certification unit 1 is placed in an operating mode whose primary purpose is to conduct a Pulse Frequency Test (step 802). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(b) Next, the user is instructed to connect the “Pulse Characterization Test Head” (not shown) to the certification unit 1 and the test does not proceed until connection of the proper test head is detected (step 804). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. Also as part of step 804, the certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 806). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 808). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(e) Next, the user is instructed to point the output of the laser unit under test 9 at the optical interface stand 11 of the test head(s) and to re-orient the laser unit under test 9 in relation to said optics 11 until the “Power/Aiming” indicator of the certification unit 1 turns green (step 810). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(f) Next, the Pulse Characterization Test Head samples the pulses in the output 10a of the laser unit under test 9 and performs an analysis, previously described, to determine the pulse frequency of the output 10a of the laser unit under test 9.(g) Next, the measured pulse frequency is presented to the user (step 814). Said presentation may be via display 20 of the certification unit 1 or via the screen of local computer 2 if connected.(h) Next, a comparison is made between said presented pulse frequency and the pulse frequency at which the laser unit under test 9 is specified to operate (step 816). If said presented pulse frequency is not within a predetermined and proper range of the pulse frequency at which the laser unit under test 9 is specified to operate, the laser unit under test 9 fails certification (step 824). The “Pulse Frequency” test is then concluded at step 826 and no further testing takes place; otherwise,(i) If said presented pulse frequency is within said predetermined and proper range of the pulse frequency at which the laser unit under test 9 is specified to operate, the user records this result (step 818). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(j) It is next determined if the “Pulse Frequency” test is to be repeated at another different power supply voltage (step 820). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another different power supply voltage, execution of the test returns to step 806.(k) When the “Pulse Frequency” test has been successfully concluded at all desired power supply voltages, the laser unit under test 9 is considered to have passed the “Pulse Frequency” test and is eligible to continue the test process (step 822). The “Pulse Frequency” test is then concluded at step 826. FIG. 12 shows a flow chart 2000-8 of a “Pulse Width” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, certification unit 1 is placed in an operating mode whose primary purpose is to conduct a Pulse Width Test (step 902). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(b) Next, the user is instructed to connect the “Pulse Characterization Test Head” (not shown) to the certification unit 1 and the test does not proceed until connection of the proper test head is detected (step 904). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. Also as part of step 904, the certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 906). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 908). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(e) Next, the user is instructed to point the output of the laser unit under test 9 at the optical interface stand 11 interfaced to the test head(s) and to re-orient the laser unit under test 9 in relation to said optics 11 until the “Power/Aiming” indicator of the certification unit 1 turns green (step 910). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(f) Next, the Pulse Characterization Test Head samples the pulses in the output 10a of the laser unit under test 9 and performs an analysis, previously described, to determine the pulse width of the output 10a of the laser unit under test 9 (step 912).(g) Next, the measured pulse width is presented to the user (step 914). Said presentation may be via display 20 of the certification unit 1 or via the screen of local computer 2 if connected.(h) Next, a comparison is made between said presented pulse width and the pulse width at which the laser unit under test 9 is specified to operate (step 916). If said presented pulse width is not within a predetermined and proper range of the pulse width at which the laser unit under test 9 is specified to operate, the laser unit under test 9 fails certification (step 924). The “Pulse Width” test is then concluded at step 926 and no further testing takes place; otherwise,(i) If said presented pulse width is within said predetermined and proper range of the pulse width at which the laser unit under test 9 is specified to operate, the user records this result (step 918). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(j) It is next determined if the “Pulse Width” test is to be repeated at another different power supply voltage (step 920). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another different power supply voltage, execution of the test returns to step 906.(k) When the “Pulse Width” test has been successfully concluded at all desired power supply voltages the laser unit under test 9 is considered to have passed the “Pulse Width” test and is eligible to continue the test process (step 922). The “Pulse Width” test is then concluded at step 926. FIG. 13 shows a flow chart 2000-9 of an “Optical Power” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, certification unit 1 is placed in an operating mode whose primary purpose is to conduct an Optical Power Test (step 1002). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(b) Next, the user is instructed to connect the “Optical Power Test Head” (not shown) to the certification unit 1 and the test does not proceed until connection of the proper test head is detected (step 1004). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. Also as part of step 1004, the certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 1006). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 1008). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(e) Next, the user is instructed to point the output of the laser unit under test 9 at the input of the external power sensor 104 (see FIG. 3e) attached to the test head and to re-orient the laser unit under test 9 in relation to said power sensor until the “Power/Aiming” indicator of the certification unit 1 turns green (step 1010). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(f) Next, the Optical Power Test Head measures the current from said power sensor and performs an analysis, previously described, to determine the optical power of the output 10a of the laser unit under test 9 (step 1012).(g) Next, the measured optical power is presented to the user (step 1014). Said presentation may be via display 20 of the certification unit 1 or via the screen of local computer 2 if connected.(h) Next, a comparison is made between said presented optical power and the optical power at which the laser unit under test 9 is specified to operate (step 1016). If said presented optical power is not within a predetermined and proper range of the optical power at which the laser unit under test 9 is specified to operate, the laser unit under test 9 fails certification (step 1024). The “Optical Power” test is then concluded at step 1026 and no further testing takes place; otherwise,(i) If said presented optical power is within said predetermined and proper range of the optical power at which the laser unit under test 9 is specified to operate, the user records this result (step 1018). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(j) It is next determined if the “Optical Power” test is to be repeated at another different power supply voltage (step 1020). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another different power supply voltage, execution of the test returns to step 1006.(k) When the “Optical Power” test has been successfully concluded at all desired power supply voltages the laser unit under test 9 is considered to have passed the “Optical Power” test and is eligible to continue the test process (step 1022). The “Optical Power” test is then concluded at step 1026. FIG. 14 shows a flow chart 2000-10 of a “Wavelength” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, certification unit 1 is placed in an operating mode whose primary purpose is to conduct a Wavelength Test (step 1102). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(b) Next, the user is instructed to connect the “Wavelength Test Head” (not shown) to the certification unit 1 and the test does not proceed until connection of the proper test head is detected (step 1104). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. Also as part of step 1104, the certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 1106). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 1108). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(e) Next, the user is instructed to point the output of the laser unit under test 9 at the optical interface stand 11 interfaced to the test head(s) and to re-orient the laser unit under test 9 in relation to said optics 11 until the “Power/Aiming” indicator of the certification unit 1 turns green (step 1110). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(f) Next, the Wavelength Test Head performs any necessary setup and communication tasks related to the spectrometer 64 (see FIG. 3c) and then performs an analysis, previously described, to determine the operating wavelength of the output 10a of the laser unit under test 9 (step 1112).(g) Next, the measured wavelength is presented to the user (step 1114). Said presentation may be via display 20 of the certification unit 1 or via the screen of local computer 2 if connected.(h) Next, a comparison is made between said presented wavelength and the wavelength at which the laser unit under test 9 is specified to operate (step 1116). If said presented wavelength is not within a predetermined and proper range of the wavelength at which the laser unit under test 9 is specified to operate, the laser unit under test 9 fails certification (step 1124). The “Wavelength” test is then concluded at step 1126 and no further testing takes place; otherwise,(i) If said presented wavelength is within said predetermined and proper range of the wavelength at which the laser unit under test 9 is specified to operate, the user records this result (step 1118). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(j) It is next determined if the “Wavelength” test is to be repeated at another, different power supply voltage (step 1120). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another, different power supply voltage, execution of the test returns to step 1106.(k) When the “Wavelength” test has been successfully concluded at all desired power supply voltages the laser unit under test 9 is considered to have passed the “Wavelength” test and is eligible to continue the test process (step 1122). The “Wavelength” test is then concluded at step 1126. FIG. 15 shows a flow chart 2000-11 of a “Speed Simulation” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, certification unit 1 is placed in an operating mode whose primary purpose is to conduct a Speed Simulation Test (step 1202). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(b) Next, the user is instructed to connect the “Speed Simulation Test Head” (not shown) to the certification unit 1 and the test does not proceed until connection of the proper test head is detected (step 1204). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. Also as part of step 1204, the certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 1206). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 1208). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(e) Next, the user is instructed to point the output of the laser unit under test 9 at the optical interface stand 11 interfaced to the test head(s) and to re-orient the laser unit under test 9 in relation to said optics 11 until the “Power/Aiming” indicator of the certification unit 1 turns green (step 1210). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(f) Next, the Speed Simulation Test Head measures the pulses in the output 10a of the laser unit under test 9 and performs calculations as previously described to control a laser, in a fashion previously described, thereby producing a return signal, also previously described, which is directed to the laser unit under test 9 as an input signal 10b (step 1212).(g) Next, an “expected speed” is presented to the user (step 1214). Said presentation may be via display 20 of the certification unit 1 or via the screen of local computer 2 if connected.(h) Next, the user is instructed to compare the speed displayed by the laser unit under test 9 to the “expected speed” that was presented to the user in step 1214. Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. If the result of said comparison is that the speed displayed by the laser unit under test 9 is not within a specified range of the aforementioned “expected speed,” the laser unit under test 9 fails certification (step 1224). The “Speed Simulation” test is then concluded at step 1226 and no further testing takes place; otherwise,(i) If said comparison indicates that the speed displayed by the laser unit under test 9 is within a specified range of the aforementioned “expected speed,” the user records this result along with the actual speed displayed by the laser unit under test 9 (step 1218). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(j) It is next determined if the “Speed Simulation” test is to be repeated at another, different power supply voltage (step 1220). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another, different power supply voltage, execution of the test returns to step 1206.(k) When the “Speed Simulation” test has been successfully concluded at all desired power supply voltages, the laser unit under test 9 is considered to have passed the “Speed Simulation” test and is eligible to continue the test process (step 1222). The “Speed Simulation” test is then concluded at step 1226. FIG. 16 shows a flow chart 2000-12 of an “Internal Clock Frequency” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, certification unit 1 is placed in an operating mode whose primary purpose is to conduct an Internal Clock Frequency Test (step 1302). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(b) Next, the user is instructed to connect the “Internal Clock Frequency Test Head” (not shown) to the certification unit 1 and the test does not proceed until connection of the proper test head is detected (step 1304). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. Also as part of step 1304, the certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(c) Next, the user is instructed to connect the probe of the “Internal Clock Frequency Test Head” (not shown) to the laser unit under test 9 (step 1306). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(d) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 1308). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(e) Next, the user is instructed to turn the laser unit under test 9 on if required (step 1310). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(f) Next, the Internal Clock Frequency Test Head samples the pulses in the clock signal 164 of the laser unit under test 9 and performs an analysis, previously described, to determine the frequency of the clock signal 164 of the laser unit under test 9 (step 1312).(g) Next, the measured frequency is presented to the user (step 1314). Said presentation may be via display 20 of the certification unit 1 or via the screen of local computer 2 if connected.(h) Next, a comparison is made between said presented frequency and the frequency at which the internal clock of laser unit under test 9 is specified to operate (step 1316). If said presented frequency is not within a predetermined and proper range of the clock frequency at which the laser unit under test 9 is specified to operate the laser unit under test 9 fails certification (step 1324). The “Internal Clock Frequency” test is then concluded at step 1326 and no further testing takes place; otherwise,(i) If said presented frequency is within said predetermined and proper range of the clock frequency at which the laser unit under test 9 is specified to operate, the user records this result (step 1318). Said recording may be made manually by the user or automatically by the local computer 2 if connected.(j) It is next determined if the “Internal Clock Frequency” test is to be repeated at another, different power supply voltage (step 1320). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another, different power supply voltage, execution of the test returns to step 1308.(k) When the “Internal Clock Frequency” test has been successfully concluded at all desired power supply voltages, the laser unit under test 9 is considered to have passed the “Internal Clock Frequency” test and is eligible to continue the test process (step 1322). The “Internal Clock Frequency” test is then concluded at step 1326. FIG. 17 shows a flow chart 2000-13 of a “Horizontal Beam Width” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, the user is instructed to set up the Beam Test Apparatus (step 1402). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. The Beam Test Apparatus, not shown, consists of three retro-reflective discs which are of a size and relative placement that satisfies the requirements set forth by the International Association of Chiefs of Police (IACP) for beam characteristics testing. The Beam Test Apparatus is required to be placed at a physical location such that the center target is at a distance of typically 202.5 feet from the user. The skilled person will appreciate that other distances as mathematically determined may be used for the test stand location.(b) Next, certification unit 1 is placed in an operating mode whose primary purpose is only to vary the power supply voltage to the laser unit under test 9 (step 1404). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 1406). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 1408). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. The certification unit 1 may retrieve the serial number and calibration information of the test head and retain it locally for later use or may transmit the information to local computer 2 if connected.(e) Next, the user is instructed to hold the laser unit under test 9 in an upright position (e.g. in its normal operating orientation), aim it so that the reticule of the laser unit under test 9 is pointed at the center target of the Beam Test Apparatus and then, to observe the measured distance reported by the laser unit under test 9 (step 1410).(f) If the measured distance reported by the laser unit under test 9 does not match the known distance to the center target of the beam test apparatus (step 1412) the laser unit under test 9 fails certification (step 1422). The “Horizontal Beam Width” test is then concluded at step 1424 and no further testing takes place; otherwise,(g) If the measured distance reported by the laser unit under test 9 matches the known distance to the center target of the beam test apparatus, the user records this result (step 1414). Since this test is typically conducted outdoors, away from the test bench, users may elect to test several laser guns in a “batch” mode and manually record the results at this point for later entry into the local computer 2.(h) It is next determined if the “Horizontal Beam Width” test is to be repeated at another, different power supply voltage (step 1416). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another, different power supply voltage, execution of the test returns to step 1406.(i) When the “Horizontal Beam Width” test has been successfully concluded at all desired power supply voltages the laser unit under test 9 is considered to have passed the “Horizontal Beam Width” test. Since this test is typically conducted outdoors, away from the test bench, users may elect to test several laser guns in a “batch” mode and manually record their results; and, after all laser units are tested enter said results into the local computer 2 (step 1418) in a “batch” mode as well. Regardless of when or how data entry is accomplished, the laser unit under test 9 is eligible to continue the test process (step 1420) and the “Horizontal Beam Width” test is considered to be concluded at step 1424. FIG. 18 shows a flow chart 2000-14 of a “Vertical Beam Width” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, the user is instructed to set up the Beam Test Apparatus (step 1502). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. The Beam Test Apparatus, not shown, consists of three retro-reflective discs which are of a size and relative placement that satisfies the requirements set forth by the International Association of Chiefs of Police (IACP) for beam characteristics testing. The Beam Test Apparatus is required to be placed at a physical location such that the center target is at a distance of typically 202.5 feet from the user. The skilled person will appreciate that other distances as mathematically determined may be used for the test stand location.(b) Next, certification unit 1 is placed in an operating mode whose primary purpose is only to vary the power supply voltage to the laser unit under test 9 (step 1504). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 1506). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 1508). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(e) Next, the user is instructed to hold the laser unit under test 9 in a horizontal position (e.g. at a right angle to its normal operating orientation), aim it so that the reticule of the laser unit under test 9 is pointed at the center target of the Beam Test Apparatus and then, to observe the measured distance reported by the laser unit under test 9 (step 1510).(f) If the measured distance reported by the laser unit under test 9 does not match the known distance to the center target of the beam test apparatus (step 1512) the laser unit under test 9 fails certification (step 1522). The “Vertical Beam Width” test is then concluded at step 1524 and no further testing takes place; otherwise,(g) If the measured distance reported by the laser unit under test 9 matches the known distance to the center target of the beam test apparatus, the user records this result (step 1514). Since this test is typically conducted outdoors away from the test bench, users may elect to test several laser guns in a “batch” mode and manually record the results at this point for later entry into the local computer 2.(h) It is next determined if the “Vertical Beam Width” test is to be repeated at another, different power supply voltage (step 1516). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another, different power supply voltage, execution of the test returns to step 1506.(i) When the “Vertical Beam Width” test has been successfully concluded at all desired power supply voltages the laser unit under test 9 is considered to have passed the “Vertical Beam Width” test. Since this test is typically conducted outdoors away from the test bench, users may elect to test several laser guns in a “batch” mode and manually record their results; and, after all laser units are tested enter said results into the local computer 2 (step 1518) in a “batch” mode as well. Regardless of when or how data entry is accomplished, the laser unit under test 9 is eligible to continue the test process (step 1520) and the “Vertical Beam Width” test is considered to be concluded at step 1524. FIG. 19 shows a flow chart 2000-15 of a “Sight Alignment” test that may be applied to laser unit under test 9 and, which may comprise some or all of the following general sequence of actions according to a non-limiting, exemplary aspect of the invention. (a) First, the user is instructed to set up the Beam Test Apparatus (step 1602). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected. The Beam Test Apparatus, not shown, consists of three retro-reflective discs which are of a size and relative placement that satisfies the requirements set forth by the International Association of Chiefs of Police (IACP) for beam characteristics testing. The Beam Test Apparatus is required to be placed at a physical location such that the center target is at a distance of typically 202.5 feet from the user. The skilled person will appreciate that other distances as mathematically determined may be used for the test stand location.(b) Next, certification unit 1 is placed in an operating mode whose primary purpose is only to vary the power supply voltage to the laser unit under test 9 (step 1604). Said mode selection may be accomplished via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(c) Next, certification unit 1 may, as necessary, apply a specified voltage to receptacle 15 for use by the laser unit under test 9 (step 1606). Said voltage may be specified via user select switches 19 of the certification unit 1 or via commands from local computer 2 if connected.(d) Next, the user is instructed to turn the laser unit under test 9 on if required (step 1608). Said instruction may be from prior training of the user or may be displayed on the screen of local computer 2 if connected.(e) Next, the user is instructed to hold the laser unit under test 9 in an upright position (e.g. in its normal operating orientation), aim it so that the reticule of the laser unit under test 9 is pointed at the center target of the Beam Test Apparatus, and then, to observe the measured distance reported by the leaser unit under test 9 (step 1610).(f) Next the user is instructed to “sweep” the reticule of the laser unit under test 9 back and forth across all three targets of the beam test apparatus (step 1612) and verify that the measured distance reported by the laser unit under test 9 changes as expected when it is pointed at each of the targets.(g) If the measured distance reported by the laser unit under test 9 does not change as expected (step 1614) the laser unit under test 9 fails certification (step 1624). The “Sight Alignment” test is then concluded at step 1628 and no further testing takes place; otherwise,(h) If the measured distance reported by the laser unit under test 9 changes as expected, the user records this result (step 1616). Since this test is typically conducted outdoors away from the test bench, users may elect to test several laser guns in a “batch” mode and manually record the results at this point for later entry into the local computer 2.(i) It is next determined if the “Sight Alignment” test is to be repeated at another, different power supply voltage (step 1618). Said determination may be made manually by the user or automatically by local computer 2 if connected. If the determination is to repeat the test at another, different power supply voltage, execution of the test returns to step 1606.(j) When the “Sight Alignment” test has been successfully concluded at all desired power supply voltages the laser unit under test 9 is considered to have passed the “Sight Alignment” test. Since this test is typically conducted outdoors away from the test bench, users may elect to test several laser guns in a “batch” mode and manually record their results; and, after all laser units are tested enter said results into the local computer 2 (step 1620) in a “batch” mode as well. Regardless of when or how data entry is accomplished the laser unit under test 9 is eligible to continue the test process (step 1622), and the “Sight Alignment” test is considered to be concluded at step 1626. The detailed description set forth above is directed to an apparatus embodiment and method embodiment used to test and measure the accuracy and performance of a laser speed gun, wherein the apparatus included modular, plug-and-play type test heads associated with various test measurements as described. Another embodiment of the invention is a self-contained, portable apparatus in which the circuitry enabling the various functions of the modular, plug-and-play test heads has been internalized; i.e., all circuitry required to enable the test and measurement of parameters required to provide certification of the laser gun(s) under test in various jurisdictions are contained within a self-contained, portable apparatus having size and weight characteristics that enable hand-held transport by the user. FIG. 20 shows a block schematic diagram of a main circuit board 2000-16 that contains thereon the necessary components and equivalent test head(s) circuitry to operate similarly to the way the modularized apparatus would operate as described above. For example, the components and circuitry shown in FIGS. 3b-3g corresponding respectively to the pulse characterization test head, pulse wavelength test head, distance measurement test head, optical power measurement test head, speed simulation test head, internal clock frequency test head, as well as a power supply, display, laser, fiber optic coils, spectrometer, power sensor, optical detector, etc. are now all included on and/or interfaced to the main board 2000-16; e.g., fiber optic connector 2044, spectrometer 2064, power sensor 2104, optical detector 2126, external power supply 2031, display 2032, laser 2030, fiber optic coils 2085, bidirectional circuitry interface for spectrometer 2021, analog input circuitry for optical power test 2022, analog input circuitry for pulse width test, pulse frequency test, double pulse test and speed simulation test 2023, analog output circuitry for speed simulation test 2024 main FPGA 2052, which performs all digital analysis and digital calculations for pulse width, pulse frequency, double pulse, wavelength, optical power, speed simulation, long and short distance simulation, and which sends appropriate data to the main processor 2001, which selects and runs tests, gets information from the main FPGA 2052, controls the display of information on display 2032 and, sends information to the optional PC (not shown). The use of the terms “a” and “an” and “the” and similar references in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to”) unless otherwise noted. The term “connected” is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening. The recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples or exemplary language (e.g., “such as”) provided herein is intended merely to better illuminate embodiments of the invention and does not impose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. While the invention is susceptible to various modifications and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms or methods disclosed, but to the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the appended claims. |
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abstract | It is an object of the present invention to obtain a containment concrete cask which has heat removal capacity maintained at the conventional level or beyond it and which prevents radiation from leaking to the outside. In a concrete cask, a shielding body composed of concrete and heat transfer fins made from metal are provided between an inner shell and an outer shell made from metal, and an accommodation portion for accommodating a radioactive substance is provided inside the inner shell. The accommodation portion has a containment structure to be insulated from the outside of the cask. In the heat transfer fins, the portions thereof at the outer shellside are provided in contact with the outer shell and the portions thereof at the inner shell side are cut so as to form a separation portion with respect to the inner shell. |
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abstract | A method of operating a nuclear reactor reduces the number of reload fuels to be loaded into the nuclear reactor in the second and the following operation cycles. |
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046413367 | description | DETAILED DESCRIPTION OF THE INVENTION In the drawing, reference numeral 1 designates an X-ray tube which generates X-radiation that is directed to a patient P and restricted to a suitable beam of rays 3 for imaging by diaphragm 2. The radiation penetrated through the patient is recorded on a film 4. X-ray tube 1 and the support of film 4 are preferably fixed together for providing fixed imaging coordinates (not shown in figure). The patient is positioned on the imaging coordinates by means of ear plugs 5 or the like supports. This is to ensure that a given part of each patient, e.g. the ear cavity, will be imaged on the same spot in a film square. The device also comprises an adjustable nasion and/or forehead support 6 whose distance from ear plugs is indicated with D. Thus, this distance is a patientwise measure the same way as the mutual distance between ear plugs, i.e. the width dimension W of a patient's skull. According to the invention, dimension D is utilized for the adjustment of soft tissue filter means 7. This dependence and adjustment is designated by a control signal 9. The adjustment can be effected manually by a control knob 8 which is preferably fitted with a proper control scale. Also for distance D, the apparatus is provided with a numerical control scale according to which said control knob scale is preferably precalibrated for facilitating the adjustment. The control scale of distance D and setting mechanisms of support or measuring means 6 as well as setting mechanisms of supports 5 are not illustrated in detail in the figure, as they represent conventional technology and are generally available in cephalostats. In practice, ear plugs 5 are in the cross-sectional plane perpendicular to X-rays bound to the imaging coordinates, whereby the patientwise variation of dimension D is effected by adjusting support or measuring means 6. Instead of the above-described manual control, the adjustment of filter means 7 can be preferably automated in a manner that the control elements of filter means 7 are directly controlled to effect necessary resetting actions on the basis of the dimensional data obtained of the patientwise positioning e.g. by means of sensor elements. When effected by means of modern microprocessor technology, the question is merely about a simple programming procedure. Since it is also rather simple to find out dimension W or the width of a patient's skull from cephalostats by means of ear supports 5, said dimension generally correlating rather well with dimension D, said control of filter means may be effected also on the basis of dimension W, if so desired. Also, supporting of filter means 7 can of course be effected in a manner different from the figure. The essential point is to effect the positional control of filter means in a controllable manner with respect to imaging coordinates. In addition to the position of a soft tissue filter, it may become necessary to adjust the slope or V-shape of a filter, which depends on the width of a patient's skull. The slope control can be effected e.g. by adapting the filter means to be rotatable around an axis substantially perpendicular to X-rays and to the direction in which the position of filter means is displaced. See FIG. 2. The invention is not limited to the above-described embodiment but a plurality of modifications thereof are conceivable within the scope of the annexed claims. |
claims | 1. A system for curing a quantity of curable material, comprising:a dispenser in communication with the quantity of curable material, said dispenser capable of dispensing a dispensed portion of the curable material;a base portion including a recess defined by a plurality of planar faces including:a central first face,a pair of second faces, each face of said pair of second faces extending from an opposite side of the first face and being disposed at a first angle with respect to said first face, anda pair of third faces, each face of said pair of third faces extending from a separate second face and being disposed at a second angle with respect to said first face different from the first angle;a light-emitting diode mounted on one each of said first, second, and third faces; anda refractive optical culmination device positioned to intercept light emitted from each said light-emitting diode and to at least one of intensify and direct said light emitted from said light-emitting diode to cure said dispensed portion of the curable material. 2. The system of claim 1, wherein each said optical culmination device is positioned to intensify and direct said light emitted from said one light-emitting diode to cure said dispensed portion of the curable material. 3. The system of claim 1, wherein said optical culmination device is substantially aligned with one of said first, second, and third faces. 4. A system for curing a quantity of curable material, comprising:a dispenser in communication with the quantity of curable material, said dispenser being capable of dispensing a dispensed portion of the curable material;a base including a plurality of elongate faces, each of said elongate faces defining a longitudinal length extending in a longitudinal direction;a plurality of light-emitting diodes, multiple diodes of said plurality of light-emitting diodes being mounted on each of said faces and being linearly arranged in the longitudinal direction thereof; anda plurality of elongate, cylindrical transparent optical culmination devices, each device being positioned to intercept light emitted from at least one light-emitting diode of said plurality of diodes and at least one of intensify and direct said light emitted from said at least one light-emitting diode as the intercepted light passes through the transparent optical culmination device to cure said dispensed portion of the curable material, each optical culmination device of said plurality of culmination devices extending in the longitudinal direction of the corresponding face and being substantially aligned with the respective multiple of light-emitting diodes mounted on said corresponding face. 5. The system of claim 1, further comprising a printer, said printer including said dispenser. 6. A system of claim 1 wherein said second angle is less than 90 degrees. |
