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abstract | A system for treating target cells with both positive and negative ions comprises a bi-polar beam delivery system configured to create and deliver both positive ion beams and negative ion beams. The bi-polar beam delivery system comprises a bi-polar accelerator configured to accelerate positive and negative ions in the same direction making such a bi-polar beam delivery system practical. |
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abstract | A radiation detector for a computed tomography scanner includes a plurality of radiation detector modules. Each detector module includes an anti-scatter module, at least one radiation absorbing mask and a detector subassembly module. The anti-scatter module includes radiation absorbing anti-scatter plates. The detector subassembly module includes a substrate and an array of detector elements. The radiation absorbing mask is a photoetched grid, formed of a radiation absorbing material and is positioned between the anti-scatter module and the detector elements of array. The strip of the grid, that is parallel to the anti-scatter plates, is wider than each anti-scatter plate. The detector module is aligned with a spatial focus by inserting the alignment pins into the alignment openings of the radiation absorbing mask and the alignment openings of the detector subassembly module. |
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043615341 | description | Before describing the apparatus and technique in detail it will be helpful to consider the mathematics associated with the present invention. In a sample containing both aluminium and silicon, the grade of aluminium, Al, is related to the number of counts, G, recorded of gamma rays emitted by .sup.27 Mg at 0.844 MeV and/or 1.015 MeV, and to the sample weight, W, by the equation: EQU Al=a.sub.0 +a.sub.1 G+a.sub.2 W. (1) The constant coefficients a.sub.0, a.sub.1 and a.sub.2 are determined from linear regression analysis by calibrating the responses G and W of the apparatus against the aluminium content of known samples using linear regression analysis. The number of counts G is determined from the equation EQU G=G.sub.T -kJ, (2) where G.sub.T is the total number of gamma rays recorded in an energy window encompassing the 0.844 MeV and/or 1.015 peaks, J is the total number of counts recorded of 1.78 MeV gamma rays, and k is a constant. The term kJ is used to subtract the spectral continuum due to both the Compton scattered 1.78 MeV gamma radiation and background due to the neutron source. Thus EQU Al=a.sub.0 +a.sub.1 G.sub.T +a.sub.2 W+a.sub.3 J, (3) where a.sub.3 =-a.sub.1 K. Similarly, the chemical concentration of silicon, Si, in the sample can be related to the number of counts per unit time, H, of 1.78 MeV gamma rays due to the .sup.28 Si(n,p).sup.28 Al reaction and the sample weight, W, by: EQU Si=b.sub.0 +b.sub.1 H+b.sub.2 W, (4) where b.sub.0, b.sub.1 and b.sub.2 are constant coefficients obtainable from regression analysis by calibrating the responses H and W against the silicon content of known samples using linear regression analysis. In practice, with bulk bauxite samples, however, the total number of counts per unit time due to 1.78 MeV gamma rays from .sup.28 Al, J, contains two indistinguishable components H and I, where I is the component contributed by thermal neutron activation of .sup.27 Al. The number of counts, I, is proportional to the product of the number of thermal neutrons, N.sub.t, measured during irradiation and the aluminium concentration of the sample. Because the number of counts, G.sub.T, previously referred to, are related to the aluminium concentration, and since N.sub.t is proportional to the thermal neutron flux within the sample, the actual silicon concentration in the sample is given by: EQU Si=b.sub.0 +b.sub.3 J+b.sub.4 G.sub.T N.sub.t +b.sub.2 W, (5) where b.sub.3 and b.sub.4 are regression coefficients, and where b.sub.0, b.sub.2, b.sub.3 and b.sub.4 are calibration coefficients determined by linear regression analysis as described above. Equations (3) and (5) are used in analysis of materials in accordance with the present invention. The experimental arrangement devised to test the present invention, and illustrated in FIG. 1, comprises a neutron source 10 and thermal neutron detector 11 located close to a railway track 12 on which a small sample of material 13 can be moved. Also close to the track 12, but remote from the neutron source 10 and detector 11, is a gamma ray detector 14, suitably shielded by a lead screen 15 and a masonry shield 16. In the experimental facility shown in FIG. 1, the neutron source was 20 Ci of Am-Be, giving an estimated output of 4.4.times.10.sup.7 n/s. The samples of material 13 were contained in a rectangular brass box 17 (25.times.25.times.4 cm deep) and were irradiated by fast neutrons from underneath. The neutron source 10 was enclosed within a cyclindrical shell 21 of cadmium (see FIG. 2) which prevented the thermal neutrons emitted by the source from reaching the sample 13. The thermal neutron flux generated within the sample 13 was monitored by thermal neutron detector 11, which was a high efficiency neutron detector (filled to a pressure of 4 atmospheres with a mixture of .sup.3 He and Kr) which was also located beneath the sample container and adjacent to the neutron source. After irradiation by source 10 for 6 minutes, the sample 13 was transferred within 15 seconds to a position immediately above the gamma detector 14, which comprised a 127.times.127 mm NaI(T1) scintillation detector. The distance between the neutron source 10 and gamma detector 14 was about 7 meters. This separation between source and detector added a considerable component of distance shielding to the already appreciable shielding against source radiation provided by concrete brick structures 16 and 26 built around both the NaI(T1) detector 14 and the neutron source assemblies. The lead shield 15, of thickness 3 cm, which was built around the body of the scintillation detector 14 so as to leave only the upper plane surface exposed for measurements, provided further reduction of background radiation. Spectrum stabilization was obtained using 0.662 MeV gamma rays from a .sup.137 Cs source (not shown in the drawings) which provided a reference peak for a Canberra Industries Model 1520 analogue spectrum stabilizer. The energy spectra of gamma rays detected by the scintillation detector 14 were analysed in the initial phases of the development of the method by a Tracor Northern 4096-channel pulse height analyser (model TN-1700). At a later stage, when energy-pulse height calibrations had been fully established, Ortec single channel analysers, digital counters and a timer were used, as shown in FIG. 2, for their greater suitability to plant or mine site operating requirements. The amplifiers used were a Tennelec linear amplifier for the scintillation detector 14 and an Ortec spectroscopy amplifier for the neutron detector 11. Output from the digital counters was obtained with a strip printer. The partly schematic and partly block form diagram of FIG. 2 is essentially a more comprehensive illustration of the apparatus shown in FIG. 1. In particular, the high energy neutron source 10 and the thermal neutron detector 11 are shown more explicitly, with the neutron source 10 encased in cadmium shielding 21 and the source 10 and detector 11 positioned within masonry shielding 26. A single high voltage power supply 22 services both the thermal neutron detector 11 and the gamma ray detector 14. The output signal from the thermal neutron detector 11 is first amplified in gain control unit 23, and if the signal, when amplified, exceeds a required threshold value (determined by threshold device 24), it is supplied to the input of a digital counter 25. The output from counter 25 is fed into processor 32, which is usually a microprocessor or small computer, programmed to effect the required analysis from its three input signals. The other two input signals to the processor 32 are signals indicative of the values G and J (see the above description). These signals are derived from the gamma rays received by the gamma detector 14 as a result of the decay of, respectively, the .sup.28 Al and .sup.27 Mg isotopes formed during the irradiation of the sample. These inputs are obtained after the output of detector 14 has been processed by amplifier 26, a gamma ray discriminator, and digital counters 28 and 28A. The gamma ray discriminator has been shown in the drawing as two gamma ray single channel analysers 27 and 27A. In practice, these devices 27 and 27A may be a single unit comprising a multi-channel analyser with outputs from channels which have energy windows, typically about 0.35 MeV wide, centred on 0.844 MeV, 1.015 MeV and 1.78 MeV. Presettable timer 31 controls the operation of the digital counters 28 and 28A. Timer 31 will be synchronized with, but operating sequentially to, pre-settable timer 30 which controls the operation of the digital counter 25. The output from the processor 32 may be recorded. For example, it may be stored on magnetic tape, magnetic disc, magnetic card, punched tape, punched card, or on any other suitable medium. Alternatively, or additionally, the output from the processor 32 may be presented as a digital display, a paper print-out, or on a chart recorder. Those skilled in this field will appreciate that the actual form of the presentation of the output from processor 32 may be chosen to suit the requirements of the owner or operator of the equipment. Accordingly, a single, unspecified display unit 33 has been included in FIG. 2. In one example of the experimental testing of the present invention, bauxite samples were dried to less than 5 percent (by weight) free moisture and crushed to -6 mm particle size. It should be noted, however, that this amount of pre-treatment is not essential. The bauxite samples contained aluminium in the range from 26 wt. percent to 32 wt. percent, whilst the silicon concentrations ranged from 0.9 wt. percent to 4.5 wt. percent. The mass of the sample used for irradiation was about 4 kg. As expected, when the bauxite was irradiated with fast neutrons, the gamma ray spectra were dominated by the 1.78 MeV gamma ray peak due to .sup.28 Al, and by a spectral continuum of gamma rays which had undergone Compton scattering both within the detector and within the bulk sample. This continuum underlies the spectral peaks at 1.015 and 0.844 MeV due to .sup.27 Mg. The Comptom scattering processes in this example were dominated by gamma rays which initially had energies of 1.78 MeV, 1.014 MeV and 0.844 MeV originating from the sample, and 0.662 MeV due to the .sup.137 Cs stabilization reference source. In the case of bauxite, again as expected, the interferences from other constituents, such as the natural radioactive nuclides, was minimal, and those from .sup.56 Mn at 0.846 MeV, 1.811 MeV and 2.113 MeV were very small. (This nuclide, with a 2.57 hr. half life, can arise from the .sup.55 Mn(n,.gamma.).sup.56 Mn reaction, or from a .sup.56 Fe(n,p).sup.56 Mn reaction; the first of these reactions will contribute negligible .sup.56 Mn owing to the extremely low concentration of manganese in Australian bauxites, despite the relatively large cross section of 13.3 barns for that reaction; the second reaction, involving iron, contributes more .sup.56 Mn than the first, but constitutes a constant level of about 2 percent interference, the variation of which is only about 1 percent of the gamma ray signal from .sup.27 Mg.) Another source of spectral interference which occurred in this example arose from the neutron activation of the copper constituent of the brass sample container, which contributed a small peak at 1.05 MeV. It was necessary, therefore, to exclude from calculations all count data that would have been recorded in a narrow energy window, about 0.1 MeV wide, centred at 1.05 MeV. Apart from interferences to the spectral peaks due to .sup.28 Al and .sup.27 Mg from monoenergetic gamma rays emitted by minor constituents of the sample and sample container, there was also substantial interference from the continuum of scattered gamma radiation. The extent of interference with the 1.78 MeV spectral peak appeared to be insignificant owing to negligible gamma radiation apparent at higher energies. However, the 0.844 MeV gamma ray peak due to .sup.27 Mg received considerable interference from the substantial underlying continuum caused by Comptom scattering of the 1.78 MeV gamma radiation from the decay of .sup.28 Al and background from the neutron source. One technique that could have been used to overcome the interference problem when using multichannel pulse height analysers for neutron activation analysis is that which is described in the specification of Australian Pat. No. 468,970. That method entails an estimation of the underlying continuum which is based on the number of counts in an energy channel close to the relevant spectral peak. However, in the present experimental arrangement, an alternative method was effectively implemented with the use of single channel analysers for the activation analysis of bauxite. The method simply entailed the establishment of two particular energy windows. One window, centred at 0.844 MeV, is approximately 0.1 MeV wide. The other window, about 0.35 MeV wide, encompasses the 1.78 MeV peak. Implementation of these two energy-window conditions alone worked well because the counts accumulated within the spectral continuum occurring within the first narrow window are proportional, with good approximation, to the number of counts due to .sup.28 Al, 1.78 MeV gamma radiation. The counts recorded in these two windows were respectively denoted by G.sub.T and J in equations (3) and (5) for purposes of either determining the calibration coefficients, a.sub.i and b.sub.j, or for determining the chemical concentrations of silicon and aluminium in samples when calibrations, and hence coefficients, were already known. After performing a number of experiments with well-blended, effectively homogeneous, ore samples of accurately known composition, the data from the activation analysis were fitted against the known chemical assays for aluminium and silicon by linear regression analysis, in order to determine the constant coefficients in equations (3) and (5). The respective precisions for silicon and aluminium determinations in bulk samples were obtained in terms of the sample standard deviations (s) as shown below: (a) When using equations (3) and (5), and the method of the present invention, PA0 (b) When the contribution by gamma rays from .sup.27 Mg at 0.844 MeV is omitted from equation 5, PA0 (c) When the contributions both by the gamma rays from .sup.27 Mg at 0.844 MeV and thermal neutrons measured below the sample container are omitted from equation 5, for Al: s=0.43 percent Al PA1 for Si: s=0.14 percent Si PA1 for Si: s=0.19 percent Si PA1 for Si: s=0.82 percent Si As shown by the smaller standard deviations for the results obtained using the present invention, the present invention compares most favourably with alternatives (b) and (c). Comparisons between neutron activation determinations for aluminium and silicon, expressed as alumina (Al.sub.2 O.sub.3) and silica (SiO.sub.2) respectively, and determinations by conventional analysis are shown in FIGS. 3 and 4. The calibration equations used to calculate the neutron activation determinations of alumina and silica in FIGS. 3 and 4 were as follows: EQU Al.sub.2 O.sub.3 =71.04-0.946G.sub.T -9.636W-0.242 J (6) EQU SiO.sub.2 =12.93+0.665J-0.0477G.sub.T N.sub.t -2.61W (7) where J and G.sub.T are expressed in thousands of counts, N.sub.t in millions of counts, and W in kilograms. It will be clear to those skilled in this art that (a) the container 17 need not be of brass and thus need not generate a significant component of the gamma spectra being studied, (b) the rail and bulk sample of the experimental arrangement described above can be substituted by a conveyor belt carrying ore (or other material) between a neutron irradiation station and a downstream gamma monitoring station, to enable on-stream analysis for silicon and aluminium of the material being carried by the belt, and (c) the rail and bulk sample of the experimental arrangement described above can be substituted by the stationary walls and surrounding rock of a borehole, and both the source and detector can be simultaneously moved in the borehole to enable borehole logging for silicon and aluminium. For such an arrangement, the high energy neutron source, the thermal neutron detector and the gamma ray detector will be mounted on a borehole probe, which can then be lowered into a borehole to any required position to analyse the rock surrounding the borehole. Normally the signal processing equipment will not be included on the probe, but will be connected to the source and detectors by long cables. |
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048088315 | abstract | A sealed container for either wet or dry radioactive samples to be counted by an associated counter. The container includes a carrier having an aperture formed therethrough. A window is connected to one side of the carrier and defines a cavity with the carrier. The cavity is accessible via at least one aperture in the carrier. A tab is removably attached to another side of the carrier for sealing the aperture. |
056688474 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a radiation emitting device, and particularly to a system and a method for adjusting the radiation delivered to an object in a radiation treatment device. 2. Description of the Related Art Radiation-emitting devices are generally known and used, for instance as radiation therapy devices for the treatment of patients. A radiation therapy device generally comprises a gantry which can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment. A linear accelerator is located in the gantry for generating a high-energy radiation beam for therapy. This high energy radiation beam can be an electron radiation or photon (X-ray) beam. During treatment, this radiation beam is trained on one zone of a patient lying in the isocenter of the gantry rotation. In order to control the radiation emitted toward an object, a beam-shielding device such as a plate arrangement or collimator is usually provided in the trajectory of the radiation beam between the radiation source and the object. This beam-shielding device defines a field on the object to which a prescribed amount of radiation is to be delivered. The radiation delivered to an object may be analyzed into primary and scattered components. The primary radiation is made up of the initial or original photons emitted from the radiation source, and the scattered radiation is the result of the photons scattered by the plate arrangement itself. The beam's radiation output in free space increases because of the increased collimator scatter, which is added to the primary beam. In other words, a point in the field is subjected not only to direct radiation, that is the primary component, but also to radiation that is scattered from the plate arrangement. The ratio of the radiation output in air with the scatterer to the radiation output without the scatterer for a reference field (for instance 10.times.10 cm) is commonly called the "output factor" or the collimator scatter factor. The concept and definition of the output factor are well understood in the art. Thus, due to these scattered photons, the dose rate applied to the surface of the object changes dependent on the size of the opening in the plate arrangement, that is, on the field size. This means that the radiation emitted to the same spot, for instance in the center of the radiation beam onto the object, changes according to the size of the opening in the plate arrangement. When the plate arrangement shows only a small opening, then the accumulated dose at the same spot is less than the accumulated dose at the same spot when the opening is big. Frequently, special filters or absorbing blocks are located in the trajectory of the radiation beam to modify its isodose distribution. A most commonly used filter is the wedge filter. This is a wedge-shaped absorbing block which causes a progressive decrease in the intensity across the beam, resulting in isodose curves that are modified relative to their normal positions. Such wedge filters are usually made of dense material, such as lead or steel, or other absorbing material. The presence of a wedge filter decreases the output of the radiation-emitting device and this decrease must be taken into account in treatment calculations. This effect is characterized by the so-called "wedge factor", defined as the ratio of doses with and without the wedge at a point in the object along the central axis of the radiation beam. The wedge factor depends on the material, size and angle of the wedge. Wedges, and particular the wedge factor, are described in Faiz M. Khan, Ph.D, "The Physics of Radiation Therapy", Williams & Wilkins, pages 234 to 238. The delivery of radiation by such a radiation therapy device is prescribed and approved by an oncologist. Actual operation of the radiation equipment, however, is normally done by a therapist. When the therapist administers the actual delivery of the radiation treatment as prescribed by the oncologist, the device is programmed to deliver that specific treatment. When programming the treatment, the therapist has to take into consideration the output factor and has to adjust the dose delivery based on the plate arrangement opening in order to achieve the prescribed radiation output on the surface of the object. This adjustment can be made according to known calculations, but the therapist normally has to do them manually, which can easily lead to errors. In the context of radiation therapy, a miscalculation can lead to either a dose that is too low and is ineffective, or that is too high and dangerous; a large error, for example, a misplaced decimal point, can be lethal. U.S. Pat. No. 5,148,032 discloses a radiation treatment device in which isodose curves in the object are adjusted both by a plate arrangement, which includes at least one movable plate that is controlled during irradiation, and by varying the radiation output of the radiation beam during irradiation, so that a wide range of variations in the possible isodose curves is obtained. A wedge-shaped isodose distribution is established, for example, by moving one plate at a constant speed while simultaneously changing the radiation output of the radiation beam. In this radiation treatment device there is no physical absorbing block in the trajectory of the radiation beam, and the therapist has to take this into account. What is needed is a method, and corresponding system, for adjusting the delivery of radiation to the object in order to make sure that the actually delivered radiation output is exactly the same as the desired radiation output, independent of the use of a wedge function. SUMMARY OF THE INVENTION According to the invention, radiation output delivered to an object from a radiation source is adjusted by generating a radiation beam having a variable radiation output and a substantially lossless beam path from a radiation source to the object. The beam path is delimited by moving at least one beam-shielding device such as a movable plate. An irradiated field of the object is defined. The radiation output of the beam is varied as a predetermined function of the position of the beam-shielding device, a wedge factor of the radiation output thereby varying according to a predetermined profile, in which the wedge factor is defined as the ratio between a reference radiation output along a reference axis of the beam with a predetermined physical wedge in the beam path and an actual radiation output of the beam in a substantially lossless beam path. The radiation output is varied such that the wedge factor is constant regardless of the size of the irradiated field, and is preferably equal to unity. |
claims | 1. A system comprising:for a nuclear fission traveling wave burnfront propagating along first and second dimensions in a nuclear fission reactor core, first electrical circuitry configured to determine a desired shape of the nuclear fission traveling wave burnfront along the second dimension within a plurality of nuclear fission fuel subassemblies according to a selected set of dimensional constraints;second electrical circuitry configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations in the nuclear fission reactor core toward respective second locations in the nuclear fission reactor core in a manner responsive to the desired shape; anda subassembly configured to migrate selected ones of the plurality of nuclear fission fuel subassemblies responsive to the second electrical circuitry. 2. The system of claim 1, wherein the second electrical circuitry is further configured to determine an existing shape of the nuclear fission traveling wave burnfront. 3. The system of claim 1, wherein the second electrical circuitry is further configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner to establish the desired shape. 4. The system of claim 1, wherein the second electrical circuitry is further configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner to maintain the desired shape. 5. The system of claim 1, wherein the second electrical circuitry is further configured to determine a time when to migrate the selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. 6. The system of claim 1, wherein:the first dimension includes an axial dimension; andthe second dimension includes a radial dimension. 7. The system of claim 1, wherein:the first dimension includes an axial dimension; andthe second dimension includes a lateral dimension. 8. The system of claim 1, wherein:the first dimension includes a lateral dimension; andthe second dimension includes an axial dimension. 9. The system of claim 1, wherein:the first locations are intermediate the second locations and an exterior of the nuclear fission reactor core. 10. The system of claim 9, wherein an attribute of position within the nuclear fission reactor core of the second locations and the first locations include geometrical proximity to a central portion of the nuclear fission reactor core. 11. The system of claim 9, wherein the inward locations and the outward locations are based on neutron flux such that neutron flux at the inward locations is greater than neutron flux at the outward locations. 12. The system of claim 9, wherein the inward locations and the outward locations are based on reactivity such that keffective at the inward locations is greater than keffective at the outward locations. 13. The system of claim 1, wherein:the first locations include inward locations; andthe second locations include outward locations. 14. The system of claim 13, wherein the inward locations and outward locations are based on geometrical proximity to a central portion of the reactor core. 15. The system of claim 13, wherein the inward locations and the outward locations are based on neutron flux such that neutron flux at the inward locations is greater than neutron flux at the outward locations. 16. The system of claim 13, wherein the inward locations and the outward locations are based on reactivity such that keffective at the inward locations is greater than keffective at the outward locations. 17. The system of claim 1, wherein the second electrical circuitry is further configured to determine rotation of at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 18. The system of claim 1, wherein the second electrical circuitry is further configured to determine inversion of at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 19. The system of claim 1, wherein the subassembly includes a nuclear fuel handling apparatus. 20. The system of claim 1, wherein the subassembly is further configured to radially migrate selected ones of the plurality of nuclear fission fuel subassemblies from respective first locations toward respective second locations. 21. The system of claim 1, wherein the subassembly is further configured to spirally migrate selected ones of the plurality of nuclear fission fuel subassemblies from respective first locations toward respective second locations. 22. The system of claim 1, wherein the subassembly is further configured to axially translate selected ones of the plurality of nuclear fission fuel subassemblies. 23. The system of claim 1, wherein the subassembly is further configured to rotate selected ones of the plurality of nuclear fission fuel subassemblies. 24. The system of claim 1, wherein the subassembly is further configured to invert selected ones of the plurality of nuclear fission fuel subassemblies. 25. A nuclear fission traveling wave reactor comprising:a nuclear fission traveling wave reactor core;a plurality of nuclear fission fuel subassemblies received in the nuclear fission traveling wave reactor core, each of the plurality of nuclear fission fuel subassemblies being configured to propagate a nuclear fission traveling wave burnfront therein along first and second dimensions in the nuclear fission reactor core;first electrical circuitry configured to determine a desired shape of the nuclear fission traveling wave burnfront along the second dimension within a plurality of nuclear fission fuel subassemblies according to a selected set of dimensional constraints;second electrical circuitry configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations in the nuclear fission reactor core toward respective second locations in the nuclear fission reactor core in a manner responsive to the desired shape; anda subassembly configured to migrate selected ones of the plurality of nuclear fission fuel subassemblies responsive to the second electrical circuitry. 26. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine an existing shape of the nuclear fission traveling wave burnfront. 27. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner to establish the desired shape. 28. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine a migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner to maintain the desired shape. 29. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine a time when to migrate the selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations in a manner responsive to the desired shape. 30. The reactor of claim 25, wherein the plurality of nuclear fission fuel subassemblies are elongate along the second dimension. 31. The reactor of claim 25, wherein the first dimension is substantially orthogonal to an elongated axis of the plurality of nuclear fission subassemblies. 32. The reactor of claim 25, wherein the first dimension and the second dimension are substantially orthogonal to each other. 33. The reactor of claim 25, wherein:the first dimension includes a radial dimension; andthe second dimension includes an axial dimension. 34. The reactor of claim 25, wherein:the first dimension includes an axial dimension; andthe second dimension includes a radial dimension. 35. The reactor of claim 25, wherein:the first dimension includes an axial dimension; andthe second dimension includes a lateral dimension. 36. The reactor of claim 25, wherein:the first dimension includes a lateral dimension; andthe second dimension includes an axial dimension. 37. The reactor of claim 25, wherein:the first locations are intermediate the second locations and an exterior of the nuclear fission reactor core. 38. The reactor of claim 37, wherein an attribute of position within the nuclear fission reactor core of the second locations and the first locations include geometrical proximity to a central portion of the nuclear fission reactor core. 39. The reactor of claim 37, wherein the inward locations and the outward locations are based on neutron flux such that neutron flux at the inward locations is greater than neutron flux at the outward locations. 40. The reactor of claim 37, wherein the inward locations and the outward locations are based on reactivity such that keffective at the inward locations is greater than keffective at the outward locations. 41. The reactor of claim 25, wherein:the first locations include inward locations; andthe second locations include outward locations. 42. The reactor of claim 41, wherein the inward locations and outward locations are based on geometrical proximity to a central portion of the reactor core. 43. The reactor of claim 41, wherein the inward locations and the outward locations are based on neutron flux such that neutron flux at the inward locations is greater than neutron flux at the outward locations. 44. The reactor of claim 41, wherein the inward locations and the outward locations are based on reactivity such that keffective at the inward locations is greater than keffective at the outward locations. 45. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine rotation of at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 46. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine inversion of at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 47. The reactor of claim 25, wherein the selected set of dimensional constraints includes a predetermined maximum distance along the second dimension. 48. The reactor of claim 25, wherein the selected set of dimensional constraints is a function of at least one burnfront criteria. 49. The reactor of claim 48, wherein the burnfront criteria includes neutron flux. 50. The reactor of claim 48, wherein the burnfront criteria includes neutron fluence. 51. The reactor of claim 48, wherein the burnfront criteria includes burnfront location within at least one of the selected ones of the plurality of nuclear fission fuel subassemblies. 52. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine a radial migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations. 53. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine a spiral migration of selected ones of the plurality of nuclear fission fuel subassemblies along the first dimension from respective first locations toward respective second locations. 54. The reactor of claim 25, wherein the second electrical circuitry is further configured to determine an axial translation of selected ones of the plurality of nuclear fission fuel subassemblies. 55. The reactor of claim 25, wherein the desired shape includes a shape chosen from a substantially spherical shape of the nuclear fission traveling wave burnfront, a shape conforming to a selected continuously curved surface, a shape that is substantially rotationally symmetrical around the second dimension, and a shape having substantial n-fold rotational symmetry around the second dimension. 56. The reactor of claim 25, wherein the desired shape of the nuclear fission traveling wave burnfront is asymmetrical. 57. The reactor of claim 25, wherein the subassembly includes a nuclear fuel handling apparatus. 58. The reactor of claim 25, wherein the subassembly is further configured to radially migrate selected ones of the plurality of nuclear fission fuel subassemblies from respective first locations toward respective second locations. 59. The reactor of claim 25, wherein the subassembly is further configured to spirally migrate selected ones of the plurality of nuclear fission fuel subassemblies from respective first locations toward respective second locations. 60. The reactor of claim 25, wherein the subassembly is further configured to axially translate selected ones of the plurality of nuclear fission fuel subassemblies. 61. The reactor of claim 25, wherein the subassembly is further configured to rotate selected ones of the plurality of nuclear fission fuel subassemblies. 62. The reactor of claim 25, wherein the subassembly is further configured to invert selected ones of the plurality of nuclear fission fuel subassemblies. |
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042809215 | claims | 1. A method for immobilizing and solidifying and reducing the volume of hazardous waste material which comprises blending substantially anhydrous powdered waste material with powdered metal, and subjecting the admixture to a pressure of at least 10 tons/in.sup.2 for sufficient time to provide a strong solid of reduced volume and wherein the amount of said powdered metal is up to about 20% by weight based on the weight of solid waste material and is at least sufficient to immobilize and solidify said waste when subjected to said pressure. 2. The method of claim 1 wherein said waste material has a diameter of about 1 micron to about 1/16 inch. 3. The method of claim 1 wherein said waste material is low level radioactive waste material. 4. The method of claim 1 wherein said powdered metal is selected from the group consisting of powdered iron, powdered nickel, powdered bronze alloys, powdered aluminum, and powdered steels. 5. The method of claim 1 wherein said powdered metal is powdered iron. 6. The method of claim 1 wherein the amount of said metal is at least about 1.5% by weight based upon the weight of the solid waste material. 7. The method of claim 1 wherein the amount of powdered metal is about 1.5 to about 3% by weight based upon the weight of the solid waste material. 8. The method of claim 1 wherein the powdered metal is employed in amounts of about 2 to about 3% by weight based upon the weight of the solid waste material. 9. The method of claim 1 wherein the powdered metal has a particle size distribution as follows: 10. The method of claim 1 wherein the pressure is 10 to about 50 tons per square inch. 11. The method of claim 1 wherein the mixture of solid waste material and powdered metal is subjected to the pressure for at least about 3 seconds. 12. The method of claim 1 wherein the composition also includes about 3 to about 5% by weight of a solid lubricant. 13. The method of claim 12 wherein said lubricant is powdered: petroleum wax, graphite, or molybdenum disulphide. 14. A strong, reduced volume, self-supporting solid obtained by the method of claim 1. 15. The method for immobilizing, solidifying and reducing the volume of hazardous waste material which comprises stacking a plurality of the strong solids produced by the method of claim 1, inserting the resulting stack into a container, conveying the container with the stack to an encapsulation station, and filling the free space in the container with a sealant to thereby encapsulate the solids and render them waterproof, chemically inert and leachproof. 16. The method of claim 1 wherein the powdered metal has a diameter of about 25 microns to about 1/32 inch. 17. The method of claim 1 which is carried out in the absence of a sintering step. 18. The method of claim 1 wherein the powdered waste material is selected from the group consisting of low level radioactive materials, spent acids, spent salts, spent caustics, cyclone separator particles, solids from electroplating sludges, solid residues from chemical etching, catalyst fines, pigment residues from paint facilities, high sulfur residues from paper pulp manufacturing, and residues from mineral acid, agricultural, pesticide, and drug manufacturing. 19. The method of claim 18 wherein the waste material is mixed with a powdered metal selected from the group consisting of powdered iron, powdered nickel, powdered bronze alloys, powdered aluminum, and powdered steels. 20. A solid having a compressive strength of at least 800 pounds per square inch obtained by the method of claim 19. 21. A solid having a compressive strength of at least 800 pounds per square inch obtained by the method of claim 1. 22. A solid having a compressive strength of at least 800 pounds per square inch and containing 1.5 to 20 percent by weight of powdered metal, based on the weight of the solid waste material, obtained by the method of claim 1. |
044420650 | description | DETAILED DESCRIPTION FIG. 1 shows a nuclear reactor including a containment structure 12 and a primary reactor vessel 14 containing the central core structure, arranged in a generally conventional configuration, with the surface of the earth being generally indicated by the line 16. The new structure which has been retrofitted to the nuclear reactor includes an isolation tube 18, and a core catcher heat exchanger structure 20. The floor of the containment structure 12 has been thinned down at 22, so that, in the unlikely event of a melt-down of the core 14, the floor 22 will be penetrated by the melted down fragments, and they will descend into the isolation tube 18 and eventually down into the core catcher heat exchanger structure 20. The isolation tube or conduit 18 includes transverse sheets, such as thin sheets of steel 24, and suitable layers of shock absorbing material which is relatively light in weight, such as sand, as shown by reference numerals 26, supported by the sheet material 24. Similar arrangements may be provided in the central area of the heat exchanger 20 to delay the descent of the molten core and related material, so that a slow controlled descent is achieved which will not destroy the heat exchanger walls by undue shock. The isolation tube 18 is preferably provided with an inner steel liner 28 (see FIG. 2), a layer of refractory material 30, such as carbon, and then an additional outer steel jacket 32. The entire assembly including the isolation tube 18 and the core-catcher heat exchanger 20 is enclosed in a reinforced concrete shell 34. As best shown in FIG. 2, the core-catcher heat exchanger includes the inner walls 36 and the outer walls 38 which may be extensions of the walls 28 and 32 respectively, which enclose the isolation conduit. Incidentally, it should be noted that the break 40 as schematically indicated between the isolation conduit 80 and the heat exchanger portion 20 of the structure is included to indicate that the action indicated by the circulation arrows 42, 44, and 46 would not occur with the support plates 24 and the sand 26 in the indicated position in FIG. 2, but these structures are merely shown for purposes of greater detail than is possible in FIG. 1. Of course, once the molten material has descended into the heat exchanger area 20, the sand and support plates 26 and 24 would have served their delaying function and would be reduced to molten form. In FIG. 2, the lower circulating arrow 46 represent the cooling action of the heaviest material, uranium oxide, which would descend to the bottom of the heat exchanger structure. Lighter weight material, such as molten steel and the like would be located in the next higher zone as indicated by the circulating arrows 44, while still lighter weight material, such as the sand, or other flux which may be provided within the isolation conduit and the heat exchanger structure, would be floating on top where the arrows 42 are present. The cooling jacket 48 between the inner wall 36 and the outer wall 38 is filled with water, and this automatically circulates through the lower input conduit 50 and the upper output conduit 52, which are connected as shown in FIG. 1 to the cooling structure 54. Molten uranium oxide normally has a melting point in the order of 2100 or 2200 degrees centigrade, which is well above the melting point of approximately 1400 or 1500 degrees centigrade for the inner steel lining 36 which faces the molten uranium oxide. However, the high thermal conductivity of the steel wall relative to that of uranium oxide insures that the steel will not differ significantly in temperature from the adjacent cooling water. In practice, therefore, the uranium oxide immediately adjacent the steel walls of the heat exchanger will solidify and form a "frozen" or solid layer against the steel wall, and the uranium oxide may thus be thought to form its own container within which the cooling action progresses. Of course, the water within the jacket 48 is heated rapidly and circulates through the large conduits 50 and 52 to the water tower 54, where much of the water may boil off, in the course of a month or two, as the molten core material and other miscellaneous molten debris cools down. Instead of a cooling tower 54, water may be drawn from, or returned to, any large body of water, such as a nearby lake, river, or ocean. Of course, with the thick steel walls and the construction as described above, the water does not become radioactive, and accordingly, there is no concern with the boiling off of the water from the water tower 54. Incidentally, the inner wall 36 of the heat exchanger 20 must be firmly supported by structural members, some of which are indicated schematically at 56, to support the very substantial weight of the molten core materials. In FIG. 1, the elevator or hoist structure 62, the vertical shaft 64, and the two horizontal shafts 66 and 68 have been shown to indicate one construction technique whereby the core-catcher arrangements could be retrofitted to an existing nuclear facility. Initially, the vertical shaft would be constructed in accordance with conventional mining techniques, with the two horizontal access tunnels 66 and 68 being dug to the indicated points directly under the core 14. With the relatively small diameter of the isolation tube and core-catching heat exchanger structure, most of the construction work can be accomplished while the reactor is still operating normally. This is particularly important, because the cost of shutdown may be in the order of several hundred thousand dollars per day. However, for a brief period of several days, while the reduced thickness floor 22, and the upper section of the isolation tube 18 are being constructed and positioned, the reactor must be briefly shut down. The input and output water conduits 50 and 52 may follow the access tunnels 66 and 68 during their substantially horizontal sections, and holes for the vertical sections of these conduits may be bored with conventional drilling equipment. In the foregoing discussion, attention has been concentrated on the below-ground structure; however, in some cases, when a melt-down would occur, the core structure might hang up within the containment structure 12, with high levels of heat being generated within this structure 12. In order to accommodate this eventuality, the heat exchanger structure 72 is provided to absorb heat in its section 74 extending within the containment structure 12, and dissipates the absorbed heat in the portion 76 which is within the cooling water 78 inside the cooling tower 54. A substantial protective shield 80 may be provided to protect the heat exchanger structure 74, from the possibly violent events associated with the possible melt-down of the reactor 14. With both the heat exchanger 72 and the core-catcher heat exchanger 20 being coupled to the single water tower 54, it has the capacity to absorb the core-decay heat, whether most of the heat is generated within the structure 12, or if the core, as expected, decends down into the core catching heat exchanger 20. When conventional reactors utilizing slow neutrons and water to slow down the speed of the neutrons, are employed, no special precautions need be taken with regard to the core catcher heat exchanger geometry to prevent it from going "critical" and generating additional heat. However, in the case of fast breeder reactors, there could be some possibility if the mass of the material was sufficiently great, that such criticality could occur. Accordingly, for reactors of this type, a longer and thinner vertically extending heat exchanger could be used, or alternatively a diverging geometry of the type shown in FIG. 3 could be employed. In FIG. 3, the structure, including the inner steel walls 36 and the outer steel walls 38, as well as the concrete enclosing structure 34 would be substantially the same, with a cooling jacket 48, all substantially as shown in FIG. 2. However, at the lowermost end of the heat exchanging structure, with sufficient volume to hold the heavy fast-breeder material, a series of branching arms 92 are provided. The input conduit 50 may be connected by suitable manifold piping 94 to the lower end of the water jacket enclosing each of the branching conduits 92. In addition, the concrete structure 34 is enlarged at its lower end 96 to fully enclose the lower end of the structure. It has been determined that, if the branching conduits 92 are oval, and if the distances across the conduits in the shorter cross-sectional direction are maintained less than about one foot, or about 30 centimeters, there will be no danger of the fast-breeder reactor material going critical. Incidentally, as noted above, the diameter of a nuclear reactor containment shell would normally be in excess of 100 feet, probably in the order of 125 feet. Further, the diameter of the isolation tube and the core catcher, is preferably in the order of two or three meters, or about 10 feet. Translated into the terms of cross-sectional area, the base of a nuclear containment structure would normally be greater than 10,000 square feet or 1,000 square meters, while the cross-sectional area of the isolation tube and the core catcher heat exchanger would normally be in the order of 100 square feet, or ten square meters. Translating these figures into percentages, the transverse dimension of the isolation tube and core catcher structure will normally be less than 10 percent or less than 20 percent of the transverse dimension of the base of the containment structure; and the cross-sectional area of the isolation tube and the core catcher structure will normally be less than 5 percent of the cross-sectional area of the base of the containment structure. For completeness, the following additional patents are cited as being of interest, although they have the shortcomings as noted hereinabove: U.S. Pat. No. 3,640,451, granted Mar. 14, 1972; No. 3,702,802, granted Nov. 14, 1972; No. 3,719,556, granted Mar. 6, 1973; No. 3,964,966, granted June 22, 1976; No. 4,003,785, granted Jan. 18, 1977; No. 4,028,179, granted June 7, 1977; No. 4,072,561, granted Feb. 7, 1978; No. 4,073,682, granted Feb. 14, 1978, and No. 4,113,560, granted Sept. 12, 1978. In closing, it is to be understood that the foregoing description and the drawings relate to specific embodiments of the invention. Other arrangements may be employed in the implementation of the invention without departing from the spirit and scope thereof. For example, instead of using steel for the lining of the isolation tube and the heat exchanger, other high temperature resistant, high strength materials could be employed. Similarly, instead of using sand and steel supporting sheets in the isolation tube and the heat exchanger, other inert material, such as plastic sheets and dirt, for example, or nearly any other material for slowing down the descent of the core, absorbing shock and avoiding steam explosions, could be employed. Further, other arrangements for conducting heat away from the core catching reactor in a passive manner, could be employed instead of the water cooling arrangement. In addition, the cross sectional dimensions of the water jackets and the strength of the supporting elements between the walls of the water jackets would be proportioned to accomodate the maximum heat flow and maximum stresses required by these portions for the particular nuclear reactor under consideration. It is to be understood, therefore, that such alternatives and other similar ones are within the scope of the present invention. |
claims | 1. A lightweight collimator, having at least a top and a bottom and incorporating shielding about a cylindrical detector having at least a top and a bottom, said detector affixed near said top of said collimator for collecting collimated radiation through said bottom of said collimator, at least said shielding shaped externally according to the quartic relationship: L 0 2 = y 2 + [ y 2 z 2 ( y + D ) 2 ] where y is the minimum thickness of encased shielding needed to shield said collimator from un-collimated radiation entering said collimator at a distance, z, along said longitudinal axis of said collimator, z measured from the bottom of said detector, and D is the inner diameter of said collimator as established by the outer diameter of said detector,wherein at least said shielding incorporated in said collimator has a variable wall thickness that decreases gradually from a thickness L0 at the end of said collimator containing said detector to a thickness, y, measured at a distance, z, away from the bottom of said detector. 2. The collimator of claim 1 made by machining solid shielding material. 3. The collimator of claim 1 made by pouring molten shielding material into forms shaped in accordance with said quartic relationship. 4. The collimator of claim 1 in which said radiation comprises at least gamma rays and said detector is at least a gamma ray detector. 5. The collimator of claim 4 in which said shielding material comprises at least in part lead. 6. A method for making a lightweight collimator for collecting radiation, said collimator having at least a top and a bottom, said collimator for collecting collimated radiation through said bottom of said collimator, comprising:providing a cylindrical detector, said detector having at least a top and a bottom, wherein said detector is affixed near said top of said collimator;providing a cylindrical tube having an inside diameter of at least the outside diameter of said detector, said tube for collecting said radiation;connecting said cylindrical tube to said detector so as to be in operable communication with said bottom of said detector;providing shielding to be incorporated within said collimator and about said detector and said cylindrical tube, at least said shielding to be shaped in accordance with the quartic relationship: L 0 2 = y 2 + [ y 2 z 2 ( y + D ) 2 ] where y is the minimum thickness of encased shielding needed to shield said collimator from un-collimated radiation entering said collimator at a distance, z, along said longitudinal axis of said collimator, z measured from the bottom of said detector, and D is the inner diameter of said collimator as established by the outer diameter of said detector;fabricating a configuration to enclose said detector, said shielding, and said tube; andenclosing said detector, said shielding and said tube in said configuration, wherein said collimator is shaped externally according to said quartic relationship, and wherein at least said shielding material has a variable wall thickness that decreases gradually from a thickness L0 at said top of said collimator to a thickness, y, measured at a distance, z, away from said bottom of said detector. 7. The method of claim 6 said shielding made by machining solid shielding material. 8. The method of claim 6 said shielding made by pouring molten shielding material into forms shaped in accordance with said quartic relationship. 9. The method of claim 6 said radiation comprising at least gamma rays and said detector comprising at least a gamma ray detector. 10. The method of claim 9 said shielding material comprising at least in part lead. |
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abstract | A nuclear power system includes a reactor vessel that includes a reactor core mounted within a volume of the reactor vessel. The reactor core includes one or more nuclear fuel assemblies configured to generate a nuclear fission reaction. The nuclear power system further includes a containment vessel sized to enclose the reactor vessel such that an open volume is defined between the containment vessel and the reactor vessel. A boron injection system is positioned in the open volume of the containment vessel and includes an amount of boron sufficient to stop the nuclear fission reaction or maintain the nuclear fission reaction at a sub-critical state. The boron injection system is positioned to deliver the amount of boron into the open volume. |
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claims | 1. A method comprising:providing a target;directing a first amplified light beam toward the target to cause an interaction between the target and the first amplified light beam, the interaction between the target and the first amplified light beam forming a first plasma and a remaining portion of the target;allowing the first plasma to expand to form a collection of pieces from the remaining portion, the collection of pieces extending along the direction of propagation of the first amplified light beam; anddirecting a second amplified light beam toward the collection of pieces, the second amplified light beam having an energy sufficient to convert at least some of the pieces of the collection of pieces into a plasma that emits EUV light, whereinthe collection of pieces comprises non-ionized pieces of a target material that emits EUV light when in a plasma state. 2. The method of claim 1, wherein the first plasma does not emit EUV light. 3. The method of claim 1, wherein the first plasma is formed at a surface of the remaining portion of the target. 4. The method of claim 3, wherein allowing the first plasma to expand comprises allowing time to elapse after the interaction between the first amplified light beam and the target. 5. The method of claim 3, wherein the collection of pieces spreads into a non-spherical volume. 6. The method of claim 1, wherein at least some of the pieces in the collection of pieces are separated by voids. 7. The method of claim 1, wherein at least some of the pieces in the collection of pieces make physical contact with at least one other piece in the collection of pieces. 8. The method of claim 1, wherein the collection of pieces comprises a mist of particles of a target material that emits EUV light when in a plasma state. 9. The method of claim 1, wherein the first amplified light beam has a temporal duration. 10. The method of claim 9, wherein the temporal duration is 5-20 picoseconds (ps). 11. The method of claim 9, wherein the temporal duration is 150 ps or less. 12. The method of claim 1, whereinthe second amplified light beam interacts with the collection of pieces at a target location,the second amplified light beam has a beam diameter in a direction that is different from a direction of propagation of the second amplified light beam, andat the target location, the collection of pieces has a spatial extent in the direction, the spatial extent of the collection of pieces being at least as large as the beam diameter of the second amplified light beam. 13. The method of claim 1, wherein the collection of pieces has a spatial extent in at least one dimension that is greater than a spatial extent of the target in the same dimension. 14. The method of claim 1, wherein the target comprises a coalesced piece of a target material a target material that emits EUV light when in a plasma state. 15. The method of claim 14, wherein the target material comprises tin. 16. The method of claim 1, wherein the first amplified light beam comprises a pulse of light, the pulse of light comprising a leading edge that interacts with the target before any other portion of the pulse of light, and the interaction between the leading edge and the target forms the first plasma. 17. The method of claim 16, further comprising causing an interaction between a portion of the first amplified light beam that occurs after the leading edge and the first plasma, the first plasma absorbing at least some the first amplified light beam that occurs after the leading edge. 18. The method of claim 1, wherein the collection of pieces forms a hemisphere-shaped volume. 19. The method of claim 18, wherein the hemisphere-shaped volume comprises a planar portion and a rounded portion, the second amplified light beam interacting with the planar portion prior to interacting with the rounded portion. 20. A method comprising:providing a target, the target comprising a target material that emits extreme ultraviolet (EUV) light when in a plasma state;directing a first amplified light beam toward the target to cause an interaction between the first amplified light beam and the target, the interaction forming a first plasma and a remaining portion of the target; andallowing the first plasma to expand at a surface of the remaining portion of the target to transform the remaining portion of the target into a collection of pieces, the collection of pieces comprising pieces of the target material and extending along a direction of propagation of the first amplified light beam, wherein a density of the collection of pieces increases along a direction that is parallel to a direction of propagation of the second amplified light beam. 21. The method of claim 20, further comprising:directing a second amplified light beam toward the collection of pieces, the second amplified light beam having an energy sufficient to convert the pieces of target material to a plasma that emits EUV light. 22. An extreme ultraviolet (EUV) light source comprising:a first source that produces at least one pulse of light having a temporal duration of 5-20 picoseconds (ps);a second source that produces an amplified light beam having an energy sufficient to convert a target material to a plasma that emits EUV light;a target material delivery system that provides a target to a target location, the target comprising the target material, whereinan interaction between a pulse of light from the first source and the target generates a shock wave that breaks the target into a collection of pieces that extends along the direction of propagation of the first amplified light beam, andan interaction between the amplified light beam and the collection of pieces generates a plasma that emits EUV light. 23. The light source of claim 22, wherein the first source and the second source are part of the same source. 24. The light source of claim 22, wherein the at least one pulse of light produced by the first source has a first wavelength, and the amplified light beam produced by the second source has a second wavelength, the first and second wavelengths being different. 25. The light source of claim 24, wherein the first wavelength comprises 1.06 microns (μm), and the second wavelength comprises 10.6 μm. 26. A method comprising:providing a target;directing a first amplified light beam toward the target to cause an interaction between the target and the first amplified light beam, the interaction between the target and the first amplified light beam forming a first plasma and a remaining portion of the target;allowing the first plasma to expand to form a collection of pieces from the remaining portion, the collection of pieces extending along the direction of propagation of the first amplified light beam; anddirecting a second amplified light beam toward the collection of pieces, the second amplified light beam having an energy sufficient to convert at least some of the pieces of the collection of pieces into a plasma that emits EUV light, whereinthe collection of pieces comprises a mist of particles of target material that emits EUV light when in a plasma state. 27. The method of claim 26, wherein the collection of pieces forms a hemisphere-shaped volume. 28. The method of claim 27, wherein the hemisphere-shaped volume comprises a planar portion and a rounded portion, the second amplified light beam interacting with the planar portion prior to interacting with the rounded portion. 29. The method of claim 26, wherein the at first amplified light beam has a first wavelength, and the second amplified light beam has a second wavelength, the first and second wavelengths being different. 30. The method of claim 26, wherein the mist of particles is distributed throughout a volume, and the first amplified light beam has an intensity of 2×1012 W/cm2. 31. A method comprising:providing a target;directing a first amplified light beam toward the target to cause an interaction between the target and the first amplified light beam, the interaction between the target and the first amplified light beam forming a first plasma and a remaining portion of the target;allowing the first plasma to expand to form a collection of pieces from the remaining portion, the collection of pieces extending along the direction of propagation of the first amplified light beam; anddirecting a second amplified light beam toward the collection of pieces, the second amplified light beam having an energy sufficient to convert at least some of the pieces of the collection of pieces into a plasma that emits EUV light, whereinthe first amplified light beam has a temporal duration of 5-20 ps. |
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claims | 1. A method for producing 225Ac, comprising:a method (X) for purifying a 226Ra-containing solution, comprising an adsorption step (R1) of allowing a 226Ra ion to adsorb onto a resin carrier having a function of selectively adsorbing a divalent cation by bringing a 226Ra-containing solution (a) into contact with the carrier under an alkaline condition, and an elution step (R2) of eluting the 226Ra ion from the carrier under an acidic condition;a method for producing a 226Ra target, comprising an electrodeposition liquid preparation step (R4) of preparing an electrodeposition liquid by using a purified 226Ra-containing solution (b) obtained by the method (X), and an electrodeposition step (R5) of electrodepositing a 226Ra-containing substance on a substrate by using the electrodeposition liquid; anda step (A1) of irradiating a 226Ra target produced by the method for producing a 226Ra target with at least one kind selected from a charged particle, a photon, and a neutron by using an accelerator to produce 225Ac. 2. The method for producing 225Ac according to claim 1, whereinthe carrier has a divalent cation-exchange group. 3. The method for producing 225Ac according to claim 1, whereinthe carrier has an iminodiacetic acid group. 4. The method for producing 225Ac according to claim 1, the method (X) further comprises a step (R3) of performing anion exchange by passing a solution containing a 226Ra ion eluted in the elution step (R2) through an anion exchange resin. 5. The method for producing 225Ac according to claim 1, whereinthe 226Ra-containing solution (a) is obtained by separating an 225Ac component from a solution in which a 226Ra target irradiated with at least one kind selected from a charged particle, a photon, and a neutron by using an accelerator has been dissolved. 6. The method for producing 225Ac according to claim 1, whereinthe carrier is charged in a tube. 7. The method for producing 225Ac according to claim 1, further comprisinga purification method (Y) comprising the steps:(R6) of allowing a 226Ra ion to adsorb onto a carrier having a function of selectively adsorbing a divalent cation by bringing a 226Ra-containing solution (c) after the electrodeposition step (R5) into contact with the carrier under an alkaline condition; and(R7) of eluting the 226Ra ion from the carrier under an acidic condition, whereina purified 226Ra-containing solution (d) obtained by the purification method (Y) is mixed with the purified 226Ra-containing solution (b), and an electrodeposition liquid is prepared in the electrodeposition liquid preparation step (R4). 8. The method for producing 225Ac according to claim 7, the purification method (Y) further comprises a step(R8) of performing anion exchange by passing a solution containing a 226Ra ion eluted in the elution step (R7) through an anion exchange resin. 9. The method for producing 225Ac according to claim 1, further comprising the steps:(A2) of dissolving the 226Ra target irradiated in the irradiation step (A1); and(A3) of separating a colloidal 225Ac component by alkalizing the solution obtained in the dissolution step (A2). |
