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050911465 | claims | 1. In a fuel bundle for a boiling water reactor having: a plurality of vertically aligned spaced apart fuel rods for forming a fuel rod group within said fuel bundle for generation of a fission reaction in the presence of water moderator, a lower tie plate for admitting water moderator through said lower tie plate to the interstitial volume between said fuel rods and supporting said vertically aligned and spaced apart fuel rods, an upper tie plate for permitting water and steam to be discharged from the top of the fuel bundle and maintaining said vertically aligned and spaced apart fuel rods in upstanding spaced apart side-by-side relation, a surrounding fuel channel for confining moderator flow along a path over the fuel rods and from said lower tie plate to said upper tie plate; at least one of said fuel rods being a part length rod extending from the lower tie plate vertically less than the full length to the upper tie plate ending interior of the fuel bundle at a disposition wherein the upper end of the part length rods defines with respect to said surrounding fuel rods an empty volume overlying said partial length rod under said upper tie plate, the improvement to said fuel bundle comprising: at least one steam vent tube overlying at least one of said part length rods; means supporting said steam vent tube in said volume overlying said part length rod, said steam vent tube being supported in the volume of said fuel bundle between the end of said part length rod and said upper tie plate; said steam vent tube defining an opening disposed to said end of said part length rod for the receipt of steam moderator within said void overlying said part length rod; said steam vent tube further defining an opening disposed to said upper tie plate and away from the end of said part length rod for the discharge of steam moderator from said fuel bundle. a plurality of vertically aligned spaced apart fuel rods for forming a fuel rod group within said fuel bundle for generation of a fission reaction in the presence of water moderator; a lower tie plate for admitting water moderator through said lower tie plate to the interstitial volume between said fuel rods and supporting said vertically aligned and spaced apart fuel rods; an upper tie plate for permitting water and steam to be discharged from the top of the fuel bundle and maintaining said vertically aligned and spaced apart fuel rods in upstanding spaced apart side-by-side relation; a surrounding fuel channel for confining moderator flow along a path over the fuel rods and from said lower tie plate to said upper tie plate; at least one of said fuel rods being a part length rod extending from the lower tie plate vertically less than the full length to the upper tie plate ending interior of the fuel bundle at a disposition wherein the upper end of the part length rods defines with respect to said surrounding fuel rods an empty volume overlying said partial length rod under said upper tie plate; at least one steam vent tube overlying at least one of said part length rods; means supporting said steam vent tube in said volume overlying said part length rod, said steam vent tube being supported in the volume of said fuel bundle between the end of said part length rod and said upper tie plate; said steam vent tube defining an opening disposed to said end of said part length rod for the receipt of steam moderator within said void overlying said part length rod; said steam vent tube further defining an opening disposed to said upper tie plate and away from the end of said part length rod for the discharge of steam moderator from said fuel bundle. providing a plurality of vertically aligned spaced apart fuel rods for forming a fuel rod group within said fuel bundle for generation of a fission reaction in the presence of water moderator; providing a lower tie plate for admitting water moderator through said lower tie plate to the interstitial volume between said fuel rods and supporting said vertically aligned and spaced apart fuel rods; providing an upper tie plate for permitting water and steam to be discharged from the top of the fuel bundle and maintaining said vertically aligned and spaced apart fuel rods in upstanding spaced apart side-by-side relation; providing a surrounding fuel channel for confining moderator flow along a path over the fuel rods and from said lower tie plate to said upper tie plate; providing at least one of said fuel rods extending from the lower tie plate vertically less than the full length to the upper tie plate ending interior of the fuel bundle at a disposition wherein the upper end of the part length rods defines with respect to said surrounding fuel rods an empty volume overlying said partial length rod under said upper tie plate; providing at least one steam vent tube overlying at least one of said part length rods; supporting said steam vent tube in said volume overlying said part length rod, said steam vent tube being supported in the volume of said fuel bundle between the end of said part length rod and said upper tie plate; defining an opening in said steam vent tube disposed to said end of said part length rod for the receipt of steam moderator within said void overlying said part length rod; defining an opening in said steam vent tube disposed to said tie plate for the discharge of steam moderator from said fuel bundle; and, reacting said fuel bundle in the presence of water moderator to form in the upper tow phase region of said fuel bundle adjacent said part length rod a two phase mixture of steam and liquid moderation whereby steam finds a preferential flow path in said steam vent tube form the top of said part length rod to said upper tie plate. 2. The invention of claim 1 and wherein said fuel bundle has a plurality of part length rods. 3. The invention of claim 2 and wherein said fuel bundle has said plurality of part length rods spaced apart one from another. 4. The invention of claim 1 and wherein said steam vent tube overlies a plurality of part length rods. 5. The invention of claim 1 and wherein said steam vent tube includes a plurality of apertures in the side walls of said steam vent tube for permitting fluid communication through the side walls of said steam vent tube. 6. The invention of claim 5 and wherein said apertures are configured to preferentially admit steam interior of said steam vent tube. 7. The invention of claim 5 and wherein said apertures are configured to preferentially discharge water from the interior of said steam vent tube. 8. The invention of claim 1 and wherein said steam vent tube overlying said part length rod is square. 9. The invention of claim 1 and wherein said steam vent tube overlying said part length rod is round. 10. The invention of claim 1 and wherein said steam vent tube includes means for classifying water flowing in the interior of said steam vent tube to the exterior of said steam vent tube. 11. A fuel bundle for boiling water reactor comprising: 12. The invention of claim 11 and wherein said fuel bundle has a plurality of part length rods. 13. The invention of claim 12 and wherein said fuel bundle has said plurality of part length rods spaced apart one from another. 14. The invention of claim 1 and wherein said steam vent tube overlies a plurality of part length rods. 15. The invention of claim 11 and wherein said steam vent tube includes a plurality of apertures in the side walls of said steam vent tube for permitting fluid communication through the side walls of said steam vent tube. 16. The invention of claim 15 and wherein said apertures are configured to preferentially admit steam interior of said steam vent tube. 17. The invention of claim 15 and wherein said apertures are configured to preferentially discharge water from the interior of said steam vent tube. 18. The invention of claim 11 and wherein said steam vent tube overlying said part length rod is square. 19. The invention of claim 11 and wherein said steam vent tube overlying said part length rod is round. 20. The invention of claim 11 and wherein said steam vent tube include means for classifying water flowing in the interior of said steam vent tube to the exterior of said steam vent tube. 21. A process for improving the outflow of generated steam in a fuel bundle for a boiling water reactor including the steps of: |
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claims | 1. A packaging for transporting and/or storing radioactive materials, the packaging delimiting a housing cavity intended to receive a mass of radioactive materials, said housing cavity being at least partly defined by a lateral body, a bottom and a lid mounted removably on the lateral body, the bottom and the lid being spaced apart from each other along a longitudinal axis of the packaging, and the lateral body extending between a first axial end on the lid side and a second axial end on the bottom side,wherein the lateral body has a thickness-change zone defining a transition surface, the lateral body comprising a reduced-thickness part extending from the transition surface towards the first axial end of the lateral body, said reduced-thickness part comprising an internal surface laterally delimiting a hollowed-out zone of the lateral body, also delimited axially by the transition surface,wherein the packaging comprises an insert body extending around the longitudinal axis, arranged removably in said hollowed-out zone, and having an internal surface laterally delimiting a part of the housing cavity,and wherein the internal surfaces are spaced apart from each other so as to have a minimum radial separation greater than 30 mm. 2. The packaging according to claim 1, wherein the insert body:a) is independent of the lateral body and of the lid;b) forms an integral part of the lid, which also comprises a main part for axial closing off of the housing cavity defining an axial-end surface of said housing cavity, the insert body being arranged projecting axially in the direction of the bottom from the axial-end surface; orc) is formed by combining a primary portion,the primary portion forming an integral part of the lid, which also comprises a main part for axial closing off of the housing cavity defining an axial end surface of said housing cavity, the primary portion including firstly a lateral wall forming the internal surface and arranged projecting axially in the direction of the bottom from the axial end surface, and secondly a fixing flange arranged at an axial end of the lateral wall and configured to be in abutment against the transition surface,the secondary portion being independent of the lateral body and of the lid, and arranged radially between the internal surface of the reduced-thickness part of the lateral body, and the assembly formed by the lateral wall of the primary portion and the main part of said lid. 3. The packaging according to claim 2, further comprising means for fixing the lid on the lateral body, the fixing means passing through the insert body and the transition surface of the lateral body. 4. The packaging according to claim 3, wherein, in case c), said fixing means pass through the fixing flange of the primary portion of the insert body. 5. The packaging according to claim 1, wherein a sealing system is gripped axially between the transition surface of the lateral body and an axial end of the insert body. 6. The packaging according to claim 1, wherein the lid is entirely covered laterally by the reduced-thickness part of the lateral body. 7. The packaging according to claim 1, it further comprising an additional lid fixed to the lateral body. 8. The packaging according to claim 1, further comprising an impact-damping cap covering at least part of the lid, as well as the first axial end of the lateral body. 9. The packaging according to claim 1, wherein the internal surface of the insert body laterally delimits an axial section of the housing cavity, the axial section extending over an axial length greater than or equal to 50 mm. 10. The packaging according to claim 1, wherein the transition surface of the lateral body forms an internal shoulder. 11. A parcel comprising the packaging according to claim 1, loaded with a mass of radioactive materials housed in the housing cavity, the mass of radioactive materials being located partly laterally opposite the insert body. 12. A method for discharging a mass of radioactive materials housed in the housing cavity of the packaging according to claim 1, the method comprising the following steps:removing the lid and the insert body, so as to release an annular space of the hollowed-out zone between the internal surface of the reduced-thickness part and an external surface of a top portion of the mass;introducing a handling device into the annular space, in order to connect the handling device to the external surface of the mass; andextracting the mass out of the cavity, by means of the handling device. 13. The parcel according to claim 11, wherein the mass of radioactive materials is in the form of a barrel. 14. The packaging according to claim 1, wherein the insert body is a ring. |
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claims | 1. A method of making an electro-optic window having reduced RF and microwave transmission characteristics, the method comprising:providing a window that is formed from a material that is substantially transparent to at least one of infra-red, visible and UV radiation;forming on a surface of the window a grid of channels;sputtering over the surface of the window a layer of a material having one of electrically conductive and dielectric properties to substantially fill the channels of the grid;selectively etching the surface of the window, thereby removing the sputtered material from the surface while leaving the channels of the grid substantially filled with the material, creating a corresponding grid pattern of the material within the channels, and thereby rendering the window non transmissive to RF/MICROWAVE radiation; andtreating the material as required to render the grid usable to reduce the RF/MICROWAVE transmission characteristics of the window. 2. The method according to claim 1, wherein the material is a metal. 3. The method according to claim 1, wherein the step of forming on a surface of the window a grid of channels comprises forming the grid of channels by laser etching the window material. 4. The method according to claim 1, wherein the step of forming on a surface of the window a grid of channels comprises forming the grid of channels by chemically etching the window material. 5. The method according to claim 1, wherein the step of forming on a surface of the window a grid of channels comprises:forming a mould in the shape of an EO window, the mould defining a positive grid formation whereby to impart to a moulded window a negative grid formation on one surface of the window;forming a sol of a material suitable for sintering and pouring the sol into the mould;converting the sol to a gel by the application of heat;drying the gel whereby to impart to the gel a permanent shape corresponding to that of the mould; andvitrifying the gel by sintering whereby to form a sintered EO window having the grid of channels formed on one surface thereof. 6. The method according to claim 1, further comprising a step of forming a capping layer configured to cover the grid and attach to the window surface by:forming a mould;forming a sol and pouring the sol into the mould;converting the sol to a gel by the application of heat;drying the gel whereby to impart to the gel a permanent shape reflecting that of the mould; andvitrifying the gel by sintering whereby to form a said capping layer. |
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046831096 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, there is illustrated a debris removal system, generally designated by the numeral 20, constructed in accordance with and embodying the features of the present invention, and disposed for use in a spent fuel pool 21 of a nuclear power plant. The spent fuel pool 21 is generally rectangular and has vertical side walls 22, vertical end walls 23 and a bottom wall 24. Mounted on and substantially covering the bottom wall 24 are a plurality of fuel assembly racks 25, each being generally in the form of an elongated vertical tube substantially square in transverse cross section. Each rack 25 has four side walls 26, each provided at the upper end thereof with an outwardly flared flange 27 (see FIG. 6). The upper edges of the flanges 27 are substantially coplanar in a plan 28 (FIG. 2) and cooperate to form a square grid of racks 25, the inclination of the flanges 27 creating separating spaces between adjacent racks 25. Each of the racks 25 is dimensioned to accommodate a single nuclear fuel assembly 30, which may typically have a length of between 11 and 14 feet. In use, the spent fuel pool 21 is filled with water to a depth of between 40 and 50 feet. Thus, the plane 28 at the top of the fuel assembly racks 25 is typically disposed at least 30 feet below the surface of the water in the pool 21. Referring to FIGS. 2 and 8, each nuclear fuel assembly 30 is a generally rectangular array of a plurality of elongated fuel rods 31, each having a bottom end plug 32, and a plurality of control rod guide thimble tubes 33. The thimble tubes 33 are somewhat longer than the fuel rods 31 and project predetermined distances above and below the ends thereof. The spacing between the fuel rods 31 and thimble tubes 33 is maintained by a plurality of longitudinally spaced-apart grid straps 35 (one shown). The fuel assembly 30 also includes a top nozzle 37 (FIG. 2) connected to the upper ends of the thimble tubes 33 and a bottom nozzle 38 connected to the lower ends of the thimble tubes 33, the bottom nozzle 38 having an upper surface 39 disposed at a slight distance (typically less than one inch) below the lower ends of the fuel rods 31. In normal operation, spent fuel assemblies 30 are lowered, as by an overhead crane cable 237 and handling tool (not shown), into the pool 21 and into a selected one of the racks 25 for storage. It is an aspect of the present invention, that the spent fuel pool 21 is utilized for performing certain operations on a fuel assembly 30, in particular the removal of debris therefrom. In this regard, the debris removal system 20 includes a work platform 40, adapted to be mounted at the top plane 28 on the racks 25, a support stand 60, mountable on the work platform 40, and a tool manipulation assembly 80, which is also mountable on the work platform 40 adjacent to the support stand 60, as indicated in FIGS. 1 and 2. Thus, when a fuel assembly 30 is suspended above the work platform 40, operations can be performed on it, as will be explained in greater detail below. Referring now also to FIGS. 3-6, the work platform 40 has a generally cruciform frame 41, including a pair of elongated, parallel angle beams 42 and a pair of parallel angle beams 43, disposed substantially perpendicular to the beams 42 and securely fastened thereto, as by welding. Support pads 44 interconnect the lower ends of the vertical flanges of the angle beams 42, and similarly interconnect the angle beams 43 to form a rigid framework, the support pads 44 being spaced apart longitudinally of the beams 42 and 43. A flat, octagonal deck 45 overlies and is fixedly secured to the horizontal flanges of the beams 42 and 43, which flanges are substantially coplanar. Integral with the deck 45 around its perimeter is a short upstanding flange 46. The deck 45 has a substantially square opening 47 therethrough centrally thereof, having dimensions slightly greater than the transverse dimensions of one of the fuel assembly racks 25, and being located at the intersection of pairs of beams 42 and 43. Respectively fixedly secured to the beams 43 and projecting upwardly therefrom through complementary openings in the deck 45 are a pair of locating pins 49 (see FIG. 10), for a purpose to be explained more fully below. Referring to FIGS. 6 and 8, there is mounted on the work platform 40 a guide fixture 50, which includes a substantially square support plate 51 which overlies and is fixedly secured to the upper surface of the deck 45. The support plate 51 has a square opening therethrough centrally thereof which is aligned in registry with the opening 47 in the deck 45. Fixedly secured to the support plate 51 within the opening therethrough and extending vertically downwardly therefrom is a square tube 52 dimensioned substantially the same as one of the racks 25. The tube 52 has four vertical walls 53, each provided at the upper end thereof with a laterally outwardly flared flange 54 which projects above the support plate 51. Four positioning members 55 are respectively fixedly secured to the outer surfaces of the walls 53 at the lower ends thereof. Each positioning member 55 is an angle member and includes an inclined guide surface 56 on the vertical flange thereof, and has a laterally outwardly extending horizontal bearing flange 57. In use, the work platform 40 is lowered into position on the top of the racks 25, with the tube 52 of the guide fixture 50 in vertical alignment with a selected one of the racks 25. More particularly, the parts are positioned and arranged so that the walls 53 of the tube 52 will be respectively substantially coplanar with the walls 26 of the selected rack 25. The bearing flanges 57 will rest upon the upper edges of the flanges 27 of the selected rack 25, with the guide surfaces 56 in engagement with the inner surfaces of the flared flanges 27, this engagement serving to aid in guiding the tube 52 into accurate registry with the rack 25. The support pads 44 are positioned so that they will respectively rest upon the upper edges of the flanges 27 of two adjacent racks 25. Preferably, there are also provided on the work platform 40, three lifting lugs 59 (see FIG. 3), projecting upwardly from the deck 45 and adapted for engagement with a triangular lifting frame (not shown) to facilitate movement of the work platform 40, as by an overhead crane cable 238 (FIG. 2) to and from its work position on the racks 25. It can be seen that when the work platform 40 is mounted in this work position, illustrated in FIGS. 6 and 8, the guide fixture 50 serves accurately to guide an associated fuel assembly 30 into the selected rack 25, as will be explained in greater detail below. Referring now to FIGS. 3 and 7-9, the support stand 60 includes a generally rectangular frame 61, having a pair of elongated, parallel bottom rails 62. Fixedly secured to the bottom rails 62 and projecting vertically upwardly therefrom at longitudinally spaced-apart locations thereon are eight posts 63, four on each of the bottom rails 62. Preferably, the bottom rails 62 and the posts 63 are all right angle members. The posts 63 on each bottom rail 62 are interconnected at their upper ends by a corresponding one of a pair of beams 64, which respectively overlie the bottom rails 62. The upper surface of each of the beams 64 is provided along the inner edge thereof with a recessed bearing surface 65, which extends longitudinally of the beam 64 and terminates just short of the opposite ends thereof. There are also provided two acute angle support brackets 66, which respectively overlie the bottom rails 62 parallel thereto, with each bracket 66 interconnecting the two posts 63 closest to one end of the associated bottom rails 62, approximately midway along the vertical extent of the posts 63. Mounted on the support brackets 66 is a non-metallic deflector shield 67, which may be formed of a suitable plastic, such as polypropylene. The deflector shield 67 is of generally cruciform shape, having four laterally outwardly extending and downwardly sloping tongues or arms 68, two of which overlie the support brackets 66 and are fixedly clamped thereto by clamp bars 68a, and the other two of which extend longitudinally between the bottom rails 62. The deflector shield 67 has a square opening 69 therethrough centrally thereof and dimensioned substantially the same as the transverse dimensions of a fuel assembly rack 25. Mounted on the support stand 60 is a generally square sliding support plate 70, which has integrally secured to the bottom surface thereof, two perpendicularly intersecting stiffening ribs 71 and 72. The opposite side edges of the support plate 70 respectively rest upon the bearing surfaces 65 of the beams 64, in sliding engagement therewith. Two elongated rectangular retaining plates 73 are respectively fixedly secured to the upper surfaces of the beams 64 and extend the length thereof, the inner edges of the retaining plates 73 overlying the adjacent edges of the sliding support plate 70 for cooperation with the recessed bearing surfaces 65 to constrain the support plate 70 against vertical movement. Mounted on the upper surface of the support plate 70 and projecting upwardly therefrom are four positioning corners 75, disposed generally at the corners of an imaginary square with the same dimensions as the opening 69 in the deflector shield 67. Each of the positioning corners 75 has an outwardly flared upper end 76. Two cross beam angles 79 extend transversely of the support stand 60 and interconnect the posts 63 which are interconnected by the support brackets 66. The longitudinally extending tongues 68 of the deflector shield 67 respectively overlie and rests upon the cross beams 79. In use, the support plate 70 is slidably movable longitudinally of the support stand 60 between a supporting position, illustrated in solid line in FIG. 7, and a retracted position, illustrated in phantom in FIG. 7. When the support plate 70 is in its supporting position, the positioning corners 75 define the corners of the square which is substantially congruent and vertically aligned with the openings 69 in the deflector shield 67. In this position, the support plate 70 is adapted to receive thereon the lower end of a fuel assembly 30, this lower end being guided into position by the positioning corners 75, accurately and stably to retain the fuel assembly 30 in position on the support plate 70, as is indicated in FIG. 8. It will be appreciated that the fuel assembly 30 remains supported by the overhead crane, the support plate 70 serving merely to stabilize the position of the fuel assembly 30 in a vertical orientation. When the support plate 70 is disposed in its retracted position, it uncovers the opening 69 in the deflector shield 67 and the aligned guide fixture 50 and the underlying fuel assembly rack 25, thereby permitting the fuel assembly 30 to be lowered into the rack 25. Referring now to FIGS. 3 and 10-15, the tool manipulation assembly 80 will be described. The tool manipulation assembly 80 includes a generally rectangular support frame 81, which resembles an open picture frame, and is comprised of an elongated base channel 82, a pair of upstanding post channels 83 and a head channel 84, best shown in FIG. 10. Fixedly secured to the base channel 82 and extending from opposite sides thereof perpendicular thereto are two spaced-apart pairs of foot channels 85 (FIGS. 10 and 14), which serve to stabilize the support frame 81. Respectively disposed adjacent to the two pairs of foot channels 85 and extending vertically upwardly therefrom within the support frame 81 are two mounting angles 86, which are arranged as mirror images of each other. Each of the mounting angles 86 has a flange 87, which is fixedly secured to one flange of the base channel 82 parallel thereto, and a flange 88 which is fixedly secured to one flange of the adjacent foot channel 85 parallel thereto. Each mounting angle 86 is provided with a pair of inclined braces 89 (FIGS. 10 and 14), which respectively extend from the two foot channels 85 of the adjacent pair thereof to the flange 88, and are fixedly secured to each, as by welding. The upper end of the flanges 87 are respectively coupled to the adjacent post channels 83 by two horizontally extending brace angles 90 (FIG. 10). Fixedly secured to the top of the head channel 84 intermediate the ends thereof are two spaced-apart, upstanding lifting lugs 91. Disposed on the head channel 84 between the lifting lugs 91 is an annular rig pad 92, which is aligned with a complementary opening through the head channel 84. Fixedly secured to the head channel 84 and projecting downwardly therefrom between the lifting lugs 91 is a funnel 93. Mounted on the support frame 81 is a drive assembly 100 (FIG. 10), which operates to effect an "X-Y-Z" movement of an associated tool, i.e., movement along any of three orthogonal axes. For purposes of illustration, the "Z" direction will be considered to be the vertical direction, the "X" direction will be considered to be the horizontal direction parallel to the plane of the support frame 81, i.e., parallel to the direction of elongation of the base channel 82, and the "Y" direction will be considered to be the horizontal direction perpendicular to the plane of the support frame 81. Also, the side of the support frame 81 which faces the support stand 60, i.e., the side on which the funnel 93 is mounted, will arbitrarily be considered to be the front or forward side of the tool manipulation assembly 80, while the opposite side will be considered to be the back or rearward side. The drive assembly 100 includes a mounting angle 94 (FIGS. 10 and 11) which is fixedly secured to the base channel 82 intermediate the foot channels 85 and extends vertically upwardly therefrom. Two vertically disposed drive cylinders 95 are respectively disposed on opposite sides of one of the flanges of the mounting angle 94 and are fixedly secured thereto, as by mounting brackets 96. The cylinders 95 respectively have piston rods 97 which project vertically upwardly therefrom and are secured to a lift frame 101 for effecting vertical reciprocating movement thereof. More particularly, the lift frame 101 is a generally rectangular configuration of angle members, including a pair of parallel angle side beams 102, each having a horizontally disposed flange 103 and a vertically disposed flange 104, and a pair of angle end beams 105, each having a horizontally disposed flange 106 and a vertically disposed flange 107, the beams 102 and 105 being fixedly secured together, as by welding. The piston rods 97 are fixedly secured to the horizontal flange 103 of one of the side beams 102. Two vertically oriented pillow blocks 109 are respectively fixedly secured to the outer surfaces of the vertical flanges 107 of the end beams 105. The pillow blocks 109 respectively receive therethrough two guide shafts 110. Each shaft 110 is supported by two shaft hangers 111 fixedly secured to the upper and lower ends thereof, the shaft hangers 111 in turn being securely mounted on the flange 88 of the adjacent one of mounting angles 86. The pillow blocks 109 are freely slidable along the guide shafts 110 for guiding the vertical movement of the lift frame 101, i.e., movement in the "Z" direction. Also respectively fixedly secured to the flanges 88 of the mounting angles 86 adjacent to the upper ends thereof, are two pulley brackets 112. Each pulley bracket 112 has two arms 113 extending longitudinally of the support frame 81 and respectively rotatably carrying sheaves or pulleys 114 and 115 adjacent to the distal ends thereof. Two cables 116 are respectively associated with the pulley brackets 112. In particular, each cable 116 is trained over the pulleys 114 and 115 of the associated pulley bracket 112, the cable 116 having one end thereof secured by an anchor 117 to the adjacent end of the lift frame 101, and having the other end thereof secured, as by U-bracket 118, to an associated one of two counterweights 119. The counterweights 119 serve to counterbalance the lift frame 101 and the portions of the drive assembly 100 carried thereby, so as to minimize the force which must be exerted by the drive cylinders 95 to effect vertical movement of the lift frame 101. Mounted on the lift frame 101 is a lateral frame 120, which is movable in the "X" direction, i.e., horizontally left and right, as viewed in FIG. 10. The lateral frame 120 is generally in the shape of an elongated channel having a rectangular bottom wall 121 and a pair of upstanding rectangular side walls 122. Each of the side walls 122 is provided on the inner surface thereof with an elongated groove 123 extending the length thereof adjacent to the distal edge thereof (FIGS. 11, 13 and 15). Fixedly secured to the bottom wall 121 of the lateral frame 120 intermediate the ends thereof, and projecting laterally therefrom perpendicular to the side walls 122, is an angle bracket 124, closed at the distal end thereof by a rectangular end plate 125. An elongated angle member 126 is secured to the horizontal flange 106 of one of the end beams 105 of the lift frame 101, the angle member 126 extending parallel to the side beams 102 substantially midway therebetween, and extending from adjacent the midpoint of the lift frame 101 outwardly therebeyond to a point near the adjacent one of the post channels 83. An elongated drive cylinder 127 is disposed along the angle member 126, being fixedly secured thereto by foot brackets 128, the cylinder 127 having a horizontal piston rod 129 extending from the inner end thereof and fixedly secured to the end plate 125. Thus, it will be appreciated that the piston rod 129 is coupled to the lateral frame 120 for effecting reciprocating horizontal movement thereof to the left and right, as viewed in FIG. 10, with respect to the lift frame 101. This horizontal movement is guided by two pillow blocks 130 which are fixedly secured to the bottom wall 121 of the lateral frame 120 and are respectively disposed for sliding movement along guide shafts 131 and 132, each of which is supported at the opposite ends thereof by a pair of shaft hangers 133 which are fixedly secured to the horizontal flanges 106 of the end beams 105. Disposed within the lateral frame 120 is an elongated video camera 135, having one end thereof seated in a saddle bracket 136, mounted for pivotal movement about a pivot pin 137 spanning the side walls 122 of the lateral frame 120. The camera 135 is secured to the saddle bracket 136 by a pair of clamps 138. An adjustment screw 139 extends through an opening in the bottom wall 121 of the lateral frame 120 for engagement with the camera 135 to adjust the inclination thereof for proper viewing of the portion of the fuel assembly 30 being worked on. An angle bracket 140 spans the side walls 122 of the lateral frame 120 adjacent to the right-hand end thereof, as viewed in FIG. 11, above the camera 135. The vertical flange of the angle bracket 140 has an arcuate recess 141 therein to accomodate adjustment of the inclination of the camera 135. Also respectively fixedly secured to the side walls 122 and projecting rearwardly therefrom (to the right, as viewed in FIGS. 11 and 12) are two elongated angle members 142 and 143, interconnected at their distal ends by a cross bar 144. An elongated drive cylinder 145 is disposed between the angle members 142 and 143 parallel thereto, and has the opposite ends thereof secured, as by foot brackets 146, respectively to the angle bracket 140 and the cross bar 144. The cylinder 145 has a horizontal piston rod 147 which projects forwardly therefrom (to the left, as viewed in FIGS. 11 and 12). Mounted on the lateral frame 120 is a longitudinal frame 150, which includes a support plate 151 spanning and secured to the upper edges of a pair of elongated, parallel side plates 152 at one end thereof, the side plates 152 being disposed substantially parallel to the side walls 122 of the lateral frame 120. The side plates 152 are interconnected at the other end thereof by a cross bar 153. The lower edges of the side plates 152 are spaced by spacers 154 from four roller bearings 155, two of the roller bearings 155 being disposed at spaced-apart locations along each of the side plates 152 and secured to the lower edges thereof by shoulder screws 156 (FIG. 13). The roller bearings 155 are freely rotatable on the shoulder screws 156 and are disposed for rolling engagement in the grooves 123 in the side walls 122 of the lateral frame 120. The piston rod 147 is coupled by nuts 157 to the cross bar 153. Thus, it will be appreciated that the cylinder 145 operates to effect a reciprocating horizontal sliding movement of the longitudinal frame 150 forwardly and rearwardly of the support frame 81 in the " Y" direction (to the left and right as viewed in FIGS. 11 and 12), with respect to the lateral frame 120. Two plunger fittings 158 are respectively threadedly engaged in complementary bores in the support plate 151, each of the fittings 158 having an upwardly spring-biased plunger pin 159 engageable with a tool mount carriage 160. The tool mount carriage 160 comprises a turret plate 161 having four equiangularly spaced-apart recesses 161a in the bottom surface thereof (FIG. 13), arranged so that any two opposed ones thereof may respectively receive the plunger pins 159 therein. The turret plate 161 has four radially outwardly extending arms 162 respectively aligned with the recesses 161a. An axial bore 163 (FIG. 11) is formed vertically through the center of the turret plate 161 and is lined with a bushing 164. Received through the bushing 164 is a shoulder screw 165, the head of which is seated in a large circular recess 166 disposed centrally at the top surface of the turret plate 161. The shoulder screw 165 is threadedly engaged with the support plate 151 intermediate the ends thereof, the turret plate 161 being spaced from the support plate 151 by a spacing washer 167. The turret plate 161 is rotable on the shoulder screw 165. The plunger pins 159 frictionally ride along the bottom surface of the turret plate 161 and seat in opposed ones of the recesses 161a when two opposed ones of the arms 162 are aligned in the "Y" direction, with the other two arms 162 aligned in the "X" direction parallel to the lateral frame 120, as illustrated in the drawings, this constituting a work configuration of the tool mount carriage 160. Thus, it will be appreciated that the tool mount carriage 160 is disposable in four work configurations in which, respectively, the four arms 162 project forwardly (to the left, as viewed in FIGS. 11 and 12) of the support frame 81 in the "Y" direction toward the associated fuel assembly 30 (see FIGS. 2 and 3). The engagement of the plunger pins 159 in the recesses 161a serves resiliently to hold the tool mount carriage 160 in the selected one of its work configurations, so as to prevent accidental movement of the tool mount carriage from that configuration, while accommodating ready indexing of the tool mount carriage 160 to another selected work configuration by the application of minimal rotational force. Each of the arms 162 has a radial bore 168 formed at the distal end thereof, the inner end of each bore 168 communicating with the central recess 166. Each arm 162 also has formed in the upper surface thereof an elongated slot 169 which communicates with the radial bore 168, all for the purpose of respectively accommodating four tool holder assemblies 170 which are identical in construction, wherefore only one will be described in detail. Referring in particular to FIGS. 11-13 and 15, each tool holder assembly 170 includes a bushing 171 lining the distal end of the associated radial bore 168, and slidably coaxially receiving therein an elongated shaft 172. The shaft 172 has an internally threaded axial bore 173 in the outer end thereof (see FIG. 16). A collar 174 encircles the shaft 172 adjacent to its outer end, and may be secured in place, as by a set screw. Disposed in surrounding relationship with the shaft 172 and trapped between the bushing 171 and the collar 174 is a helical compression spring 175. Mounted on top of the turret plate 161 is a generally bail-shaped bracket 176 having a pair of depending legs 177, each provided with an outturned attachment foot 178, the feet 178 being respectively fixedly secured by suitable fasteners to opposed ones of the arms 162. Mounted on top of the bracket 176 intermediate the ends thereof and projecting upwardly therefrom is a short hex stud 179, for use in rotating the tool mount carriage 160 among its several work configurations, as will be explained more fully below. The tool mount carriage 160 also has an alarm assembly 180, which includes a generally bail-shaped strap 181 fixedly secured to and spanning the legs 177 of the bracket 176. Carried by the strap 181 intermediate the ends thereof is a limit switch 182 having a depending actuating lever 183 (FIGS. 13 and 15). An elongated metal strap 184 is aligned with two opposed ones of the arms 162 and spans the central recess 166 in the turret plate 161. Received through complementary openings in the strap 184 adjacent to its opposite ends are two shoulder screws 185, which respectively extend downwardly through the associated ones of the slots 169 in the arms 162 and are threadedly engaged respectively with the shafts 172 of the associated ones of the tool holder assemblies 170, adjacent to the inner ends thereof. The strap 184 carries two longitudinally spaced-apart clips 186, each carrying an upwardly projecting actuator pin 187. An elongated strap 188 overlies the strap 184 perpendicular thereto, being aligned with the other two arms 162. The ends of the strap 188 are spaced from the top surface of the arms 162 by spacers 188a (FIG. 13) to ensure clearance of the strap 184. Two of the shoulder screws 185 are received through complementary openings in the strap 188 and the spacers 188a and through the aligned ones of the slots 169, and are respectively threadedly engaged with the other two tool holder shafts 172 adjacent to the inner ends thereof. The strap 188 carries two longitudinally spaced-apart upstanding actuator pins 189 (FIGS. 12 and 13). In operation, it will be appreciated that the strap 184 and its associated shoulder screws 185 and tool holder shafts 172 move horizontally as a unit, axially of the shafts 172. Similarly, the strap 188 and its associated shoulder screws 185 and tool holder shafts 172 move as a unit. The springs 175 of each such unit are balanced so as to resiliently urge the tool holder assemblies 170 thereof radially outwardly to extended conditions, illustrated in FIGS. 11 and 12, wherein the shoulder screws 185 are respectively centered in the associated slots 169. If a radially inwardly directed force is exerted on one of the tool holder assemblies 170, it moves the shaft 172 thereof radially inwardly, against the urging of the associated compression spring 175, to a retracted condition, illustrated in FIG. 15. It will be appreciated that this effects a corresponding movement of the strap 184 (or 188) and a radial outward movement of the aligned one of the tool holder shafts 172 on the opposite side of the tool mount carriage 160. When the parts reach the retracted position illustrated in FIG. 15, one of the actuator pins 187 (or 189) will engage the switch lever 183, actuating the limit switch 182 to generate a signal. Preferably, the length of the slots 169 is such that this signal will be generated before the shoulder screw 185 bottoms out at the end of the slot 169. The signal generated by the switch 182 may be an alarm to provide an indication that the shaft 172 is near the end of its retraction travel, or may be coupled to the drive assembly 100 for automatically terminating the movement thereof which occasioned the retraction of the tool holder assembly 170, as will be discussed further below. The tool mount carriage 160 can simultaneously carry four different tools, a number of such tools useful for removing debris from a fuel assembly 30 being illustrated in FIGS. 16-23. In FIG. 16, there is illustrated a pick tool 200 (also indicated in FIG. 8), which includes an externally threaded mounting lug 201 adapted for threaded engagement in the axial bore 173 in any one of the tool holder shafts 172. Integral with the mounting lug 201 is an elongated rod or shaft 202 provided with a curved pick 203 at its distal end. This tool may be useful for picking lodged debris to free it from the fuel assembly 30. In FIG. 17, there is illustrated a water lance tool 210 which includes a mounting lug 211 for mounting on a tool holder shaft 172. Integral with the mounting lug 211 is an elbow fitting 212, one end of which is coupled to a water conduit 213, which is in turn coupled to an associated source of pressurized, demineralized water (not shown). The other arm of the elbow fitting 212 is coupled to a hollow lance tube 214, which has an elongated flattened portion 215 open at its distal end. It will be appreciated that water fed through the fitting 212 is expelled from the distal end of the lance tube 214 for dislodging debris or washing away loose debris. The pressure of the stream of water emitted from the lance tube 214 is increased by reason of the reduced cross-sectional area of the flattened portion 215. In FIGS. 18 and 19, there is illustrated a modified version of the water lance tool 210, wherein the distal end of the flattened portion 215 is welded or soldered shut, as at 216. The bottom of the flattened portion 215 is provided with an elongated opening 217 therein adjacent to the closed end 216. Thus, it will be appreciated that the water will be emitted through the opening 217 in a direction perpendicular to the longitudinal axis of the tool 210. In FIGS. 20 and 21, there is illustrated a brush tool 220 which includes an externally threaded mounting lug 221 for mounting to the associated tool holder shaft 172. The mounting lug 221 is provided with an axial slot 222 in its outer end, in which is received a shaft 223, which comprises an elongated flat strap folded back upon itself, as at a fold 224, the free folded-together ends being received in the slot 222 and fixedly secured to the mounting lug 221, as by welding. A plurality of elongated bristles 225, which may be formed of metal, are trapped between the folds of the shaft 223 adjacent to the distal end thereof, and may additionally be secured in place by a suitable epoxy adhesive. The folded halves of the shaft 223 are secured together by a plurality of spot welds 226 along the length thereof, the spot welds 226 also serving to secure the bristles 225 in place. Preferably, the bristles 225 have a length so that they can simultaneously brush the lower ends of the fuel rods 31 and the upper surface 39 of the fuel assembly bottom nozzle 38. In FIGS. 22 and 23, there is illustrated a tweezers tool 230, which is another modification of the water lance tool 210. More specifically, two pincer arms 234 and 235 are respectively fixedly secured, as by soldering or welding, to the opposite edges of the flattened portion 215 of the lance tube 214, adjacent to the distal end thereof. The pincer arms 234 and 235 are curved, so that their distal ends are disposed for opposing engagement with each other. Normally, the pincer arms 234 and 235 are biased so that the distal ends thereof are spread apart. Integral with the pincer arm 234 and projecting therefrom toward the pincer arm 235 is an inclined vane 236, which is disposed across the distal end of the lance tube 214 in the path of the jet of water emitted therefrom. When a stream of water is ejected from the lance tube 214, in strikes the vane 236, driving the pincer arm 234 upwardly to a closed condition, wherein its distal end is in clamping engagement with the distal end of the other pincer arm 235, as illustrated in FIG. 22. When the water jet is turned off, the tweezers tool 230 is reopened. It will be appreciated that this tool is useful for grasping particles of debris. The overall operation of the debris removal system 20 will now be explained. Initially, the work platform 40 is lowered into position in the spent fuel pool 21 on the racks 25, with the guide fixture 50 disposed in vertical alignment with a selected one of the fuel assembly racks 25. The support stand 60 is then lowered into position on the work platform 40, with the opening 69 in the deflector shield 67 disposed in vertical alignment with the guide fixture 50. Suitable locating pins (not shown) on the work platform 40 may be arranged to cooperate with the support stand 60 to facilitate accurate positioning thereof. The desired tools, such as tools 200, 210, 220 and 230, are respectively mounted in the tool holder assemblies 170 of the tool manipulation assembly 80. Then, the entire tool manipulation assembly 80 is lowered into position on the work platform 40, with the forward side of the support frame 81 facing the support stand 60, as illustrated in FIGS. 2 and 3, the locating pins 49 being receivable in complementary openings in the foot channels 85 to facilitate accurate positioning of the tool manipulation assembly 80. Preferably a suitable lifting tool (not shown) is provided for coupling to the support frame 81 for raising and lowering it. This tool will engage the lifting lugs 59 and 91 and has a nose portion which seats in the rig pad 92, securely to brace the lifting tool in position. All of the drive cylinders 95, 127 and 145 are hydraulic cylinders, which may be water driven, and it will be appreciated that before lowering of the tool manipulation assembly 80 into place, all of these drive cylinders are coupled by suitable elongated flexible conduits to an associated source of pressurized water or other suitable drive fluid. Preferably, these drive cylinders will be coupled through associated control valves located at a control console 240 (FIG. 3) disposed at a remote site. Similarly, it will be appreciated that the pressurized water supply is also coupled to the water conduits 213 of the tools 210 and 230 through suitable control valves (not shown), which are also controllable from the remote control site. The cabling for the video camera 135 and any associated lighting therefor will also be coupled to the necessary power and monitoring equipment, which is also located at the remote control console site. All of the necessary electrical and hydraulic connections between the tool manipulation assembly 80 and the control console 240 are diagrammatically designated at 239 in FIG. 3. When the debris removal system 20 has been mounted in place in the spent fuel pool 21, the fuel assembly 30 to be worked upon is lowered into position over the support stand 60. Generally, the greatest accumulation of debris will be at the lower end of the fuel assembly 30, specifically in the region between the bottom nozzle 38 and the first grid strap 35. Accordingly, the sliding support plate 70 is disposed in its supporting position covering the opening 69 in the deflector shield 67. The fuel assembly 30 is lowered until the bottom nozzle 38 thereof is disposed in its supported position, illustrated in FIG. 8, in engagement with the sliding support plate 70 and centered within the positioning corners 75. In this configuration, the fuel assembly 30 is lightly supported and stabilized by the sliding support plate 70, the primary support for the fuel assembly 30 still being provided by the overhead crane cable 237. Preferably, the parts of the debris removal system 20 are dimensioned so that when the fuel assembly 30 is seated on the sliding support plate 70, the upper surface 39 of the bottom nozzle 38 will be spaced above the deck 45 approximately the same distance as are the tool holder assembly shafts 172 when the drive assembly 100 is disposed in its lowest position, illustrated in FIG. 10, so that the tools 200-230 can reach as low as the upper surface 39. In a constructional model of the invention, the lift frame 101 is capable of approximately a 3-inch vertical travel in the "Z" direction, so that the tools 200-230 can be moved up substantially to the level of the first grid strap 35 when the fuel assembly 30 is seated on the sliding support plate 70. The lateral frame 120 is capable of approximately a 10-inch travel along the guide shafts 131 and 132 in the "X" direction, for moving the tool mount carriage 160 between the solid line position and the far right broken line position illustrated in FIG. 10. The longitudinal frame 150 is capable of an approximately 11 inch travel along the lateral frame 120 in the "Y" direction between the solid line and broken line positions illustrated in FIG. 11. The fuel assembly 30 is approximately 9 inches square in transverse cross section, and the proximity of the tool manipulation assembly 80 to the support stand 60 and the lengths of the tools 200-300 are such, that the tools 200-230 can reach transversely completely across the fuel assembly 30. It will be appreciated that the remote operator operates the drive cylinders 95 to effect vertical movement of the tools 200-230, operates the drive cylinder 127 to effect horizontal movement thereof in the "X" direction back and forth alongside the fuel assembly 30, and operates the drive cylinder 145 to effect horizontal movement of the tools 200-230 in the "Y" direction toward and away from the fuel assembly 30. The video camera 135 is oriented so as to afford the most complete view of the region of the fuel assembly 30 being worked on. Preferably, the camera 135 is arranged to provide a view of the entry into the fuel assembly 30 channel spaces between the fuel rods 31, and to see approximately 5 rods deep into the fuel assembly 30. Thus, since the fuel assembly 30 is greater than 5 rods deep, it will be appreciated that in order to obtain effective viewing of operation on all parts of the fuel assembly 30, it may be necessary to rotate the fuel assembly 30 to obtain a clear view of all sides thereof while they are being worked on. The water lance tools 210 are used to direct either horizontal or downward jets of water at debris particles to dislodge them. Such dislodged particles fall to the upper surface 39 of the bottom nozzle 38, from which they can be brushed by the use of the brush tool 220. The pick tool 200 is also useful for dislodging debris particles, and is particularly useful when debris is wrapped around a fuel rod 31 or grid element. Debris particles which are brushed off the bottom nozzle 38 fall onto the deflector shield 67, and are guided thereby outwardly beyond the perimeter of the support stand 60 and onto the deck 45. The peripheral flange 46 prevents debris from rolling off the edge of the deck 45. This debris can later be removed from the deck 45 by suitable cleaning equipment, either while the work platform is submerged or after it has been removed from the spent fuel pool 21. While most of the debris accumulates at the lower end of the fuel assembly 30, it may also be necessary to remove debris from upper portions of the fuel assembly 30. To permit access to these upper portions, the fuel assembly 30 is lifted slightly from the support stand 60, permitting the sliding support plate 70 to be slid back to its retracted position, illustrated in broken line in FIG. 7, for uncovering the opening 69 in the deflector shield 67. This movement of the sliding support plate 70 could be effected by a cable or the like secured thereto and operated remotely by suitable drive means (not shown). Once the sliding support plate 70 has been retracted, the fuel assembly 30 can be lowered through the opening 69 in the deflector shield 67, and through the guide fixture 50 into the underlying rack 25 the amount necessary to bring the portion of the fuel assembly 30 to be worked upon within reach of the tool manipulation assembly 80. It is an important aspect of the present invention that the tool manipulation assembly 80 is arranged so as effectively to prevent damage to the fuel assembly 30 during operation of the debris removal system 20. More particularly, the tool manipulation assembly 80 is designed to prevent any of the tools 200-230 from engaging the fuel assembly 30 with forces sufficient to damage it. This protection is achieved in several ways. First of all, the drive cylinders 95, 127 and 145 are arranged to limit the maximum motive forces which can be applied thereby to relatively small values. More particularly, the hydraulic pressure is preferably limited so that the forces applied thereby are limited to a few pounds, preferably less than 4 pounds for the horizontal movements. The vertical movement of the drive assembly 100 is counterbalanced by the counterweights 119, so that this movement also can be effected by the exertion of only a few pounds of force by the drive cylinders 95. To further ensure against the application of damaging forces to the fuel assembly 30, each of the tool holder assemblies 170 comprises a compliant or yieldable mounting for the associated tool which is designed to yield along the axis of the tool holder shafts 172 at a force below the minimum force necessary to damage the fuel assembly 30. This force is determined by the springs 175, which can be changed to set the limiting force as low as 2.5 pounds or as high as 10 pounds, depending upon the application. Referring in particular to FIGS. 11, 13 and 15, when a tool engages the fuel assembly 30 while being advanced forwardly in the "Y" direction by movement of the longitudinal frame 150 to the left, as viewed in FIG. 11, with a force greater than the biasing force of the spring 175, the spring 175 will yield and compress, allowing the tool holder shaft 172 to retract with respect to the tool mount carriage 160 from its normally extended condition, illustrated in FIG. 11, to a retracted condition, illustrated in solid line in FIG. 15. Thus, the tool will remain motionless with respect to the fuel assembly 30, while the tool mount carriage 160 continues to advance, preventing the force on the fuel assembly 30 from building up past the yield point of the spring 175. As the tool holder shaft 172 is retracted, the shoulder screw 185 moves the strap 184 (or 188) in a retracting direction (to the right, as viewed in FIG. 15) until the actuator pin 187 (or 189) engages the switch lever 183 for actuating the limit switch 182 to generate the alarm signal. Preferably, the length of the slot 169 in the turret plate arm 162 is such that when the switch 182 is actuated, there is still clearance between the shoulder screw 185 and the end of the slot 169 (see FIG. 15). This permits the advance of the longitudinal frame 150 to be terminated, either manually or automatically, before the shoulder screw 185 bottoms out in the slot 169, thereby ensuring that the force exerted on the fuel assembly 30 will not increase past the yield point of the spring 175. The longitudinal frame 150 can then be retracted and the drive assembly 100 repositioned to avoid the offending contact with the fuel assembly 30. Preferably, the plunger fittings 158 are also designed so that the tool mount carriage 160 can be rotated from one of its work configurations with the exertion of only a few pounds of force. Thus, in the event that the fuel assembly 30 should be side loaded by a tool, as during movement of the lateral frame 120 in the "X" direction, the tool mount carriage 160 can rotate to avoid overloading of the fuel assembly 30. It is another feature of the present invention that the tool mount carriage 160 can be selectively moved to place different tools into a work configuration, without having to remove the entire tool manipulation assembly 80 from the spent fuel pool 21. When it is desired to change the tool being used, the drive assembly 100 is operated to move the tool mount carriage 160 to the center position, illustrated in broken line in FIG. 10, wherein the hex stud 179 is positioned immediately beneath the funnel 93 in vertical alignment therewith. A suitable tool such as a lug wrench may then be lowered manually through the spent fuel pool 21, as with an elongated rod, for insertion through the funnel 93 and into engagement with the hex stud 179 to rotate the tool mount carriage 160. In this regard, the tool mount carriage 160 will tend to snap into each of its work configurations by engagement of the plunger pins 159 in the recesses 161a, so that the operator will be able to tell when the tool mount carriage is accurately positioned in a work configuration. It will also be appreciated that, if it is necessary to change the tools on the tool mount carriage 160, such as to provide a different set of tools for performing a different type of operation, or to replace damaged or worn tools or the like, this can be effected by removal of only the tool manipulation assembly 80 from the spend fuel pool 21, without having to disturb the support stand 60 or the work platform 40. In an operational model of the present invention, the support frame 81 is preferably formed of aluminum for light weight, while the remaining parts of the tool manipulation assembly 80, as well as the work platform 40 and the support stand 60, are preferably formed of stainless steel. the support frame 81 is approximately 3 feet long, by approximately 2 feet high, by approximately 11/2 feet wide, although it will be appreciated that the dimensions of the debris removal system 20 can be changed as needed, depending upon the particular application. While the debris removal system 20 has been described in connection with the removal of debris from a nuclear fuel assembly 30, it will be appreciated that it could be utilized for other purposes. Thus, other tools, such as various types of transducers or sensors, could be mounted on the tool mount carriage 160 for performing other operations, such as measurement, inspection, repair or the like, on the fuel assembly 30. Also, while the system 20 has been described for use in operating on a fuel assembly 30, it could be utilized in other applications in a nuclear fuel plant, such as for use in dissecting a rubbled core. From the foregoing, it can be seen that there has been provided an improved system for removing debris from a nuclear fuel assembly, the system permitting remote manipulation of a plurality of tools to minimize man-rem exposure, the system being characterized by the accurate manipulation of the tools with minimal forces and effectively preventing the application of damaging forces to the associated fuel assembly. |
056087683 | abstract | In a fuel bundle assembly for a nuclear reactor wherein a plurality of fuel rods and tie rods extend between upper and lower tie plates and wherein some of the fuel rods are partial length fuel rods extending between the lower tie plate and a spacer located between the upper and lower tie plates, an improved end plug is provided for at least each of the partial length fuel rods, each end plug secured between a respective partial length fuel rod and the lower tie plate. The end plug includes an upper portion constructed of a first alloy material and including an exterior fuel rod receiving surface and a tapped hole in a lower end thereof, and a lower portion constructed of a second alloy material and including upper and lower threaded sections, the upper threaded section receivable within the tapped hole and the lower threaded section receivable within a tapped hole in the lower tie plate. The threaded end plug may be used with full length fuel rods as well as bundle tie rods. A related method of removing the fuel rod with the improved end plug from the lower tie plate is also disclosed. |
description | This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-9552, filed on Jan. 23, 2017; the entire contents of which are incorporated herein by reference. Embodiments described herein relate generally to an X-ray diagnostic apparatus and a display method. In inspection using an X-ray diagnostic apparatus in the related art, there is a case of observing a region of interest with high-resolution while observing a wide region of a subject in bird's-eye view. In recent years, as the X-ray diagnostic apparatus used for such inspection, there is known an X-ray diagnostic apparatus including a detector that includes both of a first detector including a large visual field part employing a thin film transistor (TFT) array and a second detector the visual field of which is smaller than that of the first detector and the pixel pitch of which is fine, the second detector using a complementary metal oxide semiconductor (CMOS). In such an X-ray diagnostic apparatus, for example, the first detector and the second detector are used in a switching manner in accordance with use to display one of a first X-ray image based on a signal output from the first detector and a second X-ray image based on a signal output from the second detector. According to an embodiment, an X-ray diagnostic apparatus includes an X-ray tube, an X-ray collimator, an X-ray detector and processing circuitry. The X-ray tube is configured to radiate X-rays. The X-ray collimator is configured to adjust an irradiation region of the X-rays radiated by the X-ray tube. The X-ray detector includes a first detector and a second detector having a smaller detection area than a detection area of the first detector. The X-ray detector is configured to be able to detect the X-rays radiated by the X-ray tube with the first detector and the second detector at the same time. The processing circuitry is configured to generate a synthesized image obtained by synthesizing a first X-ray image generated based on an output from the first detector that detected the X-rays radiated in the irradiation region adjusted by the X-ray collimator, and a second X-ray image generated based on an output from the second detector that detected the X-rays radiated in the irradiation region adjusted, the synthesized image having an image size corresponding to an aspect ratio of the irradiation region. The processing circuitry is configured to cause a display to display the synthesized image. The following describes embodiments of an X-ray diagnostic apparatus and a display method in detail with reference to the attached drawings. The X-ray diagnostic apparatus and the display method according to the present application are not limited to the following embodiments. First, the following describes the entire structure of an X-ray diagnostic apparatus according to a first embodiment. FIG. 1 is a diagram illustrating a configuration example of an X-ray diagnostic apparatus 100 according to the first embodiment. As illustrated in FIG. 1, the X-ray diagnostic apparatus 100 according to the first embodiment includes a high voltage generator 11, an X-ray tube 12, an X-ray collimator 13, a tabletop 14, a C-arm 15, an X-ray detector 16, a C-arm rotating/moving mechanism 17, a tabletop moving mechanism 18, C-arm/tabletop mechanism control circuitry 19, collimator control circuitry 20, processing circuitry 21, an input interface 22, a display 23, image data generation circuitry 24, a storage 25, and image processing circuitry 26. In the X-ray diagnostic apparatus 100 illustrated in FIG. 1, each processing function is stored in the storage 25 as a computer-executable program. Each of the C-arm/tabletop mechanism control circuitry 19, the collimator control circuitry 20, the processing circuitry 21, the image data generation circuitry 24, and the image processing circuitry 26 is a processor that implements a function corresponding to each program by reading out and executing the program from the storage 25. In other words, each circuitry that has read out each program has a function corresponding to the program that has been read out. The word “processor” used in the above description means, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a circuit such as an application specific integrated circuit (ASIC) and a programmable logic device (for example, a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA)). The processor reads out and executes the program stored in the storage to implement the function. Instead of storing the program in the storage, the program may be directly embedded in the circuit of the processor. In this case, the processor implements the function by reading out and executing the program embedded in the circuit. Each processor according to the embodiment is not necessarily configured as a single circuit. Alternatively, a plurality of independent circuits may be combined to be one processor to implement the function. The high voltage generator 11 generates high voltage under control by the processing circuitry 21, and supplies the generated high voltage to the X-ray tube 12. The X-ray tube 12 generates X-rays using the high voltage supplied from the high voltage generator 11. The X-ray collimator 13 narrows the X-rays generated by the X-ray tube 12 to be selectively emitted to a region of interest of a subject P under control by the collimator control circuitry 20. For example, the X-ray collimator 13 includes four slidable collimator blades. The X-ray collimator 13 causes these collimator blades to slide to narrow the X-rays generated by the X-ray tube 12 to be emitted to the subject P under control by the collimator control circuitry 20. The X-ray collimator 13 includes an additional filter for adjusting radiation quality. For example, the additional filter is set in accordance with inspection. The tabletop 14 is a bed on which the subject P is placed, and is arranged on a couch (not illustrated). The subject P is not included in the X-ray diagnostic apparatus 100. The X-ray detector 16 detects the X-rays transmitted through the subject P. For example, the X-ray detector 16 includes detection elements arranged in a matrix. Each detection element converts the X-rays transmitted through the subject P into electric signals to be accumulated, and transmits the accumulated electric signals to the image data generation circuitry 24. The X-ray detector 16 according to the present embodiment includes two detectors having different pixel pitches. FIGS. 2A and 2B are diagrams illustrating a configuration example of the X-ray detector 16 according to the first embodiment. FIG. 2A illustrates a vertical cross-sectional view of the X-ray detector 16. FIG. 2B illustrates a top view of the X-ray detector 16. For example, as illustrated in FIG. 2A, the X-ray detector 16 includes a first photodetector 16a, a second photodetector 16b, and a scintillator 16c. The first detector is constituted of the first photodetector 16a and the scintillator 16c, and the second detector is constituted of the second photodetector 16b and the scintillator 16c. The scintillator 16c converts the X-rays emitted from the X-ray tube 12 into light. The first photodetector 16a includes, for example, a two-dimensional image sensor employing a thin film transistor (TFT) array made of amorphous silicon, and detects the light converted by the scintillator 16c to output an electric signal. The second photodetector 16b includes, for example, a two-dimensional image sensor employing a complementary metal oxide semiconductor (CMOS) transistor, and detects the light converted by the scintillator 16c to output the electric signal. Hereinafter, the electric signal output by the first photodetector 16a is referred to as a first electric signal, and the electric signal output by the second photodetector 16b is referred to as a second electric signal. In this way, the scintillator 16c is shared by the first photodetector 16a and the second photodetector 16b. In other words, the X-ray detector 16 includes the scintillator 16c that converts the X-rays emitted from the X-ray tube 12 into light, and the first photodetector 16a and the second photodetector 16b that share the scintillator 16c and detect the light converted by the scintillator 16c to output the electric signal. Each of the first photodetector 16a and the second photodetector 16b outputs the electric signal obtained by detecting the light converted by the scintillator 16c at the same time. As illustrated in FIG. 2A, the first photodetector 16a and the second photodetector 16b include a plurality of elements as constituent units of pixels. Each of the elements converts a fluorescent image obtained through X-ray incidence into an electric signal to be accumulated in a photo diode (PD). FIG. 2A exemplifies a case in which the first photodetector 16a includes eight elements in one column and the second photodetector 16b includes eight elements in one column. The pixel pitch of the elements of the second photodetector 16b is finer than the pixel pitch of the elements of the first photodetector 16a. In the example illustrated in FIG. 2A, the pixel pitch of each of the elements of the first photodetector 16a corresponds to the pixel pitch of two elements of the second photodetector 16b. That is, on an XY-plane of the X-ray detector 16, one element of the first photodetector 16a corresponds to four elements of the second photodetector 16b. Thus, resolution of the second photodetector 16b is higher than that of the first photodetector 16a. As illustrated in FIG. 2B, a visual field size of the first photodetector 16a is larger than that of the second photodetector 16b. That is, as illustrated in FIG. 2B, the second photodetector 16b has a size to be overlapped with part of a detection area of the first photodetector 16a. Thus, the second photodetector 16b collects high-resolution X-ray image data in the region overlapping with the first photodetector 16a. In the X-ray diagnostic apparatus 100, the X-ray collimator 13 includes four collimator blades, and these collimator blades are slid under control by the collimator control circuitry 20. For example, in the X-ray diagnostic apparatus 100, as illustrated in FIG. 2B, the X-ray collimator 13 includes collimator blades 13a to 13d. The collimator blade 13a is arranged in parallel with one side of the first photodetector 16a and the second photodetector 16b, and is slid in a direction of a double-headed arrow 51 to adjust an X-ray irradiation region. The collimator blade 13b is arranged in parallel with one side of the first photodetector 16a and the second photodetector 16b and in parallel with the collimator blade 13a, and is slid in a direction of a double-headed arrow 52 to adjust the X-ray irradiation region. The collimator blade 13c is arranged in parallel with one side of the first photodetector 16a and the second photodetector 16b and in a direction orthogonal to the collimator blade 13a and the collimator blade 13b, and is slid in a direction of a double-headed arrow 53 to adjust the X-ray irradiation region. The collimator blade 13d is arranged in parallel with one side of the first photodetector 16a and the second photodetector 16b and in parallel with the collimator blade 13c, and is slid in a direction of a double-headed arrow 54 to adjust the X-ray irradiation region. Detection sensitivity of the first photodetector 16a is higher than that of the second photodetector 16b. In the second photodetector 16b employing the CMOS, a maximum X-ray incident amount tends to be smaller than that of the first photodetector 16a employing the amorphous silicon. Thus, in the second photodetector 16b, a dynamic range is lowered in a case of emitting high-dose of X-rays and collecting X-ray image data having a high signal to noise (S/N) ratio. In the second photodetector 16b, an amount of residual components of the electric signal is smaller than that of the first photodetector 16a. In the first photodetector 16a, a generated electric charge is trapped at a trap level within the photo diode. On the other hand, in the second photodetector 16b, the electric charge generated in the photo diode is less trapped in the CMOS due to a characteristic thereof. Returning to FIG. 1, the C-arm 15 holds the X-ray tube 12, the X-ray collimator 13, and the X-ray detector 16. The C-arm 15 rotates around the subject P lying on the tabletop 14 at high speed like a propeller by a motor arranged in a supporting part (not illustrated). The C-arm 15 is supported to be rotatable about each of XYZ-axes, that is, three axes orthogonal to each other, and individually rotates about each axis by a driving unit (not illustrated). The X-ray tube 12 and the X-ray collimator 13 are arranged to be opposed to the X-ray detector 16 across the subject P with the C-arm 15. FIG. 1 exemplifies a case in which the X-ray diagnostic apparatus 100 is a single plane, but the embodiment is not limited thereto. Alternatively, the X-ray diagnostic apparatus 100 may be a biplane. The C-arm rotating/moving mechanism 17 is a mechanism for rotating and moving the C-arm 15. The C-arm rotating/moving mechanism 17 can also change a source image receptor distance (SID) as a distance between the X-ray tube 12 and the X-ray detector 16. The C-arm rotating/moving mechanism 17 can also rotate the X-ray detector 16 held by the C-arm 15. The tabletop moving mechanism 18 is a mechanism for moving the tabletop 14. The C-arm/tabletop mechanism control circuitry 19 adjusts rotation or movement of the C-arm 15, and movement of the tabletop 14 by controlling the C-arm rotating/moving mechanism 17 and the tabletop moving mechanism 18 under control by the processing circuitry 21. For example, the C-arm/tabletop mechanism control circuitry 19 controls rotatography for collecting projection data at a predetermined frame rate while rotating the C-arm 15 under control by the processing circuitry 21. The collimator control circuitry 20 controls an irradiation region of X-rays emitted to the subject P by adjusting an aperture of the collimator blade included in the X-ray collimator 13 under control by the processing circuitry 21. The image data generation circuitry 24 generates projection data using the electric signal converted from the X-ray by the X-ray detector 16, and stores the generated projection data in the storage 25. Specifically, the image data generation circuitry 24 generates first projection data from the first electric signal output by the first photodetector 16a, generates second projection data from the second electric signal output by the second photodetector 16b, and stores each piece of the generated projection data in the storage 25. For example, the image data generation circuitry 24 performs current/voltage conversion, analog (A)/digital (D) conversion, and parallel/serial conversion on the first electric signal and the second electric signal received from the X-ray detector 16, and generates the first projection data based on the first electric signal and the second projection data based on the second electric signal. The image data generation circuitry 24 stores the generated first projection data and second projection data in the storage 25. The storage 25 receives and stores the projection data generated by the image data generation circuitry 24. For example, the storage 25 stores the first projection data based on the first electric signal and the second projection data based on the second electric signal. The storage 25 also stores volume data and an X-ray image generated by the image processing circuitry 26. The storage 25 stores a synthesized image synthesized by the processing circuitry 21. Details about the synthesized image will be described later. The storage 25 stores the programs corresponding to various functions that are read out and executed by the respective circuitry illustrated in FIG. 1. By way of example, the storage 25 stores the program corresponding to a synthesizing function 211 and the program corresponding to a control function 212 that are read out and executed by the processing circuitry 21. The image processing circuitry 26 generates an X-ray image by performing various pieces of image processing on the projection data stored in the storage 25 under control by the processing circuitry 21 described later. Alternatively, the image processing circuitry 26 directly acquires the projection data from the image data generation circuitry 24 under control by the processing circuitry 21 described later, and generates the X-ray image by performing various pieces of image processing on the acquired projection data. For example, the image processing circuitry 26 generates the first X-ray image by performing image processing on the first projection data based on the first electric signal. The image processing circuitry 26 generates the second X-ray image by performing image processing on the second projection data based on the second electric signal. The image processing circuitry 26 can store the X-ray image after image processing in the storage 25. For example, the image processing circuitry 26 can perform various pieces of processing using an image processing filter such as a moving-average (smoothing) filter, a Gaussian filter, a median filter, a recursive filter, and a band-pass filter. The image processing circuitry 26 reconstructs reconstruction data (volume data) from the projection data collected through rotatography. For example, the image processing circuitry 26 reconstructs first reconstruction data from the first projection data collected through rotatography. The image processing circuitry 26 reconstructs second reconstruction data from the second projection data collected through rotatography. The image processing circuitry 26 stores the reconstructed volume data in the storage 25. The image processing circuitry 26 generates a three-dimensional image from the volume data. For example, the image processing circuitry 26 generates a volume rendering image and a multi planar reconstruction (MPR) image from the volume data. The image processing circuitry 26 then stores the generated three-dimensional image in the storage 25. The input interface 22 is implemented by a trackball, a switch button, a mouse, a keyboard, and the like for performing setting for a predetermined region (for example, a noticed region such as a region of interest), and a foot switch for emitting X-rays, for example. The input interface 22 is connected to the processing circuitry 21, and converts an input operation received from an operator into the electric signal to be output to the processing circuitry 21. The display 23 displays a graphical user interface (GUI) for receiving an instruction from the operator, various images generated by the image processing circuitry 26, and a synthesized image synthesized by the processing circuitry 21. The processing circuitry 21 controls the operation of the entire X-ray diagnostic apparatus 100. Specifically, the processing circuitry 21 reads out, from the storage 25, the program corresponding to the control function 212 for controlling the entire device to be executed to perform various pieces of processing. For example, the control function 212 controls the high voltage generator 11 in accordance with an instruction from the operator transferred from the input interface 22 and adjusts voltage to be supplied to the X-ray tube 12 to control ON/OFF and an amount of X-rays to be emitted to the subject P. For example, the control function 212 controls the C-arm/tabletop mechanism control circuitry 19 in accordance with the instruction from the operator, and adjusts rotation or movement of the C-arm 15, and movement of the tabletop 14. For example, the control function 212 controls the collimator control circuitry 20 in accordance with the instruction from the operator and adjusts apertures of the collimator blades 13a to 13d included in the X-ray collimator 13 to control the irradiation region of the X-rays emitted to the subject P. The control function 212 controls image data generation processing performed by the image data generation circuitry 24, image processing performed by the image processing circuitry 26, analysis processing, or the like in accordance with the instruction from the operator. The control function 212 controls the display 23 to display a GUI for receiving the instruction from the operator, an image stored in the storage 25, and the like. As illustrated in FIG. 1, the processing circuitry 21 according to the first embodiment executes the synthesizing function 211 in addition to the control function 212 described above. Details about the synthesizing function 211 will be described later. The processing circuitry 21 is an example of processing circuitry according to claims. The entire structure of the X-ray diagnostic apparatus 100 has been described above. With this configuration, the X-ray diagnostic apparatus 100 according to the present embodiment enables efficiency of inspection to be improved. Specifically, the X-ray diagnostic apparatus 100 enables the X-ray image of a wide region to be observed, and enables a more noticed region to be observed as a high-definition X-ray image by compensating for a region other than a region of a high-definition second X-ray image collected by the second photodetector 16b with the first X-ray image collected by the first photodetector 16a in collecting the X-ray image using the first photodetector 16a having a large visual field size and the second photodetector 16b with high resolution (high definition). For example, in inspection using the X-ray detector 16 illustrated in FIG. 2B, there may be a case in which a wide region of the subject is first observed in bird's-eye view through the first X-ray image of a wide region collected by the first photodetector 16a, and a region of interest is observed with high-resolution through the high-definition second X-ray image collected by the second photodetector 16b. By way of example, in a case of giving coil embolization treatment for a cerebral aneurysm, the first X-ray image of a wide region is observed when a catheter is inserted from an artery of a groin to be guided to a cerebral artery, and the high-definition second X-ray image is observed when the cerebral aneurysm is embolized with a coil. The detection area of the high-resolution second photodetector 16b is small, so that the region of interest does not entirely fall within the detection area in some cases. In this case, typically, the first X-ray image of a wide region (the X-ray image photographed in the detection area of the first photodetector 16a) and the high-definition second X-ray image (the X-ray image photographed in the detection area of the second photodetector 16b) are alternately checked. However, it is complicated to alternately check the first X-ray image of a wide region and the high-definition second X-ray image, and there may be the problem that the X-rays are emitted to an unnecessarily wide region and radiation exposure may be increased. The X-ray diagnostic apparatus 100 then partially widens a photographing range so as to accommodate the entire region of interest in photographing the high-definition second X-ray image, and synthesizes the first image photographed by the first photodetector 16a and the second X-ray image photographed by the second photodetector 16b to be displayed. Accordingly, all regions of interest can be displayed at the same time, and efficiency of inspection can be improved. Additionally, increase in radiation exposure can be reduced. The following describes an example of processing performed by the X-ray diagnostic apparatus 100 according to the first embodiment. The synthesizing function 211 according to the first embodiment generates a synthesized image obtained by synthesizing the first X-ray image generated from the electric signal output from the first photodetector 16a based on the X-rays emitted in the irradiation region after being adjusted by the X-ray collimator 13 and the second X-ray image generated from the electric signal output from the second photodetector 16b based on the X-rays emitted in the irradiation region after being adjusted while matching image sizes thereof. First, in the X-ray diagnostic apparatus 100, an instruction for adjusting the X-ray irradiation region is received via the input interface 22. That is, the input interface 22 receives the operation of designating the X-ray irradiation region with the collimator blades 13a to 13d of the X-ray collimator 13. FIG. 3 is a diagram illustrating an example of the operation of designating the X-ray irradiation region according to the first embodiment. For example, the input interface 22 receives an operation of sliding the collimator blades 13a to 13d illustrated in the upper diagram of FIG. 3. The operation of designating the X-ray irradiation region can be executed through an optional operation. For example, the control function 212 causes the display 23 to display a perspective image collected by the second photodetector 16b and a GUI for moving the collimator blades 13a to 13d, and the input interface 22 receives the operation of sliding the collimator blades 13a to 13d. By way of example, as illustrated in the upper diagram of FIG. 3, the control function 212 causes the GUI to be displayed, the GUI indicating the collimator blades 13a to 13d along respective sides of the high-definition X-ray image (perspective image) collected by the second photodetector 16b. The input interface 22 receives a slide operation for the collimator blades 13a to 13d displayed along the perspective image. For example, as illustrated in a lower diagram of FIG. 3, the input interface 22 receives an operation of sliding the collimator blade 13a in a direction of an arrow 55 and an operation of sliding the collimator blade 13d in a direction of an arrow 56. Accordingly, for example, an X-ray image including a region 60 and the like other than the second X-ray image can be collected. Accordingly, for example, an X-ray image including a region 60 and the like other than the second X-ray image can be collected. That is, in the X-ray diagnostic apparatus 100, the image data generation circuitry 24 generates the second projection data from the second electric signal detected in the detection area of the second photodetector 16b, and the image processing circuitry 26 generates the second X-ray image from the second projection data. In the X-ray diagnostic apparatus 100, at the same time, the image data generation circuitry 24 generates the first projection data from the first electric signal detected in the region surrounded by the collimator blades 13a to 13d, and the image processing circuitry 26 generates the first X-ray image from the first projection data. The synthesizing function 211 generates a synthesized image obtained by synthesizing the first X-ray image and the second X-ray image generated by the image processing circuitry 26. Specifically, the synthesizing function 211 generates the synthesized image obtained by synthesizing the first X-ray image and the second X-ray image while matching the image sizes thereof. As described above, the first photodetector 16a and the second photodetector 16b in the X-ray detector 16 have different pixel pitches (resolution). Thus, when they are simply synthesized, the image sizes are mismatched. Thus, the synthesizing function 211 adjusts the image sizes of the first X-ray image and the second X-ray image based on the pixel pitch of the first photodetector 16a and the pixel pitch of the second photodetector 16b. That is, the synthesizing function 211 adjusts the image sizes of the first X-ray image and the second X-ray image so that the subject in the first X-ray image and the subject in the second X-ray image are displayed in the same ratio when being displayed on the display 23. FIGS. 4 and 5 are diagrams for explaining an example of processing performed by the synthesizing function 211 according to the first embodiment. For example, as illustrated in FIG. 4, when the image processing circuitry 26 generates a first X-ray image I1 and a second X-ray image I2, the synthesizing function 211 generates the synthesized image in which the subject in the first X-ray image and the subject in the second X-ray image are displayed in the same ratio. The synthesizing function 211 determines a side serving as a reference of the image size of the synthesized image in accordance with an aspect ratio of the X-ray irradiation region, and changes the image sizes of the first X-ray image I1 and the second X-ray image I2 in accordance with a length of the determined side. That is, the synthesizing function 211 determines the image sizes based on the X-ray irradiation region received via the input interface 22. In this case, first, the synthesizing function 211 acquires positional information of the collimator blades 13a to 13d that are slidingly moved by being controlled by the collimator control circuitry 20, and calculates the X-ray irradiation region based on the acquired positional information. For example, the synthesizing function 211 calculates the X-ray irradiation region surrounded by the collimator blades based on the positional information of the collimator blades 13a to 13d in the lower diagram of FIG. 3. The synthesizing function 211 determines a side serving as a reference of the image size in the calculated X-ray irradiation region. Specifically, the synthesizing function 211 determines a long side of the X-ray irradiation region to be a side serving as a reference of the image size. For example, the synthesizing function 211 determines, to be a side serving as a reference of the image size, the long side of the X-ray irradiation region (a side in a vertical direction in the drawing) illustrated as a rectangle in FIG. 3. The synthesizing function 211 then changes the image sizes of the first X-ray image I1 and the second X-ray image I2 so that the length of the side serving as a reference of the image size of the synthesized image is matched with the length of a corresponding side of a display region of the synthesized image on the display 23. For example, as illustrated in FIG. 5, when the display 23 includes two displays including a first display having a display region R1 and a second display having a display region R2, and causes the first display to display the synthesized image, the synthesizing function 211 adjusts the image size so that the size of the synthesized image is matched with the display region of the synthesized image in a display region R1 of the first display. For example, in a case of displaying the synthesized image in the entire display region R1 of the first display, the synthesizing function 211 changes the image size so that the length of the side serving as a reference is matched with a corresponding side of the display region R1. That is, the synthesizing function 211 changes the image size of the synthesized image so that the length of the long side of the synthesized image (a side in the vertical direction in the drawing) is matched with the length of a corresponding side of the display region R1 (a side in the vertical direction in the drawing). For example, the synthesizing function 211 magnifies the first X-ray image I1 as an image corresponding to the side serving as a reference to be displayed being matched with upper and lower sides of the display region R1. That is, the synthesizing function 211 changes the image size of the first X-ray image I1 so that the long side of the first X-ray image I1 is displayed being matched with the upper and lower sides of the display region R1. That is, the synthesizing function 211 changes the image size of the first X-ray image I1 so that a pixel on the long side of the first X-ray image I1 is assigned to a pixel in the vertical direction of the display region R1 of the display 23. The synthesizing function 211 then changes the image size of the second X-ray image I2 so that the subject in the second X-ray image I2 and the subject in the magnified first X-ray image I1 are displayed in the same ratio. That is, the synthesizing function 211 assigns a pixel in the second X-ray image I2 to a pixel in the display region R1 so that the ratio of the subject becomes the same as the ratio of the subject in the magnified first X-ray image I1. Returning to FIG. 1, the control function 212 causes the display 23 to display the synthesized image. For example, the control function 212 causes the synthesized image of the first X-ray image I1 and the second X-ray image I2 to be displayed in the display region R1 of the first display of the display 23. Accordingly, the observer can observe the entire region of interest at the same time, and the efficiency of inspection can be improved. In the above example, exemplified is a case in which one first X-ray image I1 and one second X-ray image I2 are collected to be synthesized. Also in a case of a moving image such as a perspective image, the synthesized image is similarly generated as described above. That is, the synthesizing function 211 generates a plurality of synthesized images from a plurality of first X-ray images I1 collected at a first frame rate and a plurality of second X-ray images I2 collected at a second frame rate. When the first frame rate is the same as the second frame rate, the synthesizing function 211 sequentially generates the synthesized image with the first X-ray image I1 and the second X-ray image I2 that are collected at the same time. On the other hand, when the first frame rate is different from the second frame rate, the synthesizing function 211 generates the synthesized image in accordance with a higher one thereof. By way of example, when the second frame rate is twice the first frame rate, the synthesizing function 211 assigns the same first X-ray image I1 to successive two frames in the second X-ray image I2 that is sequentially collected to generate the synthesized image. That is, the synthesizing function 211 sequentially assigns one frame of the first X-ray image I1 that is sequentially collected for every two successive frames in the second X-ray image I2 that is sequentially collected, and sequentially generates the synthesized image. The control function 212 causes a plurality of synthesized images that are sequentially generated to be displayed in the display region R1 of the display 23 in a time series manner to display a moving image. In the embodiments described above, exemplified is a case in which the long side of the X-ray irradiation region is along the vertical direction. However, the embodiment is not limited thereto. For example, when the long side of the X-ray irradiation region is along a horizontal direction, the side serving as a reference of the image size becomes a side along the horizontal direction. Next, the following describes processing performed by the X-ray diagnostic apparatus 100 according to the first embodiment with reference to FIG. 6. FIG. 6 is a flowchart illustrating a processing procedure of the X-ray diagnostic apparatus 100 according to the first embodiment. Steps S101, S102, and S105 illustrated in FIG. 6 are steps at which the processing circuitry 21 reads out, from the storage 25, the program corresponding to the control function 212 to be executed. Steps S103 and S104 are steps at which the processing circuitry 21 reads out, from the storage 25, the program corresponding to the synthesizing function 211 to be executed. At Step S101, the processing circuitry 21 controls the X-ray collimator 13 to adjust the X-ray irradiation region. At Step S102, the processing circuitry 21 collects the first X-ray image and the second X-ray image. At Step S103, the processing circuitry 21 determines the side serving as a reference of the image size in accordance with the aspect ratio of the X-ray irradiation region. At Step S104, the processing circuitry 21 changes the image sizes of the first X-ray image and the second X-ray image so that the length of the side serving as a reference is matched with the length of a corresponding side of the display region, and generates the synthesized image. At Step S105, the processing circuitry 21 causes the display 23 to display the generated synthesized image. As described above, according to the first embodiment, the X-ray collimator 13 adjusts the irradiation region of the X-rays generated by the X-ray tube 12. The X-ray detector 16 includes the scintillator 16c that converts the X-rays emitted from the X-ray tube 12 into light, and the first photodetector 16a and the second photodetector 16b that share the scintillator 16c and detect the light converted by the scintillator 16c to output the electric signal. The synthesizing function 211 generates the synthesized image obtained by synthesizing the first X-ray image generated from the electric signal output from the first photodetector 16a based on the X-rays emitted in the irradiation region after adjustment by the X-ray collimator 13, and the second X-ray image generated from the electric signal output from the second photodetector 16b based on the X-rays emitted in the irradiation region after adjustment while matching the image sizes thereof with each other. The control function 212 causes the display 23 to display the synthesized image. Thus, the X-ray diagnostic apparatus 100 according to the first embodiment can cause the X-ray image including the entire region of interest to be displayed, and can improve efficiency of inspection. The X-ray diagnostic apparatus 100 according to the first embodiment can suppress increase in radiation exposure by emitting the X-rays only to the region of interest. According to the first embodiment, the synthesizing function 211 determines the side serving as a reference of the image size of the synthesized image in accordance with the aspect ratio of the irradiation region, and changes the image size of the first X-ray image and the second X-ray image in accordance with the length of the determined side. Accordingly, the X-ray diagnostic apparatus 100 according to the first embodiment enables the synthesized image to be generated considering a display size. According to the first embodiment, the synthesizing function 211 determines the long side of the irradiation region to be the side serving as a reference of the image size. Accordingly, the X-ray diagnostic apparatus 100 according to the first embodiment enables the image size to be determined considering a maximum size of the X-ray image. According to the first embodiment, the synthesizing function 211 changes the image sizes of the first X-ray image and the second X-ray image so that the length of the side serving as a reference of the image size of the synthesized image is matched with the length of a corresponding side of the display region of the synthesized image on the display 23. Accordingly, the X-ray diagnostic apparatus 100 according to the first embodiment can generate the synthesized image matched with the display region of the display 23, and enables an image suitable for observation to be displayed. Next, the following describes a second embodiment. The configuration of the X-ray diagnostic apparatus 100 according to the present embodiment is basically the same as the configuration of the X-ray diagnostic apparatus 100 illustrated in FIG. 1. Thus, the following mainly describes differences from the X-ray diagnostic apparatus 100 according to the first embodiment. A component having the same function as that of the component illustrated in FIG. 1 is denoted by the same reference numeral, and redundant description will not be repeated. In the first embodiment described above, described is a case of displaying the synthesized image on a two-screen monitor (a monitor of a normal size). The second embodiment describes a case of displaying the synthesized image on a large-screen monitor. The synthesizing function 211 according to the second embodiment determines the image size of the synthesized image in accordance with the X-ray irradiation region. In a case of displaying the synthesized image on the large-screen monitor, the control function 212 according to the second embodiment changes the display region of the synthesized image on the display 23. Specifically, the control function 212 changes the size of the display region of the synthesized image on the display 23 in accordance with the X-ray irradiation region, and displays the synthesized image generated by the synthesizing function 211 in the changed display region. FIG. 7 is a diagram for explaining an example of processing performed by the control function 212 according to the second embodiment. For example, as illustrated in the upper diagram of FIG. 7, the display 23 is a large screen, and an overall display region R10 includes a region R11 for displaying the synthesized image, a region R12 for displaying a reference image, a region R13 for displaying a polygraph, a region R14 for displaying a Dose Tracking System (DTS), a region R15 for displaying a road map, and a region R16 for displaying a photographed image. For example, the control function 212 changes the size of the region R11 in accordance with the X-ray irradiation region. By way of example, the control function 212 magnifies the region R11 as illustrated in the lower diagram of FIG. 7. The control function 212 changes at least one of the size and the position of the display region for displaying a display target other than the synthesized image on the display 23 to change the size of the region R11 for the synthesized image, and causes the synthesized image to be displayed in the changed region R11. For example, as illustrated in the lower diagram of FIG. 7, the control function 212 reduces the size of the regions R12 to R16 and changes placement thereof to secure a space for magnifying the region R11, and magnifies the region R11 utilizing the secured space. The synthesizing function 211 generates the synthesized image matched with the size of the region R11 magnified by the control function 212. For example, the synthesizing function 211 magnifies the first X-ray image I1 to be matched with the second X-ray image I2 while keeping the display size of the high-definition second X-ray image I2 as much as possible. That is, the control function 212 changes the size of the display region so that the size of the second X-ray image I2 on the display 23 is kept to be substantially constant. Accordingly, when the display 23 has a large screen, the control function 212 can cause the entire region of interest to be displayed while causing the high-definition second X-ray image I2 to be displayed larger. Thus, in changing the display region of the synthesized image, the control function 212 acquires the size of the first X-ray image and the second X-ray image from the X-ray irradiation region, and changes the size and the placement of the display region while displaying the acquired size to be maximum so that the region for the other display target is not smaller than a required size. Next, the following describes processing performed by the X-ray diagnostic apparatus 100 according to the second embodiment with reference to FIG. 8. FIG. 8 is a flowchart illustrating a processing procedure of the X-ray diagnostic apparatus 100 according to the second embodiment. Steps S201, S202, S204, and S205 illustrated in FIG. 8 are steps at which the processing circuitry 21 reads out, from the storage 25, the program corresponding to the control function 212 to be executed. Step S203 is a step at which the processing circuitry 21 reads out, from the storage 25, the program corresponding to the synthesizing function 211 to be executed. At Step S201, the processing circuitry 21 controls the X-ray collimator 13 to adjust the X-ray irradiation region. At Step S202, the processing circuitry 21 collects the first X-ray image and the second X-ray image. At Step S203, the processing circuitry 21 changes the image sizes of the first X-ray image and the second X-ray image in accordance with the X-ray irradiation region. At Step S204, the processing circuitry 21 changes the display region of the display 23 in accordance with the image size of the synthesized image. At Step S205, the processing circuitry 21 causes the display 23 to display the generated synthesized image. As described above, according to the second embodiment, the synthesizing function 211 determines the image size of the synthesized image in accordance with the irradiation region. The control function 212 changes the size of the display region of the synthesized image on the display 23 in accordance with the irradiation region, and causes the synthesized image generated by the synthesizing function 211 to be displayed in the changed display region. Accordingly, the X-ray diagnostic apparatus 100 according to the first embodiment enables the entire region of interest to be displayed while causing the high-definition second X-ray image I2 to be displayed larger. According to the second embodiment, the control function 212 changes at least one of the size and the position of the display region for displaying a display target other than the synthesized image on the display 23 to change the size of the display region of the synthesized image, and causes the synthesized image to be displayed in the changed display region. Thus, the X-ray diagnostic apparatus 100 according to the first embodiment enables the synthesized image to be displayed in a larger region. As a result, the entire region of interest is enabled to be displayed larger while causing the high-definition second X-ray image I2 to be displayed larger. The first and the second embodiments have been described above, but various different embodiments may be implemented in addition to the first and the second embodiments. The components of the devices illustrated in the drawings of the first and the second embodiments are merely conceptual, and it is not required that it is physically configured as illustrated necessarily. That is, specific forms of distribution and integration of the devices are not limited to those illustrated in the drawings. All or part thereof may be functionally or physically distributed/integrated in arbitrary units depending on various loads or usage states. All or any part of processing functions executed by the respective devices may be implemented by a CPU and a program that is analyzed and executed by the CPU, or may be implemented as hardware using wired logic. The display method described in the above embodiments can be implemented by executing the control program prepared in advance by a computer such as a personal computer and a workstation. The display program may be distributed via a network such as the Internet. The control program may be recorded in a computer-readable recording medium such as a hard disk, a flexible disk (FD), a CD-ROM, an MO, and a DVD, and may be executed by being read out from the recording medium by the computer. As described above, according to at least one of the embodiments, efficiency of inspection can be improved. While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. |
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abstract | A charged-particle multi-beam exposure apparatus (1) for exposure of a target (41) uses a plurality of beams of electrically charged particles, which propagate along parallel beam paths towards the target (41). For each particle beam an illumination system (10), a pattern definition means (20) and a projection optics system (30) are provided. The illuminating system (10) and/or the projection optics system (30) comprise particle-optical lenses having lens elements (L1, L2, L3, L4, L5) common to more than one particle beam. The pattern definition means (20) defines a multitude of beamlets in the respective particle beam, forming its shape into a desired pattern which is projected onto the target (41), by allowing it to pass only through a plurality of apertures defining the shape of beamlets permeating said apertures, and further comprises a blanking means to switch off the passage of selected beamlets from the respective paths of the beamlets. |
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claims | 1. A wall segment ( 10 ) for a device enclosing a work zone to protect against laser beams of a laser source ( 38 ), the wall segment ( 10 ) comprising an inner wall ( 12 ) adjacent to the work zone and an outer wall ( 14 ) substantially parallel to the inner wall ( 12 ) and further away from the work zone than the inner wall ( 12 ), characterized in that the inner wall ( 12 ) and the outer wall ( 14 ) are both metallic sheet metal, the inner wall ( 12 ) is provided with a coating ( 16 ) at least on a side surface of the inner wall ( 12 ) facing the work zone, and a side surface of the outer wall ( 14 ) facing the inner wall ( 12 ) being of lesser absorption capability with respect to laser radiation than the coating ( 16 ). 2. The wall segment as claimed in claim 1 , characterized in that the coating ( 16 ) is black paint. claim 1 3. The wall segment as claimed claim 1 , characterized in that at least one partition ( 24 , 28 ) is mounted between the inner wall ( 12 ) and the outer wall ( 14 ). claim 1 4. The wall segment as claimed in claim 1 , characterized in that the at least one partition ( 28 ) is made of metal. claim 1 5. Wall segment as claimed in claim 4 , characterized in that one partition ( 26 ) is fitted at least on one of its sides ( 32 ) with a coating ( 18 ). claim 4 6. Wall segment as claimed in claim 5 , characterized in that the partition ( 26 ) adjacent to the outer wall ( 14 ) is fitted with a highly absorbent coating of paint ( 30 ) and that the absorption of the partition ( 24 ) adjacent to the inner wall ( 12 ) is low. claim 5 7. A wall segment ( 10 ) for a device enclosing a work zone to protect against laser beams of a laser source ( 38 ), the wall segment ( 10 ) comprising an inner wall ( 12 ) adjacent to the work zone and an outer wall ( 14 ) substantially parallel to the inner wall ( 12 ) and further away from the work zone than the inner wall ( 12 ), characterized in that the inner wall ( 12 ) and the outer wall ( 14 ) are both metallic sheet metal, the inner wall ( 12 ) is provided with a coating ( 16 ) provided to absorb laser radiation at least on a side surface of the inner wall ( 12 ) facing the work zone, and a side surface of the outer wall ( 14 ) facing the inner wall ( 12 ) being of lesser absorption capability with respect to laser radiation than the coating ( 16 ); wherein at least one partition ( 24 , 28 ) is made of one of iron sheet metal and graphite-coated sheet metal; one partition ( 26 ) is fitted at least on one of its sides ( 32 ) with a black-paint coating ( 18 ); and the partition ( 26 ) adjacent to the outer wall ( 14 ) is fitted with a coating of paint ( 30 ) provided to a absorb laser radiation so that the coating ( 16 ) on incidence of a laser beam begins to burn and that the absorption of the partition ( 24 ) adjacent to the inner wall ( 12 ) is being of lesser absorption capability with respect to the laser radiation than the coating of paint ( 30 ). 8. The wall segment as claimed in claim 1 , characterized in that a spacing ( 34 ) between the inner wall ( 12 ) and the outer wall ( 14 ) corresponds approximately to the diameter of an initial beam of the laser source ( 38 ). claim 1 9. Wall segment as claimed in claim 1 , characterized in that the spacings ( 36 ) between adjacent walls and/or partitions such as between the inner wall ( 12 ) and the partition ( 24 ) or between the partition ( 24 ) and the partition ( 26 , 28 ) or between the partition ( 24 , 26 , 28 ) and the outer wall ( 14 ) corresponds approximately to the diameter of the initial beam of the laser source ( 38 ). claim 1 10. Wall segment as claimed in claim 1 , characterized in that the spacing ( 34 , 36 ) of adjacent walls and/or partitions ( 12 , 14 , 24 , 26 , 28 ) is at least 60 mm. claim 1 11. Wall segment as claimed in claim 1 , characterized in that the distance ( 40 ) between the wall segment ( 10 ) and the laser source ( 38 ) is at least four-fold to five-fold the focal length of the fiber optics. claim 1 12. Wall segment as claimed in claim 1 , characterized in that the end faces ( 42 , 44 ) of the multi-shell wall component ( 10 ) are closed. claim 1 13. Wall segment as claimed in claim 12 , characterized in that the boreholes ( 50 ) are present in a vertical, upper zone, in the zone of the end face 942 ). claim 12 14. Wall segment as claimed in claim 1 , characterized in that a smoke or gas sensor ( 46 , 48 ) connected to a control is mounted between the inner wall ( 12 ) and the outer wall ( 14 ). claim 1 15. Wall segment as claimed in claim 14 , characterized in that at least two sensors ( 46 , 48 ) are mounted at different positions in the wall component ( 10 ). claim 14 16. Wall segment as claimed in claim 1 , characterized in that the inner and outer walls ( 12 ) and ( 14 ) resp. and any partition(s) ( 24 , 26 , 28 ) mounted in-between comprise essentially mutually flush polycarbonate or glass panes. claim 1 17. Wall segment as claimed in claim 16 , characterized in that the panes consist of at least two, more sequentially mounted layers. claim 16 18. A protective device against laser beams with at least one wall segment as claimed in claim 1 , characterized in that the protective device is a framework consisting of steel beams and that the walls and/or partitions ( 14 , 16 , 24 , 26 , 28 ) are affixed to this framework. claim 1 19. The wall segment as claimed in claim 1 , wherein said inner wall and outer walls are made of one of iron and steel. claim 1 20. The wall segment as claimed in claim 4 , wherein the at least one partition ( 24 , 28 ) is made of one of iron sheet metal, a steel sheet metal, and a graphite-coated sheet metal. claim 4 21. The wall segment as claimed in claim 5 , wherein said coating ( 18 ) is a black-paint coating ( 30 ). claim 5 22. A laser beam protective device comprising: a first outer wall having a first surface facing towards a laser source, said first surface having a first coating of a material of relatively low absorptivity and high reflectivity; and a second inner wall disposed between said first outer wall and said laser source, said second inner wall having an inner side facing said laser source and having a second coating of material of relatively high absorptivity; wherein said second coating burns when exposed to said laser beam. 23. The laser protective device according to claim 22 , wherein said first outer and said second inner wall are made of a metallic material. claim 22 24. The laser protective device according to claim 22 , further comprising: claim 22 at least one gas sensor disposed between said inner and outer walls to detect gas emitted when said second coating of said second inner wall burns from exposure to said laser beam. 25. The wall segment as claimed in claim 1 , characterized in that the coating ( 16 ) is provided to absorb a laser radiation so that the coating ( 16 ) on incidence of a laser beam begins to burn and the side surface of the outer wall ( 14 ) facing the inner wall ( 12 ) being of lesser absorption capability with respect to the laser radiation than the coating ( 16 ). claim 1 26. A wall segment ( 10 ) for a device enclosing a work zone to protect against laser beams of a laser source ( 38 ), the wall segment ( 10 ) comprising an inner wall ( 12 ) adjacent to the work zone and an outer wall ( 14 ) substantially parallel to the inner wall ( 12 ) and further away from the work zone than the inner wall ( 12 ), characterized in that the inner wall ( 12 ) and the outer wall ( 14 ) are both metallic sheet metal, the inner wall ( 12 ) is provided with a coating ( 16 ) of black paint at least on a side surface of the inner wall ( 12 ) facing the work zone, and a side surface of the outer wall ( 14 ) facing the inner wall ( 12 ) being of lesser absorption capability than the coating ( 16 ). 27. The wall segment as claimed in claim 26 , characterized in that the coating ( 16 ) is provided to absorb a laser radiation so that the coating ( 16 ) on incidence of a laser beam begins to burn and the side surface of the outer wall ( 14 ) facing the inner wall ( 12 ) being of lesser absorption capability with respect to the laser radiation than the coating ( 16 ). claim 26 28. The wall segment as claimed in claim 1 , wherein the coating has a high absorption capability of such kind that the coating on incidence of the laser beam begins to burn. claim 1 29. The wall segment as claimed in claim 25 , wherein the coating ( 16 ) is black paint. claim 25 |
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claims | 1. A nuclear reactor unit comprising:a containment vessel;a nuclear reactor located in the containment vessel, the nuclear reactor having a reactor vessel that has a reactor vessel wall; anda buffer salt contained in the containment vessel,the buffer salt being in thermal contact with the reactor vessel wall,the nuclear reactor, when running, generating a heat output that produces a first reactor vessel wall temperature,the buffer salt being in a solid state when at a temperature equal to or below the first reactor vessel wall temperature,the nuclear reactor, when external cooling is lost, generating heat that produces a second reactor vessel wall temperature greater than the first reactor vessel wall temperature,the buffer salt absorbing a portion of the decay heat, wherein absorption of the portion of the decay heat raises the temperature of the buffer salt, the buffer salt melting and becoming a liquid buffer salt when at the second reactor wall temperature,the containment vessel maintaining the liquid salt in thermal contact with the reactor vessel wall. 2. The nuclear reactor of claim 1 wherein convective heat transfer in the liquid state is higher than conductive heat transfer in the solid state. 3. The nuclear reactor of claim 1 wherein the buffer salt is a thermal insulator in the solid state and a thermal conductor in the liquid state. 4. The nuclear reactor of claim 1 wherein the liquid buffer salt conducts heat between the reactor vessel and the containment vessel. 5. The nuclear reactor of claim 4 wherein the containment vessel is in thermal contact with an exterior heat absorbing material. 6. The nuclear reactor of claim 5 wherein the exterior heat absorbing material includes water. 7. The nuclear reactor of claim 1 wherein the containment vessel comprises an inner wall and an outer wall, the inner wall being in thermal contact with the reactor vessel wall, the buffer salt being located between the inner wall and the outer wall. 8. The nuclear reactor of claim 1 wherein the nuclear reactor is a molten salt nuclear reactor. |
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summary | ||
047476451 | abstract | To separate ultraviolet (UV) radiation emitted from a light source (9) from impinging on infrared (IR) filters, in which the respective filters filter the radiation from the light source to result in controlled spectral distribution simulating, at least approximately, sunlight, an outer UV filter (10) is located in a first section, adjacent a first mirror-filter combination (11), alternatingly located in polygonal form, for example square (FIG. 2) or triangular (FIG. 3) or in cylindrical form (FIGS. 5,6) surrounding the light source. The first mirror-filter combination includes a first UV mirror (12) having its mirror surface directed towards the light source and, externally thereof, a IR filter (13). A sandwich assembly of a second mirror-filter combination (14) is located interiorally of the sections, the sandwich assembly having an inner UV mirror (15), reflecting inwardly, an outer UV mirror (16) reflecting outwardly, and a IR filter (17) located intermediate the mirrors, the second mirror-filter combination being so positioned with respect to the UV filter (10) to place the UV filter entirely within the optical shadow of radiation emitted from the light source, so that the radiation is separated into UV and IR and visible light components, UV radiation being passed only through the UV filter and prevented from reaching any IR filter. |
description | The present invention relates to a radiation system and a lithographic apparatus that includes a radiation system. A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning” direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. In addition to EUV radiation, radiation sources used in EUV lithography generate contaminant material that may be harmful for the optics and the working environment in which the lithographic process is carried out. Such is especially the case for EUV sources operating via a plasma produced discharge source, such as a plasma tin source. Such a source typically comprises a pair of electrodes to which a voltage difference can be applied. In addition, a vapor is produced, for example, by a laser beam that is targeted to, for example, one of the electrodes. Accordingly, a discharge will occur between the electrodes, generating a plasma, and which causes a so-called pinch in which EUV radiation is produced. In addition to this radiation, the discharge source typically produces debris particles, among which can be all kinds of microparticles varying in size from atomic to complex particles, which can be both charged and uncharged. It is desired to limit the contamination of the optical system that is arranged to condition the beams of radiation coming from an EUV source from this debris. Conventional shielding of the optical system primarily includes a system comprising a high number of closely packet foils aligned parallel to the direction of the light generated by the EUV source. A so-called foil trap, for instance, as disclosed in EP 1491963, uses a high number of closely packed foils aligned generally parallel to the direction of the light generated by the EUV source. Contaminant debris, such as micro-particles, nano-particles and ions can be trapped in walls provided by the foil plates. Thus, the foil trap functions as a contamination barrier trapping contaminant material from the source. Due to the arrangement of the platelets, the foil trap is transparent for light, but will capture debris either because it is not travelling parallel to the platelets, or because of a randomized motion caused by a buffer gas. It is desirable to improve the shielding of the radiation system, because some (directed, ballistic) particles may still transmit through the foil trap. According to an aspect of the invention there is provided a radiation system for generating a beam of radiation that defines an optical axis. The radiation system includes a plasma produced discharge source constructed and arranged to generate EUV radiation. The discharge source includes a pair of electrodes constructed and arranged to be provided with a voltage difference, and a system constructed and arranged to produce a discharge between the pair of electrodes so as to provide a pinch plasma between the electrodes. The radiation system also includes a debris catching shield constructed and arranged to catch debris from the electrodes, to shield the electrodes from a line of sight provided in a predetermined spherical angle relative the optical axis, and to provide an aperture to a central area between the electrodes in the line of sight. According to an aspect of the invention, there is provided a lithographic apparatus that includes a radiation system for generating a beam of radiation that defines an optical axis. The radiation system includes a plasma produced discharge source constructed and arranged to generate EUV radiation. The discharge source includes a pair of electrodes constructed and arranged to be provided with a voltage difference, and a system constructed and arranged to produce a discharge between the pair of electrodes so as to provide a pinch plasma between the electrodes. The radiation system also includes a debris catching shield constructed and arranged to catch debris from the electrodes, to shield the electrodes from a line of sight provided in a predetermined spherical angle relative the optical axis, and to provide an aperture to a central area between the electrodes in the line of sight. The lithographic apparatus also includes a patterning device constructed and arranged to pattern the beam of radiation, and a projection system constructed and arranged to project the patterned beam of radiation onto a substrate. Other aspects, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims. FIG. 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or EUV radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive or reflective projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W. The illumination and projection systems may include various types of optical components, such as refractive, reflective, diffractive or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. The support structure supports, i.e. bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.” The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix. The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, or any combination thereof, as appropriate for the exposure radiation being used. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”. As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask). Alternatively, the apparatus may be of a transmissive type (e.g. employing a transmissive mask). The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. Referring to FIG. 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The illuminator IL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may comprise various other components, such as an integrator and a condenser. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. The radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor IF1 can be used to accurately position the mask MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies. The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the mask table MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. 2. In scan mode, the mask table MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the mask table MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. 3. In another mode, the mask table MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed. In FIG. 2 a schematic first embodiment is shown of a radiation system according to an aspect of the invention. In particular, there is shown a radiation system 1 for generating a beam of radiation 2 defining an optical axis 3. The radiation system 1 includes a plasma produced discharge source 4 for generating EUV radiation. The discharge source includes a pair of electrodes 5 that are constructed and arranged to be provided with a voltage difference, and a system that typically includes a laser 6 for producing a vapor between the pair of electrodes so as to provide a discharge 7 between the electrodes 5. It has been found that debris 8 coming from the radiation system 1 is primarily produced on or near the electrodes 5. These effects also cause a generation of a so-called pinch which develops between the electrodes 5. Typically, the EUV light that is generated is produced by an electron transition in a Tin atom (or another suitable material, for example, Lithium or Xenon), which is ionized multiple times of electrons in the discharge process. It was found that debris particles 8, in particular, ballistic particles of the kind that may contaminate the downstream optics, are mainly produced on or near the electrodes 5 in debris producing zones 9, where the central EUV source light is mainly produced in the pinch zone 10 that is distanced from the debris producing zones 9. Thus, for a plasma produced discharge source 4, the debris producing zones 9 are typically distanced from the EUV radiation producing pinch zone 10. This effect can be utilized by the illustrated embodiment, which according to an aspect of the invention comprises a shield 11 to shield the electrodes 5 from a line of sight provided in a predetermined spherical angle relative the optical axis 3 and to provide an aperture 12 to a central area between the electrodes in the line of sight. Accordingly, debris 8, which is generated in the debris producing zone 9 initially (in the absence of additional electromagnetic fields, however, see the embodiment illustrated in FIG. 5-FIG. 7) travels substantially in straight lines from the zone 9. Thus, a shield 11 that shields the electrodes 5 from a line of sight in a predetermined spherical angle around the optical axis 3 is able to trap these debris particles 8, so that in the line of sight a substantial amount of debris 8 is prevented from entering downstream optics (not shown). Additionally, the shield 11 substantially does not shield the radiation coming from the EUV radiation producing pinch zone 10, since it provides an aperture 12 to a central area (conforming to a designated pinch zone 10) between the electrodes 5 in the line of sight, which accordingly can travel into the downstream optics substantially unhindered by the shield 11. In this way, the debris (which comes from the electrodes) may be stopped by the shield, without stopping the EUV radiation. Practically, it is convenient to shield both electrodes, since it is probable that both electrodes generate debris-producing zones that can attribute in debris 8 production. The shielding effect can be further optimized by placing the shields 11 close enough, preferably, a distance ranging between 0.5 and 25 mm to any of the electrodes, to shield a maximum spherical angle of the debris producing zone 9. To minimize a distance with the electrodes, the heat load will be so high on the shield 11 that it is preferably provided as a fluid jet 13, for example, of molten Tin. Such a jet could have a length of about 75 mm and a thickness of several mm, for example ranging from 0.5 to 3 mm. It is noted that fluid jets are per se known from U.S. 2006-0011864 which discloses electrodes in a plasma discharge source in the form of fluid jets, however, there is not disclosed a shield or at least one fluid jet provided near an electrode of a pair of electrodes. Accordingly, preferably, the debris catching shield 11 is provided, as illustrated, by a pair of fluid jets 13, arranged oppositely and generally parallel to a longitudinal axis of the electrodes 5. It may however, in certain embodiments, possible to direct the plasma production substantially towards one of the electrodes 5, which one electrode will accordingly be a major contributor in producing debris 8. Such debris may vary in size and travel speed. For instance, one can have micro-particles: these are micron-sized particles with relatively low velocities. In addition, there may be produced nano-particles, which are nanometer-sized particles with typically quite high velocities; atomic debris, which are individual atoms that act as gaseous particles; and ions, which are ionised high-velocity atoms. It is noted that in one embodiment, the fluid jet 13 may be provided near an electrode of the pair of electrodes without substantially being configured to shield the electrodes from a line of sight provided in a predetermined spherical angle relative the optical axis and to provide an aperture to a central area 10 between the electrodes in the line of sight (unlike the embodiment shown in FIG. 2). In such an embodiment, according to another aspect of the invention, the fluid jet 13 may be accelerating the recombination rate of the plasma, which may increase the frequency of the EUV source 4 and accordingly may provide a higher power output of the radiation system. Specifically, the fluid jet 13 may comprise molten Tin, although other materials may be feasible to provide the same recombining effect, including, for example water or a liquid gas, such as liquid nitrogen or liquid argon. An advantage of the latter is that it may evaporate and thus may leave no further traces in the system. Additionally, the fluid is preferably of an electrically conductive material and may be kept at ground potential, although other materials, such as argon and nitrogen may also be used. The advantage of the fluid jets is that the obstruction is continuously replaced and can thus withstand very high heat loads. However, in other embodiments, it may be possible, to provide a shield 11 that is positioned at generally the same distance nearby the electrodes 5 as discussed hereabove with reference to FIG. 2, but that is not formed by a fluid jet, but by a moving element (not shown), for example, an axially moving metal strip, that moves generally parallel to an electrode longitudinal axis, and which may be cooled by providing coolant in a container, for guiding the moving element there through. FIG. 3 shows schematically an embodiment of the invention, showing a shield in the form of a plurality of fluid jets 13, arranged in radial direction relative from the central area 10 between electrodes 5 in the line of sight. In such an embodiment, the fluid jets 13 are provided adjacent to each other, and may be generally aligned to form a static configuration of generally radially oriented platelets 14, relative to the central area 10. Although within the general context of the invention, preferably, these platelets are oriented to shield the electrodes 5 from a line of sight provided between the platelets 14, this embodiment may also have practical applications with the platelets oriented to include the electrodes 5 in a line of sight provided between the platelets 14. These applications may benefit from the heat load capacity of the shield 11 that is provided by the fluid jets 13. A further advantage is that the jets 13 by nature are not contaminated by debris depositions since they are continuously renewed. This is in contrast with a conventional foil trap solution where solid platelets 14 (foils) are used to provide shielding from debris 8. These conventional platelets therefore may suffer from contamination which may hinder a proper transmission of the EUV radiation. In particular, especially for plasma produced discharge sources 4 operated with Tin plasma, a suitable material for the fluid jets may also be Tin or a compound comprising Tin, such as for example Ga—In—Sn, which may be suitable to have a lower melting point and easier handling properties. Furthermore, although FIG. 3 shows an embodiment wherein the jets 13 are dimensioned with a general circular form, other form, including strip forms may be feasible, thus providing a shield 11 comprising platelets 14 in the form of single jets, generally of the form as depicted in FIG. 4. A thickness of such liquid foil may be typically 0.5-1 mm, which is slightly thicker than conventional foil thicknesses that are about 0.1 mm thick. It is noted that thin liquid foils are discussed in T. Inamura, H. Tamura, H. Sakamoto, “Characteristics of Liquid Film and Spray Injected from swirl Coaxial Injector”; Journal of Propulsion and Power 19 (4), 623-639 (2003). In this publication, cone-shaped foils are produced. However, preferably, according to an aspect of the invention, a slit-shaped nozzle is used, in particular, for providing straight-formed jets that are radially oriented relative to a centre zone 10 wherein a pinch can develop. In addition, this static embodiment may be combined with a rotating foil trap, known per se from EP 1491963 and, of course, with other embodiments described in the current document. Under certain circumstances, fluid jets may not be stable—i.e. they may spontaneously divide into droplets with a diameter approximately equal to the jet diameter. This means that it may only be possible to create continuous jets if the diameter is relatively large (>˜0.5 mm). Therefore, it may be advantageous to use jets that intentionally consist of closely spaced droplets that can have a very small and controllable size, with a controllable distance between droplets. The ability to create such stable droplet chains (40 μm diameter with about 40 μm distance) was presented in the EUVL Sematech conference in Barcelona (Conference 7870, 17 Oct. 2006) by David Brandt (session 3-SO-04) for use as a laser target in a LPP EUV source. The stability of the droplet chains means that different configurations may be employed, depending upon which functional aspects (recombination and/or debris catching) need to be optimized. FIGS. 13a-e show examples of such configurations. FIG. 13a depicts a continuous jet 13 in which the recombination surface is moving in the direction T. FIG. 13b depicts a stable train of droplets 113, moving in direction T, which for the purposes of this invention may be considered to be a jet 13. The stability of the droplet chains means that these chains may be positioned adjacent to each other to add an extra degree of flexibility when implementing the invention. FIG. 13c shows two adjacent chains of droplets 113, effectively creating a jet 13, extended in one direction compared to the jet 13 of FIG. 13b. A disadvantage of a droplet chain is that debris has a possible path to pass through the fluid jet. FIG. 13d and FIG. 13e show how the droplet chains can be shifted in the direction of movement T with respect to each other to effectively create a virtual continuous jet 13 for debris having a trajectory in the plane of the figure and perpendicular to the direction of movement T of the jet. FIG. 4 in addition shows a further embodiment according to an aspect of the invention, wherein the debris catching shield, herebelow also indicated as a foil trap 15 comprises a static configuration of generally radially oriented platelets 14, relative to the central area 10, wherein the platelets 14 are oriented to shield the electrodes 5 from a line of sight provided between the platelets 14. In this embodiment, at least some of the platelets are of a solid nature, in particular, of foils used in a so called conventional foil trap. It is noted that WO 99/42904 A1 discloses a foil trap of generally the same configuration; however, the publication does not discuss that the platelets 14 are configured to shield the electrodes 5 from a line of sight provided in a predetermined spherical angle relative the optical axis and to provide an aperture to a central area 10 between the electrodes in the line of sight. In comparison with conventional rotating foil traps of the type as disclosed in EP1491963, this static foil trap configuration may have an advantage in easier cooling properties, since, in an embodiment, this static foil trap configuration can be cooled using static coolant circuits devised on or in proximity of the platelets 14. Since the configuration is static, accordingly, cooling may be much simpler and therefore, the configuration can be easily scaled to higher power levels of the source. In addition, this configuration has as a benefit that it does not require moving parts, which may provide constructional advantages since the required strength and dimensions of the platelets 14 may be of a different order than the rotating conventional construction, which requires complex parts such as air bearings and high tension materials that can withstand centrifugal tension forces applied to the platelets. Thus, according to the proposed embodiment, the radially oriented platelets 14 are aiming at the pinch zone 10 thus substantially unhindering transmittance of EUV-radiation 16. This foil trap 15 will fill up with debris at certain locations so a slow rotation around the optical axis (e.g. once a day) could be useful to make sure no debris will contaminate the next foil trap 15 or other optics. This may be useful, since in a preferred embodiment, the optical axis may be 45 degrees with respect to a level plane. This principle could also be designed in combinations of concentric circles and plates. In addition, the geometry of the depicted embodiment, including static radially oriented platelets 14, may have stacking dimensions that have high gas resistance wherein a distance between the platelets may be in an order of 0.5-2 mm, preferably about 1 mm. Accordingly, atomic debris may be trapped easier. Also, a high gas resistance may help to allow a lower buffer gas pressure near the pinch zone 10, which may resulting in a higher efficiency EUV power. Typically, such a buffer gas may be Argon gas. In addition to the thermal cleaning techniques illustrated with reference to the FIG. 10-FIG. 12 presented herebelow, the platelets 14 may provided as a material of porous characteristics for removing the debris from the platelets through capillary action. For instance, by using foil material with porous characteristics (e.g. sintered materials) Tin can be taken out of the optical path and drained (or buffered in an exchangeable element). Accordingly, lifetime of the debris suppression system may be increased and downtime due to foil trap cleaning may be minimized. In addition to the above-discussed cleaning technique, the radiation system may comprise an excitator 17 (see FIG. 4) for removing the debris from the platelets 14 through mechanical excitation of the platelets 14. For example, by rotating the module fast enough (˜2000-3000 RPM as an indication) on a temporarily basis, the tin may be spun of the relevant foils, and may be caught by a getter 18. In an embodiment, the revolution axis is the optical axis, but other axes of revolution may also be possible. A combination of rotation and vibration is also an option. Accordingly, the excitator may comprise a centrifuge for removing the debris from the platelets through centrifugal action and advantageously a getter 18 for catching debris 8 removed from the platelets. Also, the foil could be externally excitated (longitudinal waves) so a flow of tin in a predefined direction may be present. Also (directional) accelerations/vibrations can be used to give excitation profile(s) (pending between stick/slip effect of the droplets) to the entire module instead of each separate foil. FIG. 5 discloses a further embodiment of the arrangement described with reference to FIG. 4. In this embodiment, a deflecting electromagnetic field unit 19 is disposed between the electrodes 5 and a shield, in this embodiment illustrated as foil trap 15. By applying an electromagnetic field, charged debris particles 8 traveling from the debris producing zones 9 can be deflected, which accordingly can be used to virtually expand the distance between the EUV radiation producing pinch zone 10 and the debris producing zones 9 as will be made even more clear with reference to FIG. 7. In FIG. 5, the deflecting field is produced by a pair of electrodes 20 arranged oppositely to the optical axis. Accordingly, a static electric field is generated according to which the electrically charged particles can be deflected. In FIG. 6, in contrast to the embodiment depicted in FIG. 5, or in addition to it, the electromagnetic deflecting field is provided as a static magnetic field 21, due to magnet elements 26 (see FIG. 8) arranged around the optic axis 3. For a front view of this configuration, see FIG. 8. Although various static field configurations are feasible, an optimally defined field is provided as a quadrupole field, arranged for deflecting substantially all electrically charged particles 8 traveling generally in a direction towards the optical system (not shown), towards a plane 22 oriented along the radially oriented platelets 14 and generally parallel to a length axis of the electrodes 5. Preferably, as is also shown in the Figure, this plane 22 is provided along the optical axis 3. However, it may be possible to select another region that is more off axis to deflect the particles thereto. Accordingly, charged debris particles can be deflected more easily towards the platelets 14 of the foil trap 15, which virtually increases the distance between the electrodes 5. Consequently, fewer platelets 14 may be needed to achieve a given extent of debris suppression. Accordingly, a typical distance may range between 0.5 and 3 mm, preferably about 2 mm. This significantly increases the optical transmission of the foil trap. The principle of operation in FIG. 6 is as follows. The rectangle 10 indicates an acceptance width of the foil trap in the absence of a magnetic field and is accordingly generally corresponding to a zone 10 from where EUV radiation is produced. However, particles 8 generated near the edges of the zone 10 (accordingly, produced from a debris producing zone 9) may travel unhindered through the shield, in this embodiment illustrated as foil trap 15, without being intercepted, as illustrated by the trajectory 23. By applying a magnetic field of the type as indicated (with a conventional arrow indication), such debris particles 8 are deflected towards the optical axis 3. For example, the particle with trajectory 23 may be deflected to follow the solid line 24 and no longer be transmitted through the foil trap 15. This is because on entrance of the foil trap, the particle appears to originate from a point outside the acceptance width 10 as indicated by the other dashed line 25. In other words, the application of the magnetic field effectively narrows down an effective acceptance width of the shield, which width defines a zone from where debris particles could enter the system unhindered. Accordingly, for a given dimensioning of the acceptance width, the optical transmission may be improved by reducing the number of platelets 11 and applying a magnetic field. A typical distance for the acceptance width of the foil trap in the absence of a magnetic field may be ranging from about 0.5 to about 2 mm, preferably about 1 mm. For typical foil trap dimensions (inner radius 30 mm, relative to a central zone 10, outer radius 139 mm), this leads to a foil trap with 137 foils having an optical transmission of approximately 63%. As the Figure shows, in a preferred embodiment, the distance d, d′ between the platelets 14 may vary, wherein typically a distance d towards the optical axis 3 may increase relative to distances d′ away from the optical axis 3. FIG. 7 shows how the source of the particles, that is, the debris producing zone 9 can be virtually shifted over a distance d to a virtual debris producing zone 9′ by applying the magnetic field. Accordingly, an effective acceptance width may be reduced. In the presence of a magnetic field B, a particle with charge q and velocity v experiences a Lorentz force given byF=qv×B (1) Consequently, if the direction of the magnetic field is perpendicular to the velocity, the particle follows a circular trajectory with radius R equal to R = mv qB ( 2 ) In the present embodiment, the angular deflection α due to the magnetic field depends on the distance over which the field is applied, which is approximately equal to the inner radius of the foil trap r0. The deflection angle is given by sin α=r0/R as shown in FIG. 3. The apparent point of departure of the particle is accordingly displaced over a distance d given byd=r0 sin α−R(1−cos α) (3)which for small values of α reduces to d = r 0 2 2 R ( 4 ) By substituting Eq. (2), the following expression relating the displacement d to the characteristic parameters q, m and v of the debris particles is obtained: d = qBr 0 2 2 mv ( 5 ) Using permanent magnets or electromagnets, a magnetic field of the order of 1 T can fairly easily be achieved. When a magnetic field is applied so that the displacement d is equal to 0.5 mm for a certain type of debris, the acceptance width for that debris accordingly effectively decreases by a factor of 2 compared to the earlier mentioned value of 1 mm acceptance width. One can therefore construct a foil trap that has an acceptance width of 2 mm and still obtain the same extent of debris mitigation. Such a foil trap may have only 69 foils and an optical transmission of 70%. Thus, the optical transmission is significantly improved by applying a magnetic field. FIG. 8 shows a front view, seen along the optic axis, of the electrodes 5 and a quadrupole magnet configuration of magnets 26. In this configuration, the North-South lines of opposing magnets 26 are oriented alternating and generally parallel to the longitudinal axis of the electrodes 5. Accordingly, a magnetic field may be produced that follows the orientation depicted in FIG. 6, that is, with a general direction of the magnetic field on either sides of the optic axis 3 in a plane generally parallel to the length axis of the electrodes, to deflect the particles inwards towards a plane 22 coaxial with the optic axis 3. Accordingly, for typical configurations, positively charged particles are focused to a vertical plane (by focusing in the horizontal direction and spreading in the vertical direction). Alternatively, a similar (but less well-defined) deflecting field may be obtained by placing two identical magnetic poles on opposite sides of the optical axis. FIG. 9 shows a further embodiment of the static configuration of generally radially oriented platelets 14 described with reference to FIG. 4. In this embodiment, instead of solid monolithic platelets 14, in at least some of the platelets 14, traverses 27 are provided oriented generally transverse to the platelets 14. This embodiment may provide thermal isolation to the further downstream platelets 14, as seen from the EUV source 4. In addition to it, possibly by applying fluid jets as shown in FIG. 3, preferably on a proximal side of the platelets 14 relative to the EUV source 4, the heat load to the platelets 14 can be further managed. In addition, a gas 28 can be guided through the traverses 27 of the platelets 14, which may be used for cleaning purposes of the platelets 14, for example, a hydrogen radical gas. Accordingly, the platelets 14 can be cleaned to prevent debris depositing on the platelets 14, thereby preventing a situation in which EUV light will no longer be able to pass through the platelets. Preferably, the foil trap may be cleaned without having to take the foil trap out of the system. The principle of additional traverses in the shown foil trap embodiment could also be used for other types of foil traps, in particular, in non-static foil traps. In addition to, or alternatively, the traverses may be used as a buffer gas to provide a buffer gas zone within a zone in side the platelets, in order to be able to further trap, for example, neutral nanoparticles which may diffuse through the platelets 14 and may cause contamination of the optical system provided downstream (not shown). FIG. 9A shows a side view of an embodiment with traverses 27, which may be provided with alternating use of wires 29 and platelet parts 30. FIG. 9B shows an embodiment with only wires 29; to provide a configuration similar to the fluid jet configuration depicted in FIG. 3. FIG. 9C in addition shows a top view generally seen along an axis parallel to the length axis of the electrodes 5, of the platelet embodiment depicted in FIG. 9A. The more open structure of FIG. 9B has an advantage when integrating foil trap cleaning based on hydrogen radicals, because it becomes easier to bring the reactive H radicals to the surface of the foils, and it becomes easier to transport the reaction products out of the foil trap 15. However, the drawback is that the flow resistance of the foil trap 15 becomes lower, which may make it more difficult to achieve a high buffer gas pressure. Therefore one needs to optimize the amount of openings in the platelets. The preferred embodiment therefore is in most cases a partially open foil structure, as shown in FIG. 9A. Furthermore, in a preferred embodiment H cleaning is integrated with the wired structures shown in the figures by providing an electric current supply 31, which is connected to at least some of the wires 29 of a platelet 14. At least some of the wires 29 in the platelet are now interconnected in order to allow a current to run through several wires 29 simultaneously. With a high enough current (for example, 20 A for a 0.4 mm thick wire), the wires will form a filament that will reach temperatures of about 2000 0C where typically H2 molecules will dissociate, generating H radicals. These H radicals can then react with Sn to form gaseous SnH4, which is pumped out of the system. In order to add H2 to the system, the embodiment therefore further comprises a H2 gas inlet 32 and the embodiment comprises a vacuum pump 33 to remove gas from the system (as shown in FIG. 9C). Alternatively, it is possible to remove debris from the capture shield using evaporation. FIG. 10 shows a graph of a calculation that was performed to calculate the removal rate of tin and lithium, for temperatures in a range of 200-800° C. In addition, for tin a removal rate of about 0.1 nm/hour was calculated for a temperature of about 900 K, and a rate of about 1 E5 nm/hour for a temperature of about 1400 K, with an almost exponential increase. Thus, in a range between these temperature values, by providing a heating system (which may be EUV source 4) the debris catching shield, in particular a foil trap 15 of the kind as shown in FIG. 4 may be selectively heated to elevate a temperature of the debris shield to a temperature for evaporating debris from the debris catching shield. In addition a gas supply system is provided which may in use serve for providing a buffer gas flow between the platelets, and which may off line be used for cleaning purposes, in particular, for providing a gas flow to evacuate evaporated debris from the debris catching shield. A particular preferable elevation temperature of the debris catching shield for a tin plasma source may be at least 900 K for offline cleaning purposes. Accordingly an alternative may be provided for chemically reactive cleaning, which may be harmful to the optics system. For a temperature of the platelets 14 of 940 K (667 C) a Tin evaporation of 0.4 nm/hour may be achievable. Advantageously, a lithium plasma source is used since lithium has a significantly higher vapor pressure than tin (about 9 orders of magnitude) and as a consequence also a significantly higher removal rate (removal rate of 0.4 nm/hr requires temperature of only 550 K (277 C). This allows applying evaporative cleaning of lithium-contaminated surfaces at significantly lower temperatures than evaporative cleaning of tin-contaminated surfaces; evaporative cleaning of collector shells contaminated with lithium is feasible. FIG. 11 shows a general schematic illustration of the cleaning principle explained hereabove with reference to FIG. 10. In particular, a platelet 14 is heated, so that debris 8 deposed thereon will be evaporated. By providing a gas flow 34 along the platelet 14, the evaporated debris, for example, tin vapor 35, will be carried away from the platelet, through which the platelet can be cleaned. Although FIG. 11 has been explained with reference to a gas flow along a platelet 14 of a foil trap, the cleaning principle can be used generally, to clean EUV mirror surfaces in particular, of downstream optical elements such as a collector element. In FIG. 11, the object to be cleaned (a platelet 14 or mirror optic) is heated while a gas is flowing over the mirror in order to transport the tin vapor away from the mirror. Heating can be done with a heating device, but it is also possible to temporarily reduce active cooling of the object, and use the heat generated by the EUV source. In FIG. 12 this technique is used for the collector 36 of an EUV lithography setup. In this embodiment the collector shells are heated one-by-one, in order to evaporate the tin from the reflective side of the collector shell, and to deposit the tin vapor on the backside of the collector shell below. When a collector shell 37 is heated, it will typically evaporate tin on both sides of the shells. This means that also the backside of the shell will evaporate tin and deposit this on the reflective surface of the collector shell above. To prevent this it is preferable to heat the center shell first, and then continue with the next shell, etc. Thus by cleaning the collector shells in the right order and controlling the temperature of the collector shell at the same time, it is possible to minimize (re)deposition on the reflective surface. Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers. The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below. |