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claims | 1. A nuclear power plant system comprising:a nuclear reactor;a steam turbine that uses steam generated in a pressure vessel included in the nuclear reactor; anda radioactive material separating and removing apparatus placed on corrugated plates of a dryer arranged in the pressure vessel, or placed in a steam passage extended between the pressure vessel and an inlet of the steam turbine, the radioactive material separating and removing apparatus including a surface having superhigh hydrophilic TiO2 and adapted to trap thereon radioactive corrosion products contained in a plurality of water drops so that the radioactive corrosion products firmly adhere on the surface, in order to separate and remove radioactive corrosion products from the plurality of water drops. 2. A nuclear power plant system comprising:a nuclear reactor having a pressure vessel which generates steam therein;a steam turbine that uses the steam generated by the nuclear reactor; anda dryer arranged in the pressure vessel to dry the steam to be supplied to the steam turbine, the dryer having a plurality of corrugated plates defining therebetween passages through which a multiphase flow containing the steam, water drops and radioactive substances flows, wherein the corrugated plates have surfaces having superhigh hydrophilic TiO2. 3. The nuclear power plant system according to claim 2, wherein the superhigh hydrophilic TiO2 is formed in fiber. 4. The nuclear power plant system according to claim 2, wherein the surface of the corrugated plates are coated with a coating containing TiO2 and SiO2. 5. The nuclear power plant system according to claim 2, wherein each of the corrugated plates includes thereon a p-type oxide film and the superhigh hydrophilic TiO2 is a coating on the p-type oxide film, and wherein the superhigh hydrophilic TiO2 is an n-type oxide. 6. The nuclear power plant system according to claim 2, wherein the dryer is provided with a means for creating an electric field or a magnetic field between adjacent corrugated plates, adapted so that minute radioactive particles contained in the multiphase flow are biased toward the corrugated plates by the electric field or the magnetic field. 7. The nuclear power plant system according to claim 6, wherein the means for creating an electric field or a magnetic field comprises a photocell including:an n-type semiconductor, which is the superhigh hydrophilic TiO2 deposited on the corrugated plates; anda film of a corrosion product, which is a p-type semiconductor, produced by a corrosion of surfaces of the corrugated plates. |
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abstract | A system to track movement of an object travelling through an imaged subject is provided. The system includes an imaging system to acquire a fluoroscopic image and operable to create a three-dimensional model of a region of interest of the imaged subject. A controller includes computer-readable program instructions representative of the steps of calculating a probability that an acquired image data is of the object on a per pixel basis in the fluoroscopic image, calculating a value of a blending coefficient per pixel of the fluoroscopic image dependent on the probability, adjusting the fluoroscopic image including multiplying the value of the blending coefficient with one of a greyscale value, a contrast value, and an intensity value for each pixel of the fluoroscopic image. The adjusted fluoroscopic image is combined with the three-dimensional model to create an output image illustrative of the object in spatial relation to the three-dimensional model. |
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abstract | An interconnected corrugated carbon-based network comprising a plurality of expanded and interconnected carbon layers is disclosed. In one embodiment, each of the expanded and interconnected carbon layers is made up of at least one corrugated carbon sheet that is one atom thick. In another embodiment, each of the expanded and interconnected carbon layers is made up of a plurality of corrugated carbon sheets that are each one atom thick. The interconnected corrugated carbon-based network is characterized by a high surface area with highly tunable electrical conductivity and electrochemical properties. |
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description | This application claims priority to, and the benefit of, co-pending U.S. provisional application entitled “HIGH EFFICIENCY CONTINUOUS-FLOW PRODUCTION OF RADIOISOTOPES” having Ser. No. 62/338,162, filed May 18, 2016, the contents of which are incorporated by reference in their entirety. This invention was made with government support under award NRC-HQ-11-G-38-0037 awarded by the Nuclear Regulatory Commission and award DE-NE-0000361 awarded by the Department of Energy. The government has certain rights in the invention. The present disclosure generally relates to methods of making radioisotopes and radioisotopes produced therefrom. Radionuclides used for medical applications must exhibit certain properties. Ideally the radionuclides should be obtained in a carrier free form with high specific activity, so a minimum amount can be administrated with maximum effect. This prevents chemical toxicity effects and overexposure of healthy tissues and organ. The radionuclide must have a relatively short half-life so that after serving its desired purpose it will decay and not cause excess damage to the surrounding organs and tissues. The radioisotope of interest should be obtained in a form so it can easily chelate to site-specific ligands that can facilitate its incorporation into radiopharmaceuticals. For diagnostic purposes the radioisotope must have an image-able gamma ray. For therapeutic applications the radionuclide should have beta or alpha emissions with energy levels suitable for delivering a therapeutic dose to the target tissue. Several of the lanthanide elements have suitable characteristics for use as medical radionuclides. In addition to their desirable nuclear properties they also have some beneficial chemical properties. In solution, the lanthanide elements predominantly exist in the +3 valence state and all exhibit similar chemical characteristics. This enables the application of the same synthesis route and procedure for the synthesis of different lanthanide compounds. A major challenge encountered in reactor produced radioisotopes for medical application is achieving high specific activity. If production of the nuclide is by a (n, γ) reaction, achieving high specific activity may require long irradiation times, sometimes not feasible for short-lived medical isotopes, or separation of isotopes with only ˜1 amu difference in atomic mass, which, for lanthanides, is an energy intensive and overall challenging task. Radioisotopes are produced via nuclear reactors or particle accelerators. When produced using nuclear reactors via the direct (n,gamma) method, often high specific activity radioisotopes with minimum carrier (stable isotope) cannot be obtained, due to the fact that the target isotope and the produced radioisotope are the same element and conventional separation techniques cannot easily be applied to separate the product radioisotope from the target152Sm+neutron(n)→153Sm+γ High specific activity can be achieved in reactor produced radioisotopes with high neutron fluxes and long irradiation times but the product will always contain a considerable amount of stable isotope carrier. One primary application of radioisotopes is in the medical field, were they are used for diagnostic purposes such as medical imaging and therapeutic applications such as cancer treatment. One major requirement for the applicability of radionuclides in medicine strongly relies on achievable specific activity. The radionuclides should be obtained with high specific activity so a minimal concentration can be administered with maximum effect, to prevent chemical toxicity complications. Prior studies have been performed on high specific activity radioisotope production via the Szilard-Chalmers method. Those studies take advantage of radioisotope separation and processing post irradiation. There are some major drawbacks associated with post irradiation separation and processing such as, retention of the recoiled and separated radioisotopes due to recombination or isotope exchange with the original target, further neutron capture of the product radioisotope, resulting in the formation of undesired radioisotope by-products and the need for exotic and costly hot cell facilities for post irradiation processing. There remains a need for improved methods of producing high specific activity radioisotopes that overcome the aforementioned deficiencies. Other systems, methods, features, and advantages of the high specific activity radioisotopes and methods of producing high specific activity radioisotopes will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. The proposed technology can be used for producing high specific activity radioisotopes using an innovative experimental setup, for fields such as but not limited to: medical, radiopharmaceuticals, industrial applications, radioisotope power systems for space exploration and scientific research. The methods can take advantage of the recoil characteristics of atoms upon neutron capture to separate a radioisotope product with increased specific activity. The methods can address the challenges of obtaining reactor-produced radioisotopes with high specific activity by: taking advantage of the recoil characteristics of an atom upon neutron capture and using an innovative experimental setup. The produced radioisotopes are ideal for nuclear medicine applications among many other applications. The objective of the disclosure is to introduce methods of producing radioisotopes with high specific activity in a nuclear reactor using the Szilard-Chalmers method. The Szilard-Chalmers effect occurs upon neutron capture and emission of prompt gamma rays, imparting recoil energy to the product radioisotope and ejecting the radioisotope in the opposite direction. Upon the presence of an immiscible capture matrix in contact with the target during irradiation, the recoiling radionuclide can be captured and separated from the bulk of the inactive material leading to a radioisotope product with increased specific activity compared to direct neutron activation method typically used. We propose an innovative experimental setup to instantaneously separate the radioactive recoil product formed during irradiation from the bulk of non-radioactive ions. The instant separation prevents the recoiled radioactive nucleus from reforming its original bonds with the target matrix and chemically separates it from the non-radioactive target matrix, resulting in a low carrier radioisotope product with increased specific activity. In addition an irradiation target was developed, by coating porous Styrene divinylbenzene XAD-4 resins with a polyvinyl alcohol lanthanide mixture. Irradiation of the synthesized resins resulted in enrichment factors up to 2 times higher compared to the lanthanide powder targets initially used. The proposed methods are useful particularly for nuclear medicine applications, such as diagnostic purposes such as medical imaging and therapeutic applications such as cancer treatment. For medical applications the radioisotope should ideally be in a carrier free form with high specific activity, which is a challenge encountered in radioisotope production via nuclear reactors. The Szilard-Chalmers method coupled with the experimental setups described herein can address the mentioned challenges. Additionally the methods can be used for the production of radioisotopes such as 238Pu, which is used by NASA to power deep space missions. The proposed method addresses the major challenge current 238Pu production methods face. In various aspects, methods of producing radionuclides with high specific activity are provided. The methods can include causing a liquid capture matrix to flow in contact with a target comprising a target nuclide; irradiating the target with ionizing radiation or particles to produce the radionuclides that are ejected from the target and into the capture matrix in contact with the target; and causing the liquid capture matrix containing the radionuclides to flow from the target to recover the capture matrix comprising the radionuclides with high specific activity. The methods can include producing a variety of radionuclides from a variety of target nuclides and from a variety of reactions. In various aspects, the radionuclides are produced from the target nuclide via a reaction selected from the group consisting of a (n, γ) reaction, a (γ, n) reaction, a (n, 2n) reaction, a (n,p) reaction, a (n,α) and a (n,fission) reaction. The reactions can be initiated by applying radiation selected from the group consisting of neutron radiation, gamma radiation, and a combination thereof. In various aspects, the radiation is thermal neutron radiation, epithermal radiation, or a neutron radiation having a neutron energy above 0.4 eV. For example, the radiation can include Cadmium neutrons, EpiCadmium neutrons, slow neutrons, resonance neutrons, intermediate neutrons, or fast neutrons. The target nuclides can be any target nuclide suitable for the reactions described, e.g. having a suitable capture cross section for the specific reaction that produces the radionuclides. The target nuclide can be selected from the group consisting of elements having atomic number from 21 to 102. In various aspects, the target nuclide is a lanthanide or an actinide. In some aspects, the target nuclide is 23Na, 31P, 37Cl, 50Cr, 55Mn, 75As, 81Br, 89Y, 98Mo, 104Ru, 127I, 152Sm, 185Ho, 174Yb, 175/176Lu, 185Re, 187Re, 194Pt, 197Au or 237Np. The target nuclides can have a variety of organic ligands attached thereto. The radionuclides can be ejected from the target by breaking one or more bonds with the ligands. The ligands can be small molecules having one or more donor atoms selected from the group consisting of oxygen, nitrogen, and a combination thereof. In various aspects, the ligands are acetylacetonate, picolinate, 8-hydroxyquinolinate, dimethylglyoximate, oxalate, 4-aminobenzoate, glycinate, or derivatives thereof. In various aspects, the target contains a support structure having a large surface area, wherein the target nuclide is in a thin coating on the support structure. This type of target structure can provide for larger enrichment factors as compared to a powder target. Suitable support structures can include mesoporous resin materials, e.g. having a surface area of about 500 m2/g to about 1000 m2/g. In various aspects, the support structure is a copolymer of styrene and divinylbenzene. In one or more aspects, the thin coating on the support structure has a thickness that is less than the recoil range of the target nuclide. In various aspects, the target is largely insoluble in the liquid capture matrix. The liquid capture matrix can be, for instance, water or other polar liquid. In various aspects, the liquid capture matrix has a pH of about 3 to 5. The methods can produce radionuclides with large enrichment factors, e.g. enrichment factors of about 3 to 30. A variety of radionuclides with high specific activity are produced by the methods described herein. In some aspects, the method includes wherein the target nuclide is 237Np, and wherein the radionuclide is 238Np that decays to produce 238Pu. In some aspects, the method includes wherein the target nuclide is 98Mo, and wherein the radionuclide is 99Mo that decays to produce 99mTc. In various aspects, methods of producing high specific activity radionuclides are provided. Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, and as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. The skilled artisan will recognize many variants and adaptations of the embodiments described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein. All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference and are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present disclosure is not entitled to antedate such publication by virtue of prior disclosure. Further, the dates of publication provided could be different from the actual publication dates that may need to be independently confirmed. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described. Functions or constructions well-known in the art may not be described in detail for brevity and/or clarity. Embodiments of the present disclosure will employ, unless otherwise indicated, techniques of radiochemistry, nanotechnology, organic chemistry, material science and engineering and the like, which are within the skill of the art. Such techniques are explained fully in the literature. It should be noted that ratios, concentrations, amounts, and other numerical data can be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited values of about 0.1% to about 5%, but also include individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure, e.g. the phrase “x to y” includes the range from ‘x’ to ‘y’ as well as the range greater than ‘x’ and less than ‘y’. The range can also be expressed as an upper limit, e.g. ‘about x, y, z, or less’ and should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘less than x’, less than y′, and ‘less than z’. Likewise, the phrase ‘about x, y, z, or greater’ should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘greater than x’, greater than y′, and ‘greater than z’. In some embodiments, the term “about” can include traditional rounding according to significant figures of the numerical value. In addition, the phrase “about ‘x’ to ‘y’”, where ‘x’ and ‘y’ are numerical values, includes “about ‘x’ to about ‘y’”. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined herein. The articles “a” and “an,” as used herein, mean one or more when applied to any feature in embodiments of the present invention described in the specification and claims. The use of “a” and “an” does not limit the meaning to a single feature unless such a limit is specifically stated. The article “the” preceding singular or plural nouns or noun phrases denotes a particular specified feature or particular specified features and may have a singular or plural connotation depending upon the context in which it is used. The term “thermal neutron,” as used herein, refers to a free neutron that is in thermal equilibrium with its surroundings or is essentially in thermal equilibrium with its surroundings. A thermal neutron is said to be in equilibrium with its surroundings when, for a given temperature, the neutron is travelling at the most probable velocity for a Maxwell-Boltzmann distribution of neutrons at this temperature. The most probable velocity at a given temperature (vT) for a Maxwell-Boltzmann distribution of neutrons can be given by the formula v T = 2 kT m where k is the Boltzmann's constant; T is the temperature, and m is the neutron mass. The thermal neutron can have a velocity of about 2100 m s−1 to 2500 m s−1, about 2120 m s−1 to 2480 m s−1, about 2140 m s−1 to 2260 m s−1, or about 2200 m s−1. A neutron is said to be essentially in thermal equilibrium with its surroundings when, for a given temperature, it has a velocity within ±10%, ±5%, or ±1% of the most probable velocity for a Maxwell-Boltzmann distribution of neutrons at this temperature. Methods of Producing Radionuclides Various methods of producing radionuclides are provided. In one or more aspects, the methods include producing radionuclides with high specific activity in nuclear reactors using the Szilard-Chalmers method (FIG. 1). The Szilard-Chalmers method works such that upon neutron capture of the target isotope (152Sm) there is an increase in energy due to the binding energy of that neutron, this excess energy is released in the form of prompt gamma rays which imparts a certain amount of recoil energy to the capturing nucleus. This recoil energy is often enough to break the chemical bonds holding the radionucleus (153Sm) in the target compound, and eject it in the opposite direction. The recoiling radionucleus is usually in a different chemical form than the target so if there is an immiscible capture matrix in contact with the target that can capture and separate the recoiling radionucleus from the bulk of the inactive material, the radioisotopes can be obtained with high specific activity Depending on the mass of the target radionuclide and the energy of the prompt gamma ray, the recoil energy is often enough to break the chemical bonds holding the capturing radionuclide in the compound and eject it in the opposite direction. The recoil energy of the capturing radionuclide by the (n, γ) reaction is calculated according to the following equation: E R = E y 2 2 × m A × c 2 ≈ E y 2 2 × A × 931.5 where ER is the recoil energy in MeV, mA is the mass of the radiating atom, c is the speed of light, A is the atomic number of the recoiling atom, Eγ is the energy of the prompt gamma ray in MeV and 931.5 MeV/u is the conversion factor from atomic mass scale to energy. It can be seen that isotopes with small mass numbers (A) and large prompt gamma energies (Eγ) result in larger recoil energy (ER) values. The larger the recoil energy the higher the probability of the radioisotope being ejected away from the target matrix and separated as a pure radioisotope product with high specific activity. The radionuclide can be produced from the target nuclide via a reaction such as a (n, γ) reaction, a (γ, n) reaction, a (n, 2n) reaction, a (n, p) reaction, a (n, α) reaction, or a (n, fission) reaction. In various aspects, the methods include using a liquid capture matrix that can be easily separated from the target to produce the radionuclides with high specific activity. The liquid capture matrix can be water or other polar liquid. The pH of the liquid capture matrix can be adjusted, for example to optimize the specific activity of the radionuclide in the capture matrix. In various aspects, the pH of the liquid capture matrix is about 2 to 12, about 3 to 10, about 3 to 8, about 3 to 7, about 3 to 5, about 2 to 3, about 3 to 4, about 4 to 5, about 5 to 6, about 6 to 7, about 7 to 8, about 8 to 9, or about 9 to 10. The liquid capture matrix can be easily separated from the target. For example, the target can be contained inside a compartment such as a mobile-phase filter compartment through which the liquid capture matrix can flow. The method can include causing a liquid capture matrix to flow in contact with a target containing a target nuclide. The methods can include using a pump or other system to flow a liquid capture matrix through, over, or around the target so as to contact the target. The flow can be a continuous flow. The flow rate can be adjusted to optimize the specific activity of the radionuclide in the capture matrix. The target can be insoluble or essentially insoluble in the capture matrix, e.g. having a solubility about 0.05 M, about 0.01 M, about 0.005 M, about 0.004 M, about 0.003 M, about 0.002 M, about 0.001 M, or less. The methods can include irradiating the target with ionizing radiation or particles to produce the radionuclides that are ejected from the target and into the capture matrix in contact with the target. The radiation can include neutron radiation, gamma radiation, or a combination thereof. The radiation can be thermal neutron radiation. The radionuclides can be produced via a Szilard-Chalmers reaction and ejected into the liquid capture matrix. The methods can then include causing the liquid capture matrix containing the radionuclides to flow from the target to recover the capture matrix containing the radionuclides with high specific activity. In various aspects, the recovered radionuclides can be carrier free or essentially carrier free, e.g. having a specific activity of about 1 millicurie/microgram (mCi/μg) to 20 mCi/μg, about 1 mCi/μg to 10 mCi/μg, about 5 mCi/μg to 10 mCi/μg, about 5 mCi/μg to 15 mCi/μg, about 8 mCi/μg to 20 mCi/μg, or about 10 mCi/μg to 20 mCi/μg, about 0.0001 mCi/μg to 1 mCi/μg. The methods can be applied to a variety of targets and target nuclides. The target nuclide can be a nuclide having a cross section for neutron capture and prompt y emission or, for other types of radiation, the target nuclide can be any element that has a cross section for the radiation. In some embodiments, the target nuclide can be any element having atomic number from 11-102, 11-20, 57-71, 89-102 and 21-102. In one or more aspects, the target nuclide is selected from the group of 23Na, 31P, 37Cl, 50Cr, 55Mn, 75As, 81Br, 89Y, 98Mo, 104Ru, 127I, 152Sm, 165Ho, 174Yb, 175/176Lu, 185Re, 187Re, 194Pt, 197Au, and 237Np. In various aspects, the target nuclide is a lanthanide or an actinide. In some aspects, the target nuclide is 237Np, and the radionuclide is 238Np that decays to produce 238Pu. In some aspects, the target nuclide is 98Mo, and the radionuclide is 99Mo that decays to produce 99mTc. In some aspects, the target nuclide has one or more organic or inorganic ligands attached thereto, and the radionuclides are ejected from the target by breaking one or more bonds with the ligands. The ligands can be a ligand that forms a stable complex with the target nuclide. The organic ligand can be a small molecule having one or more donor atoms such as oxygen and/or nitrogen. The organic ligands can include acetylacetonate, picolinate, 8-hydroxyquinolinate, dimethylglyoximate, oxalate, 4-aminobenzoate, glycinate, or a derivative thereof. For example, the experimental setup can include a mobile phase filter (VICI) compartment containing the irradiation target, where it's housed in a PEEK material container. The PEEK container has an inlet port that connects the filter compartment directly to a continuous fluid pump, which continuously pumps the capture matrix through the target were its then filtered out into the PEEK container. The container has a separate outlet port that terminates in a collection reservoir and allows sample collection. The PEEK container system was used in Example 3 for both pre-irradiation solubility test and recoil/irradiation studies in addition to post irradiation monitoring of the solid/capture matrix system. For irradiation purposes the exemplary setup includes a hollow aluminum tube, also known as the flow loop terminus (FLT) that terminates in the outer ring position of the UC-Irvine TRIGA® reactor core. FIG. 2 depicts a schematic of an exemplary embodiment of how radioisotopes with high specific activity can be produced via continuous-flow Szilard-Chalmers method using Samarium Acetylacetonate (Sm(C5H8O2)3) as a representative irradiation target. The samarium irradiation target 150 is housed in the compartment 110 of a mobile phase filter unit 120, contained in the reaction vessel 130. During irradiation the capture matrix 100 flows through the irradiation target 150, separating any recoiled radioisotopes 160 from the irradiation target isotope 170. The radioisotope rich capture matrix 180 is accumulated in the reaction vessel 130 and continuously pumped out and collected during the irradiation process. In some aspects, during this process the target isotope 170 has little to no solubility in the capture matrix 100 and maximum transfer of the radioisotope 160 to the capture matrix allows 100 for improved separation. During irradiation the irradiation target 150 can be continuously contacted with fresh capture matrix 100, post contact the capture matrix 100 containing the recoiled ionic radionuclide 160 can be collected in sample vials surrounded by shielding. The setup can allow instantaneous separation of the capture matrix containing the recoiled nucleus 180 from the bulk of the inactive material during irradiation. The rapid separation of the recoiled nucleus 160 can prevent the radioisotope from reforming its original bonds with the target matrix and in turn prevents retention of the radionuclide 160 in the irradiation target 150 (FIG. 2). In various aspects the steps of the procedure can be modified to increase the specific activity of the radionuclide and/or to increase the enrichment factor. The enrichment factors can be determined by the equation Enrichment Factor ( EF ) = X * ( capture matrix ) X ( capture matrix ) / X * ( target ) X ( target ) where X+(capture matrix) and X+(target) are the concentration of the radionuclide in the capture matrix and target, respectively, and where X (capture matrix) and X (target) are the concentrations of the target nuclide in the capture matrix and target, respectively. In various aspects, the enrichment factor can be about 2 to 100, about 3 to 50, about 3 to 30, about 5 to 30, about 10 to 30, about 15 to 30, about 15 to 25, about 10 to 20, about 20 to 30, about 30 to 40, or about 40 to 50. In various aspects, the specific activity of the radionuclide in the capture matrix is about 10 mCi/μg, 20 mCi/μg, 30 mCi/μg, 40 mCi/μg, 50 mCi/μg, or more. A variety of targets including the target nuclide can be used with methods described herein. The target can include the target nuclide and a polymer matrix supporting the target nuclide. The polymer matrix can include a variety of polymers. The polymers can include water soluble polymers such as polyvinyl alcohol or cellulose ethers. The polymers can be in the form of thin sheets or films incorporating the target nuclide. The polymers can be in the form of polymeric microparticles incorporating the target nuclide. In some aspects, the target included a support structure having a large surface area, e.g. a surface area of about 500 m2/g to 1500 m2/g, about 500 m2/g to 1200 m2/g, about 600 m2/g to 1200 m2/g, about 600 m2/g to 800 m2/g, about 700 m2/g to 900 m2/g, about 800 m2/g to 1000 m2/g, or about 900 m2/g to 1100 m2/g. The target nuclide can be in a thin layer on the surface or the outside of the support structure so as to increase the contact area with the capture matrix. The support structure can be a microporous or a mesoporous resin. The support structure can be a hydrophobic resin. In some aspects, the support structure is a copolymer of styrene and divinylbenzene. The polymer incorporating the target nuclide can be in a coating on the surface of the support structure. The coating of the target nuclide on the support structure can have a variety of thicknesses. In some aspects, the thickness is less than the recoil range of the target nuclide when exposed to the radiation, ionizing radiation, particles, or a combination thereof. Now having described the embodiments of the present disclosure, in general, the following Examples describe some additional embodiments of the present disclosure. While embodiments of the present disclosure are described in connection with the following examples and the corresponding text and figures, there is no intent to limit embodiments of the present disclosure to this description. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of embodiments of the present disclosure. Synthesis of Lanthanide Complexes A number of well-defined temperature and air stable lanthanide complexes with ligands containing oxygen or nitrogen donor atoms were synthesized according to previous literature methods with slight modifications (Zeisler S K, Weber K; J Radioanal. Nucl. Chem., 227:105-109 (1998); Tomar B S, et al.; Radiochim Acta 98:499-506 (2010)). The following general synthesis procedure was adapted for the synthesis of samarium acetylacetonate, samarium oxalate, samarium 4-aminobenzoate, holmium oxalate, and holmium 4-aminobenzoate. 5 mmol of the lanthanide nitrate (Ho, 99.9%, Strem chemicals; Sm, 99.9%, Acros Organics) was dissolved in enough boiling 0.01 M HCl (36.5-38%, EMD chemicals) to dissolve the lanthanide nitrate salt. The solution was evaporated to remove any unreacted acid. The resulting residue was dissolved in 20 mL of ultrapure water (>18.2 MO) and removed from heat. A five-fold excess of the ligand was added to the solution under constant stirring (2,4-pentadione, i.e. acetylacetone, 99% Acros Organics; 4-aminobenzoate, 99% Sigma Aldrich, oxalic acid, 99.9% Fisher Scientific). The pH of the mixture was adjusted to 5.5-6 by drop-wise addition of 14.5 M ammonia (Ammonium hydroxide 29.14% Fisher Scientific). The precipitate was separated from the solution by vacuum filtration and dried in an oven at 75° C. for 45 min. Samarium 8-hydroxyquinolinate and holmium 8-hydroxyquinolinate were synthesized according to the following general procedure: 1 mmol of the lanthanide nitrate was dissolved in 50 mL of ethanol (95%, Gold Shield Chemicals). 