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040299686 | abstract | Racks for storing spent nuclear fuel elements in a spent fuel storage pool are placed in the pool one above the other. Guide pins and guide pin receptacles mate for the alignment of the racks one above the other. A frame-like support removably holds the racks one above the other. Interengaging members between the racks and the frame-like support retain the racks in position relative to the frame-like support. |
044328940 | abstract | A detergent-containing radioactive liquid waste originating from atomic power plants is concentrated to have about 10 wt. % detergent concentration, then dried in a thin film evaporator, and converted into powder. Powdered activated carbon is added to the radioactive waste in advance to prevent the liquid waste from foaming in the evaporator by the action of surface active agents contained in the detergent. The activated carbon is added in accordance with the COD concentration of the radioactive liquid waste to be treated, and usually at a concentration 2-4 times as large as the COD concentration of the liquid waste to be treated. A powdery product having a moisture content of not more than 15 wt. % is obtained from the evaporator, and pelletized and then packed into drums to be stored for a predetermined period. |
description | The present application claims the benefit of priority from U.S. Provisional Patent Application No. 60/639,774, filed Dec. 29, 2004, the entire content of which is incorporated herein by reference. The present invention relates to a lithographic apparatus, an illumination system, a filter system, and a method for cooling a support of such a filter 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. 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 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 a lithographic apparatus, the size of features that can be imaged onto the substrate is limited by the wavelength of the projection radiation. To produce integrated circuits with a higher density of devices, and hence higher operating speeds, it is desirable to image smaller features. While most current lithographic projection apparatus employ ultraviolet light generated by mercury lamps or excimer lasers, it has been proposed to use shorter wavelength radiation, in the range of 5 to 20 nm, in particular around 13 nm. Such radiation is termed extreme ultra violet (EUV) or soft X-ray and possible sources include, for example, laser produced plasma sources, discharge plasma sources, or synchrotron radiation from electron storage rings. These types of radiation require that the beam path in the apparatus be evacuated to avoid beam scatter and absorption. Because there is no known material suitable for making a refractive optical element for EUV radiation, EUV lithographic apparatus must use mirrors in the radiation (illumination) and projection systems. Even multilayer mirrors for EUV radiation have relatively low reflectivities and are highly susceptible to contamination, further reducing there reflectivities and hence throughput of the apparatus. This may impose further specifications on the vacuum level to be maintained and may necessitate especially that hydrocarbon partial pressures be kept very low. In a typical discharge plasma source, plasma is formed by an electrical discharge. The plasma may then be caused to compress so that it becomes highly ionized and reaches a very high temperature, thereby causing the emission of EUV radiation. The material used to produce the EUV radiation is typically xenon or lithium vapor, although other gases, such as krypton or tin or water, may also be used. However, these gases may have a relatively high absorption of radiation within the EUV range and/or be damaging to optics further downstream of the projection beam and their presence should therefore be minimized in the remainder of the lithographic apparatus. A discharge plasma source is disclosed, for example, in U.S. Pat. Nos. 5,023,897 and 5,504,795, both of which are incorporated herein by reference. In a laser produced plasma source, a jet of, for example, (clustered) xenon may be ejected from a nozzle, for example, produced from an ink-jet like nozzle as droplets or thin wire. At some distance from the nozzle, the jet is irradiated with a laser pulse of a suitable wavelength for creating a plasma that subsequently will radiate EUV radiation. Other materials, such as water droplets, ice particles, lithium or tin, etc. may also be ejected from a nozzle and be used for EUV generation. In an alternative laser-produced plasma source, an extended solid (or liquid) material is irradiated to create a plasma for EUV radiation. Laser produced plasma sources are, for example, disclosed in U.S. Pat. Nos. 5,459,771, 4,872,189, and 5,577,092, all of which are incorporated herein by reference. During generation of EUV radiation, particles are released. These particles, hereinafter referred to as debris particles, include ions, atoms, molecules, and small droplets. These particles should be filtered out of the EUV radiation, as these particles may be detrimental to the performance and/or the lifetime of the lithographic apparatus, in particular the illumination and projection system thereof. International Patent Application Publication No. WO 99/42904, incorporated herein by reference, discloses a filter that is, in use, situated in a path along which the radiation propagates away from the source. The filter may thus be placed between the radiation source and, for example, the illumination system. The filter includes a plurality of foils or plates that, in use, trap debris particles, such as atoms and microparticles. Also, clusters of such microparticles may be trapped by these foils or plates. These foils or plates are orientated such that the radiation can still propagate through the filter. The plates may be flat or conical and may be arranged radially around the radiation source. The source, the filter and the projection system may be arranged in a buffer gas, for example, krypton, whose pressure is about 0.5 torr. Contaminant particles then take on the temperature of the buffer gas, for example, room temperature, thereby sufficiently reducing the particles velocity before the end of the filter. This enhances the likelihood that the particles are trapped by the foils. The pressure in this known contaminant trap is about equal to that of its environment, when such a buffer gas is applied. International Patent Application Publication No. WO 03/034153, incorporated herein by reference, discloses a contaminant trap that includes a first set of foils and a second set of foils, such that radiation leaving the source first passes the first set of foils and then the second set of foils. The plates, or foils, of the first and second set define a first set of channels and a second set of channels, respectively. The two sets of channels are spaced apart, leaving between them a space into which flushing gas is supplied by a gas supply. An exhaust system may be provided to remove gas from the contaminant trap. The pressure of the gas and the space between the two sets of channels may be relatively high so that debris particles are efficiently slowed down, further enhancing the likelihood that debris particles are trapped by the second set of foils. The first and second set of channels provide a resistance to the gas when the gas moves from the space between the two sets of channels in the channels of either the first or the second set. Hence, the presence of the gas is more or less confined to the space between the two sets of channels. Even though the platelets or foils are positioned such that radiation diverging from the radiation source can easily pass through the contaminant trap, the foils or platelets do absorb some EUV radiation and, therefore, some heat. Moreover, these foils are heated by colliding debris particles. This may result in a significant heating of the foils and heating of a supporting structure that supports the foils. This may lead to thermal expansion of the foils and of the supporting structure. As optical transmission of the contaminant trap is very important in a lithographic apparatus, the deformation of a foil due to thermal expansion of the foil should be minimized. European Patent Application Publication No. EP 1 434 098 addresses this problem by providing a contamination barrier, i.e. a foil trap or contaminant trap, that includes an inner ring and an outer ring in which each of the foils or plates is slidably positioned at at least one of its outer ends in grooves of at least one of the inner ring and outer ring. By slidably positioning one of the outer ends of the foils or plates, the foils or plates can expand in a radial direction without the appearance of mechanical tension, and thus without thermally induced deformation of the plate or foil. The contamination trap may include cooling means arranged to cool one of the rings to which the plate or foils are thermally connected. It is desirable to provide a lithographic apparatus having a filter system, or an illumination system having a filter system, or a filter system itself, in which the foil trap can both be rotated, in order to actively intercept debris particles, and be cooled. According to an aspect of the invention, there is provided a lithographic apparatus that includes an illumination system configured to condition a radiation beam, a projection system configured to project the radiation beam onto a substrate, and a filter system for filtering debris particles out of the radiation beam. The filter system includes a plurality of foils for trapping the debris particles, a support for holding the plurality of foils, and a cooling system that has a surface that is arranged to be cooled. The cooling system and the support are positioned with respect to each other such that a gap is formed between the surface of the cooling system and the support. The cooling system is further arranged to inject gas into the gap. According to an aspect of the invention, there is provided an illumination system configured to condition a radiation beam. The illumination system includes a filter system for filtering debris particles out of the radiation beam. The filter system includes a plurality of foils for trapping the debris particles, a support for holding the plurality of foils, and a cooling system that has a surface that is arranged to be cooled. The cooling system and the support are positioned with respect to each other such that a gap is formed between the surface of the cooling system and the support. The cooling system is further arranged to inject gas into the gap. According to an aspect of the invention, there is provided a filter system for filtering debris particles out of a radiation beam that is usable for lithography, in particular EUV lithography. The filter system includes a plurality of foils for trapping debris particles, a support for holding the plurality of foils, and a cooling system that has a surface that is arranged to be cooled. The cooling system and the support are positioned with respect to each other such that a gap is formed between the surface of the cooling system and the support. The cooling system is further arranged to inject gas into the gap. According to an aspect of the invention, there is provided a method for cooling at least a support for foils of a filter system for filtering debris particles out of a radiation beam that is usable for lithography, in particular EUV lithography. The method includes positioning a cooled surface with respect to the support such that a gap is formed between the cooled surface and the support, and injecting gas into the gap. As according to each of the above-mentioned aspects of the invention, a gap is provided and a gas is used to transfer heat from the support to the cooling system, the support can rotate while the cooling system remains stationary. As the gas is injected into the gap, the gas experiences much resistance in its movement from the confinement of the gap. The gas will only slowly leak into the surroundings and does therefore not result in a sharp increase in the pressure of the surroundings. FIG. 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus includes: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, EUV radiation, or X-ray 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 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. 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 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” as 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” as 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 in which 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 a radiation beam from a radiation source SO. In a path along which radiation propagates from the source SO towards the illumination IL, a filter system FS is provided. The filter system FS substantially transmits the radiation and filters debris particles out of the radiation. The illuminator IL and the filter system may be regarded as at least a part of an illumination system. The source and the lithographic apparatus may together 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 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 and the illuminator IL, together with the beam delivery system if required, may be referred to as a radiation system. The illuminator IL may include 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 include 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 may 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. FIG. 2 schematically depicts a part of a lithographic apparatus, an illumination system, and a filter system according to an embodiment of the invention. Foil F1 and foil F2 are part of a filter system for trapping debris particles. The filter system also includes a support, in FIG. 2 shown as part S1 and part S2. It is possible that part S1 and part S2 both belong to one ring-shaped support. FIG. 2 may be seen as showing a schematic cross-section of such a ring-shaped support. A symmetry axis SA is schematically represented by line L. Foil F1 and foil F2 may both be connected to an axis of the support. In that case, this axis may coincide with line L. However, it is also possible that foil F1 and foil F2 are not connected to each other, as will be shown later. In an embodiment where the support, including support parts S1 and S2, is ring-shaped, symmetry axis SA may coincide with a virtual straight line that extends through a predetermined position that is intended to coincide with a source from which radiation is generated. It is further possible that foil F1 and foil F2 are connected, i.e. form together one foil. It is in such an embodiment possible that support S1 and support S2 are separated supports, separated by the foil. For example, support S1 may represent a cross-section of an outer ring, while support S2 represents a cross-section of an inner ring. In that situation, line L does not represent a symmetry-axis. It is also possible that line L represents a plane of symmetry and that the filter system includes a plurality of foils that are parallel to each other. The filter system includes a cooling system CS. This cooling system CS may include parts CS1 and CS2. In cases where the respective support is ring-shaped, the respective cooling system CS may also be ring-shaped. Line L may in some embodiments thus also represent the symmetry axis of the cooling system CS. For a further description of the part of the filter system shown in FIG. 2, reference is only made to the upper part, i.e. above line L. The description of the upper part also holds for the lower part. The cooling system CS1 has a surface A1 that is arranged to be cooled. The cooling system CS1 and the support S1 are positioned with respect to each other such that a gap G is formed between the surface A1 of the cooling system CS1 and the support S1. The cooling system CS1 is further arranged to inject gas into the gap G. The gas and its flow direction is indicated by dotted arrows. The path P between an entrance position EP at which the gas enters the gap G and an exit position XP from which the gas exits the gap G forms in the embodiment shown in FIG. 2 a meandering path P. As the path P is a meandering path, gas injected into the gap experiences a large resistance when flowing from the entrance position EP towards the exit position XP. Such a meandering path provides resistance to leakage of gas from the gap G towards its surrounding. It is also possible that the path is a straight path. The resistance experienced by the gas when moving towards exit position XP is then lower, as compared to the embodiment shown. The support S1 may be provided with a recess R1 for holding the gas before the gas exit gap G. The pressure in this recess may be about 1000 Pa, whereas the pressure of the surrounding may be about 10 Pa. The recess R1 may thus provide a buffer in which injected gas cools the support S1. The gap G may be such that a smallest distance between the surface A1 and the support S1 is in a range that varies from about 20 micrometers to about 200 micrometers. The gap may also be such that the smallest distance between the surface A1 and the support S1 is in a range that varies from about 40 micrometers to about 100 micrometers. The surface A1 of the cooling system CS1 is arranged to be cooled with a fluid. For this purpose, the cooling system CS1 may include a channel that extends in a subsurface of surface A1. In use, water, that is, relatively cool water, may enter channel entrance CEA and run through the channel C, and leave the channel at channel exit CX. In that case, the subsurface of surface A1 will be cooled with water still about as cool as the water that enters the channel C at channel entrance CEA. The cooling system CS1 may also be arranged to cool the gas before injecting the gas into the gap G. Instead of having an entrance for water at a position indicated by channel entrance CEA, it may be advantageous to let water into the channel at a position indicated by CEG, so that water first runs along an injection channel IC through which in use gas is injected into the gap G. This allows for cooling the gas in the injection channel IC or for further keeping the gas cool in the injection channel in cases where the gas has been cooled before entering the injection channel IC. It is, of course, also possible that the injection channel IC and the surface A1 are cooled by independent cooling mechanisms. Instead of using water, any other suitable cooling medium may be used. Although not shown, it will be clear that entrances and exits of channel C are connected with supplies and exhausts, respectively, such that no water and/or any other cooling medium used for cooling the cooling system will enter the surroundings of the cooling system and/or the filter system. Gas injected via injection channel IC into the gap G may be Argon, or any other gas that has good cooling properties and is relatively inert. When the filter system is exposed to EUV radiation and filters debris particles out of the path along which the EUV radiation propagates towards a collection system, and the filter system rotates at about 3,000 rpm in a vacuum environment, the foils and their support(s) are likely to absorb about 1 kW of power as a result of absorption of EUV radiation, and impact of debris particles on foils. Without wishing to be bound by any theory, it is indicated that it is possible to remove an amount of heat equal to about 1.3 kW when Argon gas is injected into the gap G such that a pressure of about 1000 Pa in the recess R1 is reached, the temperature difference between the support and the cooled surface of the cooling system CS1 is about 200 K, and the surface A1 includes an area of about 1.26*10−2 m2. The heat transfer coefficient in this connection is taken to be about 0.7 W/m2*K*Pa and the efficiency is assumed to be about 0.85. The shortest distance between the support S1 and the surface A1 in the gap is assumed to be between about 40 and about 100 micrometers. Pressure in the surroundings may in that case be about 10 mbar. In this assessment, the material of which the support is made, is assumed to be stainless steel having a thickness of about 2 cm and a diameter of about 200 mm. FIG. 3 depicts another part of a lithographic apparatus, illumination system, and filter system according to an embodiment of the invention. In this situation, the support S1 and S2 include parts of a ring-shaped support that is rotatably arranged around a symmetry axis SA and a cooling system CS, which may, in use, remain stationary with respect to the support of which parts S1 and S2 are schematically shown. The foils F1, F2 extend radially with respect to the symmetry axis SA. There may be one injection channel IC, splitting in a part leading towards recess R1 and a part leading towards recess R2. Further structural features are the same as depicted in FIG. 2. The cooling system CS shown in FIG. 3 works the same as the cooling system shown in FIG. 2. It is possible that the support S1, S2 is rotatable due to a driving mechanism that transmits forces towards an outer ring (not shown) to which the foils F1, F2 in such an embodiment are connected. However, it also possible that the support S1, S2 are actually connected to cooling system CS via, for example, thermally insulating connections, and that the cooling system CS drives rotation of the support S1, S2. In this latter embodiment, it is not necessarily the case that the foils F1, F2 are connected to, for example, an outer ring. The combinations of a cooling system CS1 and support S1, (as well as S2 and SR), may form at least a part of a heat sink HS1 (as well as HS2). Such a heat sink may be used in embodiments shown by FIGS. 4-12. FIG. 4 schematically depicts a filter system FS which is arranged to filter, in use, debris particles out of a predetermined cross-section of the radiation as emitted by a source (not shown). The filter system FS of FIG. 4 is shown as viewed from a predetermined position that is, in use, intended to coincide with a position from which the source generates radiation. The foils F1, F2 are represented by lines for a reason, which will become clear later on. In this example, the predetermined cross-section is a section of the filter system FS as extending between a part referred to as S1 and a part referred to as S2. In this example, the predetermined cross-sections is thus a substantially ring-shaped cross-section. The filter system FS includes a first set of foils F1 and a second set of foils F2 for trapping the debris particles. Each foil F1 of the first set is thermally connected to a support S1, in this case, a first ring FR. Each foil F2 of the second set is thermally connected to a support S2, in this case, second ring SR. The first ring FR and the second ring SR are spatially separated and have the same axis RA. Each foil F1 of the first set extends towards the second ring SR and each foil F2 of the second set extends towards the first ring FR. In other words, the support S1 may be ring-shaped, and the support S2 may also be ring-shaped. Each foil F1 of the first set of foils F1 is, for example, soldered to the support S1. Each foil F2 of the second set of foils F2 is, for example, soldered to the support S2. The foils F1, F2 may be made of a material including substantially molybdenum. The supports may also be made of a material including substantially molybdenum. The filter system FS further includes a first heat sink HS1 and a second heat sink HS2. Each foil F1 of the first set is thermally connected to the first heat sink HS1 and each foil F2 of the second set is thermally connected to the second heat sink HS2. In use, through each foil F1 of the first set, heat is conducted towards substantially the first heat sink HS1. Through each foil F2 of the second set, heat is conducted towards substantially the second heat sink HS2. The first set of foils F1 extends substantially in a first section of the predetermined cross-section, and the second set of foils F2 extends substantially in a second section of the predetermined cross-section. The first section includes all foils F1 of the first set and the second section includes all foils F2 of the second set. The first section and the second section are substantially non-overlapping. It can be seen in FIG. 4 that the foils F1, F2 may be much shorter as compared to a situation in which each foil would extend from support S1 towards support S2. The amount of heat per foil F1, F2 to be transferred towards the respective heat sink is much less as compared to the amount of heat that would have to be transferred to a heat sink in a situation where a foil were to be connected to one of the supports S1 or S2 and where the foil were to extend over the full distance between the support S1 and the support S2 to which it may or may not be connected. For structural strength of the foils F1, F2 and/or for spacing the foils F1, F2 equally, substantially thermally insulating and relatively stiff wires may connect the free ends of the foils F1, F2. For the sake of clarity these wires are not shown in any of the Figures. It is also possible, as shown in FIGS. 4-7, that the foils F1, F2 of the first set and the second set, respectively, are apart from their connection with respective heat sink HS1, HS2, and unconnected with respect to any other part of the filter system FS. This allows for a good optical transmission of the filter system FS, as well as a single path per foil for conducting heat away from the respective foil. The relative dimensions of the first and second section, as well as the relative dimensions of the first foils F1 and the second foils F2, may be chosen such that all of the filter system FS remains, in use, below a predetermined maximum temperature when, in use, exposed to the radiation beam. Also, the cooling power of the respective heat sinks HS1, HS2 may be chosen such that all of the filter system FS remains below a predetermined maximum temperature when exposed to the radiation beam. In general, the filter system FS may thus be arranged such that all of the filter system FS remains below that predetermined maximum temperature. As shown in FIG. 4, one foil F1 of the first set and one foil F2 of the second set extend in substantially the same virtual plane. A distance in that virtual plane between the foil F1 of the first set and the foil F2 of the second set is selected so as to maintain a gap between the foil F1 of the first set and the foil F2 of the second set when, in use, the foil F1 of the first set and the foil F2 of the second set reach their respective maximum temperatures. This means that when, for each foil, their maximum thermal expansion is reached, the foils within one virtual plane will still not thermally connect. Each foil F1, F2 coincides with a virtual plane that extends through the predetermined position which is in use intended to coincide with a source (not shown) from which the radiation is generated. Hence, the foils F1, F2 are represented by lines in FIGS. 4-7. In use, the radiation will propagate along the foils F1, F2. As the foils F1, F2 of a filter system FS according to an embodiment of the invention will remain below a predetermined maximum temperature when exposed to, for example, EUV radiation, it is possible to design the filter system such that the predetermined temperature is below the temperature at which, for example, tin droplets, formed by tin debris particles, will not evaporate away from the foils F1, F2 when the foil is heated up. FIG. 5 shows an embodiment of a filter system according to the invention in which a foil F1 of the first set extends for a relatively small part between two foils F2 of the second set, and vice versa. This may have the advantage that a sudden peak in optical transmission due to the gap present between the foils F1 of the first set and the foils F2 of the second set, as will occur in the embodiment shown in FIG. 4, will not occur in the embodiment shown in FIG. 5. Furthermore, if the filter system FS were to be rotated around a rotation axis RA, there would not be an angular section present in the predetermined cross-section through which debris particles may move along a direction into which the radiation propagates without being intercepted by the foils F1, F2. It is possible to apply a number of second foils F2 that is smaller than the number of applied first foils F1, so as to allow a similar distance between all the foils F1, F2. FIG. 6 shows an embodiment of a filter system FS according to the invention in which a gap remains possible between a first foil F1 and a second foil F2, which both extend within the same virtual plane. However, as the lengths of the foils F1, and the lengths of the foils F2 alternate in a tangential direction, each gap between a first foil F1 and a second foil F2 is “covered” by either a first foil F1 or a second foil F2 when the filter system rotates around the rotation axis RA. FIG. 7 shows an embodiment of a filter system FS according to the invention in which both the first set of foils F1 and the second set of foils F2 are more or less randomly distributed over, respectively, the first section and the second section of the predetermined cross-section. This may have the advantage that a possible inhomogeneity in the optical transmission of the filter system FS is more or less spread out over the entire predetermined cross-section. In other words, some peaks in optical transmission may still occur, but the relative height is much lower. As indicated before, at least a part of the filter system FS may be movable such that each foil F1 of the first set and/or each foil F2 of the second set may, in use, catch debris particles actively by intercepting debris particles in their course along a path along which the radiation propagates. FIG. 8 and FIG. 9 both show a part of an embodiment of a filter system according to the invention. FIG. 8 and FIG. 9 may both be regarded as a side view, in relation to FIGS. 4-7. The first support S1, in this case the first ring FR, is shown to have a conical shape. The second support S2, in this case the second ring SR, is shown to be cylindrical in shape. It is, of course, also possible that the second ring SR is conically in shape. FIGS. 8 and 9 show a cross-section along a line I-I, which is shown in each of the FIGS. 4 to 7. Also is shown that the rotational axis RA may extend along a virtual line VL and that a source SO may be positioned such that it coincides with the line VL. In the embodiment shown in FIG. 8, the predetermined cross-sections may include foils F extending from first ring FR to the second ring SR and being connected to at least first ring FR or second ring SR, as shown in FIG. 8. However, as shown in FIG. 9, the predetermined cross-section may also include two sets of foils F1, F2 in one of the fashions shown in FIG. 4 to FIG. 7. It also applies to at least one foil extending between support S1 and support S2 that this foil coincides with a straight virtual plane, that extends through the predetermined position, i.e. the position which in use coincides with the source. For the embodiment shown in FIGS. 8 and 9, it further holds that between the foil and the predetermined position, in use, coinciding with a source SO, a tensed wire TW extends within the aforementioned straight virtual plane. This means that radiation propagating from the source SO that would hit the foil if the tensed wire TW were not present, will now hit, and heat, the tensed wire TW, instead of that foil. As a result, the foil will be in the shadow of the tensed wire TW, will not absorb (EUV) radiation, and will consequently not be heating up due to absorbance of (EUV) radiation. This significantly reduces the temperature that the foil will reach under operational circumstances. The tensed wire TW may be connected to the foil F. It may, for example, apply that a frontal part of a foil is effectively a tensed wire by providing a row of perforations between that frontal part and a remaining part of the foil. As shown in FIG. 8, it is possible that the tensed wire TW is held tight by a resilient element RE, such as a spring. It is possible that the tensed wire TW is thermally insulated from the foil F. The tensed wire TW may be made out of a material that includes tantalum and/or tungsten if the wire is not an integral part of the foil. In the embodiment shown in FIG. 8, the tensed wire TW extends fully along a diameter of the first ring FR. As shown in FIG. 9, it is possible that two tensed wires TW are used. Each tensed wire TW may extend from a position on the first support S1 to a closest position on the second support S2. FIG. 10 schematically depicts a filter system FS for filtering debris particles out of the radiation beam. The filter system shown in FIG. 10 is depicted as viewed from a predetermined position that is in use intended to substantially coincide with a source from which the radiation is generated. The filter system FS includes a plurality of foils F for trapping the debris particles. As will be clear later on, from this viewing position, the foils are seen as lines. FIG. 11 and FIG. 12 show one of these foils F, in, respectively, a perspective view and view similar to that of FIG. 10. Each of the foils F includes two parts FP1, FP2 that have a mutually different orientation. The two parts FP1, FP2 are connected to each other along a substantially straight connection line CL, which is more clearly shown in FIG. 11. Each of the two parts FP1, FP2 coincide with a virtual plane (not shown) that extends through the predetermined position from which the filter system FS is seen in FIG. 10. This is schematically indicated by the virtual straight lines VSL. As indicated earlier, this predetermined position is, in use, intended to substantially coincide with a source SO from which the radiation is generated. The source SO is schematically indicated in FIG. 11. The straight connection line CL also coincides with a virtual straight line VSL that extends through the predetermined position, i.e. through the position that is intended to substantially coincide with the source SO from which the radiation is generated. In use, radiation, generated from the source SO, propagates through the filter system. Only a small portion of the radiation will hit the foils frontally and may as such be absorbed by the foil, thereby resulting in heating the foil. Debris particles, traveling along a path into which the radiation propagates, may be trapped by the foils F as their direction of velocity is likely to have a component towards one of the foils F. It is also possible to rotate the foil trap such that the foils intercept the debris particles when these particles travel through the channels C formed by the foils F. In addition to the absorbance of radiation, the foils F also heat up, due to the impact of these particles. The filter system FS includes a support S to which a first part FP1 of the two parts FP1, FP2 is connected at a first position P1 of the support S, a second part FP2 of the two parts FP1, FP2 being connected at a second position P2 of the support S. In the embodiment shown in FIG. 10, the support S includes an inner ring IR and an outer ring OR. The inner ring IR and the outer ring OR are coaxial. A distance D between the first position P1 and the second position P2 is fixed. The foils may be made of a material substantially including molybdenum. Also, the support S may be made of a material that substantially includes molybdenum. The foils F may have been connected to the support S by soldering. The behavior of the foil trap shown in FIG. 10 when, in use, is as follows. Each part FP1, FP2 of a foil F expands when heated up. The expansion occurs substantially within a plane in which the respective part lies. The expansion of the foil F is accommodated for by a movement of the connection line substantially sideways with respect to the overall orientation of the foil. The extent to which the connection line moves sideways when accommodating for the thermal expansion is even more predictable when the distance between position P1 and position P2 is fixed. Foil F when heated up is in FIG. 12 schematically shown by a dashed line. A new orientation of the foil F, when heated up, has become predictable due to the position of the connection line CL. As the straight connection line coincides with a virtual straight line that extends through the predetermined position which is, in use, intended to substantially coincide with a source SO from which the radiation is generated, and each of the two parts FP1, FP2 coincide with a virtual plane that extends through that predetermined position, a new position and orientation of the foil will only cause a minimal drop in optical transmission, if at all. Furthermore, it is possible, for example, to experimentally determine the thermal expansion and the new position of a foil when heated up, and to design the filter system such that when the filter system is exposed to the absorbance of EUV radiation and/or impact of debris particles, the foil adopts a orientation which allows for optimal transmission of (EUV) radiation. Each part of the two parts FP1, FP2 may coincide with a virtual plane that is a straight plane. The controllability and predictability would then be even more straight forward. However, it is possible that each part, or one of the parts FP1, FP2 includes a curvature. The embodiment shown in FIGS. 10 and 12 is focused on a cylindrical or conical filter system FS, i.e. a filter system having a cylindrical or conical outer ring and possibly a cylindrical or conical inner ring. However, in principal, any other shape of the support and the filter system is possible. Fixation of the distance D between position P1 and position P2 of the support S is relative to the thermal expansion of the foil F. It is thus possible that the distance D may slightly increase due to expansion of the support, i.e. in this case inner ring IR and outer ring OR. Schematically is shown in FIGS. 10 and 12 that a support may be cooled by a cooling system CS. For the sake of clarity, this cooling system CS is only shown to be present at the outer ring OR. It is, however, equally possible to provide cooling a system CS at the inner ring IR. The cooling system may be constructed as shown in FIG. 2 and FIG. 3. 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. Although specific reference may have been made above to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example, imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography, a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured. The terms “radiation” and “beam” as 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). 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. 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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abstract | According to the present invention, there is provided a semiconductor manufacturing apparatus having: a process flow information creating section which registers an exposure device as a device for performing the pattern writing processing and an electron beam direct writing device as an alternative to the exposure device, when creating process flow information by sequentially registering processing conditions of processings in a semiconductor manufacturing process; and a control section which searches for information on the pattern writing processing based on the process flow information before the pattern writing processing, determines whether or not a mask used by the exposure device for performing the pattern writing processing searched for is installed in the exposure device, and sets the exposure device to perform the pattern writing processing in the case where it has been determined that the mask is installed in the exposure device, or sets the electron beam direct writing device to perform the pattern writing processing in the case where it has been determined that the mask is not installed in the exposure device. |
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abstract | A lifting drive for a radiation filter in a mammography device is provided. The lifting drive includes a recording apparatus that accommodates the radiation filter. The recording apparatus is embodied so that the radiation filter is operatively supported to allow movement for executing a lifting movement in at least one lifting direction. A first drive element is operable to create a drive movement. A first movement transmission element is operable to transmit the drive movement to the recording apparatus. The recording apparatus is operable to convert the drive movement into the lifting movement. A shape of the first movement transmission element is operable to be changed, so that the drive movement is able to be transmitted over different paths. |
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description | This application 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. Problem 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 a multiplexed proton based imaging 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 multiplexed proton tomography imaging apparatus and method of use thereof. In one embodiment, 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. For example, 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. 37B, an X-ray and positively charged particle double exposure image is described. As described, supra, the first detector array 1322, responsive to X-rays, is exposed to X-rays, such as the first cone beam 1392 and/or the second cone beam 1394, after passing through the patient 730. Before, after, and/or concurrently, the first detector array 1332 is exposed to the positively charged particles, such as the residual charged particle beam 267, after passing through the patient. Essentially, the first detector array 1322 comprises: (1) a material that is responsive to both X-rays and positively charged particles, such as protons or (2) comprises a composition of materials, where one component is responsive to X-rays and another component is responsive to positively charged particles. Typically, material of the first detector array 1332 is responsive and/or designed for X-ray detection, but has a smaller, typically much smaller, responsivity to positively charged particles. For instance, for a given thickness of a material, the material may absorb 99% of the X-rays while 90% of incident protons transmit through the material. However, the 10% of the incident protons leave a physical response behind on the essentially X-ray film or slab, which is detected and used to form the positively charged particle aspect of a particle-X-ray image, denoted herein as a pX-double exposure image or pX-image. Generally, a proton interacts with a nucleus via a strong interaction, either elastically or inelastically. In the elastic interaction, the proton scatters at some angle while losing momentum. In the inelastic interaction, the proton is absorbed in the interaction. The two types of interactions interact differently with detector materials. Further, the positively charged particles interact with atomic electrons, which results in a small loss of energy of the proton while knocking an electron out of orbit, such as to a higher energy level or to a free electron, either of which are detectable, such as from secondary emission or electron capture, integration, and flow. The secondary emission is an indirect measurement using a scintillator material that, responsive to transfer of energy from the X-ray and/or particle, emits a photon that is detected using a traditional detector array, such as a photodetector, photodiode array, CCD, and/or thin film transistor. The thin film transistor is optionally additionally used to directly detect the X-ray and/or charged particle. All detectors described herein are optionally and preferably two-dimensional detector arrays. All two-dimensional detector arrays described herein are optionally used, with relative rotation of the imaging beam and the sample, to generate three-dimensional images, such as via tomography. A first advantage of the X-ray and positively charged particle double exposure image is that both the X-ray and the positively charged particle are optionally delivered simultaneously or near simultaneously, such as within 0.001, 0.01, 0.1, 1, 2, 5, or 10 seconds of one another, which allows a double exposure of the patient in a fixed position, such as between patient movement, respirations, and/or twitches, each of which complicate overlaying images in software in terms of position, rotation, and non-linear distortion. A second advantage of the X-ray and positively charged particle double exposure two-dimensional image is that the X-ray and the positively charged particles interact with different components of the patient 730 and/or interact differently with the same components of the patient 730. Thus, the resultant image has more information than a purely X-ray image, where the additional fully integrated signal, the pX-image, results from the interaction of the positively charged particles and the patient 730. Dual Exposure Imaging Still referring to FIG. 37B, dual exposure imaging is described. While double exposure imaging, as used herein, exposes a detector material using both X-rays and positively charged particles, a dual exposure image uses the positively charged particles to expose two detectors. In one case, the positively charged particles expose the essentially X-ray detector to form the pX-image, and residual imaging particles 3730, after passing through the pX-image detector, are detected using a charged particle detector, such as the scintillation material 710. If the X-ray detector also uses scintillation, the X-ray detector is referred to herein as a first scintillation material and the scintillation material 710 is referred to herein as a second scintillation material. In the first case, the multitude of charged particles interact with the pX-image detector using any of the mechanisms described above. In another case, a given charged particle, of an imaging set of the positively charged particles, interacts, such as elastically, with the first essentially X-ray detector and proceeds to interact with the second scintillation material. Thus, as described above, a portion of the set of positively charged particles interact with the pX-ray detector and an intersecting and/or non-intersection portion of the set of positively charged particles interact with the scintillation material 710. 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. 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. 37A, an X-ray detector is optionally used to detect positively charged particles, such as protons. As the mass of a proton is extremely large compared to an X-ray, a resolution enhancement over a traditional X-ray image is obtained as the protons scatter less and/or differently than X-rays in transmittance through the patient 730. Still referring to FIG. 37A, the X-ray detector is optionally used to simultaneously detect X-rays and protons, yielding a physically obtained X-ray/proton fused image by the response of the detector element itself, not necessitating a post processing step combining a first image, such as an X-ray image with a second image, such as a proton image. Still referring to FIG. 37A, optionally and preferably fiducials, such as described supra, are used to determine the relative position of the source elements, the patient 730, and the detector elements, where relative positions are used for targeting, imaging, and/or aligning resulting images. Referring now to FIG. 37B, the simultaneous/single patient position X-ray and proton imaging system 3700 is further illustrated with optional beam position determination sheets, such as the first sheet 760 and the second sheet 770 described above, which allow for a more precise, and with the use of fiducials, more accurate determination of paths of individual protons through the patient 730 and tumor 720 thereof. Referring still to FIG. 37B, the simultaneous/single patient position X-ray and proton imaging system 3700 is further illustrated with an optional positively charged particle beam diffusing element 3720. As described above, a single proton is transmitted to the scintillation material 710 at a given, typically very short, time period, which allows calculation of a path of the proton through the patient 730. At the next short period of time, the process is repeated targeting another volume of the patient 730. However, with a diffusing element 3720, the narrow diameter proton beam, a necessity for a small synchrotron, is expanded or diffused by the diffusing element 3720, so that on average, the single proton calculations still work, but the system is multiplexed to allow detection of multiple protons simultaneously using the beam determination sheets and position of scintillation on the scintillation material 710, which is optionally enhanced using the multiplexed scintillation detector 1600, where elements of the array of scintillation sections 1610 are optionally physically separated. The positively charged particle beam diffusing element 3720 is optionally a proton dense material, such as a plastic, and/or a material changing direction of an incident particle. The positively charged particle beam optionally and preferably transmits through a section of the positively charged particle beam diffusing element 3720 comprising a set of atoms, where at least 10, 20, 30, 40, or 50 percent of said set of atoms comprise a form of hydrogen. With or without the diffusing element 3720, beam expander, or scattering material. Optionally, the nozzle system 146, also referred to as an exit nozzle and/or particle beam exit nozzle, the scanning system 140, first axis control 143, the vertical control, the second axis control 144, and/or the horizontal control are rapidly varied to distribute the treatment beam 269, and the resultant residual charged particle beam 267, to perform pseudo multi-plex imaging, where the pseudo multi-plex imaging is not simultaneously irradiating separate quadrants of a detector array, but rather rapidly scanning/switching between irradiation positions. Multiplexed Proton Imaging Referring now to FIG. 38A and FIG. 38B, a multiplexed proton imaging system 3800 is illustrated. For clarity of presentation, a proton is used in this section to represent a positively charged particle, such as C4+ or C6+. As a proton transmits through the patient 730, the proton interacts with the patient 730 and is redirected and/or scattered from a prior vector to a posterior vector. As described, supra, a path of the proton is optionally determined using imaging sheets, which give off photons upon passage of the proton, and photon detectors. However, the rate of imaging is limited by scanning time associated with steering the proton beam and flux rate, as only one proton path at a time is determined due to the relaxation time of the imaging sheets and scintillation material 710. Imaging multiple proton paths simultaneously, referred to as multiplexed proton imaging, is described herein. Still referring to FIG. 38A and FIG. 38B, multiple protons are directed by the nozzle system 146 along a given vector at a given time, where herein a simultaneous time is a time period between passage of protons less than a relaxation time of the imaging sheets, a relaxation time of the scintillation material 710, a fifty percent decay in flux of emitted photons from an imaging sheet after passage of positively charged particles, and/or less than 0.1, 0.01, 0.001, 0.0001, 0.00001, 0.000001, 0.0000001, or 0.00000001 seconds. The multiple protons in the proton beam are expanded, radially, using a proton beam expander and/or as illustrated using the diffusing element 3720. For clarity of presentation, two proton paths are illustrated at a simultaneous time or first time, t1, but the number of paths simultaneously determined is optionally greater than 2, 3, 4, 5, 10, 50, 100, or 1000. As illustrated, a first prior path 3811 is determined using a first sheet 760 coupled with a first detector 812 and a second sheet 770 optically coupled to a second detector 814. As the first sheet is two dimensional and the first detector 812 is a detector array, a first prior path position of a first proton in the plane of the first sheet is optionally and preferably determined at the same as a second prior path position of a second proton in the plane of the first sheet. The process is repeated using the second sheet 770 and the second detector and the results combined to determine the first prior path 3811 and the second prior path 3812 of the simultaneous first and second protons. Similarly, a first posterior vector 3821 and a second posterior vector 3822 are determined using a third sheet 780 and a fourth sheet 790 and associated detectors, not illustrated. As described, supra, the first prior vector 3811 and the first posterior vector 3822 are used to calculate a first probable path 3831 of the first proton through the patient 730 and the second prior vector 3812 and the second posterior vector 3822 are used to calculated a second probable path 3832 of the second proton through the patient 730. Differences in residual energy between the first proton and the second proton, as detected by depth of penetration into the scintillation material 710, yields additional information as to what materials were encountered in the patient 730 along the first probable path 3831 and the second probable path 3832, respectively. Still referring to FIG. 38A and FIG. 38B, the efficiency of multiplexing, also referred to as the number of simultaneous proton path determinations, increases as resolution of the detection system increases and/or as even expansion of the proton beam improves, such as with a proton radial beam cross-section expander. Statistically, some sets of simultaneous protons will pass through a set of paths that are not resolved, leading to a software discarding function removing those imaging elements. However, the simultaneous proton paths will probabilistically vary at the next time, such as a second time, t2, and each time thereafter allowing an accumulation of accepted proton imaging paths that increases at a rate faster than a series of individual measurements, such as acquired using a scanning proton beam and/or as limited by relaxation times of the sheets, such as the first sheet 760, and the scintillation material 710 of a scintillation system. Notably, the multiplexed proton imaging system 3800 is optionally and preferably combined with: (1) relative movement/rotation of the patient 730 and nozzle system 146 and associated generation of a three-dimensional image through the use of tomography algorithms and/or (2) variation of an energy of the protons from the synchrotron 130. The multiplexed proton imaging system 3800 is optionally used with the detector array 1410, the set of detector arrays 1700, and/or a non-uniform detector stack of detector layers 3034, described supra. Double Exposure Imaging Still referring to FIG. 37B, a method of double exposure imaging is described. Herein, double exposure imaging is performed using hardware. While further processing of the resultant image is optionally and preferably performed, the double exposure occurs at the detector level through exposure to both X-rays and positively charged particles, simultaneously and/or in either order. Subsequent superimposition to overlay an X-ray image and a positively charged particle image is not necessary or required. An example illustrates double exposure imaging. 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: ν⊥ 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(TI); cadmium tungstate, CdWO4; bismuth germanate; cadmium tungstate, CdWO4; calcium tungstate, CaWO4; cesium iodide, CsI; doped cesium iodide; cesium iodide doped with thallium, CsI(TI); 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 sate 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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description | The disclosed subject matter relates to computer and related electronic systems networks. More particularly, this disclosure relates to a novel and improved method and system for visualizing network performance characteristics. Most network engineers are very familiar with tools that report statistics on individual components such as links, routers, and servers. These infrastructure monitors have been around for a long time. Newer to the market are performance monitoring appliances that report end-to-end statistics and the end-user experience. These appliances provide a comprehensive view of the enterprise, without the need for desktop or server agents. They measure how well response time Service Level Agreements (SLAs) are being met. They also help solve a wide variety of problems with solutions that lead to significant reductions in operating costs. End-to-end performance monitoring can be extremely useful as a proactive method for both rapid troubleshooting and performance management of enterprise networks and server aggregations. Such monitoring has been successfully implemented to quickly identify and resolve the myriad of performance issues associated with networks, servers, and applications. The use of end-to-end performance monitoring appliances has uncovered serious inefficiencies with load balancers, poorly designed applications, by passed proxy servers, ineffective cache servers, aggressive active agents, and badly designed “redundant” networks. They can provide the “big-picture” view of networks and applications to answer questions that are critical for the end-user experience. These questions may include knowing what impact server consolidation will have on users. Such applications can help address which will work better on a particular network, a thick or thin clients configuration. Also performance monitoring applications can help identify which of sites are in greatest need of upgrades or downgrades, and which web pages are the slowest to download Drill-down troubleshooting capabilities can reveal metrics that can save weeks or months of time in identifying and resolving issues. Analyses that previously required six weeks to complete with packet sniffing tools may be accomplished in minutes when end-to-end performance monitoring appliances are properly configured. Because they continuously monitor applications, such appliances notice and report even difficult intermittent issues that cannot readily be reproduced. If a problem occurred at 3:00 a.m. the previous morning, their stored reports can be used for a post-mortem analysis. There is no need to wait for a recurrence in order to capture the behavior the way legacy troubleshooting tools require. End-to-end performance monitoring appliances with intelligent thresholds can alert a network performance management team to a developing problem before the problem severely impacts customers. Such proactive management and high-level views allow network managers to discover new ways to optimize the network. Unfortunately, known end-to-end performance monitoring and management systems fail to provide completely satisfactory operation. There are several existing response-time monitoring tools (e.g., NetIQ's Pegasus and Compuware's Ecoscope) that require a hardware and/or software agent be installed near each client site from which end-to-end or total response times are to be computed. The main problem with this approach is that it can be difficult or impossible to get the agents installed and keep them operating. For a global network, the number of agents can be significant; installation can be slow and maintenance painful. For an eCommerce site, installation of the agents is not practical; requesting potential customers to install software on their computers probably would not meet with much success. A secondary issue with this approach is that each of the client-site agents must upload their measurements to a centralized management platform; this adds unnecessary traffic on what may be expensive wide-area links. A third issue with this approach is that it is difficult to accurately separate the network from server delay contributions. To overcome the issue with numerous agent installs, some companies (e.g., KeyNotes and Mercury Interactive) offer a subscription service whereby one may use their preinstalled agents for response-time monitoring. There are two main problems with this approach. One is that the agents are not monitoring “real” client traffic but are artificially generating a handful of “defined” transactions. The other is that the monitoring does not generally cover the full range of client sites—the monitoring is limited to where the service provider has installed agents. Developers continue to improve methods and systems for testing networks, servers, and services for availability and performance. Among what is needed is the ability to visualize the operations of a computer network for identifying performance management issues and problems, together with probable causes of related problems. Techniques for visualizing network performance characteristics are disclosed, which techniques improve both the operation of the associated networks and support more associated performance management functions. According to one aspect of the disclosed subject matter, there is here provided a method and system for visualizing and monitoring quality of service of a computing network. The method includes the steps and the system includes the structures for monitoring application network transactions and behaviors for the computing network. The computing network includes one or more client subnets accessing one or more servers. The monitoring may be independent of client site monitors. The method and system gather statistical data relating to at least one network, a server and associated applications and generate a plurality of measurements of at least one quality of service indicator. The quality of service indictors relate to the performance of the computer network. The method and system further display the plurality of measurements of the at least one quality of service indicator according to the date and time of gathering the statistical data and displaying graphically the degree by which each of said plurality of measurements of the quality of service indicator varies from a predetermined threshold quality of service level for the computing network. According to another aspect of the disclosed subject matter, here is disclosed a method and system for visualizing and monitoring the performance of a computer network that include the steps and structures for displaying graphically a plurality of averaged network quality of service indicators. The averaged network quality of service indicators are associated on a radial plot and visually interlinked to form a nominal performance polygon. The nominal performance polygon includes a plurality of corners. Each of said corners corresponds to a separate one of the plurality averaged quality of service indicators. The method and system furthermore dynamically measure a plurality of network quality of service indicators. Each of the plurality of network quality of service indicators corresponds to one of the plurality of averaged network quality of service indicators. The method and system display graphically the dynamically measured plurality of network quality of service indicators as a radial plot point on the radial plot and visually interlink the radial plot points for forming a dynamic performance polygon. The dynamic performance polygon relates to the dynamic performance of the computer network. The disclosed subject matter allows monitoring the dynamic performance of the computer network by dynamically comparing variations in said dynamic performance polygon with said nominal performance polygon. A technical advantage of the disclosed subject matter includes the ability to directly compare metrics or measurements of different network quality of service indicators, regardless of the particular units of measure that may associate with the different indicators. Because the method and system here disclosed compare normalized indicator measurements to averaged values of network quality of service indicator, the indicators may be in milliseconds, percents, counts, or other measurement units. These and other aspects of the disclosed subject matter, as well as additional novel features, will be apparent from the description provided herein. The intent of this summary is not to be a comprehensive description of the claimed subject matter, but rather to provide a short overview of some of the subject matter's functionality. Other systems, methods, features and advantages here provided will become apparent to one with skill in the art upon examination of the following FIGUREs and detailed description. It is intended that all such additional systems, methods, features and advantages that are included within this description, be within the scope of the accompanying claims. FIG. 1 shows geographically a computer network that spans the globe and to which the teachings of the disclosed subject matter may apply. Across the globe 10, a computer network 12, which may actually include an association of many networks, communicates connects different sites 14 to one another. In such a computer network, addressing performance changes arising from new application deployments, determining how best to satisfy near future network and user needs, and performing proactive and reactive trouble shooting all require network managers and technicians a variety of performance management functions. These performance management functions must resolve how network managers respond to problems as they arise. FIG. 2 shows, therefore, shows computer network performance environment 20. Computer network performance environment 20 includes performance management functions 22, which communicate and interoperate with fault management functions 24, configuration management functions 26, accounting management functions 28, and security management functions 30. Performance management functions 22 ensure the efficient utilization of computer network 12 resources. This includes minimizing the impact of resource contention to make processes continuously and efficiently operate. Using fault management functions 24, configuration management functions 26, accounting management functions 28, and security management functions 30, performance management functions 22 ensure that each application/user receives what is required over all time-scales by optimally using available resources, such as device CPU resources, memory resources, and bandwidth resources. Performance management functions 22 to which the disclosed subject matter relates provide (a) proactive, measurement-based management functions for permitting, root cause/routing bottleneck diagnosis using fault management functions 24; (b) capacity planning and design, server location decisions, technology evaluations, and requirement predictions using configuration management functions 26; (c) cost/performance trade-off analyses using accounting management functions 28, and privacy and intrusion detection and prevention policies and procedures using security management functions 30. In addressing these characteristics of performance management environment 20, the disclosed subject provides a method and system for visualizing network performance characteristics. FIG. 3 relates more directly the visualization method and system of the disclosed subject matter to network optimization system 40, which provides many computer network 12 performance management functions. Network optimization system 40 permits troubleshooting enterprise application problems and optimizing computer network 12 performance. Network optimization system 40, therefore includes performance management functions 22 for ensuring consistent delivery of business critical applications, documenting information technology service levels and improving the end user's experience. One embodiment of network optimization system 40 associates router 42, application statistics function 44, network devices 46, and program databases 48 to communicate with program databases 50. Network specific databases 50 communicate with analysis functions on workstation 52. Using the analysis functions of network optimization system 40, workstation 52 provides report visualization functions 54, as described herein. Network optimization system 40 may be such as described in commonly assigned U.S. patent application Ser. No. 10/962,331 entitled “Dynamic Incident Tracking and Investigation in Service Monitors,” by Cathy Anne Fulton et al. Although described with particular reference to a computing environment that includes personal computers (PCs), a wide area network (WAN) and the Internet, the claimed network optimization system 40 subject matter can be implemented in any information technology (IT) system in which it is necessary or desirable to monitor performance of a network and individual system, computers and devices on the network. Those with skill in the computing arts will recognize that the disclosed embodiments have relevance to a wide variety of computing environments in addition to those specific examples described below. In addition, the methods of the disclosed invention can be implemented in software, hardware, or a combination of software and hardware. The hardware portion can be implemented using specialized logic; the software portion can be stored in a memory and executed by a suitable instruction execution system such as a microprocessor, PC or mainframe. All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. In the context of this document, a “memory,” “recording medium” and “data store” can be any means that contains, stores, communicates, propagates, or transports the program and/or data for use by or in conjunction with an instruction execution system, apparatus or device. Memory, recording medium and data store can be, but are not limited to, an electronic, magnetic, optical, electromagnetic, infrared or semiconductor system, apparatus or device. Memory, recording medium and data store also includes, but is not limited to, for example the following: a portable computer diskette, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), and a portable compact disk read-only memory or another suitable medium upon which a program and/or data may be stored. FIG. 3A is a block drawing of an exemplary computing environment 40 that supports the claimed subject matter. FIG. 3A illustrates an example of a suitable computing system environment 40 on which the invention may be implemented. The computing system environment 40 is only one example of a suitable computing environment and is not intended to suggest any limitation as to the scope of use or functionality of the invention. Neither should the computing environment 40 be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary operating environment 40. The invention is operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well known computing systems, environments, and/or configurations that may be suitable for use with the invention include, but are not limited to: personal computers, server computers, hand-held or laptop devices, tablet devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like. The invention may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The invention may also be practiced in distributed computing environments wherein tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in local and/or remote computer storage media including memory storage devices. With reference to FIG. 3A, an exemplary system within a computing environment for implementing the invention includes a general purpose computing device in the form of a computer 41. Components of the computer 41 may include, but are not limited to, a processing unit 43, a system memory 47, and a system bus 45 that couples various system components including the system memory to the processing unit 43. The system bus 45 may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus also known as Mezzanine bus. The computer 41 typically includes a variety of computer readable media. Computer readable media can be any available media that can be accessed by the computer 10 and includes both volatile and nonvolatile media, and removable and non-removable media. By way of example, and not limitation, computer readable media may comprise computer storage media and communication media. Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the computer 41. Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of the any of the above should also be included within the scope of computer readable media. The system memory 47 includes computer storage media in the form of volatile and/or nonvolatile memory such as read only memory (ROM) 49 and random access memory (RAM) 51. A basic input/output system 53 (BIOS), containing the basic routines that help to transfer information between elements within computer 41, such as during start-up, is typically stored in ROM 49. RAM 51 typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit 43. By way of example, and not limitation, FIG. 3A illustrates operating system 55, application programs 57, other program modules 59 and program data 61. The computer 41 may also include other removable/non-removable, volatile/nonvolatile computer storage media. By way of example only, FIG. 3A illustrates a hard disk drive 65 that reads from or writes to non-removable, nonvolatile magnetic media, a magnetic disk drive 77 that reads from or writes to a removable, nonvolatile magnetic disk 79, and an optical disk drive 81 that reads from or writes to a removable, nonvolatile optical disk 83 such as a CD ROM or other optical media. Other removable/non-removable, volatile/nonvolatile computer storage media that can be used in the exemplary operating environment include, but are not limited to, magnetic tape cassettes, flash memory cards, digital versatile disks, digital video tape, solid state RAM, solid state ROM, and the like. The hard disk drive 65 is typically connected to the system bus 45 through a non-removable memory interface such as interface 63, and magnetic disk drive 77 and optical disk drive 81 are typically connected to the system bus 45 by a removable memory interface, such as interface 75. The drives and their associated computer storage media, discussed above and illustrated in FIG. 3A, provide storage of computer readable instructions, data structures, program modules and other data for the computer 41. In FIG. 3A, for example, hard disk drive 65 is illustrated as storing operating system 67, application programs 69, other program modules 71 and program data 73. Note that these components can either be the same as or different from operating system 55, application programs 57, other program modules 59, and program data 61. Operating system 67, application programs 69, other program modules 71, and program data 73 are given different numbers hereto illustrate that, at a minimum, they are different copies. A user may enter commands and information into the computer 41 through input devices such as a tablet, or electronic digitizer 93, a microphone 91, a keyboard 89 and pointing device 87, commonly referred to as a mouse, trackball or touch pad. Other input devices (not shown) may include a joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit 43 through a user input interface 85 that is coupled to the system bus, but may be connected by other interface and bus structures, such as a parallel port, game port or a universal serial bus (USB). A monitor 111 or other type of display device is also connected to the system bus 45 via an interface, such as a video interface 109. The monitor 111 may also be integrated with a touch-screen panel or the like. Note that the monitor and/or touch screen panel can be physically coupled to a housing in which the computing device 41 is incorporated, such as in a tablet-type personal computer. In addition, computers such as the computing device 41 may also include other peripheral output devices such as speakers 117 and printer 115, which may be connected through an output peripheral interface 113 or the like. The computer 41 may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer 103. The remote computer 103 may be a personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer 41, although only a memory storage device 105 has been illustrated in FIG. 3A. The logical connections depicted in FIG. 3A include a local area network (LAN) 97 and a wide area network (WAN) 101, but may also include other networks. Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets and the Internet. For example, in the present invention, the computer system 41 may comprise the source machine from which data is being migrated, and the remote computer 103 may comprise the destination machine. Note however that source and destination machines need not be connected by a network or any other means, but instead, data may be migrated via any media capable of being written by the source platform and read by the destination platform or platforms. When used in a LAN networking environment, the computer 41 is connected to the WAN 101 through a network interface or adapter 95. When used in a WAN networking environment, the computer 41 typically includes a modem 99 or other means for establishing communications over the WAN 101, such as the Internet. The modem 99, which may be internal or external, may be connected to the system bus 45 via the user input interface 85 or other appropriate mechanism. In a networked environment, program modules depicted relative to the computer 41, or portions thereof, may be stored in the remote memory storage device. By way of example, and not limitation, FIG. 3A illustrates remote application programs 107 as residing on memory device 105. It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used. In the description that follows, the invention will be described with reference to acts and symbolic representations of operations that are performed by one or more computers, unless indicated otherwise. As such, it will be understood that such acts and operations, which are at times referred to as being computer-executed, include the manipulation by the processing unit of the computer of electrical signals representing data in a structured form. This manipulation transforms the data or maintains it at locations in the memory system of the computer, which reconfigures or otherwise alters the operation of the computer in a manner well understood by those skilled in the art. The data structures where data is maintained are physical locations of the memory that have particular properties defined by the format of the data. However, while the invention is being described in the foregoing context, it is not meant to be limiting as those of skill in the art will appreciate that several of the acts and operation described hereinafter may also be implemented in hardware. In network optimization system 40, router 42 collects flow-based statistics on network traffic, such as protocols used, ports used, and other information. Application statistics functions may be dedicated services that gather application-level information and statistics through protocols, such as SNMP that may, for example, follow the RMON2 standard. In addition, network optimization system 40 uses network devices 46 to acquire statistics that may be gathered through SNMP. Response time data may be collected from individual program databases, such as an end-to-end database. Network specific databases 50 may receive the information from these network resources and generate a highly scalable network-specific database that uses data-mining techniques and data pre-processing functions to process a large set of statistical information. At workstation 52, computer network 12 analysis and reporting functions occur. In essence, workstation 52 provides dynamic incident tracking and investigation supporting various performance management functions 22. From workstation 52, the disclosed subject matter provides report visualization functions 54 as an output of the present method and system for visualizing network performance characteristics. One aspect of network optimization system 40 includes application response time functions that quickly track and measure end-user response time. The application response time functions operate without desktop or server agents and separate response time into application, network, and server delay components. The application response time functions, therefore, enable rapid troubleshooting of application performance bottlenecks. Network optimization system 40 also includes automated processes to measure and analyze application response time for all user transactions. Report visualization functions 54 permit comparing response times and other computer network 12 performance indictors against intelligent baselines. Moreover, network optimization system 40 may automatically investigate the cause of problems as they occur. Network optimization system 40 also provides report analyzer functions that operate on workstation 52 and in conjunction with report visualization functions 54. The result is a flexible analysis engine that enables network managers to understand how application traffic impacts computer network 12 performance. Using report visualization functions 54 and the associated analysis tools of workstation 52, the present embodiment allows identifying which applications are using excessive bandwidth, the location of such users, and when such applications are being used. Report analyzer functions of workstation 52 cooperate with network specific databases 50 to store and report enterprise-wide router 42 data and application statistics 44, for extended periods of time (e.g., an entire year). Such storage in network specific databases 50 allows network managers to make important cost reduction, troubleshooting, capacity planning, and traffic analysis decisions. Network optimization system 40 separates application response times into network, server, and application delays, and generates alarms based on customer defined thresholds. However, network optimization system 40 does not require the deployment of agents on workstations within computer network 12. Network optimization system 40 collects large amounts of data from multiple sources and presents them as meaningful information and can aggregate data for reporting and analysis. Network optimization system 40 provides custom exception reporting and may drill down from the enterprise level to individual hosts and conversations occurring on computer network 12. In addition, network optimization system 40 enables a variety of computer network 12 advisory services to occur. That is, network optimization system 40 permits analyzing application response times without deploying client-side agents. Using the disclosed subject matter, network optimization system 40 permits the analysis of huge volumes of data from multiple sources for rapid identification by application of network traffic and congestion sources. As such, network optimization system 40 enables advisory service for making recommendations that translate into lower network costs and improved response, thus making advantageous use of the visualizations herein described. FIG. 4 shows application response time data plot 50 for one embodiment of the disclosed subject matter. The data of FIG. 4 may be derived from a single server or a cluster of servers. Response time data plot 60 plots time in seconds along axis 62 against calendar date and time, along axis 64. Threshold bar 66 sets a limit (e.g., 1 second) for response time plot 68. When response time plot 68 exceeds threshold bar 66, network optimization system 40 presents through report visualization functions 54 a violation report. Values reported for response time plot 68, in one embodiment, results from the accumulation of separate plots of the constituent components of the traffic response time delays. This may include network round trip time (RTT) delays, retransmission delays, data transfer delays, server response delays and connect time delays. In particular as response time plot 68 shows, server response delays 70 are the major contributor to the total response time plot 68. Thus, as traffic occurs on a computer network, as indicated by traffic plot 72, delays, as peaks in response time plot 68 show, result in traffic reductions, as valleys in traffic plot 72 exhibit. Violations of various service agreements, for example, may relate to the degree by which response time plot 68 exceeds threshold bar 66 time limit, e.g., one second. For example, peak 74 may be viewed as a major violation, since the response time exceeds threshold bar by approximately two seconds. Peak 76, which exceeds threshold bar by slightly more than one second, may be viewed as an intermediate violation. Finally, peak 78 may be considered a minor violation, since the one-second threshold bar 66 is exceeded by less than 0.25 seconds. Response time data plot 50 shows a specific server. The present embodiment may also provide information for a single interface. However, other embodiments may also provide for multiple servers, i.e., at a next level of granularity. Thus, using one diagram, it is possible to determine the aggregate violations of a set of servers. This potentially provides such additional valuable information that may be useful for managing the operation of a network. FIG. 5 provides violation intensity chart 80 that may be generated using the disclosed subject matter. In violation intensity chart 80, “Hours in Day” axis 82 crosses “Days” axis 84 to permit recording the specific time and day on which a violation occurs. Violation intensity chart 80 relates response time plot 68 to threshold bar 66 by providing a visualization of the degree by which response time plot 68 exceeds threshold bar 66. Thus, as exploded regions 86 and 88 show, violation intensity chart 80 presents tick marks of varying colors or other differentiating characteristics to demonstrate the degree by which response time plot exceeds threshold bar 66. In the illustrated example, a red tick mark 90 (which may appear alternatively as vertical hash marks) may relate to major violation peak 74 (FIG. 4), an orange tick mark 92 (which may appear alternatively as diagonal hash marks) relate to intermediate violation peak 76, and a yellow tick mark 94 (which may appear alternatively as horizontal hash marks) may relate to minor violation peak 78. Particularly attractive features of violation intensity charts include workday regions 96 and weekend regions 98. Workday regions 96 brackets the hours during which a company generally works. Weekend regions 98 highlights the weekend days. Identifying these time and day regions, violation intensity chart 80 allows a network manager to focus attention on specific violation periods. Thus, for example, in the event that an excessive number of red tick marks 90 arise in work hour regions 96 and outside of weekend regions 98 time response violation may be a major concern for computer network 12 which requires immediate attention. On the other hand, if red tick marks 90 only occur during weekend regions 98 and outside work hour regions 96, then immediate action may not be appropriate. The shadings in color intensity provide the ability to determine utilization, as well as violations. The shadings in color intensity also provide the ability to determine the degree of the utilization and/or violation of a particular network. In addition to violation intensity chart 80, the disclosed subject matter provides meaningful visualizations of associated and interdependent network quality of service indicators. FIG. 6, therefore, illustrates the generation of a server print plot 100, which integrates network performance measurements from network optimization system 40. In the example of FIG. 6, server print plot 100 (so named by virtue of providing a signature or distinct finger print of computer network 12 operations) may provide measurement visualizations from six computer network 12 quality of service indicators. Response time plot 102, as already described, may plot composite response times versus date-time slots. Refused sessions plot 104 plots refused TCP/IP sessions for particular date-time slots against total sessions. Total sessions plot 106 plots total numbers of users against day-time slots. Also, traffic volume plot 108 provides both “to server” and “from server” volume statistics for computer network 12. FIG. 6 integrates statistics from plots 102 through 108 to facilitate visualizing computer network 12 operations. In FIG. 6, server print plot axes include SRT axis 110, percent (%) refused sessions axis 112, volume (to) axis 114, volume (from) axis 116, total sessions axis 118, and burstiness axis 120. Nominal performance polygon 122 relates to nominal or average performance of computer network 12 over a predetermined or defined period of time. Nominal performance polygon 122 may be formed as a regular polygon by normalizing the respective average quality of service indicator (e.g., SRT) along SRT axis 110 and with relation to the other quality of service indicators, which, likewise may be normalized to their respective axes. Dynamic performance polygon 124, which may or may not be a regular polygon, provides measured quality of service indicator statistics relative to the normalized and averaged quality of service indicators of nominal performance polygon 122. Server print plot 100 displays key indicators for a network problem solution into one diagram. With prior approaches there may be the need to have use up to three browsers and many different plots at a single time to see all of the information appearing in server print plot 100. FIG. 6 also demonstrates what normal or nominal behavior occurs on a particular network. In reviewing an entire time period (e.g., month), FIG. 6 shows the different metrics normalized to a single plot. By determining a relative range for each metric, then FIG. 6 measures dynamic performance according to the various metrics. Based on this, FIG. 6 provides a precise measurement on the plot of the dynamic information relative to the nominal value of the associated indicator. Thus, all indicators reported on FIG. 6 are measured dynamically and quantitatively against the nominal values over the specified time period. FIGS. 7 and 8 show dynamic performance polygons and nominal performance polygons deriving from operation of the disclosed subject matter. In particular, FIG. 7 depicts on network print plot 130 nominal performance polygon 132 and dynamic performance polygon 134. Network print plot 130 includes for visualization network RTT axis 136, percent (%) byte loss axis 138, volume (to) axis 140, volume (from) axis 142, total sessions axis 144, retransmission axis 146, and users axis 148. Nominal performance polygon 132 takes the form of a regular seven-sided polygon. As FIG. 7 depicts, nominal performance polygon 132 represents nominal behavior of a computer network 12 during a period, such as Aug. 1, 2003 through Sep. 1, 2003. Clearly, different period quality of service indicators may be represented for network print plot 130 according to a network manager's preferences and needs. Dynamic performance polygon 134 of FIG. 7, in contrast to nominal performance polygon 132, presents a non-regular shape. The example of dynamic performance polygon, in particular, dynamic performance polygon 134 exceeds nominal values of nominal performance polygon 132 along network RTT axis 136, volume (to) axis 140, volume (from) axis 142, total sessions axis 144, and users axis 146. On the other hand, dynamic performance polygon 134 presents quality of service indicator values below nominal performance polygon 132 along percent (%) byte loss axis 138 and retransmission axis 146. The example of FIG. 7 may be interpreted as a heavily used network. Actually, however, the measured indicators do not show faulty or defective operation of the network. The network, while handling more than usual traffic, may need to have its computer network 12 capacity increased, if the dynamic quality of service indicators continue over a period of time to indicate the statistics of FIG. 7. In FIG. 8, server print plot 150 provides the ability to compare dynamic performance polygon 152 to nominal performance polygon 154. Dynamic performance polygon, in this example, presents real-time normalized statistics for the time 11:50 on Jun. 12, 2003. In contrast, nominal performance polygon 154 displays normalized nominal behavior for the period of Jun. 1, 2003 through Jul. 1, 2003. Quality of service indicators for server print plot 150 include those displayed by SRT axis 156, percent (%) refused sessions axis 158, volume (to) axis 160, volume (from) axis 162, total sessions axis 164, and burstiness axis 166. Dynamic performance polygon 152 reports nominal percent (%) refused sessions and nearly nominal burstiness statistics. However, IRST, volume (to), volume (from), and total sessions statistics all appear to exceed nominal values. FIG. 8 specifically references measurements against data gathered over time and averaged. The present embodiment plots dynamic measurements against the averaged information. Dynamic performance polygon 152 demonstrates that many more than the average number of sessions are occurring. If this were not so high, it might be interpreted that the network flows more traffic volume, conducting more sessions, and the server response was simply working hard. Because a great deal of volume flows into the server, a problem may exist in computer network 12. For example, a server may be mis-configured. On the other hand, such server may be in a multi-tiered environment. So, what dynamic performance polygon 152 shows may not be an extreme problem. However, the plot alerts the engineer to a potential problem, and focuses the investigation to some form of mis-configuration, such as when data being unexpectedly pushed to the server, or to the fact the server is involved in a multi-tiered application (which is also sometimes not known to the network engineer). FIG. 9 depicts on network print plot 170 time varying dynamic performance polygons for reporting variations in computer network performance. In particular, network print plot 170 displays nominal performance polygon 172 relating to the performance measurement period between 1:00 a.m. February 27 and 1:00 a.m. Feb. 28, 2003. For comparison purposes, network print plot 170 presents five dynamic performance polygons, all taken on Feb. 27, 2003, and at five minute intervals. Specifically, dynamic performance polygon 174 relates to time 1:38 a.m.; dynamic performance polygon 176 relates to time 1:43 a.m.; dynamic performance polygon 178 relates to time 1:48 a.m.; dynamic performance polygon 180 relates to time 1:53 a.m.; and dynamic performance polygon 182 relates to time 1:58 a.m. Network print plot 170 portrays computer network 12 quality of service indicators along network round trip time (NRTT) axis 184, percent (%) byte loss axis 186, volume (to) axis 188, volume (from) axis 190, total sessions axis 192, retransmission axis 194, and users axis 196. FIG. 9, therefore, details in a more comprehensive fashion the information heretofore described. Dynamic performance polygon 182 will result in a violation determination by network optimization system 40. By the time a violation is determined, however, dynamic performance polygon 182 demonstrates a high network roundtrip measurement, together with high volume (from). These indications may not truly be a problem. However, because the measurements are significantly above normal, an investigation should occur. With this information, there is the need to determine the cause for at least two of the indicators being out of range. The analyses should, therefore, be of what the causes are and what the side effects are of the out of range conditions. Dynamic performance polygons 174 through 180 provide information in reverse order from the violation. This allows a view of dynamic performance polygon 180, which occurs only five minutes before dynamic performance polygon 182. Dynamic performance polygon 180 shows a large percentage byte loss. Another out of specification indicator is the retransmission indicator. There was also more volume to the server. Going back one more frame to dynamic performance polygon 178, it is possible to see that the only indicator that is out of specification is the number of users. By continuing to back up the measurements, it is possible to isolate the first out of range indicator. This may assist in determining the root cause of the network malfunctions or mis-configurations. In dynamic performance polygon 174, the total sessions and users indicators are high. Thus, what caused the network to malfunction was the presence of too many sessions and users. This situation, however, is not at all apparent from the measurement, i.e., dynamic performance polygon 182 that resulted in the service agreement violation. That is, the violation was an effect, and certainly not a cause of the network malfunction. This demonstrates the dynamic, interrelated nature of computer network 12 and how a network degradation may affect different quality of service indicators. Thus, using the combination of dynamic performance polygons and nominal performance polygons in server and network print plots, there is the potential for indicating correlations and causalities. The disclosed subject matter may provide the ability to determine a network violation at some period before it occurs. In such case, there may be the ability to respond to an indicator change and, thereby, take preemptive action that could reduce or eliminate serious network effects. Such preemptive action may include avoiding over-use of network resources or timing of excessive network loading to occur at more optimal times. In yet a further embodiment of the disclosed subject matter, there is the ability to associate a plurality of server or network print plots. It may be possible to categorically identify the different violations that occur by viewing a broad array of server or network print plots. Upon categorically identifying such violations, based on the server or network print plots, the disclosed server or network print plots may provide insights into how to categorically eliminate network violations or out of range conditions. By categorically eliminating problems, based on the characteristic server or network print plots that such problems generate, the disclosed subject matter may very significantly improve overall network operations. Moreover, by creating and diagnosing categories of server or network print plots, the present embodiment may suggest correlations between different categories of network conditions that generate characteristic server print plots. By responding to server or network print plot data, even prior to an out of range condition arising, the disclosed subject matter may even more significantly improve overall network performance. On an even larger scale, by associating categories of server or network print plots from various points of a network system, the disclosed subject matter may provide real-time data for assisting in the diagnosis of network problems at many different levels. Thus, in addition to providing comparisons of real time visualizations of computer network 12 performance, the disclosed subject matter allows for the aggregation of statistics over longer periods of time. Such aggregations enable trend analyses for both longer term and larger scale performance management functions. For example, FIGS. 10 and 11 display overall network exception status information for a particular computer network 12. Although the information presented by FIGS. 10 and 11 is the same in the example, the two plots appear in different forms. FIG. 10, for example, reports in overall network exception status bar chart 200 exception status for the months of 9-2004 (September) in bar 202, 10-2004 (October) in bar 204, 11-2004 (November) in bar 206, and 12-2004 (December) in bar 208, all across axis 210. The “hours in violation” axis 204 varies, in this example, from 0 to 5000 hours for presenting the cumulative hours that computer network 12 violates the applicable service agreement. Violations may vary from unwanted peer-to-peer traffic, as bar 202 portion 210 relates to the more common violations appearing in all bars 202 through 208. That is, violations may include NetBIOS over 25 percent (%) violation 212, overall utilization over 80 percent (%) violation 214, unexpectedly high management traffic violation 216, and unwanted real-time streaming protocol (RSTP) traffic violation 218. FIG. 10, therefore, provides a clear visualization of the cumulative exception status for computer network 12. In contrast, FIG. 11 shows overall network exception status point chart 220 for visualizing the exception status of computer network 12 during the same reporting period of FIG. 10. Overall network exception status point chart 220 uses “hours in violation axis” 222, which ranges from 0 to 2600 hours for displaying exception status variations in computer network 12 on a per violation basis. Thus, for overall computer network 12 exceptions occurring during the period 9-2004 through 12-2004, plot 224 reports variations in the NetBIOS over 25 percent (%) violation, plot 226 reports variations in overall utilization being over 80 percent (%), plot 228 reports the unexpectedly high management traffic violation, plot 230 reports the unwanted peer-to-peer traffic violation, and plot 232 reports unwanted RTSP violations. While FIGS. 10 and 11 relate to overall network statistics, FIG. 12 presents violation trend bar chart 240 that further demonstrates the ability of the disclosed subject matter to aid in performance management of computer network 12. FIG. 12 presents in violation trend bar chart 240, a specific violation, i.e., unwanted RSTP traffic, is reported on a per site 14 basis. Chart 240 of FIG. 12 may, for example, be generated in response to a “drill in” of plot 232 in FIG. 11. Moreover, individual site 14 violation data is reported over specific time periods. Thus, for the New York Gateway Interface, for example, bar 242 reports the hours in violation for October 2004 for unwanted RTSP traffic, here approximately 550 hours. Bars 244 and 246 report the same type of data for the months of November (approx. 510 hours) and December 2004 (approx. 540 hours), respectively. In the example of FIG. 12, computer network 12 includes forty-two sites 14. However, violation trend bar chart 240, for the sake of simplicity and clarity, only displays the six sites demonstrating the more significant violations, based on a dynamic algorithm. In the example, these include the Taiwan interface site in bars 248, the Fairbanks interface site in bars 250, the Saigon interface site in bars 252, the Santa Fe interface site in bars 254, and the Milan interface site in bars 256. In summary, therefore, the disclosed subject matter provides a method and system for visualizing and monitoring quality of service of a computing network. The method includes the steps and the system includes the structures for monitoring application network transactions and behaviors for the computing network. The computing network includes one or more client subnets accessing one or more servers. The monitoring may be independent of client site monitors. The method and system gather statistical data relating to at least one network, a server and associated applications and generate a plurality of measurements of at least one quality of service indicator. The quality of service indictors associate with the performance of the computer network. The method and system further display the plurality of measurements of the at least one quality of service indicator according to the date and time of gathering the statistical data and displaying graphically the degree by which each of said plurality of measurements of the quality of service indicator varies from a predetermined threshold quality of service level for the computing network. In further summary, the disclosed subject matter provides a method and system for visualizing and monitoring the performance of a computer network that include the steps and structures for displaying graphically a plurality of averaged network quality of service indicators. The averaged network quality of service indicators relate to a radial plot and visually interlinked to form a nominal performance polygon. The nominal performance polygon includes a plurality of corners. Each of said corners corresponds to a separate one of the plurality averaged quality of service indicators. The method and system furthermore dynamically measure a plurality of network quality of service indicators. Each of the plurality of network quality of service indicators corresponds to one of the plurality of averaged network quality of service indicators. The method and system display graphically the dynamically measured plurality of network quality of service indicators as a radial plot point on the radial plot and visually interlink the radial plot points for forming a dynamic performance polygon. The dynamic performance polygon relates to the dynamic performance of the computer network. The disclosed subject matter allows monitoring the dynamic performance of the computer network by dynamically comparing variations in said dynamic performance polygon with said nominal performance polygon. The foregoing description of the preferred embodiments, therefore, is provided to enable any person skilled in the art to make or use the claimed subject matter. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the innovative faculty. Thus, the claimed subject matter is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. |
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058617019 | summary | BACKGROUND FIELD OF THE INVENTION The invention relates to methods and apparatus for conversion of charged particle kinetic energy to electrical energy. METHODS OF ENERGY CONVERSION During the 1950's major attempts were made to use nuclear power sources in satellites because of their relatively long life and high energy density. These cumbersome units were required to generate kilowatts of electrical power and were in great demand. Although rudimentary technology for direct conversion from nuclear to electrical energy had been developed in the prior two decades, direct methods were not widely used for satellite applications. Instead, indirect conversion methods (i.e., those involving an intermediate heating step) were favored because they produced relatively large quantities of electrical power at higher efficiencies than were achieveable by direct methods. Subsequently, as lower power applications for long-life batteries became more numerous, interest was again focused on direct production of electrical currents using radionuclide sources. See U.S. Pat. No. 2,728,867, issued Dec. 27, 1955 (Wilson), incorporated herein by reference. Wilson describes the use of charged particle (beta) emission and collection plates to establish a potential (voltage) in a capacitor type arrangement. Such batteries were generally designed to produce relatively low currents at relatively high terminal voltages (kilovolts, for example), reflecting their design and the relatively high energy of the alpha, beta, gamma or X-radiation involved. For an example of a photoelectric generator, see U.S. Pat. No. 4,178,524, issued Dec. 11, 1979 (Ritter), incorporated herein by reference. While high-voltage direct conversion batteries have found many uses, however, they are not ideally suited to many modern solid-state electronic applications. The past four decades of integrated microcircuit development have been characterized by decreasing power requirements and a shift from analog to digital technology. Many electronic power supplies now operate in the range of three to five volts DC, delivering microwatts to milliwatts. Indeed, power requirements for electronic applications in general have been reduced by more than an order of magnitude over the past decade and are continuing to decline. But the currently available long-life batteries are still practically limited by their design to operation at terminal voltages far in excess of what is needed for most microelectronic applications. Lower Voltage Sources Using Secondary Emission Secondary electron emission from an emitter toward a collector can substantially improve performance in a long-life, low voltage (but relatively high-current) battery. If several relatively lower-energy electrons are ejected from a secondary emitter which is struck by a relatively high-energy alpha or beta particle, twin benefits result. The energy of the alpha or beta particle is effectively reduced, even as the maximum current available to a circuit which carries the secondary electrons is increased. See U.S. Pat. No. 2,527,945, issued Oct. 31, 1950 (Linder), incorporated herein by reference. To maximize secondary emission, particles radiated from a relatively high-energy (primary emitter) source would preferably be slowed to an energy level compatible with the secondary emitter. A device using this technique is described in U.S. Pat. No. 2,858,459, issued Oct. 28, 1958 (Schwarz), incorporated herein by reference. This device incorporates a moderating layer of radiation-resistant material (the absorber) both to slow high-energy primary particles and to prevent the drift of secondary electrons back to the source. Unfortunately, all of the available lower-energy secondary electrons may not flow in an external circuit as desired if some of them are repelled back toward the secondary emitter by the negative space charge surrounding the collector. This problem has been recognized for many years, and was addressed in vacuum tube applications by placing the anode sufficiently close to the multiplying (secondary emission) electrode to substantially reduce space charge effects. See U.S. Pat. No. 2,164,892, issued Jul. 4, 1939 (Banks), incorporated herein by reference. Note, however, that if the secondary electrons are made sufficiently energetic to penetrate the space charge (so the collector actually captures all of the electrons from the secondary emitter), a further problem results. Some of the captured electrons may impart sufficient energy to other electrons in the collector to cause their ejection and subsequent drift back toward the secondary emitter or even toward the source. Thus, battery performance may be adversely affected by what is effectively a leakage current comprising electrons secondarily emitted from the collector. One method proposed for reducing this leakage current involves placing a grid, which is biased at a relatively low negative potential, between the collector and the source. It is evident that inclusion of such grids and the power supplies to establish suitable bias potential would significantly complicate both battery construction and operation. Lower Voltage Sources Using p-n Junctions Another method of directly producing relatively low-voltage electrical power using a relatively high-energy radionuclide source is to irradiate a semiconductor device comprising one or a plurality of p-n semiconductor junctions connected in series or parallel. See U.S. Pat. No. 3,094,634, issued Jun. 18, 1963 (Rappaport), and U.S. Pat. No. 3,706,893, issued Dec. 19, 1972 (Olsen et al.), both incorporated herein by reference. But the p-n junction devices of Rappaport and Olsen et al. do not incorporate the advantages of secondary electron emission, and they are used with relatively low-energy radionuclide sources (such as promethium-147) because of the substantially increased likelihood of damage to semiconductors exposed to relatively higher-energy sources (such as strontium-90). Thus, radiation energy limitations, excessive leakage currents, and high terminal voltages have combined with cost, safety and fabrication problems to limit the use of nuclear energy sources in relatively low-power applications. A long-life low-voltage power source adapted for use with modem integrated microcircuits (preferably having a specific energy density of about one watt-hour per gram) would find many uses but is not commercially available. Further, the devices and methods referenced above can not be used to produce such a power source. SUMMARY OF THE INVENTION The present invention includes methods and apparatus for building a charged-particle powered electrical source (an improved battery) for continuously-powered low-energy applications such as, e.g., integrated microcircuits and/or sensors (the improved battery often being small enough to be incorporated on the same substrate or otherwise in a modular assembly with the microcircuits and/or sensors). An improved battery comprises at least one primary energy source (for producing a plurality of primary charged particles having kinetic energy) and a plurality of plate pairs or cells in which an electrical potential exists between the plates of a plate pair, the cells being electrically connected. Cells may be connected, for example, in series (negative plate of a first cell to positive plate of a second cell) or in parallel (positive and negative plates of a first cell connected respectively to positive and negative plates of a second cell), or certain cell groups may be connected in series while other cell groups are connected in parallel. Each cell comprises a secondary emitter plate (for producing secondary electrons) spaced apart from (and sufficiently electrically insulated from) a collector plate (for collecting secondary electrons emanating from the secondary emitter plate), the secondary emitter intercepting at least a portion of the primary charged particles from at least one primary energy source. Primary charged particles may comprise non-nuclear energetic particles (electrons, protons, ions) and/or energetic particles from nuclear decay (alpha particles, beta particles, positrons). The maximum kinetic energy of primary charged particles is preferably equivalent to at least twice a predetermined maximum cell potential (that is, the maximum potential between the two plates of any plate pair). Primary charged particles are identified in the present invention as charged particles which, when intercepted by a secondary emitter plate, may impart sufficient kinetic energy to one or more (secondary) electrons to cause their emission from the emitter plate. If only a portion of a primary charged particle's total kinetic energy is imparted to secondary electrons emitted from a single emitter plate, the particle's movement may continue with reduced kinetic energy until the particle is intercepted by another emitter plate with the possible emission of one or more additional secondary electrons. Note that a secondary electron itself may have sufficient kinetic energy so that, when subsequently intercepted by one or more secondary emitter plates, one or more additional secondary electrons may be emitted. For any embodiment of the improved battery, a majority of primary charged particles (preferably substantially all of them) will carry either a negative charge or a positive charge. In the improved battery, the (relatively higher) kinetic energies of (relatively few) intercepted primary charged particles are incrementally converted to (relatively lower) kinetic energies of (relatively many) secondary electrons. These incremental kinetic energy conversions take place as the primary charged particles each pass through a plurality of cells comprising relatively thin plates. Note that the moderating layer of Schwarz is not present as such in preferred embodiments of the improved battery of the present invention. The moderating layer of Schwarz slowed relatively high-energy charged particles by converting a portion of their kinetic energy to heat. An additional portion of intercepted-particle kinetic energy was converted to the (relatively low) kinetic energy of secondary electrons which could not materially contribute to external electrical current flow because of the relatively high cell potential described in Schwarz. In contrast, each of the relatively thin plates of the improved battery preferably produces relatively large numbers of secondary electrons (preferably with minimal production of heat) in light of the electron interaction cross-section characterization curve. While characterized as having relatively low kinetic energy, secondary electrons in an improved battery nevertheless are preferably sufficiently energetic to traverse the space separating emitter plate from collector plate. Effectively collecting and retaining these relatively low-energy secondary electrons makes them available for flow in an external circuit, an outcome which was neither described nor suggested in Schwarz. Each interception by a secondary electron emitter plate of the improved battery of a primary charged particle thus preferably incrementally reduces the kinetic energy of the particle (that is, reduces the particle's kinetic energy by an amount less than the particle's total kinetic energy) while imparting at least a portion of the kinetic energy increment to a plurality of secondary electrons. Each secondary electron then preferably has an imparted kinetic energy at least equivalent to (preferably slightly exceeding) a predetermined cell electrical potential. In other words, when a preferred electron kinetic energy is measured in eV (electron volts), its numerical value preferably slightly exceeds the predetermined (equivalent) cell electrical potential measured in V (volts). The total of kinetic energy imparted to secondary electrons emerging from any secondary electron emitter plate intercepting a primary charged particle is preferably substantially equal to the increment by which the energy of that primary charged particle is reduced through interaction with that emitter plate. Note that primary charged particles which pass through the secondary emitter plate of a cell will in general also pass through the collector plate of the same cell. The effects of these passages, however, differ. In any cell of an improved battery, the emitter and collector plates are distinguished by at least one functional characteristic, that being the relatively higher yield from the emitter of secondary electrons having imparted kinetic energies at least equivalent to the predetermined cell electrical potential following cell interception of a plurality of primary charged particles. This relatively higher secondary electron yield in emitter plates will preferably be obtained by appropriate choices of plate materials, plate coatings, and/or plate geometry. For example, insulating materials generally yield more secondary electrons than conductive materials in similar applications. Differential secondary electron emission from secondary emitter plates and collector plates can also be attained through emitter plate coatings (such as magnesium oxide over platinum or carbon) which increase secondary electron emission relative to that of a collector plate comprising, for example, a thin (for example, about 100 nm thickness) carbon film. Still another method to achieve a desired cell plate differential in secondary electron emission is through control of plate geometry to maximize the probability of interaction with primary charged particles and minimize self absorption of secondary electrons in emitter plates. Additionally or alternatively, collector plate geometry may be controlled to minimize the probability of interaction with primary charged particles and maximize self absorption of secondary electrons. To enhance both the emission of low energy secondary electrons from the emitter plate and the subsequent capture and retention of these secondary electrons by the (preferably relatively closely spaced compared to emitter plate dimensions) collector plate, improved batteries of the present invention preferably operate at a maximum cell potential (that is, between the collector plate and the secondary electron emitter plate of each cell) not to exceed about 50 V. Even more preferably, maximum cell potential for many microelectronic power applications is less than about 3 V to about 10 V. Additionally, materials for cell plates are preferably chosen to maximize enhancement factor (1) below comprising Fermi energy levels (F) and material work functions (W) of the emitter (subscript e) and collector (subscript c) plates. EQU (F.sub.c -F.sub.e)+(W.sub.c -W.sub.e) (1) Note that material constraints for certain improved battery designs may require that either of the differences in expression (1) above be maximized even if the other difference is not maximized or is even relatively unfavorable. In general, however, both differences are preferably maximized where practical. Methods for Building an Improved Battery As noted above, the present invention includes a method of making a charged-particle powered battery. The method comprises providing at least one primary energy source for producing a plurality of primary charged particles having kinetic energy. In addition, a plurality of electrically connected cells is arranged proximate each primary energy source, each cell comprising a secondary emitter plate for producing secondary electrons spaced apart from a collector plate for collecting secondary electrons emanating from the secondary emitter plate. At least one secondary emitter intercepts at least a portion of the primary charged particles from at least one primary energy source. Given such a battery configuration, one may then apply a variety of design criteria alternatively to subsequent steps in building an improved battery. For example, as a first alternative, a preferred cell potential is chosen for each cell of the plurality of cells, and a composition (comprising, for example, one or more radioisotopes which each predominantly produce a desired charged particle type having a desired maximum energy) is established for each primary energy source. The preferred energy source composition is such that, with each cell of the plurality of cells having a cell potential substantially equal to the preferred cell potential, at least a portion of the primary charged particles have kinetic energy sufficient to impinge on at least two of the secondary emitter plates. As a second alternative when considering a given primary energy source, one may choose a preferred cell potential for each cell of the plurality of cells such that at least a portion of the primary charged particles from the given source impinge on at least two of the secondary emitter plates. A third alternative when considering a given primary energy source and a preferred cell potential for each cell comprises choosing a preferred geometry for each emitter plate and collector plate of each cell of the plurality of cells such that at least a portion of the primary charged particles impinge on at least two of the secondary emitter plates. Preferred methods of making an improved battery may also comprise an additional step comprising choosing materials for each collector plate and each emitter plate so that cell collector Fermi energy levels exceed cell emitter Fermi energy levels for each cell. Analogously one may choose materials for each collector plate and each emitter plate so that cell collector material work functions exceed cell emitter material work functions for each cell. And one may also choose materials for each collector plate and each emitter plate so that cell collector Fermi energy levels exceed cell emitter Fermi energy levels for each said cell and cell collector material work functions exceed cell emitter material work functions for each said cell. Note that at least a portion of the primary charged particles in preferred embodiments of the improved battery preferably have kinetic energy which is incrementally reduced on interaction with at least one secondary emitter plate, and the chosen cell potential preferably is less than about 50 V and even more preferably less than about 3 V to about 10 V. |
06021175& | claims | 1. An x-ray filter comprising x-ray radiation absorbing material having a first region for absorbing x-ray radiation to decrease exposure of the cervical spine and a second region shaped opening therein which allows higher x-ray transmission therethrough in the upper thoracic spine area of the body of a patient than in the cervical spine area of the body of the patient, the edges of said radiation absorbing material disposed between the faces of the radiation absorbing material and delineating the shaped opening being beveled. 2. The x-ray filter of claim 1 wherein the opening is generally triangular. 3. The x-ray filter of claim 2 wherein the beveled edges are oppositely oriented to define a first inclined surface adjacent the opening and facing forward and a second inclined surface adjacent the opening of facing rearward. 4. The x-ray filter of claim 3 and further comprising a lead tap attached to the first region. 5. The x-ray filter of claim 1 wherein the absorbing material contains aluminum. 6. The x-ray filter of claim 1 wherein the filter has a thickness of at least about 15 to 30 mm. 7. The x-ray filter of claim 1 wherein the shaped opening creates a generally trapezoidal pattern of higher x-ray transmission. 8. An x-ray filter comprising first and second filter blocks of x-ray radiation absorbing material which are positioned adjacent one another to form a first radiation absorbing region and a second region having a shaped opening which allows higher x-ray transmission than the first region, the shaped opening being defined by a first beveled surface of the first filter block and a second beveled surface of the second filter block, the first beveled surface facing toward a front of the x-ray filter and the second beveled surface facing toward a rear of the x-ray filter. 9. The x-ray filter of claim 8 and further comprising third and fourth filter blocks adjacent the first and second filter blocks, the first, second, third and fourth filter blocks together defining the opening in a central portion of the x-ray filter. 10. The x-ray filter of claim 9 wherein the third filter block has a third beveled surface which faces toward the rear of the x-ray filter and the fourth filter block has a fourth beveled surface which faces toward the front of the x-ray filter. 11. The x-ray filter of claim 9 wherein the opening produces a generally octagonal pattern of higher x-ray transmission. 12. The x-ray filter of claim 8 wherein the opening is generally triangular. 13. The x-ray filter of claim 8 wherein the opening produces a generally trapezoidal pattern of higher x-ray transmission. 14. The x-ray filter of claim 8 wherein the first and second filter blocks have a thickness of greater than about 15 mm. 15. An x-ray filter comprising x-ray radiation absorbing material comprising a plurality of x-ray radiation absorbing members having oppositely beveled surfaces which define a triangular shaped opening which allows higher x-ray transmission in a generally trapezoidal shaped exposure pattern. 16. An x-ray filter comprising x-ray radiation absorbing material having a first region for absorbing x-ray radiation to decrease exposure and a second region shaped opening therein which allows higher x-ray transmission therethrough in a hip region of the body of a patient than in areas of the body of the patient adjacent to a head an neck of a femur in the hip region, the edges of said radiation absorbing material disposed between the faces of the radiation absorbing material and delineating the shaped opening being beveled. 17. The x-ray filter of claim 16 wherein the opening is generally diamond-shaped. 18. The x-ray filter of claim 17 wherein the beveled edges are oppositely oriented to define first inclined surfaces adjacent the opening and facing forward and second inclined surfaces adjacent the opening of facing rearward. 19. The x-ray filter of claim 16 wherein the absorbing material contains aluminum. 20. The x-ray filter of claim 16 wherein the shaped opening creates a generally octagonal pattern of higher x-ray transmission. |
045490830 | claims | 1. An X-ray imaging device for directly displaying X-ray images on a screen, comprising: a layer of phosphor crystals arranged on said screen; at least one cathode for emitting electrons which impinge on said phosphor screen, said crystals being excited by said electrons so as to display said X-ray image by a steady cathodoluminescence; wherein said phosphor crystal excitation is controlled by the persistent polarization and depolarization thereof, said crystals emitting said steady cathodoluminescence only when depolarized and said crystals comprising a material which is depolarized when X-rays irradiate said persistently polarized crystals. 2. An X-ray image device according to claim 1, wherein said phosphor screen is continuously and uniformly irradiated by electrons which are emitted from said at least one cathode and which have been accelerated by a potential in a predetermined voltage range subsequent to the momentary application of a negative electric field which has been applied across said phosphor screen; wherein, when X-rays momentarily irradiate said phosphor screen, the areas of said phosphor screen which have been irradiated by said X-rays continuously emit cathodoluminescence until said negative electric field is again momentarily applied across said phosphor screen. 3. An X-ray imaging device according to claim 2, further comprising a means for deriving a time varying signal corresponding to said displayed X-ray images, said means for deriving including a means for generating and controlling a read electron beam which is scanned over said phosphor screen and including a current detecting means for generating a signal corresponding to current flowing in collecting electrodes which are disposed in said device, wherein said signal generated by said current detecting means comprises said time varying signal. 4. An X-ray imaging device according to claim 1, wherein said cathodoluminescence intensity and X-ray image contrast on said phosphor screen are improved by application of a predetermined potential to one of either collecting electrodes, electrodes which are placed in front of said at least one cathode, or electrodes placed in front of said phosphor screen. 5. An X-ray imaging device according to claim 4, further comprising a means for deriving a time varying signal corresponding to said displayed X-ray images, said means for deriving including a means for generating and controlling a read electron beam which is scanned over said phosphor screen and including a current detecting means for generating a signal corresponding to current flowing in collecting electrodes which are disposed in said device, wherein said signal generated by said current detecting means comprises said time varying signal. 6. An X-ray imaging device according to claim 1, wherein said phosphor screen is placed on a face plate and comprises a powder of phosphor crystals which emit brilliant cathodoluminescence when incident electrons have penetrated thereinto, and which are persistently polarized when an external electric field has been applied thereto and which are depolarized when subsequently irradiated by X-rays. 7. An X-ray imaging device according to claim 6, wherein said face plate of said device comprises a glass plate which has a low X-ray absorption coefficient. 8. An X-ray imaging device according to claim 6, wherein said phosphor crystals comprise an oxide, oxysulfide, oxyhalide, aluminate, silicate, or halide of at least one element selected from gadolinium, lanthanum, yttrium and lutetium, which has been activated with at least one element selected from terbium, praseodymium, cerium, europium, dysprosium, and samarium. 9. An X-ray imaging device according to claim 6, wherein said phosphor crystals comprise zinc sulfide or zinc-cadmium sulfides containing one of either copper or silver as an activator and one of either a group III-a or a VII-a element as a coactivator. 10. An X-ray imaging device according to claim 6, wherein said phosphor crystals comprise zinc silicate which has been activated with one of either manganese or calcium tungstate. 11. An X-ray imaging device according to claim 6, further comprising a means for deriving a time varying signal corresponding to said displayed X-ray images, said means for deriving including a means for generating and controlling a read electron beam which is scanned over said phosphor screen and including a current detecting means for generating a signal corresponding to current flowing in collecting electrodes which are disposed in said device, wherein said signal generated by said current detecting means comprises said time varying signal. 12. An X-ray imaging device according to claim 1, wherein said phosphor screen is placed on a face plate and comprises a thin film of phosphor crystals which emit brilliant cathodoluminescence when incident electrons have penetrated thereinto, and which are persistently polarized when an external electric field has been applied thereto and which are depolarized when subsequently irradiated by X-rays. 13. An X-ray imaging device according to claim 12, wherein said phosphor crystals comprise an oxide, oxysulfide, oxyhalide, aluminate, silicate, or halide of at least one element selected from gadolinium, lanthanum, yttrium and lutetium, which has been activated with at least one element selected from terbium, praseodymium, cerium, europium, dysprosium, and samarium. 14. An X-ray imaging device according to claim 12, wherein said phosphor crystals comprise zinc sulfide or zinc-cadmium sulfides containing one of either copper or silver as an activator and one of either a group III-a or a VII-a element as a coactivator. 15. An X-ray imaging device according to claim 12, wherein said phosphor crystals comprise zinc silicate which has been activated with one of either manganese or calcium tungstate. 16. An X-ray imaging device according to claim 12, wherein said face plate of said device comprises a glass plate which has a low X-ray absorption coefficient. 17. An X-ray imaging device according to claim 1, wherein said phosphor crystals comprise an oxide, oxysulfide, oxyhalide, aluminate, silicate, or halide of at least one element selected from gadolinium, lanthanum, yttrium and lutetium, which has been activated with at least one element selected from terbium, praseodymium, cerium, europium, dysprosium, and samarium. 18. An X-ray imaging device according to claim 1, wherein said phosphor crystals comprise zinc sulfide or zinc-cadmium sulfides containing one of either copper or silver as an activator and one of either a group III-a or a VII-a element as a coactivator. 19. An X-ray imaging device according to claim 1, wherein said phosphor crystals comprise zinc silicate which has been activated with one of either manganese or calcium tungstate. 20. An X-ray imaging device according to claim 1, further comprising a means for deriving a time varying signal corresponding to said displayed X-ray images, said means for deriving including a means for generating and controlling a read electron beam which is scanned over said phosphor screen and including a current detecting means for generating a signal corresponding to current flowing in collecting electrodes which are disposed in said device, wherein said signal generated by said current detecting means comprises said time varying signal. |