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044877420 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 diagrammatically shows a fast neutron nuclear reactor of the integrated type. The reactor core 10 is immersed in a volume 12 of cooling liquid metal (normally sodium) contained within a vertically axed vessel 14. The upper part of vessel 14 is sealed by a horizontal sealing slab 16, which rests by its periphery on a vessel shaft 18. The main vessel 40 is duplicated within the vessel shaft 18 by a safety vessel 12 which, like vessel 14 is suspended on slab 16. The components placed above slab 16 are disposed in a confinement enclosure 19, whereof only part is shown in FIG. 1. In reactors of the integrated type, like that diagrammatically shown in FIG. 1, slab 16 is traversed by a series of components necessary for the operation of the reactor. Thus, in its central part, the slab supports a system of rotary plugs 22 and in its peripheral part intermediate exchangers 24 and pre-vacuum pumps 26 regularly distributed around the core. An inner vessel 28 defines within vessel 14 a "hot" collector 30 containing the "hot" liquid metal issuing into the upper end of core 10 and a "cold" collector 32 in which is collected the liquid metal leaving exchangers 24. The liquid metal is then taken up by pumps 26 in order to be passed through the pipes 34 into a support 36 ensuring both the supply of liquid metal to core 10 and the supporting of the said core on the bottom of vessel 14 by means of flooring 38. Thus, in operation, the liquid metal permanently circulates through the core. Exchangers 24 ensure the extraction of the heat given off by the fission reaction. This heat is then transferred to a not shown secondary circuit before being used in the turbines of a water/vapour or steam circuit for generating electricity. According to the invention, in the interior of vessel 14 are also provided the evaporators 42 of the residual power removal devices 40. These devices 40, whereof only is shown in FIG. 1, pass through slab 16 and make it possible, in the case of a stoppage of the pre-vacuum pumps 26, to ensure an appropriate cooling of the hot liquid metal contained in collector 30, so as to remove the residual power of the reactor. FIG. 2 illustrates on a larger scale the constructional details of one of the devices 40. Each of the devices 40 comprises an evaporator 42 positioned below slab 16 and immersed in liquid metal 12, a condenser 44 positioned above slab 16 and within the reactor enclosure 19 (FIG. 1) and an adiabatic collector 46 passing through slab 16 to link evaporator 42 with condenser 44. As is more clearly shown in FIGS. 2 and 3, the evaporator 42 comprises a bundle of straight, vertical tubes 48 sealed at their lower end so as to have a glove finger-like configuration. Tubes 48 are entirely positioned below the free level 13 of liquid metal 12. In order to ensure, in the manner described hereinafter, the piping of the liquid phase of the heat transfer fluid contained in device 40, the inner wall of each of the tubes 48 is covered with a capillary structure 50. Each of the tubes 48 is fixed in the vicinity of its upper open end to a horizontal tube plate 52, which at the same time defines the lower end of adiabatic collector 46. Obviously, this fixture takes place in a tight manner, e.g. by welding. Evaporator 42 also comprises a ferrule 54 welded to the tube plate 52 and surrounding the bundle of tubes 48 . Ferrule 54 serves to pipe or channel the flow of liquid metal 12 around tubes 48. For this purpose, in its upper part in the vicinity of tube plate 52, ferrule 54 has inlet ports 56 and is open in its lower part. Thus, it establishes a flow of liquid metal 12 by a thermosiphon effect between ports 56 and the lower opening of said ferrule. In the same way, this configuration of ferrule 54 enables it to freely downwardly expand at the same time as tubes 48. It can be seen in FIG. 3 that the upper end of each of the tubes 48 projects above the tube plate 52 by a given height. This feature makes it possible to define a buffer reservoir 57 in the lower part of a vertical pipe 58, which extends ferrule 54 above tube plate 52 to define the adiabatic collector 44. The buffer reservoir 57 formed in this way above the tube plate 52 also constitutes the supply overflow for the capillary structure lining the interior of each of the tubes 48. As is illustrated in FIG. 3, the uniform distribution of the flow of heat transfer fluid in the liquid state in each of the tubes can be obtained by making sawtooth-like slits 60 at the upper end of each of the tubes and by making a row of holes 62 in the side wall of the tubes. Obviously, these two solutions can be separated from one another, i.e. the upper end of each of the tubes can be provided with slits like slits 60, or can be provided with holes like holes 62. On referring once again to FIG. 2, it can be seen that the existence of the adiabatic collector 46, constituted by pipe 58 is imposed by the distance separating the free level 13 of the liquid metal contained in the vessel and below which must be positioned evaporator 42 from the entrance into condenser 44 positioned above slab 16. In the said collector, the flow of the heat transfer fluid in the vapour phase undergoes an inevitable pressure drop, which reduces the axial flow. In order to reduce this pressure drop to the greatest possible extent and reduce the diameter of the passage through slab 16 by collector 46, it has been chosen in the manner indicated hereinbefore to connect the tubes 48 of evaporator 42 to a single condenser 44 via a single vertical pipe 58 ensuring the collection of the vapour or steam reduced in tubes 48. This solution significantly reduces the pressure drops in the adiabatic collector in a minimum proportion of 20% compared with other possible solutions, such as that consisting of having a group of individual heat pipes, each having an adiabatic zone and a condenser. Preferably, the inner wall of the vertical pipe 58 is covered on its inner face by a capillary structure 64 which, like capillary structure 50 of each of the tubes 48, makes it possible to prevent entrainments of the heat transfer fluid in the liquid phase by the gaseous phase leaving tubes 48 and regularizes the liquid film returning to evaporator 42 via buffer reservoir 57. According to another, not shown, constructional variant, capillary structure 64 can be replaced by at least one small diameter pipe for returning the liquid to the buffer reservoir 57. In the embodiment of the invention shown in FIG. 2, the condenser 44 comprises a caisson or box 66 resting via a cylindrical skirt 68 on the reactor slab 16. The vertical pipe 58 defining the adiabatic collector 46 is extended upwards within box 66 to issue into four bends 70, which are positioned at 90.degree. from one another. Bends 70 drop down again towards a toroidal supply collector 72 of the actual condenser. The latter comprises fin tubes 74 distributed e.g. over 10 circular and concentric levels or layers so as to form an annular bundle. The lower ends of tubes 74 issue into a toroidal condensate-receiving collector 76, similar to collector 72 and positioned below the latter. More specifically, the ends of the tubes 74 are sealingly fixed to the collectors 72 and 76 e.g. by welding. Collectors 72 and 76, as well as the bundle of tubes 74, are arranged coaxially with respect to the vertical pipe 58. The heat transfer fluid in the liquid phase forming in collector 76 is recycled towards the adiabatic collector 46 by bent pipes 78, which issue into pipe 58 at the upper end of the capillary structure 64 formed within the latter. FIG. 2 shows that the pipes 78 are bent in siphon-like manner, so as to form a hydraulic seal, whose developed height corresponds to the difference of the vapour pressures. In the embodiment shown in FIG. 2, condenser 44 is cooled by means of atmospheric air. The air is sucked into box 66 by a lateral pipe 80 under the effect of the pressure reduction created in the box by a vertical chimney or flue 82 positioned above the latter. FIG. 4 shows that the box 66 is shaped like a centrifugal fan helix level with the bundle of tubes 74, which makes it possible for the cooling air to circulate relatively homogeneously with the bundle. To permit the putting into operation or out of operation of the device shown in FIG. 2, vents 84 are positioned in the lateral pipe 80 at the entrance to box 66. Finally, a biological shield 86 is provided within the supporting skirt 68. According to a not shown constructional variant, condenser 44 can be connected to the assembly constituted by evaporator 40 and adiabatic collector 46 by a flange joint, in such a way that the disassembly of said joint enables the evaporator to be repaired. Preferably, the heat transfer fluid in device 40 is mercury. Preference is given to this product because of the wide temperature range in which it can be used (170.degree. to 600.degree. C.) its low vapour pressure (2 to 11 bars) in the considered temperature range (390.degree. to 530.degree. C.), the high axial heat transfer level which it permits, its dissolving in sodium in the case of a leak, as well as its radiation behaviour, when compared with other products which can be used such as potassium, sodium and sulphur. As is illustrated by the arrows in FIGS. 2 to 4, the present device operates in the following way. Mercury in the filled state at the bottom of tubes 48 of evaporator 42 is heated by the liquid metal 12 contained in the reactor vessel and which circulates in natural convection between inlet ports 58 and the outlet opening formed at the lower end of ferrule 54. Thus, the mercury is vaporized and rises in vertical pipe 58 in order to enter the supply collector 72 via bent pipe 70. When the device is put into operation by opening vents 84, the pressure drop created in box 66 as a result of the suction of air through chimney or flue 82, makes air circulate through the bundle of fin tubes 74, which has the effect of condensing the mercury, whose liquid phase is collected in collector 76. This liquid phase is then transferred by pipes 78 and capillary structure 64 into buffer reservoir 57, from where it drops again into each of the tubes 48 via capillary structures 50. Thus, cooling is brought about on reactor shutdown without any external mechanical energy supply, because the device functions entirely in natural convection. Furthermore, within the maximum power limits which can be removed with condenser 44 as a function of the mercury vapour temperature, it should be noted that an increase in the vaporization temperature of the mercury and consequently the axial power transferred corresponds to any increase in the temperature of the liquid metal 12 within the vessel. Thus, the device is self-regulating. In the embodiment described with reference to FIGS. 2 to 4, reactor enclosure 19 (FIG. 1) must be traversed by large-size air ducts in the form of supply pipe 80 and flue 82. Moreover, the dimensions of condenser 44 above slab 16 are relatively large as a result of the presence of other components. To obviate these disadvantages, FIGS. 5 and 6 show a second embodiment of the invention, which differs from the embodiment of FIGS. 2 to 4 through the different design of the condenser and through the arrangement of said condenser outside the reactor enclosure. For simplification purposes, the same reference numerals, increased by 100, are used for designating the same elements as in the first embodiment. FIG. 5 shows the right-hand part of the reactor vessel shown in FIG. 1 and it is possible to see the main vessel 114 containing liquid metal 112, the safety vessel 120 duplicating the main vessel 114, slab 116 which supports vessels 114 and 120 and whose peripheral edge rests on the vessel shaft 118, internal vessel 128 separating the hot collector 130 from the cold collector 132, as well as a heat exchanger 124. FIG. 5 also shows a residual power removal device 140 comprising an evaporator 142 immersed in the liquid metal 112, a condenser 144 positioned above slab 116 and outside reactor building 119 in this embodiment, as well as the adiabatic collector 146. Evaporator 142 and adiabatic collector 146 are identical to those described relative to the first embodiment. However, apart from its positioning outside enclosure 119, condenser 114 is of a different design to that of the preceding embodiment. Thus, although this condenser also has a box 166 resting via a ferrule 168 on the structure of the vessel shaft 118 and although the cooling air is supplied and removed by means of a lateral pipe 180 and a flue 182, it can be seen that the actual condenser is formed by two planar bundles of fin tubes 174 (FIG. 6), arranged in accordance with a dihedron having a horizontal edge or an edge which is inclined slightly relative to the horizontal. The edge of the thus formed dihedron is materialised by the vapour supply pipe 188, which extends the pipe 158 constituting the adiabatic collector 146 and traverses enclosure 119 in order to enter box 166. This supply pipe 188 is linked with two supply collectors 172 into which issues the upper end of each of the bundles of tubes 174. The lower end of these bundles issues into the condensate-receiving collectors 176. Like pipe 188, collectors 172 and 176 are rectilinear and substantially horizontal. More specifically, it can be seen in FIG. 6 that collectors 176 are positioned ebelow the supply collectors 172 and on either side of the vertical plane passing through pipe 188. Moreover, the collectors 172, 176, as well as the tube bundles 174 are arranged substantially symmetrically with respect to said plane. Obviously, as in the first embodiment, collectors 176 are connected to pipe 158 within the capillary structure of the latter by siphon-like bent pipes 178. As is shown in FIGS. 5 and 6, the air supply by pipe 180, after opening vents 184, takes place by means of the dihedron formed by tubes 174, so as to aid natural convection. Thus, the air passes through the tube bundles before escaping through flue 182. Obviously, the invention is not limited to the embodiments described in exemplified manner hereinbefore and in fact covers all variants thereof. Thus, it is readily apparent that the fluid cooling condenser 144 is not limited to atmospheric air or even to gases and could optionally be water, although the safety function which must be fulfilled by the devices for cooling the reactor on shutdown make it preferable to carry out cooling by atmospheric air. In the same way, it is obvious that the arrangements of the condensors described with reference to FIGS. 2 to 4 and FIGS. 5 to 6 can optionally be reversed. Thus, it would be possible to place within the reactor enclosure a condenser of the type described with reference to FIGS. 5 and 6. Conversely, it would also be possible to place outside the enclosure a condenser of the type described with reference to FIGS. 2 to 4. Finally, it is obvious that this residual power removal device can be used both in a loop-type reactor and in an integrated reactor. |
051587424 | summary | TECHNICAL FIELD The present invention relates generally to nuclear reactor plants, and, more specifically, to isolation cooling of a nuclear reactor therein. BACKGROUND ART In a conventional nuclear reactor plant, a nuclear reactor such as a boiling water reactor (BWR) is submerged in reactor water within a pressure vessel, and the pressure vessel is disposed inside a containment building. During operation, the reactor core boils the reactor water to generate reactor steam which is suitably channeled to a steam turbine, for example, for generating electrical power. The pressure vessel is suitably sized and configured for containing the relatively high pressures of the reactor steam which may be about 70 kg/cm.sup.2 for example. The containment building, in turn, is sized and configured for also containing such relatively high reactor steam pressures in the event of failure of the pressure vessel or the reactor steam lines therefrom. The containment building also is effective as a radioactive shield for containing radioactivity therein. The building is typically made of thick concrete and is metal lined. In one type of failure mode of the reactor plant, the reactor may become isolated from its normal cooling and water makeup systems, and a conventional isolation condenser is provided to cool the reactor in such event. In another failure mode, a pressure boundary failure such as the failure of one of the reactor steam pipes within the containment building may release hot steam under reactor pressure inside the containment building, and the isolation condenser may also be used to cool that released steam. In either occurrence, as the reactor core is shut down, decay heat is generated which in turn continues to generate reactor steam which must be quenched and cooled to prevent unacceptable temperature and pressure rises within the pressure vessel and/or the containment building. The isolation condenser is typically a conventional heat exchanger having a plurality of tubes therein which are disposed within an isolation pool of water outside the containment building, and the reactor steam from the pressure vessel or from within the containment building is suitably channeled to the isolation condenser and between its tubes for cooling the steam and transferring the heat thereof to the isolation pool water. The reactor steam is condensed on the tubes and is conventionally drained back to the pressure vessel and reused to carry more heat away from the reactor core. In order for the isolation condenser to be effective for maximizing heat transfer from the reactor steam to the pool water, the tubes must be relatively thin and single walled, but, they must be also strong enough to contain the relatively high pressure of the reactor steam being channeled therethrough. Since the reactor steam is channeled through the containment building and through the condenser tubes disposed outside thereof, the tubes themselves provide only a single barrier against release of the reactor steam, which is radioactive. If one or more of the condenser tubes fails during operation, the reactor steam will leak into the isolation pool and be released through a conventional vent to the atmosphere, which therefore would release radiation to the atmosphere outside the containment building. In order to reduce the risk of radioactive steam release from the condenser in the event of a failure thereof, conventional isolation valves are provided both in the conduits leading from the pressure vessel or containment building to the isolation condenser and in the conduits returning the condensed steam back to the pressure vessel. The isolation valves are normally closed valves which must be energized to open during operation so that, upon any failure of the isolation condenser which might release steam therefrom, the fail-safe condition will allow the valves to close upon interruption of power thereto which will stop the flow of reactor steam to the isolation condenser and, therefore, prevent any further release of radiation to the atmosphere. Accordingly, this exemplary conventional isolation condenser system provides a single barrier against release of radioactive steam and is an active system in part since power must be provided to the isolation valves to keep them open during operation while allowing the fail-safe closure thereof in the event of interruption of power thereto to reduce the risk of inadvertent release of radiation in the event of isolation condenser tube failure. OBJECTS OF THE INVENTION Accordingly, one object of the present invention is to provide a new and improved reactor steam isolation cooling system. Another object of the present invention is to provide an isolation cooling system having redundant barriers against leakage of radioactive steam. Another object of the present invention is to provide a passive isolation cooling system having a normally open shutoff valve for allowing passive operation upon loss of power thereto. DISCLOSURE OF INVENTION A reactor steam isolation cooling system includes a containment building surrounding a reactor pressure vessel having a reactor core for generating reactor steam. An isolation pool is disposed outside the containment building and is vented to the atmosphere. An isolation condenser includes a plurality of heat pipes collectively defining at one end thereof a condenser assembly disposed outside the containment building and inside the isolation pool, and at an opposite end thereof an evaporator assembly extending inside the containment building. Reactor steam is selectively channeled to the evaporator assembly for heating a working liquid therein and condensing the reactor steam to form reactor condensate for return to the pressure vessel. The working liquid is vaporized in the evaporator assembly and flows to the condenser assembly wherein it releases heat into the isolation pool with the working condensate therefrom returning to the evaporator assembly. |
058752234 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1a shows a boiling water fuel assembly 1 which comprises a long tubular container, of rectangular cross section, referred to as fuel channel 2. The fuel channel 2 is open at both ends so as to form a continuous flow passage through which the coolant of the reactor flows. The fuel assembly 1 comprises a large number of equally long tubular fuel rods 3, arranged in parallel in a bundle, in which pellets 4 of a nuclear fuel are arranged. The fuel rods 3 are arranged spaced from each other in four orthogonal sub-bundles by means of a cruciform support means 8 (see also FIG. 1b). The respective sub-bundle of fuel rods 3 is retained at the top by a top tie plate 5 and at the bottom by a bottom tie plate 6. The fuel rods 3 in the respective sub-bundle are kept spaced apart from each other by means of spacers 7 and are prevented from bending or vibrating when the reactor is in operation. The spacer according to the invention may, of course, also be used in a boiling water reactor which lacks the cruciform support means 8 and instead is provided with, for example, one or more water tubes. FIG. 2 shows a pressurized-water reactor fuel assembly 1 comprising a number of elongated tubular fuel rods 3 and control rod guide tubes 8 arranged in parallel. In the fuel rods 3, pellets 4 of a nuclear fuel are arranged. The control rod guide tubes 8 are retained at the top by a top nozzle 5 and at the bottom by a bottom nozzle 6. The fuel rods 3 are kept spaced apart from each other by means of spacers 7. FIG. 3 shows the spacer 7 which comprises an orthogonal grid structure of sleeves 9. Each sleeve 9 is intended to position an elongated element 3 extending therethrough. The elongated element 3 may consist, for example, of a fuel rod or a control rod guide tube. The sleeves 9 are thus intended to be joined together with other similar sleeves into a preferably orthogonal grid structure. At least the majority of the sleeves 9 are internally provided with four supports 10. The supports 10 comprise elongated embossments facing the center of the sleeve 9. The elongated embossments give an all-sided positioning of the elongated element 3 extending through the sleeve. The supports 10 are evenly distributed along the circumference of the sleeve 9. The supports 10 extend along the whole length of the sleeve. In FIG. 4 a fragment of the spacer according to FIG. 2 is shown in a view from above. This figure shows that the supports 10 position an elongated element 3 extending through the sleeve. FIG. 5 shows the fragment in FIG. 4 in a view from the side. The upstream edge of the sleeve 9, in relation to the coolant flowing through the assembly, is provided with a wavy form. The wavy edge of the sleeve 9 is suitably made such that that part of the upstream edge 9a, at which the sleeve is joined to an adjacently located sleeve 9 in the grid structure of the spacer, encounters the upwardly-flowing coolant after the coolant has encountered the edge 9b disposed between the joints 9a. In this way, a foreign matter which adheres to the upstream edge of the spacer is oriented transversely of the flow direction and between the elongated element 3, that is, as far away from the surface of the elongated element 3 as possible. In FIG. 4, such a foreign matter 11, in the form of a wire cutting, is shown. The captured foreign matter 11 will thus be oriented so as to make contact with that part of the wavy edge 9a which is disposed at the joint with adjacently disposed sleeves 9 in the grid structure and substantially diagonally across the flow channel 12 which is formed between the sleeves in an orthogonal grid structure. Because of the elongated and inwardly-facing supports 10, the upstream first edge 9b of the sleeve 9 is arranged making contact with the elongated element 3. In this way, foreign matter is prevented from passing in between the sleeve 9 and the elongated element 3. Oblique edges 9c, that is, edges forming an angle v with the axial direction of the spacer, are formed between the part edges 9a, 9b. The oblique edges 9c guide and orient the foreign matter so that it will make contact with the part edge 9a. In this way, the foreign matter which is stopped against the upstream edge of the spacer is diverted away from the surface of the elongated elements 3. |
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summary | ||
abstract | A radiation image storage panel comprises a stimulable phosphor layer, which contains a stimulable phosphor, and a light reflecting layer, which contains a light reflecting substance and is overlaid on one surface of the stimulable phosphor layer. A scattering length of the light reflecting layer with respect to light having wavelengths falling within a stimulation wavelength range for the stimulable phosphor is at most 5 xcexcm. The light reflecting substance may be a white pigment. The light reflecting substance may have a bulk density of at most 1 mg/cm3 or a BET specific surface area of at least 1.5 m2/g. The light reflecting substance may have a mean particle size falling within the range of 1/4 of the stimulation wavelengths to two times as large as the stimulation wavelengths. The radiation image storage panel is capable of emitting light having a high intensity and furnishing a radiation image having good image quality with a high sharpness. |
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abstract | An X-ray beam emitter including a vacuum chamber having a target window. An electron generator is positioned within the vacuum chamber for generating electrons that are directed at the target window for forming X-rays. The X-rays pass through the target window in an X-ray beam. |
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044473885 | abstract | Bolts of a liquid metal fast breeder reactor, each bolt provided with an internal chamber filled with a specific, unique radioactive tag gas. Detection of the tag gas is indicative of a crack in an identifiable bolt. |
description | This application claims priority to U.S. Provisional Patent Application No. 61/096,044, filed Sep. 11, 2008, the disclosure of which is incorporated herein by reference. The present invention is related to glassy liquid crystalline compositions, and more particularly, the present invention is related to cholesteric glassy liquid crystalline compositions having hybrid chiral-nematic groups. Liquid crystals are spontaneously ordered fluids characterized by a uniaxial, lamellar, helical, or columnar arrangement in nematic, smectic, cholesteric, or discotic mesophase, respectively. By preserving these molecular arrangements in the solid state via cooling through glass transition temperature (Tg), glassy liquid crystals (GLCs) represent a unique material class potentially useful for organic optoelectronics. Whereas all liquids are expected to vitrify at a sufficiently rapid cooling rate, most organic materials, including liquid crystals, tend to crystallize upon cooling through the melting point, Tm. Crystallization of liquid crystals essentially destroys the desired molecular order that prevails in the fluid state, resulting in polycrystalline films that scatter light or impede charge transport. The first known or reported attempt to synthesize GLCs in 1971 yielded materials with a low Tg and poor morphological stability, namely, the tendency to crystallize from the glassy state. Subsequent efforts have produced GLCs that can be categorized into (i) laterally or terminally branched, one-string compounds with a Tg mostly around room temperature; (ii) twin molecules with an above-ambient Tg but generally lacking morphological stability; (iii) cyclosiloxanes functionalized with mesogenic and chiral pendants; (iv) carbosilane dendrimers exhibiting a low Tg; (v) macrocarbocycles with mesogenic segments as part of the ring structure; and (vi) pentaerythritol as the central core to yield widely varying Tg and morphological stability. In particular, cholesteric GLCs are potentially useful as large area non-absorbing polarizers, optical notch filters and reflectors, and polarizing fluorescent films. Moreover, cholesteric GLC films can serve as a one-dimensional photonic bandgap for circularly polarized lasing. Comprising separate chiral and nematic pendants, cholesteric GLCs have been synthesized either by a statistical approach, which requires intensive workup procedures to arrive at pure components, or by deterministic approaches, which require long synthesis schemes. Cholesteric GLCs with hybrid pendants having both chiral and nematic moieties chemically bonded to a volume-excluding core addresses the problems of complexity and cost associated with previous cholesteric GLC systems with separate chiral and nematic pendants. However, previous attempts at hybrid pendants have met with little or no success. For example, hybrid pendants with a chiral tail yielded exclusively smectic mesomorphism (Delavier et al., U.S. Pat. No. 5,840,097), and cyanotolan with a chiral spacer to a cyclohexane core failed to achieve mesomorphism (Shi et al., Liq. Cryst., 1994, 17, 413). Based on the foregoing, there is an ongoing unmet need for cost effective preparation of cholesteric glassy liquid crystals with elevated phase transition temperatures, stability against crystallization from the glassy state, and selective reflection across the visible to near infrared region. In one aspect, the present invention provides cholesteric GLC compositions comprising compounds with the following general structure:AL-chiral spacer moiety-L-nematic moiety)z The compounds comprise a volume-excluding core (VEC) (A) and at least one hybrid chiral-nematic pendant moiety (Ch), which is a hybrid pendant moiety with a chiral spacer moiety connected (via a chemical bond) by a linker group (L) to a nematic moiety. The Ch pendants are constructed by combining rigid nematic moieties with flexible chiral spacers intended to partially decouple nematic moieties from volume-excluding cores with a degree of chiral preference to induce the formation of cholesteric mesoporphism. The geometric dissimilarity between the core and the pendant structures is essential to the formation of glassy liquid crystals and their stability against crystallization. The GLC materials of the present invention have desirable mechanical properties for device fabrication and durability. The materials have film- and fiber-forming abilities and morphological stability (e.g., the monodomain cholesteric GLC films retain a glassy state and preserve high orientational order without crystallization). We have GLC films which have been morphologically stable for at least 3 years. In one embodiment, the GLC compositions of the present invention are formed as thin films (e.g., deposited by melt processing or spin coating). Such thin films can range in film thickness from 2 to 22 microns depending on the material types and the spectral range of interest. In another embodiment, the GLC compositions of the present invention are formed as fibers. For example, such fibers can be used in optical communication applications. In one aspect, the present invention provides a method for preparing oriented thin films of cholesteric glassy thin films. The method comprises the steps of: (a) depositing a thin film of an alignment polymer on a substrate; (b) irradiating the polymer with linearly polarized ultraviolet radiation to create a thin film such that the of the polymer molecules are oriented relative to the direction of the linear polarization of the ultraviolet radiation; (c) depositing a thin film of the composition of claim 1 on alignment surface from step b); and (d) annealing the substrate from c) at a temperature above the glass transition temperature of the composition of claim 1, which is the Tg of the compound comprising the composition. Optionally, a second substrate is provided which is prepared according to steps a) and b) above. This substrate is placed on the substrate from c) prior to annealing such that the alignment surface of the second substrate is opposed to the thin film of composition 1 on the substrate from c) and the molecular alignment of the two substrates is the same. The compositions of the present invention can be used in applications of chiral liquid crystalline materials in organic optical devices requiring compositions capable of forming both right- and left-handed helical structures. Chiral-nematic liquid crystalline compositions of the present invention, which form clear, transparent films that absorb no light in the visible region but do selectively reflect visible and near-infrared circularly-polarized light, are especially useful large-area non-absorbing (circular) polarizers, optical notch filters, reflectors (mirrors), polarizing fluorescent films and lasers (e.g. one-dimensional photonic bandgap for circularly polarized lasing). In one aspect, the present invention provides cholesteric GLC compositions comprising compounds with the following general structure:AL-chiral spacer moiety-L-nematic moiety)z The compounds comprise a volume-excluding core (VEC) (A) and at least one hybrid chiral-nematic pendant moiety (Ch), which is a hybrid pendant moiety with a chiral spacer moiety connected (via a chemical bond) by a linker group (L) to a nematic moiety. The number of potential Ch moieties is dependant on the structure of the VEC, e.g. a phenyl VEC can be substituted with 1 to 3 Ch groups. The number of Ch groups, z, is from 1 to 20, including all integers from 1 to 20. The chiral spacer moiety of the hybrid chiral-nematic group is connected to the VEC by a linker group (L). The Ch pendants are constructed by combining rigid nematic moieties with flexible chiral spacers intended to partially decouple nematic moieties from volume-excluding cores with a degree of chiral preference to induce the formation of cholesteric mesoporphism. The geometric dissimilarity between the core and the pendant structures is essential to the formation of glassy liquid crystals and their stability against crystallization. In one embodiment, all substitutions on the VEC are Ch moieties. For example, see compounds I, II, and IV in Chart 1. In another embodiment, the VEC is substituted with at least one Ch moiety and at least one moiety that is not a Ch moiety (for example, see compounds VI (substituted with a nematic moiety) and VII (substituted with an acid moiety) in Chart 1). Other examples of non-Ch moieties include alkyl moieties and alkylaryl moieties, either of which can be unsaturated or otherwise substituted with functional groups such as alcohols, halogens, nitriles, isonitriles, ether, esthers, amides, and the like. The nematic moities discussed herein are also examples of non-Ch moieties. The VEC is a single ring or multi-ring structure with one or more substitution points which can be substituted with Ch groups. Each ring of the single ring or multi-ring structure independently has 4 to 8 carbons, including all integers between 4 and 8. Examples of multi-ring structures are multiple rings which are directly connected, multiple rings with common carbons, or fused-ring structures, and the like. The number of rings in a multi-ring structure can be from 2-10, including all integers between 2 and 10. Examples of VECs include, but are not limited to, a phenyl ring, a cyclohexane ring, a (1s,4s)-bicyclo[2.2.2]oct-2-ene multi-ring structure, an adamantane (tricycle[3.3.1.13,7]) multi-ring structure, or a cubane (pentacyclo[4.2.02,5.03,8.04,7]) multi-ring structure. In various embodiments, the VEC is a monosubstituted phenyl ring, a 1,3-substituted phenyl ring, or 1,3,5-substituted phenyl ring. In one embodiment, the VECs can comprise at least one expander moiety (E). The expander moiety is comprised of a linker group (L) and an expander ring structure (ER) which is a single ring or a multi-ring structure. The expander moiety is connected to one or more Ch moieties, can increase the number of possible chiral-nematic group substitution positions on the VEC. Each ring of the single ring or multi-ring structure independently has 4 to 8 carbons, including all integers between 4 and 8. Examples of single ring expander ring structures include phenyl rings, cyclohexyl rings, or pyridine rings. An example of a multi-ring expander ring structure is a naphthalene ring. The number of E moieties is 1 to 10, including all integers from 1 to 10. An example of an expander moiety is a phenyl ring connected to the VEC by a linker group (such as an ester group). In one embodiment the compounds of the present invention have the following general structure: The number E groups, y, is from 1 to 10, including all integer in between 1 and 10. The number of Ch groups, z, is from 1 to 20. The following are examples of VECs: Examples of compounds of the present invention include, but are not limited to, the following. The chiral spacer moiety of the Ch moiety has at least one chiral center. For example, the chiral spacer moiety is an alkyl chain of 2 to 15, including all integers between 2 and 15, carbons and contains one or two chiral centers. The chain, optionally, includes one or more functional group(s) such as ester or amide groups. The chiral spacer should have sufficient flexibility to enable the Ch pendant groups to self-organize Examples of molecules used to form chiral spacer moieties include, but are not limited to, the following: The chiral spacer groups shown above have a functional group, e.g., a hydroxyl group or bromide, which is reacted to join the spacer, or spacer-linker, or spacer-linker-nematic group to the VEC or expander group via a linker. A linker group (L) is any functional group that can be used to connect the core and the expander ring of the expander moiety, the chiral spacer moiety with the core or expander moiety, and the chiral spacer moiety with the nematic moiety. Either terminus of the functional group can be used to connect either moiety. Examples of functional groups which can be linker groups include, but are not limited to, the following: The nematic moiety is joined to the chiral spacer group by a linker group. Structures with a stable nematic liquid crystalline phase are suitable nematic moities. The nematic moiety is a multi-aromatic ring aromatic moiety. For example, the nematic moiety can have 2 to 15, including all integers in between 2 and 15, aromatic rings. The aromatic rings can be present as fused-ring structures (e.g., a naphthalene structure) or non-fused ring structures (e.g., a biphenyl structure) or individual rings. Individual adjacent rings (or ring structures) can be connected directly, such as by a single bond, or via an unsaturated alkyl chain comprising two carbons (e.g., a ethylene moiety) or a functional group such as an ether, esther, amide, thioether, thioesther, or the like. The moiety can be completely conjugated or partially conjugated. The moiety can include carbon-carbon multiple bonds (alkenyl or alkynl groups) which can conjugate different ring structures in the moiety. Without intending to be bound by any particular theory, it is considered that the nematic moiety provides rigidity to the molecule due to planar conjugation in the moiety. Examples of nematic moieties useful in the compounds of the present invention include, but are not limited to, the following: The nematic moieties can be substituted, as indicated by the X group in the structures above, or un-substituted, in which case X is a hydrogen. Groups suitable for substitution include, halides, nitro groups, alkyl groups, alkoxy groups, cyano and isocyano groups, and thiocyano and isothiocyano groups, and the like. Examples of X groups as substituents on the nematic moiety useful in the present invention, include but are not limited to, the following: The compounds of the present invention can have molecular weights ranging from 500 to 5000 amu. In one embodiment, the GLC materials of the present invention have a molecular weight of less than 2000 amu. While the core and hybrid pendants are crystalline as separate entities, the chemical hybrid, with a proper flexible chiral spacer moiety connecting the two, readily vitrifies into a GLC structure on cooling. In one embodiment, the GLC compositions consist essentially of the compounds of the present invention. In another embodiment, the GLC compositions consist of the compounds of the present invention. In various other embodiments, the GLC compositions of the present invention comprise, consist essentially of, or comprise one or more of the compounds of the present invention. The compounds comprising the GLC compositions of the present invention can be synthesized using a variety of synthetic methodologies, including single-step and multi-step processes. For example, the compounds can be synthesized starting with the core and adding each successive component (e.g., linker(s), chiral spacer moiety/moieties, linker group(s), and nematic moiety/moieties). As another example, the Ch group could be independently synthesized and the pre-prepared Ch group reacted with the linker group, the combination of which is then connected with the core, or the core, which had already been reacted with linker group(s). As yet another example, individual parts of the compound can be pre-prepared and these pre-prepared parts reacted to form the compound (e.g., a core-linker-chiral spacer part and a linker-nematic moiety part can be pre-prepared and subsequently, reacted to form the desired compound). In any of these examples, the components can contain reactive groups which are not part of the final compound. Illustrations of the preparation of exemplary compounds are provided in the Examples. The compounds of the present invention can be synthesized in a cost-effective manner. The synthesis of previous compounds used to form GLCs employed synthetic schemes based on costly and time-consuming protection-deprotection and separation methodology. The protection-deprotection methodology requires multiple steps. In one example, this methodology requires six steps. In comparison, compounds of the current invention can be synthesized in a single step (assuming the Ch pendant groups have been separately prepared). In addition to the savings in materials costs and time, the efficiency of the preparation of compounds of the present invention is increased. For example, compounds of the present invention have been prepared with a 70% yield as compared to previous GLC precursors which were prepared with a yield of less than 10%. As an example of compounds of the present invention, cholesteric GLCs were successfully developed using 4′-cyanobiphenyl-4-yl benzoate nematogens and enantiomeric 2-methylpropylene spacers to a phenyl ring core. A systematic investigation of these compounds was conducted for mesomorphic behavior, morphological stability, and optical properties in relation to the extent of substitution and regioisomerism. Amenability to photo-alignment on coumarin-containing polymer films was also tested with a morphologically stable cholesteric GLC of the present invention. Key findings regarding the compounds of this system are recapitulated as follows: Glass-forming ability generally improves with an increasing substitution with hybrid chiral-nematic mesogens on the benzene ring. The para-disubstituted and the monosubstituted systems lack glass-forming ability for the compounds of this system. With respect to the substituted benzene systems, with Tg at 73° C. and Tc at 295° C., the 1,3,5-trisubstituted system is preferred. Left at room temperature for months, the cholesteric GLC films prepared with meta- and ortho-isomers in addition to 1,3,5-trisubstituted system have remained noncrystalline, evidence of superior morphological stability. Morphologically stable cholesteric GLC films based on compounds of the present invention were characterized for their selective reflection properties. Left-handed helical stacking emerged with (S)-3-bromo-2-methylpropanol as the chiral precursor. Films of the 1,3,5-trisubstituted and meta-disubstituted systems show a λR at 413 and 422 nm, respectively, whereas that of the ortho-isomer system exhibits a λR at 860 nm. Replacing one of the hybrid chiral-nematic mesogens in the 1,3,5-trisubstituted system by a nematogen loosens the helical pitch to yield a λR at 630 nm, still shorter than the ortho-isomer despite the dilution by nematogen. Computational chemistry revealed the closer packing involving chiral spacers in the meta-isomer than the ortho-isomer, thus the stronger helical twisting in the former than the latter. The ortho-isomer is amenable to photo-alignment on films of methacrylate homopolymers and a maleimide-norbornene copolymer containing pendant coumarin monomers to a varying extent. With an extent of coumarin dimerization of about 0.25 as a result of linearly polarized UV-irradiation, the films of a methacrylate polymer with a hexamethylene spacer produced a 7 μm-thick monodomain cholesteric GLC film with selective reflection properties equivalent to mechanical alignment on rubbed polyimide films. In contrast, the rigid and bulky polymer backbone and the short flexible spacer in the maleimide-norbornene copolymer produced a polydomain cholesteric GLC film with inferior selective reflection characteristics. These observations were interpreted by the rotational mobility of pendant coumarin monomers relative to the polarization axis of irradiation. The GLC materials of the present invention have desirable mechanical properties for device fabrication and durability. The materials have film- and fiber-forming abilities and morphological stability (e.g. the monodomain cholesteric GLC films retain a glassy state and preserve high orientational order without crystallization). In one embodiment, morphological stability means that films of the GLC materials do not exhibit detectable (such as by microscopy or x-ray diffraction) for a period of time when stored at ambient temperature (e.g., 65-70° C.). For example, the materials can be stable for 6 months, 1 year, or 2 years. We have GLC films which have been morphologically stable for at least 3 years. Conventional liquid crystal polymers are generally difficult to fabricate into large-area thin films due to high melt viscosity. However, because of their chemical purity, favorable rheological properties, and short and uniform mechanical relaxation time, the GLC materials can be processed into defect-free films. For example, the GLC materials can be melt processed for use in optical elements. In one embodiment, the GLC compositions of the present invention are formed as (e.g. deposited by melt processing) thin films. Such thin films can range in film thickness from 2 to 22 microns depending on the material types and the spectral range of interest. The thin films can be deposited over an area of up to, for example, one ft by one ft by vacuum filling the gap above the glass transition temperature (Tg) between glass substrates. In another embodiment, the GLC compositions of the present invention are formed as fibers. For example, such fibers can be used in optical communication applications. In one aspect, the present invention provides a method for preparing oriented thin films of cholesteric glassy thin films. The method comprises the steps of: (a) depositing a thin film of an alignment polymer on a substrate; (b) irradiating the polymer with linearly polarized ultraviolet radiation to create a thin film the surface of which is an alignment surface, such that the polymer molecules are oriented relative to the direction of the linear polarization of the ultraviolet radiation; (c) depositing a thin film of the composition of claim 1 on alignment surface from step b); and (d) annealing the substrate from c) at a temperature above the Tg of the composition of claim 1. Optionally, a second substrate coated with a thin film of a same or different alignment polymer prepared according to steps a) and b) above is provided. This substrate is placed on the substrate from c) prior to annealing such that the alignment surface of the second substrate is apposed to the thin film of composition 1 on the substrate from c) and the molecular alignment of the two substrates is the same. The annealing step results in a film of composition 1 that is oriented. By oriented is it meant that the molecular axes of the liquid crystals of the thin film are uniaxially oriented relative to a predetermined direction (i.e., the direction dictated by the linearly polarized irradiation used to prepare the alignment polymer or alignment polymers in the case where two alignment surfaces are used). The orientation can be assessed by determining the optical properties of the oriented film. For example, a film is oriented if on impinging unpolarized light on a thin film 40-50%, including all integers between 40 and 50%, of the light is reflected or transmitted and/or the degree of circular polarization of the reflected and/or transmitted light is 90 to 100%, including all integers between 90 and 100%. Based on these values the orientational order parameter can be calculated. The substrate can be any planar surface on which a thin film of the alignment polymer can be deposited. For example, glass substrates can be used. The alignment polymer is any polymer which on irradiation with linearly polarized UV radiation (typically, 300 to 320 nm) creates a surface which can orient a thin film of the composition of claim 1 when the composition is annealed. After irradiation, the alignment polymer should be such that a thin film of the composition of claim 1 can be formed on the exposed surface of the alignment polymer thin film. For example, after irradiation the alignment polymer should be insoluble in common solvents (e.g., chloroform). Examples include the coumarin-containing polymers discussed in Example 1 (e.g., methacrylate homopolymers, maleimide-norbornene copolymers containing varying numbers of pendant coumarin monomers), cinnamate-based polymers and azobenzene-based polymers. The axis selectivity of the alignment polymer determines whether the polymer molecules are oriented parallel or perpendicular to the direction of the linearly polarized light. For example, for maleimide-norbornene copolymers containing varying numbers of pendant coumarin monomers the degree of coumarin monomer dimerization can be from 0.2 to 0.5 while maintaining molecular orientation of the alignment polymer parallel to the linearly polarized ultraviolet radiation used to irradiate the polymer. The annealing step is carried out at temperatures above the Tg of the composition of claim 1 used to form the thin film on the alignment substrate. The annealing temperature should be such that thin film of the GLC composition of claim 1 is not degraded. For example, temperatures of 1 to 25 degrees Celsius, including all integers between 1 and 25 degrees Celsius, above the Tg can be used. In another example, temperatures of 10 to 15 degrees Celsius, including all integers between 10 to 15 degrees Celsius, above the Tg can be used. The annealing step is carried out until the thin-film is oriented. Typically, the annealing step is carried out for 15 to 30 minutes, depending on the composition and film thickness used. In another aspect, the present invention provides an oriented thin film comprising a GLC composition of the present invention. In one embodiment, the oriented thin-film is present on a substrate. In another embodiment, the oriented thin film is present as a one layer of a multilayer composition of one or more thin-films, and molecular axes of the composition are uniaxially ordered. For example, the multilayer composition can include a substrate, an alignment polymer thin film, and an oriented GLC thin film. As another example, the film stack can include a substrate, an alignment polymer thin film, an oriented GLC thin film, an alignment polymer thin film, and another substrate. Optical quality films prepared from GLC materials of the present invention can be used for circular polarizers, circular-polarized fluorescence films, optical notch filters and reflectors, filters for laser protection, latching electro-optical devices for optical communication, and low-threshold and efficient circularly polarized lasers. The supramolecular structure of a chiral-nematic liquid-crystal film comprised of GLC compositions of the present invention can be described a cholesteric mesophase that includes a helical stack of quasi-nematic layers in the Grandjean (or homogeneous) orientation, which is characterized by handedness and helical pitch length, p. Handedness describes the direction in which twisting of the nematic director occurs from one layer to the next, and p is defined as the distance over which the director rotates by 360°. The property of selective reflection can be described in terms of λR=p(ne+no)/2, in which ne and no are the extraordinary and ordinary refractive indices of the quasi-nematic layer, respectively. When unpolarized white light, which consists of equal amounts of left-handed (LH) and right-handed (RH) circularly polarized components, propagates through a LH film the LH circularly polarized component in the neighborhood of λR is selectively reflected, while the RH component is completely transmitted. A sufficiently thick, singlehanded cholesteric film is capable of reflecting 50% of incident unpolarized light within the selective reflection band. Outside the selective reflection band, incident light is transmitted regardless of its polarization state. It follows that a stack of RH and LH chiral-nematic films (or a single film comprising both RH and LH chiral-nematic films) tuned at the same λR will reflect 100% of incident unpolarized light within the selective reflection band without attenuating the rest of the spectrum. For example 2 to 22 micron, including all integers between 2 and 22 microns, thick films of the GLC compositions are typically sufficient to reflect/transmit light with wavelengths from visible (blue) wavelengths to near-IR wavelengths. Generally, the film thickness and refractive index of the GLC composition(s) will dictate what wavelengths of light interact with the films (e.g., GLC compositions with a high refractive index will require thinner films to reflect/transmit light relative to compositions with a lower refractive index. The compositions of the present invention can be used in applications of chiral liquid crystalline materials in organic optical devices requiring compositions capable of forming both right- and left-handed helical structures. When a film of such a composition is applied to a substrate or surface, the helical structures are capable of forming and maintaining the Grandjean texture, in which the helical axis is perpendicular to the substrate surface, to enable the selective reflection of circular-polarized light. An enantiomeric chiral pair of liquid crystalline compositions of the present invention prepared into two separate films, characterized as a right-handed and a left-handed helix, are capable of selectively reflecting right-handed and left-handed circular-polarized light, respectively. Chiral-nematic liquid crystalline compositions of the present invention, which form clear, transparent films that absorb no light in the visible region but do selectively reflect visible and near-infrared circularly-polarized light, are especially useful large-area non-absorbing (circular) polarizers, optical notch filters, reflectors (mirrors), polarizing fluorescent films and lasers (e.g. one-dimensional photonic bandgap for circularly polarized lasing). The following examples are presented to illustrate the present invention. They are not intended to limiting in any manner. Materials and Methods Material Synthesis. All chemicals, reagents, and solvents were used as received from commercial sources without further purification except tetrahydrofuran (THF) that had been distilled over sodium and benzophenone. The 1-[(tert-butyldimethylsily)oxy]-3,5-benzenedicarboxylic acid was synthesized according to literature references. Compounds IX through XI and their intermediates were synthesized according to Reaction Scheme 3. (S)-2-(3-Hydroxy-2-methylpropoxy)-6-bromonaphthalene, 4. Acetonitrile (60 mL) was added to a mixture of 6-bromo-2-naphthol (2.7 g, 12 mmol), (S)-(+)-3-bromo-2-methylpropanol (2.0 g, 13 mmol), potassium carbonate (2.5 g, 18 mmol), and a catalytic amount of potassium iodide. After refluxing overnight, the solid residue was removed from the reaction mixture by filtration, and the filtrate was evaporated to dryness under reduced pressure. The solid residue was purified by gradient column chromatography on silica gel with hexane:methylene chloride (1:10) to pure methylene chloride to yield 4 (1.5 g, 43%). 1H NMR spectral data (400 MHz, CDCl3): δ (ppm) 1.08 (d, 3H, —CH3), 1.76 (s, 1H, HO—), 2.26 (m, 1H, —CH2CH(CH3)CH2—), 3.74 (d, 2H, HOCH2—), 4.05 (d, 2H, —CH2OAr), 7.11-7.17 (m, 2H, aromatics), 7.47 (d, 1H, aromatics), 7.58 (d, 1H, aromatics), 7.64 (d, 1H, aromatics), 7.90 (s, 1H, aromatics).(S)-2-(3-Hydroxy-2-methylpropoxy)-6-(4-cyanophenyl)naphthalene, Ch3-OH. In a mixture of 4 (1.5 g, 5.1 mmol), 4-cyanophenyl boronic acid (0.82 g, 5.6 mmol), and tetrakis(triphenylphosphine)palladium(0) (0.29 g, 0.25 mmol), toluene (20 mL) and 2M Na2CO3 solution (15 ml, 30.5 mmol) were added. The reaction mixture was stirred under argon at 90° C. overnight. Upon cooling to room temperature, ethyl acetate was added to the reaction mixture. The organic layer was separated and washed with brine before dry over anhydrous magnesium sulfate. Upon evaporating off the solvent, the solid residue was purified by gradient column chromatography on silica gel with hexane:methylene chloride (1:10) to pure methylene chloride to yield Ch3-OH (0.95 g, 59%). 1H NMR spectral data (400 MHz, CDCl3): δ (ppm) 1.10 (d, 3H, —CH3), 1.76 (t, 1H, HO—), 2.28 (m, 1H, —CH2CH(CH3)CH2—), 3.76 (d, 2H, HOCH2—), 4.10 (d, 2H, —CH2OAr), 7.21 (d, 2H, aromatics), 7.67 (d, 1H, aromatics), 7.73-7.83 (m, 6H, aromatics), 7.98 (s, 1H, aromatics).1-Hydroxy-3,5-benzenedicarboxylic acid, bis[(R)-3-[4-[(4′-cyanobiphenyl-4-yl)oxy carbonyl]phenoxy]-2-methylpropyl]ester, 5. To a solution of 1-[(tent-Butyldimethyl sily)oxy]-3,5-benzenedicarboxylic acid (0.36 g, 1.2 mmol), Ch2-OH (1.00 g, 2.6 mmol), and TPP (0.71 g, 2.7 mmol) in anhydrous tetrahydrofuran (15 mL), DEADC (0.47 g, 2.7 mmol) was added dropwise. The reaction was stirred under argon at room temperature overnight. The solvent was then removed under reduced pressure, and the solid residue was purified by gradient column chromatography on silica gel with methylene chloride:hexane 100:10 to 100:5. The tert-butyldimethylsily ether was hydrolyzed with Cs2CO3 (0.19 g, 0.59 mmol) in the mixture of N,N-dimethylformamide (15 mL) and water (1.5 mL). After stirring at room temperature for 1 h, the reaction mixture was extracted with ethyl acetate. The extracted solution was washed with brine and dry over anhydrous magnesium sulfate. Upon evaporating off the solvent, the solid residue was purified by gradient column chromatography with acetone in methylene chloride from 0 to 3% to yield 5 (0.95 g, 87%). 1H NMR spectral data (400 MHz, CDCl3): δ (ppm) 1.21 (d, 6H, —CH3), 2.53 (m, 2H, —CH2CH(CH3)CH2—), 4.06 (d, 4H, —CH2OAr), 4.43 (m, 4H, —COOCH2—), 5.50 (s, 1H, HO—), 6.99 (d, 4H, aromatics), 7.29 (d, 4H, aromatics), 7.63 (d, 4H, aromatics), 7.65-7.74 (m, 10H, aromatics), 8.14 (d, 4H, aromatics), 8.25 (s, 1H, aromatics)1-Hydroxy-3,5-benzenedicarboxylic acid, bis[(R)-3-[[[6-(4-cyanophenyl)naphthyl]-2-yl]oxy]-2-methylpropyl]ester, 6. The procedure for the synthesis of 5 was followed to prepare 6 using Ch3-OH (0.51 g, 1.6 mmol) instead of Ch2-OH in 65% yield (0.51 g). 1H NMR spectral data (400 MHz, CDCl3): δ (ppm) 1.18 (d, 6H, —CH3), 2.52 (m, 2H, —CH2CH(CH3)CH2—), 4.06 (m, 4H, —CH2OAr), 4.43 (m, 4H, —COOCH2—), 6.22 (s, 1H, HO—), 7.16 (t, 4H, aromatics), 7.63 (d, 2H, aromatics), 7.69-7.79 (m, 14H, aromatics), 7.94 (s, 2H, aromatics), 8.25 (s, 1H, aromatics).1,3,5-Benzenetricarboxylic acid, tris[(R)-3-[[[6-(4-cyanophenyl)naphthyl]-2-yl]oxy]-2-methylpropyl]ester, IX. The procedure for the synthesis of II was followed to prepare IX using Ch3-OH (0.41 g, 1.1 mmol) instead of Ch2-OH in 73% yield (0.33 g). 1H NMR spectral data (400 MHz, CDCl3): δ (ppm) 1.17 (d, 9H, —CH3), 2.52 (m, 3H, —CH2CH(CH3)CH2—), 4.05 (d, 6H, —CH2OAr), 4.45 (m, 6H, —COOCH2—), 7.15 (t, 6H, aromatics), 7.64 (d, 3H, aromatics), 7.69-7.78 (m, 18H, aromatics), 7.94 (s, 3H, aromatics), 8.85 (s, 3H, aromatics).1,3,5-Benzenetricarboxylic acid, tris[3,5-benzenedicarboxylic acid, bis[(R)-3-[4-[(4′-cyanobiphenyl-4-yl)oxycarbonyl]phenoxy]-2-methylpropyl]ester]phenyl ester, X. 1,3,5-Benzenetricarboxylic acid (0.063 g, 0.30 mmol), 5 (0.89 g, 0.97 mmol), and DPTS (0.27 g, 0.91 mmol) were dissolved in a mixture of anhydrous methylene chloride (5 mL) and anhydrous N,N-dimethylformamide (2 mL). DCC was quickly added to the reaction mixture, which was stirred under argon at room temperature overnight. Upon filtering off white solids, the filtrate was diluted with additional methylene chloride. The solution was washed with 1M hydrochloric acid and brine before being dried over magnesium sulfate. The crude product was collected by evaporation under reduced pressure and purified by gradient column chromatography on silica gel with 0 to 0.5% methanol in chloroform to yield X (0.10 g, 11%). 1H NMR spectral data (400 MHz, CDCl3): δ (ppm) 1.19 (d, 18H, —CH3), 2.53 (m, 6H, —CH2CH(CH3)CH2—), 4.04 (d, 12H, —CH2OAr), 4.47 (m, 12H, —COOCH2—), 6.98 (d, 12H, aromatics), 7.28 (d, 12H, aromatics), 7.60 (d, 12H, aromatics), 7.66 (d, 12H, aromatics), 7.70 (d, 12H, aromatics), 8.13 (d, 18H, aromatics), 8.62 (s, 3H, aromatics), 9.26 (s, 3H, aromatics).1,3,5-Benzenetricarboxylic acid, tris[3,5-benzenedicarboxylic acid, bis[(R)-3-[[[6-(4-cyanophenyl)naphthyl]-2-yl]oxy]-2-methylpropyl]ester]phenyl ester, XI. The procedure for the synthesis of X was followed to prepare XI using 6 (0.47 g, 0.60 mmol) instead of 5 in 11% yield (0.048 g). 1H NMR spectral data (400 MHz, CDCl3): δ (ppm) 1.20 (d, 18H, —CH3), 2.53 (m, 6H, —CH2CH(CH3)CH2—), 4.05 (d, 12H, —CH2OAr), 4.46 (m, 12H, —COOCH2—), 7.15 (t, 12H, aromatics), 7.61 (d, 6H, aromatics), 7.67-7.79 (m, 36H, aromatics), 7.91 (s, 6H, aromatics), 8.81 (s, 6H, aromatics), 8.64 (s, 3H, aromatics), 9.18 (s, 3H, aromatics). FIG. 1b shows the DSC thermograms of compounds identified in Example 2. Compound IX is a morphologically stable cholesteric GLC, with Tg at 85° C. and Tc at 161° C. Because of nonlinearity caused by naphthalene in the nematic moiety, the Tc is lower for IX than II. Compounds with an extended core, X and XI, were prepared with Ch2-OH and Ch3-OH, respectively. Normally, Tg increases with an increasing number of pendant groups. While the invention has been described through illustrative examples and embodiments, routine modifications to the described examples and embodiments will be apparent to those skilled in the art and such modifications are intended to be within the scope of the present invention. |
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047770090 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to nuclear power and particularly to the control of recirculating steam generators in pressurized water nuclear steam supply systems (NSSS). More specifically, the present invention is directed to automatic water level controls for steam generators of nuclear power systems. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character. 2. Description of the Prior Art The nuclear steam generator of a pressurized water nuclear power plant is typically controlled as a function of three primary operating parameters which are monitored, i.e., water level (L) steam flow (W.sub.S) and feedwater flow W.sub.fw). The signals corresponding to the monitored parameters are processed in proportional/integral and lead/lag circuits to generate a feedwater flow demand signal for controlling the amount of water introduced into the steam generator for the production of steam. The principal concern, and therefore the operating parameter on which the control action is primarily based, is the steam generator water level. In practice, the control of the steam generators of NSSS has proven to be an unusally difficult task. As a result, a significant proportion of major nuclear power plant outages have been caused by reactor trips due to steam generator operation outside the desired range. Many of these outages are due to reactor trips on low or high steam generator water levels. Typically, about 80 percent of steam generator low water level trips occur below 20 percent system rated power, and nearly 90 percent of the high water level trips occur below 20 percent power. The problem of maintaining steam generator water level within proper limits is particularly acute during plant startup, when the operators have had relatively little experience in steam generator water level control. A major complexity incident to steam generator control, particularly at low power levels, resides in the water recirculation characteristics of the system including the steam generator. Thus, during low power operation, the sensitivity of the steam generator water level to changes in feedwater flow increases. Also, at low power there is a seemingly anomolous behavioral characteristic which is manifested by an initial decrease in steam generator water level when there is an increase in the feedwater flow. This behaviour often confuses the operator, and usually causes the operator to further increase the feedwater flow, causing a further decrease in the water level and introducing "positive feedback" into the system which may lead to uncontrolled oscillation of the water level and to a reactor trip. Conventional controllers, even of the above-mentioned three parameter type, are unreliable at low power operation because the steam flow and feedwater flow signals are themselves not reliable under such operating conditions. In most instances, because of this known lack of reliability, the operators elect to manually control the water level. Attempts at manual control have met with only limited success to date. SUMMARY OF THE INVENTION It is thus an object of the present invention to provide a control technique for a recirculating steam generator in a nuclear steam supply system and particularly a method which is capable of automatic water level control over the full power operating range of the steam supply system. In accordance with the invention, there is provided a control system and a method of control for a recirculating nuclear steam generator that takes into account the power related variations in the dynamic characteristics of the steam generator. Thus, the present invention automatically controls the feedwater flow rate to a steam generator to maintain satisfactory downcomer water level during steady-state operation and during the following load maneuvers: (a) 10 percent steps in NSSS load between 15 percent and 100 percent NSSS power. PA0 (b) 1 percent/minute ramps in NSSS load between 0 percent and 15 percent NSSS power and 5 percent/minute ramps in NSSS load between 15 percent and 100 percent NSSS power. PA0 (c) Load rejections of any magnitude. PA0 (a) Reactor trip PA0 (b) Loss of a Feedwater Pump during two feedwater pump operation. PA0 (c) High steam generator downcomer water level. The present invention also provides for automatic operation in the event of the following plant conditions: In accomplishing the foregoing, the present invention automatically opens and closes, in a sequential manner, the downcomer and economizer feedwater control valves. Additionally, the invention coordinates the adjustment of the economizer feedwater control valve, the downcomer feedwater control valve and main feedwater pump speed setpoint to automatically regulate the feedwater flow between 0 percent and 100 percent NSSS power to control the steam generator water level. In accordance with a preferred embodiment, the invention regulates the feedwater flow rate to control the steam generator downcomer, i.e., steam generator, water level after a reactor trip by sensing the T.sub.AVG signal from the associated primary coolant loop. This action minimizes the possibility of overcooling the primary coolant loop after a reactor trip. The system automatically returns to the low power level control mode when steam generator water level returns to its setpoint. A control system in accordance with the invention is configured to minimize the necessity for separate adjustments by the operator during manual operation of the feedwater pump speed setpoint and the feedwater control valves. This minimizes operator actions and thus minimizes possible operator error. A particularly unique feature of the invention is its ability to position the feedwater control valves as a function of power speed such that at low flow rates feedwater flow is predominantly regulated by valves while pump speed control is the primary mechanism for feedwater flow adjustment at high flow rates. In the practice of the invention, a signal commensurate with the measured steam generator water level is passed through a lead-lag circuit. The lead improves the control responsiveness and compensates for the delays in the steam generator process, while the lag improves the steady state response and the stability margin. The lead and lag settings are automatically varied with power level to compensate for the dynamic characteristics of the steam generator. The thus processed water level signal is then passed through a proportional-integral controller, where the gain and reset rate are also adjusted as a function of power to further compensate for the steam generator dynamic characteristics. |
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claims | 1. An X-ray device comprising:an X-ray source;a settable collimator;an X-ray detector; anda data processing unit which calculates a reduction in radiation dose brought about by the collimator. 2. The X-ray device of claim 1 further comprising a display unit for displaying the calculated reduction in radiation dose. 3. The X-ray device of claim 2 wherein the reduction in the radiation dose is quantified by the ratio of the radiation cross-sectional areas with and without the collimator. 4. The X-ray device of claim 2 wherein the reduction in the radiation dose is quantified by the ratio of the area dose products with and without the collimator. 5. The X-ray device of claim 1, wherein the data processing unit calculates the reduction in the radiation dose (DR) by using the relationship:DR=DAPb/DAP0·100%where DAPb is an area dose product with filters in place, and DAP0 is an area dose product with a completely open shield. 6. The X-ray device of claim 2, further including:an imaging region for receiving a subject to be imaged;a reconstruction processor that reconstructs received x-rays into an image representation of the subject, wherein the display unit displays the image representation and the reduction in dose concurrently. 7. An X-ray device, comprising:a) an X-ray radiation source;b) a settable collimator for limiting, locally damping and/or filtering a bundle of X-rays;c) an X-ray detector; andd) means for detecting a reduction in the radiation dose brought about by the collimator. 8. An X-ray device as claimed in claim 7, further comprising a data processing unit for controlling the generation of images and for processing recorded X-ray images, which data processing unit is connected to the X-ray radiation source, the collimator and the X-ray detector and is set up for the purpose of detecting the current setting of the collimator and determining therefrom the reduction in the radiation dose brought about by the collimator. 9. An X-ray device as claimed in claim 7, further comprising a display unit for displaying a recorded X-ray image, and displaying the detected reduction in the radiation dose as text and/or as graphics. 10. An X-ray device as claimed in claim 7, further comprising a display unit for displaying imaging parameters, and displaying the radiation dose as text and/or as graphics. 11. An x-ray device as claimed in claim 7, wherein the collimator includes a shutter, and iris for limiting cross-sectional area of an x-ray beam from the x-ray source, and filter elements with adjustable x-ray transparency for adjusting a spectrum of the x-rays. 12. A method of setting the collimator of an X-ray device, wherein, based on the current setting of the collimator and possibly other components of the X-ray device, the reduction in the radiation dose brought about by the collimator is determined and displayed. 13. A method as claimed in claim 12, wherein the reduction in the radiation dose is quantified by the ratio of the radiation cross-sectional areas with and without the collimator. 14. A method as claimed in claim 12, wherein the reduction in the radiation dose is quantified by the ratio of the area dose products with and without the collimator. 15. A method as claimed in claim 14, wherein the area dose product with collimator is calculated as a function of characteristics of the X-ray radiation source of the X-ray device. 16. A method as claimed in claim 12, wherein the reduction in the radiation dose is displayed as text and/or as graphics. 17. A method as claimed in claim 12, wherein the reduction in back-scattering of the X-ray radiation and/or the improvement in image quality is determined from the reduction in the radiation dose. 18. A method as claimed in claim 12, wherein the radiation dose reduction is displayed during a patient examination to indicate the reduction in radiation dose in real time during the examination. 19. A method as claimed in claim 16, further including:disposing a subject in an imaging region of the x-ray device;reconstructing received x-rays into an image representation;displaying the image representation and the reduction in dose concurrently. 20. The method of claim 12, wherein the step of determining the radiation dose (DR) brought about by the collimator includes using the relationship:DR=DAPb/DAP0·100%where DAPb is an area dose product with filters in place, and DAP0 is an area dose product with a completely open shield. |
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052664945 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a simplified schematic of a typical soil washing concept is illustrated, in which contaminated soil, generally 1, is transported through a soil washing system, generally 2, which may comprise chemical extraction or physical separation or combinations thereof, depending on the contaminant being removed from the soil. The contaminated concentrates or effluent removed from the soil washing system 2 can comprise one or two streams, a radioactive/heavy metal stream 3a and an organics stream 3b. The radioactive/heavy metal stream 3a is typically concentrated for disposal or processing as recovered metal ore feed. The organics are typically rendered more environmentally acceptable either through biotreatment or thermal degradation. The clean soil which is recovered 4 is typically returned to the site. The process illustrated in FIG. 1 reduces the volume of contaminants and therefore the cost of remediating the contaminated site. The soil washing process is based upon commonly available mineral treatment processes for handling larger particles. Several of these soil washing processes have been successfully employed in Europe for several years for washing contaminated soils. Examples include the clean-ups at HWZ Bodemsanering B.V. where 98% of the PNA's were removed. See "Extractive Methods for Soil Decontamination; A General Survey and Review of Operational Treatment Installations," J. W. Assink Contaminated Soil, First International TNO Conference on Contaminated Soil, Nov. 11-15, 1985, UTRECHT, the Netherlands, p. 655, incorporated by reference herein. As another example, at a clean-up in Hamburg, 90% of the heavy metal and organic contents were removed by simple size classification. See "Sand From Dredge Sludge--Development of Process for the Mechanical Treatment of Dredged Material", J. Werther, et al., First International TNO Conference on Contaminated Soil, Nov. 11-15, 1985 UTRECHT, the Netherlands, p. 887, incorporated by reference herein. Referring to FIG. 2, a particular embodiment of a soil washing process is illustrated. This process is described in a copending U.S. patent application Ser. No. 529,092 now U.S. Pat. No. 5,128,068, Jul. 7, 1992, commonly owned by the asignee of the present invention. Initially, the excavated soil 1 is processed to remove large rocks and debris. This step is not shown in FIG. 2. The soil is then processed in a mechanical size separator 10 such as for instance a rotating drum or vibrating screen device to sort and prewash the feed soil with a contaminant mobilizing solution, provided through line 12. Large pieces of soil, for instance larger than 5 mm are washed with the contaminant mobilizing solution, rinsed with water supplied through line 14, checked for residual contaminants, and returned to the site as recovered soil. The contaminant mobilizing solution (or process stream) used to wash the soil will be dependent upon the contamination to be removed. For soluble contaminants, the solution will contain a leaching agent. Many suitable leaching agents are known and common leaching agents suitable for leaching radioactive compounds include for example potassium carbonate, sodium carbonate, acetic acid, sodium hypochloride, and others. Leaching agents for contaminants typically found in contaminated soils and the like are well known. For dispersible contaminants, the contaminant mobilizing solution contains a suitable surfactant. Again, suitable surfactants for dispersing contaminants such as oil, grease, polychlorinated biphenyls, etc., are also known. The contaminant mobilizing solution may contain various combinations of leaching agents and surfactants, again, depending on the contaminants in the soil to be cleaned. The effluent of soil particles smaller than 5 mm. and contaminant mobilizing solution discharged from the mechanical separator 10 through line 16 is then processed in a countercurrent flow size separator such as the mineral jig 18. In the jig 18, additional contaminant mobilizing solution supplied through line 13 flows upwardly countercurrent to the effluent. The fines are carried upwardly with the upward flow of contaminant mobilizing solution to form a slurry which is discharged through a line 20. These fines typically include heavy metal particles. The velocity of the upward flow of contaminant containing solution in the mineral jig 18 is set to separate fines of a desired size, for example fines smaller than 60 microns in diameter. The slurry discharged in the line 20 includes, in addition to the fines, contaminant mobilizing solution which contains leached and dispersed metals and organics. Heretofore, mineral jigs such as that disclosed in U.S. Pat. No. 4,873,253, have only been operated in a concurrent flow mode. We preferably operate the mineral jig 18 in a countercurrent flow mode. For such countercurrent flow operation, the jig can be operated with a stroke length of 1/2 to 3/4 inch, a pulse frequency of 300 to 400 per minute, an upflow rate of contaminant mobilizing solution of 1 to 8 liters per minute, an underflow rate of 1 to 3 liters per minute, with one layer of balls 3/16 inch in diameter or greater to provide a soil under flow of 80 to 95 percent and soil over the top of 20 to 5 percent. The intermediate sized particles between 5 mm and 60 microns in diameter, which are discharged from the bottom of the mineral jig 18, are abraded in an attrition scrubber 22a which dislodges mineral slime or fines from them. Another attrition scrubber 22 may precede the mineral jig 10. The intermediate sized particles and the dislodged fines discharged from the attrition scrubber 22a through line 24 are rinsed in a second countercurrent flow size separator such as the second mineral jig 26 operated in the manner discussed above in connection with jig 18. The countercurrent flow in the second mineral jig 26 is wash water which flows upwardly at a velocity again selected to separate the dislodged fines, typically of 60 microns in diameter and smaller. The slurry of fines and wash water is discharged through line 28. The remaining intermediate sized particles discharged from the second mineral jig 26 are processed in a density separator such as a cross-current flow jig 30 to extract higher density heavy metal solid waste particles. The mineral jig 30, which is similar to the jigs 18 and 26 is operated in the cross-current flow mode with a stroke length of 1/2to 3/16 inch, a pulse frequency of 100-400/min, a water upflow rate of 1 to 8 liters/min, one to three layers of balls less than 3/16 inch to provide soil over the top of 80 to 95 percent and a soil underflow of 20 to 5 percent. The cross-current flow carrying the intermediate sized soil particles is discharged through a line 32 into dewatering apparatus such as, for instance, a clarifier 34 or a hydroclone. Sludge from the clarifier 34 is pumped by a pump 36 onto a drying pad 38. The dried particles recovered from the drying pad are checked for cleanliness and returned to the site as additional cleaned soil. Water removed by the clarifier 34 is circulated by a pump 40 through a line 42 as the countercurrent wash water for the second mineral jig 26, and through line 44 as the cross-current flow for the density separator jig 30. The two waste slurry streams in the lines 20 and 28 from the first and second mineral jigs 18 and 26, respectively, are discharged into precipitation equipment 46 to which is added a precipitant to precipitate the dissolved metals. A sulfide or other suitable agent can be used to precipitate the dissolved metals present in a particular contaminated soil. These precipitates and fine soil particles will be highly contaminated with organics and heavy metals. A flocculant, such as for example Nalco 7182, an anionic polymer that does not interfere with trace metal absorption and co-precipitation, supplied by the Nalco Chemical Company, Naperville, Ill., is added to the precipitates and fines conveyed from the precipitation equipment 46 through a line 48 to dewatering apparatus 50 which may include for instance Bardles-Mozley concentrator 52 which separate micron size particles of high specific gravity. Simultaneously, fine particles are washed by the high shear, orbital shaking of the table. Fine soil solution which is washed from the table is passed through high intensity matrix magnetic separators which remove micron sized particles coated with weakly paramagnetic hydroxides containing inorganic contaminants. Solids from the remaining solution are then separated from the stream by either filtration or flocculation settling and pelletizing in apparatus 54. The organically contaminated fractions can be further treated biologically, chemically or thermally and returned to the site. Concentrated solids removed by the Bartles-Mozley concentrator 52 can be disposed of or sold as a concentrate. The filtrate is passed through the line 55 to an activated carbon bed 56 to remove all organics before being sent through line 58 for recycling. The recycled solution is discharged in the one of two contaminant containing solution makeup tanks 60 and 62 which is not currently being used to feed the process. Makeup chemicals 61 may be supplied and/or recycled to the makeup tanks 60 and 62. The contaminated activated carbon in the bed 56 can be thermally or chemically treated or buried. The recycled contaminant mobilizing solution is analyzed and an active component such as caustic or emulsifier are made up on a batch basis in the off-line makeup tank 60 or 62. Contaminant mobilizing solution from the active one of the tanks 60 and 62 is pumped by the pump 64 or 66, respectively, through the line 12 to the mechanical size separator 10 and through the line 13 to the first mineral jig 18. Referring again to FIG. 2, excavated feed soil (representative contaminated soil sample) is first processed to remove large rocks and debris and yield a pre-washed feed soil 3 by processing the feed soil 16 in a rotating drum or vibrating screen 10 to prewash the feed soil 16 using extractant 12 and remove larger particles greater than a nominal one-inch in diameter. Large particles, 4, generally greater than 48 mesh, which are more likely to be uncontaminated, have been washed with a leach solution, rinsed with water and are returned to the site. The remaining contaminated soil is then processed in one or more attrition scrubbers 22 followed by a mineral jig 18 which provides counter-current contact between soils less than 48 mesh and greater than 44 microns and the leach solution. The fines, generally less than 44 microns, are carried over with the wash solution which contains leached organics and metals, 20, 28. The contaminants are precipitated from this stream and removed using flocculation, for example by adding NaOH, and Na.sub.2 SiO.sub.3. The washed soils less than 48 mesh and greater than 44 microns are then abraded in a second attrition scrubber 22a and rinsed in a second counter-current mineral jig 26, treated for removal of high specific gravity metal contaminants in a specific gravity separator 30, monitored and returned to the site. The fines and wash water go to the flocculation and dewatering system 50 for precipitation and removal. One of the problems associated with remediating a contaminated site, regardless of the particular soil washing technique being used, is how to inexpensively determine whether or not the particular soil washing process is both a technically and economically feasible remediation approach. We have found that it is possible to run a bench scale or reduced scale process on virtually any soil sample using only a few pounds of sample to determine the appropriate processing parameters for a full scale soil cleaning operation. The bench scale tests can be run in a small area, remotely if needed, which makes the invention suitable for use with hazardous or radioactive materials which must be treated with special care. The essential steps of the process include first identifying the contaminated particle size ranges contained in the soil sample, followed by identifying an effective extractant for use in connection with the contaminants contained in that sample, followed by identification of an effective leachate treatment approach for use with respect to the particular soil and contaminants of the sample. Each of these three aspects to the process will now be discussed in greater detail. Before engaging in the process of the present invention, it is necessary to first obtain a representative contaminated soil sample from the site of interest which contains contaminated soil for which cleaning is desired. In this regard, it may be preferable to obtain a number of samples from various locations at the site in order to establish that soil processing parameters and needs are consistent throughout the site. Every effort should be made to obtain a soil sample which fairly represents the characteristics of the contaminated soil contained in the site as a whole, in terms of particle size, contaminant contained in the soil, etc. Once a representative contaminated soil sample is obtained from the site, according to the present invention it is necessary to evaluate that sample to determine the various particle size ranges making up the sample and the weight fraction of each range in that sample. Any suitable particle size classifying apparatus may be used for this function, although we have found sieves, preferably USA standard testing sieves meeting ASTM E-11 specifications to perform acceptably. The sieves to be used in classifying the particle size ranges are identified by sieve size for example, Nos. 10, 20, 50, 100, 200, and 325. Other sieve sizes may of course be used depending on the characteristics of the particular soil sample being tested. Each sieve is first weighed empty and placed on top of a receiver container in order of decreasing size. For example, in the array of sieves identified above, the No. 325 sieve would be on the bottom and the No. 10 sieve would be on the top. The soil sample to be evaluated is weighed and placed on top of the uppermost sieve. The soil sample is then sprayed with water until no further fines removal through the sieve is observed. Next, the top sieve is removed and the next sieve is sprayed as previously until no further fines removal is observed. This procedure is repeated until all of the sieves have been adequately rinsed. The rinsed sieves are then weighed and dried in a hood or low temperature oven at about 50.degree. C. After drying, the dried sieves are again weighed and the weight of dried soil sample contained on each sieve is determined. All of the effluent water from the sieving process, that is, water containing solids of smaller particle size than are held by the smallest mesh sieve, in this case, less than 325 mesh solids, is filtered. This is accomplished in known fashion, for example, by weighing the filter paper, then weighing the filter paper plus the collected wet solids, drying the solids in a hood or low temperature oven, weighing the dry solids and weighing the filtrate. Care should be taken that the temperature of the drying does not drive off the more volatile organic contaminants. After all of the dried solids are classified, including the dried filtrate, the solids are examined through analysis for contaminants of interest. In this way, it is possible to determine which contaminants are more heavily associated with which classification of soil sizes. The particular method of evaluating the dry solids for contaminants of interest is not critical, so long as it is tailored to the particular contaminants of interest and is suitable for analyzing dried solids. Examples of analysis procedures for determining contaminants of interest include, e.g., mass spectrometry, IR spectrometry, gas chromatography, or any other known analysis method. An example of the type of data generated by this procedure is shown in FIG. 3, which illustrates the correlation between particle size ranges and two contaminants of interest, mercury and uranium, for one soil sample. The second phase of the process of the invention involves the identification of an effective extractant for use in connection with the particular soil of interest. In this phase of the process, extraction testing is used to determine the optimal conditions for removing the contaminants identified in the first step from the soil or soil fraction. Specifically, extractants testing is preferably performed on those size fractions of soil exhibiting levels of contamination above acceptable levels. This second step examines the effects of extractant chemistry, extractant concentration, extractant solution-to-soil-weight ratio, and contact time on the efficiency of contaminant removal from the soil. In this regard, once contaminants of interest have been identified, it is possible to determine what extractants or combination of extractants could be used for extracting each contaminant. Ideally, the extractants are themselves relatively non-toxic, since in most cases they will reenter the site. For metals, the objective is generally to solubilize the metal with the extractant. For organics, the goal may also be to solubilize, e.g. with surfactants. In either case, the objective is to determine the lowest effective concentration of active extractant possible, to minimize the cost of the soil cleaning process. Thus, this second step may involve running a bench scale soil washing process on the same soil using the same extractant, but in different concentrations to determine the best economies of the soil washing system. This step is carried out using equipment which mimics the soil washing process to be used on the full scale site. In the description immediately following, the specific procedures in this second step have been selected to mimic the soil washing process presented in FIG. 2. Of course, any soil washing process could benefit from the invention, and the scope of this invention should in no way be construed to be limited to a bench scale soil washing process that mimics the process of FIG. 2. The equipment used in this step includes sieves such as those used in the first phase of the process just described, a balance such as a Fisher Scientific XT-3000 DR, and a food blender or bench attrition mill. In initiating the second step, the appropriate sieves to be used are identified once again. As previously described, typical sieve sizes may include but are not limited to numbers 10, 20, 50, 100, 200 and 325. The particular sieves used will, of course, depend upon the actual soil being tested, the results of the wet screen contaminant identification described above in step 1 and the process being modeled. Each sieve size should be chosen to represent a point in the soil washing process where a major stream of material is to be removed from the process. Preferably, these points correlate to a range of particle sizes identified in the first step as bearing the most significant share of the contaminants of interest. In this particular embodiment, screens used include 1 inch, 48 mesh (297 micron) and 325 mesh (44 micron). A known amount of the representative contaminated soil sample is placed on the largest sieve, which is positioned over a collection container. Preferably, this soil sample is selected from the same sample used to produce the particle size characteristics in step 1, however, preferably the soil used in step 1 is not reused in step 2. That is, preferably fresh contaminated soil having the same characteristics as the soil used in step 1 is used for step 2. The soil sample is sprayed with a known amount of an extractant solution while sieving the sample vigorously. Examples of extractant solutions include, for example, leachants, surfactants, water, detergent solutions, oxidizing and reducing agents, etc. The type of extractant used depends upon the contaminants of interest, which contaminants are identified as set forth in step 1. After spraying the uppermost sieve with the known amount of extractant solution, the sieve is then sprayed with a known amount of rinse water, again, while sieving the sample vigorously. After the sieve is rinsed, it is removed from above the container, dried as previously described and weighed. The dried product remaining on the screen is then analyzed for the contaminant of interest. The contents of the receiver container are placed into the blender or bench scale attrition mill/scrubber and processed for a predetermined amount of time, generally several minutes. The next largest sieve is then placed on top of a receiver container, in this case, the 48 mesh sieve. The contents of the blender or bench scale scrubber are then poured over the 48 mesh screen which is sprayed with a known amount of rinse water while sieving vigorously. After the sieve is sufficiently rinsed, it is removed, dried as previously described and weighed to determine the amount of dried soil sample contained on the screen. This dried product is then analyzed for the contaminant of interest. The contents of the receiver container are once again placed into the blender or bench scale scrubber and processed for a predetermined amount of time, generally several minutes. The next largest sieve, in this case the 325 mesh sieve, is then placed on the top of a receiver container and the contents of the blender or bench scale scrubber are poured onto this sieve. The effluent running through the screen is collected in the receiver container and placed into a storage container. The contents of this screen are then emptied into a blender or bench scale scrubber along with a known amount of extractant and processed for a predetermined amount of time, again, generally several minutes. The contents of the blender or scrubber or then poured once again onto the 325 mesh sieve which is sprayed with a known amount of rinse water while sieving vigorously. After the sieve has been rinsed, it is removed, dried and weighed as previously described and the dried product is analyzed for the contaminant of interest. The above procedure is preferably repeated using at least one additional extractant to determine which extractants extract the greatest amount of contaminant of interest from the particular soil being studied. Also, different concentrations of the same extractants may be used to determine the lowest effective concentration for extraction of the contaminants of interest. The third phase of the soil sample bench scale evaluation process involves the identification of an effective leachate treatment approach for the soil of interest. Removing contaminants from the soil requires that these liberated contaminants be treated, either for recycle or disposal. For example, heavy metal contaminants may be removed by floculation and filtration. Organics may be pyrolized. As used herein, the term "leachate treatment" refers to all methods whereby contaminants, after removal from soils and as contained in leach solutions, fines and wash solutions, are rendered more environmentally acceptable, e.g., by fixing, e.g., in a concrete matrix, or smelting, in the case of metals, or pyrolizing, in the case of organics. In this third phase, all wash solution, leachate and fines are tested to define a suitable treatment process. Various methods for treatment include pH adjustment, precipitation, flocculation and/or absorption. Precipitation methods include hydroxide or sulfide precipitation or water glass co-precipitation in the case of metal contaminants, and calcium chloride precipitation for organic contaminants. Flocculation includes chemical or electrolytic flocculation and removal using mechanically aided devices or settling tanks. Absorption media include ion exchange resins, zeolites, activated carbon and treated clays, for example. The choice of specific treatment techniques selected depends on the type and level of the contaminants. In this example, it is assumed that the fines are contaminated and must be removed and dewatered. This is the situation facing the typical contaminated soil site. The extractant will be assumed to contain the solubilized contaminant which is a metal and which is removable on an ion exchange column. The equipment used in this phase includes a 500 ml. beaker, a 1 inch diameter by 18 inch high glass column, a pH meter, a pipette for adding reagents, and a variable speed laboratory stirrer. In this phase of the process, a sample of fines slurry from the above step 2 is obtained and placed in the 500 ml. beaker. In this example, a 400 ml. sample of fines slurry was obtained. The pH of the fines slurry was adjusted to about 6.7 using HCl in order to precipitate humic materials. The amount of HCl added to achieve the desired pH is recorded. This pH adjusted solution is then analyzed for the concentration of the contaminant of interest. While gently stirring with the laboratory stirrer, flocculent solution is then added to the 40 ml. sample until flocs form and material settles from the solution. The amount of floc solution added to obtain this settling is recorded. Additionally, the volume of settled floc formed is recorded. The settled slurry is then filtered. Next, the filtrate is carefully poured onto the resin bed which has been filled with water to the top of the resin, and the resin bed is drained from the bottom until all of the filtrate has been processed. The amount of resin required to absorb all of the metal contaminant is estimated. This estimated amount of resin is removed from the top of the column. Next, the resin which has been removed from the column is stripped with a known volume of regenerating solution and the concentration of the contaminant of interest in the regenerating solution is measured. The recovery of the contaminant by the regenerating solution compared to the amount of contaminant poured into the column from the filtrate is the removal efficiency for the resin column. EXAMPLE 1 A soil contaminated with a mixture of mercury and uranium was tested. The soil washing process tested was substantially the same as that illustrated in FIG. 2. The results of the soil fraction/contaminant screening process are illustrated in FIG. 3. This information was used to develop the leachate system. Typical product results for the bench scale tests are shown in Table 1. Based on the success of the bench scale tests, a pilot test was carried out with about 50 pounds of soil using an actual attrition scrubber and a mineral jig. These results are shown in Table 2. There exists as illustrated a very good agreement in performance between the two tests shown in Tables 1 and 2. Referring again to FIG. 3 it is clear that the 250 micron particle size represented a logical cut point for this particular soil sample since most of the uranium contamination occurred in particle sizes less than 250 microns while most of the mercury contamination occurred in the particle size fractions greater than 250 microns. TABLE 1 ______________________________________ Results of Bench Scale Treatability Test Particle Size Residual Soil Contaminant Levels Fraction Treatment Uranium Mercury ______________________________________ .sup. <250 micron Segregation 890 ppm 4500 ppm by Sieving 250 << 200 micron Batch Contact 30-45 ppm 90-150 ppm with 18g/l NaOCl, pH 6 ______________________________________ TABLE 2 ______________________________________ Results of Pilot Scale Treatability Test Residual Soil Contaminant Levels Product Treatment Stream Uranium Mercury ______________________________________ Attrition scrub a) -250 micron 735 ppm 2000 ppm with 20g/l b) +250 micron 20-50 ppm 100-135 ppm NaOCl, pH 6 followed by mineral jig ______________________________________ EXAMPLE 2 In this example, soil contaminated with a mixture of gasoline, diesel oil and lead will be evaluated. The extractant to be used for this example is a commercial detergent, comprising a solution of NP90 (Henkel Corporation, Ambler, Pa. 19002) and Asee 799 (Witco Corporation, Houston, Tex. 77245) in water. The detergent solution is pH adjusted to about 12 with NaOH. A first detergent solution will include 1% of both NP90 and Asee 799. A second detergent will include 0.5% of both NP90 and Asee 799. Use a sample splitter to remove a 500-gram aliquot of soil. This aliquot is wet-sieved into three fractions,>2 mm, 50 micron<<2 mm, and <50 micron. The fractions larger than 2 mm are rinsed with water and the washed solids assayed for organics and lead. Next, the 50 micron <<2 mm fraction is contacted with the first detergent solution in an attrition scrubber for about 20 seconds. The solids are then rinsed with water and resieved to the same three size fractions to estimate the extent of particle attrition. These solids are then assayed for the presence of organics and lead. Next, the <50 micron fines are filtered from the combined wash (detergent) and rinse solutions collected from the previous steps. The solutions are treated with sodium oxalate followed by electrocoagulation, both with and without precipitation using CaCl.sub.2, and the effluent is assayed for organics and lead. The above procedures are then repeated using the second detergent solution. During the bench scale treatment process of this example, the following samples are collected for assay for contaminants: 1. One sample from each of the three dry sieve sizes (before washing). (Total three samples.) PA0 2. Two samples from each of the three wet sieve sizes for each wash solution used. (Total 12 samples.) PA0 3. Three liquid samples, one before and one after treatment, without CaCl.sub.2 and with CaCl.sub.2 precipitation for each leachate. (Total 6 samples.) |
claims | 1. A device for disinfecting an enclosed area by use of ultraviolet radiation, comprising:a fixture that is attached to a fixed architectural partition that forms a part of the enclosed area and is positioned overhead in the enclosed area;an ultraviolet-C radiation emitter located in said fixture, wherein the ultraviolet-C radiation emitter is positioned to direct ultraviolet-C radiation from overhead and toward a wall of the enclosed area; anda plurality of radiation sensors that are positioned with the enclosed area and spaced apart from each other and apart from the fixture, and the plurality of radiation sensors are positioned in the enclosed area and below the ultraviolet-C radiation emitter to receive ultraviolet-C radiation emitted by the ultraviolet-C radiation emitter and reflected from the wall of said enclosed area, wherein said ultraviolet-C radiation reflected from the wall to said plurality of sensors is measured, and a controller terminates emission of ultraviolet-C radiation from said ultraviolet-C radiation emitter after a predetermined accumulated dosage of radiation is received by each of said radiation sensors. 2. A device for disinfecting an enclose area by use of ultraviolet radiation as described in claim 1, wherein said fixed architectural partition is a ceiling, and said fixture and said ultraviolet-C radiation emitter located in said fixture are attached to said ceiling. 3. A device for disinfecting an enclosed area by use of ultraviolet radiation as described in claim 1, wherein said fixed architectural partition is a ceiling, and said fixture and said ultraviolet-C radiation emitter located in said fixture are attached to said ceiling, and wherein a radiation sensor that receives ultraviolet-C radiation reflected from architectural partitions is attached to said ceiling and positioned so as to not receive direct ultraviolet-C radiation from said ultraviolet-C emitter attached to said ceiling. 4. A device for disinfecting an enclosed area by use of ultraviolet radiation, as described in claim 1, wherein said fixture that is attached to the fixed architectural partition of the enclosed area comprises a cover that blocks ultraviolet-C radiation emission, and wherein said cover is positioned over said ultraviolet-C radiation emitter located in said fixture to cover said ultraviolet-C radiation emitter when said ultraviolet-C radiation emitter is not in operation, and wherein said cover is moved away from covering said ultraviolet-C radiation emitter when said ultraviolet-C radiation emitter is in operation to allow ultraviolet-C radiation to be emitted into said enclosed area, and wherein said cover covers said ultraviolet-C radiation emitter when said controller causes termination of emission of ultraviolet-C radiation from said ultraviolet-C radiation emitter. 5. A device for disinfecting an enclosed area by use of ultraviolet radiation as described in claim 1, wherein a first radiation sensor that receives ultraviolet-C radiation reflected from architectural partitions is located on one of said architectural partitions and a second radiation sensor is located underneath equipment or furniture that is present is said enclosed area, and the second radiation sensor is positioned below the ultraviolet-C radiation emitter, wherein first radiation sensor and said second radiation sensor each receive reflected ultraviolet-C radiation and measure said reflected ultraviolet-C radiation and cause termination of emission of ultraviolet-C radiation from said ultraviolet-C radiation emitter after a predetermined accumulated dosage of radiation is received by each of said first radiation sensor and said second radiation sensor. 6. A device for disinfecting an enclosed area by use of ultraviolet radiation as described in claim 1, wherein said fixed architectural partition is a second wall of the enclosed area, and said fixture and said ultraviolet-C radiation emitter located in said fixture are attached overhead and to said second wall. 7. A device for disinfecting an enclosed area by use of ultraviolet radiation as described in claim 1, wherein said fixture further comprises a light emitter that emits visible light. 8. A device for disinfecting an enclosed area by use of ultraviolet radiation, as described in claim 1, wherein said fixture further comprises a light emitter that emits visible light, and said fixture further comprises a cover that blocks ultraviolet-C radiation emission while said cover simultaneously permits emission of visible light. 9. A device for disinfecting an enclosed area by use of ultraviolet radiation, as described in claim 1, wherein said wall of said enclosed area is coated so as to reflect not less than five (5%) percent of the ultraviolet-C radiation directed at said wall. 10. A device for disinfecting an enclosed area by use of ultraviolet radiation as described in claim 1, wherein said fixed architectural partition is a ceiling, and said fixture and said ultraviolet-C radiation emitter located in said fixture are attached to said ceiling, and wherein a second fixed architectural partition is a second wall, and a second fixture and a second ultraviolet-C radiation emitter located in said second fixture are attached to said second wall, and wherein said fixture and said second fixture are spaced apart. 11. A device for disinfecting an enclosed area by use of ultraviolet radiation, as described in claim 1, wherein said fixture that is attached to the fixed architectural partition of the enclosed area comprises a cover that blocks ultraviolet-C radiation emission, and wherein said cover is positioned over said ultraviolet-C radiation emitter located in said fixture to cover said ultraviolet-C radiation emitter when said ultraviolet-C radiation emitter is not in operation, and wherein said cover is moved away from covering said ultraviolet-C radiation emitter when said ultraviolet-C radiation emitter is in operation to allow ultraviolet-C radiation to be emitted into said enclosed area, and wherein said cover covers said ultraviolet-C radiation emitter when said controller causes termination of emission of ultraviolet-C radiation from said ultraviolet-C radiation emitter or when a motion sensor located in said enclosed area senses motion. 12. A device for disinfecting an enclosed area by use of ultraviolet radiation, as described in claim 1, wherein the ultraviolet-C radiation emitter is positioned overhead and in a corner of the enclosed area and the ultraviolet-C radiation emitter is positioned to direct ultraviolet-C radiation to the wall. 13. A device for disinfecting an enclosed area by use of ultraviolet radiation, as described in claim 1, wherein the ultraviolet-C radiation emitter is positioned overhead in a corner of the enclosed area to direct ultraviolet-C radiation from overhead to a diagonally opposite corner of the enclosed area that comprises the wall. 14. A device for disinfecting an enclosed area by use of ultraviolet radiation, as described in claim 1, wherein the ultraviolet-C radiation emitter is positioned adjacent to a ceiling of the enclosed area and generally horizontally to direct ultraviolet-C radiation from overhead and downwardly toward the wall of the enclosed area, and wherein the ultraviolet-C radiation emitter is positioned to direct ultraviolet-C radiation at the wall and toward the enclosed area at an angle of not less than 150 degrees from the plane of the ceiling. 15. A device for disinfecting an enclosed area by use of ultraviolet radiation, as described in claim 1, further comprising a second fixture that is attached to a fixed architectural partition that forms a part of the enclosed area and is positioned overhead in the enclosed area; andan ultraviolet-C radiation emitter located in the second fixture, wherein the ultraviolet-C radiation emitter is positioned to direct ultraviolet-C radiation from overhead and toward a second wall of the enclosed area. 16. A device for disinfecting an enclosed area by use of ultraviolet radiation, as described in claim 1, wherein the ultraviolet-C radiation emitter located in the fixture is positioned to direct ultraviolet-C radiation to the entirety of the enclosed area from overhead. 17. A device for disinfecting an enclosed area by use of ultraviolet radiation, as described in claim 1, wherein a sensor of the plurality of sensors is recessed in the fixed architectural partition in the enclosed area. 18. A device for disinfecting an enclosed area by use of ultraviolet radiation, as described in claim 1, wherein a sensor of the plurality of sensors is positioned within a device comprising a shield and said device is positioned to shield the sensor from receiving direct radiation from the ultraviolet-C radiation emitter. |
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abstract | A vertical spring wedge restores a tight fitup against an adjacent structure, such as between an inlet mixer and an adjacent restrainer bracket in a boiling water nuclear reactor jet pump. The vertical spring wedge includes a U-shaped bracket including a pair of guiding portions and a pair of bracket holes. A pair of wedge assemblies are coupled with the bracket, each of the wedge assemblies including a wedge segment attached to a spring-loaded guide rod. The guide rods are displaceable in the bracket holes between a retracted position and an extended position. The wedge segments engage the guiding portions, and a combination of the bracket and wedge assemblies have a first width when the guide rods are in the retracted position and have a second width wider than the first width when the guide rods are in the extended position. |
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045335141 | summary | This invention relates to a nuclear reactor degassing method and a degassing system therefor, and more particularly it relates to a degassing method and degassing system which can be advantageously adapted in nuclear reactors for lowering the dissolved oxygen concentration in the coolant in the reactor vessel. It is known that, in the water cooling type nuclear reactors, particularly in the boiling water type ones, the concentration of the oxidizing material such as dissolved oxygen in the coolant is a highly influential factor for the corrosion of feed water piping. In order to suppress the corrosion on feed water piping, it has been proposed to adjust the dissolved oxygen concentration in the coolant flowing in the piping (U.S. Pat. No. 3,663,725). Also, a nuclear reactor degassing method in which dissolved oxygen in the coolant in the nuclear reactor pressure vessel is removed at the time of start-up of the reactor to mitigate the risk of stress corrosion cracking of the pressure vessel and the structures therein was proposed in Japanese Laid-Open Patent Application No. 39791/79 (U.S. Pat. No. 4,293,382). An object of this invention is to decrease the dissolved oxygen concentration in the coolant in the nuclear reactor vessel during the reactor start-up period. Another object of this invention is to decrease the dissolved oxygen concentration in the coolant in the nuclear reactor vessel at the time of shutdown of the reactor. A salient feature of this invention resides in that the coolant in the nuclear reactor vessel is sprayed while in a highly heated state into the space in the vessel and the gas in the space is extracted from the nuclear reactor vessel. |
056082240 | description | BEST MODE FOR CARRYING OUT THE INVENTION A target changer for use in an accelerator incorporating various features of the present invention is illustrated generally at 10 in the figures. The target changer 10 is designed for the automated and remote changing of targets on accelerator beamlines. The target changer 10 minimizes the number of connections required to service the target. Further, the target changer 10 is designed to minimize the time required to install or remove a target. The target changer 10 generally includes a ring collimator assembly 14 which includes means for shaping the beam and defines a vacuum window assembly 20, a carousel barrel 36 which provides eight ports 38 for accelerator targets, a carousel hub 46 which distributes water and helium cooling to the targets 40, and a chain drive mechanism 88 which provides the remote positioning of the carousel barrel 36, as shown in FIG. 1. Further, a modular target design allows any target 40 to be installed in any port 38, and an umbilical system provides for the quick installation and removal of any target 40. Referring to FIG. 2, a bombarding beam tube 12 is mounted to the ring collimator assembly 14. The first end of the beam tube 12 is mated to the accelerator vacuum tank (not shown). The ring collimator assembly 14 defines a means for shaping the beam and a vacuum window assembly 20. Preferably, the means for shaping the beam is a ring collimator 16. In the preferred embodiment, the ring collimator 16 is a carbon puck that is ring shaped into a very specific 7 mm diameter. The ring collimator 16 intercepts the beam edge such that only the core of the beam is utilized to eventually bombard the target. The collimator 16 is grounded such that the charge that is deposited by the protons hitting the ring collimator 16 is conducted back to the beam tube 12 and vacuum tank. The ring collimator assembly 14 is isolated from the target 40 via an insulating washer 18. The insulating washer 18 serves as a charge isolator to electrically isolate the ring collimator 16 from the target 40. In the preferred embodiment, the insulating washer 18 is a kapton film. The vacuum window assembly 20 includes a vacuum window 22, a vacuum window support 21 and a vacuum window spacer flange 23. The vacuum window support 21 retains and supports the vacuum window 22. The vacuum window spacer flange 23 receives the vacuum window 22 and its support 21 and provides space between the vacuum window 22 and lower end of the ring collimator assembly 14. The vacuum window spacer flange 23 defines a helium jet 26 which is directed toward the vacuum window 22 and cools the vacuum window 22 with helium. The helium jet 26 is in communication with a helium channel 25 which is in turn in communication with a helium supplier 24. Helium is supplied to the helium supplier 24 via an annular space 27 defined between the ring collimator assembly 14 and the carousel hub 46. Two o-rings 30 are situated, one above and one below the annular space 27, to prevent leakage. The target changer 10 defines only one vacuum window assembly 20 for use with all targets 40. Prior art systems define a vacuum window assembly for each target. The disadvantage of having a vacuum window assembly for each target is that gate valves or other expensive devices are required to maintain a vacuum. The configuration of the present device eliminates such considerations. The carousel barrel 36 defines a plurality of ports 38 and a means for circulating cooling fluid for the target 40 and the target window 32. Each of the ports 38 is configured to receive a target 40 which is held in place by an umbilical 42. In the preferred embodiment, the carousel barrel 36 defines eight ports 38. The ring collimator assembly 14 interfaces with one port and the carousel hub 46 interfaces with the remaining ports. Each target 40 defines a target window 32, a target window spacer flange 34, a target body 43 and a product tube 35, as shown in FIG. 2. The target window spacer flange 34 provides spacing between the target window 32 and the upper end of the target 40. Further, the target window spacer flange 34 defines at least one helium jet 28 for blowing recirculated helium gas on the target window 32. In the embodiment depicted, two helium jets 28 are defined by the target window spacer flange 34 and the helium jets 28 are in communication with the helium inlet 29 defined by the respective port 38. The product tube 35 extends through the length of the target 40 to the rear end thereof. The target body 43 holds a selected target material 41 which can be a gas, liquid, solid or mixture thereof. O-rings 58 are utilized to create a seal between the port 38 and the target 40. The target 40 is retained within the port 38 via the umbilical 42. The umbilical 42 serves three main purposes: (1) to provide a means for directing the product within the product tube(s) 35 away from the system 10, (2) to make the necessary high pressure connections throughout the target 40, and (3) to retain the target body 43 and spacer flange 34 in the port 38. The umbilical 42 defines at least one product line 44 which mates with product tube 35, when the umbilical 42 is installed, and delivers the product to a delivery point at a location exterior to the target changer system 10. The product line 44 is flexible, and preferably, it is fabricated from 1/16" OD Polyether ether ketone (PEEK) or stainless steel tubing. The umbilical 42 includes a captured socket head screw 45 that screws into the carousel barrel 36. Upon securely screwing the screw 45 into the barrel 36, a high pressure seal is established between the target window spacer flange 34 and the target window 32 and between the target window 32 and the target body 43. The carousel barrel 36 and the ports 38 are configured such that the cooling fluid for the target 40, preferably water, is introduced into the carousel barrel 36 and flows into a first port and circulates through the remaining ports before exiting the last or eighth port which is adjacent to the first port. The first port defines a channel 48 for the entrance of water into the port and the last port defines an outlet 50 for the outlet of water from the port, as shown in FIGS. 2, 3 and 4. Each of the remaining ports defines two openings 52, one in communication with the port in front of and one in communication with the port to the rear of the port. The first port defines an outlet opening 52 in communication with the opening 52 defined by the second port and the last port defines an inlet opening 52 in communication with the outlet opening 52 of the seventh port. In the preferred embodiment, the target 40 defines a threaded portion 54 on the exterior thereof to promote high velocity flow around the outside of the target 40, as shown in FIG. 2. In the preferred embodiment, recirculated helium gas is utilized to cool the target window 32. Each port 38 defines a helium inlet 29 which is configured to be in communication with the helium supplier 24 of the ring collimator assembly 14 when that particular port 38 is aligned with the ring collimator assembly 14. An o-ring 31 is utilized to provide a seal between the helium supplier 24 and the helium inlet 29 of the port 38. The carousel hub 46 is configured to distribute and collect water and helium and to permit rotation of the carousel barrel 36. Water and helium are distributed to and collected from the system via a water supply tube 68, a water outlet tube 64, a helium supply tube 62 and a helium outlet tube 66, as shown in FIG. 5. The water supply tube 68 is in communication with a water delivery channel 70 and the water outlet tube 64 is in communication with a water outlet channel 72. The delivery and outlet channels 70, 72 are defined by the carousel hub 46, as shown in FIGS. 2, 3 and 4. The delivery channel 70 is in communication with a gland 49 which is in turn in communication with the water inlet 48 defined by the first port. The water outlet channel 72 is in communication with a second gland 51 which is in turn in communication with the water outlet 50 of the last port. Of course, it will be noted that the flow around the barrel 36 can be reversed simply by switching the water supply and outlet tubes. Helium is introduced via the helium supply tube 62. The supply tube 62 is in communication with the annular space 27 defined between the carousel hub 46 and the ring collimator assembly 14. Helium cools the vacuum window 22 and the target window 32, as described above. The helium flows into the disc shaped space 74 between the barrel 36 and the ring collimator assembly 14 and carousel hub 46. The helium exits through an exit port 76 defined by the carousel hub 46, shown in FIG. 3. The exit port 76 is in communication with the outlet tube 66 for the helium. A plurality of o-rings 78 are utilized to insure proper seals where necessary to prevent leakage of helium and water, as depicted in FIG. 2. The carousel hub 46 includes a hub tube 80, preferably fabricated from stainless steel, imbedded therein. The carousel barrel 36 rotates with respect to this hub tube 80 via two bearings 82, 84. As shown in FIGS. 1 and 2, the lower bearing 84 is secured to the barrel 36. In the preferred embodiment, the hub tube 80 defines a passage therethrough for accommodating and protecting the product line(s) 44 of each umbilical 42. Each product line 44 exits the end of the hub tube 80 facing the accelerator and extends to a delivery point. It will be noted that although only one product line is shown in FIG. 2, each umbilical defines at least one product line. If eight targets are installed, at least eight product lines extend through the hub tube. The rotation of the carousel barrel 36 is controlled via a motor 86 and a chain and sprocket system 88, as shown in FIGS. 1 and 6. The motor 86 is mounted on a motor bracket 98 which is secured to the carousel hub 46 via two studs 100. The chain and sprocket system 88 is controlled by the motor 86 and includes a large sprocket 92 mounted on the exterior of the carousel barrel 36, a pinion 94, driven by the motor 86 and a chain 90 fitted to the pinion 94 and the large sprocket 92 of the carousel barrel 36. The alignment of any one port 38 with the ring collimator assembly 14 is provided by an 8:1 ratio between the pinnion 94 and the large sprocket 92. The ports 38 are set an equal 45.degree. apart in the carousel barrel 36. Therefore, one full 360.degree. revolution of the motor 86 corresponds to a rotation of the barrel 36 by 45.degree.. Therefore, the notch in the cam 95 on the motor shaft is adjusted such that said notch is in line with a microswitch 97, when any one port 38 is aligned with the collimator 14. The microswitch 97 engages the notch on the cam 95 at every full revolution of the motor 86, and therefore every time a port 38 is aligned with the collimator assembly 14. The alignment of a particular target 40 can be done remotely, outside the shield. The main concern with the rotation of the carousel barrel 36 is that the product lines 44 within the hub tube 80 are not twisted to the point that they rip. To prevent injury to the product lines 44, the rotation of the carousel barrel 36 is limited to 315.degree. of motion. The limited degree of motion is accomplished by securing an "L" bracket 96 to the exterior of the carousel barrel 36. The "L" bracket 96 is configured to stop at the motor bracket mounting stud 100, preventing the carousel barrel 36 from rotating beyond that point and stalling the motor 86. With the limited degree of rotation, the product lines 44 become twisted but not to the extent that they are damaged. To avoid the need to adjust the target position, an alignment fixture is used during installation of the target changer on to the accelerator to establish beam position coming out of the machine. Once the position is determined, the iron surface where the target changer is to be mounted is drilled at specific points and to specific depths. Then the target changer can be mounted on pins of uniform dimension. The adjustment is not lost if the target changer is removed, or even if a different target changer is installed in the same position. Operation of the alignment fixture can be done remotely (outside the shield) and dynamically (while beam is running). To use the target changer 10, the targets 40 are inserted into respective ports 38 and respective umbilicals 42 are secured in the carousel barrel 36 to establish the high pressure seals. The target 40 to be bombarded is aligned with the ring collimator assembly 14 by rotating the barrel 36 via the motor 86 to the selected position. Circulation of the water and the helium is established. The selected target materials 41 are inserted in the targets 40 via the product lines(s) 44 and product tube(s) 35. Bombardment of the target is performed, and the product leaves the target 40 via the product tube(s) 35, moves into the product lines 44 and is subsequently delivered away from the device 10. From the foregoing description, it will be recognized by those skilled in the art that a target changer offering advantages over the prior art has been provided. Specifically, the target changer provides a modular feature which minimizes the number of connections necessary for installing the targets. Further, the target changer is configured to minimize the time necessary to install or remove a target. Additionally, there is no impact on vacuum integrity when changing targets. Moreover, a change from one installed target to another can be done remotely (outside of the shield). Initial alignment of the target changer is performed by an alignment fixture, which can be operated remotely (outside of the shield) and dynamically (while the beam is running). While a preferred embodiment has been shown and described, it will be understood that it is not intended to limit the disclosure, but rather it is intended to cover all modifications and alternate methods falling within the spirit and the scope of the invention as defined in the appended claims. Having thus described the aforementioned invention, |
043427219 | abstract | A sodium-cooled fast reactor comprises at least one auxiliary heat exchanger constituted by a plurality of vertical heat-exchange modules each provided with a coolant circuit. A vertical cylindrical passage for each auxiliary heat exchanger extends through the reactor vault roof. The passage diameter is larger than the diameter of a heat-exchange module but smaller than the overall dimension of the auxiliary heat exchanger in horizontal cross-section. Each passage is closed by a shield plug after the modules have been placed in position, the modules being disposed around an axial extension of each shield plug. |
046631127 | abstract | Method for determining the contents of a fuel rod within a testing range extending in the longitudinal direction of the fuel rod, characterized by the features that. (a) the position of a test coil concentrically surrounding the fuel rod is changed from the beginning to the end of the testing range, and PA1 (b) in the process, the impedance of the test coil is measured as a function of its position, PA1 (c) the test coil is fed with an a-c voltage, PA1 (d) the frequency of which is so low that the measurement value in the region of a fuel pellet of pure uranium dioxide is clearly distinguished from that which is measured in the region of a doped fuel pellet. |
claims | 1. A probe for a scanning type microscope which obtains substance information of a surface of a specimen by a tip end of a nanotube probe needle fastened to a cantilever, characterized in that a nanotube is fastened to said cantilever by a deposit of decomposed components produced by resolving an organic gas by use of an ion beam in a focused ion beam apparatus and scattering light molecules composing the organic gas. 2. The probe for a scanning type microscope according to claim 1 , wherein said deposit comprises carbon atoms accumulated by using a hydrocarbon gas as said organic gas. claim 1 3. The probe for a scanning type microscope according to claim 1 , wherein said deposit comprises metal atoms accumulated by nuns an organic-metallic gas as said organic gas. claim 1 4. The probe for a scanning type microscope according to claim 1 , wherein said cantilever is coated with a conductive substance. claim 1 5. A probe for a scanning microscope produced by focused ion beam machining, characterized in that an unnecessary portion of a nanotube probe needle fastened to a cantilever is cut off by irradiating an ion beam at a tip end portion of said nanotube probe needle, and thus a length of said tip end portion of said nanotube probe needle is regulated to a predetermined length. 6. A probe for a scanning microscope produced by focused ion beam machining, characterized in that a part of nanotube components is charged by beaming ions at a tip end portion of a nanotube probe needle fastened to a cantilever, thus changing physical and chemical properties of said probe needle. 7. The probe for a scanning type microscope according to claim 6 , wherein said ions are one selected from the group consisting of fluorine, boron, gallium, and phosphorus. claim 6 8. The probe for a scanning type microscope according to claim 5 , wherein in cutting-off of said unnecessary portion, said nanotube is cut in an oblique direction thereof. claim 5 |
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061987875 | description | DESCRIPTION OF THE INVENTION Hereinafter, as one embodiment of a method of handling a nuclear reactor and an apparatus used in the handling method according to the present invention, an atomic power plant station having a boil water type nuclear reactor will be explained by taking as an exemplified example. However, the present invention will be applied to an atomic power plant station having another type of nuclear reactor. In a nuclear reactor building 11 of an atomic power plant station having a boil water type nuclear reactor shown in FIG. 1, a nuclear reactor pressure vessel 3 is provided and this nuclear reactor pressure vessel 3 is stored by a nuclear reactor storing vessel 21. In the nuclear reactor pressure vessel 3, as shown in FIG. 2, as an internal structure a steam dryer 5 and a vapor-liquid separator 8 and a shroud 1 etc. are provided. In a space of an operation floor 9 of the nuclear reactor building or containment 11, an overhead crane 8 is provided, and the overhead crane 8 is used in the working of the operation floor 9. In the operation floor 9, a dryer separator pool 7 which is abbreviated as "DS pool" and a nuclear reactor well pool 10 which communicates to an interior portion of the nuclear reactor pressure vessel 3 are provided. Among the internal structures, since the shroud 1 is a component which surrounds a reactor core of the nuclear reactor, among the internal structures the shroud 1 most strongly recieves the radiation. In this embodiment according to the present invention, the working for exchanging over the shroud 1 will be explained. The nuclear reactor pressure vessel 3 in the nuclear reactor building 11 of the atomic power plant station receives the fuels of the nuclear reactor and is a vessel to which a primary cooling member comprised the liquid is inserted. The reactor core to which the fuels of the nuclear reactor are mounted is surrounded by the shroud 1, and this shroud 1 is formed with a stainless steel cylindrical structure which isolates a flow in the cooling member which raises in the nuclear reactor and a re-circulation flow which descends a ring shape portion between an inner wall of the nuclear reactor pressure vessel 3. In this embodiment according to the present invention, the shroud 1 which is a subject of a carry-in working and a carry-out working between the inside and the outside of the nuclear reactor building 11 is a main large weight product among the machines and the apparatuses for constituting the atomic power plant station and has 70 tons weight. The internal structure receives the high concentration radioactive rays because the internal structure is a machinery product which is passed through a primary system coolant and this internal structure is covered by a reinforce concrete shielding wall or a steel plate concrete shielding wall. Further, a surrounding of the internal structure is stored in a steel shape nuclear reactor storing container 21 and this internal structure works a role of the prevention of the leakage of the radiation. These atomic power plant stations, during a periodic inspection a damage state of the internal structure of the nuclear reactor is inspected, according to the demand, the internal structure is mended, however from the aspects of the economical performance and the prevention preservation, even in a midway of the durable years, there is a case over which the internal structure is exchanged. To carry out the exchange-over for the internal structure, first of all to a sealing roof of the nuclear reactor building 11 which is positioned at a just above of the well pool 10 an opening 61 is formed as shown in FIG. 12. The opening portion 61 is closed once according to a curing sheet 63 or a rolling system shutter 62. In a case where an outside shielding wall 31 is installed at a roof portion of the nuclear reactor building 11, the carry-in and carry-out use opening 61 is provided at the outside shielding wall 31 and this opening 61 has a size in which a cask 41 is enable to pass through. At the same time, a large scale lifting machine 91 which is a large scale crawler crane is installed at a vicinity of the nuclear reactor building 11. In a case of the installation of the large scale lifting machine 91, as shown in FIG. 12, the ground for an operation area of the large scale lifting machine 91 is strengthened as an establishment ground 71. Further, as shown in FIG. 12, at the ground within a loading working radius range of the large scale lifting machine 91, an underground reservoir 81 is formed and an inlet port of this underground reservoir 81 is opened upwardly. Next, the carry-out working of the shroud 1 to the nuclear reactor building is carried out and in this carry-out working the cask 41 is used. The cask 41 is pulled up and supported by a wire rope 12 from the lifting balance 51, as shown in FIG. 5. The cask 41 is constituted by a lower portion opened container having an inlet port at a lower portion. And at the ceiling portion of this cask 41, a penetrating hole 54 is provided and in this penetrating hole 54 a wire rope 13 of a hoisting device 52 is passed through. This hoisting device 52 is installed to the lifting balance 51 and then the wire rope 13 is wounded up or paid out according to a remote operation. A hook 14 is provided to this wire rope 13. The lifting balance 51 and a hook block 93 of the large scale lifting machine 91 are connected by a wire rope 28 and the lifting balance 51 is pulled up and supported by the large scale lifting machine 91 to lift up and lift down freely. The combination equipment of the above stated lifting balance 51, the hoisting device 52, and the cask 41 is prepared at the outer side of the nuclear reactor building 11. As shown in FIG. 6(a) and FIG. 6(b), to close the inlet port 27 provided at a bottom portion of the cask 41, at an outer periphery of a cask bottom plate 42, mail screws 42a of the cask bottom plate 42 is provided to engage with female screws 42b which are processed at an inner wall face of the lower portion of the cask 41. The cask bottom plate 42 is mounted to the bougie car 43 through a receiving table 46. The bougie car 43 is stridden over the well pool 10 and DS pool 7 and is installed to run freely on a rail 15 which is laid along to the well pool 10 and DS pool 7. The construction of the receiving table 46 is as following. Namely, as shown in FIG. 14, the receiving table is constituted by a rotary table 17 which is mounted on the bougie car 43 to rotate freely toward a horizontal direction through a thrust bearing 16, an ascend and descend table 19 which is mounted on the rotary table 17 through an air pressure cylinder apparatus 18, an inner gear 20 which is fixed to the above stated rotary table 17, and a motor 23 for rotating and driving a pinion 22. The manner for extending and contracting a piston rod of the air pressure cylinder apparatus 18 and the drive control of the motor 23 can be carried out from a remote place. Accordingly, when the pinion 22 is rotated and driven by the motor 23, the inner gear 20 and the rotary table 17 are rotated at the same time at a horizontal face. Further, by extending and contracting the piston rod of the air pressure cylinder apparatus 18 the ascend and descend table 19 can be moved toward the upward and downward direction, and then the ascend and descend table 19 can give the rotation operation and the ascending and descending operation to the cask bottom plate 42. In place of the respective screws 42a and 42b of the cask 41 to the cask bottom plate 42, as shown in FIG. 7(a) and FIG. 7(b), faucet structures 44a and 44b can be employed. Further, as shown in FIG. 8(a) and FIG. 8(b), a bolt 24 is passed through a flange 45b which is fixed to the cask 41, and a structure can be employed in which the cask bottom plate 42 is fastened to the cask according to the bolt 24 which is passed through a bolt passing-through hole 45a and a nut 25. As stated in above, the preparation of the exchangeover working is carried out, the exchange-over working is carried out as following. FIG. 3 and FIG. 4 show an outline exchange-over working procedure in which the shroud 1 being the internal structure of the nuclear reactor is an object for exchanging over. To exchange over of the shroud 1, firstly a working for taking out the already established shroud 1 in the nuclear reactor pressure vessel 3 precedes. As the taking-out procedure, a cover 4 of the nuclear reactor pressure vessel 3 is released and the water is filled in the nuclear reactor pressure vessel 3 and in the well pool 10 to shield the radioactive rays and to prevent the diffusion of the radioactivity to the operation floor 9. After that, the steam dryer 5 and the vapor-liquid separator 6 are lifted out from the nuclear reactor pressure vessel 3 according to the overhead crane 8 and are laid in the water in DS pool 7. Further, the steam dryer 5 and the vapor-liquid separator 6 are provided temporally and are stored. In this case, the vapor-liquid separator 6 and a shroud head are formed as one body and are lifted out. Further, the vapor-liquid separator 6 and the shroud head are laid in the water in DS pool 7 and are stored. Next, the fuels in the nuclear reactor pressure vessel 3 are taken out from the nuclear reactor pressure vessel 3 to a suitable place and are stored. Next, the water in the well pool 10 and the nuclear reactor pressure vessel 3 is drawn out and the radioactivity cleaning working in the nuclear reactor pressure vessel 3 is carried out. Next, the curing sheet 63 which has closed the opening 61 of the nuclear reactor building 11 and the rolling system shutter 62 are operated to close the opening 61 and the opening 61 is performed to have an opened state. After that, until the restoration of the opening 61, the pressure in the space of the nuclear reactor building 11 at least the operation floor 9 is maintained to a negative pressure condition to have a lower pressure than the pressure in the outside of the nuclear reactor building 11. The maintaining means is carried out using a ventilation apparatus which is arranged at the space of the operation floor 9. Next, the lifting balance 51 is lifted up according to the large scale lifting machine 91 and the hoisting device 52 and the cask 41 are lifted up at the same time, and further the lifting balance 51, the large scale lifting machine 91 and the hoisting deice 52 are lifted from the opening 61 and to carry out to approach to the well pool 10. Accordingly, the pull-up supporting condition between the lifting balance 51 according to the large scale lifting machine 91 and the large scale lifting machine 91 and the hoisting device 52 is maintained. For this reason, the working, in which the lifting balance 51, the hoisting device 52, and the cask 41 are separated from the large scale lifting machine 91 and are reached to the operation floor 9, is not carried out. With the above stated process, the carry-in of the empty cask 41 is performed. After the carry-in of the empty cask 41 has carried out, the opening 61 is performed to have a narrow opening in which the wire rope for lifting up the lifting balance 51 of the large scale lifting machine 91 can be passed through by closing the curing sheet 63 and the rolling system shutter 62. By combining the procedure for maintaining at the above stated negative pressure condition, the atmosphere in the nuclear reactor building 11 is prevented to the utmost from leaking to the outside of the nuclear reactor building 11. Next, the wire rope 13 is paid out according to the hoisting device 52 and the hook lifting down working is carried out to approach the hook 14 toward the shroud 1. Further, the nuclear reactor internal structure slinging working is carried out, in such a nuclear reactor internal structure slinging working, the wire rope 26 is paid out between a unitary structure which is constituted by the hook 14, the upper portion lattice plate and the shroud 1. Next, the lifting-up working for lifting up the wire rope 13 according to the hoisting device 52 is carried out and then the shroud 1 is pulled up and supported as shown in FIG. 5, and the shroud 1 is stored gradually to the inner side of the cask 41 and as a result the receipt in the cask working is carried out. Next, the bougie car 43 is run along to the rail 15 and is stopped just above the well pool 10. Then the cask bottom plate which is mounted on the bougie car 43 can be positioned just under the cask 41. Next, the ascend and descend table 19 of the receiving table 46 is pushed up according to the air pressure cylinder apparatus 18 and the ascend and descend table 19 is rotated toward the horizontal direction, then with the female screws 42b of the cask 41 the male screws 42a of the cask bottom plate 42 is engaged, the inlet port 27 of the cask 41 is closed, accordingly the cask hole enclosing working is finished. To more ensure the closing condition of the cask hole, a boundary portion between the cask bottom plate 42 and the cask 41 is performed to weld and to fix according to the welding manner and to carry out the seal welding. Further, the shroud 1 is lifted down on the cask bottom plate 42 according to the hoisting device 52 and the respective wire ropes 13 and 26 are given a condition where the shroud 1 is given the tension where the shroud 1 is not failed down. The construction to which the hole closing working about the cask 41 is employed are exemplified according to the two examples shown in addition to those shown in FIG. 6(a) and FIG. 6(b), however in the constructions shown in FIG. 7(a) and FIG. 7(b), the cask bottom portion is formed with the faucet system and the closed condition is shown. The shroud 1 is lifted up to above from the floor of the operation floor 9, and on the bougie car 43 the cask bottom portion having the faucet structure 44a through the receiving table 46 is mounted on and the shroud 1 is run and moved at just under the cask 41. The cask bottom portion 42 is raised similarly to in the above, the faucet structure 44a is inserted into the cask 41 and after that the cask bottom portion 42 is rotated toward the horizontal direction. Then the cask bottom portion 42 is aligned to the position where the faucet structure 44b is fitted into faucet structure 44b at the cask side in the cask 41 and the receiving table 46 is retarded toward the lower portion from the cask bottom portion 42 and even those faucet structures between the cask 41 and the cask bottom plate 42 are meshed and fixed. According to the commands, the boundary portion between the cask 21 and the cask bottom plate 42 are fixed according to the welding manner or the sealing welding manner and then the closing condition of the inlet port 27 of the cask 41 is performed more surely. In the examples shown in FIG. 8(a) and FIG. 8(b), similarly to the examples shown in FIG. 6(a) and FIG. 6(b), the cask bottom portion 42 is positioning aligned by aligning to just under of the inlet port 27 of the cask 41. After that, at the position of the bolt 24 a bolt through-out hole 45a is rotated the cask bottom plate 42 toward the horizontal direction by the cask bottom plate 42 according to the receiving table 46 to coincide with the upward and downward directions. After that by the receiving table 46 the cask bottom plate 42 is arisen and the bolt 24 is passed through the bolt passing-through hole 45a and the screw portion of the bolt 24 which is come out toward the lower portion from the bolt passing-through hole 45a is engaged with the nut 25 and the nut 25 is tied up and then at the lower end of the cask 41 the cask 41 is adhered and accordingly the hole closing working is carried out. In this case, according to the demands the boundary portion of the cask 41 and the cask b bottom plate 42 is fixed to and seal-welded according to the welding manner and then the sealing condition to the inlet port 27 of the cask 41 can be performed surely. Further, when the sealing condition of the shroud 1 according to the cask 41 is performed surely to transfer, according to the hoisting device 52 the shroud 1 is received in the cask 41 and after the hole closing working of the inlet port 27 of the cask 41, the wire rope 13 of the hoisting device 52 is pulled out and the shroud 1 is set down on the cask bottom plate 42. The the hook 14 and the wire rope 13 together is taken out from an upper portion passing-through hole 54 and then the hole closing working of the upper portion passing-through hole 54 is carried out. The hole closing working may be the screw system in which the cover is screws to the upper portion passing through hole 54 or may be the welding system in which the cover is welded to the upper portion passing-through hole 54 or may be flange system in which using the bolt and the nut the cover is fastened to the cask 41. With the above stated structure, now the element in which the atmosphere in the cask 41 leaks to the outside of the cask 41 become nothing. When the cask hole closing working has finished, next, as shown in FIG. 9(a) and FIG. 9(b), a lifting rope 92 is wound out from a large scale lifting machine 91 according to the large scale lifting machine 91 and a hook block 93 of the large scale lifting machine 91 which is lifted to the lifting rope 92 is lifted near to the opening 61. With this structure, further the lifting balance 51 which is lifted up from the hook block 93, the hoisting device 52 and the cask 41 are lifted near to the opening 61. Next, it will enter the opening passing-through working, firstly the rolling system shutter 62 is opened and further the opening 61 is opened, next by the large scale lifting machine 91 the lifting rope 92 is wound up further from the large scale lifting machine 91 and to the opening 61 the lifting balance 51, the hoisting device 52 and the cask 41 are passed through. As shown in FIG. 11, the rolling system shutter 62 is closed and further then the opening 61 is closed. After that the above stated opening passing-through working is performed, the lifting balance 51, the hoisting device 52 and the cask 41 are lifted up toward the upper portion from the nuclear reactor building 11 and then the lifting up working in which the lifting balance 51, the hoisting device 52 and the cask 41 are carried out to the upper portion of the outside of the nuclear reactor building 11 is carried out. In the condition in which the rolling system shutter 62 is opened, from the opening 61 the atmosphere in the nuclear reactor building 11 is tried to leak toward the outside of the nuclear reactor building 11, however the pressure in the nuclear reactor building 11 is managed to a lower negative pressure condition than the pressure in the outside of the nuclear reactor building 11. Accordingly, the leakage of the atmosphere in the nuclear reactor building 11 is checked and the restraint of the radioactivity diffusion toward the outside of the atmosphere in the nuclear reactor building 11 can be strengthened. This rolling system shutter 62 is formed by making the large scale of a construction of a diaphragm mechanism of a camera and the opening 61 can be opened according a move of four diaphragm blades toward a radial direction. In place of the rolling system shutter 62, as shown in FIG. 10(a) and FIG. 10(b), the shape of the opening 61 can be formed with a quadrangle shape and from four sides of the quadrangle shape directing toward a center of the opening 61, four curing sheets 63 are spread by proceeding to the horizontal direction and the opening 61 is closed, in reversely by folding the four curing sheets 63 the opening is opened, according a construction for opening and closing the opening 61 can be employed. Another means for preventing the leakage of the atmosphere to the minimum through the opening 61 from in the nuclear reactor building equipment 11, there is a method for enclosing the cask 41, as shown in FIG. 10(a) and FIG. 10(b). Namely, in the above stated another method, firstly the cask 41 is lifted by approaching the cask 41 to the opening 61 through the large scale lifting machine 91 and holding under this condition the lifting balance 51, the hoisting machine 52 and the cask 41 are enclosed by a sheet which is installed sealable to four sides of the opening 41 and between a space of the cask 41 from the sheet 64 and a space of the operation floor at an outside the communication of the atmosphere can be prevented. After that, the curing sheet 63 is folded at a side of the four sides of the opening 41 and the opening 61 is opened and after the lifting balance 51, the hoisting machine 52 and the cask 41 are lifted at a height of the cask 41 as shown in FIG. 11, and then the shroud 1 is stored from the nuclear reactor building 11 and are carried out the outside. Even when the opening 61 is opened, since there is a possibility in which only the atmosphere at the space of the cask 41 side from the sheet is leaked at the maximum, a safety can be attained, and further in a case of the open of the opening 61, even the rush-in matters from the outside of the nuclear reactor building 11 and the atmosphere are entered into the space of the operation floor 9, the rush-in matters and the atmosphere are enclosed by the sheet 64, accordingly the diffusion of the atmosphere in the space of the operation floor 9 can be prevented. Next, after the lifting of the cask 41 which has stored the shroud 1 is carried out toward the upper portion of the nuclear reactor building 11, by swirling the boom of the large scale lifting machine the cask 41 is positioned at the just upper portion of an underground reservoir 81, accordingly the swirl working is carried out. Next, the cask 41 is fixed in the underground reservoir 81 and then the storage storing and fixing working is carried out. Next, the wire rope 12 is taken off from the cask 41 and the cask 41 is taken off from the lifting balance. Further, the wire rope 13 is cut off, for example, and the connection between the hoisting machine 52 and the shroud 1 is released, the slinging-out working is carried out, and next the inlet port of the underground reservoir 81 is covered and closed, then the carry-out working is finished. In a case of the decomposition of the atomic power plant station, in place of the above stated carry-out working a newly shroud is carried in the nuclear reactor pressure vessel 3 and then in this case the installation working is not accompanied with. However, in a case of the replace working of the shroud 1, after the finish of the carry-out working, the carry-in working of a newly shroud in the nuclear reactor building equipment 11 is accompanied with. The above stated carry-in working is carried out in accordance with the working process which is indicated as the carry-in working at a right side of FIG. 13. Namely, first of all, the new shroud is transported at the goods receipt position where the new shroud can be lifted by a trailer etc., accordingly the nuclear reactor internal structure transportation working is carried out. Next, between a hook block 93 of the large scale lifting machine 91 and the new shroud, the nuclear reactor internal structure slinging working for laying the wire rope is carried out. Next, the new shroud is lifted up at the goods receipt position according to the large scale lifting machine 91 and by swirling the boom of the large scale lifting machine 91 toward the horizontal direction the new shroud is positioned just above of the opening 61, according the lifting-up and swirling working is carried out. Next, the opening 61 is opened by operating the rolling system shutter 62 or the curing sheet 63 and the new shroud is lowered according to the large scale lifting machine 91 and the opening 61 is passed through and entered into the nuclear reactor building 11. Next, the opening 61 is closed, except for a clearance in which the lifting rope 92 can be passed through, according to the rolling system shutter 62 and the curing sheet 63, accordingly the lowering and opening passing-through working is carried out. In this above stated case, since the pressure in the nuclear reactor building 11 is managed to have the lower negative pressure management condition than the pressure in the outside of the nuclear reactor building 11, the leakage of the atmosphere in the nuclear reactor building equipment 11 can be checked and the radioactivity diffusion toward the outside of the atmosphere in the nuclear reactor building 11 can be prevented. Next, the new shroud is lifted down further and entered into the nuclear reactor pressure vessel 3 and this new shroud is set at the position where the previous established shroud 1 has existed, accordingly the nuclear reactor internal structure installation and setting working is carried out. Next, the wire rope which is laid out between the new shroud and the hook block 93 is taken out from the new shroud, accordingly the slinging-out working is carried out. After that, the above stated hook block 93 is lifted out at the outside of the nuclear reactor building 11 and then the carry-in working is finished. After that, the opening is restored to the original state, accordingly the carry-in and carry-out use opening restoration working is carried out. Next, the large scale lifting machine 91 is decomposed and withdrawn. According to the invention, since the container which is lifted in the nuclear reactor building is positioned above the internal structure of the nuclear reactor pressure vessel under a lifted condition and the internal structure is inserted in the container under the lifted condition, and since in the nuclear reactor building, there are unnecessary to carry out an assembly of the container a lowering of the container to a floor in the nuclear reactor building, a horizontal move on the floor, a connection and a release to a lifting means of the container after the lowering, and a connection working during the lowering and further it can transfer to the lifting out working, leaving the container with the lifted condition the internal structure can be stored in the container and the internal structure can be carried out speedy at the outside of the nuclear reactor building, and further the container can be shield the diffusions of the radioactive rays and the radioactivity from the internal structure, as a result the effects of the diffusion of the radioactivity in the nuclear reactor building and the restraint of the radiation exposure can be attained. According to the invention, as the container the cask is used. According to the invention, by accompanying the cask with the hoisting device the cask and the hoisting device are lifted in the nuclear reactor building, after the lifting-in according to the hoisting device which is arranged at the outer side of the cask the internal structure can be lifted up from the nuclear reactor pressure vessel and the internal structure can be stored in the cask and the internal structure can be carried out more speedy at the outside of the nuclear reactor building and the radioactive rays in the cask from the internal structure can be shielded according to the cask, as a result the effects can be obtained such effects are that the hoisting device which is arranged at the outer side of the cask does not strongly recieve radiation and it may be dispensed with to make little a part which becomes to a radioactive waste material. According to the invention, since the cask bottom portion member is carried in to the lower portion of the inlet port of the cask according to the bougie car and the inlet port of the cask is closed by the cask bottom portion member and the move of the cask bottom portion member is carried out according to the bougie car and further the cask is lifted up always and the space for enable to carry in the cask bottom portion to the lower portion of the inlet port of the cask is obtained easily, as a result the closure working can be carried out speedy, and also the inlet port of the cask can be closed at the height near to the operation floor, the effects in which the diffusion of the radioactivity into the nuclear reactor building and the restraint of radiation exposure can be attained more effectively. According to the invention, using the same crane since the lifting-out of the cask from the nuclear reactor building to the lifting-in to the reservoir can be carried out consistently, the carry-in working of the internal structure to the reservoir can be speedy by lessening the intermittent working. According to the invention, by limiting to the passing-through of the cask to the opening, the opening is opened widely according to the opening and closing apparatus and the leakage of the atmosphere in the nuclear reactor building to the outside of the nuclear reactor building which occurs by the open of the opening can be restrained and further the inside of the nuclear reactor building is formed to the negative pressure in comparison with the outside of the nuclear reactor building and the occurrence of the flow of the atmosphere from the opening to the outside of the nuclear reactor building can be deprived of and then the leakage of the atmosphere in the nuclear reactor building to the outside of the nuclear reactor building can be restrained from an aspect of the pressure, and further employing a complex means of the opening and closing apparatus and the pressure adjustment the leakage of the atmosphere in the nuclear reactor building to the outside of the nuclear reactor building can be deprived of, and as a result an effect in which the discharge of the radioactivity to the outside portion can be avoided at the utmost. According to the invention, in a case where the cask is lifted out to the outside of the nuclear reactor building through the opening, since the leakage of the atmosphere in the nuclear reactor building from the opening is shielded according to a sheet for enclosing the cask and since the leakage of the atmosphere in the nuclear reactor building from the opening is prevented, as a result an effect in which the discharge of the radioactivity to the outside portion can be avoided at the utmost. According to the invention, an effect in which the shroud as the internal structure is handled collectively and effectively by not subdividing the shroud can be obtained. According to the invention, since the internal structure in the nuclear reactor can be exchanged speedy and as a result an effect in which the time of the re-operation of the nuclear reactor using the renewed internal structure of the nuclear reactor can be hastened. According to the invention, in addition to the effect of the invention defined in claim 9, the shroud as the internal structure is carried out collectively from the nuclear reactor building by not subdividing the shroud and as a result an effect in which the shroud is exchanged speedy can be obtained. According to the invention, the cask which is lifted by the crane from the outside of the nuclear reactor building equipment is lifted together with the hoisting device in the nuclear reactor building from the opening of the nuclear reactor building, and the cask which is lifted in the nuclear reactor building and the hoisting device are held by chinning the crane and the hoisting device which is lifted up according to the crane lifts the internal structure and then the internal structure carried out the double chinning state, and the internal structure is lifted up further according to the hoisting device and drawn in the cask, after the internal structure is drawn in and stored, under the stored condition of the internal structure the internal structure and the cask are passed through together with the opening of the nuclear reactor building according to the crane and is lifted up, then the operation for carrying out the nuclear reactor building to the outside can be obtained. According to this operation, since the internal structure is stored in the cask and is treated, the scattering of the radioactive and the radioactivity material from the internal structure can be restrained according to the cask and under the chinning condition of the hoisting device and the cask according to the crane the storing working of the internal structure in the cask can be carried out, and as a result an effect in which the internal structure can be treated speedy without the accompanying of the attachment and detachment working of the cask to the crane in the nuclear reactor building can be attained. According to the invention, since the inlet port of the lower end of the cask is closed according to the cask bottom plate, the radiation ray exposure of the operators and the diffusion of the radioactive material from the internal structure can be restrained. According to the invention, since the working for closing the inlet port of the cask is carried out speedy using the boggier car, an effect for providing the handling apparatus of the internal structure of the nuclear reactor in which the more speedy carry-out of the internal structure of the nuclear reactor can be provided. According to the invention, an effect in which the shroud as the internal structure can be handled speedy by not subdividing the shroud can be obtained. |