4 mmol of 8-hydroxyquinolinate (99%, Sigma Aldrich) was gradually dissolved in 50 mL of ethanol. The 8-hydroxyquinolinate ethanolic solution was added to the lanthanide solution under constant stirring. The mixture was heated to boiling for 35 min. Precipitate formation was instantaneously visible. After 35 min the mixture was removed from heating, stirring continued until the mixture was at room temperature. The precipitate was separated from the mixture by vacuum filtration and dried in the oven at 75° C. for 45 min. Pre-Irradiation Solubility Tests The solubility of the lanthanide complexes in the water capture matrix was determined by mixing a few milligrams of the lanthanide-containing target solid thoroughly with 0.5 mL of ultra-pure H2O then separating the solution from the solid utilizing centrifugal filter tubes (EMD Millipore). A second wash of the solid was obtained using the same procedure. The solid and the washes were submitted for neutron activation analysis in order to determine the solubility of the lanthanide containing target in H2O. Recoil and Irradiation In order to determine the recoil characteristics of the activated lanthanide nucleus from the bulk of the inactive material and investigate the Szilard-Chalmers reaction, a few milligrams of the lanthanide-containing target was mixed with 0.5 mL of H2O on the filter of the centrifugal filter tubes. The solid (target matrix) was irradiated in contact with the water (capture matrix). The samples were irradiated at the University of California Irvine TRIGA reactor with a neutron flux of 8×1010n cm−2 s−1 for 20 min. Post Irradiation Sample Handling Post irradiation, the samples were left to cool for a predetermined amount of time to allow any short-lived radioisotopes to decay, before being transferred to the laboratory for treatment and analysis. The capture matrix was filtered and separated from the solid in order to separate any recoiled radiolanthanide. The solid residue and capture matrix were collected for analysis of the activity of the radiolanthanide. The pre-irradiation solubility test washes along with standards were also prepared for analysis. The samples were analyzed for radiolanthanide activity using a High Purity Germanium detector (HPGe) at the representative gamma energy of the radiolanthanide of interest. The 153Sm activity of the samarium samples were measured at the gamma energy of Ev=103 keV and 166Ho in the holmium samples were measured at Ev=81 keV. Solubility and Recoil of the Lanthanide Complexes The percent activity of the nuclide of interest in the different samples (wash, target, capture matrix) is shown in Table 1 for compounds (1)-(7). All the samples for a particular compound were irradiated as a group, along with standards for calibration purposes and direct comparisons of activities. In samples that were not treated post irradiation by separation (e.g. as in the case of target and capture matrix) the activity of the radiolanthanide is directly related to the total concentration of the corresponding lanthanide. The count rate measured in each sample was normalized to a single point in time to account for decay during measurements. Both pre-irradiation washes were collected to give an indication of the solubility of the lanthanide complex in the capture matrix (H2O). The second wash was obtained to determine if the lanthanide activity detected in the first wash was actually due to solubility of the lanthanide containing target or due to factors such as impurities or the presence of uncomplexed lanthanide that came off in the first wash. The percent activity of the radiolanthanide retained in the solid compound was indicative of the amount of the produced radiolanthanide that did not recoil into the capture matrix and was retained in the target. Radiolanthanides that recoiled out but reformed bonds with the solid compound would appear as retained as well. The percent activity in the capture matrix indicates the amount of radioisotopes transferred to the capture matrix during irradiation that did not reform bonds with the target matrix. Activity in the capture matrix may also reflect dissolution of the target matrix rather than recoil. TABLE 1Extraction yield and retention of the studied radiolanthanides% Activity% Activity% Activity in% Activity inCompoundin wash 1in wash 2targetcapture matrix(1) Samarium acetylacetonate7.0 ± 2.32.1 ± 1.346.2 ± 7.644.7 ± 6.9 (2) Samarium 4-aminobenzoate27.3 ± 3.0 26.8 ± 2.9 23.0 ± 2.722.9 ± 2.6 (3) Samarium oxalate<1<198.7 ± 5.41.2 ± 0.3(4) Samarium 8-hydroxyquinolinate<1<190.4 ± 9.59.2 ± 2.2(5) Holmium 8-hydroxyquinolinate1.4 ± 0.9<193.7 ± 9.54.4 ± 1.5(6) Holmium 4-aminobenzoate7.0 ± 1.67.7 ± 1.771.0 ± 6.514.3 ± 2.3 (7) Holmium oxalate<1<199.7 ± 3.8<1 Samarium acetylacetonate (1) in Table 1 shows slight indication of solubility, which decreases with the second wash. The 153Sm activity detected in the capture matrix indicates the possibility of the Szilard-Chalmers effect and recoil of the target radioisotope into the capture matrix. Samarium 4-aminobenzoate (2) was soluble in water as was holmium 4-aminobenzoate (6) with both washes indicating the same amount of solubility; therefore these compounds were not good candidates under the proposed experimental conditions. The samarium (3) and holmium oxalate (7) compounds were found to be insoluble in water with minimal activity detected in both pre-irradiation washes. The majority of activity remained retained in the solid target. The activity detected in the capture matrix was enough to consider samarium or holmium oxalate as potential candidates for further studies of the Szilard-Chalmers reaction with different experimental environments to enhance the recoil effect. The low yield in the capture matrix indicates that the oxalate compounds had either high stability, such that the recoil energy was not capable to overcome the binding energy holding the compound together or that the compounds had fast kinetics such that as soon as the target radioisotope recoiled away from its original position it instantly reformed its original bonds in the target matrix. The solubility of samarium 8-hydroxyquinolinate (4) in water was low and the retention of the 153Sm in the target was large. The 153Sm activity detected in the capture matrix may be attributed to both solubility and the Szilard-Chalmers effect. Holmium 8-hydroxyquinolinate (5) showed low solubility in the first wash and decreasing solubility in the second wash, with the majority of the activity retained in the target. The 166Ho activity detected in the capture matrix indicates the possibility of recoil of 166Ho from the target into the capture matrix. Between the Sm and Ho compounds tested, samarium acetylacetonate (1) and holmium 8-hydroxyquinolinate (5) showed the highest indication of the Szilard-Chalmers effect. Hence, these compounds were chosen for enrichment factor determination. Determination of Enrichment Factors The irradiated holmium 8-hydroxyquinolinate and samarium acetylacetonate samples were allowed to decay to near background levels, and then re-irradiated at the same flux and irradiation time as the first irradiation for the purpose of determining the enrichment factors. No post-treatment of the samples were made, as the aim was to determine the amount of 152Sm or 165Ho in the samples, respectively. Thus, the activity found after the second irradiation would reflect the amount of non-radioactive (target) lanthanide isotopes found in the capture matrix. If the re-irradiation produces the same number of radioisotopes in the capture matrix as the first irradiation, i.e. ZA+1X(1st irradiation)=ZA+1X(2nd irradiation), then there was no isotope enrichment and the activity from the first irradiation was from the dissolution and/or degradation of the target matrix. The assumption is that the target isotope (152Sm or 165Ho) was not consumed to any significant degree during the irradiation. On the other hand if ZA+1X(1st irradiation)>ZA+1X(2nd irradiation) radioisotope enrichment has occurred. In this case the radioisotopes in the capture matrix from the first irradiation are due to the Szilard-Chalmers reaction and not activation of cold atoms present in the capture matrix due to either solubility or degradation of the target in the capture matrix. The following equation was used to determine the enrichment factor such that if the ratio of produced radioisotope ZA+1X to the number of the inactivated target isotope ZAX in the capture matrix was greater than the number of radioisotopes produced ZA+1X to the number of inactive target isotopes ZAX in the target ( i . e . Z A + 1 X ( capture matrix ) Z A X ( capture matrix ) > Z A + 1 X ( target ) Z A X ( target ) )enrichment of the radioisotope has occurred by the Szilard-Chalmers Reaction. Enrichment Factor ( EF ) = Z A + 1 X ( capture matrix ) Z A X ( capture matrix ) / Z A + 1 X ( target ) Z A X ( target ) An EF>1 indicates that the ratio of ZA+1X/ZAX was higher in the capture matrix than in the target matrix, therefore the specific activity was enhanced and there was indication of radioisotope enrichment. The enrichment factors for samarium acetylacetonate and holmium 8-hydroxyquinolinate were found to be 1.19 and 1.51, respectively. The enrichment factors obtained in our work were lower compared to previous studies done on lanthanide complexes using the Szilard-Chalmers method. Zeisler and Weber studied the Szilard-Chalmers effect in similar holmium complexes and were able to obtain enrichment factors between 3 and 66 (Zeisler S K, Weber K; J Radioanal Nucl Chem, 227:105-109 (1998)). A study done by Zhemosekov et al. on the Szilard-Chalmers effect in a Ho-DOTA complex resulted in enrichment factors between 7.3 and 90 (Zhemosekov, et al., Radiochima Acta, 100:669-674 (2012)). Nassan et al. obtained enrichment factors up to 107 from neutron irradiated holmium-tris(cyclopentadienyl) compounds (Nassan et al., Nukleonika, 56:263-267 (2011)). However, in these previous works the enrichment factor was calculated differently, or no information was provided on how it was calculated. The low enrichment factor could be attributed to the following: (i) degradation of the target as a result of exposure to ionizing radiation during the irradiation, leading to breakdown of the target and release of the stable isotope into the capture matrix and hence lower enrichment factors; (ii) delay in separating the irradiated target from the capture matrix leading to the recoiled atom having time to reform its original bonds or possibly isotopic exchange with the stable isotope; (iii) insufficient recoil energy to break the bonds of the target molecule and release the radioisotope into the capture matrix. For example 153Sm emits 160 prompt gamma rays upon neutron capture, resulting in recoil energies between 0.0028 and 121.7 eV. Electrostatic bond energies are on the order of a few electron volts. Thus in some cases the recoil energy is small compared to the bond energy of the target molecule and the radioisotope remains retained in the target; (iv) unfavorable location of the recoiling atom in the target; the recoil energy may be enough to eject the radioisotope but the radioisotope may not reach the capture matrix leading to further retention of the radiolanthanide in the target. Irradiation of ammonium molybdate phosphate solid powder for 15 min at a neutron flux of 8×1011 n cm−2 s−1 yielded the following results (Table 2). Sample 1 is ammonium molybdate phosphate powder irradiated and contacted with water post irradiation for solubility and radioisotope recoil studies. The irradiated sample 1 was washed twice with water (wash 1 and wash 2) to determine separation of the recoiled Molybdenum-99 (99Mo) and solubility of the Molybdenum compound in the water capture matrix. Wash 1, Wash 2, and the irradiated molybdenum target were all analyzed for 99Mo activity using gamma spectroscopy at the prominent 99Mo peak of 141 KeV. In sample 2 ammonium molybdate phosphate was irradiated in contact with a water capture matrix. Post irradiation the capture matrix was separated from the irradiation target and washed an additional time to determine post irradiation solubility (wash 1). The irradiation target, capture matrix and wash 1 were analyzed via gamma spectroscopy under similar conditions to sample 1. TABLE 2Extraction yield and retention of radioactive Molybdenum-99% Activity% Activity% Activity in% Activity inCompoundin wash 1in wash 2targetcapture matrixSample 1:<1<199.2N/AAmmoniumMolybdatePhosphateSample 2:1.3N/A92.26.5AmmoniumMolybdatePhosphate Sample 1 in Table 2 shows minimal indication of 99Mo in both wash 1 and 2, with over 99% of the molybdenum retained in the target. The small fraction of 99Mo in the washes indicates that the recoiled radioisotope was not efficiently separated, which can be due to isotopic exchange of the recoiled radioisotope and retention of the radioisotope in the target. Furthermore with respect to sample 1 it can be seen that the Molybdenum compound is minimally soluble in the capture matrix, with less than 1% 99Mo activity detected in the capture matrix. In sample 2 the 99Mo activity detected in the capture matrix in contact with the target during irradiation indicates the Szilard-Chalmers effect and recoil of the target radioisotope into the capture matrix. After the capture matrix was separated from the molybdenum target it was washed an additional time (wash 1), which indicates slight solubility of the molybdenum target with 1.3% of (99Mo) transferred to wash 1. The higher percent 99Mo transferred to the capture matrix in contact with the irradiation target during irradiation as opposed to contacting the target with capture matrix post irradiation, demonstrates the recoil and transfer of the radioisotope into an immiscible phase (capture matrix) preventing recombination or isotopic exchange with the original target and therefore yielding better results compared to sample 1. A number of experiments were performed to look at the Szilard-Chalmers effect and recoil of the radioisotope using the exemplary continuous-flow experimental procedure described above and depicted in FIG. 2. For these experiments a number of lanthanide containing compounds were synthesized and used as is, in a solid powder form as the irradiation target. The criteria for choosing the capture matrix was such that the irradiation target had to be insoluble in the capture matrix to prevent dissolution of the stable isotope that would, as a result, lower the specific activity. The experiments were carried out using water as the capture matrix. Post irradiation the capture matrices collected and the original irradiation target were analyzed both for stable isotope and radioisotope content in order to determine enrichment factors. Following the preliminary proof of concept experiments (example 1), the irradiation setup was enhanced in order to further optimize the enrichment factors and experimental conditions in addition to addressing some of the challenges encountered in the previous chapter, that lead to low enrichment factors. The proposed set up was such that the capture matrix flowed through the target continuously during irradiation and was then collected outside of the reactor core. The continuous flow instantaneously separated any radioisotope that had recoiled into the capture matrix, preventing potential, recombination, retention, isotopic exchange with the original target and successive neutron capture of the product radioisotope. Furthermore the setup was such that the irradiation target was placed in a filtering compartment, which allowed the capture matrix to filter out in all directions. Therefore the capture matrix was continuously contacted with the target material and filtered out through the bottom or sides of the filter unit, resulting in a higher concentration of separated radioisotopes (FIG. 3). The equation below was used to determine the enrichment factor such that if the ratio of produced radioisotope ZA+1X to the number of the inactivated target isotope ZAX in the capture matrix was greater than the number of radioisotopes produced ZA+1X to the number of inactive target isotopes ZAX in the target ( i . e . Z A + 1 X ( capture matrix ) Z A X ( capture matrix ) > Z A + 1 X ( target ) Z A X ( target ) )enrichment of the radioisotope has occurred by the Szilard Chalmers Reaction. Enrichment Factor ( EF ) = Z A + 1 X ( capture matrix ) Z A X ( capture matrix ) / Z A + 1 X ( target ) Z A X ( target ) An EF>1 indicates that the ratio of ZA+1X/ZAX is higher in the capture matrix than in the target matrix, therefore the specific activity is enhanced and there is indication of radioisotope enrichment. The enrichment factors were calculated using the above equation. The maximum enrichment factors for the compounds tested are summarized in Table 3. TABLE 3Maximum Enrichment Factors for Lanthanide CompoundsTarget CompoundRadioisotopeEnrichment FactorHolmium 8-hydroxyquinolinate166Ho11.26Holmium acetylacetonate166Ho14.83Samarium 8-hydroxyquinolinate153Sm11.19Samarium acetylacetonate153Sm3.56 For example an enrichment factor of 11.19 for samarium 8-hydroxyquinolinate results in a 91.6% increase of the samarium-153 specific activity compared to just irradiating the target under the same conditions, without the Szilard-Chalmers continuous flow radioisotope production and separation process. The flow-loop system can be easily installed in any research reactor or radioisotope production facility and be used for radioisotope production using the Szilard-Chalmers method. The proof of concept experiments performed verifies that the Szilard-Chalmers method coupled with the unique flow loop setup results in a radioisotope product with higher specific activity compared to the typical neutron irradiation of a target. Additional experiments were performed to examine the impact of the pH of the capture matrix, using a 10−4M HNO3 capture matrix. The results for Holmium 8-Hydroxyquinolate and Samarium 8-hydroxyquinolate targets are presented in Table 4. TABLE 4Maximum Enrichment factors for lanthanide compounds with 10−4M HNO3 capture matrix.Target CompoundRadioisotopeEnrichment FactorHolmium 8-Hydroxyquinolinate166Ho4.54Samarium 8-Hydroxyquinolinate153Sm1.37 The lanthanide irradiation targets used for the initial experiments (mentioned above) were solid powders of samarium and holmium complexed with ligands containing oxygen or nitrogen donor atoms. The ideal irradiation target should be thin with a large surface area such that the recoil range of the formed radioisotope product exceeds the thickness of the target and the product radioisotope can be ejected into the capture matrix. With the mentioned experimental setup and procedure, most likely only the radioisotopes formed on the surface of the packed powder target in contact with the capture matrix had the opportunity to recoil, be ejected and separated from the target by the capture matrix. The recoil range of the formed radioisotopes below the surface in contact with the capture matrix would be small compared to the distance from the capture matrix, leading to retention of the formed product in the target matrix. A large surface area of the target in contact with the capture matrix leads to an increase of the formed radioisotope product having the opportunity to recoil into the capture matrix, resulting in higher enrichment and an increase in specific activity. In an effort to look into diverse irradiation targets containing a high lanthanide content, larger lanthanide containing surface area and higher stability towards the irradiation field, the synthesis of additional target material that would fit into the mentioned criteria was investigated. One class of material that was appealing and considered as a promising agent for intra-arterial therapy and the treatment of liver malignancies was: radioactive holmium acetylacetone microspheres (HoAcAc-MS). The microspheres are loaded with holmium acetylacetonate (an irradiation target used in Example 3, with promising results, Table 3) and prepared by a solvent evaporation method 1. Vente M A D, Nijsen J F W, Roos R, et al (2009) Neutron activation of holmium poly(L-lactic acid) microspheres for hepatic arterial radioembolization: a validation study. Biomed Microdevices 11:763-772. doi: 10.1007/s10544-009-9291-y 2. Mumper R J, Jay M (1992) Poly(L-lactic acid) microspheres containing neutron-activatable holmium-165: a study of the physical characteristics of microspheres before and after irradiation in a nuclear reactor. Pharm Res 9:149-154. 3. Zielhuis S W, Nijsen J F W, de Roos R, et al (2006) Production of GMP-grade radioactive holmium loaded poly(L-lactic acid) microspheres for clinical application. Int J Pharm 311:69-74. doi: 10.1016/j.ijpharm.2005.12.034 4. Nijsen J F, Zonnenberg B A, Woittiez J R, et al (1999) Holmium-166 poly lactic acid microspheres applicable for intra-arterial radionuclide therapy of hepatic malignancies: effects of preparation and neutron activation techniques. Eur J Nuc Med 26:699-704. 5. Bult W, Seevinck P R, Krijger G C, et al (2009) Microspheres with ultrahigh holmium content for radioablation of malignancies. Pharm Res 26:1371-1378. doi: 10.1007/s11095-009-9848-8]. Previous studies performed concluded that HoAcAc-MS can endure neutron activation with a nominal thermal neutron flux of 5×1012 n·cm−2s−1 and heating to 200° C. and still maintain their structural integrity [Ref: Vente M A D, Nijsen J F W, Roos R, et al (2009) Neutron activation of holmium poly(L-lactic acid) microspheres for hepatic arterial radioembolization: a validation study. Biomed Microdevices 11:763-772. doi: 10.1007/s10544-009-9291-y]. In order to further develop an irradiation target that is porous and has a large surface area in contact with the capture matrix we developed an irradiation target by coating an inert solid support resin (Styrene divinylbenzene XAD-4 resin) with a Poly-vinyl Alcohol (PVA)/lanthanide mixture. The following procedure was used for the synthesis of Holmium Acetylacetonate polyvinyl alcohol XAD-4 resins: Similar to the HoAcAc PVA material synthesis, 0.5130 g of HoAcAc was dissolved in 9.2 mL chloroform (solution A). 1.2664 g of PVA was dissolved in 90 mL boiling H2O (solution B). Solution A was added to Solution B and 2.0394 g of cleaned XAD-4 resin was added to the emulsion and stirred at 700 rpm at room temperature for 72 hours until the majority of the solvent evaporated. The resultant pink colored resins were collected and dried. A similar procedure was utilized for the synthesis of Holmium 8-Hydroxyquinolinate polyvinyl alcohol XAD-4 resins. TABLE 5Maximum Enrichment factor for lanthanide PVA XAD-4 resinTarget CompoundRadioisotopeEnrichment FactorHoAcAc PV A XAD-4 resin166Ho24.36 Preliminary experiments were performed using the HoAcAc PVA XAD-4 resins and the flow loop setup for Szilard-Chalmers studies. The obtained enrichment factor for the resin (Table 5) was significantly higher compared to the powder target previously used (Table 3). The resin can be used as an irradiation target for radioisotope production using the Szilard-Chalmers method in addition to other applications such as in radiopharmaceuticals for cancer therapy. The Plutonium-238 radioisotope has a number of applications such as use in radioisotope power systems as a long-lived heat source to power space missions (Witze A (2014) Nuclear Power Desperately Seeking Plutonium. Nat. News) or in nuclear powered cardiac pacemakers (Huffman F N, Norman J C (1974) Nuclear-fueled cardiac pacemakers. Chest 65:667-672. doi: 10.1378/chest.65.6.667). The decay heat of 238Pu can be converted to electricity using radioisotope thermoelectric generator (RTG). 238Pu has a half-life of 88 years resulting in a decline in output by half over 88 years. Therefore the ability of the RTG to produce electricity declines in a slow and predictable manner. The RTG has been a power source of choice for a number of NASA's important missions into deep space were the lack of sunlight makes solar panels useless as an energy source. NASA has powered a total of 9 planetary and Apollo missions using radioisotope power systems, including the Pioneer and Voyager spacecraft. Additionally 238Pu fueled radioisotope heaters have been used on spacecraft's to warm instruments and other on-board systems. Currently 238Pu is produced by neutron bombardment of large Neptunium-237 targets for periods of up to 1 year (Howe S D, Crawford D, Navarro J, Ring T (2013) Economical Production of Pu-238. Nucl. Emerg. Technol. Sp. (NETS 2013)), according to the following mechanism:237Np+n→238Np→(β−,2.117 days)→238Pu,such that the 237Np with a neutron capture cross section of 170 barns captures a neutron to produce 238Np which then beta decays with a half-life of 2.117 days to 238Pu. A disadvantage of this production route is that the intermediate radioisotope of 238Np has a large fission cross-section of 2600 barns therefore a majority of the 238Np has fissioned before decaying to 238Pu. The developed continuous flow setup is an ideal method for Pu-238 production. Such that upon neutron capture of 237Np, the imparted recoil energy will eject the formed 238Np into the capture matrix were it is separated from the irradiation target and instantly pumped out the reactor core. Once the 238Np has left the reactor core via the capture matrix it is no longer exposed to the neutron flux and therefore the 238Np cannot fission. Since this is a continuous process the 238Np can be collected and left to decay to 238Pu, which is the product of interest. The proposed 238Np/238Pu production route can address the major obstacles involved in efficient 238Pu production. The Szilard-Chalmers method coupled with the continuous flow setup is more efficient in 238Pu production and as a result produces a product with higher specific activity. It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations, and are set forth only for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiments of the disclosure without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure. |
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049816403 | abstract | A vertical cell is provided for receiving a nuclear fuel assembly having a bundle of fuel rods retained at the nodes of a regular lattice and a skeleton formed of two end pieces connected together by tie rods and grids spaced apart along the tie rods. The structure of the cell has a cross-section corresponding to that of the assembly to be received and carries mechanisms for retaining the grids and the lower end piece, and a comb mechanism for holding the rods at their nominal spacing. The comb mechanism comprises at least two sets of combs carried by a frame fixed to the structure. The combs of each set are guided on the frame, and jacks move them towards and away from each other in a direction transversal to the movement of the combs of the other set. One of the grid retention mechanisms comprises jaws pivotably mounted on the structure and connected to simultaneous control jacks which move the jaws between a position in which they release the grid situated immediately below the comb mechanism and another position in which the jaws grip the grid on all sides thereof. |
046541705 | claims | 1. A method of decontaminating metal surfaces having an inorganic coating thereon which contains radioactive substances and spinel-like chromium oxides comprising: (A) passing over said coating a decontamination solution which comprises (B) passing over said coating a composition heated to about 50.degree. to about 120.degree. C., said composition consisting essentially of (C) passing said decontamination solution over said coating. 2. A method according to claim 1 wherein said alkali metal hypohalite is selected from the group consisting of sodium and potassium hypobromite, hypochlorite, hypoiodite, and mixtures thereof. 3. A method according to claim 1 wherein said alkali metal hypohalite is sodium hypobromite. 4. A method according to claim 1 wherein the concentration of said alkali metal hypohalite is about 0.1 to about 2%. 5. A method according to claim 1 including the additional last steps of repeating steps (A) and (B). 6. A method according to claim 1 including the additional steps of rinsing said coating with water after steps (A) and (B). 7. A method according to claim 1 wherein said chelate is nitrilotriacetic acid. |
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053435052 | claims | 1. Device for the recovery of a molten nuclear reactor core, comprising beneath the core (1) vertical partitions (4) defining separate volumes (5,6), certain of the volumes (5) being empty and the other of the volumes (6) being filled with coolant, the coolant-filled volumes being surmounted by a refractory material layer (7), wherein the partitions (4) are generally parallel, the coolant-filled volumes (6) forming channels in which the coolant circulates substantially horizontally. 2. Device for the recovery of a molten core according to claim 1, wherein the partitions (4) are generally straight. 3. Device for the recovery of a molten core according to claim 1, wherein the partitions (4) extend horizontally beyond a vertical well (2) in which the core is located. 4. Device for the recovery of a molten core according to claim 1, wherein the partitions (4) are composed of metal. 5. Device for the recovery of a molten core according to claim 1, wherein the channels (6) extend between a raised coolant source (10) and a vaporized coolant outlet (13). 6. Device for the recovery of a molten core according to claim 5, wherein the coolant source (10) is separated from the channels (6) by a valve (12) when the coolant is heated. 7. Device for the recovery of a molten core according to claim 1, wherein the empty and coolant-filled volumes (5, 6) are surmounted by a continuous heat absorption material layer (8) which surmounts the refractory material layer. 8. Device for the recovery of a molten core according to claim 7, wherein the heat absorption material is silica concrete. 9. Device for the recovery of a molten core according to claim 1, comprising a refractory material enclosure (9) which surrounds an area located above the empty and coolant-filled volumes (5, 6). 10. Device for the recovery of a molten core according to claim 1, wherein the refractory material is a refractory concrete. 11. Device for the recovery of a molten core according to claim 5, wherein the coolant source (10) is separated from the channels (6) by an automatically opening device when the coolant is heated. |
042138248 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT The sole drawing illustrates a preferred embodiment of a nuclear steam generating plant 10 including a vertically positioned pressure vessel 11 contained within a containment 12 of circular cross section. The pressure vessel 11 forms a pressurized container for a consolidated nuclear steam system (not shown in detail). The containment 12 consists of an outer cylindrical containment wall 13 topped by an outer upper head 14, and an inner cylindrical containment wall 15 topped by an inner upper head 16. An annular shaped chamber 20 is formed by the boundaries of the outer and inner walls, 13 and 15 respectively, and the inner upper head 16; and, an upper chamber 17 is formed between the upper inner and outer heads, 16 and 14 respectively, and the upper portion of the outer wall 13. The outer upper head 14 and inner upper head 16 are provided with removable sections, 18 and 19, respectively. A vertically disposed cylindrical shell 21, radially spaced in close proximity about the lower portion of the pressure vessel 11, cooperates with a horizontally disposed floor 22 to divide the containment into two compartments designated as the dry well 23 and wet well 24. A second cylindrical shell 25 is disposed in the wet well 24, radially spaced between the cylindrical shell 21 and the lower portion inner containment wall, thus subdividing the wet well into an inner annular region 26, and an outer annular region 27. Suppression pool water is contained only within the inner annular region 26 to a level 30 located so as to substantially fill the region. In the embodiment shown in the sole drawing, the centerline 51 of the pressure vessel 11 is not coincident with the centerline 52 of the containment 12. Although not essential to the practice of the invention, the centerlines 51, 52 are typically offset in order to facilitate the location of auxiliary equipment (not shown) in the dry well 23. Hence, it should be understood that cylindrical shell 21, in the embodiment illustrated in the drawing, is not concentrically circumscribed by the cylindrical shell 25. A plurality of vertically disposed perforated pressure suppression pipes 31, only two (31A, 31B) of which are shown for clarity, are substantially located within annular region 26 and extend through the horizontal floor 22 such that their upper extremity extends into the dry well 23. The lower end of each pressure suppression pipe 31 longitudinally extends partly into a ring collar 32 which is radially spaced thereabout to permit expansion of the pipe while precluding excessive lateral movements. Low pressure rupture discs 33 seal the upper end of the pressure suppression pipes. The upper volume of the inner annular region 26 is divided into circumferential upper portions by baffles 34, extending downward from the floor 22 to a level below that of the liquid level 30. The baffles 34 are circumferentially disposed between the vapor suppression pipes 31. Rupture discs 35 are provided above the water level 30 in the cylindrical shell 25. One rupture disc 35 is generally provided between each pair of circumferentially adjacent baffle plates 34. Feed 36 and returns 37 cooling pipe connections are provided within the inner annular region 26 and are attached to a cooling system (not shown). The feed 36 and return 37 cooling pipe connections provide means for circulating and cooling the water of the suppression pool which is heated due to convection from the pressure vessel and from the absorption of gamma radiation escaping from the core. A feedwater inlet pipe 40 and a steam outlet pipe 41 penetrate the outer and inner containment walls, 13 and 15 respectively, pass through the dry well 23, and extend into the pressure vessel 11. While only one inlet and one outlet pipe are illustrated, a plurality of these pipes would generally be disposed at spaced intervals about the pressure vessel and throughout the containment. A sealed conduit 42 traverses the outer annular region 27 and connects with a fluid tight passage 43 leading to a lower region 44 which is located below the pressure vessel. Instrument lines 45 from outside (not shown) of the containment are routed through the dry well to the lower region and enter the bottom of the reactor via the conduit 42, passages 43 and lower region 44. In operation, the reactor core 50 which is illustrated schematically, is disposed significantly below the suppression pool water level 30 in the annular region 26 which directly circumscribes the lower portion of the pressure vessel. Chambers 17 and 20 are water filled to afford biological shielding from the ionizing radiation which emanates from the reactor core. In ship propulsion applications, under normal conditions, the height of the water level 30 precludes significant reduction of the shielding achieved when the vessel achieves extreme attitudes. The baffled arrangement of the upper portion of the suppression pool effectively prevents air located above the water level 30 from shifting to the higher portion of the inner annular region during the pitch and roll of the vessel in which the reactor plant is located. All process penetrations into the pressure vessel 11 are made in the dry well compartment, thus the dry well 23 initially receives the discharge fluid upon a loss of coolant accident. As the dry well pressurizes the discs 33 rupture allowing the flow of fluid and air through the pressure suppression pipes 31 and into the suppression pool where the condensible gases released from the pressure vessel condense. The inner annular region, in turn, pressurizes causing the discs 35 to burst into the outer annular region, thereby relieving the pressure build up in the inner annular region. Means (not shown) are provided for draining the upper chamber 17. The center sections 18 and 19 of the upper outer head 14 and inner head 16 are removable for servicing, installation and removal of major components, and refueling of the reactor. The use of the water filled double wall containment arrangement permits elimination or a substantial reduction in the thickness of the biological shield of concrete (not shown) traditionally used resulting in an overall reduction in containment weight. The division of wet well and utilization of the waterless outer annular region 27 results in an increased suppression pool height which, in itself, and in conjunction with the inner region baffles 34 enhances the additional radiation shielding provided by the suppression pool. It will be evident to those skilled in the art that changes may be made, e.g. the use of sand for biological shielding purposes in chamber 20, or that parts of the invention may be used without other parts described herein, without departing from the spirit of the invention covered in the claims. |
039731316 | summary | FIELD OF THE INVENTION This invention relates to pulsed neutron logging tools for use in well bores, and more particularly, to a system for switching functions of a downhole pulsed neutron tool for obtaining measurements of different earth formation properties without requiring separate cable conductors or removing the tool from the well bore. BACKGROUND OF THE INVENTION In the search for earth formations containing hydrocarbons, a well bore is drilled and instruments are passed along the well bore to make measurements. From the measurements, the formation lithology, porosity, and other factors from which the presence of hydrocarbons can be deduced are measured. More often than not, several different types of measurements are necessary for formation analysis and it is necessary to obtain multiple types of measurements with separate tools. When logging tools are run separately, there is always a problem of correlating the depth in addition to the time consumed in removing and rerunning other tools. The loss of valuable rig time is an important commercial consideration. Where a single tool obtains multiple measurements, there is the problem of communication of power and signals between the surface and the tool over the electrical logging cable. For nuclear well logging, it is desirable to use a type of cable as disclosed in a copending application entitled "Well Logging System and Method Using An Armored Coaxial Cable and Compensation Circuit", Ser. No. 192,883 filed Oct. 27, 1971 and which is assigned to the assignee of the present invention. This is a triaxial (or armored coaxial) type of cable and it has desirable bandwidth capabilities for enhancing the measurement and preserving the shape of electrical pulses generated in the downhole equipment. As would be expected with this type of cable which has a limited number of conductors, certain types of measurements cannot be simultaneously made. In nuclear logging, for example, it is desirable to have a capability for obtaining a carbon/oxygen log and a thermal neutron decay time log on one pass through the well bore. While the equipment for obtaining these logs is similar, there are different neutron pulse frequencies, operating voltages, voltages and timing functions, so that obtaining both logs with one run of the tool requires downhole switching and control functions. In the practice of the present invention, a logging tool is provided with a high energy neutron generator (14 MeV) and a gamma ray detector. Thus, zones of interest can be found for further measurements related to carbon/oxygen content. This type of measurement is typically run at a much lower logging speed and uses a different neutron pulse duration and frequency. There are other factors which differentiate a thermal decay tool from carbon/oxygen tool. For example, a C/O tool may have a source detector spacing up to four inches more than a spacing required for a thermal decay tool. In regard to neutron pulse frequency and neutron generator pulse width, a thermal neutron decay time tool can operate at 1 KHz for neutron burst repetition with an ion source duration of 75 microseconds. A C/O tool on the other hand, has a neutron pulse repetition frequency of about 20 KHz and a 20 microsecond ion source pulse width. The measurements of gamma rays for thermal neutron decay time measurements occur at a time after the neutron burst. On the other hand, measurements for C/O ratio are made during the burst of neutron energy since inelastic scattering is measured. One of the advantages of a C/O tool is that it is substantially salinity independent, whereas a thermal neutron decay time tool is limited to areas of fairly high salinity. SUMMARY OF THE INVENTION The well logging system of the present invention has a source of high energy neutrons (a D-T reaction accelerator tube) and a gamma ray detector located at a compromise spacing for optimum counting of gamma rays both during a burst of neutrons and after a burst of neutrons. This enables measurement of both thermal neutron decay time and carbon/oxygen ratio. The downhole tool is provided with independent channels which provide operations to generate trigger pulses at different neutron pulse repetition frequencies and to provide desired neutron pulse duration dimensions for each operating frequency. The independent operation channels are selected by use of a control signalling technique which selects one of the channels for operation. A downhole switch is responsive to a control signal for stepwise altering the voltage on the target of the neutron generator tube, thereby controlling the relative number of neutrons generated in each neutron pulse and compensating for the compromise in spacing. In the surface equipment, provision is made by switches for using timing pulses to gate detector signals for each type of measurement. |