048812471 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS As a nuclear power reactor operates, the quantity of fissionable material in the fuel rods decreases. The term "burnup" denotes this depletion of fissionable content. As burning occurs, certain radioactive isotopes are produced which spontaneously emit fast neutrons. The greater the burnup, the greater will be the production of these isotopes, and thus the emission rate of these fast neutrons will increase. There are five isotopes which account for more than 99% of a fuel assembly's fast neutron emission. These are .sup.242 Cm, .sup.244 Cm, .sup.238 Pu, .sup.239 Pu, and .sup.240 Pu. The plutonium isotopes dominate the emission up to about 200 effective full power days of reactor operation, at which point they count for 50% of the neutron activity. Thereafter, the curium isotopes become more important, account for 64%, 83%, 97%, and 99% after 210, 300, 600, and 900 effective full power days, respectively. FIG. 1 gives a typical relationship between the effective full power reactor days and the spontaneous neutron emission rate of an assembly that is assumed to have resided in the reactor for that length of time. The graph in FIG. 1 comes from calculations based on the method described in the publication Origin--The ORNL Isotope Generation and Depletion Code, by M. J. Bell, ORNL-4628, Oak Ridge National Laboratory, Oak Ridge, TN, May 1973. FIG. 1 corresponds to a reactor operating at a thermal power of 4100 MW, with an initial uranium enrichment of 3.20% .sup.235 U, with a total fuel load of 103.6 metric tons of uranium, divided among 193 fuel assemblies, and operating with an average thermal neutron flux of 4.26.times.10.sup.13 n/(cm.sup.2 -s). It is the capture by .sup.238 U of these neutrons and the subsequent neutron capture by the thus newly formed isotopes that, together with the emission of beta particles, produce the neutron-emitting isotopes of curium and plutonium. The quantity of these isotopes produced depends almost entirely on the total number of thermal neutrons to which an assembly is exposed, as does the thermal energy released due to fission by the fuel in the assembly. The calculated curve shows a linear relationship between the neutron emission rate and the reactor exposure time. The calculated curve has a formula given by EQU in y=m ln.times.b where y is the assembly neutron emission rate; x is the reactor exposure time and m and b are constants. The constants m and b are determined by normal procedures for fitting linear relationships, i.e. the x and y values are used for two points to determine the two unknowns. The values obtained were m=3.92 and -6.62. By inserting these values and taking the anti-logarithm of both sides, one obtains the following equation: Neutron emission rate (n/s)=1.34.times.10.sup.-3 [reactor exposure (days)] .sup.3.92. This equation can be further modified to the following equation: reactor exposure=746.3 (emission rate).sup.-3.92. This equation would be employed to determine reactor exposure directly from the emission rate, which, in turn, is obtained from the measured neutron counts. This invention is based on a measurement of this total neutron activity of an assembly and the correlation of that activity to the burnup of the fuel. We have also found that perturbations in fast neutron emission due to reactor down time are insignificant and err on the conservative side anyway. FIG. 2 illustrates the apparatus for measuring the fast neutron emission rate from spent fuel rods. In FIG. 2, a fuel rod assembly 1 containing fuel rods 2 is lowered into a positioning frame 3, such as a single element of a standard spent fuel storage rack. The frame, fuel rod assembly, and remaining apparatus are surrounded with water 4, which may or may not contain dissolved boron. Lead bricks 5 prevent gamma rays and some thermal neutrons from reaching neutron detector 6, and cadmium sheets 7 prevent any remaining thermal neutrons from reaching neutron counter 6. A polyethylene moderator 8 slows down the fast neutrons to the thermal energy range so as to activate neutron counter 6. A certain fraction of the fast neutrons emitted by the spent fuel will interact with counter 6, each producing an electrical pulse. The counting rate of these pulses is directly proportional to the emission rate of fast neutrons from the assembly. Since there is a one-to-one correspondence between emission rate and burnup, there is also a one-to-one correspondence between counting rate and burnup. The actual inventory buildup pattern of curium and plutonium in a fuel assembly will proceed at different rates for different reactor and fuel assembly designs but will be the same over the lifetime of a given reactor or for a given reactor design. As one step in the method of this invention, it is necessary to use the apparatus to measure the fast neutron counting rate from a nuclear fuel assembly of known burnup from a given type of reactor. The burnup of nuclear fuel can be determined by maintaining a careful history of the fuel in the reactor or by a chemical analysis. Either method is technically and economically prohibitive for use on large quantities of fuel, but is practical for a small sample. By dividing the neutron emission rate give from a calculated curve (such as in FIG. 1) by the coutning rate for a fuel sample having that reactor time, a proportionality constant between the emission rate from a sample of known burnup and the counting rate from samples of unknown burnup can be determined. When the neutron counting rate of nuclear fuel of unknown burnup is measured, multiplication by the proportionality constant will give the emission rate and, from the curve, the reactor time which is a measurement of the amount of burnup. Examples of devices suitable for measuring neutron emissions via counting rate include a boron-10 lined neutron detector and a U-235 lined fission detector. The boron 10 detector is preferred because it is about 20 times more sensitive, although it is more affected by gamma rays and thus requires more lead shielding. Both of these types of detectors detect thermal neutrons, so it is necessary to surround the detector with water or polyethylene to change the fast neutrons to thermal neutrons. It is also necessary to exclude gamma rays from the detector by surrounding it with lead, which also excludes some of the thermal neutrons, and to exclude any remaining thermal neutrons by surrounding it with cadmium. In addition, the associated counting electroncis such as a power supply, amplifier, discriminator, and scaler are required as is well known in the art. The associated electronics are not located underwater, but at a location remote from the counter and fuel assembly, electrical connections being made with standard cables also well known in the art. EXAMPLE 1 A test was conducted to determine roughly the sensitivity of the burnup measurement. The experimental arrangement was similar to that shown in FIG. 2. The detector was a two inch diameter by four inch long BF.sub.3 neutron counter. Adjacent to the detection system was a simulated portion of a fuel assembly in a plexiglass tank. The rod spacing and geometry approximated those of a real assembly. For the test, ten simulated rods were fabricated, five containing eight enriched uranium fuel peelets (about 3%) and five containing eight fuel pellets of natural enrichment (0.72%). The total length of each stack of eight pellets was about 12 centimeters. They were housed in aluminum cylinders. A 5.2 microgram .sup.252 Cf source (0.375 inch diameter by about 1 inch long) provided the fission spectrum of neutrons simulating emissions of the cirium and plutonium isotopes. The neutron emission rate was about 1.25 times 10.sup.7 neutrons per second. In the first series of runs, the five enriched rods were placed in the first row of a 5 by 5 grid and the five natural rods were placed in the second row. The source was then moved from the fifth row to the first row in the third column, displacing the fuel rods in rows 1 and 2. In the second series of tests, no fuel rods were used. Neutron count rates were measured and recorded during successive 10 second perios for the .sup.252 Cf source in the five positions in the third column. All but two points of these series were repeated using a 2,000 ppm concentration of boron in the water. The results are given in the following table: ______________________________________ Boron Simulated Concen- Fuel Rods tration CF-252 Source Position In Position In Water Row 1 Row 2 Row 3 Row 4 Row 5 ______________________________________ 0 ppm 17.5 14.4 11.2 8.5 6.3 Yes 2000 ppm 16.6 13.4 10.3 -- -- 0 ppm 15.6 12.1 8.8 6.2 4.5 No 2000 ppm 15.4 11.8 8.6 6.2 4.4 ______________________________________ The highest counting rate waas obtained for the fuel rods in position in a water bath due to the reduced shielding because of the displaced water and to the additional fast neutrons of fission reactions in the fuel rodds. The addition of boron decreased the counting raate, but not appreciably. The decrease is due to primarily to the reduced number of thermal neutrons available for fission reactions in the fuel rods. Experiments show that the reduction in shielding due to the displaced water and the fission neutron production in the rods together cause only a 10% increase in the total counting rate. Also, since there is a negligibly small difference between count rates with pure waater and with borated water, the experiments indicaate that an insignificant number of thermal neutrons were able to penetrate the lead and cadmium shields. Accordingly, the apparatus is indeed sensitive to only the fast neutrons. All four experiments demonstrate that the counting rate drops rather sharply as the neutron source location moves farther into the assembly. Thus, in a practical application, the technique would be most sensitive to the burnup in the first few outside layers of rods. If there were any differences in burnup across the cross-sectional area of an assembly, it would be likely that the interior rods would have a higher burnup. In that sense, the application of the proposed method would provide conservative estimates of burnup. The fact that excellent counting rates were obtained using a relatively weak .sup.252 Cf source suggests that sizable counting rates would be obtained in a practical application. EXAMPLE 2 This example illustrates how the burnup of a fuel assembly of unknown burnup would be calculated for a particular reactor design and initial uranium enrichment, given the curve shown in FIG. 1 and a reading of 161.9 counts per second when an assembly having a known burnup of 600 effective full power days was measured in an apparatus as illustrated in FIG. 2. Since the corresponding emission rate for the assembly of known burnup is 9.92.times.10.sup.7 neutrons per second (from FIG. 1), the emission to-reading conversion factor is 9.92.times.10.sup.7 .div.161.9=6.13.times.10.sup.5 emitted neutrons per neutron count. If the counting rate from an assembly of unknown burnup were then measured to be 812.4 counts per second, its emission rate would be obtained through multiplication by the conversion factor yielding 812.4.times.6.13.times.10.sup.5 =4.98.times.10.sup.8 neutrons emitted per second. From the graph in FIG. 1, the unknown burnup corresponding to this emission rate is then determined to be 900 effective full power days. |
045267448 | description | DESCRIPTION OF PREFERRED EMBODIMENTS In FIGS. 1-3, the numeral 1 designates a fuel channel device for a fuel assembly intended for a boiling water reactor. The vertical center line of the fuel assembly is designated 1' in FIG. 1. The fuel channel device 1 surrounds sixty-four fuel rods 2 and 2', which are evenly distributed among four partial bundles, each of which is surrounded by a partial fuel channel 3 as shown in FIGS. 3 and 4. An upper portion of the fuel channel device 1, having a length L and being above the location of the fuel rods 2, as shown in FIGS. 1, 3, 6, and 12, has a projection in an imaginary horizontal plane extending through the mid-portion of the fuel rods, forming a square with rounded corners, the square surrounding the partial bundles in such a way that each of the four quadrants of the square surrounds one partial bundle. The partial fuel channels 3 have been formed by dividing the fuel channel of the fuel assembly into four parts along a vertical distance of approximately the same length as the fuel rods, by means of a hollow stiffening device of cruciform cross-section. The stiffening device has a vertical center line 4' and four stiffening wings 4. Each wing 4 comprises a vertical passageway or flow path 5' for relatively cold moderator water. The stiffening device is composed of four elongated, vertical sheet metal elements or channel walls 6, 6', 6", 6"' of L-shaped cross-section extending along a predominant part of the vertical extension of the fuel rods below the upper portion of length L. In this specification, "predominant" is used in its commonly accepted sense to indicate prevalence over all others in magnitude. Each stiffening wing 4 comprises two parallel sheet metal portions arranged in mutually spaced relationship to each other, each metal portion belonging to a corresponding L-shaped sheet metal element. In each stiffening wing, as shown in FIGS. 1 and 3, a plurality of mutually confronting nozzles 7, made in the sheet metal elements, are welded together by a welding seam 7' so as to form a plurality of hydraulic connections between adjacent partial fuel channels 3. However, the channel walls 6, 6', 6", 6'" prevent horizontal communication between passageways 5' and the interior of each partial fuel channel 3. The fuel channel device 1 is made of Zircaloy.RTM. and is welded to a Zircaloy.RTM. sleeve 15 having a lower portion made with square cross-section. The sleeve 15 is screwed to a lower part base 16, which at its lowermost part has a central, downwardly directed inlet opening for the water flow supplied to the fuel assembly. A water tube 17 is fixed in the middle of the lower part 16 by means of a plurality of radially directed arms 18, which are welded to the lower part 16 and the water tube 17. Each partial fuel channels 3 comprises a partial bundle of sixteen fuel rods, which are supported by a corresponding bottom tie plate or grid 19 as shown in FIGS. 1 and 4. The four bottom grids rest on the upper end of the water tube 17 and on a plurality of axial projections 20, provided in the upper end portion of the lower part 16. Each partial bundle is provided with a plurality of spacer devices 21 arranged vertically one after the other, only one being shown in FIG. 1, and with a partial top tie plate or grid 22 as shown in FIGS. 1-3. The lower ends of the elongated L-shaped sheet metal elements 6, 6', 6", 6'" are arranged in four horizontal slots 23, formed in the upper end of the water tube 17 as shown in FIGS. 1 and 4, whereby the interior of the stiffening device is hydraulically connected to the water tube 17. Each stiffening wing 4 is provided with a tight bottom 24, the radially inner edge of which forms part of the circumference of a central inlet opening 25, intended for a flow of moderator water flowing through the flow paths 5' and 5". Each water flow path 5' communicates with the surrounding interassembly core space via a plurality of nozzles 13 arranged along the length of each stiffening wing 4, as shown in FIGS. 1, 3 and 4; In each partial bundle, two of the sixteen fuel rods are made as tie rods 2', that is, adapted for force transmission. Similarly to the other fuel rods 2, the tie rods 2' are arranged with the axially extending pins of their lower end plugs in corresponding through-holes in the bottom tie plate 19 and with the axially extending pins of their upper end plugs in corresponding, substantially hollow-cylindrical portions of the partial tip tie plate 22. In the tie rods 2' the upper end pins 25 are passed through the partial top grid 22 and provided with nuts 25', and the lower end pins 26 are passed through the bottom grid 19 and provided with nuts 26', as shown in FIG. 1. The other fuel rods 2, however, are arranged in the bottom grid with freedom of movement in a direction vertically upward. In this arrangement, the tie rods 2' can transmit tensile force from above to the bottom grids. Each partial top grid 22 is formed with sixteen fuel rod positions arranged in a square lattice and comprises sixteen substantially hollow-cylindrical portions 27 as shown in FIG. 3 and a plurality of connecting portions, one of which constitutes a middle portion and is designated 28', the others being designated 28. Just as the hollow-cylindrical portions, the middle portions 28 and 28' constitute integral parts of the partial top grid. The connecting portions 28 and 28' connect the hollow-cylindrical portions to each other and, together with external surfaces thereof, define a plurality of passageways or openings 29 for reactor coolant formed in the partial top grid 22. The central connecting portion 28' is directly connected to the four hollow-cylindrical portions 27 located nearest the mid-point of the partial top grid. The axes of two of these four portions 27 lie in a vertical plane passing through the mid-point of the partial top grid, but not through the center line of the fuel assembly. Each of these two hollow-cylindrical portions surrounds an end pin 25 in a corresponding tie rod 2' of the partial assembly as shown in FIGS. 1 and 2. In each partial top grid the central connecting portion 28 is provided at its mid-point with a threaded hole 30, and the four partial top grids are attached to a common top tie plate or lifting plate 31 arranged within the upper portion of lenght L, as shown in FIGS. 1, 2, 2A, 2B and 6 by means of four screw bolts 32, each of which is passed through a vertical hole 32' in the top tie plate 31 and screwed into a corresponding hole 30 in such a way that upwardly-facing surfaces of the partial top grids 22 are passed against downwardly-facing surfaces of the top tie plate 31. Thus, the common tie plate 31 can transmit tensile force from above to the four partial top grids 22 which, in turn, can transmit tensile force via tie rods 2' to the bottom grids 19, thereby facilitating simultaneous removal of all four partial bundles in one lifting operation. Each head of the screw bolts 32 makes contact with a corresponding upwardlyfacing surface portion 36 of the top tie plate 31. The top tie plate 31 is formed with four corner portions 40, which together with four intermediate horizontal, rod-shaped portions 41 form a substantially square frame which fits, with no mentionable play, within the previously mentioned upper portion of the fuel channel device 1. The corner portions 40, the rod-shaped portions 41 and a spider 42 constitute integral parts of the top tie plate 31. Two of the corner portions 40 are each provided with a hole 43 for the purpose of facilitating the passage of reactor coolant, whereas the other two support a lifting loop 33, which at each end is attached to the top tie plate by means of two through-going horizontal pins 34, which are passed through corresponding holes 34' in a lug 35, provided in the top tie plate, and fixed by means of welding. Alternatively, the lifting loop 33 may be constructed as an integral part of the top tie plate 31. The top tie plate 31 is provide in one of the corners with two, substantially vertically directed leaf springs 37 shown in FIGS. 1, 2 and 2A, which make contact with the inner side of a lifting lug 38 welded to the upper edge of the fuel channel device. The lifting lug is dimensioned, together with a lifting lug of the same kind arranged at the opposite corner, to be loaded with the weight of the entire fuel assembly. Further, the top tie plate is provided at opposite corners with two, substantially vertically directed leaf springs 37', intended to make contact with vertical surfaces in the top tie plate of the reactor core (not illustrated). In each corner the top tie plate 31 has two downwardly-directed projections 39 with vertical rest surfaces, which make contact with corresponding vertical surface portions of the partial top grids 22. The top tie plate 31 supports a distribution channel 44 for sprinkling water, channel 44 running along a predominant part of the circumference of the fuel assembly, as shown in FIG. 2. Alternatively, instead of the partial top grid 22, it is possible to use the partial top grid 22' shown in FIG. 3A, in which one central connecting portion is designated 28'" and the other 28". The connecting portions connect together sixteen hollow-cylindrical portions 27'. The two diagonally extending connecting portions are each positioned immediately below a corresponding arm of the spider 42 of the top tie plate. As is shown in FIG. 1, the top tie plate 31 has on its underside several portions which make contact with hollow-cylindrical portions 27 of partial top grids 22 and are provided with bores or cylindrical recesses 45 which are adapted for receiving corresponding end pins of the fuel rods 2 when these are expanded due to high temperature. The fuel assembly shown in FIGS. 6, 7 and 8 differs from that described above only in that the common top tie plate 46 and the partial top grids 47 deviate from the corresponding details in the fuel assembly described above. The top tie plate 46 has in each quadrant seven drilled holes 45' adapted for receiving fuel rod end pins, and is provided with a lifting loop 48 which constitutes an integral part. Upwardly-facing surfaces of the top tie plate constitute the bottom in a water distribution channel 49. Each partial top grid has a plurality of hollow-cylindrical portions 50 and a central connecting member which is designated 51, the other connecting members between the portions 50 being designated 52. Each member 51 has a centrally disposed threaded hole 53. Four bolts 54 are passed through the top tie plate 46 through corresponding holes 55 and screwed into four corresponding holes 53. Each quadrant of the top tie plate 46 has at least five diagonally directed, elongated portions extending between vertical fuel rod axes. The horizontal projections of these portions mainly cover the corresponding connecting portions 51 and 52 of the partial top grids 47. The fuel assembly comprises in total eight tie rods. In each partial bundle, two of these tie rods are positioned with their axes in a vertical plane through the center line of the partial bundle and the fuel assembly. The embodiment shown in FIGS. 9, 10 and 11 differs from that described above as regards the design of the common top tie plate 56 and the four partial top grids 57. Each partial top grids 57 has sixteen hollow-cylindrical portions corresponding to sixteen fuel rod positions. Each partial bundle comprises two tie rods 2', the top pins of which are designated 25 and are arranged in two hollow-cylindrical portions, designated 58, each provided with a nut 25'. Each partial top grid is attached to the top tie plate 56 by means of two upwardly extended hollow-cylindrical portions 60, which are each provided with a solid threaded end portion 59. Each of the threaded end portions 59 is passed through a hole 59' in the top tie plate 56 and are each provided with a nut 61. The holes 45" have the same purpose as the holes 45 and 45' shown in FIGS. 1 and 7, respectively. In the embodiments of FIGS. 1 to 11, bolts 32, 54 and 59-61 are accessible from above the fuel assembly so that the common top tie plates 31, 46 and 56 can be removed from the fuel channel. As a result, individual partial bundles and their associated bottom grids and top grids can be removed from the fuel channel as separate units. Of course, where the common top tie plates are left in place, all of the bottom grids, fuel rods, top grids and the common top tie plate can be removed as a unit from the fuel channel. The fuel assembly shown in FIGS. 12 and 13 differs from the other fuel assemblies in that its upper end is constructed in a different way. The fuel assembly comprises four partial bundles of fuel rods 2 and 2', each partial bundle comprising two tie rods 2'. The fuel channel system 1 is divided into four partial fuel channels 3 by means of four supporting wings 4 and is provided with two lifting lugs 38 in the same way as is shown in FIG. 1. Each of the four partial bundles is provided with a bottom grid 19. The fuel assembly is constructed with a top tie plate 62 which, in accordance with the above-described common top tie plates, serves the purpose of positioning the four partial bundles. In addition, the top tie plate functions as a common top grid to position of the fuel rods in each partial bundle in relation to each other. This is because common top grid 62 is formed with sixty-four hollow-cylindrical portions 64, corresponding to a fuel rod position each. The top tie plate or grid 62 is provided with a lifting loop 63 which constitutes an integral part. Each tie rod 2' is passed through a bottom grid 19 with its lower end pin 26, which provided with a nut 26', the upper end pin 25 in a corresponding way being passed through the top tie plate or grid 62 and being provided with a nut 25'. Just as the top tie plates described above, the top tie plate or grid 62 is arranged in an upper portion of the fuel channel sysem 1. This portion is not divided into four parts since it is disposed above the supporting wings 4. In the embodiment of FIGS. 12 and 13, nuts 25' are accessible from above the fuel assembly so that the top tie plate 62 can be removed from the fuel channel. Thus, individual partial bundles and their associated bottom grids and tie rods can be removed from the fuel channel as separate units. Of course, where the top tie plate is left in place, all of the bottom grids, fuel rods, tie rods and the top tie plate can be removed as a unit from the fuel channel. The drawings only show fuel assemblies having sixty-four fuel rod positions. The invention also comprises fuel assemblies having a greater or smaller number of fuel rod positions, for example a fuel assembly having four partial assemblies and twenty-five fuel rod positions in each partial assembly. |
description | The invention relates to the field of nuclear imaging. More specifically, the present invention relates to a collimating system for use in nuclear imaging, such as for example a collimating system for tomography, a corresponding tomography system and a method of collimating. Single Photon Emission Computed Tomography (SPECT) is a biomedical imaging technique that is often used in nuclear medicine to image functional processes. The gamma camera detects photons that are emitted due to decay of the tracer that was injected in the patient. The camera measures projections at different angles, which can then be used to reconstruct a 3D image of the distribution of the labeled molecules in the patient. An important part of a SPECT scanner is the collimator. The collimator is used to only transmit gamma rays with certain directions. Behind this collimator is a detector that converts the gamma ray in a measurable signal. Two main types of collimators are known, being the parallel-hole collimator and the pinhole collimator. Pinhole collimators are used to select gamma rays from a cone. The projection of a pinhole collimator on a flat detector is a circular or elliptical region. The efficiency of a pinhole collimator is typically very low because the aperture of a pinhole needs to be small in order to have a good resolution. To increase the efficiency of a pinhole collimator, multiple pinholes can be placed on the same collimator. To maximize the number of pinholes, an optimal usage of the detector area is necessary. Typically, a tradeoff has to be made when using pinholes on rectangular detectors. The projections of the different pinholes will either overlap, or some valuable detector area will not be used. Overlap is often undesirable because the detections in the regions of overlap will be more ambiguous. However, a combination of overlapping and non-overlapping data can improve the reconstruction quality. In the case of a full-ring detector, a cylindrical multi-pinhole collimator is typically used. The number of pinholes on the collimator is restricted by the size of the detector, the radius of the collimator, the field-of-view and the amount of overlap allowed on the detector. This restriction can be a problem for data-completeness, e.g. when the restricted amount of pinholes is less than 60. When the field-of-view is small, the detector is very large and/or the radius of the collimator is also large, data-completeness might not be a problem. In order to successfully reconstruct a 3D image, we need projections under different angles. 60 projections are typically used in clinical practice. It is an object of embodiments of the present invention to provide good methods and systems for collimating. It is an advantage of embodiments according to the present invention that the collimator has no rotating parts and does not need to be rotated, as enough collimating apertures can be provided for obtaining data-completeness. It is an advantage of embodiments of the present invention that data completeness can be obtained for tomography, without introducing large problems of overlap. It is an advantage of embodiments of the present invention that overlapping projections can selectively be taken into account and that such a selection can be a dynamic selection, depending on the object to be imaged and the information to be obtained. It thus is an advantage of embodiments according to the present invention that the amount of overlap can be adjusted through different set-ups. It is an advantage of embodiments according to the present invention that a more efficient use can be made of the available detector surface positioned after the collimator, compared to e.g. conventional pinhole systems. It is an advantage of embodiments according to the present invention that the collimator can be made thinner, allowing more collimating apertures to be placed next to each other. It is an advantage of embodiments according to the present invention that overlap between radiation stemming from different non-shut collimating apertures can be controlled more precisely and more efficient usage is made of the available detector area. It is an advantage of the embodiments that one or more problems mentioned in the background can be reduced or solved. It is an advantage of the embodiments of the present invention that the collimating system does not need to rotate. Collimators are made of heavy collimating material, like for example lead, tungsten or alloys of these materials. Rotating such a heavy collimator with a high precision is a technical challenge that can be avoided by embodiments of the present invention. The above objective is accomplished by a method and device according to the present invention. In one aspect, the present invention relates to a collimating system for collimating radiation received under different angles for performing tomography, the collimating system comprising a static collimator comprising a plurality of collimating apertures, shutters for selectively and temporarily shutting at least two of said collimating apertures wherein the shutters have a shutting element for closing the at least two collimating apertures, and at least one collimating element distinct from the shutting element for collimating radiation passing through non-shut collimating apertures in a direction so as to control overlap between radiation stemming from different non-shut collimating apertures. Selectively shutting may comprise or may be individually shutting collimating apertures or groups of collimating apertures. Selectively shutting apertures or groups of collimating apertures may be or may comprise selecting for each aperture or for each group of apertures to shut or not to shut it, and shutting or not shutting the collimating aperture or group of collimating apertures correspondingly. It is an advantage of embodiments according to the present invention that overlap of radiation stemming from different collimating holes can be controlled. It is an advantage of embodiments of the present invention that the amount of overlap may be adjusted through different set-ups or different types of applications. The at least one collimating element may be provided for collimating radiation in axial direction, in transaxial direction or in a combination of both directions. Where in embodiments of the present invention reference is made to collimation in transaxial direction, reference is made to collimation in a plane perpendicular to the axial direction. The collimating elements are distinct from the shutting elements. Where in embodiments of the present invention reference is made to collimating elements that are distinct from the shutting elements, reference is made to collimating elements that are functionally distinct from the shutting elements, i.e. whereby collimation does not occur by exclusively using the shutting elements. The shutting element may have a thickness of at least 0.5 mm over its shutting area for blocking radiation passing through the collimating apertures. Where in embodiments of the present invention reference is made to the shutting area, reference is made to the area that needs to be blocked for preventing radiation passing through the collimating aperture to reach the detector. It is an advantage of embodiments according to the present invention that accurate shutting can be provided. It is an advantage of embodiments according to the present invention that sufficiently absorbing material can be provided for blocking radiation from the collimating hole, so that no erroneous detection is obtained and an appropriate background radiation level can be reached. In some embodiments, the thickness of the shutting element may be at least 0.5 mm or e.g. at least 1 mm or more. The static collimator may be at least partially ring-shaped and the collimating apertures may be positioned on a same collimator ring. Embodiments of the present invention may be especially suitable for ring-shaped multi-aperture collimators, wherein currently often rotating collimators need to be used to avoid or reduce overlap resulting in disturbing interaction of the rotating system. The at least one collimating element may be part of one of the shutters. The at least one collimating element and the shutting element may be fabricated from one block of material, forming one unitary element. In such an embodiment the at least one collimating element and shutting element are operated and controlled simultaneously. Moving shutting elements for closing at least two collimating apertures will then move the associated at least one collimating element for collimating radiation passing through certain non-shut collimating apertures to control overlap, for instance for collimating radiation passing through one or more neighbouring non-shut collimating apertures. Non-static collimating elements, such as for instance simultaneously moving shutting elements and collimating elements, have the advantage that the degree of freedom for designing and positioning the collimating elements may be increased. If the degree of freedom for designing and positioning the collimating elements increases, the precision with which overlap can be controlled may be further increased. The at least one collimating element and the shutting element may form two separate elements. In such an embodiment the at least one collimating element and corresponding shutting element may be operated and controlled simultaneously, meaning that moving shutting elements for closing at least two collimating apertures will move the associated at least one collimating element for collimating radiation passing through certain non-shut collimating apertures to control overlap, for instance for collimating radiation passing through one or more neighbouring non-shut collimating apertures. In such an embodiment the collimating elements and shutting elements may alternatively be operated and controlled independently from one another. The at least one collimating element may be part of one of the shutters such that a shutter having a shutting element for shutting a predetermined collimating aperture comprises at least one collimating element shaped for controlling collimation of radiation passing through another collimating aperture. In some embodiments, the another collimating aperture may be a collimating aperture neighbouring the predetermined collimating aperture. It is an advantage of embodiments according to the present invention that the additional collimating can be easily introduced by adding a collimating element for collimating radiation from a given collimating hole to a shutter for shutting a neighbouring collimating hole. The latter avoids the need for introduction of an additional complete separate and further collimator. The at least one collimating element may comprise a slanted surface of the shutter. The at least one collimating element may be part of an additional collimator configured with respect to the static collimator for controlling overlap between radiation stemming from different non-shut collimating apertures. It is an advantage of embodiments according to the present invention that the static collimator can also be used by a further collimating element, i.e. that it allows for configuring with other optional elements. The additional collimator may be a collimator ring providing collimation in a direction determining overlap between radiation stemming from different non-shut collimating holes. The at least one collimating element may comprise radiation transparent windows in the additional collimator made of absorbing material. The at last one collimating element may be a non-static element, meaning that it is movable with respect to the at least one collimating aperture. The at least one collimating element and the shutting element may be operated and controlled simultaneously or independently from one another. The at least one collimating element may be a movable element with respect to the collimating apertures. The movement may be for example by a pneumatic, hydraulic or electric actuator, embodiments of the present invention not being limited thereto. For blocking, shutters may for example be moved in front of a collimating aperture or away from the collimating aperture, e.g. by shifting, translating, rotating, . . . . The movement may be performed for example by a pneumatic, hydraulic or electric actuator embodiments of the present invention not being limited thereto. At least one of the shutters or shutting elements, a subset of the shutters or shutting elements, or each of the shutters or shutting elements may be individually controllable. Individually controllable shutters or shutting elements may allow for each aperture or for each group of apertures to shut or not to shut it. Individually controllable shutters or shutting elements or subsets of shutters or shutting elements may allow shutting at least two of said collimating apertures independently from one another. The at least one collimating element, a subset of the collimating elements, or each of the collimating elements may be individually controllable. The collimating system may comprise a controller programmed for controlling the shutters for opening the collimating apertures in a predetermined manner. It is an advantage of embodiments according to the present invention that shutting of collimating holes can be performed in an automated way, without the need for human interaction, e.g. without the need for human interaction during measurements. The controller may be programmed for alternatingly and temporarily opening the shutting elements for collimating apertures, e.g. non-neighbouring collimating apertures. It is an advantage of embodiments according to the present invention that separate shutting control of collimating holes can be obtained, allowing simultaneous use of apertures that are sufficiently far distantiated from each other and collimated to avoid or limit overlap of the radiation to be detected. The controller may be programmed for individually controlling a subset or each of the shutters and or shutting elements allowing for closing at any time any of the plurality of collimating apertures. The controller may be programmed for individually controlling a subset or each of the at least one collimating element. The controller may be programmed for alternatingly and temporarily opening shutting elements for a subset of collimating apertures such that over a predetermined time period, all collimating apertures have been un-shut. It is an advantage of embodiments according to the present invention that embodiments of the present invention for example allow emulating a rotational collimator using a static collimator. The latter allows for example to replace a rotational collimator with a limited number of apertures, whereby avoiding rotation of a collimator provides detecting data in a less disturbed measurement environment. For example, the electromagnetic influences of a motor for rotating the collimator can be avoided. The static collimator may be at least partially ring-shaped. Embodiments of the present invention may be especially suitable for ring-shaped multi-aperture collimators, wherein currently often rotating collimators need to be used to avoid or reduce overlap resulting in disturbing interaction of the rotating system. The number of apertures may be at least 15, e.g. at least 24. The number of apertures may be at least 30, e.g. at least 45, e.g. at least 60. It is an advantage of embodiments according to the present invention that the number of collimating apertures is not strongly restricted by the field-of-view of the system, as the collimating apertures can be shut alternatingly and therefore do not need to be used simultaneously. The static collimator may be ring shaped and may be for use with a ring shaped detector and the number of apertures may fulfill the following equation number of apertures > π acos ( R FOV R d ) - a cos ( R FOV R c ) wherein Rd is the radius of the detector, Rc is the radius of the static collimator and RFOV is the transaxional field-of-view The present invention also relates to an imaging system comprising a detector, a collimating system as described above, and a correlator for correlating signals detected using the detector with collimated apertures un-shut at the moment of detection. The imaging system may be a biomedical imaging system. The imaging system may be a system for performing tomography. The imaging system may be a single photon emission computed tomography system. The present invention also relates to a method for imaging an object, the method comprising selectively and temporarily shutting at least two of a plurality of collimating apertures of a static collimator using shutters having a shutting element for closing the collimating apertures thereby alternatingly and temporarily opening shutting elements for collimating apertures or subsets of collimating apertures, detecting the radiation transmitted through the un-shut collimating apertures, correlating the detected radiation with the collimator apertures un-shut during the detecting, and deriving therefrom information of the object of interest. Alternatingly and temporarily opening shutting elements for collimating apertures may be alternatingly and temporarily opening shutting elements for non-neighbouring collimating apertures. The alternatingly and temporarily opening shutter elements may be such that a rotation of the static collimator is emulated. Separately and temporarily shutting shutters may be separately and temporarily shutting shutters having a shutter element, the shutting element having a thickness of at least 0.5 mm over its shutting area for blocking radiation stemming from an object of interest passing through the collimating apertures. The method may comprise using collimating elements, optionally collimating elements that are distinct from the shutting elements, for collimating radiation passing through non-shut collimating apertures in a direction so as to control overlap between radiation stemming from different non-shut collimating apertures. In one aspect, the present invention relates to a collimating system for collimating radiation received under different angles for performing tomography, the collimating system comprising a static collimator comprising a plurality of collimating apertures, shutters for separately and temporarily shutting at least two of said collimating apertures, wherein the shutters having a shutting element for closing the at least two collimating apertures, and a controller for alternatingly and temporarily opening shutting elements for non-neighbouring collimating apertures. The collimating system may comprise a correlator for correlating detected radiation with the collimator apertures un-shut during the detecting, and further optionally for deriving therefrom information of the object of interest. The present invention also relates to a controller for controlling a collimating system comprising a plurality of collimating apertures and shutter elements according to a method as described above. The present invention further relates to a computer program product for, if implemented on a processing unit, performing a method as described above. The invention also relates to a data carrier storing the computer program product and the transmission of the computer program product over a network. In one aspect, the present invention also relates to a collimating system for collimating radiation received under different angles for performing tomography, the collimating system comprising, a static collimator comprising a plurality of collimating apertures, shutters for separately and temporarily shutting at least two of said collimating pinholes, wherein the shutters having a shutting element for closing said at least two collimating pinholes, the shutting element having a thickness of at least 0.5 mm over its shutting area for blocking radiation passing through the collimating pinholes. Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Any reference signs in the claims shall not be construed as limiting the scope. In the different drawings, the same reference signs refer to the same or analogous elements. The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention. Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein. Moreover, the terms top, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein. It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B. Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments. Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination. In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description. Where in embodiments of the present invention reference is made to an open shutter or an open or un-shut collimating aperture, reference is made to a state of the shutter, e.g. associated with the collimating aperture, such that at least some radiation passing the collimating aperture is able to reach the detector. The shutter may for example be shifted, rotated or more generally moved away from the aperture so that it is not blocking radiation. Where in embodiments of the present invention reference is made to a closed shutter or to a closed or shut collimating aperture, reference is made to a state of the shutter, e.g. associated with the collimating aperture, such that the majority and preferably substantially all radiation passing the collimating aperture is blocked by the shutter so that it does not reach the detector. Where in embodiments according to the present invention reference is made to radiation, reference may be made to electromagnetic radiation comprising amongst others gamma radiation, embodiments of the present invention not being limited thereto. For example a collimator according to embodiments of the present invention also can collimate electro-magnetic waves such as for example infrared radiation, visible radiation, UV radiation, X-rays. In a first aspect, the present invention relates to a collimating system for collimating radiation received under different angles for performing tomography. Embodiments of the present invention may be especially suitable for performing single photon emission computed tomography, although embodiments of the present invention are not limited thereto. The collimating system according to embodiments of the present invention comprises a static collimator having a plurality of collimating apertures. Such apertures may be pinholes, but also may be alternative apertures such as slats, slits, particularly shaped pinholes, etc. The collimating system according to embodiments of the present invention also comprises shutters for selectively and temporarily shutting at least two of the collimating apertures. In embodiments of the present invention, the number of collimating apertures may typically be significantly larger than would be allowed for avoiding overlap during simultaneous use. The shutters according to embodiments of the present invention have a shutting element for closing the collimating aperture. Such a shutting element thus typically allows blocking radiation passing through a collimating aperture. According to embodiments of the present invention, the collimating system also comprises at least one collimating element for collimating radiation passing through non-shut collimating apertures in a direction so as to control overlap between radiation stemming from different non-shut collimating apertures. By way of illustration, embodiments of the present invention not being limited thereto, further features and advantages will be described with reference to an exemplary system as shown in FIG. 1 to FIG. 6, comprising standard and optional features. FIG. 1 and FIG. 2 illustrate a collimating system 100 comprising a static collimator 110. The static collimator 110 is adapted for collimating radiation from different angles, without the need for rotating during operation. For example, with reference to FIG. 2, it can be seen that by alternatingly shutting different apertures 112, radiation from different apertures is allowed to pass and optionally be further collimated by collimating elements 140. It also can be seen that the collimating element, placed on the shutter 120 in FIG. 2 can be placed further away from the collimator. It will not block radiation from the middle aperture when that one is open because the collimating will then also be moved away, together with the shutter. The static collimator 110 may at least be partially ring-shaped and the collimating apertures may be positioned on the same collimator ring. The static collimator alternatively also may have a different shape, such as a sphere, a polyhedron, a cube, . . . . The static collimator 110 comprises a plurality of collimating apertures 112. The collimating apertures may for example be pinholes. Alternatively, the collimating apertures may be slats, slits, particularly shaped pinholes, etc. The number of collimating apertures that can be introduced therefore can be at least 16, at least 32, at least 64, at least 128 and may be at the upper side limited by the physical place required by the collimating apertures on the collimator. In embodiments of the present invention, the number of collimating apertures may typically be significantly larger than would be allowed for avoiding overlap during simultaneous use. Shutters may be provided on one, more or each of the collimating apertures. In other words it is an advantage of embodiments according to the present invention that the number of collimating apertures can be so large that neighbouring pinholes have overlapping projections, as the use of shutters allows closing the collimating apertures so that, if not desired, overlap on the detector can be avoided and the detections can be performed separately, e.g. shifted in time. In a ring shaped embodiment for example, i.e. when the collimating system is ring shaped and with the detector to be used also ring shaped, the number of collimating elements which would be an upper limit in an unshut prior art system for avoiding overlap and which may be larger due to the shutting possibility in embodiments of the present invention, can be calculated as following: Given a detector radius (Rd), a collimator radius (Rc), a transaxional FOV Radius (RFOV) (indicated in FIG. 7—left part, by way of illustration) and given the fact that no overlap is allowed, then the number of apertures on one ring on the collimator is normally limited to x = π acos ( R FOV R d ) - a cos ( R FOV R c ) wherein Rd is the radius of the detector, Rc is the radius of the static collimator (110) and RFOV is the transaxional field-of-view radius. When the collimating shutters described in this invention are used, the number of apertures that can be placed on one ring on the collimator is not limited to this formula any more. Similarly, also the maximum height of a further static collimating element 140 for collimating with respect to the collimator and its collimating apertures in a prior art system can be calculated: Given a detector radius (Rd), a collimator radius (Rc), a transaxional FOV Radius (RFOV), a collimator ring with x apertures and given the fact that no overlap is allowed, the height at which a collimating element can normally be placed is expressed as h = R c · tan ( π x ) tan ( a sin ( R FOV R c ) - tan ( π x ) ) with h the height of the collimating element above the collimator (towards the detector), as also indicated in FIG. 1 and FIG. 2. More particularly, in FIG. 1, it can be seen that the maximum distance at which a collimating element can be placed when it is static is at a distance h from the static collimator 110. Placing the collimating element 140 further away would block radiation from the middle apertures when it would be open (as the collimating elements in this configuration are static and do not shift together with the shutters). Alternatively, the collimating elements 140 in such a configuration could also be made moveable. With the shutting design according to embodiments of the present invention, this height can be increased further, while still allowing to obtain no overlap. Collimating further away from the aperture gives a sharper projection. The static collimator 110 typically is made of a material that is substantially blocking the radiation, except at areas where collimating apertures are present. Such material may be particularly selected as function of the radiation used in the application. Typical materials that may be used are for example tungsten, lead, platinum or gold or alloys of these materials. The static collimator 110 according to embodiments of the present invention is such that no rotation of the collimator itself is required, while providing sufficient collimating apertures so that data completeness is obtained. According to embodiments of the present invention, at least two shutters 120 are present comprising a shutting element 122 for separately and temporarily shutting at least two of the collimating apertures. The shutters according to embodiments of the present invention have a shutting element for closing one of the at least two of the collimating apertures. The shutter element may be any type of shutter. The shutter element advantageously has a thickness such that it can block radiation passing through the collimating hole. The shutter element therefore advantageously is made of a material having sufficient stopping potential for the radiation used, e.g. for gamma-radiation. The material forming the shutting element may advantageously be a high-density material. The thickness of the shutter elements may be at least 0.5 mm, e.g. at least 1 mm over the full area where they shut of the radiation. The thickness may be determined as function of the radiation that will be used for e.g. a SPECT system and may be such that less than 1%, advantageously less than 0.1%, still more advantageously less than 0.01% radiation is transmitted. The required thickness may be determined based on the required attenuation factor to be obtained. The attenuation factor is given by ρ=e−μ(E)l with 1 the thickness of the shutting element and μ(E) the attenuation coefficient of the shutter material at a certain energy E. E.g. using an isotope Tc-99m with an energy 140 keV, a thickness of tungsten shutting elements of 5 mm allows blocking at least 81.99% of the radiation. Using e.g. 1-125 with an energy of 30 keV, a thickness of a lead shutting elements of 0.1 mm allows blocking at least 96.24%. The shutter element 122 may in some embodiments be made of blocking material, such as for example tungsten, lead, platinum or gold or alloys of these materials. For blocking, shutters may for example be moved in front of a collimating aperture or away from the collimating aperture, e.g. by shifting, translating, rotating, . . . . The movement may be performed for example by a pneumatic, hydraulic or electric actuator embodiments of the present invention not being limited thereto. The shutters may be controlled individually or may be controlled in group. In one embodiment, as shown in FIG. 3, the shutters may be provided as a shuttering ring. The system shown in FIG. 3 and in more detail in FIG. 16 illustrates a static collimator 110 with 21 collimating apertures and a shuttering ring 180 comprising 7 shutters, being windows in the shuttering ring. Rotation of the shuttering ring 180 results in shutting 14 collimating apertures and simultaneously selecting 7 collimating apertures. The shuttering ring 180 allows separately shutting some collimating apertures while opening shutters for other collimating apertures. The shuttering ring 180 thus allows separately shutting some apertures while opening other apertures. According to the embodiment shown in FIG. 3 and FIG. 16, the shutters thus are implemented as a rotating ring of windows, closing or opening certain apertures. The collimating system further comprises collimating elements 140 for collimating radiation passing through non-shut collimating apertures so as to control overlap between radiation stemming from different non-shut collimating apertures. In another embodiment, as shown in FIG. 4, the shuttering ring 180 comprises collimating elements 190 for collimating radiation passing through non-shut collimating apertures so as to control overlap between radiation stemming from different non-shut collimating apertures. In this embodiment the collimating elements 190 may have an additional shutting function as using only the shutter ring 180 would not be sufficient in the example shown because the rays of the middle apertures shown in FIG. 4 would also pass through the window of the neighbouring apertures. FIG. 3 and FIG. 4 thus illustrate shutters that may be controlled simultaneously or in group. In another embodiment, individual control of the different apertures is provided by individually controlling the shutters 120. Some or all of the collimating elements 190 and the shutting elements 180 may be operated independently from each other or simultaneously. In other words, the shutters may be adapted for shutting at least two of said collimating apertures independently. An example thereof is shown in FIG. 5, whereby the individually controllable shutters 120 are illustrated. According to embodiments of the present invention, the collimating system also comprises at least one collimating element 140 for collimating radiation passing through non-shut collimating apertures 112 in a direction so as to control overlap between radiation stemming from different non-shut collimating apertures 112. The at least one collimating element is distinct from the shutting element, meaning that the collimation is not done exclusively by the shutting element. The collimating elements may take any possible shape. The collimating elements may have a slanted edge, rounded edge, may be pyramidal shaped, knive shaped, spherically shaped, etc. They advantageously may be made of high-density material. The collimating elements 140 have the function of collimating radiation, e.g. collimating gamma radiation. According to some embodiments of the present invention, the collimating elements may be introduced as separate collimating elements, not being part of the shutter. Alternatively, the collimating elements may be introduced as part of the shutters. In one embodiment, the at least one collimating element 140 may be part of the shutter 120, such that the shutter 120 having a shutting element 122 for shutting a predetermined collimating aperture 112, comprises the at least one collimating element 140 shaped for controlling collimation of radiation passing through a collimating aperture 112 neighbouring the predetermined collimating aperture 112. In embodiments of the present invention, at least one collimating element 140 may be present, a collimating element 140 may be present for some of the collimating apertures 112 or one or more collimating elements 140 may be present for each of the collimating apertures 112. By way of illustration, FIG. 5 and also FIG. 2 illustrate part of a collimating system comprising a shutter with a shutter element and a collimating element. In the particular example shown in FIG. 2, the collimating element is placed on top of the shutter. It acts as a knife, separating the circular projections. The collimating shutters in the present example are used in such a way that no two neighbouring apertures are open simultaneously, allowing separation through the collimating element of the projections obtained. In contrast or in addition to distinct collimating elements being present in the shutter, in some embodiments, the shutters also may perform an additional collimating function by partially opening the shutter elements. In other words, the shutting elements also may perform an additional collimating function. It is an advantage of the embodiments of the present invention that the blurry edge of the projections is very limited because the cut-off can happen at a relatively large distance from the pinholes. The occurrence of the blurry edge can be best explained using FIG. 6, illustrating one example wherein no further collimation is present (A), one example where the further collimation is performed close to or at the static collimator (B) and one example where the further collimation is performed at a distance from the static collimator. From FIG. 6 it can be seen that it is advantageous to have the additional collimation by the collimating elements as far as possible away from the static collimator 110 as the blurry projection then is smallest. In the different drawings, the blurry projection is indicated by reference numeral 610, whereas the sharp projection is given by reference numeral 620. The collimator thickness can then be very low. This is an advantage because of the high cost and weight of collimator material. When overlap is used, a low collimator thickness is also an advantage because the pinholes might otherwise start to intersect, which cannot be allowed for a correct functioning of the collimator. The advantage of using shutters having a collimating element for collimating can for example be understood from the following. The projection of a pinhole is a circle or an ellipse and typically a tradeoff is to be made between allowing overlap of radiation from different apertures and not using some valuable detector area. Rectangular projections would solve this problem, but a number of solutions providing such rectangular projections induces further problems: the use of slats for predetermined collimating