abstract | An apparatus, transfer cask, system, and method for defueling a nuclear reactor and transferring spent nuclear fuel from a spent nuclear fuel pool to a storage cask for long terms storage. In one aspect, the invention is an apparatus for use in transferring a canister of spent nuclear fuel from a transfer cask to a storage cask, the apparatus comprising a radiation absorbing shield surrounding a portion of a hole through which the canister can pass; means for securing the apparatus to the top surface of the storage cask; means for securing the bottom surface of the transfer cask to the apparatus; wherein the transfer cask securing means and the storage cask securing means are positioned on the apparatus so that when the apparatus is secured to both the transfer cask and the storage cask. The cavity of the transfer cask, the hole, and the cavity of the storage cask are substantially aligned; and means are included for moving the bottom lid in a horizontal direction once the bottom lid is unfastened from the bottom surface. In another aspect, the invention is a system comprising the above described apparatus, transfer cask, and a storage cask. In still another aspect, the invention is a method of using the system of the present invention to defuel a nuclear reactor and transfer the spent nuclear fuel a spent nuclear fuel pool to a storage cask. |
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claims | 1. A system, comprising:a generator-detector configured to be attached to a conduit, the generator-detector configured to measure the concentration of mercury in the conduit in a non-destructive manner down to a lower detection limit of 10 ppm±50%. 2. The system as recited in claim 1, wherein the conduit communicates a fluid. 3. The system as recited in claim 2, wherein the conduit is a portion of a pipeline for transporting oil or gas. 4. The system as recited in claim 1, wherein the generator-detector includes a spectroscopic beam generator-detector. 5. The system as recited in claim 4, wherein the generator-detector is configured to measure the concentration of mercury at two locations within the conduit, and wherein the generator-detector is configured to average the two measurements. 6. The system as recited in claim 5, wherein the two locations are about 180 degrees apart from one another. 7. The system as recited in claim 1, wherein the generator-detector uses neutron activation analysis. 8. The system as recited in claim 7, wherein the generator-detector includes a thermal neutron source and a gamma detector. 9. The system as recited in claim 1, further comprising at least one magnet configured to mechanically couple an exterior housing containing the generator-detector to the conduit. 10. The system as recited in claim 9, wherein the generator-detector is configured to project energy to an interior location of the conduit and the at least one magnet are spaced apart from a path of the energy projection. 11. The system as recited in claim 1, wherein the generator-detector is configured to measure mercury in the conduit to a lower detection limit down to 1 ppm±50%. 12. The system as recited in claim 1, wherein the generator-detector is configured for use underwater at a depth down to at least 75 meters (about 250 feet). 13. A method, comprising:mechanically coupling a device to an exterior of a conduit;directing at least two neutron beams to at least two target interior locations of the conduit; andmeasuring the concentration of mercury in the conduit using the device in a non-destructive manner by measuring the concentration of mercury at the at least two target interior locations and averaging the at least two measurements. 14. The method as recited in claim 13, wherein the conduit is a subsea pipe, and wherein the device is initially positioned on the subsea pipe by a diver. 15. The method as recited in claim 13, wherein the device includes a generator-detector and the generator-detector includes at least one of a spectroscopic beam generator-detector, a thermal neutron source, and a gamma detector. 16. The method as recited in claim 15, wherein the generator-detector is configured to measure mercury in the conduit to a lower detection limit down to at least 10 ppm±50%. 17. The method as recited in claim 16, wherein the generator-detector is configured to measure mercury in the conduit to a lower detection limit down to 1 ppm±50%. 18. The method as recited in claim 13, further including communicating a fluid through the conduit during the coupling, directing, and measuring steps. |
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description | The present invention relates to a method of characterizing the vibrational performance of a charged particle beam microscope system and the application thereof. When scanning, a charged particle beam microscope system vibrates, causing the formed scan lines to jiggle. The jiggled scan line distorts or halos the obtained scan image, so the image becomes difficult to analyze i.e. the image quality is damaged. This greatly harms the performance and reliability of the charged particle microscope system. There are various sources of vibration during a charged particle beam imaging operation, such as environmental noises and moving or rotating mechanical components in the microscope system. Currently, the vibration issue is typically handled by fine-tuning the microscope system with reference to factory or field testing results of the system performed by the manufacturer or customer. This kind of work is basically experience-based, requiring a lot of trial-and-error thus is inefficient and costly both time-wise and manpower-wise. Moreover, the test result is hard to be reproduced on another machine or even for another imaging job on the same machine. Therefore, it is desirable that the industry has a testing tool which can correctly describe the vibrational behavior of the mechanical sub-systems of the microscope system, which is one of the main contributors to the overall system vibration, and the testing effectiveness of the tool is preferably to be machine and/or imaging job independent. The embodiments of the present invention disclose a method and applications thereof for characterizing the vibrational performance of a charged particle beam microscope system having at least one encoder. One embodiment of the present invention discloses method for characterizing the vibrational performance of a charged particle beam microscope system which has at least one encoder. The method first provides a plurality of images taken by using the concerned charged particle beam microscope system, wherein the images comprise at least one imaged pattern and each of the images is taken at a predefined set of encoder frequencies. Next, the encoder frequencies are correlated with a vibration amplitude of the imaged pattern in the images. The correlating step comprises: generating, for each image, a time-domain image vibration signal representing information of the imaged pattern vibration amplitude versus an elapsed time period of the concerned image being taken; generating, for each image, a frequency-domain image vibration spectrum from the time-domain image vibration signal, wherein the frequency-domain image vibration spectrum represents information of the imaged pattern vibration amplitude versus a range of frequencies including the set of encoder frequencies; identifying, for each image, from the frequency-domain image vibration spectrum, at least one encoder frequency from the set of encoder frequencies each with a corresponding imaged pattern vibration amplitude, so as to form at least one data pair accordingly; and forming, using the formed data pairs, points on a coordinate system of imaged pattern vibration amplitude versus frequency thereby forming a system vibrational performance chart. The formed system vibrational performance chart characterizes the vibrational performance of the concerned charged particle beam microscope system, wherein the vibrational performance represents the imaged pattern vibration amplitude in individual image at at least one encoder frequency from the set of encoder frequencies at which the concerned image is correspondingly taken by using the charged particle beam microscope system. Another embodiment of the present invention discloses a computing agent for characterizing the vibrational performance of a charged particle beam microscope system which has at least one encoder. The computing agent comprises: an input member, a computing member and an output member. The input member is able to be coupled to the concerned charged particle beam microscope system for receiving, from the charged particle beam microscope system, a plurality of images formed by the charged particle beam microscope system and information of a plurality of sets of encoder frequencies, wherein each image is formed at a corresponding set of encoder frequencies, and the images comprise at least one imaged pattern. The computing member is coupled with the input member for receiving the images and information of encoder frequencies from the input member. The computing member executes the following steps: generating, for each received image, a time-domain image vibration signal representing information of a vibration amplitude of the imaged pattern versus an elapsed time period of the concerned image being formed; generating, for each received image, a frequency-domain image vibration spectrum from the time-domain image vibration signal, wherein the frequency-domain image vibration spectrum represents information of the imaged pattern vibration amplitude versus a range of frequencies including the set of encoder frequencies at which the image is correspondingly taken. The computing member then continues to execute steps of identifying, for each received image, from the frequency-domain image vibration spectrum, at least one encoder frequency from the set of encoder frequencies, each with a corresponding imaged pattern vibration amplitude, so as to form at least one data pair accordingly; and forming, using the formed data pairs, points on a coordinate system of imaged pattern vibration amplitude versus frequency thereby forming a system vibrational performance chart. The formed system vibrational performance chart characterizes the vibrational performance of the concerned charged particle beam microscope system, wherein the vibrational performance represents the imaged pattern vibration amplitude in individual image at at least one encoder frequency from the set of encoder frequencies at which the concerned image is correspondingly taken by using the charged particle beam microscope system. The output member is coupled with the computing member for receiving the system vibrational performance chart from the computing member and outputting the same for the user's interpretation. Yet another embodiment of the present invention discloses a charged particle beam microscope system which has at least one encoder. The charged particle beam microscope system comprises: a moving stage whereupon a sample is secured for imaging; a charged particle beam generator for generating a primary charged particle beam; a condenser lens module for condensing the primary charged particle beam; a probe forming objective lens module for focusing the condensed primary charged particle beam into a charged particle beam probe; a deflection module for scanning the charged particle beam probe across a surface of the sample; a detector module for collecting charged particles generated from the sample surface upon bombardment of the charged particle beam probe and generating a detection signal accordingly; an image forming module coupled with the detector module for receiving the detection signal from the detector module and forming at least one charged particle microscopic images accordingly; and a vibration characterization module for characterizing the vibrational performance of the concerned charged particle beam microscope system by correlating the working frequencies of the encoder with corresponding vibration amplitudes of an imaged pattern in the images. Accordingly, some of the embodiments of the present invention use an intrinsic element, the encoder, to assess the vibrational performance of a charged particle beam microscope system. A method and application thereof are proposed by the embodiments of the present invention. One of the major vibration sources of a charged particle beam microscope system is the moving sample stage in a continuous scan mode operation. The stage is driven by a motor. Ideally, in the continuous scan mode the motor should be controlled to keep the stage at a predetermined constant speed. To achieve this, a closed-loop control scheme is typically adapted. An encoder is included in the control system for providing feedback to the controller indicating the instant stage moving speed. The signal-generating frequency of an encoder is generally referred to as the encoder frequency. When the encoder is functioning, the encoder frequency is known to be dependent upon the speed of the stage. In other words, one stage speed corresponds to one specific encoder frequency. This specific encoder frequency, which can be seen as an excitation frequency of the concerned microscope system, will be referred to as an encoder primary frequency hereinafter. For one primary frequency, a plurality of encoder harmonic frequencies may be derived mathematically due to non-linearity of the system. The embodiments of the present invention propose a method to correlate the working encoder frequencies with the vibrational behavior of a charged particle beam microscope system at a certain stage speed, whereby characterizing the vibrational performance of the system. The proposed method can be implemented as a computing hardware, a firmware, or pure software (e.g. a computer readable medium encoded with a computer program). A charged particle beam microscope system configured to implement the proposed method is also disclosed. FIG. 1 is a schematic illustration of a charged particle beam microscope system 100 according to an embodiment of the present invention. A charged particle beam generator 110 generates a charged particle beam, and then the charged particle beam is condensed and focused by a condenser lens module 120 and an objective lens module 130, respectively, to form a charged particle beam probe 140. The formed charged particle beam probe 140 then bombards the surface of a sample 210 secured on a stage 200. The charged particle beam probe 140 is controlled by a deflection module 150 to scan the surface of the sample 210 along a first direction to form a plurality of scan lines and, in the meanwhile, the stage 200 moves along a second direction at a certain speed. This second direction is designed to be at an angle to the first direction. In one embodiment, the second direction is selected to be substantially perpendicular to the first direction. In this embodiment, this kind of scanning operation is called a continuous scan mode operation. After the charged particle beam probe 140 bombards the surface of the sample 210, secondary charged particles 160 are induced to emit from the sample surface along with other charged particles of the beam probe 140 reflected by the sample 210. These particles are then detected and collected by a detector module 170. Then, the detector module 170 generates a detection signal 171 accordingly. In this embodiment, the sample stage 200 is controlled by a closed-loop control system 310, which includes an encoder 340. The encoder 340 provides a feedback signal to a controller in the control system 310 indicating the instant position and moving speed of the sample stage 200. The encoder 340 also generates vibrations which contribute to the overall vibration of the microscope system 100. This encoder-generated vibration tends to be more significant at certain working frequencies of the encoder 340. These specific frequencies generally comprise the encoder primary frequency and its associate harmonic frequencies. An image forming module 320 coupled to the detector module 170 receives the detection signal 171 and accordingly forms a charged particle microscopic image of the sample 210. A vibration characterization module 330, which is coupled to the charged particle beam microscope system 100, for example to the image forming module 320 and the encoder 340, collects data of the obtained image from the image forming module 320 and information of the working encoder frequencies from the encoder 340 to accordingly generate a system vibrational performance chart for illustrating the vibrational performance of the concerned microscope system 100. It is noted that as mentioned earlier, the encoder primary frequency is dependent upon the moving speed of the sample stage 200. It is also noted that the encoder harmonic frequencies are mathematically derived from the encoder primary frequency and are therefore also dependent upon the stage speed. It is further noted that the speed of the stage 200 is determined by a desired imaging condition at which the image is to be taken. For example, the imaging condition may comprise parameters such as the desired pixel size, average number for a scan line/point pixel/frame image, the length of the scan lines, the sampling rate of the imaging channel of the charged particle beam microscope system, etc., or any combination thereof. In other words, the desired imaging condition gives rise to a corresponding moving speed of the stage 200. Therefore, when each image is taken at a different pre-selected imaging condition, each image is taken at a different stage speed. Further, in such case, as the encoder primary frequency (and thus the associate harmonic frequencies) is dependent on the stage speed, each image is taken at a different set of encoder frequencies corresponding to the stage speed at which the image is taken, and this frequency set is composed of one encoder primary and a plurality of harmonic frequencies derived thereof. The charged particle beam microscope system 100 may also comprises a control module 350 for setting a speed for the stage 200 according to a desired imaging condition loaded into the charged particle beam microscope system 100 through, for example, a user input means (not shown in FIG. 1). Accordingly, the control module 350 should be at least coupled to such user input means and the stage 200. The control module 350 can be implemented as a pure hardware such as an independent IC, a firmware or a pure computing program. The way in which the control module 350 is implemented and the way it is coupled with the user input means and the stage 200 is known to those skilled in the art and will not be repeated herein. In one embodiment of the present invention, a method is disclosed which can be executed by the vibration characterization module 330 to generate the aforementioned system vibrational performance chart from the obtained scan images. The method comprises steps of receiving a charged particle microscopic image, generating a time-domain image vibration signal from the received image, generating a frequency-domain image vibration spectrum from the time-domain image vibration signal, and identifying the imaged pattern vibration amplitude at an encoder primary and optionally harmonic frequencies from the frequency-domain image vibration spectrum. The encoder primary frequency and optionally harmonic frequencies along with their corresponding imaged pattern vibration amplitudes are then tabled and used to form respective points on a specific coordinate system. The process is repeated to form a plurality of such points thereby forming the system vibrational performance chart on the coordinate system. This chart describes the microscope system's vibrational performance in terms of the imaged pattern vibration amplitude at varying encoder frequencies. FIG. 2 shows a flow chart of the method. It is noted that the sample 210 may be designed to have at least one stripe pattern thereon such that the obtained scan image contains at least one imaged stripe pattern. After the image is taken, an edge detection/extraction algorithm is applied to extract the edge of the imaged stripe pattern to form the time-domain image vibration signal. The edge extraction algorithm can catch all vibrations and noises showing on the imaged stripe pattern. If the image was taken in a vibration-free environment, the extracted stripe pattern edge would be a straight line. If however, there was vibration when the image was taken, the extracted stripe pattern edge would carry “waves”. In step S10 in FIG. 2, a plurality of charged particle microscopic images of a sample are provided. Each image is taken at a pre-selected imaging condition. Each image comprises at least one imaged stripe pattern therewithin. For each image, its imaging condition corresponds to a set of encoder frequencies comprising an encoder primary frequency and associate harmonic frequencies. In step S20, a time-domain image vibration signal is generated for each of the provided charged particle microscopic images. As mentioned earlier, a vibration signal extractor for example an edge detection or extraction algorithm may be used to extract the edge of the imaged stripe pattern. The extracted edge can be treated as a signal along a time coordinate, wherein this signal carries all the vibration information of the concerned image, including the electrical and environmental noises captured during imaging. Data from the extracted edge are then used to form the time-domain image vibration signal. The formed time-domain image vibration signal shows a continuous curve composed of varying vibration amplitudes of the imaged pattern edge over an elapsed time period during which the sample was being imaged. The curve includes oscillations of various frequencies and amplitudes. For example, the curve in a time-domain image vibration signal may carry information of the encoder generated vibrations, vibration from other mechanical components in the microscope system, electrical noises, environmental noises such the human voice . . . etc. In step S30 a frequency-domain image vibration spectrum is generated from each time-domain image vibration signal. A domain transformation operator, for example the Fast Fourier Transformation (FFT), is used to transform the time-domain image vibration signal to its corresponding frequency-domain image vibration spectrum. In such transformation, all vibration information carried by the time-domain signal including the encoder generated vibration, other system vibrations, environmental noises and so on, each with varying occurrence frequencies and amplitudes, are processed to produce a full-range spectrum. The frequency-domain image vibration spectrum represents the vibration amplitudes of the imaged pattern edge versus a range of frequencies including the set of encoder frequencies defined in S10. In step S40, the encoder primary and optionally harmonic frequencies with corresponding imaged stripe pattern vibration amplitudes are identified from the frequency-domain image vibration spectrum. Recall that this encoder primary frequency is determined based on the stage speed which is determined by a pre-selected imaging condition at which the image was taken. Then, a data pair is formed accordingly which carries information of the identified encoder primary and optionally harmonic frequencies with their corresponding imaged pattern vibration amplitudes. Next in step S50, the data pair from step S40 is used to form a point on a coordinate system of (imaged pattern) vibration amplitude versus frequency. The range of the frequency axis should at least include the set of encoder frequencies (i.e. thus the encoder primary and associate harmonic frequencies) at which the concerned image was formed. The above five steps are repeated to form a plurality of such points thereby finally producing a system vibrational performance chart. This chart illustrates the vibrational characteristics of the concerned charged particle beam microscope system with regard to the encoder primary (and optionally the harmonic) frequencies. It is noted that in this embodiment, the vibrational characteristics of the concerned microscope system are expressed in the form of the vibration amplitude of the imaged stripe pattern versus the encoder primary and optionally harmonic frequencies. In other words, in the obtained system vibrational performance chart, a point with a higher value indicates a more severe vibration problem at the corresponding encoder primary/harmonic frequency. The stage speed and thus the imaging condition of an interested point in the chart can be found through checking the encoder primary and/or harmonic frequency of this point. Therefore, it can also be said that in the obtained system vibrational performance chart, a point with a higher value indicates a more severe vibration problem at the corresponding imaging condition of this point. The vibration amplitude of the imaged stripe pattern edge, or referred to as the imaged stripe pattern vibration amplitude or the imaged pattern vibration amplitude herein, can be quantified in various ways. In one embodiment of the present invention, it is estimated by measuring the degree of departure of the vibrating edge from a predefined reference. For example, as shown in FIG. 3, the reference can be an axis 301 passing through a center axis of the vibrating stripe pattern edge 302. This center axis may be obtained by averaging the relative height between individual points on the imaged stripe pattern or say the extracted edge. It is noted that the consideration of the encoder harmonic frequencies can be optional. However, if the harmonic frequency-generated vibration components reach a noticeable level, they may also be shown in the system vibrational performance chart to give further information about the vibrational behavior of the concerned charged particle beam microscope system. It is also noted that once the vibrational performance chart is generated, a threshold value can be defined for individual encoder primary/harmonic frequency to evaluate the vibrational behavior of the system at this frequency. For example, if the vibration amplitude of an imaged stripe pattern edge at a certain encoder primary/harmonic frequency exceeds a predefined threshold value, it is determined the vibrational performance of the concerned charged particle beam microscope system does not meet satisfaction at this encoder primary/harmonic frequency, otherwise it is determined the vibrational performance of the microscope system meets satisfaction at this frequency. Reference will now be made to FIG. 4, which includes FIG. 4A-1˜FIG. 4A-5, FIG. 4B-1˜FIG. 4B-5, FIG. 4C-1˜FIG. 4C-5, FIG. 4D, FIG. 4E and FIG. 4F to illustrate the formation process of the system vibrational performance chart in accordance with an embodiment of the present invention. It is noted that in this embodiment, the examined charged particle beam microscope system is selected to be a scanning electron beam microscope (SEM). First, five SEM images of a sample pattern 401, 402, 403, 404, 405 taken in a continuous scan mode are provided, as shown in FIG. 4A, which includes FIG. 4A-1, FIG. 4A-2, FIG. 4A-3, FIG. 4A-4 and FIG. 4A-5. Each of the images 401˜405 is taken at a pre-selected imaging condition described in the title of the image. Consequently, each of the images 401˜405 is taken at a specific stage speed, and thus at a specific encoder frequency set including a primary frequency and associate harmonic frequencies. Referring to FIG. 4B, which includes FIG. 4B-1, FIG. 4B-2, FIG. 4B-3, FIG. 4B-4 and FIG. 4B-5, a time-domain image vibration signal is correspondingly generated for each of the images 401˜405. As shown in FIG. 4B, these generated time-domain image vibration signals are denoted as 411, 412, 413, 414, 415, respectively. Next, individual time-domain image vibration signal 411˜415 is transformed to a corresponding frequency-domain image vibration spectrum 421, 422, 423, 424, 425, as shown in FIG. 4C, which includes FIG. 4C-1, FIG. 4C-2, FIG. 4C-3, FIG. 4C-4 and FIG. 4C-5. FIG. 4D illustrates overlapped frequency-domain image vibration spectrums 421˜425. Then, for each of the frequency-domain image vibration spectrums 421˜425, an encoder primary frequency is identified from the horizontal axis and a corresponding imaged pattern vibration amplitude is identified from the vertical axis. This encoder primary frequency-imaged pattern vibration amplitude data pair is then tabled and used to generate a point on a coordinate system of (imaged pattern) vibration amplitude versus frequency. As five such points have been formed on the coordinate system, a system vibrational performance chart for the concerned SEM is completed, as shown in FIG. 4E. It is noted that this chart only illustrates the case of the encoder primary frequency. In this embodiment, an analysis on the system vibrational behavior at the encoder harmonic frequencies also provides significant results. Detailed numbers of the encoder primary and one of the harmonic frequencies, the secondary frequency, for individual image and their corresponding imaged pattern vibration amplitude are given in Table 1. It can be seen from Table 1 that, at the encoder secondary frequency of the concerned SEM system, the imaged pattern vibration amplitude is at a noticeable level, with some even much greater than those at the primary frequencies. Therefore, for the concerned SEM system, a system vibrational performance chart at the encoder secondary frequency is necessary for a more informative tuning of the system. Such chart is illustrated in FIG. 4F. It can be seen from FIG. 4E and 4F that the system vibration performance is exceptionally unacceptable at working encoder frequencies in the vicinity of 50 Hz. Therefore, the corresponding imaging conditions at these frequencies need to be identified for rigorously testing and tuning the concerned SEM system so as to bring the curve down i.e. improve the system vibrational performance. In some cases, the hardware may be examined to find out if there is a loosened component that is generating severe vibration. After the system has been tuned, the system vibrational performance chart can be reproduced through the above process to see if the curve is lowered to an acceptable level. For example, if the imaged pattern vibration amplitude at a certain encoder primary or harmonic frequency exceeds a predefined threshold value, it is determined the system vibrational performance does not meet satisfaction at such frequency, otherwise it is determined the system vibrational performance meets satisfaction at such frequency. It is noted that the proposed method described in conjunction with FIG. 2 to FIG. 4 can be implemented in the form of the vibration characterization module 330 described in conjunction with FIG. 1. The vibration characterization module 330 can be implemented as a pure hardware such as an independent IC, a firmware or a pure computing program. For example, it can be implemented as a computer readable medium encoded with a computer program, wherein the program is able to execute the details of the proposed method as described in those embodiments in conjunction with FIG. 2 to FIG. 4. In one embodiment, the vibration characterization module 330 may be implemented as one selected from a group consisting of the following: a mainframe host, a terminal computer, a personal computer, any kind of mobile computing devices, or any combination thereof. In one embodiment, the vibration characterization module 330 is implemented as a computing agent which comprises at least an input member, a computing member and an output member. The input member can be coupled to the charged particle beam microscope system 100 for the vibration characterization module 330 to connect and access, for example, the image forming module 320 and the encoder 340. For example, the vibration characterization module 330 accesses these elements or their equivalents of the charged particle beam microscope system 100 to receive images formed by the charged particle beam microscope system 100 and information of working encoder frequencies during imaging, which comprises a plurality of sets of encoder frequencies (i.e. including a primary frequency and at least one associate harmonic frequencies), wherein each of the images is formed at a corresponding set of encoder frequencies. In one embodiment, the input member is coupled to the charged particle beam microscope system 100 through a medium selected from a group consisting of the following, or any combination thereof: cable wire, optical fiber cable, portable storage media, IR, Bluetooth, human manual input, intranet, internet, wireless network, wireless radio, etc. The computing member is coupled with the input member to receive, for example, the images and information of encoder frequencies from the input member for the use of carrying out the steps/actions described in conjunction with FIG. 2 to FIG. 4. In one embodiment, the vibration characterization module 330 may actively select a plurality of imaging conditions, each corresponding to a specific stage speed and thus a specific set of encoder frequencies (i.e. including a primary frequency and at least one associate harmonic frequencies), and instruct the charged particle beam microscope system 100 to perform imaging according to these selected imaging conditions to form corresponding images. The formed images are then fed back to the vibration characterization module 330 for analysis. In one embodiment, the selected imaging conditions may be inputted by a user through a user input means set on the vibration characterization module 330. Alternatively, the imaging conditions to be used can be picked out from those loaded into the charged particle beam microscope system 100, for example through a user input means set therewithin. Also, a mixture of imaging conditions from both the vibration characterization module 330 and the charged particle beam microscope system 100 may be used simultaneously. In one example, these imaging conditions for the purpose of characterization of a charged particle beam microscope system's vibrational performance may be pre-stored in a storage medium set in the vibration characterization module 330. As described earlier, a system vibrational performance chart would be generated at the end of the operation of the computing member. The output member is coupled to the computing member to receive the generated system vibrational performance chart therefrom and then output it for the user's interpretation. For example, the outputs can be an electronic file recognizable by a computer, a screen display or printed hard copy reports. Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims. TABLE 1ImageEncoderEncodervibrationprimaryImage vibrationsecondaryamplitudefrequency (Hz)amplitude (nm)frequency (Hz)(nm)15 nmp21.9310.1643.8524.920 nmp29.936.9658.4721.525 nmp36.547.273.0811.2530 nmp43.855.1587.712.7735 nmp51.565.49102.327.82 |
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056169280 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 numeral 11 represents the emissions absorbing portion of an apparatus of this invention, and the remainder of the apparatus, for carrying off and consuming the energy generated in portion 11, is designated by numeral 13. In portion 11 radioactive waste material 15, suitably shaped in spherical form (although other forms may also be employed and held in a suitable interior container 16, preferably of compatible material, is positioned inside an inner spherical shell of electrically conductive material (such as aluminum), and is separated from such material by dielectric 19, which may be a suitable dielectric, solid or gaseous, e.g., alumina, mica, air. An enveloping sphere 21 surrounds sphere 17 and is separated from it by dielectric 23. Sphere 21 is preferably of an electrically conductive material, such as a metal of higher atomic number than the material of sphere shell 17. Suitable such materials are copper and silver, with copper normally being preferred, but other metals may also be used. When solid dielectrics are utilized they may be the sole means for separating the sphere but when gaseous dielectrics, such as air (or a high vacuum) are employed, mechanical means (not shown), preferably of electrically insulating material, will be employed. Electrical conductors 25 and 27, which will usually be insulated copper, and/or silver wires, conduct electricity to a variable resistance 29 and/or a battery 31. Diode 33 is provided to act as a check switch on current flow, preventing battery 31 from delivering electricity to part 11 of the apparatus. Other switches (not shown) may also be provided to separate the variable resistance and the battery from the rest of the system, if desired, and the variable resistance may be made automatically variable to draw a relatively small current, due to the difference in the electrical potentials of the spherical shells 17 and 21, drawing more current when the potential difference is sufficiently high and being of decreased resistance so as to allow and promote current flow when the potential difference is lower. Also, means may be provided for automatically reversing the polarity of the battery so as initially to stimulate or induce electrical current flow between spherical shells 17 and 21. While spherical shells are shown, these may be of other suitable shapes, such as cylindrical, cubical, tetrahedronal and ellipsoidal too, and in some instances the shells may desirably be perforated to allow release (through suitable absorbers or safety means, not shown) of gaseous materials generated from the radioactive waste or generated by expansion of gases present, as heat is released from the waste. Sometimes the inner shell may be perforated to permit some radiant energy flow through such openings, as when plural pairs of shields or electrodes are employed, e.g., 4 to 200 concentric metal spheres, with separating dielectrics. In the illustration a single apparatus is illustrated but banks of such devices may be connected together, with the current produced flowing through single or multiple resistances and/or being employed to charge one or more batteries. In FIG. 1 the nuclear waste is in a suitable metal container 16 but it is contemplated that other materials of construction may be employed and sometimes it can be omitted. Concrete enclosing container 35 encloses the waste, the container for the waste, and the pair of spherical shells of electrically conductive material, but other suitable exterior containers may also be utilized. While this invention is not bound or limited by the following theory of operation, it is considered that alpha particles emitted by the radioactive waste (which usually is a complex mixture of various radioactive isotopes) tend to make the charge of the first metal absorber positive whereas beta particles and gamma rays, being more penetrating, tend to make the charge of the next contacted electrically conductive material negative, as illustrated in FIG. 1. When plural pairs of absorbers are employed the metals of low density will tend to be negative relative to the high density metals. Metals of low density, if sufficiently thick, will react with more beta particles reaching them than will metals of higher density because the high density metals, if sufficiently thin, will reflect some of the lower frequency radiation back to the more absorbing low density metal and transmit some to the next set of shielding levels. If the wastes emit gamma rays there should be several layers of combinations of insulator, low density conductor, insulator, high density conductor, etc. For example, aluminum and copper may be employed, as may be other metals and alloys, and combinations of metals (or alloys) outside the ranges specified in the Ritter patent. Magnesium, aluminum and/or titanium may be employed as the low atomic number metal, together with vanadium, chromium, manganese, iron, cobalt, nickel, copper or zinc as the higher atomic number metal. Similarly, magnesium or aluminum may be used with titanium. Also, for example, vanadium, chromium, manganese or iron may be used with cobalt, nickel, copper or zinc, with preference being to employing such combinations with atomic numbers further apart within such groups. Other such combinations that are useful include vanadium, chromium, manganese, iron, cobalt, nickel, copper or zinc with molybdenum, silver, tin, platinum, gold, mercury and/or lead. In some applications alloys or amalgams may be employed. Also, with respect to the higher atomic number materials, silver, cadmium and tin may be used with lead. Thus, while, within the broader aspects of this invention it is possible to utilize as the absorber or shield materials metals with atomic numbers below 23 in combination with those of atomic numbers above 46, it is also possible to utilize combinations of metals outside such ranges and still obtain the radiation absorbing and energy consuming effects desired. In FIG. 2 heterogeneous nuclear waste 41, in a suitable metal container 43, is surrounded by concentric absorbing materials and dielectrics, all of which are in spherical shape conforming to the shape of waste 41 and container 43. Thus, between the container for the radioactive waste and the first radiation absorbing sphere 45 of electrically conductive material there is a dielectric layer or sphere 47 and subsequently, in order, about the sphere 45 are a spherical layer 49 of dielectric, another absorbing sphere 51 of electrically conductive material, another dielectric layer 53, another metal layer 55, a dielectric layer 57 and an outer metal layer 59. Spheres 45 and 55 are of aluminum or copper, as shown, and spheres 51 and 59 are of copper or lead, respectively. The same dielectric, mica, alumina or other suitable solid, or air, may be used between the various metal spheres. Of course, other shapes than spherical may also be employed. As illustrated, in normal operation spheres 45 and 55 will usually be relatively negative and spheres 51 and 59 will be relatively positive. Conductors 61 and 63 connect the "negative" potentials of spheres 45 and 55 to line 65, which line connects to an electrical power consuming part of the circuit, not shown herein, but like that of FIG. 1. Lines 67 and 69 act to transmit the "positive" potentials from parts 51 and 59 to line 71, which is also connected to the energy consuming parts of the circuit. Of course, lines 61, 63, 65, 67, 69 and 71 are insulated to avoid any short circuits. While only two sets of pairs of electrodes, shields, or electrically conductive spheres are illustrated in FIG. 2, a multiplicity of such pairs may also be employed. Also, container 43 and/or waste 41 may be connected to line 71. In FIG. 3 there is shown a nuclear installation, battery or other source of electrical power 73, which also is a source of harmful radiation due to the presence therein of radioactive material. Numeral 75 designates a multilayered shield of alternating high Z and low Z metals, separated by dielectrics. For example, electrically conductive metal sheets 77 and 81 may be of a low Z material, such as aluminum, and sheets 79 and 83 may be of a higher Z material, such as copper or lead. Between the sheets are dieletric layers, which may be of suitable dielectric material, such as alumina, mica, silica, glass and in some cases, synthetic organic polymeric plastics. If gaseous materials are employed for the dielectric, air or high vacuum is usually preferred. Electrical connections of the more negative first and third layers and the more positive second and fourth layers and the insulated metal surface of source 73 be made to a power consuming portion of the circuitry, 85, which includes lines 87 and 89, a variable load 91, batteries to be charged, such as that at 93, and a diode 95 to prevent batteries from discharging through the radioactive source. As is seen from the drawing, voltages from energy converting device 73 and shield 75 may be combined via conductors 97 and 99, and 101 and 103 respectively. Thus, shielding 75 can protect humans and the environment from nuclear installation 73 and can be employed to help consume the radiation energy from the nuclear material in such installation. Of course, shielding 75 may be used to enclose the source of radiation 73 or may be employed to enclose and protect a "target" of such radiation, such as a room in which personnel are located, near the nuclear installation. FIG. 4 illustrates another embodiment of the invention in which an aluminum electrode 111, or "shield", in the form of an empty truncated sphere, with a few small holes in it, and insulated from surrounding container 113, has another conductive sphere 115, made of copper or silver, inside it. Radioactive waste 117 is in the container surrounding the spheres, and arrows, such as that identified by numeral 119, show some paths of radioactive emissions from a particular location 121 of the radioactive material. Instead of aluminum, other conductive materials, preferably metals, can be used as the material of the outer sphere as long as they are stable at the temperature obtaining within container 113 and as long as they are dense enough to absorb alpha particles emitted from the heterogeneous nuclear waste. Among such materials may be mentioned magnesium, titanium, copper, iron, chromium and nickel. Outer shell 111 does not have to be spherical in shape but a sphere presents the greatest variety of directional surfaces and is an excellent target for emitted radiation. Inner electrode 115, preferably of silver or copper, may also be of other conductive metals, with the identity of its electrode material depending to some extent on that of the other electrode material. For example, it is preferred that "the high Z" and "low Z" metals should be at least five atomic members apart, more preferably at least ten atomic numbers apart and most preferably twenty or more atomic numbers apart. Also, relatively high and low Z materials may be employed. Thus, two "high Z" metals or alloys may be used so long as they are a sufficient atomic number difference apart and are operative in the present invention. Electrical conductors 123 and 125, together with the outer shell source of electrical potential and the inner shell source of electrical potential, can be communicated through a load or resistance, such as that shown at 127, and the current flowing can be read by an ammeter, such as that at 129. Absorbing of alpha particles by conductors 123 and 125 may send a positive charge through the circuit but relatively high Z shield 115 will tend to be more charged than low Z 111 due to 111's greater photoelectron reactivity and its greater absorption of electrons. Also, as illustrated, the electrical potential from either of the metal spheres may be transmitted to a sink, represented by metal plate 131, in pond 133, which plate serves as a ground. At 135 is shown a battery which may be employed to induce the flow of electricity between the metal spheres or from the metal spheres to the metal plate 131. Switches for cutting off the auxiliary battery 135 are present, but are not illustrated in the drawing. As is seen from the previous description the present process affects dangerous emissions from the heterogeneous radioactive or comparable radiation source, which are converted to electrical energy, which is consumed. Thereby radiation is removed from the environment and is changed to a harmless energy form. It is well known that huge sums of money have been expended in research efforts to solve nuclear waste storage problems but despite all such efforts no prior art disclosure taught the process of this invention. Prior art efforts were directed to containing the nuclear waste, usually after concentration thereof, by storing it in a container or matrix in a remote area or deep in the earth. Often shielding was utilized which, in effect, merely contains the radiation or is itself affected by absorption of such radiation. When containment is the only effect of the shielding dangerous energy levels can be produced and when conversion of the shielding material takes place due to energy absorption, the nature of the material may change, leading to deterioration thereof. Before the present invention it was known that certain types of radiation could be converted into electrical energy (but many experts refused to believe that gamma rays could be so transformed). Still, the prior art did not teach the use of any of such conversion mechanisms for shielding the environment from dangerous emissions. In fact, such apparatuses could leak primary emissions and could generate dangerous secondary emissions. Also, for satisfactory operation of various prior art nuclear devices for producing electrical energy, such as that of the Ritter patent, purified sources of radioactivity had to be used, rather than heterogeneous wastes, such as usual nuclear wastes. The present invention allows the treatment and shielding of such wastes and also allows the protection of various sources of complex radioactive emissions, such as decommissioned nuclear plants, pools of highly radioactive materials, radioactive mill tailings, nuclear wastes being transported, nuclear wastes being processed, and stored solidified wastes that have been "vitrefied", encased in a synthetic organic resin, or embedded in ceramics or concrete. The present invention also incorporates several safety features not suggested by the prior art. For example, by drawing off radiant energy from shield material the invention allows for stabilization of such material and thereby increases its shielding life. Also, whereas in the Ritter patent an object has been to build up high voltages, thus putting a strain on the shielding and increasing the danger of accident, such is not necessary nor is it an object of the present invention, which allows for regulation of the resistance to maintain a current flow and thereby to aid the conversion of radioactivity to electricity. In other words, there is no "back pressure" on the system due to any requirement to produce a high voltage, and the present apparatus acts as a safety valve, allowing the flow of more electricity in response to any flare-ups or sudden emissions of radioactivity. The embodiment of the invention described uses form-retaining electrically conductive metal shields but such shields may also be made in the form of a flexible blanket which can be easily placed over a source of radiation or over a subject to be protected from such radiation. In such and other instances the intervening dielectric material, which will then preferably be a solid, may be molded or otherwise attached to the electrically conductive materials. Of course, in such blankets suitable conductors will be provided to carry off electricity from the shielding metals to an electrical load, where it is consumed. In employing the invention modifications may be made depending on the particular type of waste being utilized and its state of "decay". If the predominant emission is of alpha particles the load should be across contacts with the first layer of shielding and the rest of the shielding. If the predominant emission is of beta rays it is considered best to have a high Z outermost shielding layer and/or a ground as one electrode and all the other layers as the other electrode. When gamma rays are the principal radiation it is considered best to employ thin layers of relatively high Z material with thicker layers of relatively low Z material, in repeating pairs, with the current flow being between such high Z and low Z layers. Usually the various shield layers are at different distances from the radioactive source but it is also within the invention to utilize different shield electrodes at the same distance from such source. For conversion of gamma rays to harmless electricity a honeycomb form of shielding is considered to be efficient, and it is also effective for absorption of beta rays. However, in some cases, as when the metal shields deteriorate after use (some reduced amount of deterioration may be observed) only a single type of metal shielding material may sometimes be best employed, with dependence being on direct conversion, photoelectricity, Compton effect and ion pair formation for conversion of the radiation energy. Normally, as when a source of radiation is aboveground, as in a decommissioned nuclear power plant, the shielding may have to be changed as time goes by. Such changing may also be dictated by the changing nature of the radiation source, and it will be preferable to utilize shieldings for greatest effects versus various types of radiation, for example, radioactive cobalt 60 during the first years after decommissioning, and isotopes of nickel and niobium many years later (each having different peak frequencies of radiation). As described, shields may be used around a nuclear reactor or installation, and above the installation they may be in staggered form to allow air circulation (but any air emitted will be filtered and monitored for leakage of radionuclides). Liquid wastes may be shielded by means of the present invention, as may be radioactive wastes being transported in containers. Such containers may be made of shielding materials and the electrical load may be a part of the electrical system of the transporting vehicle. For example, the electricity generated from the waste being carried may be used to operate electric lights on a truck or trailer being employed, which lights will blink on and off to act as a warning that radioactive material is present. The present invention is useful for protecting humans and the environment. Even if it had been known that electricity could be produced from heterogeneous radiation including gamma rays, such "new use" of such process would be patentable, especially in the absence of any suggestion thereof in the art. Especially in view of the long felt need for such a process and the great number of researchers attempting to invent it it is considered that the process was not merely inherent in the prior art and was not obvious to those of ordinary skill in such art. Apparently the closest "prior art" to the present invention is U.S. Pat. No. 4,178,524, to Ritter. Ritter does not mention the employment of his apparatus to absorb radiation and protect the environment. In fact, he utilizes a lead housing to attenuate the radiation emitted by the source thereof. It may be inferred that the Ritter apparatus creates additional emissions. Ritter uses particular types of radioactive sources, emitting energies less than a million electron volts. Such radioactive sources of Ritter appear to be relatively pure isotopes, not heterogeneous nuclear wastes emitting large amounts of radiations of different types. Ritter specifies the employment of his particular high and low-Z materials whereas the present invention allows the use of a wide variety of such materials, for example, nuclear wastes include alpha and beta radiation emitters, but Ritter's device is limited to a source of gamma rays with less than 1 Mev power. Ritter tries to produce maximum voltage whereas such is not the purpose of this invention and in fact, preventing voltage build-up is very important. Ritter's invention is a "remote electrical generator" whereas the present apparatus is intended for use in or next to power plants, hospitals, waste processing centers or other places that generate or house nuclear wastes, and allows treatment of the wastes at such sites, thereby, at least in part, obviating the need to transport them to a dump. Finally, the Ritter patent makes no mention of consuming the energy developed in the load, especially one of variable resistance, which makes the apparatus adaptable for use with radioactive wastes of different strengths and of changing activities. Unlike the Ritter apparatus, which requires the regulation of the energy the radioactive source can emit so as to maintain it low, the present apparatus is capable of operations with high energy sources and is adaptable to consume whatever electrical energy is produced by such source, thereby aiding in continuous conversion of radiation to electrical energy. The invention has been described with respect to various illustrations and embodiments thereof but is not to be limited to these because it is evident that one of skill in the art, with the present specification and drawings before him, will be able to utilize substitutes and equivalents without departing from the invention. |
description | This application is a continuation of applicant's co-pending U.S. application Ser. No. 13/695,792, filed Jun. 3, 2013, which is a U.S. National Stage application under 35 USC § 371 of PCT/US2011/036034, filed 11 May 2011, which claims priority benefit under the Paris Convention from U.S. Provisional Application No. 61/333,467, filed May 11, 2010, U.S. Provisional Application No. 61/393,499, filed Oct. 15, 2010, and U.S. Provisional Application No. 61/444,990, filed Feb. 21, 2011, all three of which are titled “METAL FUEL ASSEMBLY,” the entire contents of all of the foregoing applications are hereby incorporated by reference. The present invention relates generally to nuclear fuel assemblies used in the core of a nuclear reactor, and relates more specifically to metal nuclear fuel elements. U.S. Patent Application Publication No. 2009/0252278 A1, the entire contents of which are incorporated herein by reference, discloses a nuclear fuel assembly that includes seed and blanket sub-assemblies. The blanket sub-assembly includes thorium-based fuel elements. The seed sub-assembly includes Uranium and/or Plutonium metal fuel elements used to release neutrons, which are captured by the Thorium blanket elements, thereby creating fissionable U-233 that burns in situ and releases heat for the nuclear power plant. Conventional nuclear power plants typically use fuel assemblies that include a plurality of fuel rods that each comprise uranium oxide fuel in a cylindrical tube. The surface area of the cylindrical tube of conventional fuel rods limits the amount of heat that can be transferred from the rod to the primary coolant. To avoid overheating the fuel rod in view of the limited surface area for heat flux removal, the amount of fissile material in these uranium oxide fuel rods or mixed oxide (plutonium and uranium oxide) fuel rods has conventionally been substantially limited. One or more embodiments of the present invention overcome various disadvantages of conventional uranium oxide fuel rods by replacing them with all metal, multi-lobed, powder metallurgy co-extruded fuel rods (fuel elements). The metal fuel elements have significantly more surface area than their uranium oxide rod counterparts, and therefore facilitate significantly more heat transfer from the fuel element to the primary coolant at a lower temperature. The spiral ribs of the multi-lobed fuel elements provide structural support to the fuel element, which may facilitate the reduction in the quantity or elimination of spacer grids that might otherwise have been required. Reduction in the quantity or elimination of such spacer grids advantageously reduces the hydraulic drag on the coolant, which can improve heat transfer to the coolant. Because the metal fuel elements may be relatively more compact than their conventional uranium oxide fuel rod counterparts, more space within the fuel assembly is provided for coolant, which again reduces hydraulic drag and improves heat transfer to the coolant. The higher heat transfer from the metal fuel rods to the coolant means that it is possible to generate more heat (i.e., power), while simultaneously maintaining the fuel elements at a lower operating temperature due to the considerably higher thermal conductivity of metals versus oxides. Although conventional uranium oxide or mixed oxide fuel rods typically are limited to fissile material loading of around 4-5% due to overheating concerns, the higher heat transfer properties of the metal fuel elements according to various embodiments of the present invention enable significantly greater fissile material loadings to be used while still maintaining safe fuel performance. Ultimately, the use of metal fuel elements according to one or more embodiments of the present invention can provide more power from the same reactor core than possible with conventional uranium oxide or mixed oxide fuel rods. The use of all-metal fuel elements according to one or more embodiments of the present invention may advantageously reduce the risk of fuel failure because the metal fuel elements reduce the risk of fission gas release to the primary coolant, as is possible in conventional uranium oxide or mixed oxide fuel rods. The use of all-metal fuel elements according to one or more embodiments of the present invention may also be safer than conventional uranium oxide fuel rods because the all-metal design increases heat transfer within the fuel element, thereby reducing temperature variations within the fuel element, and reducing the risk of localized overheating of the fuel element. One or more embodiments of the present invention provide a fuel assembly for use in a core of a nuclear power reactor (e.g., a land-based or marine nuclear reactor). The assembly includes a frame comprising a lower nozzle that is shaped and configured to mount to the nuclear reactor internal core structure, and a plurality of elongated metal fuel elements supported by the frame. Each of the plurality of fuel elements includes a metal fuel alloy kernel comprising metal fuel material and a metal non-fuel material. The fuel material includes fissile material. Each fuel element also includes a cladding surrounding the fuel kernel. The plurality of elongated metal fuel elements provide at least 70% by volume of the overall fissile material of the fuel assembly. One or more embodiments of the present invention provide a fuel assembly for use in a core of a nuclear power reactor. The assembly includes a frame including a lower nozzle that is shaped and configured to mount to the nuclear reactor internal core structure. The assembly also includes a plurality of elongated, extruded metal fuel elements supported by the frame, each of said plurality of fuel elements including a metal fuel alloy kernel including metal fuel material and a metal non-fuel material. The fuel material includes fissile material. The fuel element also includes a cladding surrounding the fuel kernel. A moderator:fuel ratio in a region of the metal fuel elements is 2.5 or less. One or more embodiments of the present invention provide a method of manufacturing a fuel assembly for use in a core of a nuclear power reactor. The method includes manufacturing each of a plurality of elongated metal fuel elements by: mixing powder metal fuel with powder metal non-fuel material, wherein the powder metal fuel material includes fissile material, sintering the mixed powder metal fuel and metal non-fuel material to create a fuel core stock, surrounding the fuel core stock with a cladding material, and co-extruding the fuel core stock and cladding material to create the fuel element. The method also includes mounting the plurality of elongated metal fuel elements to a frame of the fuel assembly. A moderator:fuel ratio in a region of the metal fuel elements may be 2.5 or less. The method may include positioning a displacer within the mixed powder metal fuel material and metal non-fuel material before said sintering such that said sintering results in a fuel core stock that includes the displacer. The fuel assembly may be placed into a land-based nuclear power reactor. According to one or more of these embodiments, the plurality of elongated metal fuel elements provide at least 60% of a total volume of all fuel elements of the fuel assembly. According to one or more of these embodiments, an average thickness of the cladding is at least 0.6 mm. According to one or more of these embodiments, the fuel assembly is thermodynamically designed and physically shaped for operation in a land-based nuclear power reactor. According to one or more embodiments, the fuel assembly may be used in combination with a land-based nuclear power reactor, wherein the fuel assembly is disposed within the land-based nuclear power reactor. According to one or more of these embodiments, with respect to a plurality of the plurality of fuel elements: the fuel material of the fuel kernel is enriched to 20% or less by uranium-235 and/or uranium-233 and comprises between a 20% and 30% volume fraction of the fuel kernel; and the non-fuel metal includes between a 70% and 80% volume fraction of the fuel kernel. With respect to the plurality of the plurality of fuel elements, the fuel material enrichment may be between 15% and 20%. The non-fuel metal of the fuel kernel may include zirconium. According to one or more of these embodiments, the kernel includes δ-phase UZr2. According to one or more of these embodiments, with respect to a plurality of the plurality of fuel elements: the fuel material of the fuel kernel includes plutonium; the non-fuel metal of the fuel kernel includes zirconium; and the non-fuel metal of the fuel kernel includes between a 70% and 97% volume fraction of the fuel kernel. According to one or more of these embodiments, the fuel material includes a combination of: uranium and thorium; plutonium and thorium; or uranium, plutonium, and thorium. According to one or more of these embodiments, the cladding of a plurality of the plurality of fuel elements is metallurgically bonded to the fuel kernel. According to one or more of these embodiments, the non-fuel metal of a plurality of the plurality of fuel elements includes aluminum. According to one or more of these embodiments, the non-fuel metal of a plurality of the plurality of fuel elements includes a refractory metal. According to one or more of these embodiments, the cladding of a plurality of the plurality of fuel elements includes zirconium. According to one or more of these embodiments, a plurality of the plurality of fuel elements are manufactured via co-extrusion of the fuel kernel and cladding. According to one or more of these embodiments, the fuel assembly, one or more fuel elements thereof, and/or one or more fuel kernels thereof includes burnable poison. According to one or more of these embodiments, the plurality of elongated metal fuel elements provide at least 80% by volume of the overall fissile material of the fuel assembly. According to one or more of these embodiments, the land-based nuclear power reactor comprises a conventional nuclear power plant having a reactor design that was in actual use before 2010. The frame may be shaped and configured to fit into the land-based nuclear power reactor in place of a conventional uranium oxide fuel assembly for the reactor. According to one or more of these embodiments, one or more of the fuel elements has a spirally twisted, multi-lobed profile that defines a plurality of spiral ribs. The spacer ribs of adjacent ones of the plurality of fuel elements may periodically contact each other over the axial length of the fuel elements, such contact helping to maintain the spacing of the fuel elements relative to each other. The fuel assembly may have a moderator to fuel ratio of at least 2.5 or 2.5 or less. The multi-lobed profile may include concave areas between adjacent lobes. According to one or more of these embodiments, the respective metal fuel alloy kernels of the plurality of metal fuel elements are formed via sintering of the fuel material and metal non-fuel material. According to one or more of these embodiments, the multi-lobed profile includes lobe tips and intersections between adjacent lobes, wherein the cladding is thicker at the tips than at the intersections. One or more embodiments of the present invention provide a method of manufacturing a fuel assembly for use in a core of a land-based nuclear power reactor. The method includes manufacturing each of a plurality of elongated metal fuel elements by mixing powder metal fuel with powder metal non-fuel material, wherein the powder metal fuel material includes fissile material. The manufacturing of each of the elongated metal fuel elements also includes sintering the mixed powder metal fuel and metal non-fuel material to create a fuel core stock, surrounding the fuel core stock with a cladding material, and co-extruding the fuel core stock and cladding material to create the fuel element. The method also includes mounting the plurality of elongated metal fuel elements to a frame of the fuel assembly comprising a lower nozzle that is shaped and configured to mount to a core of the land-based nuclear power reactor. The plurality of elongated metal fuel elements provide at least 70% by volume of the overall fissile material of the fuel assembly. The fuel assembly is thermodynamically designed and physically shaped for operation in the land-based nuclear power reactor. According to one or more of these embodiments, the method also includes positioning a displacer within the mixed powder metal fuel material and metal non-fuel material before the sintering such that the sintering results in a fuel core stock that includes the displacer. According to one or more of these embodiments, the method also includes placing the fuel assembly into the land-based nuclear power reactor. One or more embodiments of the present invention provide a nuclear reactor that includes a pressurized heavy water reactor and a fuel assembly disposed in the pressurized heavy water reactor. The fuel assembly includes a plurality of elongated metal fuel elements mounted to each other. Each of the plurality of fuel elements includes a powder metallurgy metal fuel alloy kernel comprising metal fuel material and a metal non-fuel material, the fuel material comprising fissile material. Each fuel element also includes a cladding surrounding the fuel kernel. The plurality of elongated metal fuel elements provide at least 70% by volume of the overall fissile material of the fuel assembly. Each of the fuel elements may have a spirally twisted, multi-lobed profile that defines a plurality of spiral spacer ribs. One or more embodiments of the present invention provide a nuclear reactor that includes a pressurized heavy water reactor; and a fuel assembly disposed in the pressurized heavy water reactor. The fuel assembly includes a plurality of elongated metal fuel elements mounted to each other, each of said plurality of fuel elements including: a metal fuel alloy kernel comprising metal fuel material and a metal non-fuel material, the fuel material comprising fissile material, and a cladding surrounding the fuel kernel. A moderator:fuel ratio in a region of the metal fuel elements may be 2.5 or less. According to one or more of these embodiments, the fuel assembly also includes a plurality of UO2 fuel elements supported by the frame, each of said plurality of UO2 fuel elements comprising UO2 fuel. At least some of the plurality of elongated UO2 fuel elements may be positioned laterally outwardly from the plurality of elongated metal fuel elements. The UO2 fuel may have less than 15% U-235 enrichment. According to one or more of these embodiments, a shroud separates coolant flow past the plurality of elongated UO2 fuel elements from coolant flow past the plurality of elongated metal fuel elements. One or more embodiments of the present invention provide a fuel assembly for use in a core of a nuclear power reactor. The assembly includes a frame comprising a lower nozzle that is shaped and configured to mount to the nuclear reactor internal core structure. The assembly includes a plurality of elongated, extruded metal fuel elements supported by the frame. Each of said plurality of fuel elements includes a metal fuel alloy kernel comprising metal fuel material and a metal non-fuel material, the fuel material comprising fissile material, and a cladding surrounding the fuel kernel. The assembly includes a plurality of additional elongated fuel elements supported by the frame. As viewed in a cross-section of the fuel assembly, the plurality of additional elongated fuel elements may be positioned in a single-fuel-element-wide ring that surrounds the plurality of elongated, extruded metal fuel elements. The plurality of elongated metal fuel elements may provide at least 60% of a total volume of all fuel elements of the fuel assembly. According to one or more of these embodiments, the plurality of additional elongated fuel elements each comprise a hollow rod with pelletized UO2 fuel disposed inside the rod. According to one or more of these embodiments, a portion of the fuel assembly that supports the plurality of additional elongated fuel elements is inseparable from a portion of the fuel assembly that supports the plurality of elongated, extruded metal fuel elements. According to one or more of these embodiments, the plurality of additional elongated fuel elements are not separable as a unit from the plurality of elongated, extruded metal fuel elements. According to one or more of these embodiments, the fuel assembly defines a 17×17 pattern of positions; each of the plurality of elongated, extruded metal fuel elements is disposed at one of the pattern positions; none of the plurality of elongated, extruded metal fuel elements are disposed at any of the peripheral positions of the 17×17 pattern; and each of the plurality of additional elongated fuel elements is disposed in a different one of the peripheral positions of the 17×17 pattern. According to one or more of the above embodiments, the kernel may comprise ceramic fuel material instead of metal fuel material. In one or more such embodiments, the fuel material comprises ceramic fuel material disposed in a matrix of metal non-fuel material. Conversely, in one or more metal fuel embodiments, the plurality of elongated, extruded fuel elements comprise a plurality of elongated, extruded metal fuel elements; the fuel material comprises metal fuel material; and the fuel kernel comprises a metal fuel alloy kernel comprising an alloy of the metal fuel material and the matrix of metal non-fuel material. These and other aspects of various embodiments of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. In one embodiment of the invention, the structural components illustrated herein are drawn to scale. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. In addition, it should be appreciated that structural features shown or described in any one embodiment herein can be used in other embodiments as well. As used in the specification and in the claims, the singular form of “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. FIGS. 1-3 illustrate a fuel assembly 10 according to an embodiment of the present invention. As shown in FIG. 3, the fuel assembly 10 comprises a plurality of fuel elements 20 supported by a frame 25. As shown in FIG. 3, the frame 25 comprises a shroud 30, guide tubes 40, an upper nozzle 50, a lower nozzle 60, a lower tie plate 70, an upper tie plate 80, and/or other structure(s) that enable the assembly 10 to operate as a fuel assembly in a nuclear reactor. One or more of these components of the frame 25 may be omitted according to various embodiments without deviating from the scope of the present invention. As shown in FIG. 3, the shroud 25 mounts to the upper nozzle 50 and lower nozzle 60. The lower nozzle 60 (or other suitable structure of the assembly 10) is constructed and shaped to provide a fluid communication interface between the assembly 10 and the reactor 90 into which the assembly 10 is placed so as to facilitate coolant flow into the reactor core through the assembly 10 via the lower nozzle 60. The upper nozzle 50 facilitates direction of the heated coolant from the assembly 10 to the power plant's steam generators (for PWRs), turbines (for BWRs), etc. The nozzles 50, 60 have a shape that is specifically designed to properly mate with the reactor core internal structure. As shown in FIG. 3, the lower tie plate 70 and upper tie plate 80 are preferably rigidly mounted (e.g., via welding, suitable fasteners (e.g., bolts, screws), etc.) to the shroud 30 or lower nozzle 60 (and/or other suitable structural components of the assembly 10). Lower axial ends of the elements 20 form pins 20a that fit into holes 70a in the lower tie plate 70 to support the elements 20 and help maintain proper element 20 spacing. The pins 20a mount to the holes 70a in a manner that prevents the elements 20 from rotating about their axes or axially moving relative to the lower tie plate 70. This restriction on rotation helps to ensure that contact points between adjacent elements 20 all occur at the same axial positions along the elements 20 (e.g., at self-spacing planes discussed below). The connection between the pins 20a and holes 70a may be created via welding, interference fit, mating non-cylindrical features that prevent rotation (e.g., keyway and spline), and/or any other suitable mechanism for restricting axial and/or rotational movement of the elements 20 relative to the lower tie plate 70. The lower tie plate 70 includes axially extending channels (e.g., a grid of openings) through which coolant flows toward the elements 20. Upper axial ends of the elements 20 form pins 20a that freely fit into holes 80a in the upper tie plate 80 to permit the upper pins 20a to freely axially move upwardly through to the upper tie plate 80 while helping to maintain the spacing between elements 20. As a result, when the elements 20 axially grow during fission, the elongating elements 20 can freely extend further into the upper tie plate 80. As shown in FIG. 4, the pins 70a transition into a central portion of the element 20. FIGS. 4 and 5 illustrate an individual fuel element/rod 20 of the assembly 10. As shown in FIG. 5, the elongated central portion of the fuel element 20 has a four-lobed cross-section. A cross-section of the element 20 remains substantially uniform over the length of the central portion of the element 20. Each fuel element 20 has a fuel kernel 100, which includes a refractory metal and fuel material that includes fissile material. A displacer 110 that comprises a refractory metal is placed along the longitudinal axis in the center of the fuel kernel 100. The displacer 110 helps to limit the temperature in the center of the thickest part of the fuel element 20 by displacing fissile material that would otherwise occupy such space and minimize variations in heat flux along the surface of the fuel element. According to various embodiments, the displacer 110 may be eliminated altogether. As shown in FIG. 5, the fuel kernel 100 is enclosed by a refractory metal cladding 120. The cladding 120 is preferably thick enough, strong enough, and flexible enough to endure the radiation-induced swelling of the kernel 100 without failure (e.g., without exposing the kernel 100 to the environment outside the cladding 120). According to one or more embodiments, the entire cladding 120 is at least 0.3 mm, 0.4 mm, 0.5 mm, and/or 0.7 mm thick. According to one or more embodiments, the cladding 120 thickness is at least 0.4 mm in order to reduce a chance of swelling-based failure, oxidation based failure, and/or any other failure mechanism of the cladding 120. The cladding 120 may have a substantially uniform thickness in the annular direction (i.e., around the perimeter of the cladding 120 as shown in the cross-sectional view of FIG. 5) and over the axial/longitudinal length of the kernel 100 (as shown in FIG. 4). Alternatively, as shown in FIG. 5, according to one or more embodiments, the cladding 120 is thicker at the tips of the lobes 20b than at the concave intersection/area 20c between the lobes 20b. For example, according to one or more embodiments, the cladding 120 at the tips of the lobes 20b is at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 125%, and/or 150% thicker than the cladding 120 at the concave intersections/areas 20c. The thicker cladding 120 at the tips of the lobes 20b provides improved wear resistance at the tips of the lobes 20b where adjacent fuel elements 20 touch each other at the self-spacing planes (discussed below). The refractory metal used in the displacer 110, the fuel kernel 100, and the cladding 120 comprises zirconium according to one or more embodiments of the invention. As used herein, the term zirconium means pure zirconium or zirconium in combination with other alloy material(s). However, other refractory metals may be used instead of zirconium without deviating from the scope of the present invention (e.g., niobium, molybdenum, tantalum, tungsten, rhenium, titanium, vanadium, chromium, zirconium, hafnium, ruthenium, osmium, iridium, and/or other metals). As used herein, the term “refractory metal” means any metal/alloy that has a melting point above 1800 degrees Celsius (2073K). Moreover, in certain embodiments, the refractory metal may be replaced with another non-fuel metal, e.g., aluminum. However, the use of a non-refractory non-fuel metal is best suited for reactor cores that operate at lower temperatures (e.g., small cores that have a height of about 1 meter and an electric power rating of 100 MWe or less). Refractory metals are preferred for use in cores with higher operating temperatures. As shown in FIG. 5, the central portion of the fuel kernel 100 and cladding 120 has a four-lobed profile forming spiral spacer ribs 130. The displacer 110 may also be shaped so as to protrude outwardly at the ribs 130 (e.g., corners of the square displacer 110 are aligned with the ribs 130). According to alternative embodiments of the present invention, the fuel elements 20 may have greater or fewer numbers of ribs 130 without deviating from the scope of the present invention. For example, as generally illustrated in FIG. 5 of U.S. Patent Application Publication No. 2009/0252278 A1, a fuel element may have three ribs/lobes, which are preferably equally circumferentially spaced from each other. The number of lobes/ribs 130 may depend, at least in part, on the shape of the fuel assembly 10. For example, a four-lobed element 20 may work well with a square cross-sectioned fuel assembly 10 (e.g., as is used in the AP-1000). In contrast, a three-lobed fuel element may work well with a hexagonal fuel assembly (e.g., as is used in the VVER). FIG. 9 illustrates various dimensions of the fuel element 20 according to one or more embodiments. According to one or more embodiments, any of these dimensions, parameters and/or ranges, as identified in the below table, can be increased or decreased by up to 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, or more without deviating from the scope of the present invention. Fuel Element 20 ParameterSymbolExample ValuesUnitCircumscribed diameterD9-14 (e.g., 12.3, 12.4, 12.5,mm12.6)Lobe thicknessΔ2.5-3.8 (e.g., 2.5, 2.6, 2.7, 2.8,mm2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5,3.6, 3.7, 3.8), variableMinimum cladding thicknessδ0.4-1.2 (e.g., 0.4, 0.5, 0.6, 0.7,mm0.8, 0.9, 1.0, 1.1, 1.2)Cladding thickness at the lobeδmax0.4-2.2 (e.g., 0.4, 0.5, 0.6, 0.7,mm0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4,1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1,2.2), 1.5δ, 2δ, 2.5δAverage cladding thickness0.4-1.8 (e.g., 0.4, 0.5, 0.6,mm0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3,1.4, 1.5, 1.6, 1.7, 1.8), at least0.4, 0.5, or 0.6Curvature radius of cladding at loberΔ/2, Δ/1.9, variablemmperipheryCurvature radius of fuel kernel at loberf0.5-2.0 (e.g., 0.5, 0.6, 0.7, 0.8,mmperiphery0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5,1.6, 1.7, 1.8, 1.9, 2.0), (Δ-2δ)/2, variableRadius of curvature between adjacentR2-5 (e.g., 2, 3, 4, 5), variablemmlobesCentral displacer side lengtha1.5-3.5 (e.g., 1.5, 1.6, 1.7, 1.8,mm1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5,2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2,3.3, 3.4, 3.5)Fuel element perimeter25-60 (e.g., 25, 30, 35, 40, 45,mm50, 55, 60)Fuel element area50-100 (e.g., 50, 60, 70, 80,mm290, 100)Fuel kernel area, mm230-70 (e.g., 30, 40, 50, 60, 70)mm2Enrichment≤19.7w/oU fraction≤25v/o As shown in FIG. 4, the displacer 110 has a cross-sectional shape of a square regular quadrilateral with the corners of the square regular quadrilateral being aligned with the ribs 130. The displacer 110 forms a spiral that follows the spiral of the ribs 130 so that the corners of the displacer 110 remain aligned with the ribs 130 along the axial length of the fuel kernel 100. In alternative embodiments with greater or fewer ribs 130, the displacer 110 preferably has the cross-sectional shape of a regular polygon having as many sides as the element 20 has ribs. As shown in FIG. 6, the cross-sectional area of the central portion of the element 20 is preferably substantially smaller than the area of a square 200 in which the tip of each of the ribs 130 is tangent to one side of the square 200. In more generic terms, the cross-sectional area of an element 20 having n ribs is preferably smaller than the area of a regular polygon having n sides in which the tip of each of the ribs 130 is tangent to one side of the polygon. According to various embodiments, a ratio of the area of the element 20 to the area of the square (or relevant regular polygon for elements 20 having greater or fewer than four ribs 130) is less than 0.7, 0.6, 0.5, 0.4, 0.35, 0.3. As shown in FIG. 1, this area ratio approximates how much of the available space within the shroud 30 is taken up by the fuel elements 20, such that a lower ratio means that more space is advantageously available for coolant, which also acts as a neutron moderator and which increases the moderator-to-fuel ratio (important for neutronics), reduces hydraulic drag, and increases the heat transfer from the elements 20 to the coolant. According to various embodiments, the resulting moderator to fuel ratio is at least 2.0, 2.25, 2.5, 2.75, and/or 3.0 (as opposed to 1.96 when conventional cylindrical uranium oxide rods are used). Similarly, according to various embodiments, the fuel assembly 10 flow area is increased by over 16% as compared to the use of one or more conventional fuel assemblies that use cylindrical uranium oxide rods. The increased flow area may decrease the coolant pressure drop through the assembly 10 (relative to conventional uranium oxide assemblies), which may have advantages with respect to pumping coolant through the assembly 10. As shown in FIG. 4, the element 20 is axially elongated. In the illustrated embodiment, each element 20 is a full-length element and extends the entire way from lower tie plate 70 at or near the bottom of the assembly 10 to the upper tie plate 80 at or near the top of the assembly 10. According to various embodiments and reactor designs, this may result in elements 20 that are anywhere from 1 meter long (for compact reactors) to over 4 meters long. Thus, for typical reactors, the elements 20 may be between 1 and 5 meters long. However, the elements 20 may be lengthened or shortened to accommodate any other sized reactor without deviating from the scope of the present invention. While the illustrated elements 20 are themselves full length, the elements 20 may alternatively be segmented, such that the multiple segments together make a full length element. For example, 4 individual 1 meter element segments 20 may be aligned end to end to effectively create the full-length element. Additional tie plates 70, 80 may be provided at the intersections between segments to maintain the axial spacing and arrangement of the segments. According to one or more embodiments, the fuel kernel 100 comprises a combination of a refractory metal/alloy and fuel material. The refractory metal/alloy may comprise a zirconium alloy. The fuel material may comprise low enriched uranium (e.g., U235, U233), plutonium, or thorium combined with low enriched uranium as defined below and/or plutonium. As used herein, “low enriched uranium” means that the whole fuel material contains less than 20% by weight fissile material (e.g., uranium-235 or uranium-233). According to various embodiments, the uranium fuel material is enriched to between 1% and 20%, 5% and 20%, 10% and 20%, and/or 15% and 20% by weight of uranium-235. According to one or more embodiments, the fuel material comprises 19.7% enriched uranium-235. According to various embodiments, the fuel material may comprise a 3-10%, 10-40%, 15-35%, and/or 20-30% volume fraction of the fuel kernel 100. According to various embodiments, the refractory metal may comprise a 60-99%, 60-97%, 70-97%, 60-90%, 65-85%, and/or 70-80% volume fraction of the fuel kernel 100. According to one or more embodiments, volume fractions within one or more of these ranges provide an alloy with beneficial properties as defined by the material phase diagram for the specified alloy composition. The fuel kernel 100 may comprise a Zr-U alloy that is a high-alloy fuel (i.e., relatively high concentration of the alloy constituent relative to the uranium constituent) comprised of either δ-phase UZr2, or a combination of δ-phase UZr2 and α-phase Zr. According to one or more embodiments, the 6-phase of the U-Zr binary alloy system may range from a zirconium composition of approximately 65-81 volume percent (approximately 63 to 80 atom percent) of the fuel kernel 100. One or more of these embodiments have been found to result in low volumetric, irradiation-induced swelling of the fuel element 20. According to one or more such embodiments, fission gases are entrained within the metal kernel 100 itself, such that one or more embodiments of the fuel element 20 can omit a conventional gas gap from the fuel element 20. According to one or more embodiments, such swelling may be significantly less than would occur if low alloy (α-phase only) compositions were used (e.g., at least 10%, 20%, 30%, 50%, 75%, 100%, 200%, 300%, 500%, 1000%, 1200%, 1500%, or greater reduction in volume percent swelling per atom percent burnup than if a low alloy α-phase U-10Zr fuel was used). According to one or more embodiments of the present invention, irradiation-induced swelling of the fuel element 20 or kernel 100 thereof may be less than 20, 15, 10, 5, 4, 3, and/or 2 volume percent per atom percent burnup. According to one or more embodiments, swelling is expected to be around one volume percent per atom percent burnup. According to one or more alternative embodiments of the present invention, the fuel kernel is replaced with a plutonium-zirconium binary alloy with the same or similar volume percentages as with the above-discussed U-Zr fuel kernels 100, or with different volume percentages than with the above-discussed U-Zr fuel kernels 100. For example, the plutonium fraction in the kernel 100 may be substantially less than a corresponding uranium fraction in a corresponding uranium-based kernel 100 because plutonium typically has about 60-70% weight fraction of fissile isotopes, while LEU uranium has 20% or less weight fraction of fissile U-235 isotopes. According to various embodiments, the plutonium volume fraction in the kernel 100 may be less than 15%, less than 10%, and/or less than 5%, with the volume fraction of the refractory metal being adjusted accordingly. The use of a high-alloy kernel 100 according to one or more embodiments of the present invention may also result in the advantageous retention of fission gases during irradiation. Oxide fuels and low-alloy metal fuels typically exhibit significant fission gas release that is typically accommodated by the fuel design, usually with a plenum within the fuel rod to contain released fission gases. The fuel kernel 100 according to one or more embodiments of the present invention, in contrast, does not release fission gases. This is in part due to the low operating temperature of the fuel kernel 100 and the fact that fission gas atoms (specifically Xe and Kr) behave like solid fission products. Fission gas bubble formation and migration along grain boundaries to the exterior of the fuel kernel 100 does not occur according to one or more embodiments. At sufficiently high temperatures according to one or more embodiments, small (a few micron diameter) fission gas bubbles may form. However, these bubbles remain isolated within the fuel kernel 100 and do not form an interconnected network that would facilitate fission gas release, according to one or more embodiments of the present invention. The metallurgical bond between the fuel kernel 100 and cladding 120 may provide an additional barrier to fission gas release. According to various embodiments, the fuel kernel 100 (or the cladding 120 or other suitable part of the fuel element 20) of one or more of the fuel elements 20 can be alloyed with a burnable poison such as gadolinium, boron, erbium or other suitable neutron absorbing material to form an integral burnable poison fuel element. Different fuel elements 20 within a fuel assembly 10 may utilize different burnable poisons and/or different amounts of burnable poison. For example, some of fuel elements 20 of a fuel assembly 10 (e.g., less than 75%, less than 50%, less than 20%, 1-15%, 1-12%, 2-12%, etc.) may include kernels 100 with 25, 20, and/or 15 weight percent or less Gd (e.g., 1-25 weight percent, 1-15 weight percent, 5-15 weight percent, etc.). Other fuel elements 20 of the fuel assembly 10 (e.g., 10-95%, 10-50%, 20-50%, a greater number of the fuel elements 20 than the fuel elements 20 that utilize Gd) may include kernels 100 with 10 or 5 weight percent or less Er (e.g., 0.1-10.0 weight percent, 0.1 to 5.0 weight percent etc.). According to various embodiments, the burnable poison displaces the fuel material (rather than the refractory metal) relative to fuel elements 20 that do not include burnable poison in their kernels 100. For example, according to one embodiment of a fuel element 20 whose kernel 100 would otherwise include 65 volume percent zirconium and 35 volume percent uranium in the absence of a poison, the fuel element 20 includes a kernel 100 that is 16.5 volume percent Gd, 65 volume percent zirconium, and 18.5 volume percent uranium. According to one or more other embodiments, the burnable poison instead displaces the refractory metal, rather than the fuel material. According to one or more other embodiments, the burnable poison in the fuel kernel 100 displaces the refractory metal and the fuel material proportionally. Consequently, according to various of these embodiments, the burnable poison within the fuel kernel 100 may be disposed in the δ-phase of UZr2 or α-phase of Zr such that the presence of the burnable poison does not change the phase of the UZr2 alloy or Zr alloy in which the burnable poison is disposed. Fuel elements 20 with a kernel 100 with a burnable poison may make up a portion (e.g., 0-100%, 1-99%, 1-50%, etc.) of the fuel elements 20 of one or more fuel assemblies 10 used in a reactor core. For example, fuel elements 20 with burnable poison may be positioned in strategic locations within the fuel assembly lattice of the assembly 10 that also includes fuel elements 20 without burnable poison to provide power distribution control and to reduce soluble boron concentrations early in the operating cycle. Similarly, select fuel assemblies 10 that include fuel elements 20 with burnable poison may be positioned in strategic locations within the reactor core relative to assemblies 10 that do not include fuel elements 20 with burnable poison to provide power distribution control and to reduce soluble boron concentrations early in the operating cycle. The use of such integral burnable absorbers may facilitate the design of extended operating cycles. Alternatively and/or additionally, separate non-fuel bearing burnable poison rods may be included in the fuel assembly 10 (e.g., adjacent to fuel elements 20, in place of one or more fuel elements 20, inserted into guide tubes in fuel assemblies 10 that do not receive control rods, etc.). In one or more embodiments, such non-fuel burnable poison rods can be designed into a spider assembly similar to that which is used in the Babcock and Wilcox or Westinghouse designed reactors (referred to as burnable poison rod assemblies (BPRA)). These then may be inserted into the control rod guide tubes and locked into select fuel assemblies 10 where there are no control banks for the initial cycle of operation for reactivity control. When the burnable poison cluster is used it may be removed when the fuel assembly is relocated for the next fuel cycle. According to an alternative embodiment in which the separate non-fuel bearing burnable poison rods are positioned in place of one or more fuel elements 20, the non-fuel burnable poison rods remain in the fuel assembly 10 and are discharged along with other fuel elements 20 when the fuel assembly 10 reaches its usable life. The fuel elements 20 are manufactured via powder-metallurgy co-extrusion. Typically, the powdered refractory metal and powdered metal fuel material (as well as the powdered burnable poison, if included in the kernel 100) for the fuel kernel 100 are mixed, the displacer 110 blank is positioned within the powder mixture, and then the combination of powder and displacer 110 is pressed and sintered into fuel core stock/billet (e.g., in a mold that is heated to varying extents over various time periods so as to sinter the mixture). The displacer 110 blank may have the same or similar cross-sectional shape as the ultimately formed displacer 110. Alternatively, the displacer 110 blank may have a shape that is designed to deform into the intended cross-sectional shape of the displacer 110 upon extrusion. The fuel core stock (including the displacer 110 and the sintered fuel kernel 100 material) is inserted into a hollow cladding 120 tube that has a sealed tube base and an opening on the other end. The opening on the other end is then sealed by an end plug made of the same material as the cladding to form a billet. The billet may be cylindrically shaped, or may have a shape that more closely resembles the ultimate cross-sectional shape of the element 20, for example, as shown in FIGS. 5 and 9. The billet is then co-extruded under temperature and pressure through a die set to create the element 20, including the finally shaped kernel 100, cladding 110, and displacer 120. According to various embodiments that utilize a non-cylindrical displacer 110, the billet may be properly oriented relative to the extrusion press die so that corners of the displacer 110 align with the lobes 20b of the fuel element 20. The extrusion process may be done by either direct extrusion (i.e., moving the billet through a stationary die) or indirect extrusion (i.e., moving the die toward a stationary billet). The process results in the cladding 120 being metallurgically bonded to the fuel kernel 100, which reduces the risk of delamination of the cladding 120 from the fuel kernel 100. The tube and end plug of the cladding 120 metallurgically bond to each other to seal the fuel kernel 100 within the cladding 120. The high melting points of refractory metals used in the fuel elements 10 tend to make powder metallurgy the method of choice for fabricating components from these metals. According to one or more alternative embodiments, the fuel core stock of the fuel elements 20 may be manufactured via casting instead of sintering. Powdered or monolithic refractory metal and powdered or monolithic fuel material (as well as the powdered burnable poison, if included in the kernel 100) may be mixed, melted, and cast into a mold. The mold may create a displacer-blank-shaped void in the cast kernel 100 such that the displacer 110 blank may be inserted after the kernel 100 is cast, in the same manner that the cladding 120 is added to form the billet to be extruded. The remaining steps for manufacturing the fuel elements 20 may remain the same as or similar to the above-discuss embodiment that utilizes sintering instead of casting. Subsequent extrusion results in metallurgical bonding between the displacer 110 and kernel 100, as well as between the kernel 100 and cladding 120. According to one or more alternative embodiments, the fuel elements 20 are manufactured using powdered ceramic fuel material instead of powdered metal fuel material. The remaining manufacturing steps may be the same as discussed above with respect to the embodiments using powdered metal fuel material. In various metal fuel embodiments and ceramic fuel embodiments, the manufacturing process may result in a fuel kernel 100 comprising fuel material disposed in a matrix of metal non-fuel material. In one or more of the metal fuel embodiments, the resulting fuel kernel 100 comprises a metal fuel alloy kernel comprising an alloy of the metal fuel material and the matrix of metal non-fuel material (e.g., a uranium-zirconium alloy). In one or more of the ceramic fuel embodiments, the kernel 100 comprises ceramic fuel material disposed in (e.g., interspersed throughout) the matrix of metal non-fuel material. According to various embodiments, the ceramic fuel material used in the manufacturing process may comprise powdered uranium or plutonium oxide, powdered uranium or plutonium nitride, powdered uranium or plutonium carbide, powdered uranium or plutonium hydride, or a combination thereof. In contrast with conventional UO2 fuel elements in which UO2 pellets are disposed in a tube, the manufacturing process according to one or more embodiments of the present invention results in ceramic fuel being disposed in a solid matrix of non-fuel material (e.g., a zirconium matrix). As shown in FIG. 4, the axial coiling pitch of the spiral ribs 130 is selected according to the condition of placing the axes of adjacent fuel elements 10 with a spacing equal to the width across corners in the cross section of a fuel element and may be 5% to 20% of the fuel element 20 length. According to one embodiment, the pitch (i.e., the axial length over which a lobe/rib makes a complete rotation) is about 21.5 cm, while the full active length of the element 20 is about 420 cm. As shown in FIG. 3, stability of the vertical arrangement of the fuel elements 10 is provided: at the bottom—by the lower tie plate 70; at the top—by the upper tie plate 80; and relative to the height of the core—by the shroud 30. As shown in FIG. 1, the fuel elements 10 have a circumferential orientation such that the lobed profiles of any two adjacent fuel elements 10 have a common plane of symmetry which passes through the axes of the two adjacent fuel elements 10 in at least one cross section of the fuel element bundle. As shown in FIG. 1, the helical twist of the fuel elements 20 in combination with their orientation ensures that there exists one or more self-spacing planes. As shown in FIG. 1, in such self spacing planes, the ribs of adjacent elements 20 contact each other to ensure proper spacing between such elements 20. Thus, the center-to-center spacing of elements 20 will be about the same as the corner-to-corner width of each element 20 (12.6 mm in the element illustrated in FIG. 5). Depending on the number of lobes 20b in each fuel element 20 and the relative geometrical arrangement of the fuel elements 20, all adjacent fuel elements 20 or only a portion of the adjacent fuel elements 20 will contact each other. For example, in the illustrated four-lobed embodiment, each fuel element 20 contacts all four adjacent fuel elements 20 at each self-spacing plane. However, in a three-lobed fuel element embodiment in which the fuel elements are arranged in a hexagonal pattern, each fuel element will only contact three of the six adjacent fuel elements in a given self-spacing plane. The three-lobed fuel element will contact the other three adjacent fuel elements in the next axially-spaced self-spacing plane (i.e., ⅙ of a turn offset from the previous self-spacing plane). In an n-lobed element 20 in which n fuel elements are adjacent to a particular fuel element 20, a self-spacing plane will exist every 1/n helical turn (e.g., every ¼ helical turn for a four-lobed element 20 arranged in a square pattern such that four other fuel elements 20 are adjacent to the fuel element 20; every ⅓ helical turn for a three-lobed element in which three fuel elements are adjacent to the fuel element (i.e., every 120 degrees around the perimeter of the fuel element)). The pitch of the helix may be modified to create greater or fewer self-spacing planes over the axial length of the fuel elements 20. According to one embodiment, each four-lobed fuel element 20 includes multiple twists such that there are multiple self-spacing planes over the axial length of the bundle of fuel elements 20. In the illustrated embodiment, all of the elements 20 twist in the same direction. However, according to an alternative embodiment, adjacent elements 20 may twist in opposite directions without deviating from the scope of the present invention. The formula for the number of self-spacing planes along the fuel rod length is as follows:N=n*L/h, where: L—Fuel rod length n—Number of lobes (ribs) and the number of fuel elements adjacent to a fuel element h—Helical twist pitch The formula is slightly different if the number of lobes and the number of fuel elements adjacent to a fuel element are not the same. As a result of such self-spacing, the fuel assembly 10 may omit spacer grids that may otherwise have been necessary to assure proper element spacing along the length of the assembly 10. By eliminating spacer grids, coolant may more freely flow through the assembly 10, which advantageously increases the heat transfer from the elements 20 to the coolant. However, according to alternative embodiments of the present invention, the assembly 10 may include spacer grid(s) without deviating from the scope of the present invention. As shown in FIG. 3, the shroud 30 forms a tubular shell that extends axially along the entire length of the fuel elements 20 and surrounds the elements 20. However, according to an alternative embodiment of the present invention, the shroud 30 may comprise axially-spaced bands, each of which surrounds the fuel elements 20. One or more such bands may be axially aligned with the self-spacing planes. Axially extending corner supports may extend between such axially spaced bands to support the bands, maintain the bands' alignment, and strengthen the assembly. Alternatively and/or additionally, holes may be cut into the otherwise tubular/polygonal shroud 30 in places where the shroud 30 is not needed or desired for support. Use of a full shroud 30 may facilitate greater control of the separate coolant flows through each individual fuel assembly 10. Conversely, the use of bands or a shroud with holes may facilitate better coolant mixing between adjacent fuel assemblies 10, which may advantageously reduce coolant temperature gradients between adjacent fuel assemblies 10. As shown in FIG. 1, the cross-sectional perimeter of the shroud 30 has a shape that accommodates the reactor in which the assembly 10 is used. In reactors such as the AP-1000 that utilize square fuel assemblies, the shroud has a square cross-section. However, the shroud 30 may alternatively take any suitable shape depending on the reactor in which it is used (e.g., a hexagonal shape for use in a VVER reactor (e.g., as shown in FIG. 1 of U.S. Patent Application Publication No. 2009/0252278 A1). The guide tubes 40 provide for the insertion of control absorber elements based on boron carbide (B4C), silver indium cadmium (Ag, In, Cd), dysprosium titanate (Dy2O3.TiO2) or other suitable alloys or materials used for reactivity control (not shown) and burnable absorber elements based on boron carbide, gadolinium oxide (Gd2O3) or other suitable materials (not shown) and are placed in the upper nozzle 50 with the capability of elastic axial displacement. The guide tubes 40 may comprise a zirconium alloy. For example, the guide tube 40 arrangement shown in FIG. 1 is in an arrangement used in the AP-1000 reactor (e.g., 24 guide tubes arranged in two annular rows at the positions shown in the 17×17 grid). The shape, size, and features of the frame 25 depend on the specific reactor core for which the assembly 10 is to be used. Thus, one of ordinary skill in the art would understand how to make appropriately shaped and sized frame for the fuel assembly 10. For example, the frame 25 may be shaped and configured to fit into a reactor core of a conventional nuclear power plant in place of a conventional uranium oxide or mixed oxide fuel assembly for that plant's reactor core. The nuclear power plant may comprise a reactor core design that was in actual use before 2010 (e.g., 2, 3 or 4-loop PWRs; BWR-4). Alternatively, the nuclear power plant may be of an entirely new design that is specifically tailored for use with the fuel assembly 10. As explained above, the illustrated fuel assembly 10 is designed for use in an AP-1000 or EPR reactor. The assembly includes a 17×17 array of fuel elements 20, 24 of which are replaced with guide tubes 40 as explained above for a total of 265 fuel elements 20 in EPR or 264 fuel elements 20 in AP-1000 (in the AP-1000, in addition to the 24 fuel elements being replaced with the guide tubes, a central fuel element is also replaced with an instrumented tube). The elements 20 preferably provide 100% of the overall fissile material of the fuel assembly 10. Alternatively, some of the fissile material of the assembly 10 may be provided via fuel elements other than the elements 20 (e.g., non-lobed fuel elements, uranium oxide elements, elements having fuel ratios and/or enrichments that differ from the elements 20). According to various such alternative embodiments, the fuel elements 20 provide at least 50%, 60%, 70%, 75%, 80%, 85%, 90%, and/or 95% by volume of the overall fissile material of the fuel assembly 10. Use of the metal fuel elements 20 according to one or more embodiments of the present invention facilitate various advantages over the uranium oxide or mixed oxide fuel conventionally used in light water nuclear reactors (LWR) (including boiling water reactors and pressurized water reactors) such as the Westinghouse-designed AP-1000, AREVA-designed EPR reactors, or GE-designed ABWR. For example, according to one or more embodiments, the power rating for an LWR operating on standard uranium oxide or mixed oxide fuel could be increased by up to about 30% by substituting the all-metal fuel elements 20 and/or fuel assembly 10 for standard uranium oxide fuel and fuel assemblies currently used in existing types of LWRs or new types of LWRs that have been proposed. One of the key constraints for increasing power rating of LWRs operating on standard uranium oxide fuel has been the small surface area of cylindrical fuel elements that such fuel utilizes. A cylindrical fuel element has the lowest surface area to volume ratio for any type of fuel element cross-section profile. Another major constraint for standard uranium oxide fuel has been a relatively low burnup that such fuel elements could possibly reach while still meeting acceptable fuel performance criteria. As a result, these factors associated with standard uranium oxide or mixed oxide fuel significantly limit the degree to which existing reactor power rating could be increased. One or more embodiments of the all-metal fuel elements 20 overcome the above limitations. For example, as explained above, the lack of spacer grids may reduce hydraulic resistance, and therefore increase coolant flow and heat flux from the elements 20 to the primary coolant. The helical twist of the fuel elements 20 may increase coolant intermixing and turbulence, which may also increase heat flux from the elements 20 to the coolant. Preliminary neutronic and thermal-hydraulic analyses have shown the following according to one or more embodiments of the present invention: The thermal power rating of an LWR reactor could be increased by up to 30.7% or more (e.g., the thermal power rating of an EPR reactor could be increased from 4.59 GWth to 6.0 GWth). With a uranium volume fraction of 25% in the uranium-zirconium mixture and uranium-235 enrichment of 19.7%, an EPR reactor core with a four-lobe metallic fuel element 20 configuration could operate for about 500-520 effective full power days (EFPDs) at the increased thermal power rating of 6.0 GWth if 72 fuel assemblies were replaced per batch (once every 18 months) or 540-560 EFPDs if 80 fuel assemblies were replaced per batch (once every 18 months). Due to the increased surface area in the multi-lobe fuel element, even at the increased power rating of 6.0 GWth, the average surface heat flux of the multi-lobe fuel element is shown to be 4-5% lower than that for cylindrical uranium oxide fuel elements operating at the thermal power rating of 4.59 GWth. This could provide an increased safety margin with respect to critical heat flux (e.g., increased departure from nucleate boiling margin in PWRs or maximum fraction limiting critical power ratio in BWRs). Further, this could allow a possibility of using 12 fuel elements per assembly with burnable poisons. Burnable poisons could be used to remove excess reactivity at the beginning of cycle or to increase the Doppler Effect during the heat-up of the core. Thus, the fuel assemblies 10 may provide greater thermal power output at a lower fuel operating temperature than conventional uranium oxide or mixed oxide fuel assemblies. To utilize the increased power output of the assembly 10, conventional power plants could be upgraded (e.g., larger and/or additional coolant pumps, steam generators, heat exchangers, pressurizers, turbines). Indeed, according to one or more embodiments, the upgrade could provide 30-40% more electricity from an existing reactor. Such a possibility may avoid the need to build a complete second reactor. The modification cost may quickly pay for itself via increased electrical output. Alternatively, new power plants could be constructed to include adequate features to handle and utilize the higher thermal output of the assemblies 10. Further, one or more embodiments of the present invention could allow an LWR to operate at the same power rating as with standard uranium oxide or mixed oxide fuel using existing reactor systems without any major reactor modifications. For example, according to one embodiment: An EPR would have the same power output as if conventional uranium-oxide fuel were used: 4.59 GWt; With a uranium volume fraction of 25% in the uranium-zirconium mixture and uranium-235 enrichment of approximately 15%, an EPR reactor core with a four-lobe metallic fuel element 20 configuration could operate for about 500-520 effective full power days (EFPDs) if 72 fuel assemblies were replaced per batch or 540-560 EFPDs if 80 fuel assemblies were replaced per batch. The average surface heat flux for the elements 20 is reduced by approximately 30% compared to that for cylindrical rods with conventional uranium oxide fuel (e.g., 39.94 v. 57.34 W/cm2). Because the temperature rise of the coolant through the assembly 10 (e.g., the difference between the inlet and outlet temperature) and the coolant flow rate through the assembly 10 remain approximately the same relative to conventional fuel assemblies, the reduced average surface heat flux results in a corresponding reduction in the fuel rod surface temperature that contributes to increased safety margins with respect to critical heat flux (e.g., increased departure from nucleate boiling margin in PWRs or maximum fraction limiting critical power ratio in BWRs). Additionally and/or alternatively, fuel assemblies 10 according to one or more embodiments of the present invention can be phased/laddered into a reactor core in place of conventional fuel assemblies. During the transition period, fuel assemblies 10 having comparable fissile/neutronic/thermal outputs as conventional fuel assemblies can gradually replace such conventional fuel assemblies over sequential fuel changes without changing the operating parameters of the power plant. Thus, fuel assemblies 10 can be retrofitted into an existing core that may be important during a transition period (i.e., start with a partial core with fuel assemblies 10 and gradually transition to a full core of fuel assemblies 10). Moreover, the fissile loading of assemblies 10 can be tailored to the particular transition desired by a plant operator. For example, the fissile loading can be increased appropriately so as to increase the thermal output of the reactor by anywhere from 0% to 30% or more higher, relative to the use of conventional fuel assemblies that the assemblies 10 replace. Consequently, the power plant operator can chose the specific power uprate desired, based on the existing plant infrastructure or the capabilities of the power plant at various times during upgrades. One or more embodiments of the fuel assemblies 10 and fuel elements 20 may be used in fast reactors (as opposed to light water reactors) without deviating from the scope of the present invention. In fast reactors, the non-fuel metal of the fuel kernel 100 is preferably a refractory metal, for example a molybdenum alloy (e.g., pure molybdenum or a combination of molybdenum and other metals), and the cladding 120 is preferably stainless steel (which includes any alloy variation thereof) or other material suitable for use with coolant in such reactors (e.g., sodium). Such fuel elements 20 may be manufactured via the above-discussed co-extrusion process or may be manufactured by any other suitable method (e.g., vacuum melt). As shown in FIGS. 7A, 7B, and 8, fuel assemblies 510 accordingly to one or more embodiments of the present invention may be used in a pressurized heavy water reactor 500 (see FIG. 8) such as a CANDU reactor. As shown in FIGS. 7A and 7B, the fuel assembly 510 comprises a plurality of fuel elements 20 mounted to a frame 520. The frame 520 comprises two end plates 520a, 520b that mount to opposite axial ends of the fuel elements 20 (e.g., via welding, interference fits, any of the various types of attachment methods described above for attaching the elements 20 to the lower tie plate 70). The elements 20 used in the fuel assembly 510 are typically much shorter than the elements 20 used in the assembly 10. According to various embodiments and reactors 500, the elements 20 and assemblies 510 used in the reactor 500 may be about 18 inches long. The elements 20 may be positioned relative to each other in the assembly 510 so that self-spacing planes maintain spacing between the elements 20 in the manner described above with respect to the assembly 10. Alternatively, the elements 20 of the assembly 510 may be so spaced from each other that adjacent elements 20 never touch each other, and instead rely entirely on the frame 520 to maintain element 20 spacing. Additionally, spacers may be attached to the elements 20 or their ribs at various positions along the axial length of the elements 20 to contact adjacent elements 20 and help maintain element spacing 20 (e.g., in a manner similar to how spacers are used on conventional fuel rods of conventional fuel assemblies for pressurized heavy water reactors to help maintain rod spacing). As shown in FIG. 8, the assemblies 510 are fed into calandria tubes 500a of the reactor 500 (sometimes referred to in the art as a calandria 500). The reactor 500 uses heavy water 500b as a moderator and primary coolant. The primary coolant 500b circulates horizontally through the tubes 500a and then to a heat exchanger where heat is transferred to a secondary coolant loop that is typically used to generate electricity via turbines. Fuel assembly loading mechanisms (not shown) are used to load fuel assemblies 510 into one side of the calandria tubes 500a and push spent assemblies 510 out of the opposite side of the tubes 500a, typically while the reactor 500 is operating. The fuel assemblies 510 may be designed to be a direct substitute for conventional fuel assemblies (also known as fuel bundles in the art) for existing, conventional pressurized heavy water reactors (e.g., CANDU reactors). In such an embodiment, the assemblies 510 are fed into the reactor 500 in place of the conventional assemblies/bundles. Such fuel assemblies 510 may be designed to have neutronic/thermal properties similar to the conventional assemblies being replaced. Alternatively, the fuel assemblies 510 may be designed to provide a thermal power uprate. In such uprate embodiments, new or upgraded reactors 500 can be designed to accommodate the higher thermal output. According to various embodiments of the present invention, the fuel assembly 10 is designed to replace a conventional fuel assembly of a conventional nuclear reactor. For example, the fuel assembly 10 illustrated in FIG. 1 is specifically designed to replace a conventional fuel assembly that utilizes a 17×17 array of UO2 fuel rods. If the guide tubes 40 of the assembly 10 are left in the exact same position as they would be for use with a conventional fuel assembly, and if all of the fuel elements 20 are the same size, then the pitch between fuel elements/rods remains unchanged between the conventional UO2 fuel assembly and one or more embodiments of the fuel assembly 10 (e.g., 12.6 mm pitch). In other words, the longitudinal axes of the fuel elements 20 may be disposed in the same locations as the longitudinal axes of conventional UO2 fuel rods would be in a comparable conventional fuel assembly. According to various embodiments, the fuel elements 20 may have a larger circumscribed diameter than the comparable UO2 fuel rods (e.g., 12.6 mm as compared to an outer diameter of 9.5 mm for a typical UO2 fuel rod). As a result, in the self-aligning plane illustrated in FIG. 1, the cross-sectional length and width of the space occupied by the fuel elements 20 may be slightly larger than that occupied by conventional UO2 fuel rods in a conventional fuel assembly (e.g., 214.2 mm for the fuel assembly 10 (i.e., 17 fuel elements 20×12.6 mm circumscribed diameter per fuel element), as opposed to 211.1 mm for a conventional UO2 fuel assembly that includes a 17×17 array of 9.5 mm UO2 fuel rods separated from each other by a 12.6 mm pitch). In conventional UO2 fuel assemblies, a spacer grid surrounds the fuel rods, and increases the overall cross-sectional envelope of the conventional fuel assembly to 214 mm×214 mm. In the fuel assembly 10, the shroud 30 similarly increases the cross-sectional envelope of the fuel assembly 10. The shroud 30 may be any suitable thickness (e.g., 0.5 mm or 1.0 mm thick). In an embodiment that utilizes a 1.0 mm thick shroud 30, the overall cross-sectional envelope of an embodiment of the fuel assembly 10 may be 216.2 mm×216.2 mm (e.g., the 214 mm occupied by the 17 12.6 mm diameter fuel elements 20 plus twice the 1.0 mm thickness of the shroud 30). As a result, according to one or more embodiments of the present invention, the fuel assembly 10 may be slightly larger (e.g., 216.2 mm×216.2 mm) than a typical UO2 fuel assembly (214 mm×214 mm). The larger size may impair the ability of the assembly 10 to properly fit into the fuel assembly positions of one or more conventional reactors, which were designed for use with conventional UO2 fuel assemblies. To accommodate this size change, according to one or more embodiments of the present invention, a new reactor may be designed and built to accommodate the larger size of the fuel assemblies 10. According to an alternative embodiment of the present invention, the circumscribed diameter of all of the fuel elements 20 may be reduced slightly so as to reduce the overall cross-sectional size of the fuel assembly 10. For example, the circumscribed diameter of each fuel element 20 may be reduced by 0.13 mm to 12.47 mm, so that the overall cross-sectional space occupied by the fuel assembly 10 remains comparable to a conventional 214 mm by 214 mm fuel assembly (e.g., 17 12.47 mm diameter fuel elements 20 plus two 1.0 mm thickness of the shroud, which totals about 214 mm). Such a reduction in the size of the 17 by 17 array will slightly change the positions of the guide tubes 40 in the fuel assembly 10 relative to the guide tube positions in a conventional fuel assembly. To accommodate this slight position change in the tube 40 positions, the positions of the corresponding control rod array and control rod drive mechanisms in the reactor may be similarly shifted to accommodate the repositioned guide tubes 40. Alternatively, if sufficient clearances and tolerances are provided for the control rods in a conventional reactor, conventionally positioned control rods may adequately fit into the slightly shifted tubes 40 of the fuel assembly 10. Alternatively, the diameter of the peripheral fuel elements 20 may be reduced slightly so that the overall assembly 10 fits into a conventional reactor designed for conventional fuel assemblies. For example, the circumscribed diameter of the outer row of fuel elements 20 may be reduced by 1.1 mm such that the total size of the fuel assembly is 214 mm×214 mm (e.g., 15 12.6 mm fuel elements 20 plus 2 11.5 mm fuel elements 20 plus 2 1.0 mm thicknesses of the shroud 30). Alternatively, the circumscribed diameter of the outer two rows of fuel elements 20 may be reduced by 0.55 mm each such that the total size of the fuel assembly remains 214 mm×214 mm (e.g., 13 12.6 mm fuel elements 20 plus 4 12.05 mm fuel assemblies plus 2 1.0 mm thicknesses of the shroud 30). In each embodiment, the pitch and position of the central 13×13 array of fuel elements 20 and guide tubes 40 remains unaltered such that the guide tubes 40 align with the control rod array and control rod drive mechanisms in a conventional reactor. FIG. 10 illustrates a fuel assembly 610 according to an alternative embodiment of the present invention. According to various embodiments, the fuel assembly 610 is designed to replace a conventional UO2 fuel assembly in a conventional reactor while maintaining the control rod positioning of reactors designed for use with various conventional UO2 fuel assemblies. The fuel assembly 610 is generally similar to the fuel assembly 10, which is described above and illustrated in FIG. 1, but includes several differences that help the assembly 610 to better fit into one or more existing reactor types (e.g., reactors using Westinghouse's fuel assembly design that utilizes a 17 by 17 array of UO2 rods) without modifying the control rod positions or control rod drive mechanisms. As shown in FIG. 10, the fuel assembly includes a 17 by 17 array of spaces. The central 15 by 15 array is occupied by 200 fuel elements 20 and 25 guide tubes 40, as described above with respect to the similar fuel assembly 10 illustrated in FIG. 1. Depending on the specific reactor design, the central guide tube 40 may be replaced by an additional fuel element 20 if the reactor design does not utilize a central tube 40 (i.e., 201 fuel elements 20 and 24 guide tubes 40). The guide tube 40 positions correspond to the guide tube positions used in reactors designed to use conventional UO2 fuel assemblies. The peripheral positions (i.e., the positions disposed laterally outward from the fuel elements 20) of the 17 by 17 array/pattern of the fuel assembly 610 are occupied by 64 UO2 fuel elements/rods 650. As is known in the art, the fuel rods 650 may comprise standard UO2 pelletized fuel disposed in a hollow rod. The UO2 pelletized fuel may be enriched with U-235 by less than 20%, less than 15%, less than 10%, and/or less than 5%. The rods 650 may have a slightly smaller diameter (e.g., 9.50 mm) than the circumscribed diameter of the fuel elements 20, which slightly reduces the overall cross-sectional dimensions of the fuel assembly 610 so that the assembly 610 better fits into the space allocated for a conventional UO2 fuel assembly. In the illustrated embodiment, the fuel rods/elements 650 comprise UO2 pelletized fuel. However, the fuel rods/elements 650 may alternatively utilize any other suitable combination of one or more fissile and/or fertile materials (e.g., thorium, plutonium, uranium-235, uranium-233, any combinations thereof). Such fuel rods/elements 650 may comprise metal and/or oxide fuel. According to one or more alternative embodiments, the fuel rods 650 may occupy less than all of the 64 peripheral positions. For example, the fuel rods 650 may occupy the top row and left column of the periphery, while the bottom row and right column of the periphery may be occupied by fuel elements 20. Alternatively, the fuel rods 650 may occupy any other two sides of the periphery of the fuel assembly. The shroud 630 may be modified so as to enclose the additional fuel elements 20 in the periphery of the fuel assembly. Such modified fuel assemblies may be positioned adjacent each other such that a row/column of peripheral fuel elements 650 in one assembly is always adjacent to a row/column of fuel elements 20 in the adjacent fuel assembly. As a result, additional space for the fuel assemblies is provided by the fact that the interface between adjacent assemblies is shifted slightly toward the assembly that includes fuel elements 650 in the peripheral, interface side. Such a modification may provide for the use of a greater number of higher heat output fuel elements 20 than is provided by the fuel assemblies 610. A shroud 630 surrounds the array of fuel elements 20 and separates the elements 20 from the elements 650. The nozzles 50, 60, shroud 630, coolant passages formed therebetween, relative pressure drops through the elements 20 and elements 650, and/or the increased pressure drop through the spacer grid 660 (discussed below) surrounding the elements 650 may result in a higher coolant flow rate within the shroud 630 and past the higher heat output fuel elements 20 than the flow rate outside of the shroud 630 and past the relatively lower heat output fuel rods 650. The passageways and/or orifices therein may be designed to optimize the relative coolant flow rates past the elements 20, 650 based on their respective heat outputs and designed operating temperatures. According to various embodiments, the moderator:fuel ratio for the fuel elements 20 of the fuel assembly 610 is less than or equal to 2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, and/or 1.8. In the illustrated embodiment, the moderator:fuel ratio equals a ratio of (1) the total area within the shroud 630 available for coolant/moderator (e.g., approximated by the total cross-sectional area within the shroud 630 minus the total cross-sectional area taken up by the fuel elements 20 (assuming the guide tubes 40 are filled with coolant)) to (2) the total cross-sectional area of the kernels 100 of the fuel elements 20 within the shroud 630. According to an alternative embodiment of the invention, the shroud 630 may be replaced with one or more annular bands or may be provided with holes in the shroud 630, as explained above. The use of bands or holes in the shroud 630 may facilitate cross-mixing of coolant between the fuel elements 20 and the fuel elements 650. As shown in FIG. 10, the fuel elements 650 are disposed within an annular spacer grid 660 that is generally comparable to the outer part of a spacer grid used in a conventional UO2 fuel assembly. The spacer grid 660 may rigidly connect to the shroud 630 (e.g., via welds, bolts, screws, or other fasteners). The spacer grid 660 is preferably sized so as to provide the same pitch between the fuel elements 650 and the fuel elements 20 as is provided between the central fuel elements 20 (e.g., 12.6 mm pitch between axes of all fuel elements 20, 650). To provide such spacing, the fuel elements 650 may be disposed closer to the outer side of the spacer grid 660 than to the shroud 630 and inner side of the spacer grid 660. The fuel assembly 610 and spacer grid 660 are also preferably sized and positioned such that the same pitch is provided between fuel elements 650 of adjacent fuel assemblies (e.g., 12.6 mm pitch). However, the spacing between any of the fuel elements 20, 650 may vary relative to the spacing between other fuel elements 20, 650 without deviating from the scope of the present invention. According to various embodiments, the fuel elements 20 provide at least 60%, 65%, 70%, 75%, and/or 80% of a total volume of all fissile-material-containing fuel elements 20, 650 of the fuel assembly 610. For example, according to one or more embodiments in which the fuel assembly 610 includes 201 fuel elements 20, each having a cross-sectional area of about 70 mm2, and 64 fuel elements 650, each having a 9.5 mm diameter, the fuel elements 20 provide about 75.6% of a total volume of all fuel elements 20, 650 (201 fuel elements 20×70 mm2 equals 14070 mm2; 64 fuel elements 650×π×(9.5/2)2=4534 mm2; fuel element 20, 650 areas are essentially proportional to fuel element volumes; (14070 mm2/(14070 mm2+4534 mm2)=75.6%)). The height of the fuel assembly 610 matches a height of a comparable conventional fuel assembly that the assembly 610 can replace (e.g., the height of a standard fuel assembly for a Westinghouse or AREVA reactor design). The illustrated fuel assembly 610 may be used in a 17×17 PWR such as the Westinghouse 4-loop design, AP1000, or AREVA EPR. However, the design of the fuel assembly 610 may also be modified to accommodate a variety of other reactor designs (e.g., reactor designs that utilize a hexagonal fuel assembly, in which case the outer periphery of the hexagon is occupied by UO2 rods, while the inner positions are occupied by fuel elements 20, or boiling water reactors, or small modular reactors). While particular dimensions are described with regard to particular embodiments, a variety of alternatively dimensioned fuel elements 20, 650 and fuel assemblies 10 may be used in connection with a variety of reactors or reactor types without deviating from the scope of the present invention. Depending on the specific reactor design, additional rod positions of a fuel assembly may be replaced with UO2 rods. For example, while the fuel assembly 610 includes UO2 rods only in the outer peripheral row, the assembly 610 could alternatively include UO2 rods in the outer two rows without deviating from the scope of the present invention. According to various embodiments, the portion of the fuel assembly 610 that supports the fuel elements 650 is inseparable from the portion of the fuel assembly 610 that supports the fuel elements 20. According to various embodiments, the fuel elements 20 are not separable as a unit from the fuel elements 650 of the fuel assembly 610 (even though individual fuel elements 20, 650 may be removed from the assembly 610, for example, based on individual fuel element failure). Similarly, there is not a locking mechanism that selectively locks the fuel element 650 portion of the fuel assembly to the fuel element 20 portion of the fuel assembly 610. According to various embodiments, the fuel elements 20 and fuel elements 650 of the fuel assembly 610 have the same designed life cycle, such that the entire fuel assembly 610 is used within the reactor, and then removed as a single spent unit. According to various embodiments, the increased heat output of the fuel elements 20 within the fuel assembly 610 can provide a power uprate relative to the conventional all UO2 fuel rod assembly that the assembly 610 replaces. According to various embodiments, the power uprate is at least 5%, 10%, and/or 15%. The uprate may be between 1 and 30%, 5 and 25%, and/or 10 and 20% according to various embodiments. According to various embodiments, the fuel assembly 610 provides at least an 18-month fuel cycle, but may also facilitate moving to a 24+ or 36+ month fuel cycle. According to an embodiment of the fuel assembly 610, which uses fuel elements 20 having the example parameters discussed above with respect to the element 20 shown in FIG. 10, the assembly 17 provides a 17% uprate relative to a conventional UO2 fuel assembly under the operating parameters identified in the below tables. Operating Parameter for AREVA EPR ReactorValueUnitReactor power5.37GWtFuel cycle length18monthsReload batch size1/3coreEnrichment of Fuel Element 20≤19.7w/oEnrichment of UO2 of the Rods 650≤5w/oCoolant flow rate117%rv* rv = reference value Fuel Assembly ParameterValueUnitFuel assembly design17 × 17Fuel assembly pitch215mmFuel assembly envelope214mmActive fuel height4200mmNumber of fuel rods265Fuel element 20 pitch (i.e., axis to axis spacing)12.6mmAverage outer fuel element 20 diameter12.6mm(circumscribed diameter)Average minimum fuel element 20 diameter10.44mmModerator to fuel ratio, seed region (around2.36elements 20)Moderator to fuel ratio, blanket (around the fuel rods1.9650) The fuel assemblies 10, 510, 610 are preferably thermodynamically designed for and physically shaped for use in a land-based nuclear power reactor 90, 500 (e.g., land-based LWRS (including BWRs and PWRs), land-based fast reactors, land-based heavy water reactors) that is designed to generate electricity and/or heat that is used for a purpose other than electricity (e.g., desalinization, chemical processing, steam generation, etc.). Such land-based nuclear power reactors 90 include, among others, VVER, AP-1000, EPR, APR-1400, ABWR, BWR-6, CANDU, BN-600, BN-800, Toshiba 4S, Monju, etc. However, according to alternative embodiments of the present invention, the fuel assemblies 10, 510, 610 may be designed for use in and used in marine-based nuclear reactors (e.g., ship or submarine power plants; floating power plants designed to generate power (e.g., electricity) for onshore use) or other nuclear reactor applications. The foregoing illustrated embodiments are provided to illustrate the structural and functional principles of the present invention and are not intended to be limiting. To the contrary, the principles of the present invention are intended to encompass any and all changes, alterations and/or substitutions within the spirit and scope of the following claims. |
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description | Referring now to the accompanying drawings, as an example of a preferred embodiment of a gas treatment system according to the present invention, a plasma deposition system for depositing a thin film on a substrate to be treated by utilizing the electron cyclotron resonance (ECR) will be described below. In this preferred embodiment, a gas in a vacuum vessel is extracted, and electrons are added to the gas to change particles, e.g., radicals, in the gas to negative ions. Then, the quantity of negative ions corresponding to specific radicals is analyzed by a mass spectrometer. On the basis of the results thereof, the density of radicals is estimated. In accordance with the estimated value, various process conditions for influencing radicals in plasma are controlled. FIG. 1 is a sectional view showing the whole construction of the preferred embodiment of a gas treatment system according to the present invention, and FIG. 2 is a side view schematically showing an electron adhesion type mass spectrometer for use in this gas treatment system. First, a plasma deposition system shown in FIG. 1 will be described. As shown in FIG. 1, the plasma deposition system has a vacuum vessel 1 of, e.g., aluminum. The vacuum vessel 1 comprises a first cylindrical vacuum chamber 11 arranged upward for producing plasma, and a second cylindrical vacuum chamber 12 arranged downward to be communicated with the first vacuum chamber 11. Furthermore, the vacuum vessel 1 is grounded to have zero potential. The upper end of the vacuum vessel 1 has an opening, in which a transmission window 13 formed of a material capable of transmitting microwaves, e.g., quartz, is airtightly provided to maintain vacuum in the vacuum vessel 1. Outside of the transmission window 13, a waveguide 15 connected to a microwave power supply part 14 serving as a high-frequency supply means for producing a plasma of, e.g., 2.45 GHz and 1.5 kW is provided. The microwaves produced by the microwave power supply part 14 are guided by the waveguide 15 in, e.g., a TE mode, or the microwaves guided in the TE mode are changed by the waveguide 15 to a TM mode, to be introduced into the first vacuum vessel 11 via the transmission window 13. On the side wall defining the first vacuum vessel 11, gas nozzles 16 are arranged at regular intervals in the circumferential directions thereof. A gas source (not shown), e.g., an Ar gas source, is connected to the gas nozzles 16 so as to uniformly supply Ar gas to the upper portion of the first vacuum vessel 11. In the second vacuum vessel 12, a wafer mounting table 17 having substantially the same size as that of a wafer W is supported on a supporting part 18 via an insulator (not shown) of, e.g., aluminum, so as to face the first vacuum vessel 11. An electrode is embedded in the mounting table 17, and connected to a high-frequency power supply part 19 so as to supply an ion drawing bias voltage thereto. On the other hand, as shown in FIG. 1, the upper portion of the second vacuum chamber 12, i.e., a portion communicated with the first vacuum chamber 11, is provided with a ring-shaped deposition gas supply part 20. The deposition gas supply part is designed to jet deposition gases, e.g., C4F8 and C2H4 gases, which are fed from a gas supply pipe (not shown), into the second vacuum chamber 12. Furthermore, the Ar gas and the deposition gases corresponds to treatment gases. On the side wall of the second vacuum chamber 12, a gate valve 21 for introducing wafers into the second vacuum vessel 12 is provided. To the other side of the side wall, an electron adhesion type mass spectrometer 3, which will be described later, is connected. To the bottom of the second vacuum chamber 12, exhaust pipes 22 are connected at, e.g., two positions which are symmetrical with respect to the central axis of the second vacuum chamber 12. On the periphery of the side wall defining the first vacuum vessel 11, a ring-shaped main electromagnetic coil 23 serving as a magnetic field forming means is arranged so as to be close to the first vacuum vessel 11. Beneath the second vacuum vessel 12, a ring-shaped auxiliary electromagnetic coil 24 is arranged so as to be close to the second vacuum vessel 12. Referring to FIG. 3, the electron adhesion type mass spectrometer 3 will be described below. The mass spectrometer 3 has a cylindrical body 30 comprising an introducing pipe 31, an ion passage part 32 and an ion detecting part 33, which are arranged in that order from the vacuum vessel 1. The introducing pipe 31 has an extracting port 34 on one end thereof. The extracting port 34 is arranged so as to face the vacuum vessel 1 via a hole 35 formed in the side wall of the vacuum vessel 1. The introducing pipe 31 is made of a new metal or permalloy, which is a material having a high permeability. The periphery of the introducing pipe 31 is surrounded by a metallic bellows body 36, both ends of which are airtightly mounted on a portion surrounding the base end portion of the introducing pipe 31 and a portion surrounding the hole 35, respectively. The bellows body 36 is connected to a driving part 37, such as an air cylinder, which is guided along a rail 38. Therefore, in accordance with the movement of the driving part 37, the bellows body 36 expands and contracts to allow the introducing pipe 33 into the vacuum chamber 1. Furthermore, the hole 35 may be open and closed by a lid (not shown). In this case, the first and second vacuum chambers 11 and 12 can be separated from the electron adhesion type mass spectrometer 3 by tightly closing the hole 35 by the lid, so that process conditions can be more easily controlled. In the introducing pipe 31, a first focus ring 40, a second focus ring 41, a filament 42 serving as a part of an electron adding means for adding electrons to radicals, and an electrode 43 for drawing ions are arranged in that order from the extracting port 34. The filament 42 is connected to a direct voltage source 44 capable of varying voltage. In the ion passage part 32, four rod-shaped electrodes 45 arranged in the vicinity of the periphery of the ion passage part 32 so as to extend in longitudinal directions thereof. Two pairs of the electrodes 45 facing each other serve as a quadrupole. In the ion detector 33, a third focus ring 46 and a detector 47 for detecting a current value due to negative ions are arranged in that order from the ion passage part 32. Furthermore, the body is evacuated to a predetermined degree of vacuum by means of a vacuum pump 48. The value (current value) detected by the detector 47 is fed to a kind determining part 47a, which derives the relationship between the mass number of the negative ions and the measured value (relative intensity) of the number of the negative ions, i.e., a mass spectrum, to determine the kind of the negative ions on the basis of the mass spectrum. This determination is carried out on the basis of data which are obtained by deriving the mass number at the peak of the measured value of the negative ions and deriving a correspondence between the previously prepared mass number and the kind of the negative ions on the basis of the derived mass number. The detected value is fed to a density estimating means 49. The density estimating means 49 has the function of grasping the relationship between the value of the energy of electrons emitted from the filament 42 and the measured value when the voltage of the direct voltage source 44 is varied, deriving the peak of the measured value, and estimating the density of specific radicals in plasma on the basis of the peak value. The results estimated by the density estimating means 49 are fed to the control part 5. FIG. 4 is a block diagram of a control system for controlling process conditions influencing the density of specific particles, e.g., radicals in this example, in plasma, on the basis of the estimated results obtained by the density estimating means 49. FIG. 4 shows signal lines extending from the control part 5. This point will be described later. In this preferred embodiment, an example where control signals outputted from the control part 5 control only a pulse generating part 51 for modulating the output power of the microwave power supply part 14 will be described. The operation of this preferred embodiment will be described below. First, the magnetic field formed by the electromagnetic coils 14 and 15 is associated with microwaves to cause electron cyclotron resonance, so that Ar gas supplied from the nozzles 16 and, e.g., C4F8 and C2H4 gases, supplied from the gas supply part 20 are activated to plasma, respectively. On the other hand, during a deposition treatment, the extracting port 34 of the body 30 of the electron adhesion type mass spectrometer 3 protrudes above the center of a wafer W, and the interior of the body 30 of the electron adhesion type mass spectrometer 3 is maintained to be higher vacuum than the vacuum vessel 1. Therefore, a part of plasma is drawn into the extracting port 34 to be incorporated into the body 30 via the first and second focus rings 40 and 41. Then, electrons emitted from the filament 42 are added to particles, such as radicals, contained in the plasma, so that the radicals are ionized. For example, C4F7 radicals become negative ions of C4F7xe2x80x94. As described above, a superimposed voltage of a positive or negative direct voltage U (volts) and a high-frequency voltage Vxe2x80x2 (volts) [frequency f (MHz) ] is previously supplied from power supply parts (not shown) to the electrodes 45 of two pairs of hyperbolic cylindrical rods (quadrupole). If Vxe2x80x2 is continuously varied while U/Vxe2x80x2 is maintained to be constant, ions corresponding to the respective masses can be detected by the detector 47. The kind determining part 47a prepares a mass spectrum on the basis of the detected signal from the detector as described above, and selects a mass number contained in a predetermined range of mass number, from the mass numbers at the peak values in the mass spectrum. Then, the values of U and Vxe2x80x2 are set every negative ions of the selected mass number so as to accelerate the negative ions, to vary the filament voltage to vary electron energy emitted from the filament 42, to acquire data relating to a correspondence between the value of the electron energy and the measured value of the number of ions. FIG. 5 shows an example of the acquired data. It can be seen from this figure that the peak value varies in accordance with pressure. The inventor has grasped that the peak value of the measured value of negative ions corresponds to the density of target radicals. In this preferred embodiment, it is previous grasped how much the power of microwaves increases (or decreases) with respect to the peak value of the number of negative ions (e.g., C4F7xe2x80x94), and the peak value is inputted to an automatic control circuit, which supplies a control signal to the pulse generating part 51 to control the state of plasma. In this case, the relative value of the density of radicals is grasped to control the density of radicals. FIGS. 7 and 8 show examples where the peak value varies the magnitude of microwaves with respect to radicals C3F7xe2x80x94 and C4F9xe2x80x94 obtained by negative ionizing C4F8 gas used as a treatment gas. In each of these figures, microwaves of 500 W (solid line) and 600 W (dotted line) are measured at a pressure of 20 Torr. Furthermore, data relating to the peak value and the density of specific radicals, e.g., C4F7 radicals, may be previously prepared, and the detected peak value may be applied to the data to estimate the density of radicals corresponding to the peak value to supply a control signal corresponding to the estimated value to, e.g., the pulse generating part 51. The density of radicals thus estimated can be controlled to a target value by controlling the electronic temperature of plasma. The electronic temperature of plasma can be adjusted by pulse-modulating microwaves outputted from the microwave power supply part 14. The adjusting way in the case of radicals having a density increasing as the energy increases is different from the adjusting way in the case of radicals having a density decreasing as the energy increases. For example, in the former, assuming that the microwaves are pulse-modulated by a pulse having a certain duty ratio, if the density of radicals exceeds a preset value, the duty ratio of the microwave power is increased to increase the energy of microwaves supplied to the gas, so that the density of radicals is controlled so as to decrease. In addition, in order to control the energy (power) of microwaves, the output power value of the microwave power supply part 14 may be controlled in place of the control of the duty ratio, or these controls may be combined. According to this preferred embodiment, the density of, e.g., C4F7 radicals, in plasma in the vacuum vessel 1 can be estimated, and the power of the microwave power supply part 14 is controlled on the basis of the estimated density, so that the density of radicals can be set to be an appropriate value. Therefore, it is possible to carry out a treatment wherein the dispersion in wafer W is small, e.g., the thickness and quality of the wafer W are uniform. In addition, since a gas is extracted from the gas extracting port to give electrons to the gas to ionize the gas to count negative ions, there is no problem in that precision is decreased due to soil of the window provided in the vacuum vessel. Furthermore, in the above described preferred embodiment, the density of radicals is derived during the treatment of product wafers W to be fed back to the real time control part 5 to control process conditions. However, the present invention should not be limited thereto. After a predetermined number of wafers are treated, a treatment may be carried out using a test wafer to measure the density of radicals during the treatment to set process conditions, such as the duty ratio of microwaves, on the basis of the measured value during the subsequent treatment of product wafers W to control the process conditions. In order to control the process conditions, in addition to the microwave power, current control parts 52 and 53, which are shown in FIG. 4, for controlling the current values of the main electromagnetic coil 23 and the auxiliary electromagnetic coil 24, respectively, may be controlled to change the intensity and shape of a magnetic field. Alternatively, gas flow-rate adjusting parts 54 and 55 connected to the gas nozzles 16 and the gas supply part 20, respectively, may be controlled so as to adjust the flow rates and mixing ratio of treatment gases, or the opening and closing of a butterfly valve of a pressure adjusting part 56 provided in the middle of the exhaust pipe 22 may be controlled so as to adjust the pressure in the vacuum vessel 1. Also with respect to the high-frequency power supply part 19, the power value or bias may be controlled. When a pulse modulation is carried out by means of a pulse generating part 57, the duty ratio may be controlled by the control signal via the pulse generating part 57. This is particularly effective in etching of a thin film on a wafer W. Moreover, these controls of process conditions may be combined. As the way of adjusting the process conditions, the process conditions may be previously adjusted to change the density of radicals, and a program may be prepared on the basis of the obtained data. FIG. 9 is a graph showing the variation in peak value of radicals negative-ionized by changing the flow rate of C4F8 serving as a treatment gas. In this figure, C3F7 and C4F9 are measured as examples of radicals. This figure shows that the peak value of ions decreases as the flow rate of C4F8 increases. Therefore, it can be seen that the density of radicals varies in accordance with the flow rate of the treatment gas. In the above described preferred embodiment, the estimation of the density of radicals using the density estimating means 49 has been carried out on the basis of ion count data obtained by negative ionizing target radicals, e.g., C4F7, in the electron addition type mass spectrometer 3. However, in some kinds of radicals, e.g., CF4 radicals, F-ions are dissociated by adding electrons. In such a case, the density of CF4 radicals is estimated on the basis of the measured value of the dissociated negative ions, e.g., F-ions. The present invention also includes this case. In addition, the kind of radicals should not be limited to CF4, and the specific particles should not be limited to radicals, but the particles may be molecules or atoms. Furthermore, FIG. 6 is a characteristic diagram showing the measured value of the above described F-ions. Furthermore, in this preferred embodiment, a method for estimating a distribution of concentration of radicals above a wafer may be used. In this method, the bellows 36 is expanded and contracted by means of the driving part 38 of the electron addition type mass spectrometer 3, and the counted values of negative ions at a plurality of places in radial directions of a wafer are derived by changing the position of the extracting port 34. Furthermore, according to the present invention, a nozzle may be airtightly inserted into the extracting port 34 to provide a bellows between the outside of the extracting port 34 and the periphery of the hole 35, to reciprocate the nozzle while the body 30 is fixed. The present invention may be applied to a helicon wave type system, a parallel plate type system, an inductively coupled plasma (ICP) system and so forth, other than the ECR. In addition, the invention may be applied to plasma treatments other than deposition and etching, e.g., the ashing of a resist. Moreover, the present invention may be applied to any systems for treating substrates using treatment gases, other than the plasma treatment system, e.g., a thermal CVD system. According to the treatment system of the present invention, the density of particles, e.g., radicals, in a vacuum vessel can be estimated, and factors (process conditions) influencing the state of plasma can be controlled on the basis of the estimated results, so that it is possible to carry out a good treatment. While the present invention has been disclosed in terms of the preferred embodiment in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modification to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims. |