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053012186 | abstract | A multi-layer, rolled metal foil is laser tackwelded to form a tube which can be inserted in the intermediate space between the fuel body and cladding of a metal alloy fissionable fuel element. The rolled foil has at least three foil layers at the point of tack welding. The laser welding penetration is adjusted so that the foil weld is maintained at a thickness of at least two foil layers, but does not penetrate all of the layers. The weld is designed to fail in response to fuel or blanket alloy swelling during irradiation. After weld failure, the overlapping layers slip and the multi-layer foil unrolls as the fuel swells, providing a continuous, unbroken barrier between the fuel or blanket alloy and cladding which masks defects in the barrier due to weld failure. |
abstract | In a manufacture of a probe for a scattering type near-field microscope, there is provided a method of coating, with a high reproducibility, uniform metal particles efficiently inducing a surface enhanced Raman scattering. It has been adapted such that, in the probe for the scattering type near-field microscope, one part or all of the probe due to an interaction of at least an evanescent field is coated by metal particles which don't mutually adhere and have a particle diameter of 10 nm or larger and 50 nm or smaller in radius of curvature. |
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060884207 | abstract | In a reactor core, there is charged a number of fuel assemblies composed of a channel box and a fuel bundle disposed therein, in which fuel rods adjacent to each other are arranged so as to provide a triangular shape and a ratio of a coolant channel cross section to a fuel cross section is set to be 1 or less. |
040100707 | abstract | For gas-cooled pebble-bed reactors, an absorber element in the form of a hollow, helical spiral coil is proposed, which moves directly through the pebble bed essentially through rotary motion. This form not only facilitates the penetration into greater depths of the pebble bed, but also has a substantially greater absorber effect as compared to the known, essentially cylindrical absorber rods with the same absorber volume, so that the number of absorber elements can be reduced. |
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claims | 1. An apparatus for a scanning probe microscope, comprising a measuring assembly which includesa lateral shifting unit for lateral displacement in a plane,a vertical shifting unit for vertical displacement perpendicular to the plane,a probe provided on a probe support anda specimen support to receive a specimen,the lateral shifting unit and the vertical shifting unit being operable to provide relative displacement between the specimen support and the probe support,wherein a condenser light path is, at least partially, formed through the measuring assembly between a condenser light source and the specimen support, and wherein the specimen support is located in the area of an end of the condenser light path. 2. The apparatus as claimed in claim 1, wherein the condenser light path is formed substantially centrally through the measuring assembly. 3. The apparatus as claimed in claim 1, wherein the condenser light path is formed, at least partially, through the lateral shifting unit. 4. The apparatus as claimed in claim 3, wherein the condenser light path is formed through an opening in the lateral shifting unit. 5. The apparatus as claimed in claim 1, wherein the vertical shifting unit is arranged adjacent to the condenser light path. 6. The apparatus as claimed in claim 5, wherein the vertical shifting unit comprises a plurality of vertical shifting elements which are arranged around the condenser light path. 7. The apparatus as claimed in claim 1, wherein the condenser light path extends substantially parallel to a vertical axis. 8. The apparatus as claimed in claim 1, wherein the condenser light path is formed so that condenser light is in the shape of a substantially conical condenser light cone towards the specimen support. 9. The apparatus as claimed in claim 1, wherein the condenser light path is formed through a retaining member, the vertical shifting unit being disposed on the retaining member and the retaining member being made, at least in part, of transparent material. 10. The apparatus as claimed in claim 9, wherein the retaining member is arranged substantially centrally with respect to the condenser light path. 11. The apparatus as claimed in claim 9, wherein the retaining member is held by a frame member, the condenser light path being formed through an opening in the frame member. 12. The apparatus as claimed in claim 9, wherein at least a section of an optical deflecting unit is disposed in the range of the condenser light path to deflect measuring light rays towards the probe. 13. The apparatus as claimed in claim 12, wherein at least said section of the optical deflecting unit is made of transparent material. 14. The apparatus as claimed in claim 12, wherein the optical deflecting unit is arranged substantially centrally with respect to the condenser light path. 15. The apparatus as claimed in claim 9, wherein the probe is fixed to another retaining member, at least one section of the another retaining member being disposed in the condenser light path and said at least one section of the another retaining member being made of transparent material. 16. The apparatus as claimed in claim 15, wherein the another retaining member is fixed to a further retaining member which is coupled to the vertical shifting unit and comprises an opening, the condenser light path being formed through the opening. 17. The apparatus as claimed in claim 1, wherein an optical examination unit is provided for optical examination of the specimen illuminated by condenser light. 18. The apparatus as claimed claim 17, wherein the optical exanimation unit is provided beneath the specimen support. 19. The apparatus as claimed claim 17, wherein the optical examination unit is an objective. 20. The apparatus as claimed claim 17, wherein the optical examination unit is an optical microscope. 21. The apparatus as claimed in claim 1, wherein for vertical displacement the probe support is connected to-the vertical shifting unit. 22. A method of microscopically examining a specimen on a specimen support of a scanning probe microscope, including an optical microscope, comprising the steps of:providing a measuring assembly which includes a lateral shifting unit, a vertical shifting unit, a probe provided on a probe support and a specimen support to receive a specimen;positioning a probe and the specimen support relative to each other using at least one of the lateral shifting unit for lateral displacement in a plane and the vertical shifting unit for vertical displacement perpendicular to the plane, to perform relative displacement between the probe support and the specimen support;providing a condenser light and illuminating the specimen on the specimen support using light rays from the condenser light; andguiding the light rays from the condenser light along a path which is at least partially provided through the measuring assembly. |
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048295523 | description | DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference to FIG. 1, an X-ray apparatus provided with a conventional source 20 of X-ray photon irradiation projects a beam 10 of irradiation at a subject 30, typically a localized area of the subject 30 such as a heart, a chest, a liver or other selected body area. The beam 10, FIG. 1, penetrates the subject 30 and individual photon beams thereof (hereinafter "photons") are either absorbed (one such absorbed photon is shown as photon 40), scattered (one such scattered photon is shown as photon 50), or unscattered (shown as photons 60, 70). An X-ray photon sensitive detector 100 is aligned with the path of the beam 10 emanating from source 20 behind the subject 30. Between the detector 100 and the subject is disposed a serial array 100 of strips 90. Each strip 90 comprises an X-ray photon absorptive material such as tantalum, lead, uranium or alloys, mixtures or laminates of one or more of all of the foregoing metals. As shown in FIG. 1 the array 100 comprises a series of speced strips 90 each of which has a predetermined height, H, and thickness W. Spaces 92 are provided between the strips 90, the spaces 92 typically comprising a non-X-ray absorptive material such as air, aluminum, foam and the like. Such non-absorptive spaces 92 are provided so as to allow unscattered photons such as photon 60 to travel through the array 110 and be detected by detector 100. Air is most preferred as comprising the spaces 92. Unscattered photons such as 60, 70, FIG. 1, which transmit through the subject are typically the only photons which the user wants to detect via detector 100 in order to obtain a true shadow image of the subject 30. Scattered photons such as photon 50 are typically absorbed by the array 110 of strips 90 by impinging on a face 98 of a strip 90 and thereby prevented from detection by detector 100 because such scattered photons 50 do not represent a true shadow image of the subject 30 by virtue of their scattering. Of the portion of the beam 10, FIG. 1, which ultimately transmits unscattered through the subject (generically shown as photons 60, 70), some portion of such unscattered irradiation will transmit directly through the subject 30 and the grid array 110 and ultimately be detected by detector 100 (generally represented by photon 60). However, another unscattered portion of the beam 10, as represented generically by photon 70, will transmit through the subject only to be obstructed from detection, typically by impinging on a front fact 95 of one absorptive strips 90. The grid array 110 of strips 90 is typically focussed at (i.e., angled as shown in FIG. 1) the source 20 from where the beam 10 or irradiation is emanating in order to avoid the incidental impingement of an unscattered photon ray, such as 60 or 70, on a face 98 of a strip 90. The object of the grid array 110, therefore, is to prevent or minimize scattered radiation such as photon 50 from being detected by detector 100 and allow as much unscattered, unabsorbed radiation 60, 70 to be detected as possible. Therefore, although obstructed photons 70 comprise a critical portion of the unscattered irradiation for purposes of constructing a true shadow image of the subject 30, such unscattered photons 70 are obstructed from detection in such a manner that detector 100 only detects unscattered photons 60 which transmit through subject 30 at such an angle as to pass through one of the non-absorptive spaces 92 provided between the strips 90 in array 110, FIG. 1. A small amount of scattered irradiation may reach detector 100 (now shown) by virtue of scattering through the subject at an angle which aims a scattered photon through a space 92, but the majority of scattered photons scattered toward the array 110 of strips of impinge on and be absorbed by one or more of strips 90. The strips 92 of grid array 110 shown in schematic form in FIG. 1, are most preferably comprised of tantalum. Prior grid array systems typically employ a strip density (i.e., number of strips per inch) of greater than about 50 strips per inch and most typically about 150 strips per inch, for the purpose of preventing more than about 75% of the scattered irradiation (such as photon 50) from being detected. The concomitant disadvantage in grid systems having such a great number of strips 90 is that the total strip face area 95 per inch is concomitantly increased thereby preventing a greater amount of the critical shadow image forming radiation (such as photons 60, 70) from being detected. The present invention typically employs a strip density for grid array 110 of less than about 10 strips per inch and most preferably about two strips per inch. Prior grid array systems typically employ a strip height, H, FIG. 1, of less than about 0.25 inches. The present invention preferably employs a strip height, H, of greater than 0.25 inches, preferably between about 0.25 and five inches and most preferably about three inches. As strip height H is increased, the amount of scattered radiation (such as photon 50) which is prevented from reaching detector 100 is increased. A concomitant disadvantage in increasing strip height H is that strips 90 require more precise and selective "focussing" relative to source 20 (i.e., angle alignment of strips 90 relative to source 20) in order to avoid incidental impingement of critical image forming radiation (such as photons 60, 70) on a strip face 98. The thickness W, FIG. 1, of the strips is typically selected to be less than about ten mills and most preferably about two mils. The result of the transmission of the unscattered photons through the subject toward the grid array 110 is that the detector 100 detects a shadow image consisting primarily of unscattered photons (such as photon 60) passing through spaces 92 on which is superimposed a serial array of dark lines corresponding to the thickness W of the strips 92 which have obstructed a portion of the unscattered photons (such as photon 70) from being detected. According to the invention a complete shadow image of the subject is constructed from the detector 100, FIG. 1, as if the strips 90 did not obstruct any unscattered photons from detection. Such a complete image is formed by recording the photons detected by detector 100 as a conventional analog image, converting such an analog image into a digital image, i.e., a digital array of data representative of the analog image, and creating a digital image of the dark areas of the analog image. These new areas correspond to the areas of the detector obstructed by the thickness W of the strips that prevented detection of unscattered photons. Such reconstruction is accomplished via calculating a new digital array from the original digital array according to a predetermined algorithm, formula, program or function, using a conventional digital image processing device. The detector 100, FIG. 1, typically comprises an X-ray photon sensitive material such as a gadollinium oxysulfide screen which emits fluorescent light at any given area of the screen upon impingement of photons at the given area. The degree of fluorescence over a given area of the screen will typically vary directly with the number of photons impinging on the given area of the screen. The result of projecting the beam 10 through the subject 30, therefore, is a shadow image of the photons absorbed by the subject and appearing on the screen as gradations of non-fluorescent versus fluorescent areas on the detector 100. With reference to the schematic diagram of FIG. 2, the image 130 which fluoresces from the screen detector 100 is typically received by a mirror M and reflected as light image 140 into reception by a lens L. Lens L preferably collimates the reflected image 140 and directs such collimated image into an image intensifier II which amplifies the image and is preferably coupled to a fiber-optic bundle FOB. The light image emerging from the fiber optic bundle FOB is received by a conventional analog image converter AC, typically a television camera. Other known devices such as large area sensitive solid state arrays and CCD's could also be used. The analog image converter AC, FIG. 2, is typically electronically scanned as a series of rows, typically as a series of 512 rows, each row typically comprising 512 points. Each point within, for example, a 512 by 512 array is a pixel having an established intensity (and color, if applicable or desired). As each pixel is scanned, the output from the image converter AC, FIG. 2, is fed to an analog to digital converted ADC. The ADC provides a digital representation of the intensity of each pixel which can be stored in a digital memory. The result is a digital map of pixel intensities with a one to one correspondence to each point in the analog image. The number of rows and divisions in a single row in the array may comprise more or fewer than 512 rows and/or 512 pixels per row resulting in greater or less resolution. The art of processing images, well known per se, is outlined in Boxe, Digital Image Processing (Prentice Hall, Englewood Cliffs, N.J. 1984) and references cited therein. The analog image may be recorded, and the digital data converted therefrom, in one, two, or three dimensions depending on the capability of the X-ray apparatus. Where the X-ray apparatus source, detector, and grid are rotatable in the three dimensions around the subject enabling a three dimensional photon absorption image to be recorded, a suitable three dimensional digital pixel map may be constructed from the three dimensional analog image as the detector moves in three dimensions around the subject. For purposes of explanation the discussion herein is limited to two dimensional analog images and two dimensional digital arrays representative thereof. In the exemplary case where the digital map comprises a 512.times.512 map, the map converted to two dimensions comprises a square, 512 pixels long and 512 pixels wide, i.e., a square map comprised of 262,144 equally sized pixels. Alternatively, the digital map may be constructed to represent the analog image in more or fewer pixels and in various grid shapes other than a square. In a preferred embodiment of the invention where the grid system 110 has a density of about 2 strips per inch and, the strips 90 are about 2 mils in thickness W, FIG. 1, the system 110 will obstruct about 7% of the critical unscattered photons. Assuming such a grid system embodiment and assuming the length of the strips are substantially aligned with the orientation of the length of the scanned rows of pixels, each strip 90 will obstruct the equivalent of about 2 pixel rows (each 512 pixels in length) of the digital map, wherein the pixel intensities in such rows have digital contents equivalent to zero light intensity. The present invention provides a means for calculating reconstructed data for the pixels in each such digital pixel array (as if representing areas of the detector unobstructed by the thickness W of the strips 90) from the pixels bordering such obstructed pixel arrays. Assuming the example stated above where a strip 90, FIG. 1, obstructs an array of digitally converted data, two pixels in thickness on a 512.times.512 map, FIG. 3 is shown as depicting, in schematic form, a portion of the exemplary 512.times.512 pixel map in which each square denotes a separate pixel. For example, Row X denotes a portion of a row array of data, two pixels in thickness, corresponding to an area of the detector 100 obstructed by one of strips 90, FIG. 1. Row arrays T, Y, and V,Z, FIG. 3, shown as one pixel in thickness, border row array X on the top and bottom respectively and correspond to the areas of the detector 100 detecting primarily unscattered photons immediately above and below the stirp 90 which is represented by row array X. A typical means for calculating reconstructed data for the double row X pixel 200, for example, is accomplished via a program or algorithm which selects the data from two pixels 600 and 500 bordering pixel 200 on the top and bottom, FIG. 3. The data selected from pixels 600 and 500 may be averaged and assigned to pixel 200 as reconstructed pixel data. Similarly, with respect to row X pixel 300, the data from pixels 700 and 400 may be selected, averaged and assigned as reconstructed pixel data for pixel 300. Thus two bordering pixels, each one pixel away from the row X pixel to be reconstructed (primarily because row X is two pixels in width), are typically selected to calculate the new data for a given row array X pixel. An analogous pixel selection and data averaging process is thus carried out for each pixel in each pixel row array corresponding to each strip obstructed area (now shown) of the detector and a complete reconstruction of a digital image may be effected corresponding to an analog image of the subject as if none of the unscattered photons passing through the subject were obstructed by the thicknesses W of strips 90, FIG. 1. In such an averaging process the pixels (e.g., 500, 600, FIG. 3) adjacent the photon obstructed pixels (e.g., pixel 200, FIG. 3) are identified and counted, the data of such adjacent pixels is added, and the sum of such retrieved data is divided by the number of pixels counted. As described hereinbelow, such adjacent pixels (e.g., 500, 600, FIG. 3) are preferably identified for retrieval by comparing the data stored in all adjacent pixels in the pixel map and identifying which adjacent pixels have a difference in stored data greater than a selected or predetermined value. The adjacent pixels having such differences in data greater than the selected value may thus be defined as either a photon obstructed pixel or a non-photon obstructed pixel, i.e., the pixels on either side of the edge of a portion of the digital image corresponding to the edge of a strip 90, FIG. 1, which is obstructing unscattered photons 70 from detection. Other programs and algorithms such as bi-directional pixel weighting or more complicated mathematical approximations may be utilized whereby different bordering pixels are selected and/or different calculations are carried out to arrive at reconstruction data for the row X strip obstructed pixels, FIG. 3. The pixels selected and the program or algorithm selected for use in the reconstruction process will vary according to a variety of factors including the orientation of the strips 90 relative to the pixel map, the size of the pixel grid selected for mapping the analog image, the density, height, and the thickness of the strips in the grid array. The combination of all of such variables will determine the orientation, number and location of the pixels on the digital map corresponding to the various strip obstructed areas of the detector. There are many techniques of reconstructing data for the obstructed areas of a pixel map and similarly there are many programs for manipulating the pixel data collected other than averaging. Modst preferably a related handling of the pixel data in the unobstructed areas is carried out which enhances image fidelity by reducing noise and enhancing image edges and features. Multiple exposures may be made and the values of each pixel over all the exposures averaged. This technique relies upon the statistical nature of noise to add energy on one exposure and to subtract energy on the second exposure so as to average out to near zero the total noise added or substracted over many exposures. The actual signal due to the subject image will add on each exposure. This technique can be expected to increase the image signal to noise ratio by a factor equal to the square root of the number of exposures. Another technique which may be employed is a weighted moving average. This technique improves signal to noise in real time with little time delay. This technique involves replacing the digital data of a selected pixel (to be used in reconstructing an obstructed pixel) with a weighted average of the adjacent pixels on either side of the selected pixel in question. For example, in FIG. 3 the value of pixel 600 could be calculated by the following equation: ##EQU1## Where: v(600)* is the resultant average value which replaces v(600) in the pixel map, v(598) is defined as the raw value of pixel 598, and v(599), v(600), v(601) and v(602) are the analogous raw values of the correspondingly numbered pixels and similarly for the other terms in the equation. The coefficients for each pixel value is an arbitrary weight given to that pixel which increases or decreases the effect of that pixel on the average value being calculated. In this example, the value calculated at pixel 600, FIG. 3, would not be known until pixel 602 is scanned causing a two pixel delay which is neglible in most real-time applications. This technique may be broadened by including more neighboring pixels, changing the weight given to each neighboring pixel, or by including pixels in adjacent rows above and below the pixel in question but with increased time delay and data processing requirements. In systems (such as the preferred system of the present invention) using lenses, mirrors and other typical optical devices which cause an image to be focussed onto a video camera tube, distortions occur as the tube is read out at the scene at the edge of the tube is read out. This distortion, known as parabolic distortion is corrected by analog or digital circuit techniques, the analog techniques amplify the analog video signal in a known predetermined way as the tube is scanned. This amplification compensates for the parabolic distortion. A similar compensation can be accomplished by adding to the digital values in the pixel map so as to, in effect, amplify the signal in a manner similar to the analog circuitry. With reference to FIG. 3, the following is a generally applicable and preferred reconstruction technique, which is useful in this invention where the grid strips 90 obstruct, for example, the rows X. The pattern of light striking rows T, Y, Z and V depends upon the shadow image of the subject. For example, if this shadow image contains a brighter to dim transition, i.e., an edge, running diagonally from the upper left to the lower right across the pixel map in FIG. 3 transversing the obstructed row X, reconstruction of that edge in the obstructed pixels of rows X may be accomplished by recognizing that a series of brighter pixels followed by a series of dimmer pixels, or vice versa, defines such an edge, and using a series of pixels prevents a single noise spike from creating a "false" edge. By logically relating bright to dim transitions on previous rows of the pixel map as the continuation of a single edge, the angle that the edge makes across the pixel map, FIG. 3, can be determined, and if a second edge and its angle is found transversing rows Z and V in FIG. 3, then these two edges can be determined to be a single edge traversing the obstructed rows X in FIG. 3 and the appropriate data inserted into the proper pixels in the obstructed rows X, thereby reconstructing the edge. Such a routine will maintain the fidelity of the image better than simple averaging. In the typical case, the individual strips 90 of a grid array 110 are straight along their length as shown in side crosssection in FIG. 1. A grid array may also be conprised of strips which have a different geometry such as circular or the like relative to the source 20. Where the strips 90, FIG. 1, are configured to be straight, a straight row-like pattern of pixels, such as row X, FIG. 3, may be formed on the pixel grid as corresponding to the photon obstructed areas of the recorded analog image. Typically, however, the grid strips 90, FIG. 1, may be skewed or otherwise not aligned such that straight rows of pixels are obstructed. In any grid array 110, FIG. 1 embodiment, straight, skewed, circular, or otherwise, the edge of the strips as represented by a pattern of pixels on the prixel grid may be determined by comparing the data stored in adjacent pixels to determine bright to dim transitions on the pixel map corresponding to bright to dim transitions in the recorded analog image. By identifying which adjacent pixels in the pixel map have a difference in data greater than a selected value strip edges may be defined and the pixels corresponding to the photon obstructed areas of the analog image may thus be defined as being between the defined edges. For example, with reference to FIG. 3, if pixels 597 and 598 were bright as determined by the digital representation (i.e., the digital data collected), and pixels 599, 600, 601 and 602 were dim, an edge would be defined. Accordingly, if pixels 397, 398 and 399 were bright and 400, 401 and 402 were dim, the edge is determined to be running diagonally down from left to right from pixels 598 and 399. If the pixels 498 to 502 were bright and 503 and subsequent along each row were dim, and if 698 to 703 were bright and the subsequent pixels along such row were dim, then the edge can be logically connected from 598 and 399 to 502 and 703 and inferred to have occurred at pixels 200 and 301. Thus, the appropriate values can be reconstructed at pixels 200 and 301 preserving the fidelity of the edge through the obstructed rows. Such a technique may be expanded into more or less sophisticated techniques to reconstruct data corresponding to obstructed areas of the pixel map. Also this technique is applicable for reconstructing a shadow image edge across other patterns of obstructed pixels, which represent patterns of possible grid structures other than straight strips such as curves, circles, spheres, and essentially all other geometrical patterns. A natural extension of the edge detection technique is to enhance that edge. Typically the transition from a series of bright pixels to dim pixels is gradual. The gradations depend upon the shadow image, how well the image is focussed and the ability of the ADC to distinguish various gray levels. However, once an edge has been logically discovered, the digital value of the pixels on the brighter side of the edge and may be increased the digital values on the dim side of the edge may be decreased by predetermined amounts to enhance the definition of the edges. A visual reconstruction of the edge from the enhanced digital values would produce a more pronounced visual edge. Additionally, although beyond the scope of this invention, detected edges can be analyzed. The length, contour and width of the edge can be determined, if the edge outlines an object and the area of the object can be determined. Many such features of the image can be determined which lead into areas of pattern recognition. As a general matter, the wider the digital row arrays corresponding to the strip obstructed areas of the detector become, relative to the overall size of the digital map, the more difficult it becomes to devise a predetermined pixel selection and data manipulation routine which is capable of carrying out the most accurate reconstruction of the strip obstructed pixels. Preferably the density, thickness W, and height H of the strips 90, of the grid array 110, FIG. 1, are selected to minimize obstruction of unscattered irradiation to less than about fourteen percent of the total amount of unscattered irradiation teaching the grid array 110. Preferably the density of the strips is selected to be between about one and three strips per inch (most preferably about two strips per inch), the thickness W of the strips is less than ten mils (most preferably about four mils), and the height H of the strips is preferably greater than 0.25 inches (most preferably about three inches). In addition to the reconstruction techniques discussed herein, the system may be first calibrated whereby pictures are taken with no subject and the system is programmed to learn where the obstructions are and thus where reconstruction is required upon actual photon irradiation of the subject. Here the edge detection scheme described earlier can be applied to find the edges of the obstructed areas in the pixel map. Additionally the analog scanner may be "wobbled" in order to fill in the obstructed areas in effect creating a controlled smearing of the collected analog image and noncomitant filling in of the obstructed area. A less preferred technique of filling in the obstructed areas involves moving or vibrating the grid array 110, FIG. 1, up and down and taking numerous pictures and collecting numerous digital data during the movement up and down to thereby obtain a time averaged reconstruction of obstructed areas in addition to the reconstruction routines discussed herein. It will now be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent, which is limited only by the following claims, construed in accordance with the patent law, including the doctrine of equivalents. |
summary | ||
047926929 | abstract | An irradiation apparatus for curing photopolymerizable dental fillings in situ comprises a lamp 10 for producing a convergent light beam with a convergence angle .alpha.E smaller than about 30.degree. with respect to the optical axis, and an optical wave guide 15 having an entrance surface 14 disposed in the light beam and an exit surface 16. The wave guide 15 is conical with a diameter decreasing from the entrance surface 14 to the exit surface 16 and has a refractive index of approximately .sqroot.2. At the exit surface 16, radiation of constant density and high intensity is produced within a substantially semi-spherical lobe, so that even such dental parts which are difficult to access can be irradiated and penetrated with high intensity radiation. |