apertures of the collimator for separating the different projections can block projections from neighbouring collimating apertures. A similar disadvantage can be obtained when using collimating windows in combination with the collimator. As indicated, a rotating collimating wheel with collimating windows may be used, but has the disadvantage that there is the technical burden of rotating the rather heavy collimating wheel. Another way to achieve rectangular projections is to use loftholes instead of pinholes. Loftholes are collimator holes that have a volume that differs from a conical shape. By adapting the shape of the collimator hole, the projection shape can be adapted. Lofthole projections, however, have a blurry edge. To reduce the edge, one can increase the collimator thickness or decrease the aperture size. Decreasing the aperture size also lowers the sensitivity of the system. Increasing the collimator thickness will increase the weight and the price of the collimator, since the collimator is typically made of heavy and expensive materials. In accordance with at least some embodiments of the present invention, introducing collimating elements on one or more shutters results in a good separation of the projections. A collimating element mounted on a closed shutter serves as a cut-off system for both its neighboring pinholes. When the shutter is opened, the two neighboring shutters are closed and they serve as a cut-off system for the pinhole that is open. Introduction of the collimating element on the shutter therefore may overcome the problem of closing neighbouring collimating apertures while still having the advantage that the detector area can be more efficiently used due to the rectangular projections. According to embodiments of the present invention, the collimating system 100 furthermore advantageously may comprise a controller 300, as shown in FIG. 2. Such a controller may be programmed for controlling the shutters for opening the collimating apertures in a predetermined manner Such a controller may be hardware or software based. The controller may be programmed so that shutting may be performed in an automatic and/or automated way, i.e. optionally without the need for human interaction. It is to be noticed that in alternative embodiments, control of the shutters may be performed manually or by human intervention. The controller 300 may be programmed for alternatingly and temporarily opening the shutting elements for non-neighbouring collimating apertures 112. By controlling the shutting of collimating holes, simultaneous use of apertures that are sufficiently far distantiated from each other and collimated is obtained allowing avoiding or limiting overlap of the radiation to be detected. In some embodiments, the controller 300 is programmed for alternatingly and temporarily opening shutting elements 122 for a subset of collimating apertures 112 such that over a predetermined time period, all collimating apertures 112 have been temporarily un-shut. In one example, a virtual rotation of the collimator can be emulated by accurately shutting the collimating apertures. It is known that in order to be able to reconstruct the projection data to a 3D image, the imaged object should be recorded from a minimum of angles (typically 60 angles are used in clinical practice). According to prior art, the number of collimator apertures is limited by the amount of overlap allowed. For a large number of configurations, the number of collimating apertures allowed by the amount of overlap typically is not enough for data-completeness. According to a prior art solution, a limited number of collimating apertures is used and the collimator or the detector is rotated. This movement, which introduces a number of difficulties due to the weight of the components and in view of stability of the measurements, can be overcome in embodiments of the present invention by emulating the rotation. According to embodiments of the present invention, a virtual rotation may be emulated by alternatingly shutting different collimating apertures, avoiding the need for rotating the collimator and thus resulting in more stable and accurate measurements. For example, no disturbing effects of a motor required for rotating the collimator are present. In case of small field-of-view applications, such a shutting collimating technique can allow good imaging, even without the need for further collimating elements. For larger field-of-view shutters with collimating elements according to at least some embodiments of the present invention provide a good solution for accurate measurements. In accordance with embodiments of the present techniques, it thus is possible to use a succession of shutter configurations to register the necessary projections under different angles without needing rotation and without affecting the amount of overlap. In other words, by opening the shutters in a predetermined manner, emulation of a virtual rotation of a collimator ring with limited number of collimating apertures can be obtained, allowing for example replacing a rotational collimator with limited number of apertures and thus avoiding rotation of a collimator resulting in a less disturbed measurement environment. In accordance with embodiments of the present invention, the system may be adapted for adjusting the amount of overlap on the detector, by controlling the shutters or in other words by controlling which apertures are opened. In other words, the overlap can be used as a parameter. The overlap on the detector of radiation stemming from different collimating apertures may be chosen to be zero or non existing, thus allowing to make sure for each detected photon through which aperture it was directed, or it may be chosen to have some overlap, of which the amount can be chosen, to optimize the amount of radiation captured. It is an advantage of the embodiments of the present techniques that the amount of overlap can be adjusted. The shutters are configurable, so one can first do a scan without overlap and then do another scan with overlap. This can improve the reconstructed image quality. By way of illustration, an exemplary multi-pinhole collimator is shown in FIG. 7. In the left part of the figure, the shutters are configured such that there is no overlap. In the right part of the figure, another shutter configuration is used. More shutters are opened and there is a small amount of overlap. In some embodiments, the control of the shutters may be performed by the controller or in other words, the controller can be programmed so that a predetermined amount of overlap is obtained, optionally variable over time. Whereas in the present aspect the collimating system is described as being characterized by the shutters and the at least one collimating element, it is to be understood that the present invention in some embodiments alternatively also relates to a collimating system as described above, wherein no additional collimating element is present, but which is characterized by the presence of shutters for separately and temporarily shutting collimating apertures. Optionally also a controller for alternatingly and temporarily opening shutting elements for non-neighbouring collimating apertures may be present. Such a controller then can also be further characterised in that through control of the shutters in a predetermined manner, it allows for emulating a virtual rotation of the collimating system. In one aspect, the present invention also relates to an imaging system for tomography using a collimating system as described above. Such an imaging system, which may for example be a SPECT imaging system, although embodiments of the present invention are not limited thereto, comprises a collimating systems as described in the first aspect or in an embodiment thereof, a detector element, and a correlator or correlating means for correlating, at different moments in time, signals detected using the detector with a set of collimated apertures un-shut at the moment of detection. The system may be a bio-imaging system. By way of illustration, embodiments of the present invention not being limited thereto, an example of an imaging system is discussed with reference to FIG. 8 to FIG. 10, indicating standard and optional features. FIG. 8 is a schematic illustration of an exemplary imaging system 400, in the present example being a SPECT system, which includes a collimator assembly, also referred to as collimating system 100, and a detector 410 assembly. The detector 410 in the present example is a full ring gamma detector, radiated using a cylindrical collimator 110 comprising a plurality of pinholes 112. The radius of the collimator 110 will typically be as small as possible because the sensitivity of a pinhole 112 decreases when the distance to the imaged object increases. Also, the geometric resolution of a pinhole collimator increases when the distance to the imaged object increases. Therefor, the radius of the collimator will typically be fixed and as small as possible. As also indicated in the first aspect, according to prior art, the number of pinholes is limited by the amount of overlap allowed on the detector. FIG. 9 is an illustration of a prior art pinhole-configuration without overlap. If the radius of the collimator and the detector are not changed and more pinholes are added to the cylinder, the projections will start to overlap, as shown in FIG. 10. Overlap is often undesirable because the detections in the regions of overlap will be more ambiguous. However, a combination of overlapping and non-overlapping data can improve the reconstruction quality. According to prior art, the amount of overlap is a parameter that needs to be fixed when the collimator is designed. Nevertheless, as indicated for the first aspect, according to embodiments of the present invention, overlap can be used as a parameter and may be variable, e.g. even during imaging for the reconstruction of one and the same object. Further features and advantages of embodiments of the present invention may correspond with standard and optional features as described in the first aspect. In a further aspect, the present invention relates to a method for imaging an object in a tomography system. The method may be especially suitable for performing single photon emission computed tomography, although embodiments are not limited thereto. The method may advantageously be performed using a collimating system as described in the first aspect or an imaging system as described in the second aspect, although embodiments of the present invention are not limited thereto. The method according to embodiments of the present invention comprises selectively and temporarily shutting at least two of a plurality of collimating apertures of a static collimator, e.g. using shutters having a shutting element for closing the collimating apertures, thereby alternatingly and temporarily opening shutters for non-neighbouring collimating apertures. The method also comprises detecting the radiation transmitted through the un-shut collimating apertures. The method further comprises correlating the detected radiation with the collimator apertures un-shut during the detecting and deriving therefrom information of the object of interest. Correlating the detected radiation with the collimator apertures un-shut during the detection typically allows for more easily and in some cases unambiguously assigning certain detections to certain collimator apertures, i.e. to certain projection angles. Deriving information of the object typically may comprise reconstructing the image based on the projections obtained. Embodiments according to the present aspect may allow for emulating a virtual rotation of the collimating system used, for example by alternatingly opening one or a group of distanced, e.g. equally distanced, collimating apertures. The method thereby may be adapted for not simultaneously opening neighbouring collimating apertures. According to some embodiments of the present invention the shutting elements also may be controlled for actively collimating radiation passing through non-shut collimating apertures. As indicated above, the methods may be computer-implemented methods for performing a method for imaging or a method for designing a collimator system. Such a computer-implemented method may be implemented on a processing system that includes at least one programmable processor coupled to a memory subsystem that includes at least one form of memory, e.g., RAM, ROM, and so forth. It is to be noted that the processor or processors may be a general purpose, or a special purpose processor, and may be for inclusion in a device, e.g., a chip that has other components that perform other functions. Thus, one or more aspects of embodiments of the present invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The processor may be adapted for performing a method for designing a collimating system or for imaging an object in tomography or may comprise instructions for performing such a method. The processing system may include a storage subsystem that has at least one disk drive and/or CD-ROM drive and/or DVD drive. In some implementations, a display system, a keyboard, and a pointing device may be included as part of a user interface subsystem to provide for a user to manually input information. Ports for inputting and outputting data also may be included. More elements such as network connections, interfaces to various devices, and so forth, may be included. The various elements of the processing system may be coupled in various ways, including via a bus subsystem. The memory of the memory subsystem may at some time hold part or all of a set of instructions that when executed on the processing system implement the steps of the method embodiments described above. While a processing system as such is prior art, a system that includes the instructions to implement aspects of the methods as described above is not prior art. The present invention also includes a computer program product that provides the functionality of any of the methods according to the present invention when executed on a computing device. Such computer program product can be tangibly embodied in a carrier medium carrying machine-readable code for execution by a programmable processor. The present invention thus relates to a carrier medium carrying a computer program product that, when executed on computing means, provides instructions for executing designing a collimator according to any of the methods as described above. The term “carrier medium” refers to any medium that participates in providing instructions to a processor for execution. Such a medium may take many forms, including but not limited to, non-volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks, such as a storage device that is part of mass storage. Common forms of computer readable media include, a CD-ROM, a DVD, a flexible disk or floppy disk, a tape, a memory chip or cartridge or any other medium from which a computer can read. Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to a processor for execution. The computer program product can also be transmitted via a carrier wave in a network, such as a LAN, a WAN or the Internet. Transmission media can take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications. Transmission media include coaxial cables, copper wire and fibre optics, including the wires that comprise a bus within a computer. By way of illustration, embodiments of the present invention not being limited thereto, an example is given of the design of a static full-ring multi-pinhole collimator for brain SPECT. Brain SPECT is in clinical practice mostly performed with a dual head SPECT scanner with fan beam or parallel hole collimators. The resolution of such a system is typically about 7-8 mm, which is rather poor to image the complex structures of the human brain. In small animal SPECT, sub-millimeter resolutions are obtained using multi-pinhole collimators. Using a non-rotating full-ring multi-pinhole collimator according to an embodiment of the present invention to insert in the LaPET detector ring, should allow for brain SPECT imaging with a resolution of 4 mm or better. An example of such a system is drawn in FIG. 11. A full-ring geometry allows in the present example for having complete solid angle coverage and allows for making a stationary system. This allows doing faster dynamic imaging. In the present example the collimator is designed for the LaPet system, being a PET detector ring made of 24 LaBr3 detectors. It was in the present example chosen because of its very good energy resolution and its large axial FOV. For the design of the collimator, four important specifications were to be taken into account. The first specification is that the collimator was designed for the LaPET detector ring, described for example by Kyba et al. in IEEE Nuclear Science Symposium Conference Record: pp 4123-4128 (2007). The LaPET detector ring consists of 24 LaBr3 detectors of 27 by 60 pixels, each 4×4×30 mm large. The second specification is that the Field-Of-View (FOV) must be large enough to image a full human brain, which is assumed to be a cylinder with a radius of 110 mm and an axial length of 125 mm. The third specification is that the collimator must not rotate. The fourth specification is that the system must have a resolution of 4 mm or better. One design that is compliant with all specifications is shown in FIG. 12. The tungsten collimator has a radius of 145 mm and has two rings of 64 pinholes with a diameter of 2 mm. The rings are spaced 8.12 mm apart. The pinholes on the inferior ring see the superior part of the brain. The pinholes on the superior ring see the inferior part of the brain. An annulus is placed between the two pinhole-rings to prevent the projections from overlapping in the axial direction. Each pinhole sees half of the transaxial FOV. Given the specifications of the FOV and the properties of the LaPET detector, a maximum of 16 pinholes (8 in each ring) can simultaneously project on the detector without causing overlap. Therefore, the pinholes are equipped with collimating shutters. The shutter blocks all radiation when moved in front of a pinhole. A sequence of shutter movements is then performed to obtain an acquisition setup that simulates a rotational movement. A shutter also has a collimating element that is used to prevent the projection of the neighboring pinhole on one side from overlapping with the projection of the open pinhole on the other side. All simulations and reconstructions were based on raytracing and analytical calculations. In a first simulation, the sensitivity is calculated at each point in the FOV. Also, the mean sensitivity over a cylinder with a radius of 110 mm and a length of 125 mm is calculated. The calculations were based on the formula proposed by Mallard and Myers in Phys. Med. Biol. 8 pp 165-182 (1963). To investigate penetration through the pinhole, the mean sensitivity was also calculated with the effective pinhole diameter (dse) as proposed by Paix in Phys. Med. Biol. 12 pp 489-500 (1967). S = d se 2 sin 3 θ 16 b 2 with d se = d ( d + 2 μ tan α 2 ) + 2 μ 2 tan 2 α 2 with θ the incident angle measured from the plane of the pinhole, with dc the perpendicular distance from the point in the FOV to the pinhole, with μ the attenuation coefficient of tungsten and with α the openingsangle of the pinhole. In a second simulation, the resolution is calculated at each point in the FOV. The calculations are based on the formula proposed by Anger in Radioisotope cameras Instrumentation in Nuclear Medicine vol 1, pp 485-552 (1967) and the resolution effective diameter as proposed by Accorsi in IEEE Trans. Med. Imaging 23 pp 750-763 (2004). The resolution effective diameter depends on the direction of incidence on the pinhole plane. Therefore, there are two resolution values, one for each direction. If the plane X=0 is defined by the normal to the detector plane and the vector from the pinhole to the voxel, then the parallel direction is along the y axis and the perpendicular direction is along the x axis. R = R i 2 M 2 + ( d re ( 1 + 1 M ) ) 2 with M = h b d re // = d + ln 2 μ ( tan 2 α 2 - cot 2 θ ) cot α 2 sin θ d re ⊥ = ( d + ln 2 μ tan α 2 sin θ ) 2 - ( ln 2 μ ) 2 cos 2 θ with h the distance between the detector and the pinhole. Finally, a Defrise phantom is modeled using a grid with 0.5×0.5×0.5 mm voxels. The phantom has a radius of 110 mm and an axial length of 120 mm with 15 disks of 4 mm. The phantom is projected using a ray-tracer. The projections are then reconstructed using software OSEM to investigate data-completeness. 5 iterations and 8 subsets are used. The bed is axially shifted during acquisition (8.12 mm steps are used). The reconstructed image has 2×2×2 mm voxels. The result of the sensitivity simulation for the central slice is shown in FIG. 13. The sensitivity in the center of the FOV is 1.52e-04. The mean sensitivity of the whole FOV is 5.39-05. When penetration is modeled, the sensitivity in the center of the FOV is 2.64e-04 and the mean sensitivity is 9.40e-05. In other words, 38% of the total sensitivity is due to knife-edge penetration. This is a relatively large amount but it can be modeled and included in the reconstruction algorithm and thus should not pose any problems. The result of the resolution simulation in the central slice at different distances from the pinhole is shown in FIG. 14. The resolution in the parallel direction is very similar to the resolution in the perpendicular direction. In the center of the FOV it is 4.07 mm in the parallel direction and 4.12 mm in the perpendicular direction. An axial line profile of the reconstruction Defrise phantom shows very good agreement with the original phantom, as shown in FIG. 15. From the above simulation results, it can be seen that the resolution of a system according to embodiments of the present invention potentially can be significantly higher than using known systems. FIG. 17 shows the potential of combining overlapping and non-overlapping data to improve image quality of a multi-pinhole brain SPECT system. The system used is the same one as described in the previous example, except for the pinhole diameter, which was 3.9 mm instead of 2 mm. Projection data of a contrast phantom with 5 hot sources (7:1) for 3 different setups were obtained: without overlap (8 pinholes are opened simultaneously), with 100% overlap (16 pinholes are opened simultaneously) and with mixed overlapping and non-overlapping data (during 20% of the scan time only 8 pinholes were opened simultaneously and during the other 80% of the scan time 16 pinholes were opened simultaneously). The projection data were simulated using a ray tracer (Siddon) and Poisson noise was added afterwards. Assumption was made of 3 million counts in the projection data for the setup without overlap. The images were reconstructed using OSEM. Compared to the reconstruction from non-overlapping data, the reconstructed images with only overlapping data showed severe artifacts. These were reduced by mixing non-overlapping and overlapping data and were completely eliminated by adding body contouring. Body contouring is the initialization of the starting image of the reconstruction algorithm with an image that is zero outside and 1 inside the contours of the object. To define the body contour, a reconstruction was performed using only the non-multiplexed data (17 iterations). The body contour was defined by thresholding the resulting image and the reconstruction was then restarted using all the data and the body contour as starting image. Image quality was assessed using Contrast-Recovery-Curves (CRC) for the reconstructed contrast phantom using (a) only non-overlapping data and body contouring and (b) mixed overlapping and non-overlapping data and body contouring. These CRC curves are shown in FIG. 17, the curve for non-overlapping data shown in solid line, and the curve for mixed overlapping and non-overlapping data shown in dashed line. After each iteration we measured the noise and the mean contrast recovery (CR) (averaged over the 5 hot sources). A 5% improvement in contrast recovery was obtained compared to the setup without overlap at 58% noise. While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention may be practiced in many ways, and is therefore not limited to the embodiments disclosed. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to include any specific characteristics of the features or aspects of the invention with which that terminology is associated. |
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056339011 | abstract | A nuclear containment arrangement has a permanent pool cavity seal extending across an annular gap between a reactor pressure vessel and a refueling pool wall to provide a water tight seal therebetween. A seal plate has a support ring with a cylindrical section weldedly connected to an outer seal ring on an embedded ring. A J-shaped flexible ring attached to the seal plate allows axial and radial movement of the reactor vessel during thermal expansion and contraction. The inner portion of the seal plate overhangs the J-shaped flexible ring thereby to protect it from damage resulting from an object dropped thereon. Cooperating access holes and access hole covers in the seal plate provide access to the refueling pool cavity. Support arms underneath the seal plate are provided. Each support arm may have leveling screws to adjust the level of the seal plate. This provides a permanent pool cavity seal that permits flooding of the refueling pool for refueling with it only being necessary to remove the access hole covers for normal reactor operations. |
051611767 | abstract | An exposure apparatus includes a light source for exposing a wafer through a mask; a light blocking device being movable and effective to block light from the light source to limit an exposure zone; a positional deviation detecting system for detecting positional deviation between the mask and the wafer; and a drive control system for moving the light blocking device to execute position control therefor, on the basis of a detection signal from the positional deviation detecting system. |
summary | ||
051942143 | abstract | A plugging device, such as a tube plug, and method for plugging a tubular member, such as a nuclear steam generator tube, comprises a locking cup for securing together the plurality of members comprising the tube plug. The plugging device may comprise a first member, such as a shell of a tube plug, a second member, such as bolt means of a tube plug and an annular locking cup disposed in a bore of the first member and having outside diameter threads. The outside diameter threads of the locking cup have a deformed portion with a wave-like pattern for providing resistance during threading and unthreading of the locking cup into and out of the first member. At least one of the second member and the locking cup has at least one recess for receiving a deformable portion of the other of the second member and the locking cup for securing the first member, the second member, and the locking cup together. The metal-to-metal abutment of an outside diameter surface of the locking cup and a plug face of the shell and the metal-to-metal abutment of a taper of the bolt means and a taper of the locking cup may seal a chamber within the shell to prevent fluid flow through the tube plug. |
description | The present invention generally relates to automated testing, and more particularly relates to a system and apparatus for managing test procedures within a hardware-in-the-loop (HIL) simulation system. Hardware-in-the-loop (HIL) simulation systems offer an effective and cost efficient mechanism for testing complex electronic systems, such as a vehicular electronic control unit (ECU). Typically, an HIL simulation system includes and HIL simulator that that is coupled to, and configured to simulate the operating environment of, the electronic system under test. For example, a vehicular ECU may be coupled to an HIL simulator that is configured to simulate the other control units, sensors, and systems within a vehicle. This configuration allows the ECU to operate in substantially the same manner as it would operate within an actual vehicle. Accordingly, the HIL simulation system enables a user to test the ECU without the added complexity and cost associated with maintaining an actual vehicle. Generally, the HIL simulator is controlled by a user via a host electronic device. The host electronic device provides an HIL interface that the user may utilize to provide commands to, and receive data from, the HIL simulator. This HIL interface enables the user to determine if the electronic system under test is operating properly by issuing commands to the HIL simulator and determining if a desired response occurs. However, given the complexity of many electronic systems, including many vehicular ECUs, a user may be required to provide a large number of precisely timed commands via the HIL interface in order to comprehensively test the electronic system. Manually issuing such large numbers of precisely timed commands may be very time consuming for the user and costly for an employer. Further, there is an increased risk of user error during the testing process, which can lead to inaccurate test results. Accordingly, it is desirable to provide a system for generating and managing large numbers of commands within an HIL simulation system. In addition, it is also desirable to provide a system for automatically issuing a plurality of commands within an HIL simulation system. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. In one embodiment an apparatus is provided for managing test procedures for an HIL simulation environment. The apparatus comprises an input interface for receiving input from a user, a processor coupled to the input interface and in operable communication with the HIL simulation environment. The processor is configured to generate a test sequence comprising a plurality of test procedure references based on input from the user, wherein in each test procedure reference corresponds to a test procedure having instructions for issuing commands to, and receiving data from, the HIL simulation environment, and sequentially execute each test procedure within the generated test sequence in cooperation with the HIL simulation environment, in response to a command from the user. The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. FIG. 1 is a block diagram of an exemplary HIL simulation system 100. As depicted, system 100 includes a host electronic device 110 that is in operable communication with an HIL simulation environment 112. HIL simulation environment 112 includes an HIL simulator 114 and an electronic system 116 under test. Electronic system 116 includes one or more hardware and/or embedded software components that will be tested within system 100. In one embodiment, electronic system 116 comprises a vehicular ECU, such as a body control module or power train control module. However, it will be understood by one who is skilled in the art that electronic system 116 may be any electronic system that can be tested within a simulated environment. HIL simulator 114 is in operable communication with host electronic device 110 with electronic system 116. As depicted, HIL simulator 114 includes a processor 120 and one or more I/O modules 124. Processor 120 is configured to execute a software simulation (a “plant model”) of the operating environment for electronic system 116. The plant model may include environment variables and mathematical simulations of the dynamic systems (e.g. controllers, actuators, sensors, and/or other systems) found within the actual operating environment for electronic system 116. For example, in the case where electronic system 116 comprises a vehicular ECU, HIL simulator 114 may be configured to execute a plant model that simulates the various control units, sensors, and other systems that are found within an actual vehicle. Processor 120 is coupled to electronic system 116 via I/O module(s) 124. I/O module(s) 124 include various connectors and signal conditioners that enable processor 120 to transmit signals to, and receive signals from, electronic system 116. Ideally, the plant model and the I/O module(s) 124 allow processor 120 to substantially replicate the operating environment of electronic system 116, enabling electronic system 116 to operate within the HIL simulation environment 112 in substantially the same manner as it would within the its actual operating environment. In addition, processor 120 is configured to receive predetermined commands from the host electronic device 110. These predetermined commands may include commands to reboot the HIL simulator 114, load/reload a plant model, start/pause/stop the plant model, assign values to one or more environment variables within the plant model, and/or retrieve operational and diagnostic data from electronic system 116 or a simulated system within the plant model. Processor 120 may include one or more microprocessors, each of which may be any one of numerous known general-purpose microprocessors or application specific processors that operate in response to program instructions. In the depicted embodiment, processor 120 includes on-board RAM (random access memory) 126 and on-board ROM (read only memory) 128. The program instructions that control processor 120 may be stored in RAM 126, ROM 128, or a non-illustrated hard-drive. It will be appreciated that processor 120 may be implemented using various other circuits, not just one or more programmable processors. For example, digital logic circuits and analog signal processing circuits could also be used. Host electronic device 110, as noted above, is in operable communication with HIL simulator 114. In one embodiment, host electronic device 110 is coupled to HIL simulator 114 via a real-time communication interface, such as FireWire. As discussed in detail below, host electronic device 110 is configured to provide commands to, and receive data from, the HIL simulator 114. In addition, host electronic device enables a user to manage and perform a plurality of test procedures for testing the operation of electronic system 116 within HIL simulation environment 112. Host electronic device 110 may comprise a desktop computer, a laptop computer, and/or any other computing device having a configuration sufficient to perform the operations described herein. In the depicted embodiment, host electronic device 110 includes a display device 130, a processing unit 132, and memory 134. FIG. 2 is a block diagram of the host electronic device 110 of FIG. 1. As described above, host electronic device 110 includes display device 130, processing system 132, and memory 134. Display device 130 is in operable communication with the processing system 132 and, in response to display commands received therefrom, displays various images. It will be appreciated that display device 130 may be any one of numerous known displays suitable for rendering graphic, iconic, and/or textual images in a format viewable by a user. Non-limiting examples of such displays include various cathode ray tube (CRT) displays, flat panel displays such as, for example, liquid crystal displays (LCD) and thin film transistor (TFT) displays, or displays based on any other known technology. Processing system 132, at least in the depicted embodiment, includes an input interface 136 and a processor 138. Input interface 136 is in operable communication with processor 138 and is configured to receive input from the user and, in response to the user input, supply various signals to processor 138. Input interface 136 may be any one, or a combination, of various known user interface devices including, but not limited to, a cursor control device (CCD), such as a mouse, a trackball, or joystick, and/or a keyboard, one or more buttons, switches, or knobs. In the depicted embodiment, input interface 136 includes a CCD 140 and a keyboard 142. A user may utilize CCD 140 to, among other things, move a cursor symbol over, and select, various items rendered on the display device 130, and may utilize keyboard 142 to, among other things, input various data. Processor 138 is in operable communication with display device 130, memory 134, and input interface 136 via one or more non-illustrated cables and/or busses. Processor 138 is configured to respond to user input supplied via input interface 136 to, among other things, selectively retrieve data from memory 134, and to command display device 130 to render various graphical, icon, and/or textual images. Processor 138 may include one or more microprocessors, each of which may be any one of numerous known general-purpose microprocessors or application specific processors that operate in response to program instructions. In the depicted embodiment, processor 138 includes on-board RAM (random access memory) 146 and on-board ROM (read only memory) 148. The program instructions that control processor 138 may be stored in RAM 146, ROM 148, and/or memory 134. It will be appreciated that this is merely exemplary of one scheme for storing program instructions, and that various other storage schemes may be implemented. It will also be appreciated that processor 138 may be implemented using various other circuits, not just one or more programmable processors. For example, digital logic circuits and analog signal processing circuits could also be used. Memory 134, as noted above, is in operable communication with processor 138 and is configured to store various data. These data may include one or more software modules, including an HIL interface module 150, a test sequence management module 151, and an interpreter module 152. In addition, memory 134 may store additional data including one or more test procedures 160, 161, 162, test sequences 163, 164, and plant models 165. Software modules 150-152 and data 160-165 will be described in detail below. It will be appreciated that the memory 134 may be implemented using numerous suitable devices for receiving and storing the various data. Some non-limiting examples include static memory, magnetic disks, hard drives, floppy drives, thumb drives, compact disks, and the like. In addition, the data may be stored on separate memory devices or in separate sections of a common memory device. Moreover, the memory 134 may be disposed within the same structural casing as the processing system 132 and/or display device 130, or it may be disposed separately therefrom. Finally, it will additionally be appreciated that the processor 138 and memory 134 may be in operable communication via a local wired or wireless local area network connection or via a wide area network connection. No matter the specific manner in which the display device 130, the processing system 132, and memory 134 are implemented and in operable communication, the processing system 132 is configured, generally in response to one or more user inputs to the user interface 136, to retrieve one or more software modules (e.g., software modules 150-152) from the memory 134 and to execute each retrieved software module to perform the processes described below. A description of each of the processes associated with software modules 150-152 will now be provided. It should be noted that certain ones of these software modules (e.g., HIL interface module 150 and interpreter module 152) may be provided by one or more third-party software applications. In addition, although the depicted embodiment includes three separate software modules, it should be understood that embodiments of the present invention may include various numbers and arrangements of software modules to perform the processes described below. With reference to FIGS. 1 and 2, HIL interface module 150 includes program instructions that cause processor 138 to provide a communication interface between host electronic device 110 and HIL simulation environment 112. A user of host electronic device 110 or another software module may utilize HIL interface module 150 to transmit commands and data to, and retrieve diagnostic and operational data from, HIL simulator 114. In one embodiment, HIL interface module 150 enables the user or other software module to transmit a selected plant model 165 to HIL simulator 114. As described above, the plant model 165 is a software simulation of the operating environment for electronic system 116 and may include a plurality of environment variables and simulated dynamic systems. In addition, the user or other software module may issue commands that instruct HIL simulator 114 to reboot, load/reload plant model 165, start/pause/stop a simulation, assign a value to a selected environment variable, and/or retrieve diagnostic and operating data from the plant model and the electronic system 116. Test sequence management module 151 includes program instructions that cause processor 138 to execute a plurality of test sequence management processes. The test sequence management processes include test sequence generation/editing, test sequence analysis, test sequence performance, and test results reporting. As described below with regard to FIG. 3, in one embodiment test sequence management module 151 includes program instructions that cause processor 138 to render a graphical user interface (GUI) on display device 130. The user may interact with this GUI via input interface 136 to perform these test sequence management processes. In addition, it should be noted that while test sequence management module 151 is depicted as a single software module, it may be implemented as a plurality of separate software modules that cooperatively perform the test management processes described below. During test sequence generation/editing a user of host electronic device 110 generates and/or edits a plurality of test sequences. A test sequence includes a sequential list having one or more test procedure references and/or one or more test commands. A test procedure reference identifies a location in memory 134 where a test procedure (e.g., test procedure 160-162) is stored. These test procedures are customized software component having instructions for performing at least one test of the operation of electronic system 116 within HIL simulation environment 112. As further described below, the test procedure instructions may be written in a scripting language that is parsed and executed by interpreter module 152. In general, test procedures include instructions for creating one or more desired operating conditions within HIL simulation environment 112 and determining if one or more desired responses occur. Accordingly, a test procedure includes instructions for issuing commands to HIL simulator 114 via HIL interface module 150 and instructions for retrieving operational and diagnostic data from HIL simulator 114 via HIL interface module 150. In addition, a test procedure also includes instructions for generating a test procedure log. The test procedure log includes data describing the execution of a test procedure, such as the test procedure start time, the commands issued to HIL simulator 114, the operational and diagnostic data retrieved from HIL simulator 114, the results (e.g., pass/fail) of each test performed during execution of the test procedure, and the test procedure end time. A test command identifies a predetermined operation that is performed before, after, or between the referenced test procedures within a test sequence. As further described below, test commands may be used to ensure that HIL simulation environment 112 is in a stable state before a test procedure is executed. For example, a test command may assign default values to all of the environment variables for plant model 165, cause HIL simulator 114 to reload plant model 165, or cause HIL simulator 114 to reboot. Additional examples of test commands will be provided below. During test sequence generation/editing the user is able to add test procedure references and/or test commands to a test sequence, delete test procedure references and/or test commands from a test sequence, and change the order of the test procedure references and test commands within a test sequence. The generated/edited test sequences may be stored in memory (e.g., test sequences 163, 164) to be retrieved at a later time. Thus, this process enables the user to generate a large sequence of commands that can be executed within the HIL simulation environment 112 to test the operation of electronic system 116 with minimal input from a user. During test sequence analysis, a test sequence is analyzed to determine a count of the test procedure references and test commands, to validate the test procedure references, and to estimate its total execution time. The results of each analysis are provided to the user via a graphical or textual report that is rendered on display device 130. In one embodiment, test sequence management module 151 generates a count of the test procedure references and test commands within the test sequence by traversing the sequential list and counting each item included therein. In addition, test sequence management module 151 may validate the test procedures within a test sequence by traversing the sequential list and verifying that each test procedure reference corresponds to an actual test procedure (e.g., test procedures 160-162) stored in memory 134. Test sequence management module 151 estimates the total execution time for a test sequence based on the number and types of test commands included therein and an individual execution time for each referenced test procedure. For example, each individual test command may be associated with an individual execution time (e.g., in seconds) enabling test sequence management module 151 to generate a cumulative execution time for all of the test commands within the test sequence. Further, each referenced test procedure may be associated with a predetermined execution time (e.g., in seconds). In one embodiment, this predetermined execution time is identified within the test procedure. In this case, test sequence management module 151 determines the individual execution time for each referenced test procedure based on its predetermined execution time and an execution overhead time. The execution overhead time is based on the time required for processor 138 to retrieve the test procedure (e.g., test procedures 160-162) and other data from memory 134 in order to begin executing the test procedure instructions. Finally, test sequence management module 151 generates the total execution time for the test sequence by adding the cumulative performance time for the test commands to the individual execution times for each referenced test procedure. During test sequence performance, the test commands and referenced test procedures within a test sequence are sequentially executed by processor 138. Display device 130 may render a graphical or textual representation of the test sequence progress, including an elapsed time for each completed test procedure and test command and an elapsed time for the current test procedure or test command. In addition, at any time during the test sequence performance a user may request a stop test sequence command to terminate the performance of a test sequence (e.g., after execution of the current test procedure or test command has completed). Thus, this process enables the user to automate the execution of a large sequence of commands within the HIL simulation environment 112 to test the operation of electronic system 116. As noted above, a test procedure is a customized software component that includes instructions for performing at least one test of the operation of electronic system 116 within HIL simulation environment 112. These test procedure instructions may be written in a scripting language, such as Python, Perl, PHP, TCL, or any other suitable scripting language. Further, interpreter module 152 may comprise a software interpreter (e.g., a Python interpreter, a Perl interpreter, a PHP interpreter, a TCL interpreter, etc.) having program instructions that enable processor 138 to retrieve a test procedure (e.g., test procedures 160-162) from memory 134 and execute the test procedure instructions. In this case, test sequence management module 151 executes each referenced test procedure in cooperation with interpreter module 152. For example, each time test sequence management module 151 encounters a test procedure reference, test sequence management module 151 may submit the test procedure reference to interpreter module 152. Interpreter module 152 retrieves the corresponding test procedure from memory 134 and executes the test procedure instructions. As described above, the test procedure instructions will cause interpreter module 152 to transmit commands to, and receive diagnostic and operating data from, HIL simulation environment 112 via HIL interface module 150 and to maintain a test procedure log. In one embodiment, test sequence management module 151 monitors the test procedure log to detect one or more entries (e.g., such as a test procedure end time) signaling that interpreter module 152 has completed a submitted test procedure. Alternatively, test sequence management module 151 may communicate with interpreter module 152 to determine if the submitted test procedure is completed. Upon determining a submitted test procedure is completed, test sequence management module 151 executes the next item in the test sequence. It should be noted that alternative embodiments may utilize other test procedure instruction formats. For example, the test procedure instructions may comprise program instructions that may be executed directly by processor 138. In this case, test sequence management module 151 would include program instructions that cause processor 138 to retrieve and execute each referenced test procedure, without the need for interpreter module 152. As noted above, a test command identifies a predetermined operation that is performed before, after, or between the referenced test procedures within a test sequence. Test commands may be used to ensure that HIL simulation environment 112 is in a stable condition (e.g., an initialized state) before the execution of a referenced test procedure and/or to provide information to a user of host electronic device 110. Test commands that can be included within a test sequence include a reload plant model command, a reboot HIL simulator command, a clear environment variables command, a wait command, and a prompt command, to name a few. The operations associated with each of these commands will now be described. A reload plant model command causes the HIL simulator 114 to reload the current plant model. In one embodiment, test sequence management module 151 provides a predetermined scripting language instruction to interpreter module 152 upon encountering a reload plant mode command. In response to this scripting language instruction, interpreter module 152 issues a command to HIL interface 114 via HIL interface module 150 causing HIL interface 114 to clear memory 126 and then reload and re-initialize the current plant model 165. A reboot HIL simulator command causes the HIL simulator 114 to reboot. In one embodiment, test sequence management module 151 provides a predetermined scripting language instruction to interpreter module 152 upon encountering a reboot HIL simulator command. In response to this scripting language instruction, interpreter module 152 issues a command to HIL interface 114 via HIL interface module 150 causing HIL interface 114 clear memory 126 and reboot processor 120. A clear environment variables command causes HIL simulator to assign predetermined default values to the environment variables for the current plant model 165. In one embodiment, a record of the environment variables and their corresponding default values for plant model 165 is stored in memory 134. In this case, test sequence management module 151 may be configured to issue scripting language instructions to interpreter module 152 based on the environment variables and corresponding default values in this stored record. In response to these scripting language instructions, interpreter module 152 issues commands to HIL interface 114 via HIL interface module 150 causing HIL interface 114 to assign the appropriate default value to each environment variable of plant model 165. The wait command causes test sequence management module 151 to pause for a period of time that is substantially equal to a requested wait period. In one embodiment, the wait command includes the value of the wait period (e.g., in seconds). Further, the prompt command causes test sequence management module 151 to display a message to the user via display device 130. In one embodiment, the prompt command includes a timeout period (e.g., a value representing the length of a time period in seconds) and the message. In this case, test sequence management module 151 displays the message via display device 130 and pauses for a period of time that is substantially equal to the timeout period. During test results reporting, one or more reports describing the performance of a test sequence are generated and displayed to the user. In one embodiment, test sequence management module 151 may store each test procedure log that is generated during performance of a test sequence in memory 134. The test procedure logs may be stored in a compressed format or in an uncompressed format. Further, test sequence management module 151 may convert each test procedure log into a format (e.g., an HTML document) that can be viewed and understood by a user via display device 130. Finally, test sequence management module 151 may generate a summary test sequence report based on the test procedure logs generated during a test sequence. The summary test procedure report may include an elapsed time for each executed test procedure and a summary of the results for each test (e.g., pass/fail) performed during execution of the test procedure. The summary test sequence report may be displayed via display device 130 in graphical or textual format and/or stored in memory 134. FIG. 3 is a depiction of an exemplary user interface 200 for managing a plurality of test sequences. With reference to FIGS. 2 and 3, user interface 200 is a GUI that is rendered on display device 130 in response to command signals received from processor 138 as it executes Test Sequence Management Module 151. User interface 200 includes a test sequence display area 210 configured to display items (e.g., test commands and test procedure references) within a displayed test sequence. As depicted, the displayed test procedure includes a prompt command 240, a reboot HIL simulator command 241, a wait command 242, a reload plant model command 243, a plurality of test procedure references 244, 245, 246, and a clear environment variables command 247. Each of these items 240-247 is associated with a check box 250, 251, 252, 253, 254, 255, 256, 257 that can be selected (e.g., check boxes 250, 252, and 253) or unselected (e.g., check boxes 251 and 254-257) by a user. In addition, the user may highlight an item 240-247 by utilizing CCD 140 to move a cursor symbol over and select the item. User interface 200 also includes a plurality of selectable buttons, including an exit button 270, a perform test sequence button 271, a store test sequence button 272, a remove selected items button 273, a move item up button 274, a move item down button 275, an add test procedure reference button 276, a wait button 277, a prompt button 278, a reload plant model button 279, a reboot HIL simulator button 280, and a clear environment variables 281. The user selects exit button 270 to exit user interface 200 and the store test sequence button 272 to store the displayed test procedure in memory 134. In response to store test sequence button 272, processor 138 may cause display device 130 to render a graphical or textual interface that enables the user to select a location in memory 134 where the displayed test sequence will be stored. The remove selected items button 273 may be selected to remove items (e.g., items 240, 242, and 243) associated with selected check boxes from the test sequence. In addition, the move item up button 274 and move item down button 275 may be selected to relocate the highlighted item within test sequence display area 210, enabling the user to change the order of the commands and/or test procedures 240-247 in the test sequence. Buttons 276-281 enable a user to insert items (e.g., test commands or test procedure references) within the displayed test sequence. In one embodiment, the new item is inserted after the currently highlighted item (e.g., prompt command 240) within the displayed test sequence. The user selects add test procedure reference button 276 to add a selected test procedure reference to the displayed test sequence. In response, to add test procedure reference button 276, processor 138 may cause display device 130 to render a graphical or textual interface that enables the user to select a desired test procedure reference. Further, the user selects the wait button 277 to insert a wait command within the displayed test procedure. In response to wait button 277, processor 138 causes display device 130 to render a graphical or textual interface that enables the user to select a wait period. Further still, the user selects the prompt button 278 to insert a prompt command within the displayed test sequence. In response to prompt button 278, processor 138 causes display device 130 to render a graphical or textual interface that enables the user to enter a message and a timeout period. The reload plant model button 279, reboot HIL simulator button 280, and clean environment variables button 281 enable the user to respectively insert a reload plant model command, reboot HIL simulator command, or a clear environment variables command. In addition, the user selects display button 271 to cause processor 138 to perform the displayed test sequence. Processor 138 then accesses test sequence management module 151 to sequentially execute the test commands and reference test procedures within the displayed test sequence. Finally, user interface 200 includes a menu bar 310 having a plurality of selectable menu categories. These selectable menu categories include a file menu category 320, an add menu category 321, an edit menu category 322, and a tools menu category 323. The user may select menu categories 320-323 to cause corresponding menus to be rendered on display device 130. Each menu includes a plurality of selectable menu items that the user may select to perform one of the test sequence management processes described above. File menu category 320 corresponds to a menu that includes menu items which enable the user to retrieve an existing test sequence from memory 134, store the displayed test sequence, and view a test procedure log or a summary test sequence report. Further, add menu category 321 corresponds to a menu that includes menu items which enable the user to insert a test procedure reference and the test commands described above within the displayed test sequence. In addition, edit menu category 322 corresponds to a menu that includes menu items which enable the user to select to select/unselect all of the checkboxes 250-258 within test sequence display area 210, remove items (e.g., items 240, 242, and 243) that are associated with a selected check box (e.g., check boxes 250, 252, and 253), and remove all of the items 240-147 from the displayed test sequence. Finally, tools menu category 323 corresponds to a menu that includes menu items which enable a user to perform the test sequence analysis processes described above. While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof. |
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claims | 1. An apparatus comprising:at least one control rod comprising a neutron absorbing material;a control rod drive mechanism (CRDM) unit; anda control rod/CRDM coupling connecting the control rod and the CRDM unit such that the CRDM unit provides at least one of gray rod control and shutdown rod control for the at least one control rod;wherein the control rod/CRDM coupling includes a connecting rod having an average density greater than the density of stainless steel at room temperature, wherein the connecting rod comprises:a hollow or partially hollow connecting rod tube;a filler disposed in the interior volume of the hollow or partially hollow connecting rod tube, the filler comprising a material having a density greater than the density of stainless steel at room temperature, anda welded plug sealing off the interior volume of the hollow or partially hollow connecting rod tube with the filler disposed in the interior volume. 2. The apparatus as set forth in claim 1, wherein the hollow or partially hollow connecting rod tube is made of stainless steel. 3. The apparatus as set forth in claim 1, wherein the filler has a density of at least 16.2 grams per cubic centimeter at room temperature. 4. The apparatus as set forth in claim 1, wherein the hollow or partially hollow connecting rod tube comprises a material having a first density and the material comprising the filler has a density that is at least twice the first density. 5. The apparatus as set forth in claim 1, wherein the connecting rod further comprises:an additional element disposed in the hollow or partially hollow connecting rod tube, the additional element not being the filler comprising a material having a density greater than the density of stainless steel at room temperature, the additional element preventing the filler from moving inside the hollow or partially hollow connecting rod tube. 6. The apparatus as set forth in claim 1, wherein the connecting rod further comprises:a compressed spring disposed in the hollow or partially hollow connecting rod tube and pressing against the filler. 7. The apparatus as set forth in claim 6, wherein the spring is disposed below the filler in the hollow or partially hollow connecting rod tube such that the spring at least contributes to dissipating kinetic energy accrued by the filler during a SCRAM. 8. The apparatus as set forth in claim 3, wherein the hollow or partially hollow connecting rod tube is made of stainless steel. 9. The apparatus as set forth in claim 2, wherein the filler comprises a material selected from the group consisting of tungsten, depleted uranium, molybdenum, and tantalum. 10. The apparatus as set forth in claim 1, wherein the filler comprises a material selected from the group consisting of tungsten, depleted uranium, molybdenum, and tantalum. 11. An apparatus comprising:at least one control rod comprising a neutron absorbing material;a control rod drive mechanism (CRDM) unit; anda connecting rod having its lower end connected with the control rod and its upper end connected with the CRDM unit such that the CRDM unit provides at least one of gray rod control and shutdown rod control for the at least one control rod;wherein the connecting rod comprises (i) a hollow or partially hollow stainless steel rod tube having a length of 250 centimeters or greater and (ii) a filler material disposed inside the hollow or partially hollow stainless steel rod tube, the filler material having a density greater than the density of stainless steel at room temperature. 12. The apparatus of claim 11 wherein the at least one control rod comprises a plurality of control rods and the apparatus further comprises:a spider via which the lower end of the connecting rod is connected with the plurality of control rods. 13. An apparatus comprising:at least one control rod comprising a neutron absorbing material;a control rod drive mechanism (CRDM) unit;a connecting rod having its lower end connected with the control rod and its upper end connected with the CRDM unit such that the CRDM unit provides at least one of gray rod control and shutdown rod control for the at least one control rod; anda detachable attachment assembly via which the lower end of the connecting rod connects with the at least one control rod, the detachable attachment assembly including mating male and female attachment components;wherein the connecting rod comprises (i) a hollow or partially hollow rod tube made of a rod tube material and (ii) a heavy material disposed inside the hollow or partially hollow rod tube, the heavy material having a density greater than the density of the rod tube material, the heavy material disposed inside the hollow or partially hollow rod tube being different from the male and female attachment components of the detachable attachment assembly. 14. The apparatus of claim 13 wherein the rod tube material is stainless steel. 15. The apparatus of claim 14 wherein the heavy material comprises tungsten. 16. The apparatus of claim 14 wherein the heavy material comprises depleted uranium. 17. The apparatus of claim 14 wherein the heavy material comprises molybdenum. 18. The apparatus of claim 14 wherein the heavy material comprises tantalum. 19. The apparatus of claim 13 wherein the heavy material comprises tungsten. 20. The apparatus of claim 13 wherein the heavy material comprises depleted uranium. 21. The apparatus of claim 13 wherein the heavy material comprises molybdenum. 22. The apparatus of claim 13 wherein the heavy material comprises tantalum. 23. The apparatus of claim 13 wherein the heavy material has a density that is at least twice the density of the rod tube material. 24. The apparatus of claim 23 wherein the rod tube material is stainless steel. 25. The apparatus of claim 13 wherein the at least one control rod comprises a plurality of control rods and the apparatus further comprises:a spider via which the lower end of the connecting rod is connected with the plurality of control rods, the spider including the female attachment component of the detachable attachment assembly and the lower end of the connecting rod including the male attachment component of the detachable attachment assembly. 26. The apparatus as set forth in claim 1, wherein the hollow or partially hollow connecting rod tube has a length of 250 centimeters or greater. 27. The apparatus as set forth in claim 13, wherein the hollow or partially hollow connecting rod tube has a length of 250 centimeters or greater. 28. The apparatus as set forth in claim 11, wherein the connecting rod further comprises:a welded plug sealing off the interior volume of the hollow or partially hollow connecting rod tube. 29. The apparatus as set forth in claim 13, wherein the connecting rod further comprises:a welded plug sealing off the interior volume of the hollow or partially hollow connecting rod tube. 30. The apparatus as set forth in claim 1, further comprising:a detachable attachment assembly via which a lower end of the connecting rod connects with the at least one control rod, the detachable attachment assembly including mating male and female attachment components;wherein the filler disposed in the hollow or partially hollow rod tube is different from the male and female attachment components of the detachable attachment assembly. 31. The apparatus as set forth in claim 11, further comprising:a detachable attachment assembly via which the lower end of the connecting rod connects with the at least one control rod, the detachable attachment assembly including mating male and female attachment components;wherein the filler disposed inside the hollow or partially hollow stainless steel rod tube is different from the male and female attachment components of the detachable attachment assembly. 32. An apparatus comprising:at least one control rod comprising a neutron absorbing material;a control rod drive mechanism (CRDM) unit; anda connecting rod having its lower end connected with the control rod and its upper end connected with the CRDM unit such that the CRDM unit provides at least one of gray rod control and shutdown rod control for the at least one control rod;wherein the connecting rod comprises (i) a hollow or partially hollow rod tube made of a rod tube material and (ii) a heavy material comprising depleted uranium disposed inside the hollow or partially hollow rod tube, the heavy material having a density greater than the density of the rod tube material. 33. The apparatus of claim 32 wherein the rod tube material is stainless steel. |