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description | This application is a continuation of U.S. patent application Ser. No. 11/486,197 entitled “Radiopharmaceutical Pig” filed on 13 Jul. 2006, now U.S. Pat. No. 7,459,246 which is a continuation of U.S. patent application Ser. No. 10/527,301 entitled “Polymer Pharmaceutical Pig and Associated Method of Use and Associated Method of Production” filed on 9 Mar. 2005, now U.S. Pat No. 7,165,672 which claims priority to PCT Application No. PCT/US03/31823 filed on 7 Oct. 2003, which claims priority to U.S. Provisional Patent Application No. 60/419,161 filed on 17 Oct. 2002, the entire disclosures of which are hereby incorporated by reference in their entireties. A pharmaceutical pig is used for transportation of liquid radiopharmaceuticals. A radiopharmacy typically dispenses a liquid radiopharmaceutical into a syringe, which is then placed in a pharmaceutical pig for transport to a medical facility. The pharmaceutical pig reduces unwanted exposure from the radioactive material and protects the syringe from damage. After delivery, the pharmaceutical pig is opened, the syringe is removed and the radiopharmaceutical is administered to a patient. The used syringe is put back in the pharmaceutical pig and returned to the radiopharmacy for disposal. Some radiopharmacies are independently owned and others are owned and operated in nationwide networks by Cardinal Health, Inc., having a place of business at 7000 Cardinal Place, Dublin, Ohio 43017 and Mallinckrodt Inc., a business of Tyco International, Ltd. Conventional pharmaceutical pigs are used on a daily basis by radiopharmacies across the country. Many of the conventional pigs in current use are formed from plastic and lead. Of course, the lead is used as shielding material for the radiopharmaceutical. Conventional plastic/lead pharmaceutical pigs are typically configured in a two-part or a three-part design, discussed in greater detail below. Other conventional pharmaceutical pigs are formed from plastic and tungsten. The tungsten is an alternative shielding material to lead, but it is much more expensive. The pharmaceutical pigs that are currently used with syringes are elongate devices sized to enclose a single syringe that holds a dose for a single patient. Conventional two-part pharmaceutical pigs are available from Biodex Medical Systems, Inc. of Shirley, N.Y. (“Biodex”) and are commonly used in the Mallinckrodt system of radiopharmacies. Conventional three-part pharmaceutical pigs are produced by Cardinal Health, Inc. and are shown in U.S. Pat. No. 5,519,931. These conventional three-part pharmaceutical pigs are believed to be in widespread use in the Cardinal Health, Inc. system of radiopharmacies to transport conventional syringes. The Biodex two-part pharmaceutical pig is formed from: a) an outer plastic shell having a removable plastic top that threadibly engages a plastic base; and b) an inner shield having an upper lead section that fits in the plastic top and a lower lead section that fits in the plastic base. Conventional syringes are transported in this two-part pharmaceutical pig. However, because of the possibility of contamination, the lower section of the pharmaceutical pig is washed and disinfected after each use in the Mallinckrodt system of radiopharmacies. There is a three-part pharmaceutical pig disclosed in U.S. Pat. No. 5,519,931, assigned to Syncor International Corp., which is formed from the following components: a) an outer shell having a removable plastic top that threadibly engages a plastic base; b) an inner shield having an upper lead section that fits in the plastic top and a lower lead section that fits in the plastic base; and c) an inner disposable liner having a removable plastic cap that connects to a plastic base. A conventional syringe is contained in the disposable plastic liner, which fits into the lead portion of the pharmaceutical pig. There is also a pharmaceutical pig disclosed in U.S. Pat. No. 6,425,174, which is also assigned to Syncor International Corp., that includes an upper shield and a lower shield that nest within an upper outer shell and a lower outer shell, respectively. There is a separate sharps container, having an upper cap and a lower housing, that nests within the upper shield and the lower shield, respectively. John B. Phillips is listed as the inventor on several patents for a three-part pharmaceutical pig having: a) an outer plastic shell; b) an inner lead shield; and c) a removable inner liner to hold a syringe. The Phillips' patents are as follows: U.S. Pat. Nos. 5,611,429; 5,918,443; and 6,155,420. The removable inner liner in the Phillips' design has a flared hexagonal shaped section sized to surround the finger grip of the syringe and hold it securely in place during transit. Conventional three-part lead/plastic pharmaceutical pigs, such as the Syncor design or the Phillips design described above, rely on a removable inner liner having a cap and base to contain the syringe and prevent contamination of the lead shielding material with the radiopharmaceutical. However, both the two-part lead/plastic pharmaceutical pig and the three-part lead/plastic pharmaceutical pig have exposed lead on the interior. There is a need for a new design that protects the lead from inadvertent contamination by the liquid radiopharmaceutical. Lead is a very porous material that can absorb the radiopharmaceutical. Moreover, lead, as a material, might be construed as being hygienically challenging. Many conventional three-part lead/plastic pharmaceutical pigs use a threaded design to connect the cap and the base. Some of these prior art designs require several turns to connect the cap and the base. In a busy radiopharmacy, there is a need for a faster and easier way to attach the cap to the base. However, the cap is typically not locked into place, therefore, rough transportation and a failure to provide the requisite number of turns can result in the cap untwisting slightly from the base during transit with a potential spill of radioactive pharmaceutical fluid resulting therefrom. Another issue is that the base of a conventional pharmaceutical pig is generally cylindrical making the pharmaceutical pig prone to tipping and falling over on its side. The present invention is directed to overcoming one or more of the problems set forth above. These deficiencies and shortcomings include, but are not limited to, exposed lead, numerous turns required to attach the cap to the base, absence of a locking mechanism to secure the cap to the base and a cylindrical base where the bottom portion of the base has substantially the same diameter as the top portion of the base so that the pharmaceutical pig is prone to tipping and falling over on its side. A pharmaceutical pig is sized and arranged to transport a single syringe containing a unit dose of a radiopharmaceutical from a radiopharmacy to a medical facility such as a doctor's office, clinic or hospital. After the radiopharmaceutical has been administered to a patient, the used syringe is put back into the pharmaceutical pig and returned to the radiopharmacy for proper disposal. The present invention may be used with conventional syringes or safety syringes. In one aspect of this present invention, a polymer pharmaceutical pig is disclosed. The polymer pharmaceutical pig includes an elongate polymer base having a base shell that completely encloses a base shielding element and having a first hollow center section and an elongate polymer cap that is removably attached to the elongate polymer base, the elongate polymer cap, having a second hollow center and a cap shell that completely encloses a cap shielding element. Moreover, for convenience and ease of use, the amount of rotation of the elongate polymer cap in relation to the elongate polymer base for removably attaching the elongate polymer base to the elongate polymer cap is minimized, i.e., preferably less than three hundred and sixty degrees (360°), more preferably less than one hundred and eighty degrees (180°) and optimally less than ninety degrees (90°). Preferably, a locking detent is located in the threaded interconnections to secure the elongate polymer base to the elongate polymer cap. The polymer material utilized in the base shell and the cap shell can include virtually any type of plastic and is preferably polycarbonate resin, e.g., LEXAN® material, while the base shielding element and the cap shielding element can be made of virtually any type of material that blocks radiation emitted from the radiopharmaceutical. This material preferably includes lead as well as tungsten and metallic-filled polymers, with lead being the most preferred material due to the low cost and ease of manufacturing. Preferably, the elongate polymer cap is substantially cylindrical and the bottom portion of the elongate polymer base is substantially bell-shaped. Moreover, the elongate polymer base of the pharmaceutical pig preferably includes a top portion having a first diameter, a middle portion having a second diameter and a bottom portion having a third diameter, where the second diameter of the middle portion is less than the first diameter of the top portion and is less than the third diameter of the bottom portion. The elongate polymer cap of the pharmaceutical pig preferably includes a top portion having a fourth diameter and a bottom portion having a fifth diameter, where the fourth diameter of the top portion is less than the fifth diameter of the bottom portion. In the preferred design, the top portion of the elongate base includes a plurality of flattened portions, where at least one flattened portion of the plurality of flattened portions includes an arch-like portion and the bottom portion of the elongate base includes a plurality of flattened portions, wherein at least one flattened portion of the plurality of flattened portions includes an arch-like portion. The bottom portion of the elongate cap base includes a plurality of flattened portions, where at least one flattened portion of the plurality of flattened portions includes an arch-like portion. Optimally, at least one flattened portion of the plurality of flattened portions in the top portion of the elongate base is substantially aligned with the at least one flattened portion of the plurality of flattened portions in the bottom portion of the elongate cap. In another aspect of this present invention, an assembly including a pharmaceutical pig sized and arranged to transport a syringe is disclosed. The assembly includes a syringe having a needle, a barrel, a pair of wing-shaped finger grips, and a plunger, and a pharmaceutical pig including an elongate polymer base that completely encloses a base shielding element. The elongate polymer base having a first hollow center section that is sized to surround the needle and at least a portion of the barrel of the syringe and an elongate polymer cap that is removably attached to the elongate polymer base. The elongate polymer cap completely encloses a cap shielding element and the elongate polymer cap includes a second hollow center section that is sized to surround at least a portion of the plunger of the syringe. In still another aspect of this present invention, a method for transporting a syringe in a pharmaceutical pig, the syringe having at least a needle, a barrel, a pair of wing-shaped finger grips, and a plunger is disclosed. The method includes placing a syringe containing a liquid radiopharmaceutical in a pharmaceutical pig having an elongate polymer base that completely encloses a base shielding element. The elongate polymer base having a first hollow center section that is sized to surround the needle and at least a portion of the barrel of the syringe and an elongate polymer cap that is removably attached to the elongate polymer base. The elongate polymer cap completely encloses a cap shielding element and the elongate polymer cap having a second hollow center section that is sized to surround at least a portion of the plunger of the syringe. This is followed by transporting the pharmaceutical pig containing the syringe to a medical facility and then transporting the pharmaceutical pig and the used syringe back to the radiopharmacy for disposal of the used syringe. In yet another aspect of this present invention, a method for producing a pharmaceutical pig is disclosed. The method includes molding a base shielding element in a first mold, molding a cap shielding element in a second mold. This is followed by inserting the base shielding element within a third mold and injecting molten polymer material into the third mold so that when the polymer material hardens, the base shielding element is completely enclosed by the polymer material to form an elongate base. This is then followed by inserting the cap shielding element within a fourth mold and injecting molten polymer material into the fourth mold so that when the polymer material hardens, the cap shielding element is completely enclosed by the polymer material to form an elongate cap. These are merely some of the innumerable illustrative aspects of this present invention and should not be deemed an all-inclusive listing. These and other aspects will become apparent to those skilled in the art in light of the following disclosure and accompanying drawings. FIG. 1 is a perspective view of the embodiment of the pharmaceutical pig of the present invention that is generally indicated by numeral 10. There is an elongate base 12 and an elongate cap 14. The elongate base 12 and the elongate cap 14 of the pharmaceutical pig 10 can be formed in any of a wide variety of shapes and sizes, however, a substantially cylindrical shape is preferred. Preferably, the elongate base 12 includes a top portion that is generally indicated by numeral 16 having a first diameter, a middle portion that is generally indicated by numeral 18 having a second diameter and a bottom portion that is generally indicated by numeral 20 having a third diameter. The elongate cap 14 includes a top portion that is generally indicated by numeral 22 having a fourth diameter and a bottom portion that is generally indicated by numeral 24 having a fifth diameter. In the preferred embodiment, the second diameter of the middle portion 18 of the elongate base 12 is less than the first diameter of the top portion 18 of the elongate base 12. The second diameter of the middle portion 18 of the elongate base 12 is also less than the third diameter of the bottom portion 20 of the elongate base 12 to create a bell-shape. Also, in the preferred embodiment, the fourth diameter of the top portion 22 of the elongate cap 14 is less than the fifth diameter of the bottom portion 24 of the elongate cap 14. The elongate base 12 for the pharmaceutical pig 10, preferably includes a first plurality of flattened portions 28, e.g., four (4), that each include an arch-like portion 30 located on the bottom portion 20 of the elongate base 12 of the pharmaceutical pig 10. The bottom portion 20 of the elongate base 12 is preferably bell-shaped to prevent tipping and includes a domed, bottom surface 32 to reduce material cost, as shown in FIGS. 4 and 5. Referring again to FIGS. 1 and 2, the top portion 16 of the elongate base 12 for the pharmaceutical pig 10, preferably and optionally, includes a second plurality of flattened portions, e.g., four (4), that preferably alternate between rectangular portions 36 and rectangular portions that each have a downwardly extending arch-like portion 34. The elongate cap 14 for the pharmaceutical pig 10, preferably and optionally, includes a third plurality of flattened portions 40, e.g., four (4), that each include an arch-like portion 41. The top portion 22 is preferably circular and includes a flat top surface 42, as shown in FIG. 1, which can be labeled as well as easily transported within a delivery case that can hold a multiple number of pharmaceutical pigs 10. There is a plurality of threaded interconnections, which is generally indicated by numeral 44, as shown in FIG. 2. Preferably, but not necessarily, there are four (4) threads 45. Preferably, with the present pharmaceutical pig 10 of the present invention, the amount of turns required to secure the elongate base 12 to the elongate cap 14 is minimized. The preferred amount of turning being one turn (360°) or less, with a more preferred amount of turning being one-half of a turn (180°) or less and the most preferred amount of turning being one-quarter of a turn (90°) or less. The pitch of the threads 45 can vary greatly depending on the parameters of the pharmaceutical pig 10, with the most preferred value of pitch being 1.38 for the threads 45. Referring now to FIG. 3, there is a series of locking detents 46 that secure the elongate base 12 to the elongate cap 14. These locking detents 46 lock the elongate base 12 to the elongate cap 14 when the threads 45 of the elongate cap 14 and the elongate base 12 are completely engaged. The elongate cap 14 is flush against the elongate base 12 after having completed the maximum amount of turning, e.g., one-quarter of a turn (90°) to seal the elongate cap 14 against the elongate base 12 in fluid-tight relationship. This seal is present without the presence of an additional component that requires replacement and maintenance, such as an o-ring. Located within the elongate cap 14 and elongate base 12 is a cap shielding element that is generally indicated by numeral 48 and the base shielding element that is generally indicated by numeral 54, respectively, as shown in FIGS. 4 and 5. These shielding elements 48 and 54 are typically formed from lead because it is relatively inexpensive and easy to form. Moreover, these shielding elements 48 and 54 can be formed from any material that blocks the radiation that is emitted from the radiopharmaceutical. For example, tungsten is a suitable shielding element, but it is more expensive than lead and more difficult to form or mold. Metallic-filled polymer composite materials such as the ECOMASS® compounds produced by Engineered Materials, a M. A. Hanna Company having a place of business in Norcross, Ga. can also be used as shielding material. The cap shielding element 48 has a closed end 52 and an open end 50. The walls 56 of the cap shielding element 48 are of generally uniform thickness. The base shielding element 54 has a closed end 58 and an open end 60. The walls 62 of the base shielding element 54 are of generally uniform thickness. As shown in FIG. 5 and best illustrated in FIG. 6, the walls 62 of the base shielding element 54 form a protrusion 64, which is preferably but not necessarily triangular, which forms an angle T when measured against the inside wall of the base shielding element 54. The base shielding element 54 includes a ledge near the open end 60 that forms a shoulder 66. Referring again to FIGS. 4 and 5, the cap shielding element 48 of the elongate cap 14 is completely enclosed by a cap shell 70 having an outer cap shell portion 72 and an inner cap shell portion 74. Also, the base shielding element 54 of the elongate base 12 is completely enclosed by a base shell 76 having an outer base shell portion 78 and an inner base shell portion 80. The cap shell 70 and base shell 76 are preferably made of polymer material. This can include virtually any type of plastic, however, the most preferred type of material is a polycarbonate resin. A specific type of polycarbonate resin, which can be utilized with the present invention, can be purchased under the mark LEXAN®, which is a federally registered trademark of the General Electric Company, having a place of business at One Plastics Avenue, Pittsfield, Mass. 01201. LEXAN® is very lightweight, but is also known for its impact resistance, clarity, stability and heat resistance. The preferred method of forming the cap shell 70 and base shell 76 so that the cap shell 70 and base shell 76 enclose and seal the cap shielding element 48 of the elongate cap 14 and the base shielding element 54 of the elongate base 12, respectively, is by the process of molding. Although the polymer material can be molded in two parts and then melted or welded to provided the complete enclosure of the cap shielding element 48 of the elongate cap 14 and the base shielding element 54 of the elongate base 12, the preferred method of molding the polymer material is by a “two-shot” or “overmolding” process. Examples of this “two-shot” or “overmolding” process are described in: U.S. Pat. No. 4,750,092, which issued to Werther on Jun. 7, 1988 and was assigned to Kollmorgen Technologies Corporation, which is incorporated herein by reference; U.S. Pat. No. 6,381,509, which issued to Thiel et al. on Apr. 30, 2002; and was assigned to Mattec, Inc, which is incorporated herein by reference; and U.S. Pat. No. 6,405,729, which issued to Thornton on Jun. 18, 2002, which is incorporated herein by reference. A significant advantage of the present invention is that no inner liner is utilized. This is a significant advantage since inner liners are typically discarded after each use. This reduces cost and eliminates waste. As also shown in FIG. 5, there is a syringe 83, having: a needle 87 shown in phantom; a barrel 86; a plunger 85; and finger grips 93 which are sometimes called wings. The finger grips 93 may be hexagonal, circular or polygonal; they may fully or partially surround the barrel 86. The finger grips 93 are captured between the previously described shoulder portion 66 formed in the inner base shell portion 80 of the base shell 76 and the inner cap shell portion 74 of the cap shell 70. The syringe 83 is therefore prevented from lateral movement inside the pharmaceutical pig 10 during transit. The needle 87 and at least a portion of the barrel 86 are positioned in a first hollow center section 91 of the elongate base 12. At least a portion of the plunger 85 is positioned in a second hollow center section 89 of the elongate cap 14. The pharmaceutical pig 10 is believed to comply with the revised Bloodborne Pathogens Standard (29 C.F.R. Sectional 1910.1030(d)(2)) promulgated by the Occupational Safety and Health Administration by fully meeting their definition of a “sharps container” by providing a container that is: puncture resistant; capable of being labeled or color-coded; leakproof on the sides and bottom; and does not require a healthcare provider to reach by hand into the container where the sharp has been placed. Method of Use for the Pharmaceutical Pig 10: A prescription is called in, faxed in, or otherwise given to a radiopharmacy. The pharmacist enters the prescription in a computer and prints out the labels. A self-adhesive label can be attached to the pharmaceutical pig 10 in a conventional fashion. In the alternative, a label can be attached to the pharmaceutical pig with the flexible sleeve (not shown), without the need for adhesives. A separate label is affixed to a safety syringe or a conventional syringe. The syringe 83 is filled with a radiopharmaceutical in accordance with the prescription. The filled syringe 83 is assayed. In other words, the activity of the radiopharmaceutical in the syringe 83 is measured in a dose calibrator to verify that it complies with the prescription. The filled syringe 83 is put in the pharmaceutical pig 10 and then closed. The pharmaceutical pig 10 is wipe tested for contamination. If the pharmaceutical pig 10 passes the wipe test, it is placed in a delivery container. The delivery containers used by some Mallinckrodt Inc. pharmacies have interior padding of rubber foam. Several pharmaceutical pigs 10 may be placed in a single delivery container. Before leaving the radiopharmacy, the delivery container and the pharmaceutical pigs 10 are wipe tested and surveyed. If the delivery container passes, a DOT label is affixed to the outside of the delivery container and it is delivered to a medical facility. The pharmaceutical pigs 10 are then opened and the syringe 83 is placed in an injection shield. The radiopharmaceutical is administered to the patient. The delivery case with the pharmaceutical pigs 10 and used syringes 83 are then returned to the radiopharmacy. The syringe 83 is removed from the pharmaceutical pig 10 and placed in a disposal bin. The pharmaceutical pig 10 is then washed and dried. The pharmaceutical pig 10 is then ready to be reused. Method of Producing the Pharmaceutical Pig 10: This involves first molding the base shielding element 54 by pouring molten, nuclear shielding, material into a first mold (not shown). The preferred substance is lead, as opposed to tungsten or metallic-filled polymers, due to cost considerations and ease of molding. When the base shielding element 54 has solidified, the base shielding element 54 is then placed into an injection molding machine (not shown). The polymer material, e.g., polycarbonate resin, is then injected and flows into a third mold, having a mold cavity, which surrounds the base shielding element 54. After an application of temperature and pressure, a solidified elongate base 12 is released from the mold. This elongate base 12 includes the base shielding element 54, which is now completely enclosed by a base shell 76. The base shell 76 includes an inner base shell portion 80 that is adjacent to the needle 87 and barrel 86 of the syringe 83 and an outer base shell portion 78 that forms the outer surface of the elongate base 12. In the same manner, the cap shielding element 48 is created by pouring molten, nuclear shielding, material into a second mold (not shown). As with the base shielding element 54, the preferred substance is again lead. When the cap shielding element 48 has solidified, the cap shielding element 48 is placed into an injection molding machine (not shown). The polymer material, e.g., polycarbonate resin, is then injected and flows into a fourth mold, having a mold cavity, which surrounds the cap shielding element 48. After an application of temperature and pressure, a solidified elongate cap 14 is released from the mold. This elongate cap 14 includes the cap shielding element 48, which is now completely enclosed by the cap shell 70. The cap shell 70 includes an inner cap shell portion 74 that is adjacent to the plunger 85 of the syringe 83 and an outer cap shell portion 72 that forms the outer surface of the elongate cap 14. Although a preferred embodiment of the pharmaceutical pig 10, a method of use of the pharmaceutical pig 10 and a method of production for the pharmaceutical pig 10 have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it is understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit for the invention as set forth and defined by the following claims. |
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description | Nuclear reactors generate energy from a nuclear chain reaction (i.e., nuclear fission) in which a free neutron is absorbed by the nucleus of a fissile atom in a nuclear fuel, such as Uranium-235 (235U). When the free neutron is absorbed, the fissile atom splits into lighter atoms, and releases more free neutrons to be absorbed by other fissile atoms, resulting in a nuclear chain reaction, as is well understood in the art. Thermal energy released from the nuclear chain reaction is converted into electrical energy through a number of other processes also well known to those skilled in the art. The advent of nuclear power reactors adapted to burn nuclear fuel having low fissile content levels (e.g., as low as that of natural uranium) has generated many new sources of burnable nuclear fuel. These sources include waste or recycled uranium from other reactors. This is not only attractive from a cost savings standpoint, but also based upon the ability to essentially recycle spent uranium back into the fuel cycle. Recycling spent nuclear fuel stands in stark contrast to disposal in valuable and limited nuclear waste containment facilities. For these and other reasons nuclear fuel and nuclear fuel processing technologies that support the practices of recycling nuclear fuel and burning such fuel in nuclear reactors continue to be welcome additions to the art. In some embodiments of the present invention, a fuel bundle for a nuclear reactor is provided, and comprises a plurality of fuel elements each including a first fuel component of recycled uranium; and a second fuel component of at least one of depleted uranium and natural uranium blended with the first fuel component, wherein the blended first and second fuel components have a first fissile content of less than 1.2 wt % of 235U. Some embodiments of the present invention provide a fuel bundle for a nuclear reactor, wherein the fuel bundle comprises a first fuel element including recycled uranium, the first fuel element having a first fissile content of no less than 0.72 wt % of 235U; and a second fuel element including at least one of depleted uranium and natural uranium, the second fuel element having a second fissile content of no greater than 0.71 wt % of 235U. Some embodiments of the present invention provide a fuel bundle for a nuclear reactor, wherein the fuel bundle comprises fuel elements containing fissile content of 235U, and each of the fuel elements of the fuel bundle has a fissile content of 235U between about 0.9 wt % 235U and 5.0 wt % 235U. Furthermore, at least one of the fuel elements is a poisoned low-enriched uranium fuel element including a neutron poison in a concentration greater than about 5.0 vol %. Some embodiments of the present invention provide a method of operating a pressurized heavy water nuclear reactor in which a first fuel bundle is provided that is made up of a plurality of fuel elements each having a fissile content of 235U between about 0.9 wt % 235U and 5.0 wt % 235U, at least one of the fuel elements being a poisoned low-enriched uranium fuel element including a neutron poison in a concentration greater than about 5.0 vol %. The first fuel bundle is inserted into a pressure tube of the pressurized heavy water nuclear reactor. The pressurized heavy water nuclear reactor is operated to burn the fuel elements, producing a power output at least as great as a fuel bundle of natural uranium while providing a negative fuel temperature coefficient (FTC), a negative power coefficient (PC), and a coolant void reactivity (CVR) that is lower than that provided by operating the pressurized heavy water nuclear reactor with natural uranium fuel. In some embodiments, any of the fuel bundles and methods just described are utilized in a pressurized heavy water reactor, wherein the fuel bundles are located within one or more tubes of pressurized water that flow past the fuel bundles, absorb heat from the fuel bundles, and perform work downstream of the fuel bundles. Other aspects of the present invention will become apparent by consideration of the detailed description and accompanying drawings. Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of embodiment and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. A number of nuclear fuels according to various embodiments of the present invention are disclosed herein. These fuels can be used in a variety of nuclear reactors, and are described herein with reference to pressurized heavy water reactors. Such reactors can have, for example, pressurized horizontal or vertical tubes within which the fuel is positioned. An example of such a reactor is a Canadian Deuterium Uranium (CANDU) nuclear reactor, a portion of which is shown schematically in FIG. 5. Other types of reactors can have un-pressurized horizontal or vertical tubes with holes in them. Pressurized heavy water nuclear reactors are only one type of nuclear reactor in which various nuclear fuels of the present invention can be burned. Accordingly, such reactors are described herein by way of example only, it being understood that the various fuels of the present invention can be burned in other types of nuclear reactors. Similarly, the various fuels of the present invention described herein can be positioned in any form within a nuclear reactor for being burned. By way of example only, the fuel can be loaded into tubes or can be contained in other elongated forms (each of which are commonly called “pins” or “elements”, referred to herein only as “elements” for sake of simplicity). Examples of elements used in some embodiments of the present invention are indicated at 22 in FIGS. 1-4, and are described in greater detail below. In the case of fuel contained within tubes, the tubes can be made of or include zirconium, a zirconium alloy, or another suitable material or combination of materials that in some cases is characterized by low neutron absorption. Together, a plurality of elements can define a fuel bundle within the nuclear reactor. Such fuel bundles are indicated schematically at 14 in FIG. 5. The elements of each bundle 14 can extend parallel to one another in the bundle. If the reactor includes a plurality of fuel bundles 14, the bundles 14 can be placed end-to-end inside a pressure tube 18. In other types of reactors, the fuel bundles 14 can be arranged in other manners as desired. With continued reference to FIG. 5, when the reactor 10 is in operation, a heavy water coolant 26 flows over the fuel bundles 14 to cool the fuel elements and remove heat from the fission process. The nuclear fuels of the present invention are also applicable to pressure tube reactors with different combinations of liquids/gasses in their heat transport and moderator systems. In any case, coolant 26 absorbing heat from the nuclear fuel can transfer the heat to downstream equipment (e.g., a steam generator 30), to drive a prime mover (e.g., turbine 34) to produce electrical energy. Canadian Patent Application No. 2,174,983, filed on Apr. 25, 1996, describes examples of fuel bundles for a nuclear reactor that can comprise any of the nuclear fuels described herein. The contents of Canadian Patent Application No. 2,174,983 are incorporated herein by reference. The various nuclear fuels of the present invention can be used (e.g., blended) in conjunction within one or more other materials. Whether used alone or in combination with other materials, the nuclear fuel can be in pellet form, powder form, or in another suitable form or combination of forms. In some embodiments, fuels of the present invention take the form of a rod, such as a rod of the fuel pressed into a desired form, a rod of the fuel contained within a matrix of other material, and the like. Also, fuel elements made of the fuels according to the present invention can include a combination of tubes and rods and/or other types of elements. As described in greater detail below, fuels according to various embodiments of the present invention can include various combinations of nuclear fuels, such as depleted uranium (DU), natural uranium (NU), and reprocessed or recycled uranium (RU). As used herein and in the appended claims, references to “percentage” of constituent components of material included in nuclear fuel refers to percentage weight, unless specified otherwise. Also, as defined herein, DU has a fissile content of approximately 0.2 wt % to approximately 0.5 wt % of 235U (including approximately 0.2 wt % and approximately 0.5 wt %), NU has a fissile content of approximately 0.71 wt % of 235U, and RU has a fissile content of approximately 0.72 wt % to approximately 1.2 wt % of 235U (including approximately 0.72 wt % and approximately 1.2 wt %). Recycled Uranium Reprocessed or recycled uranium (RU) is manufactured from spent fuel created from nuclear power production using light water reactors (LWRs). A fraction of the spent fuel is made up of uranium. Therefore, chemical reprocessing of spent fuel leaves behind separated uranium, which is referred to in the industry as reprocessed or recycled uranium. Natural Uranium (NU) contains only the three isotopes 234U, 235U, and 238U. However, after irradiation in a LWR and cooling, the resulting RU has an isotopic composition different from natural uranium. In particular, RU includes four additional types of uranium isotopes that are not present in natural uranium: 236U and 232U, 233U, and 237U (generally considered impurities). Accordingly, the presence of these four additional isotopes can be considered a signature for RU. It should also be understood that the isotopic composition of RU is dependent on many factors, such as the initial 235U content in the fuel prior to irradiation (i.e., fresh fuel), the origin(s) of the fuel, the type of reactor in which the fuel was burned, the irradiation history of the fuel in the reactor (e.g., including burnup), and the cooling and storage periods of the fuel after irradiation. For example, most irradiated fuels are cooled for at least five years in specially engineered ponds to ensure radiological safety. However, the cooling period can be extended to 10 or 15 years or longer. RU often includes chemical impurities (e.g., Gadolinum) caused by fuel cladding, fuel doping, and separation and purification methods used on the RU. These chemical impurities can include very small quantities of transuranic isotopes, such as Plutonium-238 (238Pu), 239Pu, 240Pu, 241Pu, 242Pu, Neptunium-237 (237Np), Americium-241 (241Am), Curium-242 (242Cm) and fission products, such as Zirconium-95/Niobium-95 (95Zr/95Nb), Ruthenium-103 (103Ru), 106Ru, Cesium-134 (134Cs), 137Cs, and Technetium-99 (99Tc). Other impurities often present in RU include: Aluminum (Al), Boron (B), Cadmium (Cd), Calcium (Ca), Carbon (C), Chlorine (Cl), Chromium (Cr), Copper (Cu), Dysprosium (Dy), Flourine (F), Iron (Fe), Magnesium (Mg), Manganese (Mn), Molybdenum (Mo), Nickel (Ni), Nitrogen (N), Phosphorous (P), Potassium (K), Silicon (Si), Sodium (Na), Sulphur (S), and Thorium (Th). Depleted Uranium As stated above, depleted uranium (DU) has a fissile content of approximately 0.2 wt % to approximately 0.5 wt % of 235U (including approximately 0.2 wt % and approximately 0.5 wt %). DU is uranium primarily composed of the isotopes Uranium-238 (238U) and Uranium-235 (235U). In comparison, natural uranium (NU) is approximately 99.28 wt % 238U, approximately 0.71 wt % 235U, and approximately 0.0054 wt % percent 234U. DU is a byproduct of uranium enrichment, and generally contains less than one third as much 235U and 234U as natural uranium. DU also includes various impurities, such as: Aluminum (Al), Boron (B), Cadmium (Cd), Calcium (Ca), Carbon (C), Chlorine (Cl), Chromium (Cr), Copper (Cu), Dysprosium (Dy), Flourine (F), Gadolinium (Gd), Iron (Fe), Magnesium (Mg), Manganese (Mn), Molybdenum (Mo), Nickel (Ni), Nitrogen (N), Phosphorous (P), Potassium (K), Silicon (Si), Sodium (Na), Sulphur (S), and Thorium (Th). Blended Fuel It will be appreciated that in many applications, the uranium content of many nuclear fuels is too high or too low to enable such fuels to be burned in a number of nuclear reactors. Similarly, the constituent components of RU (234U, 235U, 236U, and 238U) and the above-described impurities (232U, 233U, and 237U) typically found in RU can prevent RU from being a viable fuel in many reactors. However, the inventors have discovered that by blending RU with DU, the fissile content of 235U in the resulting nuclear fuel can be brought into a range that is acceptable for being burned as fresh fuel in many nuclear reactors, including without limitation pressurized heavy water nuclear reactors (e.g., pressurized heavy water nuclear reactors having horizontal fuel tubes, such as those in CANDU reactors). Similar results can be obtained by blending RU with NU to reduce the fissile content of 235U in the resulting nuclear fuel to an acceptable range for being burned as fresh fuel. Whether blended with DU or NU, RU can be blended using any method known in the art, such as but not limited to using an acid solution or dry mixing. In some embodiments, the nuclear reactor fuel of the present invention includes a first fuel component of RU and a second fuel component of DU that have been blended together to have a combined fissile content of less than 1.2 wt % of 235U. In such fuels, the RU can have a fissile content of approximately 0.72 wt % of 235U to approximately 1.2 wt % of 235U. In other embodiments, the RU in such fuels can have a fissile content of approximately 0.8 wt % of 235U to approximately 1.1 wt % of 235U. In other embodiments, the RU in such fuels can have a fissile content of approximately 0.9 wt % of 235U to approximately 1.0 wt % of 235U. In still other embodiments, the RU in such fuels can have a fissile content of approximately 0.9 wt % of 235U. In each of these embodiments, the DU of such fuels can have a fissile content of approximately 0.2 wt % of 235U to approximately 0.5 wt % of 235U. Accordingly, by blending lower 235U fissile content DU with the higher 235U fissile content RU, the resulting blended RU/DU nuclear fuel can have a fissile content of less than 1.0 wt % of 235U in some embodiments. In other embodiments, the resulting blended RU/DU nuclear fuel can have a fissile content of less than 0.8 wt % of 235U. In other embodiments, the resulting RU/DU nuclear fuel can have a fissile content of less than 0.72 wt % of 235U. In still other embodiments, the resulting RU/DU nuclear fuel can have a fissile content of approximately 0.71 wt % of 235U, thereby resulting in a natural uranium equivalent fuel generated by blending RU and DU. In some embodiments, the nuclear reactor fuel of the present invention includes a first fuel component of RU and a second fuel component of NU that have been blended together to have a combined fissile content of less than 1.2 wt % of 235U. In such fuels, the RU can have a fissile content of approximately 0.72 wt % of 235U to approximately 1.2 wt % of 235U. In other embodiments, the RU in such fuels can have a fissile content of approximately 0.8 wt % of 235U to approximately 1.1 wt % of 235U. In other embodiments, the RU in such fuels can have a fissile content of approximately 0.9 wt % of 235U to approximately 1.0 wt % of 235U. In still other embodiments, the RU in such fuels can have a fissile content of approximately 0.9 wt % of 235U. Accordingly, by blending lower 235U fissile content NU with the higher 235U fissile content RU, the resulting blended RU/NU nuclear fuel can have a fissile content of less than 1.0 wt % of 235U in some embodiments. In other embodiments, the resulting blended RU/NU nuclear fuel can have a fissile content of less than 0.8 wt % of 235U. In other embodiments, the resulting RU/NU nuclear fuel can have a fissile content of less than 0.72 wt % of 235U. In still other embodiments, the resulting RU/NU nuclear fuel can have a fissile content of approximately 0.71 wt % of 235U, thereby resulting in a natural uranium equivalent fuel generated by blending RU and NU. In some embodiments, RU is blended with both DU and NU to produce fuels having the same 235U fissile contents or content ranges described above in connection with blended RU/DU and blended RU/NU nuclear fuels. In such cases, the 235U fissile contents and content ranges of RU, and the 235U fissile contents and content ranges of DU can be the same as those described above. The nuclear fuels according to the various embodiments of the present invention can include a burnable poison (BP). For example, any of the nuclear fuels described herein can include a blend of RU and DU with a burnable poison (BP), or a blend of RU and NU with a burnable poison (BP). The burnable poison can be blended with the various RU/DU blends, RU/NU blends, and RU/DU/NU blends described herein. Fuel Bundle Constructions Nuclear fuel blending (as described above) is a powerful manner of producing fresh nuclear fuels from otherwise unusable RU. However, such blending is only one technique by which RU can be utilized for burning in many types of reactors, including pressurized heavy water reactors. In many applications, the blended RU fuels described herein can be used with great efficiency in fuel bundles depending at least in part upon the locations of such blended fuels in the fuel bundles. Also, RU can even be successfully utilized in fuel bundles without necessarily being blended as described above. Instead, when RU is included in particular locations in a fuel bundle, has certain 235U fissile contents, and/or is used with targeted combinations of DU and/or NU, the resulting fuel bundle has highly desirable characteristics. These characteristics include greater fuel burnup control and low coolant void reactivity (described below). FIGS. 1-4 illustrate various embodiments of a nuclear fuel bundle for use in a nuclear reactor, such as the pressurized heavy water reactor 10 shown schematically in FIG. 5. In particular, each of FIGS. 1-4 illustrates a cross-sectional view of a number of embodiments of a fuel bundle 14 positioned in a pressure tube 18. The fuel arrangements illustrated in each of FIGS. 1-4 are provided by way of example, it being understood that other fuel arrangements within the fuel bundles of FIGS. 1-4 are possible, and fall within the spirit and scope of the present invention. It should also be noted that the characteristics (including 235U fissile contents and 235U fissile content ranges) of the various fuels described in connection with FIGS. 1-4 below (RU, DU, NU, RU/DU blends, RU/NU blends, and RU/DU/NU blends) are provided above. Heavy water coolant 26 is contained within the pressure tube 18, and occupies subchannels between the fuel elements 22 of the fuel bundle 14. The fuel elements 22 can include a central element 38, a first plurality of elements 42 positioned radially outward from the central element 38, a second plurality of elements 46 positioned radially outward from the first plurality of elements 42, and a third plurality of elements 50 positioned radially outward from the second plurality of elements 46. It should be understood that in other embodiments, the fuel bundle 14 can include fewer or more elements, and can include elements in configurations other than those illustrated in FIGS. 1-4. For example, the fuel elements 22 can be positioned parallel to one another in one or more planes, elements arranged in a matrix or array having a block shape or any other cross-sectional shape, and elements in any other patterned or patternless configuration. The pressure tube 18, the fuel bundle 14, and/or the fuel elements 22 can also be configured in various shapes and sizes. For example, the pressure tubes 18, fuel bundles 14, and fuel elements 22 can have any cross-sectional shapes (other than the round shapes shown in FIGS. 1-5) and sizes desired As another example, the fuel elements 22 within each fuel bundle 14 can have any relative sizes (other than the uniform size or two-size versions of the fuel elements 22 shown in FIGS. 1-4). In the embodiments of FIGS. 1 and 2, a 37-element fuel bundle is illustrated in which all of the fuel elements 22 have a uniform cross-sectional size (or diameter, in the case of elements having a round cross-sectional shape). The first plurality of elements 42 in each of FIGS. 1 and 2 includes six elements arranged in parallel with one another in a generally circular pattern. The second plurality of elements 46 in each of FIGS. 1 and 2 includes twelve elements also arranged in parallel with one another in a generally circular pattern. The third plurality of elements 50 in each of FIGS. 1 and 2 includes eighteen elements also arranged in parallel with one another in a generally circular pattern. The central element 38, the first plurality of elements 42, the second plurality of elements 46, and the third plurality of elements 50 are arranged concentrically such that all of the elements 22 are in parallel with one another. It should be understood that the lines included in FIGS. 1 and 2 indicating the generally circular position of the elements 22 is for illustration purposes only, and does not necessarily indicate that elements 22 are tethered together or otherwise coupled in a particular arrangement. In the embodiments of FIGS. 3 and 4, a 43-element fuel bundle 14 is illustrated. The first plurality of elements 42 in each of FIGS. 3 and 4 includes seven elements arranged in parallel with one another in a generally circular pattern. The second plurality of elements 46 in each of FIGS. 3 and 4 includes fourteen elements arranged in parallel with one another in a generally circular pattern. The third plurality of elements 50 in each of FIGS. 3 and 4 includes twenty-one elements arranged in parallel with one another in a generally circular pattern. The central element 38, the first plurality of elements 42, the second plurality of elements 46, and the third plurality of elements 50 are arranged concentrically such that all of the elements 22 are in parallel with one another. The central element 38 and each of the first plurality of elements 42 have a first cross-sectional size (or diameter, in the case of elements having a round cross-sectional shape), and each of the second plurality 46 and third plurality 50 of elements have a second cross-sectional size (or diameter, in the case of elements having a round cross-sectional shape) different from the first cross-sectional size. In particular, the first cross-sectional size is greater than the second cross-sectional size. In this regard, the term “cross-sectional shape” refers to the cross-sectional shape generated by a plane passing through the body referred to in an orientation that is perpendicular to a longitudinal axis of the body. It should also be understood that the lines included in FIGS. 3 and 4 indicating the generally circular position of the elements 22 is for illustration purposes only and does not necessarily indicate that elements are tethered together or otherwise coupled in a particular arrangement. In some embodiments, each of the fuel elements 22 of FIGS. 1-4 includes a tube filled with nuclear fuel. The tube can be made of or include zirconium, a zirconium alloy, or another suitable material or combination of materials that in some cases is characterized by low neutron absorption. The tube can be filled with one or more materials, such as nuclear fuel alone or in combination with other materials. The material(s) can be in pellet form, powder form, or in another suitable form or combination of forms. In other embodiments, each of the fuel elements 22 includes a rod formed from one or more materials (e.g., nuclear fuel alone or in combination with other materials), such as nuclear fuel contained within a matrix of other material. Also, in some embodiments, the fuel elements 22 in a bundle 14 can include a combination of tubes and rods and/or other fuel-containing elements, and the fuel elements 22 can take on other configurations suitable for the particular application. As shown in FIGS. 1-4, the fuel elements 22 can include various combinations of nuclear fuels, such as depleted uranium (DU), natural uranium (NU), and reprocessed or recycled uranium (RU). With reference first to FIG. 1, the fuel bundle 14 illustrated therein includes 37 elements. The central element 38 of FIG. 1 includes a blend of RU and DU having a first fissile content (i.e., (RU/DU)1) and/or a blend of DU and a burnable poison (BP) and/or DU. As described above, a blend (generally designated herein by the use of a slash “/” herein) of materials can be created using any method known in the art, such as but not limited to using an acid solution or dry mixing of the subject materials. Returning to FIG. 1, the first plurality of elements 42 includes a blend of RU and DU having a second fissile content (i.e., (RU/DU)2). The second plurality of elements 46 includes a blend of RU and DU having a third fissile content (i.e., (RU/DU)3) and/or NU having a first fissile content (i.e., NU1). The third plurality of elements 50 includes a blend of RU and DU having a fourth fissile content (i.e., (RU/DU)4) and/or NU having a second fissile content (i.e., NU2). In the embodiments illustrated in FIG. 1, (as well as those of other figures of the present application), materials that have been blended together are referred to with a slash “/”. However, in each such case, alternative fuel arrangements for such elements include the use of fuel elements 22 each having only one of the fuels noted, but used in combination with fuel elements 22 having the other fuel noted. The use of such elements 22 of different fuel types (e.g., in the same ring of elements 22) can be provided in place of or in addition to elements 22 having a blend of fuel types as described above. For example, the ring of (RU/DU)2 elements 22 in FIG. 1 indicates that each illustrated element 22 in the first plurality of elements 36 is a blend of RU and DU. However, alternatively or in addition, the first plurality of elements 36 can instead include one or more elements of RU and one or more elements of DU. The resulting fuel elements 22 containing RU or DU can be arranged in various configurations, such as in an alternating pattern with changing circumferential position about the fuel bundle 14. In some embodiments, the 235U fissile content of the RU/DU blends included in the fuel bundle 14 of FIG. 1 are approximately the same (from ring to ring, or with changing radial distance from the center of the fuel bundle 14). In other embodiments, the 235U fissile content of the RU/DU blends included in the fuel bundle 14 change from ring to ring, or with changing radial distance from the center of the fuel bundle 14. For example, the RU/DU blend included in at least one of the central element 38, the first plurality of elements 42, the second plurality of elements 46, and the third plurality of elements 50 in FIG. 1 can have a fissile content different than a fissile content of a blend included in one or more of the other elements. In some embodiments, an (RU/DU)1 blend included in the central element 38 of FIG. 1 generally has a lower percentage of 235U than the (RU/DU)2 blend included in the first plurality of elements 42, the (RU/DU)2 blend included in the first plurality of elements 42 generally has a lower percentage of 235U than any (RU/DU)3 blend included in the second plurality of elements 46, and any (RU/DU)3 blend included in the second plurality of elements 46 generally has a lower percentage of 235U than any (RU/DU)4 blend included in the third plurality of elements 50. Therefore, the 235U fissile content of the nuclear fuel included in the fuel bundle 14 can increase in an outward radial direction from the center of the fuel bundle 14. In other embodiments, however, the 235U fissile content decreases in an outward radial direction from the center of the fuel bundle 14. Similarly, the fissile content of any NU used in the embodiments of FIG. 1 can be approximately the same or varied with changing distance from the center of the fuel bundle 14. For example, any NU1 included in the second plurality of elements 46 can generally have a lower percentage of 235U than any NU2 included in the third plurality of elements 50. Alternatively, any NU2 included in the third plurality of elements 50 can generally have a lower percentage of 235U than any NU1 included in the second plurality of elements 46. Furthermore, in some embodiments, the particular fissile content of a particular fuel element 22 can be varied throughout one or more of the plurality of elements 42, 46, and 50 (e.g., in a circumferential direction within the fuel bundle 14) or along the longitudinal length of the fuel bundle 14. Also, a BP can be included in any or all of the fuel elements 22 of FIG. 1, such as in the center element 38 as illustrated. The following fuel bundle arrangements are based upon the fuel bundle embodiments illustrated in FIG. 1, and are presented as examples of fuel bundles having particularly desirable characteristics, but are not to be considered limiting to the scope of the present invention or the other possible embodiments contemplated by FIG. 1. As used herein, the term “ring” includes a center element alone. Center element: RU/DU 1st ring of elements 42: RU/DU 2nd ring of elements 46: RU/DU 3rd ring of elements 50: RU/DU Center element: (RU/DU)1 1st ring of elements 42: (RU/DU)2 2nd ring of elements 46: (RU/DU)3 3rd ring of elements 50: (RU/DU)4 Wherein (RU/DU)2 has a 235U fissile content greater than that of (RU/DU)1, (RU/DU)3 has a 235U fissile content greater than that of (RU/DU)1 and/or (RU/DU)2, and/or wherein (RU/DU)4 has a 235U fissile content greater than that of (RU/DU)1, (RU/DU)2, and/or (RU/DU)3. Center element: (RU/DU)1 1st ring of elements 42: (RU/DU)2 2nd ring of elements 46: (RU/DU)3 3rd ring of elements 50: NU Wherein (RU/DU)2 has a 235U fissile content greater than that of (RU/DU)1, and wherein (RU/DU)3 has a 235U fissile content greater than that of (RU/DU)1 and/or (RU/DU)2. Center element: (RU/DU)1 1st ring of elements 42: (RU/DU)2 2nd ring of elements 46: NU 3rd ring of elements 50: (RU/DU)3 Wherein (RU/DU)2 has a 235U fissile content greater than that of (RU/DU)1, and wherein (RU/DU)3 has a 235U fissile content greater than that of (RU/DU)1 and/or (RU/DU)2. Center element: (RU/DU)1 1st ring of elements 42: (RU/DU)2 2nd ring of elements 46: NU 3rd ring of elements 50: NU Wherein (RU/DU)2 has a 235U fissile content greater than that of (RU/DU)1. FIG. 2 illustrates another embodiment of a 37-element fuel bundle 14. The central element 38 of FIG. 2 includes RU having a first fissile content (i.e., RU1) and/or DU having a first fissile content (i.e., DU1). The first plurality of elements 42 of FIG. 2 includes RU having a second fissile content (i.e., RU2) and/or DU having a second fissile content (i.e., DU2). The second plurality of elements 46 includes RU having a third fissile content (i.e., RU3). The third plurality of elements 50 includes RU having a fourth fissile content (i.e., RU4). The 235U fissile contents of the RU included in each fuel element 22 can be approximately the same and/or can be varied. In those embodiments where the 235U fissile content of the RU in FIG. 2 varies, this change can be with radial distance from the center of the fuel bundle and/or with circumferential position within the fuel bundle 14, and can exist between any or all of the rings shown in FIG. 2, and/or between any or all circumferential positions of any ring. For example, in some embodiments, the RU1 included in the central element 38 generally has a lower percentage of 235U than the RU2 included in the first plurality of elements 42, the RU2 blend included in the first plurality of elements 42 generally has a lower percentage of 235U than the RU3 included in the second plurality of elements 46, and/or the RU3 included in the second plurality of elements 46 generally has a lower percentage of 235U than the RU4 included in the third plurality of elements 50. Therefore, in some embodiments, the 235U fissile content of nuclear fuel of the fuel bundle 14 increases in an outward radial direction from the center of the fuel bundle 14. However, in other embodiments, the 235U fissile content decreases in an outward radial direction from the center of the fuel bundle 14. It is to be understood that even when the fissile content of RU included in the fuel bundle 14 of FIG. 2 is varied in any of the manners described above, each fuel element 22 still has a 235U fissile content generally between and including approximately 0.72 wt % to approximately 1.2 wt % of 235U. By way of example only, the fissile content of the RU1 included in the central element 38 is chosen from the range defined above for RU, and the fissile content of the RU2 included in the first plurality of elements 42 is also chosen from the same range defined, but can be different from the fissile content chosen for the central element 38. Similarly, the fissile content of any DU used in the embodiments of FIG. 2 can be approximately the same or varied—either with radial distance from the center of the fuel bundle 14 or with change in circumferential position within the fuel bundle 14. Again by way of example only, any DU1 included in the central element 38 can generally have a lower percentage of 235U than any DU2 included in the second plurality of elements 42. Alternatively, any DU2 included in the second plurality of elements 42 can generally have a lower percentage of 235U than any DU1 included in the central element 38. Furthermore, in some embodiments, the particular fissile content of a particular fuel element 22 can be varied throughout one or more of the plurality of elements 42, 46, and 50 (e.g., in a circumferential direction within the fuel bundle 14) or along the longitudinal length of the fuel bundle 14. Also, a BP can be included in any or all of the fuel elements 22 of FIG. 2. The following fuel bundle 14 arrangement is based upon the fuel bundle embodiments illustrated in FIG. 2, and is presented as an example of a fuel bundle 14 having particularly desirable characteristics, but is not to be considered limiting to the scope of the present invention or the other possible embodiments contemplated by FIG. 2. As used herein, the term “ring” includes a center element alone. Center element: DU1 1st ring of elements 42: DU2 2nd ring of elements 46: RU1 3rd ring of elements 50: RU2 Wherein DU2 has a 235U fissile content greater than that of DU1, and wherein RU2 has a 235U fissile content greater than that of RU1. The embodiments of FIG. 3 are substantially similar to the embodiments of FIG. 1 described above, except that the fuel bundle 14 is a 43-element fuel bundle, and has non-uniformly sized fuel elements 22, as described above. Since the distribution of nuclear fuel in the central, first, second, and third pluralities of elements 38, 42, 46, and 50, respectively, is similar to FIG. 1, reference is hereby made to the description accompanying FIG. 1 above for more detail regarding the embodiments (and possible alternatives thereto) shown in FIG. 3. The following fuel bundle arrangements are based upon the fuel bundle embodiments illustrated in FIG. 3, and are presented as examples of fuel bundles having particularly desirable characteristics, but are not to be considered limiting to the scope of the present invention or the other possible embodiments contemplated by FIG. 3. As used herein, the term “ring” includes a center element alone. Center element: RU/DU 1st ring of elements 42: RU/DU 2nd ring of elements 46: RU/DU 3rd ring of elements 50: RU/DU Center element: RU/DU 1st ring of elements 42: RU/DU 2nd ring of elements 46: RU/DU 3rd ring of elements 50: NU Center element: RU/DU 1st ring of elements 42: RU/DU 2nd ring of elements 46: NU 3rd ring of elements 50: RU/DU Center element: DU/BP 1st ring of elements 42: (RU/DU)1 2nd ring of elements 46: (RU/DU)2 3rd ring of elements 50: (RU/DU)3 Wherein (RU/DU)2 has a 235U fissile content greater than that of (RU/DU)1, and wherein (RU/DU)3 has a 235U fissile content greater than that of (RU/DU)2 and/or (RU/DU)1. Center element: DU 1st ring of elements 42: (RU/DU)1 2nd ring of elements 46: (RU/DU)2 3rd ring of elements 50: (RU/DU)3 Wherein (RU/DU)2 has a 235U fissile content greater than that of (RU/DU)1, and wherein (RU/DU)3 has a 235U fissile content greater than that of (RU/DU)2 and/or (RU/DU)1. Center element: DU/BP 1st ring of elements 42: (RU/DU)1 2nd ring of elements 46: (RU/DU)2 3rd ring of elements 50: NU Wherein (RU/DU)2 has a 235U fissile content greater than that of (RU/DU)1. Center element: DU/BP 1st ring of elements 42: (RU/DU)1 2nd ring of elements 46: NU 3rd ring of elements 50: (RU/DU)2 Wherein (RU/DU)2 has a 235U fissile content greater than that of (RU/DU)1. The embodiment of FIG. 4 is substantially similar to the embodiment of FIG. 2 described above, except that the fuel bundle 14 is a 43-element fuel bundle, and has non-uniformly sized fuel elements 22, as described above. Since the distribution of nuclear fuel in the central, first, second, and third pluralities of elements 38, 42, 46, and 50, respectively, is similar to FIG. 2, reference is hereby made to the description accompanying FIG. 2 above for more detail regarding the embodiments (and possible alternatives thereto) shown in FIG. 4. The following fuel bundle arrangements are based upon the fuel bundle embodiments illustrated in FIG. 4, and are presented as examples of fuel bundles having particularly desirable characteristics, but are not to be considered limiting to the scope of the present invention or the other possible embodiments contemplated by FIG. 4. As used herein, the term “ring” includes a center element alone. Center element: DU/BP 1st ring of elements 42: RU 2nd ring of elements 46: RU 3rd ring of elements 50: RU Center element: DU 1st ring of elements 42: RU 2nd ring of elements 46: RU 3rd ring of elements 50: RU Center element: DU 1st ring of elements 42: DU 2nd ring of elements 46: RU 3rd ring of elements 50: RU The embodiments of FIGS. 3 and 4 provide examples of how the particular number of fuel elements, the fuel element arrangement (e.g., rings of elements in the illustrated embodiments), fuel element sizes, and relative fuel element sizes can change while still embodying the present invention. In some embodiments, the 235U fissile content of nuclear fuel decreases in an outward radial direction from the center of the fuel bundle 14. In other embodiments, the 235U fissile content increases in an outward radial direction from the center of the fuel bundle 14. In heavy water cooled reactors, the rate of neutron multiplication increases when coolant voiding occurs. Coolant voiding occurs, for example, when coolant starts to boil. Coolant void reactivity is a measure of the ability of a reactor to multiply neutrons. This phenomenon is due to positive coolant void reactivity, and can occur in all reactors for different scenarios. The present invention can provide a significant reduction in coolant void reactivity, and can also provide a negative fuel temperature coefficient and/or a negative power coefficient. The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention. For example, in various embodiments described and/or illustrated herein, RU and DU blends are further blended with different types of nuclear fuel or other materials to produce nuclear fuels having desired fissile contents. For example, the RU and DU can be blended (alone or as an RU/DU blend) with slightly enriched uranium (SEU) and low enriched uranium (LEU). As defined herein, SEU has a fissile content of approximately 0.9 wt % to approximately 3 wt % of 235U (including approximately 0.9 wt % and approximately 3 wt %), and LEU has a fissile content of approximately 3 wt % to approximately 20 wt % of 235U (including approximately 3 wt % and approximately 20 wt %). Also, the embodiments described herein may be used with pressure tubes larger or smaller than those used in current pressure tube reactors and may also be used in future pressure tube reactors. Furthermore, the present invention can be employed in fuel bundles having a different number and arrangement of elements, and is not limited to 43-element and 37-element fuel bundle designs and arrangements, such as those illustrated by way of example in FIGS. 1-4. For example, although the embodiments of FIGS. 3 and 4 utilize two different element sizes in the illustrated fuel bundles 14, whereas the embodiments of FIGS. 1 and 2 utilize uniform element sizes across the illustrated fuel bundles 14, it will be appreciated that any of the fuel bundles described herein can have the same or differently-sized elements in different rings and/or different circumferential positions within the fuel bundles while still falling within the spirit and scope of the present invention. As another example, larger element sizes need not necessarily be located only in the first and/or second rings of a fuel bundle 14. In other embodiments, such relatively larger element sizes are located in radially outer rings of the fuel bundle 14 (e.g., the radially outermost ring and/or ring adjacent thereto). Fuel Bundle Construction for Reduced or Negative CVR As described above, it is desirable to decrease coolant void reactivity (CVR), and even provide a negative CVR, in a pressurized heavy water nuclear reactor such as the Canadian Deuterium Uranium (CANDU) reactor. Canadian Patent No. 2,097,412, the entire contents of which are incorporated by reference herein, provides a useful background on the science of reducing coolant void reactivity, in particular in CANDU reactors. A neutron absorber or “poison” may be included along with fissile content in a fuel bundle to reduce or completely negate positive CVR values. For example, a poison may be mixed with one or more fissionable types of uranium in one or more of the elements 22 of either of the fuel bundles 14 (including the 37-element fuel bundle of FIGS. 1 and 2 and the 43-element fuel bundle of FIGS. 3 and 4). The poison may be a burnable poison such as dysprosium or gadolinium, or may alternately be a non-burnable poison such as hafnium. In order to compensate for the neutron-absorbing effect of the poison, an increase in fissionable material is necessary compared to a non-poisoned natural uranium fuel typically used in a CANDU reactor. In order to meet a particular fuel burnup target and CVR, a graded enrichment scheme may be used in constructing the fuel bundle 14. In one construction, a 37-element fuel bundle as shown in FIGS. 1 and 2 is provided in which each of the fuel elements 22 has a fissile content of 235U between about 0.9 wt % 235U and 5.0 wt % 235U, and at least one of the fuel elements 22 is a poisoned low-enriched uranium fuel element including a neutron poison in a concentration greater than about 5.0 vol %. In other words, all of the fuel elements 22 qualify as “slightly-enriched”, and may qualify as or contain “low-enriched” uranium. In some constructions, the fissile content of the at least one poisoned low-enriched uranium fuel element is at least about 3.0 wt % of 235U, and more particularly, may be between about 3.0 wt % of 235U and about 3.5 wt % of 235U. The neutron poison content of the at least one poisoned low-enriched uranium fuel element may be between about 5.0 vol % and about 8.0 vol %. In one particular example, the fissile content of the at least one poisoned low-enriched uranium fuel element is about 3.21 wt % of 235U, and the neutron poison concentration in the at least one low-enriched uranium fuel element is about 6.82 vol %. The neutron poison in this particular example may be dysprosium. The neutron poison may also be a mixture of dysprosium and another burnable poison, such as gadolinium. In the above examples, among other configurations within the scope of the invention, the at least one poisoned low-enriched uranium fuel element of the fuel bundle 14 includes the center element 38 of the bundle and each of the fuel elements of the first plurality 42 that immediately surround the center element 38. The remaining fuel elements 22 of the fuel bundle 14 (i.e., the fuel elements of the second and third pluralities 46, 50) are non-poisoned fuel elements disposed radially outside the poisoned low-enriched uranium fuel elements 38, 42. Each of the non-poisoned fuel elements 46, 50 has a fissile content of 235U not exceeding the fissile content of the poisoned low-enriched uranium fuel elements 38, 42, and at least some of the non-poisoned fuel elements 46, 50 have a fissile content of 235U that is less than the fissile content of the poisoned low-enriched uranium fuel elements 38, 42. In some constructions, the fuel elements of the second plurality 46 have a higher fissile content that the fuel elements of the third plurality 50. For example, the fuel elements of the second plurality 46 may have a fissile content between about 3.0 wt % and about 3.5 wt % 235U, and the fuel elements of the third plurality 50 may have a fissile content less than about 2.0 wt % 235U. More particularly, the fuel elements of the second plurality 46 may have a fissile content of about 3.18 wt % 235U, and the fuel elements of the third plurality 50 may have a fissile content of about 1.73 wt % 235U. In other constructions, the fissile content of the fuel elements 22 may all be the same as the poisoned low-enriched uranium fuel elements, or may at least be greater than the levels of the particular example above. In order to maintain a low CVR (i.e., less than that of a natural uranium fuel bundle), and in some cases negative CVR, with levels of fissile content greater than those of the particular example expressed above, the poisoned low-enriched uranium fuel elements 38, 42 may have a higher poison content than 6.82 vol %. For example, the poison content of the poisoned low-enriched uranium fuel elements 38, 42 may be increased up to about 20 vol % in relation to the fissile content. Although the material for the fuel elements described above may be produced by enriching natural uranium to achieve the desired fissile content, alternate sources can provide fueling flexibility. In order to limit the amount of enrichment required to produce a predetermined fissile content of 235U in a particular fuel element 22 and make use of alternate uranium sources, a quantity of low-enriched uranium may be mixed with a quantity of any one natural uranium, recycled uranium, and depleted uranium. For example, to produce a poisoned low-enriched uranium fuel element having a fissile content of 3.21 wt % 235U, a small quantity of low-enriched uranium having a fissile content greater than 3.21 wt % 235U may be mixed with recycled uranium (which has a fissile content between about 0.72 wt % 235U and 1.2 wt % 235U). If enough 235U is present in the low-enriched uranium, the mix may include recycled uranium and/or at least one of natural uranium and depleted uranium. A fuel bundle such as that described above provides a coolant void reactivity (CVR) and a fuel temperature coefficient (FTC) lower than the corresponding CVR and FTC of an equivalent natural uranium fuel bundle, without a decrease in power output, when used as fuel in a pressurized heavy water nuclear reactor. Such a fuel bundle can provide a negative CVR, a negative FTC, and a negative power coefficient (PC). The CVR with this type of fuel bundle is not very sensitive to the fuel burnup. For example, a fuel bundle as described above may yield a CVR value of −3 mk at mid-burnup. To make use of a fuel bundle including poisoned low-enriched uranium fuel elements, a fuel bundle (or multiple similar fuel bundles) with the characteristics described above is inserted into one of the pressure tubes 18 of a pressurized heavy water nuclear reactor and the reactor is operated to burn the fuel. When burned in the reactor, the fuel bundle produces a power output at least as great as a fuel bundle of natural uranium while providing a negative coolant void reactivity (CVR), a negative fuel temperature coefficient (FTC), and a negative power coefficient (PC). Therefore, upon coolant voiding inside the pressure tube, the reactivity of the fuel bundle actually decreases. A reactor designed to burn natural uranium fuel may be fueled by replacing one or more natural uranium fuel bundles with the fuel bundles including poisoned low-enriched uranium fuel elements. The reactor may operate without discrimination to which type of fuel bundles are loaded, such that no reconfiguring of the reactor for the different fuel is necessary. The replacement fuel bundles including poisoned low-enriched uranium fuel elements provide similar performance as natural uranium with an increased safety factor. The replacement fuel bundle may also reduce the dependency on fresh natural uranium supplies by taking advantage of recycled uranium and/or depleted uranium. In some constructions, one or more pressure tubes 18 are each filled with fuel bundles similar to the above-described fuel bundle. For example, each pressure tube 18 may receive 12 fuel bundles at one time. Because the lattice k-infinity of the fuel bundle having low-enriched uranium and neutron poison is higher than a similar fuel bundle of natural uranium, a conventional 8-bundle-shift fueling scheme cannot be used. Instead, a 4-bundle-shift or a 2-bundle-shift fueling scheme may be used. Furthermore, combination bundle-shifting such as a mixed 2-and-4-bundle-shift or a mixed 4-and-8-bundle-shift may be employed. Refueling the pressure tube(s) 18 may take place with one of these schemes during operation of the nuclear reactor (i.e., without shutting down the reactor). |
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042007941 | abstract | A combined fine focusing micro lens array and micro deflector assembly for use in electron beam tubes of the fly's eye type is provided. The assembly comprises a fine focusing micro lens array sub-assembly formed from a plurality of spaced-apart stacked parallel thin planar apertured silicon semiconductor lens plates each having an array of micro lens aperture openings. The lens plates each have highly conductive surfaces and are secured to glass rods for holding the plates in stacked parallel spaced-apart relationship with the apertures axially aligned in parallel. A micro deflector assembly is adjacent to the micro lens array sub-assembly. A micro deflector element axially aligned with each respective fine focusing lens element serves for deflecting an electron beam passing through along orthogonal x-y directional axes of movement normal to the electron beam path. The deflector elements are comprised by two orthogonally arrayed sets of parallel spaced-apart deflector bars with alternate bars of each set of deflector bars being interconnected electrically for common connection to a respective source of fine x-y deflection potential.. The thin planar apertured silicon lens plates comprising the micro lens array are held together in stacked parallel assembled relationship by spaced-apart glass support rods whose longitudinal axes extend at right angles to the plates and to which the planar silicon lens plates are secured at their periphery. The two orthogonally arrayed sets of parallel spaced-apart deflection bars forming the sets of micro-deflector elements likewise preferably comprise parallel plates or bars of polycrystalline silicon having a highly conductive metalized surface. The micro deflector bars likewise are held in assembled spaced-apart parallel relationship by respective sets of spaced-apart parallel supporting glass rods whose longitudinal axes extend in a plane parallel to the plane of the deflector bars but at right angles thereto and to which the ends of the deflector bars are thermally bonded. The fine focusing micro lens array and micro deflector sub-assembly thus comprised, are secured together in assembled relation by additional glass support rods being disposed about the outer peripheries of the micro lens and micro deflector sub-assemblies and being secured thereto by thermal bonding such as by fusion. |
description | The present invention relates generally to radiation-shielding systems and, more particularly, to radiation-shielding systems used in the production of radioisotopes for nuclear medicine. Nuclear medicine is a branch of medicine that uses radioactive materials (e.g., radioisotopes) for various research, diagnostic and therapeutic applications. Radiopharmacies produce various radiopharmaceuticals (i.e., radioactive pharmaceuticals) by combining one or more radioactive materials with other materials to adapt the radioactive materials for use in a particular medical procedure. For example, radioisotope generators may be used to obtain a solution comprising a daughter radioisotope (e.g., Technetium-99m) from a parent radioisotope (e.g., Molybdenum-99) which produces the daughter radioisotope by radioactive decay. A radioisotope generator may include a column containing the parent radioisotope adsorbed on a carrier medium. The carrier medium (e.g., alumina) has a relatively higher affinity for the parent radioisotope than the daughter radioisotope. As the parent radioisotope decays, a quantity of the desired daughter radioisotope is produced. To obtain the desired daughter radioisotope, a suitable eluant (e.g., a sterile saline solution) can be passed through the column to elute the daughter radioisotope from the carrier. The resulting eluate contains the daughter radioisotope (e.g., in the form of a dissolved salt), which makes the eluate a useful material for preparation of radiopharmaceuticals. For example, the eluate may be used as the source of a radioisotope in a solution adapted for intravenous administration to a patient for any of a variety of diagnostic and/or therapeutic procedures. In one method of obtaining a quantity of eluate from a generator, an evacuated container (e.g., an elution vial) may be connected to the generator at a tapping point. For example, a hollow needle on the generator can be used to pierce a septum of an evacuated container to establish fluid communication between the container and the generator column. The partial vacuum of the container can draw eluant from an eluant reservoir through the column and into the vial, thereby eluting the daughter radioisotope from the column. The container may be contained in an elution shield, which is a radiation-shielding device used to shield workers (e.g., radiopharmacists) from radiation emitted by the eluate after it is loaded in the container. After the elution is complete, the eluate may be analyzed. For example, the activity of the eluate may be calibrated by transferring the container to a calibration system. Calibration may involve removing the container from the shielding assembly and placing it in the calibration system to measure the amount of radioactivity emitted by the eluate. A breakthrough test may be performed to confirm that the amount of the parent radioisotope in the eluate does not exceed acceptable tolerance levels. The breakthrough test may involve transfer of the container to a thin shielding cup (e.g., a cup that effectively shields radiation emitted by the daughter isotope but not higher-energy radiation emitted by the parent isotope) and measurement of the amount of radiation that penetrates the shielding of the cup. After the calibration and breakthrough tests, the container may be transferred to a dispensing shield. The dispensing shield shields workers from radiation emitted by the eluate in the container while the eluate is transferred from the container into one or more other containers (e.g., syringes) that may be used to prepare, transport, and/or administer the radiopharmaceuticals. Typically, the dispensing process involves serial transfer of eluate to many different containers (e.g., off and on throughout the course of a day). The practice of using a different shielding device for dispensing than was used for elution stems from the fact that it is common industry practice to place the shielded container upside down on a work surface (e.g., tabletop surface) during the idle periods between dispensing of eluate to one container and the next. Prior art elution shields are generally not conducive for use as dispensing shields because, among other reasons, they may be unstable when inverted. For example, some elution shields have a heavy base that results in a relatively high center of gravity when the elution shield is upside down. Further, some elution shields have upper surfaces that are not adapted for resting on a flat work surface (e.g., upper surfaces with bumps that would make the elution shield unstable if it were placed upside down on a flat surface). Radiopharmacies have addressed this problem by maintaining a supply of elution shields and another supply of dispensing shields. The same generator may be used to fill a number of elution containers before the radioisotopes in the column are spent. The volume of eluate needed at any time may vary depending on the number of prescriptions that need to be filled by the radiopharmacy and/or the remaining concentration of radioisotopes in the generator column. One way to vary the amount of eluate drawn from the column is to vary the volume of the evacuated container used to receive the eluate. For example, container volumes ranging from about 5 mL to about 30 mL are common and standard containers having volumes of 5 mL, 10 mL, or 20 mL are currently used in the industry. A container having a desired volume may be selected to facilitate dispensing of a corresponding amount of eluate from the generator column. Unfortunately, the use of multiple different sizes of containers is associated with significant disadvantages. For example, a radiopharmacy may attempt to manipulate a conventional shielding device so that can be used with containers of various sizes. One solution that has been practiced is to keep a variety of different spacers on hand that may be inserted into shielding devices to temporarily occupy extra space in the radiation shielding devices when smaller containers are being used. Unfortunately, this adds complexity and increases the risk of confusion because the spacers can get mixed up, lost, broken, or used with the wrong container and may be considered inconvenient for use. For instance, some conventional spacers surround the sides of the containers in the shielding-devices, which is where labels may be attached to the containers. Accordingly, the spacers may mar the labels and/or contact adhesives used to attach the labels to the container resultantly causing the spacers to stick to the sides of the container or otherwise gum up the radiation-shielding device. Another problem with conventional radiation-shielding systems is that dispensing shields may be somewhat inconvenient to handle. Whereas elution shields may be handled between one and ten times in a typical day, which limits the importance of the ergonomics of elution shields, a dispensing shield may be handled hundreds of times in a typical day. This makes the ergonomics of dispensing shields important. Prior art dispensing shields can be relatively heavy (e.g., 3-5 pounds) and have utilitarian designs focusing on radiation-shielding and function rather than ease of handling. For example, dispensing shields can be cylindrical, have sharp edges, and lack an obvious place for gripping them. Because of the repetitive handling of dispensing shields by workers, the aggregate toll of the foregoing inconveniences can add up to discomfort, injury, and other problems. Further, each time a worker lifts a dispensing shield to transfer eluate from the container housed therein to other containers, the worker is exposed to radiation escaping the dispensing shield through the opening that is used to access the container. A worker can significantly reduce exposure to radiation in the dispensing process by gripping the dispensing shield at a place that is relatively farther from the opening rather than a place that is relatively closer to the opening. Unfortunately, prior art dispensing shields do little to discourage the practice of gripping the dispensing shield near the opening, putting the onus on the individual worker to be mindful of hand placement when handling a dispensing shield. Thus, there is a need for improved radiation-shielding systems and methods of handling containers containing one or more radioisotopes that facilitate safer, more convenient, and/or more reliable handling of radioactive materials. One aspect of the invention is directed to a radiation-shielding system that is designed to facilitate safe handling of radioactive materials by providing flexibility and convenience in the manner in which radioactive materials are enclosed in protective radiation shielding. The system includes a structure (broadly characterized as a body) having a cavity therein for receiving the radioactive material. Two openings to the cavity are provided in the body, the first of which is sized smaller than the second. The system also includes a pair of bases constructed for releasable attachment to the body generally at the second (larger) opening. One of the bases is shorter in length and/or lighter in weight than the other. Another aspect of the invention is a method of handling a radioisotope in a cavity formed in a radiation-shielding body. There are two openings into the cavity, one of which is sized smaller than the other. The container is inserted into the cavity through the larger opening and a loading base is releasably attached to the body generally at the larger opening to at least partially enclose the container in the cavity. The loading base is constructed to limit escape of radiation from the cavity through the larger of the two openings. The radioisotope is loaded into the container in the cavity through the smaller of the two openings while the loading base is attached to the body. The loading base is detached from the body. A dispensing base is releasably attached to the body generally at the larger of the two openings to at least partially enclose the container in the cavity. The dispensing base is constructed to limit escape of radiation from the cavity through the larger opening. The dispensing base has at least one of a shorter length and a lighter weight than the loading base. At least some of the radioisotope from the container is removed through the first opening to the cavity without removing the container from the cavity and while the dispensing base is attached to the body. Another aspect of the invention is directed to a radiation-shielding assembly for convenient and safe dispensing of a radioactive material. The system includes a radiation-shielding body having a cavity therein for receiving the radioactive material. There is an opening into the cavity through the body. A hand grip is attached to the body and is constructed to facilitate grasping and holding of the body during movement thereof. The hand grip has a grip surface and a guard positioned between the grip surface and the opening into the cavity that may, in one regard, be said to discourage gripping of the assembly near the opening. In another aspect, the invention is directed to a radiation-shielding assembly that provides flexibility to adapt the assembly to enclose containers of different shapes and/or sizes. The assembly has a body at least partially defining a cavity for holding the radioactive material. There is an opening into the cavity through the body. The body is constructed to limit escape of radiation from the cavity through the body. The assembly also includes a base constructed for releasable attachment to the body generally at the opening. The base is constructed to limit escape of radiation from the cavity through the opening when the base is attached to the body in a first orientation relative to the body and when the base is attached to the body in a second different orientation relative to the body. The base is constructed to position a first container at a predetermined location in the cavity when the base is attached to the body in the first orientation and to position a second container at a predetermined location in the cavity when the base is attached to the body in the second orientation. The first and second containers differ from one another in height and/or diameter. Still another aspect of the invention is directed to a method of handling radioactive materials. The method includes placing a first container in a cavity in a radiation-shielding body. There is an opening to the cavity in the body. The first container has a first size and a first shape. A base is releasably attached to the body generally at the opening while the base is in a first orientation relative to the body. The base is configured to position the first container at a predetermined location in the cavity when the base is attached to the body in the first orientation. The base is detached from the body and the first container is removed from the cavity. A second container that has a different size and/or a different shape than the first container is placed in the cavity. The base is releasably attached to the body generally at the opening while the base is in a second orientation relative to the body different than the first orientation. The base is configured to position the second container at a predetermined location in the cavity when the base is attached to the body in the second orientation. Yet another aspect of the invention is directed to a method of using a radiation-shielding assembly, such as one of the radiation-shielding assemblies described herein. With regard to this method, a first component of a radiation-shielding assembly is releasably attached to a second component of the radiation-shielding assembly while the first component is in a first orientation (relative to the second component) to define a cavity of a first size and first shape. Further, the first component can be releasably attached to the second component while the first component is in a second orientation different from the first orientation (relative to the second component) to define a cavity of at least one of a second size and a second shape different from the first size and the first shape, respectively. Various refinements exist of the features noted in relation to the above-mentioned aspects of the present invention. Further features may also be incorporated in the above-mentioned aspects of the present invention as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present invention may be incorporated into any of the aspects of the present invention. Corresponding reference characters indicate corresponding parts throughout the figures. Referring now to the figures, and first to FIGS. 1-6 in particular, one embodiment of a radiation-shielding system of the present invention, generally designated 101, is shown as a rear-loaded elution and dispensing shield combination. The system 101 may enclose a container (e.g., elution and/or dispensing vial) containing a radioisotope (e.g., Technetium-99m) that emits radiation in a radiation-shielded cavity in the system, thereby limiting escape of radiation emitted by the radioisotope from the system. Thus, the system 101 may be used to limit the radiation exposure to handlers of one or more radioisotopes or other radioactive material. For example, parts of the system 101 may be assembled to form an elution shield 103 and other parts of the system may be assembled to form a dispensing shield 105, as discussed in more detail later herein. The radiation-shielding system 101 includes a body 111 having a cavity 113 at least partially defined therein for receiving the radioactive material. The embodiment shown in the figures also includes a cap 115 and a pair of interchangeable bases 117, 119. The body 111, cap 115, and bases 117, 119 may be used to substantially enclose a container C1 (shown in phantom in FIGS. 3 and 4) in the cavity 113. The body 111 may include a circumferential sidewall 121 that at least partially defines the cavity 113. The sidewall 121 of the body 111 shown in the figures is substantially tubular, but the sidewall can have other shapes (e.g., polygonal, tapered, etc.). The sidewall 121 may be adapted to limit escape of radiation from the cavity 113 through the sidewall. For example, in some embodiments, the sidewall 121 may include (e.g., be constructed of) one or more radiation-shielding materials (e.g., lead, tungsten, depleted uranium and/or another material). The radiation-shielding material can be in the form of one or more layers (not shown). Some or all of the radiation-shielding material can be in the form of a substrate impregnated with one or more radiation-shielding materials (e.g., a moldable tungsten-impregnated plastic). Those skilled in the art will know how to design the body 111 to include a sufficient amount of one or more selected radiation-shielding materials in view of the amount and kind of radiation expected to be emitted in the cavity 113 and the applicable tolerance for radiation exposure to limit the amount of radiation that escapes through the sidewall 121 to a desired level. One end of the body 111 may have a first opening 127 to the cavity 113 and a second end of the body may have a second opening 129 to the cavity, as shown in FIGS. 3-6. The second opening 129 may be sized greater than the first opening 127. For example, the first opening 127 may be sized to prevent passage of one or more containers (e.g., containers C1 (FIGS. 3 and 4) and C2 (FIGS. 5 and 6) therethrough while permitting passage of the tip of a needle (not shown) that may be, for example, a needle on a tapping point of a radioisotope generator. As an example, the illustrated body 111 comprises an annular flange 131 extending radially inward from the sidewall 121 near the top of the sidewall. (As used herein the terms “top” and “bottom” are used in reference to the orientation of the system 101 in FIG. 3 but do not require any particular orientation of the system or its component parts). The first opening 127, which in the illustrated embodiment is a substantially circular opening, may be defined by an inner edge of the flange 131. The flange 131 may have a chamfer 133 at the opening 127 to facilitate guiding the tip of a needle toward a pierceable septum (not shown) of a container received in the cavity. The inner surface of the body 139 adjacent the flange 131 may be stepped, tapered, or a combination thereof to help align the top of a container with the first opening 127 as the container is loaded into the cavity 113. The flange 131 may be integrally formed with the sidewall 121 or manufactured separately and secured thereto. The flange 131 may include a radiation-shielding material, as described above, to limit escape of radiation from the cavity. However, the flange 131 can be substantially transparent to radiation without departing from the scope of the invention. The second opening 129 is sized to permit passage of one or more containers (e.g., C1 and C2) therethrough for loading and unloading of the containers into and out of the cavity 113. For example, the second opening 129 may have about the same size, shape, and cross sectional area as the inside of the circumferential sidewall 121. The cap 115 may be constructed for releasable engagement with the body 111 over the first opening 127 thereof. For example, the cap 115 may be constructed for releasable attachment to the body 111 or it may be designed for placement in contact with the body without any connection thereto. The cap 115 may be constructed in many different ways. As one example of a suitable cap construction, the cap 115 shown in FIGS. 3 and 5 comprises a magnetic portion 141 that attracts the body 111 (e.g., the flange 131) when the cap is placed over the end of the body to cover the first opening 127, thereby resisting movement of the cap away from the body. In some embodiments, the body 111 may be constructed of a material that is attracted by the magnetic portion 141 of the cap 115. In other embodiments, the body 111 may comprise a material having a relatively weaker attraction or no attraction to the magnetic portion 141 of the cap, and an attracting element (not shown) made of a material that has a relatively stronger attraction to the magnetic portion (e.g., iron or the like) molded into or otherwise secured to the body to enable the magnetic portion of the cap 115 to attract the body. Further, the cap and/or the body may be equipped with detents, threading snaps and/or friction fitting elements or other fasteners that are operable to releasably attach the cap to the body without the use of magnetism without departing from the scope of the invention. The cap may be removed from the body as shown in FIG. 2 to expose the first opening 127 and permit access to a container in the cavity 113 through the first opening. The cap 115 may be constructed to limit escape of radiation emitted in the cavity 113 through the first opening 127 when the cap is placed on the body 111. For example, the cap 115 may comprise one or more radiation-absorbing materials, as described above, to achieve the desired level of protection against radiation. In order to reduce costs, radiation-absorbing materials may be positioned only at a center portion of the cap (e.g., in registration with the first opening when the cap is engaged with the body) while an annular outer portion surrounding the radiation-absorbing center portion may be made from less expensive and/or lighter-weight non-radiation-absorbing materials, but this is not required for practice of the invention. Referring to FIG. 3, the first base 117 may be constructed for releasable attachment to the body 111 (e.g., as a closure for the second opening 129) to enclose a container C1 in the cavity 113 during a process (e.g., an elution process) in which radioactive material is loaded into the container. Hence, the first base may otherwise be referred to as a “loading base,” although use of that term does not imply that the system is limited to use in elution or other loading processes when the first base is attached to the body. Similarly, the assembly 103 formed by attachment of the loading base 117 to the body, may otherwise be referred to as an “elution shield,” although use of that term does not limit the assembly to use in an elution or other loading process. As seen in FIGS. 3-6, the illustrated loading base 117 comprises an extension element 151 having radiation shields 153, 155 secured at opposite ends thereof. The radiation shields 153, 155 may be permanently attached to the extension element 151, as shown in the figures, or releasably attached to the extension element (e.g., by threaded or other suitable releasable connections). The extension element 151 shown in the figures is a generally tubular structure and may be constructed of one or more relatively inexpensive, lightweight, durable materials, such as high-impact polycarbonate materials (e.g., Lexan®), nylon, and/or the like. The loading base 117, or a portion thereof (e.g., the extension element 151), may be coated with a grip enhancing coating (not shown). For example, the loading base 117 may be coated with a thermoplastic elastomer (e.g., Santoprene®, which is commercially available from Advanced Elastomer Systems, LP of Akron, Ohio) to facilitate manual gripping of the loading base. The extension element can have other shapes (e.g., polygonal, tapered, and the like) without departing from the scope of the invention. Likewise, the extension element can be constructed of other materials without departing from the scope of the invention. The loading base 117 may be constructed for releasable attachment to the body 111 in a first orientation (FIG. 3) to accommodate a first container C1 in the cavity 113 and also constructed for releasable attachment to the body in a second orientation (FIG. 5) to accommodate a second container C2 in the cavity having a different size than the first container C1. For example, the loading base 117 may comprise one or more connectors 159 (e.g., threads, bayonet connection lugs, or the like) that are operable to releasably attach the loading base to the body 111 when the loading base has a first orientation relative to the body and to releasably attach the loading base to the body when the base has a second orientation relative to the body (e.g., an orientation in which the loading base has been rotated about 180 degrees from the first orientation). As shown in FIGS. 3 and 5, one of the radiation shields 153 may be positioned generally at the second opening 129 when the loading base 117 is attached to the body 111 in its first orientation (FIG. 3) and the other radiation shield 155 may be positioned generally at the second opening when the loading base is attached to the body in its second orientation (FIG. 5). Further, the radiation shields 153, 155 may each comprise a closure surface 153a, 155a that is positioned generally at the second opening 129 and faces inward of the cavity 113 when the loading base is attached to the body 111 so the corresponding radiation shield is positioned generally at the second opening. The closure surface 155a for one of the radiation shields 155 may be designed to extend farther into the opening 229 than the closure surface 153a for the other radiation shield 153 so that the size and/or shape of the cavity 113 can be controllably varied by selectively attaching the loading base 117 to the body 111 in either of its first or second orientations. When the loading base 117 of the embodiment shown in the figures is attached to the body 111 in the orientation shown in FIG. 3, the distance D1 between the closure surface 153a and the first opening 127 is greater than the distance D2 between the other closure surface 155a and the first opening when the loading base is attached to the body in the orientation shown in FIG. 5. This may facilitate use of the system 101 with containers C1, C2 having different heights. For instance, by attaching the loading base 117 to the body 111 so a selected one of the radiation shields 153, 155 is positioned generally at the second opening 129, it is possible to position containers having different heights so they are in a predetermined location relative to the first opening (e.g., adjacent the first opening, in contact with or in close proximity to the flange 131, etc.), which may facilitate connection of the containers to a radioisotope generator. Likewise, the loading base 117 may be configured such that in a first orientation of the base the cavity accommodates a first container having a first diameter and in a second orientation the cavity accommodates a second container having a second diameter different than the first diameter. For example, one of the radiation shields 155 of the embodiment shown in FIGS. 3-6 has a sidewall 161 configured to extend into the second opening 229 when the loading base 117 is attached to the body in its second orientation. The inner surface of the sidewall 161 has a reduced cross sectional area relative to the second opening 229. Thus, the closure surface 155a of the radiation shield 155 may be characterized as forming a cup-shaped structure 163 sized to receive the bottom end of the container C2 as shown in FIG. 4. The cup-shaped structure 163 may be adapted to hold the container C2 in a predetermined location within the cavity (e.g., so the bottom of the container is aligned with the first opening 127), which may facilitate piercing of a septum (not shown) on the container by the tip of a needle inserted through the first opening. In contrast, the closure surface 153a of the other radiation shield 153 may be configured as a substantially flat surface that is substantially coextensive with the cross sectional area of the cavity 113. As shown in FIG. 3, the sidewall 121 of the body 111 can be used to position a larger diameter container C1 in a predetermined location in the cavity 113 (e.g., so the bottom of the container is aligned with the first opening 127). In other embodiments, each of the radiation shields could be designed to include a cup-shaped structure (of the same or different diameters) without departing from the scope of the invention. The system can be designed to hold two different containers in the same predetermined position or in different predetermined positions. Although the system shown in the figures is designed so that the smaller diameter container is also the shorter container, the system could also be designed so that the taller container is smaller in diameter without departing from the scope of the invention. Similarly, the system can be adapted to accommodate different sized containers that are identical in height and vary only in diameter, or vice-versa, without departing from the scope of the invention. Moreover, the closure surfaces can be distinct from the radiation shields without departing from the scope of the invention. The loading base 117 may be adapted to limit escape of radiation from the cavity 113 through the second opening 129 when the loading base is attached to the body 111 in its first orientation, in its second orientation, and/or more suitably in both orientations. For example, the radiation shields 153, 155 may comprise one or more radiation-absorbing materials (as described above) so that the first radiation shield 153 limits escape of radiation through the second opening 129 when the loading base 117 is attached to the body 111 in the first orientation and so that the second radiation shield 155 limits escape of radiation through the second opening when the loading base is attached to the body in the second orientation. The radiation shields 153, 155 may be adapted to absorb and/or reflect radiation over an area that is substantially coextensive with the second opening 129. For example, the radiation shields 153, 155 may be configured to have substantially the same cross sectional shape and size as the second opening 129 and have the connectors 159 formed thereon so that the radiation shields can be releasably attached to the body 111 to plug the second opening with radiation-absorbing material. In other embodiments of the invention, however, the radiation shields may comprise radiation-shielding materials positioned to substantially cover the second opening 129 without being received therein. Those skilled in the art will know how to design the loading base 117 to include a sufficient amount of one or more radiation-absorbing materials in appropriate locations to limit escape of radiation through the second opening 129 to a desired level. Referring to FIG. 3, the loading base 117 may be used to increase the overall length of the system 101 relative to the length of the body. For example, the extension element 151 of the loading base 117 may comprise a circumferential sidewall 171 generally corresponding to the circumferential sidewall 121 of the body 111. As those skilled in the art know, some radioisotope generators are designed to work with a shielding assembly having a particular minimum length (e.g., six inches). The loading base 117 may be assembled with a body 111 that would otherwise be too short for a particular radioisotope generator to satisfy the minimum length requirement of that generator. The extension element 151 may be transparent to radiation because other parts of the system 101 (e.g., the radiation shields 153, 155) can achieve the desired level of radiation shielding. Use of a relatively lighter-weight (e.g., non-radiation-absorbing) extension element 151 to provide the required length allows the weight of the elution shield 103 to be lighter and/or less expensive compared to a similar assembly that is constructed of relatively heavier-weight and/or more expensive materials (e.g., radiation-absorbing materials) along the entirety of the minimum length required by the particular radioisotope generator. There may be a void 173 in the loading base 117 for additional weight reduction. Referring to FIGS. 4 and 6, the second base 119 may be constructed for releasable attachment to the body 111 to enclose a container in the cavity 113 thereof during a dispensing process. Hence, the second base 119 may otherwise be referred to as a “dispensing base,” although use of that term does not imply that the system is limited to use in dispensing processes when the second base is attached to the body. Similarly, the assembly 105 formed by attachment of the dispensing base 119 to the body 111, may otherwise be referred to as a “dispensing shield,” although use of that term does not limit the assembly to use in an dispensing or other process. The dispensing base 119 shown in the figures, for example, comprises a single radiation shield 181 that acts as a closure for the second opening 129 of the body 111 when the dispensing base is attached to the body. The dispensing base 119 is constructed for selective releasable attachment to the body 111 in a first orientation in which the dispensing shield 105 accommodates a first container C1 (FIG. 4) and also constructed for releasable attachment to the body in a second orientation in which the dispensing shield 105 accommodates a second container C2 (FIG. 6) that has a different size and/or shape than the first container. Referring to FIGS. 4 and 6, for example, the dispensing base 119 may comprise connectors 183 (e.g., threads, bayonet connection lugs, or the like) that are operable to releasably attach the dispensing base to the body 111 when the dispensing base is in a first orientation relative to the body (FIG. 4) and to releasably attach the dispensing base to the body when the dispensing base is in a second orientation relative to the body (FIG. 6) that is different from (e.g., rotated about 180 degrees) from the first orientation. Further, when the dispensing base 119 is attached to the body 111 in the first orientation, a first closure surface 185 may be positioned generally at the second opening 129 and face inward of the cavity 113. When the dispensing base is attached to the body in the second orientation, a second closure surface 187 may be positioned generally at the second opening and face inward of the cavity. The closure surfaces 185, 187 of the dispensing base 119 shown in the figures are structurally analogous to the corresponding closure surfaces 153a, 155a of the loading base 117 so that the dispensing base can be adapted to accommodate different containers in the same way as the loading base. Thus, the closure surfaces 185, 187 may be configured to extend different distances into the second opening 129, thereby allowing selective variation of the distance between the respective closure surface 185, 187 and the first opening 127 in the same manner described for the loading base 117. A sidewall 189 extends above and around the circumference of one of the closure surfaces 187, thereby forming a cup-shaped structure 195 analogous to the cup-shaped structure 163 described for the loading base 117. The cup-shaped structure 195 may be used to position a container C2 at a predetermined location in the cavity 113 (e.g., so the bottom of the container is aligned with the first opening) in the same manner described for the loading base. Although the closure surfaces 153a, 155a, 185, 187 of the embodiment shown in the figures are similar in size and shape, it is also possible that the closure surfaces of the dispensing base may differ in size and/or shape from the corresponding closure surfaces of the loading base without departing from the scope of the invention. The dispensing base 119 may be substantially shorter and lighter than the loading base 117. For instance, the dispensing base 119 may lack structure that is analogous to the extension element 151 of the loading base 117 because the need to satisfy the minimum length requirement of a radioisotope generator may only apply when the radioisotope generator is being used. Omission of an extension element makes the dispensing base 119 shorter and lighter. Likewise, the use of the single radiation shield 181 in the dispensing base 119 also reduces the length and weight of the dispensing base relative to the loading base 117, which has two radiation shields 153, 155. The combined center of gravity 191 of the dispensing shield 105 (FIG. 4) is closer to the first opening 127 than the combined center of gravity 193 of the elution shield 103 (FIG. 5). This may tend to make the dispensing shield 105 more stable when placed upside down on a flat surface (as shown in FIGS. 4 and 6) than the elution shield 103 would be if it were placed upside down on the same surface. The radiation shielding system 101 may be used to provide radiation shielding for containers used to hold a radioisotope. For example, a container C1 (e.g., an evacuated elution vial) can be loaded into the cavity 113 through the second opening 129 in the body 111. After the container C1 is in the cavity 113, the loading base 117 may be attached to the body 111 as shown in FIG. 3 to form the elution shield 103 and substantially enclose the container in the cavity. The closure surface 153a and sidewall 121 of the body 111 position the container in a predetermined location in the cavity, which in the illustrated embodiment is approximately in contact with the flange 131 and in alignment with the first opening 127. The cap 115 may be removed (if present) to expose the first opening 127. Then, the container C1 may be connected to a radioisotope generator through the now exposed first opening 127 (e.g., by inserting the tip of a needle associated with a tapping point on the radioisotope generator into the container through the first opening). The container C1 is at least partially filled with an eluate comprising a radioisotope (e.g., Technetium-99m) produced by the generator. When a desired amount of eluate has been loaded into the container C1, the container may be disconnected from the radioisotope generator and the cap 115 replaced over the first opening to limit escape of radiation through the first opening. The container C1 may be transported in the cavity 113 to another location where the eluate is analyzed (e.g., where its activity is calibrated and a breakthrough test is performed). The loading base 117 may be detached from the body 111 to allow the container C1 to be removed from the cavity 113 through the second opening 129 for the analysis. After the eluate has been analyzed, the container C1 can be reloaded in the cavity 113 through the second opening 129. The dispensing base 119 may be attached to the body 111, as shown in FIG. 4, in place of the loading base 117 to form the dispensing shield 105 and re-enclose the container C1 in the cavity 113. The dispensing shield 105 may be inverted and placed first opening 127 down on a work surface 197 (e.g., a radiation-absorbing coaster). When a worker (e.g., a radiopharmacist) is ready to dispense some of the eluate from the container C1 to another container (e.g., syringe), he or she may lift the body 111 off the work surface 197, thereby exposing the first opening 127. The worker may dispense some or all of the eluate from the container C1 through the now exposed first opening 127. For example, the worker may pierce a septum (not shown) of the container C1 by inserting the tip of a needle attached to a syringe through the first opening 127 and drawing some or all of the eluate out of the container using the syringe. When a desired amount of the eluate has been dispensed from the container C1, the dispensing shield 105 may be replaced on the work surface 197 until more of the eluate is needed. When the container C1 is emptied of eluate or the eluate is no longer desired, the dispensing base 119 can be detached from the body 111 and the container C1 removed from the cavity 113 through the second opening 129. The second smaller container C2 may then be loaded into the cavity 113 through the second opening 129. The loading base 117 may be attached to the body as shown in FIG. 5 so the closure surface 155a and sidewall 161 position the container in a predetermined location, which in the illustrated embodiment is in contact with the flange 131 and in alignment with the first opening 127. Then the elution process can be repeated as described above, resulting in a desired amount of eluate being loaded into the container C2. After the elution process the container C2 may be transported in the cavity 113 to another location as described previously for the first container C1. The loading base 117 may be detached from the body 111 to allow the container C2 to be removed from the cavity 113 through the second opening 129 for the analysis. After the analysis is complete, the container C2 may be replaced in the cavity 113 through the second opening 129. Then the dispensing base 119 may be attached to the body, as shown in FIG. 6, in place of the loading base 117. The eluate may be dispensed from the container C2 in substantially the same manner described for the first container C1. Referring now to FIGS. 7-12E, another embodiment of a radiation-shielding system of the present invention, generally designated 201, is shown as a rear-loaded elution and dispensing shield combination. Like the radiation-shielding system 101 described above, the system 201 may enclose a container (e.g., elution and/or dispensing vial) containing a radioisotope (e.g., Technetium-99m) that emits radiation in a radiation-shielded cavity, thereby limiting escape of radiation emitted by the radioisotope from the system. Thus, the system may be used to limit the radiation exposure to handlers of one or more radioisotopes or other radioactive material. The radiation-shielding system 201 has a body 211 having a cavity 213 at least partially defined therein for receiving the radioactive material. The radiation-shielding system shown in FIG. 7 also includes a cap 215 and a pair of interchangeable bases 217, 219. The body 211, cap 215, and bases 217, 219 may be used to substantially enclose a container C1 (shown in phantom in FIG. 9) in the cavity 213, as is described in more detail below. The body 211 and cap 215 of the system shown in the figures may be substantially analogous to the body 111 and cap 115 of the system 101 shown in FIGS. 1-6. For example, the body 211 may have first and second openings 227, 229 that are analogous to the first and second openings 127, 129 of the body 111 shown in FIGS. 3-6. The system 201 shown in the figures includes a loading base 217 constructed for releasable attachment to the body 211 generally at the second opening 229 to form an elution shield 203. The loading base 217 shown in the figures (e.g., FIG. 9), for example, comprises connectors 259 (e.g., threads, bayonet connection lugs, or the like) that are operable to releasably attach the loading base to the body 211. The loading base 217 may be operable to limit escape of radiation from the cavity 213 through the second opening 229 when attached to the body 211. With reference to FIG. 9, the loading base 217 may comprise a tubular structure 251 having a radiation shield 253, which may comprises one or more radiation-absorbing materials as described previously, secured at one end so that the radiation shield is positioned generally at the second opening 229 when the loading base 217 is attached to the body 211. The other end of the tubular structure 251 may be closed (as shown in FIG. 9) or open (not shown). The tubular structure 251 may be constructed of a lightweight material (e.g., high-impact plastic) that is substantially transparent to radiation. The loading base may have a void 273 therein to reduce weight of the elution shield 203. The loading base 217, or a portion thereof (e.g., the tubular structure 251), may be coated with a grip enhancing coating (not shown) to facilitate manual gripping of the loading base. For instance, a thermoplastic elastomer (e.g., Santoprene®) is one example of a suitable grip enhancing coating material. The loading base 217 may be operable in combination with the body 211 to provide an elution shield 203 having enough length to satisfy a minimum length requirement for a particular radioisotope generator, in the same manner described above in connection with the loading base 117 of system 101. It will be understood by those skilled in the art that the design of the loading base 217 can be varied substantially without departing from the scope of the invention. Although the system 201 shown in FIG. 7 has a different loading base than was described in connection with system 101, it is understood that the system 201 can be modified to use the same loading base 117 as the system 101 described previously without departing from the scope of the invention. Likewise, the system 201 can be modified to use a loading base having virtually any size and shape without departing from the scope of the invention. Referring now to FIG. 10, the system 201 further comprises an ergonomic dispensing base 219 that is constructed for releasable attachment to the body 211 generally at the second opening 229 to form a dispensing shield 205. For example, the dispensing base 219 may generally be constructed in the form of a sheath adapted to receive at least the bottom portion of the body 211 therein, in which case the body 211 is partially sheathed by the dispensing base when the base 219 and body 211 are assembled to form the dispensing shield 205. The dispensing base 219 may have a closed end 265 and may comprise any suitable connectors (e.g., threads, bayonet connection lugs, or the like) for releasably attaching the dispensing base to the body 211. For example, in the embodiment shown in the figures, the dispensing base 219 comprises bayonet connection lugs 283 for releasably attaching the dispensing base to the body 211 using a bayonet connection (e.g., the same bayonet connection used to releasably attach the loading base 217 to the body 211). The dispensing base 219 may be adapted to limit escape of radiation from the cavity 213 through the second opening 229 when it is attached to the body 211. For example, the dispensing base 219 may comprise one or more radiation-absorbing materials, as described above. Again, those skilled in the art will know how to provide a sufficient amount of radiation-absorbing materials in the dispensing base 219 to achieve a desired level of protection against radiation exposure. The dispensing base 219 may be designed with a concentration of radiation-absorbing materials positioned generally at the second opening 229 (not shown) when the dispensing base is attached to the body. In some embodiments, the entire dispensing base may be constructed of radiation-shielding materials (e.g., metal or tungsten-impregnated plastic). The dispensing base 219 comprises a hand grip 275 that is adapted to fit comfortably in the palm of a person's hand. The hand grip 275 may comprise one or more types of grip enhancing features (e.g., grooves 275a (FIG. 12A), raised bumps 275b (FIG. 12B), finger indentations 275c (FIG. 12C), flats 275d (FIG. 12D), raised ridges 275e (FIG. 12E), combinations thereof, and the like) to improve the ability of a person to grip the dispensing base 219 by the hand grip. A grip enhancing coating (not shown) may be applied to the dispensing base 219, or a portion thereof (e.g., the hand grip 275), to facilitate manual gripping of the dispensing base. A thermoplastic elastomer (e.g., Santoprene®) is one example of a suitable grip enhancing coating material. A knob 277 may be formed at one end of the hand grip 275 (e.g., at the closed end 265 of the dispensing base 219) to reduce the risk that the dispensing base will accidentally slip out of a person's grasp. The dispensing base 219 may comprise a finger guard 279 positioned between the hand grip 275 and the first opening 227 of the body 211 when the dispensing base is attached to the body to discourage workers from gripping the dispensing base too close to the first opening and thereby being exposed to unnecessarily high radiation. As best shown in FIG. 9, for example, the finger guard 279 may comprise an annular flange 293 extending at least in part transversely outward of the hand grip 275 surface. The outer diameter of the finger guard 279 may be sized to make it more convenient to grip the dispensing base 219 by the hand grip 275 than at the finger guard or any location between the finger guard and the first opening 227. The distance between the finger guard 279 and the first opening 227 can be increased as needed to provide a desired level of protection against exposure of workers' hands to radiation escaping through the first opening. The finger guard 279 may also comprise one or more radiation-shielding materials to shield the hand of a person handling the dispensing shield 205 from radiation escaping through the first opening 227. Further, the finger guard 279 may be constructed of a material that is substantially impervious to penetration by a needle to protect a worker from accidental injury while inserting a needle into the dispensing shield. Although FIG. 11 illustrates a user gripping the dispensing base 219 by wrapping a hand at least partially around the circumference of the base, it is further contemplated that the benefits of the finger guard 279 also inure to a user who grips the dispensing base by its closed end 265 (e.g. by wrapping a hand at least partially over the end of the base 219 so the knob 277 is in the palm of the hand or by wrapping a hand at least partially around the circumference of the knob). Further, it may be desirable in some cases for a user grip the dispensing base 219 by the closed end 265 thereof (e.g., by the knob 277). For example, this may be a desirable practice from the standpoint of increasing the distance between the user's hand and the first opening 227 (e.g., to further reduce exposure of the user's hand to radiation). If that is the case, it is contemplated that the finger guard may be moved closer to the closed end of the dispensing base (and therefore farther from the first opening). For example, the finger guard may be closer to the end of the dispensing base than it is to the first opening 227. Moreover, if desired, the distance between the finger guard and the closed end of the dispensing base may be short enough (e.g., so that the finger guard is adjacent the closed end) that there is insufficient space between the finger guard and the closed end of the dispensing base for a user to wrap a hand around the side of the dispensing base between the finger guard and the end of the base to thereby encourage a user to grip the dispensing base at the closed end thereof. The operation of the radiation-shielding system 201 is similar in many ways to the operation of the radiation system 101 described above. A container C1 (e.g., an evacuated elution vial) may be loaded into the cavity 213 through the second opening 229. Then the loading base 217 may be releasably attached to the body 211 to enclose the container C1 within the elution shield 203. If present at this time, the cap 215 may be removed from the body 211 to permit the container C1 to be connected to a radioisotope generator through the now exposed first opening 227, as described above. When a desired amount of radioactive eluate has been loaded into the container C1, the container may be disconnected from the radioisotope generator. The cap 215 may be replaced over the first opening 227 to limit escape of radiation through the first opening while the container C1 is carried to a location where the eluate can be analyzed. The loading base 217 may be detached from the body 211 and the container C1 removed from the cavity 213 through the second opening 229 to analyze the eluate (e.g., in a calibration system). When the analysis of the eluate is complete, the container C1 may be replaced in the cavity 213 through the second opening 229. The dispensing base 219 may be releasably attached to the body 211 to enclose the container C1 in the dispensing shield 205. The cap 215 may be removed to permit initial access to the first opening 227 for the dispensing process. Thereafter, the body 211 may be placed upside down on a work surface (e.g., a radiation-shielding coaster 197 operable to limit escape of radiation through the first opening 227) until it is time to dispense some or all of the remaining eluate to another container (e.g., syringe). A worker (e.g., a radiopharmacist) may grab the dispensing shield 205 by the hand grip 275 of the dispensing base 219 with one hand and lift the body 211 off the work surface 197 to access the container C1 through the first opening 227. For example, the tip of a needle attached to a syringe may be inserted into the cavity 213 through the first opening 227 to pierce the septum of the container C1 and draw eluate out of the container into the syringe. If the worker accidentally misses the first opening 227, the guard 279 may deflect the needle away from the hand that is holding the dispensing shield 205, thereby protecting the worker from injury. The ergonomic hand grip 275 makes it easy to hold the dispensing shield 205. Some people may prefer to grab the dispensing base 217 by palming the knob 277 in their hand. Others may prefer to wrap their fingers around the hand grip 275, in which case any grip enhancements 275a, 275b, 275c, 275d, 275e of the grip can make their grip more secure. The finger guard 279 discourages people from placing their hands too close to the first opening 227 when lifting the body 211 off the work surface 197, thereby preventing unnecessary exposure to radiation escaping through the first opening 227. Further, in embodiments of the system 201 in which the finger guard 279 comprises radiation-absorbing materials, the finger guard may shield the person's hand from a portion of the radiation escaping through the first opening 227, thereby further reducing exposure to radiation. When a desired amount of the eluate has been transferred from the container C1 in the dispensing shield 205 to another container, the person may replace the body 211 upside down on the work surface 197 until it is time to transfer eluate to another at which time the dispensing process may be repeated. When the container C1 is empty or its contents are no longer desired, the dispensing base 219 may be detached from the body 211 and the container taken out of the cavity 213 through the second opening 229. Then the entire process may be repeated with another container. Although various assembly components of the radiation-shielding system described above have generally cylindrical shapes, the geometric shapes of one or more of the various components may be varied without departing from the scope of the invention. Furthermore, if desired, a loading base could be designed to provide more than two options for varying the amount of space in the cavity for greater flexibility in adapting the system for use with various different sized containers without departing from the scope of the invention. In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. When introducing elements of the present invention or various embodiments thereof, the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Moreover, the use of “top” and “bottom” and variations of these terms is made for convenience, but does not require any particular orientation of the components. As various changes could be made in the above systems and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying figures shall be interpreted as illustrative and not in a limiting sense. |