claims | 1. A retention and alignment system for nuclear fuel rods comprising:an upper nozzle plate and a lower nozzle plate;at least one nuclear fuel rod having an upper end and a lower-most end and extending axially along a longitudinal axis between the upper and lower nozzle plates;at least one first precision magnet incorporated onto the lower-most end of the at least one nuclear fuel rod; andat least one second precision magnet incorporated onto the lower nozzle plate in a position confronting the at least one first precision magnet along the longitudinal axis, the first precision magnet having at least one of a magnetic north or south polarity and the second precision magnet having at least one of a magnetic south or north polarity opposite the polarity of the confronting first precision magnet to effect magnetic attraction between the confronting first and second precision magnets. 2. The retention and alignment system recited in claim 1 wherein each of the at least one first and second precision magnets has at least one paired section, each section of the pair having a polarity opposite the polarity of the other section of the pair, wherein the polarity of each section of the pair is selectively switchable to the opposite polarity to selectively switch one of the first or second precision magnets from a locked configuration wherein confronting precision magnet sections attract each other to an unlocked position wherein confronting precision magnet sections repel each other. 3. The retention and alignment system recited in claim 2 wherein each of the at least one first and second precision magnets has at least a second paired section, each second paired section having a polarity opposite the polarity of the other second paired section, and the polarity of the opposing sections is switched by rotating one of the first and second precision magnets to position the second paired section of a section of one of the first and second precision magnets opposite the first paired section of the other of the first and second precision magnets such that opposing sections have the same polarity. 4. The retention and alignment system recited in claim 1 wherein each of the at least one first and second precision magnets has at least one paired section, each section of the pair having a polarity the same as the polarity of the other section of the pair, wherein the polarity of each section of the pair is selectively switchable to the opposite polarity to selectively switch one of the first or second precision magnets from a locked configuration wherein confronting precision magnet sections attract each other to an unlocked position wherein confronting precision magnet sections repel each other. 5. The retention and alignment system recited in claim 4 wherein each of the at least one first and second precision magnets has at least a second paired section, each second paired section having a polarity the same as the polarity of the other second paired section, and the polarity of the opposing sections is switched by rotating one of the first and second precision magnets to position the second paired section of a section of one of the first and second precision magnets opposite the first paired section of the other of the first and second precision magnets such that opposing sections have the opposite polarity. 6. The retention and alignment system recited in claim 1 wherein each of the at least one first and second precision magnets comprises a plurality of paired sections, each section of a pair within the plurality of paired sections having one of the same polarity as the other section of the pair or the opposite polarity of the other section of the pair, wherein the polarity of each section is selectively switchable to the opposite polarity to selectively switch one of the first or second precision magnets from a locked configuration wherein at least a majority of the confronting precision magnet sections attract each other to an unlocked position wherein at least the majority of the confronting precision magnet sections repel each other. 7. The retention and alignment system recited in claim 6 wherein the polarity of each section is selectively switchable to the opposite polarity by rotating at least one of the first and second precision magnets. 8. The retention and alignment system recited in claim 1 wherein the at least one first precision magnet comprises a first precision magnet incorporated onto the lower-most end of the at least one fuel rod, wherein the at least one second precision magnet comprises a second precision magnet incorporated onto the lower nozzle plate, and wherein the first precision magnet and the second precision magnet are configured to axially retain the nuclear fuel rod between the upper and lower nozzles. 9. The retention and alignment system recited in claim 1 further comprising at least one grid parallel to and positioned between the upper and lower nozzle plates, the at least one grid defining a perimeter and having within the perimeter, a set of grid straps extending laterally and longitudinally across the grid to define at least one cell having an interior and an exterior, the at least one cell being configured to receive the at least one fuel rod passing axially through the interior of the cell;at least one third precision magnet incorporated onto one of the grid straps in the interior of the cell;at least one fourth precision magnet incorporated onto a side of the fuel rod passing through the cell in a position confronting the at least one third precision magnet, the third precision magnet having at least one of a magnetic north or south polarity and the fourth precision magnet having at least one of a magnetic north or south polarity the same as the polarity of the confronting third precision magnet to effect magnetic repulsion between the confronting third and fourth precision magnets for maintaining a gap between the fuel rod and the grid strap onto which the confronting third precision magnet is incorporated. 10. The retention and alignment system recited in claim 9 wherein there are a plurality of cells and a plurality of fuel rods, and wherein only one of the fuel rods extends axially through any one of the cells. 11. The retention and alignment system recited in claim 10 wherein each cell through which one of the fuel rods passes has at least two third precision magnets incorporated onto different grid straps of the cell and the fuel rod has at least two fourth precision magnets, each fourth precision magnet positioned on the fuel rod to confront a different one of the at least two third precision magnets incorporated onto the grid straps. 12. The retention and alignment system recited in claim 10 further comprising at least one retention member positioned in each cell to maintain the gap between the fuel rod and at least one of the grid straps of the cell. 13. The retention and alignment system recited in claim 1 wherein the lower nozzle plate comprises a plurality of cupped portions for seating the lower-most end of the at least one nuclear fuel rod, and each cupped section has one of the at least one first precision magnets incorporated therein. 14. The retention and alignment system recited in claim 1 further comprising a path for coolant flow along each of the at least one nuclear fuel rod. 15. A retention and alignment system, comprising:an end plug, comprising:a boss section configured to operably couple to a fuel rod; anda lower-most end surface comprising a first magnet pair, the first magnet pair comprising:a first magnet comprising a first polarity; anda second magnet comprising a second polarity, wherein the second polarity is opposite the first polarity; anda nozzle plate comprising a surface, wherein the lower-most end surface is configured to be seated upon the surface of the nozzle plate, the surface comprising a second magnet pair configured to confront the first magnet pair, the second magnet pair comprising:a third magnet comprising the second polarity; anda fourth magnet comprising the first polarity. 16. The retention and alignment system of claim 15, wherein the nozzle plate and end plug are configurable between an unlocked configuration and a locked configuration. 17. The retention and alignment system of claim 16, wherein the end plug is rotatable relative to the nozzle plate to transition the end plug and the nozzle plate between the unlocked configuration and the locked configuration. 18. The retention and alignment system of claim 16, wherein the nozzle plate and end plug are configurable in the unlocked configuration based on:the first magnet confronting the fourth magnet; andthe second magnet confronting the third magnet. 19. The retention and alignment system of claim 16, wherein the nozzle plate and end plug are configurable in the locked configuration based on:the first magnet confronting the third magnet; andthe second magnet confronting the fourth magnet. 20. A retention and alignment system, comprising:an end plug, comprising:a boss section configured to operably couple to a fuel rod; anda lower-most end surface configured to be seated on a surface of a nozzle plate, wherein the lower-most end surface comprises:a first pair of magnets comprising a first polarity; anda second pair of magnets comprising a second polarity;wherein the nozzle plate comprises a third pair of magnets comprising the second polarity and a fourth pair of magnets comprising the first polarity;wherein the first pair of magnets is configured to magnetically couple to the third pair of magnets; andwherein the second pair of magnets is configured to magnetically couple to the fourth pair of magnets. 21. The retention and alignment system of claim 20, wherein the lower-most end surface of the plug comprises a first flat surface, and wherein the surface of the nozzle plate comprises a second flat surface. |
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059498374 | description | BEST MODE FOR CARRYING OUT THE INVENTION A. The Nonproliferative Light Water Thorium Nuclear Reactor Turning now to a detailed consideration of a first preferred embodiment of the present invention known as the nonproliferative light water thorium nuclear reactor, FIG. 1 illustrates a nuclear reactor core 10 comprised of a plurality of fuel assemblies 12, known as seed-blanket units (SBUs), that are arranged in a generally hexagonal configuration, and are themselves hexagonal in cross section. The core 10 is of the same geometrical configuration and dimensions as a conventional Russian light water reactor known as the VVER-1000 so that it can be easily retrofitted into a VVER-1000, and is formed of 163 of the SBU fuel assemblies 12. The difference between the core 10 and the VVER-1000 reactor core lies in the composition of the SBUs 12 as will be discussed in greater detail below. It will be understood that the shape and arrangement of the core 10 and the SBUs 12 can be modified as necessary to facilitate retrofitting into any type of conventional light water pressurized water reactor (PWR). For example, conventional PWRs in the United States and other countries employ fuel assemblies having square cross sections, and the SBUs 12 would also have square cross sections if they were designed to be retrofitted into such a PWR. Surrounding the core 10 is a reflector 14 which is preferably comprised of a plurality of reflector assemblies 16 as illustrated in FIGS. 1 and 5.1-5.9. Each of the reflector assemblies 16 preferably contains a mixture of water and core barrel/pressure vessel metal. Alternatively, each of the reflector assemblies 16 could also be formed predominantly of thorium oxide. FIG. 2 illustrates the composition of each of the SBU fuel assemblies 12. Each of the SBUs 12 includes a centrally located seed region 18 and an annular blanket region 20 which surrounds the seed region 18. The seed region 18 is comprised of a plurality of seed fuel rods 22 which are preferably formed of uranium-zirconium alloy containing U-235/U-238 initially enriched to as high as 20% U-235, which is the maximum enrichment that is considered to be nonproliferative, i.e., incapable of being utilized to manufacture nuclear weapons. While it is not necessary to maximize the initial U-235 enrichment to 20%, it is preferable to employ this enrichment level to minimize plutonium production in the seed during reactor operation. Alternatively, the fuel rods 22 can be made of cermet fuel with uranium oxide particles embedded in a zirconium alloy matrix. The use of zirconium alloy (zircalloy) in the seed fuel rods 22 is preferred over oxide type fuel because the zirconium alloy fuel has a much higher thermal conductivity. As will be discussed in greater detail below, this is important because it reduces the amount of space needed in the SBU 12 for heat removal, and thereby increases the amount of space available for water moderator. The seed region 18 also contains a plurality of water tubes 24 for reception of water moderator (or conventional burnable poison rods and/or control rods as discussed in greater detail below) to control reactivity in the seed region 18. The blanket region 20 contains a plurality of blanket fuel rods 26 which are preferably formed of mixed thorium-uranium oxide. The initial uranium oxide volume content in the thorium-uranium mixture is preferably in the range of approximately 2-10%, and is employed to help fuel the blanket region 20 on start up before the thorium has had a chance to absorb neutrons from the seed, and generate the blanket's own fissile fuel, U-233. As in the seed fuel rods 22, the uranium oxide contained in the blanket fuel rods 24 is preferably U-235/U-238 enriched initially as high as the maximum nonproliferative ratio of 20:80. The seed-blanket core 10 operates in accordance with the following simplified equation for the power sharing between the seed 18 and the blanket 20: EQU P.sub.b /P.sub.s =.epsilon.(K.sub.b /(1-K.sub.b))(K.sub.s-1)/K.sub.s In the foregoing equation, K.sub.s and K.sub.b are the multiplication factors of the seed and blanket respectively. P.sub.s and P.sub.b are the powers generated in the seed and blanket respectively, while .epsilon. is the fast effect, which is slightly over 1. The seed multiplication factor, K.sub.s, is greater than 1, and the blanket multiplication factor, K.sub.b, is less than 1. Thus, the blanket is subcritical, and the seed acts as a source of neutrons for the blanket. In order to maximize the amount of energy produced from thorium, it is necessary to make the fraction of the core power produced in the blanket 20 as high as possible. This is accomplished by making K.sub.s as high as possible, and it has been determined that K.sub.s can be as high as 1.70, while K.sub.b is selected between approximately 0.85 and 1. The number of neutrons absorbed by U-238 in the seed 18 must be minimized. Most of the neutrons absorbed in U-238 are in what is called the resonance energy region marked by closely spaced energy intervals of extremely high absorption. On the other hand, most of the fissions in U-235 occur at lower energies in the thermal region where the average neutron energy is in near equilibrium with the ambient temperature of the light water moderator. By making the water content of the seed 18 as high as practicable, the number of neutrons in the resonance region is decreased, and thus, fewer neutrons are captured by the U-238. Reduction of U-238 captures produces two favorable effects. First, the multiplication factor of the seed, K.sub.s, is raised, thereby increasing the fraction of core power produced in the blanket as discussed above, and second, the formation of plutonium is minimized since it is the U-238 neutron captures which forms the plutonium. The amount of water that can be placed in the seed region 18 is limited by the need to have enough room for the fuel rods 22 to permit adequate heat removal from the same. The volume and surface area of the fuel rods must therefore not be reduced to the point where the power density in the core rises beyond operational limits dictated by the reactor's cooling system. By fabricating the seed fuel elements 22 out of uranium/zirconium alloy, which has a much higher thermal conductivity than does oxide fuel, the water moderator/fuel volume ratio in the seed 18 can be made as high as 4 or 5 to 1 as compared with less than 2 to 1 in a conventional uranium core. The water moderator/fuel ratio in the seed 18 should therefore be selected between approximately 2.5 and 5.0, and most preferably between 3.0 and 3.5. Another advantage to the high moderator/fuel volume ratio in the seed 18 is that it substantially reduces the quantity of high level radioactive waste generated in the seed 18. In particular, because the seed spectrum is very thermal due to the large water fraction, very few transuranic or minor actinides will be produced. It is these actinides, with half lives of millions of years, that require very long term storage in underground repositories. The 10 year blanket life coupled with the reduced actinide production from the nonproliferative core 10 therefore produces less radioactive waste materials and also less long term heat generation. This results in underground repository space requirements being significantly reduced. In addition, low level waste is also somewhat reduced because no boric acid is dissolved in the water moderator for normal operation, and thus no tritium is generated in the core. It should be noted that the reason boric acid is not employed in the water moderator is that it would unacceptably lower the multiplication factor in the blanket region 20. The moderator/fuel ratio in the blanket region 20 is also a very important parameter, however, it is governed by different constraints. In particular, the situation in the blanket 20 is more complex because too much water reduces K.sub.b by absorbing too many neutrons coming from the seed fuel elements, and thereby taking them away from the thorium. On the other hand, too little water in the blanket increases the loss to protactinium. When thorium absorbs a neutron, it forms protactinium, which after a 27.4 day half-life, decays into fissionable U-233. During this interval, protactinium is vulnerable to absorbing a neutron and thereby forming nonfissionable U-234. This is a double loss of both a neutron and a prospective U-233 nucleus. Research indicates that to minimize this loss, the optimum value of the water/fuel ratio in the blanket 20 should be selected between approximately 1.5 and 2.0, and preferably approximately 1.7. Preferably, the seed region 18 comprises between approximately 25 and 40 percent of the total volume in the SBU 12. This range of values is also determined based upon competing considerations. First, the core 10 is designed to burn as much thorium as possible, thus the blanket region 20 must be made as large as practical. On the other hand, the seed region 18 cannot be made so small that the power density therein rises too high for the reasons given previously. The range of 25-40 percent has been determined to provide the optimum balance of these competing in considerations. Still another important design aspect of the SBU 12 is the central seed/annular blanket configuration. In Applicant's previously published International Application, Publication No. WO85/01826, a seed-blanket core is disclosed which employs an annular seed with both an inner, central blanket section and an outer, surrounding blanket section. Such an arrangement cannot be made nonproliferative because the thin, annular seed has a correspondingly small "optical thickness" which causes the seed spectrum to be dominated by the much harder spectrum of the inner and outer blanket sections. This results in higher thermal neutron energies, and a resulting increased production of Pu-239 in the seed. The central seed arrangement of the SBU 12 overcomes this drawback by making the seed section 18 thick enough to avoid excessive interaction with thermal neutrons crossing from the blanket section 20 into the seed section 18. The referenced core and fuel assembly parameters for the core 10 and each of the SBUs 12 are presented in Tables 1 and 2, respectively, below. These parameters were selected to provide a complete compatibility of the SBU fuel assembly with an existing (typical) VVER-1000 plant. TABLE 1 ______________________________________ Core Parameters Parameter ______________________________________ Total Power (MWth) 3000 Average Power Density 107 (w/cm.sup.3) Average Moderator Temp., .degree.C. 306 Number of SBUs in Core 163 Number of Control Rod 61 Clusters (CRC) Number of Control Rods 12 per CRC Blanket Fuel U + Th(O.sub.2) Seed Fuel U/Zr Alloy Seed Reload Schedule 54 Seed/Cycle (.apprxeq.1 Year) Blanket Reload Schedule 163 Blankets/9 Cycles (.apprxeq.10 Years) ______________________________________ TABLE 2 ______________________________________ SBU Parameters Parameter Seed Blanket ______________________________________ Outer Radius of Fuel 0.310 0.380 Pellet, cm Outer Radius of Gas Gap, -- 0.3865 cm Outer Radius of Cladding, 0.370 0.4585 cm Cell Radius, cm 0.6652 0.6731 Pitch, cm 1.267 1.282 Moderator/Fuel Volume Ratio 3.18 1.68 Number of Fuel Rods 156 162 Number of Water Tubes 12 0 Number of Other Tubes 1 0 Seed Total Weight, tH.M. 6.71 -- Blanket Total Weight, tH.M. -- 35.82 U (In Blanket) t -- 3.11 ______________________________________ To provide additional reactivity control during each seed cycle, the SBU 12 can be modified as illustrated in FIG. 3 to include a plurality of burnable poison containing rods 28 and 30 which are positioned at spaced locations in the seed section 18. In the example illustrated in FIG. 3, the first group of burnable poison rods 28 comprise standard Westinghouse burnable poison rods known as WABAs as are presently utilized in conventional PWR fuel systems. These rods are formed of a composite material consisting of boron-10, boron-11, carbon, aluminum and oxygen. The second group of burnable poison containing rods 30 comprise uranium/zircalloy seed fuel rods which have been modified to contain a small percentage of natural gadolinium. Any number and combination of the burnable poison containing rods 28 and 30 can be employed as necessary. In the example illustrated in FIG. 3, each SBU 12 contains 12 of the WABAs 28 and 6 of the gadolinium/fuel rods 30. Both types of burnable poison rods have their advantages. The WABAs provide a more uniform control of reactivity until the end of each reactor fuel cycle, while the gadolinium/fuel rods 30 provide a large negative reactivity input for the first third of the reactor cycle life. FIG. 4 illustrates the reactivity level K in each of the SBUs 12 as a function of full power days for each of four seed control variations: no poison, gadolinium poison, boron poison and combined gadolinium and boron poison. As illustrated, the combination of both types of poison control results in the flattest reactivity curve. Conventional control rods are also preferably employed to compensate the excess reactivity in the reactor core. In addition, the control rods can be employed for emergency shutdown (scram) of the reactor and compensation for power transients resulting from Xe oscillations and moderator temperature transients. The control rods are assembled into control rods clusters (CRCs) with 12 control rods per CRC. As noted in Table 1, it is not necessary that each of the SBUs 12 include a CRC, and calculations indicate that it is sufficient to place place one CRC in each of 61 of the 163 SBUs in the core. In the operation of the nonproliferative light water thorium nuclear reactor core 10, a once-through fuel cycle is employed in which all of the fuel rods in both the seed and blanket regions 18 and 20 are used in the reactor core only once. However, a unique fuel management scheme is employed in which the seed and blanket fuel assemblies follow separate fuel management paths. In particular, each of the seed fuel rods 22 remains in the reactor core for more than one seed fuel cycle (approximately 13 months), preferably three cycles, however, only a fraction (preferably 1/3) of the seeds is replaced at the end of each seed fuel cycle. Preferably, the positions of the SBUs 12 in the core 10 are also shuffled at the end of each seed fuel cycle to improve the power distribution throughout the core. In contrast, each of the blanket fuel rods 24 remains in each SBU 12 for the entire life of the blanket 20, which is preferably 9 fuel cycles, or approximately 10 years. This fuel management scheme combined with the seed-blanket arrangement and associated core parameters allows approximately 80-90% of the uranium in the seed fuel elements 22 to be consumed before they are removed from the core 10. As a result, the spent seed fuel rods 22 are of no economic or nuclear value since so little of the original U-235 loading remains. In addition, this extended burn-up of the seed fuel rods causes a buildup of Pu-238 which is sufficiently high to completely denature the small amount (approximately 30 kg. per year) of Pu-239 that is produced in the seed 18. More specifically, approximately 8-9% of the total plutonium produced by the reactor core 10 is Pu-238. Since Pu-238 is a heat generator which produces approximately 300 times the amount of heat generated by Pu-239, weapons grade plutonium, such a high percentage of Pu-238 prevents the plutonium produced by the reactor core from being used for weapons purposes. In particular, numerous studies have determined that reactor grade plutonium cannot be used for weapons purposes, even by refrigerating the weapons down to 0.degree. F., where the content of Pu-238 equals or exceeds 4.9% by weight. At these concentrations, the heat generated by the Pu-238 causes the high explosives to melt and the plutonium to eventually melt also, or at least change phase from its normal Alpha Phase to Delta Phase. The phase change decreases its density and substantially increases its critical mass. Since the nonproliferative core 10 produces concentrations of Pu-238 well in excess of 4.9%, this effectively renders the discharged plutonium essentially nonproliferative. The multiple batch fuel management scheme is illustrated in greater detail in FIGS. 5.1 through 5.9 which show a pie slice section of approximately one-fifth of the SBUs 12 in the core 10. Each of the FIGS. 5.1-5.9 shows the fuel loading map for each of the nine seed fuel cycles which correspond to one blanket fuel cycle. The fuel loading maps reflect the basic approach adopted, i.e., a three batch fuel management scheme. This means that at all cycles, with the exception of the transient cycles one and two, there are three seed batches: fresh, once-burned and twice-burned. These are designated on the reload maps as F, O and T, respectively. Another major factor influencing the reload pattern is the heavy use of burnable poisons which are capable of suppressing local power peaks. It should also be noted that the majority of the fresh fuel is not loaded at the core periphery, but is distributed predominantly within the middle part of the core at positions 6, 8, 10 and 12, and near peripheral positions 20, 21, 23, 26 and 32. Additional information shown in FIGS. 5.1-5.9 shows the distribution of the U-Gd and WABA poison rods within the core. The elaborate burnable poison distribution reflects the complexity of the reload patterns and the low leakage configurations used in this design. Those SBUs having CRCs are also indicated by a C. At the beginning of core life, i.e., cycle one, all fresh seed fuel assemblies are loaded. In order to achieve a reasonable radial power distribution, three different uranium enrichments and weight fractions are used. As indicated in FIG. 5.1, a first third of the SBUs 12 contains seed fuel rods having 9.5% by volume uranium enriched to 12% by weight U-235, a second third of the SBUs 12 contain seed fuel rods having 14.5% by volume uranium enriched to 17% by weight U-235, and the remaining third of the SBUs 12 contain seed fuel rods having 17% by volume uranium enriched to 20% by weight U-235. The target fresh fuel enrichment of 20% by weight of U-235 was used thereafter for each of the following cycles 3-9. Thus, cycles one and two are transient cycles, while cycles 3-9 are quasi-equilibrium cycles. The fresh fuel enrichment was constant at 20% U-235 by weight, but the weight fraction of uranium in the U/Zr alloy was varied to assure 300 full power days of operation which correspond to one seed fuel cycle. Since the reactor is not usually operated at full power during the entire fuel cycle, it is estimated that the actual length of the seed fuel cycle is approximately 13 months. B. The Plutonium Incinerator The second preferred embodiment of the present invention is another seed-blanket reactor core design known as the plutonium incinerator. As the name implies, the goal of this embodiment of the invention is to consume as much weapons or reactor grade plutonium as possible. This is in contrast to the goal of the first preferred embodiment of the invention which is to derive as much energy as possible from the thorium fuel in the blanket. As will be discussed in greater detail below, the completely different goal of the plutonium incinerator dictates that completely different core parameters be employed. The preferred form of the plutonium incinerator embodiment is illustrated in FIG. 6, and comprises a reactor core 100, again formed from a plurality of SBUs 102. The core 100 has a generally circular cross section, and 89 of the SBUs 102, each of which has a square cross section. It should be noted once again that the size and shape of the reactor core is arbitrary, and can be varied as necessary to achieve a desired power output, and/or accommodate retrofitting into any type of conventional core. Each of the SBUs 102 includes a central seed region 104 and an annular blanket region 106. The total percentage of the SBU volume occupied by the seed region 104 is chosen in this embodiment to be as large as possible, preferably between approximately 45 and 55%, so that as much plutonium can be burned in the seed as possible. A reflector 108 made of any suitable material, such as thorium oxide, surrounds the core 102. One preferred form of the SBU 102 is illustrated in FIG. 7. As illustrated, the seed region 104 is comprised of a first plurality of seed fuel rods 110 formed of plutonium (weapons or reactor grade) and zirconium alloy, or alternatively, cermet fuel. A plurality of water holes 112 are uniformly spaced throughout the seed region 104 for reception of control rod pins. First and second pluralities of burnable poison containing rods 114 and 116 are also uniformly positioned throughout the seed region 104. The burnable poison containing rods 114 are preferably formed of a mixture of the seed fuel and gadolinium. These can be of two types, the first type having a gadolinium concentration of 0.36 g/cc, and the second type having a gadolinium concentration of 0.72 g/cc. The burnable poison containing rods 116 preferably comprise conventional WABA poison rods. Any combination of the two types of burnable poison containing rods 114 and 116 can be employed as desired. The blanket region 106 contains a plurality of blanket fuel rods 118 formed predominantly of thorium oxide. Preferably, a small percentage, less than approximately 1% by volume, of plutonium oxide is mixed with the thorium oxide in the blanket fuel rods 116 to keep the blanket multiplication factor high during initial reactor operation. In addition, it is very important that approximately 2-5% by volume uranium tailings (natural uranium with most of its U-235 isotope removed) are added to the thorium to denature the U-233 which is formed in the thorium during reactor operation by nonfissile isotopes, U-236 and U-238. This is necessary because, unlike in the first preferred embodiment in which a small amount of enriched uranium is added to the blanket fuel rods which itself can generate these nonfissile isotopes, the plutonium added to the blanket fuel rods in the plutonium incinerator embodiment is incapable of generating these nonfissile isotopes. The moderator/fuel volume ratio in the seed region 104 is selected to be much higher than in a conventional reactor core, however, the reasons for doing so are different than in the nonproliferative embodiment of the present invention. In particular, the moderator/fuel ratio is selected to be between approximately 2.5 and 3.5, and preferably between 2.5 and 3.0. This effect further increases the control poison reactivity worth therein, thereby making the reactor much easier to control. As in the nonproliferative core embodiment, the moderator/fuel ratio in the blanket region is selected to be between approximately 1.5 and 2.0. Example values for the main core and SBU parameters for the plutonium incinerator embodiment of the present invention are provided in Tables 3 and 4 below: TABLE 3 ______________________________________ Main Core Parameters Parameter Value ______________________________________ Power Level, MWth 3250 Number of SBUs in Core 89 Equivalent Diameter of Core, cm 380 Active Height of Core, cm 365 Average Power Density, w/cc 78.5 ______________________________________ TABLE 4 ______________________________________ Additional Core Parameters Parameter Seed Blanket ______________________________________ Number of Fuel Rods/SBU 264 384 Number of Water Holes/SBU 25 0 Distance Across Flats, cm 25.5 35.7 % of SBU Volume 51 49 Fuel Pin Diameter, mm 8.7 8.7 Fuel Rod Diameter, mm 9.7 9.7 Pitch, mm 15.0 12.75 Moderator/Fuel Volume 2.54 1.49 Ratio Fuel Type Metallic Oxide Composite Fuel Material 2.4 Vol 0.55 Vol % Pu % PuO.sub.2 97.6 Vol 94.45-97.45 % Zirc- Vol % ThO.sub.2 alloy 2.0-5.0 Vol % U tailings Core Heavy Metal Loading, 2300 Pu 60,700 Th kg 392 Pu 100 U tailings ______________________________________ In the operation of the plutonium incinerator core 100, the seed fuel rods 110 and the blanket fuel rods 118 reside in the core for two years, and are discharged simultaneously. This fuel reload scheme is optimal from the point of view of the plutonium inventory reduction rate, but probably is suboptimal from the thorium utilization point of view. However, this is not a concern since the goal of the plutonium incinerator core 100 is to maximize consumption of plutonium. Preferably, the fuel management scheme adopts a two-batch core with a standard out-in pattern. The reload configuration and accumulated burnup for the once and twice burnt fuel assemblies are illustrated in the core map of FIG. 8. The accumulated burnup for the once burnt assemblies is approximately 15 GWD/T and the discharge fuel averages approximately 31 GWD/T. Three different types of fuel assemblies are illustrated in the core map of FIG. 8. Type A assemblies employ 20 of the gadolinium based burnable poison rods 14, each having a gadolinium concentration of 0.36 g/cc, type B fuel assemblies also contain 20 of the gadolinium based burnable poison rods 114, however, these have a gadolinium concentration of 0.72 g/cc, and type C fuel assemblies contain 20 of the gadolinium based burnable poison rods 114 with a gadolinium concentration of 0.72 g/cc, as well as 20 of the WABA burnable poison rods 116. The annual charge of Pu-239 in the plutonium incinerator core 100 is approximately 1350 kg. Each year, 500 kg of plutonium are discharged from the reactor thus leaving a net destruction rate of approximately 850 kg of total plutonium, although only approximately 200 kg of Pu-239 remains since the rest of the remaining plutonium is in the form of the other plutonium isotopes, Pu-240, 241 and 242. An equilibrium cycle based on a standard sized LWR fuel assembly utilizing the seed-blanket concept will give the equivalent results. The advantages of using the thorium fuel cycle for incinerating Pu-239 in a seed-blanket reactor result from the neutronic properties of thorium, namely its high thermal absorption cross-section. This leads to a high initial Pu inventory, and therefore to high consumption of Pu per unit energy. Driving the thorium blanket with Pu fissile material causes a high Pu power share and therefore efficient Pu incineration. Use of a conventional homogenous light water reactor (LWR) core design presents a controllability problem. Excess reactivity of a fuel cycle based on Pu is of the same value of a similar uranium based cycle, while reactivity worth of a standard control mechanism is significantly lower. The Pu-based fuel is characterized by a very high thermal absorption cross-section, which is competing with control poison material for thermal neutrons. The results of a conventional homogeneous assembly design indicate that the effectiveness of control rods, soluble boron and burnable poisons is reduced by approximately a factor of 2 as compared with conventional LWR values. The obvious solutions to this problem are to improve the reactivity control worth of different control mechanisms, such as utilization of more potent absorbers and/or increasing moderator/fuel volume ratio of the core. Unfortunately, such solutions have a negative impact on safety and economic performance parameters of the reactor. The thorium based seed-blanket design provides a unique solution to this problem which does not carry economic or operational penalties. Since the control rods and/or burnable poison rods are only positioned in the seed region 104 of each SBU 102, the control effectiveness of these is substantially increased because the power density of the seed portion is much higher than that of the core average. Thus, the neutron importance function in the seed is very high, thereby increasing the reactivity worth of the control and poison rods. In addition, the high moderator/fuel volume ratio in the seed region improves power distribution within the SBU, thereby further increasing the control poison reactivity worth. C. Summary In summary, the present invention provides two novel thorium based seed-blanket reactor core arrangements which are particularly significant in that they provide economical, viable solutions to the problems of nuclear proliferation and weapons grade nuclear fuel destruction, while at the same time providing an economic reliable source of electrical power. The nonproliferative embodiment of the present invention is ideal for use by lesser developed countries because it eliminates any concern that the reactor fuel or waste materials will be used for making nuclear weapons, since neither of them can be used for this purpose. The plutonium incinerator embodiment is particularly attractive for use in providing an excellent means by which stockpiled weapons and reactor grade plutonium can be conveniently destroyed. In both embodiments, the seed-blanket core arrangement is necessary to provide the desired results. Without it, the nonproliferative embodiment would not work, i.e., would generate proliferative waste materials. In the plutonium incinerator, the seed-blanket arrangement is needed to insure proper reactor control, and prevent generation of significant new amounts of Pu-239. Although the invention has been disclosed in terms of a number of preferred embodiments, it will be understood that numerous other variations and modifications could be made thereto without departing from the scope of the invention as defined in the following claims. |