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claims | 1. A lithographic projection apparatus comprising: an illumination system constructed and arranged to supply a projection beam of radiation; a mask table constructed to hold a mask; a substrate table constructed to hold a substrate; and a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; and further comprising: two vacuum chambers separated by a chamber wall incorporating a channel structure comprising adjacent narrow channels separated by walls that are substantially parallel to a propagation direction of said radiation so as to pass said radiation from one of said vacuum chambers to the other one, said propagation direction being substantially along an optical axis of said apparatus. 2. An apparatus according to claim 1 , wherein a width of said channels increases or decreases along said optical axis in accordance with passing of a diverging or converging beam of radiation, respectively. claim 1 3. An apparatus according to claim 1 , wherein said channel structure comprises a honeycomb structure. claim 1 4. An apparatus according to claim 1 , wherein a cross-sectional dimension of said channels in a radial direction perpendicular to said optical axis is larger than another cross-sectional dimension of said channels in a tangential direction around said optical axis. claim 1 5. An apparatus according to claim 4 , wherein said width in the tangential direction is in the range from 0.1 to 2 mm. claim 4 6. An apparatus according to claim 4 , wherein said width in the radial direction is in the range from 5 to 50 mm. claim 4 7. An apparatus according to claim 1 , wherein a length of said channel is in the range from 5 to 70 mm. claim 1 8. An apparatus according to claim 1 , wherein said apparatus further comprises a radiation source contained in one of said vacuum chambers. claim 1 9. An apparatus according to claim 1 , wherein said radiation source is a plasma source for generating extreme ultraviolet radiation. claim 1 10. An apparatus according to claim 9 , wherein said radiation source is a discharge plasma source. claim 9 11. An apparatus according to claim 1 , wherein the radiation is extreme ultraviolet radiation having a wavelength in the range from 0.5 to 50 nm. claim 1 12. A method of manufacturing a device using a lithographic projection apparatus comprising: an illumination system constructed and arranged to supply a projection beam of radiation; a mask table constructed to hold a mask containing a mask pattern; a substrate table constructed to hold a substrate that is at least partially covered by a layer of radiation-sensitive material; and a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate, and further comprising: two vacuum chambers separated by a chamber wall incorporating a channel structure comprising adjacent narrow channels separated by walls that are substantially parallel to a propagation direction of said radiation so as to pass said radiation from one of said vacuum chambers to the other one, said propagation direction being substantially along an optical axis of said apparatus, said method comprising the step of: using the projection beam of irradiation to project an image of at least a portion of the mask pattern onto a target portion on the substrate. 13. A device manufactured according to the method of claim 12 . claim 12 14. A method according to claim 12 , wherein said illumination system comprises a radiation source contained in one of said vacuum chambers. claim 12 15. A method according to claim 12 , wherein said illumination system comprises a plasma source for generating extreme ultraviolet radiation. claim 12 16. A method according to claim 12 , wherein said radiation source is a discharge plasma source. claim 12 17. A method according to claim 12 , wherein a width of said channels increases or decreases along said optical axis in accordance with passing of a diverging or converging beam of radiation, respectively. claim 12 18. A method according to claim 12 , wherein said channel structure comprises a honeycomb structure. claim 12 19. A method according to claim 12 , wherein a cross-sectional dimension of said channels in a radial direction perpendicular to said optical axis is larger than another cross-sectional dimension of said channels in a tangential direction around said optical axis. claim 12 20. A method according to claim 19 , wherein said width in the tangential direction is in the range from 0.1 to 2 mm. claim 19 21. A method according to claim 19 , wherein said width in the radial direction is range from 5 to 50 mm. claim 19 22. A method according to claim 12 , wherein a length of said channels is in the range from 5 to 70 mm. claim 12 23. A method according to claim 12 , wherein the radiation is extreme ultraviolet radiation having a wavelength in the range from 0.5 to 50 nm. claim 12 |
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abstract | The invention pertains to a process for separating at least one first chemical element E1 from at least one second chemical element E2 coexisting in a mixture in the form of oxides, comprising the following steps: a) a step to solubilise a powder of one or more oxides of the said at least one first chemical element E1 and a powder of one or more oxides of the said at least one second chemical element E2 in a medium comprising at least one molten salt of formula MF—AlF3 wherein M is an alkaline element, after which there results after this step a mixture comprising the said molten salt, a fluoride of the said at least one first chemical elements E1 and a fluoride of the said at least one second chemical element E2; b) a step to contact the mixture resulting from step a) with a medium comprising a metal in the liquid state, the said metal being a reducing agent capable of predominantly reducing the said at least one first chemical element E1 relative to the said at least one second chemical element E2, after which there results after this step a two-phase medium comprising a first phase called metal phase comprising the said at least one first chemical element E1 in oxidation state 0, and a second phase called saline phase comprising the molten salt of above-mentioned formula MF—AlF3 and a fluoride of the said at least one second chemical element E2. |
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abstract | An apparatus for automatically loading a fuel pellet for manufacturing a nuclear fuel rod is provided. The apparatus includes a tray transfer unit that horizontally transfers the tray, a fuel pellet alignment unit that aligns fuel pellets arranged in the tray, a measurement unit that measures an entire length of the fuel pellets arranged in a row on the tray, a controller that compares an accumulated measured length with a set length, a waiting table located adjacent to the tray transfer unit to store a redundancy fuel pellet, and a fuel pellet movement unit that is driven by the controller and moves the fuel pellets between the tray and the waiting table. |
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description | This application claims the benefit of a priority under, 35 USC 119 to French Patent Application No. 01 13357 filed Oct. 17, 2001, the entire contents of which are hereby incorporated by reference. The invention relates to antiscattering grids and particularly to antiscattering grids used in X-ray imaging. A radiology imaging apparatus may comprise an X-ray source and an image receiver between which the object, of which it is wished to produce an image, is positioned. The beam emitted by the source passes through the object before reaching the detector. It is partly absorbed by the internal structure of the object so that the intensity of the beam received by the detector is attenuated. The overall attenuation of the beam after having passed through the object is directly related to the absorption distribution in the object. The image receiver may comprise an optoelectronic detector or enhancing film/screen pair sensitive to the intensity of the radiation. The image generated by the receiver corresponds in principle to the distribution of the overall attenuations of the rays due to having passed through the internal structures of the object. One part of the radiation emitted by the source is absorbed by the internal structure of the object and the other part is either transmitted (primary or direct radiation) or scattered (secondary or scattered radiation). The presence of scattered radiation results in the contrast of the image obtained being degraded and the signal/noise ratio being reduced. One solution to this problem comprises interposing one or more “antiscattering” grids between the object to be X-rayed and the image receiver. This grid is usually formed by a series of parallel plates made of a material that absorbs the X-rays. In a grid identified as a “focused” grid (using the terminology defined by the CEI 60627 standard relating to “X-ray imaging diagnostic equipment—characteristics of the antiscattering grids for general use and for mammography”), all the planes of the plates intersect along the same straight line passing through the focal point of the radiation emitted by the source. A antiscattering grid may comprise a series of oriented parallel plates made of a material which strongly absorbs the X-rays, for example, lead, and are held together between inter-plate members made of a material more transparent to X-rays than the plates, such as, for example, aluminum or cellulose fibers (paper or wood). A disadvantage for such a grid is that the grid is unable to reduce the degree of radiation scattered in a direction parallel to the plane of the plates. Crossed grids having two series of absorbent plates, in which the two plates are positioned perpendicular to each other, reduce this disadvantage. The crossed grids allow two-dimensional filtering to be obtained and thus further reduce the solid angle with which a point on the receiver sees the object. However, the presence of inter-plate members between the plates reduces the transmission of the direct radiation through the grid. Consequently, the X-ray dose needed to obtain an image of good quality must be increased (particularly in mammography). There are several structural arrangements for obtaining grids without inter-plate members. One structural arrangement is two-dimensional filtering comprising superposing one-dimensional grids. U.S. Pat. No. 5,307,394 describe an antiscattering device comprising the superposition of several grids. Each grid has parallel absorbent plates separated by openings, the plates being positioned at an angle of between 0 and 89.9° with respect to the central beam perpendicular to the plane of the receiver. The grids have a thickness such that the ratio of the thickness of the grid to the distance between the plates is greater than 1. This arrangement provides filtering of the rays whose angle of incidence is high. Another structural arrangement comprises producing two-dimensional grids directly in a one-piece support. U.S. Pat. No. 5,389,473 describes a method of manufacturing an antiscattering grid, comprising producing a grid from a glass plate, making openings in the plate by photoetching and chemical etching (for example using hydrofluoric acid). Such a method results in an array of cells separated by partitions being formed. The partitions are then covered with a layer of material that absorbs the X-rays. WO 94/17533 describes an antiscattering grid comprising a lattice formed in a glass plate, the lattice comprising cells separated by partitions. The partitions are covered with a layer of absorbent material, not only inside the cells but also along their edges corresponding to the upper and lower surfaces of the glass plate. In the field of mammography, another type of two-dimensional grid has been developed. U.S. Pat. No. 5,606,589 describe an antiscattering grid comprising thin metal sheets micro-etched to form a lattice. The sheets are superposed so as to form a focused grid. The sheets are held stacked together by adhesive bonding. U.S. Pat. No. 5,814,235 describes a method of manufacturing such a grid. The method comprises forming, by photoetching in a metal foil, a lattice structure comprising cells separated by segments extending in transverse directions. The foils are then individually immersed in a bath of adhesive. The foils are then stacked on top of each other so as to align the segments in order to form partitions between the cells and then clamped together in position. This method makes it possible in particular to obtain strong grids. U.S. Pat. No. 6,075,840 generalizes this type of grid for applications other than mammography. The disadvantage with the above methods is that they are based on the chemical etching of layers of materials and consequently result in a significant loss of material, and hence high costs. Moreover, a disadvantage with the antiscattering grids in general is that they mask part of the image receiver and leave their impression on the image obtained. A solution to this problem comprises slightly shifting the grid during image acquisition. Thus, the image obtained comprises the superposition of images, for which the grid lies in different positions. In certain cases, it is possible to translate the grid only in a single direction (in particular in mammography, in which the direction of displacement is parallel to the patient's thoracic cage). In this case, the impressions of the segments or of the partitions which are positioned parallel to the direction of displacement of the grid remain on the image obtained. U.S. Pat. No. 5,970,118 describes an antiscattering grid formed in a glass plate in which the partitions of the cells are not parallel to the side of the grid parallel to the direction of displacement of the latter. For example, the grid may comprise cells having a square shape and oriented at 35° with respect to an edge of the grid parallel to the direction of displacement. An embodiment provides a grid that is two dimensional for limiting the filtering of the direct radiation. An embodiment provides an antiscattering grid for radiation, particularly for an X-ray imaging apparatus, of the type comprising a substrate having a plurality of metallized partitions that together define a plurality of cells distributed over the substrate. The partitions allow passage of radiation emitted from a source lying in line with the grid, and absorbing the radiation not coming directly from this source. In an embodiment of the invention the substrate is made of a polymer material. The polymer material is less absorbent of the radiation and therefore permits more of the direct radiation to pass through. This feature permits in particular the reduction of the radiation doses administered to the object. In an embodiment the external surfaces of the substrate are not metallized, thereby allowing some of the direct radiation to pass through the substrate. This makes it possible to further increase the quality of the image without increasing the radiation doses administered to the object. In an embodiment as the substrate is less absorbent of radiation the gird has less strict dimensioning constraints while still exhibiting superior performance. An embodiment is a method for the manufacture of such grids. An embodiment is a method of manufacturing an antiscattering grid comprising a substrate made of a polymer material, in which the substrate is formed by radiation curing of a monomer sensitive to the radiation. The method may comprise, for example, laser photolithography (and in particular the technique known as “stereolithography”) or X-ray lithography. The method of manufacturing an antiscattering grid may comprise: (a) forming, for example, by stereolithography, a substrate having a plurality of partitions which together define a plurality of cells distributed over the said substrate; and (b) depositing a layer of metal on the surface of the substrate. In an embodiment of the method, the substrate of the grid may be formed from a wide range of low-density materials. It may, for example, comprise an epoxy resin or an acrylic resin. These materials have a density and an atomic number that are low enough to have low radiation absorption, particularly for X-rays. Forming the substrate by, for example, stereolithography, allows small cells to be obtained. In particular, in an embodiment of the invention, there may be two broad types of grids. A grid may have cells with openings of about 200 μm (micrometers) to about 300 μm and comprising partitions having a thickness of about 50 μm to about 100 μm. A grid having a pitch of about 50 μm to about 100 μm and comprising partitions having a thickness of about 20 μm to about 50 μm. FIG. 1 shows schematically the principle of operation of an antiscattering grid 1 mounted in a radiology apparatus. The grid 1 is positioned in front of a detector screen 42 so that the radiation source 44 is located at the focal point O of the grid 1. One part of the direct radiation D emitted by the source 44 passes through an object 46, the image of which it is wished to obtain, without undergoing distortion. Another part d of the radiation is scattered by the object 46 so that it strikes the grid at an angle α to the focusing direction of the grid 1. Since the internal partitions of the grid 1 are focused, they absorb the scattered radiation d. FIG. 2 shows more specifically the paths of the radiation, during image acquisition, through an antiscattering grid of an embodiment. The grid comprises a substrate 2 made of a polymer material, comprising partitions 8 which define cells 12. The internal walls of the cells 12 are covered with a metal layer 14. A part D1 of the direct radiation D passes through the grid 1 via the substrate 2, while another part D2 passes through the grid 1 via the cells 12. Because of the low density of the polymer of which the substrate 2 is formed, the radiation D1 undergoes little attenuation. The internal walls of the cells 12 are covered with a metal layer 14 that absorbs the scattered radiation d striking the grid 1 at too great an angle α to the focusing direction of one of the cells 12. An embodiment is directed to two types of grids. A first type, of which the grids have an opening x of about 200 μm to about 300 μm and comprise partitions having a thickness e of about 50 μm to about 100 μm; and a second type of finer grids with a pitch of about 50 μm to about 100 μm and comprising partitions having a thickness e of about 20 μm to about 50 μm. Grids for a radiology apparatus, for example, in mammography, may have a ratio of the thickness of the grid to the distance between the partitions of between 3 and 5. The disclosed embodiments makes it possible to obtain grids having ratios greater than 8, whether the grids are linear or crossed. This feature ensures filtering of the rays whose angle of incidence deviates, even slightly, from the direction of direct radiation and consequently results in grids having extremely high rejection properties. In the case of grids of the first type mentioned above, a grid thickness e of greater than about 1.6 mm or about 2.4 mm, and less than about 3 mm, is obtained (should the ratio reach 10). In the case of grids of the second type, a grid thickness e of greater than about 0.4 mm or about 0.8 mm, and less than about 1 mm, is obtained (should the ratio reach 10). It may be advantageous to choose to manufacture a grid having a pitch equal to the period of the digital detector of the camera. This feature makes it possible to eliminate the gain modulations introduced by the grid and prevent a deflection generated by the superposition of the grid and of the detector from being obtained. FIG. 3 shows the overall shape of a substrate 2 of a focused antiscattering grid according to one embodiment. The substrate is in the form of a substantially planar element, of thickness e, having two principal faces, an upper face 4 and a lower face 6. The substrate is composed of intersecting partitions 8 defining cells 12 passing through the substrate from one of its principal faces to the other. The substrate 2 is “focused”, that is to say by definition, the planes containing the partitions 8 between the cells 12 all have the same focal point O, as shown in FIG. 4. In FIG. 3, the cells 12 are square in shape and define a quasi-periodic pattern (or instead one in which the pitch or the period varies continuously). The pitch may correspond to the distance between two successive parallel partitions. Cells having various polyhedral shapes are possible. However, in an embodiment cells preferably have the shape of a parallelogram. A parallelogram is that category of shapes which minimizes as far as possible the surface area occupied by the partitions and therefore makes it possible to minimize the absorption of the grid. It will also be understood that the partitions separating the cells are not necessarily aligned. They may be parallel and offset from one cell to the next. This gives the grid some advantages. In particular, this feature makes it possible to minimize the generation of impressions of the partitions on the image obtained when these impressions are approximately parallel to the direction of displacement of the grid. One embodiment of a substrate is described as follows. The substrate 2 is designed by computer-aided design. The geometrical features of the substrate 2 are defined according to the desired properties of the grid. From these geometrical features, a polyhedral surface model is generated which can be exported to the STL (standing for stereolithography) format. This format allows an object to be described in the form of a polyhedron having triangular facets. Next, the sections of the substrate 2 to be produced by successive cutting of parallel horizontal planes are defined. The distance between each section corresponds to the thickness of a layer. FIG. 5 shows a first step in the manufacture of a substrate by stereolithography. A precursor fluid 22 (for example photosensitive liquid acrylate or epoxy resins) is contained in a tank 24 kept at a high pressure (between 300 kPa and 7000 kPa) by means of a pump device 26 connected to the tank 24 and in communication with the precursor fluid 22. The tank 24 is closed in its upper part by a window 28 (made of quartz, sapphire or silica). FIG. 5 shows a platform 34, the principal surface of which is parallel to the free surface of the fluid 22 and is mounted on an elevator (not shown) which can be translationally actuated perpendicular to the plane of the platform 34. FIG. 5 shows a source 32 emitting a beam through a lens 36 to an arrangement of mirrors 38. The source 32 is, for example, an ultraviolet laser source. The mirrors 38 are used to deflect the beam emitted by the source 32 onto the free surface of the precursor fluid 22. The mirrors are positionally controlled by a computer so as to perform a point-by-point scan of the layer of fluid 22 close to its free surface. The ultraviolet radiation emitted by the source 32 causes local curing of the precursor fluid 22. The mirrors 38 are controlled so that the beam draws on the surface of the fluid a pattern corresponding to the lower surface of the substrate 2. When a first layer of polymer has been thus produced, the elevator is actuated in order to lower the platform 34 supporting the cured layer by a height corresponding to the thickness of one layer (the thickness of a layer is determined by the level of viscosity of the precursor fluid chosen—it is generally less than one-tenth of a millimeter). Next, the source again draws a new pattern in order to create a second layer on the first layer. Each cured layer is in the form of a lattice comprising segments defining openings. The layers are produced in succession so that the segments of two adjacent layers are superposed, thus forming the partitions of the cells of the substrate. The final substrate obtained is a one-piece substrate. FIG. 6 shows an intermediate step during which a layer 52 of polymer is produced by stereolithography on that part 54 of the substrate that has already been produced. The final substrate 2 obtained is a one-piece substrate. When the substrate 2 has been completed, the precursor fluid 22 contained in the tank 24 that has not reacted is drained off. As shown in FIG. 4, the relative positions and dimensions of the openings and of the segments vary progressively from one layer to the next. In this way, it is possible to construct a substrate 2 having focused cells 12 for the purpose of obtaining a focused grid. One particular way of implementing an embodiment of the method in which point-by-point stereolithography is used has been described. It will be understood that it is possible to use other rapid prototyping techniques such as, for example, whole-layer stereolithography, in which the source illuminates the surface of the fluid through a mask defining a complementary shape of the pattern to be produced. In a second step, the surface of the substrate 2 is metallized, by a chemical vapor deposition (CVD) process. The detail of a grid 1 thus obtained is shown in FIG. 7. Such a method is used to obtain a metal layer 14 having a thickness of the order of a few μm. The absorbent metals preferably used are gold (in the form of a layer from 2 μm to 5 μm in thickness), copper (in the form of a layer from about 10 μm to about 20 μm in thickness), tantalum (in the form of a layer from about 2 μm to about 10 μm in thickness) or possibly lead. These materials may be used by themselves, in combination or in association with other materials. It is also possible to employ other metallization processes such as, for example, physical vapor deposition (PVD) or electrolysis. It is also possible to deposit a first thin layer on the substrate by sputtering and then to deposit a second layer on the first layer by an electroplating technique. In a third step, those parts of the metal layer provided on or covering the upper surface 4 and the lower surface 6 of the substrate are removed. In one embodiment the metal layer can be removed by abrasion. In another embodiment the metal layer can be removed by plasma etching. When using plasma etching the semi-finished grid is place in a plasma reactor. The reactor may be of type used in the manufacture of micro electro mechanical systems (MEMS) or semiconductor integrated circuits. A plasma reactor of this type is available from Alcatel Micro Machining Systems (MMS) or Plasma Etch Inc. Plasma etching occurs in a vacuum and uses radio frequency energy to create plasma. The ions of the plasma react with the metallic layer that is to be removed. In an alternative embodiment, simple dry plasma etching may be used. In simple dry plasma etching, gas contained in the reactor forms a simple plasma. The particle of metal located on the exposed surface of the metallic layer is removed by the impact of the ions contained in the plasma. In a further alternative embodiment, plasma etching in the presence of active gas may be used. A reactive gas, for example, SF6, is introduced into the plasma so as to produce a combined physical and chemical etching. In a still further embodiment, laser ablation may be used. In laser ablation, the metallic layer is exposed to a focused radiation beam provided by a laser source. Laser ablation provides mechanical etching of the particles of metal. The laser source may a laser emitting in the ultraviolet band, such as Excimer laser sources. The laser source is controlled so as to sweep over the surface of the grid. The size of the laser spot generated by the radiation beam depends on the power of the source and the ablation threshold of the metal to be removed. The duration of the ablation process depends on the spot size, the pulse frequency of the laser source (in the case of a pulsed laser source), the thickness of the metal layer to be removed and the area of surface to be treated. The upper and lower surfaces can be de-coated one at a time. However, it is possible to de-coat both surfaces simultaneously using two laser source or one laser source and a beam splitter. The removal of the metal layer by plasma etching or laser ablation is more advantageous than removal by abrasion. Plasma etching or laser ablation provides a substantially uniform removal of the metal layer from desired surfaces of the grid and provides a substantially clean cut of the metal layer at the edges of the cell walls. A substantially uniform removal and cut of the metal layer may maintain a high transmission of the radiation through the grid. The described techniques for removal of the metallic layer are easy to implement through available manufacturing and industrial processes and tools with reasonable and acceptable costs. It is also possible, after the metallization step, to fill the cells 12 with a polymer similar to the polymer of which the substrate 2 is made. Using this additional operation, the antiscattering grid is made homogeneous and the attenuation is thus distributed uniformly, in order to reduce any artifacts that it generates on the images obtained. This is mainly so in the case of grids having a thickness of less than about 1 mm, the attenuation of which is negligible. The manufacture of a plane grid has been described, but it is also possible to produce in the same way, grids comprising a substrate made of a polymer material of different shape. For example, the thickness of the grid is not necessarily constant. Thus, grids called “roof-shaped” grids (the terminology used in the CEI standard) may be produced. One skilled in the art may make various modifications in structure and/or function and/or steps and equivalents thereof to the disclosed embodiments without departing from the scope and extent of the invention as recited in the claims. |
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claims | 1. A Boiling Water Reactor (BWR) external cooling system, comprising:a suppression pool configured to provide cooling for the BWR;closed cooling coils contacting and coiled around a cross-sectional outer periphery of the suppression pool; anda heat sink fluidly coupled to the cooling coils to provide a flow of cooling fluid through the cooling coils,wherein the system does not breach the suppression pool or any other primary containment structure, and the suppression pool is a torus shape with the cross-sectional outer periphery being circular, the cooling coils encircling the circular cross-sectional outer periphery of the suppression pool. 2. The BWR external cooling system of claim 1, further comprising:a pump, fluidly coupled to the heat sink; andan inlet pipe connecting the pump to the cooling coils to provide the flow of cooling fluid through the cooling coils. 3. The BWR external cooling system of claim 2, further comprising:an outlet pipe connected to the cooling coils to discharge warm water from the cooling coils back to the heat sink. 4. The BWR external cooling system of claim 2, wherein the pump is driven by a diesel generator. 5. The BWR external cooling system of claim 2, further comprising:a control valve in the inlet pipe. 6. The BWR external cooling system of claim 5, further comprisinga controller for controlling at least one of the pump and the control valve, the controller being positioned in a remote location relative to the suppression pool. 7. The BWR external cooling system of claim 1, wherein the heat sink is one of a man-made or natural body of water. 8. The BWR external cooling system of claim 3, wherein the inlet pipe and the outlet pipe form a closed system with the cooling coils such that the inlet pipe provides the flow of cooling fluid to the cooling coils and the outlet pipe returns all of the cooling fluid to the heat sink. 9. The BWR external cooling system of claim 8, wherein the cooling fluid is a liquid. 10. The BWR external cooling system of claim 1, wherein the flow of cooling fluid through the cooling coils occurs without the need for electrical power to be provided to the external cooling system. 11. The BWR external cooling system of claim 10, wherein the flow of cooling fluid through the cooling coils occurs via a gravity draining of the cooling fluid from the heat sink through the cooling coils. 12. The BWR external cooling system of claim 11, wherein an elevation of the heat sink is above an elevation of the suppression pool. 13. The BWR external cooling system of claim 10, wherein the flow of cooling fluid through the cooling coils is not drained back into the heat sink. 14. The BWR external cooling system of claim 10, wherein the flow of cooling fluid through the cooling coils is not returned to the heat sink. |
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050154362 | summary | BACKGROUND OF THE INVENTION The present invention relates to a water-cooled direct cycle nuclear power plant, and to a method for controlling iron concentration in cooling water in order to further decrease radioactive corrosion product concentration in reactor water. A control method of a prior art for controlling corrosion product concentration in feed water is disclosed in Japanese Patent Laid-Open No. 61-79194, where .sup.58 Co..sup.60 Co ion concentration in reactor water is controlled at low level by maintaining Fe/Ni concentration ratio in a range of 2 to 10. However, in this control method, a sufficient consideration is not paid to the case where the nickel concentration is further decreased. In the above prior art, the control is carried out only in dependence on Fe/Ni concentration ratio in feed water. In this control method, .sup.60 Co ion concentration was frequently higher than an expected value, although .sup.58 Co ion concentration may be maintained at low level. Namely, the Fe/Ni concentration ratio is not a sufficient control index. SUMMARY OF THE INVENTION The object of the present invention is to provide a water-cooled direct cycle nuclear power plant having a control means which controls iron concentration in feed water at a suitable level in order to maintain .sup.60 Co ion concentration in reactor water at low level even when nickel concentration becomes relatively low in feed water. The above-mentioned object of the present invention is achieved by a water-cooled direct cycle nuclear power plant, which includes a nuclear reactor, a turbine, a condenser, a purifying means and a feed water heater successively arranged as main constituent elements, and further comprises means for measuring iron concentration in cooling water and means for injecting iron into cooling water for controlling iron amount in cooling water at optimum level. The iron-injecting means includes a processing unit which calculates iron concentration increment to be added on the basis of the data obtained by the above-mentioned iron concentration measuring means in order to supply the iron amount into cooling water for realizing an iron accumulation rate not less than 0.5 mg/m.sup.2 /hr on fuel rod surface, and a control unit for supplying the calculated amount of iron to feed water. In the present invention, iron concentration in cooling water is measured, iron accumulation rate on fuel rod surface is calculated based on the measured data, and iron amount to be injected from iron-injecting means is controlled so as to maintain the calculated iron accumulation rate to be not less than 0.5 mg/m.sup.2 /hr. To maintain Fe/Ni ratio in feed water in a range of 2 to 10 is effective for changing nickel and cobalt adhered to fuel rod surface into chemically stable and almost insoluble ferrite oxide (NiFe.sub.2 O.sub.4, CoFe.sub.2 O.sub.4, etc.), and decreasing the amount of activated .sup.58 Co or .sup.60 Co dissolving into reactor water in comparison with a case where nickel and cobalt are adhered on fuel rod as a monooxide. However, as shown in FIG. 2-A, .sup.60 Co is considered to dissolve into reactor water not from the whole portion of corrosion product adhered on fuel rod surface, but only from a portion of a certain thickness of the product which serves as a dissolvable layer. In consequence, in case iron accumulation layer is thin as shown in FIG. 2-B, the most portion of .sup.60 Co accumulated on fuel rod surface contributes to the dissolution into reactor water, while in case iron accumulation layer is thick as shown in FIG. 2-C, only a part of accumulated .sup.60 Co contributes to the dissolution. Since the half life of .sup.60 Co is about five years, which is relatively long in comparison with an usual plant operation cycle of one year, the specific activity of Co adhered to fuel rod is regarded as monotonously increasing along time lapse. Actually, the .sup.60 Co concentration increasing rate in reactor water caused by plant operation is usually rather small in comparison with the increase of the specific activity. This is for the reason that, as mentioned above, only a part of .sup.60 Co adhered to fuel rod contributes to the dissolution. In other words, it may be understood that an iron layer newly adhered to fuel rod has a function to shield a dissolution of .sup.60 Co from an oldly adhered layer having a higher specific activity into reactor water. With this view point, a relation between iron accumulation rate on fuel rod and .sup.60 Co concentration increase rate in reactor water is calculated, result of which is shown in FIG. 3, showing a tendency that the latter becomes smaller as the former becomes greater. From this figure, it is found that the .sup.60 Co concentration increase rate in reactor water becomes small in a case where the iron accumulation rate on fuel rod is not less than 0.5 mg/m.sup.2 / hr. Therefore, iron concentration can be controlled at an optimum level by using iron accumulation rate as a control index. However, if iron amount accumulated on fuel rod become unnecessarily great, heat transfer from fuel rod to reactor water is deteriorated with a risk of causing failures of fuel cladding tubes; and .sup.54 Mn and .sup.59 Fe, which are generated by iron activation, increases, causing a increase of total radioactive concentration. Therefore, it is required to limit the amount of iron to be accumulated. In this text, the nuclear reactor is of a type where water is used as a coolant and boiled on fuel rod surfaces such as seen in a boiling water reactor or advanced thermal reactor. The term of iron concentration means a concentration of all irons existing in cooling water including ionized Fe, not-ionized iron hydroxide, iron oxide etc. regardless of their chemical states. The iron concentration measuring means is a device which can measure the iron amount included in a sampled specimen for atomic absorption or ion chromatograph in a dissolved and ionized state of iron. The control means for controlling iron amount in cooling water at an optimum level is a device comprising a memory and a calculator required for deducing an iron accumulation rate on fuel rod surface from the measured iron concentration, and a control unit constituted by a flow rate control valve or a pump of variable flow rate required for controlling iron-injecting rate according to the calculated results of the calculator. The iron-injecting means is a device comprising an iron generating means by virtue of ionizing or cladding through electrolytic analysis, or a water tank containing water including iron constituent, and a pump for injecting the water including iron constituent into the cooling water. |
abstract | The shutters (2) in an X-ray device which include at least a radiation source (1), a diaphragm device (8) with shutters (2) and a recording (3) and image processing unit (4), are provided with hole and/or edge patterns (11-14) which reproduce non-anatomical patterns in the radiation image; the shutter edges (15) are detected in the radiation image in the image processing unit on the basis of such patterns, so that only the directly irradiated part of the patient is displayed. |
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045405123 | abstract | Disclosed is a process for separating and recovering boric acid from water containing solids which include boric acid and radionuclides. In the first step, the water is separated from the solids by evaporation of the water at a temperature under 130.degree. F. In the second step, an alcohol selected from the group consisting of methanol, ethanol, propanol, isopropanol, and mixtures thereof is added to the remaining solids in the amount of at least 1.4 times that stoichiometrically required to react with the boric acid to form boron alkoxide and water to about 100 mole % in excess of stoichiometric. In the third step, the boron alkoxide is separated from the remaining solids by evaporation of the boron alkoxide. In the fourth step, water is added to the volatilized boron alkoxide to form boric acid and an alcohol. And finally, the alcohol is separated from the boric acid by evaporating the alcohol. |
claims | 1. An electron beam lithography apparatus for concentrically drawing a plurality of circles on a substrate by applying an electron beam while rotating the substrate, comprising:a beam deflection portion for deflecting the electron beam to change an irradiation position of the electron beam;a synchronization signal generation portion for generating a synchronization signal in synchronization with the rotation of the substrate;a controller for controlling the beam deflection portion on the basis of the synchronization signal in order to deflect the electron beam in a rotational radial direction of the substrate and in a rotational tangential direction of the substrate relative to the circle path and in the same rotational direction of the substrate, while drawing transition is performed from one circle to another circle; anda beam cutoff portion for cuffing off the irradiation of the electron beam on the substrate, for a period when the electron beam is deflected in the rotational radial direction. 2. The electron beam lithography apparatus according to claim 1, wherein the controller deflects the electron beam in the rotational tangential direction of the substrate relative to the circle path and in the same direction as the movement of the substrate before drawing transition is performed from the one circle to the another circle. 3. The electron beam lithography apparatus according to claim 1, wherein the controller deflects the electron beam in the rotational tangential direction relative to the circle path to overwrite a portion of the circle including a drawing connection position. 4. The electron beam lithography apparatus according to claim 1, wherein the beam cutoff section varies an intensity of the electron beam applied to the substrate at a predetermined rate before or after a period when the electron beam is deflected in the rotational radial direction. 5. An electron beam lithography method for drawing a plurality of circles on a substrate by applying an electron beam while rotating the substrate, the method comprising:a transition controlling step of deflecting the electron beam in a rotational radial direction of the substrate and in a rotational tangential direction of the substrate relative to the circle path and in the same rotational direction of the substrate, upon performing drawing transition from one circle to another circle; anda beam cutoff step of cutting off the irradiation of the electron beam on the substrate, for a period when the electron beam is deflected in the rotational radial direction. 6. The electron beam lithography method according to claim 5, wherein the transition controlling step includes a step of deflecting the electron beam in the rotational tangential direction of the substrate relative to the circle path and in the same direction as the movement of the substrate before drawing transition is performed from the one circle to the another circle. 7. The electron beam lithography method according to claim 5, wherein the transition controlling step deflects the electron beam in the rotational tangential direction relative to the circle path to overwrite a portion of the circle including a drawing connection position. 8. The electron beam lithography method according to claim 5, comprising the step of varying an intensity of the electron beam applied to the substrate at a predetermined rate before or after a period when the electron beam is deflected in the rotational radial direction. 9. An apparatus comprising a drawing controller for applying an electron beam on a substrate to draw a plurality of circles, configured for deflecting the electron beam in a rotational radial direction of the substrate and in a rotational tangential direction of the substrate relative to the circle path and in the same rotational direction of the substrate, upon performing drawing transition from one circle to another circle. 10. The apparatus recited in claim 9, wherein the drawing controller is further configured for cutting off the irradiation of the electron beam on the substrate, for a period when the electron beam is deflected in the rotational radial direction. 11. The apparatus recited in claim 9, wherein before the drawing transition from the one circle to the another is performed, the electron beam is deflected in the rotational tangential direction of the substrate relative to the circle path and in the same rotational direction of the substrate. 12. The apparatus recited in claim 9, wherein the drawing controller is configured for deflecting the electron beam in the rotational tangential direction relative to the circle path to overwrite a portion of the circle including a drawing connection position. 13. The apparatus recited in claim 9, wherein the drawing controller is configured for varying an intensity of the electron beam applied to the substrate at a predetermined rate before or after a period when the electron beam is deflected in the rotational radial direction. |
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abstract | Compositions comprising high levels of high specific activity copper-64, and process for preparing said compositions. The compositions comprise from about 2 Ci to about 15 Ci of copper-64 and have specific activities up to about 3800 mCi copper-64 per microgram of copper. The processes for preparing said compositions comprise bombarding a nickel-64 target with a low energy, high current proton beam, and purifying the copper-64 from other metals by a process comprising ion exchange chromatography or a process comprising a combination of extraction chromatography and ion exchange chromatography. |
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summary | ||
061750514 | claims | 1. A method for deactivating liquid alkali metal coolant and/or alkaline earth metal coolant removed from a nuclear reactor system, the method comprising the steps of: a) mixing an ammoniacal liquid with a liquid alkali metal coolant and/or alkaline earth metal coolant removed from a nuclear reactor coolant system in a reaction vessel to form a reaction mixture containing solvated electrons and alkali and/or alkaline earth metal cations; b) introducing a precipitating agent to the reaction mixture of step (a) to form a precipitating alkali metal salt and/or alkaline earth metal salt; and c) separating the alkali and/or alkaline earth metal salts from the ammoniacal liquid for disposal and/or further treatment. a) creating a reaction mixture in a closed reaction vessel comprising: b) introducing a precipitating agent that ionizes in the anhydrous liquid ammonia, the precipitating agent introduced in a sufficient amount to precipitate an alkali metal salt; and c) separating the anhydrous ammonia to yield the alkali metal salt for disposal or further treatment. a) introducing and circulating anhydrous liquid ammonia in the coolant system until the anhydrous liquid ammonia contains dissolved alkali metal to form a reaction mixture; b) introducing the reaction mixture to a closed vessel; c)introducing an ionizable precipitating agent into the closed reaction vessel thereby forming an alkali metal salt; and d) separating the anhydrous ammonia to yield the alkali metal salt for disposal or further treatment. a) mixing anhydrous liquid ammonia with molten alkali metal in a closed vessel to form a reaction mixture; b) introducing a hazardous waste material to the mixture of step (a) to form a precipitating alkali metal salt and detoxify the hazardous waste; and c) separating the anhydrous ammonia to yield the alkali metal salt and detoxified waste for disposal or further treatment. a) mixing anhydrous liquid ammonia with a precipitating agent in a closable reaction vessel wherein the precipitating agent is ionized in the anhydrous liquid ammonia; b) introducing a liquid alkali metal to the mixture of step (a) to form a precipitating alkali metal salt; and c) separating the anhydrous ammonia to yield the alkali metal salt for disposal or further treatment. 2. The method of claim 1 wherein the liquid alkali metal coolant is sodium and the precipitating agent is a member selected from the group consisting of ammonium chloride, ammonium nitrate and copper chloride. 3. The method of claim 1 wherein the precipitating agent is in a stoichiometric amount to provide sufficient anions to combine with the alkali metal cations to form a precipitatable metal salt. 4. The method of claim 2 wherein the ammoniacal liquid is anhydrous liquid ammonia. 5. The method of claim 2 wherein the precipitating agent has a reducible anion when ionized in ammoniacal liquid to be reduced by solvated electrons in the reaction vessel. 6. The method of claim 5 wherein the amount of moles of the alkali metal is at least twice the amount of moles of the precipitating agent. 7. The method of claim 1 wherein the alkali metal is a member selected from the group consisting of sodium, potassium, lithium and a mixture thereof. 8. The method of claim 1 wherein the ammoniacal liquid is anhydrous liquid ammonia maintained at a pressure and temperature to remain in a liquefied phase in the reaction vessel. 9. The method of claim 5 wherein the precipitating agent is in at least a stoichiometric amount to consume solvated electrons generated by the dissolving alkali metal. 10. A method for deactivating liquid alkali metal removed from a coolant system of a nuclear reactor, the method comprising the steps of: 11. The method of claim 10 wherein the precipitating agent is a member selected from the group consisting of ammonium chloride and ammonium nitrate. 12. The method of claim 10 wherein the precipitating agent is introduced in a stoichiometric amount to provide sufficient anions to combine with the alkali metal cations to form the precipitating alkali metal salt. 13. The method of claim 10 wherein the precipitating agent has a reducible anion to be reduced by solvated electrons in the reaction vessel. 14. The method of claim 10 wherein the precipitating agent is water. 15. The method of claim 13 wherein the amount of moles of the alkali metal is at least twice the amount of moles of the precipitating agent. 16. The method of claim 10 wherein the alkali metal is a member selected from the group consisting of sodium, potassium, lithium and a mixture thereof. 17. A method for deactivating solidified alkali metal encrusted on surfaces within a coolant system of a nuclear reactor, the method comprising the steps of: 18. A method for deactivating alkali metal coolant and/or alkaline earth metal coolant used in a nuclear reactor system, the method comprising: solubilizing and/or ionizing the alkali metal coolant and/or alkaline earth metal coolant and a precipitating agent in an ammoniacal liquid, introducing the precipitating agent in a sufficient amount to combine with the ionized alkali metal and/or alkaline earth metal to form an alkali metal salt and/or alkaline earth metal salt. 19. A method for deactivating molten alkali metal removed from a coolant system of a nuclear reactor while detoxifying a hazardous waste, the method comprising the steps of: 20. A method for deactivating liquid alkali metal removed from a coolant system of a nuclear reactor, the method comprising the steps of: |
abstract | The design of a compact, high-efficiency, high-flux capable compact-accelerator fusion neutron generator (FNG) is discussed. FNG's can be used in a variety of industrial analysis applications to replace the use of radioisotopes which pose higher risks to both the end user and national security. High efficiency, long lifetime, and high power-handling capability are achieved though innovative target materials and ion source technology. The device can be sealed up for neutron radiography applications, or down for borehole analysis or other compact applications. Advanced technologies such as custom neutron output energy spectrum, pulsing, and associated particle imaging can be incorporated. |
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050858246 | claims | 1. A drive system comprising: a gantry including a bridge having longitudinal and transverse axes and supported by spaced first and second end frames joined to first and second drive trucks for moving said bridge along said transverse axis; first means for driving said first drive truck; second means for driving said second drive truck being independent from said first driving means; and means for controlling said first and second driving means for reducing differential transverse travel between said first and second drive trucks, due to a skewing torque acting on said bridge, to less than a predetermined maximum, said controlling means being in the form of an electrical central processing unit and including: said first and second driving means include first and second motors driving first and second transmissions, respectively, said first and second transmissions driving first and second driven wheels of said first and second drive trucks, respectively; said gantry further includes a trolley selectively movable along said bridge longitudinal axis, and a main hoist joined to said trolley; said differential transverse travel being effected by at least one of backlash in said first and second transmissions and transverse flexibility of said bridge; and said travel control means including a predetermined correction model indicative of said at least one of said backlash and said transverse flexibility. 2. A drive system according to claim 1 wherein said controlling means is effective for subtracting said travel error signal from said at least one command signal for decreasing velocity of said respective one of said first and second drive trucks which travels more than the other thereof. 3. A drive system according to claim 1 wherein said controlling means is effective for adding said travel error signal to said at least one command signal for increasing velocity of said respective one of said first and second drive trucks which tends to travel less than the other thereof. 4. A drive system according to claim 1 wherein said controlling means is effective for adding said travel error signal to said first command signal for increasing velocity of said first drive truck which tends to travel less than said second drive truck; and subtracting said travel error signal from said second command signal for decreasing velocity of said second drive truck. 5. A drive system according to claim 1 wherein: 6. A drive system according to claim 5 wherein said travel control means further includes first and second travel sensors for providing first and second travel signals indicative of transverse positions of said first and second drive trucks, respectively, and said travel error signal is proportional to the difference of said first and second travel signals. 7. A drive system according to claim 6 wherein said first and second travel sensors measure rotational position of first and second undriven wheels of said first and second drive trucks, respectively. 8. A drive system according to claim 6 wherein said first and second transmissions each include reduction chain drives for reducing rotational speed from said first and second motors to said first and second driven wheels, respectively. 9. A drive system according to claim 6 wherein said first and second transmissions each include reduction gear drives for reducing rotational speed from said first and second motors to said first and second driven wheels, respectively. 10. A drive system according to claim 6 wherein said first and second velocity control means each includes first and second motor sensors for providing first and second feedback signals indicative of rotational velocity of said first and second motors, respectively, and means for subtracting said first and second feedback signals from said first and second command signals, respectively, for providing first and second velocity error signals for controlling said first and second motors, respectively. 11. A drive system according to claim 10 wherein said gantry is a nuclear refueling platform and said main hoist is effective for raising and lowering a nuclear fuel bundle. 12. A drive system according to claim 11 wherein said controlling means is effective for subtracting said travel error signal from said at least one command signal for decreasing velocity of said respective one of said first and second drive trucks which travels more than the other thereof. 13. A drive system according to claim 6 wherein said travel control means correction model is indicative of both said backlash and said transverse flexibility. 14. A drive system according to claim 13 further including guide rails upon which said first and second driven wheels are movable, and wherein said travel control means correction model is indicative also of slippage between said first and second driven wheels and said guide rails. |
047864621 | abstract | A novel concrete core support structure for nuclear reactors is described. |
042591562 | abstract | In a device for coupling pipelines in a pressure vessel of a nuclear reactor having a first piping section sealingly extending through the pressure vessel-housing wall and fastened thereto, and a second piping section sealingly connected to the first piping section, as well as a core container fastened within the pressure vessel, the core container having a cover, and steam separators forming, together with the core-container cover, a structural unit, the second piping section being also included with the core-container cover and with the steam separators fastened to the cover in the structural unit and, when the pressure vessel is opened, the second piping section together with the core-container cover being liftable out of the pressure vessel and being reinsertable into the pressure vessel, the first and the second piping sections being in mutual contact at coaxial sealing surface portion formed thereon at the sealed connecting location thereof, said sealing surface portions being placeable into a nominal location of sealing connection thereof through the weight per se of the structural unit of the core-container cover and the steam separators as well as through bracing forces for the core-container cover, the bracing forces being oriented in axial direction of the pressure vessel, and means for affording relative motion dependent upon thermal expansion, of the sealing surface portions within a predetermined tolerance range without impairing sealing action thereof. |