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description | This application is a continuation application of non-provisional patent application Ser. No. 13/451,102, entitled RADIATION DETECTOR SYSTEM AND METHOD, filed Apr. 19, 2012. This application claims benefit under 35 U.S.C. §120 and incorporates by reference U.S. Utility Patent Application for RADIATION DETECTOR SYSTEM AND METHOD by inventors Adam Gregory Bogorodzki, Janusz Skierski, Hieronim Stanislaw Teresinski, and George G. Y. Yan, filed electronically with the USPTO on Apr. 19, 2012, with Ser. No. 13/451,102, EFS ID 12583812, confirmation number 1406. All of the material in this patent application is subject to copyright protection under the copyright laws of the United States and of other countries. As of the first effective filing date of the present application, this material is protected as unpublished material. However, permission to copy this material is hereby granted to the extent that the copyright owner has no objection to the facsimile reproduction by anyone of the patent documentation or patent disclosure, as it appears in the United States Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. Not Applicable Not Applicable The present invention generally relates to systems and methods for the detection of radiation, more particularly, but not by way of limitation, to the use of these devices to detect alpha, beta, and gamma radiation. While not limitive of the invention teachings, the present invention may in some circumstances be advantageously applied to categories including U.S. Patent Classification 250/367. The current detection technologies for ionizing radiation in contamination monitoring are gas flow and thin plastic scintillation. The present invention proposes a radiation detector incorporating an integrated radiation detection methodology that provides a compact and sensitive radiation detector for a variety of system applications. Within the prior art of radiation detectors as applied to whole body radiation contamination monitors, conventional prior art systems typically utilize gas flow detectors or thin plastic scintillation detectors or combinations of these two as generally illustrated in FIG. 1 (0100). This diagram indicates that in the context of a whole body radiation contamination detector/monitor/scanner typically is configured to detect radiation on a human subject (0101) via means of a number of gas flow radiation detectors (0102, 0103, 0104) in conjunction with a thin plastic scintillation radiation detector (0105). Within this context, integrated scintillation detectors are not used in contamination monitoring, other than hand and foot monitors. Existing solutions for beta/gamma detection imposes significant physical separation between the beta and gamma detectors (gamma detector further away from monitored object), resulting in: Gamma signal attenuated by the beta detector; and Reduced gamma signal due to R-squared law distance from the monitored object. Exemplary prior art covering multi-band radiation detection includes the following: U.S. Pat. No. 7,683,334 for SIMULTANEOUS BETA AND GAMMA SPECTROSCOPY; U.S. Pat. No. 7,388,206 for PULSE SHAPE DISCRIMINATION METHOD AND APPARATUS FOR HIGH-SENSITIVITY RADIOISOTOPE IDENTIFICATION WITH AN INTEGRATED NEUTRON-GAMMA RADIATION DETECTOR; U.S. Pat. No. 5,514,870 for FAST CSI-PHOSWICH DETECTOR; and U.S. Pat. No. 5,399,869 for PHOSWICH DETECTORS HAVING OPTICAL FILTER FOR CONTROLLING PULSE HEIGHT AND RISE TIME OF OUTPUT FROM SCINTILLATOR. This prior art does not teach any methodology by which multi-band radiation detectors may be economically fabricated to address a wide variety of system applications, including but not limited to whole body radiation contamination detectors/monitors/scanners. While the use of multi-detector whole body radiation contamination detectors/monitors/scanners has been field-proven for many years, they have certain limitations. The prior art as detailed above suffers from the following deficiencies: Gas Flow Detector Limitations Applicable for alpha and beta radiation only. Use of gas adds inconvenience and operational cost. Has some negative environmental impact by releasing methane or CO2 into the atmosphere. Available gamma option suffers from physical separation between monitored body and gamma detectors that are located behind gas detectors resulting in reduced gamma detection efficiency.Thin Plastic Scintillation Detector Limitations Practical only for beta or beta/alpha detection without discrimination. Available gamma option suffers from physical separation between monitored body and gamma detectors that are located behind gas detectors, thus reducing gamma detection efficiency. More compact detectors, with increased sensitivity to alpha, beta, and gamma ionizing radiation would improve the performance of whole body contamination monitors. Additional possible applications for a compact radiation detector are for laundry radiation monitors and tool & articles radiation monitors, where cost and smaller physical space requirements are important considerations. However, the prior art does not teach how such compact and integrated detectors can be fabricated, despite the fact that integrated scintillation detectors have been studied for some spectroscopy applications. While some of the prior art may teach some solutions to several of these problems, the core requirement for multiple radiation detectors to detect a multiplicity of radiation types in these prior art systems has not been addressed by the prior art. Accordingly, the objectives of the present invention are (among others) to circumvent the deficiencies in the prior art and affect the following objectives: (1) Provide for a radiation detector system and method that integrates scintillation detectors to detect a multiplicity of radiation types. (2) Provide for a radiation detector system and method that improves detector efficiency and sensitivity by integrating a multiplicity of detectors in a compact physical structure. (3) Provide for a radiation detector system and method that reduces the cost of whole body radiation contamination detectors/monitors/scanners. (4) Provide for a radiation detector system and method that increases radiation signal detection efficiency. (5) Provide for a radiation detector system and method that reduces crosstalk between alpha, beta, and gamma radiation detection signals. (6) Provide for a radiation detector system and method that minimizes electronic noise between the detected radiation signals. (7) Provide for a radiation detector system and method to discriminate different radiation types with a single integrated detector and photomultiplier tube (PMT). (8) Provide for a radiation detector system and method that permits whole body radiation contamination systems to be significantly cost reduced. (9) Provide for a radiation detector system and method that increases beta sensitivity by using an anti-coincident discrimination technique to reduce gamma background in the beta channel. While these objectives should not be understood to limit the teachings of the present invention, in general these objectives are achieved in part or in whole by the disclosed invention that is discussed in the following sections. One skilled in the art will no doubt be able to select aspects of the present invention as disclosed to affect any combination of the objectives described above. The present invention system generally comprises a photomultiplier tube in conjunction with radiation scintillation materials to detect alpha, beta, and gamma radiation. The photomultiplier tube output is shape amplified before being fed through discriminators to detect the individual radiation types. The discriminator outputs are then fed to an anti-coincidence analysis module that determines whether individual alpha, beta, and gamma pulses are valid and should be counted by corresponding alpha, beta, and gamma pulse radiation counters. The present invention system may incorporate any selected combination of the above characteristics to achieve the overall design goals consistent with the objectives detailed above. The system may be augmented by a radiation detection method to affect alpha/beta/gamma radiation detection/monitoring/scanning in a variety of contexts. The method may be implemented in a variety of applications, including but not limited to whole body radiation contamination detectors, laundry radiation scanners, tool/article radiation detectors, and the like. Integration of this and other preferred exemplary embodiment methods in conjunction with a variety of preferred exemplary embodiment systems described herein is anticipated by the overall scope of the present invention. While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detailed preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiment illustrated. The numerous innovative teachings of the present application will be described with particular reference to the presently preferred embodiment, wherein these innovative teachings are advantageously applied to the particular problems of a RADIATION DETECTOR SYSTEM AND METHOD. However, it should be understood that this embodiment is only one example of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others. The present invention may be utilized as a radiation detector in a wide variety of contexts which may include radiation monitoring and/or scanning applications. Thus, the term “detector” or “detection” should be given its broadest possible meaning to include, among other things, radiation monitoring and/or radiation scanning. The present invention may be utilized as a radiation detector in a wide variety of contexts wherein more than one band of radiation must be detected. While the disclosed embodiment is capable of simultaneously detecting alpha, beta, and gamma radiation, the invention should not be limited to simultaneous detection of these three radiation groups. For example, the present invention specifically anticipates that embodiments may be constructed to detect alpha/beta, beta/gamma, or alpha/beta/gamma radiations. These embodiments may be specifically tailored to detect these combinations or in some configurations be configurable to detect these radiation band combinations in response to some form of data entry, possibly via a computer system running software read from a computer readable medium. The present invention may incorporate a variety of scintillation materials in a variety of mechanical configurations in order to affect the detection of radiation in a number of radiation types. Within this document the term “array stack” may be used to describe the configuration of the scintillation material, but it should not be construed a limiting the scope of the invention. “Array Stack” should be given its broadest possible meaning when applied to multi-layer scintillation materials used to detect radiation when used in conjunction with a photomultiplier tube or tubes. The present invention makes no limitation on the ordering of scintillation plates in the radiation detector. The present invention as depicted herein may include specified “nominal” values in some preferred exemplary embodiments. These values should not be deemed as limitive of the invention scope and are merely typical values. The present invention anticipates a wide variety of scintillation materials may be used in the construction of the ISD described herein. Within this context, many preferred system embodiments will utilize an alpha scintillation plate comprising a scintillation material having a medium time constant, a beta scintillation plate comprising a scintillation material having a short time constant, and a gamma scintillation plate comprising a scintillation material having a long time constant. Within this context, the terms “short”, “medium”, and “long” are relative in nature only and may vary widely based on application. Thus, these terms are not limitive of the scope of the invention. While the present invention is applicable to a wide variety of applications, several are preferred. Of these, a whole body radiation detector/monitor/scanner application is generally illustrated in FIG. 2 (0200) wherein the human subject (0201) is scanned using several integrated radiation scanners (0202, 0203, 0204) as will be discussed herein. The present invention at its broadest level may be described a depicted by the system block diagram in FIG. 3 (0300). Generally speaking, the invention system utilizes a scintillation array stack (0301) as the radiation detection mechanism. This array stack (0301) feeds a photomultiplier tube (0302) whose output is converted by shaping amplifiers (0303) for use by discriminators (0304) to select various radiation types based on the output of the shaping amplifiers (0303). The discriminator (0304) output is then fed into an anti-coincidence module that ensures that only radiation of a proper band is triggered for counting. Finally, the anti-coincidence module (0305) output is fed into radiation counters (0306) that count radiation event within each radiation band. This system block diagram does not limit the number of any element depicted in FIG. 3 (0300) and may be applied to any number of radiation band combinations, including but not limited to alpha/beta, beta/gamma, or alpha/beta/gamma radiations as indicated above. An exemplary system construction for a preferred embodiment of the present invention is generally illustrated in FIG. 4 (0400), wherein the radiation detector comprises an integrated body structure (0401) with associated photomultiplier tube (PMT) wiring harness/bulkhead (0402). This structure (0400) may be better understood by inspecting the assembly view of FIG. 5 (0500), wherein the detector case (0501) and photomultiplier tube (0502) are integrated with a beta particle shield (0503) and a number of scintillation plates such as a beta scintillator (0504) alpha scintillator (0505) and gamma scintillator incorporated into the detector case (0501) that are responsive to radiation externally impinging the overall structure (0500). Within this context, the alpha particle detector (0505) may comprise a thin foil covered with alpha sensitive material (such as ZnS), optically bonded to a foil covered with beta sensitive material (0504). To prevent high energy beta radiation from impinging on the gamma sensitive substrate enclosure (0501) (typically PVT) a beta blocker (0503) can be inserted between the gamma scintillator enclosure (0501) and the beta scintillator (0504). A photomultiplier tube (PMT) (0502) is inserted within the plastic substrate enclosure (0501), thus significantly increasing the detection of radiation as compared to the configurations detailed in the prior art. The scintillation materials for detecting alpha, beta and gamma radiation are chosen so that their time constants are medium, short, and long, respectively. The layers (0503, 0504, 0505) and substrate (0501) are encapsulated in light-tight wrapping with only the PMT electrical leads exposed (0402) for connection to a preamplifier or other electronics as a single unit. This entire assembly, including one PMT (0502) may be termed an Integrated Scintillation Detector (ISD) and assembled in a variety of configurations, one preferred embodiment as indicated in FIG. 4 (0400). This integrated construction methodology results in significant cost savings, since only one PMT is utilized to detect all alpha, beta, and gamma radiation. The operation of an exemplary radiation detection electronics portion of the system can best be described by the system block diagram of FIG. 6 (0600). While FIG. 6 (0600) illustrates a general block diagram of the signal conditioning and anti-coincidence circuit associated with one (ISD), it should be noted that a multiplicity of ISDs may be deployed for typical system applications, such as the whole body radiation detection/monitoring/scanning systems. A disclosed method is detailed herein to identify the pulses coming from the alpha, beta, and gamma scintillators through a single PMT. Key to this disclosed method is a scheme to evaluate the decay time constants of the pulse from the PMT and decide what sort of radiation is received. The electrical waveform is typically choppy and noisy due to the physical nature of the alpha and beta radiation and scintillator response. The objectives of the signal conditioning and anti-coincidence circuit are: increase signal detection efficiency; reduce crosstalk between the alpha, beta, and gamma signals; and minimize electronic noise. Referring to FIG. 6 (0600), within one preferred exemplary embodiment of the invention there are three main sub-functions in this methodology: analog signal processing, digital signal processing, and anti-coincidence. Analog Signal Processing The PMT assembly (0601) may optionally contain a preamplifier (0602) that amplifies the signal from PMT with an optimal gain of approximately 5. This optional preamplifier (0602) substantially increases noise immunity. The optionally amplified PMT signal is first processed by a shaping amplifier (0603) comprising a series of DC-coupled wide bandwidth amplifiers and filters. Classic LC filters are preferred because the operating frequencies are generally in MHz range. The signal then goes to the comparators that process beta pulses (0604). Other pulses are present at this stage as well (see the digital processing section below). The second stage shaping amplifier (0605) optimally consists of a unity gain buffer followed by a low pass 10 MHz, 3-pole filter. The filter typically reduces amplification in pass band by a factor of 2 due to impedance matching. The signal is then inspected by comparators that process alpha pulses (0606). Beta pulses are assumed to be already filtered out at this point. The third stage shaping amplifier (0607) optimally has high gain of approximately 100 and it is followed by a low pass, 3 pole, 3 MHz filter. The output goes to comparators that process gamma pulses (0608). While many methodologies are possible to implement the discriminator modules (0604, 0606, 0608) generally illustrated in FIG. 6 (0600), one preferred embodiment of this functionality is generally illustrated in FIG. 7 (0700). The discriminator modules (0604, 0606, 0608) measure the pulse amplitude and length in the beta, alpha, and gamma channels respectively. Each discriminator module has a number of comparators (0711, 0712) with thresholds set on the logarithmic scale (0713). The number of comparators (0711, 0712) and threshold levels (0713) are chosen to cover the range of amplitudes of alpha, beta and gamma pulses. The digital processing starts when the selected low level comparator is triggered in any channel (0720) and ends when all comparators in all the channels become inactive (0720). The length of the pulse in each channel is then measured (0731, 0732) for the duration of time when the selected upper level comparator is activated (0741, 0742). The resulting time is then assessed whether it fits in a bracket of valid pulse lengths for the channel. If it does, the pulse in that channel is considered valid, otherwise it is not valid. As generally illustrated in FIG. 6 (0600), the anti-coincidence module (0609) makes a determination whether the resulting pulse is alpha, beta, or gamma. It works according to the following logic. If alpha pulse is valid, then the resulting pulse is alpha and alpha counter (0611) is advanced, else if gamma pulse is valid, then the resulting pulse is gamma and gamma counter (0612) is advanced, else if beta pulse is valid, then the resulting pulse is beta and beta counter (0610) is advanced, else the pulse is rejected and no counter is advanced. This decision logic is generically illustrated in FIG. 8 (0800), wherein the depicted truth table can be utilized to implement this functionality both within the digital and analog domains. Thus, while the anti-coincidence analysis module is thought to be optimally implemented using digital logic, the present invention anticipates that this functionally could also be implemented within the analog domain. The avoidance of hard logic “0” and “1” values in this truth table anticipates the use of analog decision making techniques that incorporate logic levels with more than two stable states such as neural nets and the like. A preferred exemplary embodiment of the present invention as applied to alpha-beta radiation detection is generally illustrated in the system block diagram of FIG. 9 (0900). In this configuration, the radiation detector (0901) (typically an ISD incorporating scintillation plate stack and photomultiplier tube with optional embedded preamplifier) generates output that is amplified by an alpha/beta amplifier (0902) and compared using beta pulse amplitude comparators (0903). Additionally, the output of the alpha/beta amplifier (0902) is alpha filtered (0904) and used as input to alpha pulse amplitude comparators (0905). Control logic (0906) (typically in the form of a microprocessor or microcontroller) takes the comparator outputs (0903, 0905) and performs pulse width discrimination and other analyses to determine what type of radiation pulse has been detected and in what quantity. This system may also include digital controls to affect gain modulation of one or more amplifiers in the system. Ancillary support circuitry may typically include a high voltage power supply control and test circuitry (0907), high voltage power supply (0908), oscillator (0909), voltage regulator (0910), serial interface (0911), communications connector interface (0912), and/or in-circuit programming provisions (0913). One skilled in the art will recognize that while the ancillary support circuits detailed herein are typical of a practical system configuration, they may be augmented or modified widely based on the particular application context. A preferred exemplary embodiment of the present invention as applied to beta-gamma radiation detection is generally illustrated in the system block diagram of FIG. 10 (1000). In this configuration, the radiation detector (1001) (typically an ISD incorporating scintillation plate stack and photomultiplier tube with optional embedded preamplifier) generates output that is amplified by a beta/gamma amplifier (1002) and compared using beta pulse amplitude comparators (1003). Additionally, the output of the beta/gamma amplifier (1002) is fed to a gamma amplifier (1004) and used as input to gamma pulse amplitude comparators (1005). Control logic (1006) (typically in the form of a microprocessor or microcontroller) takes the comparator outputs (1003, 1005) and performs pulse width discrimination and other analyses to determine what type of radiation pulse has been detected and in what quantity. This system may also include digital controls to affect gain modulation of one or more amplifiers in the system. Ancillary support circuitry may typically include a high voltage power supply control and test circuitry (1007), high voltage power supply (1008), oscillator (1009), voltage regulator (1010), serial interface (1011), communications connector interface (1012), and/or in-circuit programming provisions (1013). One skilled in the art will recognize that while the ancillary support circuits detailed herein are typical of a practical system configuration, they may be augmented or modified widely based on the particular application context. An exemplary photomultiplier tube configuration useful in some preferred embodiments of the present invention is generally illustrated in FIG. 11 (1100). In this context the photomultiplier tube (1101) is powered by a high voltage power supply in conjunction with a resistive divider. Output from the photomultiplier tube (1101) may be optionally amplified before being used as input for other components within the overall radiation detection system. Within this context, some preferred embodiments utilize a preamplifier (1102) proximal to the photomultiplier tube (1101) to improve noise immunity and obtain optimal detector sensitivity. While many preamplifiers may be suitable for this application, the use of a model AD8099 Ultra-Low Distortion High Speed Op Amp from Analog Devices, Inc. is preferred in many embodiments. The present invention may in some preferred embodiments utilize a variety of amplifier configurations to process the radiation pulse signatures obtained from the radiation detector (as typically illustrated in FIG. 11 (1100)). To this end, an exemplary alpha/beta amplifier (1201) and gamma amplifier (1202) configuration are generally illustrated in FIG. 12 (1200). The use of a model AD8099 Ultra-Low Distortion High Speed Op Amp from Analog Devices, Inc. is preferred in many of these exemplary invention embodiments. The shaping amplifier configurations (1201, 1202) generally illustrated in FIG. 12 (1200) may also incorporate a wide variety of digitally switched beta and/or gamma gain modulation inputs that modify the feedback behavior of the operational amplifiers in response to digital controls from the control logic (0906, 1006) generally depicted in FIG. 9 (0900) and FIG. 10 (1000). A preferred exemplary embodiment of an alpha filtering block (FIG. 9 (0904)) useful in some invention embodiments is generally illustrated in FIG. 12 (1200). This filtering block may be utilized in some preferred embodiments with the alpha/beta/gamma amplifiers (1201, 1202) illustrated in FIG. 12 (1200). While amenable to a wide variety of implementations, a preferred embodiment of an alpha amplitude detector is generally illustrated in FIG. 14 (1400). Here a cascading string of comparators (nominally 8) are used in conjunction with a resistive divider string and appropriate filtering to provide instantaneous determination of the amplitude threshold associated with the alpha pulses. Note that the input to this comparator string is derived from the alpha filter described in FIG. 13 (1300). One skilled in the art may approach this design with different implementations without departing from the spirit of the invention. While amenable to a wide variety of implementations, a preferred embodiment of a beta amplitude detector is generally illustrated in FIG. 15 (1500). Here a cascading string of comparators (nominally 8) are used in conjunction with a resistive divider string and appropriate filtering to provide instantaneous determination of the amplitude threshold associated with the beta pulses. One skilled in the art may approach this design with different implementations without departing from the spirit of the invention. While amenable to a wide variety of implementations, a preferred embodiment of a gamma amplitude detector is generally illustrated in FIG. 16 (1600). Here a cascading string of comparators (nominally 12) are used in conjunction with a resistive divider string and appropriate filtering to provide instantaneous determination of the amplitude threshold associated with the gamma pulses. One skilled in the art may approach this design with different implementations without departing from the spirit of the invention. The present invention has application to a variety of radiation detection contexts, several of which are preferred. One of these is in the construction of a whole body radiation detector/monitor/scanner. This whole body detector/monitor/scanner application may be constructed in a wide variety of configurations, with one preferred embodiment presented in FIG. 17 (1700). Within this context, a plethora of radiation detectors (1711, 1712, 1713, 1714, 1721, 1722, 1723, 1724, 1731, 1732, 1733, 1734) may be arrayed to detect radiation over an extended spatial area and/or volume. Arraying of integrated scintillation detectors (ISD) as described in FIG. 4 (0400) and FIG. 5 (0500) in this application permits simultaneous acquisition of different types of radiation while allowing more accurate analysis of acquired data resulting from improved sensitivity (reduced detector-to-source distance) and reduced scanning time. The present invention has application to a variety of radiation detection contexts, several of which are preferred. One of these is in the construction of a laundry radiation detector/monitor/scanner. As generally illustrated in FIG. 18 (1800), the prior art in this field utilized multiple radiation detectors (1801, 1802) that were stacked and arranged to cover a conveyor belt (1803). As mentioned previously, this approach suffers from poor detection sensitivity and high implementation cost. This laundry radiation detector/monitor/scanner application may be constructed using the present invention as depicted in FIG. 19 (1900), wherein only a single radiation detector element (1901) is necessary to achieve the functionality of the prior art, while simultaneously increasing detector sensitivity and reducing overall system cost. The present invention has application to a variety of radiation detection contexts, several of which are preferred. One of these is in the construction of a tool and article radiation detector/monitor/scanner. As generally illustrated in FIG. 20 (2000), the prior art in this field utilized multiple radiation detectors (2001, 2002) that were arranged on the faces of a box structure (2003) to permit radiation inspection of tools and/or other articles. As mentioned previously, this approach suffers from poor detection sensitivity and high implementation cost. This tool/article radiation detector/monitor/scanner application may be constructed using the present invention as depicted in FIG. 21 (2100), wherein only a single radiation detector element (2101) is necessary to achieve the functionality of the prior art, while simultaneously increasing detector sensitivity and reducing overall system cost. There are several advantages to the present invention system/method as detailed herein. Many of these deal with the compact nature of the resulting radiation detector. Compared to the prior art, the distance between the plastic gamma scintillator and the monitored object is significantly reduced. FIG. 1 (0100) illustrates the relative distances in the prior art between the plastic gamma scintillator (0105) and the front face of the alpha/beta detector (0103) is approximately 51 mm. The distance between the front face of the alpha/beta detector and the subject person (0101) being monitored in a whole body radiation monitor system context varies depending upon the body shape (morphology) of the individual (0101) being monitored. With the implementation of the present invention in a whole body radiation monitor system, the separate plastic gamma scintillator (0105) is eliminated as generally illustrated in FIG. 2 (0200). Since the strength of the ionizing radiation signal is inversely proportional to the square of the distance between the signal source and detector, from FIG. 1 (0100) it can be seen that the gamma signal detected by the plastic gamma detector (0105) would be inversely proportional to the square of the sum of the distances to the individual detectors (including the thickness of the alpha/beta detector (0103). Using typical numbers, the distance on average between the person (0101) and the plastic gamma detector=50 mm+50 mm+30 mm=130 mm. In contrast with the prior art, the present invention situates the plastic gamma detector (0202) about 50 mm from the subject person (0201) being monitored. Applying the R-squared law, the gamma detection sensitivity in a whole body radiation monitor utilizing the present invention compared to the prior art configuration illustrated in FIG. 1 (0100) is increased by a factor of (130/50)*(130/50)=6.76. Additional benefits of the present invention may include reduced physical space requirements, since a whole body radiation monitor typically uses 25 or more radiation detectors in its construction (see FIG. 17 (1700)). The simplified mechanical design due to the elimination of the separate plastic gamma detectors also results in significantly reduced overall system cost. The compact nature of the ISD modules in this application drastically reduces the overall space requirements for whole body radiation monitor systems as compared to the prior art. Finally, the increased sensitivity of the ISD configuration disclosed herein can result in significantly reduced scanning times in whole body monitoring radiation monitoring systems, a significant improvement in throughput capability as compared to the scanning time possible with the multi-detector methodologies and configurations taught by the prior art. The present invention system anticipates a wide variety of variations in the basic theme of construction, but can be generalized as a radiation detector system comprising: (a) scintillation array stack; (b) photomultiplier tube; (c) shaping amplifier; (d) discriminator; (e) anti-coincidence module; and (f) radiation counter; wherein the scintillation array stack is responsive to more than one band of radiation; the scintillation array stack is in proximity to the photomultiplier tube, the photomultiplier tube receiving excitation input from the scintillation array stack; the shaping amplifier receives the output of the photomultiplier tube and produces one or more radiation pulses based on the excitation and output of the photomultiplier tube; the discriminator receives the radiation pulses and produces a pulse output depending on whether the radiation pulses fit a threshold and pulse width profile associated with a radiation type; and the anti-coincidence module receives the pulse output and increments an associated radiation counter based on whether the pulse output is valid for the radiation type associated with the radiation counter. This general system summary may be augmented by the various elements described herein to produce a wide variety of invention embodiments consistent with this overall design description. The present invention system anticipates a wide variety of variations in the basic theme of construction, with an alternative ISD embodiment generalized as a radiation detector system comprising: (a) scintillation array stack; (b) photomultiplier tube; (c) shaping amplifier; (d) discriminator; (e) anti-coincidence module; and (f) radiation counter; wherein the scintillation array stack comprises scintillation materials forming an integrated scintillation detector (ISD) further comprising beta scintillator plate, alpha scintillator plate, and gamma scintillator plate stacked with no inter-layer gaps within a detector case; the scintillation array stack is in proximity to the photomultiplier tube, the photomultiplier tube receiving excitation input from the scintillation array stack; the shaping amplifier receives the output of the photomultiplier tube and produces one or more radiation pulses based on the excitation and output of the photomultiplier tube; the discriminator receives the radiation pulses and produces a pulse output depending on whether the radiation pulses fit a threshold and pulse width profile associated with a radiation type; and the anti-coincidence module receives the pulse output and increments an associated radiation counter based on whether the pulse output is valid for the radiation type associated with the radiation counter. This general system summary may be augmented by the various elements described herein to produce a wide variety of invention embodiments consistent with this overall design description. In some preferred embodiments the present invention system may primarily comprise an integrated scintillation detector (ISD), this generalized as a radiation detector system comprising an integrated scintillation detector (ISD), the ISD comprising: (a) alpha scintillator plate; (b) beta scintillator plate; (c) beta particle shield plate; (d) gamma scintillator plate; (e) photomultiplier tube; and (f) detector case; wherein the alpha scintillator plate, the beta scintillator plate, the beta particle shield plate, and the gamma scintillator plate are stacked to form a scintillation array stack with no inter-layer gaps between the plates; the scintillation array stack is housed within the detector case; the photomultiplier tube is housed within the detector case; the scintillation array stack is in proximity to the photomultiplier tube within the detector case; and the photomultiplier tube is oriented to receive excitation input from the scintillation array stack. This general system summary may be augmented by the various elements described herein to produce a wide variety of invention embodiments consistent with this overall design description. The present invention may be utilized in the context of an overall radiation detection system as generally illustrated in FIG. 22 (2200), wherein the radiation detector system (2201) described herein is connected to a computer system (2202) under control of software retrieved from a computer readable medium (2203). This software may permit an operator (2204) via a graphical user interface (GUI) (2205) or other interface to control or direct the computer system in this capacity. Data associated with the detection of radiation impinging on the radiation detector (2201) in this context may also be logged to a database (2206) that may be accessed locally by the computer system (2202) or remotely via a computer network. While the present invention may be implemented in a wide variety of hardware platforms, one preferred embodiment utilizes an integrated microcontroller as generally depicted in FIG. 23 (2300). Within this context, the discriminators (2304, 2306, 2308), analysis module (2309) and counters (2310, 2311, 2312) may be embodied in a microcontroller (2320) or other integrated circuit operating under software read from a computer readable medium. Note that the output of the shaping amplifiers (2302, 2305, 2307) may be input to this processing subsystem (2320) in analog form and flash converted to digital data as needed to determine pulse amplitudes. Software residing on this microcontroller (2320) can also facilitate the pulse width analysis functions (2309) as well as pulse counting functions (2310, 2311, 2312). Further integration of the system is possible wherein the shaping amplifiers (2303, 2304, 2305) are either integrated separately (2330) onto a single integrated circuit, or equivalently fully integrated with the control logic wherein the subsystems (2320) and (2330) are combined into an application specific integrated circuit (ASIC). One skilled in the art will recognize that this level of integration is well within the capabilities of one of ordinary skill in the semiconductor arts and thus need not be further detailed herein. The present invention method anticipates a wide variety of variations in the basic theme of implementation, but can be generalized as a radiation detector method as illustrated in the flowchart of FIG. 24 (2400), the method operating in conjunction with a radiation detector system comprising: (a) scintillation array stack; (b) photomultiplier tube; (c) shaping amplifier; (d) discriminator; (e) anti-coincidence module; and (f) radiation counter; wherein the scintillation array stack is responsive to more than one band of radiation; the scintillation array stack is in proximity to the photomultiplier tube, the photomultiplier tube receiving excitation input from the scintillation array stack; the shaping amplifier receives the output of the photomultiplier tube and produces one or more radiation pulses based on the excitation and output of the photomultiplier tube; the discriminator receives the radiation pulses and produces a pulse output depending on whether the radiation pulses fit a threshold and pulse width profile associated with a radiation type; and the anti-coincidence module receives the pulse output and increments an associated radiation counter based on whether the pulse output is valid for the radiation type associated with the radiation counter; wherein the method comprises the steps of: (1) collecting radiation from a scintillation array stack with a photomultiplier tube (2401); (2) shape amplifying the output of the photomultiplier tube to produce shape amplified waveforms (2402); (3) determining the radiation pulse type using detection thresholds and pulse durations from the shape amplified waveform (2403); (4) if the radiation pulse type is determined to be an alpha pulse, incrementing the alpha pulse counter and proceeding to step (1) (2404); (5) if the radiation pulse type is determined to be a gamma pulse, incrementing the gamma pulse counter and proceeding to step (1) (2405); (6) if the radiation pulse type is determined to be a beta pulse, incrementing the beta pulse counter and proceeding to step (1) (2406); and (7) ignoring the radiation pulse as invalid and proceeding to step (1) (2407). Note that this method may incorporate displays, audible alarms, or other type of human and/or computer interfaces in conjunction with data logging and/or mathematical analysis of the collected radiation pulse count information. This general method summary may be augmented by the various elements described herein to produce a wide variety of invention embodiments consistent with this overall design description. The present invention also anticipates an ISD method variation in the basic theme of implementation, this variant generalized as a radiation detector method as illustrated in the flowchart of FIG. 24 (2400), the method operating in conjunction with a radiation detector system comprising: (a) scintillation array stack; (b) photomultiplier tube; (c) shaping amplifier; (d) discriminator; (e) anti-coincidence module; and (f) radiation counter; wherein the scintillation array stack comprises scintillation materials forming an integrated scintillation detector (ISD) further comprising alpha scintillator plate, beta scintillator plate, beta particle shield plate, and gamma scintillator plate stacked with no inter-layer gaps within a detector case; the scintillation array stack is in proximity to the photomultiplier tube, the photomultiplier tube receiving excitation input from the scintillation array stack; the shaping amplifier receives the output of the photomultiplier tube and produces one or more radiation pulses based on the excitation and output of the photomultiplier tube; the discriminator receives the radiation pulses and produces a pulse output depending on whether the radiation pulses fit a threshold and pulse width profile associated with a radiation type; and the anti-coincidence module receives the pulse output and increments an associated radiation counter based on whether the pulse output is valid for the radiation type associated with the radiation counter; wherein the method comprises the steps of: (1) collecting radiation from a scintillation array stack with a photomultiplier tube (2401); (2) shape amplifying the output of the photomultiplier tube to produce shape amplified waveforms (2402); (3) determining the radiation pulse type using detection thresholds and pulse durations from the shape amplified waveform (2403); (4) if the radiation pulse type is determined to be an alpha pulse, incrementing the alpha pulse counter and proceeding to step (1) (2404); (5) if the radiation pulse type is determined to be a gamma pulse, incrementing the gamma pulse counter and proceeding to step (1) (2405); (6) if the radiation pulse type is determined to be a beta pulse, incrementing the beta pulse counter and proceeding to step (1) (2406); and (7) ignoring the radiation pulse as invalid and proceeding to step (1) (2407). Note that this method may incorporate displays, audible alarms, or other type of human and/or computer interfaces in conjunction with data logging and/or mathematical analysis of the collected radiation pulse count information. This general method summary may be augmented by the various elements described herein to produce a wide variety of invention embodiments consistent with this overall design description. The present invention anticipates a wide variety of variations in the basic theme of construction. The examples presented previously do not represent the entire scope of possible usages. They are meant to cite a few of the almost limitless possibilities. This basic system and method may be augmented with a variety of ancillary embodiments, including but not limited to: An embodiment wherein the scintillation materials are chosen to detect alpha and beta radiation. An embodiment wherein the scintillation materials are chosen to detect beta and gamma radiation. An embodiment wherein the scintillation materials are chosen to detect alpha, beta, and gamma radiation. An embodiment wherein the scintillation materials are chosen to detect alpha, beta, and gamma radiation with the time constants of the scintillation materials being medium, short, and long, respectively. An embodiment wherein the radiation detector is constructed in an array, the array incorporated into a whole body radiation contamination scanner. An embodiment wherein the radiation detector is incorporated into a laundry radiation scanner. An embodiment wherein the radiation detector is incorporated into a tool/article radiation scanner. An embodiment wherein the output of the photomultiplier tube is conditioned by a preamplifier. An embodiment wherein the radiation detector forms an integrated scintillation detector (ISD) wherein the scintillation array stack is constructed as a closely formed structure having no inter-layer gaps, the ISD presenting a reduced overall thickness profile while simultaneously increasing the beta/gamma radiation sensitivity of the radiation detector. An embodiment wherein the alpha scintillation plate comprises a scintillation material having a medium time constant. An embodiment wherein the beta scintillation plate comprises a scintillation material having a short time constant. An embodiment wherein the gamma scintillation plate comprises a scintillation material having a long time constant. An embodiment wherein radiation impinging on the scintillation array stack results in emissions from the scintillation array stack that are input to the photomultiplier tube, the emissions simultaneously detecting any impinging alpha and beta radiation by the photomultiplier tube. An embodiment wherein radiation impinging on the scintillation array stack results in emissions from the scintillation array stack that are input to the photomultiplier tube, the emissions simultaneously detecting any impinging beta and gamma radiation by the photomultiplier tube. An embodiment wherein radiation impinging on the scintillation array stack results in emissions from the scintillation array stack that are input to the photomultiplier tube, the emissions simultaneously detecting any impinging alpha, beta, and gamma radiation by the photomultiplier tube. One skilled in the art will recognize that other embodiments are possible based on combinations of elements taught within the above invention description. A radiation detector system/method that simultaneously detects alpha/beta, beta/gamma, or alpha/beta/gamma radiation within an integrated detector has been disclosed. The system incorporates a photomultiplier tube with radiation scintillation materials to detect alpha/beta/gamma radiation. The photomultiplier tube output is then shape amplified and fed through discriminators to detect the individual radiation types. The discriminator outputs are fed to an anti-coincidence and pulse width and timing analysis module that determines whether individual alpha/beta/gamma pulses are valid and should be counted by corresponding alpha/beta/gamma pulse radiation counters. The system may include a radiation detection method to affect alpha/beta/gamma radiation detection in a variety of contexts. The system/method may be implemented in a variety of applications, including but not limited to whole body radiation contamination detectors, laundry radiation scanners, tool/article radiation detectors, and the like. |
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abstract | A short use or disposable system and method for adaptive window-capable radiation protection provides a disposable outer covering for securing one or more flexible and overlappable radiation shield members relative to a user using a variety of features including pockets, pocket defining members, fitting aid members, and fixing and releasing points. Features allow conveniently securing multiple layers of reusable shields in disposable coverings and providing pre-selected and assembled shielding kits for specific uses. Variants provide adaptive shielding sheets that may be customized to a particular patient need or injury profile. |
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summary | ||
050680838 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to nuclear reactor fuel assemblies, and more particularly, to improved dashpot constructions for a control rod guide thimble of the fuel assembly. 2. Description of the Prior Art In a typical nuclear reactor, the reactor core includes a large number of fuel assemblies each composed of top and bottom nozzles with a plurality of elongated transversely spaced hollow guide thimbles extending longitudinally between the nozzles and a plurality of transverse support grids axially spaced along and attached to the guide thimbles. A plurality of elongated fuel elements or rods are supported by the transverse grids between top and bottom nozzles and transversely spaced apart from one another and from the guide thimbles. The fuel rods contain fissile material and are grouped by the grids in an array which provides a neutron flux in the core sufficient to support a high rate of nuclear fission and thus the release of a large amount of energy in the form of heat. A liquid coolant is pumped upwardly through the core in order to extract some of the heat generated in the core for the production of useful work. Clusters of elongated control rods are mounted to drive mechanisms above the fuel assemblies and in alignment with the hollow guide thimbles. During operation of the nuclear reactor, the control rods can be inserted into the fuel assemblies via the channels defined therein by the hollow guide thimbles. The control rods are used to control the nuclear reaction occurring within the fuel assemblies of the reactor core, allowing power level to increase upon withdrawal and reducing power level upon insertion of the control rods. In case of a need to quickly reduce power in the reactor core, the control rods are released from their drive mechanism and allowed to fall rapidly into the fuel assembly. If not controlled, the impact of the control rods on the fuel assembly could conceivably damage it. Therefore, deceleration and braking of the control rods is accomplished by providing a constriction to the flow of coolant in the form of a reduced diameter lower end portion of each guide thimble. Coolant flowing upwardly through the lower end portion of the guide thimble becomes trapped by the entering control rod forming a dashpot which effectively decelerates and brakes the control rod prior to impact: with the fuel assembly. Historically, the dashpot has been formed by swaging the lower end portion of the guide thimble to a smaller diameter size, leaving the remainder of the guide thimble at the desired diameter size. This process is expensive to perform and forms a conical transition between the reduced diameter lower end portion and the remainder of the tube which is difficult to control. The reduced diameter lower end portion of the prior art dashpot design also requires additional components to position and attach the lowermost or bottom grid or grids of the fuel assembly in place, further increasing the expense and difficulty of manufacture. The rest of the grids and a top nozzle fitting are assembled and joined by means for a bulged mechanical swaging of the guide thimble onto a plurality of identical larger sleeves that attach to the grids and to the top nozzle. Consequently, a need exists for an alternative approach to dashpot construction so as to overcome the problems associated with the prior art dashpot design. One approach is disclosed in U.S. Pat. No. 4,655,990 to Leclercq wherein the constriction is formed by insertion of a smaller diameter tube or tube sections inside the lower end portion of the guide thimble. While the particular constructions of this patent provide a start in the right direction, they are not perceived as an optimum solution to all of the problems. SUMMARY OF THE INVENTION The present invention provides improved dashpot constructions designed to satisfy the aforementioned needs. The objective of the present invention is to fabricate the dashpot from a main tube of the guide thimble and an auxiliary tube of the proper size with little or no additional processing of the tubes so employed. The embodiments of the dashpot constructions of the present invention accomplish this objective with no more than a weld or bulge joint to join the main and auxiliary tubes and an end flare provided on the auxiliary tube to form the transition. Some of the embodiments provide an outside diameter which is a continuation of the same outside diameter of the main tube of the guide thimble, whereas others provide a smaller outside diameter requiring the addition of the same components for attachment of the bottom grid(s) as used heretofore. Accordingly, the present invention relates to a dashpot in a control rod guide thimble having an elongated main hollow tube. The dashpot comprises: (a) a lower tubular portion of the main tube; (b) an auxiliary hollow tube inserted in the lower portion of the main tube and having an outside diameter slightly less than an inside diameter of the main tube to permit a close fitting relationship between an exterior surface of the auxiliary tube and an interior surface of the main tube lower portion; and (c) an end plug attached to a lower end portion of the auxiliary tube. The auxiliary tube has an upper end portion with an inside surface portion in axial cross-section flaring upwardly and outwardly to provide a tapered transition extending between and connecting an interior surface of the auxiliary tube with the exterior surface thereof. Several embodiments of the dashpot are disclosed. These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described illustrative embodiments of the invention. |
claims | 1. A method for installing a locking retainer in a tube to maintain internal components within the tube under compression comprising the steps of:a) providing an elongated retainer spring having large and small diameter sections with the large diameter section of a size for an interference fit with the interior diameter of the tube and the smaller diameter section of a size having a clearance with the interior diameter of the tube;b) inserting a smaller diameter section of an elongated tool into the large diameter section of the elongated retainer spring;c) engaging a transition between the smaller diameter section of the elongated tool and a larger diameter section of the elongated tool against a transition between the large and small diameter sections of the elongated retainer spring;d) inserting the combined tool and retainer spring into an open end of the tube containing internal components with an end of the small diameter section of the retainer spring entering the tube first;e) advancing the combined tool and retainer spring within the tube to compress the small diameter section of the retainer spring against an adjacent internal component until an end of the tool engages the adjacent internal component enabling the spring to apply a selected axial preload on the internal components in the tube; andf) withdrawing the tool from the retainer spring while maintaining the large diameter section of the retainer spring in engagement with the interior diameter of the tube to maintain the axial preload on the internal components. 2. A method according to claim 1, including advancing the combined tool and retainer spring within the tube to engage the spring transition with the interior diameter of the tube and subsequently rotating the combined tool and retainer spring to advance the large diameter section of the retainer spring into the tube. 3. The method according to claim 1 wherein the tube comprises a nuclear fuel rod. 4. The method according to claim 3 wherein the internal components comprise fuel pellets. |
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description | This application is a divisional of U.S. patent application Ser. No. 13/607,940, filed Sep. 10, 2012, now U.S. Pat. No. 9,959,944, which claims the benefit of U.S. Provisional Application No. 61/623,332, filed Apr. 12, 2012, the disclosures of which are incorporated by reference herein. The following relates to the nuclear power reactor arts, neutron reflector arts, and related arts. In a nuclear reactor, fissile material is arranged in the reactor such that the neutron flux density resulting from fission reactions is sufficient to maintain a sustained fission process. In a commercial reactor, fissile material is typically provided in the form of fuel rods mounted in modular, elongated fuel assemblies which are generally square or hexagonal in cross section. A plurality of such fuel assemblies are arranged together to form a reactor core which is contained inside a cylindrical stainless steel core basket. This entire assembly, in turn, is mounted inside a pressure vessel. In a typical configuration, reactor coolant flows downward in an annular space between the core basket and the pressure vessel, reverses direction in a lower plenum of the vessel, flows upward through openings in a lower end plate at the bottom of the reactor core, and upward through the fuel assemblies where it is heated by the reactor core. The heat extracted by the reactor coolant from the core is utilized to generate electricity thereby lowering the temperature of the reactor coolant which is recirculated through the reactor in a closed loop. In boiling water reactor (BWR) designs, the primary coolant boils inside the pressure vessel and the resulting primary coolant steam is piped through a recirculating loop to drive a turbine. In pressurized water reactor (PWR) designs the primary coolant remains in a subcooled liquid state and heats secondary coolant in an external steam generator, and the secondary coolant drives a turbine. In a variant PWR design, the steam generator is located inside the pressure vessel (i.e., an integral PWR) and a secondary coolant circuit flows into the pressure vessel to feed the steam generator. In the fission process, free neutrons are generated. In a thermal nuclear reactor, these neutrons are slowed, i.e. thermalized, by ambient water which is advantageous as thermalized neutrons are more likely to stimulate additional fission events as compared with faster neutrons. However, neutrons originating near the outer boundary of the reactor core may travel outside the reactor core and be lost. To improve overall efficiency and to increase burn rate for the outer fuel assemblies, it is known to include a core former, or radial reflector, between the reactor core and the core basket. The objective is to reflect neutrons traveling out of the core back toward the core to enhance burn of the fuel assemblies. The welds, bolts, or other fasteners of the radial reflector experience high radiation flux, and can be prone to damage or failure due to the harsh operating environment with the reactor. Repair of any such damage is difficult or impossible due to the extremely radioactive environment. Moreover, the radial reflector can impede natural circulation around the reactor core, which may be problematic for any emergency core cooling system (ECCS) that relies upon natural circulation. In some instances radial reflectors are known to cause jetting of coolant laterally onto the fuel assemblies. Jetting is generally undesirable as excessive wear may result over time. According to one aspect, an apparatus comprises a nuclear reactor core comprising fissile material and a core former surrounding the nuclear reactor core. The core former comprises one or more single-piece annular rings wherein each single-piece annular ring comprises neutron-reflecting material. In some embodiments the core former comprises a stack of two or more single-piece annular rings wherein each single-piece annular ring comprises neutron-reflecting material. In some embodiments the stack of single-piece annular rings is self-supporting. In some embodiments the stack of single-piece annular rings does not include welds or fasteners securing adjacent single-piece annular rings together. According to another aspect, an apparatus comprises a nuclear reactor core comprising fissile material, a core former surrounding the nuclear reactor core and including one or more single-piece annular rings wherein each single-piece annular ring comprises neutron-reflecting material, and a core basket containing the nuclear reactor core and the core former. In some embodiments an annular gap is defined between the core former and the core basket. In some embodiments an annular gap is defined between the core former and the core basket and the core former comprises a self-supporting stack of single-piece annular rings wherein each single-piece annular ring comprises neutron-reflecting material. In some embodiments the outer surface of the core former includes axially extending channels. In some embodiments the core former does not include welds and does not include fasteners. According to another aspect, a method comprises: constructing a core former by stacking a plurality of single piece annular rings wherein each single piece annular ring comprises neutron-reflecting material; and loading a nuclear reactor core inside the core former by disposing fuel assemblies comprising fissile material inside the core former. In some embodiments the method further includes, after the constructing and loading, operating a nuclear reactor comprising primary coolant disposed in a pressure vessel that also contains the constructed core former and loaded nuclear reactor core in order to heat the primary coolant. In some embodiments the method further comprises forging each single-piece annular ring. In some embodiments the method further comprises casting each single-piece annular ring. In some embodiments the method further comprises rolling and welding one or more plates to form each single-piece annular ring With reference to FIGS. 1-3, a core former as disclosed herein is described in the context of an illustrative nuclear reactor of the pressurized water reactor (PWR) type. The nuclear reactor includes a pressure vessel 10, only a lower portion of which is shown diagrammatically in phantom in FIG. 1. The lower portion of the pressure vessel contains a reactor core constructed as an array of fuel assemblies. For illustrative purposes, FIG. 1 shows a single fuel assembly 12 being loaded into the reactor. (The loading is done using a crane or other lifting apparatus, not shown). The fuel assembly 12 is shown diagrammatically, and typically includes a structural skeleton of spacer grids and upper and lower end fittings or nozzles supporting the fuel rods with guide tubes interspersed amongst the fuel rods to provide conduits for control rods, instrumentation, or the like (details not illustrated). FIG. 3 shows an overhead or top view including the complete nuclear reactor core 14 constructed as an array of fuel assemblies 12. The illustrative reactor core of FIG. 3 includes 69 fuel assemblies, but more or fewer fuel assemblies can be included depending upon the size of the core and the sizes of the constituent fuel assemblies. The illustrative fuel assemblies 12 are all of equal size, and the layout of the fuel assemblies in the reactor core can be varied. The reactor core 14 is contained in a core former 16 which in turn is contained in a core basket 18. The reactor core 14 can have substantially any configuration compatible with a light water reactor. In the illustrative configuration shown in FIG. 3, the reactor core includes 69 PWR type fuel assemblies each having a 17×17 array of fuel rods supported by a bottom grid structure that is part of a core former 16. The upper portion of the nuclear reactor is not shown, but typically includes a hollow cylindrical central riser defining an inner cylindrical plenum conducting primary coolant exiting from the top of the reactor core 14 upward. This is sometimes called the “hot leg” of the primary coolant circuit. A downcomer annulus is defined between the central riser and the pressure vessel 10, and provides the downward flowing “cold leg” of the primary coolant circuit which returns primary coolant to the bottom of the nuclear core 14. The reactor optionally includes other components such as internal steam generators, a reactivity control sub-system including control rods coupled with external or internal control rod drive mechanisms (CDRM), an optional internal pressurizer, and so forth. Other vessel configurations and reactor types are also contemplated, including PWR designs with external steam generators, integral PWR designs with steam generators disposed inside the pressure vessel, various BWR designs, and so forth. The core former 16 provides lateral support of the fuel assemblies and is constructed as a stack of single-piece annular rings 24. Each annular ring is a single-piece component, for example a single-piece forged or cast stainless steel ring. A single-piece may also be formed by rolling and welding one or more plates. Each annular ring is suitably a monolithic element without joints or seams. The stack of annular rings 24 is optionally a self-supporting stack, with the upper end of each ring supporting the lower end of the next-higher ring in the stack. On the other hand, if the reactor core is of sufficiently low profile it is contemplated to employ as few as a single annular ring in constructing the core former. In FIG. 1, the illustrative core former 16 is shown concentrically arranged with core basket 18 (e.g., a lower shroud), a portion of the core basket 18 being removed in FIG. 1 to expose the core former 16 for purposes of illustration. FIG. 4 illustrates a top view of a single core former ring 24. The core former ring 24 is an annular element having a cylindrical outer surface 28 and an inner 32 shaped to conform with the outer periphery of the reactor core 14 (see also FIG. 3). More generally, the outer surface 28 should conform with the inner surface of the core basket, which is cylindrical in the case of illustrative core basket 18. With particular reference to FIGS. 1 and 2, in the axial direction, that is, the direction transverse to the plane of the annular ring 24, the number of rings 24 in the stack is sufficient for the core former 16 to be at least coextensive with the axial extent of the reactor core 14. Said another way, the “height” of the core former 16 should be equal to or greater than the “height” of the reactor core 14 that is placed within the core former 16. Advantageously, the core former 16 does not include any welds, bolts, or other fasteners. Rather, the stack of annular rings 24 is self-supporting. For manufacturing convenience, it is advantageous for the rings 24 of the stack to be interchangeable. However, in some embodiments the uppermost ring and/or the lowermost ring may be different. By way of illustrative example, the core former 16 includes five annular rings 24, of which the three middle single-piece annular rings 24 are interchangeable, the lowermost ring 24L omits any bottom-surface features intended to mate with a “further-below” ring (since it is not aligning with a ring located below it) and the uppermost ring 24u similarly omits any upper-surface features intended to mate with a “further-above” ring. Additionally, the uppermost ring 24u includes pins 36 on the upper surface for lateral and rotational alignments of components, such as upper internals, located above the uppermost ring 24u. Additional pins or other core former retention features may be included to keep the rings from moving vertically. In some embodiments the weight of the annular rings 24, either alone or in combination with the weight of components located above the uppermost ring 24u, may be sufficient to prevent vertical movement, in which case no mounting or retention features are needed. As noted, the radially inner surface 32 of each ring 24 conforms to the shape of the core (e.g., plurality of fuel assemblies 12) and the radially outer surface 28 is cylindrical or otherwise shaped to conform with the inner surface of the core basket 18. In some embodiments there is a relatively small gap (e.g., annular, flow passage) defined between the outer surface 28 of the core former 16 and the inner diameter or surface of the core basket 18 for the circulation of water. This gap serves as a thermal sleeve, and also allows bypass flow outside of the core which can be useful in some emergency core cooling system designs. In one embodiment, gamma heating increases the temperature of the core former rings 24 and bypass flow provides cooling. The thermal sleeve functionality helps accommodate the thermal difference from the hot leg to the cold leg of the nuclear reactor cooling system, and reduces stresses within the core former 16 that can be generated because of such thermal gradient. The flow bypass functionality is useful in the event of a loss of primary coolant flow, as the thermal sleeve also acts as a bypass flow channel, allowing water to travel in a natural circulation loop vertically downwards through the thermal sleeve, exit the core former 16 at the bottom, and turn and enter the core where it exits the top of the core and again turns and enters the thermal sleeve to repeat the loop. During normal operation, the bulk of the primary coolant flow enters the bottom of the core former 16 and flows upward through the reactor core 14, and only a small portion of the total flow travels upward through the thermal sleeve. Optionally, more bypass flow can be provided (or the amount of bypass flow can be designed) by increasing the size of the thermal sleeve or by providing bypass flow slots or channels 40 in the outer surfaces 28 of the rings 24 of the core former 16. In the stack of rings, these channels 40 extend the entire axial length of the core former 16 to allow more bypass flow in addition to the thermal sleeve. The size, shape, and location of these slots can be chosen to provide a desired level of bypass flow. Instead of or in addition to the bypass flow slots 40 on the outside surface 28 of the core former 16, one or more holes could be drilled axially through the stack of core former rings. The core former 16 and the reactor core 14 are disposed in the core basket 18. In the illustrative embodiment, the core basket 18 is suspended from a mid-flange 44 (indicated diagrammatically in FIG. 1) of the pressure vessel 10 by mounting brackets 42. Other arrangements are also contemplated, including support of the core basket from below, e.g. by feet or pedestals resting on a lower surface of the pressure vessel. The core former 16 is intended to act as a neutron reflector. (Said another way, the core former 16 can alternatively be considered to be a neutron reflector 16). Toward this end, the annular rings 24 of the core former 16 are made of stainless steel or another suitable corrosion resistance neutron reflective material in order to provide neutron reflection so as to more efficiently burn the fuel in the periphery fuel assemblies. The lack of welds, bolts or other threaded fasteners, or the like in some embodiments is advantageous as welds or fasteners can suffer failures due to irradiation imbrittlement and differential thermal expansion created from the radiation and heat output by the reactor core 14. In addition, the core former 16 has few components, e.g. five rings 24 in the illustrative core former 16 and optional additional components such as the illustrative upper constraint pins 36. While five annular rings 24 are employed in the illustrative core former 16, other numbers of rings (down to as few as a single ring) can be arranged or stacked axially to produce a core former of a desired height. The quantity, size, and geometry of each of the rings can vary to create a wide range of core formers. Adjacent rings can include mating features on for interlocking and/or restricting radial and/or axial movement between the rings. For example, the as seen in FIGS. 2 and 4, adjacent rings can be keyed together by a key/keyway interlocking configuration 50 to prevent relative rotation between adjacent rings. In some embodiments, the stack of single-piece annular rings 24 is self-supporting. However, it is alternatively contemplated to include lateral support, for example via the surrounding core basket, in order to prevent the stack from leaning or to provide load transfer from the core basket into the core former or from the core former to the core basket. With reference to FIG. 4 and with further reference to FIG. 5, mating surfaces of adjacent rings 24 of the stack can include an annular joint 60 that provides a tortuous path for (lateral) fluid flow into or out of the core former 16 via the joints between the rings 24. FIG. 5 shows a side sectional view of a portion of a ring 241 and a ring 242 stacked on top of the ring 241. As seen in FIG. 5, the top surface of the lower ring 241 includes a circumferential groove or recess 62 that mates with a circumferential protrusion 64 on the bottom surface of the upper ring 242. FIG. 5 shows the upper surface of one of the rings 24 including the circumferential groove or recess 62. (The circumferential protrusion 64 is on the bottom surface of the ring 24 and hence is not visible in FIG. 4). This configuration forms the illustrative annular joint 60 in the form of a shiplap joint that provides enhances alignment of the rings in the stack while also reducing leakage through the interface between the rings. The joint configuration further inhibits coolant from flowing between adjacent rings and subsequently spraying or otherwise jetting into the fuel assemblies. The lowermost ring 24L of the stack omits the circumferential protrusion 64 (since there is no further-below ring with which to mate), and similarly the uppermost ring 24u omits the circumferential groove or recess 62. Other suitable annular joints providing the desired tortuous flow path through the joint include mating grooves/protrusions. The illustrative core former 16 surrounds the entire height of the reactor core 14, but is still contained within the core basket 18. The core former 16 in one embodiment is made of stainless steel to reflect neutrons that leave the core region back into the core to continue the nuclear reaction. The rings comprising the core former 16 can be forged or cast, for example. As mentioned, one preferred material is stainless steel. The rings can have a wide range of radial thicknesses. The thickness should be chosen to provide adequate neutron reflection, and should also be sufficient to ensure structural integrity of the stack of annular rings 24. A relatively thicker core former may be used to enhance burn-up of the periphery fuel assemblies, for example in the context of a small modular reactor (SMR) having a relatively small core, and/or in the context of a reactor design intended for operation without performing occasional fuel shuffling. More generally, the disclosed core former designs are suitable for use in nuclear reactors of any size, and are suitable for use in conjunction with fuel shuffling or without fuel shuffling. The term “fuel shuffling” refers to the process of occasionally shutting down the reactor and moving fuel assemblies to different locations within the reactor core so that the fuel in each fuel assembly is more thoroughly consumed than would be the case if each fuel assembly remained in a single location within the reactor core for the entire useful life of the fuel. The exemplary embodiments have been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. |
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description | 1. Field of the Invention The present invention relates to a lithographic apparatus and a method of cleaning a collector included in such a lithographic apparatus. 2. Description of the Related Art A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning” direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate. In some current designs for lithographic apparatus, radiation in the EUV range (with wavelengths typically of 5-20 nm) is used to transfer a pattern from a mask onto a substrate. Radiation produced by an EUV light source is collected by a EUV collector and then directed into an illumination system. When an EUV source based on Sn is used, it will also produce Sn particles that may contaminate the EUV collector. In order to achieve sufficient lifetime for the lithography apparatus, it is required that these Sn particles are removed from the EUV collector mirror (this will be referred to as ‘cleaning’). Currently there are two methods available for removing these Sn contaminations. In recent experiments, it has been demonstrated that with hydrogen radicals (or a mixture of hydrogen with another gas) it is possible to remove Sn contaminations from a substrate. Another possible method is halogen cleaning. In this method halogens form a volatile Sn-halogen molecule, which evaporates and is transported out of the collector with a gas flow. Besides the Sn contamination, the collector may be contaminated with Sn-oxides. In order to remove the Sn-oxides as well, they first need to be reduced to Sn. This is done using hydrogen radicals. Both these cleaning methods require hydrogen radicals and therefore implementation of hydrogen radicals in the EUV collector is very important. One of the requirements for efficiently cleaning a collector surface is a sufficiently large flux of hydrogen radicals on the collector surface. A large flux may be achieved at a relatively high pressure but at very high pressures hydrogen radicals are quickly lost due to three-body recombination. At low pressures the radicals are quickly lost due to recombination on wall surfaces. A possible pressure range wherein a sufficiently high flux can be established and wherein recombination of radicals is limited, is at pressures above 10 kPa. At these pressures, a high velocity flow through the collector is needed in order to clean the whole collector. However, the velocity achievable is limited by the maximum pumping capacity of the system. It is desirable to provide a method of cleaning a collector of an EUV lithographic apparatus using hydrogen radicals wherein a sufficiently high velocity of the hydrogen radicals is achieved with a limited pumping capacity. Accordingly, there is provided a lithographic apparatus including a collector configured to collect radiation from a radiation source, the collector including a plurality of shells forming separate compartments; a cleaning arrangement including a gas inlet and a gas outlet, the arrangement being configured to clean surfaces of the plurality of shells by guiding a gas flow from the inlet through the compartments to the outlet, wherein the cleaning arrangement includes a distribution system configured to divide the gas flow into several sub flows, each of the sub flows corresponding to one or more of the compartments, and a control system configured to control the relative amount of the sub flows. According to yet another aspect, there is provided a cleaning arrangement including a gas inlet and a gas outlet, the arrangement being configured to clean surfaces of shells of a collector of a lithographic apparatus by guiding a gas flow from the inlet through compartments of said collector to the outlet, wherein the cleaning arrangement includes a distribution system configured to divide the gas flow into several sub flows, each of the sub flows corresponding to one or more of the compartments, and a control system configured to control the relative amount of the sub flows. According to another aspect of the invention, there is provided a method of cleaning a collector of a lithographic apparatus, the collector including a plurality of collector shells forming separate compartments configured to receive radiation at a first open end of the collector and to deliver radiation at a second open end of the collector, wherein the method include guiding a gas flow through the compartments in order to clean surfaces of the plurality of shells; dividing the gas flow into several sub flows, each of the sub flows corresponding to one of the compartments; and controlling the relative amount of the sub flows. According to another aspect of the invention, there is provided a collector for a lithographic apparatus, the collector including a plurality of tubular shells forming separate compartments, and cross walls extending in radial direction and subdividing the compartments. Throughout the text unless indicated otherwise, the terms “hydrogen” and “hydrogen radicals” include their isotopes as well, in particular, deuterium and tritium. FIG. 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus includes a collector CO configured to collect radiation from a radiation source SO. An illumination system (illuminator) IL is configured to condition a radiation beam B (e.g. UV radiation or EUV radiation). A support (e.g. a mask table) MT is configured to support a patterning device (e.g. a mask) MA and is connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters. A substrate table (e.g. a wafer table) WT is configured to hold a substrate (e.g. a resist-coated wafer) W and is connected to a second positioner PW configured to accurately position the substrate in accordance with certain parameters. A projection system (e.g. a refractive projection lens system) PS is configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. including one or more dies) of the substrate W. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. The support supports, e.g. bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support may be a frame or a table, for example, which may be fixed or movable as required. The support may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit. The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix. The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”. As here depicted, the apparatus is of a reflective type (e.g. employing a reflective mask). Alternatively, the apparatus may be of a transmissive type (e.g. employing a transmissive mask). The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). In such “multiple stage” machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. The lithographic apparatus may also be of a type wherein at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, e.g. water, so as to fill a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure. Referring to FIG. 1, the illuminator IL receives radiation from a collector CO which receives radiation from the radiation source SO. The source SO and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the radiation beam may be passed from the source SO via the collector CO to the illuminator IL with the aid of a beam delivery system BD including, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO, the collector CO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system. The illuminator IL may include an adjuster AD for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components, such as an integrator IN and a condenser. The illuminator IL may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section. The radiation beam B is incident on the patterning device (e.g., mask MA), which is held on the support (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF2 (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor IF1 (e.g. an interferometric device, linear encoder or capacitive sensor) can be used to accurately position the mask MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the mask MA, the mask alignment marks may be located between the dies. The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the mask table MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. 2. In scan mode, the mask table MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the mask table MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in the scanning direction) of the target portion. 3. In another mode, the mask table MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above. Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed. Referring to FIG. 2, the collector CO includes a plurality of coaxial shells 20, 21, 22, 23 forming separate compartments 50, 51, 52, 53. A cleaning arrangement includes a gas inlet 30 and a gas outlet 32, and is configured to clean surfaces of the plurality of shells 20-23 by guiding a gas flow from the inlet 30 through the compartments 50, 51, 52, 53 to the outlet 32. The cleaning arrangement further includes a distribution system configured to divide the gas flow into several sub flows 40, 41, 42, 43, each of said sub flows corresponding to one of the compartments 50, 51, 52, 53 respectively. In an embodiment, the shells 20-23 are substantially tubular concentric walls so as to form substantially tubular compartments 50, 51, 52, 53, see FIG. 2. FIG. 2 shows an embodiment wherein the distribution system includes tubes 60, 61, 62, 63 configured to direct the respective sub flows 40, 41, 42, 43 into the different compartments 50, 51, 52, 53 respectively. In this embodiment, the distribution system further includes a cap 75 which is configured to close an entrance of the collector CO. The tubes 60-63 are connected to the cap 75, in a way which will be discussed below with reference to FIGS. 3 and 4. As can be seen from FIG. 2, the cap 75 includes rings 76, 77, 78, 79 which meet the circular outer ends of the shells 20-23. The lithographic apparatus includes a control system configured to control the relative amount of the sub flows 40, 41, 42, 43. The control system includes a plurality of valves 70, 71, 72, 73 for controlling the sub flows 40, 41, 42, 43 respectively. The control system further includes a control unit 74 that is configured to control the valves 70, 71, 72, 73 depending on predefined conditions. The control unit 74 may, for example, be a computer including memory to store instructions and a processor to execute instructions. By controlling the valves 70, 71, 72, 73, it is possible to, for example, clean each of the compartments 50, 51, 52, 53 of the collector CO separately. As shown in FIG. 2, the valve 73 is open and the other valves, i.e. valves 70, 71, 72 are closed. Because these compartments are smaller than the complete collector volume, they need a relatively low flow rate to create sufficient velocity of the cleaning gas and therefore the pumping capacity does not need to be as high. FIG. 3 is a schematic front view of the cap 75. For reasons of simplicity only two tubes 62, 63 are shown. As was explained above, the sub flow 42 flowing through tube 62 is controlled by valve 72 and the sub flow 43 flowing through tube 63 is controlled by valve 73. Both tubes 62 and 63 are split up into four end tubes. In this example, tube 62 is split up into end tubes 62A, 62B, 62C and 62D, and tube 63 is split up into end tubes 63A, 63B, 63C and 63D. FIG. 3 shows a possible configuration on how the end tubes 62A, 62B, 62C, 62D, 63A, 63B, 63C, 63D can be connected to the cap 75. Outlets of the end tubes 62A, 62B, 62C, 62D, 63A, 63B, 63C, 63D are depicted by circles 62A′, 62B′, 62C′, 62D′, 63A′, 63B′, 63C′, 63D′. FIG. 3 further shows the rings 76, 77, 78 of the cap 75. The further distribution of the sub flows 42 and 43 into four sub flows results in a better distribution of the sub flows in the respective compartments 52, 53. FIG. 4 is a perspective view of a possible arrangement of the distribution system showing the tubes 62, 63 and the end tubes 62A-62D, 63A-63D connected to the cap 75. Referring to FIG. 5, the control system includes a diaphragm 80 having diaphragm blades 81, 82, 83, 84, 85, 86, 87. The diaphragm 80 is placed at the entrance of the collector CO so as to obstruct at least part of the openings of at least some of the compartments 50, 51, 52, 53. The diaphragm 80 can be opened and closed depending on the control parameters which may be defined to control the relative amount of the sub flows through the compartments 50, 51, 52, 53. In FIG. 5, the shells 22 and 23 of the collector CO are visible and depicted as circles. Because of the particular aperture of the diaphragm 80, the shells 20, 21 are not visible in FIG. 5. They are depicted in FIG. 5 by dashed circles. The diaphragm 80 may obstruct for example only the outer compartment 53 so as to let the cleaning gas flow through compartments 50, 51 and 52. It should be appreciated that other configurations are possible. During cleaning of the collector CO, the diaphragm 80 can dynamically be controlled so as to obstruct different parts of the collector opening at different moments in time. Referring to FIG. 6, the control system includes a ring 88 which may be moved in front of the entrance or exit of the collector CO. FIG. 6 shows the ring 88 during a transition from a non-obstructive state to an obstructive state in which the ring 88 will close part of the entrance of compartment 53. The ring 88 can be moved depending on the control parameters which may be defined to control the relative amount of the sub flows through the compartment 53. By reducing the opening of the largest entrance (i.e. the entrance of compartment 53) the flow-resistance of the compartment 53 is increased. This results in a relatively larger flow-resistance of compartment 53 as compared to the other compartments 50, 51, 52. And in turn, this results in a better distribution of the gas flow through all the compartments 50, 51, 52, 53 of the collector CO. It should be appreciated that the ring 88 could also be a static ring positioned in front of one or more of the compartments. To prevent the ring 88 from obstructing the radiation, the ring 88 may be positioned in front of the outer compartment 53 and outside the radiation beam coming from the radiation source SO. The collector CO may be cleaned using a cleaning gas which includes H radicals. The lithographic apparatus may include a H radical source at the entrance of each compartment 50, 51, 52, 53. Referring to FIG. 7, filaments 90 are positioned in the cap 75. The filaments are heated by a current and will produce H radicals when a gas containing H2 is pumped through the cap 75. Producing the H radicals at the entrance of the compartments 50, 51, 52, 53 results in a local production of H radicals and therefore a loss of H radicals in the tubes is avoided. Referring to FIG. 8, the collector CO includes a plurality of substantially tubular shells 20, 21, 22, 23 forming separate compartments 50, 51, 52, 53. The collector CO includes cross walls 100, 101, 102, 103 extending in radial direction and subdividing the compartments 50, 51, 52, 53. By subdividing the compartments 50, 51, 52, 53, more sub flows can be defined which flow through even smaller sub compartments. When cleaning only some of the sub compartments at a time, a further reduction of the pump capacity needed is possible. It should be noted that instead of placing the distribution system and the control system at the upstream side of the collector CO (i.e. the side facing the source SO), it is also possible to place the distribution system and the control system at the downstream side of the collector (i.e. the side facing the illuminator IL). It should be appreciated that the distribution system including the cap 75 and the tubes 60, 61, 62, 63 can be combined with the control system including the diaphragm 80. It should also be appreciated that it is possible to place the distribution system described with reference to FIG. 2 at the upstream side of the collector CO and the diaphragm 80 shown in FIG. 5 at the down stream side of the collector. Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be appreciated that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. It should be appreciated that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers. The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams. The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components. While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein. The descriptions above are intended to be illustrative, not limiting. For example, the diaphragm 80 or the ring 88 may be placed inside (for example half way in) the collector CO instead of at the entrance or exit. It will be apparent to one skilled in the art that such modifications may be made to the invention as described without departing from the scope of the claims set out below. |
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claims | 1. An adapter device for radiation protective garments, said device comprising:a lower member having a main body that includes a top surface, a bottom surface, and a pair of elongated shafts extending orthogonally from the top surface;a pair of shaft connectors that are each configured to engage one of the elongated shafts;an upper member having a main body that includes a top surface, a bottom surface, and a pair of shaft apertures extending from the top surface to the bottom surface thereof,said upper member further including a protrusion extending orthogonally from the top surface of the main body, and having an aperture disposed thereon; anda user engagement unit that includes an upper shoulder strap and a lower shoulder strap that are configured to be removably secured together, said upper shoulder strap including another pair of shaft apertures disposed along a middle section thereof,wherein each of the pair of shaft apertures and the another pair of shaft apertures include a dimension that is suitable for receiving the elongated shafts,the elongated shafts include a generally parallel orientation with each other,each of the shafts include a plurality of embedded screw threads, andeach of the shafts further include an aperture disposed along a distal end, said aperture being configured to receive a locking pin. 2. The device of claim 1, wherein the main body of each of the lower member and the upper member includes an elongated curved and generally rectangular shape. 3. The device of claim 2, wherein the main body of each of the lower member and the upper member include complementary dimensions to each other. 4. The device of claim 1, wherein the user attachment unit is configured to be interposed between the lower member and the upper member, and each of the pair of shaft apertures and the another pair of shaft apertures are configured to align with each other to form a pair of uniform pathways. 5. The device of claim 1, further comprising:a padded section that is positioned along the bottom surface of the lower member. 6. The device of claim 1, wherein the protrusion is located along a central portion of the upper member, and the protrusion aperture includes a shape and dimension that is suitable for receiving a hook from an overhead suspension device. 7. The device of claim 1, wherein the upper shoulder strap and the lower shoulder strap are removably secured together via quick release fasteners. 8. The device of claim 7, wherein said quick release fasteners include a pair of buckle receivers and a pair of buckle tongues. 9. The device of claim 1, wherein the upper member and the lower member are constructed from a plastic material that does not reflect X-rays. 10. The device of claim 1, wherein the upper member and the lower member are coated with a radiation shielding material. 11. The device of claim 1, further comprising:one or more strips of adhesive material that are disposed along the upper strap, said material being configured to engage a protective garment that is in contact with the upper strap. 12. The device of claim 1, further comprising a padded layer that is disposed along a portion of the lower shoulder strap. 13. An adapter device for radiation protective garments, said device comprising:a lower member having a main body that includes a top surface, a bottom surface, and a pair of elongated shafts extending orthogonally from the top surface;a pair of shaft connectors that are each configured to engage one of the elongated shafts;an upper member having a main body that includes a top surface, a bottom surface, and a pair of shaft apertures extending from the top surface to the bottom surface thereof,said upper member further including a protrusion extending orthogonally from the top surface of the main body, and having an aperture disposed thereon; anda user engagement unit that includes an upper shoulder strap and a lower shoulder strap that are configured to be removably secured together, said upper shoulder strap including another pair of shaft apertures disposed along a middle section thereof,wherein each of the pair of shaft apertures and the another pair of shaft apertures include a dimension that is suitable for receiving the elongated shafts,wherein the upper shoulder strap and the lower shoulder strap are removably secured together via quick release fasteners, and said quick release fasteners include a pair of buckle receivers and a pair of buckle tongues. 14. An adapter device for radiation protective garments, said device comprising:a lower member having a main body that includes a top surface, a bottom surface, and a pair of elongated shafts extending orthogonally from the top surface;a pair of shaft connectors that are each configured to engage one of the elongated shafts;an upper member having a main body that includes a top surface, a bottom surface, and a pair of shaft apertures extending from the top surface to the bottom surface thereof,said upper member further including a protrusion extending orthogonally from the top surface of the main body, and having an aperture disposed thereon; anda user engagement unit that includes an upper shoulder strap and a lower shoulder strap that are configured to be removably secured together, said upper shoulder strap including another pair of shaft apertures disposed along a middle section thereof,wherein each of the pair of shaft apertures and the another pair of shaft apertures include a dimension that is suitable for receiving the elongated shafts, andwherein the upper member and the lower member are coated with a radiation shielding material. |
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claims | 1. A charged particle multi-beam system comprising:a charged particle source configured to generate at least one beam of charged particles;a stage configured to hold a flat substrate to be inspected; anda particle-optical component disposed in a beam path of the at least one beam of charged particles downstream of the charged particle source, the particle-optical component comprising:a first multi-aperture plate having a plurality of apertures and a second multi-aperture plate having a plurality of apertures, wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed therebetween;wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the plurality of apertures of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the second multi-aperture plate; andwherein a first width of the gap at a location of a first aperture of the plurality of apertures of the first multi-aperture plate is by at least 5% greater than a second width of the gap at a location of a second aperture of the plurality of apertures of the first multi-aperture plate;wherein the system further comprises:a voltage supply system configured to apply different electric potentials to the first and second multi-aperture plates of the particle-optical component; andat least one focusing particle-optical lens disposed in the beam path of the at least one charged particle beam downstream of the particle-optical component and configured to focus charged particle beamlets having traversed the particle-optical component onto the flat substrate. 2. The system according to claim 1, wherein the first multi-aperture plate has a first surface facing towards the second multi-aperture plate, and the second multi-aperture plate has a first surface facing towards the first multi-aperture plate, wherein each first surface has an area comprising plural apertures of the respective plurality of apertures, and wherein at least one of the first surfaces is a planar surface within the area. 3. The system according to claim 2, wherein the at least one first surface is a curved surface within the area. 4. The system according to claim 2, wherein the at least one first surface is a convex surface within the area. 5. The system according to claim 2, wherein the at least one first surface is a concave surface within the area. 6. The system according to claim 1, wherein the first multi-aperture plate has a first surface facing towards the second multi-aperture plate, and the second multi-aperture plate has a first surface facing towards the first multi-aperture plate, and wherein shapes of the first surfaces are symmetric with respect to each other relative to a plane extending between the first and second multi-aperture plates. 7. The system according to claim 1, wherein the first multi-aperture plate has a first surface facing towards the second multi-aperture plate, and the second multi-aperture plate has a first surface facing towards the first multi-aperture plate, and wherein a shape of at least one of the first surfaces is symmetric relative to an axis extending transversely to the first and second multi-aperture plates. 8. The system according to claim 1, wherein the second width is in a range of from about 100% to about 1000% of a diameter of the second aperture. 9. The system according to claim 1, wherein the first width is in a range of from about 150% to about 1500% of a diameter of the first aperture. 10. The system according to claim 1, wherein, for substantially each aperture of the plurality of apertures of the first multi-aperture plate, a diameter of the aperture of the plurality of apertures of the first multi-aperture plate is substantially equal to a diameter of a corresponding aperture of the plurality of apertures of the second multi-aperture plate aligned with the aperture of the first multi-aperture plate. 11. The system according to claim 1, wherein a diameter of the apertures of the pluralities of apertures is in a range of from about 0.5 μm to about 180 μm. 12. The system according to claim 1, wherein a distance between centers of adjacent apertures of the plurality of apertures of the first multi-aperture plate is in a range from about 5 μm to about 200 μm. 13. The system according to claim 1, wherein at least one of the first and second multi-aperture plates is made of silicon. 14. The system according to claim 1, further comprising a mounting structure mounting the first multi-aperture plate relative to the second multi-aperture plate. 15. The system according to claim 14, wherein the mounting structure comprises at least one actuator for adjusting a position of the first multi-aperture plate relative to the second multi-aperture plate. 16. The system according to claim 1, further comprising a third multi-aperture plate having a plurality of apertures and arranged such that the first multi-aperture plate is disposed between the third multi-aperture plate and the second multi-aperture plate, and wherein the plurality of apertures of the third multi-aperture plate is arranged such that each aperture of the plurality of apertures of the third multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the first multi-aperture plate. 17. The system according to claim 16, wherein a diameter of an aperture of the third multi-aperture plate is smaller than a diameter of a corresponding aperture of the first multi-aperture plate aligned with the aperture of the third multi-aperture plate. 18. The system according to claim 16, wherein a diameter of an aperture of the third multi-aperture plate is 99% or less of a diameter of a corresponding aperture of the first multi-aperture plate aligned with the aperture of the third multi-aperture plate. 19. The system according to claim 16, further comprising a mounting structure mounting the third multi-aperture plate relative to the first multi-aperture plate. 20. The system according to claim 19, wherein the mounting structure comprises at least one actuator for adjusting a position of the third multi-aperture plate relative to the first multi-aperture plate. 21. The system according to claim 1, wherein the charged particle source is an electron source and the at least one beam of charged particles is at least on beam of electrons. 22. The system according to claim 1, wherein the electric potentials are in a range from 0 to 5000V. 23. The system according to claim 1, further comprising a detector arrangement for detecting at least one of secondary particles and radiation emitted by the specimen as a result of being exposed to the charged particles. 24. The system according to claim 1, wherein the voltage supply system configured to apply the different electric potentials in order to compensate at least one particle-optical aberration of the at least one focusing particle-optical lens. 25. A particle-optical component for manipulating a plurality of beamlets of charged particles, the particle-optical component comprising:a first multi-aperture plate having a plurality of apertures and a second multi-aperture plate having a plurality of apertures, wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed therebetween;wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the plurality of apertures of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the second multi-aperture plate; andwherein a first width of the gap at a location of a first aperture of the plurality of apertures of the first multi-aperture plate is by at least 5 greater than a second width of the gap at a location of a second aperture of the plurality of apertures of the first multi-aperture plate;the particle-optical component further comprising a fourth aperture plate having at least one aperture, the first multi-aperture plate being disposed between the fourth aperture plate and the second multi-aperture plate, and further comprising a mounting structure comprising at least one actuator for displacing the fourth aperture plate relative to the first multi-aperture plate such that in a first position one aperture of the at least one aperture of the fourth aperture plate is in alignment with a first aperture of the first multi-aperture plate and in a second position different from the first position the one aperture is in alignment with a second aperture of the first multi-aperture plate. 26. A method of operating a particle-optical system, comprising:positioning a testing aperture plate having at least one aperture in a first position relative to a multi-aperture component comprising a plurality of apertures such that in the first position, a first set of apertures of the testing aperture plate is in alignment with a first set of apertures of the multi-aperture component, with the respective sets of apertures comprising at least one aperture each;transmitting a set of beamlets of charged particles through the first set of apertures of the testing aperture plate and the first set of apertures of the multi-aperture component aligned therewith;determining at least one of positions, shapes and dimensions of the transmitted beamlets in a predetermined plane and a total intensity or individual intensities of the transmitted beamlets;positioning the testing aperture plate in a second position relative to the multi-aperture component such that the first set of apertures of the testing aperture plate is in alignment with a second set of apertures of the multi-aperture component;transmitting a set of beamlets of charged particles through the first set of apertures of the testing aperture plate and the second set of apertures of the multi-aperture component aligned therewith; anddetermining at least one of positions, shapes and dimensions of the transmitted beamlets in the predetermined plane and a total intensity or individual intensities of the transmitted beamlets. 27. The method according to claim 26, further comprising at least one of adjusting at least one of an optical property and a position of the multi-aperture component and adjusting an optical property of the particle-optical system, based an the at least one of positions, shapes and dimensions of the transmitted beamlets in the predetermined plane and the total intensity or individual intensities of the transmitted beamlets. 28. A particle-optical arrangement, comprising:a charged particle source for generating at least one beam of charged particles; andat least one particle-optical component comprising:a first multi-aperture plate having a plurality of apertures and a second multi-aperture plate having a plurality of apertures, wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed therebetween;wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the plurality of apertures of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the second multi-aperture plate;wherein a first width of the gap at a location of a first aperture of the plurality of apertures of the first multi-aperture plate is by at least 5 greater than a second width of the gap at a location of a second aperture of the plurality of apertures of the first multi-aperture plate;wherein the at least one particle-optical component is arranged such that the second multi-aperture plate is traversed by a beam path of the charged particles downstream of the first multi-aperture plate; andwherein the particle-optical arrangement further comprises a first electrode traversed by the beam path of the charged particles upstream of the first multi-aperture plate;a second electrode traversed by the beam path of the charged particles downstream of the second multi-aperture plate; anda voltage supply system configured to apply different electric potentials to the first and second multi-aperture plates and the first and second electrodes. 29. The particle-optical arrangement according to claim 28, further comprising a voltage supply system configured to apply different electric potentials to the first and second multi-aperture plates. 30. The particle-optical arrangement according to claim 29, further comprising a controller having a first control portion configured to control the voltage supply system based upon a total beam current of a plurality of charged particle beamlets downstream of the particle-optical component. 31. The particle-optical arrangement according to claim 30, further comprising a current detector for detecting the total beam current of the plurality of charged particle beamlets. 32. The particle-optical arrangement according to claim 30, wherein the controller has a second control portion for adjusting beam currents of the plurality of charged particle beamlets, and wherein the first control portion is responsive to a setting of the second control portion. 33. The particle-optical arrangement according to claim 28, wherein the voltage supply system is configured to apply voltages to the first electrode and the first multi-aperture plate such that an electrical field generated upstream of the first multi-aperture plate in a vicinity thereof is a decelerating field for the charged particles of the beam of charged particles. 34. The particle-optical arrangement according to claim 28, wherein the voltage supply system is configured to apply voltages to the first electrode and the first multi-aperture plate such that an electrical field generated upstream of the first multi-aperture plate in a vicinity thereof is an accelerating field for the charged particles of the beam of charged particles. 35. The particle-optical arrangement according to claim 28, wherein the voltage supply system is configured to apply voltages to the second electrode and the second multi-aperture plate such that an electrical field generated downstream of the second multi-aperture plate in a vicinity thereof is an accelerating field for the charged particles of the beam of charged particles. 36. The particle-optical arrangement according to claim 28, wherein the voltage supply system is configured to apply voltages to the second electrode and the second multi-aperture plate such that an electrical field generated downstream of the second multi-aperture plate in a vicinity thereof is a decelerating field for the charged particles of the beam of charged particles. 37. The particle-optical arrangement according to claim 28, further comprising a third electrode traversed by the beam path of the charged particles between the first electrode and the first multi-aperture plate, wherein the voltage supply system is further configured to apply an electric potential to the third electrode. 38. The particle-optical arrangement according to claim 28, further comprising a fourth electrode traversed by the beam path of the charged particles between the second multi-aperture plate and the second electrode, wherein the voltage supply system is further configured to apply an electric potential to the fourth electrode. 39. The particle-optical arrangement according to claim 28, further comprising at least one focusing particle-optical lens disposed in the beam path of the charged particle beam. 40. The particle-optical arrangement according to claim 39, further comprising a voltage supply system configured to apply different electric potentials to the first and second multi-aperture plates, for compensating at least one particle-optical aberration of the at least one focusing particle-optical lens. 41. The particle-optical arrangement according to claim 40, wherein the at least one particle-optical aberration is at least one of a field curvature and a spherical aberration. 42. The particle-optical arrangement according to claim 28, wherein the voltage supply system is configured to apply electric potentials to the first and second electrodes such that a first electrical field is generated upstream of the first multi-aperture plate and a second electrical field different from the first electrical field is generated downstream of the second multi-aperture plate;further comprising at least one focusing particle-optical lens disposed downstream of the second multi-aperture plate in the beam path of the charged particles;wherein the voltage supply system is further configured to apply different electric potentials to the first and second multi-aperture plates, for compensating at least one particle-optical aberration of the at least one focusing particle-optical lens. 43. A method of manipulating charged particle beamlets, the method comprising:applying a predetermined first electric potential to a first multi-aperture plate and a predetermined second electric potential different from the predetermined first potential to a second multi-aperture plate;transmitting a plurality of charged particle beamlets through apertures of a first multi-aperture plate having a plurality of apertures and, subsequently, through a second multi-aperture plate having a plurality of apertures,and transmitting the plurality of charged-particle beamlets through at least one focusing particle-optical lens;wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed therebetween;wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the plurality of apertures of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the second multi-aperture plate;wherein a first width of the gap at a location of a first aperture of the plurality of apertures of the first multi-aperture plate is by at least 5% greater than a second width of the gap at a location of a second aperture of the plurality of apertures of the first multi-aperture plate; andwherein the applied predetermined electric potentials are chosen such that at least one particle-optical aberration of the at least one focusing particle-optical lens is compensated. 44. The method according to claim 43, wherein the predetermined electric potentials are in a range of from 0 to about 5000 V. 45. A particle-optical arrangement, comprising:a charged particle source for generating at least one beam of charged particles; at least one magnetic lens configured to generate a first magnetic field in a path of the at least one beam;at least a first multi-aperture plate having a plurality of apertures, wherein the at least first multi-aperture plate is disposed to be traversed by a beam path of the at least one beam of charged particles;at least one coil arrangement configured to generate a second magnetic field such that a magnetic flux density at the at least first multi-aperture plate is substantially zero. 46. A particle-optical arrangement according to claim 45, further comprising a second multi-aperture plate having a plurality of apertures, wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed therebetween;wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of the apertures of the second multi-aperture plate;wherein a first width of the gap at a location of a first aperture of the plurality of apertures of the first multi-aperture plate is by at least 5% greater than a second width of the gap at a location of a second aperture of the plurality of apertures of the first multi-aperture plate. 47. The particle-optical arrangement according to claim 46, wherein the first multi-aperture plate has a first surface facing towards the second multi-aperture plate, and the second multi-aperture plate has a first surface facing towards the first multi-aperture plate, wherein each first surface has an area comprising plural apertures of the respective plurality of apertures, and wherein at least one of the first surfaces is a curved surface within the area. 48. A method of manipulating charged particle beamlets, the method comprising:generating at least one of a charged-particle beam and a plurality of charged-particle beamlets;transmitting the at least one of the charged-particle beam and the plurality of charged-particle beamlets through at least one magnetic lens generating a first magnetic field;transmitting the at least one of the charged-particle beam and the plurality of charged-particle beamlets through at least one multi-aperture plate having a plurality of apertures; andgenerating a second magnetic field by applying a predetermined electric current to a coil arrangement traversed by the plurality of charged particle beamlets such that the second magnetic field at least partially compensates the first magnetic field and a magnetic flux density at the at least one multi-aperture plate is substantially zero. 49. A method of focusing a plurality of charged particle beamlets, the method comprising:transmitting at least one of a charged particle beam and a plurality of charged-particle beamlets through a first multi-aperture plate and a second multi-aperture plate, each having a plurality of apertures, with centers of the first and second multi-aperture plates being spaced a distance w0 apart,applying a first electric potential U1 to the first multi-aperture plate,applying a second electric potential U2 to the second multi-aperture plate, the second electric potential being different from the first electric potential;at least one of generating an electrical field traversed by the beam path upstream of the first multi-aperture plate and an electrical field traversed by the beam path downstream of the second multi-aperture plate, such that a first field strength E1 of an electrical field upstream and in the vicinity of the first multi-aperture plate differs from a second field strength E2 of an electrical field downstream and in the vicinity of the second multi-aperture plate by at least about 200 V/mm,wherein for charged particles having a charge q and having and a kinetic energy Ekin upon traversing the first multi-aperture plate, the following relationship is fulfilled: 0.0001 ≤ 3 4 · q w 0 · E kin ( U 1 - U 2 ) 2 E 1 - E 2 ≤ 0.2 . 50. The method according to claim 49, wherein a distance between the first and second multi-aperture plates increases with increasing distance from the center thereof such that a field strength of an electrical field generated by applying the first and second electrical potentials U1 and U2 in between the first and second multi-aperture plates decreases with increasing distance from the center. 51. A particle-optical arrangement, comprisinga first multi-aperture plate having a plurality of apertures and a second multi-aperture plate having a plurality of apertures, wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed therebetween; anda magnetic lens arrangement comprising a first pole piece and a second pole piece and a coil for inducing magnetic flux in the first and second pole pieces;wherein the first multi-aperture plate is magnetically coupled to or integrally formed with the first pole piece of the magnetic lens arrangement and the second multi-aperture plate is magnetically coupled to or integrally formed with the second pole piece of the magnetic lens arrangement;wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the plurality of apertures of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the second multi-aperture plate; andwherein a first width of the gap at a location of a first aperture of the plurality of apertures of the first multi-aperture plate is by at least 5 greater than a second width of the gap at a location of a second aperture of the plurality of apertures of the first multi-aperture plate. 52. A method of focusing a plurality of charged particle beamlets, the method comprising:generating an electrical field of at most 5000 V/mm between a first multi-aperture plate having a plurality of apertures and a first electrode such that the first multi-aperture plate has a first focusing power F1, wherein the first electrode is spaced a distance of at least 1 mm apart from the first multi-aperture plate;transmitting at least one of a charged particle beam and a plurality of charged-particle beamlets through the electrical field, the plurality of apertures of the first multi-aperture plate and the first electrode;transmitting the at least one of the charged particle beam and the plurality of charged-particle beamlets through apertures of a particle-optical component comprising at least a second multi-aperture plate having a plurality of apertures, the particle-optical component being configured and operated so as to provide a second focusing power F2, wherein the second focusing power F2 of the particle-optical component is at least five times smaller than the first focusing power F1. 53. A particle-optical component, comprising a first multi-aperture plate having a plurality of apertures,a second multi-aperture plate having a plurality of apertures,a fourth aperture plate having at least one aperture,a mounting structure comprising at least one actuator for displacing the fourth aperture plate relative to the first multi-aperture plate to a first position and to a second position, which is different from the first position,wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed therebetween;wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the plurality of apertures of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the second multi-aperture plate; andwherein the first multi-aperture plate is disposed between the fourth aperture plate and the second multi-aperture plate. 54. The particle-optical component according to claim 53, wherein one aperture of the at least one aperture of the fourth aperture plate is in alignment with a first aperture of the first multi-aperture plate in the first position and the one aperture is in alignment with a second aperture of the first multi-aperture plate in the second position. 55. A particle-optical component, comprisinga first multi-aperture plate having a plurality of apertures;a third multi-aperture plate having a plurality of apertures,wherein the plurality of apertures of the third multi-aperture plate is arranged such that each aperture of the plurality of apertures of the third multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the first multi-aperture plate, and wherein a diameter of an aperture of the third multi-aperture plate is smaller than a diameter of a corresponding aperture of the first multi-aperture plate aligned with the aperture of the third multi-aperture plate; anda voltage supply system configured to apply different electric potentials to the first and third multi-aperture plates of the particle-optical component. 56. The particle-optical component according to claim 55, further comprising a second multi-aperture plate having a plurality of apertures, wherein the second multi-aperture plate is spaced apart from the first multi-aperture plate such that a gap is formed therebetween; wherein the plurality of apertures of the first multi-aperture plate is arranged such that each aperture of the plurality of apertures of the first multi-aperture plate is aligned with a corresponding aperture of the plurality of apertures of the second multi-aperture plate; and wherein the third multi aperture plate is arranged such that the first multi-aperture plate is disposed between the third multi-aperture plate and the second multi-aperture plate. 57. The particle-optical component according to claim 55, wherein a diameter of an aperture of the third multi-aperture plate is less than 99% of a diameter of a corresponding aperture of the first multi-aperture plate aligned with the aperture of the third multi-aperture plate. |
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summary | ||
051724022 | claims | 1. An exposure apparatus, comprising: a radiation source generating a non-uniformness in illuminance including x-rays generally in a direction in one dimension with respect to a predetermined exposure region; illuminance measuring means for measuring an illuminance distribution in the direction in one dimension in the exposure region and in an area adjacent thereto; shutter means having a leading edge effective to start exposure in the exposure region and a trailing edge effective to stop the exposure; a memory with a drive table for setting a drive curve for the leading and trailing edges in accordance with the measured illuminance distribution; shutter driving means for causing the leading and trailing edges to move through the exposure region in the direction in one dimension, independently of each other, in accordance with said drive table; edge position detecting means for detecting, with an illuminance detector of said illuminance measuring means and at two different points spaced in the direction in one direction, a position of a shadow of one of the leading and trailing edges; and coordinate conversion means for effecting conversion of a coordinate system of said drive table and a coordinate system for the positioning of said illuminance detector during the illuminance distribution measurement, in accordance with results of the edge position detection. moving the shutter so that one of the leading and trailing edges of the shutter is related to the exposure region; projecting an exposure beam including x-rays between the leading and trailing edges of the shutter and to at least a portion of the exposure region; determining a position of a shadow of the one edge formed by the exposure beam with respect to a stage coordinate system related to the movement of the chuck; and adjusting the shutter on the basis of the determination in said determining step. moving a shutter having an edge so that the edge is related to a predetermined exposure region; projecting an exposure beam including X-rays to the edge of the shutter and to at least a portion of the exposure region; determining a position of a shadow of the edge of the shutter formed by the exposure beam with respect to a predetermined coordinate system related to movement of a movable chuck; adjusting the shutter in accordance with the determination in said determining step; placing a substrate on the chuck; moving the chuck so that the substrate is related to the exposure region; and controlling the exposure of the substrate with the exposure beam through the shutter. a chuck for holding a substrate to be exposed; a stage for moving said chuck in accordance with a stage coordinate system; a shutter having an edge, for controlling exposure of the substrate, held by said chuck, with an exposure beam including X-rays; a shutter driving mechanism for displacing said edge of said shutter in accordance with a shutter coordinate system; a first detector for detecting the exposure beam and producing a corresponding output; a second detector for determining a position of a shadow of said edge of said shutter formed by the exposure beam, with respect to the stage coordinate system, on the basis of the output of said first detector; and a processor for determining the relationship between a position of said edge of said shutter with respect to the shutter coordinate system and the position of the shadow of said edge of said shutter with respect to the stage coordinate system, on the basis of the determination by said second detector. a chuck for holding a substrate to be exposed; a stage for moving said chuck in accordance with a stage coordinate system; a shutter having an edge, for controlling exposure of the substrate, held by said chuck, with an exposure beam including X-rays; a shutter driving mechanism for displacing said edge of said shutter in accordance with a shutter coordinate system; and a detector for determining, with respect to the stage coordinate system, a position of a shadow of said edge of said shutter formed by the exposure beam which edge is positioned with respect to the shutter coordinate system. projecting the edge of the shutter on a predetermined plane with an exposure beam including X-rays; detecting a position of the projected edge of the shutter; and adjusting the shutter in accordance with the detection in said detecting step. projecting the edge of the shutter on a predetermined plane; detecting a position of the projected edge of the shutter; adjusting the shutter on the basis of said detection in said detecting step; and exposing the substrate with radiation including X-rays while controlling the exposure through the adjusted shutter. 2. A method of adjusting a shutter device of an exposure apparatus having a movable chuck for holding a substrate to be exposed, and an exposure region related to the exposure of the substrate, said shutter device having a movable shutter with a leading edge and a trailing edge, said method comprising the steps of: 3. A method according to claim 2, wherein said adjusting step comprises the step of determining the relationship between a position of the edge with respect to a shutter coordinate, set in relation to the shutter, and a position of the shadow with respect to the stage coordinate system. 4. A method according to claim 2, wherein said adjusting step comprises the step of adjusting at least one of a position and an attitude of the shutter with respect to the exposure beam. 5. A method according to claim 2, wherein the exposure beam includes at least one of light of a g-line, light of an i-line, light of an excimer laser and light of X-rays. 6. An exposure method for the manufacture of semiconductor devices, comprising the steps of: 7. An exposure apparatus, comprising: 8. An apparatus according to claim 7, wherein said chuck and said first detector are movable as a unit with said stage. 9. An apparatus according to claim 7, wherein the exposure beam includes at least one of light of a g-line, light of an i-line, light of an excimer laser, and light of X-rays. 10. An exposure apparatus, comprising: 11. An apparatus according to claim 9, further comprising an adjuster for adjusting an attitude of said shutter with respect to the exposure beam, in accordance with the determination made by said detector. 12. An apparatus according to claim 10, wherein the exposure beam includes at least one of light of a g-line light of an i-line, light of an excimer laser, and light of X-rays. 13. A shutter adjusting method for use in an exposure apparatus for the manufacture of semiconductor devices, for adjusting a shutter with an edge, comprising the steps of: 14. A method according to claim 13, wherein the exposure beam includes at least one of light of a g-line, light of an i-line, light of an excimer laser, and light of X-rays. 15. A method according to claim 14, wherein the light of X-rays is produced from a synchrotron radiation source. 16. A method of patterning a substrate through exposure of the substrate while controlling the exposure with a shutter having an edge, said method comprising the steps of: 17. A method according to claim 16, wherein the radiation includes at least one of light of a g-line, light of an i-line, light of an excimer laser and light of X-rays. 18. A method according to claim 17, wherein the light of X-rays is produced from a synchrotron radiation source. |
056082231 | summary | FIELD OF THE INVENTION The present invention concerns an ion implantation device which implants charged particles, especially ions, into substrates such as semiconductor wafers. BACKGROUND ART Generally, ion implantation devices of this type are used to implant ions of a predetermined chemical species into semiconductor wafers in semiconductor manufacturing processes. Furthermore, such ion implantation devices include ion implantation devices with a so-called "mechanical scanning system" in which implantation is efficiently performed by a) positioning a multiple number of semiconductor wafers around the circumference of a rotation disk, b) causing said disk to rotate so that all of the semiconductor wafers are scanned at a high speed, and c) causing relative movement of the ion beam at a comparatively low speed in the radial direction of the rotating disk, so that the individual semiconductor wafers are scanned at a low speed. Recently, in ion implantation devices, there has been a demand for an increase in the ion beam current in order to improve the productivity of semiconductor devices by shortening the ion implantation time. Hopes have been place in the abovementioned ion implantation devices with mechanical scanning systems as ion implantation devices capable of handling such large-current ion beams. However, in cases where a large-current ion beam is used, particles of impurities are created by sputtering which occurs as a result of parts other than the semiconductor wafers (e.g., the rotating disk) being irradiated by the ion beam. These impurity particles become mixed with the desired ions, and adhere to the semiconductor wafers, so that said semiconductor wafers become contaminated (below, this will be referred to as "contamination"). When impurity elements other than the desired ions thus become mixed with said ions and adhere to the wafers, the yield of semiconductor devices drops conspicuously. Furthermore, it has also been indicated that in cases where the chemical species of ions being implanted is changed after certain ions have been implanted, contamination caused by the element previously being implanted (i.e., cross contamination) occurs. Various methods have been proposed in order to prevent such contamination or cross contamination. For example, in Japanese Patent Application Kokai No. 61-116746, an ion implantation device is disclosed in which contamination caused by sputtering of the rotating disk is prevented by constructing a scanning arm assembly in which wafer attachment paddles are installed at equal intervals in a circular arrangement around a central hub, and wafers are attached to the tips of said paddles. This ion implantation device is constructed so that the scanning arm assembly is caused to rotate at high speed, and so that a cycloidal movement is performed at a low speed about the axis of the bottom part of the scanning arm assembly. In such a construction, since wafer attachment paddles are installed as a disk, the portions of said paddles that are exposed to the ion beam can be reduced, so that the portions of the disk exposed to the ion beam can be greatly reduced; furthermore, as a result of the aforementioned cycloidal movement, the entire surface of each wafer can be irradiated with the/on beam. However, in the abovementioned ion implantation device using wafer attachment paddles, although the speed of the aforementioned cycloidal movement is controlled so that said speed is proportional to the distance from the axis of rotation, no consideration is given to fluctuations where there are changes in the ion beam current during the aforementioned low-speed cycloidal movement, the device cannot adequately respond to said changes; as a result, ions cannot be uniformly implanted. One object of the present invention is to provide an ion implantation device a) which can reduce sputtering caused by exposure of the disk to the ion beam, and b) which can adequately respond to changes in the ion beam current during ion beam implantation. DISCLOSURE OF THE INVENTION The present invention provides an ion implantation device which is characterized by the fact that in an ion implantation device equipped with a disk which allows a plurality of wafers to be positioned at intervals around the circumference of said disk, said disk is constructed so that there is at least one place on said disk where the spacing between the aforementioned wafers is different from the spacing elsewhere. In the above construction, respective ion beam charges passing between the wafers (which are separated from each other by different spacing) are successively compared over time, so that fluctuations in the ion beam current are detected. Furthermore, the speed of the aforementioned low-speed scanning in the radial direction of the disk with respect to the axis of rotation is controlled so that even if there are fluctuations in the ion beam current during ion beam implantation, ions can be implanted into the respective semiconductor wafers in a substantially uniform manner . |
abstract | The invention refers to a spacer for holding a number if elongated fuel rods intended to be located in a nuclear plant and to a fuel unit having such spacers. The spacer encloses a number of cells, which each has a longitudinal axis and is arranged to receive a fuel rod in such a way that the fuel rod extends in parallel with the longitudinal axis. Each cell is formed by a sleeve-like member. Each sleeve-like member is manufactured in a sheet-shaped material that is bent to the sleeve-like shape. |
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051679051 | summary | BACKGROUND OF THE INVENTION This invention generally relates to apparatus for sealing conduits and more particularly relates to a foldable nozzle dam having a foldable extrusion-resistant seal or gasket for sealing conduits, such as the primary nozzles of a nuclear steam generator. Before discussing the current state of the art, it is instructive first to briefly describe the structure and operation of a typical nuclear steam generator. In this regard, a typical nuclear steam generator generally comprises a shell and a plurality of U-shaped heat transfer tubes disposed in the shell, the U-shape of the tubes defining a first tube leg portion and a second tube leg portion interconnected by a U-bend tube portion. The shell defines an inlet plenum and an outlet plenum therein such that the first tube leg portion of each U-shaped tube is in fluid communication with the inlet plenum and the second tube leg portion of each tube is in fluid communication with the outlet plenum. Also in fluid communication with the inlet plenum is an inlet primary nozzle attached to the shell for delivering a radioactive primary fluid into the inlet plenum. Moreover, in fluid communication with the outlet plenum is an outlet primary nozzle attached to the shell for allowing the primary fluid to exit the outlet plenum and thus exit the steam generator in the manner discussed hereinbelow. In addition, the steam generator shell also includes a plurality of relatively small diameter manway openings therethrough for allowing access to the inlet and outlet plena so that maintenance can be performed in the steam generator. In this typical nuclear steam generator, each manway opening has a diameter substantially less than the inside diameters of the inlet and outlet nozzles. During operation of the nuclear steam generator, the radioactive primary fluid, which is heated by the fission reaction of a nuclear reactor core, flows through the tubes as a nonradioactive secondary fluid of lower temperature circulates around the tubes. More specifically, the primary fluid flows from the nuclear reactor core where it is heated, through the inlet nozzle and into the inlet plenum. The primary fluid then flows into the first tube leg portion of each heat transfer tube, through the U-bend portion of each tube, out the second tube leg portion of each tube and then into the outlet plenum, whereupon it exits the outlet nozzle and the steam generator. Moreover, as the primary fluid exits the steam generator, it is returned to the nuclear reactor core to be reheated. Of course, as the primary fluid flows through the heat transfer tubes, it gives up its heat to the secondary fluid circulating around the tubes for producing steam in a manner well known in the art. Such a typical nuclear steam generator is more fully disclosed in U.S. Pat. No. 4,079,701 entitled "Steam Generator Sludge Removal System" issued Mar. 21, 1978 to Robert A. Hickman et al. Periodically, it is necessary to shut down the nuclear reactor core for refueling. At that time, it is cost advantageous also to simultaneously perform maintenance on the steam generator. During such maintenance activities, a reactor cavity, which encloses a reactor vessel containing the reactor core, is partially drained of primary fluid to a level that is below the elevation of the inlet and outlet nozzles of the steam generator. Of course, for safety reasons the nuclear reactor core is not uncovered when the reactor cavity is partially drained of primary fluid. Thus, it will be appreciated that this process of partially draining the reactor cavity to an elevation that is below the inlet and outlet nozzles of the steam generator also drains the heat transfer tubes as well as the inlet and outlet plena of the steam generator. After the steam generator tubes and the inlet and outlet plena are drained of primary fluid, nozzle dams are inserted through the relatively small diameter manways and installed in the mouths of the inlet and outlet nozzles to block the nozzles. Once these dams are installed, the reactor cavity can be refilled with primary fluid for the refueling operation, the reactor cavity being refilled to a level above the elevation of the inlet and outlet plena. Therefore, refilling of the reactor cavity with primary fluid can be accomplished without interfering with maintenance activities being performed in the steam generator plena because the nozzle dams which block the inlet and outlet nozzles prevent the radioactive primary fluid from rising into the inlet and outlet plena. Moreover, simultaneously performing reactor refueling and steam generator maintenance activities reduces the total time the nuclear reactor core is shut down, thereby recapturing revenue that would otherwise be lost when reactor refueling and steam generator maintenance are performed in seriatim. In addition, as stated hereinabove, the manway openings have a diameter smaller than the inside diameter of the inlet and outlet nozzles. Therefore, a problem in the art is to provide a nozzle dam that is not only capable of passing through the relatively small diameter manways but also capable of being disposed across the relatively larger inside diameters of the inlet and outlet nozzles to block the nozzles. Of course, once installed across the inlet or outlet nozzle, the nozzle dam should be fluid-tight so that primary fluid will not rise into the inlet and outlet plena to interfere with maintenance activities being performed in the steam generator. In this regard, the nozzle dam may include at least two parts sized to pass through the inlet or outlet nozzle, the two parts having a seal or gasket therebetween to seal the nozzle dam so that the nozzle dam is fluid-tight. The seal or gasket, which is intended to be clamped between the two parts for creating a seal therebetween, may have at least one aperture for passage of clamping means therethrough. However, applicants have observed that the aperture of the seal or gasket may extrude away from the clamping means when the two parts are tightly clamped together, thus enlarging the fluid flow path defined by the aperture surrounding the clamping means. This is undesirable because such enlargement of the flow path compromises the ability of the seal or gasket to perform its intended function of providing a nozzle dam that is fluid-tight. Therefore, another problem in the art is to provide a nozzle dam having a seal or gasket that resists extrusion away from such clamping means so that the nozzle dam is fluid-tight. Steam generator nozzle dams having seals are known. One such nozzle dam is disclosed in U.S. Pat. No. 4,637,588 entitled "Non-Bolted Ringless Nozzle Dam" issued Jan. 20, 1987 in the name of John J. Wilhelm et al. and assigned to the assignee of the present invention. This patent discloses a nozzle dam having one or more seal assemblies, each seal assembly including a foldable circular seal plate encircled with an inflatable seal which is disposable in frictional engagement with the nozzle wall. However, this patent does not appear to disclose a nozzle dam having an extrusion-resistant seal or gasket. Another nozzle dam having a seal assembly is disclosed in U.S. Pat. No. 4,671,326 entitled "Dual Seal Nozzle Dam and Alignment Means Therefore" issued Jun. 9, 1987 in the name of John J. Wilhelm et al. and assigned to the assignee of the present invention. This patent discloses a seal assembly including a foldable circular seal plate having a center section hingedly connected to two side sections. However, this patent does not appear to disclose a nozzle dam having an extrusion-resistant seal or gasket. An extrusion-limiting seal or gasket is disclosed in U.S. Pat. No. 4,181,313 entitled "Seals And Gaskets" issued Jan. 1, 1980 in the name of Edward F. H. B. Hillier et al. According to this patent, a seal or gasket, which has at least one aperture providing a fluid passageway and which is intended in use to be clamped by clamping means between surfaces of two parts to be sealed, comprises an elastically-compressible material and a relatively-incompressible material bonded therein, the relatively-incompressible material forming an extrusion-limiting barrier which extends at least partway around the aperture. However, this patent does not appear to disclose a foldable nozzle dam having a foldable extrusion-resistant seal or gasket. An anti-extrusion sealing device is disclosed in U.S. Pat. No. 4,468,042 entitled "Anti-Extrusion Sealing Device With Interlocked Retainer Portions" issued Aug. 28, 1984 in the name of Aaron J. Pippert et al. According to this patent, a relatively soft body, including a sealing portion, and a harder body, which serves as an anti-extrusion device for the soft body, are permanently joined together by mating mechanical interlock formations. However, this patent does not appear to disclose a foldable nozzle dam having a foldable extrusion-resistant seal or gasket. Thus, although the above-recited patents may disclose nozzle dams and anti-extrusion seal devices, these patents do not appear to disclose a foldable nozzle dam having a foldable extrusion-resistant seal or gasket, the nozzle dam being foldable for passing through the relatively small diameter steam generator manway and being unfoldable for placement across the larger diameter of the nozzle in combination with a foldable seal or gasket attached to the nozzle dam, the seal or gasket being extrusion-resistant for providing a nozzle dam that is fluid-tight. Therefore, what is needed is a foldable nozzle dam having a foldable extrusion-resistant seal or gasket for sealing conduits, such as the primary nozzles of a nuclear steam generator. SUMMARY OF THE INVENTION A typical nuclear power plant includes a nuclear reactor core for producing heat and a steam generator in fluid communication with the nuclear reactor core for generating steam. The steam generator includes inlet and outlet primary nozzles attached to the steam generator. At times it is necessary to perform maintenance in the steam generator. To safely and satisfactorily perform this maintenance, it is prudent first to seal or block the inlet and outlet primary nozzles of the steam generator. Therefore, disclosed herein is an apparatus for sealing or blocking conduits, such as the primary nozzles of a nuclear steam generator. In general, the apparatus comprises an annular bracket surrounding the open end of the conduit, the bracket having a circular opening transversely therethrough and a top surface thereon and having a periphery portion sealingly attached to the open end of the conduit, the periphery portion having a plurality of spaced-apart holes transversely therein; a cover plate mounted on the bracket for covering the opening of the bracket, the cover plate having a periphery portion having a plurality of spaced-apart bores transversely therethrough; a plurality of elongated fasteners engaging the holes of the bracket and the bores of the cover plate for tightly connecting the cover plate to the bracket; and extrusion-resistant seal means interposed between the bracket and the cover plate for providing a fluid-tight seal therebetween, the seal means having a periphery portion having a plurality of spaced-apart transverse apertures for receiving the fasteners therethrough, the seal means intimately engaging the top surface of the bracket for providing a fluid-tight seal between the cover plate and the bracket, the seal means being configured to resist extrusion away from the fasteners as the cover plate is tightly connected to the bracket. More specifically, the invention comprises an annular bracket sealingly attached to the rim of the open end of the primary nozzle, the bracket having a plurality of threaded holes therein. Mounted atop the bracket is a foldable nozzle dam that includes a generally arcuate-shaped first side section hingedly connected to a generally arcuate-shaped second side section. Each arcuate-shaped side section includes a cut-out centrally formed along the straight portion thereof, the cut-outs defining a generally rectangular opening when the hinged side sections are moved into the same plane with respect to each other. Covering the rectangular opening and removably connected to each side section is a generally rectangular center section. When the side sections are moved into the same plane with respect to each other and when the center section is connected to the side sections, the center section and the side sections define a nozzle dam having a generally circular configuration for covering the circular opening defined by the bracket. The periphery portions of the center section and of the side sections have bores therethrough capable of being coaxially aligned with the threaded holes in the bracket. A plurality of threaded bolts extend through the bores in the nozzle dam and into the threaded holes in the bracket for removably connecting the nozzle dam to the bracket. Interposed between the nozzle dam and the bracket is an elastomeric foldable extrusion-resistant seal member for providing a seal therebetween so that the primary nozzle may be suitably sealed. The periphery of the seal member has a plurality of apertures for receiving each bolt therethrough. The seal member is attached, such as by contact cement, to the side sections of the nozzle dam. In one embodiment of the seal member, the seal member comprises in transverse section a plurality of layers bonded or laminated together, such as by a suitable adhesive. In this embodiment of the seal member, a generally annular first layer is sealingly attached to the bottom of a generally circular second layer. The first layer has an outside diameter that is substantially the same as the outside diameter of the nozzle dam. The second layer has a diameter that is also substantially the same as the outside diameter of the nozzle dam and covers the full surface of the nozzle dam. The first layer is of a material that is softer than the second layer. In this regard, the first layer may be EPDM (ethylene propylene diene monomer) rubber having a Shore A durometer hardness of between 40 and 60. The second layer may be EPDM rubber having a Shore A durometer hardness of between 60 and 80. The dual hardness of the seal member allows it to be extrusion-resistant and also allows it to intimately engage the top surface of the bracket for creating an effective seal between the nozzle dam and the bracket, which nozzle dam and/or bracket may have surface imperfections that could otherwise lead to leakage. In another embodiment of the seal member, the seal member comprises in transverse section a plurality of regions fused or molded together rather than laminated layers bonded together. In this embodiment of the seal member, a generally annular first region is molded with a generally circular second region. The first region has an outside diameter that is substantially the same as the outside diameter of the nozzle dam. The second region has a diameter that is also substantially the same as the outside diameter of the nozzle dam. The first region is of a material that is softer than the second region. In this regard, the first region may be EPDM rubber having a Shore A durometer hardness of between 40 and 60. The second region may be EPDM rubber having a Shore A durometer hardness of between 60 and 80. The molded configuration of the molded seal member allows it to be mounted on the nozzle dam assembly more easily than the laminated seal member. The molded seal member is formed in a shop-fabricated, press-cure process. The laminated seal member, on the other hand, requires that the annular first layer be formed separately from the second layer. The next step for assembling the laminated seal member is to mat and glue the two layers together. This step for producing the laminated seal member requires that the first layer be precisely matted and glued to the second layer. The gluing operation must result in laminated layers that are not buckled and that do not contain air bubbles therebetween; that is, the laminated layers must be substantially uniformly glued to each other across their entire interface. If the laminated layers are not precisely matted and glued, then the layers must be separated, the gluing removed and the operation repeated. Thus, the laminated seal member requires more labor-intensive assembly steps than the molded seal member and is therefore more costly to produce. During installation in the primary nozzle, the nozzle dam is drawn toward the bracket as the bolts threadably engage the holes of the bracket. As the nozzle dam is drawn toward the bracket, a compressive force will act perpendicularly on each opposing face or side of the seal member because the seal member is interposed between the nozzle dam and the bracket. This compressive force acting perpendicularly against each side of the seal member will tend to cause the seal member to extrude laterally outwardly away from each bolt. Such lateral extrusion of the seal member as the nozzle dam is tightly clamped or connected to the bracket will tend to enlarge the aperture that defines the annular gap or fluid flow path around each bolt. This is undesirable because creation of such an enlarged flow path will compromise the ability of the seal member to perform its intended function of providing a nozzle dam that is fluid-tight. Thus, according to the invention, the seal member is configured to be extrusion-resistant so that the seal member will not laterally extrude away from each bolt in a manner that adversely enlarges the fluid flow path around each bolt. An object of the present invention is to provide an apparatus for sealing or blocking the open end of a conduit. Another object of the present invention is to provide a foldable extrusion-resistant seal or gasket for sealing the primary nozzles of a nuclear steam generator. A feature of the invention is the provision of an extrusion-resistant laminated seal member having in transverse cross-section a plurality of bonded layers of differing hardnesses. Another feature of the invention is the provision of an extrusion-resistant molded seal member having in transverse cross-section a plurality of fused or molded regions of differing hardnesses. An advantage of the invention is that the configuration of the seal member allows it to be extrusion-resistant so that the seal member will not substantially laterally extrude away from bolts passing therethrough so that the fluid flow path surrounding the bolts is not adversely enlarged. These as well as additional objects, features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments with reference to the several figures. |
052763358 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A cask body for storing and transporting highly radioactive materials according to this invention may be accomplished using an inner shell which can be made of steel or similar structurally strong material, with a number of layers of depleted uranium wire circumferentially wound on the inner shell to create a radioactive shield against emanation of radioactivity from materials stored within the inner shell. The wire can be wound tightly, tensilely stressed onto the inner shell to apply a compressive stress on the inner shell, thereby increasing its strength and durability. The shield itself may be a few inches thick and the cask may be six or more feet in diameter and six or more feet high for typical applications. A casting of depleted uranium in a copper jacket (to prevent rapid oxidation) is hot worked such as in a looping mill, into an intermediate diameter, for example from 3/8 to 5/16 inch. It is then cold drawn to a final size and shape, for example a round cross section with a diameter of 1/8 to 1/16 inch, or a rectangular cross section of 1/10 to 1/4 inch. This wire may then be used to create the wire wound depleted uranium shield. If there is a large transition from the hot working size to the cold drawn size, further heat treating may be used to soften the metal and then final shaping through cold drawing may be effected. After this, the depleted uranium wire can be used to wind cylindrical or spiral shields for the cask body cover and base members according to this invention to form a completed cask. The hot working eliminates and heals voids, cracks and holes that might normally occur in cast material. It also recrystallizes the structure from cast dendrites to regular crystalline wrought material which is more ductile and tougher. By using wire to form the shield instead of castings, any desired shape can be fabricated without the requirement for new casting molds. In this way large capital investment for melting and casting dies and furnaces is eliminated. In addition, the wire wound shield creates a single continuous structure (without the added cost and complexity of designing joints for castings) which will not only be structurally sound but will avoid leakage of radioactive radiation. The final wire form can be round, square, flat, hexagonal, or any polygonal shape. Even round wire with its inherent voids can be used by simply adding additional layers to compensate for the total void, so that the total length of the path through the shielding material is sufficient to attenuate the radiation. The voids may be minimized by running the wire in the same direction from layer to layer: that is, in a left-hand helix or a right-hand helix continuously. A further advantage of using wire is that the quality of the shielding can be tested before the cask is complete. Delaying inspection until after the completion of the cask introduces two problems. The expense of fabricating the device has already been endured before it is known whether the quality is acceptable. In addition, once the shielded cask is completed it is difficult to inspect in the typical manner using X-rays since it is an effective shielding device. By using a wire-wound shield, there is provided the opportunity to inspect the wire before it is wound into a shield. This can be done very quickly "on the fly" as the wire goes past an inspection station, and since the wire is quite thin, X-rays or ultrasonics can be effectively used to determine its uniformity and structure. Although the wire has been disclosed to herein as being drawn to size, it may as well be done by other techniques, such as by rolling for example. When the wire is wound into the shield, the layers are staggered so that the joints between the wire do not overlap and create an escape path for the radiation. The cask body can contain an outer shell spaced from the inner shell to cover and protect the depleted uranium. The outer shell may be the same shape as the inner shell, and it may be fixed to the inner shell to form a single unitary body with superior strength and rigidity containing the depleted uranium wire-wound shield between the two shells. The cask may be completed by a base member and a cover member which caps each end of the body. Each of the members can include an inner plate and a number of layers of depleted uranium wire wound on the inner plate to create a radioactive shield against emanation of radioactivity from the material stored within the cask. A depleted uranium plug may be used on each inner plate as the central point on which the depleted uranium wire is wound, either spirally or circumferentially about the plug. The base and cover members may include outer plates spaced from the inner plates and covering and protecting the depleted uranium wire. The depleted uranium plug can be tapered so that it automatically induces a staggering of the joints between the wire from layer to layer to avoid escape paths through which the radiation can escape. There is shown in FIG. 1 the inner shell 10 of a cask body according to this invention on which is wound circumferentially a shield 12 of depleted uranium wire. As shell 10 is rotated about its central axis 14, the depleted uranium wire 16 is wound on it by a wire-winding machine 18 of conventional design in the same manner as wire would be wound on a conventional wire or cable bobbin or reel. As wire 16 is cast back and forth across shell 10 rotated by drive 9, the wire is wound circumferentially, first in a left-hand helix, then in a right-hand helix. However, alternatively, wire winder 18, a wire winding traversing mechanism, is operated to stop and rewind only in the same direction: that is, always in a left-hand spiral or always in a right-hand spiral. When this is accomplished, the strands of round wire will lie within the joints between the wires of subordinate layers so as to minimize the voids between them. Thus in FIG. 2, where the wire has been laid in a left-hand helix, wire strands 20, 22 and 24 of the lower layer, shown in full lines, create gaps at joints 26 and 28. When the next layer is applied, strands 30 and 32, shown in phantom, will lie over joints 26 and 28, minimizing the voids 34, 36, 38 shown in FIG. 3. If the layers were applied in a more conventional manner, first in a left-hand helix then in a right-hand helix, the strands would crisscross as shown in FIG. 4, where the strands of the lower layer 40 slant to the left and the strands of the the upper layer 42 slant to the right. The voids can be eliminated in a number of ways. For example, the wire can be made square, rectangular, or flat as indicated in FIG. 5, where the strands 44 and 46 in the upper layer are staggered so that they cover the joints 48 and 50 created between strands 52, 54 and 56. While in FIG. 5 the overlap of the two layers is shown to be 50%, the actual amount of overlap is adjusted for the number of layers and the diameter of the wire. For example, in FIG. 6, a number of layers 60 far in excess of two can be applied to build the shield since the overlap is in the range of only 1 or 2%. By winding alternately and continuously from left to right and right to left, in FIG. 6B, adjacent layers of wire have their joints angled to each other, thereby additionally inhibiting joint alignment. Other shapes of wire also eliminate voids. For example the hexagonal wires 70 in the upper layer 72, FIG. 7, nest without voids in the junctions formed by hexagonal strands 74 in the lower layer 76. The completed cask body 11, FIG. 8, is shown having a cylindrical outer shell 82 matching in shape cylindrical inner shell 10 and welded to it at junctions 84 and 86 to form a single unitary structure with four-layer wire-wound depleted uranium shield 12 between them. The method of fabricating cask body 11 includes casting an ingot 100, FIG. 9, of depleted uranium. Then in step 102, hot working the depleted uranium into a rod or wire of material of a diameter from 3/8 to 5/16 inch, for example, in an extrusion press such as a 1400 ton Loewy hydropress or a grooved roll rod rolling mill. Following this in step 104, the wire or rod is cold drawn to a final size and shape such as a round wire with a diameter of 1/8 to 1/16 inch or a rectangular wire 1/10 by 1/4 inch. Since the drop in size between the hot working and the cold drawing is substantial, a further heat treatment may be provided in step 106 to soften the depleted uranium wire, after which a final shaping by cold drawing can be accomplished in step 108. Following this, in step 110, the wire may be wound circumferentially about inner shell 10 and then circumferentially or spirally wound in step 112 on a plate to form the cover and base members. End caps, which may take the form of identically fabricated base member 120 and cover member 122, may be used to close the ends of cask body 11, FIG. 8. Each such member, as shown in FIG. 10, includes an inner plate 124 on which is wound spirally, circumferentially or both, a number of layers of depleted uranium wire. An outer plate 128 may be fixed to inner plate 124 to form a protective covering over the depleted uranium wire 126 which constitutes radioactivity shield 130. An annular wall is provided by inner plate 124 and outer plate 128 complete with shielding 130 in order to complete the closure of cask body 11 and eliminating any possible line of sight escape paths for radiation. A depleted uranium plug 140 may be used at the center of members 120, 122 to form a center point about which the wire may be wound. Plug 140 may be formed with tapered wall 142 as shown in FIG. 11 with respect to plug 140a. The taper is set so that each successive layer of wire windings 144 is offset with respect to the others so that no direct line of sight through junctions is permitted. In order to remove potential line of sight leakage along tapered wall 142, that wall can be formed with a helical, curved groove 142a, FIG. 11B, for circular wire, or a stepped surface 142b, FIG. 11C, for wire with a rectilinear cross-section. The spiral winding of depleted uranium wire 126a about plug 140 on inner plate 124a as shown in FIG. 12 can be accomplished by a spiral winding device which includes a drive table 150, FIG. 13, driven by drive system 152 to rotate inner plate 124a while wire 126a is fed through a radially traversing feeder arm 154 in a conventional way. Completed cask 180, FIG. 14, is shown including cask body 11 with cover member 120b and base member 122b installed on it. In this embodiment, cover member 120b and base member 122b each include an annular recess 182, 184 which overlaps and engages the ends of cask body 11. Although specific features of the invention are shown in some drawings and not others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. Other embodiments will occur to those skilled in the art and are within the following claims: |
054835631 | abstract | Zirconium or zirconium alloy components of a cylindrical shape are cleaned with an ice blasting process to produce a defect-free bondline in multi-layered tubing suitable for nuclear fuel cladding and the chemical processing industry. The ice blasting process improves the integrity of the metallurgical bond by removing foreign contamination that can initiate non-bonding defects. |
061608653 | summary | FIELD OF THE INVENTION AND RELATED ART This invention relates to a synchrotron radiation intensity measuring system for measuring the intensity of synchrotron radiation and also to an X-ray exposure apparatus wherein the exposure amount is controlled on the basis of measurement by such measuring system. In another aspect, the invention is concerned with a device manufacturing method which uses such exposure apparatus. In X-ray exposure apparatuses for use in an X-ray lithographic process in one field of use of synchrotron radiation, since the synchrotron radiation has a shape of sheet-like beam and sufficient exposure region is not provided, an X-ray mirror is used to expand the sheet-like beam in a direction perpendicular to the synchrotron orbit. It is an important factor to maintain uniform exposure amount upon the surface of a substrate such as a wafer, irradiated thereby. To this end, it is required to precisely control the attitude of or relative position of the X-ray mirror with respect to the sheet-like beam, emitted from a synchrotron ring. Further, if during the X-ray exposure process the relative positional relation between the X-ray mirror and the sheet-like beam varies due to vibration, temperature change or fluctuation of the sheet-like beam, uniformness of exposure amount can not be retained, and non-uniform exposure results. In consideration of this, it is desired that the synchrotron ring, the X-ray mirror and the X-ray exposure apparatus are mounted very precisely. Additionally, use of some mechanism for cancelling any external vibration is desired. U.S. Pat. No. 5,448,612 shows an apparatus wherein a beam position detector is provided on a support member for an X-ray mirror to detect relative positional deviation of the X-ray mirror relative to the beam. Driving means controls the attitude of the X-ray mirror on the basis of the result of detection by the detector. A dual-element detector disposed in a vertical direction are used to control the attitude of an X-ray mirror so that the outputs of the detector elements are balanced. Also, on the basis of the sum signal of the outputs of the two detector elements or of an output of one of them, the intensity of synchrotron radiation is calculated. Although in the above-described example the intensity of synchrotron radiation can be calculated on the basis of an output signal of a detector, if the intensity distribution in a direction perpendicular to the synchrotron radiation varies as a result of a change in accumulated current of a synchrotron ring, for example, the intensity of synchrotron radiation and the output signal of the detector are not exactly proportionally correlated with each other. Thus, in that occasion, an error occurs in calculation of the synchrotron radiation intensity. If the exposure amount is controlled on the basis of it, there may occur an error in exposure amount. SUMMARY OF THE INVENTION It is an object of the present invention to provide a synchrotron radiation intensity measuring system by which the intensity of synchrotron radiation can be measured precisely and quickly with simple procedure. It is another object of the present invention to provide an X-ray exposure apparatus by which exposure amount can be controlled precisely on the basis of measurement made by use of such intensity measuring system. In accordance with an aspect of the present invention, there is provided a synchrotron radiation measuring system, comprising: an X-ray detector movable in a direction of intensity distribution of synchrotron radiation to follow shift of the synchrotron radiation; and computing means for reserving therein one of (i) a relation between a signal of said X-ray detector and the intensity of synchrotron radiation and (ii) a relation among a signal of said X-ray detector, the level of vacuum at a synchrotron ring and the intensity of synchrotron radiation; wherein the intensity of synchrotron radiation is measured through said computing means on the basis of an output signal of said X-ray detector. In one preferred form of this aspect of the present invention, said computing means reserves therein a relation between a signal of said X-ray detector and the intensity of synchrotron radiation, and, when the intensity of synchrotron radiation is I and the output of said X-ray detector is v, the relation satisfies a condition: EQU I(v)=a.sub.0 +a.sub.1 v+a.sub.2 v.sup.2 +a.sub.3 v.sup.3 + . . . In another preferred form of this aspect of the present invention, said computing means reserves therein a relation among a signal of said X-ray detector, the level of vacuum at the synchrotron ring and the intensity of synchrotron radiation, and, when the intensity of synchrotron radiation is I and the output of said X-ray detector is v, the relation satisfies a condition: EQU I(v)=a.sub.0 (p)+a.sub.1 (p)v+a.sub.2 (p)v.sup.2 +a.sub.3 (p)v.sup.3 + . . . where a.sub.0, a.sub.1, a.sub.3, . . . , are coefficients which are a function of vacuum level p of the synchrotron ring. In a further preferred form of this aspect of the present invention, said X-ray detector has two elements which are disposed in array along the direction of intensity distribution of the synchrotron radiation. In accordance with another aspect of the present invention, there is provided an X-ray exposure apparatus, comprising: a synchrotron radiation intensity measuring system as recited above; and control means for controlling exposure amount on the basis of measurement by said measuring system. In one preferred form of this aspect of the present invention, said control means comprises means for controlling exposure time. In another preferred form of this aspect of the present invention, said exposure time controlling means comprises shutter control means for controlling a driving speed or a driving pattern for a shutter thereby to control the exposure time. Use of computing means which reserves therein one of (i) a relation between a signal of said X-ray detector and the intensity of synchrotron radiation and (ii) a relation among a signal of said X-ray detector, the level of vacuum at a synchrotron ring and the intensity of synchrotron radiation, enables high precision and high speed calculation of the intensity of synchrotron radiation on the basis of an output of the X-ray detector which detects a sheet-like beam of synchrotron radiation. Further, because of capability of high precision and high speed calculation of synchrotron radiation intensity, exposure time can be controlled through control of a driving speed or driving pattern for a shutter on the basis of the result of calculation. Thus, high precision exposure amount control is assured. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. |
048760579 | claims | 1. Process for the control of a nuclear reactor having a core containing fissile material assemblies, the fission of the nuclei of said materials being brought about by interactions with neutrons and producing in turn neutrons, said nuclear reactor also having a means for regulating the neutron flux in the reactor core and the power given off by said reactor core, said regulating means comprising at least one assembly of control rods displaceable in said reactor core, said process being characterized in that: (A) iteratively there is a determination of the neutron fluxes .phi.(j,g) for each zone or mesh j 1.ltoreq.j.ltoreq.J of a group of meshes corresponding to the volume of the reactor core and for each velocity group g 1.ltoreq.g.ltoreq.G of a plurality of velocity groups for the neutrons; and the numbers of neutrons or sources S(j) emitted by each mesh j, 1.ltoreq.j.ltoreq.J, per volume and time unit, the determination of said values consisting of repeating the following sequence of operations until said values converge: (B) the regulating means is controlled as a function of the neutron fluxes .phi.(j,g) and powers P(j). effective macroscopic diffusion section .SIGMA.s(j,g g') of the neutrons of the velocity group g, 1.ltoreq.g.ltoreq.G in the velocity group g', g'.noteq.g, effective macroscopic absorption section .SIGMA.a(j,g) of the neutrons of velocity group g, 1.ltoreq.g.ltoreq.G, effective macroscopic fission section .SIGMA.f(j,g) of the neutrons of velocity group g, 1.ltoreq.g.ltoreq.G. effective macroscopic diffusion sections .SIGMA.s.sup.0 (j,g g'), whose values are the possible values for said core, an effective macroscopic absorption section .SIGMA.a.sup.0 (j,g), whose value is a possible value for said core, an effective macroscopic fission section .SIGMA.f.sup.0 (j,g) of value equal to zero. 2. Process according to claim 1, wherein the distribution of neutrons in the core is defined by all the following parameters for each j, 1.ltoreq.j.ltoreq.J: 3. Process according to claim 1, wherein the predetermined interaction probabilities of the neutrons in the core can be defined for each mesh j, 1.ltoreq.j.ltoreq.J and each velocity group g, 1.ltoreq.g.ltoreq.G by: 4. Process according to claim , wherein for each mesh j 1.ltoreq.j.ltoreq.J all the second neutron flux components .phi..sup.1 (j,g), 1.ltoreq.g.ltoreq.G is determined as the solution of the system with G linear equations: ##EQU21## 5. Process according to claim 1, wherein the first component .phi..sup.0 (j,g) are calculated in accordance with the relations: ##EQU22## in which v(j) is the volume of the mesh j. 6. Process according to claim 1, wherein the new sources NS(j) are calculated in accordance with the relations: ##EQU23## in which .nu. is the average number of new neutrons per volume unit in the core. 7. Process according to claim 3, wherein G=2, the neutron fluxes .phi.(j,1) and .phi.(j,2) for each mesh j, 1.ltoreq.j.ltoreq.J being calculated according to the relations: ##EQU24## 8. Process according to claim 7, wherein the new sources NS(j) are calculated according to the equation: EQU NS(j)=.nu...SIGMA.f(j,1)..phi.(j,1)+.nu...SIGMA.f(j,2)..phi.(j,2) 9. Process according to claim 3, wherein for each mesh j 1.ltoreq.j.ltoreq.J, all the second neutron flux components .phi..sup.1 (j,g).sup.(m) 1.ltoreq.g.ltoreq.G is determined iteratively, the values .phi..sup.1 (j,g).sup.(n,m) obtained at the nth iteration being calculated as the solution of the system with G linear equations: ##EQU25## in which m is a time index, the neutron fluxes being calculated at instants t=t.sub.0 +m..DELTA.t, n is the iteration index for the calculation of the neutron fluxes at each instant t, .phi.(j,g).sup.(m-1) is the neutron flux obtained at the time iteration m-1 and v.sub.g is the average velocity of the neutrons of the velocity group g. 10. Process according to claim 1, wherein the first neutron flux components .phi.(j,g) are calculated as a function of predetermined coupling matrixes [.psi.g.sup.PREC ] for the delayed neutrons, whereof each element .psi.g.sup.PREC (j,k) represents the mean flux in the mesh j, for the velocity group g associated with a source uniformly distributed in mesh k and emitting one neutron per second in accordance with a delayed neutron emission spectrum .chi..sub.g.sup.PREC. 11. Process according to claim 10, wherein the first neutron flux components are calculated in accordance with the equation: ##EQU26## in which m is a time index, the neutron fluxes being calculated at instants t=t.sub.0 +m..DELTA.t, n is the iteration index for the calculation of the neutron fluxes at each instant t and S.sub.k.sup.PREC is the source, in mesh k, linked with delayed neutron precursors. 12. Process according to claim 11, wherein the sources S.sub.k.sup.(n,m) and S.sub.k.sup.PREC(n,m) are calculated in accordance with the equations: ##EQU27## in which .beta. is the total number of delayed neutrons per fission neutron and ##EQU28## in which .lambda.i is the radioactive decay constant of the precursor and Ci(j).sup.(n,m) is the concentration of the precursor i in mesh j at instant t.sub.0 +m..DELTA.t and at iteration n. 13. Process according to claim 12, wherein the new sources are calculated in accordance with equation: ##EQU29## 14. Process according to claim 1, wherein the neutron fluxes .phi.(j,g) and sources S(j) being iteratively calculated, said neutron fluxes are initialized to the value zero and said sources to a constant non-zero value. 15. Process according to claim 1, wherein the neutron fluxes .phi.(j,g) and sources S(j) are iteratively calculated at an instant t, the said neutron fluxes and said sources being initialized with the values obtained by said process at a preceding instant t-1. |