047675934 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Structure: With reference to FIG. 1, there is illustrated a partial elevational, sectional view of a typical multiple shell pressure vessel 10 of the present invention. Pressure vessel 10 comprises, basically, a first inner pressure vessel 12, a second inner pressure vessel 14 disposed concentric about said first inner pressure vessel and spaced apart therefrom to define first interstitial space 16, an outer pressure vessel 18 disposed concentric about said second inner pressure vessel 14 and spaced apart therefrom to define second interstitial space 20. Pressure vessel shell 12 can be fabricated from stainless steel or stainless steel clad carbon steel. The wall thickness or structural configuration of vessel shell 12 is designed to withstand any compression forces due to the pressure from the filler material contained under pressure in interstices 16 and 20 without buckling. Pressure vessel 10 further comprises a reactor coolant inlet port 24 comprising a generally cylindrical inner inlet conduit 26 attached, at one end, to first inner pressure vessel 12, and at its other end to flange 42, conduit 26 being in fluid communication with the interior of inner pressure vessel 12. Reactor coolant inlet port 24 further comprises an outer inlet conduit 27 disposed concentric about inner inlet conduit 26 and spaced apart therefrom to define inlet port interstitial space 32. One end of outer inlet conduit 27 is attached to second inner pressure vessel 14, placing first interstitial space 16 in fluid communication with inlet port interstitial space 32. Inlet port outer conduit 27 also comprises spacer conduit 30, a first bellows 34 attached at one end to vessel flange 40 and second bellows 36 attached, at one end, to outer flange 42 and, at the other end, to conduit 30 to allow for thermal expansion and contraction of inner inlet port conduit 26. Reactor coolant outlet port 44, located proximate the opposite side of pressure vessel 10, is of identical construction as inlet port 24. Pressure vessel 10 also comprises a top bolting flange 46, to which are attached, as by continuous, full penetration welds 47, 48 and 49 (see FIG. 2) or the like, the top rims of first inner pressure vessel 12, second inner pressure vessel 14 and outer pressure vessel 18, respectively. Top bolting flange 46 is also provided with an extended peripheral rim or lip 50 adapted to engage pressure vessel peripheral support ledge 52. Ledge 52 is a part of the building housing the reactor pressure vessel and is designed to support and cradle pressure vessel 10. A removable pressure vessel head 60, comprising a head bolting flange 62 attached, as by a continuous, full penetration weld or the like, to hemispherical forged head cover 64, is adapted to engage and be bolted to top flange 46 by head bolts 66. Pressure vessel head 60 may also contain numerous small penetrations (not shown) for control rod drives, fuel rod standpipes, etc. Interstitial spaces 16, 20 and 32 are filled with a low melting point, high boiling point material selected from the group consisting of, lead, tin, antimony, bismuth, cadmium, or sodium and potassium, and mixtures thereof. Chemical compositions or compounds containing boron or cadmium may also be added to the molten filler material. Alloys of these materials can be formulated to have various melting points. Table 1 illustrates the melting points of both the pure elements and various formulations for alloys thereof. TABLE 1 ______________________________________ Melting Point Composition in percent Alloys Deg. Fahr. Pb Sn Cd Bi Na K ______________________________________ Pure lead 628 100 0 0 0 0 0 Pure tin 450 0 100 0 0 0 0 Lipowitz 140 26 13 10 51 0 0 Wood's 158 26 13 12 49 0 0 Rose's 230 28 22 0 50 0 0 Sodium 208 0 0 0 0 100 0 Potassium 144 0 0 0 0 0 100 ______________________________________ It can be seen that the various percentages of alloying materials can be adjusted to achieve a particular melting point for a particular pressure vessel operating temperature. For most applications, the melting point of the filler material should be close to or preferably somewhat higher than the operating temperatures of the pressure vessel shells so that they are "plastic" or "flowable" during operation to avoid any interlayer friction or shear forces. The filler material must also be substantially incompressible, a characteristic typical of the materials of Table 1. In addition, the filler material must also be good thermal conductors, also a characteristic typical of the materials of Table 1 . Also, the filler materials should have a thermal expansion that is only slightly more than the thermal expansion of the pressure vessel shells. If not, when the filler material cools down from the molten state, it will contract faster than the shells. When the molten material freezes, it will further contract. In order to alleviate these conditions, any one or combination of the following procedures must be followed: (a) The fillers must be pressurized at the time of filling and closing off of the interstices. (b) The pressure vessel shells must be heated to a non-uniform temperature profile as shown in FIGS. 10 and 11. (c) A combination of pressurization of the fillers and non-uniform heating of the shells must be empIoyed. These procedures are necessary in order to obtain a residual positive pressure of the filler material in all the interstices upon cooling of pressure vessel 10 from the temperatures at the time of filling, to the normal or service operating condition temperatures. If these procedures are not followed, vacuum pockets, air pockets or "nests" may develop anywhere in the filler spaces. In addition, these procedures are necessary to insure that sufficient filler pressure exists to maintain the wall of inner pressure vessel 12 in compression, or at least in a state of very low tension. Since the portion of the pressure vessel most vulnerable to tensile stress cracking due to thermal and pressure transients is in the region of vessel penetrations, FIG. 2 is an illustration of a typical configuration of a coolant inlet or outlet penetration. The inlet port or vessel penetration 24 illustrated in FIG. 2 comprises an inner conduit 26 having a flared portion 70 proximate one end that is attached, as by continuous, full penetration weld 72 or the like, to first inner pressure vessel 12. The other end of conduit 26 is attached, as by continuous, full penetration weld 73 or the like, to outer flange 42. An outer conduit 27 comprising a first bellows 34 attached at one end to vessel flange 40 and at its other end to outer conduit flange 29, a second bellows 36 having one end attached to port outer flange 42 and at its other end to outer conduit flange 28. Flanges 28 and 29 are attached to and spaced apart by outer conduit member 30. Outer conduit 27 is attached to pressure vessel 10 by means of cylindrical member 74, having a flared end 75. Cylindrical member 74 is first attached, as by continuous, full penetration weld 76 to flange 40. The flared end 75 of member 74 is attached, as by continuous full penetration weld 78, to second inner pressure vessel shell 14. Interstitial space 32 between conduits 26 and 27 is thus in fluid communication with interstitial space 16 of pressure vessel 10. In order to seal off interstitial space 20 at port 24, cylindrical member 80, having a flared end 81, is first attached, as by continuous, full penetration weld 84 or the like to sealing flange 82. Sealing flange 82 is attached, as by continuous, full penetration weld 86 or the like, to the outer surface of cylindrical member 74. The flared end 81 of cylindrical member 80 is attached, as by continuous, full penetration weld 88, or the like, to outer pressure vessel shell 18, thus sealing off interstitial space 20 around port 24. It can be seen that when the incompressible material selected from Table 1 is pressurized to a sufficient degree to maintain the wall of inner pressure vessel 12 in compression, then the probability of crack initiation or propagation in the region around the vessel penetration is reduced or eliminated. With reference to FIG. 3, there is illustrated the method of maintaining the spacing between concentric pressure vessel shells 12 and 14. Typically this method would also apply to the spacing between pressure vessel shells 14 and 18 although not shown in FIG. 3. A set of radial spacers 90 are attached, as by welding or the like, to the outer side of pressure vessel shell 12 with a similarly shaped base centering spacer 92 attached, as by welding or the like, to the bottom of first inner pressure vessel shell 12 coincident with the vertical axis of rotation of the concentric vessels. A set of radial spacers 94a and 94b are attached to the inside surface of second inner pressure vessel shell 14 and disposed on each side of radial spacers 90 to act as a guide when nesting one concentric pressure vessel within the other. A centering guide 96 is attached to the inside surface of pressure vessel shell 14 coincident with the vertical axis of rotation of the pressure vessel shells to act as a guide for member 92. A set of radial spacers 98 and base centering spacer 99 are attached to the outside of second inner pressure vessel shell 14 in readiness for assembly of the outer pressure vessel shell. Assembly: The pressure vessel of the present invention is assembled in the following manner. First, top flange 46 is place top down on a flat supporting surface. Second, first inner pressure vessel shell 12 is placed with its open end abutting bottom inside edge of flange 46 (now facing up) and attached thereto as by continuous, full penetration weld 47 or the like. The welds are then inspected by ultrasound or other means and repaired if defective. Third, second inner pressure vessel shell 14 is dropped over first inner pressure vessel shell 12 guided by radial members 90 and radial guides 94a and 94b. The rim of the open end of second inner pressure vessel shell 14 is attached, as by continuous, full penetration weld 48 or the like to top flange 46. The welds are then inspected by ultrasound or other means and repaired if defective. Fourth, outer pressure vessel shell 18 is then dropped over second inner pressure vessel shell 14 guided by guide members similar to those for shells 12 and 14. The rim of the open end of outer pressure vessel 18 is attached, as by weld 49 or the like, to top flange 46. The welds are then inspected by ultrasound or other means and repaired if defective. Fifth, port conduits 26 are then attached to inner pressure vessel shell 12, as by continuous, full penetration weld 72 or the like (FIG. 2). The welds are then inspected by ultrasound or other means and repaired if defective. Sixth, the flared end of cylindrical member 74 is attached, as by continuous, full penetration weld 78 or the like, to second inner pressure vessel shell 14. The welds are then inspected by ultrasound or other means and repaired if defective. Seventh, the flared end of cylindrical member 80 is attached, as by continuous, full penetration weld 88 or the like, to outer pressure vessel shell 18. The welds are then inspected by ultrasound or other means and repaired if defective. Eighth, closure flange 82 is attached, as by continuous, full penetration weld 84 or the like, to the end of cylindrical member 80 and to the outer side of cylindrical member 74, as by continuous, full penetration weld 86 or the like. Flange 40 is welded, as by continuous, full penetration weld 76, to cylindrical member 74. The welds are then inspected by ultrasound or other means and repaired if defective. Ninth, outer conduit 27 is pre-assembled by welding flanges 28 and 29 to outer conduit member 30, then welding one end of bellows 34 and 36 to flanges 29 and 28, respectively, and finally welding the other end of bellows 36 to flange 42 and bellows 34 to flange 40. This outer conduit assembly 27 is then slipped over inner conduit or sleeve 26 with the other end of bellows 34 welded to flange 40. Flange 42 is then welded, as by continuous, full penetration weld 73 or the like, to inner conduit 26. The assembled pressure vessel is now ready for filling interstices 16, 20 and 32 with the low melting point, high boiling point, substantially incompressible material selected from Table 1 . Filling Method: The assembled pressure vessel 10 is now placed in a furnace and heated. The heating may be accomplished by various means, such as, gas fired burners, an array of space heaters or by resistance heaters wrapped about the exterior of the vessel or the like. The vessel assembly may be heated uniformly or non-uniformly to pre-calculated specific temperatures exceeding the melting point temperature of the low melting point material being used. Non-uniform heating in the radial direction may be accomplished by the simultaneous heating from the outside of the pressure vessel while cooling the inside of the assembled vessel with air or other gases. The filler material is then heated to a temperature equal to the average of the temperatures of the adjacent pressure vessel shells. Filling can be accomplished by one of several methods. In the first method, with reference to FIGS. 5 and 6, a peripheral header 100 containing the molten filler material selected from Table 1, is placed in fluid communication with, for example, interstice 16 through conduit 114 fluidly communicating header 100 with hole 116 in top flange 46 Hole 116 is, in turn connected in fluid communication with conduit 118 passing down through interstice 16 with its outlet 120 proximate the bottom of pressure vessel 10. A vent hole 111 (FIG. 6) in top bolting flange 46 allows gases to escape during the filling operation. After filling is completed, vent hole 111 is sealed off by cap 122. Additional filler material is then pumped into interstice 16 until a predetermined design pressure is reached, at which time valve 124 is closed. Interstice 20 can be filled in a similar manner using conduit 102, hole 104 and conduit 106 and valve 126. Shell temperatures are then reduced to permit the filler materials to freeze. With reference to FIG. 9, there is illustrated a pressure profile across the multiple shell pressure vessel 10 of the present invention at close-off of the molten material during the filling operation. Pressure P.sub.2 is established to maintain pressure vessel shell 12 in compression. In certain instances, it is possible to fill one interstice while the temperature of the interstice material in the adjacent interstice is frozen, i.e., below the melting point of the material. With respect to FIGS. 10 and 11, by maintaining the proper temperature gradient across the combined pressure vessel shell configuration, the temperature in the interstice being filled can be maintained above its melting point while the temperature in the adjacent interstice is below the melting point. In FIG. 10 interstice 16 has been filled with molten lead as the filler material. The temperature gradient across pressure vessel shells 12, 14 and 18 is maintained highest (T.sub.5) at outer pressure vessel shell 18 and lowest (T.sub.6) at inner pressure vessel shell 12. The molten lead in interstice 16 is maintained at 700 deg. F. which is above its 628 deg. F. melting point. With reference to FIG. 11, the temperature gradient T.sub.5 to T.sub.6 has shifted downward so that the temperature of the lead in interstice 16 is now 600 deg. F. and the temperature in interstice 20 is 700 deg. F. Thus, the lead in interstice 16 is below its melting point and, therefore, frozen, while the lead in interstice 20 is above its melting point. An alternative method of filling interstices 16 and 20 is illustrated in FIGS. 12 and 13 where the temperature across the pressure vessel shells in constant. For this second method, filler materials of different melting points are used while the pressure vessel shells are heated to a uniform temperature above the highest melting point. The first filler material having the highest melting point is placed in the first interstice, then sealed off and pressurized. The shells are cooled to the freezing point of the first filler material but above the melting point of the second filler material. the second filler material is then placed in the second interstice, rhen sealed off and pressurized. The shell can then be cooled down to allow the second filler material to freeze. In FIG. 12, the temperature of all pressure vessel shells is maintained at 700 deg. F. while interstice 16 is filled with molten lead and then pressurized. In FIG. 13, the temperature of all pressure vessels is lowered and maintained at a temperature of 550 deg. F. allowing the lead in interstice 16 to freeze while filling interstice 20 with molten tin, having a melting point of 450 deg. F., and then pressurized. Constant Pressure Differential: With reference to FIG. 7, there is illustrated a pressure regulator 150 for maintaining the pressure in interstice 16 at a constant multiple of the pressure inside first inner pressure vessel shell 12. This device is important in maintaining this constant multiple during transient pressure events which might otherwise cause critical tensile stresses in the wall of inner pressure vessel shell 12. Pressure regulator 150 comprises, basically, a first inner bellows 152 having one open end attached to the inner surface of first inner pressure vessel shell 12 and its other open end attached to regulator piston head 159. Pressure regulator 150 further comprises a second bellows 156, with piston 154 attached, concentrically disposed about first bellows 152 and spaced apart therefrom to define annular bellows space 158. Hole 160 in first inner pressure vessel shell 12 allows the interior of first bellows 152 to fluidly communicate with interstice 16. Hole 162 in the wall of first inner pressure vessel 12 allows annular bellows space 158 to communicate with conduit 164, which, in turn, is in fluid communication with a gas pressure control system (not shown), common in the art, outside pressure vessel 10. Annular bellows space 158 is adapted to be filled with a compressible gas. It can be seen that, in accordance with well known laws of physics, the pressure multiple or "ratio" between the inside of first pressure vessel shell 12 and interstice 16 will be governed by the following relationship: EQU P.sub.0 .times.A.sub.0 =P.sub.1 .times.A.sub.1 where P.sub.0 =pressure of fluid inside first inner pressure vessel shell 12. PA1 A.sub.0 =cross-sectional area of second bellows 156. PA1 P.sub.l =pressure of fluid in interstice 16. PA1 A.sub.l =cross-sectional area of first bellows 152. PA1 M=Multiple of pressure in interstice 16 relative to pressure inside first inner pressure vessel 12. therefore: EQU M=P.sub.1 /P.sub.0 =A.sub.0 /A.sub.1 where By using low strength welds for bellows 152 and 156 when attaching them to pressure vessel shell 12 or at other locations, it is possible to provide a "fail-safe" rupture mechansim. If filler material in interstice 16 overheats due to a LOCA and expands beyond a predetermined limit, the weak welds will fail and filler material containing Boron or Cadmium will be injected into the main pressure vessel to "poison" the coolant and stop or seriously reduce the nuclear chain reaction. Leak Detection: With reference to FIG. 8, there is illustrated a method for detecting leaks in critical welds within pressure vessel 10. In FIG. 8, a leak detection system 200 is illustrated for the critical welds 47 and 49 used to respectively attach first inner pressure vessel shell 12 and outer pressure vessel shell 18 to top bolting flange 46. The leak detection system comprises a first leak detection chase channel 202 attached, as by welding or the like, to the outside of first inner pressure vessel shell 12 immediately below weld 47 and also to top bolting flange 46 to provide a gas-tight conduit peripherally about vessel 12 and weld 47. Hole 204 in top bolting flange 46 is adapted to be in fluid communication with leak detector 210 through conduit 212. The leak detection system further comprises a second leak detection chase channel 220 attached, as by welding or the like, to the inside of outer pressure vessel shell 18 immediately below weld 49 and also to top bolting flange 46 to provide a gas-tight conduit peripherally about the inside of vessel 18 and weld 49. Hole 222 in top bolting flange 46 is adapted to be in fluid communication with leak detector 230 through conduit 232. Any leakage of radioactive material through weld 47 or a pressure rise or drop in chase channels 202 and 220 will be detected by leak detectors 210 and 230, respectively. With respect to FIG. 14, there is illustrated a temperature gradient profile across a prior art multiple shell pressure vessel wall in which the concentrically disposed pressure vessel shells are heat shrunk over each other. It will be noted in FIG. 14 that the overall temperature drop across the vessel wall is relatively high. Such a condition tends to create substantial stresses in the vessel walls. FIG. 15, is a temperature gradient profile across the multiple shell pressure vessel of the present invention in which the interstices have been filled with the thermally conductive materials previously described. It will be noted that the overall temperature drop across the pressure vessel wall configuration of the present invention is more uniform and substantially less than that for the pressure vessel of FIG. 14. Although the pressure vessel of the present invention has been described in specific terms, those terms are not intended to limit the scope of the present invention, such scope being limited only as stated in the claims. |
description | This patent application claims priority from Application Serial No. u20110312, titled DEVICE FOR FORMATION OF LIGHT FIELD WITH CELLULAR INTENSITY DISTRIBUTION IN TRANSVERSAL SECTION filed on Apr. 19, 2011. This disclosure relates generally to controlling microparticles and, more particularly, to controlling microparticles through a light field having controllable intensity and periodicity of maxima thereof. Gradient light beams may be utilized for capturing and/or shifting of microparticles (e.g., influencing ensembles of micro-objects in microtechnology and/or nanotechnology applications with aims including but not limited to regulating movement and/or mixing thereof with regard to organic tissues as part of therapy and/or prophylaxis and influencing materials during localized laser processing). The mechanism of particle capturing may be based on aligning particle dipoles along the direction of a light field. When the light field contains a strong gradient, the particles may be attracted to a region of strongest electric field. The gradient may influence particles in a plane perpendicular to the axis of the light field. When the longitudinal gradient force balances a dispersion force, the particles having higher refractive index than that of the environment may be captured and localized in intensity maxima of the light field. The particles having lower refractive index than that of the environment may be retracted in local intensity minima of the light field. Optical tweezers utilized for manipulating viruses and bacteria, inducing cellular synthesis in immunology and molecular genetics, capturing and shifting chromosomes, changing mobility of human spermatozoa and trans-membrane proteins etc. may be created based on the aforementioned principle. Gradient light fields may also be utilized for creating optical pumps, funnels and the like with an aim of filtrating particles and/or influencing living and non-living matter. Devices utilized for forming gradient light fields may not allow for locally rounded intensity maxima to be formed. Although a Fresnel biprism allows formation of a static gradient light field in the form of parallel strips, the Fresnel biprism may not allow formation of a variable gradient light field in addition to not enabling formation of a light field having locally rounded intensity maxima. An optical setup including a source of laser radiation, a telescope-collimator and a pyramid with four edges may enable formation of a gradient light field (e.g., a quadrabeam). However, the aforementioned gradient light field may be static, with a multitude of periodically distributed intensity maxima having same magnitudes in a transverse direction. Disclosed are a method, a device and/or a system of controlling microparticles through a light field having controllable intensity and periodicity of maxima thereof. In one aspect, a method includes providing a capability to control divergence of a coherent light beam having an axially symmetrical distribution of intensity thereof through an optical divergence controller, and directing an output of the optical divergence controller related to the controlled divergence of the coherent light beam onto a glass prism. The glass prism includes a planar shape onto which a pyramidal structure is formed. The glass prism is positioned such that the output of the optical divergence controller is incident on a planar surface of the planar shape or the pyramidal structure. The method also includes controlling a distance between maxima of an output light field of the glass prism and intensity thereof through controlling the divergence of the coherent light beam through the optical divergence controller and/or varying a distance between the optical divergence controller and the glass prism, and utilizing the output light field of the glass prism in controlling microparticles in a microtechnology or a nanotechnology application. In another aspect, an optical device includes an optical divergence controller to provide a capability to control divergence of a coherent light beam having an axially symmetrical distribution of intensity thereof, and a glass prism including a planar shape onto which a pyramidal structure is formed. The glass prism is positioned such that an output of the optical divergence controller is incident on a planar surface of the planar shape or the pyramidal structure. Controlling the divergence of the coherent light beam through the optical divergence controller and/or varying a distance between the optical divergence controller and the glass prism enables controlling a distance between maxima of an output light field of the glass prism and intensity thereof. The output light field of the glass prism is configured to be utilized in controlling microparticles in a microtechnology or a nanotechnology application. In yet another aspect, an optical system includes an optical divergence controller to provide a capability to control divergence of a coherent light beam having an axially symmetrical distribution of intensity thereof, and a glass prism including a planar shape onto which a pyramidal structure is formed. The glass prism is positioned such that an output of the optical divergence controller is incident on a planar surface of the planar shape or the pyramidal structure. The optical system also includes an ensemble of microparticles. Controlling the divergence of the coherent light beam through the optical divergence controller and/or varying a distance between the optical divergence controller and the glass prism enables controlling a distance between maxima of an output light field of the glass prism and intensity thereof. The output light field of the glass prism is configured to be utilized in controlling the ensemble of microparticles. The methods and systems disclosed herein may be implemented in any means for achieving various aspects, and may be executed in a form of a machine-readable medium embodying a set of instructions that, when executed by a machine, cause the machine to perform any of the operations disclosed herein. Other features will be apparent from the accompanying drawings and from the detailed description that follows. Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows. Example embodiments, as described below, may be used to provide a method, a device and/or a system of controlling microparticles through a light field having controllable intensity and periodicity of maxima thereof. Although the present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments. FIG. 1 shows an optical system 100, according to one or more embodiments. In one or more embodiments, optical system 100 may include a laser source 102 and a telescope collimator 104 configured to form a collimated coherent beam of light with axially symmetrical distribution of intensity. In one or more embodiments, the collimated coherent beam of light may be directed onto an optical divergence controller 106 that is configured to control divergence of the collimated coherent beam of light. In one example embodiment, optical divergence controller 106 may be a spherical lens with varying focal distance. Depending on the adjustment of optical divergence controller 106, convergent or divergent light beams may be generated therefrom. In one or more embodiments, optical system 100 may include a glass prism 108 onto which the convergent or the divergent beam from optical divergence controller 106 is incident. In one example embodiment, glass prism 108 may include a rectangular cuboid onto which a square pyramid is formed. In one or more embodiments, a pyramidal surface of glass prism 108 may be a pure pyramid; alternately, the pyramidal surface may be a pyramid truncated on an edge thereof in a different manner (e.g., truncated on a square-shaped plane, a round-shaped plane, arbitrarily truncated). The shape(s) of glass prism 108 shown in FIG. 1, therefore, should not be considered limiting. In one example embodiment, glass prism 108 may be positioned such that the light beam is incident on a planar surface of the rectangular cuboid, with the square pyramid (an example shape) being along the direction of incidence; it should be noted that glass prism 108 may also be positioned such that the light beam is incident on a prism side thereof (and similarly for other variations of glass prism 108). In one or more embodiments, when a convergent light beam is incident on glass prism 108, a convergent quadrabeam may be formed, with the convergent quadrabeam representing a cellular field in which the distance between maxima (or, cell period) decreases proportionally with distance. In one or more embodiments, when a divergent light beam is incident on glass prism 108, a divergent quadrabeam may be formed, with the divergent quadrabeam representing a cellular field in which the distance between maxima (or, cell period) increases with distance. In one or more embodiments, through increasing divergence of the beam incident on glass prism 108 through optical divergence controller 106, the intensity of maxima of the cellular field and distances between maxima thereof (or, cell period) may be increased. Likewise, through decreasing divergence of the beam incident on glass prism 108 through optical divergence controller 106, the intensity of maxima of the cellular field and the distances between maxima thereof (or, cell period) may be decreased. In one or more embodiments, with an increase in a width (or, dimension along the direction of incidence of the beam) of the square pyramid portion of glass prism 108, the distance between maxima of the cellular field (or, cell period) may increase. Likewise, with decrease in the width of the square pyramid portion of glass prism 108, the distance between maxima of the cellular field (or, cell period) may decrease. Thus, it may be possible to tune the distance between the maxima of the cellular field (or, cell period) through tuning divergence and/or through utilizing glass prisms (e.g., glass prism 108, or, another glass prism instead of glass prism 108) of varying widths. FIG. 1 also shows a microscope 110 and a Charge Coupled Device (CCD) camera 112 to observe, register and/or investigate the cellular field. It is obvious that the aforementioned devices have been included merely for illustrative purposes, and that other devices within an experimental setup are within the scope of the exemplary embodiments. FIG. 2 shows a ray diagram of a convergent beam incident on glass prism 108, according to one or more embodiments. FIG. 3 shows a ray diagram of a divergent beam incident on glass prism 108, according to one or more embodiments. FIG. 4 shows a perspective view of glass prism 108, according to one or more embodiments. FIG. 5 shows the longitudinal distribution of a convergent cellular field as a function of distance between glass prism 108 and optical divergence controller 106. As seen in FIG. 5, when the distance between glass prism 108 and optical divergence controller 106 is increased (from 10 mm to 50 mm to 90 mm), the distance between maxima in the intensity distribution across a transverse section of the convergent cellular field decreases. The beam incident on glass prism 108 may be more convergent as the distance between glass prism 108 and optical divergent controller 106 is increased, thereby contributing to the distance between maxima in the cellular field being reduced. FIG. 6 shows the longitudinal distribution of a divergent cellular field as a function of distance between glass prism 108 and optical divergence controller 106. As seen in FIG. 6, when the distance between glass prism 108 and optical divergence controller 106 is increased (from 10 mm to 50 mm to 90 mm), the distance between maxima in the intensity distribution across a transverse section of the divergent cellular field increases. The beam incident on glass prism 108 may be more divergent as the distance between glass prism 108 and optical divergent controller 106 is increased, thereby contributing to the distance between maxima in the cellular field being increased. Thus, in one or more embodiments, optical system 100 may allow for formation of a gradient light field with a cellular distribution of intensity in a transverse section thereof, the cellular distribution including a set of controllable periodically distributed intensity maxima. In one or more embodiments, the cell period of the cellular field may be controlled/regulated in an arbitrary plane perpendicular to an axis of symmetry thereof. Exemplary embodiments may, therefore, allow for dosated (e.g., through laser) influence on ensembles of micro-objects (e.g., micro-particles) in microtechnology and nanotechnology applications as discussed above in the Background section. Referring back to FIG. 1, a sample 124 (e.g., micro-particles) may be placed (e.g., in a sample holder 122) such that particles of sample 124 are configured to interact with the gradient light field to be influenced thereby; in other words, sample 124 may be placed between glass prism 108 and microscope 110. In one example embodiment, sample holder 122 may be a cuvette; it should be noted that sample holder 122 may be made of various types of materials (e.g., glass). In one or more embodiments, sample holder 122 may/may not serve to shape the gradient light field. FIG. 7 shows a process flow diagram detailing the operations involved in controlling microparticles through a light field having controllable intensity and periodicity of maxima thereof, according to one or more embodiments. In one or more embodiments, operation 702 may involve providing a capability to control divergence of a coherent light beam having an axially symmetrical distribution of intensity thereof through optical divergence controller 106. In one or more embodiments, operation 704 may involve directing an output of optical divergence controller 106 related to the controlled divergence of the coherent light beam onto glass prism 108. In one or more embodiments, glass prism 108 may include a planar shape onto which a pyramidal structure is formed. In one or more embodiments, glass prism 108 may be positioned such that the output of optical divergence controller 106 is incident on a planar surface of the planar shape or the pyramidal structure. In one or more embodiments, operation 706 may involve controlling a distance between maxima of an output light field of glass prism 108 and intensity thereof through controlling the divergence of the coherent light beam through optical divergence controller 106 and/or varying a distance between optical divergence controller 106 and glass prism 108. In one or more embodiments, operation 708 may then involve utilizing the output light field of glass prism 108 in controlling microparticles in a microtechnology or a nanotechnology application. Although the present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. |