description | The present invention will be described below in detail with reference to the embodiments shown in to FIGS. 2 to 7. FIG. 2 shows an overall schematic view of a radiographic system. A radiographic apparatus 11 includes an X-ray image detecting apparatus 12 having a detecting surface on which a plurality of photoelectric conversion elements are disposed two-dimensionally. As will be described below, the X-ray image detecting apparatus 12 includes an X-ray image detector in which X-ray grids, fluorescent substances (which serve, as is well known, to convert incident X-rays to light of a predetermined wave-length; such substances, and any and all arrangements that can transform X-rays to light, are herein referred to sometimes as an X-ray converter or conversion member) and the photoelectric conversion elements are constituted together as a unit, i.e., integrated in one united body. X-rays irradiated from an X-ray generator 13 having an X-ray tube are applied to a person S as a subject being examined for diagnosis, and X-rays that have passed through the person S are detected by the X-ray image detecting apparatus 12. Thus-obtained image data is digitally processed by an image processing apparatus 14 including a computer, and the image data that has been processed is stored in the computer as well as displayed on a display unit 15 as an X-ray image of the person being examined. FIG. 3 is shows a sectional view of an X-ray image detector 21 built in the X-ray image detecting apparatus 12. The X-ray image detector 21 is arranged such that a plurality of photoelectric conversion elements 23 are disposed two-dimensionally on the plane of an insulation substrate 22, the plane extending in the direction perpendicular to the sheet surface of FIG. 3, and further, a grid unit 24 is disposed on the photoelectric conversion elements 23, that is, at a side toward incident X-rays. In addition, the spaces between the photoelectric conversion elements 23 are arranged as insensitive regions 25, which have no sensitivity to fluorescence. A glass sheet is used as the insulation substrate 22 because it does not chemically act on semiconductor devices that form the photoelectric conversion elements 23 and the like, endures the high temperatures involved in semiconductor manufacturing processes, is stable dimensionally, and is able to have a high degree of flatness. The grid unit 24 has grids which are formed of foils 26 composed of lead having a large x-ray absorption ratio, and the spaces between the respective grids are filled with fluorescent substances 27 and intermediate substances 28, sequentially in this order, in a direction opposite to the direction from which X-rays are incident. A photoelectric conversion element 23 is disposed just under a corresponding fluorescent substance 27, which is located between each pair of grids, and as well, each photoelectric conversion elements 23 is disposed so as to avoid a portion shaded by a foil 26, and the shaded portion is arranged as an insensitive region 25. The thickness of each foil 26 is in approximate agreement with the width of the insensitive region 25. The fluorescent substances 27 located between the respective grids are spatially separated from each other by the foils 26 in order to prevent crosstalk in which fluorescence L2 generated by the fluorescent substances 27 on the respective photoelectric conversion elements 23 is incident on adjacent photoelectric conversion elements 23. The intermediate substances 28 are disposed to reinforce the foils 26 having low rigidity and composed of aluminum, paper, wood, synthetic resin or carbon-fiber-reinforced resin, or the like, having a small X-ray absorption ratio. The fluorescent substances 27 are partitioned by the foils 26, and the intermediate substances 28 are laminated or layered on the fluorescent substances 27. While the foils 26 are mainly composed of lead, when the surfaces thereof are arranged as reflecting surfaces for reflecting fluorescence, fluorescence generated by the fluorescent substances 27 is reflected on the foils 26, which increases the amount of fluorescence incident on corresponding photoelectric conversion elements 23, thereby improving the S/N of a detection signal. FIG. 4 is a sectional view of the X-ray image detector 21 shown in FIG. 3 when it is viewed from a direction D (an x-ray incident direction). Each photoelectric conversion element 23 is formed in an approximate square shape, and each grid formed by the foils 26 have a slit or strip shape. The grids are filled with intermediate substances 28 having a slit shape formed in accordance with the shape of the grids. The photoelectric conversion elements 23 formed just under the intermediate substances 28, each having the approximately square shape, are distributed two-dimensionally. Insensitive regions 29 are formed between the respective photoelectric conversion elements 23. Note that it is not always necessary that the girds formed by an X-ray grid be formed in a shape of stripes, and they may instead be formed in a matrix shape. In this case, the respective grids may be formed in a quadrangular shape (a square shape or a rectangular shape) or may be formed in a polygonal shape other than a quadrangular shape, for example, in a hexagonal honeycomb shape. Since primary X-rays L1 are incident on the grid unit 24 in approximately parallel to the foils 26, they pass through the intermediate substances 28 and reach the fluorescent substances 27 and make it emit the fluorescence L2, to which the photoelectric conversion elements 23 have sensitivity, in the fluorescent substances 27. While the fluorescence L2 is emitted at various angles, it does not reach other adjacent photoelectric conversion elements 23 because it does not pass through the foils 26. In contrast, since scattered X-rays L3 are incident on the grid unit 24 obliquely to (i.e., not parallel to) the foils 26 but at a certain angle with respect to it, most of the scattered X-rays L3 are absorbed by the foils 26, and the ratio of them that reach the fluorescent substances 27 or the photoelectric conversion elements 23 is small. Since the foils 26 exist only on the insensitive regions 25 between the photoelectric conversion elements 23, they do not block the X-rays to be intrinsically detected that are not scattered by the subject and incident toward the fluorescent substances 27 on the photoelectric conversion elements 23. Therefore, the reduction of the transmittance of X-rays, which is determined by the ratio of the thicknesses of the intermediate substances 28 and the foils 26 (opening ratio), does not occur in this arrangement, while this reduction is a problem in the conventional art employing the moving grid. When, for example, it is assumed in the conventional example shown in FIG. 1 that the foils 7 have a thickness of 43 xcexcm and the intermediate substances 8 have a thickness of 207 xcexcm, about 17% of the arrangement (43/(43+207)) blocks the transmission of X-rays, and thus their opening ratio is 83%. In contrast, in this embodiment, an opening ratio of 100% can be secured while having the grid unit 24. This means that sensitivity can be improved about 20% while using the same photoelectric conversion elements 23, which permits a reduction in dosage received by persons being examined. Further, in the X-ray image detector of this embodiment, the foils 26 exhibit multiplied actions not only removing the scattered X-rays L3 incident on the foils 26 but also solving the problem which is caused by the diverged component or the scattered component of the fluorescence L2 by spatially separating the fluorescent substances 27. That is, the foils 26 reduce the above-mentioned crosstalk between adjacent photoelectric conversion elements. By this arrangement, the MTF can be improved, and an excellent X-ray image can be taken. Further, while the fluorescent substances 27 are formed continuously in the direction perpendicular to the sheet surface (the depth direction) of FIG. 3 in the above embodiment, the fluorescent substances 27 located on the insensitive regions 29 may be removed in correspondence to the approximately square shape of the photoelectric conversion elements 23. In this case, the MTF also will be improved in this direction (the depth direction). The grid unit 24 arranged as described above, of which a grid ratio (i.e., height of the foil of the grid as shown in the Figures divided by spacing between adjacent vertical foils of the grid) is preferably set to at least 3:1, can achieve a large effect for removing the scattered X-rays L3. FIG. 5 shows a sectional view of a second embodiment of the X-ray image detecting apparatus of the present invention, wherein the same components as used in the first embodiment are denoted by the same reference numerals. The second embodiment is different from the first embodiment as described below. That is, in the first embodiment, the grid unit 24 is arranged as a parallel grid all foils of which are disposed parallel to each other, whereas in the second embodiment, a grid unit 32 of an X-ray image detector 31 is arranged as a converging grid foils of which are tilted symmetrically with respect to a center line Z acting as a symmetrical axis. Specifically, foils 33a in the vicinity of the center line Z are disposed perpendicular to the detecting surfaces of photoelectric conversion elements 23, and foils 33b in the periphery of the grid unit 32 are tilted with respect to the direction of the center line Z. The angle xcex8 of foils 33 with respect to the normal Y of the detecting surfaces of the photoelectric conversion elements 23 is 0 in the vicinity of the center line Z, and increases with distance of the foil 33 from the center line Z. Note that the extending lines of all the foils 33 (i.e., the planes of all the foils) intersect with each other at one point (focal point) on the center line Z. Ordinarily, a radiographic system is arranged such that this focal point is in approximate agreement with the emitting point of an X-ray source from which X-rays emit. When an X-ray image is taken using the converging grid together with an X-ray tube having an emitting point located at the focal point of the converging grid, a still more excellent image can be obtained which does not have any vignetting caused by the foils 33 even in the periphery of the grid unit 32, that is, in which the intensity of X-rays is not reduced even in the periphery thereof. FIG. 6 is a sectional view of a third embodiment of the X-ray image detecting apparatus 41 of the present invention. In the previous embodiments, the flourescent substances in the grid unit of the X-ray image detector are partitioned by the grid foils. In the third embodiment, however, partitions 43, which are different from grid foils 26, are disposed only in the portions where flourescent substances 27 are partitioned so that adjacent flourescent substances can be spatially separated from each other by the partitions 43. The partitions 43 have a property that they do not transmit the fluorescence L2, since they block it by reflecting or absorbing it, while they may absorb the X-rays in a small amount. In a grid unit 42 arranged as described above, the foils 26 can remove scattered X-rays incident downward, and as well, the partitions 43 can prevent the diverged or scattered component of the fluorescence L2 generated in the fluorescent substances from invading into adjacent regions, whereby occurrence of crosstalk can be prevented. Further, the portion of the grid unit 42 excluding the fluorescent substances 27 and the partitions 43 has a structure in which only the foils 26 and intermediate substances 28 are alternately disposed, and thus the portion of the grid unit 42 can be simply made by a conventional manufacturing method. Note that, as a modification, a similar function also can be obtained in an arrangement in which the portions of the partitions 43 are composed of simple cavities, the fluorescent substances 27 are spatially separated for each grid, and a reflecting layer or a shading layer is formed on a side of each fluorescent substance 27. FIG. 7 shows a sectional view of a fourth embodiment of the X-ray image detecting apparatus of the present invention. Each of the foils 26 of a grid unit 52 of an X-ray image detector 51 is supported with its lower end inserted into one of a plurality of grooves 53a formed on the upper surface of a resin plate 53. Further, a plurality of recesses 53b are formed on the lower surface of the resin plate 53 at the same pitch as the foils 26 and are filled with fluorescent substances 27. That is, the fourth embodiment has a structure in which the fluorescent substances 27 are spatially separated in correspondence to the spaces between the respective foils. Note that the resin plate 53 has a property that it blocks fluorescence emitted from the fluorescent substances 27 by reflection, absorption or the like. Otherwise, the resin plate 53b is provided with this property. In contrast, the upper ends of the foils 26 are held by a resin plate 54 having grooves 54a formed thereon at the same pitch as the grooves 53a. The grid unit 52 has sufficient rigidity because the foils 26 are held by the grooves 53a and 54a, which permits the spaces between the foils 26 to be arranged as cavities 55 without being filled with intermediate substances. This arrangement can avoid a loss caused when X-rays pass through the intermediate substances, in addition to being able to remove any scattered X-rays and crosstalk that is caused by fluorescence. For example, when the intermediate substances 28 in the first embodiment are composed of aluminum having a thickness of 2 mm, they have a transmittance for the X-rays L1 of about 70%. That is, sensitivity can be improved about 40% (≈1/0.7xe2x88x921) by the removal of the intermediate substances. As a result, compatibility can be established between a further reduction in the dosage received by the subject and improvement of image quality. Note that rigidity may be further improved by providing cover portions or bonded layers on the surfaces of the grid foils, in the spaces between the grid foils and the fluorescent substances, or in the spaces between the fluorescent substances and the photoelectric conversion elements. The employment of the grid unit 52 arranged as described above can remove a large amount of a scattered X-ray component, and can reduce crosstalk between the respective photoelectric conversion elements due to converged fluorescence, whereby image contrast can be improved, and as well, a decrease in the intensity of X-rays can be reduced when they transit the grid unit. That is, the reduction of the dosage received by subjects and the improvement of image quality, which are ordinarily inconsistent with each other, can be satisfied at the same time. The X-ray image detecting apparatus using the X-ray image detectors of all of the embodiments described above has such advantages as high reliability, less expensive cost and easy maintenance because it can obtain an excellent image without the need for a mechanism for moving an X-ray grid. Further, it is needless to say that the above-mentioned third and fourth embodiments may employ a converging grid, as in the second embodiment. As described above, according to the X-ray image detecting apparatus of the present invention, an excellent image having high contrast can be obtained while reducing the dosage received by the subject. While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 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. |
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description | The disclosed methods and systems relate to diagnostic imaging systems, and more specifically to systems and methods for obtaining stereoscopic x-ray images. X-ray technology has found many practical uses in medical, industrial, and scientific fields. One of the more familiar uses of x-rays is as a diagnostic tool in the fields of medicine and dentistry. As such, x-rays are used to visualize anatomical structures and detect the presence of pathology, disease or abnormal anatomy. Advances in x-ray technology include the use of digital x-ray equipment, wherein images are captured digitally. The use of digital x-ray equipment can greatly reduce a patient's exposure to potentially harmful radiation, while providing sharper image detail and ease of processing. However, the usefulness of x-ray technology has been limited by the difficulty in providing three-dimensional information of the object being examined. Studies in the field of dentistry have shown that for a more accurate diagnosis, two or three radiographs taken at different angles are necessary. Those radiographs are conventionally viewed individually by the examiner and processed and compared in the examiner's brain to be visualized in 3 dimensions. Several systems have been devised to obtain three dimensional information, including transmission X-ray microscopes and Computerized Axial Tomography (CAT) scanners. These systems combine x-ray transmission systems with tomographical reconstruction methods to enable recreation of three-dimensional information from sets of flat cross-sectional images. The systems rely on a large number of different cross-sectional images of an object taken from many different angles. The digital image data is processed in a computer to yield a three-dimensional picture that can display the object being examined in great detail. The systems, however, are complicated and generally expensive, making them somewhat inaccessible and unaffordable. In addition, the amount of the radiation necessary to produce a CAT image is very high compared to standard two-dimensional images. What is needed, then, is a system and method for extracting three-dimensional information from two-dimensional x-ray images that is relatively simple to use, is accessible and affordable, yet provides limited exposure of a patient or other object to radiation. Disclosed are systems and methods for obtaining stereoscopic x-ray images. The method includes taking two digital x-ray views of the same object from differing positions. The included angle between the axes of the x-rays for each position generally coincides with that formed by a pair of eyes viewing the object, though larger angles can be used. The x-rays can be taken by two x-ray generators within a single housing or within separate but attached housings. The x-ray generators are spaced apart and aimed at the object to form the appropriate angle. Care is taken not to move the object. Preferably, the x-ray generators have dual collimators to take the views. In this case, the time between taking the two x-rays need only be as long as the image capture time of the sensor being used, which lessens the chance of the object moving. The digital data from the sensor for each position is processed in the normal manner to provide an image of the object from each position. The two resulting images are displayed in a manner such that only the image corresponding to the viewer's eye position is received at that eye. Current methods of displaying three-dimensional (3D) images can be used. For example, the images can be polarized and viewed through corresponding polarized eyeglasses. Preferably, the images can be displayed on a 3D liquid crystal display (LCD) screen, such as the Sharp Actius™ RD3D. On such screens, the two images are overlapped, but use separate pixels for each image. An LCD filter restricts the angle at which light from the pixels can be viewed, such that the image corresponding to the viewer's left eye can only be viewed by the left eye and vice versa. Other screens are formed with ridges that restrict the viewing angle for each pixel. Other means for viewing stereoscopic images include eyeglass video displays that present the separate images to the corresponding eye, or a 3D viewer using mirrors to reflect the corresponding image from two monitors to the respective eye of the viewer. In one embodiment, a system for obtaining a stereoscopic x-ray image of a target includes at least one housing, a pair of spaced apart x-ray tubes within the at least one housing, each x-ray tube generating x-rays when energized, a collimator associated with each x-ray tube and a digital image sensor spaced opposite the target from the collimators. A longitudinal axis of each collimator is aligned between its associated x-ray tube and the target. Each collimator filters the x-rays from its associated x-ray tube such that x-rays not travelling towards the target are limited. The digital image sensor detects x-rays from the x-ray tubes and outputs sensor data for each x-ray tube for forming the stereoscopic x-ray image. In some aspects, the x-ray tubes may be located within a single housing. In one aspect, the system can include a processor in communication with the digital image sensor to receive the sensor data and output image data, and a display in communication with the processor to receive the image data and output the stereoscopic x-ray image for viewing. The display can further include a filter to restrict viewing of a portion of the stereoscopic x-ray image corresponding to x-rays detected by the sensor from one of the x-ray tubes to viewing from one eye of a viewer wherein a position of the eye with respect to the display corresponding to a position of the one of the x-ray tubes with respect to the object. The display can be a liquid crystal display and the filter can restrict an angle at which light from a pixel of the liquid crystal display can be viewed. The display can be an eyeglass display having a separate display for each eye of a viewer, wherein each display presents a portion of the stereoscopic x-ray image corresponding to x-rays detected at the sensor from one of the x-ray tubes. A transformer can convert incoming power to a voltage differential required to energize the x-ray tubes to emit x-rays. A power switch can be configured to limit the incoming power. A transfer switch can be configured to transfer energizing power from one x-ray tube to the other x-ray tube. A timer can be configured to activate the transfer switch. In one embodiment, a method of obtaining a stereoscopic x-ray image of a target can include energizing a first x-ray tube to emit x-rays in a direction towards the target, energizing a second x-ray tube spaced apart from the first x-ray tube to emit x-rays in a direction towards the target, detecting emitted x-rays at a sensor to obtain sensor data, processing the sensor data to obtain image data and displaying the image data to provide a stereoscopic x-ray image of the target. In some aspects, the method can include maintaining the positions of the first and second x-ray tubes, the sensor and the target during energizing and detecting. The method can include connecting to a power supply and transforming power from the power supply to provide a differential voltage at the x-ray tubes sufficient to energize the x-ray tubes. The method can include limiting the power from the power supply to that required for energizing the first and the second x-ray tubes. In one aspect, detecting can include downloading the sensor data obtained by detecting the x-rays emitted from the first x-ray tube to a processor and downloading the sensor data obtained by detecting the x-rays emitted from the second x-ray tube to the processor. Prior to energizing the second x-ray tube, power to the first x-ray tube may be cut and the sensor data obtained by detecting the x-rays emitted from the first x-ray tube can be cleared from the sensor. In one aspect, displaying can include filtering the stereoscopic x-ray image to restrict viewing of a portion of the stereoscopic x-ray image corresponding to x-rays detected by the sensor from one of the x-ray tubes to viewing from one eye of a viewer at a position of the eye with respect to the display corresponding to a position of the one of the x-ray tubes with respect to the object. Filtering can include restricting an angle at which light from a pixel of a liquid crystal display can be viewed. In one aspect, displaying can include displaying a first portion of the stereoscopic x-ray image corresponding to x-rays detected by the sensor from the first x-ray tube to a first eye of a viewer and displaying a second portion of the stereoscopic x-ray image corresponding to x-rays detected by the sensor from the second x-ray tube to a second eye of the viewer. To provide an overall understanding, certain illustrative embodiments will now be described; however, it will be understood by one of ordinary skill in the art that the apparatus described herein can be adapted and modified to provide apparatus for other suitable applications and that other additions and modifications can be made without departing from the scope of the systems and methods described herein. Unless otherwise specified, the illustrated embodiments can be understood as providing exemplary features of varying detail, and therefore, unless otherwise specified, features, components, modules, and/or aspects of the illustrations can be otherwise combined, separated, interchanged, and/or rearranged without departing from the disclosed systems or methods. Additionally, the shapes and sizes of components are also exemplary and unless otherwise specified, can be altered without affecting the disclosed systems or methods. Throughout the entirety of the present disclosure, use of the articles “a” or “an” to modify a noun can be understood to be used for convenience and to include one, or more than one of the modified noun, unless otherwise specifically stated. FIG. 1 illustrates a schematic representation of a system 10 for producing stereoscopic x-ray images. A transformer 12 within housing 14 of system 10 is connected to a power supply 3 via power switch 16. Power switch 16 may be remotely located so as not to expose an operator to radiation. Transformer 12 converts incoming power from power supply 3 to provide a high voltage differential across the electrode pairs (not shown) of x-ray tubes 18a and 18b. X-ray tubes 18a, 18b operate in the manner of known x-ray tubes to emit x-rays. For example, current to the cathode of the electrode pair heats a filament, which sputters electrons to a tungsten anode at high speed. A high speed electron can knock loose an electron from a tungsten atom's lower orbital and an electron from a higher orbital can fall to the lower energy level, releasing a high energy x-ray photon. Transfer switch 20 can transfer current from x-ray tube 18a to x-ray tube 18b and vice versa. Switch 20 can include timer 22 for automatic transfer of current. Collimator tubes 24a, 24b absorb unwanted x-rays to effectively limit the emitted x-rays to a direction along their longitudinal axes 26a, 26b. In this manner, the emitted x-rays are filtered so that only those travelling essentially parallel to axes 26a, 26b and generally convergent on target 5 are allowed through the collimator tubes 24a, 24b. Pure aluminum disks 28a, 28b may be placed in the path of the x-ray beams to filter out low energy x-rays whose wave lengths are such that they would not penetrate the object and hence would not be useful for producing images. Image sensor 30 digitally captures the x-ray photons passing through object 5 and the digital sensor data captured by sensor 30 is input to processor 32 (as illustrated by arrow 34). Processor 32 processes the sensor data obtained from each x-ray tube 18a, 18b to obtain image data for a pair of two-dimensional images 36a, 36b that are displayed on display 38. The two resulting images 36a, 36b are displayed in a manner such that only the image for the x-ray tube corresponding to the viewer's eye position is received at that eye, thus providing a 3D image 36 to the user. Known methods for displaying 3D images may be utilized. For example, the images can be polarized and/or colored and viewed through corresponding polarized and/or colored eyeglasses. Preferably, the images can be displayed on a 3D LCD screen, such as the Sharp Actius™ RD3D. On such screens, the two images are overlapped, but use separate pixels for each image. An LCD filter restricts the angle at which light from the pixels can be viewed, such that the image corresponding to the viewer's left eye can only be viewed by the left eye and vice versa. Other types of displays include screens formed with ridges that restrict the viewing angle for each pixel; eyeglass video displays that present the separate images to the corresponding eye; 3D viewers using mirrors to reflect the corresponding image from two monitors to the respective eye of the viewer; and other means as are known in the art. FIG. 2 is a block diagram of a method 100 by which system 10 provides stereoscopic x-ray images for viewing. X-ray system 10 is activated (102) using power switch 16. When system 10 is activated, current flows (104) to transformer 12. Power switch 16 may limit the amount of current that flows to transformer 12 to that required for system 10 to obtain the image data for forming the stereoscopic image. Power switch 16 may work in conjunction with transfer switch 20 and timer 22 to limit the total time of exposure, i.e., the time during which the object 5 is exposed to x-rays. Transformer 12 converts (106) the incoming power to provide the necessary high voltage differential across the electrode pairs of a first of the x-ray tubes 18a, 18b so as to energize (108) the tube. For the sake of illustration, but not limitation, the systems and methods are described herein with x-ray tube 18a being the first energized x-ray tube and x-ray tube 18b being the second energized x-ray tube. It will be understood that the order in which the x-ray tubes are energized does not affect the operation of the systems or methods described. When x-ray tube 18a has been energized for a time sufficient to obtain sensor data at image sensor 28 for forming a digital image, as determined by timer 22 at block 110, switch 20 is activated to cut power to x-ray tube 18a, as at block 112. Image sensor 28 may download (114) the sensor data obtained from x-rays emanating from x-ray tube 18a to processor 30. After a time sufficient for image sensor 28 to clear, as determined by timer 22 at block 116, switch 20 is activated (118) such that the output from transformer 12 is directed to x-ray tube 18b to energize x-ray tube 18b (120). When x-ray tube 18b has been energized for a time sufficient to obtain sensor data at image sensor 28 for forming a digital image, as determined by timer 22 at block 122, switch 20 is activated to cut power to x-ray tube 18b, as at block 124. Timer 22 may operate in conjunction with switch 16 to limit power to transformer 12, such that when power to x-ray tube 18b is cut, switch 16 may be activated to cut power to transformer 12, as indicated by dashed block 126. Switch 16 may independently cut power to transformer 12 after a preset amount of time as a fail-safe measure. Image sensor 28 may download (128) the sensor data obtained from x-rays emanating from x-ray tube 18b to processor 30. For illustration purposes, downloading of the sensor data from image sensor 28 to processor 30 (blocks 114, 128) is shown following the cutting of power to x-ray tubes 18a, 18b. However, depending on the configuration of image sensor 28 and processor 30, image sensor 28 may download the sensor data to processor 30 while x-ray tubes 18a, 18b are energized or both during and after x-ray tubes 18a, 18b are energized. Processor 30 processes (130) the sensor data to obtain image data corresponding to a two-dimensional x-ray image for x-ray tube 18a and a two-dimensional x-ray image for x-ray tube 18b. The image data is forwarded (132) to display 36. Using the image data from processor 30, display 36 displays (134) the image data such that a viewer perceives a 3D x-ray image of the target, as described with relation to display 36. Although the stereoscopic x-ray system and method have been described relative to specific embodiments thereof, they are not so limited. Obviously many modifications and variations may become apparent in light of the above teachings. For example, timer 22 can be configured with power switch 16, or separately along power line 40 feeding transformer 12. Alternately, x-ray tubes 24a, 24b may each be located within a housing that may be attached together to form housing 14. Similarly, each x-ray tube 24a, 24b may have its own transformer 12 and transfer switch 20 may be configured with power switch 16 to transfer power between the transformers 12. Elements, components, modules, and/or parts thereof that are described and/or otherwise portrayed through the figures to communicate with, be associated with, and/or be based on, something else, can be understood to so communicate, be associated with, and or be based on in a direct and/or indirect manner, unless otherwise stipulated herein. Many additional changes in the details, materials, and arrangement of parts, herein described and illustrated, can be made by those skilled in the art. |
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abstract | The invention relates to compositions and methods for coating a zirconium alloy cladding of a fuel element for a nuclear water reactor. The composition includes a master alloy including one or more alloying elements selected from chromium, silicon and aluminum, a chemical activator and an inert filler. The alloying element(s) is deposited or are co-deposited on the cladding using a pack cementation process. When the coated zirconium alloy cladding is exposed to and contacted with water in a nuclear reactor, a protective oxide layer can form on the coated surface of the cladding. |
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046631100 | abstract | A fusion blanket includes a chamber wall, a multiplication section, an enrichment section and a reflector in radially outward succession, respectively. The chamber wall isolates the fusion reaction chamber from the remainder of the blanket. Fusion neutrons bombard atoms in the multiplication section to free further neutrons which are then available for breeding fuel. The enrichment section contains fertile fuel of sufficient dilution to maximize the enrichment rate and minimize fast fission. Materials may be included in the multiplication section and the enrichment section to reduce thermal neutron flux, thereby suppressing thermal fission. Additionally, tritium may be bred in both sections. The fertile material is exposed to neutron bombardment until the desired enrichment is achieved. The particles may be removed and mixed to minimize nonuniformities in enrichment. The particles may then be fabricated into fuel elements for fission reactors. |
047939621 | abstract | In order to transfer a bundle of rods of or from a nuclear fuel assembly into a storage case, the bundle is placed in a waiting position above a cassette provided with recesses. The rods are then introduced into the recesses by lowering them by gravity. When the cassette is full, it is brought into the extension of the case by interposing a transformation member. By simultaneously exerting a thrust on all the rods, the latter are compactly transferred into the case. |
047939613 | summary | FIELD OF THE INVENTION This invention relates to a method and a source for producing positively charged molecular ions of hydrogen (H.sub.2.sup.+) or deuterium ((D.sub.2.sup.+). BACKGROUND OF THE INVENTION Neutral beam injection has proven to be an effective way to heat plasmas in tokamaks as well as mirror devices. Multi-amperes of neutral atoms have already been obtained from deuterium ions for energies as high as 120 keV. In some future fusion reactors, such as the Mirror Fusion Test Facility at the Lawrence Livermore Laboratory, high currents of lower energy (40 keV) deuterium atoms are required in certain neutral beam lines. In that respect, it is more advantageous to form the neutral atoms from the molecular D.sub.2.sup.+ ions and accelerate them to twice the energy (80 keV). In passing through the gas neutralizer, these D.sub.2.sup.+ ions will first dissociate and will then be neutralized to form two atomic particles with half the original D.sub.2.sup.+ ion energy However, this technique is useful only if ion sources that can generate a high percentage (>70%) of D.sub.2.sup.+ ions are available. SUMMARY OF THE INVENTION One principal object of the present invention is to provide a novel method and apparatus for generating a high concentration of H.sub.2.sup.+ or D.sub.2.sup.+ ions by using a new and improved multicusp ion source. The basic principle in achieving a high percentage of H.sub.2.sup.+ or D.sub.2.sup.30 ions is to extract them from the source as soon as they are produced. Otherwise they will react with background gas molecules to form tri-atomic ions H.sub.3.sup.+ or D.sub.3.sup.+ or be dissociated by electrons. The former reaction H.sub.2.sup.+ + H.sub.2 .fwdarw.H.sub.3.sup.+ +H have a very short mean free path length .lambda.. Assuming a background neutral gas density of approximately 3. 3.times.10.sup.13 cm.sup.-3 and a cross-section .sigma. of approximately 6.times.10.sup.-15 cm.sup.2, 80=(n.sub.o .sigma.).sup.-1 is estimated to be about 5 cm. Thus the distance traversed by the H.sub.2.sup.+ ion before it arrives at the extaactor electrode cannot exceed this value. This in turn sets a limit on the length of the source chamber. Among the novel features of this invention is the provision of a short ion source, both physically and electrically. This is accomplished by placing the filaments close to the plasma grid which is connected electrically to the ion source shell. The plasma grid thus becomes part of the anode. Also, the length and width of the source is approximately 40 cm.times.10 cm, for example, but the depth is only about 6 cm, for example. Because the physical distance from the filaments to the plasma grid is substantially less than the mean free path for neutralization or capture of a H.sub.2.sup.+ ion, the ratio of the desired ion to total ions is about 80%. The same applies to D.sub.2.sup.+ ions. The positive ions are extracted from the source by a negative voltage which may vary widely, according to the application, from 300 volts or lower to 40 keV, or higher, for example. The source utilizes a multicusp magnetic field, produced by rows of magnets, for example, which may be of the samarium-cobalt type. Such magnetic field on the back plate reduces the effective path length and loss of the positive ions before they are extracted from the source. In turn, it increases the primary electron path length by making it difficult for these electrons to be lost to the surfaces protected by the magnetic field. |
041773853 | abstract | A method and apparatus for the storage of fuel in a stainless steel egg crate structure within a storage pool. Fuel is initially stored in a checkerboard pattern or in each opening if the fuel is of low enrichment. Additional fuel (or fuel of higher enrichment) is later stored by adding stainless steel angled plates within each opening, thereby forming flux traps between the openings. Still higher enrichment fuel is later stored by adding poison plates either with or without the stainless steel angles. |
description | The present disclosure relates to a passive fire response system configured to release an ionic liquid. Metal fires in a contained space are known as pool fires. A pool fire will burn at the surface where sodium is exposed to air and water. Often, a catch pan is placed in areas where metal fires are likely to occur to contain and/or mitigate interaction of the fire with structural materials. Metal fires generate a significant amount of heat. Moreover, when sodium reacts with water, hydrogen gas is produced resulting in hydrogen detonation with oxygen. At least one example embodiment provides a passive fire response system. In some example embodiments, a passive fire response system is configured to suppress a metallic fire. The system includes a reservoir containing an ionic liquid, at least one outlet in communication with the reservoir, a valve arranged between the reservoir and the outlet, a sensor configured to sense at least one of a hydrogen concentration and a temperature and/or heat, and a controller configured to open the valve and release the ionic liquid if an output from the sensor indicates that at least one of a threshold hydrogen concentration and a threshold temperature has been met and/or exceeded. In at least one example embodiment, the sensor is a temperature sensor and/or a hydrogen sensor. The passive fire response system is arranged in a chamber having a ceiling, and the sensor is positioned at the ceiling. In some example embodiments, the reservoir is located above the sensor. In at least one example embodiment, the chamber may house a sodium fast reactor. A catch pan is positioned below the sodium fast reactor. In some example embodiments, the controller is configured to open at least one valve when a temperature of at least about 75° C. is sensed by the sensor. In other example embodiments, the controller is configured to open at least one valve when a hydrogen concentration of at least about 50 parts per hundred million (pphm) is sensed by the sensor. In at least one example embodiment, the passive fire response system is gravity driven. In other example embodiments, the system can further include a pump configured to pump the ionic liquid from the reservoir through the at least one outlet in response to an output from the controller. In at least one example embodiment, the reservoir is refillable. The valve may be electronically actuated. In at least one example embodiment, the ionic liquid is asymmetric and does not crystallize at room temperature. The ionic liquid is liquid at room temperature. The ionic liquid reacts with sodium to produce stable, non-reactive salt byproducts. In at least one example embodiment, the passive fire response system includes a temperature control system configured to maintain the ionic liquid in the reservoir at a temperature ranging from about 10° C. to about 30° C. In some example embodiments, a method of passively suppressing a metallic fire is provided. The method includes sensing at least one of a temperature and a hydrogen concentration in a chamber, and automatically opening a valve to release an ionic liquid from a reservoir if the sensed at least one of the temperature and the hydrogen concentration is greater than or equal to at least one of a threshold temperature and a threshold hydrogen concentration has been met and/or exceeded. In at least one example embodiment, a method of manufacturing a passive fire response system is provided. The method includes positioning a reservoir containing an ionic liquid above a catch pan of a sodium fast reactor, establishing an outlet extending from the reservoir to the catch pan, positioning a sensor adjacent a ceiling of a chamber containing the sodium fast reactor, and connecting a control system to the sensor. In at least one example embodiment, the sensor is configured to sense at least one of a hydrogen concentration and a temperature generated by a metallic fire. The control system is configured to release the ionic liquid from the reservoir via the outlet if an output from the sensor indicates that the at least one of the hydrogen concentration and the temperature equals or exceeds at least one of a threshold hydrogen concentration and a threshold temperature. Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. Some detailed example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the example embodiments set forth herein. Accordingly, while example embodiments are capable of various modifications and alternative forms, example embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures. It should be understood that when an element or layer is referred to as being “on,” “connected to,” “coupled to,” or “covering” another element or layer, it may be directly on, connected to, coupled to, or covering the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout the specification. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It should be understood that, although the terms first, second, third, 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, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of example embodiments. Spatially relative terms (e.g., “beneath,” “below,” “lower,” “above,” “upper,” and the like) may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It should be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” 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. The terminology used herein is for the purpose of describing various example embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. 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, including 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. In at least one example embodiment, a passive fire response system configured to suppress a metallic fire is provided. As shown in FIGS. 1-3, in some example embodiments, the passive fire response system 10 is configured to suppress a metallic fire. The passive fire response system 10 can be located in a housing 12, such as a steam generator building, of a sodium fast reactor or other type of reactor. The system 10 includes a reservoir 14, at least one outlet 28 in communication with the reservoir 14, a valve 16 arranged between the reservoir 14 and the outlet 28, and a sensor 18. In at least one example embodiment, a catch pan 26 may be positioned on a floor 24 of the housing 12. The catch pan 26 is configured to catch sodium spilled from a reactor, such as a sodium fast reactor. In some example embodiments, the valve 16 may be electronically actuated. If more than one outlet 28 is included in the system 10, the system may include one valve 16 for each outlet 28 or a single valve for all outlets 28. In at least one example embodiment, the outlet 28 releases the ionic liquid 46 into and/or onto the catch pan 26 during a fire. In other example embodiments, the outlets 28 could include nozzles (not shown) that could provide targeted spraying of fire within the housing 12. In at least one example embodiment, the reservoir 14 contains an ionic liquid 46. The reservoir 14 may be refillable and may include an inlet (not shown) through which the reservoir 14 may be refilled. Suitable ionic liquids 46 include those set forth in U.S. Patent Application Publication No. 2011/0039467 to Xu, filed Aug. 9, 2010, the entire content of which is incorporated herein by reference thereto. In some example embodiments, the ionic liquid 46 is asymmetric and does not crystallize at room temperature. The ionic liquid 46 is liquid at room temperature. In at least one example embodiment, the ions of the ionic liquid 46 are able to react with sodium in the housing 12 to produce environmentally stable and unreactive salt byproducts. The ionic liquids 46 can also include mixtures of certain materials that produce a liquid with an ionic character, but without water or oxygen components. For example, a corn oil and sodium bicarbonate mixture may produce a non-aqueous liquid having an ionic character, which can mitigate the spread of fire and the corrosion of components as a result of fire byproducts. In at least one example embodiment, the sensor 18 is configured to sense at least one of a hydrogen concentration 50 and a temperature and/or heat 52 generated by a metallic fire 44. During metallic fires 44, high temperatures may be generated and hydrogen may be produced when sodium reacts with water. Maximum temperatures and hydrogen concentrations tend to occur at localized hot areas at a ceiling 22 and/or on walls of the housing 12. Thus, in some example embodiments, the sensor 18 is positioned on the ceiling 22 of the housing 12 so that the sensor 18 will quickly sense an increase in temperature and/or hydrogen concentration. In at least one example embodiment, the sensor 18 is a temperature sensor 54 that is configured to sense temperatures. The controller 20 receives an output from the temperature sensor, compares the output to a threshold temperature and determines whether the sensed temperature is greater than or equal to the threshold temperature. The threshold temperature is about 75° C. In some example embodiments, the sensor 18 is a hydrogen sensor 53 that is configured to sense a hydrogen concentration. The controller 20 receives the output from the hydrogen sensor, compares the output to a threshold hydrogen concentration, and determines whether the sensed hydrogen concentration is greater than or equal to the threshold hydrogen concentration. The threshold hydrogen concentration is about 50 parts per hundred million (pphm). Thus, the controller 20 receives an output from the sensor 18, and compares the output to at least one of the threshold temperature and threshold hydrogen concentration to determine if the thresholds have been met. If the at least one of the threshold hydrogen concentration and the threshold temperature has been met and/or exceeded, the controller 20 is configured to open the valve 16 and release the ionic liquid 46 from the reservoir 14 via the at least one outlet 28. In at least one example embodiment, the passive fire response system 10 may include both the temperature sensor 54 and the hydrogen sensor 53. When sodium reacts with water, hydrogen is produced and rapidly diffuses. The hydrogen sensor 53 can quickly sense a change in hydrogen concentration before the temperature is greater than or equal to the threshold temperature. Once the hydrogen threshold is sensed, the controller 20 receives an output from the hydrogen sensor 53 and the controller 20 then compares the output from the hydrogen sensor 53 to the threshold hydrogen concentration. If the output from the sensor 53 exceeds the threshold hydrogen concentration, the controller 20 sends a signal to open the valve 16 and release ionic liquid 46 from the reservoir 14 via at least one outlet 28. Once the ionic liquid 46 is released, the fire may or may not be controlled depending on how large the fire has become. If the fire is not under control, the temperature will continue to rise. The temperature sensor 54 senses temperature increases. The controller 20 receives an output from the temperature sensor 54 and compares the output to the threshold temperature. If the temperature meets and/or exceeds the threshold temperature, the controller 20 sends a signal to open one or more additional valves 16 and release additional ionic liquid 46 from the reservoir 14 via at least one outlet 28. Thus, the passive fire response system 10 may be tailored to release measured amounts of ionic liquids 46 based on the outputs from the sensors 18 that are received by the controller 20. In some example embodiments, the reservoir 14 is positioned above the sensor 18 and the release of the ionic liquid 46 from the reservoir 14 is gravity driven. In other example embodiments, as shown in FIG. 3, the passive fire response system 10 may include a pump 32 configured to pump the ionic liquid 46 from the reservoir 14 when the valve 16 is opened by the controller 20 in response to an output received from the sensor 18 if the controller 20 compares the output to the threshold temperature and/or threshold hydrogen concentration and determines that the thresholds have been met and/or exceeded. In at least one example embodiment, as shown in FIG. 3, the system 10 may also include a temperature control system 30 configured to maintain the ionic liquid 46 at a temperature ranging from about 10° C. to about 30° C. As shown in FIGS. 2 and 3, the passive fire response system 10 is positioned in the housing 12 that contains a sodium fast reactor 34. The sodium fast reactor includes a sodium inlet 36, a sodium outlet 38, a steam outlet 40, and a feed water inlet 42. By treating a metallic fire with an ionic liquid, stable, non-reactive salt byproducts are produced. The energy of formation of certain byproducts produced using this system is shown in FIG. 4. At certain temperature ranges during a metallic fire, these byproducts are more stable than the fire reaction products. For example, sodium carbonate and sodium chloride can be produced using the system 10, and these reaction products do not result in caustic corrosion that may otherwise be associated with metallic fires. In some example embodiments, a method of passively suppressing a metallic fire is provided. The method may include sensing at least one of a temperature and a hydrogen concentration in a chamber with a sensor. The method may also include automatically opening a valve to release an ionic liquid from a reservoir if the controller determines that an output from the sensor has met and/or exceeded at least one of a threshold temperature and a threshold hydrogen concentration. In another example embodiment, a method of manufacturing a passive fire response system is provided. The method may include positioning a reservoir containing an ionic liquid above a catch pan of a sodium fast reactor and/or other type of reactor, establishing an outlet extending from the reservoir to the catch pan, and positioning a sensor adjacent a ceiling of a chamber containing the sodium fast reactor. The sensor is configured to sense at least one of a hydrogen concentration and a temperature generated by a metallic fire. The method may also include connecting a control system to the sensor. The control system may be configured to release the ionic liquid from the reservoir via the outlet if an output from the sensor indicates that at least one of a threshold hydrogen concentration and a threshold temperature has been met and/or exceeded. The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure. |
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description | The nuclear thermal-hydraulic stability of a BWR is more stable at lower reactor output if the core flow rate is the same. In view of that point, an embodiment of the present invention is based on the concept below. The liquid (coolant) surface varying function of the spectral shift rod is applied to the non-rated power operation to drop a level of the water surface in a rising pipe at a low core flow rate near the low end at the automatic flow control range. Correspondingly, an amount of the coolant (water) in fuel assemblies is relatively reduced and a moderating rate of neutrons is also reduced, thereby producing a lower reactor output than the case of the water surface being not formed. This lowering of the reactor output necessarily increases an allowance for the nuclear thermal-hydraulic stability of a reactor core at the low end at the automatic flow control range. A BWR core according to a preferred embodiment of the present invention will be described below with reference to FIGS. 1 to 7. The BWR includes a core shroud 3 disposed inside a reactor pressure vessel 8. Within the core shroud 3, a core 1 is formed of a number of fuel assemblies 2 arrayed in the form of a square lattice. Upper end portions of the fuel assemblies 2 are supported by an upper lattice plate 4, which is fixed to an upper portion of the core shroud 3, in such a manner that the fuel assemblies 2 are restrained from moving horizontally. A core lower portion supporting plate 6 is mounted to the core shroud 3 and is positioned at a lower end portion of the core 1. Control rods 11 each having a cruciform cross-section are inserted between the fuel assemblies 2 through control rod guide pipes 5, and are driven by control rod driving mechanism 9 provided below the reactor pressure vessel 8. Fuel support pieces 10, shown in FIG. 2, are provided respectively at the top portion of the control rod guide pipes 5 and penetrates the core lower portion supporting plate 6. Four fuel assemblies 2 are inserted in and held by four insertion holes 10a formed in the fuel support piece 10, respectively. A load of the fuel assemblies 2 is finally supported by a bottom plate 8a of the reactor pressure vessel 8 through the fuel support piece 10, the control rod guide pipe 5, and a housing 9a of the control rod driving mechanism 9. In a side surface of the fuel support piece 10, four orifices are formed to take in a coolant (cooling water) flowing externally. These orifices lob are communicated respectively with the corresponding insertion holes 10a. An inner diameter d of the orifice 10b differs depending on the type of the reactor. In this embodiment, the diameter d is about 6.2 cm that is primarily used in BWRs having electric power of 1.1 million KW class. The fuel support piece 10 has a cross-shaped hole 10c which is formed between the four insertion holes 10a and receives the control rod 11. A plurality of internal pumps 20 are provided at the bottom the reactor pressure vessel 8. Each of the internal pumps 20 comprises a pump portion 21 including an impeller, and a motor portion 22 including a motor coupled to the impeller. The pump portion 21 is arranged in an annular passage 23 formed between the reactor pressure vessel 8 and the core shroud 3. The motor portion 22 is positioned outside the reactor pressure vessel 8. The core 1 is constructed, as shown in FIG. 3, by arranging each four fuel assemblies 2 around one control rod 11. Each control rod 11 is positioned adjacent to two sides of each fuel assembly 2. A detailed structure of the fuel assembly 2 will be described below with reference to FIGS. 4, 5, 6 and 7. The fuel assembly 2 comprises 74 fuel rods 12 arrayed in the form of a 9-row, 9-column square lattice, two water rods (spectral shift rods) 13 arrange in an area capable of accommodating seven fuel rods 12, a plurality of spacers 14 for holding spacings between adjacent ones of the fuel rods 12 and the water rods 13 to set values, and an upper tie plate 15 and a lower tie plate 16 for holding respectively upper and lower end portions of the fuel rods 12 and the water rods 13. A channel box 17 surrounds an outer periphery of a bundle of fuel rods 12 held together by the fuel spacers 14. Each of the fuel rods 12 comprises, though not shown, a cladding pipe which is made of a zirconium alloy and is filled with uranium fuel pellets containing U-235, U-238, etc. The fuel rods 12 include full-length fuel rods 12a having a fuel effective length L (corresponding to a portion where the fuel pellets are present) equal to a normal full length, and partial-length fuel rods 12b having a fuel effective length L shorter than that of the full-length fuel rods 12a. The total length of the partial-length fuel rod 12b is shorter than that of the full-length fuel rods 12a. The fuel assembly 2 is made up of 66 full-length fuel rods 12a and 8 partial-length fuel rods 12b. The partial-length fuel rods 12b are arranged in the second layer counting from the outermost side, as shown in FIG. 5. The lower tie plate 16 comprises, as shown in FIG. 6, a lower end portion 16a and a fuel rod holding portion 16b. The lower end portion 16a has an opening formed therein for introducing the cooling water supplied through the insertion hole 10a in the fuel support piece 10. The fuel rod holding portion 16b has a plurality of through holes 18 for introducing the cooling water to a cooling water passage 19 formed between the fuel rods 12, and holds the lower end portions of the fuel rods 12. A flow passage area ratio r (=S1/S2) of a total cross-sectional area (total cross-sectional area as viewed in a section Bxe2x80x94B in FIG. 6) S1 of all the through holes 18 to a total cross-sectional area (total cross-sectional area as viewed in a section Vxe2x80x94V in FIG. 4) S2 of the cooling water passage 19 in the channel box 17 is 0.3. The water rod 13 comprises, as shown in FIG. 7, a rising pipe 13a for introducing upward the cooling water introduced from the interior of the lower tie plate 16, and a falling pipe 13b communicated with an upper end portion of the rising pipe 13a for introducing downward the cooling water introduced from the rising pipe 13a. The rising pipe 13a has a cooling water inlet 25 formed at its lower end portion. The cooling water inlet 25 is positioned at the same height as (or lower than) the fuel rod holding portion 16b. The falling pipe 13b has a cooling water outlet 26 formed at its lower end portion. A height (outlet height) h from an upper surface of the fuel rod holding portion 16b to the cooling water outlet 26 is set to satisfy the following relationship: xe2x88x922.1r2+2.2rxe2x88x920.3xe2x89xa6(h/L) less than xe2x88x922.2r2+1.8r+0.04xe2x80x83xe2x80x83(1) The upper surface of the fuel rod holding portion 16b lies substantially at the same level as the lower end position of the fuel effective length L of the fuel rod 12. The position at which the rising pipe 13a of the water rod 13 communicates with the falling pipe 13b thereof lies near (or above) the upper end of the fuel effective length L of the full-length fuel rod 12a. The height from the upper surface of the fuel rod holding portion 16b to the communicating portion between the rising pipe 13a and the falling pipe 13b is about 3.7 m (the fuel effective length L). The operation of this embodiment will be described below. Upon driving of the internal pumps 20, the cooling water is forced to flow in a lower plenum 24 through the annular passage 23. The cooling water flows into the interior of the fuel support piece 10 through the orifices 10b, and is then introduced to the interior of the lower tie plate 16 through a cooling water passage formed in the fuel support piece 10. Most of the cooling water flows into the cooling water passage 19 via the through holes 18 to cool the fuel rods 12a and 12b. Because of a pressure loss due to a throttling effect developed by the through holes 18, the pressure of the cooling water after having passed the through holes 18 is lower than the pressure of the cooling water before passing the through holes 18. The remainder of the cooling water introduced to the interior of the lower tie plate 16 flows into the rising pipe 13a of the water rod 13 through the cooling water inlet 25. After rising in the rising pipe 13a, the cooling water falls in the falling pipe 13b and then flows out externally of the water rod 13 through the cooling water outlet 26. Since the pressure loss caused by the through holes 18 is negligible for the flow of the cooling water passing the water rod 13, a surface of the cooling water (liquid) is formed in the rising pipe 13a at a level corresponding to a pressure difference resulted from the pressure loss due to the throttling effect developed by the through holes 18. More specifically, a height (water surface level) H from the upper surface of the fuel rod holding portion 16b to the water surface formed in the rising pipe 13a is expressed by; H=(P1xe2x88x92P2)/(xcfx81xc3x97g)xe2x80x83xe2x80x83(2) where P1 is the pressure at the cooling water inlet 25, P2 is the pressure at the cooling water outlet 26, xcfx81 is the density of the cooling water in the rising pipe 13a, and g is the acceleration of gravity. Since the pressure P2 is reduced as the outlet height h increases, the water surface level H rises as the outlet height h increases. In this embodiment, the problems in the rated power operation and the non-rated power operation are solved by utilizing such a property of the water surface level in the rising pipe 13a. Specifically, in the rated power operation, the cooling water is always filled in the rising pipe 13a, and therefore influences of a transient event can be suppressed with sufficient reliability. Also, in the non-rated power operation, the water surface level in the rising pipe 13a is lowered to reduce an amount of the cooling water in the fuel assemblies 2, whereby the reactor output can be suppressed to improve the nuclear thermalhydraulic stability sufficiently. These two types of functions will be described below one by one. First, the inventors studied influences of the outlet height h and the water surface level H in the rated power operation, and obtained results shown in FIG. 8. The results of FIG. 8 were obtained by employing a core (comparative core) having the same structure as the core 1 of this embodiment, and determining values of the water surface level H with analysis while the outlet height h was changed variously, on condition that the comparative core is at the rated power and the core flow rate is minimum, i.e., that the reactor output is 100% of the rated value and the core flow rate is 90% of the rated value. Incidentally, the flow passage area ratio r in the comparative core is fixed to 0.3 as with this embodiment. The rising pipe 12a in the comparative core has however no limitations in length. In the graph of FIG. 8, the horizontal axis represents the outlet height h in units of nodes scaled by 24-division of the fuel effective length L. The water surface level H represented by the vertical axis means the height (m) from the upper surface of the fuel rod holding portion 16b to the water surface. As is apparent from FIG. 8, as the outlet height h increases, the water surface level H also increases. For example, the water surface level H takes H≈2.6 (m) at h=1 (node), takes H≈3.7 (m) at h≈4.5 (node), and amounts to H≈7.2 (m) at h≈12 (node). Accordingly, assuming that the length of the rising pipe 13a is, e.g., 3.7 m corresponding to the fuel effective length L, if the coolant outlet 26 is positioned near the upper surface of the fuel rod holding portion 16b (namely, h≈0) as disclosed in the above-cited JP, A, 63-73187, U.S. Pat. No. 5,023,047, U.S. Pat. No. 5,640,435, and Hitachi Hyoron, Vol. 74, No. 10 (1992), the water surface is formed at a level corresponding to H≈2.5 m, and a portion of the rising pipe 13a above the water surface becomes a vapor zone. On the other hand, if the outlet height h is set to satisfy hxe2x89xa74.5, Hxe2x89xa73.7 (m) is obtained, thus meaning that the water surface is not formed in the rising pipe 13a and the rising pipe 13a is fully filled with the cooling water. In this case, a limit height h0 of the outlet height h capable of filling the rising pipe 13a with the cooling water is 4.5 (node). Additionally, the reason why the water surface level H does not change smoothly with respect to an increase of the outlet height h in FIG. 8 is that the cross-sectional area of the cooling water passage in the fuel assembly 2 is partially reduced at the positions of the fuel spacers 14 and the pressure loss is increased correspondingly. Such an h-H characteristic also varies depending on the flow passage area ratio r. Specifically, a larger flow passage area ratio r reduces the throttling effect developed by the through holes 18 and hence the pressure loss, whereby an increasing rate of the water surface level H with respect to the outlet height h lowers. As a result, the limit height h0 of the outlet height h capable of filling the rising pipe 13a with the cooling water is increased. Then, the inventors studied influences of the limit height h0 of the outlet height h in the rated power operation, and obtained results shown in FIG. 9. The characteristic of FIG. 9 was obtained by, as with the case of FIG. 8, employing a core (comparative core) having the same structure as the core 1 of this embodiment, and determining values of the limit height h0 of the outlet height h with analysis, at which H=3.7 is obtained, while the flow passage area ratio r was changed variously from 0.2 to 0.4, on condition that the comparative core is at the rated power and the core flow rate is minimum. Incidentally, in the graph of FIG. 9, the vertical axis represents the limit height h0 as a relative value with the fuel effective length L set to 100%. As is apparent from FIG. 9, as the flow passage area ratio r increases, the limit height h0 also increases. For example, the limit height h0 takes h0≈6 (%) at r=0.2, h0≈17 (%) at r=0.3, and h0≈24 (%) at r=0.4. The characteristic curve of FIG. 9 is expressed by: h0=xe2x88x92210r2+220rxe2x88x9230xe2x80x83xe2x80x83(3) In a region lying on and above the characteristic curve expressed by the formula (3), i.e., in a region meeting; h0xe2x89xa7xe2x88x92210r2+220rxe2x88x9230xe2x80x83xe2x80x83(4) Hxe2x89xa73.7 is obtained. This means that when the length of the rising pipe 13a is 3.7 m corresponding to the fuel effective length L, the rising pipe 13a can be kept fully filled with the cooling water. Accordingly, if the outlet height h (m) satisfies the following relationship on condition that the flow passage area ratio r is in the range of 0.2xe2x89xa6rxe2x89xa60.4; h/Lxe2x89xa7xe2x88x922.1r2+2.2rxe2x88x920.3xe2x80x83xe2x80x83(5) the rising pipe 13a of 3.7 m can be kept fully filled with the cooling water. In the core 1 of this embodiment, it is possible to always maintain the water surface level H not lower than 3.7 m and to keep the rising pipe 13a of 3.7 m fully filled with the cooling water during the rated power operation by satisfying the conditions of 0.2xe2x89xa6rxe2x89xa60.4 and xe2x88x922.1r2+2.2rxe2x88x920.3xe2x89xa6h/L. Accordingly, unlike the conventional structure wherein the water surface is formed in the rising pipe during the rated power operation, if there should occur a transient event such as an abrupt increase of the core flow rate due to, e.g., an abnormal condition occurred in the control system for the internal pumps 20, a rising rate of the reactor output would be small because the rising pipe 13a is originally fully filled with the cooling water. As a result, this embodiment can suppress influences of the transient event with sufficient reliability. In other words, safety of the reactor can be further improved. While the above description has been made, by way of example, in connection with the case under conditions of the core being at the rated power and the core flow rate being 90% of the rated value, when the core flow rate is larger than 90% of the rated value, a value of the right side (P1-P2) in the formula (2) becomes larger and the water surface level H rises as compared with that resulted in the above case of the minimum core flow rate. Next, the inventors studied influences of the outlet height h and the water surface level H in the non-rated power operation during which the core flow rate and the reactor output are lower than those in the rated power operation, and obtained results shown in FIG. 10. The results of FIG. 10 were obtained by employing a core (comparative core) having the same structure as the core 1 of this embodiment, and determining values of the water surface level H with analysis while the outlet height h was changed variously, under condition at the above-described low end at the automatic flow control range in the non-rated power operation (here, on condition that the reactor output is 90% of the rated value and the core flow rate is 65% of the rated value). Incidentally, as with the case of FIG. 8, the flow passage area ratio r is fixed to 0.3 and the rising pipe 12a has no limitations in length. The horizontal axis and the vertical axis represent the same parameters as those in the graph of FIG. 8. As is apparent from FIG. 10, similarly to the case of FIG. 8, as the outlet height h increases, the water surface level H also increases. However, the values of the water surface level H are smaller as a whole than those in FIG. 8. For example, the water surface level H takes H≈1.4 (m) at h=1 (node), H≈3.7 (m) at h≈9.5 (node), and H≈4.6 (m) at h≈12 (node). Accordingly, assuming that the length of the rising pipe 13a is, e.g., 3.7 m corresponding to the fuel effective length L, if the outlet height h is set to satisfy h less than 9.5, the water surface appears in the rising pipe 13a, and a vapor zone is formed in a portion of the rising pipe 13a above the water surface. In this case, a limit height h1 of the outlet height h capable of forming the water surface in the rising pipe 13a is 9.5 node. Then, the inventors studied influences of the limit height h1 of the outlet height h in the non-rated power operation, and obtained results shown in FIG. 11. The characteristic of FIG. 11 was obtained by, as with the case of FIG. 9, determining values of the limit height h1 of the outlet height h with analysis, at which H=3.7 is obtained, while the flow passage area ratio r was changed variously from 0.2 to 0.4. In the graph of FIG. 11, the vertical axis represents the limit height h1 as a relative value like that in FIG. 9. As is apparent from FIG. 11, similarly to the case of FIG. 9, as the flow passage area ratio r increases, the limit height h1 also increases. However, an increasing rate of the limit height h1 is smaller than in FIG. 9. The reason is that because the cooling water outlet 26 is positioned much above the upper surface of the fuel rod holding portion 16b, the pressure loss in the cooling water passage 19 