051606976 | claims | 1. Lower connector for a fuel assembly of a nuclear reactor, said lower connector comprising an adapter plate (2) of square shape traversed by water passage orifices (8, 9), and a filtration plate (11) pierced with holes of small dimensions and located in abutment with said adaptor plate (2), said water passage orifices of said adaptor plate being arranged completely symmetrically to one another in relation to medians (6, 6') and diagonals (5, 5') of said adaptor plate (2), each sector (7a, 7b, 7c, 7d, 7e, 7f, 7g, 7h) of said adaptor plate (2) delimited by a median (6, 6') and a diagonal (5, 5') comprising orifices (8) having an oblong shape in cross-section, and said holes in said filtration plate (11) comprising sets of said holes (15) arranged in zones of said filtration plate (11) aligned with water-passage orifices (8) of said adaptor plate. 2. Lower connector according to claim 1, wherein said adaptor plate (2) further comprises water passage orifices (9) of cylindrical shape and of circular cross-section, arranged completely symmetrically in relation to said medians (6, 6') and to said diagonals (5, 5') of said adaptor plate. 3. Lower connector according to claim 1 or 2, wherein said adaptor plate (22) further comprises orifices (30, 31) in the form of a triangle with rounded corners. 4. Lower connector according to claim 1, wherein said sectors (7a to 7h) are triangular, some of the orifices (8) of oblong shape in each said triangular sector having a cross-section a longitudinal axis of which points in a direction parallel to a first median (6, 6') of said adaptor plate, and the others of said orifices of oblong shape have a cross-section the longitudinal axis of which points in a direction parallel to a second median (6, 6') of said adaptor plate (2). 5. Connector according to claim 1, wherein said adaptor plate comprises, in each of said zones (7a, 7b to 7h), holes (9a) for fastening guide tubes of a said fuel assembly to said lower connector and holes (9b) for fastening said filtration plate (11) to said adaptor plate (2) which are of cylindrical shape and of circular cross-section and which are arranged completely symmetrically in relation to said diagonals (5, 5') and to said medians (6, 6') of said adaptor plate (2). 6. Connector according to claim 1, wherein said orifices (8, 28) having cross-sections of oblong shape and arranged within a zone (7a to 7h; 27a to 27h) delimited by a median (6, 6'; 26, 26') and a diagonal (5, 5'; 25, 25') constitute sets of orifices (8a, 8b, 8c, 8d, 8e, 8f, 8g; 28a, 28b to 28h) having different lengths in their axial direction. 7. Lower connector according to claim 4, wherein in each of said zones (7a to 7h), said adaptor plate comprises ten oblong orifices (8a, 8b, 8c, 8d, 8e, 8f) having a cross section the longitudinal axis of which points in a first direction parallel to a first median (6) of said adaptor plate (2), and two orifices (8g) having a cross section the longitudinal axis of which points in a second direction parallel to a second median (6') of said adaptor plate (2). 8. Connector according to claim 1, wherein said filtration plate (11) comprises orifices of rectangular shape, in which are arranged filtration sets (15) in the form of sieves, superposed on said water passage orifices (8, 9) of said adaptor plate (2). 9. Connector according to claim 8, wherein said sieves consist of ligaments (16) of small cross-section, at least some of said ligaments comprising reinforcing struts (16') the cross-section of which is larger than a cross-section of said ligaments delimiting cells of said sieves (15). |
039880753 | description | DESCRIPTION OF THE INVENTION Referring now more particularly to FIG. 1, there is shown a partially cutaway sectional view of a nuclear fuel assembly 10. This fuel assembly consists of a tubular flow channel 11 of generally square cross section with a lifting bale 12 extending above channel 11 and a nose piece at the lower end of channel 11 (not shown due to the lower portion of assembly 10 being omitted). The upper end of channel 11 is open at 13 and the lower end of the nose piece is provided with coolant flow openings. An array of fuel elements 14 is enclosed in channel 11 with one fuel element 14 being shown in partial section, and the array is supported therein by means of upper end plate 15 and a lower end plate (not shown due to the lower portion being omitted). The liquid coolant ordinarily enters through the openings in the lower end of the nose piece, passes upwardly around fuel elements 14, and discharges at upper outlet 13 in a partially vaporized condition for boiling reactors or in an unvaporized condition for pressurized reactors at elevated temperatures. Referring now to FIG. 2 in addition to FIG. 1, a nuclear fuel element or rod 14 is shown in partial sectional view constructed in accordance with the teachings of this invention. The fuel element includes fuel material 16, here shown as a plurality of fuel pellets of fissionable and/or fertile material positioned within a structural cladding or container 17. In some cases the fuel pellets may be of various shapes; in other cases different fuel forms such as particulate fuel may be used. The physical form of the fuel is immaterial to this invention. Various nuclear fuel materials may be used including uranium compounds, plutonium compounds, thorium compounds, and mixtures thereof. A preferred fuel is uranium dioxide or a mixture comprising uranium dioxide and plutonium dioxide. The container is sealed at its ends by means of end plugs 18 which may include studs 19 to facilitate the mounting of the fuel rod in the assembly. A cavity or plenum 20 is provided at one end of the fuel element to permit longitudinal expansion of the fuel material and accumulation of gases released from the fuel material. A helical member 21 is positioned within space 20 and serves to maintain the position of the fuel during handling and transportation of the fuel elements. Cladding 17 is secured to end plugs 18 by means of circumferential welds 22. Common cladding materials are stainless steel alloys, aluminum and its alloys and zirconium and its alloys. The fuel element is designed to provide an excellent thermal contact between the fuel cladding and the fuel material, a minimum of parasitic neutron absorption and resistance to bowing and vibration which is occasionally caused by flow of the coolant at high velocity. Referring to FIGS. 2 and 3, there is positioned in the plenum 20 inside helical member 21 (preferably a stainless steel helical member 21), a hollow container 23, preferably a metallic container such as a stainless steel container, having a multiplicity of gas permeable openings in one portion of the container, preferably one end or cap 25 of the container, permitting gases and liquids entering the plenum 20 to enter the container 23. In container 23 is disposed an additive of a getter 24 comprised of barium or barium alloys containing one or more metal alloying components in addition to barium such as aluminum, zirconium, nickel, titanium and combinations of the foregoing. The getter is preferably in particulate form, to maximize the surface area per unit weight of the getter available to react with the gases and liquids entering container 23. Generally the alloying components will constitute up to 15 weight percent of the alloy with the balance being barium. However certain advantageous alloys above 15 weight percent are also contemplated in this invention. One such preferred alloy is about 50 weight percent aluminum with the balance being barium; another such alloy is about 10 weight percent nickel, about 40 weight percent aluminum with the balance being barium; and still another such alloy is about 15 to about 20 weight percent zirconium with the balance being barium. While FIGS. 2 and 3 present a preferred embodiment of the getter of this invention, additional physical forms of the getter can be utilized in plenum 20 including foil, sheet, films, wire, rod, bar and combinations of the foregoing. These other physical forms may be placed in the plenum, preferably inside the helical member 20 and preferably in a container such as stainless steel container 23. The container 23 in FIGS. 2 and 3 is preferably in the form of a right circular cylinder although any other configuration for the container is suitable. One end or cap 26 and the cylindrical wall portion 28 are solid metal, preferably a stainless steel, and the other end or cap 25 is preferably a screen material and preferably stainless steel screen of about 400 to about 32 mesh. The container is assembled by welding, brazing or otherwise sealing the solid end and the screen end into the hollow cylindrical wall portion 28. The ends or caps 25 and 26 are preferably concave or recessed into the cylinder as shown in FIG. 3 to facilitate welding. An effective amount of the getter is charged into the container with one end open, preferably the screen end open, and an end closure is then effected typically by spot welding. Preferably about 5 .+-. 1 grams of getter are used in a fuel rod containing about 5 kilograms of sintered nuclear fuel material (or generally about one gram of getter per kilogram of fuel material). Larger quantities of getter are used in powder fuel rods and in fuel rods suspected of containing large amounts of deleterious gases. The preferred use of the getter container 23 disclosed herein results in additional advantages. The container 23 insures retention of the particulate getter and any reaction products resulting from reaction of the getter with reactive gases in the fuel element. In this manner particulate material from the plenum will not be capable of entering the portion of the fuel element occupied by the nuclear fuel and the getter reaction products will be retained in the plenum, the lower temperature portion of the fuel element. This keeps the getter reaction products at lower temperatures and minimizes the chance of exposing the reaction products to higher temperatures tending to release the reactive gases combined to form the reaction product. The container 23 is easy to load, can be fabricated within very close dimensional tolerances, and has excellent dimensional stability due to the strength of the metal forming the cylindrical wall portion. Further the strength of the metal forming the cylindrical wall portion minimizes deformation of the container during handling and assembly of the fuel element. In another embodiment of the container, one or more openings can be made in one portion of the cylindrical wall portion 28 to give gases access to the getter. This embodiment may retain the screen end cap 25 or have a solid end cap replace the screen end cap 25. The getter used in the nuclear fuel element of this invention and its properties will now be described in detail. It has been discovered that a material suitable for controlling moisture and other reactive gases by chemically combining with such gaseous materials, namely a getter, should have a combination of properties. One desirable property is the minimization of any free hydrogen after the chemical reaction of the getter with water, as the minimization of free hydrogen prevents any possible hydride failures of cladding for nuclear fuel elements. Thus the getter should react approximately stoichiometrically with the water and water vapor (both herein called water) and in such a way that there is a negligible net source of hydrogen from the reaction. The getter should also rapidly react with the water at the temperature prevailing in the system in which the getter is utilized. The getter should generally have a low neutron cross section and be inexpensive to fabricate. The getter should also have the property of reacting with hydrogen, other reactive gases such as carbon monoxide, carbon dioxide, oxygen, nitrogen, and hydrogen-containing compounds such as hydrocarbons. Barium and the barium alloys disclosed herein have the foregoing properties and can be readily purchased or fabricated in a form of small particles having a Tyler Screen mesh size in the range of about No. 1 to No. 8, giving a high surface area for reaction with any reactive gases present in the fuel element. Barium alloys containing one or more metals in addition to barium such as aluminum, zirconium, nickel, titanium and combinations thereof can be readily obtained commercially and when available in the foregoing size range provide a high surface area reactive with any reactive gases present in the fuel element. The impurity content of the barium-containing materials is not critical to the development of the foregoing getter properties and substantial amounts of impurities can be included in the fabricated barium-containing materials as long as the surface of the barium-containing materials has barium effectively exposed for reaction. In practice it has been discovered that oxygen contents up to several thousand parts per million in the barium-containing materials are tolerable. Nitrogen contents up to about 750 parts per million are tolerable in utilization of the barium-containing materials. The other impurities found in the barium-containing materials used in this invention which do not hinder their use as getters in nuclear fuel rods include hydrogen and carbon. Metallic impurities found in the barium-containing materials which do not hinder use of the barium-containing materials as getters are hafnium in amounts up to about 1000 parts per million or more, iron in amounts up to about 1000 parts per million or more and chromium in amounts up to about 1000 parts per million or more. The fact that the impurity content of the barium-containing materials is not critical to their utilization as moisture getters enables fabrication of the barium-containing materials from corresponding low-grade metallic components. Since the barium-containing materials are utilized in the plenum of the fuel elements, small amounts of impurities of high neutron absorption cross section offer negligible interference. The barium-containing materials used in this invention have the property of reacting with water for long periods of time at a rapid rate of reaction over a temperature range of about room temperature (typically about 70.degree. F) up to fuel element plenum temperature (typically 650.degree. .+-. 100.degree. F) without becoming passive. During reaction with water, the barium-containing materials leave substantially no free hydrogen so cladding used in association with the getters of this invention would be exposed to substantially no hydrogen thereby eliminating formation of metallic hydrides which ultimately lead to weakening or failure of the cladding. This minimum release of hydrogen during the reaction of the barium-containing materials with water indicates a substantially stoichiometric reaction of the barium-containing materials with water. Studies indicate that the barium-containing materials used in this invention readily react with hydrogen over a temperature range of room temperature to reactor operating temperatures so that these materials are efficient hydrogen getters. The barium-containing materials also react with hydrogen-containing compounds such as hydrocarbons and with other gases such as nitrogen, carbon dioxide, carbon monoxide and oxygen. The barium-containing materials have a low neutron cross section required for use in nuclear applications when the impurities having high neutron cross section are minimized. As will be apparent to those skilled in the art, various modifications and changes may be made in the invention described herein. It is accordingly the intention that the invention be construed in the broadest manner within the spirit and scope as set forth in the accompanying claims. |
claims | 1. A control apparatus for an injection molding machine, said apparatus having a neural network and operating so that information on test molding is inputted to the neural networks, a quality prediction function is determined by repeating the estimation of weight factors and thresholds on the neural networks as many times as the number of test molding cycles, and mass-production molding is begun with the quality prediction function, said control apparatus further comprising:an upper/lower control limit determination unit for setting an upper control limit and a lower control limit for each of the monitor values that indicate the state in each part of a molding machine; anda function revision need determining unit for setting the range between the upper control limit and lower control limit set by the upper/lower control limit determination unit as the control range, and outputting a revision command for the quality prediction function and/or generating an alarm signal from an alarm signal generating unit when the monitor values acquired during mass-production molding have deviated from the control range. 2. The control apparatus of claim 1, wherein the upper control limit is a maximum value selected from the monitor groups obtained in test molding, and the lower control limit is a minimum value selected from the monitor groups obtained in test molding. 3. The control apparatus of claim 1, the control apparatus performing control wherein an alarm signal is generated from the alarm signal generating unit when the monitor values acquired during mass-production molding have deviated from the control range, and the quality prediction function is revised and/or the operation of the molding machine is stopped either when the alarm signal has continued for a specific number of times or when the cumulative number of alarm signals has reached a specific number. 4. The control apparatus of claim 1, wherein the control apparatus comprises a calculation unit for predicting quality values by providing the monitor values to the quality prediction function, and a satisfactory product determination unit for ascertaining that the molded articles are satisfactory when the quality prediction value predicted by the calculation unit is within the required quality, and ascertaining that the molded articles are unsatisfactory when the quality prediction value does not comply with the required quality. |
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summary | ||
abstract | In a nuclear reactor, in-core stability is improved, power density is increased, and an economical natural-circulation reactor (or partial forced-circulation reactor) is achieved. The reactor core has a void reactivity coefficient between xe2x88x920.07 and xe2x88x920.03% xcex94k/k/% void fraction. This void reactivity coefficient range is achieved by, for example, the design of the by-pass portion and channel box, the enrichment distribution along the axial direction, the provision of blanket areas, and/or the arrangement of water rods and fuel rods within a channel box. |
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abstract | Provided is a passive containment spray system including: a spray coolant storage unit that communicates with a containment accommodating a reactor vessel and maintains equilibrium of pressure between the spray coolant storage unit and the containment; a spray pipe that is installed within the containment in such a manner that when an accident occurs, a coolant supplied from the spray coolant storage unit is sprayed into the containment through the spray pipe due to an increase in pressure within the containment; and a connection pipe one end of which is inserted into the spray coolant storage unit in such a manner as to provide a flow path along which the coolant flows and the other end of which is connected to the spray pipe in such a manner that the coolant is passively supplied to the spray pipe through the connection pipe therein. |
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claims | 1. A method of performing microbeam radiation therapy for a subject, comprising:producing a high-energy radiation fan beam, wherein the width of the fan beam in a first direction is greater than the width of the fan beam in a second direction;shaping the fan beam; andproducing a relative movement between the subject and the fan beam to irradiate the subject through a collimator to produce high-dose regions alternating with low-dose regions,wherein the collimator is affixed to the subject. 2. The method of claim 1, wherein shaping the fan beam includes adjusting the width of the fan beam in the first direction while producing a relative movement between the subject and the fan beam in the second direction. 3. The method of claim 2, wherein the width of the fan beam is adjusted to correspond to a desired treatment region in the subject. 4. The method of claim 2, wherein adjusting the width of the fan beam in the first direction includes adjusting the position of a set of adjustable jaws configured to block a portion of the high-energy radiation beam. 5. The method of claim 2, wherein adjusting the width of the fan beam in the first direction includes placing a filter in the path of the fan beam. 6. The method of claim 1, wherein shaping the fan beam includes adjusting the intensity profile of the fan beam. 7. The method of claim 6, wherein a filter is used to adjust the intensity profile of the fan beam. 8. The method of claim 6, wherein the collimator includes a filter that is used to adjust the intensity profile of the fan beam. 9. The method of claim 1, further comprising receiving a radiation treatment profile and wherein shaping the fan beam includes shaping the fan beam based upon the radiation treatment profile. 10. A microbeam radiation therapy system, comprising:a high-energy beam source configured to produce a high-energy radiation beam;a collimator with slits, wherein the collimator only passes the high-energy radiation beam through the slits, and wherein the collimator is affixed to a subject; anda beam shaper configured to spatially limit and filter the high-energy radiation beam. 11. The system of claim 10, wherein the beam shaper adjusts the shape of the high-energy radiation beam. 12. The system of claim 11, wherein the shape of the high-energy radiation beam is adjusted to correspond to a desired treatment region. 13. The system of claim 11, wherein the high-energy radiation beam is a fan beam and the beam shaper includes a set of adjustable jaws configured to block a portion of the fan beam. 14. The system of claim 11, wherein the beam shaper includes a filter in the path of the high-energy radiation beam. 15. The system of claim 11, wherein the beam shaper is configured to adjust the intensity profile of the high-energy radiation beam. 16. The system of claim 10, wherein the beam shaper is part of the collimator. 17. The system of claim 10, wherein the beam shaper includes a plurality of slidable leafs configured to provide an opening in the beam shaper. 18. The system of claim 10, wherein the beam shaper includes a filter having a spatially varying thickness. 19. The system of claim 10, wherein the high-energy radiation beam is a fan beam and wherein the high-energy beam source varies the peak energy of the fan beam based upon a radiation treatment profile. 20. A method of performing microbeam radiation therapy for a subject, comprising:producing a high-energy radiation beam;shaping and attenuating the high-energy radiation beam using a filter;passing the shaped and attenuated beam through a collimator to produce high-dose regions alternating with low-dose regions; andirradiating the subject with the shaped, attenuated, and collimated beam,wherein the collimator is affixed to the subject. |
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summary | ||
claims | 1. A collimator system comprising:a collimator comprising:at least one aperture configured to allow radiation to pass through;at least one outer annulus configured to reduce radiation passing through at an amount depending on the material and the thickness of said at least one outer annulus; andtwo carriages associated with said collimator, said carriages movable by at least one motor thereby moving said collimator in a 2-dimensional plane. 2. The collimator system of claim 1, wherein said collimator further comprises at least one inner annulus between said at least one aperture and said at least one outer annulus, said at least one inner annulus having changing thickness. 3. The collimator system of claim 2, wherein said thickness changes as a function of the distance from said at least one aperture, starting at a low thickness on the side of each one of said at least one apertures and ending at the thickness of said at least one outer annulus on the side of said at least one outer annulus. 4. The collimator system of claim 1, wherein said carriages movable by at least one motor along a track. 5. The collimator system of claim 4, wherein said tracks are perpendicular to each other. 6. The collimator system of claim 4, wherein said tracks are non-parallel. 7. The collimator system of claim 1, wherein said at least one motor is configured to rotate between an x-ray source's pulses and stop during said x-ray source's pulses. 8. A method of controlling a Region of Interest (ROI) in an image of an x-ray irradiated area, comprising:providing:a collimator comprising:at least one aperture configured to allow radiation to pass through;at least one outer annulus configured to reduce radiation passing through at an amount depending on the material and the thickness of said at least one outer annulus; andtwo carriages associated with said collimator, said carriages movable by at least one motor thereby moving said collimator in a 2-dimensional plane;determining a location on said image; andmoving said two carriages, thereby moving said collimator to place at least one of said at least one aperture according to said determined location. 9. The method of claim 8, further comprising:providing:a plurality of radiation attenuating plates, each one of said plates having an aperture;means for selecting a radiation attenuating plate; anda plate changing mechanism comprising:a body comprising on one face thereof said plurality of radiation attenuating plates;wherein said at least one aperture of said collimator comprises one aperture configured to receive any of said plurality of radiation attenuating plates; andmoving said body to bring a selected one of said plurality of radiation attenuating plates to said aperture of said collimator. 10. The method of claim 8, wherein said collimator further comprises at least one inner annulus, each said at least one inner annulus between a respective one of said at least one aperture and a respective one of said at least one outer annulus, each said at least one inner annulus having changing thickness. 11. The method of claim 10, wherein each said at least one inner annulus thickness changes as a function of the distance from an inner annulus respective aperture, starting at a low thickness on the side of said respective aperture and ending at the thickness of said inner annulus respective outer annulus on the side of said respective outer annulus. 12. The method of claim 8, wherein said two carriages are movable along a track. 13. The method of claim 8, wherein said two carriages are movable along two non-parallel tracks. 14. The method of claim 8, wherein said at least one motor is configured to rotate between an x-ray source's pulses and stop during said x-ray source's pulses. 15. The method of claim 9, wherein said body is highly transparent to radiation. 16. The method of claim 9, wherein said body has one of: a circular shape and an anchor like shape. 17. The method of claim 9, wherein said radiation attenuating plates are made of copper. |
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summary | ||
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abstract | An imaging system includes a detector configured to detect X-rays from an X-ray source. The detector includes multiple photodetector elements. The imaging system also includes an anti-scatter grid disposed over the detector, wherein the anti-scatter grid includes multiple radiation absorbing elements. At least a portion of one or more of the radiation absorbing elements of the multiple radiation absorbing elements is disposed on each photodetector element, and a total area of each respective portion of the one or more radiation absorbing elements disposed on each photodetector element is substantially equal. |
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abstract | Among other things, an applicator means (20) for x-ray radiation therapy for the irradiation of surfaces, as well as a radiation therapy device are described, having an applicator element (21) for taking up a probe tip or a radiation source element of a radiation source means (11). In order to further develop applicator means (20) in such a way that it is especially suitable also for the irradiation of surfaces, it is provided that applicator element (21) for adjusting different beam characteristics has at least one element (27) for influencing the beam, in particular a lens element, which is disposed in an exchangeable manner at/in applicator element (21). In addition, an advantageous fastening means is described, by means of which applicator means (20) can be attached and fixed on the surface to be treated. |
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description | This application is a continuation-in-part of U.S. patent application Ser. No. 15/467,840 filed Mar. 23, 2017, which is a continuation-in-part of U.S. patent application, which is a continuation-in-part of U.S. patent application Ser. No. 15/402,739 filed Jan. 10, 2017, which is a continuation-in-part of U.S. patent application Ser. No. 15/348,625 filed Nov. 10, 2016, which is a continuation-in-part of U.S. patent application Ser. No. 15/167,617 filed May 27, 2016, which is a continuation-in-part of U.S. patent application Ser. No. 15/152,479 filed May 11, 2016, which is a continuation-in-part of U.S. patent application Ser. No. 14/216,788 filed Mar. 17, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 13/087,096 filed Apr. 14, 2011, which claims benefit of U.S. provisional patent application No. 61/324,776 filed Apr. 16, 2010, all of which are incorporated herein in their entirety by this reference thereto. Field of the Invention The invention relates generally to imaging and treating a tumor. Discussion of the Prior Art Cancer Treatment Proton therapy works by aiming energetic ionizing particles, such as protons accelerated with a particle accelerator, onto a target tumor. These particles damage the DNA of cells, ultimately causing their death. Cancerous cells, because of their high rate of division and their reduced ability to repair damaged DNA, are particularly vulnerable to attack on their DNA. Patents related to the current invention are summarized here. Proton Beam Therapy System F. Cole, et. al. of Loma Linda University Medical Center “Multi-Station Proton Beam Therapy System”, U.S. Pat. No. 4,870,287 (Sep. 26, 1989) describe a proton beam therapy system for selectively generating and transporting proton beams from a single proton source and accelerator to a selected treatment room of a plurality of patient treatment rooms. Imaging Lomax, A., “Method for Evaluating Radiation Model Data in Particle Beam Radiation Applications”, U.S. Pat. No. 8,461,559 B2 (Jun. 11, 2013) describes comparing a radiation target to a volume with a single pencil beam shot to the targeted volume. P. Adamee, et. al. “Charged Particle Beam Apparatus and Method for Operating the Same”, U.S. Pat. No. 7,274,018 (Sep. 25, 2007) and P. Adamee, et. al. “Charged Particle Beam Apparatus and Method for Operating the Same”, U.S. Pat. No. 7,045,781 (May 16, 2006) describe a charged particle beam apparatus configured for serial and/or parallel imaging of an object. K. Hiramoto, et. al. “Ion Beam Therapy System and its Couch Positioning System”, U.S. Pat. No. 7,193,227 (Mar. 20, 2007) describe an ion beam therapy system having an X-ray imaging system moving in conjunction with a rotating gantry. C. Maurer, et. al. “Apparatus and Method for Registration of Images to Physical Space Using a Weighted Combination of Points and Surfaces”, U.S. Pat. No. 6,560,354 (May 6, 2003) described a process of X-ray computed tomography registered to physical measurements taken on the patient's body, where different body parts are given different weights. Weights are used in an iterative registration process to determine a rigid body transformation process, where the transformation function is used to assist surgical or stereotactic procedures. M. Blair, et. al. “Proton Beam Digital Imaging System”, U.S. Pat. No. 5,825,845 (Oct. 20, 1998) describe a proton beam digital imaging system having an X-ray source that is movable into a treatment beam line that can produce an X-ray beam through a region of the body. By comparison of the relative positions of the center of the beam in the patient orientation image and the isocentre in the master prescription image with respect to selected monuments, the amount and direction of movement of the patient to make the best beam center correspond to the target isocentre is determined. S. Nishihara, et. al. “Therapeutic Apparatus”, U.S. Pat. No. 5,039,867 (Aug. 13, 1991) describe a method and apparatus for positioning a therapeutic beam in which a first distance is determined on the basis of a first image, a second distance is determined on the basis of a second image, and the patient is moved to a therapy beam irradiation position on the basis of the first and second distances. There exists in the art of charged particle cancer therapy a need for accurate, precise, and rapid imaging of a patient and/or treatment of a tumor using charged particles in a complex room setting. The invention comprises an intervening object compensating semi-automated cancer treatment plan generation and/or cancer treatment apparatus and method of use thereof. Elements and steps in the figures are illustrated for simplicity and clarity and have not necessarily been rendered according to any particular sequence. For example, steps that are performed concurrently or in different order are illustrated in the figures to help improve understanding of embodiments of the present invention. The invention comprises a method and apparatus for planning for and optionally treating a tumor of a patient using positively charged particles in a presence of an intervening object, comprising the steps of: (1) positioning the intervening object between the tumor of the patient and an exit surface of an output nozzle system connected to a synchrotron using a beam transport system; (2) predetermining an energy reduction of the positively charged particles resultant from the positively charged particles traversing the intervening object along a beam treatment path as a function of relative rotation of the patient and the beam treatment path; (3) generating a radiation treatment plan adjusting energy of the positively charged particles delivered from the synchrotron to the intervening object to yield a desired beam treatment energy of the positively charged particles entering the tumor after compensating for the energy reduction; and (4) optionally detecting a set of the positively charged particles after traversing the intervening object to yield a signal, where the signal is used with knowledge of energy of the positively charged particles exiting the synchrotron to pre-determine the energy reduction along the beam treatment path. In combination, the above described embodiment is used with an X-ray imaging and charged particle beam treatment or imaging system comprising the steps of: rotating an X-ray imaging system, configured to deliver the X-rays, around both a first rotation axis and the patient; imaging the patient using X-rays from the X-ray imaging system; and passing the positively charged particles through an exit port of a nozzle system, the nozzle system connected to a synchrotron via a first beam transport line, the positively charged particles passing into the patient from the exit port along a z-axis and at least one of: (1) treating the tumor with the positively charged particles and (2) imaging the patient with residual charged particles comprising the positively charged particles after transmitting through the patient. In one case, a first cone beam X-ray source and a second cone beam X-ray source are positioned on a first side of the patient and at least one two-dimensional X-ray detector is positioned on an opposite side of the patient from the first cone beam X-ray source. In combination, the above described embodiment is used with a multiplexed proton tomography imaging apparatus and method of use thereof. For example, a method for imaging a tumor of a patient comprises the steps of: (1) simultaneously detecting spatially resolved positively charged particle positions passing through each of a set of cross-section planes, where the cross-section planes are both prior to and posterior to the patient along a path of the positively charged particles; (2) determining a prior vector for each of the individual positively charged particles entering a patient using the detected positions; (3) determining a posterior vector for each of the individual positively charged particles exiting the patient using the detected positions; (4) generating a path, a best path, and/or a probable path of each positively charged particle through the patient; and (5) generating an image of the patient using the n probable proton paths. In one case, an imaging system: (1) delivers a set of n protons from a synchrotron: through a beam transport system exit nozzle, through a proton radial cross-section beam expander, through a first prior imaging sheet, through a second prior imaging sheet, through a patient position, through at least one posterior imaging sheet, and into a scintillation material of a beam energy scintillation detector system, where the first prior imaging sheet is positioned between the proton radial cross-section beam expander and the patient position, where the second prior imaging sheet is positioned between the proton radial cross-section beam expander and the patient position; (2) simultaneously detects spatially resolved both prior and posterior position photon emissions, resultant from passage of multiple protons; (4) determines both a prior vector and a posterior vector for each proton; and (5) determines a path for each proton through the patient and uses the determined paths, optionally and preferably with residual energy determinations, to generate an image of the patient. In combination, a method of double exposure imaging of a tumor of a patient is performed using hardware, using a detector responsive to both X-rays and positively charged particles, simultaneously, and/or in either order. The preferably near-simultaneous double exposure yields enhanced resolution due to the imaging rate versus patient movement, no requirement of a software overlay step, and associated errors, of the X-ray based image and the positively charged particle based image, and enhancement of an X-ray image, the enhancement resultant from a differing physical interaction of the positively charged particles with the patient compared to interactions of X-rays and the patient. Further, resolution enhancements utilize individual particle tracking, as measured using detection screens, to determine a probable intra-patient path. Optionally, residual energy positively charged particles, having passed through a primarily X-ray detector, are used to generate a second/dual image at a secondary detector, such as a detector based on scintillation resultant from proton absorbance. In combination, a method for imaging a tumor of a patient using X-rays and positively charged particles comprises the steps of: (1) generating an X-ray image using the X-rays directed from an X-ray source, through the patient, and to an X-ray detector, (2) generating a positively charged particle image: (a) using the positively charged particles directed from an exit nozzle, through the patient, through the X-ray detector, and to a scintillator, the scintillator emitting photons when struck by the positively charged particles and (b) generating the positively charged particle image of the tumor using a photon detector configured to detect the emitted photons, where the X-ray detector maintains a static position between said the nozzle and the scintillator during the step of generating a positively charged particle image. Individual images are optionally and preferably collected as a function of relative rotation of the patient and the imaging elements to form a three-dimensional image, such as via tomography. In combination, a method and apparatus is described for determining a position of a tumor in a patient for treatment of the tumor using positively charged particles in a treatment room. More particularly, the method and apparatus use a set of fiducial markers and fiducial detectors to mark/determine relative position of static and/or moveable objects in a treatment room using photons passing from the markers to the detectors. Further, position and orientation of at least one of the objects is calibrated to a reference line, such as a zero-offset beam treatment line passing through an exit nozzle, which yields a relative position of each fiducially marked object in the treatment room. Treatment calculations are subsequently determined using the reference line and/or points thereon. The inventor notes that the treatment calculations are optionally and preferably performed without use of an isocenter point, such as a central point about which a treatment room gantry rotates, which eliminates mechanical errors associated with the isocenter point being an isocenter volume in practice. For example, a set of fiducial marker detectors detect photons emitted from and/or reflected off of a set of fiducial markers positioned on one or more objects in a treatment room and resultant determined distances and/or calculated angles are used to determine relative positions of multiple objects or elements in the treatment room. Generally, in an iterative process, at a first time objects, such as a treatment beamline output nozzle, a specific portion of a patient relative to a tumor, a scintillation detection material, an X-ray system element, and/or a detection element, are mapped and relative positions and/or angles therebetween are determined. At a second time, the position of the mapped objects is used in: (1) imaging, such as X-ray, positron emission tomography, and/or proton beam imaging and/or (2) beam targeting and treatment, such as positively charged particle based cancer treatment. As relative positions of objects in the treatment room are dynamically determined using the fiducial marking system, engineering and/or mathematical constraints of a treatment beamline isocenter is removed. In combination, a method and apparatus for imaging a tumor of a patient using positively charged particles, comprising the steps of: (1) sequentially delivering from an output nozzle, connected to a first beam transport line, to the patient: a first set of the positively charged particles comprising a first mean energy and a second set of the positively charged particles comprising a second mean energy, the second mean energy at least two mega electron Volts different from the first mean energy; (2) after transmission through the patient, sequentially detecting: a first residual energy of the first set of the positively charged particles and a second residual energy of the second set of the positively charged particles; and (3) determining a water equivalent thickness of a probed path of the patient using the first residual energy and the second residual energy. The detection step optionally uses a scintillation material and/or an X-ray detector material to detect the residual energy positively charged particles. Use of a half-maximum of a Gaussian fit to output of the detection material as a function of energy, preferably using three of more detected residual energies, yields a water equivalent thickness of the sampled beam path. In combination, an apparatus and method of use thereof are used for directing positively charged particle beams into a patient from several directions. In one example, a charged particle delivery system, comprising: a controller, an accelerator, a beam path switching magnet, a primary beam line from the accelerator to the path switching magnet, and a plurality of physically separated beam transport lines from the beam path switching magnet to a single patient treatment position is used, where the controller and beam switching magnet are used to direct sets of the positively charged particles through alternatingly selected beam transport lines to the patient, tumor, and/or an imaging detector. Optionally, during a single session and at separate times, a single repositionable treatment nozzle is repositioned to interface with each beam transport line, such as to a terminus of each beam transport line, which allows the charged particle delivery system to use one and/or fewer beam output nozzles that are moved with nozzle gantries. A single nozzle with first and second axis scanning capability along with beam transport lines leading to various sides of a patient allow the charged particle delivery system to operate without movement and/or rotation of a beam transport gantry and an associated beam transport gantry. Beam transport line gantries are optional as one or more of the beam transport lines are preferably statically positioned. In combination, a beam adjustment system is used to perform energy adjustments on circulating charged particles in a synchrotron previously accelerated to a starting energy with a traditional accelerator of the synchrotron or related devices, such as a cyclotron. The beam adjustment system uses a radio-frequency modulated potential difference applied along a longitudinal path of the circulating charged particles to accelerate or decelerate the circulating charged particles. Optionally, the beam adjustment system phase shifts the applied radio-frequency field to accelerate or decelerate the circulating charged particle while spatially longitudinally tightening a grouped bunch of the circulating charged particles. The beam adjustment system facilitates treating multiple layers or depths of the tumor between the slow step of reloading the synchrotron. Optionally, the potential differences across a gap described herein are used to accelerate or decelerate the charged particle after extraction from the synchrotron without use of the radio-frequency modulation. In combination, an imaging system, such as a positron emission tracking system, optionally used to control the beam adjustment system, is used to: dynamically determine a treatment beam position, track a history of treatment beam positions, guide the treatment beam, and/or image a tumor before, during, and/or after treatment with the charged particle beam. In combination, an imaging system translating on a linear path past a patient operates alternatingly with and/or during a gantry rotating a treatment beam around the patient. More particularly, a method for both imaging a tumor and treating the tumor of a patient using positively charged particles includes the steps of: (1) rotating a gantry support and/or gantry, connected to at least a portion of a beam transport system configured to pass a charged particle treatment beam, circumferentially about the patient and a gantry rotation axis; (2) translating a translatable imaging system past the patient on a path parallel to an axis perpendicular to the gantry rotation axis; (3) imaging the tumor using the translatable imaging system; and (4) treating the tumor using the treatment beam. In combination, a method for imaging and treating a tumor of a patient with positively charged particles, comprises the steps of: (1) using a rotatable gantry support to support and rotate a section of a positively charged particle beam transport line about a rotation axis and a tumor of a patient; (2) using a rotatable and optionally extendable secondary support to support, circumferentially position, and laterally position a primary and optional secondary imaging system about the tumor; (3) image the tumor using the primary and optional secondary imaging system as a function of rotation and/or translation of the secondary support; and (4) treat, optionally concurrently, the tumor using the positively charged particles as a function of circumferential position of the section of the charged particle beam about the tumor. In combination, a method and apparatus for imaging a tumor of a patient using positively charged particles and X-rays, comprises the steps of: (1) transporting the positively charged particles from an accelerator to a patient position using a beam transport line, where the beam transport line comprises a positively charged particle beam path and an X-ray beam path; (2) detecting scintillation induced by the positively charged particles using a scintillation detector system; (3) detecting X-rays using an X-ray detector system; (4) positioning a mounting rail through linear extension/retraction to: at a first time and at a first extension position of the mounting rail, position the scintillation detector system opposite the patient position from the exit nozzle and at a second time and at a second extension position of the mounting rail, position the X-ray detector system opposite the patient position from the exit nozzle; (5) generating an image of the tumor using output of the scintillation detector system and the X-ray detector system; and (6) alternating between the step of detecting scintillation and treating the tumor via irradiation of the tumor using the positively charged particles. In combination, a method or apparatus for tomographically imaging a sample, such as a tumor of a patient, using positively charged particles is described. Position, energy, and/or vectors of the positively charged particles are determined using a plurality of scintillators, such as layers of chemically distinct scintillators where each chemically distinct scintillator emits photons of differing wavelengths upon energy transfer from the positively charged particles. Knowledge of position of a given scintillator type and a color of the emitted photon from the scintillator type allows a determination of residual energy of the charged particle energy in a scintillator detector. Optionally, a two-dimensional detector array additionally yields x/y-plane information, coupled with the z-axis energy information, about state of the positively charged particles. State of the positively charged particles as a function of relative sample/particle beam rotation is used in tomographic reconstruction of an image of the sample or the tumor. In another example, a method or apparatus for tomographic imaging of a tumor of a patient using positively charged particles respectively positions a plurality of two-dimensional detector arrays on multiple surfaces of a scintillation material or scintillator. For instance, a first two-dimensional detector array is optically coupled to a first side or surface of a scintillation material, a second two-dimensional detector array is optically coupled to a second side of the scintillation material, and a third two-dimensional detector array is optically coupled to a third side of the scintillation material. Secondary photons emitted from the scintillation material, resultant from energy transfer from the positively charged particles, are detected by the plurality of two-dimensional detector arrays, where each detector array images the scintillation material. Combining signals from the plurality of two-dimensional detector arrays, the path, position, energy, and/or state of the positively charged particle beam as a function of time and/or rotation of the patient relative to the positively charged particle beam is determined and used in tomographic reconstruction of an image of the tumor in the patient or a sample. Particularly, a probabilistic pathway of the positively charged particles through the sample, which is altered by sample constituents, is constrained, which yields a higher resolution, a more accurate and/or a more precise image. In another example, a scintillation material is longitudinally packaged in a circumferentially surrounding sheath, where the sheath has a lower index of refraction than the scintillation material. The scintillation material yields emitted secondary photons upon passage of a charged particle beam, such as a positively charged residual particle beam having transmitted through a sample. The internally generated secondary photons within the sheath are guided to a detector element by the difference in index of refraction between the sheath and the scintillation material, similar to a light pipe or fiber optic. The coated scintillation material or fiber is referred to herein as a scintillation optic. Multiple scintillation optics are assembled to form a two-dimensional scintillation array. The scintillation array is optionally and preferably coupled to a detector or two-dimensional detector array, such as via a coupling optic, an array of focusing optics, and/or a color filter array. In combination, an ion source is coupled to the apparatus. The ion source extraction system facilitates on demand extraction of charged particles at relatively low voltage levels and from a stable ion source. For example, a triode extraction system allows extraction of charged particles, such as protons, from a maintained temperature plasma source, which reduces emittance of the extracted particles and allows use of lower, more maintainable downstream potentials to control an ion beam path of the extracted ions. The reduced emittance facilitates ion beam precision in applications, such as in imaging, tumor imaging, tomographic imaging, and/or cancer treatment. In combination, a state of a charged particle beam is monitored and/or checked, such as against a previously established radiation plan, in a position just prior to the beam entering the patient. In one example, the charged particle beam state is measured after a final manipulation of intensity, energy, shape, and/or position, such as via use of an insert, a range filter, a collimator, an aperture, and/or a compensator. In one case, one or more beam crossing elements, sheets, coatings, or layers, configured to emit photons upon passage therethrough by the charged particle beam, are positioned between the final manipulation apparatus, such as the insert, and prior to entry into the patient. In combination, a patient specific tray insert is inserted into a tray frame to form a beam control tray assembly, the beam control tray assembly is inserted into a slot of a tray receiver assembly, and the tray assembly is positioned relative to a gantry nozzle. Optionally, multiple tray inserts, each used to control a beam state parameter, are inserted into slots of the tray receiver assembly. The beam control tray assembling includes an identifier, such as an electromechanical identifier, of the particular insert type, which is communicated to a main controller, such as via the tray receiver assembly. Optionally and preferably, a hand control pendant is used in loading and/or positioning the tray receiver assembly. In combination, a gantry positions both: (1) a section of a beam transport system, such as a terminal section, used to transport and direct positively charged particles to a tumor and (2) at least one imaging system. In one case, the imaging system is orientated on a same axis as the positively charged particle, such as at a different time through rotation of the gantry. In another case, the imaging system uses at least two crossing beamlines, each beamline coupled to a respective detector, to yield multiple views of the patient. In another case, one or more imaging subsystem yields a two-dimensional image of the patient, such as for position confirmation and/or as part of a set of images used to develop a three-dimensional image of the patient. In combination, multiple linked control stations are used to control position of elements of a beam transport system, nozzle, and/or patient specific beam shaping element relative to a dynamically controlled patient position and/or an imaging surface, element, or system. In combination, a tomography system is optionally used in combination with a charged particle cancer therapy system. The tomography system uses tomography or tomographic imaging, which refers to imaging by sections or sectioning through the use of a penetrating wave, such as a positively charge particle from an injector and/or accelerator. Optionally and preferably, a common injector, accelerator, and beam transport system is used for both charged particle based tomographic imaging and charged particle cancer therapy. In one case, an output nozzle of the beam transport system is positioned with a gantry system while the gantry system and/or a patient support maintains a scintillation plate of the tomography system on the opposite side of the patient from the output nozzle. In another example, a charged particle state determination system, of a cancer therapy system or tomographic imaging system, uses one or more coated layers in conjunction with a scintillation material, scintillation detector and/or a tomographic imaging system at time of tumor and surrounding tissue sample mapping and/or at time of tumor treatment, such as to determine an input vector of the charged particle beam into a patient and/or an output vector of the charged particle beam from the patient. In another example, the charged particle tomography apparatus is used in combination with a charged particle cancer therapy system. For example, tomographic imaging of a cancerous tumor is performed using charged particles generated with an injector, accelerator, and guided with a delivery system. The cancer therapy system uses the same injector, accelerator, and guided delivery system in delivering charged particles to the cancerous tumor. For example, the tomography apparatus and cancer therapy system use a common raster beam method and apparatus for treatment of solid cancers. More particularly, the invention comprises a multi-axis and/or multi-field raster beam charged particle accelerator used in: (1) tomography and (2) cancer therapy. Optionally, the system independently controls patient translation position, patient rotation position, two-dimensional beam trajectory, delivered radiation beam energy, delivered radiation beam intensity, beam velocity, timing of charged particle delivery, and/or distribution of radiation striking healthy tissue. The system operates in conjunction with a negative ion beam source, synchrotron, patient positioning, imaging, and/or targeting method and apparatus to deliver an effective and uniform dose of radiation to a tumor while distributing radiation striking healthy tissue. In combination, a treatment delivery control system (TDCS) or main controller is used to control multiple aspects of the cancer therapy system, including one or more of: an imaging system, such as a CT or PET; a positioner, such as a couch or patient interface module; an injector or injection system; a radio-frequency quadrupole system; a ring accelerator or synchrotron; an extraction system; an irradiation plan; and a display system. The TDCS is preferably a control system for automated cancer therapy once the patient is positioned. The TDCS integrates output of one or more of the below described cancer therapy system elements with inputs of one or more of the below described cancer therapy system elements. More generally, the TDCS controls or manages input and/or output of imaging, an irradiation plan, and charged particle delivery. In combination, one or more trays are inserted into the positively charged particle beam path, such as at or near the exit port of a gantry nozzle in close proximity to the patient. Each tray holds an insert, such as a patient specific insert for controlling the energy, focus depth, and/or shape of the charged particle beam. Examples of inserts include a range shifter, a compensator, an aperture, a ridge filter, and a blank. Optionally and preferably, each tray communicates a held and positioned insert to a main controller of the charged particle cancer therapy system. The trays optionally hold one or more of the imaging sheets configured to emit light upon transmission of the charged particle beam through a corresponding localized position of the one or more imaging sheets. For clarity of presentation and without loss of generality, throughout this document, treatment systems and imaging systems are described relative to a tumor of a patient. However, more generally any sample is imaged with any of the imaging systems described herein and/or any element of the sample is treated with the positively charged particle beam(s) described herein. Charged Particle Beam Therapy Throughout this document, a charged particle beam therapy system, such as a proton beam, hydrogen ion beam, or carbon ion beam, is described. Herein, the charged particle beam therapy system is described using a proton beam. However, the aspects taught and described in terms of a proton beam are not intended to be limiting to that of a proton beam and are illustrative of a charged particle beam system, a positively charged beam system, and/or a multiply charged particle beam system, such as C4+ or C6+. Any of the techniques described herein are equally applicable to any charged particle beam system. Referring now to FIG. 1A, a charged particle beam system 100 is illustrated. The charged particle beam preferably comprises a number of subsystems including any of: a main controller 110; an injection system 120; a synchrotron 130 that typically includes: (1) an accelerator system 131 and (2) an internal or connected extraction system 134; a beam transport system 135; a scanning/targeting/delivery system 140; a nozzle system 146; a patient interface module 150; a display system 160; and/or an imaging system 170. An exemplary method of use of the charged particle beam system 100 is provided. The main controller 110 controls one or more of the subsystems to accurately and precisely deliver protons to a tumor of a patient. For example, the main controller 110 obtains an image, such as a portion of a body and/or of a tumor, from the imaging system 170. The main controller 110 also obtains position and/or timing information from the patient interface module 150. The main controller 110 optionally controls the injection system 120 to inject a proton into a synchrotron 130. The synchrotron typically contains at least an accelerator system 131 and an extraction system 134. The main controller 110 preferably controls the proton beam within the accelerator system, such as by controlling speed, trajectory, and timing of the proton beam. The main controller then controls extraction of a proton beam from the accelerator through the extraction system 134. For example, the controller controls timing, energy, and/or intensity of the extracted beam. The controller 110 also preferably controls targeting of the proton beam through the scanning/targeting/delivery system 140 to the patient interface module 150. One or more components of the patient interface module 150, such as translational and rotational position of the patient, are preferably controlled by the main controller 110. Further, display elements of the display system 160 are preferably controlled via the main controller 110. Displays, such as display screens, are typically provided to one or more operators and/or to one or more patients. In one embodiment, the main controller 110 times the delivery of the proton beam from all systems, such that protons are delivered in an optimal therapeutic manner to the tumor of the patient. Herein, the main controller 110 refers to a single system controlling the charged particle beam system 100, to a single controller controlling a plurality of subsystems controlling the charged particle beam system 100, or to a plurality of individual controllers controlling one or more sub-systems of the charged particle beam system 100. Still referring to FIG. 43, a first input to the semi-automated radiation treatment plan development system 4300, used to generate the radiation treatment plan 4310, is a requirement of dose distribution 4320. Herein, dose distribution comprises one or more parameters, such as a prescribed dosage 4321 to be delivered; an evenness or uniformity of radiation dosage distribution 4322; a goal of reduced overall dosage 4323 delivered to the patient 730; a specification related to minimization or reduction of dosage delivered to critical voxels 4324 of the patient 730, such as to a portion of an eye, brain, nervous system, and/or heart of the patient 730; and/or an extent of, outside a perimeter of the tumor, dosage distribution 4325. The automated radiation treatment plan development system 4300 calculates and/or iterates a best radiation treatment plan using the inputs, such as via a computer implemented algorithm. Each parameter provided to the automated radiation treatment plan development system 4300, optionally and preferably contains a weight or importance. For clarity of presentation and without loss of generality, two cases illustrate. In a first case, a requirement/goal of reduction of dosage or even complete elimination of radiation dosage to the optic nerve of the eye, provided in the minimized dosage to critical voxels 4324 input is given a higher weight than a requirement/goal to minimize dosage to an outer area of the eye, such as the rectus muscle, or an inner volume of the eye, such as the vitreous humor of the eye. This first case is exemplary of one input providing more than one sub-input where each sub-input optionally includes different weighting functions. In a second case, a first weight and/or first sub-weight of a first input is compared with a second weight and/or a second sub-weight of a second input. For instance, a distribution function, probability, or precision of the even radiation dosage distribution 4322 input optionally comprises a lower associated weight than a weight provided for the reduce overall dosage 4323 input to prevent the computer algorithm from increasing radiation dosage in an attempt to yield an entirely uniform dose distribution. Each parameter and/or sub-parameter provided to the automated radiation treatment plan development system 4300, optionally and preferably contains a limit, such as a hard limit, an upper limit, a lower limit, a probability limit, and/or a distribution limit. The limit requirement is optionally used, by the computer algorithm generating the radiation treatment plan 4310, with or without the weighting parameters, described supra. Referring now to FIG. 1B, an example of a charged particle cancer therapy system 100 is provided. A main controller receives input from one, two, three, or four of a respiration monitoring and/or controlling controller 180, a beam controller 185, a rotation controller 147, and/or a timing to a time period in a respiration cycle controller 148. The beam controller 185 preferably includes one or more or a beam energy controller 182, the beam intensity controller 340, a beam velocity controller 186, and/or a horizontal/vertical beam positioning controller 188. The main controller 110 controls any element of the injection system 120; the synchrotron 130; the scanning/targeting/delivery system 140; the patient interface module 150; the display system 160; and/or the imaging system 170. For example, the respiration monitoring/controlling controller 180 controls any element or method associated with the respiration of the patient; the beam controller 185 controls any of the elements controlling acceleration and/or extraction of the charged particle beam; the rotation controller 147 controls any element associated with rotation of the patient 830 or gantry; and the timing to a period in respiration cycle controller 148 controls any aspects affecting delivery time of the charged particle beam to the patient. As a further example, the beam controller 185 optionally controls any magnetic and/or electric field about any magnet in the charged particle cancer therapy system 100. One or more beam state sensors 190 sense position, direction, intensity, and/or energy of the charged particles at one or more positions in the charged particle beam path. A tomography system 700, described infra, is optionally used to monitor intensity and/or position of the charged particle beam. Referring now to FIG. 1C, an illustrative exemplary embodiment of one version of the charged particle beam system 100 is provided. The number, position, and described type of components is illustrative and non-limiting in nature. In the illustrated embodiment, the injection system 120 or ion source or charged particle beam source generates protons. The injection system 120 optionally includes one or more of: a negative ion beam source, an ion beam focusing lens, and a tandem accelerator. The protons are delivered into a vacuum tube that runs into, through, and out of the synchrotron. The generated protons are delivered along an initial path 262. Optionally, focusing magnets 127, such as quadrupole magnets or injection quadrupole magnets, are used to focus the proton beam path. A quadrupole magnet is a focusing magnet. An injector bending magnet 128 bends the proton beam toward a plane of the synchrotron 130. The focused protons having an initial energy are introduced into an injector magnet 129, which is preferably an injection Lambertson magnet. Typically, the initial beam path 262 is along an axis off of, such as above, a circulating plane of the synchrotron 130. The injector bending magnet 128 and injector magnet 129 combine to move the protons into the synchrotron 130. Main bending magnets, dipole magnets, turning magnets, or circulating magnets 132 are used to turn the protons along a circulating beam path 264. A dipole magnet is a bending magnet. The main bending magnets 132 bend the initial beam path 262 into a circulating beam path 264. In this example, the main bending magnets 132 or circulating magnets are represented as four sets of four magnets to maintain the circulating beam path 264 into a stable circulating beam path. However, any number of magnets or sets of magnets are optionally used to move the protons around a single orbit in the circulation process. The protons pass through an accelerator 133. The accelerator accelerates the protons in the circulating beam path 264. As the protons are accelerated, the fields applied by the magnets are increased. Particularly, the speed of the protons achieved by the accelerator 133 are synchronized with magnetic fields of the main bending magnets 132 or circulating magnets to maintain stable circulation of the protons about a central point or region 136 of the synchrotron. At separate points in time the accelerator 133/main bending magnet 132 combination is used to accelerate and/or decelerate the circulating protons while maintaining the protons in the circulating path or orbit. An extraction element of an inflector/deflector system is used in combination with a Lambertson extraction magnet 137 to remove protons from their circulating beam path 264 within the synchrotron 130. One example of a deflector component is a Lambertson magnet. Typically the deflector moves the protons from the circulating plane to an axis off of the circulating plane, such as above the circulating plane. Extracted protons are preferably directed and/or focused using an extraction bending magnet 142 and optional extraction focusing magnets 141, such as quadrupole magnets, and optional bending magnets along a positively charged particle beam transport path 268 in a beam transport system 135, such as a beam path or proton beam path, into the scanning/targeting/delivery system 140. Two components of a scanning system 140 or targeting system typically include a first axis control 143, such as a vertical control, and a second axis control 144, such as a horizontal control. In one embodiment, the first axis control 143 allows for about 100 mm of vertical or y-axis scanning of the proton beam 268 and the second axis control 144 allows for about 700 mm of horizontal or x-axis scanning of the proton beam 268. A nozzle system 146 is used for directing the proton beam, for imaging the proton beam, for defining shape of the proton beam, and/or as a vacuum barrier between the low pressure beam path of the synchrotron and the atmosphere. Protons are delivered with control to the patient interface module 150 and to a tumor of a patient. All of the above listed elements are optional and may be used in various permutations and combinations. Ion Extraction from Ion Source A method and apparatus are described for extraction of ions from an ion source. For clarity of presentation and without loss of generality, examples focus on extraction of protons from the ion source. However, more generally cations of any charge are optionally extracted from a corresponding ion source with the techniques described herein. For instance, C4+ or C6+ are optionally extracted using the ion extraction methods and apparatus described herein. Further, by reversing polarity of the system, anions are optionally extracted from an anion source, where the anion is of any charge. Herein, for clarity of presentation and without loss of generality, ion extraction is coupled with tumor treatment and/or tumor imaging. However, the ion extraction is optional used in any method or apparatus using a stream or time discrete bunches of ions. Diode Extraction Referring now to FIG. 2A and FIG. 2B, a first ion extraction system is illustrated. The first ion extraction system uses a diode extraction system 200, where a first element of the diode extraction system is an ion source 122 or first electrode at a first potential and a second element 202 of the diode extraction system is at a second potential. Generally, the first potential is raised or lowered relative to the second potential to extract ions from the ion source 122 along the z-axis or the second potential is raised or lowered relative to the first potential to extract ions from the ion source 122 along the z-axis, where polarity of the potential difference determines if anions or cations are extracted from the ion source 122. Still referring to FIG. 2A and FIG. 2B, an example of ion extraction from the ion source 122 is described. As illustrated in FIG. 2A, in a non-extraction time period, a non-extraction diode potential, A1, of the ion source 122 is held at a potential equal to a potential, B1, of the second element 202. Referring now to FIG. 2B, during an extraction time period, a diode extraction potential, A2, of the ion source 122 is raised, causing a positively charged cation, such as the proton, to be drawn out of the ion chamber toward the lower potential of the second element 202. Similarly, if the diode extraction potential, A2, of the ion source is lowered relative a potential, B1, then an anion is extracted from the ion source 122 toward a higher potential of the second element 202. In the diode extraction system 200, the voltage of a large mass and corresponding large capacitance of the ion source 122 is raised or lowered, which takes time, has an RC time constant, and results in a range of temperatures of the plasma during the extraction time period, which is typically pulsed on and off with time. Particularly, as the potential of the ion source 122 is cycled with time, the ion source 122 temperature cycles, which results in a range of emittance values, resultant from conservation of momentum, and a corresponding less precise extraction beam. Alternatively, potential of the second element 202 is varied, altered, pulsed, or cycled, which reduces a range of emittance values during the extraction process. Triode Extraction Referring now to FIG. 2C and FIG. 2D, a second ion extraction system is illustrated. The second ion extraction system uses a triode extraction system 210. The triode extraction system 210 uses: (1) an ion source 122, (2) a gating electrode 204 also referred to as a suppression electrode, and (3) an extraction electrode 206. Optionally, a first electrode of the triode extraction system 210 is positioned proximate the ion source 122 and is maintained at a potential as described, infra, using the ion source as the first electrode of the triode extraction system. Generally, potential of the gating electrode 204 is raised and lowered to, as illustrated, stop and start extraction of a positive ion. Varying the potential of the gating electrode 204 has the advantages of altering the potential of a small mass with a correspondingly small capacitance and small RC time constant, which via conservation of momentum, reduces emittance of the extracted ions. Optionally, a first electrode maintained at the first potential of the ion source is used as the first element of the triode extraction system in place of the ion source 122 while also optionally further accelerating and/or focusing the extracted ions or set of ions using the extraction electrode 206. Several example further describe the triode extraction system 210. Still referring to FIG. 43, a second input to the semi-automated radiation treatment plan development system 4300, is a patient motion 4330 input. The patient motion 4330 input comprises: a move the patient in one direction 4332 input, a move the patient at a uniform speed 4333 input, a total patient rotation 4334 input, a patient rotation rate 4335 input, and/or a patient tilt 4336 input. For clarity of presentation and without loss of generality, the patient motion inputs are further described, supra, in several cases. Still referring to FIG. 43, in a first case the automated radiation treatment plan development system 4300, provides a guidance input, such as the move the patient in one direction 4332 input, but a further associated directive is if other goals require it or if a better overall score of the radiation treatment plan 4310 is achieved, the guidance input is optionally automatically relaxed. Similarly, the move the patient at a uniform rate 4333 input is also provided with a guidance input, such as a low associated weight that is further relaxable to yield a high score, of the radiation treatment plan 4310, but is only relaxed or implemented an associated fixed or hard limit number of times. Still referring to FIG. 43, in a second case the computer implemented algorithm, in the automated radiation treatment plan development system 4300, optionally generates a sub-score. For instance, a patient comfort score optionally comprises a score combining a metric related to two or more of: the move the patient in one direction 4332 input, the move the patient at a uniform rate 4333 input, the total patient rotation 4334 input, the patient rotation rate 4335 input, and/or the reduce patient tilt 4336 input. The sub-score, which optionally has a preset limit, allows flexibility, in the computer implemented algorithm, to yield on patient movement parameters as a whole, again to result in patient comfort. Still referring to FIG. 43, in a third case the automated radiation treatment plan development system 4300 optionally contains an input used for more than one sub-function. For example, a reduce treatment time 4331 input is optionally used as a patient comfort parameter and also links into the dose distribution 4320 input. Still referring to FIG. 43, a third input to the automated radiation treatment plan development system 4300 comprises output of an imaging system, such as any of the imaging systems described herein. Still referring to FIG. 43, a fourth optional input to the automated radiation treatment plan development system 4300 is structural and/or physical elements present in the treatment room 1222. Again, for clarity of presentation and without loss of generality, two cases illustrate treatment room object information as an input to the automated development of the radiation treatment plan 4310. Still referring to FIG. 43, in a first case the automated radiation treatment plan development system 4300 is optionally provided with a pre-scan of potentially intervening support structures 4422 input, such as a patient support device, a patient couch, and/or a patient support element, where the pre-scan is an image/density/redirection impact of the support structure on the positively charged particle treatment beam. Preferably, the pre-scan is an actual image or tomogram of the support structure using the actual facility synchrotron, a remotely generated actual image, and/or a calculated impact of the intervening structure on the positively charge particle beam. Determination of impact of the support structure on the charged particle beam is further described, infra. Still referring to FIG. 43, in a second case the automated radiation treatment plan development system 4300 is optionally provided with a reduce treatment through a support structure 4344 input. As described supra, an associated weight, guidance, and/or limit is optionally provided with the reduce treatment through the support structure 4344 input and, also as described supra, the support structure input is optionally compromised relative to a more critical parameter, such as the deliver prescribed dosage 4321 input or the minimize dosage to critical voxels 4324 of the patient 730 input. Still referring to FIG. 43, a fifth optional input to the automated radiation treatment plan development system 4300 is a doctor input 4236, such as provided only prior to the auto generation of the radiation treatment plan. Separately, doctor oversight 4230 is optionally provided to the automated radiation treatment plan development system 4300 as plans are being developed, such as an intervention to restrict an action, an intervention to force an action, and/or an intervention to change one of the inputs to the automated radiation treatment plan development system 4300 for a radiation plan for a particular individual. Still referring to FIG. 43, a sixth input to the automated radiation treatment plan development system 4300 comprises information related to collapse and/or shifting of the tumor 720 of the patient 730 during treatment. For instance, the radiation treatment plan 4310 is automatically updated, using the automated radiation treatment plan development system 4300, during treatment using an input of images of the tumor 720 of the patient 730 collected concurrently with treatment using the positively charged particles. For instance, as the tumor 720 reduces in size with treatment, the tumor 720 collapses inward and/or shifts. The auto-updated radiation treatment plan is optionally auto-implemented, such as without the patient moving from a treatment position. Optionally, the automated radiation treatment plan development system 4300 tracks dosage of untreated voxels of the tumor 720 and/or tracks partially irradiated, relative to the prescribed dosage 4321, voxels and dynamically and/or automatically adjusts the radiation treatment plan 4310 to provide the full prescribed dosage to each voxel despite movement of the tumor 720. Similarly, the automated radiation treatment plan development system 4300 tracks dosage of treated voxels of the tumor 720 and adjusts the automatically updated tumor treatment plan to reduce and/or minimize further radiation delivery to the fully treated and shifted tumor voxels while continuing treatment of the partially treated and/or untreated shifted voxels of the tumor 720. Intervening Object As the positively charged particle beam travels along a treatment beam path in the treatment room 1222, in some situations the positively charged particle beam passes through an object, referred to herein as an intervening object, which decelerates and/or redirects the positively charged particles. Herein, predetermining an impact of the intervening object on the positively charged particle beam is described and compensating for the impact is described. Referring now to FIG. 44, a method for determining an impact of an object 4400 on the positively charged particle beam is described. Herein, an intervening object 4410 is any inanimate and/or non-biological object in the treatment room 1222 between an exit surface of the nozzle system 146 and a terminal point of the charged particle beam in the tumor as determined by the Bragg peak. Examples of intervening objects 4410 comprise: a patient couch, a patient support element, an implant, an embedded element in the patient 730, and/or a prosthesis. Parameters defining the intervening object 4410 and/or the physical intervening object 4410 itself is provided to the method for determining an impact of an object 4400. Still referring to FIG. 44, in a first case, the intervening object 4410 is pre-scanned 4420, such as with an X-ray system, a positron emission system, and/or a positively charged particle beam system. For example, a three-dimensional (3D) computed tomography (CT) proton beam image of the intervening object is obtained. In the radiation treatment plan 4310, described supra, a determination is made for each treatment beam, of a set of treatment beam covering relative motion and/or translation of the nozzle system and the patient, whether or not the charged particle beam will traverse the intervening object 4410 and if so, what cross-section of the intervening object 4410 is traversed at each position along a pathway through the intervening object 4410. For each voxel of the intervening object 4410 along the treatment path, a deceleration and/or redirection/scattering of the treatment beam is calculated. By integrating the impact of the intervening object 4410 across the voxels traversed, a total deceleration and/or net direction/scattering change of the positively charged particle beam is predetermined. Subsequently, in a generation of the radiation treatment plan step 4440 or in the auto-generate the radiation treatment plan step 4226, the incident energy of the positively charged particles for each incident treatment vector of the radiation treatment plan 4310 is adjusted to increase the energy of the initial charged particle beam to compensate for the loss of energy or deceleration of the positively charged particle beam resultant from passage through the intervening object. Similarly, in the generation of the radiation treatment plan step 4440 or in the auto-generate the radiation treatment plan step 4226, the incident vector/direction of the positively charged particles for each incident treatment vector of the radiation treatment plan 4310 is adjusted to compensate for redirection of the initial charged particle beam to account for redirection of the treatment beam resultant from passage through the intervening object. Still referring to FIG. 44 and still referring to the first case of pre-scanning the object 4420, two approaches are used to measure the impact of the intervening object 4410 on the positively charged particle beam. In a first approach, the initial energy and direction of a treatment beam mimic traverses an actual treatment path 4424 through the intervening object 4410 and a residual energy and/or altered direction of the treatment beam mimic is measured, such as with the tomography apparatus and/or tomography imaging system described supra. In this first approach, the energy and/or vector of a particular incident treatment beam is adjusted to compensate for a directly measured impact of the intervening object 4410 on the particular incident treatment beam to yield a planned treatment beam in the radiation treatment plan. In a second approach, the 3D CT image of the intervening object 4410 is used to calculate impact to a transformed and/or proposed incident treatment path 4424 through the intervening object 4410, where the proposed incident treatment path is a combination of voxels crossing many layers of the 3D CT image of the intervening object. Similar to the first approach, in the second approach, a residual energy and/or altered direction of the proposed treatment path is adjusted to compensate for the calculated impact, using real image data, of the intervening object 4410 on the proposed incident treatment beam to yield a planned treatment beam in the radiation treatment plan. The first case finds particular utility for standard items, such as a standard implanted item, or for an item readily available in the treatment room, such as a patient support/positioning/movement system element. Still referring to FIG. 44, in a second case, impact of the intervening object 4410 on the positively charged particle treatment beam is pre-calculated 4430 using known physical properties. For example, physical parameters such as material type, material density, and shape of the intervening object 4410 are coded into a 3D model of the intervening object 4410. Similar to the first case, the 3D model of the intervening object 4410 is used to determine a deceleration and/or altered direction of a proposed treatment path and the model data is used to adjust a proposed treatment beam to a planned treatment beam that accounts for the purely calculated impact of the intervening object 4410 on the treatment beam. One method of pre-calculating impact of the intervening object 4410 on a treatment beam is via use of finite element analysis 4432. The second case finds particular utility for compensating for an implanted object, such as a hip replacement, titanium bone support, plate, fastener, or other medically implanted item, especially a custom implant. Still referring to FIG. 44, in a third case, an actual image, such as a 3D CT image, of the intervening object 4410 is combined with model based calculations of impact of the intervening object 4410 on an incident particle beam, such as through use of known physical material properties, chemical properties, physical shape, and/or chemical/physical state of the intervening object. The resulting hybrid measured-calculated impact of the intervening object 4410 on a proposed treatment beam is used to generate an actual treatment beam vector in the radiation treatment plan 4310, which is generated 4440 and/or auto-generated 4226. Automated Adaptive Treatment Referring now to FIG. 45, a system for automatically updating the radiation treatment plan 4500 and preferably automatically updating and implementing the radiation treatment plan is illustrated. In a first task 4510, an initial radiation treatment plan is provided, such as the auto-generated radiation treatment plan 4226, described supra. The first task is a startup task of an iterative loop of tasks and/or recurring set of tasks, described herein as comprising tasks two to four. In a second task 4520, the tumor 720 is treated using the positively charged particles delivered from the synchrotron 130. In a third task 4530, changes in the tumor shape and/or changes in the tumor position relative to surrounding constituents of the patient 730 are observed, such as via any of the imaging systems described herein. The imaging optionally occurs simultaneously, concurrently, periodically, and/or intermittently with the second task while the patient remains positioned by the patient positioning system. The main controller 110 uses images from the imaging system(s) and the provided and/or current radiation treatment plan to determine if the treatment plan is to be followed or modified. Upon detected relative movement of the tumor 720 relative to the other elements of the patient 730 and/or change in a shape of the tumor 730, a fourth task 4540 of updating the treatment plan is optionally and preferably automatically implemented and/or use of the radiation treatment plan development system 4300, described supra, is implemented. The process of tasks two to four is optionally and preferably repeated n times where n is a positive integer of greater than 1, 2, 5, 10, 20, 50, or 100 and/or until a treatment session of the tumor 720 ends and the patient 730 departs the treatment room 1222. Automated Treatment Referring now to FIG. 46, an automated cancer therapy treatment system 4600 is illustrated. In the automated cancer therapy treatment system 4600, a majority of tasks are implemented according to a computer based algorithm and/or an intelligent system. Optionally and preferably, a medical professional oversees the automated cancer therapy treatment system 4600 and stops or alters the treatment upon detection of an error but fundamentally observes the process of computer algorithm guided implementation of the system using electromechanical elements, such as any of the hardware and/or software described herein. Optionally and preferably, each sub-system and/or sub-task is automated. Optionally, one or more of the sub-systems and/or sub-tasks are performed by a medical professional. For instance, the patient 730 is optionally initially positioned in the patient positioning system by the medical professional and/or a tray insert 510 is loaded into a tray assembly 400 by the medical professional. Optional and preferably automated, such as computer algorithm implemented, sub-tasks include one or more and preferably all of: receiving the treatment plan input 4300, such as a prescription, guidelines, patient motion guidelines 4330, dose distribution guidelines 4320, intervening object 4310 information, and/or images of the tumor 720; using the treatment plan input 4300 to auto-generate a radiation treatment plan 4226; auto-positioning 4222 the patient 730; auto-imaging 4224 the tumor 720; implementing medical profession oversight 4238 instructions; auto-implementing the radiation treatment plan 4520/delivering the positively charged particles to the tumor 720; auto-reposition the patient 4521 for subsequent radiation delivery; auto-rotate a nozzle position 4522 of the nozzle system 146 relative to the patient 730; auto-translate a nozzle position 4523 of the nozzle system 146 relative to the patient 730; auto-verify a clear treatment path using an imaging system, such as to observe presence of a metal object or unforeseen dense object via an X-ray image; auto-verify a clear treatment path using fiducial indicators 4524; auto control a state of the positively charge particle beam 4525, such as energy, intensity, position (x,y,z), duration, and/or direction; auto-control a particle beam path 4526, such as to a selected beamline and/or to a selected nozzle; auto implement positioning a tray insert 510 and/or tray assembly 400; auto-update a tumor image 4610; auto-observe tumor movement 4530; and/or generate an auto-modified radiation treatment plan 4540/new treatment plan. Still yet another embodiment includes any combination and/or permutation of any of the elements described herein. The main controller, a localized communication apparatus, and/or a system for communication of information optionally comprises one or more subsystems stored on a client. The client is a computing platform configured to act as a client device or other computing device, such as a computer, personal computer, a digital media device, and/or a personal digital assistant. The client comprises a processor that is optionally coupled to one or more internal or external input device, such as a mouse, a keyboard, a display device, a voice recognition system, a motion recognition system, or the like. The processor is also communicatively coupled to an output device, such as a display screen or data link to display or send data and/or processed information, respectively. In one embodiment, the communication apparatus is the processor. In another embodiment, the communication apparatus is a set of instructions stored in memory that is carried out by the processor. The client includes a computer-readable storage medium, such as memory. The memory includes, but is not limited to, an electronic, optical, magnetic, or another storage or transmission data storage medium capable of coupling to a processor, such as a processor in communication with a touch-sensitive input device linked to computer-readable instructions. Other examples of suitable media include, for example, a flash drive, a CD-ROM, read only memory (ROM), random access memory (RAM), an application-specific integrated circuit (ASIC), a DVD, magnetic disk, an optical disk, and/or a memory chip. The processor executes a set of computer-executable program code instructions stored in the memory. The instructions may comprise code from any computer-programming language, including, for example, C originally of Bell Laboratories, C++, C#, Visual Basic® (Microsoft, Redmond, Wash.), Matlab® (MathWorks, Natick, Mass.), Java® (Oracle Corporation, Redwood City, Calif.), and JavaScript® (Oracle Corporation, Redwood City, Calif.). Herein, any number, such as 1, 2, 3, 4, 5, is optionally more than the number, less than the number, or within 1, 2, 5, 10, 20, or 50 percent of the number. Herein, an element and/or object is optionally manually and/or mechanically moved, such as along a guiding element, with a motor, and/or under control of the main controller. The particular implementations shown and described are illustrative of the invention and its best mode and are not intended to otherwise limit the scope of the present invention in any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation, and other functional aspects of the system may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and/or physical couplings between the various elements. Many alternative or additional functional relationships or physical connections may be present in a practical system. In the foregoing description, the invention has been described with reference to specific exemplary embodiments; however, it will be appreciated that various modifications and changes may be made without departing from the scope of the present invention as set forth herein. The description and figures are to be regarded in an illustrative manner, rather than a restrictive one and all such modifications are intended to be included within the scope of the present invention. Accordingly, the scope of the invention should be determined by the generic embodiments described herein and their legal equivalents rather than by merely the specific examples described above. For example, the steps recited in any method or process embodiment may be executed in any order and are not limited to the explicit order presented in the specific examples. Additionally, the components and/or elements recited in any apparatus embodiment may be assembled or otherwise operationally configured in a variety of permutations to produce substantially the same result as the present invention and are accordingly not limited to the specific configuration recited in the specific examples. Benefits, other advantages and solutions to problems have been described above with regard to particular embodiments; however, any benefit, advantage, solution to problems or any element that may cause any particular benefit, advantage or solution to occur or to become more pronounced are not to be construed as critical, required or essential features or components. As used herein, the terms “comprises”, “comprising”, or any variation thereof, are intended to reference a non-exclusive inclusion, such that a process, method, article, composition or apparatus that comprises a list of elements does not include only those elements recited, but may also include other elements not expressly listed or inherent to such process, method, article, composition or apparatus. Other combinations and/or modifications of the above-described structures, arrangements, applications, proportions, elements, materials or components used in the practice of the present invention, in addition to those not specifically recited, may be varied or otherwise particularly adapted to specific environments, manufacturing specifications, design parameters or other operating requirements without departing from the general principles of the same. Although the invention has been described herein with reference to certain preferred embodiments, one skilled in the art will readily appreciate that other applications may be substituted for those set forth herein without departing from the spirit and scope of the present invention. Accordingly, the invention should only be limited by the Claims included below. Still referring to FIG. 2C and FIG. 2D, optionally and preferably geometries of the gating electrode 204 and/or the extraction electrode 206 are used to focus the extracted ions along the initial ion beam path 262. Still referring to FIG. 2C and FIG. 2D, the lower emittance of the electron cyclotron resonance triode extraction system is optionally and preferably coupled with a downbeam or downstream radio-frequency quadrupole, used to focus the beam, and/or a synchrotron, used to accelerate the beam. Still referring to FIG. 2C and FIG. 2D, the lower emittance of the electron cyclotron resonance triode extraction system is maintained through the synchrotron 130 and to the tumor of the patient resulting in a more accurate, precise, smaller, and/or tighter treatment voxel of the charged particle beam or charged particle pulse striking the tumor. Still referring to FIG. 2C and FIG. 2D, the lower emittance of the electron cyclotron resonance triode extraction system reduces total beam spread through the synchrotron 130 and the tumor to one or more imaging elements, such as an optical imaging sheet or scintillation material emitting photons upon passage of the charged particle beam or striking of the charged particle beam, respectively. The lower emittance of the charged particle beam, optionally and preferably maintained through the accelerator system 134 and beam transport system yields a tighter, more accurate, more precise, and/or smaller particle beam or particle burst diameter at the imaging surfaces and/or imaging elements, which facilitates more accurate and precise tumor imaging, such as for subsequent tumor treatment or to adjust, while the patient waits in a treatment position, the charged particle treatment beam position. Any feature or features of any of the above provided examples are optionally and preferably combined with any feature described in other examples provided, supra, or herein. Ion Extraction from Accelerator Referring now to FIG. 3, both: (1) an exemplary proton beam extraction system 300 from the synchrotron 130 and (2) a charged particle beam intensity control system 305 are illustrated. For clarity, FIG. 3 removes elements represented in FIG. 1C, such as the turning magnets, which allows for greater clarity of presentation of the proton beam path as a function of time. Generally, protons are extracted from the synchrotron 130 by slowing the protons. As described, supra, the protons were initially accelerated in a circulating path, which is maintained with a plurality of main bending magnets 132. The circulating path is referred to herein as an original central beamline 264. The protons repeatedly cycle around a central point in the synchrotron 136. The proton path traverses through a radio frequency (RF) cavity system 310. To initiate extraction, an RF field is applied across a first blade 312 and a second blade 314, in the RF cavity system 310. The first blade 312 and second blade 314 are referred to herein as a first pair of blades. In the proton extraction process, an RF voltage is applied across the first pair of blades, where the first blade 312 of the first pair of blades is on one side of the circulating proton beam path 264 and the second blade 314 of the first pair of blades is on an opposite side of the circulating proton beam path 264. The applied RF field applies energy to the circulating charged-particle beam. The applied RF field alters the orbiting or circulating beam path slightly of the protons from the original central beamline 264 to an altered circulating beam path 265. Upon a second pass of the protons through the RF cavity system, the RF field further moves the protons off of the original proton beamline 264. For example, if the original beamline is considered as a circular path, then the altered beamline is slightly elliptical. The frequency of the applied RF field is timed to apply outward or inward movement to a given band of protons circulating in the synchrotron accelerator. Orbits of the protons are slightly more off axis compared to the original circulating beam path 264. Successive passes of the protons through the RF cavity system are forced further and further from the original central beamline 264 by altering the direction and/or intensity of the RF field with each successive pass of the proton beam through the RF field. Timing of application of the RF field and/or frequency of the RF field is related to the circulating charged particles circulation pathlength in the synchrotron 130 and the velocity of the charged particles so that the applied RF field has a period, with a peak-to-peak time period, equal to a period of time of beam circulation in the synchrotron 130 about the center 136 or an integer multiple of the time period of beam circulation about the center 136 of the synchrotron 130. Alternatively, the time period of beam circulation about the center 136 of the synchrotron 130 is an integer multiple of the RF period time. The RF period is optionally used to calculated the velocity of the charged particles, which relates directly to the energy of the circulating charged particles. The RF voltage is frequency modulated at a frequency about equal to the period of one proton cycling around the synchrotron for one revolution or at a frequency than is an integral multiplier of the period of one proton cycling about the synchrotron. The applied RF frequency modulated voltage excites a betatron oscillation. For example, the oscillation is a sine wave motion of the protons. The process of timing the RF field to a given proton beam within the RF cavity system is repeated thousands of times with each successive pass of the protons being moved approximately one micrometer further off of the original central beamline 264. For clarity, the approximately 1000 changing beam paths with each successive path of a given band of protons through the RF field are illustrated as the altered beam path 265. The RF time period is process is known, thus energy of the charged particles at time of hitting the extraction material or material 330, described infra, is known. With a sufficient sine wave betatron amplitude, the altered circulating beam path 265 touches and/or traverses a material 330, such as a foil or a sheet of foil. The foil is preferably a lightweight material, such as beryllium, a lithium hydride, a carbon sheet, or a material having low nuclear charge components. Herein, a material of low nuclear charge is a material composed of atoms consisting essentially of atoms having six or fewer protons. The foil is preferably about 10 to 150 microns thick, is more preferably about 30 to 100 microns thick, and is still more preferably about 40 to 60 microns thick. In one example, the foil is beryllium with a thickness of about 50 microns. When the protons traverse through the foil, energy of the protons is lost and the speed of the protons is reduced. Typically, a current is also generated, described infra. Protons moving at the slower speed travel in the synchrotron with a reduced radius of curvature 266 compared to either the original central beamline 264 or the altered circulating path 265. The reduced radius of curvature 266 path is also referred to herein as a path having a smaller diameter of trajectory or a path having protons with reduced energy. The reduced radius of curvature 266 is typically about two millimeters less than a radius of curvature of the last pass of the protons along the altered proton beam path 265. The thickness of the material 330 is optionally adjusted to create a change in the radius of curvature, such as about ½, 1, 2, 3, or 4 mm less than the last pass of the protons 265 or original radius of curvature 264. The reduction in velocity of the charged particles transmitting through the material 330 is calculable, such as by using the pathlength of the betatron oscillating charged particle beam through the material 330 and/or using the density of the material 330. Protons moving with the smaller radius of curvature travel between a second pair of blades. In one case, the second pair of blades is physically distinct and/or is separated from the first pair of blades. In a second case, one of the first pair of blades is also a member of the second pair of blades. For example, the second pair of blades is the second blade 314 and a third blade 316 in the RF cavity system 310. A high voltage DC signal, such as about 1 to 5 kV, is then applied across the second pair of blades, which directs the protons out of the synchrotron through an extraction magnet 137, such as a Lambertson extraction magnet, into a transport path 268. Control of acceleration of the charged particle beam path in the synchrotron with the accelerator and/or applied fields of the turning magnets in combination with the above described extraction system allows for control of the intensity of the extracted proton beam, where intensity is a proton flux per unit time or the number of protons extracted as a function of time. For example, when a current is measured beyond a threshold, the RF field modulation in the RF cavity system is terminated or reinitiated to establish a subsequent cycle of proton beam extraction. This process is repeated to yield many cycles of proton beam extraction from the synchrotron accelerator. In another embodiment, instead of moving the charged particles to the material 330, the material 330 is mechanically moved to the circulating charged particles. Particularly, the material 330 is mechanically or electromechanically translated into the path of the circulating charged particles to induce the extraction process, described supra. In this case, the velocity or energy of the circulating charged particle beam is calculable using the pathlength of the beam path about the center 136 of the synchrotron 130 and from the force applied by the bending magnets 132. In either case, because the extraction system does not depend on any change in magnetic field properties, it allows the synchrotron to continue to operate in acceleration or deceleration mode during the extraction process. Stated differently, the extraction process does not interfere with synchrotron acceleration. In stark contrast, traditional extraction systems introduce a new magnetic field, such as via a hexapole, during the extraction process. More particularly, traditional synchrotrons have a magnet, such as a hexapole magnet, that is off during an acceleration stage. During the extraction phase, the hexapole magnetic field is introduced to the circulating path of the synchrotron. The introduction of the magnetic field necessitates two distinct modes, an acceleration mode and an extraction mode, which are mutually exclusive in time. The herein described system allows for acceleration and/or deceleration of the proton during the extraction step and tumor treatment without the use of a newly introduced magnetic field, such as by a hexapole magnet. Charged Particle Beam Intensity Control Control of applied field, such as a radio-frequency (RF) field, frequency and magnitude in the RF cavity system 310 allows for intensity control of the extracted proton beam, where intensity is extracted proton flux per unit time or the number of protons extracted as a function of time. Still referring FIG. 3, the intensity control system 305 is further described. In this example, an intensity control feedback loop is added to the extraction system, described supra. When protons in the proton beam hit the material 330 electrons are given off from the material 330 resulting in a current. The resulting current is converted to a voltage and is used as part of an ion beam intensity monitoring system or as part of an ion beam feedback loop for controlling beam intensity. The voltage is optionally measured and sent to the main controller 110 or to an intensity controller subsystem 340, which is preferably in communication or under the direction of the main controller 110. More particularly, when protons in the charged particle beam path pass through the material 330, some of the protons lose a small fraction of their energy, such as about one-tenth of a percent, which results in a secondary electron. That is, protons in the charged particle beam push some electrons when passing through material 330 giving the electrons enough energy to cause secondary emission. The resulting electron flow results in a current or signal that is proportional to the number of protons going through the target or extraction material 330. The resulting current is preferably converted to voltage and amplified. The resulting signal is referred to as a measured intensity signal. The amplified signal or measured intensity signal resulting from the protons passing through the material 330 is optionally used in monitoring the intensity of the extracted protons and is preferably used in controlling the intensity of the extracted protons. For example, the measured intensity signal is compared to a goal signal, which is predetermined in an irradiation of the tumor plan. The difference between the measured intensity signal and the planned for goal signal is calculated. The difference is used as a control to the RF generator. Hence, the measured flow of current resulting from the protons passing through the material 330 is used as a control in the RF generator to increase or decrease the number of protons undergoing betatron oscillation and striking the material 330. Hence, the voltage determined off of the material 330 is used as a measure of the orbital path and is used as a feedback control to control the RF cavity system. In one example, the intensity controller subsystem 340 preferably additionally receives input from: (1) a detector 350, which provides a reading of the actual intensity of the proton beam and/or (2) an irradiation plan 360. The irradiation plan provides the desired intensity of the proton beam for each x, y, energy, and/or rotational position of the patient/tumor as a function of time. Thus, the intensity controller 340 receives the desired intensity from the irradiation plan 350, the actual intensity from the detector 350 and/or a measure of intensity from the material 330, and adjusts the amplitude and/or the duration of application of the applied radio-frequency field in the RF cavity system 310 to yield an intensity of the proton beam that matches the desired intensity from the irradiation plan 360. As described, supra, the protons striking the material 330 is a step in the extraction of the protons from the synchrotron 130. Hence, the measured intensity signal is used to change the number of protons per unit time being extracted, which is referred to as intensity of the proton beam. The intensity of the proton beam is thus under algorithm control. Further, the intensity of the proton beam is controlled separately from the velocity of the protons in the synchrotron 130. Hence, intensity of the protons extracted and the energy of the protons extracted are independently variable. Still further, the intensity of the extracted protons is controllably variable while scanning the charged particles beam in the tumor from one voxel to an adjacent voxel as a separate hexapole and separated time period from acceleration and/or treatment is not required, as described supra. For example, protons initially move at an equilibrium trajectory in the synchrotron 130. An RF field is used to excite or move the protons into a betatron oscillation. In one case, the frequency of the protons orbit is about 10 MHz. In one example, in about one millisecond or after about 10,000 orbits, the first protons hit an outer edge of the target material 130. The specific frequency is dependent upon the period of the orbit. Upon hitting the material 130, the protons push electrons through the foil to produce a current. The current is converted to voltage and amplified to yield a measured intensity signal. The measured intensity signal is used as a feedback input to control the applied RF magnitude or RF field. An energy beam sensor, described infra, is optionally used as a feedback control to the RF field frequency or RF field of the RF field extraction system 310 to dynamically control, modify, and/or alter the delivered charge particle beam energy, such as in a continuous pencil beam scanning system operating to treat tumor voxels without alternating between an extraction phase and a treatment phase. Preferably, the measured intensity signal is compared to a target signal and a measure of the difference between the measured intensity signal and target signal is used to adjust the applied RF field in the RF cavity system 310 in the extraction system to control the intensity of the protons in the extraction step. Stated again, the signal resulting from the protons striking and/or passing through the material 130 is used as an input in RF field modulation. An increase in the magnitude of the RF modulation results in protons hitting the foil or material 130 sooner. By increasing the RF, more protons are pushed into the foil, which results in an increased intensity, or more protons per unit time, of protons extracted from the synchrotron 130. In another example, a detector 350 external to the synchrotron 130 is used to determine the flux of protons extracted from the synchrotron and a signal from the external detector is used to alter the RF field, RF intensity, RF amplitude, and/or RF modulation in the RF cavity system 310. Here the external detector generates an external signal, which is used in a manner similar to the measured intensity signal, described in the preceding paragraphs. Preferably, an algorithm or irradiation plan 360 is used as an input to the intensity controller 340, which controls the RF field modulation by directing the RF signal in the betatron oscillation generation in the RF cavity system 310. The irradiation plan 360 preferably includes the desired intensity of the charged particle beam as a function of time and/or energy of the charged particle beam as a function of time, for each patient rotation position, and/or for each x-, y-position of the charged particle beam. In yet another example, when a current from material 330 resulting from protons passing through or hitting material is measured beyond a threshold, the RF field modulation in the RF cavity system is terminated or reinitiated to establish a subsequent cycle of proton beam extraction. This process is repeated to yield many cycles of proton beam extraction from the synchrotron accelerator. In still yet another embodiment, intensity modulation of the extracted proton beam is controlled by the main controller 110. The main controller 110 optionally and/or additionally controls timing of extraction of the charged particle beam and energy of the extracted proton beam. The benefits of the system include a multi-dimensional scanning system. Particularly, the system allows independence in: (1) energy of the protons extracted and (2) intensity of the protons extracted. That is, energy of the protons extracted is controlled by an energy control system and an intensity control system controls the intensity of the extracted protons. The energy control system and intensity control system are optionally independently controlled. Preferably, the main controller 110 controls the energy control system and the main controller 110 simultaneously controls the intensity control system to yield an extracted proton beam with controlled energy and controlled intensity where the controlled energy and controlled intensity are independently variable and/or continually available as a separate extraction phase and acceleration phase are not required, as described supra. Thus the irradiation spot hitting the tumor is under independent control of: time; energy; intensity; x-axis position, where the x-axis represents horizontal movement of the proton beam relative to the patient, and y-axis position, where the y-axis represents vertical movement of the proton beam relative to the patient.In addition, the patient is optionally independently translated and/or rotated relative to a translational axis of the proton beam at the same time.Beam Transport The beam transport system 135 is used to move the charged particles from the accelerator to the patient, such as via a nozzle in a gantry, described infra. Charged Particle Energy The beam transport system 135 optionally includes means for determining an energy of the charged particles in the charged particle beam. For example, an energy of the charged particle beam is determined via calculation, such as via equation 1, using knowledge of a magnet geometry and applied magnetic field to determine mass and/or energy. Referring now to equation 1, for a known magnet geometry, charge, q, and magnetic field, B, the Larmor radius, ρL, or magnet bend radius is defined as: ρ L = v ⊥ Ω c = 2 Em qB ( eq . 1 ) where: v⊥ is the ion velocity perpendicular to the magnetic field, Ωc is the cyclotron frequency, q is the charge of the ion, B is the magnetic field, m is the mass of the charge particle, and E is the charged particle energy. Solving for the charged particle energy yields equation 2. E = ( ρ L qB ) 2 2 m ( eq . 2 ) Thus, an energy of the charged particle in the charged particle beam in the beam transport system 135 is calculable from the know magnet geometry, known or measured magnetic field, charged particle mass, charged particle charge, and the known magnet bend radius, which is proportional to and/or equivalent to the Larmor radius. Nozzle After extraction from the synchrotron 130 and transport of the charged particle beam along the proton beam path 268 in the beam transport system 135, the charged particle beam exits through the nozzle system 146. In one example, the nozzle system includes a nozzle foil covering an end of the nozzle system 146 or a cross-sectional area within the nozzle system forming a vacuum seal. The nozzle system includes a nozzle that expands in x/y-cross-sectional area along the z-axis of the proton beam path 268 to allow the proton beam 268 to be scanned along the x-axis and y-axis by the vertical control element and horizontal control element, respectively. The nozzle foil is preferably mechanically supported by the outer edges of an exit port of the nozzle or nozzle system 146. An example of a nozzle foil is a sheet of about 0.1 inch thick aluminum foil. Generally, the nozzle foil separates atmosphere pressures on the patient side of the nozzle foil from the low pressure region, such as about 10−5 to 10−7 torr region, on the synchrotron 130 side of the nozzle foil. The low pressure region is maintained to reduce scattering of the circulating charged particle beam in the synchrotron. Herein, the exit foil of the nozzle is optionally the first sheet 760 of the charged particle beam state determination system 750, described infra. Charged Particle Control Referring now to FIG. 4A, FIG. 4B, FIG. 5, FIG. 6A, and FIG. 6B, a charged particle beam control system is described where one or more patient specific beam control assemblies are removably inserted into the charged particle beam path proximate the nozzle of the charged particle cancer therapy system 100, where the patient specific beam control assemblies adjust the beam energy, diameter, cross-sectional shape, focal point, and/or beam state of the charged particle beam to properly couple energy of the charged particle beam to the individual's specific tumor. Beam Control Tray Referring now to FIG. 4A and FIG. 4B, a beam control tray assembly 400 is illustrated in a top view and side view, respectively. The beam control tray assembly 400 optionally comprises any of a tray frame 410, a tray aperture 412, a tray handle 420, a tray connector/communicator 430, and means for holding a patient specific tray insert 510, described infra. Generally, the beam control tray assembly 400 is used to: (1) hold the patient specific tray insert 510 in a rigid location relative to the beam control tray 400, (2) electronically identify the held patient specific tray insert 510 to the main controller 110, and (3) removably insert the patient specific tray insert 510 into an accurate and precise fixed location relative to the charged particle beam, such as the proton beam path 268 at the nozzle of the charged particle cancer therapy system 100. For clarity of presentation and without loss of generality, the means for holding the patient specific tray insert 510 in the tray frame 410 of the beam control tray assembly 400 is illustrated as a set of recessed set screws 415. However, the means for holding the patient specific tray insert 510 relative to the rest of the beam control tray assembly 400 is optionally any mechanical and/or electromechanical positioning element, such as a latch, clamp, fastener, clip, slide, strap, or the like. Generally, the means for holding the patient specific tray insert 510 in the beam control tray 400 fixes the tray insert and tray frame relative to one another even when rotated along and/or around multiple axes, such as when attached to a charged particle cancer therapy system 100, nozzle system 146, dynamic gantry nozzle, or gantry nozzle, which is an optional element of the nozzle system 146, that moves in three-dimensional space relative to a fixed point in the beamline, proton beam path 268, and/or a given patient position. As illustrated in FIG. 4A and FIG. 4B, the recessed set screws 415 fix the patient specific tray insert 510 into the aperture 412 of the tray frame 410. The tray frame 410 is illustrated as circumferentially surrounding the patient specific tray insert 510, which aids in structural stability of the beam control tray assembly 400. However, generally the tray frame 410 is of any geometry that forms a stable beam control tray assembly 400. Still referring to FIG. 4A and now referring to FIG. 5 and FIG. 6A, the optional tray handle 420 is used to manually insert/retract the beam control tray assembly 400 into a receiving element of the gantry nozzle, nozzle system 146, or dynamic gantry nozzle. While the beam control tray assembly 400 is optionally inserted into the charged particle beam path 268 at any point after extraction from the synchrotron 130, the beam control tray assembly 400 is preferably inserted into the positively charged particle beam proximate the nozzle system 146 or dynamic gantry nozzle as control of the beam shape is preferably done with little space for the beam shape to defocus before striking the tumor. Optionally, insertion and/or retraction of the beam control tray assembly 400 is semi-automated, such as in a manner of a digital-video disk player receiving a digital-video disk, with a selected auto-load and/or a selected auto-unload feature. Patient Specific Tray Insert Referring again to FIG. 5, a system of assembling trays 500 is described. The beam control tray assembly 400 optionally and preferably has interchangeable patient specific tray inserts 510, such as a range shifter insert 511, a patient specific ridge filter insert 512, an aperture insert 513, a compensator insert 514, or a blank insert 515. As described, supra, any of the range shifter insert 511, the patient specific ridge filter insert 512, the aperture insert 513, the compensator insert 514, or the blank insert 515 after insertion into the tray frame 410 are inserted as the beam control tray assembly 400 into the positively charged particle beam path 268, such as proximate the nozzle system 146 or dynamic gantry nozzle. Still referring to FIG. 5, the patient specific tray inserts 510 are further described. The patient specific tray inserts comprise a combination of any of: (1) a standardized beam control insert and (2) a patient specific beam control insert. For example, the range shifter insert or 511 or compensator insert 514 used to control the depth of penetration of the charged particle beam into the patient is optionally: (a) a standard thickness of a beam slowing material, such as a first thickness of Lucite, an acrylic, a clear plastic, and/or a thermoplastic material, (b) one member of a set of members of varying thicknesses and/or densities where each member of the set of members slows the charged particles in the beam path by a known amount, or (c) is a material with a density and thickness designed to slow the charged particles by a customized amount for the individual patient being treated, based on the depth of the individual's tumor in the tissue, the thickness of intervening tissue, and/or the density of intervening bone/tissue. Similarly, the ridge filter insert 512 used to change the focal point or shape of the beam as a function of depth is optionally: (1) selected from a set of ridge filters where different members of the set of ridge filters yield different focal depths or (2) customized for treatment of the individual's tumor based on position of the tumor in the tissue of the individual. Similarly, the aperture insert is: (1) optionally selected from a set of aperture shapes or (2) is a customized individual aperture insert 513 designed for the specific shape of the individual's tumor. The blank insert 515 is an open slot, but serves the purpose of identifying slot occupancy, as described infra. Slot Occupancy/Identification Referring again to FIG. 4A, FIG. 4B, and FIG. 5, occupancy and identification of the particular patient specific tray insert 510 into the beam control tray assembly 400 is described. Generally, the beam control tray assembly 400 optionally contains means for identifying, to the main controller 110 and/or a treatment delivery control system described infra, the specific patient tray insert 510 and its location in the charged particle beam path 268. First, the particular tray insert is optionally labeled and/or communicated to the beam control tray assembly 400 or directly to the main controller 110. Second, the beam control tray assembly 400 optionally communicates the tray type and/or tray insert to the main controller 110. In various embodiments, communication of the particular tray insert to the main controller 110 is performed: (1) directly from the tray insert, (2) from the tray insert 510 to the tray assembly 400 and subsequently to the main controller 110, and/or (3) directly from the tray assembly 400. Generally, communication is performed wirelessly and/or via an established electromechanical link. Identification is optionally performed using a radio-frequency identification label, use of a barcode, or the like, and/or via operator input. Examples are provided to further clarify identification of the patient specific tray insert 510 in a given beam control tray assembly 400 to the main controller. In a first example, one or more of the patient specific tray inserts 510, such as the range shifter insert 511, the patient specific ridge filter insert 512, the aperture insert 513, the compensator insert 514, or the blank insert 515 include an identifier 520 and/or and a first electromechanical identifier plug 530. The identifier 520 is optionally a label, a radio-frequency identification tag, a barcode, a 2-dimensional bar-code, a matrix-code, or the like. The first electromechanical identifier plug 530 optionally includes memory programmed with the particular patient specific tray insert information and a connector used to communicate the information to the beam control tray assembly 400 and/or to the main controller 110. As illustrated in FIG. 5, the first electromechanical identifier plug 530 affixed to the patient specific tray insert 510 plugs into a second electromechanical identifier plug, such as the tray connector/communicator 430, of the beam control tray assembly 400, which is described infra. In a second example, the beam control tray assembly 400 uses the second electromechanical identifier plug to send occupancy, position, and/or identification information related to the type of tray insert or the patient specific tray insert 510 associated with the beam control tray assembly to the main controller 110. For example, a first tray assembly is configured with a first tray insert and a second tray assembly is configured with a second tray insert. The first tray assembly sends information to the main controller 110 that the first tray assembly holds the first tray insert, such as a range shifter, and the second tray assembly sends information to the main controller 110 that the second tray assembly holds the second tray insert, such as an aperture. The second electromechanical identifier plug optionally contains programmable memory for the operator to input the specific tray insert type, a selection switch for the operator to select the tray insert type, and/or an electromechanical connection to the main controller. The second electromechanical identifier plug associated with the beam control tray assembly 400 is optionally used without use of the first electromechanical identifier plug 530 associated with the tray insert 510. In a third example, one type of tray connector/communicator 430 is used for each type of patient specific tray insert 510. For example, a first connector/communicator type is used for holding a range shifter insert 511, while a second, third, fourth, and fifth connector/communicator type is used for trays respectively holding a patient specific ridge filter insert 512, an aperture insert 513, a compensator insert 514, or a blank insert 515. In one case, the tray communicates tray type with the main controller. In a second case, the tray communicates patient specific tray insert information with the main controller, such as an aperture identifier custom built for the individual patient being treated. Tray Insertion/Coupling Referring now to FIG. 6A and FIG. 6B a beam control insertion process 600 is described. The beam control insertion process 600 comprises: (1) insertion of the beam control tray assembly 400 and the associated patient specific tray insert 510 into the charged particle beam path 268 and/or dynamic gantry nozzle 610, such as into a tray assembly receiver 620 and (2) an optional partial or total retraction of beam of the tray assembly receiver 620 into the dynamic gantry nozzle 610. Referring now to FIG. 6A, insertion of one or more of the beam control tray assemblies 400 and the associated patient specific tray inserts 510 into the dynamic gantry nozzle 610 is further described. In FIG. 6A, three beam control tray assemblies, of a possible n tray assemblies, are illustrated, a first tray assembly 402, a second tray assembly 404, and a third tray assembly 406, where n is a positive integer of 1, 2, 3, 4, 5 or more. As illustrated, the first tray assembly 402 slides into a first receiving slot 403, the second tray assembly 404 slides into a second receiving slot 405, and the third tray assembly 406 slides into a third receiving slot 407. Generally, any tray optionally inserts into any slot or tray types are limited to particular slots through use of a mechanical, physical, positional, and/or steric constraints, such as a first tray type configured for a first insert type having a first size and a second tray type configured for a second insert type having a second distinct size at least ten percent different from the first size. Still referring to FIG. 6A, identification of individual tray inserts inserted into individual receiving slots is further described. As illustrated, sliding the first tray assembly 402 into the first receiving slot 403 connects the associated electromechanical connector/communicator 430 of the first tray assembly 402 to a first receptor 626. The electromechanical connector/communicator 430 of the first tray assembly communicates tray insert information of the first beam control tray assembly to the main controller 110 via the first receptor 626. Similarly, sliding the second tray assembly 404 into the second receiving slot 405 connects the associated electromechanical connector/communicator 430 of the second tray assembly 404 into a second receptor 627, which links communication of the associated electromechanical connector/communicator 430 with the main controller 110 via the second receptor 627, while a third receptor 628 connects to the electromechanical connected placed into the third slot 407. The non-wireless/direct connection is preferred due to the high radiation levels within the treatment room and the high shielding of the treatment room, which both hinder wireless communication. The connection of the communicator and the receptor is optionally of any configuration and/or orientation. Tray Receiver Assembly Retraction Referring again to FIG. 6A and FIG. 6B, retraction of the tray receiver assembly 620 relative to a nozzle end 612 of the dynamic gantry nozzle 610 is described. The tray receiver assembly 620 comprises a framework to hold one or more of the beam control tray assemblies 400 in one or more slots, such as through use of a first tray receiver assembly side 622 through which the beam control tray assemblies 400 are inserted and/or through use of a second tray receiver assembly side 624 used as a backstop, as illustrated holding the plugin receptors configured to receive associated tray connector/communicators 430, such as the first, second, and third receptors 626, 627, 628. Optionally, the tray receiver assembly 620 retracts partially or completely into the dynamic gantry nozzle 610 using a retraction mechanism 660 configured to alternately retract and extend the tray receiver assembly 620 relative to a nozzle end 612 of the gantry nozzle 610, such as along a first retraction track 662 and a second retraction track 664 using one or more motors and computer control. Optionally the tray receiver assembly 620 is partially or fully retracted when moving the gantry, nozzle, and/or gantry nozzle 610 to avoid physical constraints of movement, such as potential collision with another object in the patient treatment room. For clarity of presentation and without loss of generality, several examples of loading patient specific tray inserts into tray assemblies with subsequent insertion into an positively charged particle beam path proximate a gantry nozzle 610 are provided. In a first example, a single beam control tray assembly 400 is used to control the charged particle beam 268 in the charged particle cancer therapy system 100. In this example, a patient specific range shifter insert 511, which is custom fabricated for a patient, is loaded into a patient specific tray insert 510 to form a first tray assembly 402, where the first tray assembly 402 is loaded into the third receptor 628, which is fully retracted into the gantry nozzle 610. In a second example, two beam control assemblies 400 are used to control the charged particle beam 268 in the charged particle cancer therapy system 100. In this example, a patient specific ridge filter 512 is loaded into a first tray assembly 402, which is loaded into the second receptor 627 and a patient specific aperture 513 is loaded into a second tray assembly 404, which is loaded into the first receptor 626 and the two associated tray connector/communicators 430 using the first receptor 626 and second receptor 627 communicate to the main controller 110 the patient specific tray inserts 510. The tray receiver assembly 620 is subsequently retracted one slot so that the patient specific ridge filter 512 and the patient specific aperture reside outside of and at the nozzle end 612 of the gantry nozzle 610. In a third example, three beam control tray assemblies 400 are used, such as a range shifter 511 in a first tray inserted into the first receiving slot 403, a compensator in a second tray inserted into the second receiving slot 405, and an aperture in a third tray inserted into the third receiving slot 407. Generally, any patient specific tray insert 510 is inserted into a tray frame 410 to form a beam control tray assembly 400 inserted into any slot of the tray receiver assembly 620 and the tray assembly is not retracted or retracted any distance into the gantry nozzle 610. Tomography/Beam State In one embodiment, the charged particle tomography apparatus is used to image a tumor in a patient. As current beam position determination/verification is used in both tomography and cancer therapy treatment, for clarity of presentation and without limitation beam state determination is also addressed in this section. However, beam state determination is optionally used separately and without tomography. In another example, the charged particle tomography apparatus is used in combination with a charged particle cancer therapy system using common elements. For example, tomographic imaging of a cancerous tumor is performed using charged particles generated with an injector, accelerator, and guided with a delivery system that are part of the cancer therapy system, described supra. In various examples, the tomography imaging system is optionally simultaneously operational with a charged particle cancer therapy system using common elements, allows tomographic imaging with rotation of the patient, is operational on a patient in an upright, semi-upright, and/or horizontal position, is simultaneously operational with X-ray imaging, and/or allows use of adaptive charged particle cancer therapy. Further, the common tomography and cancer therapy apparatus elements are optionally operational in a multi-axis and/or multi-field raster beam mode. In conventional medical X-ray tomography, a sectional image through a body is made by moving one or both of an X-ray source and the X-ray film in opposite directions during the exposure. By modifying the direction and extent of the movement, operators can select different focal planes, which contain the structures of interest. More modern variations of tomography involve gathering projection data from multiple directions by moving the X-ray source and feeding the data into a tomographic reconstruction software algorithm processed by a computer. Herein, in stark contrast to known methods, the radiation source is a charged particle, such as a proton ion beam or a carbon ion beam. A proton beam is used herein to describe the tomography system, but the description applies to a heavier ion beam, such as a carbon ion beam. Further, in stark contrast to known techniques, herein the radiation source is preferably stationary while the patient is rotated. Referring now to FIG. 7, an example of a tomography apparatus is described and an example of a beam state determination is described. In this example, the tomography system 700 uses elements in common with the charged particle beam system 100, including elements of one or more of the injection system 120, the accelerator 130, a positively charged particle beam transport path 268 within a beam transport housing 320 in the beam transport system 135, the targeting/delivery system 140, the patient interface module 150, the display system 160, and/or the imaging system 170, such as the X-ray imaging system. The scintillation material is optionally one or more scintillation plates, such as a scintillating plastic, used to measure energy, intensity, and/or position of the charged particle beam. For instance, a scintillation material 710 or scintillation plate is positioned behind the patient 730 relative to the targeting/delivery system 140 elements, which is optionally used to measure intensity and/or position of the charged particle beam after transmitting through the patient. Optionally, a second scintillation plate or a charged particle induced photon emitting sheet, described infra, is positioned prior to the patient 730 relative to the targeting/delivery system 140 elements, which is optionally used to measure incident intensity and/or position of the charged particle beam prior to transmitting through the patient. The charged particle beam system 100 as described has proven operation at up to and including 330 MeV, which is sufficient to send protons through the body and into contact with the scintillation material. Particularly, 250 MeV to 330 MeV are used to pass the beam through a standard sized patient with a standard sized pathlength, such as through the chest. The intensity or count of protons hitting the plate as a function of position is used to create an image. The velocity or energy of the proton hitting the scintillation plate is also used in creation of an image of the tumor 720 and/or an image of the patient 730. The patient 730 is rotated about the y-axis and a new image is collected. Preferably, a new image is collected with about every one degree of rotation of the patient resulting in about 360 images that are combined into a tomogram using tomographic reconstruction software. The tomographic reconstruction software uses overlapping rotationally varied images in the reconstruction. Optionally, a new image is collected at about every 2, 3, 4, 5, 10, 15, 30, or 45 degrees of rotation of the patient. Herein, the scintillation material 710 or scintillator is any material that emits a photon when struck by a positively charged particle or when a positively charged particle transfers energy to the scintillation material sufficient to cause emission of light. Optionally, the scintillation material emits the photon after a delay, such as in fluorescence or phosphorescence. However, preferably, the scintillator has a fast fifty percent quench time, such as less than 0.0001, 0.001, 0.01, 0.1, 1, 10, 100, or 1,000 milliseconds, so that the light emission goes dark, falls off, or terminates quickly. Preferred scintillation materials include sodium iodide, potassium iodide, cesium iodide, an iodide salt, and/or a doped iodide salt. Additional examples of the scintillation materials include, but are not limited to: an organic crystal, a plastic, a glass, an organic liquid, a luminophor, and/or an inorganic material or inorganic crystal, such as barium fluoride, BaF2; calcium fluoride, CaF2, doped calcium fluoride, sodium iodide, NaI; doped sodium iodide, sodium iodide doped with thallium, NaI(Tl); cadmium tungstate, CdWO4; bismuth germanate; cadmium tungstate, CdWO4; calcium tungstate, CaWO4; cesium iodide, CsI; doped cesium iodide; cesium iodide doped with thallium, CsI(Tl); cesium iodide doped with sodium CsI(Na); potassium iodide, KI; doped potassium iodide, gadolinium oxysulfide, Gd2O2S; lanthanum bromide doped with cerium, LaBr3(Ce); lanthanum chloride, LaCl3; cesium doped lanthanum chloride, LaCl3(Ce); lead tungstate, PbWO4; LSO or lutetium oxyorthosilicate (Lu2SiO5); LYSO, Lu1.8Y0.2SiO5(Ce); yttrium aluminum garnet, YAG(Ce); zinc sulfide, ZnS(Ag); and zinc tungstate, ZnWO4. In one embodiment, a tomogram or an individual tomogram section image is collected at about the same time as cancer therapy occurs using the charged particle beam system 100. For example, a tomogram is collected and cancer therapy is subsequently performed: without the patient moving from the positioning systems, such as in a semi-vertical partial immobilization system, a sitting partial immobilization system, or the a laying position. In a second example, an individual tomogram slice is collected using a first cycle of the accelerator 130 and using a following cycle of the accelerator 130, the tumor 720 is irradiated, such as within about 1, 2, 5, 10, 15 or 30 seconds. In a third case, about 2, 3, 4, or 5 tomogram slices are collected using 1, 2, 3, 4, or more rotation positions of the patient 730 within about 5, 10, 15, 30, or 60 seconds of subsequent tumor irradiation therapy. In another embodiment, the independent control of the tomographic imaging process and X-ray collection process allows simultaneous single and/or multi-field collection of X-ray images and tomographic images easing interpretation of multiple images. Indeed, the X-ray and tomographic images are optionally overlaid to from a hybrid X-ray/proton beam tomographic image as the patient 730 is optionally in the same position for each image. In still another embodiment, the tomogram is collected with the patient 730 in the about the same position as when the patient's tumor is treated using subsequent irradiation therapy. For some tumors, the patient being positioned in the same upright or semi-upright position allows the tumor 720 to be separated from surrounding organs or tissue of the patient 730 better than in a laying position. Positioning of the scintillation material 710 behind the patient 730 allows the tomographic imaging to occur while the patient is in the same upright or semi-upright position. The use of common elements in the tomographic imaging and in the charged particle cancer therapy allows benefits of the cancer therapy, described supra, to optionally be used with the tomographic imaging, such as proton beam x-axis control, proton beam y-axis control, control of proton beam energy, control of proton beam intensity, timing control of beam delivery to the patient, rotation control of the patient, and control of patient translation all in a raster beam mode of proton energy delivery. The use of a single proton or cation beamline for both imaging and treatment facilitates eases patient setup, reduces alignment uncertainties, reduces beam state uncertainties, and eases quality assurance. In yet still another embodiment, initially a three-dimensional tomographic proton based reference image is collected, such as with hundreds of individual rotation images of the tumor 720 and patient 730. Subsequently, just prior to proton treatment of the cancer, just a few 2-dimensional control tomographic images of the patient are collected, such as with a stationary patient or at just a few rotation positions, such as an image straight on to the patient, with the patient rotated about 45 degrees each way, and/or the patient rotated about 90 degrees each way about the y-axis. The individual control images are compared with the 3-dimensional reference image. An adaptive proton therapy is subsequently performed where: (1) the proton cancer therapy is not used for a given position based on the differences between the 3-dimensional reference image and one or more of the 2-dimensional control images and/or (2) the proton cancer therapy is modified in real time based on the differences between the 3-dimensional reference image and one or more of the 2-dimensional control images. Charged Particle State Determination/Verification/Photonic Monitoring Still referring to FIG. 7, the tomography system 700 is optionally used with a charged particle beam state determination system 750, optionally used as a charged particle verification system. The charged particle state determination system 750 optionally measures, determines, and/or verifies one of more of: (1) position of the charged particle beam, such as the treatment beam 269, (2) direction of the treatment beam 269, (3) intensity of the treatment beam 269, (4) energy of the treatment beam 269, (5) position, direction, intensity, and/or energy of the charged particle beam, such as a residual charged particle beam 267 after passing through a sample or the patient 730, and (6) a history of the charged particle beam. For clarity of presentation and without loss of generality, a description of the charged particle beam state determination system 750 is described and illustrated separately in FIG. 8 and FIG. 9A; however, as described herein elements of the charged particle beam state determination system 750 are optionally and preferably integrated into the nozzle system 146 and/or the tomography system 700 of the charged particle treatment system 100. More particularly, any element of the charged particle beam state determination system 750 is integrated into the nozzle system 146, the dynamic gantry nozzle 610, and/or tomography system 700, such as a surface of the scintillation material 710 or a surface of a scintillation detector, plate, or system. The nozzle system 146 or the dynamic gantry nozzle 610 provides an outlet of the charged particle beam from the vacuum tube initiating at the injection system 120 and passing through the synchrotron 130 and beam transport system 135. Any plate, sheet, fluorophore, or detector of the charged particle beam state determination system is optionally integrated into the nozzle system 146. For example, an exit foil of the nozzle 610 is optionally a first sheet 760 of the charged particle beam state determination system 750 and a first coating 762 is optionally coated onto the exit foil, as illustrated in FIG. 7. Similarly, optionally a surface of the scintillation material 710 is a support surface for a fourth coating 792, as illustrated in FIG. 7. The charged particle beam state determination system 750 is further described, infra. Referring now to FIG. 7, FIG. 8, and FIG. 9A, four sheets, a first sheet 760, a second sheet 770, a third sheet 780, and a fourth sheet 790 are used to illustrated detection sheets and/or photon emitting sheets upon transmittance of a charged particle beam. Each sheet is optionally coated with a photon emitter, such as a fluorophore, such as the first sheet 760 is optionally coated with a first coating 762. Without loss of generality and for clarity of presentation, the four sheets are each illustrated as units, where the light emitting layer is not illustrated. Thus, for example, the second sheet 770 optionally refers to a support sheet, a light emitting sheet, and/or a support sheet coated by a light emitting element. The four sheets are representative of n sheets, where n is a positive integer. Referring now to FIG. 7 and FIG. 8, the charged particle beam state verification system 750 is a system that allows for monitoring of the actual charged particle beam position in real-time without destruction of the charged particle beam. The charged particle beam state verification system 750 preferably includes a first position element or first beam verification layer, which is also referred to herein as a coating, luminescent, fluorescent, phosphorescent, radiance, or viewing layer. The first position element optionally and preferably includes a coating or thin layer substantially in contact with a sheet, such as an inside surface of the nozzle foil, where the inside surface is on the synchrotron side of the nozzle foil. Less preferably, the verification layer or coating layer is substantially in contact with an outer surface of the nozzle foil, where the outer surface is on the patient treatment side of the nozzle foil. Preferably, the nozzle foil provides a substrate surface for coating by the coating layer. Optionally, a binding layer is located between the coating layer and the nozzle foil, substrate, or support sheet. Optionally, the position element is placed anywhere in the charged particle beam path. Optionally, more than one position element on more than one sheet, respectively, is used in the charged particle beam path and is used to determine a state property of the charged particle beam, as described infra. Still referring to FIG. 7 and FIG. 8, the coating, referred to as a fluorophore, yields a measurable spectroscopic response, spatially viewable by a detector or camera, as a result of transmission by the proton beam. The coating is preferably a phosphor, but is optionally any material that is viewable or imaged by a detector where the material changes spectroscopically as a result of the charged particle beam hitting or transmitting through the coating or coating layer. A detector or camera views secondary photons emitted from the coating layer and determines a position of a treatment beam 269, which is also referred to as a current position of the charged particle beam or final treatment vector of the charged particle beam, by the spectroscopic differences resulting from protons and/or charged particle beam passing through the coating layer. For example, the camera views a surface of the coating surface as the proton beam or positively charged cation beam is being scanned by the first axis control 143, vertical control, and the second axis control 144, horizontal control, beam position control elements during treatment of the tumor 720. The camera views the current position of the charged particle beam or treatment beam 269 as measured by spectroscopic response. The coating layer is preferably a phosphor or luminescent material that glows and/or emits photons for a short period of time, such as less than 5 seconds for a 50% intensity, as a result of excitation by the charged particle beam. The detector observes the temperature change and/or observe photons emitted from the charged particle beam traversed spot. Optionally, a plurality of cameras or detectors are used, where each detector views all or a portion of the coating layer. For example, two detectors are used where a first detector views a first half of the coating layer and the second detector views a second half of the coating layer. Preferably, at least a portion of the detector is mounted into the nozzle system to view the proton beam position after passing through the first axis and second axis controllers 143, 144. Preferably, the coating layer is positioned in the proton beam path 268 in a position prior to the protons striking the patient 730. Referring now to FIG. 1 and FIG. 7, the main controller 110, connected to the camera or detector output, optionally and preferably compares the final proton beam position or position of the treatment beam 269 with the planned proton beam position and/or a calibration reference to determine if the actual proton beam position or position of the treatment beam 269 is within tolerance. The charged particle beam state determination system 750 preferably is used in one or more phases, such as a calibration phase, a mapping phase, a beam position verification phase, a treatment phase, and a treatment plan modification phase. The calibration phase is used to correlate, as a function of x-, y-position of the glowing response the actual x-, y-position of the proton beam at the patient interface. During the treatment phase, the charged particle beam position is monitored and compared to the calibration and/or treatment plan to verify accurate proton delivery to the tumor 720 and/or as a charged particle beam shutoff safety indicator. Referring now to FIG. 10, the position verification system 179 and/or the treatment delivery control system 112, upon determination of a tumor shift, an unpredicted tumor distortion upon treatment, and/or a treatment anomaly optionally generates and or provides a recommended treatment change 1070. The treatment change 1070 is optionally sent out while the patient 730 is still in the treatment position, such as to a proximate physician or over the internet to a remote physician, for physician approval 1072, receipt of which allows continuation of the now modified and approved treatment plan. |