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description | This application is a continuation of U.S. patent application Ser. No. 10/994,911 filed Nov. 22, 2004, now U.S. Pat. No. 7,084,410, and titled “CONFIGURATION MANAGEMENT AND RETRIEVAL SYSTEM FOR PROTON BEAM THERAPY SYSTEM, which is also a continuation of U.S. patent application Ser. No. 10/744,697 filed Dec. 22, 2003, now U.S. Pat. No. 6,882,244, and titled “CONFIGURATION MANAGEMENT AND RETRIEVAL SYSTEM FOR PROTON BEAM THERAPY SYSTEM,” and claims the benefit of U.S. Provisional Application No. 60/438,281 filed Jan. 2, 2003. 1. Field of the Invention The present invention relates to particle radiation therapy systems and, in particular, concerns an improved data storage system that reduces the effects of single point failures for radiation beam therapy systems. 2. Description of the Related Art Particle radiation therapy involves coordinating complex systems and devices to enable targeting of specific cancerous regions of a patient. In particular, proton beam therapy utilizes one or more precisely aligned particle streams to irradiate cancer or tumor cells. The energized protons disrupt targeted cells or tissue so as to effectively halt the progression of the disease. In proton beam therapy, the patient should be accurately positioned with respect to the one or more beams so that the stream irradiates only the desired target region. Otherwise, the stream may damage other healthy cells within the patient's body. Specific alignment in this manner requires numerous control systems to maintain accurate and precise dosage delivery to a plurality of patients during prescribed treatments. As described in U.S. Pat. No. 4,870,287, a proton treatment facility may comprise a proton energy source, an injector, an accelerator, a beam transport system, a switchyard, and a plurality of treatment stations so as to accommodate multiple patients. Each treatment station may comprise a plurality of treatment components such as treatment platforms, gantry structures, and patient monitoring components. Additionally, control and monitoring of the proton treatment facility may be directed by computer and hardware subsystems, which coordinate the activities of each treatment station using software configurable components. Moreover, control system activities may include beam intensity management, beam position orientation and modification, digital imaging performance, safety condition monitoring, and various other treatment functions. Together these systems form a highly complex collection of hardware and software components. The complexity of the proton treatment facility may be further magnified by managing multiple treatment stations where additional requirements for system redundancy and selective control of each treatment station is required. The complex architecture of proton therapy systems present numerous obstacles for coordinating control of a high volume patient throughput. On a typical treatment day, prescribed treatment dosages may be configured for many patients using a plurality of treatment stations, whereby delivery of simultaneous treatments may effect concurrent treatment dosages between patients. For example, each treatment station may require a different proton beam energy delivery, wherein the overall energy is calculated and produced at the source, the switchyard diverts the proper amount of proton beam energy to each treatment station, and the multiple gantries are positioned to deliver the diverted energy to the target regions of the patients on the treatment platforms. To elicit the coordination control of multiple treatment stations, conventional proton beam therapy control systems use either a centralized computer system, such as a database server, or separate computer subsystems to localize control. The problem with a centralized computer system is that, if one or more treatment components fails to function or goes offline, the system as a whole may shut down. Also, if the centralized computer fails, the treatment components may stop functioning because they rely on the centralized computer for operational instructions. Unfortunately, with the high volume of treatments to be delivered, a system shut down would be inconvenient, costly, and reduce treatment efficiency. Some treatments may be delayed or postponed for another day, which inconveniences everyone including the patient and the system operators. In other circumstances, a delayed or postponed treatment may degrade the therapy provided, wherein the treatment time may need to be reduced or the dosage modified to accommodate a larger number of treatments in a reduced period of time. Additionally, delayed treatments may also incur additional treatment costs due to extended periods of operation, where system operators are paid overtime wages and the treatment delivery systems remain operable for longer periods of time. Therefore, a centralized computer alone is not the answer due to unavoidable failures that may occur during treatment delivery, which may endanger some patients. Since patient safety is a great concern, some conventional proton beam therapy control systems use separate computer subsystems to localize control to particular treatment components. The problem with localized control is that each component requires a system operator to manually enter prescribed treatment and operational parameters for each patient at each treatment station. Unfortunately, the length of each treatment would be extended due to the additional time needed to enter prescribed parameters for each patient treatment and system operation. Also, the high volume of treatments to be delivered would need to be reduced to accommodate the additional time or additional system operators would need to be hired to extend the treatment day, which results in additional operational costs. Hence, there is a need for an improved proton beam therapy control system that manages multiple treatment delivery components and coordinates delivery of simultaneous treatments without compromising patient safety. There is also a need for an improved proton beam therapy control system that reduces the adverse effects of centralized computer failures if one or more treatment components fails to function. Additionally, this system architecture should be able to accommodate the complexity associated with proton beam therapy control systems while maintaining an acceptable level of user interactive simplicity so as to facilitate configuration, maintenance, and development in an efficient manner. The aforementioned needs are satisfied by a radiation beam therapy system having a plurality of treatment devices including a radiation beam source and a beam transport device. In one embodiment, the radiation beam therapy system comprises a database component that stores subsets of parameters associated with selected treatment devices, wherein the parameters comprise instructional information that can be used to configure the selected treatment devices for operation. In addition, the radiation beam therapy system comprises an interface component that allows a user to modify the subsets of parameters associated with selected treatment devices stored in the database. Moreover, the radiation beam therapy system comprises a management component that extracts subsets of parameters from the database and generates data storage elements comprising the extracted subsets of parameters in a format recognizable by the selected treatment devices, wherein the data storage elements permit configuration of the selected treatment devices based, at least in part, on the instructional information comprised therein, the management component further distributes the data storage elements to the selected treatment devices to thereby permit the selected treatment devices to operate independently of the database component. In one aspect, operation of the selected treatment devices includes a treatment mode of operation. The plurality of treatment devices includes at least one of a charged particle source, an accelerator, and a beam transport system. The source or accelerator includes a proton synchrotron and the beam transport system includes a plurality of steering and focussing magnets with beam sensors distributed along an evacuated beam transport tube. The beam transport system connects to a series of switchyards that include an array of dipole bending magnets which deflect the beam to any one of a plurality of beam focussing and deflection optics leading to respective treatment locations having rotatable gantries. Also, a beam delivery system may be located within each rotatable gantry, which may be adapted to deliver therapeutic radiation doses to a patient lying on a treatment platform according to a specific patient treatment plan. In another aspect, the subsets of parameters include treatment data, configuration parameters, operational parameters, and control settings for the selected treatment devices. The selected treatment devices are software controlled instruments that require at least one of the subsets of parameters for operation and treatment. The database component comprises a centralized database server, which stores configuration and operational information, such as data, parameters, and control settings, for the selected treatment devices in a manner so as to provide easy access to the stored configuration and operational information, wherein parameter retrieval and modification are easily performed by the centralized database server via requests from the interface component. The centralized database server provides configuration management activities, which may include record keeping and version/revision control. The management component reduces the occurrence of single point failures by generating appropriate data storage elements and distributing the data storage elements to the selected treatment devices. The distribution of data storage elements by the management component affords the selected treatment devices operational independence from the database component due to the associated reliance on the data storage elements for parameter retrieval and operational configuration. In still another aspect, the radiation beam therapy system comprises at least one communication link between the management component and the selected treatment devices so as to distribute the generated data storage elements to the selected treatment devices. The subsets of parameters are stored in the database component in at least one of database table structures, records, and values. The data storage elements are arranged in a consolidated information set that is recognizable by the selected treatment devices. The consolidated information set exploits the native functionality of the selected treatment devices in a manner such that an additional numerical or supplemental program or application may be unnecessary for the selected treatment devices to recognize the configuration parameter values from the data storage elements. The data storage elements comprise a data type that is stored and accessed in a file-oriented manner as is suitable for each selected treatment devices. The data storage elements comprise a data type that is stored and accessed in an address-oriented manner as is suitable for each selected treatment devices. The data storage elements comprise one or more volatile or non-volatile system control files. The data storage elements comprise one or more system control files including flat files. The one or more system control files include one or more flat files. In still another aspect, the management component sends configurable parameters to each treatment device, and wherein a selected treatment device retrieves usable parameters from the configurable parameters. Additionally, the management component selectively sends configurable parameters to each treatment device representing usable parameters by each treatment device. The aforementioned needs are also satisfied by a radiation beam therapy system comprising a plurality of distributed functional components whose operation is coordinated to elicit a selected operational mode. In one embodiment, the system comprises a database component that stores a plurality of parameters associated with the distributed functional components. In addition, the system comprises an interface component that allows a user to select an operational mode for which the database component identifies appropriate subsets of parameters that are associated with the distributed functional components and generates at least one system control file containing an appropriate subset of parameters used to configure a selected distributed functional component to operate in such a manner to elicit the selected operational mode. Moreover, the system comprises a control file distribution component that provides each of the distributed functional components with the appropriate system control file such that the functional components are able to operate substantially independently of the database component while eliciting the selected operational mode. The aforementioned needs are also satisfied by a radiation beam therapy system comprising, in one embodiment, a plurality of treatment devices including a radiation beam source and a beam transport device and a database that stores subsets of specific parameters associated with selected treatment devices, wherein the specific parameters comprise a logical collection of instructional information that can be used to configure the selected treatment devices for operation. In addition, the system comprises an interface that allows a user to modify the subsets of specific parameters associated with selected treatment devices stored in the database. Moreover, the system comprises a management component that extracts selected subsets of specific parameters from the database and generates system control files comprising the extracted subsets of specific parameters in a format recognizable by the selected treatment devices, wherein the system control files permit configuration of the selected treatment devices based, at least in part, on the instructional information comprised therein, the management component further distributes the system control files to the selected treatment devices to thereby permit the selected treatment devices to operate independently of the database. Furthermore, the subsets of specific parameters comprise, for example, subsets of instrument specific parameters. The aforementioned needs are also satisfied by a radiation beam therapy system having a plurality of functional components including a radiation beam source and a beam transport device. In one embodiment, the system comprises a database that stores subsets of configurable parameters associated with the operation of the functional components, the database further comprising an interface component that allows a user to modify the stored subsets of configurable parameters. In addition, the system comprises a management component that retrieves subsets of configurable parameters associated with selected functional components from the database, the management component further generating control files from the stored configurable parameters, and subsequently distributing the generated control files to the identified functional components such that the identified functional components can operate independently. The aforementioned needs are also satisfied by a radiation beam therapy system comprising, in one embodiment, at least one functional component that can be configured for treatment delivery via a subset of configurable parameters and a database component that stores the subset of configurable parameters as a logical collection of information, the database component having a user interface that allows a user to modify the logical collection of information. In addition, the system comprises a management component that communicates with the database component and the at least one functional component, wherein the management component identifies the subset of configurable parameters associated with the at least one functional component, generates a first file from the identified subset of configurable parameters, and distributes the first file to the at least one functional component so that, upon reception of the first file, the at least one functional component can extract the subset of configurable parameters from the first file and configure itself for treatment delivery. The aforementioned needs are also satisfied by a method for managing a plurality of distributed instruments used in treatment delivery for a radiation beam therapy system. In one embodiment, the method comprises storing operational instructions for each instrument within a centralized configuration management system having a database component in which the operational instructions are maintained and selecting an operational mode for the radiation beam therapy system and identifying a subset of operational instructions stored in the database component for each of the distributed instruments to be used in configuring the radiation beam therapy system to function in the selected operational mode. In addition, the method comprises generating a data storage element for each of the distributed instruments containing the required operational instructions necessary to configure each distributed instrument to function in such a manner so as to result in the radiation beam therapy system functioning in the selected operational mode. Moreover, the method comprises transferring the data storage element to the distributed instruments thereby providing the necessary operational instructions for a selected distributed instrument to operate without requiring further access to the centralized configuration management system to elicit functioning of the radiation beam therapy system in the desired operational mode. In one aspect, generating a data storage element includes generating a plurality of data storage elements. Also, generating a data storage element includes generating at least one flash memory element. Additionally, generating a data storage element includes generating at least one system control file. Moreover, transferring the data storage element to the distributed instruments includes transmitting the data storage element to the distributed instruments. The aforementioned needs are also satisfied by a method of configuring a radiation beam therapy system having a plurality of functional components for directing a beam to at least one of a plurality of treatment locations. In one embodiment, the method comprises maintaining a plurality of configurable parameters in a database, the configurable parameters used to coordinate the function of the plurality of functional components thereby eliciting operational control of the radiation beam therapy system and selecting an operational mode in which the beam is to be directed to a particular treatment location with a desired set of operational parameters. In addition, the method comprises identifying subsets of parameters from the plurality of configurable parameters maintained in the database that are used to configure and control the functional components in such a manner so as to direct the beam to the selected treatment location with the desired set of operational parameters. Moreover, the method comprises generating at least one system control file which reflects the subsets of parameters used to configure and control the functional components and distributing the at least one system control file to at least one of the plurality of functional components thereby directing the operation of the functional components. These and other objects and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings. In complex, multi-processor software controlled systems, it may be important to provide treatment configurable parameters that are easily modified by an authorized user to prepare the software controlled system for various modes of operation. In one embodiment, a configuration management system of the present invention provides a centralized database server, which stores configuration and operational information, such as data, parameters, and control settings, for the software controlled systems. Advantageously, the database approach provides easy access to the stored configuration and operational information, wherein parameter retrieval and modification are easily performed by the configuration management system via requests from a user interface system. Additionally, the configuration management system provides configuration management activities, which may include record keeping and version/revision control as will be described in greater detail herein below. In conventional treatment delivery systems, the treatment delivery components access operational and configuration parameters directly from the database component using a single point acquisition approach. Single point acquisition requires a direct dependence on the database component for operation and parameter retrieval via a direct communication link between the treatment delivery devices and the database component. As a result of operational dependence, if a network problem occurs and the database component is offline or unavailable, then the conventional treatment delivery systems are forced to shut down and patient treatments may be terminated until the database component is functionally online or available. Single point failures are disadvantageous to patient health, treatment stability, and operational efficiency. Conversely, the present invention reduces the occurrence of single point failures by generating a static document, such as a flat text file, read-only file, or flash memory element, comprising operational and configuration parameters and distributing the static document to the treatment delivery components. The distribution of static documents affords the treatment delivery components operational independence from the database component due to the associated reliance on the static documents for parameter retrieval and operational configuration. Although a communication link may be used to distribute the generated static document or system control file to the treatment delivery components, operational reliance is advantageously shifted to the static document. The scope and functionality of the static documents or system control files will be described in greater detail herein below. Moreover, for ease of updating and retrieval, configuration parameters, for example, may be stored in the database table structures as records or values. When generating the static document or system control file, the retrieved configuration parameter values may be arranged in a consolidated information set that is recognizable by the treatment delivery components. Advantageously, the consolidated information set exploits the native functionality of the treatment delivery devices in a manner such that an additional numerical or supplemental program or application may be unnecessary for the treatment delivery devices to parse the configuration parameter values from the static document. Moreover, the static documents or system control files provide fast, localized parameter retrieval capability and independent operational capabilities for the software controlled systems as will be further described in greater detail herein below. Reference will now be made to the drawings wherein like numerals refer to like parts throughout. FIG. 1 illustrates one embodiment of a clinically-based radiation beam therapy system, such as, for example, a proton beam therapy system (PBTS) 10, that may used in a particle radiation treatment facility. In one embodiment, the proton beam therapy system 10 may comprise a plurality of treatment delivery components including a charged particle source 11, an accelerator 12, and a beam transport system 14. Additionally, the source/accelerator 11, 12 may comprise, for example, a proton synchrotron and the beam transport system 14 may comprise, for example, a plurality of steering and focussing magnets with beam sensors distributed along an evacuated beam transport tube. In one aspect, the beam transport system 14 connects to a series of switchyards 16 that may comprise an array of dipole bending magnets which deflect the beam to any one of a plurality of beam focussing and deflection optics 26 leading to respective treatment locations having rotatable gantries 18. Moreover, a beam delivery system 20 may be located within each rotatable gantry 18, which may be adapted to deliver therapeutic radiation doses to a patient 24 lying on a treatment platform 22, according to a specific patient treatment plan. An exemplary proton beam treatment system is more fully disclosed in U.S. Pat. No. 4,870,287, which is hereby incorporated by reference in its entirety. In operation, charged particle beams of a predefined energy may be generated by the proton synchrotron 12 and transported by the beam transport system 14 to the switchyards 16. The switchyards 16 may be configured to select a one or more gantries 18 for transport of radiation thereto. Each rotatable gantry 18 is capable of orienting the beam delivery system 20 relative to the target location of the patient 24. Beam orientation allows directed deposition of radiation to a predefined location along the rotation axis or a so-called isocenter. Additionally, to facilitate accurate and precise dosage delivery to one or more of the patients 24, the beam delivery system 20 may be positioned, configured, and calibrated for radiation delivery according to prescribed specifications of the patient treatment plan. One of the central components of the proton beam therapy system 110 is the radiation delivery system 20, designed to deliver precise dose distributions to a target volume within a patient. In general, such delivery systems are comprised of components which may either modify or monitor specific properties of a radiation beam relevant to the treatment plan. The beam delivery system 20 may, for example, comprise a device to spread or otherwise modify the beam position and profile, a dispersive element to modify the beam energy and a plurality of beam sensors to monitor such properties. Additional disclosure relating to the radiation delivery system 20 is provided in U.S. Pat. No. 4,870,287. FIG. 2 illustrates one embodiment of a central configuration of a particle radiation treatment facility 50 that may be used to provide proton beam therapy treatments to patients in a manner as previously described with reference to FIG. 1. The particle radiation treatment facility 50 may comprise the proton beam therapy system (PBTS) 10 of FIG. 1, a user interface system 52, and a configuration management system 54 that may be used to generate one or more static documents or system control files 56 for the PBTS treatment delivery components 11, 12, 14, 16, 18, 20 of the PBTS 10. In addition, the one or more generated system control files 56 may be distributed to the PBTS 10 by the configuration management system 54 in a manner so as to provide configuration data and parameters in a recognizable format to the PBTS treatment delivery components 11, 12, 14, 16, 18, 20. In one embodiment, the user interface system 52 may comprise a generally known computer workstation, such as a personal computer, that may be used to retrieve and modify the configuration parameters for the PBTS 10. One or more users, such as system operators, field service engineers, medical physics personnel, facility administrators, etc., may update PBTS configuration data, parameters, and/or control settings in the configuration management system 54 via the user interface system 52. The user interface system 52 provides access to data, parameters, and control settings that may be used to configure the previously mentioned PBTS treatment delivery components in the PBTS 10. The PBTS 10 may be given access to the configuration data through the system control files 56 that may be generated and provided by the configuration management system 54. It should be appreciated that there may be more than one user interface system 52 to the configuration management system 54 without departing from the scope of the present teachings. However, for safety reasons, a preferred embodiment may comprise one designated user interface system 52 to the configuration management system 54 to update configuration data, parameters, and control settings for the PBTS treatment delivery components 11, 12, 14, 16, 18, 20 in the PBTS 10. It should be appreciated that there are configurable parameters and control settings that may apply to software related components as well as the hardware related components. Some software and hardware components that may be configured through the configuration management system 54 may include, but are not limited to, power supplies, tesla meters, sensors, detectors, timing control systems, user interfaces, network configurations, and safety systems. In one embodiment, the configuration management system 54 may comprise a generally known centralized computer system, such as a database server, that may be used to store the PBTS configuration data and parameters in database components, such as files, in a manner so as to be easily retrievable by the user interface system 52 when prompted by a user. Advantageously, the manipulation of the configuration data and parameters through the configuration management system 54 allows for maintaining configuration data and parameter integrity as well as providing an interactive interface to the user. In a manner as will be described in greater detail herein below, the configuration management system 54 may comprise processing and management components that may be used to verify updated parameter settings to an acceptable operational range. For example, if the operational range of a power supply is between 0 and 500 amps, then the management component verifies that supply output is not set less than 0 amps and greater than 500 amps. In one embodiment, the configuration management system 54 uses a PBTS software application that allows authorized users to easily access and modify the PBTS configurable parameters while maintaining data integrity. The PBTS software application may be used in conjunction with common desktop environments on various platforms, such as those used with Solaris™ and X Windows™ on UNIX based platforms. In one aspect, a configurable parameter may comprise a piece of data or information needed by the PBTS 10 to configure, for example, control settings, wherein the value of the configurable parameter may vary depending on the treatment dosage and/or environment. Some of the devices in the PBTS 10 need configuration data for proper initialization. For example, magnets are configured with default output specific to their target energy. Moreover, other functional components of the PBTS 10, such as ion source, power supplies, timing, etc., may require configurable initialization data, scale factors, conversion factors, mapping, etc. As will be described in greater detail herein below, the data is accessible to the user through a graphical user interface (GUI) via the user interface system 52, and the data is stored and maintained in a database component of the configuration management system 54. When an authorized user requests a configuration update, a connection to the database component is established and any modifications to the data are applied to the database component. In addition, authorized user accounts may be created via the user interface system 52, wherein authorized users comprises varying degrees of permission or access levels, which may be determined by administrators. For example, different types of users may be granted access to data related only to a specific job function. Accelerator staff may be allowed to modify accelerator related parameters, such as magnet settings. Medical physicians may be allowed to modify treatment room related parameters, such as detectors and scattering foils. Various other users, such as field service personnel and system administrators may have access to data needed to maintain the system. Moreover, the database component of the PBTS configuration management component 54 may be initialized with two sets of data: treatment data and non-treatment data. The treatment set may comprise configuration data that has been approved for treatment operations. In most cases, there is one treatment set or one set of approved treatment data that is available. The non-treatment set may comprise configuration data that may be used for other functional operations, such as research, maintenance, and/or tuning. For the most part, authorized users are able to retrieve and view most configurable parameters. If a user has write access to a parameter, then the user is able to modify its value within an acceptable range, which will be described in greater detail herein below. However, proposed modifications related to treatment data is subject to approval by a designated administrator, wherein the designated administrator is responsible for patient treatment and approving proposed modifications to the treatment data. In one embodiment, the PBTS 10 of FIG. 1 may further comprise one or more PBTS workstations 62 that may house the hardware and software used to operate and control the PBTS treatment delivery components 11, 12, 14, 16, 18, 20 of the PBTS 10. The PBTS workstations 62 function independently from the configuration management system 54 so as to provide localized control to the PBTS 10. As previously mentioned, the user interface system 52 is used to interact with the configuration management system 54. Conversely, the PBTS workstations 62 are used to interact with the PBTS treatment delivery components 11, 12, 14, 16, 18, 20. In one embodiment, there is no direct link between the configuration management system 54 and the PBTS 10. Instead, the PBTS workstations 62 and/or the PBTS 10 access the PBTS configuration data, parameters, and control settings from the configuration management system 54 via the system control files 56. In one aspect, it should be appreciated by those skilled in the art that the configuration management system 54 provides one or more system control files 56 to the treatment delivery components 11, 12, 14, 16, 18, 20 of the treatment delivery system 10. Additionally, it should also be appreciated that the treatment delivery components 11, 12, 14, 16, 18, 20 may retrieve one or more operational parameters from the system control files 56. In another aspect, it should be appreciated by those skilled in the art that the management component is adapted to send configurable parameters to each treatment device, wherein a selected treatment device retrieves usable parameters from the configurable parameters. Moreover, the management component is further adapted to selectively send configurable parameters to each treatment device representing usable parameters by each treatment device. Advantageously, this particular embodiment provides a separation of control between the configuration management system 54 and the PBTS workstations 62. Configuration data, parameters, and control settings are more easily updated using the configuration management system 54, which offers more reliable database management and controlled parameter revision. The generation of system control files 56 allows the PBTS workstations 62 to access the PBTS configuration data, parameters, and control settings when and if the configuration management system 54 is offline or unavailable. Therefore, the PBTS 10 is able to operate independently of the configuration management system 54. During treatment delivery, the operation of the PBTS treatment delivery components 11, 12, 14, 16, 18, 20 are desirably coordinated to direct a precisely calibrated and aligned proton beam 58 towards a specific target region or isocenter 60 of the patient 24. As previously described, the patient 24 is supported by the treatment platform 22 and the gantry 18 is rotatable about an axis of rotation and is used to properly align the proton beam 58 with respect to the patient 24 and the isocenter 60. The PBTS control system 62 monitors and coordinates the operational activities of the hardware and software subsystems used to configure and direct the proton beam 58 as well as insure patient safety. Patient safety is a primary concern in radiation treatment and strict control over the PBTS 10 must be maintained at all times to insure that the proton beam 58 is accurately and precisely directed with an appropriate intensity or energy level. It should be appreciated that a more in depth discussion relating to the PBTS control system 62 is more fully disclosed in U.S. Pat. No. 5,260,581, which is hereby incorporated by reference in its entirety. In addition, the PBTS 10 including the PBTS workstations 62 may utilize the system control files 56 to access configuration data, parameters, and control settings from the configuration management system 54. In one embodiment, the system control files 56 may comprise a series of strings or characters in one or more recognizable files or formats that may be parsed by the PBTS 10, PBTS workstations 62, or the functional components 11, 12, 14, 18, 20 of the PBTS 10 to retrieve configuration data, parameters, etc. stored in a control file format, such as, for example, a flat file, binary file, flash memory file, etc. One advantage to using flat files is that flat files are human readable, but various other file structures, such as binary files, may be used by those skilled in the art without departing from the scope or functionality of the present teachings. Moreover, in one aspect, the system control files 56 may be delineated using a reference identifier, such as a comma, hyphen, semi-colon, etc. Alternatively, strings may be delineated using codes that signify tabs or new lines. Additionally, a sequentially oriented group of characters that are not likely to be found in the record itself may serve as the reference identifier for string parsing. In various embodiments, system control files 56 may be file and/or address oriented and stored in a variety of different formats. For example, a file-oriented schema may comprise a “textual document” (e.g. based on the ASCII character set) which is stored and accessed as a discrete file using a non-volatile data storage device (e.g. a hard disk drive, optical drive, tape drive, flash memory device, etc.). Likewise, an address-oriented schema may comprise system control file information stored in a manner that may be accessible at selected locations within a volatile or non-volatile memory or storage device (e.g. bits/bytes of information stored at a particular memory address). It will further be appreciated that the information contained in the system control file may be represented in numerous different manners, such as for example, using binary, octal, hexadecimal, html or other data types/representations. These data types may be stored and accessed in file-oriented, address-oriented, or other organizational manners as is suitable for each instrument or device which is desirably configured to use the system control file information. In certain embodiments, the system control files 56 may comprise, for example, data files or formats stored in various types of data storage elements, such as flash memory, read-only memory, etc. As is generally known, programmable read-only memory (PROM) is read-only memory (ROM) that can be modified once by a user. Since PROM processes are relatively inflexible, many PROM chips designed to be modified by users may be implemented with erasable programmable read-only memory (EPROM) or electrically erasable programmable read-only memory (EEPROM), which can be programmed, erased and reprogrammed multiple times. In addition, flash memory represents a type of non-volatile memory that can be erased and reprogrammed in units of memory blocks. Other types of devices that may be used in accordance with the present teachings may include magnetic and optical data storage formats, such as compact disks, floppy disks, tape drives, etc. Therefore, in general, it should be appreciated that system control files may comprise various types of data storage or memory elements having various compositions without departing from the scope of the present invention. Moreover, the access configuration data, parameters, and control settings from the configuration management system 54 may be stored on the various types of data storage or memory elements so as to provide system control files 56 to the operational and treatment devices 11, 12, 14, 18, 20 of the PBTS 10. Once the configuration data, parameters, etc. are identified and retrieved from the system control file 56, the PBTS control system 62 or the functional components 11, 12, 14, 18, 20 of the PBTS 10 may use the retrieved data, parameters, etc. to configure its functional and operational components for delivery of treatment. It should be appreciated that the PBTS 10 may receive and interpret the PBTS system control files 56 as read-only formatted files that may