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039506517 | abstract | A method of defining the radiation beam for medical therapy in which the beam is shaped by an aperture in an easily formable, radiation absorbing member. The member is formed by compressing a mixture of granulated heavy metal, such as tungsten, with powdered pressure sensitive adhesive into a shape-retaining box. The member is cut to define the aperture desired, and preferably the cutting is done so that the aperture walls parallel the beam that will pass therethrough. |
description | The present application hereby claims priority under 35 U.S.C. § 119 to German patent application number DE 102017200653.6 filed Jan. 17, 2017, the entire contents of which are hereby incorporated herein by reference. At least one embodiment of the invention generally relates to an X-ray detector with an arrangement of a pixelated second electrode and a scattered radiation grid for increasing signal stability and a medical device for this purpose. Counting direct-conversion X-ray detectors or integrating indirect-conversion X-ray detectors can be used in X-ray imaging, for example in computed tomography, angiography or radiography. X-rays or photons can be converted into electric pulses in direct-conversion X-ray detectors by way of a suitable converter material. The converter material used can for example be CdTe, CZT, CdZnTeSe, CdTeSe, CdMnTe, InP, TlBr2, HgI2, GaAs, Si or other materials. The electric pulses are evaluated by evaluation electronics, for example an integrated circuit (application specific integrated circuit, ASIC). In counting X-ray detectors, incident X-rays are measured by counting the electric pulses triggered by the absorption of X-ray photons in the converter material. The height of the electric pulse is generally proportional to the energy of the absorbed X-ray photon. This enables the extraction of spectral information from a comparison of the height of the electric pulse with a threshold value. Generally, a scattered radiation grid is embodied on the radiation incidence side of the X-ray detector. The scattered radiation grid suppresses or reduces the detection of the X-ray photons scattered in the object. This enables image artifacts to be reduced. Known from DE 10 2014 216 756 A1 is a first X-ray projection with a first distribution of first intensity values, which is recorded by an X-ray detector with a plurality of detector elements, wherein these include a collimator and an X-ray source that interacts with the X-ray detector. Each of the first intensity values is assigned to one of the detector elements in each case. A determination of shading of the detector elements by the collimator enables the localization of foci of the first intensity values. Herein, the determination of the shading on the first distribution and the localization step is based on the previously determined shading. Furthermore, each focus is assigned to one of the detector elements in each case. Known from DE 10 2014 201 772 A1 is a direct-conversion X-ray detector, which comprises a semiconductor used for detecting X-rays. The detector further comprises on the underside, i.e. on the side facing away from the X-rays, a pixelated anode attached to the semiconductor. The anode is divided into a plurality of subpixels. In each case, adjacently arranged subpixels are combined to form a square counting image pixel used for the purpose of detection. Arranged between the image pixels, there is in each case a row of subpixels. These subpixels are not used for detection, i.e. they are non-counting. The non-counting subpixels have an electrically conducting link to one another. With direct-conversion X-ray detectors, high demands are placed on signal stability. Signal stability can be influenced by different parameters, such as, for example, the temperature, the voltage applied to the converter element, additional lighting and so forth. Signal stability can in particular include the reproducibility of signals or numerical values based on the electric pulses. Signal stability can be influenced by the stability of the focus, for example an X-ray source. An, in particular temporally, unstable focus can influence the shadow-casting by the scattered radiation grid, so that it, for example, changes over time. For example, shadow-casting by the grid wall can change due to an unstable focus such that shading of adjacent detector elements of the grid wall by the grid wall differs over time. The inventors have identified that, generally, shadow-casting can influence the electric field in the converter element. A charge or field drift can form in the region of the shadow-casting or the grid walls. The closer the detector element is to the region of the shadow-casting or to a grid wall, the more pronounced the charge or field drift can be. The inventors have identified that incorrect positioning of the grid wall can result in unwanted shading of a detector element. As a result of mounting tolerances, the grid walls can be, in particular minimally, out of alignment. A precise examination of the beam path of the X-rays reveals that these mounting tolerances for the grid walls result in shading of the active pixel area. The actual shadow can vary if the focus moves. In reality, the focus of the X-ray tube cannot really be aligned in a stable manner and it is not really possible to avoid slight fluctuations in position. These fluctuations cause the shadow-casting by the grid walls, and hence of the signal stability or drift, to change. The inventors have further identified that the converter element can be subject to so-called radiation drift. If X-rays with a constant photon flux are applied, the output signal of the X-ray detector is not constant over time. The causes of this can be found in the polarization of the converter material. One hypothesis is that impurities in the material are occupied and/or depopulated according to the flux. Even after irradiation with X-rays, polarization effects are still visible for a long period. This signal drift is a major cause of image artifacts. The inventors have identified that, in addition to the grid walls, pixels are subject to particularly strong signal drift. At least one embodiment of the invention discloses an X-ray detector and/or a medical device that enable increased signal stability or reduced drift. At least one embodiment of the the invention is directed to an X-ray detector. Further, at least one embodiment of the invention is directed to a medical device. At least one embodiment of the invention relates to an X-ray detector comprising a stack arrangement with a scattered radiation grid and a planar converter element comprising a first surface and a second surface. The converter element comprises a first electrode embodied on the first surface. The converter element further comprises a pixelated second electrode with two adjacent first electrode elements. The two adjacent first electrode elements, in particular in each case, comprise a first width and a first length. The two adjacent first electrode elements are embodied on the second surface opposite the first surface. The scattered radiation grid comprises a grid wall with a wall thickness along the boundary between the two adjacent first electrode elements. The grid wall is arranged such that the grid wall is arranged substantially perpendicular on the first surface. The grid wall is further arranged such that, in a projection substantially parallel to the direction of incidence of the radiation and to the surface normal of the first surface, the grid wall at least partially overlaps the two adjacent first electrode elements. The projection can at least partially overlap each of the two adjacent first electrode elements. In the projection, the grid wall can in particular additionally, at least partially, preferably completely, overlap the interspace arranged between the adjacent first electrode elements. At least one embodiment of the invention further relates to a medical device comprising an X-ray detector according to at least one embodiment of the invention. The advantages of the X-ray detector according to at least one embodiment of the invention can advantageously be transferred to the medical device according to at least one embodiment of the invention. It is advantageously possible to reduce image artifacts. It is advantageously possible to reduce the influence of fluctuation in the tube focus on image quality. The medical device can preferably be a computed-tomography system. The drawings are to be regarded as being schematic representations and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose become apparent to a person skilled in the art. Any connection or coupling between functional blocks, devices, components, or other physical or functional units shown in the drawings or described herein may also be implemented by an indirect connection or coupling. A coupling between components may also be established over a wireless connection. Functional blocks may be implemented in hardware, firmware, software, or a combination thereof. 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. Example embodiments, however, may be embodied in various different forms, and should not be construed as being limited to only the illustrated embodiments. Rather, the illustrated embodiments are provided as examples so that this disclosure will be thorough and complete, and will fully convey the concepts of this disclosure to those skilled in the art. Accordingly, known processes, elements, and techniques, may not be described with respect to some example embodiments. Unless otherwise noted, like reference characters denote like elements throughout the attached drawings and written description, and thus descriptions will not be repeated. 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. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections, 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. The phrase “at least one of” has the same meaning as “and/or”. Spatially relative terms, such as “beneath,” “below,” “lower,” “under,” “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,” “beneath,” or “under,” other elements or features would then be oriented “above” the other elements or features. Thus, the example terms “below” and “under” may 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 interpreted accordingly. In addition, when an element is referred to as being “between” two elements, the element may be the only element between the two elements, or one or more other intervening elements may be present. Spatial and functional relationships between elements (for example, between modules) are described using various terms, including “connected,” “engaged,” “interfaced,” and “coupled.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship encompasses a direct relationship where no other intervening elements are present between the first and second elements, and also an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. In contrast, when an element is referred to as being “directly” connected, engaged, interfaced, or 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. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. Also, the term “exemplary” is intended to refer to an example or illustration. When an element is referred to as being “on,” “connected to,” “coupled to,” or “adjacent to,” another element, the element may be directly on, connected to, coupled to, or adjacent to, the other element, or one or more other intervening elements may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” “directly coupled to,” or “immediately adjacent to,” another element there are no intervening elements present. 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. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Before discussing example embodiments in more detail, it is noted that some example embodiments may be described with reference to acts and symbolic representations of operations (e.g., in the form of flow charts, flow diagrams, data flow diagrams, structure diagrams, block diagrams, etc.) that may be implemented in conjunction with units and/or devices discussed in more detail below. Although discussed in a particularly manner, a function or operation specified in a specific block may be performed differently from the flow specified in a flowchart, flow diagram, etc. For example, functions or operations illustrated as being performed serially in two consecutive blocks may actually be performed simultaneously, or in some cases be performed in reverse order. Although the flowcharts describe the operations as sequential processes, many of the operations may be performed in parallel, concurrently or simultaneously. In addition, the order of operations may be re-arranged. The processes may be terminated when their operations are completed, but may also have additional steps not included in the figure. The processes may correspond to methods, functions, procedures, subroutines, subprograms, etc. Specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. This invention may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. Units and/or devices according to one or more example embodiments may be implemented using hardware, software, and/or a combination thereof. For example, hardware devices may be implemented using processing circuity such as, but not limited to, a processor, Central Processing Unit (CPU), a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), a System-on-Chip (SoC), a programmable logic unit, a microprocessor, or any other device capable of responding to and executing instructions in a defined manner. Portions of the example embodiments and corresponding detailed description may be presented in terms of software, or algorithms and symbolic representations of operation on data bits within a computer memory. These descriptions and representations are the ones by which those of ordinary skill in the art effectively convey the substance of their work to others of ordinary skill in the art. An algorithm, as the term is used here, and as it is used generally, is conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of optical, electrical, or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, or as is apparent from the discussion, terms such as “processing” or “computing” or “calculating” or “determining” of “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device/hardware, that manipulates and transforms data represented as physical, electronic quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. In this application, including the definitions below, the term ‘module’ or the term ‘controller’ may be replaced with the term ‘circuit.’ The term ‘module’ may refer to, be part of, or include processor hardware (shared, dedicated, or group) that executes code and memory hardware (shared, dedicated, or group) that stores code executed by the processor hardware. The module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces that are connected to a local area network (LAN), the Internet, a wide area network (WAN), or combinations thereof. The functionality of any given module of the present disclosure may be distributed among multiple modules that are connected via interface circuits. For example, multiple modules may allow load balancing. In a further example, a server (also known as remote, or cloud) module may accomplish some functionality on behalf of a client module. Software may include a computer program, program code, instructions, or some combination thereof, for independently or collectively instructing or configuring a hardware device to operate as desired. The computer program and/or program code may include program or computer-readable instructions, software components, software modules, data files, data structures, and/or the like, capable of being implemented by one or more hardware devices, such as one or more of the hardware devices mentioned above. Examples of program code include both machine code produced by a compiler and higher level program code that is executed using an interpreter. For example, when a hardware device is a computer processing device (e.g., a processor, Central Processing Unit (CPU), a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a microprocessor, etc.), the computer processing device may be configured to carry out program code by performing arithmetical, logical, and input/output operations, according to the program code. Once the program code is loaded into a computer processing device, the computer processing device may be programmed to perform the program code, thereby transforming the computer processing device into a special purpose computer processing device. In a more specific example, when the program code is loaded into a processor, the processor becomes programmed to perform the program code and operations corresponding thereto, thereby transforming the processor into a special purpose processor. Software and/or data may be embodied permanently or temporarily in any type of machine, component, physical or virtual equipment, or computer storage medium or device, capable of providing instructions or data to, or being interpreted by, a hardware device. The software also may be distributed over network coupled computer systems so that the software is stored and executed in a distributed fashion. In particular, for example, software and data may be stored by one or more computer readable recording mediums, including the tangible or non-transitory computer-readable storage media discussed herein. Even further, any of the disclosed methods may be embodied in the form of a program or software. The program or software may be stored on a non-transitory computer readable medium and is adapted to perform any one of the aforementioned methods when run on a computer device (a device including a processor). Thus, the non-transitory, tangible computer readable medium, is adapted to store information and is adapted to interact with a data processing facility or computer device to execute the program of any of the above mentioned embodiments and/or to perform the method of any of the above mentioned embodiments. Example embodiments may be described with reference to acts and symbolic representations of operations (e.g., in the form of flow charts, flow diagrams, data flow diagrams, structure diagrams, block diagrams, etc.) that may be implemented in conjunction with units and/or devices discussed in more detail below. Although discussed in a particularly manner, a function or operation specified in a specific block may be performed differently from the flow specified in a flowchart, flow diagram, etc. For example, functions or operations illustrated as being performed serially in two consecutive blocks may actually be performed simultaneously, or in some cases be performed in reverse order. According to one or more example embodiments, computer processing devices may be described as including various functional units that perform various operations and/or functions to increase the clarity of the description. However, computer processing devices are not intended to be limited to these functional units. For example, in one or more example embodiments, the various operations and/or functions of the functional units may be performed by other ones of the functional units. Further, the computer processing devices may perform the operations and/or functions of the various functional units without sub-dividing the operations and/or functions of the computer processing units into these various functional units. Units and/or devices according to one or more example embodiments may also include one or more storage devices. The one or more storage devices may be tangible or non-transitory computer-readable storage media, such as random access memory (RAM), read only memory (ROM), a permanent mass storage device (such as a disk drive), solid state (e.g., NAND flash) device, and/or any other like data storage mechanism capable of storing and recording data. The one or more storage devices may be configured to store computer programs, program code, instructions, or some combination thereof, for one or more operating systems and/or for implementing the example embodiments described herein. The computer programs, program code, instructions, or some combination thereof, may also be loaded from a separate computer readable storage medium into the one or more storage devices and/or one or more computer processing devices using a drive mechanism. Such separate computer readable storage medium may include a Universal Serial Bus (USB) flash drive, a memory stick, a Blu-ray/DVD/CD-ROM drive, a memory card, and/or other like computer readable storage media. The computer programs, program code, instructions, or some combination thereof, may be loaded into the one or more storage devices and/or the one or more computer processing devices from a remote data storage device via a network interface, rather than via a local computer readable storage medium. Additionally, the computer programs, program code, instructions, or some combination thereof, may be loaded into the one or more storage devices and/or the one or more processors from a remote computing system that is configured to transfer and/or distribute the computer programs, program code, instructions, or some combination thereof, over a network. The remote computing system may transfer and/or distribute the computer programs, program code, instructions, or some combination thereof, via a wired interface, an air interface, and/or any other like medium. The one or more hardware devices, the one or more storage devices, and/or the computer programs, program code, instructions, or some combination thereof, may be specially designed and constructed for the purposes of the example embodiments, or they may be known devices that are altered and/or modified for the purposes of example embodiments. A hardware device, such as a computer processing device, may run an operating system (OS) and one or more software applications that run on the OS. The computer processing device also may access, store, manipulate, process, and create data in response to execution of the software. For simplicity, one or more example embodiments may be exemplified as a computer processing device or processor; however, one skilled in the art will appreciate that a hardware device may include multiple processing elements or porcessors and multiple types of processing elements or processors. For example, a hardware device may include multiple processors or a processor and a controller. In addition, other processing configurations are possible, such as parallel processors. The computer programs include processor-executable instructions that are stored on at least one non-transitory computer-readable medium (memory). The computer programs may also include or rely on stored data. The computer programs may encompass a basic input/output system (BIOS) that interacts with hardware of the special purpose computer, device drivers that interact with particular devices of the special purpose computer, one or more operating systems, user applications, background services, background applications, etc. As such, the one or more processors may be configured to execute the processor executable instructions. The computer programs may include: (i) descriptive text to be parsed, such as HTML (hypertext markup language) or XML (extensible markup language), (ii) assembly code, (iii) object code generated from source code by a compiler, (iv) source code for execution by an interpreter, (v) source code for compilation and execution by a just-in-time compiler, etc. As examples only, source code may be written using syntax from languages including C, C++, C#, Objective-C, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5, Ada, ASP (active server pages), PHP, Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, Visual Basic®, Lua, and Python®. Further, at least one embodiment of the invention relates to the non-transitory computer-readable storage medium including electronically readable control information (processor executable instructions) stored thereon, configured in such that when the storage medium is used in a controller of a device, at least one embodiment of the method may be carried out. The computer readable medium or storage medium may be a built-in medium installed inside a computer device main body or a removable medium arranged so that it can be separated from the computer device main body. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium is therefore considered tangible and non-transitory. Non-limiting examples of the non-transitory computer-readable medium include, but are not limited to, rewriteable non-volatile memory devices (including, for example flash memory devices, erasable programmable read-only memory devices, or a mask read-only memory devices); volatile memory devices (including, for example static random access memory devices or a dynamic random access memory devices); magnetic storage media (including, for example an analog or digital magnetic tape or a hard disk drive); and optical storage media (including, for example a CD, a DVD, or a Blu-ray Disc). Examples of the media with a built-in rewriteable non-volatile memory, include but are 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. The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, data structures, and/or objects. Shared processor hardware encompasses a single microprocessor that executes some or all code from multiple modules. Group processor hardware encompasses a microprocessor that, in combination with additional microprocessors, executes some or all code from one or more modules. References to multiple microprocessors encompass multiple microprocessors on discrete dies, multiple microprocessors on a single die, multiple cores of a single microprocessor, multiple threads of a single microprocessor, or a combination of the above. Shared memory hardware encompasses a single memory device that stores some or all code from multiple modules. Group memory hardware encompasses a memory device that, in combination with other memory devices, stores some or all code from one or more modules. The term memory hardware is a subset of the term computer-readable medium. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium is therefore considered tangible and non-transitory. Non-limiting examples of the non-transitory computer-readable medium include, but are not limited to, rewriteable non-volatile memory devices (including, for example flash memory devices, erasable programmable read-only memory devices, or a mask read-only memory devices); volatile memory devices (including, for example static random access memory devices or a dynamic random access memory devices); magnetic storage media (including, for example an analog or digital magnetic tape or a hard disk drive); and optical storage media (including, for example a CD, a DVD, or a Blu-ray Disc). Examples of the media with a built-in rewriteable non-volatile memory, include but are 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. The apparatuses and methods described in this application may be partially or fully implemented by a special purpose computer created by configuring a general purpose computer to execute one or more particular functions embodied in computer programs. The functional blocks and flowchart elements described above serve as software specifications, which can be translated into the computer programs by the routine work of a skilled technician or programmer. Although described with reference to specific examples and drawings, modifications, additions and substitutions of example embodiments may be variously made according to the description by those of ordinary skill in the art. For example, the described techniques may be performed in an order different with that of the methods described, and/or components such as the described system, architecture, devices, circuit, and the like, may be connected or combined to be different from the above-described methods, or results may be appropriately achieved by other components or equivalents. At least one embodiment of the invention relates to an X-ray detector comprising a stack arrangement with a scattered radiation grid and a planar converter element comprising a first surface and a second surface. The converter element comprises a first electrode embodied on the first surface. The converter element further comprises a pixelated second electrode with two adjacent first electrode elements. The two adjacent first electrode elements, in particular in each case, comprise a first width and a first length. The two adjacent first electrode elements are embodied on the second surface opposite the first surface. The scattered radiation grid comprises a grid wall with a wall thickness along the boundary between the two adjacent first electrode elements. The grid wall is arranged such that the grid wall is arranged substantially perpendicular on the first surface. The grid wall is further arranged such that, in a projection substantially parallel to the direction of incidence of the radiation and to the surface normal of the first surface, the grid wall at least partially overlaps the two adjacent first electrode elements. The projection can at least partially overlap each of the two adjacent first electrode elements. In the projection, the grid wall can in particular additionally, at least partially, preferably completely, overlap the interspace arranged between the adjacent first electrode elements. The X-ray detector can in particular be embodied as a direct-conversion X-ray detector. The direct-conversion X-ray detector can comprise at least one detector element per grid cell. The direct-conversion X-ray detector preferably comprises a plurality of detector elements. It can comprise N×M detector elements per grid cell. It is advantageously possible to improve the dose utilization for the imaging. A first electrode element or a possible second electrode element is, for example, assigned to a detector element. The first electrode can preferably be a cathode and the pixelated second electrode an anode. The adjacent first electrode elements can be adjacent first anode elements. The second electrode element can be a second anode element. Alternatively, the first electrode can be an anode and the pixelated second electrode a cathode. The adjacent first electrode elements can be adjacent first cathode elements. The second electrode element can be a second cathode element. The first electrode and the second electrode can be connected in an electrically conductive manner to the converter element. The first electrode and the second electrode comprise an electrically conductive material. In operation, different potentials are applied to the first electrode and the second electrode so that an electric field forms between the first electrode and the second electrode. The first electrode can be embodied as planar or pixelated. The first electrode can preferably be embodied as planar. The first electrode can have a structure, for example resulting from the method for applying the first electrode to the converter element. The second electrode is pixelated. The second electrode is divided into a plurality of first electrode elements and one possible second electrode element or a plurality of possible second electrode elements. The two adjacent first electrode elements are embodied adjacent to one another. The two adjacent first electrode elements are electrically insulated from one another or not connected to one another directly in an electrically conductive manner. The two adjacent first electrode elements are demarcated from one another. A gap or an interspace is formed as a boundary between the two adjacent first electrode elements between the two adjacent first electrode elements. The first width can preferably be embodied along the direction of rotation of the computed-tomography system. The first length can preferably be embodied along the axis of rotation of the computed-tomography system. The converter element comprises a first surface and a second surface. The first surface is opposite the second surface. The first electrode is arranged on the first surface. The two adjacent second electrode elements are arranged on the second surface. In operation, the first surface is aligned toward the radiation source. The direction of incidence of the radiation is substantially parallel to the surface normal of the first surface. The second surface is embodied on the surface of the converter element facing away from the radiation source. The first surface be designated the upper side. The second surface can be designated the underside. The scattered radiation grid can be embodied as a one-, two- or three-dimensional absorber for scattered radiation. The scattered radiation grid is able to absorb scattered X-ray photons in particular, for example in the object to be examined. The scattered radiation grid can preferably be embodied as a three-dimensional absorber with an, for example regular, grid shape. The scattered radiation grid comprises at least one grid wall. The grid wall can in particular be aligned toward a point, for example an X-ray source. The wall thickness can be small compared to the height of the grid wall and/or to the length of the grid wall. The grid wall can preferably be aligned along an interspace or the boundary between the first adjacent electrode elements. In the projection, the grid wall can preferably be embodied along the boundary between the first adjacent electrode elements. Herein, the wall thickness can in particular be embodied perpendicular to the boundary. The boundary can be embodied along the first width or the first length. Along the wall height, which can be embodied along the direction of incidence of the radiation, the wall thickness can be different, for example stepped, or uniform. The grid wall can be arranged substantially perpendicular on the first surface, wherein a difference can be less than 20 degrees, preferably less than 10 degrees and particularly preferably less than 5 degrees. In particular, when in operational use, the projection is substantially parallel to the direction of incidence of the radiation. The projection is substantially parallel to the surface normal of the first surface. The direction of incidence of the radiation and the surface normal the first surface are substantially parallel. In the projection, the grid wall overlaps the planar extension of the two adjacent first electrode elements at least partially and in particular in each case. In the projection, the grid wall can additionally at least partially, preferably completely, overlap the interspace arranged between the adjacent first electrode elements along the boundary. In the projection, the grid wall can cover the interspace between the two adjacent first electrode elements, in particular completely. The inventors have identified that the signal drift can be mainly attributed to a change in the effective pixel size. Since the effective pixel size can be defined by the electrode size of a pixel or the associated field patterns in the converter material itself, it is possible to conclude that the field lines in the converter material are distorted by irradiation with X-rays. One hypothesis is that the impurity-occupation density in the converter material, and hence the polarization thereof by X-rays, can change. However, no, or virtually no, X-rays arrive at the converter element below the scattered radiation grid. It is possible for a new field distribution to form resulting in a change to the effective pixel size. Detector elements with directly adjacent grid walls can be affected to a greater degree than detector elements that do not have a directly adjacent grid wall. Detector elements with a directly adjacent grid wall on two sides can have the greatest drift effect. Detector elements with only one wall in the immediate vicinity can have a medium drift effect and detector elements without a directly adjacent grid wall have the smallest drift effect. There can be a positive or negative drift. To date, attempts have been made to configure the dead zone below the grid walls large enough or wide enough for the drift effect to disappear or be greatly reduced. However, it is known that the drift effect has a very long range and extends over a plurality of detector elements. Hence, suppression of the drift effect by dead zones is only very restrictedly possible. A field displacement can result in a change in the effective pixel size. Hence, it is possible for X-ray quanta, which are actually absorbed in the dead zone, i.e. directly next to the grid wall or under the grid wall now to be additionally counted in a counting detector element. The effective pixel size of the detector elements at the edge of a grid wall changes over time and, depending upon the status, captures more or fewer quanta, which is manifested as a drift or change in the counting rate. The inventors suggest, in at least one embodiment, an arrangement of the second electrode and the scattered radiation grid with which the adjacent first electrode elements extend at least partially within the projection of the grid wall. Hence, in the suggested arrangement, it is advantageously possible to avoid a dead zone or non-counting detector elements. Advantageously, a pixelated electrode is described in conjunction with a scattered radiation grid, which is able to meet the stability requirements under the boundary conditions of a direct-conversion X-ray detector. It is advantageously possible to minimize negative influences, for example by way of variable shading. It is advantageously possible to minimize signal fluctuations caused by tube fluctuations. The grid wall itself comprises a wall thickness. For example, the wall thickness can be approximately 100 μm. From a certain planar extension of a detector element, it is now no longer possible for each detector element to be surrounded by, for example, four walls since otherwise, although the patient is exposed to numerous X-ray photons with a dose, due to absorption in the scattered radiation grid, these are not able contribute to the imaging. With the suggested arrangement of the pixelated electrode in conjunction with the scattered radiation grid, it is possible to implement a plurality of electrode elements within a grid cell. Hence, the grid walls enable the dose loss to be kept low or kept constant compared to previous arrangements. With the arrangement of the pixelated electrode in conjunction with the scattered radiation grid, it is advantageously possible to ensure that shading caused by the grid wall conforms to stability requirements. It is advantageously possible for drift to be reduced with detector elements located in the immediate vicinity of a grid wall. It is advantageously possible to achieve improved clinical images. It is advantageously possible for spatially highly resolved events to be registered in the X-ray detector. It is advantageously possible to avoid a change in the effective pixel size due to field-line distortions. The field-line distortions can be generated on the outer edge of the pixel by the actual grid wall or by shadow-casting by the grid wall. It is advantageously possible for the influence of focusing instabilities or focusing fluctuations to be reduced. According to one embodiment of the invention, a second electrode element with a second width and a second length is embodied, in particular completely, outside the projection on the second surface. The second electrode element can, in particular, be not directly adjacent to a grid wall. The second electrode element is not arranged within the projection, which is substantially parallel to the direction of incidence of the radiation and to the surface normal of the first surface. The second electrode element is not arranged below the grid wall. An embodiment with a plurality of second electrode elements is possible. Preferably, all second electrode elements or the effective second pixel size thereof can be of the same size. Alternatively, an embodiment with second electrode elements with a different size is possible. The second electrode element can be surrounded by a first electrode element so that a detection unit can be formed. The detection unit can be enclosed by grid walls at least partially, preferably completely. The detection unit can have a sum total of first electrode elements and second electrode elements corresponding to N×M with N,M∈. The detector elements can, for example, be arranged in N rows and M columns. The detection unit can comprise N×M detector elements. The detection unit can, for example, comprise 1×1, 2×2, 4×4 or 4×6 detector elements. The detector element can be designated as subpixels. The detection unit can be designated as pixels. The detection unit can be made up of subpixels. It is advantageously possible for the influence of the shading with the second electrode elements to be reduced compared to the first electrode elements. According to one embodiment of the invention, a first planar extension of one of the adjacent first electrode elements is greater than a second planar extension of the second electrode element. The first planar extension can be defined by the area spanned by the first width and the first length. The second planar extension can be defined by the area spanned by the second width and the second length. The planar extension can correspond to the spanned area. The first electrode element is preferably partially, and in particular not completely, arranged within the projection. Within the projection, it is possible for fewer or hardly any X-rays to arrive at the converter element. Hence, the overlapping region of the first electrode element with the projection can make little contribution or no contribution at all to the counting of detected events. In order advantageously to be able to detect the same number of events, the first planar extension can be selected as greater than the second planar extension. According to one embodiment of the invention, the first width is greater than the second width and/or the first length is greater than the second length. According to one embodiment of the invention, the first width is greater than the second width. The first width of one of the adjacent first electrode elements can be greater than the second width of the second electrode element. The first planar extension can be enlarged compared to the second planar extension by a first width that is greater than the second width. It is advantageously possible for the shading of the second electrode element to be taken into account. The first width and the first length can be different or substantially the same. The second width and the second length can be different or substantially the same. According to one embodiment of the invention, the first length is greater than the second length. The first length of one of the adjacent first electrode elements can be greater than the second length of the second electrode element. The first planar extension can be enlarged compared to the second planar extension by a first length that is greater than the second length. It is advantageously possible for the shading of the second electrode element to be taken into account. According to one embodiment of the invention, one of the adjacent first electrode elements comprises a first effective pixel area, which is defined by the gradients of the field lines in regions bounding the adjacent first electrode element and/or the adjacent second electrode element. An effective pixel area can, for example, be determined by the fact that, with homogeneous irradiation of the X-ray detector with X-rays, the counted events are used as a measure for the size of the detector element. The effective pixel area can be determined by the volume assigned to the detector element in the converter element. The volume can be determined by the field lines embodied in the converter element. It is advantageously possible for the detection volume of a detector element or the first electrode element to be defined by gradients of the field lines instead of mechanical separation of the detection volumes from one another. The electric field lines assigned to a detector element can border the electric field lines of the adjacent detector elements. According to one embodiment of the invention, the second electrode element comprises a second effective pixel area, which is defined by the gradients of the field lines in regions bounding the adjacent first electrode element and/or the adjacent second electrode element. It is advantageously possible for the detection volume of a detector element or the second electrode element to be defined by gradients of the field lines instead of mechanical separation of detection volumes from one another. According to one embodiment of the invention, the first effective pixel area is defined by shading of incident radiation by the scattered radiation grid. The first effective pixel area of one of the adjacent first electrode elements is defined by shading of incident radiation in operation by the scattered radiation grid. The first effective pixel area can be defined on at least one outer edge or the boundary regions by the shadow-casting by the grid wall. The first effective pixel area can be defined on a further outer edge by the electrode-induced gradients of the field lines. The incidence of X-rays can change the gradients of the field lines, in particular within the projection of the grid wall on the converter element. The field change can advantageously no longer result in a change to the first effective pixel area. The shadow-casting by the grid wall onto the converter element or the detector element can define the active area of the detector element on at least one outer edge of the detector element. The effective pixel area can be reduced by the shading. According to one embodiment of the invention, the first effective pixel area and the second effective pixel area are substantially the same size. The first effective pixel area of one of the adjacent first electrode elements and the second effective pixel area of the second electrode element can substantially be of equal sizes. The detector elements of a detection unit can preferably have a substantially uniform effective pixel size. It is advantageously possible for the counted events of all detector elements of a detection unit to be equally weighted or compared directly to one another. It is advantageously possible for the detector elements to comprise a uniform effective pixel area. It is advantageously possible to avoid corrections to the first effective pixel area and/or second effective pixel area. According to one embodiment of the invention, the first effective pixel area and the second effective pixel area are of different sizes. The first effective pixel area of one of the adjacent first electrode elements and the second effective pixel area of the second electrode element are of different sizes. It is advantageously possible for the detector elements of a detection unit to be weighted differently. It is advantageously possible for larger detector elements to acquire more events and be used for example as an estimation of the counting for the detection unit. According to one embodiment of the invention, the surface area of the first effective pixel area and the surface area of the second effective pixel area differ by a maximum of 30 percent. The surface area of the first effective pixel area of one of the adjacent first electrode elements and the surface area of the second effective pixel area of the second electrode element differ by a maximum of 30 percent. The difference of maximum 30 percent can be compensated by calibration, for example with a spatially homogeneous photon flux and without an object to be examined in the beam path between the radiation source and the X-ray detector. It is advantageously possible to compensate differences in the surface area between different detector elements, for example caused by imprecise positioning of the scattered radiation grid. It is advantageously possible for the signal-to-noise ratio for a plurality of detector elements to be substantially the same. It is advantageously possible to avoid image artifacts. It is also possible to compensate differences of more than 30 percent, but the signal-to-noise ratio can be impaired and so image artifacts can be caused at low counting rates. According to one embodiment of the invention, the extension of the first effective pixel area along the first width and/or along the first length minus an overlapping region of the first electrode element with the grid wall in the substantially perpendicular projection and the extension of an adjacent second effective pixel area along the second width or along the second length are of equal size. According to one embodiment of the invention, the extension of the first effective pixel area along the first width minus an overlapping region of the first electrode element with the grid wall in the substantially perpendicular projection and the extension of an adjacent second effective pixel area along the second width are of equal size. The grid wall can be arranged such that it at least partially overlaps one of the adjacent first electrode elements in the substantially perpendicular projection. The extension of the first effective pixel area outside the projection along the first width can be the same size as the extension of the second effective pixel area along the second width. It is advantageously possible for the first effective pixel area irradiated by the X-rays to be of the same size as the second effective pixel area irradiated by the X-rays. According to one embodiment of the invention, the extension of the first effective pixel area along the first length minus an overlapping region of the first electrode element with the grid wall in the substantially perpendicular projection and the extension of an adjacent second effective pixel area along the second length are of equal size. The grid wall can be arranged such that it at least partially overlaps the at least one first electrode element in the substantially perpendicular projection. The extension of the first effective pixel area outside the projection along the first length is of the same size as the extension of the second effective pixel area along the second length. It is advantageously possible for the first effective pixel area irradiated by the X-rays to be the same size as the second effective pixel area irradiated by the X-rays. According to one embodiment of the invention, an extension of the first effective pixel area and/or the second effective pixel area is based, in particular in each case, on the quotient of an extension of a grid opening of the scattered radiation grid and a joint number of the first electrode elements and the second electrode elements along the extension of the grid opening of the scattered radiation grid. The joint number can correspond to the number of detector elements along the grid opening. The joint number can, for example, correspond to M or N. The extension can designate section, for example along the first width or the first length. In particular, an extension outside the projection equal to the quotient of an extension of a grid opening and the joint number along the extension of the grid opening can be assigned to the first effective pixel area of one of the adjacent first electrode elements. It is advantageously possible for the first effective pixel area irradiated by the X-rays to be the same size as the second effective pixel area irradiated by the X-rays. According to one embodiment of the invention, an extension of one of the adjacent first electrode elements is based on the sum of the first width or the first length and an extension between two adjacent first electrode elements or between the one adjacent first electrode elements and the adjacent second electrode element. An extension equal to the sum of the first width and the extension between two adjacent first electrode elements can be assigned to one of the adjacent first electrode elements. An extension equal to the sum of the first length and the extension between two adjacent first electrode elements can be assigned to one of the adjacent first electrode elements. An extension equal to the sum of the first width and the extension between the one of the adjacent first electrode elements and the adjacent second electrode element can be assigned to one of the adjacent first electrode elements. An extension equal to the sum of the first length and the extension between two adjacent first electrode elements can be assigned to one of the adjacent first electrode elements. It is advantageously possible for the first effective pixel area to be estimated using the assigned extension. According to one embodiment of the invention, furthermore a shade-capture structure is arranged between the scattered radiation grid and the converter element. The shade-capture structure comprises an X-ray absorbing material. The shade-capture structure can be produced from the same material as the scattered radiation grid. The shade-capture structure can be embodied in a grid shape. The shade-capture structure and the scattered radiation grid can have mutually matching grid-opening geometry. The wall of the shade-capture structure can be aligned to the focus of the X-ray tube. The wall of the shade-capture structure can in particular be 30 to 100 percent wider than the grid wall. It is advantageously possible for the number of scattered photons registered in the X-ray detector to be reduced. The influence of fluctuations of the tube focus can be reduced. According to one embodiment of the invention, the X-ray detector further comprises a lighting unit arranged between the scattered radiation grid and the first electrode. It is furthermore possible for a lighting unit for additional lighting of the converter element with infrared, ultraviolet or visible light to be arranged between the scattered radiation grid and the converter element. Preferably, infrared light can be used for the additional lighting. It is advantageously possible for the polarization state of the converter element to be stabilized by way of the additional lighting. In order, for example on the scattered radiation grid, to prevent scattered photons from being registered in the converter element, a shade-capture structure can be arranged below the lighting unit. At least one embodiment of the invention further relates to a medical device comprising an X-ray detector according to at least one embodiment of the invention. The advantages of the X-ray detector according to at least one embodiment of the invention can advantageously be transferred to the medical device according to at least one embodiment of the invention. It is advantageously possible to reduce image artifacts. It is advantageously possible to reduce the influence of fluctuation in the tube focus on image quality. The medical device can preferably be a computed-tomography system. FIG. 1 shows an example embodiment of the X-ray detector 1 according to the invention according to a first embodiment in a side view. The X-ray detector 1 comprises a stack arrangement with a scattered radiation grid 3 and a planar converter element 10. The converter element 10 comprises a first surface 11 and a second surface 12. The converter element 10 comprises a first electrode 15 embodied on the first surface 11. The converter element 10 further comprises a pixelated second electrode 16 with two adjacent first electrode elements 16, 17. The two adjacent first electrode elements 16, 17 comprise a first width 18 and a first length. The two adjacent first electrode elements 16, 17 are embodied on a second surface 12 opposite the first surface 11. The scattered radiation grid 3 comprises a grid wall 4 with a wall thickness along the boundary between the two adjacent first electrode elements 16, 17. The grid wall 4 is arranged such that the grid wall 4 is arranged substantially perpendicular on the first surface 11. The grid wall 4 is arranged such that, in a projection that is substantially parallel to the direction of incidence of the radiation 30 and to the surface normal 13 of the first surface 11, the grid wall 4, partially overlaps the two adjacent first electrode elements 16, 17. In operation, X-rays 31 are incident on the X-ray detector 1 along the direction of incidence of the radiation 30. FIG. 2 shows an example embodiment of the X-ray detector 1 according to the invention according to a second embodiment in a side view. The X-ray detector 1 further comprises a second electrode element 16, 27. The second electrode element 16, 27 with a second width and a second length is embodied outside the projection on the second surface 12. To ensure that the first effective pixel area and the second effective pixel area are substantially the same size, the extension 23 and the extension 24 are selected as substantially the same size. The extensions 21, 22, 22′, 23, 24 are arranged along the axis of rotation and/or along the direction of rotation. The respective extensions 21, 22, 22′, 23, 24 in the direction of rotation and along the axis of rotation can be selected as different sizes. Herein, the extension 23 is the sum of the extension 21 and the extension 22. The extension 21 is the second width or the second length. The extension 22 is the distance between two adjacent second electrode elements 16, 27 or between an adjacent first electrode element 16, 17 and a second electrode element 16, 27. The extension 22 is 30 to 100 μm. The extension 21 is 100 to 900 μm. The extension 22′ designates the distance between two adjacent first electrode elements 16, 17. The extension 22′ is preferably 30 to 100 μm or less than 30 μm. The extension 22′ is embodied within the projection. The extensions 23, 24 substantially correspond to the quotients of the extension 6, 6′ of the grid opening divided by the joint number of the detector elements 17, 27. The two adjacent first electrode elements 16, 17 are electrically isolated from one another. FIG. 3 shows an example embodiment of the X-ray detector 1 according to the invention according to a third embodiment in a top view. The scattered radiation grid 3 is arranged between the radiation source and the converter element 10. The scattered radiation grid 3 is arranged above the first surface 11. The scattered radiation grid 3 comprises an arrangement of grid walls 4 in a substantially rectangular grid arrangement. The grid walls 4 have a wall thickness 5, 5′, 5″. The wall thickness 5 of an internal grid wall 4 within the scattered radiation grid 3 can have a greater wall thickness 5 than the wall thicknesses 5′, 5″ of the grid walls 4 at the edge of the scattered radiation grid 3 or the X-ray detector 1. The scattered radiation grid 3 comprises grid openings 6, 6′, wherein the extension of the grid opening 6 along the axis of rotation can be the same as or different from the extension of the grid opening 6′ along the direction of rotation. The first width 18 and the second width 28 are aligned parallel to the axis of rotation 43. The first length 19 and the second length 29 are aligned parallel to the direction of rotation 44. The first electrode elements 16, 17 overlap (indicated by dashed lines in FIG. 3) in the projection, which is substantially parallel to the direction of incidence of the radiation and to the surface normal of the first surface 11, partially overlap the grid walls 4. The first electrode elements 16, 17, which partially overlap a grid wall 4 on two sides, have a greater planar extension than first electrode elements 16, 17, which only partially overlap a grid wall 4 on one side. The first electrode elements 16, 17, which partially overlap a grid wall 4 on two sides, all have a substantially same planar extension. The first electrode elements 16, 17, which partially overlap a grid wall 4 on one side only, all have substantially the same planar extension. The second electrode elements 16, 27 have a substantially identical second width 28 and a substantially identical second length 29. The planar extension of the second electrode elements 16, 27 is substantially constant for all second electrode elements 16, 27. The first width 18 is greater than the second width 28. The first length 19 is greater than the second length 29. For example, the grid opening 6, 6′ can correspond to a section 1, wherein the section 1 can, for example, be aligned parallel to the first width 18, second width 28, first length 19 or second length 19. The joint number of the first electrode elements 17 and the second electrode elements 27 can be n with n∈, for example 4. The extension of the first effective pixel area and/or the second effective pixel area is 1/n, i.e. for example ¼. FIG. 4 shows an example embodiment of the X-ray detector 1 according to the invention according to a fourth embodiment in a side view in a first operating state. The course of the electric field lines 14 of a second electrode element 16, 27 is shown. The course of the electric field lines 14′ of the two adjacent first electrode elements 16, 17 is shown. The electric field lines 14, 14′ are depicted in operational state without the influence of X-rays. The field lines 14,14′ are substantially embodied uniformly in the converter element 10. The first effective pixel area 20 and the second effective pixel area 26 are substantially the same size. FIG. 5 shows an example embodiment of the X-ray detector 1 according to the invention according to a fourth embodiment in a side view in a second operating state. Under the influence of X-rays 31, the field lines 14′ toward the boundary between the two adjacent first electrode elements 16, 17 can be changed, distorted or tilted. Under the influence of X-rays 31, the polarization in the converter element 10 can increase and hence the electric field, in particular outside the projection, can decrease so that the electric field within the projection can be intensified. The first effective pixel area 20 and the second effective pixel area 26 are substantially the same size. FIG. 6 shows an example embodiment of the X-ray detector 1 according to the invention according to a fifth embodiment in a side view. The X-ray detector 1 further comprises a lighting unit 8. The lighting unit 8 is configured to light the converter element 10 with additional, preferably infrared, light. The X-ray detector 1 further comprises a shade-capture structure 7. The shade-capture structure 7 is arranged between the scattered radiation grid with the grid walls 4 and the converter element 10. The shade-capture structure 7 is arranged between the lighting unit 8 and the first electrode 15. The shade-capture structure 7 is preferably arranged in the immediate vicinity of the first electrode 15. The shade-capture structure 7 comprises an X-ray absorbing material. The shade-capture structure 7 preferably comprises the same material as the scattered radiation grid 3. The walls of the shade-capture structure 7 can be embodied wider along the direction of rotation or the axis of rotation than the assigned grid walls 4 of the scattered radiation grid. A wall of the shade-capture structure can be assigned to the grid wall 4, for example in that the grid wall 4 and the wall of the shade-capture structure 7 at least partially overlap in the projection. FIG. 7 shows an example embodiment of the detector module 51 with X-ray detectors 1 according to the invention. In a preferred embodiment, the detector module 51 comprises a two-dimensional matrix or arrangement of a plurality of X-ray detectors 1. The number of detector elements can, for example, be within the region ranging from 100 to several thousands. The scattered radiation grid is not shown for reasons of simplicity. The detector elements can comprise a plurality of energy channels. The X-ray detector 1 comprises the converter element 10. The converter element 10 can be embodied as a planar direct converter comprising, for example, CdTe, CZT, CdZnTeSe, CdTeSe, CdMnTe, InP, TlBr2, HgI2, GaAs, Si or other materials as the converter material. The upper side of the converter element 10 comprises a first electrode 15. The underside of the converter element 10 comprises the second electrode 16, 17, 27. The second electrode 16, 17, 27 is connected via soldered connections 69 to the pixel electrodes 57 and the pixel electronics 67 in the ASIC 59. The soldered connections 69 can, for example, be embodied as bump bonds or solder material in conjunction with copper pillars. The joint number of detection elements 17, 27, the number of soldered connections 69, the number of pixel electrodes 57 and the number of pixel electronics 67 in the ASIC 59 are the same. The electric field between the first electrode 15 and a detector element 17, 27 determines a sensitive detection volume. The unit comprising a detection volume, a detector element 17, 27, a soldered connect 69, a pixel electrode 57 and pixel electronics 67 connected to the pixel electrode 57 forms a detector element, for example a pixel or subpixel. The ASIC 59 is connected at the underside to a substrate 61. The ASIC 59 is connected via TSV connections 63 running through the substrate 61 to peripheral electronics 65. FIG. 8 shows an example embodiment of the computed-tomography system 32 according to the invention. The computed-tomography system 32 contains a gantry 33 with a rotor 35. The rotor 35 comprises a radiation source or X-ray source 37 and the detector device 2. The detector device 2 comprises at least one X-ray detector according to the invention. The detector device 2 can comprise a detector module. The object to be examined 39 is supported on the patient bed 41 and can be moved through the gantry 33 along the axis of rotation z 43. A computing unit 45 is used to control and calculate the sectional views. An input device 47 and an output device 49 are connected to the computing unit 45. Although the invention was illustrated in more detail by the preferred example embodiment, the invention is not restricted by the disclosed examples and other variations can be derived herefrom by the person skilled in the art without departing from the scope of protection of the invention. The patent claims of the application are formulation proposals without prejudice for obtaining more extensive patent protection. The applicant reserves the right to claim even further combinations of features previously disclosed only in the description and/or drawings. References back that are used in dependent claims indicate the further embodiment of the subject matter of the main claim by way of the features of the respective dependent claim; they should not be understood as dispensing with obtaining independent protection of the subject matter for the combinations of features in the referred-back dependent claims. Furthermore, with regard to interpreting the claims, where a feature is concretized in more specific detail in a subordinate claim, it should be assumed that such a restriction is not present in the respective preceding claims. Since the subject matter of the dependent claims in relation to the prior art on the priority date may form separate and independent inventions, the applicant reserves the right to make them the subject matter of independent claims or divisional declarations. They may furthermore also contain independent inventions which have a configuration that is independent of the subject matters of the preceding dependent claims. None of the elements recited in the claims are intended to be a means-plus-function element within the meaning of 35 U.S.C. § 112(f) unless an element is expressly recited using the phrase “means for” or, in the case of a method claim, using the phrases “operation for” or “step for.” 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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052884350 | abstract | Method and apparatus for the incineration and vitrification of radioactive waste materials. Waste materials are fed into a melter containing molten glass wherein the waste is incinerated and vitrified into the glass matrix. Gases produced are combusted in an extended plenum area preferably designed to provide a residence time of at least 3 seconds. A portion of the sulfur compounds in the combustion gases are incorporated into a solid matrix of gypsum by contacting the sulfur compounds with an aqueous solution and calcium hydroxide. |
description | Field of the Invention The present invention relates to an X-ray Talbot interferometer. Description of the Related Art An X-ray phase imaging technique is an imaging technique using phase changes that occur as X-rays pass through an object. Examples of X-ray phase imaging techniques that have been proposed include a Talbot interferometer described in Japanese Patent No. 5162453. The Talbot interferometer typically includes two or three gratings each having a periodic structure. Of these gratings, a grating normally disposed near the object may be referred to as a beam splitter grating, a grating normally disposed near a detector may be referred to as an analyzer grating, and a grating normally disposed near an X-ray source may be referred to as a source grating. These gratings may each be either a grating having a one-dimensional periodic pattern, or a grating having a two-dimensional periodic pattern. The detector is normally one that is capable of acquiring a two-dimensional intensity distribution of X-rays incident on the detection surface of the detector. The beam splitter grating is typically a phase-modulation transmissive diffraction grating. X-rays incident on the beam splitter grating are diffracted by the periodic structure of the grating to form an interference pattern (also called a self-image of the grating) at a predetermined position by a so-called Talbot effect. Since the interference pattern is deformed reflecting, for example, phase changes that occur as X-rays pass through the object, information about the shape and internal structure of the object can be obtained by measuring and analyzing the intensity distribution of the interference pattern. The analyzer grating is typically a grating that has a periodic transmittance distribution, because of the periodic arrangement of X-ray transmitting portions and X-ray shielding portions. The analyzer grating is disposed at the position of the interference pattern, and thus is used for the purpose of producing moire in the intensity distribution of X-rays transmitted through the grating. The moire reflects the deformation of the interference pattern, and the period of the moire can be increased infinitely. Therefore, even when the spatial resolution of the detector to be used is not high enough to allow direct detection of the interference pattern, information about the interference pattern can be indirectly obtained by detecting moire having a large pattern period. Like the typical analyzer grating described above, the source grating is a grating having a structure where X-ray transmitting portions and X-ray shielding portions are periodically arranged. The source grating is normally disposed near an X-ray emitting spot in the X-ray source (X-ray generator), and used for the purpose of virtually forming an array of linear X-ray-emitting portions (or small X-ray-emitting spots in the case of a two-dimensional grating). A plurality of interference patterns formed by X-rays emitted from the linear X-ray-emitting portions are superimposed while displaced from each other by an integral multiple of the pattern period, in the absence of any object in the X-ray path. Thus, there is no pattern loss even when many interference patterns are superimposed, and it is possible to form a periodic pattern having generally high X-ray intensity and fringe visibility. To achieve the superimposition described above, the grating period of each grating and the distance between gratings need to be designed to meet certain conditions. A Talbot interferometer using the source grating described above may be specifically referred to as a Talbot-Lau interferometer. A Talbot interferometer using the source grating described above is disclosed in Japanese Patent No. 5162453. Hereinafter, the term “Talbot interferometer” includes a Talbot-Lau interferometer. In an imaging technique using a Talbot interferometer, detection of interference patterns or moire patterns by a detector is generally followed by analysis of the detected patterns for conversion to a more useful image. Another imaging technique is known, in which a positional relation between gratings during imaging is designed to meet specific conditions, so that a detected special moire image can be directly used as an object image. For example, in imaging techniques described in Japanese Patent No. 5162453 and “Phase-contrast imaging using a scanning-double-grating configuration”, OPTICS EXPRESS (US), 2008, Vol. 16, No. 8, pp. 5849-5867, by Y. I. Nesterets and S. W. Wilkins, imaging is performed by forming moire with a very large (ideally infinite) period, using an interferometer having a grating arrangement where an interference pattern and an analyzer grating pattern are precisely the same in direction and pitch. Here, a periodic pattern having the same period as the interference pattern may be formed on a detector, or no periodic pattern may be formed on the detector. In either case, an X-ray intensity acquired by each of a plurality of pixels of the detector is substantially the same. That is, the intensity distribution acquired by the detector is substantially uniform. The document by Y. I. Nesterets and S. W. Wilkins describes a technique in which the relative positions of gratings are adjusted such that the intensity of X-rays transmitted through the gratings is minimized in the imaging region. Then, with the beam splitter grating and the analyzer grating fixed to each other, imaging is performed while both the gratings are being scanned at the same time. With this technique, the detector can acquire an image which strongly reflects not only absorption information of the object, but also scattering information (small-angle X-ray scattering power by microparticles, fine fibers, edges of structures, etc.) along the periodic direction of the interference pattern. In this technique, differential phase information along the periodic direction of the interference pattern is strongly reflected in the image if differential phase values are large and the local phase of interference fringes is sufficiently significantly shifted, but is not strongly reflected in the image if the local phase shift is not significant enough. In other words, the image obtained by the detector does not have high sensitivity to differential phase information. Even when imaging is performed without scanning of the two gratings, the resulting image will be substantially the same if the spatial resolution of the imaging system is not particularly high. This imaging technique which performs imaging, with the grating positions adjusted to minimize the intensity of X-rays transmitted through the gratings, is similar to a so-called dark-field technique in an optical microscope. In the present specification, an imaging technique which performs imaging with such grating positions (not based on the assumption of scanning of gratings) may be referred to as a dark-field technique. Conversely, an imaging technique which performs imaging, with the relative positions of gratings adjusted such that the intensity of X-rays transmitted through the gratings is maximized in the imaging region, may be referred to as a bright-field technique in the present specification. Japanese Patent No. 5162453 describes a technique which performs imaging, with the relative positions of gratings adjusted such that the intensity of X-rays transmitted through the gratings is about the average of maximum and minimum values throughout the imaging region. In the present specification, this imaging technique may be referred to as an intermediate technique. With the intermediate technique, the detector can acquire an image which strongly reflects not only absorption information of the object, but also differential phase information (spatial differential values of the phase distribution of X-rays transmitted through the object) along the periodic direction of the interference pattern. However, with the intermediate technique, the detector can acquire very little scattering information of the object. In the present specification, a phase distribution of X-rays transmitted through the object, a differential phase distribution obtained by spatially differentiating the phase distribution, and a secondary differential phase distribution obtained by differentiating the differential phase distribution in the same direction may be collectively referred to as phase information of the object. With the use of a Talbot interferometer, when imaging is performed under conditions where the intensity distribution of X-rays transmitted through gratings is uniform in the imaging field, it is possible to acquire an image which strongly reflects not only the absorption information of the object, but also the phase information and the scattering information of the object. However, as described above, a Talbot interferometer which performs the intermediate technique is unable to acquire scattering information of the object. Also, a Talbot interferometer which performs the dark-field technique has low sensitivity to phase information of the object. The present invention provides an X-ray Talbot interferometer that is capable of acquiring scattering information, and also acquiring phase information with higher sensitivity than a Talbot interferometer of the related art which performs the dark-field technique. An X-ray Talbot interferometer according to an aspect of the present invention includes a source grating having a plurality of X-ray transmitting portions to transmit some X-rays from an X-ray source, a beam splitter grating configured to diffract the X-rays from the X-ray transmitting portions with a periodic structure to form interference patterns, an analyzer grating configured to block parts of the interference patterns, and a detector configured to detect X-rays from the analyzer grating. The beam splitter grating forms the interference patterns corresponding to the respective X-ray transmitting portions by diffracting X-rays from each of the X-ray transmitting portions with the periodic structure. The X-ray transmitting portions are arranged to form a periodic pattern in which specific spatial frequency components are enhanced by superimposing the interference patterns corresponding to the respective X-ray transmitting portions. The specific spatial frequency components are spatial frequency components contained in a sideband produced when spatial frequency components specific to the interference patterns are modulated by an object. When no object is placed between the source grating and the analyzer grating, a positional relation between the periodic pattern and a grating pattern of the analyzer grating is substantially the same over an entire imaging field. Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. Embodiments of the present invention will be described in detail with reference to the attached drawings. The same components are denoted by the same reference numerals throughout the drawings, and redundant description will be omitted. Because many X-ray Talbot interferometers (which may hereinafter be simply referred to as interferometers) use simple one-dimensional fringe interference patterns and an analyzer grating having a simple one-dimensional fringe pattern, the present embodiment will be described on the basis of such an interferometer configuration. In an X-ray Talbot-Lau interferometer of the related art, a source grating is configured to enhance carrier components in interference patterns. In other words, the interferometer of the related art has a configuration in which interference patterns formed by respective small X-ray sources of an X-ray source array virtually formed by the source grating are superimposed such that bright portions are superimposed on each other and dark portions are also superimposed on each other, whereby the contrast between bright and dark portions is enhanced. On the other hand, an interferometer of the present embodiment is configured such that parts of bright portions of interference patterns are superimposed on each other, and parts of bright portions and parts of dark portions of the interference patterns are also superimposed on each other. Thus, in the Talbot-Lau interferometer of the present embodiment, the source grating enhances specific frequency components shifted from carrier waves of the interference patterns. The details will now be described. FIG. 4 is a schematic diagram of an X-ray Talbot-Lau interferometer 1100 of a comparative example, which is an X-ray Talbot-Lau interferometer of the related art. The X-ray Talbot-Lau interferometer 1100 includes an X-ray source 110 having an X-ray emitting spot (so-called focus) 11, a source grating 12, a beam splitter grating 13, an analyzer grating 14, and a detector 15. While not shown, an object is placed near the beam splitter grating 13 for imaging. The object may be placed either upstream of the beam splitter grating 13 (i.e., between the source grating 12 and the beam splitter grating 13), or downstream of the beam splitter grating 13 (i.e., between the beam splitter grating 13 and the analyzer grating 14). In the X-ray Talbot-Lau interferometer 1100 of the related art, when no object is placed in the X-ray path, interference patterns 16a to 16c formed by X-rays transmitted through X-ray transmitting portions 121a to 121c of the source grating 12 are superimposed while displaced from each other exactly by an interference pattern period dIP. That is, a relative displacement d0C′ between a plurality of interference patterns superimposed on each other is equal to dIP. Thus, the interference patterns 16a to 16c formed by X-rays from the X-ray transmitting portions 121a to 121c are superimposed to allow exact coincidence between their bright portions and also between their dark portions. Thus, a high-intensity periodic pattern (which is formed by superimposing a plurality of interference patterns) having the same visibility as an interference pattern formed by X-rays from a single X-ray transmitting portion can be formed on the analyzer grating 14. In other words, by superimposing the interference patterns 16a to 16c formed by X-rays from the X-ray transmitting portions 121a to 121c, spatial frequency components specific to the interference patterns 16a to 16c are enhanced. Even when the interference patterns 16a to 16c formed by X-rays from the X-ray transmitting portions 121a to 121c are superimposed while displaced from each other by an integral multiple of the pattern period, it is possible to ensure coincidence between bright portions of the interference patterns 16a to 16c and between dark portions of the interference patterns 16a to 16c. Therefore, the displacement between the interference patterns 16a to 16c may be an integral multiple of the pattern period. The spatial frequency components (i.e., components of a spatial frequency 1/dIP) specific to the interference patterns 16a to 16c can be considered as being enhanced when the displacement between the interference patterns 16a to 16c is equal to either the pattern period or an integral multiple of the pattern period. For the interference patterns 16a to 16c formed by X-rays from the X-ray transmitting portions 121a to 121c of the source grating 12 to be superimposed on each other while displaced exactly by the pattern period or an integral multiple of the pattern period, a grating period d0C of the source grating 12 can be defined as follows: d 0 C = n 1 × d IP × L 01 L 12 where n1 is a positive integer, L01 is the distance between the source grating 12 and the beam splitter grating 13, and L12 is the distance between the beam splitter grating 13 and the analyzer grating 14. Here, the distance between components is the distance between the centers of the components. In the equation, n1 is a value representing the number of pattern periods by which the superimposed interference patterns are displaced from each other. This means that when n1=1, the interference patterns are superimposed while displaced from each other by the pattern period, as in the case of the interference patterns 16a to 16c illustrated in FIG. 4. On the other hand, in an X-ray Talbot interferometer 100 of the present embodiment, as illustrated in FIG. 1, interference patterns 6a to 6c formed by X-rays from X-ray transmitting portions 21a to 21c of a source grating 2 are superimposed while displaced from each other by a distance, which is different from the interference pattern period dIP in the absence of any object. That is, in the X-ray Talbot interferometer 100 of the present embodiment, the displacement d0′ between the interference patterns 6a to 6c formed by X-rays from the X-ray transmitting portions 21a to 21c is not equal to the interference pattern period dIP. Therefore, bright and dark portions of the interference patterns 6a to 6c formed by X-rays from the X-ray transmitting portions 21a to 21c overlap each other without exact coincidence between bright portions and between dark portions. In this case, the grating period d0 of the source grating 2 can be expressed as follows: d 0 = n 1 × d IP × L 01 L 12 ( 1 + α 1 ) ( 1 ) where α1 is a deviation ratio representing the degree of deviation from conditions that allow the interference patterns 6a to 6c to coincide with each other. Note that α1 is not equal to 0 (α1≠0) while it can take a negative value. When α1 is 0, the design conditions of the source grating 2 are the same as those in the comparative example. In the case of α1≠0, superimposing the interference patterns 6a to 6c formed by X-rays from the X-ray transmitting portions 21a to 21c enhances components contained in a sideband resulting from modulation of spatial frequency components specific to the interference patterns 16a to 16c by the presence of the object, instead of enhancing the spatial frequency components specific to the interference patterns 16a to 16c. As described above, a displacement between interference patterns in a typical Talbot-Lau interferometer may be an integral multiple of 2 or more of the pattern period. Similarly, in the Talbot-Lau interferometer of the present embodiment, a displacement between interference patterns may be designed by giving a certain deviation ratio to an integral multiple of 2 or more of the pattern period. However, the design where n1 is an integer of 2 or more is disadvantageous and generally undesirable in that the X-ray transmittance of the entire source grating is lowered. Therefore, the case of n1=1 will be mainly described. Note that −1/n1<α1<1/n1 is satisfied. In FIGS. 1 and 4, for the convenience of explanation, the interference patterns formed by X-rays from the X-ray transmitting portions are shown at different positions in the horizontal direction. However, the interference patterns 6a to 6c are actually formed on the analyzer grating 4 and the interference patterns 16a to 16c are actually formed on the analyzer grating 14. Hence, for example, the distance between the source grating 2 and the interference pattern 6a is equal to the distance between the source grating 2 and the interference pattern 6b. A general configuration of the X-ray Talbot interferometer according to the present embodiment will now be described. FIG. 1 is a schematic diagram of the X-ray Talbot interferometer 100 according to the present embodiment. The X-ray Talbot interferometer 100 includes the source grating 2 having the X-ray transmitting portions 21a to 21c to transmit some X-rays from an X-ray source 10, and a beam splitter grating 3 configured to diffract the X-rays from the X-ray transmitting portions 21a to 21c of the source grating 2 to form the interference patterns 6a to 6c corresponding to the respective X-ray transmitting portions 21a to 21c. The X-ray Talbot interferometer 100 also includes an analyzer grating 4 configured to block some of the X-rays forming the interference patterns 6a to 6c, and a detector 5 configured to detect the intensity of the X-rays from the analyzer grating 4. The X-ray Talbot interferometer 100 can form an X-ray Talbot interferometer system, together with an object information acquiring unit and an image display unit. The object information acquiring unit may be formed by a computing device including a processor and a storage unit. The object information acquiring unit is capable of recording object information acquired by the detector 5 and outputting the object information to the image display unit. The image display unit may be formed by a display device or a printer. FIG. 1 illustrates an example where the X-ray source 10 configured to emit X-rays to the source grating 2 forms the X-ray Talbot interferometer 100, together with the three gratings 2, 3, and 4, and the detector 5. Alternatively, the X-ray source 10 may be configured to be separated from, and used in combination with, the X-ray Talbot interferometer 100. In the present invention and the present specification, the term “Talbot interferometer” includes both a Talbot interferometer that includes an X-ray source and a Talbot interferometer that does not include an X-ray source (but may include a space for the X-ray source). Each component of the X-ray Talbot interferometer 100 will now be described. The X-ray source 10 emits X-rays to the source grating 2. The X-rays to be emitted may be either continuous X-rays or characteristic X-rays. The energy of the X-rays typically ranges from 2 keV to 100 keV. A wavelength selection filter may be provided as appropriate, for example, between the X-ray source 10 and the source grating 2. FIG. 2A illustrates a grating pattern of the source grating 2. The source grating 2 has a one-dimensional periodic structure where X-ray transmitting portions (which may be referred to as openings) 21 having a high X-ray transmittance and X-ray shielding portions 22 having a low X-ray transmittance are arranged in one direction. The source grating 2 is disposed near X-ray emitting spot 1 of the X-ray source 10 to virtually form an array of linear X-ray-emitting portions (or small X-ray-emitting spots in the case of using a two-dimensional grating). FIG. 2B illustrates a grating pattern of the beam splitter grating 3. The beam splitter grating 3 is a phase-modulation diffraction grating having a one-dimensional periodic structure where phase-advance portions 31 and phase-delay portions 32 are arranged in one direction. The phase-advance portions 31 and the phase-delay portions 32 have a width ratio of 1:1 in the direction of arrangement. The pattern and the amount of phase modulation of the beam splitter grating 3 may be selected from various patterns and values suitable for generally known Talbot interferometers, and are not particularly limited here. Note that the amount of phase modulation refers to a phase difference between X-rays transmitted through the phase-advance portions 31 and the phase-delay portions 32. A beam splitter grating with a phase difference of π rad or π/2 rad is typically used as the beam splitter grating 3, but a beam splitter grating with a phase difference other than that may be used as the beam splitter grating 3. An amplitude-modulation diffraction grating may be used as the beam splitter grating 3 while it has a disadvantage over the phase-modulation diffraction grating in terms of a significant loss of X-rays. FIG. 2C illustrates a grating pattern of the analyzer grating 4. The analyzer grating 4 has a one-dimensional periodic structure where X-ray transmitting portions 41 having a high X-ray transmittance and X-ray shielding portions 42 having a low X-ray transmittance are arranged in one direction. The X-ray transmitting portions 41 and the X-ray shielding portions 42 have a width ratio of 1:1 in the direction of arrangement. The grating patterns illustrated in FIGS. 2A to 2C are merely examples, and each grating may have, for example, a two-dimensional periodic structure. The two-dimensional periodic structure may be a square or hexagonal grating structure. The source grating 2 and the analyzer grating 4 having a two-dimensional periodic structure may have either a pattern where isolated X-ray transmitting portions are periodically arranged between X-ray shielding portions, or a pattern where isolated X-ray shielding portions are periodically arranged between X-ray transmitting portions. In the present invention and the present specification, the latter pattern of the shield grating may be referred to as an inverse grating pattern. The detector 5 may be of any type as long as it is capable of acquiring a two-dimensional X-ray intensity distribution. A line sensor having detection pixels arranged in a line may be used as the detector 5 in the present embodiment. This is because the line sensor can acquire a two-dimensional X-ray intensity distribution by using it in combination with a scanning unit which is capable of scanning in a direction crossing the array direction of the detection pixels. To reduce the time required for imaging, however, it is desirable to use an area sensor having detection pixels arranged in two directions. An imaging plate may be used as the detector 5. The spatial resolution of the detector 5 does not need to be as high as a level that allows detection of the fundamental wave of an interference pattern formed by the beam splitter grating 3. Specifically, the pixel pitch of the detection pixels may be greater than half the period of an interference pattern formed by a virtual linear X-ray-emitting portion. The present embodiment assumes that the pixel pitch of the detection pixels is much greater than the period of the interference pattern. When no object is placed between the source grating 2 and the analyzer grating 4, the positional relation between a periodic pattern formed by superimposing a plurality of interference patterns and the grating pattern of the analyzer grating 4 is substantially the same over the entire imaging field. Note that the positional relation between the periodic pattern and the grating pattern of the analyzer grating 4 refers to a local positional relation between each of bright and dark portions of the periodic pattern formed on the analyzer grating 4 and the corresponding one of transmitting and shielding portions of the analyzer grating 4 overlapping the bright and dark portions. For example, when both the periodic pattern and the grating pattern of the analyzer grating 4 have a line-and-space pattern, the positional relation between the periodic pattern and the grating pattern of the analyzer grating 4 means whether a bright portion and a shielding portion exactly coincide with each other, whether a bright portion half overlaps a shielding portion, or whether a bright portion and a transmitting portion exactly coincide with each other. In other words, the positional relation between the periodic pattern and the grating pattern of the analyzer grating 4 is the distance between the reference position of each bright portion of the periodic pattern and the reference position of the corresponding shielding portion of the analyzer grating 4. For example, the center of each bright portion in the periodic direction of the periodic pattern is defined as the reference position of the bright portion, and the center of each shielding portion in the periodic direction of the grating pattern is defined as the reference position of the shielding portion. In this case, if the distance between the center of each bright portion and the center of the shielding portion closest to the bright portion in the periodic direction of the periodic pattern is substantially the same over the entire imaging field, the positional relation between the periodic pattern and the grating pattern of the analyzer grating 4 can be considered substantially the same over the entire imaging field. If the periodic pattern and the grating pattern have periods in a plurality of directions, the positional relation between the periodic pattern and the grating pattern of the analyzer grating 4 can be considered substantially the same over the entire imaging field when the distance between the reference positions in each periodic direction is substantially the same. In the present invention and the present specification, “distance is substantially the same” means that the difference between maximum and minimum values of the distance between the reference position of each bright portion and the reference position of the shielding portion closest to the bright portion is dIP/4 or less. Also, “positional relation between the periodic pattern and the grating pattern is substantially the same over the entire imaging field” means that the distance between reference positions is substantially the same. It is preferable that the difference between maximum and minimum values of the distance between the reference position of each bright portion and the reference position of the shielding portion closest to the bright portion be dIP/8 or less. To make the positional relation between the periodic pattern and the grating pattern the same over the entire imaging field, it is only necessary that the interference patterns forming the periodic pattern and the analyzer grating 4 be the same in pitch and periodic direction. The ranges of allowable differences in pitch and periodic direction vary in accordance with the pitch and the size of the imaging field. An X-ray intensity distribution formed on the detector 5 is uniform. In the present invention and the present specification, “X-ray intensity distribution formed on the detector 5 is uniform” means that the intensity of X-rays incident on the detection surface of the detector 5 is substantially the same over the entire imaging field in the detection surface. The imaging field refers to a region obtained by projecting the imaging range of the object onto the detection surface. The imaging field typically coincides with the entire detection surface, but only part of the detection surface may serve as the imaging field. As in the case of the X-ray Talbot-Lau interferometer 1100 of the related art, the distance L01 between the source grating 2 and the beam splitter grating 3 and the distance L12 between the beam splitter grating 3 and the analyzer grating 4 may be designed such that the visibility of interference patterns is particularly high on the analyzer grating 4. Here, the design takes into account the Talbot effect produced when X-rays from each of virtual linear X-ray-emitting portions formed by the source grating 2 are diffracted by the beam splitter grating 3. By using a simple model, the following describes the effect of the present embodiment where the interference patterns formed by X-rays from the virtual linear X-ray-emitting portions are superimposed while displaced from each other by an amount not equal to the pattern period, and also describes the resulting image produced using the dark-field technique or intermediate technique. First, a coordinate system (x, y) is defined on the analyzer grating 4. The periodic direction of the interference patterns coincides with the x-axis direction. An intensity distribution gIPo(x, y) of an interference pattern on the analyzer grating 4 formed by X-rays emitted from a single point on the source grating 2 can be written as follows: g IPo ( x , y ) = a ( x , y ) + b ( x , y ) cos [ 2 π d IP x + ϕ ( x , y ) ] ( 2 ) where a(x, y) is the average intensity distribution of the interference pattern reflecting the X-ray transmittance distribution of the object, b(x, y) is the amplitude distribution of the interference pattern reflecting the X-ray transmittance distribution of the object and the X-ray small-angle scattering power distribution of the object with respect to the periodic direction of the interference pattern, and ϕ(x, y) is the phase distribution of the interference pattern reflecting a distribution obtained by differentiating, along the periodic direction of the interference pattern, the phase distribution of X-rays transmitted through the object. Note that the X-ray small-angle scattering power distribution of the object refers to the spatial distribution of power of small-angle scattering caused by microparticles and fine fibers in the object, edges in structures, and the like. Also, the distribution obtained by differentiating, in a certain direction, the phase distribution of X-rays transmitted through the object refers to the distribution of deflection angles of X-rays refracted by the object in the direction of differentiation described above. In the present invention and the present specification, information about the X-ray transmittance distribution of the object may be referred to as absorption information, information about the differential phase distribution of X-rays transmitted through the object may be referred to as differential phase information, and information about the X-ray small-angle scattering power distribution of the object may be referred to as scattering information. The phase distribution and the differential phase distribution of X-rays transmitted through the object, and a secondary differential phase distribution obtained by differentiating the differential phase distribution in the same direction may be collectively referred to as phase information of the object. Here, the spatial frequency components specific to the interference patterns in the present embodiment are spatial frequency components having a periodic direction in the x-axis direction and a spatial frequency of 1/dIP. The spatial frequency components specific to the interference patterns can be considered as being amplitude-modulated and phase-modulated by b(x, y) and ϕ(x, y) representing the object information. In the present specification, the spatial frequency components specific to interference patterns and modulated by object information may be referred to as a carrier wave. Harmonic components, instead of fundamental wave components, of the interference patterns may be used as a carrier wave. However, harmonic components of the interference patterns are generally very small as compared to fundamental wave components, and thus are rarely used as a carrier wave. By using the following equationc(x,y)=b(x,y)eiϕ(x,y) (3),equation (2) can be rewritten as follows: g IPo ( x , y ) = a ( x , y ) + 1 2 c ( x , y ) e i 2 π d IP x + 1 2 c * ( x , y ) e - i 2 π d IP x ( 4 ) where * represents a complex conjugate. Computing the two-dimensional Fourier transform of both sides leads to the following equation: G IPo ( ξ , η ) = A ( ξ , η ) + 1 2 C ( ξ - 1 d IP , η ) + 1 2 C * ( ξ + 1 d IP , η ) ( 5 ) where each capital letter represents the Fourier transform of the corresponding function (the same applies to the following equations), ξ represents a spatial frequency in the x-axis direction, and η represents a spatial frequency in the y-axis direction. The X-ray intensity distribution on the analyzer grating 4 will be discussed, which takes into account the presence of the X-ray emitting spot 1 having a spatial spread and the source grating 2. The object and the beam splitter grating 3 are approximated to be at the same position. The X-ray emitting spot 1 and the source grating 2 are also approximated to be at the same position. With respect to the position coordinates (x0, y0) in the x-axis and y-axis directions at the position of the X-ray emitting spot 1 and the source grating 2, a function representing the shape of the emission intensity distribution of the X-ray emitting spot 1 is expressed as gS(x0, y0). The transmittance distribution of the source grating 2 is expressed as t0(x0, y0). In this case, the effective emission intensity distribution gS0(x0, y0) of the X-ray emitting spot 1 can be expressed as follows:gS0(x0,y0)=gS(x0,y0)t0(x0,y0) (6).Additionally, the X-ray intensity distribution gIP(x, y) on the analyzer grating 4 can be approximately expressed as a convolution of gIPo(x, y) and a point spread function hS0(x, y) representing blurring caused by the effective emission intensity distribution of the X-ray emitting spot 1, as follows:gIP(x,y)=gIPo(x,y)*hS0(x,y) (7)where * represents a convolution. Note that gIP(x, y) differs from gIPo(x, y) in that it represents the intensity distribution of interference patterns actually formed on the analyzer grating 4 (i.e., interference patterns formed by all X-rays transmitted through the source grating 2). Also, gIP(x, y) can be considered as representing the intensity distribution of a periodic pattern formed by superimposing a plurality of interference patterns produced by X-rays from the X-ray transmitting portions 21a to 21c of the source grating 2. Additionally, hS0(x, y) can be written as follows: h S 0 ( x , y ) ∝ g S 0 ( - L 01 L 12 X , - L 01 L 12 y ) . ( 8 ) Here, hS(x, y) is a function that can be expressed as follows: h S ( x , y ) ∝ g S ( - L 01 L 12 X , - L 01 L 12 y ) . ( 9 ) Note that hS(x, y) is a point spread function in the absence of the source grating 2. If the source grating 2 has a simple sinusoidal transmittance distribution, t0(x0, y0) can be written as follows by ignoring absolute values: t 0 ( x 0 , y 0 ) = 1 + cos ( 2 π d 0 x 0 ) . ( 10 ) A relative displacement d0′ between interference patterns can be written as follows using the pitch d0 of the source grating 2 and the geometry (L12, L01) of the X-ray Talbot interferometer 100: d 0 ′ = d 0 L 12 L 01 . ( 11 ) In this case, hS0(x, y) can be written as follows: h S 0 ( x , y ) = h S ( x , y ) [ 1 + cos ( 2 π d 0 ′ x ) ] . ( 12 ) Then, HS0(ξ, η), which is the Fourier transform of hS0(x, y), can be expressed as follows: H S 0 ( ξ , η ) = H S ( ξ , η ) + 1 2 H S ( ξ - 1 d 0 ′ , η ) + 1 2 H S ( ξ + 1 d 0 ′ , η ) . ( 13 ) Thus, GIP(ξ, η), which is the Fourier transform of gIP(x, y), can be written as follows using equations (5), (7), and (13) and the convolution theorem: G IP ( ξ , η ) = G IPo ( ξ , η ) H S 0 ( ξ , η ) ≈ A ( ξ , η ) H S ( ξ , η ) + 1 4 C ( ξ - 1 d IP , η ) H S ( ξ - 1 d 0 ′ , η ) + 1 4 C * ( ξ + 1 d IP , η ) H S ( ξ + 1 d 0 ′ , η ) . ( 14 ) Here, the spatial changes of a(x, y), b(x, y), ϕ(x, y), and hS(x, y) are assumed to be much slower than dIP and d0′. As can be seen from equation (14), c(x, y) is filtered by a frequency filter HS in the process of information transmission, through the effect of the X-ray emitting spot 1 having a spatial spread and the source grating 2. As shown in equation (3), c(x, y) has information about the amplitude distribution of the interference pattern and the phase distribution of the interference pattern, and thus has absorption information, phase information, and scattering information of the object. Therefore, equation (14) indicates that the object information is filtered by the frequency filter HS. Also, the shape of the frequency filter HS is found to be determined by the emission intensity distribution of the X-ray emitting spot 1 and L01 and L12, and the position of the frequency filter HS relative to C(ξ, η) is found to be determined by the period dIP of the interference patterns, the grating period d0 of the source grating 2, and L01 and L12. FIGS. 3A to 3C illustrate changes in the spatial frequency spectrum of an interference pattern formed on the analyzer grating 4, and show a process in which GIPo(ξ, η) is converted to GIP(ξ, η) by being filtered by HS0(ξ, η) as in equation (14). Note that FIGS. 3A to 3C each show the profile of each spectrum on the ξ-axis. Also, a(x, y) and b(x, y) are assumed to be constants (i.e., independent of x and y), shape information of the object is assumed to be reflected in ϕ(x, y), and hS(x, y) is assumed to have a two-dimensional Gaussian shape. FIGS. 3A, 3B, and 3C show |GIPo(ξ, η)|, |HS0(ξ, η)|, and |GIP(ξ, η)|, respectively. A spectrum around ξ=1/dIP in FIG. 3A corresponds to components of (½)C(ξ−1/dIP, η), and a spectrum around ξ=−1/dIP in FIG. 3A corresponds to components of (½)C*(ξ+1/dIP, η). A spectrum around ξ=1/dIP in FIG. 3B corresponds to components of (½)HS(ξ−1/d0′, η), and a spectrum around ξ=−1/dIP in FIG. 3B corresponds to components of (½)HS(ξ+1/d0′, η). This example assumes a case where d0′ is slightly smaller than dIP. Therefore, the center of the filter applied around the carrier wave is located slightly to the high-frequency side of the carrier wave. FIG. 3C shows a spectrum obtained after filtering with HS0(ξ, η). In this example, the sideband structure is originally highly symmetric with respect to the carrier wave. However, by the effect of applying an asymmetric filter to the carrier wave, the original sideband structure is transformed into a less symmetric sideband structure as shown. Next, an X-ray intensity distribution will be discussed, which is eventually measured by transmitting X-rays through the analyzer grating 4 and allowing the X-rays to enter the detector 5. A transmittance distribution t2(x, y) of the analyzer grating 4 can be expressed as follows by ignoring absolute values: t 2 ( x , y ) = 1 + cos ( 2 π d 2 x - ϕ r ) ( 15 ) where d2 is the grating period of the analyzer grating 4, and ϕr is the phase of the analyzer grating 4 (corresponding to the position of the analyzer grating 4 in the x-axis direction) and is in the range of 0≤ϕr<2π. When ϕr=0, the bright portions of the interference patterns formed at the position of the analyzer grating 4 coincide with the transmitting portions of the analyzer grating 4 in the area free from the effect of the object. On the other hand, when ϕr=π, the bright portions of the interference patterns formed at the position of the analyzer grating 4 coincide with the shielding portions of the analyzer grating 4 in the area free from the effect of the object. That is, imaging performed with ϕr=0 is the bright-field technique, and imaging performed with ϕr=π is the dark-field technique. When the bright portions of the interference patterns formed at the position of the analyzer grating 4 coincide with the transmitting portions of the analyzer grating 4, the distance between the center of each bright portion and the center of the corresponding transmitting portion is 0 in the periodic direction (x-axis direction here) of the interference patterns. Similarly, when the bright portions of the interference patterns formed at the position of the analyzer grating 4 coincide with the shielding portions of the analyzer grating 4, the distance between the center of each bright portion and the center of the corresponding shielding portion is 0 in the periodic direction of the interference patterns. In the case of performing the bright-field technique, the distance between the center of each bright portion and the center of the corresponding transmitting portion may be 0 (ϕr=0). However, even when the interference patterns and the analyzer grating 4 are slightly displaced from each other, an X-ray intensity distribution having the same characteristics as the X-ray intensity distribution obtained by the bright-field technique can be obtained. The same applies to the case of performing the dark-field technique. Therefore, in the present invention and the present specification, imaging performed when the distance between the center of each bright portion and the center of the corresponding transmitting portion is less than or equal to ⅛ times the period (0≤ϕr≤π/4 or 7π/4≤ϕr<2π) is considered as the bright-field technique. On the other hand, imaging performed when the distance between the center of each bright portion and the center of the corresponding shielding portion is less than or equal to ⅛ times the period (3π/4≤ϕr≤5π/4) is considered as the dark-field technique. It is preferable that the distance between the center of each bright portion and the center of the corresponding transmitting portion be less than or equal to 1/10 times the period (0≤ϕr≤π/5 or 9π/5≤ϕr<2π), or the distance between the center of each bright portion and the center of the corresponding shielding portion be less than or equal to 1/10 times the period (4π/5≤ϕr≤6π/5). This is because the characteristics of the bright-field technique or the dark-field technique are particularly reflected in the X-ray intensity distribution. When ϕr=π/2 or ϕr=3π/2, the distance between the center of each bright portion and the center of the corresponding transmitting portion, and the distance between the center of each bright portion and the center of the corresponding shielding portion, are both ¼ times the pitch of the interference patterns. In this case, the intensity of X-rays transmitted through the analyzer grating 4 is the average of the maximum value (X-ray intensity when ϕr=0) and the minimum value (X-ray intensity when ϕr=π). When the interference patterns and the analyzer grating 4 have this positional relation, the characteristics of an X-ray intensity distribution obtained by the intermediate technique are most strongly reflected. However, even when the interference patterns and the analyzer grating 4 are slightly displaced from each other, an X-ray intensity distribution having the same characteristics as the X-ray intensity distribution obtained by the intermediate technique can be obtained. Therefore, in the present invention and the present specification, imaging performed when the distance between the center of each bright portion and the center of the corresponding transmitting portion is greater than ⅛ times the period, and the distance between the center of each bright portion and the center of the corresponding shielding portion is greater than ⅛ times the period (π/4<ϕr<3π/4 or 5π/4<ϕr<7π/4) is considered as the intermediate technique. As in the case of the source grating 2, the grating period d2 of the analyzer grating 4 may be an integral multiple of 2 or more of dIP or a value close thereto. However, again this is generally undesirable in that the X-ray transmittance is lowered. Therefore, the following describes the case where d2 has a value close to dIP. Since the analyzer grating 4 is normally disposed very close to the detection surface of the detector 5, the analyzer grating 4 and the detection surface are approximated to be at the same position. Here, the intensity distribution of X-rays transmitted through the analyzer grating 4 coincides with the X-ray intensity distribution formed on the detection surface. A point spread function (PSF) specific to intensity distribution measurement made by the detector 5 used is represented by hD(x, y). In this case, the X-ray intensity distribution gM(x, y) eventually measured can be written as follows using the intensity distribution of X-rays transmitted through the analyzer grating 4 (gIP(x, y)t2(x, y)) and the point spread function of the detector 5:gM(x,y)=[gIP(x,y)t2(x,y)]*hD(x,y) (16).Therefore, GM(ξ, η), which is the Fourier transform of gM(x, y), can be written as follows: G M ( ξ , η ) = [ G IP ( ξ , η ) * T 2 ( ξ , η ) ] H D ( ξ , η ) ≈ [ A ( ξ , η ) H S ( ξ , η ) + 1 8 C ( ξ - 1 d IP + 1 d 2 , η ) H S ( ξ - 1 d 0 ′ + 1 d 2 , η ) e i ϕ r + 1 8 C * ( ξ + 1 d IP - 1 d 2 , η ) H S ( ξ + 1 d 0 ′ - 1 d 2 , η ) e - i ϕ r ] H D ( ξ , η ) . ( 17 ) Here, terms located in a region far away from the origin in the (ξ, η) space are ignored on the assumption that their values are made sufficiently small by filtering with HD(ξ, η). Also, |HD(ξ, η)| is a function corresponding to a modulation transfer function (MTF) of the detector 5. Since d2=dIP is satisfied in the present embodiment, equation (17) can be rewritten as follows: G M ( ξ , η ) ≈ [ A ( ξ , η ) H S ( ξ , η ) + 1 8 C ( ξ , η ) H S ( ξ - ξ 0 , η ) e i ϕ r + 1 8 C * ( ξ , η ) H S ( ξ + ξ 0 , η ) e - i ϕ r ] H D ( ξ , η ) ( 18 ) where ξ0=1/d0′−1/dIP. To simplify the discussion, hS(x, y) is assumed to be an even function. Since hS(x, y) is a real function at the same time, HS(ξ, η), which is the Fourier transform of hS(x, y), is also a real even function. HS(ξ, η) may have a structure with a plurality of extremal values depending on the shape of hS(x, y). In this case, the value of ξ0 is assumed to be small enough to be contained in the main lobe at the origin in HS(ξ, η). Then, when HS (ξ−ξ0, η) and HS (ξ+ξ0, η) are each Taylor-expanded around (ξ, η)=(0, 0), and terms related to η and the second and higher order terms of ξ are ignored, GM(ξ, η) can be approximately written as follows: G M ( ξ , η ) ≈ { A ( ξ , η ) H S ( ξ , η ) + 1 8 C ( ξ , η ) [ H S ( - ξ 0 , 0 ) + ( ∂ H S ∂ ξ ) ( - ξ 0 , 0 ) ξ ] e i ϕ r + 1 8 C * ( ξ , η ) [ H S ( ξ 0 , 0 ) + ( ∂ H S ∂ ξ ) ( ξ 0 , 0 ) ξ ] e - i ϕ r } H D ( ξ , η ) = { A ( ξ , η ) H S ( ξ , η ) + 1 8 C ( ξ , η ) [ H S ( - ξ 0 , 0 ) + ( ∂ H S ∂ ξ ) ( - ξ 0 , 0 ) ξ ] e i ϕ r + 1 8 C * ( ξ , η ) [ H S ( - ξ 0 , 0 ) - ( ∂ H S ∂ ξ ) ( - ξ 0 , 0 ) ξ ] e - i ϕ r } H D ( ξ , η ) = { A ( ξ , η ) H S ( ξ , η ) + 1 8 H S ( - ξ 0 , 0 ) [ C ( ξ , η ) e i φ r + C * ( ξ , η ) e - i φ r ] + 1 8 ( ∂ H S ∂ ξ ) ( - ξ 0 , 0 ) ξ [ C ( ξ , η ) e i ϕ r - C * ( ξ , η ) e - i ϕ r ] } H D ( ξ , η ) . ( 19 ) Therefore, gM(x, y) can be approximately written as follows: g M ( x , y ) ≈ a ( x , y ) * h S ( x , y ) * h D ( x , y ) + 1 8 H S ( - ξ 0 , 0 ) [ c ( x , y ) e i ϕ r + c * ( x , y ) e - i ϕ r ] * h D ( x , y ) + 1 8 ( ∂ H S ∂ ξ ) ( - ξ 0 , 0 ) [ e i ϕ r 1 2 π i ∂ c ( x , y ) ∂ x - e - i ϕ r 1 2 π i ∂ c * ( x , y ) ∂ x ] * h D ( x , y ) = a ( x , y ) * h S ( x , y ) * h D ( x , y ) + 1 4 H S ( - ξ 0 , 0 ) b ( x , y ) cos [ ϕ ( x , y ) + ϕ r ] * h D ( x , y ) + 1 16 π ( ∂ H S ∂ ξ ) ( - ξ 0 , 0 ) × { e i ϕ r i [ ∂ b ( x , y ) ∂ x e i ϕ ( x , y ) + ib ( x , y ) ∂ ϕ ( x , y ) ∂ x e i ϕ ( x , y ) ] - e - i ϕ r i [ ∂ b ( x , y ) ∂ x e - i ϕ ( x , y ) - ib ( x , y ) ∂ ϕ ( x , y ) ∂ x e - i ϕ ( x , y ) ] } * h D ( x , y ) = a ( x , y ) * h S ( x , y ) * h D ( x , y ) + 1 4 H S ( - ξ 0 , 0 ) b ( x , y ) cos [ ϕ ( x , y ) + ϕ r ] * h D ( x , y ) + 1 8 π ( ∂ H S ∂ ξ ) ( - ξ 0 , 0 ) × { ∂ b ( x , y ) ∂ x sin [ ϕ ( x , y ) + ϕ r ] + b ( x , y ) ∂ ϕ ( x , y ) ∂ x cos [ ϕ ( x , y ) + ϕ r ] } * h D ( x , y ) . ( 20 ) On the rightmost side of equation (20), the first term represents a contrast which is based on the absorption information of the object and remains after elimination of the effect of interference fringes. The second term on the rightmost side of equation (20) represents part of the effects of amplitude modulation b(x, y) and phase modulation ϕ(x, y) of the interference fringes. For example, the second term indicates that, in the case when ϕr=π/2, in other words, in the case of a condition corresponding to imaging performed using the intermediate technique described above, the effect of ϕ(x, y) reflecting the differential phase information of the object is strongly reflected in the image. The second term also indicates that, in the case when ϕr=π, in other words, in the case of a condition corresponding to imaging performed using the dark-field technique described above, although the effect of ϕ(x, y) is not much reflected in the image unless the value of ϕ(x, y) is large enough, the effect of b(x, y) containing the scattering information of the object is strongly reflected in the image. Note that the second term is a term which maximizes its variation when ξ0=0, and shows the same characteristics as the Talbot interferometer of the related art in terms of how the effects of b(x, y) and ϕ(x, y) are reflected in the image. On the other hand, the third term on the rightmost side of equation (20) is a term that can have a non-zero value only when ξ0≠0, that is, when the displacement d0′ between interference patterns is not equal to (≠) the pattern pitch dIP of the interference patterns. The third term thus represents the unique effects of the present embodiment. The first term within braces ({ }) in the third term on the rightmost side of equation (20), ∂ b ( x , y ) ∂ x sin [ ϕ ( x , y ) + ϕ r ] ,mainly represents the effect of a differential value of b(x, y) along the x-axis direction. The differential value of b(x, y) reflects a differential value of absorption information (differential absorption information) and a differential value of scattering information (differential scattering information). The absolute value of sin [ϕ(x, y)+ϕr] is large when imaging is performed using the intermediate technique (where ϕr takes a value close to π/2 or 3π/2), and hence this term indicates that the differential absorption information and the differential scattering information have significant effects on the image in the case of imaging using the intermediate technique. On the other hand, when imaging is performed using the dark-field technique (where ϕr takes a value close to π), this term generally has no significant effect on the image. The second term within braces ({ }) in the third term on the rightmost side of equation (20), b ( x , y ) ∂ ϕ ( x , y ) ∂ x cos [ ϕ ( x , y ) + ϕ r ] ,mainly represents the effects of b(x, y) and differential value of ϕ(x, y) along the x-axis direction. The differential value of ϕ(x, y) reflects a differential value of differential phase information of the object (secondary differential phase information or wavefront curvature). The absolute value of cos [ϕ(x, y)+ϕr] is large when imaging is performed using the dark-field technique, and hence this term indicates that the secondary differential phase information has a significant effect on the image in the case of imaging using the dark-field technique. On the other hand, when imaging is performed using the intermediate technique, this term generally has no significant effect on the image. Thus, the third term on the rightmost side of equation (20) represents the effect of causing scattering information to be strongly reflected in the X-ray intensity distribution on the detector 5, in the case of using the intermediate technique which is originally unable to acquire scattering information. The third term on the rightmost side of equation (20) also represents the effect of causing phase information to be significantly reflected in the X-ray intensity distribution on the detector 5, in the case of using the dark-field technique which originally has low sensitivity to phase information. The greater the derivative of HS(ξ, η) at ξ=−ξ0, the greater the effect the third term generally has on the image. In summary, when imaging using the intermediate technique is performed with the interferometer of the present embodiment, an image which strongly reflects absorption information, differential phase information, differential absorption information, and differential scattering information can be acquired. When imaging using the dark-field technique is performed with the interferometer of the present embodiment, an image which strongly reflects absorption information, scattering information, and secondary differential phase information can be acquired. In the case of using the bright-field technique, since cos [ϕ(x, y)+ϕr], which is the second term within braces ({ }) in the third term on the rightmost side of equation (20), has a large value, an X-ray intensity distribution which more strongly reflects phase information than the related art can be formed on the detector 5, as in the case of using the dark-field technique. As described above, absorption information, phase information, and scattering information of the object can be acquired in the present embodiment. Even when the dark-field technique or bright-field technique is performed using the Talbot interferometer of the present embodiment, phase information is strongly reflected in the acquired X-ray intensity distribution by adding the third term described above. It is thus possible to acquire phase information with higher sensitivity than the dark-field technique of the related art. Other features of the present embodiment and imaging techniques will now be described. In imaging using the dark-field technique, the level of X-ray shot noise is generally low, because the X-ray intensity in the background of the image is relatively low. Therefore, in imaging using the dark-field technique, scattering information and secondary differential phase information can be acquired with a relatively high signal-to-noise (S/N) ratio. In imaging using the bright-field technique, the amount of X-rays lost by transmission through the analyzer grating 4 is small. Therefore, in imaging using the bright-field technique, it is possible not only to acquire absorption information with a relatively high S/N ratio, but also to acquire scattering information and secondary differential phase information. In the case of using the dark-field technique or bright-field technique, changes in the X-ray intensity in the background resulting from changes in the relative position of gratings are smaller than in the case of using the intermediate technique, and hence the requirement for accuracy in the alignment of gratings is lower. In the present embodiment, the frequency filter HS can be applied to the spectrum of each of C(ξ, η) and C*(ξ, η) reflecting the object information, at a position off the center of the spectrum. This allows components in the high-frequency region in c(x, y) to remain more easily, and thus can improve the spatial resolution of imaging. As described above, the gratings used in the interferometer may have a two-dimensional grating pattern, such as a square grating pattern or a hexagonal grating pattern. This is advantageous in that, in the case of using the dark-field technique or bright-field technique, scattering information for a plurality of directions and secondary differential phase information along a plurality of directions can be acquired at the same time. In the case of using the intermediate technique of the related art, differential phase information of the object for one direction can be acquired with high sensitivity. However, even when gratings with a two-dimensional grating pattern are used, differential phase information for a plurality of directions cannot be acquired at the same time. When the dark-field technique is performed in the present embodiment, either one of the source grating 2 and the analyzer grating 4 may have the inverse grating pattern described above. The range of ξ0 for achieving particularly high imaging performance in the interferometer of the present embodiment will now be described. When the X-ray emitting spot 1 is assumed to have a two-dimensional Gaussian emission intensity distribution, gS(x0, y0) can be written as follows: g S ( x 0 , y 0 ) = e - x 0 2 + y 0 2 2 σ S 2 ( 21 ) where σS is a constant that determines the size of spatial spread of the X-ray emitting spot 1. In this case, hS(x, y) can be written as follows from equation (9): h S ( x , y ) ∝ e - x 2 + y 2 2 σ S ′2 ( 22 ) where σS′ is as follows: σ S ′ = σ S L 12 L 01 . ( 23 ) In this case, HS(ξ, η), which is the Fourier transform of hS(x, y), can be expressed as follows by ignoring coefficients: H S ( ξ , η ) = e - ξ 2 + η 2 2 σ SF 2 . ( 24 ) This also has a Gaussian shape. Note however that σSF is a constant that determines the width of HS(ξ, η) and can be expressed as follows: σ SF = 1 2 πσ S ′ = 1 2 πσ S L 01 L 12 . ( 25 ) When n1=1, ξ0 can be written as follows: ξ 0 = 1 d 0 ′ - 1 d IP = - 1 d IP α 1 1 + α 1 ≈ - α 1 d IP . ( 26 ) Note that |α1|<<1. C(ξ−1/dIP, η), which is the spectrum of object information, is two-dimensionally distributed around the carrier wave at the center. As described above, ϕ(x, y) reflects a distribution obtained by differentiating, in the direction of the carrier wave, the phase distribution of X-rays transmitted through the object. In this case, the components of C(ξ−1/dIP, η) strongly appear particularly in the ξ-axis direction, which is the direction of the carrier wave. Therefore, the frequency filter HS may be shifted along the ξ-axis (ξ0≠0). If |ξ0| has a large value, many higher-frequency components in c(x, y) can be transmitted. At the same time, however, this is disadvantageous in that the total amount of signals is reduced due to loss of low-frequency components. To effectively achieve the advantages of the present embodiment while preventing such loss of low-frequency components, ξ0 may be selected to satisfy the following:0.3σSF<|ξ0|<3.0σSF (27).If the value of |ξ0| is around 0.3σSF, the interferometer can have the unique features of the present embodiment while having imaging performance relatively close to that in the case of the design of the related art. On the other hand, if the value of |ξ0| is around 3.0σSF, the amount of transmission of high-frequency components can be significantly increased, and hence the characteristics of a small-size object or structure can be particularly efficiently transmitted. However, since low-frequency components are significantly reduced, the total amount of signals is often reduced. If gS(x0, y0) has a full width at half maximum of wS, the relation wS=2σS(2 ln 2)0.5 is satisfied when gS(x0, y0) has a Gaussian shape. Therefore, expression (27) can be rewritten as follows: 0.3 2 ln 2 π w S L 01 L 12 < ξ 0 < 3.0 2 ln 2 π w S L 01 L 12 . ( 28 ) This can be roughly rewritten as follows by calculating coefficient parts and using α1: 0.1 d IP w S L 01 L 12 < α 1 < 1.1 d IP w S L 01 L 12 . ( 29 ) Expression (29) gives a suitable range of the deviation ratio α1 for determining the pitch d0 of the source grating 2 in the present embodiment. If the emission intensity distribution gS(x0, y0) of the X-ray emitting spot 1 has a typical shape (e.g., the shape of a rectangular function) other than the Gaussian shape, a suitable range of α1 substantially coincides with the range given by expression (29) while the shape of HS(ξ, η) becomes more complex. The relation between dIP and d1, which is the grating period of the beam splitter grating 3, can be generally written as follows: d IP = d 1 m L 01 + L 12 L 01 ( 30 ) where m is a positive integer. A suitable value of m is determined by the relation between the pattern of the beam splitter grating 3 and the interference patterns, but m may generally be 1 or 2. A typical example of the case of m=1 is the case of using a so-called π/2 phase modulation grating as the beam splitter grating 3. A typical example of the case of m=2 is the case of using a so-called π phase modulation grating as the beam splitter grating 3. Using harmonic components in the interference patterns as a carrier wave also corresponds to the case where m has a value other than 1. By using equation (30), expression (29) can be rewritten as follows using d1: 0.1 d 1 mw S L 01 + L 12 L 12 < α 1 < 1.1 d 1 mw S L 01 + L 12 L 12 . ( 31 ) The value of d0 in this case can be rewritten as follows using d1: d 0 = n 1 d 1 m L 01 + L 12 L 12 ( 1 + α 1 ) . ( 32 ) Additionally, d2 can be rewritten as follows: d 2 = n 2 d 1 m L 01 + L 12 L 01 ( 33 ) where n2 is a positive integer, which may be 1 (n2=1) for higher transmittance. The emission intensity distribution of the X-ray emitting spot 1 is known to be easily measured, for example, by performing imaging with a pinhole placed at a predetermined position in the X-ray path. The full width at half maximum of the emission intensity distribution, wS, can be easily measured. Therefore, it is easy to determine whether the interferometer satisfies expressions (31) and (32). Of components of the sidebands appearing in GIPo(ξ, η), the components of the upper sideband may be strongly transmitted by setting α1<0, or the components of the lower sideband may be strongly transmitted by setting α1>0. However, as described above, the object information appears not only as the amplitude modulation of the interference patterns, but also as the phase modulation of the interference patterns. Therefore, generally, the amplitude spectrum of the upper sideband and the amplitude spectrum of the lower sideband are not perfectly symmetrical. Also, depending on the type of the object, the visibility and detectability of the structure may vary significantly, in accordance with which of the upper and lower sideband components are transmitted. Therefore, on the basis of this relation, the value of α1 may be set such that, in a sideband predicted in advance, a region to be transmitted (enhanced) is located near a maximum value in a region of the frequency filter HS applied to the carrier wave. The interferometer may have a configuration which allows the user to set the size of the object the user particularly wants to observe (enhance). In this case, the interferometer may include a setting unit for the user to set the size, a computing device, and a positioning unit for positioning a determined one of a plurality of source gratings in the optical path. The computing device may include a first unit configured to determine a frequency to be enhanced on the basis of the set size, a second unit configured to determine α1 in accordance with the frequency difference (ξ0) between the determined frequency and a carrier wave, and a third unit configured to determine the source grating to be used on the basis of the determined α1. The setting unit may be, for example, a display unit configured to display a dial or buttons for entry of numerical values and also display a set numerical value. The positioning unit for positioning a determined source grating in the optical path may be a moving unit (e.g., actuator or gear) configured to move the source grating in response to a command from the computing device. Instead of selecting a source grating to be used from a plurality of source gratings, a source grating having a variable pitch (e.g., a source grating described in Japanese Patent Laid-Open No. 2011-153869) may be used. Instead of using a source grating, an X-ray source having a one-dimensional or two-dimensional array of linear X-ray emitting portions or small X-ray emitting spots may be used. This X-ray source may be produced by texturing the anode surface of an X-ray tube or arranging an array of anode materials in the X-ray tube, or by forming an array pattern on a normal anode surface with electron beams from an electron optical system. The interferometer may be configured to vary the shape of electron beams by controlling the electron optical system. This can change the period of the array of linear X-ray emitting portions or small X-ray emitting spots, and thus can easily change a spatial frequency to be particularly enhanced in the object information. When the interferometer is configured such that the positional relation between the interference patterns and the analyzer grating can be changed, the imaging technique can be selected or changed and executed, in accordance with the object or information to be acquired. If this positional relation can be changed, it is possible to perform not only an imaging technique which does not involve fringe analysis, but also an imaging technique which involves analysis of acquired moire fringes to obtain object information. When fringe analysis is performed, moire fringes with a relatively short period may be formed on the detector, or a detection result may be obtained by a phase stepping technique (fringe scanning technique). The object information obtained by fringe analysis is typically a distribution, in the acquired moire fringes, of local average values excluding intensity fluctuations caused by moire, local phase values of specific moire fringe components, and local visibility values of the specific moire fringe components. The visibility value of a moire fringe component is often defined as a value obtained by dividing the amplitude of a periodic component of moire fringes by an average value. To configure the interferometer such that the positional relation between the interference patterns and the analyzer grating can be changed, the interferometer may include a moving unit capable of moving at least one of the source grating, the beam splitter grating, and the analyzer grating. The interference patterns can be moved by moving at least one of the source grating and the beam splitter grating. The moving unit may be, for example, an actuator. The imaging technique to be used may be determined when the operator specifies the amount of movement as an instruction to the moving unit. Gratings may be automatically positioned in response to selection of an imaging mode by the operator. For automatic positioning of gratings in response to selection of an imaging mode by the operator, the interferometer may include an imaging mode instruction unit configured to give the selected imaging mode as an instruction to a movement instruction unit, and the movement instruction unit configured to give the amount of movement as an instruction to the moving unit for each grating. The movement instruction unit gives, to the moving unit for each grating, the amount of movement of the grating for appropriate positioning of the grating. The movement of a grating includes in-plane rotation of the grating. The imaging mode instruction unit and the movement instruction unit may each be formed by a computing device including a processor and a storage unit. The imaging mode instruction unit and the movement instruction unit may be formed as a single computing device. The imaging mode instruction unit, the movement instruction unit, and the object information acquiring unit may be formed as a single computing device. In the case of executing an imaging mode which involves forming moire fringes with a relatively short period on the detector and acquiring the intensity distribution of the moire fringes to perform fringe analysis, the moire fringes may have a pitch that is 2 to 20 times the pixel pitch of detection pixels. Thus, when the movement instruction unit receives an instruction to execute this imaging mode, the source grating, the beam splitter grating, and the analyzer grating are arranged such that the pitch of the moire fringes falls within this range in the absence of any object between the source grating and the detector. This imaging mode can be executed by performing imaging, with the gratings arranged as described above. In the case of executing an imaging mode which involves performing a phase stepping technique, it is required to vary the positional relation between a periodic pattern formed by a plurality of interference patterns and the analyzer grating to detect the X-ray intensity distribution multiple times. Therefore, when the movement instruction unit receives an instruction to execute this imaging mode from the imaging mode instruction unit, the position of at least one of the source grating, the beam splitter grating, and the analyzer grating is changed during multiple acquisitions of the X-ray intensity distribution. Instead of selecting an imaging mode, the operator may select, for example, the period of a periodic pattern, and the periodic direction of the periodic pattern or of the grating pattern of the analyzer grating. Although the above-described embodiment deals with a one-dimensional grating having a periodic direction in one direction, a two-dimensional grating having periods in a plurality of directions may be used. For example, when a two-dimensional grating having periodic direction in the x-axis and y-axis directions is used, it is only necessary that expressions (31), (32), and (33) be satisfied in both the x-axis and y-axis directions. The same applies to the case of using a two-dimensional grating (e.g., hexagonal grating) having periodic directions in three or more directions. A more concrete example of the present embodiment will now be described. Example 1 is a concrete example of the present embodiment. As the X-ray source, the interferometer includes an X-ray tube having a tungsten anode. The X-ray tube is configured to emit X-rays having a certain energy bandwidth, with a photon energy of about 25 keV at the center, by controlling the tube voltage or a filter. The present interferometer is designed to function effectively particularly for X-rays having a wavelength of about 0.05 nm (i.e., a photon energy of about 25 keV). The effective emission intensity distribution of the X-ray emitting spot has a two-dimensional Gaussian shape with a full width at half maximum of 500 μm. The patterns of the source grating, the beam splitter grating, and the analyzer grating are as illustrated in FIGS. 2A to 2C. The beam splitter grating is a silicon phase grating with a grating period d1 of 8.0 μm. Since the grating substrate has a 32 μm difference in thickness between the phase-advance and phase-delay portions, a phase modulation of about π rad is applied to incident X-rays with a wavelength of about 0.05 nm. Note that the phase-advance and phase-delay portions are equal in width. The source grating and the analyzer grating both have a structure in which a gold plating layer of 100 μm thick is formed on a silicon substrate to form X-ray shielding portions. The detector is a flat panel detector having a pixel pitch of 50 μm. A point spread function specific to the detector has a two-dimensional Gaussian shape with a full width at half maximum of 50 μm. The distances L01 and L12 are 800 mm and 200 mm, respectively. The source grating and the X-ray emitting spot are disposed at substantially the same position, and the analyzer grating and the detection surface of the detector are disposed at substantially the same position. In this case, d0 and d2 are calculated as 20.0(1+α1) μm and 5.0 μm, respectively, on the basis of equations (32) and (33). Here, m=2 and n1=n2=1 are set by taking into account that the beam splitter grating is a so-called π phase modulation grating. In the present example, the deviation ratio α1 is set to −0.015. This means that d0 is 19.7 μm. The value of α1 may be in the range of 0.004<|α1|<0.044 on the basis of expression (31). An aspect of the present invention can provide an X-ray Talbot interferometer that is capable of acquiring scattering information, and also acquiring phase information with higher sensitivity than a Talbot interferometer of the related art which performs the dark-field technique. While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. This application claims the benefit of Japanese Patent Application No. 2015-155461 filed Aug. 5, 2015, which is hereby incorporated by reference herein in its entirety. |
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062597671 | abstract | The invention relates to an X-ray device which operates with only a single image detection device whose format corresponds to the maximum exposure format. In order to facilitate the adjustment of the exposure field for an exposure, a respective set of exposure parameters is stored in a memory for each of the various organs to be imaged; this set includes inter alia an adjustment value for the size of the exposure field for an exposure of the relevant organ. This adjustment value is fetched and the diaphragm unit is automatically controlled in such a manner that the fetched adjustment value is (pre)adjusted. |
claims | 1. A method for measuring an information transfer limit of a transmission electron microscope by adopting a crystal thin film, of which lattice constants and structure are known, as a specimen to be assessed, and measuring a contrast of observed crystal lattice fringes, wherein:an electron beam is routed to the crystal thin film;two specific waves of the electron beam that are transmitted or diffracted are selected and used to form a lattice image; andwhile a condition for diffraction of the electron beam to be caused by the specimen, and a condition for selection of the two transmitted or diffracted waves are held intact, a change in the contrast of formed crystal lattice fringes derived from a change in the incident angle of the electron beam falling on the crystal thin film is checked in order to measure the information transfer limit. 2. The method for measuring an information transfer limit according to claim 1, wherein:the incident angle of the electron beam is changed in order to determine the tilt angle α0 of the incident electron beam, at which the contrast of crystal lattice fringes is 1/e under an achromatic condition satisfied by the two waves of the electron beam, or an associated wave number uα0=α0/λ;a half angle β of a diffraction angle corresponding to a distance ddf between adjoining ones of lattice fringes, or a wave number uβ is represented by an equation (1) below; u β = 1 d df = β 2 λ ( 1 ) using the equation (1), an information transfer limit dc is provided as the equation (2): d c = λ 2 θ 0 β = 1 2 u θ 0 u β ( 2 ) where e denotes the base of a natural logarithm and λ denotes the wavelength of an electron beam. 3. The method for measuring an information transfer limit according to claim 1, wherein:the incident angle of the electron beam is changed in order to fit the equation (3), which is a function encompassing a focal spread Δ that is an indeterminate constant, to a change in the contrast of lattice fringes derived from a change in the tilt angle α of the incident electron beam or in an associated wave number uα=α/λ;{tilde over (Φ)}(uθ)=exp(−8π2Δ2λ2uθ2uβ2) (3)the focal spread Δ that is an indeterminate constant is thus determined; andan information transfer function dc is provided as the following equation (4): d c = πΔλ 2 ( 4 ) where uβ denotes a wave number (=1/ddf) relevant to a distance ddf between adjoining ones of lattice fringes employed for measurement, and λ denotes the wavelength of the electron beam. 4. The method for measuring an information transfer limit according to claim 1, wherein the condition for diffraction of the electron beam is a condition that diffracted waves derived from the so-called Bragg diffraction is excited. 5. A transmission electron microscope, comprising:an electron source;a crystal thin film to which an electron beam radiated from the electron source is routed;an electron beam deflector disposed on the side of the electron source beyond the crystal thin film in order to change the angle of the electron beam incident on the crystal thin film;a specimen tilting system that adjusts the angle of the crystal specimen with respect to the optical axis of the electron microscope;an objective lens on which a diffracted electron beam scattered by the crystal thin film falls;an aperture system which is disposed on an opposite side of the objective lens relative to the electron source, which selects the diffracted electron beam, and whose position can be varied depending on the angle of the electron beam incident on the crystal thin film; andan observation device for use in observing a lattice image that results from interference of the selected diffracted wave and other wave and that is formed on an image plane of the objective lens, wherein:a crystal thin film whose lattice constants and structure are known is adopted as a specimen to be assessed,a contrast of crystal lattice fringes to be observed is measured in order to measure an information transfer limit of the transmission electron microscope,an electron beam is routed to the crystal thin film,two specific waves of the electron beam that are transmitted or diffracted are selected and used to form a lattice image, andwhile a condition for diffraction of an electron beam caused by the specimen and a condition for selection of the two transmitted or diffracted waves are held intact, the incident angle of the electron beam falling on the crystal thin film is changed in order to check a change in the contrast of formed crystal lattice fringes for the purpose of measuring an information transfer limit, and wherein:the incident angle of the electron beam is changed in order to determine the tilt angle α0 of the incident electron beam, at which the contrast of crystal lattice fringes is 1/e under an achromatic condition satisfied by the two selected waves of the electron beam, or an associated wave number uα0=α0/λ,a half angle β of a diffraction angle corresponding to a distance ddf between adjoining ones of lattice fringes, or an associated wave number uβ is represented by the equation (5) below: u β = 1 d df = β 2 λ ( 5 ) using the equation (5), an information transfer limit dc is provided as the following equation (6): d c = λ 2 θ 0 β = 1 2 u θ 0 u β ( 6 ) where e denotes the base of a natural logarithm and λ denotes the wavelength of the electron beam. 6. The transmission electron microscope according to claim 5, further comprising a control system that controls the electron beam deflector, specimen tilting system, and aperture system while interlocking them with one another. 7. A transmission electron microscope, comprising:an electron source;a crystal thin film to which an electron beam radiated from the electron source is routed;an electron beam deflector disposed on the side of the electron source beyond the crystal thin film in order to change the angle of the electron beam incident on the crystal thin film;a specimen tilting system that adjusts the angle of the crystal specimen with respect to the optical axis of the electron microscope;an objective lens on which a diffracted electron beam scattered by the crystal thin film falls;an aperture system which is disposed on an opposite side of the objective lens relative to the electron source, which selects the diffracted electron beam, and whose position can be varied depending on the angle of the electron beam incident on the crystal thin film; andan observation device for use in observing a lattice image that results from interference of the selected diffracted wave and other wave and that is formed on an image plane of the objective lens, wherein:a crystal thin film whose lattice constants and structure are known is adopted as a specimen to be assessed,a contrast of crystal lattice fringes to be observed is measured in order to measure an information transfer limit of the transmission electron microscope,an electron beam is routed to the crystal thin film,two specific waves of the electron beam that are transmitted or diffracted are selected and used to form a lattice image, andwhile a condition for diffraction of an electron beam caused by the specimen and a condition for selection of the two transmitted or diffracted waves are held intact, the incident angle of the electron beam falling on the crystal thin film is changed in order to check a change in the contrast of formed crystal lattice fringes for the purpose of measuring an information transfer limit, and wherein:the incident angle of the electron beam is changed in order to fit the equation (7) below, which is a function encompassing a focal spread Δ that is an indeterminate constant, to a change in the contrast of lattice fringes derived from a change in the tilt angle α of the incident electron beam or in an associated wave number uα=α/λ,{tilde over (Φ)}(uθ)=exp(−8π2Δ2λ2uθ2uβ2) (7)the focal spread Δ that is an indeterminate constant is thus determined, andan information transfer limit dc is provided as the following equation (8): d c = πΔλ 2 ( 8 ) where uβ denotes a wave number (1/ddf) relevant to a distance ddf between adjoining ones of lattice fringes employed for measurement, and λ denotes the wavelength of the electron beam. 8. A transmission electron microscope comprising:an electron source generating a electron beam;an electron beam deflector between the electron source and a specimen in order to change an angle of the electron beam incident on the specimen;a specimen-holding device which supports the specimen and possesses mechanism to tilt the specimen;an objective lens on which a diffracted electron beam of the electron beam scattered by a crystal thin film falls;an aperture system positioned below the specimen to select specified transmitted or diffracted electron beams;an observation device to observe an image on an image plane of the objective lens that results from interference of the selected electron beams; anda control system which controls the specimen-tilt to keep the angle between the specimen and the electron beam incident to the specimen to be constant, and the aperture position to track the selected electron beams, while the angle of the electron beam incident to the specimen is changed,wherein when the specimen is a crystal thin film with known crystal structure and lattice constant, the angle of the electron beam incident on the specimen is changed in order to check a change in a contrast of formed crystal lattice fringes on the image plane for purpose of measuring an information transfer limit. 9. The transmission electron microscope according to claim 8, wherein the angle between the specimen and the electron beam incident to the specimen is an angle at which diffracted waves of the diffracted electron beam derived from the so-called Bragg diffraction are excited. |
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summary | ||