comprise spreadsheets, tables, etc. Additionally, the retrieved information may also comprise a set of instructions that may be used by the PBTS 10 to configure its operational components. Advantageously, configuration may occur without depending on the processing and management components of the configuration management system 54 during delivery of treatment. Therefore, the operational components of the PBTS 10 may function in an independent manner, which reduces the adverse effects of single point failures in the configuration management system 54. The management of data, parameters, and control settings by the configuration management system 54 allows for preserving data integrity as well as insuring no duplication of data. For example, data integrity may be preserved with automatic backup, wherein the configuration management system 54 archives backup files comprising copied configuration data, parameters, etc. in a separate storage component without consent from a user. In addition, controlled access to configuration data, parameters, etc. allows the configuration management system 54 to prioritize multiple updates according pre-determined criteria so as to substantially avoid the duplication of configuration data, parameters, etc. Moreover, the PBTS 10 accesses the data, parameters, and control settings from the system control files 56, which insures that the configuration data, parameters, etc. are accessible when and if a single point failures occurs with respect to the configuration management system 54. For example, configuration of the PBTS 10 may include setting proton energy source 11, the accelerator 12, and the beam transport 14 to deliver a prescribed proton beam 58 to the switchyard 16. In addition, configuration of the PBTS 10 may also include setting the switchyard 16 to direct the prescribed proton beam 60 to a specific treatment station and the corresponding gantry 18 to orient the proton beam 60 towards a specific isocenter 60 on the patient 24. Moreover, configuration data, parameters, etc. may further include length of treatment delivery, energy strength of the proton beam, duration of radiation dosage, and radiating multiple treatment areas on the patient. It is critical to patient safety that the configuration data, parameters, etc. stored in the system control files 56 is locally accessible so that, if the configuration management system 54 goes off line for some reason, the PBTS 10 and its components may remain functional. Advantageously, generation and distribution of system control files 56 to the PBTS treatments delivery system 10 and its components by the configuration management system 54 offers control separation so that the PBTS 10 and its components rely less on the configuration management system 54 to deliver treatments to patients. In general, it should be appreciated that the PBTS control system 62 and the processing components of the configuration management system 54 may comprise, by way of example, computers, program logic, or other substrate configurations representing data and instructions, which operate as described herein. In various other embodiments, the PBTS control system 58 and the processing and management components of the configuration management system 54 may comprise controller circuitry, processor circuitry, processors, general purpose single-chip or multi-chip microprocessors, digital signal processors, embedded microprocessors, microcontrollers and the like. Additionally, it will be appreciated that in one embodiment, the program logic may be implemented as one or more components, wherein the components may be configured to execute on one or more processors. The components may include, but are not limited to, software or hardware components, modules such as software modules, object-oriented software components, class components and task components, processes methods, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, micro-code, circuitry, data, databases, data structures, tables, arrays, and variables. In one aspect, the configuration management system 54 may be implemented using applications designed for relational database development and implementation. It is further recognized that the configuration management system 54 may be implemented as spreadsheet or a single database with separate tables or as other data structures that are well known in the art such as linked lists, binary trees, and so forth. Also, the configuration management system 54 may be implemented as a plurality of databases which are collectively administered. It should also be appreciated that the structure and schema of the configuration management system 54 may be altered, as needed, to implement the relations or associations utilized to organize and categorize the information in the configuration management system 54. FIGS. 3A-3C illustrate various functional embodiments of the PBTS 10 of FIGS. 1, 2 and the configuration management system 54 of FIG. 2. For ease of discussion, FIG. 3A illustrates a simplified block diagram of the user interface system 52, the configuration management system 54, and the treatment delivery system 10. In this particular embodiment, the configuration management system 54 may comprise a management component 70, a database component 72, and a control file component 74 that are functionally interconnected so as to manage, update, and distribute PBTS configuration data, parameters, and control settings for the PBTS 10. The PBTS database system components 70, 72, 74 may comprise hardware and/or software subsystems that may be adapted for specific functionality with respect to the PBTS 10. Advantageously, the use of system control files as described herein reduces the occurrence of single point failures by generating a static document, such as, for example, a flat file, binary file, flash memory file, etc., comprising operational and configuration parameters and then distributing the static document to the treatment delivery components. In addition, the distribution of system control files allows the treatment delivery components operational independence from the database component due to the associated reliance on the system control files for operation and parameter retrieval. In one aspect, although a communication link may be used to distribute the generated system control file or static document to one or more of the treatment delivery components, operational reliance may be shifted to the distributed system control file or static document. For ease of updating and retrieval, configuration parameters, for example, may be stored in the database table structures as records or values. When generating the static document or control file, the retrieved configuration parameter values may be arranged in a consolidated information set that is recognizable by the treatment delivery components. Advantageously, the consolidated information set exploits the native functionality of the treatment delivery devices in a manner such that an additional numerical or supplemental program or application is unnecessary for the treatment delivery devices to parse the configuration parameter values from the static document. The scope and functionality of these processes will be more fully described in greater detail herein below. In one embodiment, when parameter modifications have been requested, the treatment delivery system 10 receives periodic parameter updates in the form of electronic control files from the configuration management system 54 via, for example, a communication network, such as an Ethernet, intranet, or internet communication system. In some circumstances, the treatment delivery components may send request to the configuration management system inquiring whether parameter updates are available. As will be in greater detail below, the parameter updates are sent to the treatment delivery system in a recognizable format that is easily identified by the treatment delivery components of the system. FIG. 3B further illustrates the configuration management system 54 of FIGS. 2, 3A with additional functional features associated with the database component 72. Configuration and operational parameters 80, such as data, information, and control settings, may be stored in the database component 72 of the configuration management system 54 as database files in a generally known manner. For example, each PBTS treatment delivery component 11, 12, 14, 16, 18, 20 of the PBTS 10 may have its own set of parameters 80 related to configuration and operation. A relational association may be established in the database component 72 between the particular PBTS treatment delivery component 11, 12, 14, 16, 18, 20 and its own set of parameters 80 from 1 to N. These parameters 80 may be searched for, retrieved, sorted, and edited by the management component 70 in a generally known manner so as to produce parameter update files 82 whenever an authorized user requests a parameter update via the user interface system 52. The process of updating parameters will be described in greater detail herein below. In one embodiment, the configuration data and parameters are maintained in sets. The database component 72 is responsible for maintaining approved, current, and proposed sets of configuration data and parameters. An approved set may comprise the set of parameter configurations that are acceptable for allowing treatments to proceed. Preferably, for safety reasons, there is only one approved set of configuration parameters at any one time. A current set may comprise the set of parameter configurations that the PBTS 10 is currently being configured with, which may or may not be permissible for treatments. The current set may be one of a plurality of configuration sets stored in the database component 72. A proposed set may comprise a set of parameter configurations waiting approval from a system administrator before it can be used for treatments. As illustrated in FIG. 3C, the management component 70 may be used by the configuration management system 54 to identify, retrieve, and update configuration parameters from the database component 72 and to generate system control files 56 using the control file component 74. After generating the system control files 56, the management component 70 subsequently distributes the system control files 56a, 56b, 56c, 56d, 56e to the corresponding PBTS treatment delivery systems 10a, 10b, 10c, 10d, 10e of the PBTS 10, which may include beam control systems 10a, safety systems 10b, power systems 10c, logging systems 10d, and various additional systems 10e. Beam control systems 10a may include the beam transport 14, the switchyard, the gantry 18 and the beam delivery system 20. Power systems 10c may include the proton energy source 11 and the accelerator 12. The database component 72 may function in the capacity of generally known memory devices, such as hard drives, compact discs, removable storage media, tape drives, flash memory, optical devices, integrated circuitry, etc., wherein the parameter information may easily stored, altered, and retrieved by the user interface system 52. The control file component 74 may function as relational translator that interprets database language formats into control file language formats so that configuration parameters stored in the database may translated into recognizable operational parameters for the functional components of the PBTS 10. In a complex, multi-processor software controlled system, such as the PBTS 10, it may be important to provide treatment configurable parameters that are easily modified by an authorized user to prepare the software controlled system for various modes of operation, such as modifying parameter tolerance, user access, access levels, debug output, etc. In most cases, configuration parameters are loaded by execution software of the PBTS 10 in a safe and timely manner. Moreover, the PBTS 10 often involves multiple modes of operation (treatment, research, commissioning), multiple configuration setups (passive beam delivery, active beam delivery), and multiple patient setups. In addition, there may be more than one person who has authorized access to modify data and parameter sets. In one embodiment, the configuration management system 54 provides a centralized database server, which stores configuration and operational information, such as data, parameters, and control settings, for the software controlled PBTS 10. In one embodiment, parameter modification and parameter retrieval are performed by the configuration management system 54 via requests from the user interface system 52. Moreover, the configuration management system 54 provides configuration management activities, which may include record keeping (i.e., who, when, and why modified certain parameter, has a parameter been approved for a certain mode), providing backup of the data, and version/revision control. Additionally, configuration data and parameters may be temporarily changed in a manner such that, after a designated time period, newly modified values of configuration data and parameters may revert back to previously stored values. Reversion to previous data, parameters, etc. may also occur after the system control files 56 are generated. In one aspect, modifying data and parameters may be subject to approval by an administrator, which helps to maintain data integrity and insure proper treatment dosages and delivery. The system administrator may either approve, reject, or institute a time limit for the modification availability. In some cases, if duplicate modification requests are requested by one or more authorized users and the system administrator approves all pending modification requests, then the latest modification request may override all other requests. In other cases, a time out period indicates that the system administrator is approving a proposed modification but only for a limited amount of time. In this particular situation, once the specified date and/or time have elapsed, the previous value of the data or parameter prior to the modification request will be reinstated. Advantageously, the configuration management system 54 comprises the capability to generate system control files 56 to substantially avoid problematic situations that may occur during operation of the PBTS 10. Network problems and single-point failures may occur as the result of an unexpected shutdown and/or an emergence of a corrupted file. The system control files 56 may comprise various types of control files, such as, for example, flat files, binary files, flash memory files, etc., that provide fast, localized parameter retrieval capability and independent operational capabilities for the PBTS 10. In one aspect, modifying configuration data and parameters during treatments may adversely affect the treatment delivery. Therefore, for safety reasons, system control files 56 are preferably generated between treatments. Additionally, the configuration management system 54 comprises an information management and retrieval system with adequate configuration management capabilities and fast, safe, and localized parameter retrieval. For example, the configuration management system 54 utilizes the management component 70 in conjunction with the database component 72 to provide restricted access to parameter modification, wherein authorized users are allowed to revise configuration data, parameters, etc. and unauthorized users are not granted access to the configuration data, parameters, etc. In addition, the configuration management system 54 uses the management component 70 in conjunction with the control file component 74 to generate the system control files 56 from parameter files 80, 82 for distribution of configuration parameters to the PBTS 10. In one aspect, on a periodic basis or when a parameter has been modified either temporarily or permanently, the configuration management system 54 may generate system control files 56 from the parameter files 80, 82, substantially insuring that proper syntax has been followed during generation. For example, the management component 70 has access to the programming language used by each of the treatment delivery components in the PBTS 10. In one aspect, proper syntax may comprise using a specific set of rules prescribed by the programming language to combine instructional elements into permitted constructions that will be recognizable to the designated treatment delivery component. Proper syntax may also refer to a systematic arrangement of data and instructions that may be easily parsed from the system control files 56 by the designated treatment delivery component. Moreover, the generated system control files 56 are then placed in the appropriate directories associated with the functional components of the PBTS 10. In addition, execution software used by the functional components of the PBTS 10 retrieves the appropriate system control file 56 and loads the requested configuration parameters for treatment delivery. FIG. 4A illustrates one embodiment of a logical organization of a plurality of configuration parameter values 80 in the database component 72. As previously described, there are a significant number of configuration parameter values 80 that may be applied to each PBTS treatment delivery component in the PBTS 10. Tracking the configuration parameter values for PBTS treatment delivery components can be highly complex and cumbersome. Therefore, the management component 70 may be used to map parameters to specific treatment delivery components in the PBTS 10 using a plurality of mapping tables 74. In the database component 72, the mapping tables 74 comprising deployment labels 76a, 76b, 76c to lookup keys 78 may be created to identify and retrieve configuration parameter values 80 to thereby generate a plurality of system control files 86. In one aspect, the lookup keys 78 identify where the data and parameter values 80 can be located within the database component 72, wherein each deployment label 76 points to a specific lookup key 78 where the data or parameter values 80 can be found in the database component 72. For example, a first treatment delivery component of the PBTS 10 may be mapped to a first mapping table 74a comprising a first set of deployment labels 76a. A second treatment delivery component of the PBTS 10 may be mapped to a second mapping table 74b comprising a second set of deployment labels 76b. A third treatment delivery component of the PBTS 10 may be mapped to a third mapping table 74c comprising a third set of deployment labels 76c. As illustrated in FIG. 4A, the first set of deployment labels 76a may point to lookup keys A, C, and E, (78) which may further point to configuration parameter values V1, V2, and V5 (80). The second set of deployment labels 76b may point to lookup keys B and E (78), which may further point to configuration parameter values V2 and V5 (80). The third set of deployment labels 76c may point to lookup keys A, D, E, and F (78), which may further point to configuration parameter values V1, V4, V5, and V6 (80). For the most part, parameter referencing, as indicated in FIG. 4A with a dashed line, takes place in the database component 72 in a generally known manner. In one aspect, once the configuration parameter values 80 have been identified and retrieved, the configuration parameter values 80 may be subsequently imported, as illustrated in FIG. 4A with a solid line, into the system control files 86 for distribution to the corresponding PBTS treatment delivery component in the PBTS 10. For example, the first mapping table 74a may be used to generate and distribute a first system control file 86a to the first treatment delivery component of the PBTS 10. The second mapping table 74b may be used to generate and distribute a second system control file 86b to the second treatment delivery component of the PBTS 10. The third mapping table 74c may be used to generate and distribute a third system control file 86c to the third treatment delivery component of the PBTS 10. It should be appreciated that the order in which the parameter values are retrieved may vary and may depend on the specific order in which the designated treatment delivery component parses the information from the control file. It should also be appreciated that any number of control file generation techniques may be used by one skilled in the art without departing from the scope of the present invention. As previously described, treatment parameter values may need to be updated to reflect new treatment dosages, etc. Therefore, once the configuration parameter values 80 have been identified and located in the database component 72, the configuration parameters values 80 may be replaced or revised with updated configuration parameters values 82. It should be appreciated that storing data and information is generally known in the art and any of a number of generally known storage methods may be used to store the updated configuration parameters values 80 in the database component 72. FIG. 4B illustrates one embodiment of a logical organization of configuration parameter associations 94. User input modifications 90 to specific configuration parameters may effect other dependent configuration parameters in a manner such that the dependent configuration parameter values may need to be re-calculated. In one aspect, a plurality referential locations 92 may be used to identify a plurality of parameter associations 94 corresponding to the user inputted modifications 90. For example, as illustrated in FIG. 4B, a first input modification 90a to a first configuration parameter value V1 referenced by lookup key A may point to a first referential location 92a, which may further point to a first and second parameter association 94a, 94b. Since V1 has been modified by the user, the database component 72 locates the configuration parameter values V4 and V6 associated with the lookup keys D and F. Subsequently, the configuration parameter values V4 and V6 may then be re-calculated according to a specified function, such as V4=V4+V1 and V6=V6+V1. It should be appreciated that the re-calculation function may vary depending on a particular application without departing from the scope of the present invention. Similarly, in another example, a second input modification 90a to a second configuration parameter value V2 referenced by lookup key B may point to a second referential location 92b, which may further point to a third parameter association 94c. Since V2 has been modified by the user, the database component 72 locates the configuration parameter value V1 associated with the lookup key A. Subsequently, the configuration parameter value V1 may then be re-calculated according to a specified function, such as V1=V1+V2. In addition, a third input modification 90c to a third configuration parameter value V3 referenced by lookup key C may point to a third referential location 92c, which may further point to a fourth, fifth, and sixth parameter association 94d, 94e, 94f. Since V3 has been modified by the user, the database component 72 locates the configuration parameter values V2, V5, and V6 associated with the lookup keys B, E, and F. Subsequently, the configuration parameter values V2, V5, and V6 may then be re-calculated according to a specified function, such as V2=V2+V3, V5=V5+V3, and V6=V6+V3. It should be appreciated that the order in which the configuration parameter values are re-calculated may vary depending on specific application priorities established by the user. As previously mentioned, the most recent modification may be given priority over past modifications or priority may be established by a configuration administrator. It should also be appreciated that any number of parameter association techniques may be used by one skilled in the art without departing from the scope of the present invention. FIG. 4C illustrates one example of using mapping tables 74 to generate system control files 86 associated with specific treatment delivery devices in the PBTS 10. In one embodiment, the mapping tables 74 comprise records and keys for maintaining the data as well as the actual parameters and their associated attributes. As previously described, the configuration management system 54 uses input data from authorized users via the user interface device 52 to manipulate or modify the configuration data, parameters, etc. in the database component 72. This data is made available to the treatment delivery components and devices in the PBTS 10 as a mapping from the tables to text based control files 86. For example, the power supply in the PBTS 10 may be used to energize one or more magnets in order to reach the desired energy and control the beam in a generally known manner. There are different types of power supplies and each type of power supply may be configured differently. As a result, the configuration parameters associated with the power supplies may be stored in the database component 72. As illustrated in FIG. 4C, the configuration parameters may be stored, for example, in the database component 72 using tables. In one aspect, the tables hold information that is used to look up and maintain the parameters and their values in a manner as previously described with reference to FIGS. 4A, 4B and as illustrated herein below. . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .attr1attr2. . .. . .. . .AmpScale 20000. . .. . .attrnattr1attr2. . .. . .. . .MaxAmp 20000. . .. . .attrnattr1attr2. . .. . .. . .MaxVolt 20000. . .. . .attrnattr1attr2. . .. . .. . .MinAmp−20000. . .. . .attrnattr1attr2. . .. . .. . .MinVolt−20000. . .. . .attrnattr1attr2. . .. . .. . .RampRate 720. . .. . .attrn. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. . . In one embodiment, the management component 70 of the configuration management system 54 uses the database component 72 to select necessary parameter values 80 and further uses the control file component 74 to write the parameter values 80 to control files 86. As a result, the configuration parameter values in control file form 86 are available for retrieval by the designated treatment delivery components of the PBTS 10. For example, as illustrated in FIG. 4C, the database component 72 may comprise a mapping table 74 for the power supply. The power supply mapping table 74 comprises deployment labels that point to one or more lookup keys 78 which further point to configuration parameter values 80 associated with the power supply. These configuration parameter values 80 for the power supply may be imported into a control file 86 for distribution to the power supply component of the PBTS 10. In another example, as illustrated in FIG. 4C, the database component 72 may further comprise a mapping table 74 for a timing system. The timing system mapping table 74 comprises deployment labels that point to one or more lookup keys 78 which further point to configuration parameter values 80 associated with the timing system. These configuration parameter values 80 for the timing system may be imported into a control file 86 for distribution to the timing system component of the PBTS 10. FIG. 5 illustrates one embodiment of a system configuration process 100 that may be used by the configuration management system 54 to modify parameters for the PBTS 10. The database component 72 of the PBTS configuration management component 54 is used to maintain and preserve the integrity of configuration data, parameters, etc. in a manner so as to avoid duplicating configuration settings. In addition, the stored configuration data, parameters, etc. may be easily retrieved, modified, and archived so that configuration parameters may be updated in a more efficient manner. The system configuration process 100 initiates in a start state 102 and then advances to a state 104 where a user may request a parameter update via the user interface system 52. In one embodiment, the user enters new system configuration parameters into the user interface system 52 via a computer workstation, and the requested parameter update having the new system configuration parameters is electronically sent to the configuration management system 54 for evaluation. Subsequently, upon receiving the requested parameter update, the management component 70 of the configuration management system 54 runs through a PBTS system check that compares the new system configuration parameters to a tolerance range of values. For example, if the operational range of a power supply is between 0 and 500 amps, then the management component 70 verifies that the new system configuration parameter for the power supply is not set less than 0 amps and greater than 500 amps. In a decision state 108, if one or more of the new system configuration parameters in the requested parameter update are out of tolerance range, then the prior database settings for the prior system configuration parameters are preserved and the user is notified in a state 114 and the process 100 subsequently terminates in an end state 116. Otherwise, in the decision state 108, if the new configuration parameters in the requested parameter update fall with the pre-determined tolerance ranges then the process 100 proceeds to a state 112 where the management component 70 of the configuration management system 54 performs a parameter update as described in greater detail herein below with reference to FIG. 6. Once the system configuration parameters in the database component 72 of the configuration management system 54 have been updated to the new system configuration parameters in the requested parameter update, the user is notified in the state 114, and the process 100 terminates in the end state 116. As previously described, in a complex, multi-processor software controlled system, such as the PBTS 10, it may be important to provide treatment configurable parameters that are easily modified by an authorized user to prepare the software controlled system for various modes of operation. Advantageously, the configuration management system 54 provides a centralized database, which efficiently stores configuration data, parameters, etc., for the software controlled PBTS 10. Also, parameter modification and parameter retrieval may be efficiently performed by the configuration management system 54 via requests from the user interface system 52. FIG. 6 illustrates one embodiment of a parameter update process 140 that may be used by the management component 70 of the configuration management system 54 to update system configuration parameters used by the PBTS 10. The updated parameters are easily identified and retrieved from the database files and then converted to control files for distribution to the PBTS 10. Generation and distribution of system control files 56 to the PBTS treatments delivery system 10 and its components by the configuration management system 54 offers control separation so that the PBTS 10 and its components rely less on the configuration management system 54 to deliver treatments to patients. For ease of discussion, FIG. 3B will be referenced in conjunction with FIG. 6. The parameter update process 140 initiates in a start state 142 and proceeds to a state 144 where the management component 70 of the configuration management system 54 identifies the parameters 80 associated with the requested parameter update 82 in the database component 72. In a state 146, the new system configuration parameters in the requested parameter update 82 are temporarily stored in the database component of the configuration management system 54 while waiting approval from a system administrator. After modification approval is granted, either the requested parameter update 82 is stored in a permanent manner so as to replace the previous parameters 80 with the parameter update 82, or the requested parameter update 82 is used to generate system control files 56 for a specific treatment and the previous parameters 80 are maintained in the database component 72. By temporarily storing the parameter update 82, duplication of data does not occur, and the previous parameters 80 are not lost. A temporary parameter update 82 will have a specified time period for expiration in a manner as previously described. This allows for increased treatment flexibility in that treatment dosages can vary for each treatment delivery without losing prior configuration parameters. Next, in a state 148, the management component 70 uses the control file component 74 to generate the system control file 56 with the new system configuration parameters from the requested parameter update 82. In one embodiment, the management component 70 retrieves configuration parameters from the database component 72 and queues the parameter values in a string by separating each value with a delimiter. In one aspect, the control file component 74 has prior knowledge of the order in which the parameter values will be parsed by the designated functional component of the PBTS 10. Hence, the management component 70 uses the control file component 74 to track the placement of each parameter value in the queue so that the system control file 56 will be appropriately generated with the correct parsing order. Optionally, the management component 70 may then calculate and update the checksum, which checks the generated system control file 56 for errors. In one aspect, generated system control files 56 provide checksum mechanisms to verify that generated data is current and up-to-date. When the system control files 56 are generated, the management component 70 uses a checksum algorithm to allow the detection of file corruption. The checksum method is a common form of detecting corruption in network transfer of data packets. The sending process appends a checksum to the end of the packet that the receiver uses to confirm the packet is not corrupted. There are many checksum algorithms out there. They basically take the information in the packet/file and perform mathematical operations and/or logical operations (bit shifting, bit twiddling, etc.) to “sum” the packet/file. The receiving process uses the same algorithm on the data and compares it to the checksum. If they match, there is no data corruption. Following, the configuration management system 54 establishes communication with PBTS 10 and distributes the generated system control file 56 to the appropriate functional component of the PBTS 10. Subsequently, the parameter update process 140 terminates in an end state 154. Advantageously, the PBTS 10 or its operational components accesses the data, parameters, etc. through the system control files 56. This substantially insures that the data, parameter, etc. may be accessible even when and if a single point failures occurs with respect to the configuration management system 54. In addition, configuration of the PBTS 10 or its operational components may be achieved without depending on the configuration management system 54 during treatment delivery. Therefore, the PBTS 10 and its operational components may function in an independent manner, which reduces the adverse effects of single point failures in the configuration management system 54. FIG. 7 illustrates the advantages of using the configuration management system 54 of the present invention to manage, update, and distribute configuration parameters for the PBTS 10. Advantageously, the configuration management system 54, as described herein, utilizes the positive characteristics of both database oriented file management systems and control files configuration systems. As illustrated in FIG. 7, with reference to the database management systems, the configuration management system 54 provides controlled access to configuration information, such as authentication and logging, parameter range verification before parameter is read by the PBTS 10, operational mode separation in configuration parameters, automated backup, and data integrity. In addition, the database management system may further provide revision control for a single parameter, parameter modification expiration date management, and report generation capabilities to insure the proper syntax, data integrity of the system control files. As further illustrated in FIG. 7, with reference to the control file configuration systems, the configuration management system 54 provides fast access to configuration parameters in system control files, which may take less time to access a file than accessing a field in the database, and provides localized access to configuration parameters with higher reliability, which substantially insures that parameter information is accessible in case of database server or network interruptions and/or failures. Additionally, the control file configuration system may further provide configuration information in an archived or read-only format to the user, administrator, and/or system operator. It should be appreciated that the configuration management system 54 may be added on or to existing control files configuration systems in various currently used medical devices by one skilled in the art without departing from the scope of the present invention. Although the preferred embodiment of the present invention has shown, described, and pointed out the fundamental novel features of the invention as applied to this particular embodiment, it will be understood that various omissions, substitutions and changes in the form of the detail of the device illustrated may be made by those skilled in the art without departing from the spirit of the present invention. Consequently, the scope of the invention should not be limited to the foregoing description, but should be defined by the appending claims. |
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