description | The contents of German patent application DE 10 2014 223 811.0 is incorporated by reference. In the event of conflict, the present specification controls. The invention relates to an imaging optical unit for EUV projection lithography. Furthermore, the invention relates to an optical system with such an imaging optical unit, a projection exposure apparatus with such an optical system, a production method for a microstructured or nanostructured component using such a projection exposure apparatus and a microstructured or nanostructured component produced therewith, in particular a semiconductor chip, for example a memory chip. An imaging optical unit for EUV projection lithography is known from US 2007/0 223 112 A1, U.S. Pat. No. 6,781,671, US 2010/0 149 509 A1, WO 2012/137 699 A1, US 2012/0069314 A1, EP 1 768 172 B1, WO 2004/046 771 A1 and U.S. Pat. No. 7,751,127. The configuration of a system stop for an imaging optical unit is known from U.S. Pat. No. 6,445,510 B1. It is an object of the disclosed technology to ensure a homogenization of an image-side numerical aperture using the imaging optical unit so that an unchanging high structure resolution in the image plane is made possible, independently of the field location and of an orientation of an image-side plane of incidence of the imaging light. In general, in a first aspect, the invention features an imaging optical unit for EUV projection lithography for imaging an object field in an object plane into an image field in an image plane, the imaging optical unit including a plurality of mirrors for guiding imaging light from the object field to the image field, and an aperture stop, which is tilted by at least 1° relative to a normal plane on which is perpendicular to an optical axis. The aperture stop is configured with a circular stop contour and is arranged in such a way that the following applies to mutually perpendicular planes: a deviation of a numerical aperture NAx measured in one of these planes from a numerical aperture NAy measured in the other one of these two planes is less than 0.003, averaged over the field points of the image field. A tilt of the aperture stop in relation to the normal plane which is perpendicular to the optical axis constitutes a previously unused degree of freedom for homogenizing the image-side numerical aperture. By means of such a tilted aperture stop, it is possible, in particular, to set the maximum illumination angle for an image point in the image field virtually independently of the direction of incidence and the image point position in the image field. The tilt renders it possible to variably predetermine the maximum illumination angle in a variation plane perpendicular to the tilt axis of the aperture stop by way of the respective tilt angle, independently of a plane perpendicular thereto containing the tilt axis. Hence, tilting the aperture stop relative to the normal plane ensures a change in a width corresponding to the projection of the diameter of the aperture stop in the normal plane in one of two dimensions spanning the aperture stop and hence a change in the numerical aperture predetermined by way of the width in this plane. This degree of freedom of a tilt of the aperture stop relative to the normal plane enables a homogenization of the numerical apertures, in particular in the case of off-axis fields and/or in the case of e.g. axial fields with an aspect ratio differing from 1, and therefore enables an equalization of a maximum angle of incidence, independently of the direction of incidence. Therefore, the illumination angle is defined by way of two angle coordinates, namely one angle which characterizes the illumination direction in the respectively present plane of incidence and a second angle which characterizes an azimuth orientation of the image-side plane of incidence. The homogenization of the numerical apertures NAx, NAy for the two mutually perpendicular planes, which are spanned by the z-axis parallel to the optical axis and an x-axis and by the z-axis and a y-axis lying in a meridional plane, is explained in detail in EP 1 768 172 B1 as an imaging parameter to be optimized. In order to characterize this homogenization, i.e. the deviation between the numerical apertures NAx and NAy, use can be made of the image field-side numerical aperture. The aperture stop with the circular edge can be manufactured in a cost-effective manner. A diameter of the circular aperture stop can have a variable configuration, for example in the style of an iris diaphragm. The diameter can be modifiable in a predetermined manner with the aid of an appropriate drive. The tilt of the circular aperture stop in relation to the normal plane on the optical axis has been found to be particularly suitable, for example for adapting the numerical aperture NAx and NAy. The optical axis is a common axis of rotational symmetry of the mirrors of the imaging optical unit. This assumes a configuration of the mirrors with rotationally symmetric reflection surfaces or with substantially rotationally symmetric reflection surfaces, i.e. apart from nano-asphere corrections. Such a configuration of the mirrors is not mandatory for all mirrors of the imaging optical unit. To the extent that mirrors with non-rotationally symmetric reflection surfaces are used in the imaging optical unit, the optical axis is understood to mean a reference axis which is defined by the remaining rotationally symmetric mirrors or by rotationally symmetric reference surfaces with the best fit to the non-rotationally symmetric reflection surfaces. In addition to homogenization of the numerical aperture, the tilt of the circular stop can also lead to an improvement of the telecentricity and/or ellipticity and/or trefoil imaging parameters. As a result of the homogenization, the deviation of the numerical aperture NAx from the numerical aperture NAy, averaged over the field points of the image field, can be less than 0.003, less than 0.001, less than 0.0005 or e.g. 0.0002. An even smaller deviation in the region of 0.0001 is also possible. The deviation can be 0.00001. Strictly speaking, the homogenization of the numerical apertures NAx and NAy over all field points in an image field, explained above, only relates to planes in the x-direction or y-direction. In particular, such a homogenization is advantageous for imaging H-lines or V-lines, i.e. for lines of an object structure to be imaged which extend parallel to the x-axis or parallel to the y-axis. The homogenization can also apply to different planes of incidence with arbitrary azimuth angles, i.e. to planes of incidence which have a finite angle in relation to the xz-plane of incidence or in relation to the yz-plane of incidence. Such a homogenization, even for planes of incidence tilted correspondingly in relation to the xz-plane or yz-plane, can be implemented, in particular, if structures which extend in the direction of a corresponding azimuth angle or perpendicular thereto are imaged. In some embodiments, a stop arrangement departs from the prescription of an arrangement of the stop plane in a manner coinciding with crossing points of individual imaging rays assigned to fixed illumination directions of various field points. It was found that an arrangement of the tilted circular aperture stop departing from the arrangement in the coma plane or the arrangement in a chief ray crossing plane can lead to a further improvement of imaging parameters. A corresponding statement applies to a decentration of the arrangement of the aperture stop. In order to define the coma plane and the chief ray crossing plane, the coma rays used in this document are defined below. Here, a distinction is made between free coma rays and bounding coma rays. Here, free coma rays are the rays which are transferred with maximum aperture from an off-axis article point or object point in an article plane or else object plane to an image point in the image plane by means of the imaging optical unit, with the rays intersecting at the image point also having a maximum aperture. Here, the maximum aperture of the rays intersecting at the image point, the aperture NA, is predetermined as nominal variable or setpoint value for the imaging optical unit, with, initially, no aperture stop limiting the setpoint value of the numerical aperture NA. The free coma rays are established by virtue of a telecentric centroid ray profile being assumed for each image point for the imaging beams of the image points in the image plane. Using these conditions of numerical aperture NA and telecentricity, an imaging beam to the associated object point is established for each image point, proceeding from the image points in the image plane against the projection direction of the imaging optical unit in the direction of the object plane. The rays bounding this imaging beam are referred to as free coma rays or, more simply, as coma rays below. If the coma rays are bounded by a stop—an aperture stop—the rays which just pass the edge of the stop are also referred to as bounding coma rays. The free coma rays of different article points or image points intersect along a three-dimensional intersection line, which virtually form a circle for paraxial image points, with all free coma rays of the image points approximately extending through this circle. For off-axis image points, a closed three-dimensional intersection line emerges for respectively two image points, along which three-dimensional intersection lines the free coma rays intersect, with this intersection line usually varying with the considered image points. The imaging beams of all image points of the image field provide a waist region of the imaging beam from the sum of the intersection lines. This waist region is generally referred to as a pupil. A coma plane for two image points emerges as a plane with the best fit to the sum of the intersection lines. In order to determine this plane with the best fit, i.e. in order to determine the coma plane, the three-dimensional intersection line can be averaged in such a way that the integral of the squared perpendicular distances of the intersection line along this line on the coma plane is minimal. Alternatively, it is also possible to use the distance or the magnitude of the distance for minimization when determining the coma plane. If more than two image points are considered, the coma plane emerges as that plane in which the sum of all integrals of the aforementioned type becomes minimal over all intersection lines. Below, the coma plane is also referred to as pupil plane. Below, a distinction is made between chief ray plane and chief ray crossing plane. The chief ray plane emerges as a plane perpendicular to the optical axis, which extends through the intersection point of a chief ray of an off-axis object point with the optical axis. For paraxial object points, the chief ray is virtually identical to the centroid ray of the imaging light beam, which transfers the object point in an object plane into an image point in an image plane with the maximum aperture angle by means of the imaging optical unit. Here, the chief ray of the imaging light beam can initially extend parallel to the optical axis as far as the first mirror. Likewise, the chief ray can also extend parallel to the optical axis after the last mirror of the imaging optical unit. For off-axis object points, the chief ray can deviate from the centroid ray. Furthermore, different intersection points of the chief rays emanating from these object points with the optical axis emerge for different object points. The chief ray plane is defined as the plane with the best fit in relation to these intersection points that is vertical to the optical axis. The chief ray plane is that plane perpendicular to the optical axis for which the integral of the squared distance of a chief ray intersection point from the plane becomes minimal, wherein the integral is to be formed over all intersection points of chief rays of field points of an object field with the optical axis. The chief ray plane is also referred to as paraxial pupil plane. The centroid ray is that imaging ray in a light beam which transfers an object point in the object plane into an image point in an image field plane by means of the imaging optical unit, which centroid ray extends through the energy-weighted centre in a plane perpendicular to the direction of propagation thereof, which centre emerges by integrating the light intensities of the aforementioned light beam in this plane. The chief ray crossing plane is a plane parallel to the coma plane. The chief ray crossing plane in this case extends through the region in which all chief rays of the imaging beams assigned to the image points under the aforementioned conditions of NA setpoint value and the image-side telecentricity intersect, or in which the sum of these imaging beams has the narrowest cross section thereof. That is to say, the chief ray crossing plane is tilted about the intersection point of the chief ray plane with the optical axis, determined like above by averaging, in such a way that it extends parallel to the coma plane. Both the free coma rays and the chief rays constitute an ideal case in the following figures. There, boundary or free coma rays or centre rays or chief rays for beams which extends exactly in a telecentric manner for all field points are shown. Moreover, these rays extend in the image plane with a predetermined numerical aperture of the imaging optical unit. An orientation of a tilt axis for the aperture stop relative to an object displacement direction was found to be particularly suitable. An object displacement drive can be provided for displacing the object through the object field along the object displacement direction. Certain values of the tilt angles of the aperture stopwere found to be particularly suitable for achieving the object of good homogenization of the numerical aperture. The tilt angle can be at least 2.5°, can be at least 3° or else can be even larger. The tilt angle can be smaller and can be 1.1°. The tilt angle can be 8.6°. The tilt angle can be 13°. The tilt angle can lie in the range between 5° and 15°. The tilt angle can lie in the range between 1° and 3°. Certain orientations of a tilt relative to the angle of the optical axis relative to the chief ray of the central field point were found to be suitable for improving imaging parameters, depending on the design of the imaging optical unit. What emerged unexpectedly here is that in fact both orientations can bring about an improvement, depending on the design of the imaging optical unit. A planar stop configuration can likewise be manufactured in a cost-effective manner. Alternatively, the aperture stop can be designed in such a way that it follows the form of a pupil of the imaging optical unit, which may deviate from the planar design, in three dimensions. A configuration of at least one mirror of the imaging optical unit as a free-form surface increases the degrees of freedom for the imaging optical unit. All mirrors of the imaging optical unit can be configured as free-form surfaces. Examples of free-form surface designs which can be used within projection optical unit designs are found in WO 2013/174 686 A1 and the references cited there. In some embodiments, a drive increases the adaptation possibilities for the imaging optical unit. The image-side numerical aperture can be predetermined exactly and with a sufficient number of degrees of freedom by way of the tilt drive and the optionally likewise present drive for setting the stop diameter. Further aspects of the technology relate to the improvement of imaging parameters of an imaging optical unit when instead of using a titled circular stop, an elliptical stop is used, which is displaced along a reference axis, which may be the optical axis, or perpendicular thereto, in particular parallel to an object displacement direction, for the purposes of optimizing parameters. These further aspects can be combined with the features explained above. Imaging optical units of the first aspect may be incorporated in an optical system for a projection exposure apparatus, used in production of microstructured or nanostructured components. Exemplary embodiments are explained in more detail below. A projection exposure apparatus 1 for microlithography includes a light source 2 for illumination light or imaging light 3. The light source 2 is an EUV light source, which generates light in a wavelength range of e.g. between 5 nm and 30 nm, in particular between 5 nm and 15 nm. In particular, the light source 2 can be a light source with a wavelength of 13.5 nm or a light source with a wavelength of 6.9 nm. Other EUV wavelengths are also possible. A beam path of the illumination light 3 is depicted very schematically in FIG. 1. An illumination optical unit 6 serves to guide the illumination light 3 from the light source 2 to an object field 4 in an object plane 5. Using a projection optical unit or imaging optical unit 7, the object field 4 is imaged into an image field 8 in an image plane 9 with a predetermined reduction scale. The projection optical unit 7 according to FIG. 2 for example has a reduction by a factor of 4. Other reduction scales are also possible, e.g. 5×, 6×, or 8×, or else reduction scales with a magnitude greater than 8× or with a magnitude smaller than 4×, e.g. 2× or 1×. In the projection optical unit 7, the image plane 9 is arranged parallel to the object plane 5. A portion of a reflection mask 10, which is also referred to as reticle, coinciding with the object field 4 is imaged in this case. The reticle is supported by a reticle holder 11 depicted schematically in FIG. 1, which is displaceable by way of a reticle displacement drive 12, which is likewise depicted in a schematic manner. The imaging by the projection optical unit 7 is implemented onto the surface of a substrate 13 in the form of a wafer, which is supported by a wafer holder or a substrate holder 14. The wafer holder 14 is displaced by way of a wafer displacement drive 15, which is likewise depicted schematically in FIG. 1. Between the reticle 10 and the projection optical unit 7, FIG. 1 schematically depicts a beam 15a of the illumination light 3 entering therebetween and, between the projection optical unit 7 and the substrate 13, a beam 15b of the illumination light 3 exiting from the projection optical unit 7. The illumination light 3 imaged by the projection optical unit 7 is also referred to as imaging light. The imaging rays 15b at the edge, which are incident on the image field 8, are imaging rays which ideally belong to the same absolute illumination angles of the illumination of the image field 8. The maximum angle of the exiting beam 15b in relation to the optical axis is a polar angle Θ. Θ therefore is the angle of incidence in a plane of incidence, which has an optical axis oA and a coma ray of the beam 15b. Θ ideally does not depend on the azimuth angle about the optical axis oA, i.e. on the direction of the plane of incidence. In reality, the angle of incidence Θ is a function of an azimuth angle in the image plane 9. The numerical aperture, and hence the variable determining the resolution capability of the imaging optical unit, for example of the projection lens according to FIG. 1, emerges as NA=n*sin Θ, which is a function of the azimuth angle in the image plane 9, particularly when imaging off-axis image points or an off-axis image field 8, i.e. NA[azimuth]=n*sin [Θ (azimuth)]. Here, n is the refractive index of the medium through which the exiting beam 15b propagates. By way of example, an image field-side numerical aperture of the projection optical unit 7 in the embodiment according to FIG. 2 is 0.26. This is not reproduced true to scale in FIG. 1. The image field-side numerical aperture can for example lie in the range between 0.2 and 0.7, depending on the embodiment of the projection optical unit 7. In order to facilitate the description of the projection exposure apparatus 1 and the projection optical unit 7, a Cartesian xyz-coordinate system is indicated in the drawing, from which system the respective positional relationship of the components illustrated in the figures is evident. In FIG. 1, the x-direction runs perpendicular to the plane of the drawing into the latter. The y-direction runs toward the right and the z-direction runs downward. The projection exposure apparatus 1 is of the scanner type. Both the reticle 10 and the substrate 13 are scanned in an object displacement direction parallel to the y-direction by a synchronized displacement by way of the displacement drives 12 and 15 during the operation of the projection exposure apparatus 1. A stepper type of the projection exposure apparatus 1, in which a stepwise displacement of the reticle 10 and of the substrate 13 in the y-direction takes place between individual exposures of the substrate 13, is also possible. Both the object plane 5 and the image plane 9 respectively extend parallel to the xy-plane. FIG. 1 depicts very schematically part of a beam path of the imaging light 3 between the object field 4 and the image field 8. What is shown is the beam path of a chief ray 16 of a central field point of the projection optical unit 7 routed over reflections at four mirrors M1, M2, M3 and M4 of the projection optical unit 7. This beam profile is merely indicated very schematically in FIG. 1 in order to sketch out the region around an aperture stop 18 which is still to be explained below. In addition to the mirrors M1 to M4, the projection optical unit 7 can have further mirrors and, for example, can have a total of six, eight or ten mirrors M1, . . . . The location, size and tilt of the mirrors M1 to M4 are merely shown schematically in FIG. 1 for indicating the beam path of the imaging light 3, which generally has a different detailed route. At least one of the mirrors M1, M2, . . . can have a reflection surface that is embodied as a free-form surface. The chief ray 16 crosses the optical axis oA of the projection optical unit 7 in the beam path between the mirrors M2 and M3, wherein, for example, the mirror M1 is the first mirror of the projection lens 7 in the beam path downstream of the reticle 10. The optical axis oA constitutes a reference axis, on the basis of which a mathematical representation of the optically used surfaces of the mirrors M1, M2, . . . of the projection optical unit 7 is possible. In particular, the reference axis can be an axis of rotational symmetry of these optical surfaces. The reference axis can lie in a symmetry plane of the imaging optical unit 7. A crossing point of the chief ray 16 with the optical axis oA lies in a pupil plane 17 of the projection optical unit 7 in the case of paraxial imaging. In order to distinguish this pupil plane 17 from the pupil plane defined at the outset by the coma plane, it is denoted as paraxial pupil or paraxial pupil plane below. The optical axis oA is perpendicular to a normal plane, which may coincide with the paraxial pupil plane 17, which is why the reference sign 17 is also used for the normal plane below. The aperture stop 18 of the projection optical unit 7 is arranged in the region of this crossing point of the optical axis oA with the beam path of the chief ray 16 between the mirrors M2 and M3. The aperture stop 18 is configured as a planar stop. This aperture stop 18 serves to predetermine a homogenized image-side numerical aperture NA such that the image-side numerical apertures NAx perpendicular to the plane of the drawing of FIG. 1 and NAy in the plane of the drawing of FIG. 1 are as equal as possible for all image points, i.e. NAx=NAy should be satisfied to the best possible extent. It is possible to achieve homogenization of the numerical aperture in the case of a typical numerical aperture NA of 0.25, in which the values between NAx and NAy of this numerical aperture NA vary by no more than 0.0025. An image-side numerical aperture shown in the plane of the drawing of FIG. 1 corresponds to the value NAy, since the numerical aperture in the yz-plane is depicted here. An image-side numerical aperture NAx emerges in the xz-plane perpendicular thereto. FIG. 2 elucidates an actual course of imaging rays in the imaging optical unit 7 between the object field 4 and the image field 8, which both lie at a distance from the optical axis oA, i.e. constitute off-axis fields. What is shown in FIG. 2 is the course of individual rays 24 of the imaging light 3, which belong to five field points spaced apart from one another along the y-axis, wherein respectively one chief ray 16 and coma rays 19, 20 emanate from each one of these field points. As mentioned above, the chief rays and (free) coma rays for the ideal case of a setpoint aperture NA=0.25 are depicted in this case, with the beams forming an image point extending telecentrically in the image plane 9. The basic design and the optical design data of the imaging optical unit 7 according to FIG. 2 are known from EP 1 768 172 B1, apart from the exact course of the imaging rays and, even more critically, the configuration and arrangement of the aperture stop 18. The optical axis oA of the imaging optical unit 7 is the axis of rotational symmetry of the description of the surface of mirror surfaces of the mirrors M1 to M6 of the imaging optical unit 7. FIG. 3 shows details in respect of the precise arrangement of the aperture stop 18, which is arranged in a stop plane 25. Here, the section III from FIG. 2 is depicted in a magnified manner. The calculation of the beam paths depicted in FIG. 2 and FIG. 3 (and also for the following figures which show the course of imaging beams) was initially carried out without a stop and with a constant numerical aperture NAx=NAy=0.25 for the depicted image points in order initially to depict the ray route of the beams without a stop in the case of these aperture and telecentricity conditions. After inserting the real stop 18, the latter modifies the beams extending through the imaging optical unit 7 in such a way that these intersect in the region of the edge of the stop; this has not been depicted so as to provide a better overview. Unlike in the configuration according to EP 1 768 172 B1, the aperture stop 18 has a circular configuration with a diameter of 66.254 mm. In relation to the normal plane 17 on the optical axis oA, the stop plane 25 is tilted by a tilt angle α0, the magnitude of which in the embodiment according to FIG. 2 and FIG. 3 is approximately 13°. This tilt is implemented about a tilt axis 26. The tilt axis 26 is perpendicular to the yz-plane, i.e. perpendicular to a tilt normal plane 27, which contains the object displacement direction y and in relation to which the field planes, i.e. the object plane 5 and the image plane 9, are perpendicular. The tilt normal plane 27 coincides with the meridional plane of the imaging optical unit 7. In principle, other magnitudes of the tilt angle α0 in the region of between 10° and 16° are also possible and can lead to an imaging performance of the projection optical unit that is improved over EP 1 768 172 B1, as will still be explained in conjunction with the example in FIGS. 6 to 9. This tilt about the tilt axis 26 through the tilt angle α0 is brought about in an anticlockwise direction in the orientation of FIG. 3. In the embodiment according to FIGS. 2 and 3, the tilt of the circular aperture stop 18 is such that an angle co of a stop normal NAB in relation to a chief ray 16z of a central field point is reduced in comparison with the angle γ0 of the optical axis oA in relation to this chief ray 16z of the central field point. In this case, α0<0. ε0=γ0+α0 applies. The angle γ0 simultaneously is the angle between a normal plane s (cf. the subsequent FIG. 4) in relation to the chief ray 16 and the stop plane 25. Within this meaning, the circular aperture stop 18 is thus tilted relative to the overall beam of the imaging light 3 in such a way that a projection of an area bounded by the aperture stop 18, as seen in the direction of the beam profile of this beam of the imaging light 3, is enlarged compared to a positioning of the circular aperture stop 18 perpendicular to the optical axis oA. For the purposes of a more detailed explanation of the tilt angle situation for a tilted circular aperture stop, FIG. 4 shows, in a schematic manner and in extracts, a light beam 3 through an imaging optical unit, e.g. a projection lens, which images an object point into an image point, in a region in which a chief ray 16 intersects the optical axis oA which extends along a z-axis. Depicted are an upper coma ray 19, a lower coma ray 20 and the chief ray 16 of the light beam 3 in a yz-plane, which forms a meridional plane of the optical unit. The light beam 3 has a radius s in the depicted projection. The latter emerges from the distance between the upper coma ray 19 and the intersection point of the chief ray 16 with the optical axis oA, wherein the distance s is measured perpendicular to the chief ray 16 and wherein the chief ray 16 intersects the optical axis under the angle γ. A plane perpendicular to the optical axis oA through this intersection point of chief ray 16 and optical axis oA is denoted as paraxial pupil plane 17, as described above. The paraxial pupil plane 17 intersects the upper coma ray 19 in such a way that a distance ry emerges in the y-direction perpendicular to the optical axis oA, wherein this direction e.g. corresponds to the object displacement direction in the case of a projection lens. A stop perpendicular to the optical axis oA with this radius ry in the y-direction would bound the light beam 3 in the depicted manner. The paraxial pupil plane 17 and a plane 17a perpendicular to the chief ray through the intersection point between the chief ray 16 and the optical axis oA are tilted against one another by the angle γ. In the case where the upper coma ray 19 and the chief ray 16 extend parallel to one another, the upper coma ray 19 is also perpendicular to the radius s. A radius s′ of the light beam 3 in the direction of the lower coma ray 20 is generally different from the above-described radius s in the direction of the upper coma ray 19. If the light beam 3 has a radius rx that differs from s in the x-direction (direction perpendicular to the plane of the drawing), which radius equals the distance of the coma ray, not depicted in this direction, from the intersection point of the chief ray and the optical axis in the x-direction, wherein this distance is once again determined perpendicular to the chief ray 16, the light beam cross section differs from the circular form. If rx is greater than s, the light beam depicted in FIG. 4 can be bounded by means of a circular planar stop with a radius rx if the latter is rotated or tilted about an axis of rotation 26 parallel to the x-axis through the intersection point between the chief ray 16 and the optical axis oA, through an angle α in relation to the paraxial pupil plane 17, which extends through said intersection point. If rx is greater than ry in this case, a is greater than zero. The circular stop 18 is therefore tilted in the anticlockwise direction compared with the location of the stop perpendicular to the optical axis oA in FIG. 4. With the angle ε, introduced in the context of FIG. 3, for the angle of the stop normal in relation to the chief ray 16, which has an angle γ relative to the optical axis, ε=γ+α applies, with α>0. By contrast, if rx were smaller than ry, i.e. in a case not depicted in FIG. 4, a is less than zero. In this case, the relationship ε=γ+α also applies, with α<0. This case was explained above in conjunction with FIG. 3. The following relationships: cos (γ)=s/ry; cos(γ+α)=s/rx emerge from FIG. 4, as result of which ry/rx=cos(γ+α)/cos(γ) emerges. Using this, it is possible to establish the tilt angle α in the case of a predetermined diameter rx of the circular stop and a predetermined distance value ry. It is mentioned that the light beam depicted in FIG. 4 cannot be bounded by a tilted circular planar stop in such a way that a setpoint value for the numerical aperture in the x-direction and y-direction is to be approximately equal, as averaged over all field point of the image field, for an imaging optical unit with a light beam 3 where rx is less than s. However, in this case, the stop can be approximated by an elliptic stop, the semi-minor axis of which perpendicular to the meridional plane points in the direction of the axis of rotation which extends through the intersection point of chief ray HS and optical axis oA. By way of example, this direction is perpendicular to the optical axis and perpendicular to the object displacement direction in the case of a lithographic projection lens. The semi-major axis of the elliptic stop is determined by the tilt angle γ and the spacing of the coma rays 19, 20 to be observed. This semi-major axis emerges, for example, by optimizing the image-side telecentricity and the image-side numerical apertures NAx and NAy, which should be as equal as possible for all image points. It should be mentioned that the centre point of the tilted circular stop 18, or, in accordance with a further aspect, of the elliptic tilted stop 18 can be displaced from the above-described axis of rotation or tilt axis by e.g. up to ±2 mm in the direction of the optical axis oA, i.e. in the z-direction. Using this it is possible, in particular, to optimize an x-telecentricity, as will still be shown on the basis of the following exemplary embodiments. Furthermore, a centre point or centre of these stops 18 in the y direction, i.e. in the object displacement direction, can be displaced by e.g. ±1 mm. By way of this displacement, it is possible, in particular, to optimize a y-telecentricity, which will likewise still be shown below. A mean numerical aperture of NAy_av=0.24297 emerges for the projection lens described in EP 1 768 172 B1 for a non-tilted, circular aperture stop with a diameter of rx=66.254 mm, which is arranged parallel to the object displacement direction, i.e. perpendicular to the optical axis oA. The mean numerical aperture in the x-direction is NAx_av=0.24952, and so a mean deviation of NAx_av−NAy_av=0.00655 emerges. A mean numerical aperture of NAy_av=0.25058 emerges when use is made of the elliptic stop depicted in EP 1 768 172 B1, which has a semi-major axis in the object displacement direction of ry=68.348 mm and a semi-minor axis perpendicular to the optical axis and perpendicular to the object displacement direction of rx=66.254 mm, hence resulting in a ratio of ry/rx=1.032. The mean numerical aperture in the x-direction in this case is also NAx_av=0.24952, and so a mean deviation of NAx_av−NAy_av=0.00106 emerges. This is an improvement by approximately a factor of 6 compared to the first mentioned, non-tilted circular stop. If the planar circular stop is tilted by approximately −13°, as depicted in FIGS. 2 and 3, a mean numerical aperture of NAy_av=0.24889 is obtained in the case of a tilt angle of −12.9°. Here, the mean numerical aperture in the x-direction is NAx_av=0.24984, and so a mean deviation of NAx_av−NAy_av=0.00095 emerges, constituting an improvement in the mean deviation of the numerical aperture by approximately a factor of 7 compared to the first mentioned, non-tilted circular stop. Here, the diameter of the tilted, planar and circular stop 18 was optimized to 66.366 mm. Furthermore, the centre Z of the stop was displaced in this case by the value of 1.216 mm along the optical axis oA for optimizing the telecentricity. In addition to this optimization of the telecentricity, there additionally was a displacement of the centre Z by 0.270 mm perpendicular to the optical axis oA in the y-direction. Using the optimized tilt angle of α=−12.9°, ry/rx=cos(γ+α)/cos(γ)=1.026 emerges. This example shows that the mean deviations of the numerical aperture for the image points can be further improved by means of the tilted and circular stop 18 with the planar embodiment in view of the deviations when using an elliptical stop described in EP 1 768 172 B1. It should also be particularly highlighted that the telecentricity for the lens described in EP 1 768 172 B1 can be significantly improved by means of a tilted circular stop. The aforementioned data for the stop geometry and the numerical apertures were established over sixty-five field points distributed over the image field 8. As explained in the context of FIG. 4, the numerical aperture of the individual image points in the image field 8 can be optimized by tilting the planar aperture stop 18 about an axis perpendicular to the object displacement direction and perpendicular to the optical axis oA. Here, the numerical aperture NA for an image point in general is a function of the azimuth angle at the relevant image point in the image plane, which is why (as shown above) NA(azimuth)=n*sin [Θ(azimuth)] applies for an image point. By means of the tilt angle α, about which the planar aperture stop 18 is tilted relative to the paraxial pupil plane, it is possible to optimize the numerical aperture for predetermined, but generally arbitrary azimuth angles. The above-described optimization such that the image-side numerical apertures NAx and NAy should be as equal as possible for all image field points corresponds to an azimuth angle=0° for NAx and an azimuth angle=90° for NAy. Such an optimization results in a tilt angle α. Alternatively, the numerical aperture of all image points can also e.g. be optimized to azimuth angles which respectively correspond to the maximum NAazimuth,max and minimum aperture NAazimuth,min for the respective image point such that the image-side numerical apertures NAazimuth,max and NAazimuth,min should be as equal as possible for all image points. A tilt angle α1 optimized thus generally differs from the tilt angle α, in which the image-side numerical apertures NAx and NAy are as equal as possible for all image points. Optimizations of the tilt angle of the planar stop are also possible such that the image-side numerical apertures NAazimuth should be as equal as possible for all image points, wherein this should then apply to a predetermined, fixed azimuth angle of e.g. 45°. Such an optimization of the tilt angle of a planar stop is advantageous if, for example, structures which extend under 45° in relation to the object displacement direction are imaged by the imaging optical unit. As mentioned, it is generally possible for the centre Z or the centre point of the stop to be displaced along the z-axis, i.e. along the optical axis. Displacements perpendicular to the optical axis in the y-direction (object displacement direction) are also possible, as was described in the example above of the tilted circular stop in a projection lens according to EP 1 768 172 B1. These displacements serve for the further optimization of the imaging properties, in particular for optimizing the telecentricity. For the further optimization, displacements of the stop centre point in the x-direction (perpendicular to the object displacement direction) are also possible. Therefore, a centre Z of the aperture stop 18 from FIG. 3 can for example be at a distance from the intersection point of the stop plane 25 with the optical axis oA, i.e. it is, in particular, at a distance from the optical axis oA. Depicted additionally in FIG. 3 is a coma plane 28, in which the coma rays 19, 20 from spaced apart field points intersect. This coma plane 28 is likewise perpendicular to the tilt-normal plane 27, i.e. perpendicular to the yz-plane. The stop plane 25 of the aperture stop 18 is tilted by an angle δ0≠0 in relation to this coma plane 28. In the shown exemplary embodiment, the coma plane 28 is approximately perpendicular to the chief ray 16z of the central field point. δ0=γ0−α0 applies approximately. In FIG. 3, a chief ray crossing plane 29, in which the chief rays 16 from spaced apart field points intersect, extends parallel to the coma plane 28. The stop plane 25 is also tilted by approximately the angle δ0 in relation to the chief ray crossing plane 29. The pupil plane of the projection optical unit 7 lies in the region of the planes 28, 29. The crossing points 28a, 28b of the coma rays 19, 20 on the one hand and 29a of the chief rays 16 on the other hand are at a distance from the aperture stop 18. The aperture stop optionally has a functional connection to a tilt drive 18a, to which the aperture stop 18 is connected for the tilt about the tilt axis 26. In particular, a step-free tilt of the aperture stop 18 is possible by way of the tilt drive 18a. The tilt drive 18a can be connected to a sensor arrangement, not depicted in any more detail in the drawing, for measuring the image-side numerical apertures NAx, NAy or NAazimuth (for one or more predetermined azimuth angles), wherein a tilt setpoint value can be calculated from the measurement result in a regulation unit (which is likewise not depicted here) and this setpoint value can be fed by way of an appropriate signal connection to the tilt drive 18a for regulated readjustment of a tilt actual value and hence of the value for the image-side numerical aperture, in particular NAy. Thus, the yz-plane constitutes a variation plane for the image-side numerical aperture. The scanning direction y lies in this variation plane. Imaging properties of the projection optical unit 7 with the circular aperture stop 18 arranged in the aperture plane 25 are discussed below on the basis of FIGS. 5 to 9. FIG. 5 schematically elucidates a procedure of a numerical evaluation of an imaging parameterization used here. FIG. 5 depicts a top view of the image field 8 (from FIG. 1) of the imaging optical unit 7 for an object field 4 (from FIG. 1), which may have an arcuate embodiment, assigned to this image field. In the numerical evaluation, a total of thirty-five field points FP are considered on the image field 8. Here, field points FP are selected which are lined up in one half of the image field 8 in a manner spaced apart equidistantly along the y-direction in a total of seven field point columns 301 to 307. The five field points FP which are lined up along the field point column 303 are schematically arranged in FIG. 5. Here, the field points FP are numbered in sequence, starting with the field point FP in the column 301 with the smallest y-coordinate and finishing with the field point FP35 in the column 307 with the largest y-coordinate. A Fourier expansion of a distribution of a numerical aperture NA for each one of the field points FP of the image field 8 is calculated for these thirty-five field points FP, taking into account the optical design data of the imaging optical unit 7. Here, a calculation over the field points FP covering half of the image field 8 is sufficient. To this end, individual rays 24 (see e.g. FIGS. 1 and 2) of the imaging light 3 are targeted onto the stop boundary of the circular aperture stop 18 (or, in general, of a stop situated in the imaging optical unit) against the projection direction, proceeding from each one of the thirty-five image field points FP. Examples of such numerical apertures NAi (with iε{1, 2, 3, . . . 35}) not yet optimized in respect of the tilt angle are indicated in FIG. 5 for the respective upper-most image field points FP of the field point columns 301 and 307. These numerical apertures NAi can be understood as a boundary of sub-beams of the imaging light 3, which just still pass through the aperture stop 18 starting from these image field points (against the actual beam direction of the imaging light 3) or these sub-beams describe the numerical aperture NAi emerging for an image point i due to the stop. For the purposes of optimizing a tilt location of the aperture stop 18, the stop boundary of the aperture stop 18 is scanned equidistantly over the circumference thereof. Then the respective direction cosines kx and ky in the associated image point in the image field 8 are determined for each one of these individual rays 24. This value is then converted into polar coordinates k and φ. The Fourier expansion then enables access to the deviations of the resulting numerical aperture for each one of the image field points FP from a numerical aperture constant over all illumination directions of the respective field point. FIG. 5 depicts, by way of NA7(φ) and NA35(φ), the distributions of the numerical aperture as a function of the azimuth angle φ for the image field points FP7 and FP35. Field points distributed over the whole image field 8 can be used for calculating NA. In general, the Fourier expansion can be written as: N A ( φ ) = NA 0 + ∑ L = 1 N [ a L cos L φ + b L sin L φ ] Here, NA0 is a constant contribution, φ is the azimuth angle in the image field plane in relation to an image point and aL, bL are expansion coefficients of the Fourier expansion. Leading expansion terms of this Fourier expansion can be written asNA(φ)=NA0+a1 cos φ+b1 sin φ+a2 cos 2φ+b2 sin 2φ+a3 cos 3φ+b3 sin 3φ+ . . . . These leading terms are: NA0: constant contribution of the numerical aperture independent of the azimuth (effective NA); a1: telecentricity in the x-direction; b1: telecentricity in the y-direction; √{square root over (a22+b22)}: ellipticity √{square root over (a32+b32)}: trefoil FIGS. 6 to 9 provide results of this Fourier expansion. Here, the expansion terms of the Fourier expansion are depicted up to the 3rd order for a circular stop, which is arranged in the projection optical unit described in EP 1 768 172 B1. Here, this circular stop is tilted by an angle of −13°, as was described in conjunction with FIG. 3. The stop diameter in this case is 66.254 mm. The crossing point, e.g. of the central chief ray 16z with the optical axis oA, therefore lies in the stop plane 25. FIG. 6 shows the respective first expansion term NA0 for the thirty-five field points FP. What emerges is a sawtooth-like profile, which shows that the first coefficient of the Fourier series NA0 above substantially decreases from the inner image field edge to the outer image edge in the direction of the object displacement (scanning direction). For elucidation purposes, FIG. 6 indicates an assignment of the depicted NA0 curve to individual field point columns 301, 304 and 307. The effective numerical aperture NA0 only varies very little between the values of approximately 0.2484 and 0.2496 over all thirty-five field points FP. A mean value of the numerical aperture in the xz-plane, NAx,average, emerges as 0.24954. A corresponding mean value in the yz-plane, NAy,average, emerges as 0.24867. The difference between these two mean values, which are averaged over all thirty-five field points, is 0.00087, i.e. it is less than 0.001. FIG. 7 shows the variation of the x-telecentricity and y-telecentricity telecentricity values for the field points FP1 to FP35. For the x-telecentricity telecentricity value, slightly decreasing values to a value of approximately −2 mrad emerge over these thirty-five field points, starting from a value of 0. The y-telecentricity telecentricity values vary between values of −2 mrad and −5 mrad. The y-telecentricity telecentricity values once again vary in a stepped manner, comparable with the variation of the effective numerical aperture NA0 according to FIG. 6. Here, the telecentricity specifies the angle of the centroid ray of the light beam, which extends through one of the image points FP1 to FP35, wherein the aforementioned circular stop, tilted by −13°, is arranged in the projection optical unit described in EP 1 768 172 B1 when imaging the image points. Here, the x-telecentricity is the direction cosine in the xz-plane and the y-telecentricity is the direction cosine in the yz-plane, wherein x, y and z in this case relate to a local coordinate system, the origin of which is at the considered image point, where z extends parallel to the optical axis, y extends parallel to the object displacement direction (scanning direction) and x extends perpendicular to the y-axis and z-axis. If x-telecentricity and y-telecentricity are zero for an image point, the centroid ray of the associated light beam associated with this image point is perpendicular to the image field plane 8. If the x-telecentricity is zero, the corresponding centroid ray extends in the yz-plane. Analogously, the centroid ray extends along the xz-plane when the y-telecentricity is zero. FIG. 8 shows the value of the ellipticity for the thirty-five image field points FP. The ellipticity describes the deviation of the aperture angle of a respective beam forming the respective image point by way of the inserted stop, e.g. the tilted circular stop, from the value NA0 in the direction of the main axes of the ellipse centred at the respective image point in an elliptic approximation. Here, FIG. 8 elucidates the variation of the numerical aperture along these ellipse coordinates and therefore differs from the numerical apertures in the x-direction and y-direction NAx, NAy for the corresponding image point, which is why, also, the corresponding mean values of these numerical apertures differ over the considered number of image points. Thus, in FIG. 8, the mean value over the depicted 35 field points is approximately 0.5*10−3. Averaging the numerical aperture NAx over the 35 image point yields NAx=0.24952 and approximately NAy=0.24867, from which a difference of 0.87*10−3 emerges. In practical terms, that type of averaging for optimizing the stop will be preferred which is best fitted to the structures to be imaged. By way of example, if horizontal and/or vertical structures are imaged, i.e. structures which are oriented in the direction of the x-axis and/or y-axis, an optimization of the aperture in view of NAy and/or NAx is to be preferred. If structures that are arranged at an angle not equal to 0° or 90° in relation to the x-axis and y-axis are imaged, an optimization according to FIG. 8 is to be preferred. FIG. 9 shows the variation of a further expansion term of the Fourier expansion of the numerical aperture, the so-called trefoil. This value varies between 0 and 1×10−4. The values for the ellipticity and the trefoil also vary in a stepped manner as a function of the evaluated field points FPi. Unlike the step-shaped variation of the effective numerical aperture NA0 according to FIG. 6 and of the y-telecentricity telecentricity value according to FIG. 7, the values within a respective field point column do not decrease, but slightly increase instead. FIGS. 10 to 13 depict the expansion terms of the aforementioned Fourier expansion for a further exemplary embodiment of the tilted circular stop 18, wherein the latter is displaced along the y-direction and along the z-direction, i.e. along the optical axis oA, in terms of the stop centre point Z thereof. The displacement in the y-direction or object displacement direction relative to the optical axis is 0.270 mm in this case, the displacement along the optical axis is 1.216 mm. The tilt angle is −12.95° and the post-optimized diameter is 66.366 mm. As a result of the shift in the y-direction, it is possible to see a significant improvement in the y-telecentricity (FIG. 11). Furthermore, an improvement in the x-telecentricity is achieved by a displacement along the optical axis (FIG. 11). In one exemplary embodiment of the tilted circular stop 18, the latter is only displaced along the y-direction but not along the z-direction in terms of the stop centre point Z thereof. The displacement in the y-direction or object displacement direction relative to the optical axis is 0.551 mm in this case. This y-displacement can lie in the range between 0.1 mm and 1.0 mm and, for example, can also be 0.2 mm, 0.25 mm, 0.27 mm or 0.3 mm. As mentioned above, no displacement was carried out along the optical axis. The tilt angle corresponds to that which was explained above in conjunction with FIGS. 10 to 13. A post-optimized stop diameter of the tilted and y-decentred circular stop 18 can correspond to that which was explained above in conjunction with FIGS. 10 to 13. Alternatively, the post-optimized diameter of the circular, y-decentred stop 18 can also have a different value, e.g. the value of 66.456 mm. What is found compared to the expansion terms described above in conjunction with FIGS. 6 to 9 is that the use of the “displacement in the y-direction” degree of freedom leads to a significant improvement in the y-telecentricity, the absolute magnitude of which at most reaches the value of 1.1 mrad over all measured field points. The additional use of the “displacement in the z-direction” degree of freedom described above in conjunction with FIGS. 10 to 13 then still leads to an improvement in the x-telecentricity. In absolute terms, a displacement in the z-direction is specified, proceeding from a location of a stop arrangement plane at the original design data, as mentioned in the respectively cited publications. Below, a further embodiment of an imaging optical unit 31 with the tilted, circular aperture stop 32, which can be used in the projection exposure apparatus 1 instead of the projection optical unit 7, is explained on the basis of FIGS. 14 to 19. Components and functions corresponding to those that were already explained above with reference to FIGS. 1 to 13 are provided with the same reference signs and are not discussed in detail again. In the meridional section according to FIG. 14, the individual rays 24 of three field points spaced apart from one another in the y-direction are depicted in the beam path of the imaging optical unit 31, with, once again, the chief rays 16 and the coma rays 19, 20 being shown for each one of these three field points. Apart from a configuration and arrangement of the aperture stop 32, the imaging optical unit 31 corresponds to the one according to FIG. 5a of US 2007/0 223 112 A1 with the associated description. FIG. 15 shows, in a sectional magnification, the arrangement of the once again circular aperture stop 32 of the imaging optical unit 31. The aperture stop 32 has a diameter of 51.729 mm. A diameter of 51.851 mm is also possible. The aperture stop 32 is tilted by an angle α0−1.3° about the tilt axis 26 in relation to the normal plane 17 on the optical axis oA. This tilt in relation to the normal plane 17 is brought about in the clockwise direction in the orientation according to FIGS. 14 and 15. The aperture stop 32 is tilted in such a way that the angle 130 of the stop normal NAB in relation to the chief ray 16z of the central field point is reduced compared to the angle γ0 of the optical axis oA in relation to the chief ray 16z of the central field point. ε0=γ0+α0 applies in the aperture stop 32. The coma plane 28 and the chief ray crossing plane 29 parallel thereto are once again plotted in FIG. 15. The stop plane 25 is tilted in relation to both planes. Crossing points 28a, 28b of the coma rays 19, 20 on the one hand and 29a of the chief rays 16 on the other hand are distant from the aperture stop 32. For the purposes of optimizing the y-telecentricity, a centre Z of the aperture stop 32 can be distant from the intersection point of the stop plane 25 with the optical axis oA, i.e., in particular, distant from the optical axis oA. The ideal distance in the y-direction is approximately 0.28 mm in this case for the exemplary embodiment according to FIG. 14. Furthermore, the centre of the stop can be displaced in the direction of the optical axis in relation to the chief ray plane such that there is also minimization of the x-telecentricity. A displacement value can lie in the region of 1.2 mm, but it can also, for example, be significantly larger and be e.g. 2.5 mm. FIGS. 16 to 19 show the dependence of the leading expansion terms of the Fourier expansion of the numerical aperture for the thirty-five field points FP for the circular stop tilted by −1.3° according to the exemplary embodiment according to FIG. 14 in accordance with what was already explained above in conjunction with FIGS. 6 to 9. In FIGS. 16 to 19, a tilted, circular stop, which is displaced in the y-direction and z-direction for optimizing the telecentricity, is used in the imaging optical unit 31 according to FIG. 5a of US 2007/0 223 112 A1. Here, the displacement in the y-direction is 0.28 mm and the displacement in the z-direction is 1.21 mm. The tilt angle α=−1.3°. The effective numerical aperture NA0 according to FIG. 16 varies between values of 0.2498 and 0.2501. Averaged over all thirty-five field points, a mean numerical aperture NAx,average of 0.25039 emerges in the xz-plane and a mean value NAy,average of 0.25060 emerges in the yz-plane. The difference of these mean values yields 0.00021. The x-telecentricity telecentricity value varies between the values of 0 mrad and −2 mrad and decreases monotonically between the field points FP1 and FP35. The y-telecentricity telecentricity value varies between the values of 1 mrad and −1 mrad. The ellipticity value varies between the values of 0 and 3×10−4. The trefoil value varies between the values of 2×10−5 and 3×10−5. The variations of NA0, of the telecentricity value of the y-telecentricity, of the ellipticity and of the trefoil once again have sawtooth structures for the respective field point columns 30i. In the exemplary embodiment depicted in FIG. 14, the ratio ry/rx=1.004, said ratio having been described in conjunction with FIG. 4. For the ideal tilt angle of the circular aperture stop, the ratio cos(γ+α)/cos(γ)=1.005, which has good correspondence with the ratio ry/rx=1.004. FIG. 20 is used below to explain a further embodiment of an imaging optical unit 33 with the tilted, circular aperture stop 34, which can be used in the projection exposure apparatus 1 instead of the projection optical unit 7. Components and functions corresponding to those that were already explained above with reference to FIGS. 1 to 19 are provided with the same reference signs and are not discussed in detail again. In this embodiment, the stop centre is displaced neither in the y-direction nor in the z-direction. Apart from a configuration and arrangement of the aperture stop 34, the imaging optical unit 33 corresponds to the embodiment according to FIG. 1 in US 2003/0 076 483 A1, which is also published as U.S. Pat. No. 6,781,671. Compared to the meridional section in FIG. 1 of US 2003/0 076 483 A1, the projection optical unit 33 according to FIG. 20 is depicted in a manner mirrored about an axis parallel to the xy-axis. In the embodiment according to FIGS. 20 and 21, the aperture stop 34 is also circular and has a diameter of 31.032 mm. A diameter of 31.059 mm is also possible. The aperture stop 34 is tilted in relation to the normal plane 17 by a tilt angle α0 of +8.6°. This tilt is once again implemented in the anticlockwise direction about the tilt axis 26 in the illustration according to FIG. 21. This tilt is such that the angle β0 of the stop normal NAB in relation to the chief ray 16z of the central field point is increased compared to the angle γ0 of the optical axis oA in relation to the chief ray 16z of the central field point. That is to say, ε0=γ0+α0 applies again. In the exemplary embodiment depicted in FIG. 20, the ratio ry/rx=0.920, said ratio having been described in conjunction with FIG. 4. For the ideal tilt angle of the circular aperture stop, the ratio cos(γ+α)/cos(γ)=0.929, which has good correspondence with the ratio ry/rx=0.920. FIG. 21 once again depicts the coma plane 28 and the chief ray crossing plane 29. The stop plane 25 is respectively tilted by the angle δ0 in relation to these planes. The crossing point 28a of the coma rays 19 lies in the region of the stop plane 25 and in the region of an inner boundary of the aperture stop 34. The crossing point 28b of the coma rays 20 and the crossing point 29a of the chief rays 16 are distant from the aperture stop 34. A centre Z of the aperture stop 34 is distant from the intersection point between the stop plane 25 and the optical axis oA. FIGS. 22 to 25 in turn show numerical results in the Fourier expansion of the numerical aperture when using the aperture stop 34 according to FIGS. 20 and 21. Depicted here are the results of five field points, which respectively lie in the centre of one of the field point columns 30i, which were already explained above in conjunction with the explanations according to FIGS. 2 to 19. The first term of the Fourier expansion, i.e. the effective numerical aperture NA0, varies between values of 0.248 and 0.251 when using the aperture stop 34. Averaged over the field points, a value NAx,average of 0.25137 emerges in the xz-plane and a value NAy,average of 0.24924 emerges in the yz-plane. A difference between these two mean values is 0.00213. An x-telecentricity telecentricity value lies very close to the value of 0 mrad when using the aperture stop 34. A y-telecentricity telecentricity value lies in the region between −15 and −14 mrad. An ellipticity value lies in the range between 0 and 5×10−4. A trefoil value lies in the range between 2.75 and 2.95×10−4. In FIGS. 26 to 29, a tilted, circular stop which is displaced in the y-direction and z-direction for optimizing the telecentricity is used in the imaging optical unit 33 according to FIG. 1 of US 2003/0 076 483 A1. Here, the shift is −0.410 mm in the y-direction and −0.916 mm in the z-direction. The tilt angle α=+8.09° and the stop diameter was optimized to 30.946 mm. The tilt axis is arranged analogously to FIG. 21. A comparison between FIGS. 26 to 29 and 22 to 25 shows that the ellipticity and the telecentricity are slightly better in the case of the tilted and displaced circular stop than in the case of the non-displaced tilted circular stop. The first term of the Fourier expansion, i.e. the effective numerical aperture NA0, varies between values of 0.249 and 0.252 when using an appropriately displaced and decentred stop 34. Averaged over all field points, a value NAx,average of 0.24984 emerges in the xz-plane and a value NAy,average of 0.24989 emerges in the yz-plane. A difference between these two mean values is 0.00095. Accordingly, an optimization of the tilted, circular aperture stop 34, in which the latter is only decentred in the y-direction but not displaced in the z-direction, is also possible. Here, the y-decentering can have the value of −0.839 mm. In order to compare the expansion terms of the Fourier expansion above in the case of the tilted circular stop from FIG. 6 to FIG. 9 with a non-tilted circular stop, FIGS. 30 to 33 depict the corresponding expansion terms of a circular stop with a diameter of 66.254 mm, with the stop being arranged centrally in relation to the optical axis in the chief ray plane. It is possible to see a significant reduction of NA0 of approximately 0.002 in the case of the non-tilted stop. Furthermore, the system with the non-tilted, circular stop has a y-telecentricity that is approximately 50% worse (see FIG. 31) than a system with a circular stop that is tilted by approximately −13° (see FIG. 7). A comparison of FIG. 32 and FIG. 8 yields that the ellipticity is likewise worse by approximately a factor of 4. A similar result applies to the trefoils depicted in FIGS. 9 and 33. Compared to an elliptical stop arranged centred in relation to the optical axis, which will still be described below in conjunction with FIGS. 34 to 37, it was also found that the non-tilted, circular stop has worse Fourier coefficients. A correction effect of the tilt degree of freedom for the stop is a correction of the ellipticity, as emerges, for example from the data comparison above. FIGS. 34 to 37 depict the expansion terms of the Fourier expansion up to the third order for an elliptical stop, as is arranged and used in the projection optical unit described in EP 1 768 172 B1. Here, the stop has a semi-major axis of 68.348 mm in the object displacement direction (y-direction). Furthermore, the stop is perpendicular to the optical axis. The semi-minor axis of the stop is 66.254 mm in a direction (x-direction) perpendicular to the object displacement direction (y-direction). A comparison with FIGS. 6 to 9 shows that the telecentricity, in particular the y-telecentricity, has significantly smaller values in the case of the circular stop tilted by −13° than in the case of the elliptic stop arranged perpendicular to the optical axis in the paraxial pupil plane. Furthermore, the ellipticity is significantly reduced in the case of the tilted, circular stop, and so for example, a mean value of 0.5*10−3 emerges in the case of the tilted stop, whereas the ellipticity in the case of the non-tilted elliptic stop is approximately 2*10−3 and therefore worse by approximately a factor of 4 than in the case of the tilted stop. There likewise is an improvement in the trefoil in the case of the tilted circular stop. FIGS. 38 to 41 likewise again depict the expansion terms of the Fourier expansion up to the third order for an elliptical stop, as used in the projection optical unit described in EP 1 768 172 with the dimensions specified above, wherein, however, the stop is displaced by approximately 0.7 mm in the object displacement direction (scanning direction). Hence, the centre of the elliptical stop is spaced from the optical axis in the y-direction by 0.7 mm. As emerges from the comparison of the respective FIGS. 34 to 37 and 38 to 41, a significant improvement in the y-telecentricity and in the trefoil can be achieved by small displacements of the stop centre in the direction of the object displacement direction by approximately 1.5 mm, by 0.7 mm in the shown example, wherein the expansion coefficients for the zeroth and second order remain substantially unchanged in such a stop. Furthermore, the x-telecentricity can be improved by an optionally additionally implemented displacement of the stop centre point along the optical axis, i.e. in the z-direction. The following mean values for the numerical apertures NAx and NAy in the x-direction and y-direction emerge for four of the six shown embodiments of the imaging optical unit 3 according to FIG. 3 from EP 1 768 172 B1, which are summarized in Table 1, with the graphical display of the Fourier coefficients for the non-tilted, circular stop arranged in the paraxial pupil plane being dispensed with. TABLE 1Comparison of NA characteristic values for various stopconfigurations in an imaging optical unit as per FIG. 3 of EP 1768 172 B1Table 1NAx—averageNAy—averageDifferenceTilted, circular,0.249540.248670.00087non-displacedstopTilted, circular,0.249840.248890.00095displaced stopElliptical and0.249520.250580.00106displaced stopNon-tilted,0.249520.242970.00655circular stop Table 1 shows that better results in respect of the variation of the numerical aperture of the image field can be obtained with tilted, circular aperture stops than with stops arranged in the paraxial pupil plane. Furthermore, the telecentricity can be significantly improved. In FIGS. 42 to 45, an elliptic stop arranged in the paraxial pupil plane, i.e. arranged perpendicular to the optical axis in the chief ray plane, is used in the imaging optical unit 31 according to FIG. 5a of US 2007/0 223 112 A1. Here, the centre point of this stop is displaced from the optical axis by 0.6 mm in the y-direction in order to adapt the y-telecentricity. The stop has an extent of 51.840 mm in the x-direction and 52.052 mm in the y-direction. In the case of such a non-tilted elliptic stop, the y-telecentricity can be improved by y-decentering. A comparison between FIGS. 42 to 45 and FIGS. 16 to 19 shows that the ellipticity and the telecentricity is slightly better in the case of the tilted and displaced circular stop than in the case of the displaced elliptic stop. The following mean values for the numerical apertures NAx and NAy in the x-direction and y-direction emerge for the various embodiments of the imaging optical unit 31 according to FIG. 5a from US 2007/0 223 112 A1, which are summarized in Table 2, with the graphical display of the Fourier coefficients for the non-tilted, circular stop arranged in the paraxial pupil plane being dispensed with. TABLE 2Comparison of NA characteristic values for various stopconfigurations in an imaging optical unit as per FIG. 5a fromUS 2007/0 223 112 A1Table 2NAx—averageNAy—averageDifferenceTilted, circular,0.249880.250080.00020non-displacedstopTilted, circular,0.250390.250600.00021displaced stopElliptical and0.249880.250130.00025displaced stopNon-tilted,0.249880.249120.00076circular stop Table 2 shows that better results in respect of the variation of the numerical aperture of the image field can be obtained with tilted, circular aperture stops than with stops arranged in the paraxial pupil plane. In FIGS. 46 to 49, an elliptic stop which is not displaced in the y-direction and z-direction is used in the imaging optical unit 33 according to FIG. 1 of US 2003/0 076 483 A1. The aperture stop is arranged in the paraxial pupil plane, i.e. perpendicular to the optical axis in the chief ray plane. The stop has an extent of 31.032 mm in the x-direction and 28.548 mm in the y-direction. In FIGS. 50 to 53, a displaced elliptic stop which is displaced in the y-direction and z-direction for optimizing the telecentricity is used in the imaging optical unit 33 according to FIG. 1 of US 2003/0 076 483 A1. The aperture stop is arranged in the paraxial pupil plane, i.e. perpendicular to the optical axis in the chief ray plane. Here, the centre point of this stop is displaced from the optical axis by −0.7 mm in the y-direction in order to adapt the y-telecentricity. The stop has an extent of 31.032 mm in the x-direction and 28.548 mm in the y-direction. The following mean values for the numerical apertures NAx and NAy in the x-direction and y-direction emerge for three of the four shown embodiments of the imaging optical unit 33 according to FIG. 1 from US 2003/0 076 483 A1, which are summarized in Table 3. Furthermore, the mean values for a non-tilted, circular stop in the paraxial pupil plane are specified, with the graphical display of the Fourier coefficients for the non-tilted, circular stop being dispensed with. TABLE 3Comparison of NA characteristic values for various stopconfigurations in an imaging optical unit as per FIG. 1fromUS 2003/0 076 483 A1Table 3NAx—averageNAy—averageDifferenceTilted, circular,0.251370.249240.00213non-displacedstopTilted, circular,0.251820.249970.00185displaced stopElliptical0.251360.248710.00265displaced stop, Non-tilted0.251380.270520.01913circular stop Table 3 likewise shows that tilted, circular aperture stops can achieve better results in respect of the variation of the numerical aperture of the image field than stops arranged in the paraxial pupil plane. As the various exemplary embodiments of aperture stops in the three projection lenses for EUV lithography depicted above show, it is possible to achieve a homogenization of the numerical aperture of the image field of the lens using a tilted, circular stop, which is arranged in the region of the pupil of the projection lens, by way of a tilt angle optimization and optionally by way of displacing the stop in the y-direction and/or z-direction, which correspond to the object displacement direction and the optical axis, respectively. Here, better results are achieved than with non-tilted stops arranged in the paraxial pupil plane. Furthermore, the telecentricity and trefoil can additionally be improved. The magnitude of the tilt angle α0 of the tilted, circular stop generally lies in the range between 1° and 20°, preferably in the range between 5° and 15°. The tilt angle α0 can be just as large as an angle αCR between the chief ray 16 of the central field point and the optical axis oA. The exemplary embodiments of the imaging optical units described above each have mirrors M1, M2, . . . , which can be described by way of an asphere equation, i.e. which have rotationally symmetric reflection surfaces, which are used in parts, in relation to the optical axis oA. Alternatively, an imaging optical unit not depicted in a figure can be used with an aperture stop arranged with an appropriate tilt, which optical unit contains at least one mirror embodied as a free-form surface. Examples of such free-form surfaces are described in the following publications: WO 2014 000 970 A1, WO 2013/174 686 A1, US 2013/0 088 701 A1, US 2013/0 070 227 A1, US 2012/0 274 917 A1, U.S. Pat. No. 8,018,650 B2, U.S. Pat. No. 8,810,903, US 2013/0 342 821 A1, U.S. Pat. No. 7,414,781 B2, U.S. Pat. No. 7,719,772 B2, US 2012/0 188 525 A1, U.S. Pat. No. 8,169,694 B2. For the purposes of producing a microstructured or nanostructured component, the projection exposure apparatus 1 is used as follows: initially, the reflection mask 10 or the reticle and the substrate or the wafer 13 are provided. Subsequently, a structure on the reticle 10 is projected onto a light-sensitive layer of the wafer 13 with the aid of the projection exposure apparatus 1. Then, by developing the light-sensitive layer, a microstructure or nanostructure is generated on the wafer 13 and hence the microstructured component is generated. A number of embodiments are described. Other embodiments are in the claims. |
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abstract | Devices for eliminating radioactive contamination of radioactive waste by providing adaptive processing of the decontamination solution for reuse. The plant for electrochemical decontamination of metal radioactive waste includes a pipe equipped with shut-off valves, a radioactive waste processing module that comprises a unit for electrochemical decontamination connected by a ventilation channel to the ventilation module and pipe for decontamination solution supply and discharge equipped with shut-off valves. The plant is equipped with a decontamination solution preparation module connected with a pipe for decontamination solution supply and discharge, at least one pump, while the module for decontamination solution receiving is equipped with devices for cleaning and pH correction of decontamination solution, and the unit for electrochemical decontamination of metal radioactive waste, the module for decontamination solution receiving and the decontamination solution preparation module are equipped with pH measurement elements. |
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047864630 | summary | FIELD OF THE INVENTION The invention relates to an emergency heat exchanger for cooling the primary fluid of a nuclear reactor the core of which, consisting of fuel assemblies which release heat, is immersed in a primary fluid contained in a vessel. BACKGROUND OF THE INVENTION In the case of fast-neutron nuclear reactors, the primary fluid for cooling the reactor generally consists of liquid sodium filling a stainless steel vessel of large dimensions closed by a very thick horizontal slab. When the reactor is stopped after a period of operation, it is necessary to continue the cooling of the core assemblies, because some residual radioactivity remains, generating heat in this core. In high-power nuclear reactors, the quantity of heat to be removed is large and the principal heat exchange circuit of the reactor is generally used to carry out its cooling after stopping. In the case of integrated-type reactors, this circuit incorporates intermediate sodium-sodium exchangers and pumps for circulating the primary sodium. These pumps operate at a low speed during the cooling after stopping. However, if a technical incident causes a stoppage of the normal operation of the principal cooling circuit, the core can no longer be adequately cooled. Excessive heating of the core can result in very severe accidents, so that an emergency cooling circuit, completely separate from the principal circuit, of great simplicity and high reliability, is provided. Such an emergency circuit incorporates a sodium-sodium heat exchanger partly immersed in the primary reactor fluid. This heat exchanger incorporates a bundle of tubes inside which circulates secondary sodium which heats up in contact with the primary sodium present in the reactor vessel. The secondary sodium circulated through the bundle is itself cooled outside the reactor vessel, in a sodium-air exchanger. In the case of fast-neutron reactors of high power, for example 1,500 or 1,800 Mwe, it is necessary to employ several sodium-sodium emergency exchangers immersed in the reactor vessel. It is necessary to restrict the number of these sodium-sodium emergency exchangers for cost reasons, and to reduce the number of passages in the reactor slab. The sodium-sodium emergency exchangers must therefore be relatively large. Furthermore, these heat exchangers are subjected to very high thermal stresses, with the result that their design presents technical problems which are difficult to solve. In the majority of cases, the sodium-sodium emergency exchangers are of the type with bundles of hairpin tubes immersed directly in the primary sodium. These tubes are placed inside an outer shell which is open at its base and perforated over a large part of its side surface. The U-tubes are joined at one of their ends to a first tube plate, and at their other end to a second tube plate offset relative to the first along the height of the heat exchanger. These tube plates enable the secondary sodium in the tubes to be sent to the central part of the exchanger and to be recovered at its peripheral part. The cooled sodium descends in the tube branches situated at the central part of the exchanger and rises in the tube branches situated at the periphery of the latter. While travelling in the tubes, the secondary liquid sodium heats up in thermal contact with the primary sodium through the tube walls. This results in very large temperature differences between the various parts of the exchanger. The latter can also be subjected to large temperature changes over time. This results in thermal stresses which can be very high in some parts of the exchanger, and it is necessary to design exchangers of such structure that it enables these thermal stresses to be reduced to acceptable levels. Furthermore, the tubes forming the exchange bundle must be efficiency braced to prevent their relative movement under the effects of heat and vibrations. The gives rise to problems in the assembly of the heat exchanger which are difficult to resolve. SUMMARY OF THE INVENTION The object of the invention is consequently to offer an emergency heat exchanger for cooling the primary fluid of a nuclear reactor contained in a vessel incorporating a substantially horizontal closure plate and enclosing the reactor core immersed in the primary fluid, incorporating a support flange resting on the closure plate, a bundle of exchange tubes bent into a hairpin and fixed to two tube plates, a cylindrical shell with a vertical axis surrounding the bundle which is submerged in the primary fluid, and a circuit for feeding the tubes of the bundle with a heat exchange fluid, incorporating a means of cooling the exchange fluid heated by the primary fluid arranged outside the vessel, a heat exchanger which makes it possible to restrict the thermal stresses in its various component members and has a simple structure which is permits easy assembly. To this end, the two tube plates are placed coaxially, horizontally and at the same level, one of these tube plates, of annular shape, situated peripherally relative to the second central plate, circular in shape, being fixed to a shell having a vertical axis and situated above the tube plates and connecting the latter to the support flange and to a second shell coaxial with the first, situated below the tube plates, and carrying a connecting piece of a third shell connected to the central tube plate, and each of the tubes of the bundle incorporates a vertical straight part connected to the central tube plate, a bent part for returning the tube, a vertical straight return part, a horizontal circular portion over approximately one-third of the circumference and a vertical part joining the peripheral tube plate. The invention also relates to a process for assembling the heat exchanger. |
abstract | An electron beam duplication lithography apparatus and method for focusing electrons emitted from a mask plate as a result of an application of an electric field between a mask plate and a duplication plate. Irradiation of electrons from the mask plate is assisted through an electric field lens or magnetic field lens, or a combination thereof from an electron field emission material formed into a pattern on a flat surface of a substrate. The result is that a congruent or similar pattern is lithographed by electron beam exposure onto an electron beam resist film from a field emission film having the congruent or similar pattern to be created. |
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052788830 | summary | FIELD OF THE INVENTION The present invention is directed to a spacer grid for use in nuclear reactor fuel assemblies. In particular, the invention is directed to a spacer grid for light water reactors wherein the spacer grid positions and holds the nuclear fuel rods in their intended positions while producing thermal-hydraulic characteristics favorable to heat transfer within the fuel assembly, as well as improving the fuel cycle cost by increasing nuclear fuel loading and optimizing fuel distribution. BACKGROUND In nuclear reactors intended for the generation of power, nuclear fuel assemblies are customarily of the rod type which are arranged in closely spaced parallel arrays in generally square configurations. An outer channel, usually square, surrounds the generally square configuration of fuel rods to form a fuel assembly. The means by which fuel rods are spaced ordinarily take the form of a spacer grid. An example of a spacer grid is shown and described in U.S. Pat. No. 3,654,077. A common problem in typical boiling water reactors is that the central region of the fuel assemblies may be undermoderated and overenriched. In order to increase the flow of moderator, usually water, and to improve neutron moderation and economy, an elongated central water channel is provided which forms a centrally disposed path for the flow of moderator/coolant along the length of, but physically separated from, the fuel rods. The central water channel can have any cross-sectional area and/or geometry, positioned centrally and symmetrically within the outer channel, or asymmetrically displaced from the central axis within the outer channel, and can be oriented around its central axis so that its walls which extend the length of the assembly are either parallel or non-parallel to the walls of the outer channel. The central water channel can be a square or circular tube or array of such tubes extending along the length of the fuel assembly. An example of the square central water channel is shown in U.S. Pat. No. 4,913,876. Sufficient liquid coolant is circulated through the central channel or tubes to keep the contained coolant largely or completely in the liquid phase. The presence of liquid as contrasted to gaseous moderator in the central region of the fuel assembly increases the nuclear performance of the assembly by providing a greater number of hydrogen atoms which function, in part, to slow down neutrons and thereby increase the likelihood of further fissions. The moderator coefficient of reactivity, which is the change in reactor reactivity occurring when the moderator density changes, is thus affected by maintaining liquid as contrasted to gaseous moderator in the central region in the assembly. As is well known, each fuel assembly for a boiling water type of water cooled reactor is typically enclosed by a square outer channel which confines the coolant which enters that fuel assembly to that particular fuel assembly until it exits the assembly at the top of the reactor core. The coolant passing through the fuel assembly consists of a mixture of liquid water and steam. At the bottom entrance of the fuel assembly, the coolant is liquid water having a temperature at/or approximately near its saturation temperature. As coolant flows upward through the assembly, power is transferred by the fuel rods to the coolant, steam is produced, and the fraction of steam in the coolant is increased. At the top of the fuel assembly, the coolant which has been heated by the fuel rods may be primarily steam. As a result of a high volume fraction of steam in the upper region of the reactor core, the upper region of the core becomes undermoderated and overenriched due to the presence of too few hydrogen atoms compared to the number of fissionable uranium or plutonium atoms. As a consequence, less than optimum uranium utilization results. The neutronic efficiency may be improved by decreasing the amount of fuel in the upper region of the core. One way in which this may be accomplished is by reducing the diameter of that portion of one or more of the fuel rods which extend into the upper portion of the core. Current reactor and fuel assembly designs provide for fuel rods to be loaded during fuel fabrication from the top of the fuel assembly. If conventionally designed fuel assemblies are utilized, and if fuel rods with decreased diameters in the upper region of the core are to be loaded into the assembly, the fuel rods must be inserted into the assembly from the bottom. Subsequent to reactor operation, failed fuel rods must similarly be removed from the bottom of the assembly. A failed fuel assembly would first have to be upended which could cause the relocation of cracked fuel pellet fragments within fuel rods which have not failed. Such movement of cracked fuel fragments in rods which have not failed can cause such rods to sustain subsequent fuel cladding failure. The departure from normal procedures by upending fuel assemblies would add to design complexity of the upper and lower tie plates and the fuel rods, increase the fabrication costs of the fuel assembly, as well as increase the subsequent operational costs and risks associated with failed fuel rod replacement. U.S. Pat. No. 5,084,237 issued to Patterson et al. on Jan. 28, 1992 which is incorporated by reference, relates to a side insertable spacer designed to permit rapid repair of irradiated fuel assemblies. The side insertable spacer is an example of a device which does not require upending of the fuel assemblies in order to remove the failed fuel rod(s). The side insertable spacer, however, must be used in conjunction with conventional spacers and tie plates. As is well known, improvements in fuel cycle costs may be achieved by increasing the net amount of fuel in the fuel assembly. Although increasing the diameter of the fuel rods would produce such an increase, it would also result in the concomitant increase in the resistance to coolant flow within the assembly and an increase in pressure drop. Spacer grids also contribute significantly to the resistance to coolant flow. Furthermore, since there are several grid spacers which are located at selected intervals along the length of the fuel assembly, their total contribution to resistance to coolant flow affects the maximum quantity of nuclear fuel that may be utilized in a particular fuel assembly design. It would thus be an advantage over prior art designs if a spacer grid offered lower resistance to coolant flow thereby permitting an increase in fuel rod diameter and, concomitantly, an increase in the total amount of nuclear fuel within the assembly. Once the maximum quantity of nuclear fuel has been placed within the fuel assembly, further improvements in nuclear reactor operations could be achieved if the amount of power that could be safely produced within the fuel assembly were increased. Since reactor power levels are limited by the amount of coolant flowing through the assembly as well as by local heat transfer conditions present at the surface of the fuel rods, it is highly desireable spacer grid offer as little resistance to coolant flow as is possible. It is well known that heat transfer and therefore power capability is enhanced if a continuous film of water is maintained on the surface of the nuclear fuel rods. It would therefore be an advantage over prior art designs if the spacer grid also aided in, or contributed to, maintaining a water film on the fuel rod surfaces. An example of a spacer/mixing grid which provides for circulation of cooling water about the fuel rods while offering low resistance to flow is found in U.S. Pat. No. 4,726,926 for a Mixing Grid issued to Patterson et al. which is incorporated by reference. In addition to maintaining a water film on the surface of the fuel rods, it is also desirable to transfer liquid water present on the inner walls of the outer channel and the outer walls of the inner water channel to the surface of the fuel rods. In order to insert the outer channel in its proper position over the bundle of fuel rods, a significant clearance is provided between the outer surface of the spacer grid and the inner surface of the outer channel. This clearance permits significant coolant flow between the inner walls of the outer channel and the outer perimeter of the spacer grid. Such bypass flow is undesirable because it is not as effective in the transfer of the liquid film from the channel walls to the fuel rod surfaces as is flow which passes through the spacer grid. Bypass flow can be decreased by limiting the clearance between the spacer grid and channel walls or by sealing the clearance between the spacer grid and the channel walls. Either approach renders the grid spacer susceptible to damage during the insertion or the removal of the outer channel. Copending application Ser. No. 07/747,088, entitled Boiling Water Reactor Fuel Rod Assembly With Fuel Rod Spacer Arrangement describes a fuel rod spacer arrangement wherein the fuel rods can be easily loaded into the assembly. One design which facilitates the transfer of liquid condensed on the surrounding channel to the fuel rod surfaces while maintaining an adequate clearance between the spacer grid and channel is disclosed in U.S. Pat. No. 4,749,543. However, this design suffers from the limitations that it is complex, and since it permits bypass flow, not all of the liquid is removed from the channel walls. It would therefore be an advantage over prior art devices to more effectively reduce bypass flow and remove virtually all liquid present on the inner wall of the outer channel as well as directing it to the fuel rod surfaces. Spacer grids, regardless of their design, remove or strip a portion of the liquid water which has condensed on the inner walls of the outer channel and outer wall of the central channel and transfer some of the condensed water to the fuel rod surfaces, thereby increasing the water film thickness on the fuel rods. Spacer grids also function to coalesce small liquid droplets present in the coolant flow into larger droplets and aid in directing greater quantities of such larger liquid droplets to the fuel rod surfaces contributing further to increasing the water film thickness on the fuel rods. It might thus appear that additional spacer grids could be placed at selected points along the length of the assembly to function as a flow stripper and transfer liquid coolant drops to the surface of the fuel rods. However, the use of additional spacer grids results in increases in pressure drop. It would thus be an advantage to provide a low pressure drop spacer grid and to position at least one additional low pressure drop spacer grid to reduce the distance between the spacers in the upper region of the core and enhance the formation of a water film on the fuel rods without increasing the pressure drop across the fuel assembly. Despite advances in the art of fuel assembly and spacer grid designs, a need exists for a spacer grid which has a low pressure drop, improves local heat transfer and provides for maximum fuel loading, while accommodating changes in the diameter of individual fuel rods along the length of the fuel assembly. OBJECTS OF THE INVENTION It is an object of the present invention to provide a low pressure drop spacer for a light water reactor. It is another object of the present invention to provide a method of using a low pressure drop spacer grid to increase the power capability of fuel assembly by improving local thermal conditions on the fuel rods. It is another object of the present invention to provide a low pressure drop spacer which permits the amount of fuel that may be loaded into a fuel assembly to be increased. It is yet another object of the present invention to provide a low pressure drop spacer which permits increased neutron moderation in the upper region of the core by accommodating reduced diameter fuel rods which extend into the upper portion of the core. It is yet a further object of the present invention to provide a spacer grid which reduces the amount of bypass flow. It is a further object of the present invention to provide a low pressure spacer which increases efficiency in reactor fuel cycle costs. SUMMARY OF THE INVENTION A low pressure drop spacer is disclosed for positioning and retaining the fuel rods of a nuclear fuel assembly, the fuel assembly being formed of parallel elongated fuel rods, the spacer having a perimeter strip which circumscribes a region within the assembly through which the fuel rods extend, the strip having an upstream edge and a downstream edge and being adapted to form first apertures positioned toward the upstream edge and second apertures positioned toward the downstream edge, the spacer further having grid members extending and arranged within the region to divide the region into subregions, the grid members being secured to the perimeter strips; each one of the grid members having an upstream edge and a downstream edge and being adapted to form first apertures positioned toward the upstream edge of the perimeter strip and second apertures positioned toward the downstream edge of the perimeter strip, the spacer further having a first spring fork comprising a first end strip and parallel pairs of first spring strips secured to the first end strip, each one of the parallel pairs of first spring strips extending through a corresponding one of the first apertures in the perimeter strip and a corresponding one of the first apertures in the grid members, the first fork positioned in a first plane extending in a first direction defined by the plurality of pairs of first spring strips, the spacer further having a second spring fork comprising a second end strip and parallel pairs of second spring strips secured to the second end strip, each one of the parallel pairs of second spring strips extending through a corresponding one of the second apertures in the perimeter strip and a corresponding one of the second apertures in the grid members, the second fork positioned in a second plane being substantially parallel to the first plane, the second plane extending in a second direction defined by said plurality of pairs of second spring strips such that the second spring fork is superposed on the first spring fork so as to form fuel rod passageways through which the fuel rods extend. |
050376047 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to FIGS. 1-6. These Figures show a typical Westinghouse, 3-loop pressurized, water reactor (PWR) nuclear power plant. The actual arrangements of nuclear power plants, however, vary by specific plant. Also, 2-loop and 4-loop PWR plants have similar but different arrangements, as known in the art. The present invention can be readily adapted by those of ordinary skill in the art to all these different plant arrangements, number of loops, plus non-Westinghouse PWR plant designs. FIG. 1 is a perspective view of the containment building 10 with a cutaway in the front left of a forward concrete wall 11 to show the reactor vessel 12 therein. The reactor vessel 12 is an elongated, generally cylindrically shaped member of a familiar design for use in a nuclear reactor system. The reactor vessel 12 has the usual hemispherical bottom and a plurality of inlet and outlet primary system water nozzles (not shown). In FIG. 1 the reactor vessel 12 closure head and fuel (not shown) have already been removed and the radioactive lower and upper internals, 14 and 16, respectively, have been removed and stored. The front right portion of the wall 11 is also cutaway to show the internals 14, 16 in their respective storage racks, 15, 17, in a refueling canal 18. The refueling canal 18 is located above the reactor vessel 12, with an upper flange 22 of the vessel 12 being generally coplanar with the floor or bottom 24 of the refueling canal 18. The reactor vessel 12 as shown in FIG. 1 is under the refueling condition and is ready for, e.g. in situ annealing. At this time, water in the refueling canal 18 is at maximum level 64 shown in FIGS. 1 and 6. Before introducing an annealing apparatus into the reactor vessel 12, precautions must be taken to prevent radiation emitted by the stored internals 14, 16 from being introduced into the area at which the annealing apparatus will be installed and hooked up by human assistance for operation. In this regard, a coffer dam according to the present invention is used for temporary shielding. The structure of the coffer dam will now be described with reference to FIGS. 2-6, wherein the coffer dam is generally referred to by reference numeral 30. The coffer dam 30 is cylindrical and generally includes: a plurality of segments 40; first sealing means 50 positioned between fit up flanges or edges 42 of adjacent segments 40; first connecting means 70 for attaching together the edges 42 of adjacent segments 40; second sealing means 60 positioned between a bottom flange 32 of the completed coffer dam 30 and the reactor vessel upper flange 22; and second connecting means 76 for attaching the bottom flange 32 to the reactor vessel upper flange 22. FIGS. 2a and 2b are schematic views illustrating introduction of the segments 40 according to the present invention into the containment building 10 and assembly thereof into the completed coffer dam 30. Each segment 40 is pre-fabricated in a factory and is a one-piece, curved, metal member. Although only one segment 40 is shown in FIG. 2a, a plurality of segments are assembled to form the coffer dam 30, as 40 described below. Accordingly, each segment 40 may be referred to as 40a, 40b, etc. In the preferred embodiment of the coffer dam 30 shown in FIGS. 2a, 2b and 4, each segment 40 is an elongated vertical cylindrical section, i.e. each is an equal longitudinal curved section of the total cylindrical coffer dam 30. If four segments 40 are used, each segment 40 is curved 90 degrees; if three segments, 120 degrees; and so on. In an alternate embodiment shown in FIG. 3, each segment 40 is a horizontal cylindrical section, i.e. each is a cross sectional portion of the cylinder. Further, as shown in FIG. 6, if desired the coffer dam 30 can be made of a combination of vertical and horizontal sections 40 connected together. In any case, the segment 40 size is selected, most importantly, so as to fit through the equipment hatch 28 of the containment building 10 and yet still correspond to the reactor vessel 12 size. The choice of segment 40 size and quantity can also be varied to satisfy other manufacturing, transport and plant specific conditions. Referring again to the preferred embodiment of the present invention shown in FIG. 4, each of the four vertical segments 40 can include a side port 46a46b, etc. which is used to direct the annealing apparatus connections out of the coffer dam 30 to a control station (not shown). The alternate embodiments of the segments 40 shown in FIGS. 3 and 6 can also include side ports 46 in the uppermost segments 40. As shown in FIGS. 2a and 2b, and as described more fully below, each segment 40 is brought into the containment building 10 and preferably assembled by humans in a low radiation area of the operating floor 72. In this regard, each segment 40 includes vertical and horizontal fit up flanges or edges 42. Adjacent edges 42 are mated and connected by the first connecting means 70, such as bolt and nut combinations 71. The lowermost set of horizontal fit up flanges or edges 42 form the bottom flange 32 of the completed coffer dam 30, whereas the uppermost set of horizontal fit up flanges or edges 42 form the upper flange 82 of the coffer dam 30. Each of the segments 40 can be pre-fabricated to contain the sealing means described below. Alternatively, all or some of the sealing means could be installed when the segments 40 are being assembled on the operating floor 72. More particularly, the coffer dam 30 includes the first sealing means 50 between the edges 42 of adjacent segments 40. As the first sealing means 50 strip seals 44 can be used as shown in FIGS. 4-6. Because the outside 78 of the coffer dam 30 (see FIG. 6) is in contact with refueling canal water, temperatures are reduced, allowing the first sealing means 50 to be, e.g. rubber composition or metal. Such sealing means 50 helps resolve a significant feasibility issue by allowing a plurality of segments 40 to be passed through the hatch 28 and to form the complete coffer dam 30. Once the segments 40 are connected together to form the completed coffer dam 30, the coffer dam 30 is moved and attached to the reactor vessel flange 22. As shown in FIG. 5, a seating surface 33 of the bottom flange 32 mates with a closure head seating surface 34 of the reactor vessel flange 22 with the second sealing means 60 therebetween. The type of second sealing means 60 used in this area depends on the thermal design requirements of the reactor vessel flange 22 during the annealing operation. Where high temperatures in the reactor vessel upper flange 22 area are required to minimize thermal gradients and residual stresses, the second sealing means 60 will be a thermal insulator gasket-type seal in combination with metallic and non-metallic O-rings. For those applications where low temperatures at the reactor vessel upper flange 22 can be tolerated, the second sealing means 60 can be merely low temperature O-rings. The pressure differential across the second sealing means 60 is low (max 15 PSI), thus allowing a wide range of allowable second sealing means 60, flange 32 and second connecting means 76 combinations. The bottom flange 32 of the coffer dam 30 is connected to the reactor vessel flange 22 via the second connecting means 76. Such connecting means 76 can be, e.g. a threaded bolt 38 arrangement. More particularly, the bottom flange 32 of the coffer dam 30 has sufficient holes 36 to allow the completed coffer dam 30 to be bolted to the threaded holes 37 formed in the reactor vessel 12 for receiving the closure head. This bolt down arrangement prevents a catastrophic seal failure as the flanges 32, 22 can be in intimate contact. This arrangement also resolves a significant feasibility problem of the conventional coffer dam described in the "Description of the Prior Art" section, suora, which has no bolt down feature. That is, the coffer dam was merely seated on the bottom of the refueling canal outside of the reactor vessel and employed the weight of the coffer dam to create the seal clamping force. Long handled tools (not shown) can be used from the operating floor 72 to bolt the coffer dam 30 to the reactor vessel flange 22. In this way, the lowest possible personnel exposure to radiation is obtained. If personnel were to work around the reactor vessel flange 22 to connect the coffer dam 30 directly to the flange 22, with only the reactor vessel 12 filled with water, radiation exposure to the personnel coming from the stored internals 14, 16 would be high. Nevertheless, if radiation from the stored internals 14, 16 were adequately shielded by other means, the coffer dam segments 40 can be assembled directly on the reactor vessel upper flange 22 or personnel can be used at the reactor vessel upper flange 22 to connect the bolts 38, if desired. With the coffer dam 30 installed on the reactor vessel 12, the refueling canal 18 is flooded to shield the radiation emitting from the stored internals 14, 16. As shown in FIG. 3, a conventional seal leak detection means 90, with passage to the dry side of the first and second sealing means 50, 60 can be incorporated for monitoring seal effectiveness. As shown in FIGS. 3, 5 and 6, an annealing apparatus 100 is then inserted in the reactor vessel 12, with a lower seating surface 106 of a top plate 102 thereof seated on the reactor vessel internals seating ledge 104. This structure frees up the reactor vessel closure head seating surface 34 to allow the seating surface 33 of the coffer dam 30 to be seated thereon. This change eliminates the need for sealing the top plate 102 of the annealing apparatus 100 to the vessel 12. Workmen (not shown) in the area above the annealing apparatus 100 hook up the various heater power leads 108, thermocouples 110, etc. known in the art. The power leads 108 and thermocouples 110 are led out of the coffer dam 30 through the side ports 46. These ports 46 are then closed by sealant plugs 48. The side ports 46 project above the water level 64 in the refueling canal 18 so water cannot enter the coffer dam 30. These ports 46 and the access cover plate 80, discussed below, are sealed to prevent any potential airborne radiation particles that might be released during heat up and cool down from being released to the containment atmosphere. That is, the annealing process incorporates an inward air movement concept to control airborne radiation particles. A vacuum pulls on the internal vessel volume and the exhaust is passed through an external filter. Any air leakage which might occur around seals for the thermocouples 110 and power cables 108 and the access cover plate 80 are inward. The vacuum is required only to be slightly under atmospheric pressure as there is only a slight pressure differential. The access cover plate 80 is also introduced through the equipment hatch 28. The access cover plate 80 is secured to the upper flange 82 of the coffer dam 30 by third connecting means 83 and sealed via third sealing means 88, such as an O-ring. Sealing at this point above the water line 64, significantly removed from the heat sources, allows for use of low temperature seals. The access cover plate 80 can be made of two, semi-circular sections joined to each other by fourth connecting means 84 such a hinges, pins or bolts. Of course, the access cover plate 80 could be made in more sections than two if desired. The access cover plate 80/side ports 46 combination: allows for man entry to the top of the annealing apparatus 100 for initial installation and hook-up of power leads 108, thermocouples 110, other instrumentation, and piping while the refueling canal 18 is filled; allows man entry during operation for maintenance, inspection and dismantling; no disconnections of thermocouples 110 or power leads 108 are required for man entry into the coffer dam 30; allows for easy exit of the power leads 108 and thermocouples 110; allows for easy installation of the annealing assembly 100; and allows thermocouple 110 actuation and adjustment during annealing. The coffer dam 30 according to the present invention also provides for effective control of air flow to the internal volume of the reactor vessel 12 which is maintained at a negative pressure during the annealing process to control airborne contamination. A vacuum system 112 is used for maintaining the reactor vessel 12 at a slight negative pressure. The system 112 enters the coffer dam 30 at a side port 52 with piping 54 going along the interior wall 56 of the coffer dam 30 and entering the reactor vessel 12 through a connection 58 in the annealing apparatus top plate 102. Similar routing is made for a vent line 62 to the interior of the reactor vessel 12. In contrast to the temporary shielding discussed in the above referenced co-pending application entitled "Water Filled Tanks...," wherein vertical and horizontal water tanks are used between the reactor vessel and stored internals, the coffer dam 30 of the present invention allows for water shielding of the stored internals 14, 16 even in reactors where the refueling canal 18 is small and the internals 14, 16 are installed in close proximity to the reactor vessel 12. In some instances, however, it may be desired to use both supplementary lead or steel shielding hanging on the coffer dam 30 at the closest point of the coffer dam 30 relative to the stored internals, if the radiation reading merits same. The method of assembling the coffer dam segments 40 according to the present invention will now be described in greater detail with reference to FIGS. 2-6. As seen in FIG. 2a, each pre-fabricated segment 40 can be shipped from the factory in, e.g. a strong back reusable shipping frame 66, to the reactor site. At the site the shipping frame 66 and a segment 40a are transferred to the interior of the containment building 10 through the equipment hatch 28. Once inside containment, the segment 40a is released from the shipping frame 66 and upended using a containment crane 68 in a low radiation area of the operating floor 72. This upending operation is enhanced by a shipping frame 66 which has included upending features such as pivot pins and internal rails or rollers to permit upending vertically under the natural crane hook positions without loss of control or undue loading of the segments 40 or the shipping frame 6. As suggested above, each segment 40 can be pre-fabricated at the factory to include the first, second and third sealing means, where necessary, or the sealing means can be installed when the coffer dam segments 40 are assembled on the operating floor. Then, with the segments 40 assembled and the seals captured in place, the coffer dam 30 is lowered onto the reactor vessel flange 22 and connected in sealing relation to the reactor vessel 12. The next step in the annealing process is to introduce the annealing apparatus 100 into the reactor vessel 12 and pump the remaining water from the reactor vessel 12 and coffer dam. A suitable annealing apparatus is described in the above-referenced application entitled "Modular Annealing Apparatus For In Situ Reactor Vessel Annealing And Related Method of Assembly." Once the annealing apparatus 100 is inserted into the reactor vessel 12, the power leads 108, thermocouples 110, etc. are led by the workmen out the side ports 46 to the control station. The access cover plate 80 is then introduced into the containment building 10 and connected in sealing relation as described above via the bolts 86. FIGS. 3 and 4 illustrate the annealing apparatus 100 in the reactor vessel 12 and the complete coffer dam 30 installed above the annealing apparatus 100. In these embodiments, side ports 46 and an access cover plate 80 are used. In contrast, FIG. 6 is a perspective view of an alternate embodiment, wherein the side ports 46 and cover 80 are not used; the connections (not shown) for the annealing apparatus 100 are led directly out the top of the coffer dam 30. Once the annealing apparatus 100 is inserted and hooked up, annealing of the reactor vessel is performed. As would be understood by one having ordinary skill in the art, after annealing is performed, the coffer dam 30 can be disassembled and removed from the containment building 10 by merely reversing the steps described above. In this way, the coffer dam 30 can be reused by transporting same to other reactors. Further, should the coffer dam 30 require repairs, the entire coffer dam 30, a segment 40 thereof or the access cover plate 80 can be transported back to the factory where the repair can be performed. The foregoing is considered illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. For example, although the present invention is described as particularly suitable to annealing operations, the invention is also equally applicable to other situations where the internals are stored and some work must be performed in the reactor vessel such as scheduled inspections or weld repairs. Accordingly, all suitable modifications and equivalents may be resorted to that fall within the scope of the invention and the appended claims. |
043307116 | claims | 1. A container combination suitable for the transportation and storage of irradiated fuel elements of nuclear reactors comprising, in combination, a removable inner container which is usable by itself for storage in a correspondingly laid out fuel element storehouse and an outer container wherein the two containers each has its own cover, each said container having a bottom and said outer container having jacket means and wherein: (a) the thickness of the bottom and the jacket means of the outer container are such that they serve as shielding against gamma and neutron radiation; (b) said inner container is axially fixed in said outer container with the cover of the inner container spaced from and out of contact with the cover of said outer container; (c) said outer container and jacket means have an interior wall which taper inwardly toward said bottom of said outer container to an extent whereby the radial position of said inner container in said outer container is fixed by contact between the exterior of said inner container with at least said jacket means adjacent said bottom of said outer container; and (d) sealing means urging the outer wall of said inner container tightly against the inner wall of said outer container. 2. A container combination according to claim 1 wherein there is provided a holding down device means between the cover of the outer container and the cover of the inner container, recesses are provided in the outer container jacket means and the holding down device means is received in said recesses and can exert force on the cover of the container whereby the inner container is fixedly axially. 3. The container combination as claimed in claim 1 wherein the outer wall of said inner container is tapered adjacent its bottom to correspond to the taper on said inner wall of said outer container whereby a snug fit is obtained when said inner container is placed inside said outer container. 4. A container combination according to claim 1 wherein the jacket means has therein cooling conduit means adapted to be connected to the outside. 5. The container combination as claimed in claim 4 wherein the inner wall of said outer container is provided with a plurality of hollow recesses which are integrated into said cooling conduit means. 6. A container combination according to claim 5 wherein the cover of the inner container is so dimensioned that it provides substantially for shielding against gamma and neutron radiation. 7. A container combination according to claim 4 wherein the cover of the inner container is so dimensioned that it provides substantially for shielding against gamma and neutron radiation. |
abstract | The invention is a process for manufacturing a nano aluminum/alumina metal matrix composite and composition produced therefrom. The process is characterized by providing an aluminum powder having a natural oxide formation layer and an aluminum oxide content between about 0.1 and about 4.5 wt. % and a specific surface area of from about 0.3 and about 5 m2/g, hot working the aluminum powder, and forming a superfine grained matrix aluminum alloy. Simultaneously there is formed in situ a substantially uniform distribution of nano particles of alumina. The alloy has a substantially linear property/temperature profile, such that physical properties such as strength are substantially maintained even at temperatures of 250° C. and above. |
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claims | 1. A cooling system for a nuclear reactor module, comprising:a nuclear reactor pressure vessel that houses primary coolant;a steam generator configured to lower a temperature of the reactor pressure vessel by transferring heat from the primary coolant to a secondary coolant that circulates through the steam generator and releasing at least a portion of the secondary coolant as steam;a containment vessel at least partially surrounding the reactor pressure vessel, which forms a containment region therebetween, wherein the containment region is dry during normal operation of the nuclear reactor module;a temperature monitor configured to monitor temperature of the pressure vessel;at least one conduit that enables the containment region to receive water from a source of water; anda controller in operative connection with the temperature monitor, wherein the controller is configured to cause a non-emergency shut down of the nuclear reactor module, including:causing, during the non-emergency shut down, the steam generator to release steam to lower the temperature of the reactor pressure vessel, andcausing, during the non-emergency shut down, water from the source of water to be introduced into the containment region through at least one conduit in response to a determination that the temperature of the reactor pressure vessel indicated by the temperature monitor has been lowered to a threshold cooling temperature as a result of the steam release. 2. The cooling system of claim 1, wherein the containment vessel is at least partially submerged in a reactor bay pool and at least one conduit receives water from the reactor bay pool. 3. The cooling system of claim 1, wherein the threshold cooling temperature is above a boiling temperature of the secondary coolant, and wherein the introduction of the water into the containment region operates to lower the temperature of the reactor pressure vessel to below the boiling temperature of the secondary coolant. 4. The cooling system of claim 3, wherein the threshold cooling temperature is approximately 250 degrees Fahrenheit. 5. The cooling system of claim 1, wherein the containment vessel retains at least some of the water introduced into the containment region through at least one conduit and submerges a majority of the reactor pressure vessel. 6. The cooling system of claim 5, wherein the containment vessel is configured to increase an internal pressure in response to the introduction of water into the containment region, and maintain the water within the containment region as the pressure equilibrates within the containment vessel. 7. A cooling system for a nuclear reactor module, the nuclear reactor module including a nuclear reactor pressure vessel that houses primary coolant, a steam generator configured to lower a temperature of the reactor pressure vessel by transferring heat from the primary coolant to a secondary coolant that circulates through the steam generator and releasing at least a portion of the secondary coolant as steam, and a containment vessel at least partially surrounding the reactor pressure vessel, which forms a containment region therebetween, wherein the containment region is dry during normal operation of the nuclear reactor module, the cooling system comprising:a temperature monitor configured to monitor temperature of the pressure vessel;a fill pipe that enables the containment region to receive water; anda controller in operative connection with the temperature monitor, wherein the controller is configured to:cause a non-emergency shut down of the nuclear reactor module,cause, during the non-emergency shut down, the steam generator to release steam to lower the temperature of the reactor pressure vessel, andcause, during the non-emergency shut down, water to be introduced into the containment region through the fill pipe in response to a determination that the temperature of the reactor pressure vessel indicated by the temperature monitor has been lowered to a threshold cooling temperature as a result of the steam release. 8. The cooling system of claim 7, wherein the fill pipe receives water from a reactor bay pool that at least partially retains the containment vessel. 9. The cooling system of claim 7, wherein the controller introduces the water into the containment region to lower the temperature of the reactor pressure vessel to below the boiling temperature of the secondary coolant. 10. The cooling system of claim 7, wherein the threshold cooling temperature is approximately 250 degrees Fahrenheit. 11. The cooling system of claim 7, wherein the controller is configured to fill the containment region with water to submerge a majority of the reactor pressure vessel. 12. The cooling system of claim 7, wherein the controller is configured to maintain the water within the containment region as pressure equilibrates within the containment vessel. |
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062263412 | summary | This invention relates generally to neutronic reactors, and more specifically to devices for preventing neutronic chain reactions from exceeding safe operating limits. All neutronic reactors are constructed with as much excess reactivity as is possible considering the available reactor control system, the excess reactivity of a neutronic reactor being defined as the amount that the reproduction ratio of a neutronic reactor under most favorable conditions exceeds unity. The reproduction ratio of a neutronic reactor is the ratio of the number of neutrons in any given generation to the number of neutrons in the preceding generation within the actual pile structure. The excess reactivity of a neutronic reactor determines the magnitude of isotope production and other neutron-absorbing activities which the reactor may accomplish, and also determines the flexibility which is possible in operating the reactor. The existence of excess reactivity in a reactor makes desirable both regulating control means and safety control means for the reactor. Regulating control means are necessary in order to maintain the reproduction ratio of the reactor at unity during constant power operation, and to make adjustments in the power level of the reactor. Safety control means are desirable in order to shut down the reactor more rapidly when unsafe operating conditions develop than is possible with the regulating control means. There are many causes of unsafe operating conditions which make it desirable to shut down a neutronic reactor. If the reactor "period" becomes too short for any reason, it is desirable to shut down the reactor, the reactor period being the time required for the neutron flux density within the reactor to increase by a factor of e, or 2.718. In those reactors which employ cooling means and operate at substantial power levels, it is also desirable to shut down the reaction if there is a decrease in the flow of the coolant. There are also many other reasons for providing a safety control system to shut down a neutronic reactor, and the safety control system may be coupled to any of these dangerous conditions. A number of safety control systems have been developed in the neutronic reactor art. In one of these systems, neutron-absorbing rods are disposed within channels which extend into the active portion of the reactor, the active portion being the region of the reactor in which the fissionable material is disposed. The rods of neutron-absorbing materials are mechanically biased to enter the active portion of the reactor when released, either by the attraction of gravity or some impelling force. Another safety system provides a channel extending through the active portion of the reactor and means to impel bodies of neutron-absorbing material into the channel in response to an unsafe condition. The application of John J. Goett, Ser. No. 595,189, entitled "Reactor Control", filed May 22, 1945, now U.S. Pat. No. 2,773,823, discloses such a system provided with a centrifugal impeller for driving balls of neutron-absorbing materials into a reactor. It has been found that neither of these systems is entirely satisfactory. Both of the systems are complicated by the fact that it is desirable to keep the ambient atmosphere from the active portion of the reactor to as great an extent as possible, since both nitrogen and oxygen present in the ambient atmosphere have relatively large neutron capture cross-sections. For this reason, it is generally necessary to provide liners for all channels entering into the active portion of the reactor, and to seal the channels from the atmosphere within the reactor. It is also to be noted, that the liners themselves introduce added neutron losses into the reactor. Considerations of neutron economy also dictate that the channels extending into the active portion of the reactor be confined to as small a cross-section as possible. As a result, the rod safety system permits relatively small clearance between the rods and the rod liners, and hence it is possible for some of the rods to jam within the channels in the reactor before the rod is effectively inserted into the active portion of the reactor. The problem of jamming is further complicated in neutronic reactors which use graphite or other solid crystalline moderator structures by the fact that distortion of the solid moderator structure results from the bombardment of the structure by the high energy neutrons which are present in neutronic chain reactions. The shifting of graphite blocks in reactors employing moderators thus constructed, may so distort the channels for the safety control devices, that rods could not be made to enter into the active portion of the reactor effectively, hence causing the entire safety system to fail. The rod type of safety system, however, has some distinct advantages over other types of control, such as the impelled ball system described above. A rod may readily by recovered from its channel in the active portion of the reactor, whereas it is difficult to remove neutron-absorbing balls from the channels extending through the active portion of the reactor, both as a mechanical problem and as a health physics problem, since the neutron-absorbing balls will remain highly radio-active even after the neutronic reaction has ceased. Hence, it is an object of the present invention to provide a safety system for a neutronic reactor which is both neutronically safe and physically convenient. Another object of the present invention is to provide a safety system which provides two separate safety operations, the failure of one operation actuating the second operation, thereby greatly reducing the probability of a failure of the safety system. Further, it is an object of the present invention to accomplish the provision of a safety system having two separate operations without introducing into the neutronic reactor additional neutron-absorbing materials or additional neutronically deleterious channels. |
description | This application claims the benefit of Provisional Patent Application Ser. No. 60/311,453, filed 2001 Aug. 8 by the present inventor. Not applicable. Not applicable. 1. Field of Invention This invention relates to hot nuclear fusion reactions of heavy and light Hydrogen and other fusion reactive gases for the production and recovery of energy. 2. Description of Prior Art Electric illumination supplies a basic need of modern society. To this end, inventors created several types of electric lights. U.S. Pat. No. 514,170 to Tesla (1894), which is hereby incorporated by reference, discloses a partially evacuated, bulb shaped glass enclosure with a central target. This central electrode is attached by a stalk containing an electrically conductive element. The conducting element is attached to a source of high voltage, high frequency electrical potential. This alternating potential ionizes and then alternately attracts and repels the positive ions of rarefied gases present in the bulb. These ions reach such speeds, that the central refractory electrode, due to the force of impact of these high speed ions, glows incandescently, becoming a source of light. This starts occurring at frequencies of 20 KHz (thousand Hertz) and above, and at potentials of 20 kV AC (thousand volts alternating current) and above. A reliable source of power supplies a basic need of modern society. To this end, inventors created several types of nuclear reactors. U.S. Pat. No. 3,530,497 to International Telephone and Telegraph Corporation (1970), U.S. Pat. No. 3,258,402 to Farnsworth (1966) and U.S. Pat. No. 3,386,883 to Farnsworth (1968), which is hereby incorporated by reference, collectively describe the “Farnsworth fusor.” The “Farnsworth fusor” utilizes the phenomenon of electrostatic confinement of ionized gases as its principle mode of operation as a controlled nuclear-fusion reactor. These reactors are limited to cylindrical, spherical, or toroidal vessels. These reactors have control grids. These reactors have a cathode. These reactors depend upon thermionic emission. These reactors have ion guns. These reactors utilize direct currents as their principle drive potential. These reactors function with internal electrodes. These electrodes are therefore exposed to the extreme heat generated by the reaction. This results in decreased reliability since these vital structures are close to the reaction and are detrimentally affected by the extreme levels of heat generated by nuclear reactions. The varied reactor shapes available to the “Farnsworth fusor”, and the internal structures required for it's operation, limit the efficiency of energy transfer from the nuclear-fusion reaction to the power absorption medium. The invention relates to particle acceleration and neutron tubes. My study of sonoluminescence or bubble fusion, lead to my conceiving of the idea of developing an apparatus in which the theory of raising the temperature and pressure of a plasma for the generation of fusion reactions is abandoned. In it's place is a means of generation of fusion reactions which is solely dependent upon particle collision velocity. High temperatures and momentarily high pressures do occur during the operation of this device. But, high temperature and pressure are not the operational determinants of this invention's operation. They are secondary results of it's operation only. The primary operational determinant is particle collision velocity. Sufficient particle collision velocity is obtained by the acceleration of particles to sufficient velocities which generate collision velocities sufficient for fusion reactions to occur. This invention is a particle accelerator and is not a confinement reactor. It is novel in that it utilizes alternating potential acceleration in order to produce a particle motion pattern in which particles alternately collide with a target, resulting in fusion, and then are alternately accelerated away from the target stopping the fusion reactions. Such an on off nature of the device provides many advantages as will be described in this application. Previous references to a collapsing bubble were purely analogies used to explain the expanding and collapsing nature of this particle movement. As indicated above, the understanding of the nature of this invention was first understood by me while studying sonoluminescence. In the “bubble” analogy I found a convenient means of attempting to portray the particle movements of this invention. That I should use such a description should be understood in the light that my inspiration for this invention came while studying such bubble behavior. What became very apparent to me at that time was the importance of dropping the concern over the raising of plasma temperature and pressure as done in confinement processes. These processes mimic the conditions of the core of the Sun. It became obvious that such attempts are futile here on Earth. The Sun's great mass and gravitational fields make such operation applicable to such a region. The conditions on Earth make such operation inherently inefficient. This invention rectifies this situation by solely applying it's operational energy to the ionization and subsequent acceleration of the contained particles and ions. It becomes efficient by not wasting energy on increases in plasma temperature and pressure, parameters not directly related to fusion. This device is a radially and axially concentric, alternating potential neutron tube. Previous references to other processes were no more than word pictures used in an attempt to describe the operation of this device. This device does not use actual sonoluminescence, imploding bubbles, or cavitation phenomenon. Such earlier references were word picture analogies only. It is also important to realize that with this invention I discard confinement theory and it's reliance on compression to temperatures needed to achieve nuclear reaction. This invention also does not rest upon theories of bubble cavitation or sonoluminescence. The observed fact that these processes do not achieve sufficient temperatures for temperature dependent fusion reaction processes is not relevant to this invention. This device is solely velocity dependent. It is not temperature or pressure dependent. Nikola Tesla patented an “Incandescent Electric Light” on Feb. 6, 1894, U.S. Pat. No. 514,170, which is hereby incorporated by reference. This patent discloses an evacuated, bulb shaped glass enclosure with a central target. This target is connected to one terminal of a high voltage, high frequency alternating current AC power supply. The other terminal of the power supply is connected to earth ground. The alternating potentials generate an alternating electric field emanating outward from the target. This field ionizes and accelerates ions to and from this target at high speeds. At sufficient voltages, these impacts cause the central target to glow incandescently. Tesla's apparatus functioned as a source of light. My invention is a modification of this apparatus so that it may function as a fusion reactor. At radio frequency, RF, the effective ground point on Tesla's device is at the outer layer of the glass envelope. As a result, the outermost point of the contained electric field assumes the shape of this envelope. The asymmetry of the resultant electric field did not sufficiently hamper the device's function as an electric light. However, such asymmetry of the electric field would lead to inadequate focus of the ions onto the central target electrode for fusion reactions to occur. Additionally, location of RF ground at the outer surface of the envelope also allows for internal arcing between the central target and the inner surface of the envelope. Such arcing takes the form of the plasma filaments commonly seen in such devices which today are referred to as plasma lamps. Such arcing is visually pleasing in a lighted lamp, but would prevent the device from producing reliable fusion reactions. Additionally, Tesla's device contained an inner conductive sleeve extending over the insulated stalk, proceeding along this stalk and in contact with the target electrode. This sleeve would further interfere with the electric field symmetry rendering the device in operable for fusion reactions. Tesla's device includes no provisions for reactor cooling or from insulation from heat released within the energy absorber jacket. Tesla's device includes no provisions for the introduction or removal of contained gases. Tesla's device provides for a conceptual model for this invention. But significant modifications and changes were needed to transform this concept from a light bulb into a fusion reactor. Applications include a power source and a neutron source. Neutron sources are used in radiography, nuclear devices, medical treatments, and in various measuring devices. The invention is a spherical fusion reactor with a central target electrode. A spherical, insulated envelope contains a concentrically located spherical target electrode. This envelope contains rarefied fusion reactive gas. The envelope is suspended in an insulating and cooling medium. This medium is contained within a thermally insulated container. This container is suspended within an energy absorbing medium held within another container. A source of high voltage, high frequency alternating potential is connected between the central target electrode and earth ground. A Deuterium (or Deuterium and Tritium, D-T) ion plasma is produced within this envelope by electric fields present between the target and the ground plane. This field is present when the target is at a different electric potential with reference to the ground plane. The intensity of this field is in proportion to the potential difference between the target and the ground plane. The direction of this field is determined by the relative charge polarities between the target and the ground plane. With reference to a positive ion, with a positive charge on the target and a negative charge on the ground plane, the electric field direction would be such that a positively charged particle would move radially outward from the target. With a negative charge on the target and a positive charge on the ground plane, a positively charged particle would move radially inward toward the target. The rate of acceleration of a charged particle within this field is in proportion to the intensity of this field. The intensity of this field is in proportion to the potential difference between the target and the ground plane. With an alternating potential placed between the target and the ground plane, an electric field varying in intensity and polarity is produced. The maximum intensity is proportional to the peak voltage applied. As the potential difference is rising, the electric field intensity is increasing. The electric field intensity becomes sufficiently intense for electric field ionization. Once ionization occurs, the positive and negative ions are accelerated in opposite directions. The alternating potential applied is of such a magnitude that it has not reached it's peak value at the point of ionization. The intensity of this potential continues to increase until the field reaches such intensity that sufficient particle acceleration for fusion reactions to occur is produced. It is during the polarity of alternation in which inward acceleration of positive ions occurs, that these ions are accelerated with fusion reactive velocities to the central target. These particles impact with the target and each other with velocities sufficient for fusion. These fields change in polarity with the polarity potential changes of the alternating current. The ions within this enclosed space alternately accelerate inward to the target electrode, and alternately accelerate outward toward the envelope. The spherical target electrode is suspended from the envelope by an insulated stalk. When the target electrode is biased negative, with respect to earth ground, ions within this enclosed space accelerate to the target electrode producing D-D or D-T reactions. The target is loaded with D or T by the impact of the D or T ions. Envelopment of the reactor envelope within an insulating cooling medium provides for cooling of the reactor and isolates the reactor chamber from RF ground potential. This permits a uniform equipotential surface to be developed along the inner lining of the reactor envelope. This surface is spherical and concentrically aligned with the central target electrode. This produces a uniformly spherical electric field within the reactor envelope. This allows the electric field to focus the ions onto the target when they are accelerating inward to the target. The electric fields must be symmetrical in order to allow for fusion reactions to occur at the target. RF ground potential must be sufficiently removed from the outer surface of the reactor envelope for reliable functioning. This design provides for the removal of the RF ground potential location to be located external to the thermally insulated container holding the insulating and cooling medium. In some embodiments, this RF ground potential location may also be located externally more distant from this point. Electrical insulation of the internal and external surfaces of the reactor envelope from RF ground provides for uniformly symmetrical electric fields within the reactor chamber. Envelopment of the reactor insulating and cooling medium within a thermally insulated container provides for the outward transport of energy radiations with restriction of inward passage of heat energy. This reduces the thermal load of the reactor and the contained insulating and cooling medium from reabsorption of heat produced within the absorber medium. This invention provides a highly controllable and efficient hot fusion reactor. AC drive current provides for both ionization and target impact. The cyclic on of nature of this inventions operation allow fine power increment control and the means for both introducing and extracting gases to and from fusion reactions. Fine power control is obtained by the fact that the reaction is turning on and off at a high rate. Duty cycle and pulse control allow the number of reactions per given time period to be varied. In example, if the drive frequency is 50,000 Hertz, the net power output of the system can be varies in 1/50,000 per second increments by varying the number of alternations per time period in which the applied potential is of sufficient intensity to permit fusion reactions. Introduction and extraction of gases can be accomplished during and after the portion of alternation in which positive ions are accelerated outward. Control of the waveform can also let the electric field be momentarily ended in order to facilitate electron and ion recombination. Gas injection and extraction can take place during these time periods. Most significantly, the alternation polarity nature of the drive potential provides a time means in which portions of time where the central reacting mass is disassembled. This is subsequently followed by radial acceleration of ions outward providing for a time in which gas exchange may occur. All the prior art with regards to particle acceleration and neutron tube fusion reactors do not involve reversal of particle direction as does this invention. Such devices work, but work only as one shot devices. It can operate on both the D-D and the D-T reactions. The presence of a physical target limits power levels to those levels within which the target will survive. FIG. 1 shows a non conducting spherical reactor envelope 21 having an internal insulated stalk 22 extending centrally from which a spherical target electrode 11 is located centrally, coaxially, and fixedly within envelope 21. An open space is defined between spherical electrode 11 and the inner surface of spherical envelope 21. This defined space contains rarefied Deuterium gas 235. This gas 235 may also consist of Tritium, or mixture of Deuterium and Tritium, or any other fusion reactive gases. This space also provides a location for the generation of an alternating electric field. This alternating electric field provides for the ionization of gases contained therein. It also provides for the alternately radial inward acceleration and the alternately radial outward acceleration of ionized gases contained therein. The collapsing of ionized gases provides for ions impacting the spherical target, for the impact of ions with one another, and for such impacts to occur at fusion reactive velocities. The outward radial acceleration of ionized gases provides for a gas distribution allowing for gas extraction from the enclosed space and for a gas distribution allowing for gas introduction into the enclosed space. The fusion contained gas is at a predetermined pressure from 0.00000001 Torr and 760 Torr, preferably from 0.0001 to 1 Torr, in particular about 0.01 Torr. The spherical envelope of insulating material 21 enclosing a space provides for the following: a sealed space containing gas at a predetermined pressure, an insulating surface providing a location for the stopping of the outward movement of electrons, a location of a equipotential of electric charge accumulation, and the development of a spherically symmetrical electric field. Envelope 21 is suspended within insulating and cooling medium 241 by a second insulated stalk 22 which passes through insulated cap 230 and insulating feedthru 42. Insulating and cooling medium 241 is contained within thermally and electrically insulated container 237. Insulated container 237 is suspended within radiation absorber and cooling medium 242 which is contained by heat absorbent container 238. Insulated container's 237 partial radius is concentrically centered on spherical target 11 and spherical envelope 21. The insulating and cooling medium 241 separates and distances RF, radio frequency, ground potential from locations: within the reactor chamber, along the inner surface of the reactor chamber, along the outer surface of the reactor chamber, and to places external to the thermally and electrically insulated enclosure. This separation and distancing of the RF ground potential provides for: a symmetrically developed field within the reactor, an electric field of evenly developed intensity radially outward from the target, the prevention of internal arcing, and the reduction of capacitive reactance loading of the power supply. High voltage, high frequency alternating current source/power supply 130 is connected by wire 13 between ground potential point 153 and spherical target electrode 11. Heat absorbent container 238 is also connected by wire 13 and ground potential point 153. In the present embodiment target 11 is Titanium, wire 13 is copper, envelope 21, stalk 22, and feedthru 42 are made of glass. Internal insulated stalk 22 is radiused to permit a tight fit with spherical target electrode 11. Insulated cap 230 and container 237 are made of double layered glass with a vacuum insulation as per standard practice of those experienced in this art. Heat absorbent container 238 is steel. Insulating and cooling medium 241 is transformer oil. Radiation absorber and cooling medium 242 is water. Gas 235 is Deuterium. Power supply 130 and ground potential point 153 are per standard practice of those experienced in the art. Inside the surrounding envelope 21 is spherical target 11. Target 11 is the site of nuclear reactions and provides a surface: for ions impacting the spherical target, for the impact of ions with one another, and for such impacts to occur at fusion reactive velocities. Target 11 may also be composed of other materials capable of permitting and surviving nuclear reactions. AC potential applied between the target 11 and ground 153 produce an alternating electric field within. Typically, about 100 KV, kilovolts, RMS, root mean square, to 150 KV RMS is to be placed between the inner surface of envelope 235 and the surface of spherical target 11. This is the net voltage between these points. There will be a voltage drop through envelope 21 and the ground potential point 153. This additional voltage drop will vary as a result of the AC potential frequency and the makeup of the intervening structures. This will vary with the differing embodiments of this invention. The potential provided by power supply 130 is at a predetermined voltage from 10 KV AC RMS to 25,000,000 AC RMS, preferably from 50 KV AC RMS to 500 KV AC RMS, in particular from 100 KV AC RMS to 250 KV AC RMS. This potential is at a predetermined frequency from 60 Hertz to 1,000,000 Hertz, preferably 10,000 Hertz to 100,000 Hertz, in particular from 20,000 Hertz to 50,000 Hertz. Using an example of 100 KV RMS, factoring for the internal resistance losses of the power supply and adding a 50 percent safety factor, the puncture breakdown of the insulating medium 241 should be about 840 KV. The transformer oil of this embodiment has a puncture breakdown of about 50 KV per millimeter, mm, at 60 Hz. This comes to about 1.7 cm, centimeters. A thickness of 10 cm should be entirely adequate. With the net operating voltage of the reactor being 100 KV RMS, the power supply should put out 200 KV RMS for peak efficiency of energy transfer. Insulating and cooling medium 241 is a major functional change in order to make this invention function as a nuclear reactor. All previous devices have the earth ground point 153 within the reactor chamber, at the reactor chamber itself, or along the outer surface of the reactor chamber. This will function adequately at DC, direct current, potentials. However, because of the characteristics of AC potentials, this will not reliably work at AC frequencies. Functioning becomes even more difficult as the frequency of the AC increases. I will briefly recite these problems. They are addressed and resolved by the insulating and cooling medium 241 and by the concentrically and spherically placed relationship between spherical target electrode 11 and the spherical inner surface of insulated envelope 21. This invention can also work with shapes other than spheres, such as toroids, cylinders, and spiral helix shapes. But the symmetrical relationship between a given reactor envelope and it's correspondingly shaped target electrode must be maintained for operation as a fusion reactor. Fusion requires the overcoming of intense near inter particle repulsive forces as the particles collide. This requires an evenly and symmetrically developed electric field between the target electrode and the inner surface of it's containing envelope. Electric field asymmetry and variation will allow for scattering, rather than collision of particles. Lack of fusion would be the result. Sufficient impact for incandescence of the target may permit illumination, but it would prevent fusion. Removal of RF ground potential from beyond the outer surface of insulated reactor envelope 21 to the outer surface of insulated container 237 or beyond permits the development of a nearly equal potential difference point along the inner surface of insulated reactor envelope 21. As a result, a symmetrical electric field will develop in the enclosed space between the target electrode 11 and the inner surface of the reactor envelope 21. Focus of ions onto the surface of the target electrode is the result. Worked results later presented on a example embodiment of this invention indicate at 50 KHz about 99.99 percent of the applied AC potential appears between the inner surface of spherical reactor chamber 21 and target electrode 11. This is about 0.01 percent voltage variation within this electric field. Without insulating and cooling medium 241 this would be impossible. Suspension of such a device within an atmosphere conductive at RF frequencies would lead to considerable voltage variation along both the outer and inner surfaces of insulated spherical envelope 21. The result would be internal arcing and the formation of plasma filaments short circuiting the potential difference between these locations. The presence of increasing amounts of capacitive reactance with increasing frequency of AC potential would sufficiently load down the power supply to make practical delivery of sufficient acceleration voltage at reasonable power levels impossible. Conductance of AC through this capacitance would also cause overheating. It would result in the target electrode to have to dissipate more power than the resultant fusion reactions would be permitted to produce. Such a device would consume more drive power than energy produced. This is permitted when the device is operated as a neutron generator or source. It precludes operation of the device as a net producer of energy. Another advance in this invention is the enclosure of the insulating and cooling means 241 within a thermally insulated container 237. This permits the outward radiation of power, particulate radiations, and waveform radiations, but restricts the inward movement of heat energy released within the absorber medium 242 from moving backward into the reactor thereby increasing it's heat loading. It provides for the absorption of emitted radiations from the reactor. This allows for: the harnessing of said radiations to do work, the shielding of the external environment of the reactor from radiations, and the cooling of the contained reactor and it's associated internal components. Target 11 is the location of fusion reactions. A varying and polarity reversing electric field is formed between this centrally located target 11 and the inner surface of spherical envelope 21. This field will be evenly distributed and symmetrical. On both alternations, at sufficient potential, the enclosed rarefied Deuterium gas 235 is ionized. After ionization, the gas is either accelerated to the envelope 21 or to the target 11 depending on the given polarity of the field at that instant. On inward passage of the ions, generally with potentials exceeding 100 KV to about 150 KV, the ions impact with each other at the target surface with fusion reactive velocities. Considering application of 141 KV peak AC applied at 50 Khz, the duty cycle of the instantaneous potential exceeding 100 KV is about 25 percent. These voltages can be scaled up or down for given operational considerations. The Deuterium gas 235 is at a pressure of about 0.01 Torr. Prior to operation, the reactor is evacuated and is then baked without, and then with Deuterium gas present. This is to cleanse the contents of contaminant gases. The reactor is placed into operation. Deuterium gas 235 is delivered at the proper pressure and the reacted gases are removed by associated plumbing apparatus, not described. The gas alternately ionizes and impacts the target electrode 11 resulting in fusion reactions. The polarity reverses and the gas deionizes. The gas is then reionized and is propelled outward to the reactor envelope 21. This is the operational principle of this invention. The alternating electric field provides for a continuos on off nature of the reactions, and for the alternating radial inward and then radial outward acceleration of the contained gas. These principals allow for reaction stability, controllability, safety, and the ongoing injection and extraction of fuel and waste gases to permit continuos ongoing operation. The operational embodiment of this invention is applicable to power production and neutron production. The physical target version of this invention limits the device to given power levels. The following worked embodiment has a 1 cm target electrode diameter. Such a device can dissipate no more than about 250 watts. This example is for demonstration and calculating purposes only. Up scaling of the target electrode to 10 cm allows of about 25 KW, kilowatts, 20 cm of about 100 KW, and 50 cm of about 628 KW. These power levels can be further increased by placing cooling passages within the target electrode. Such modification would be a future improvement of this basic invention. As part of another patent application, the target electrode 11 is replaced by a virtual target representing a point in space. Such a device could easily operate within megawatt power levels. This invention is also able to operate with other shapes such as toroids, cylinders, and helixes. Gases other than straight Deuterium may be used, such as Tritium, Deuterium Tritium mixtures, and other fusion reactive gases. Catalyst gases such as Methane or Deuterane may be used to increase efficiency. FIG. 2 shows representations of sine wave potentials with amplitude increasing from left to right. The upsweep of the sine wave curve is represented by 166. A fusion threshold is shown at 165. Potentials above this magnitude cause fusion as indicated by portions of the curve 172. The down sweep of the sine wave curve is represented by 167. The change of polarity is represented by 168. The action of this alternating potential is detailed in the last drawings of 4-7. The next five FIGS. 3 through 7 will be discussed together. They show the same arrangement of layers as built. However, they show the functional changes as a negative potential is placed upon the target electrode. Shown is the subsequent ionization of the contained gas. This continues with the differential acceleration of charged particles. The formation of a new capacitor in the reactor. The charging of this new capacitor. The formation of a capacitive voltage divider. The increased acceleration of positive ions. All of this occurs during the negative alternation and occurs before the peak potential of the negative alternation is reached. This represents less than the first 90 degrees of an AC alternation. On the application of the subsequent reverse alternation, the reverse occurs. This is not detailed, for it does not illustrate the particle acceleration resulting in nuclear reactions. But what does happen is the stopping of the nuclear reactions and the disassembly of the central reacting mass. The positive ions are accelerated outward to the reactor envelope. They transfer energy to the reactor envelope upon impact. This becomes one of the means of transport of energy out from the reaction center. FIG. 3 shows a partial cross section of a spherical reactor and central target electrode and the intervening material between this reactor and ground potential. It shows the conductive and non conductive layers which form a capacitive voltage divider across the power supply. It includes a schematic representation of the capacitance across the power supply. At this instant in time no voltage is applied by the power supply. The representations in the following figures are basically the same excepting for the changes made as a result of the power supply applying an increasingly negative potential between the target electrode and ground potential. FIG. 4 represents the time period when an initial negative voltage is applied to the target electrode. It shows an electric field within the reactor chamber which is becoming a capacitor. This time is represented as the initial part of the up sweep of the sine curve shown as 166. The electric field has not reached sufficient intensity to ionize the contained gas. FIG. 5 represents a time period after initial ionization of the gas within the reactor. In time it is still during the sine wave up sweep shown at 166, but it is at an increased intensity at a latter time during the cycle. It shows the initial differential acceleration of charged particles. Positively charged particles are accelerated radially inward towards the target electrode. Negative electrons are accelerated radially outward towards the reactor vessel envelope. A net current flows through the capacitor at this time. This current is composed of positive ions moving inward and electrons moving outward. FIG. 6 represents a the time period in which the power supply continues to provide a further increasing negative potential to the target electrode. It represents a time in the cycle shifted right from that time in FIG. 5. It still is during the up sweep region 166. Some of the electrons have reached and stopped at the inner surface of the reactor envelope. This represents a decrease in current through this capacitor forming within the reactor. The electrons collecting at the inner surface of the envelope begin to form the plate of this new capacitor within the reactor. The inward proceeding positive charges continue to increase in velocity at this time. FIG. 7 represents a the time period within an AC voltage potential in which the power supply continues to provide a further increasing negative potential to the target electrode. It represents a time within the cycle represented by region 172 through the cycle peak amplitude. All of the electrons have stopped at the inner lining of the reactor envelope. These electrons form the plate of a capacitor within the reactor. At this time the current flow through this capacitor is at a minimum. The capacitor is charging with increasing potential difference across it's plates. This capacitor is in series connection within the capacitive voltage divider between the terminals of the power supply. A portion of the total power supply output potential is now across this capacitor within the reactor. The magnitude of the voltage across the new capacitor 128 within the reactor is in reverse relationship to that capacitor's value of capacitance with respect to the total capacitance of the voltage divider. The plates of this capacitor consist of the target electrode centrally and the electron layer peripherally. The increasing negative potential charges this capacitor to higher and higher potentials as the negative alternation continues to increase in intensity. The central target electrode is negative with respect to the outer plate of this capacitor formed by the electrons stopped at the inner layer of the reactor envelope. As the power supply continues to provide an increasing potential, the voltage between the inner layer of the reactor envelope and the central target electrode reaches an intensity sufficient to accelerate the positive ions to the target with fusion reactive energies and velocities. Once the crest of the peak electric field intensity passes during region 172, fusion continues for a period of time due to particle inertia acquired during acceleration. Inward acceleration actually continues during the down sweep of the sine wave curve at 167. The amount of inward acceleration becomes progressively less to where the forces of mutual repulsion predominate and the assembled reacting mass begins to disassemble. All inward acceleration ceases by polarity change point 168. During the next 180 degrees of the sine wave cycle, the process repeats, but with opposite effects. Electrons are accelerated inward and positive ions are accelerated outward. This cycle repeats over and over as driven by the repetitive oscillation nature of the drive potential. The operational embodiment of this invention is a worked example of how this invention functions. A small 250 watt device is presented. This device operates with a power gain of about three which is very good for fusion power sources. But increased efficiencies can be expected on upsizing this example. It is given is to demonstrate the utility of this invention. This 250 watt device consists of a Titanium target spherical electrode of 1 cm in diameter. It is in a glass envelope which has an inside diameter of 21 cm. It contains Deuterium gas at a pressure of about 0.01 Torr. It is within a vacuum insulated flask with an inside radius of 41 cm containing transformer oil. The capacitance between the internal electrode and the inner surface of the envelope is about 0.03 picofarads, which will be referred to as C1. The capacitance between this surface and a RF ground located at the outside of the insulated flask is about 26 picofarads, and is referred to as C2. The capacitive reactance of C1 is about 106 million ohms at 50 Khz. The capacitive reactance of C2 is about 122 thousand ohms at 50 KHz. The AC potential applied is 100 KV RMS. Peak operational current is about 2.96 ma, milliamps. The net duty cycle where the instantaneous applied voltage is to the target is 100 KV or greater with respect to ground is about 25 percent. The device will be operated at an average power of 250 watts. This corresponds to about 80 watts per square cm of target electrode. This is the operational parameters for a Tungsten cathode operating in a vacuum tube. This is taken from “Electron Tube Design,” by the Electron Tube Division of Radio Corporation of America, a privately issued edition for internal use by employees, first printing 1962, which is hereby incorporated by reference. There are no figures available for Titanium. It is assumed that the thermal qualities of Titanium will approximately equal or exceed that of Tungsten. At 80 watts per square cm, the electrode will be at a temperature of about 2600 degrees Kelvin and have an operational life of about 10,000 hours. The heating due to ion impact is about 23.5 watts per square cm for a total of about 75 watts. Operating at 80 watts per square cm is about 250 watts total power output, with 75 watts input. This represents a power gain of about 333 percent. This is a significant increase over the 105 to 110 percent recently obtained with other fusion reactors. The device can operate at a reduced power level even at higher power gain levels. It can be also upscaled for better efficiency. In the descriptions above, the reader has seen several embodiments of my invention. There are differing applications for these reactors. One example is a fixed power plant for the generation of electricity. Another example is a portable reactor part of a jet engine powering an aircraft. These very different applications make best use of differing embodiments of my invention. In the descriptions above, I have put forth theories of operation that I believe to be correct, such as the way charged particles move in the reactor. While I believe these theories to be correct, I don't wish to be bound by them. While there have been described above the principals of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and is not as a limitation to the scope of the invention. |
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