corresponding to a level difference from the upper surface of the fuel rod holding portion 16b to the cooling water outlet 26 is increased and the influence of the flow passage area ratio r is reduced. Further, the values of the limit height h1 itself are larger as a whole than those in FIG. 9. For example, the limit height h1 takes h1≈32 (%) at r=0.2, h1≈37 (%) at r=0.3, and h1≈41 (%) at r=0.4. The characteristic curve of FIG. 11 is expressed by: h1=xe2x88x92220r2+180r+4xe2x80x83xe2x80x83(6) In a region below the characteristic curve expressed by the formula (6), i.e., in a region meeting; h1 less than xe2x88x92220r2+180r+4xe2x80x83xe2x80x83(7) H less than 3.7 is obtained. This means that when the length of the rising pipe 13a is 3.7 m corresponding to the fuel effective length L, the water surface can be formed in the rising pipe 13a. Accordingly, if the outlet height h (m) satisfies the following relationship on condition that the flow passage area ratio r is in the range of 0.2xe2x89xa6rxe2x89xa60.4; h/L less than xe2x88x922.2r2+1.8r+0.04xe2x80x83xe2x80x83(8) the water surface can be formed in the rising pipe 13a of 3.7 m and a vapor zone can be formed in a portion of the rising pipe 13a above the water surface. In the core 1 of this embodiment, it is possible to set the water surface level H to be lower than 3.7 m and to form the water surface in the rising pipe 13a and a vapor zone above the water surface at least at the low end at the automatic flow control range in the non-rated power operation by satisfying the conditions of 0.2xe2x89xa6rxe2x89xa60.4 and h/L less than xe2x88x922.2r2+1.8r+0.04. With this embodiment, therefore, the void fraction in the fuel assemblies 2 can be increased to reduce the neutron moderating effect, whereby the reactor output can be suppressed to improve the nuclear thermal-hydraulic stability of the core 1 sufficiently in the non-rated power operation. Additionally, it is a principal rule that operation of the reactor below the core flow rate range at the rated power is performed, as mentioned above, when the reactor is started and stopped. During such operation, a possibility that there occurs an event like an abrupt increase of the core flow rate, such as assumed in the above (1), is much lower than during the rated power operation. Therefore, the formation of the water surface in the rising pipe 13a, when the reactor is in the low core flow rate range as encountered in the starting and stopping periods thereof, hardly raises significant problems in comparison with the period of the rated power operation. According to this embodiment, as described above, since the outlet height h is set to satisfy the relationship of xe2x88x922.1r2+2.2rxe2x88x920.3xe2x89xa6h/L less than xe2x88x922.2r2+1.8r+0.04 under condition of 0.2xe2x89xa6rxe2x89xa60.4, influences of the transient event during the rated power operation can be suppressed with sufficient reliability, while the nuclear thermal-hydraulic stability of the core during the non-rated power operation can be sufficiently improved. This embodiment can also provide an advantage below. In the conventional structure wherein the water surface is formed in the rising pipe during the rated power operation, no problems occur in usual reactor output control because the level of the water surface in the rising pipe can be approximately calculated based on the core flow rate. However, when there is a need for achieving a core control ability with higher accuracy, it is required to actually measure the water surface level by a detector or the like. Manufacture of such a detector or the like pushes up a cost and reduces economy of the reactor. Also, a difficulty arises in installing the detector in a limited space inside the fuel assembly. According to this embodiment, the rising pipe 13a is fully filled with water during the rated power operation. Thus, since the reactor output control is performed on condition that the rising pipe 13a is always fully filled with water, highly accurate control can be achieved in this embodiment without providing such a detector or the like. As a result, this embodiment can improve economy of the reactor in comparison with the conventional structure. The above-mentioned advantages can also be provided in the case of using fuel assemblies having the fuel effective length L other than 3.7 m. Specifically, neutrons leak in a considerable amount to the outside of the core near at the upper end of the fuel effective length L, and change of the fuel effective length L at the upper end of the fuel effective causes no significant influence upon the pressure loss characteristic in the lower portion of the fuel assembly 2. Thus, even if the fuel effective length L is changed on the order of 0.1 m, the same advantages as described above can be obtained. The through holes 18 in the fuel rod holding portion 16b are simply cylindrical in shape, and the total cross-sectional area S1 of the through holes 18 as viewed in the section taken along line Bxe2x80x94B in FIG. 6 gives a minimum value of the total cross-sectional area S1. When the through holes 18 have, for example, any other complex shape, the total cross-sectional area S1 is given by a minimum total cross-sectional area of the through holes 18 in the direction of height thereof. In this embodiment, the orifices 10b in the fuel support piece 10 are formed in the side surface of the fuel support piece 10. However, so long as the same pressure loss characteristic is obtained by the through holes 18 which restrict an expanded flow of the cooling water, the orifices 10b may be formed in a lower surface, an oblique surface as viewed from the horizontal surface, or a curved surface. Further, the shape of each orifice 10b is not necessarily required to be circuit, but may be, e.g., elliptic, rectangular or triangular so long as the same pressure loss characteristic is obtained based on the restriction of an expanded flow of the cooling water. The water rod 13 is not necessarily required to have the structure shown in FIG. 7. So long as the conditions of the above formulae (5) and (8) are satisfied, the water rod 13 may have the structure of a water rod having a rising passage and a falling passage, as disclosed in JP, A, 63-73187 and JP, B, 7-89158, for example. Also, the overall length of the water rod 13 is not limited to 3.7 m, but may be longer than 3.7 m. Further, the position at which the rising pipe 13a and the falling pipe 13b communicate with each other is not necessarily limited to the vicinity of the upper end of the water rod 13. It is just essential that the length of the communicating position between both the pipes to the lower end of the water rod is about 3.7 m or more. These modifications can also provide similar advantages as described above. While this embodiment uses the fuel assembly having a 9-row, 9-column array of fuel rods, the present invention is also applicable to a fuel assembly having a 10-row, 10-column array of fuel rods. While the inner diameter d of the orifices 10b in the fuel support piece 10 is set to about 6.2 cm in this embodiment, the inner diameter d may have other value in some cases. In an advanced boiling water reactor (ABWR), for example, the fuel support piece 10 having the orifices 10b with the inner diameter d of about 5.6 cm is primarily employed. A BWR core including such a fuel support piece will be described below as another embodiment of the present invention. In another embodiment, the construction except the fuel support piece is the same as that of the above embodiment (first embodiment) having been described in connection with FIGS. 1 to 7. (A) Case of d≈5.6 (cm) For a core which has the same structure as the first embodiment and includes the fuel support piece 10 having the orifices 10b with the inner diameter d of about 5.6 cm, the inventors studied influences of the limit height h0 of the outlet height h in the rated power operation, and obtained results shown in FIG. 12. Also, the inventors studied influences of the limit height h1 of the outlet height h at the low end at the automatic flow control range (where the reactor output and the core flow rate are respectively about 70% and about 50% of those in the rated power operation), and obtained results shown in FIG. 13. The FIGS. 12 and 13 correspond respectively to FIGS. 9 and 11 for the first embodiment. As is apparent from FIG. 12, for example, the limit height h0 takes h0≈12 (%) at r=0.2, h0≈=24 (%) at r=0.3, and h0≈28 (%) at r=0.4. The characteristic curve of FIG. 12 is expressed by: h0=xe2x88x92420r2+340rxe2x88x9240xe2x80x83xe2x80x83(9) In a region lying on and above the characteristic curve expressed by the formula (9), i.e., in a region meeting; h0xe2x89xa7xe2x88x92420r2+340rxe2x88x9240xe2x80x83xe2x80x83(10) Hxe2x89xa73.7 is obtained. This means that when the length of the rising pipe 13a is 3.7 m corresponding to the fuel effective length L, the rising pipe 13a can be kept fully filled with the cooling water during the rated power operation. Accordingly, if the outlet height h (m) satisfies the following relationship on condition that the flow passage area ratio r is in the range of 0.2xe2x89xa6rxe2x89xa60.4; h/Lxe2x89xa7xe2x88x924.2r2+3.4rxe2x88x920.4xe2x80x83xe2x80x83(11) the rising pipe 13a of 3.7 m can be kept fully filled with the cooling water. As is apparent from FIG. 13, for example, the limit height h1 takes h1xe2x88x9254 (%) at r=0.2, h1≈56 (%) at r=0.3, and h1≈58 (%) at r=0.4. The characteristic curve of FIG. 13 is expressed by: h1=xe2x88x9253r2+50r+46xe2x80x83xe2x80x83(12) In a region below the characteristic curve expressed by the formula (12), i.e., in a region meeting; h1 less than xe2x88x9253r2+50r+46xe2x80x83xe2x80x83(13) H (the water surface level in the rising pipe) less than 3.7 is obtained. This means that when the length of the rising pipe 13a is 3.7 m corresponding to the fuel effective length L, the water surface can be formed in the rising pipe 13a. Accordingly, if the outlet height h (m) satisfies the following relationship on condition that the flow passage area ratio r is in the range of 0.2xe2x89xa6rxe2x89xa60.4; h/L less than xe2x88x920.53r2+0.5r+0.46xe2x80x83xe2x80x83(14) the water surface can be formed in the rising pipe 13a of 3.7 m and a vapor zone can be formed in a portion of the rising pipe 13a above the water surface. With this embodiment wherein the inner diameter d of the orifices 10b in the fuel support piece 10 is set to about 5.6 cm, similar advantages as those in the first embodiment can also be obtained by setting the outlet height h so as to satisfy the condition of: xe2x88x924.2r2+3.4rxe2x88x920.4xe2x89xa6(h/L) less than xe2x88x920.53r2+0.5r+0.46 (B) Case of Inner Diameter d being Larger Than 5.6 cm but Smaller Than 6.2 cm Comparing the first embodiment with the embodiment (second embodiment) described in the above (A), it is seen that the relationship between the outlet height h and the water surface level H is changed depending on the inner diameter d of the orifices 10b formed in the side surface of the fuel support piece 10. Accordingly, there exists some range of the outlet height h which can be used in one of the first and second embodiments, but cannot be used in the other. To cope with such a range of the outlet height h, two types of water rods 13 each comprising the rising pipe 13a and the falling pipe 13b require to be fabricated depending on the inner diameter d of the orifices 10b, thus resulting in an increased production cost. In view of the above, by taking the logical product of the conditions expressed by the formulae (5) and (8) and the conditions expressed by the formulae (11) and (12), the outlet height h can be used for any of d≈5.6 cm, d≈6.2 cm, and 5.6 cmxe2x89xa6dxe2x89xa66.2 cm. The resulting logical product is given by a region between the characteristic curve of FIG. 12 and the characteristic curve of FIG. 11, the region being expressed by: xe2x88x924.2r2+3.4rxe2x88x920.4xe2x89xa6(h/L) less than xe2x88x922.2r2+1.8r+0.04xe2x80x83xe2x80x83(15) Similar advantages as those in the first embodiment can also be obtained by a core constructed by loading fuel assemblies including the water rods 13 for each of which the outlet height h is set to satisfy the condition of the above formula (15). Further, since those fuel assemblies can be loaded in cores provided with fuel support pieces having orifices with its inner diameter d ranging from about 5.6 cm to about 6.2 cm, fuel economy can be improved. |
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description | The present invention relates to an irradiation planning apparatus for making, for example, an irradiation plan for a charged particle irradiation system that radiates charged particles to a target, an irradiation planning program, an irradiation plan determining method, and a charged particle irradiation system. Conventionally, there have been proposed an apparatus that conducts a heavy charged particle therapy by radiating charged particles to an affected area such as cancer cells. In a heavy charged particle therapy such as a carbon filament therapy, it is desirable to realize a uniform clinical effect in the target. For achieving this, it is possible to define a clinical dose which is the product of an absorbed dose and a relative biological effectiveness (RBE), and make an irradiation plan so that the clinical dose is uniform in the target. FIG. 4(A) is a diagram illustrating irradiation spots to which charged particles of a single ion species are to be radiated. FIG. 4(A) shows a longitudinal section of a target viewed from the lateral side of the traveling direction of the beam. In the apparatus that conducts a heavy charged particle therapy, as illustrated in the drawing, spots SP disposed on the surface perpendicular to the irradiation direction are arranged in the irradiation direction with respect to a tumor region 182 located behind a body surface 188, and thus the spots SP are arranged three-dimensionally. The apparatus that conducts a heavy charged particle therapy sequentially radiates a beam of ion species to the spots SP from the direction of the arrow illustrated in the drawing and conducts irradiation in a manner of filling the tumor region 182. FIG. 4(B) illustrates a depth dose distribution chart by such a carbon filament therapy. In this chart, depth distributions of a clinical dose 191, an RBE 192, and an ion species irradiation dose 193 are shown. In designing a clinical dose that is uniform in the target in the carbon filament therapy, the quality (LET) distribution of carbon filament for realizing this is determined almost uniquely. Here, when the RBE 192 involves errors 192a, 192b, large distortions 191a, 191b occur in the distribution of the clinical dose 191, and the clinical dose distribution can greatly deteriorate. RBE depends on quality of radiation (particle species or LET), dose level, cell strain, end point and so on, and RBE itself is accompanied by a large error. Therefore, it is desired to reduce the error in RBE for preventing significant deterioration in the clinical dose distribution. There have been proposed a method and an apparatus for charged particle beam irradiation capable of radiating charged particles from a plurality of directions by having a rotary irradiation device (see Patent Document 1). With this apparatus, since charged particles can be radiated from the plurality of directions, it is possible to reduce the irradiation dose on normal sites by widely dispersing the dose to be radiated to the normal sites. Radiation of the charged particles from the plurality of directions can also reduce an error in RBE. Increased irradiation directions, however, lead to several disadvantages. First, increased irradiation directions disadvantageously increase a burden on a staff engaged in the therapy. In addition, increased irradiation directions disadvantageously lead to a large increase in exposure volume of normal tissues. There is a disadvantage that a rotary gantry like a rotary irradiation device of Patent Document 1 is bulky. Also, there is a disadvantage that a rotary gantry for heavy charged particles has not been practically used in an actual therapy because of difficulties in its construction and operation. Besides the above, since occurrence of a delayed effect such as cerebral necrosis from the planned therapeutic volume (PTV) after the therapy is reported for part of sites such as a cerebral tumor, it is desired to develop an irradiation method capable of effectively controlling only cancer cells without injuring normal cells contained in a tumor. Patent Document 1: Japanese Patent Laid-open Publication No. 2000-202047 In light of the above problems, it is an object of the present invention to provide an irradiation planning apparatus, an irradiation planning program, an irradiation plan determining method, and a charged particle irradiation system capable of realizing irradiation with desirable dose distribution with respect to a target. The present invention provides an irradiation planning apparatus for determining an irradiation parameter of a charged particle irradiation system that radiates charged particles generated by an ion source to a target by accelerating the charged particles by means of an accelerator, the irradiation planning apparatus having composite irradiation parameter determining means that determines the irradiation parameter with respect to one target by combining the charged particles of a plurality of kinds of ion species, or an irradiation planning program, an irradiation plan determining method, and a charged particle irradiation system for the irradiation planning apparatus. In the present invention, it is possible to provide an irradiation planning apparatus, an irradiation planning program, an irradiation plan determining method, and a charged particle irradiation system capable of achieving irradiation with desirable dose distribution with respect to one target. Hereinafter, one embodiment of the present invention will be described by referring to the attached drawings. FIG. 1 is a block diagram showing a configuration of a charged particle irradiation system 1. The charged particle irradiation system 1 includes a plurality of ion sources 2 (2A, 2B, 2C), a multiple ion source connector 3, a linear accelerator 4, a synchrotron 5, a conveyance system 6, a fixed radiator 20, a rotary gantry 22, and a controlling apparatus 50 for controlling these. To the controlling apparatus 50, a planning apparatus 70 that transmits therapy planning data is connected. The ion source 2 is a device that removes an electron from an atom to generate an ion, and includes a first ion source 2A for drawing an ion species of the first kind, a second ion source 2B for drawing an ion species of the second kind, and a third ion source 2C for drawing an ion species of the third kind. The first to third ion sources 2 are configured to generate different kinds of ions, e.g., oxygen ions, carbon ions, and helium ions, respectively. The multiple ion source connector 3 is a connector that selectively connects the first ion source 2A to the third ion source 2C to the linear accelerator 4. The multiple ion source connector 3 appropriately switches the ion source 2 for supplying the linear accelerator 4 with ion species, to any one of the first ion source 2A to the third ion source 2C under the control by the controlling apparatus 50. The linear accelerator 4 is a kind of accelerator, and accelerates the charged particles supplied from the ion source 2 to have a predetermined energy by means of an electromagnet, and supplies the charged particles to the synchrotron 5. The synchrotron 5 is a kind of accelerator, and further accelerates the charged particles incident from the linear accelerator 4 on a circling orbit by means of an electromagnet to make the charged particles have high energy. The conveyance system 6 conveys the charged particles drawn by an emitter 11 from the synchrotron 5 to an irradiation device 25 by means of an electromagnet. The emitter 11 is provided at a connecting part between the synchrotron 5 and the conveyance system 6, and emits the charged particles to the conveyance system 6 from the synchrotron 5 under the control by the controlling apparatus 50. A switch 12 is provided on the conveyance system 6, and switches the therapy rooms 9 (9A, 9B, 9C) accommodating the irradiation device 25 to which the charged particles conveyed by the conveyance system 6 are to be conveyed under the control by the controlling apparatus. The fixed radiator 20 provided in each of the therapy rooms 9A, 9B radiates charged particles from the irradiation device 25 provided at its trailing end. The rotary gantry 22 provided in the therapy room 9C can change the irradiation direction of charged particles by rotation, and radiates charged particles from the irradiation device 25 at the trailing end toward the changed irradiation direction. The irradiation device 25 controls a position in the XY direction of charged particles (planar direction perpendicular to the radiation direction of charged particles) by means of a X-direction scanning magnet and a Y-direction scanning magnet, and controls a stop position in the Z direction of charged particles (traveling direction of charged particles) by means of an energy changing part (range shifter), and measures the irradiation dose of charged particles for each irradiation spot by means of a scanning monitor. In other words, the irradiation device 25 functions as a scanning irradiation device that controls the three-dimensional position of an irradiation spot of charged particles while measuring the irradiation dose. This scanning irradiation device three-dimensionally scans a pencil beam in which charged particles are narrowed down, and conducts a therapy in a manner of filling the tumor. The controlling apparatus 50 has a CPU (central processing unit) 51 and a memory 52. The memory 52 stores various programs and data including a control program 60, current value changing pattern data 66, irradiation parameter data 67, and maximum depth data 68. The CPU 51 operates by using the data such as the current value changing pattern data 66, and the irradiation parameter data 67 in accordance with the program such as the control program 60. By this operation, the controlling apparatus 50 functions as an ion source switching section 61, an accelerator controlling section 62, an irradiation position controlling section 63, a stop position controlling section 64, and a dose monitoring section 65. The CPU 51 also functions as a multiple ion species irradiation controller that conducts a control of making the ion source switching section 61 switch the ion species, making the accelerator controlling section 62 accelerate with an appropriate current, and making the irradiation position controlling section 63 and the stop position controlling section 64 sequentially change the irradiation spot. The ion source switching section 61 conducts a control of switching the ion source for generating charged particles to either one of the first ion source 2A to the third ion source 2C. This makes it possible to switch the ion species between spills. The accelerator controlling section 62 reads out an appropriate current value changing pattern from the current value changing pattern data 66 in accordance with the ion species supplied from the ion source 2, and controls the current value to be flown in the electromagnet of the accelerator 4 in accordance with this current value changing pattern. The irradiation position controlling section 63 controls and drives the X-direction scanning magnet and the Y-direction scanning magnet of the irradiation device 25 to control the position in the plane perpendicular to the traveling direction (position in the XY direction) of charged particles to be emitted to the target. The stop position controlling section 64 controls and drives the energy changing part of the irradiation device 25 to control the stop position of charged particles in the traveling direction of the charged particles (Z direction). The dose monitoring section 65 acquires an irradiation dose for each irradiation spot measured by a dose monitor of the irradiation device 25. The current value changing pattern data 66 is pattern data of current values to be flown in the electromagnets of the linear accelerator 4, the synchrotron 5, and the linear accelerator 4 for individual ion species. The memory 52 storing the current value changing pattern data 66 functions as a current pattern memory. The irradiation parameter data 67 is data including spot number, X position, Y position, energy, irradiation amount, and ion species. The energy indicates an irradiation position in the Z direction. The irradiation amount indicates the number of charged particles to be radiated, or a dose. The ion species consists of appropriate information from which the ion species to be radiated can be identified, for example, ion species name, ion species number, or ion source ID indicating which one of the first ion source 2A to the third ion source 2C is to be used as the ion source. The irradiation parameter data 67 is received from the planning apparatus 70 and stored in the memory 52. The maximum depth data 68 stores maximum depths of individual ion species that can be radiated by the charged particle irradiation system 1. These maximum depths are smaller in heavier ion species, and larger in lighter ion species. Therefore, the settings may be provided not for light ion species, but only for part of heavy ion species that can be used. Besides the above, the controlling apparatus 50 also executes a control of emitting charged particles from the emitter 11 and a control of switching the destination of irradiation of charged particles by the switch 12. The switching of the irradiation spot and the switching of the ion species by the controlling apparatus 50 may be conducted in an appropriate order. For example, after completion of irradiation to all the irradiation spots with one ion species, the ion species may be switched to the next ion species, or after irradiating a predetermined range of irradiation spots with all ion species, the irradiation spots may be switched to the next predetermined range of irradiation spots. The predetermined range of irradiation spots can be appropriately set in such a manner that it is the whole of the irradiation spots in the plane perpendicular to the irradiation direction at one depth position of the irradiation direction, or it is one irradiation spot. Since it is necessary to change the current value to be flown in the synchrotron 5 or the like in accordance with the current value changing pattern data 66 when the ion species is changed, it is desired to irradiate all the irradiation spots sequentially with each ion species. This charged particle irradiation system 1 allows generation of the charged particles of the plurality of kinds of different ion species by the ion source 2, and allows irradiation of one target with accelerated charged particles of various ion species while switching the plurality of kinds of ion species. The planning apparatus 70 is a computer having a CPU 71, a memory 72, an input part 74, and a display part 75, and functions as an irradiation planning apparatus or a therapy planning apparatus. The memory 72 stores various programs including a planning program 73 as an irradiation planning program, and various data. The CPU 71 operates using data in the memory 72 in accordance with a program such as the planning program 73. By this operation, the planning apparatus 70 generates the irradiation parameter data 67, and transmits the irradiation parameter data 67 to the controlling apparatus 50. The input part 74 is configured by input devices such as a keyboard and a mouse, and receives an input operation, for example, by a person who is planning the therapy. The display part 75 is configured by a display device such as a display for displaying characters and images, and displays various images including CT captured image, MRI image and PET image, and various regions (GTV, CTV, PTV) and so on. By means of the charged particle irradiation system 1 configured as described above, it is possible to execute an intensity modulated composite ion therapy (IMCIT) that radiates charged particles while modulating the beam intensity by using a plurality of kinds of ion species based on the irradiation parameter data 67. Next, an operation for creating the irradiation parameter data 67 using a plurality of kinds of ion species by the planning apparatus 70 will be described. The intensity modulated composite ion therapy of the present invention sequentially determines “which ion species m”, “to which spot i”, and “how many wi, m” is to be radiated, by inverse planning. The spot i indicates the spot number of the irradiation parameter data 67. First, the planning apparatus 70 selects the number of ion species M to be radiated, and the ion species, and creates a dose kernel for irradiation of each spot for each ion species. The dose kernel di, m(r) indicates a dose applied to a position r in a patient body by a pencil beam of ion species m radiated to the spot i. The dose kernel di, m(r) reflects physical characteristics of each ion species. The physical characteristics used herein include extension of beam due to scattering, and an amount of generated fragments, and LET (Linear Energy Transfer). In a therapy planning of the intensity modulated composite ion therapy, it is possible to determine the irradiation parameters (wi, m) for the purpose by formulating the evaluation index f of the repetitive operation by a least square method or the like depending on the purpose. <1> First Evaluation Index f As the first example, an evaluation index f can be calculated by Mathematical formula 1 and Mathematical formula 2 below. f ( w m ) = ∑ j ∈ T ( Q T o H ′ [ ∑ m = 1 M D j ( w m ) - D T m a x ] 2 + Q T u H ′ [ D T m i n - ∑ m = 1 M D j ( w m ) ] 2 ) + ∑ j ∈ O Q O o H ′ [ ∑ m = 1 M D j ( w m ) - D O m a x ] 2 [ Mathematical formula 1 ] D j ( w m ) = ∑ i = 1 N d i , m ( r j ) w i , m ≡ ∑ i = 1 N d i , m w i , m [ Mathematical formula 2 ] The evaluation index f represented by [Mathematical formula 1] consists of three terms. The first term and the second term are operations for a target. The target used herein refers to an irradiation region that is determined based on a tumor-invasion region specified by a physician or the like while an irradiation error or the like is taken into account. The third term is an operation for OAR (Organ At Risk). The first term represents a penalty for the value over the maximum allowable value, and is multiplication of QTO and H′ [(subtraction)]2. The (subtraction) part is a formula that subtracts a maximum dose DTmax which is the maximum allowable value, from a dose applied to each position j (three-dimensional position in the patient body, preferably specified with higher resolution than the resolution for the position specified by the spot i) of the target when wm nuclides of a plurality of kinds of ion species m are radiated. The H′ [ ] part represents a Heaviside function, and the value is fetched when the value of the (subtraction) part is positive, and zero is assigned when it is negative. Therefore, when the dose is less than or equal to the maximum allowable value, the first term is zero which is assigned for an appropriate value, and does not increase the evaluation index f. QTO is a penalty coefficient, and when it is set large, the value over the maximum allowable value calculated by H′ [(subtraction)]2 greatly influences the evaluation index f. The second term represents a penalty for the value under the minimum allowable value, and is multiplication of QTU and H′ [(subtraction)]2. The (subtraction) part is a formula that subtracts a dose applied to each position j (three-dimensional position in the patient body) of the target when wm nuclides of a plurality of kinds of ion species m are radiated from a minimum dose DTmin which is the minimum allowable value. The H′ [ ] part does not increase the evaluation index f when the dose is more than or equal to the minimum allowable value because the second term is zero which is assigned for an appropriate value. QTU is a penalty coefficient, and when it is set large, the value under the minimum allowable value calculated by H′ [(subtraction)]2 greatly influences the evaluation index f. The third term represents a penalty for the value over the maximum allowable value of dose that can be radiated to organ at risk, and is multiplication of QOO and H′ [(subtraction)]2. The (subtraction) part is a formula that subtracts a maximum dose DOmax which is the maximum allowable value, from a dose applied to each position j (three-dimensional position in the patient body) of the target when wm nuclides of a plurality of kinds of ion species m are radiated. The H′ [ ] part does not increase evaluation index f when the dose is less than or equal to the maximum allowable value because the first term is zero which is assigned for an appropriate value. QTO is a penalty coefficient, and when it is set large, the value over the maximum allowable value calculated by H′ [(subtraction)]2 greatly influences the evaluation index f. For example, assuming the case where a peripheral region of the target is set as OAR, and coefficient of a risk degree QOO of the third term is set at a large value, the number wi, m of ion species m to be radiated to each spot i is optimally determined so that the evaluation index f (wm) is minimum in the inverse planning that inversely calculates an optimum irradiation method from the optimum dose distribution. Therefore, by setting the coefficient of risk degree QOO at a large value, it is possible to determine “to which position”, “with which ion species”, and “how much” irradiation is to be made for minimizing the dose application to the peripheral region of the target while keeping a necessary and sufficient dose (first term, second term) for the target. By using the first evaluation index f, it is possible to increase dose concentration to the tumor, compared with the conventional example where only one kind of ion species is used. <2> Second Evaluation Index f As a second example, an evaluation index f can be calculated by Mathematical formula 3 below. f ( w m ) = ∑ j ∈ T ( Q T o H ′ [ ∑ m = 1 M D j ( w m ) - D T m a x ] 2 + Q T u H ′ [ D T m i n - ∑ m = 1 M D j ( w m ) ] 2 ) + ∑ j ∈ T ′ Q T o H ′ [ LET T ′ m i n - LET j ( w m = 1 , M ) ] 2 [ Mathematical formula 3 ] The third term of [Mathematical formula 3] represents a penalty for the case where the irradiation amount to a region T′ of high-grade tumor is less than the minimum allowable value, and is multiplication of QT′O and H′ [(subtraction)]2. The (subtraction) part is a formula that subtracts an energy amount LET applied to each position j (three-dimensional position in the patient body) of the target when wm nuclides of a plurality of kinds of ion species m are radiated, from a minimum energy amount LETT′min which is the minimum allowable value. The H′ H part does not increase the evaluation index f when the dose is more than or equal to the minimum allowable value because the third term is zero which is assigned for an appropriate value. QTO is a penalty coefficient, and when it is set large, the value under the minimum allowable value calculated by H′ [(subtraction)]2 greatly influences the evaluation index f. By adding the third term of [Mathematical formula 3] as described above, it is possible to provide a limit that prevents LET of a partial region (T′) in the tumor from being lower than a certain value LETTmin. By using the second evaluation index f, it is possible to provide an effective therapy in accordance with, for example, difference in radiation sensitivity between normal cells and cancer cells contained in the tumor. <3> Third Evaluation Index f As the third example, an evaluation index f can be calculated by the following Mathematical formula 4. f ( w m ) = ∫ α m i n α m ax ∑ j ∈ T ( Q T o H ′ [ ∑ m = 1 M D j ( α , w m ) - D T m a x ] 2 + Q T u H ′ [ D T m i n - ∑ m = 1 M D j ( α , w m ) ] 2 ) ϕ ( α ) ⅆ α [ Mathematical formula 4 ] In [Mathematical formula 4], parameter a defining a biological effect is varied within the range of assumed errors αmin≦α≦αmax, and a weight wm for each ion species with which dose distribution in the target falls within the allowable values shown by the following mathematical formula [5] for every a is optimally determined for individual ion species. Here, φ(α) represents probability (probability density function) of assuming α. D T m i n ≤ ∑ m = 1 M D j ( α , w m ) ≤ D T m ax [ Mathematical formula 5 ] By using this third evaluation index f, it is possible to provide a robust therapy that is insusceptible to relative biological effectiveness (RBE) and irradiation, and registration error. <4> Setting of Depth Limit for Individual Ion Species A dose kernel cannot be created for a depth exceeding the maximum accelerable energy for ion species (nuclide). For this reason, maximum depths for individual ion species are registered in the maximum depth data 68, and ion species that is selectable are limited. As a result, for the depth exceeding the maximum accelerable energy for a certain ion species, an ion species that is lighter than the certain ion species is radiated. For example, in a facility having a synchrotron capable of radiating 16 cm for oxygen, 22 cm for carbon, and 66 cm for helium, the position exceeding 22 cm is automatically irradiated with helium by registering the specification in the therapy plan, and imposing the limitation. As a result, the advantages of lower prices and smaller sizes of the heavy charged particle therapy apparatus equipped with the charged particle irradiation system 1 are obtained. By formulating the objective functions of inverse planning in conformance with the purpose as shown in <1> to <4> with the use of the flexibility associated with the use of a plurality of kinds of ion species, it is possible to automatically determine irradiation parameters that are consistent with the purpose. FIG. 2 is a flowchart of a process executed by the CPU 71 of the planning apparatus 70 to generate the irradiation parameter data 67 in accordance with the planning program 73. The CPU 71 executing this process functions as composite irradiation parameter determining means. First, the CPU 71 receives input of data about target/organ at risk based on data obtained by separate CT imaging from the input part 74 (step S1). This data input is made by a physician, for example by surrounding respective regions of GTV and CTV in a CT captured image displayed in the display part 75. GTV is a macroscopic tumor volume that can be observed in an image or by palpation, whereas CTV is a clinical target volume including GTV and a microscopic progression range. At this time, the planning apparatus 70 also permits input of an allowable evaluation value C for which the evaluation index f is a sufficiently small value. The CPU 71 determines an irradiation direction in which a pencil beam is radiated for the input data of target/organ at risk (step S2). This determination can be achieved by appropriate methods including input by an operator, or determination by the CPU 71 in accordance with a preset algorism for determining an irradiation direction. The CPU 71 determines an ion species to be radiated (step S3). Here, the number of ion species is determined as M, and ion species is determined as m=1, M. Since this determination of ion species depends on the ion species that can be radiated from the ion source 2, the determination may be made by reading out data of the ion species that can be radiated, preliminarily stored in the memory 72 of the planning apparatus 70. The determination may be conducted by an appropriate method, for example, by inputting a plurality of kinds of ion species (for example, three kinds) to be used among a plurality of kinds of ion species (for example, four kinds) that are selectable in the charged particle irradiation system 1, by a therapy planner, or by an appropriate algorism. The CPU 71 prescribes doses for a target/organ at risk (step S4). Here, a therapy planner inputs a maximum allowable value Dmax, a minimum allowable value Dmin and the like shown in [Mathematical formula 1] to [Mathematical formula 5] at the input part 74 under a physician's direction. The CPU 71 determines an irradiation position of a pencil beam (step S5). The irradiation position is determined by arranging beam spots densely three-dimensionally for the entire region of PTV (which is to be a target). The entire irradiation position determined in this manner is a target T, and each one of the irradiation positions is a spot to which a pencil beam of ion species is to be radiated. PTV refers to a planned target volume including CTV and an irradiation error. The CPU 71 sets the part corresponding to GTV in the irradiation position as a high-grade malignant target T′, and the periphery of the irradiation position as a protective region O which is OAR. The CPU 71 creates a dose kernel d (i, m) of a pencil beam (step S6). Here, i represents an irradiation position (spot ID), and m represents a volume. The CPU 71 determines an initial value of a weight w (i, m) of a pencil beam (step S7). This initial value is determined by the CPU 71 on the basis of a rough order regarding the number of nuclides to be radiated to the spot. The CPU 71 calculates a dose D based on the weight (step S8). This dose calculation gives candidates for the irradiation parameter data 67 that determines the position, the ion species, and the amount to be radiated. The CPU 71 derives an evaluation index f so that the dose is necessary and sufficient to the target, and exposure to organ at risk is not more than allowable values (step S9). The CPU 71 repeats steps S8 to S9 while updating the weight w (i, m) of the pencil beam and adding a variable n by 1 (step S11) until the evaluation index f is less than C or the variable n is larger than N (step S10: No). C represents an allowable evaluation value indicating that the evaluation index f is sufficiently small and allowable, and N represents the maximum number of repetition. Therefore, when the evaluation index f is less than C and is sufficiently small, or the maximum number of repetition is reached, the repetitive operation ends. As to updating of the weight w (i, m), it is desired to update the data of the entire region to be irradiated. Besides, the value currently stored and the value obtained by the calculation of this time may be compared for each spot, and the value of the spot may be updated when the value obtained by the calculation of this time is preferred. When the evaluation index f is less than C, or the variable n is larger than N (step S10: Yes), the CPU 71 outputs the irradiation parameter data 67 to the controlling apparatus 50 (step S12), and ends the process. Through these operations, the planning apparatus 70 can generate the irradiation parameter data 67 using a plurality of kinds of ion species. The controlling apparatus 50 of the charged particle irradiation system 1 can irradiate one target (irradiation region of one patient) with any one of the plurality of kinds of ion species switched in accordance with the irradiation parameter data 67. As described above, by having the ion sources 2A to 2C, and switching the energy and the ion species during a single irradiation from one direction by conducting switching of ion species, acceleration, drawing and irradiation, it is possible to realize any dose/dose distribution in the tumor. By the irradiation parameter data 67 thus generated, the arrangement of ion species to be radiated to the tumor is set, for example, in the manner as shown in the irradiation ion species distribution chart of FIG. 3(A). FIG. 3(A) is a longitudinal section of irradiation ion species distribution viewed from the lateral side of the beam traveling direction. Irradiation spots SP are three-dimensionally arranged so that the entire target 80 is filled. In this example, the front side of the irradiation direction (the side closer to a body surface 88) and the peripheral part in the XY direction are set as a first irradiation region 82 mainly composed of a heavy ion species (oxygen O in this example), the center part of the tumor is set as a second irradiation region 83 mainly composed of a lighter ion species (carbon C in this example), and the back side of the irradiation direction is set as a third irradiation region 84 mainly composed of a further lighter ion species (helium He in this example). By irradiating in this manner, it is possible to achieve irradiation with desired quality of radiation for each site (each of the irradiation regions 82, 83, 84) in the target 80 by combining the advantage of the heavy ion species having characteristics of small scattering, large generation quantity of fragments, and high LET, and the advantage of the light ion species having characteristics of large scattering, small generation quantity of fragments, and low LET. In brief, the charged particle irradiation system 1 can concentrate the dose at the target 80 while minimizing exposure to the peripheral normal tissues by irradiating the periphery of the target (peripheral part perpendicular to the irradiation direction) with a heavy ion species to make the scattering small, and irradiating the downstream side of the target (back side of the irradiation direction) with a light ion species to reduce the application of dose to the back side of the target due to fragments, and irradiating the upstream side of the target (front side of the irradiation direction) with a heavy ion species to make LET high. For the irradiation regions 82, 83, 84, the irradiation setting can be made appropriately, for example, radiating a single ion species to each irradiation spot, or radiating to each irradiation spot a combination of a plurality of kinds of ion species in different proportions of irradiation amounts (the number of radiated charged particles) for different ion species, or making irradiation spots to be irradiated with a single ion species, and irradiation spots to be irradiated with a plurality of kinds of ion species coexist. FIG. 3(B) shows a depth dose distribution chart radiated by the controlling apparatus 50 using a plurality of kinds of ion species in accordance with the irradiation parameter data 67 by an intensity modulated composite ion therapy. As described with FIG. 3(A), FIG. 3(B) shows an example of the case where the front side of the irradiation direction (the part of small depth, upstream side) is irradiated with a heavy ion species, and the back side of the irradiation direction (the part of large depth, downstream side) is irradiated with a light ion species. As illustrated in the drawing, the charged particle irradiation system 1 keeps gentle distribution of quality (LET) in the target by combining a first ion species irradiation dose 94, a second ion species irradiation dose 95 and a third ion species irradiation dose 96 indicating physical amount of energy for a clinical dose 91 (Dclin). In the illustrated example, the charged particle irradiation system 1 irradiates the front side of the irradiation direction with oxygen which is a heavy ion species at a proportion larger than those of other ion species to achieve the first ion species irradiation dose 94, irradiates the center or its periphery of the irradiation direction with carbon which is the second heavy ion species at a proportion larger than those of other ion species to achieve the second ion species irradiation dose 95, and irradiates the back side of the irradiation direction with helium which is a lighter ion species than the above at a proportion larger than those of other ion species to achieve the third ion species irradiation dose 96. In this manner, the charged particle irradiation system 1 can realize a uniform clinical dose distribution in the target while appropriately changing the quality of radiation (particle species and LET) by combining a plurality of kinds of ion species. As a result, the distribution of quality of radiation (LET) in the target can be kept gentle by combination of the plurality of kinds of ion species, and distortions 91a, 91b in the distribution of the clinical dose 91 can be suppressed to low levels even when errors 92a, 92b occur in a RBE 92. By optimizing the quality distribution by means of the plurality of kinds of ion species in accordance with the radiation sensitivity of normal cells or cancer cells in a tumor, the charged particle irradiation system 1 can kill only the cancer cells while conserving the normal cells. By using a light ion species for irradiation of a deep site, the charged particle irradiation system 1 can treat a deep site of the body with an accelerator of low acceleration energy. Generally, high acceleration energy is required for a heavy ion species to reach a deep site, however, according to the present invention, a deep site can be treated with low acceleration energy by using a light ion species, and thus the acceleration energy required as a whole can be reduced. Therefore, it is possible to achieve cost reduction and downsizing of the accelerator, which contributes to the spread of the heavy charged particle therapy. In addition, by using the plurality of kinds of ion species, the charged particle irradiation system 1 can desirably set spatial distribution of not only dose but also quality even in the single field irradiation from one direction, and improve the concentration of dose to the tumor compared with the conventional case using a single ion species. The charged particle irradiation system 1 can provide a therapy that is insusceptible to relative biological effectiveness (RBE) and irradiation, and registration error. The charged particle irradiation system 1 can also provide an effective therapy depending on the difference in radiation sensitivity between normal cells and cancer cells contained in a tumor. The charged particle irradiation system 1 can realize the dose distribution and the quality distribution to be given into the target without necessity of a large-scale apparatus like a rotary gantry. The present invention is not limited to the configuration of the aforementioned embodiment, but many embodiments are available. The present invention is applicable to a charged particle irradiation system that radiates a beam of charged particles to a target. 1: Charged particle irradiation system 2: Ion source 2A: First ion source 2B: Second ion source 2C: Third ion source 4: Linear accelerator 5: Synchrotron 67: Irradiation parameter data 68: Maximum depth data 70: Planning apparatus 71: CPU 72: Memory 73: Planning program |
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abstract | The present disclosure relates to an extreme ultraviolet (EUV) radiation source having an angled primary laser, and an associated method of formation. In some embodiments, the EUV radiation source has a fuel droplet generator that provides fuel droplets to an EUV source vessel along a first trajectory. A primary laser is configured to generate a primary laser beam along a second trajectory that intersects the first trajectory at a non-perpendicular angle. A collector mirror is configured to focus the EUV radiation to an exit aperture of the EUV source vessel not linearly aligned with the second trajectory of the primary laser beam. By focusing the EUV radiation to an exit aperture not linearly aligned with the second trajectory, a protection element configured to block remnants of the primary laser beam can be located at a position that does not reduce a power of the focused EUV radiation. |
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claims | 1. A system comprising:a neutron reflector assembly configured to surround a nuclear reactor core during a sustained nuclear fission reaction; andthe neutron reflector assembly being further configured to adjust fast neutron flux and thermal neutron flux within the reactor core by altering reflectivity characteristics of reflector material in the neutron reflector assembly during a sustained nuclear fission reaction;wherein the neutron reflector assembly includes a plurality of cylindrical tubes containing reflector material, at least two of the tubes in the plurality of tubes having different radius values. 2. The system of claim 1, further comprising:a heat exchanger, wherein the neutron reflector assembly is in thermal communication with the heat exchanger. 3. The system of claim 2, further comprising:a molten nuclear fuel salt in the nuclear reactor core, wherein the neutron reflector assembly is in thermal communication with the molten nuclear fuel salt. 4. The system of claim 3, further comprising:a tube and shell heat exchanger, wherein the neutron reflector assembly is in thermal communication with the molten nuclear fuel salt via the tube and shell heat exchanger. 5. The system of claim 1, wherein the reflector material includes a flowing liquid neutron reflector. 6. The system of claim 5, further comprising a flowing liquid neutron reflector spillover reservoir. 7. The system of claim 1, wherein the neutron reflector assembly includes a plurality of refractory clad sleeves. 8. The system of claim 1, further comprising a plurality of neutron moderating members, each neutron moderating member selectively insertable into neutron reflector assembly. 9. The system of claim 5, wherein the flowing liquid neutron reflector is molten lead. 10. The system of claim 5, wherein the flowing liquid neutron reflector is molten lead-bismuth. 11. The system of claim 5, wherein the neutron reflector assembly is further configured to maintain the flowing liquid neutron reflector in a creeping flow. 12. The system of claim 1, wherein the neutron reflector assembly includes a flowing liquid moderator. 13. The system of claim 1, wherein the neutron reflector assembly includes a primary static neutron reflector sub-assembly and a secondary dynamic neutron reflector sub-assembly. 14. The system of claim 1, wherein the neutron reflector assembly includes a plurality of cylindrical tubes flowing reflector material in neutronic communication with the nuclear reactor core during the sustained nuclear fission reaction. 15. A system comprising:a neutron reflector assembly configured to surround a nuclear reactor core during a sustained nuclear fission reaction;the neutron reflector assembly being further configured to adjust fast neutron flux and thermal neutron flux within the reactor core by altering reflectivity characteristics of reflector material in the neutron reflector assembly during a sustained nuclear fission reaction;a heat exchanger, wherein the neutron reflector assembly is in thermal communication with the heat exchanger; anda molten nuclear fuel salt in the nuclear reactor core, wherein the neutron reflector assembly is in thermal communication with the molten nuclear fuel salt. 16. The system of claim 15, wherein the heat exchanger is a tube and shell heat exchanger. 17. The system of claim 15, wherein the heat exchanger is a tube and shell heat exchanger and the neutron reflector assembly is in thermal communication with the molten nuclear fuel salt via the tube and shell heat exchanger. 18. The system of claim 15, wherein the reflector material includes a flowing liquid neutron reflector. 19. The system of claim 18, further comprising a flowing liquid neutron reflector spillover reservoir. 20. The system of claim 15, wherein the neutron reflector assembly includes a plurality of refractory clad sleeves. 21. The system of claim 15, further comprising a plurality of neutron moderating members, each neutron moderating member selectively insertable into neutron reflector assembly. 22. The system of claim 18, wherein the flowing liquid neutron reflector is molten lead. 23. The system of claim 18, wherein the flowing liquid neutron reflector is molten lead-bismuth. 24. The system of claim 18, wherein the neutron reflector assembly is further configured to maintain the flowing liquid neutron reflector in a creeping flow. 25. The system of claim 15, wherein the neutron reflector assembly includes a flowing liquid moderator. 26. The system of claim 15, wherein the neutron reflector assembly includes a primary static neutron reflector sub-assembly and a secondary dynamic neutron reflector sub-assembly. 27. The system of claim 15, wherein the neutron reflector assembly includes a plurality of cylindrical tubes flowing reflector material in neutronic communication with the nuclear reactor core during the sustained nuclear fission reaction at least two of the tubes in the plurality of tubes having different radius values. |
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abstract | Disclosed herein are a nuclear fuel rod for fast reactors, which includes an oxide coating layer formed on the inner surface of a cladding, and a manufacturing method thereof. The nuclear fuel rod for fast reactors, which includes the oxide coating layer formed on the inner surface of the cladding, can increase the maximum permissible burnup and maximum permissible temperature of the metallic fuel slug for fast reactors so as to prolong the its lifecycle in the fast reactors, thus increasing economic efficiency. Also, the fuel rod is manufactured in a simpler manner compared to the existing method, in which a metal liner is formed, and the disclosed method enables the cladding of the fuel rod to be manufactured in an easy and cost-effective way. |
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claims | 1. A separate type safety injection system, comprising:a coolant injection unit connected to a reactor coolant system by a safety injection pipe such that coolant stored therein is injected into the reactor coolant system by a pressure difference when a loss-of-coolant-accident (LOCA) occurs;a gas injection unit disposed at a position higher than the coolant injection unit, and configured to pressurize the coolant injected into the reactor coolant system, by introducing gas stored therein to an upper part of the coolant injection unit in the loss-of-coolant-accident;a connection pipe configured to connect the upper part of the coolant injection unit and a lower part of the gas injection unit such that gas within the gas injection unit is introduced to the upper part of the coolant injection unit; andan orifice formed on an inner side of the connection pipe to contract a flow cross-sectional area of the gas introduced to the coolant injection unit, the orifice being configured to allow increases of a flow velocity and a flow rate of gas introduced to the coolant injection unit when a pressure difference between the coolant injection unit and the gas injection unit increases to a critical value and configured to passively limit the flow velocity and the flow rate of the gas introduced to the coolant injection unit as a critical flow velocity and a critical flow rate by forming choked flow when the pressure difference between the coolant injection unit and the gas injection unit is more than the critical value. 2. The separate type safety injection system of claim 1, wherein the coolant injection unit is provided with a coolant tank for storing the coolant therein,wherein the gas injection unit is provided with a gas tank for storing the gas therein, andwherein the coolant tank and the gas tank are connected to each other by the connection pipe. 3. The separate type safety injection system of claim 2, further comprising a throttle member installed at the safety injection pipe such that a flow rate of the coolant injected into the reactor coolant system is restricted, and configured to contract a flow cross-sectional area of the safety injection pipe. 4. The separate type safety injection system of claim 2, further comprising a check valve installed at the safety injection pipe such that the coolant inside the reactor coolant system is prevented from back-flowing and leaking into the separate type safety injection system. 5. The separate type safety injection system of claim 2, wherein at least part of the orifice protrudes from an inner side wall of the pipe line formed by the connection pipe or the partition wall. 6. An integral type reactor comprising:a core makeup tank configured to inject coolant into a reactor coolant system using a gravity force and pressure balance when an accident occurs on the reactor, by reaching a pressure equilibrium state with the reactor coolant system; anda separate type safety injection system connected to the reactor coolant system, and configured to inject coolant stored therein into the reactor coolant system when a loss-of-coolant-accident (LOCA) occurs,wherein the separate type safety injection system comprises:a coolant injection unit connected to a reactor coolant system by a safety injection pipe such that coolant stored therein is injected into the reactor coolant system by a pressure when the loss-of-coolant-accident occurs;a gas injection unit disposed at a position higher than the coolant injection unit, and configured to pressurize the coolant injected into the reactor coolant system, by introducing gas stored therein to an upper part of the coolant injection unit in the loss-of-coolant-accident;a connection pipe configured to connect the upper part of the coolant injection unit and a lower part of the gas injection unit such that gas within the gas injection unit is introduced to the upper part of the coolant injection unit; andan orifice formed on an inner side of the connection pipe to contract a flow cross-sectional area of the gas introduced to the coolant injection unit, the orifice being configured to allow increases of a flow velocity and a flow rate of gas introduced to the coolant injection unit when a pressure difference between the coolant injection unit and the gas injection unit increases to a critical value and configured to passively limit the flow velocity and the flow rate of the gas introduced to the coolant injection unit as a critical flow velocity and a critical flow rate by forming choked flow when the pressure difference between the coolant injection unit and the gas injection unit is more than the critical value. 7. The integral type reactor of claim 6, wherein the coolant injection unit is provided with a coolant tank for storing the coolant therein, andwherein the gas injection unit is provided with a gas tank for storing the gas therein,wherein the coolant tank and the gas tank are connected to each other by the connection pipe. 8. The integral type reactor of claim 7, further comprising a throttle member installed at the safety injection pipe such that a flow rate of the coolant injected into the reactor coolant system is restricted, and configured to contract a flow cross-sectional area of the safety injection pipe. 9. The integral type reactor of claim 7, further comprising a check valve installed at the safety injection pipe such that the coolant inside the reactor coolant system is prevented from back-flowing and leaking into the separate type safety injection system. 10. The integral type reactor of claim 7, wherein at least part of the orifice protrudes from an inner side wall of the pipe line formed by the connection pipe or the partition wall. 11. The integral type reactor of claim 6, further comprising an isolation valve installed at a pipe which connects a lower end of the core makeup tank with the reactor coolant system, and configured to be open by an actuation signal generated when a related accident occurs, such that the coolant is injected into the reactor coolant system from the core makeup tank. 12. The integral type reactor of claim 6, further comprising a pressure balancing pipe having one end connected to the reactor coolant system and another end connected to the core makeup tank, such that a pressure balance is formed at the core makeup tank. 13. The integral type reactor of claim 6, further comprising a passive residual heat removal system configured to remove heat of the core by circulating a fluid stored therein to a steam generator inside the reactor coolant system, when an accident occurs on the reactor. 14. The integral type reactor of claim 13, further comprising an isolation valve installed at a pipe which connects the passive residual heat removal system with the reactor coolant system, and configured to be open by an actuation signal. |
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abstract | The beam irradiation apparatus is featured by including a transport pipe which is vacuum-evacuated to be used as a transport channel of a beam taken out from an accelerator, a quadrupole magnet which modulates the beam diameter of the beam so that the beam is incident on an irradiation target existing in the atmosphere while maintaining the focusing angle of the beam, and one or more longitudinally movable range shifters which are provided to be capable of changing the distance to the irradiation target of the beam, and which modulate the beam range by reducing the energy of the beam by allowing the beam to pass through the movable range shifter, and is featured in that the beam is irradiated onto the irradiation target by modulating the beam diameter and the beam range. |
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abstract | The invention comprises an apparatus to repair a fuel assembly to accomplish a load lift comprising a main body, an upper section, a connection configured between the main body and the upper section and a lower section connected to the main body. The invention also comprises an inner adjusting body with a top and a bottom wherein a mandrel is connected to the bottom, the mandrel configured to actuate a holding body upon actuation of the inner adjusting body, the inner adjusting body positioned inside the upper section, the main body and the lower section and an actuator connected to the upper section, the actuator configured to actuate the inner adjusting body. |
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claims | 1. An emergency core cooling system for a reactor vessel using water as a coolant and a moderator, and receiving therein a reactor core on which nuclear fission occurs, the emergency core cooling system comprising:a containment structure surrounding the entire reactor system including the reactor vessel and condensing a vapor discharged from the reactor vessel to obtain water when emergency core cooling is performed;a reactor cavity that surrounds the reactor vessel and in which said water condensed in the containment structure is collected due to gravity;a first cavity pipe extending through the reactor vessel to an interior thereof, wherein said first cavity pipe has a first cavity pipe opening in said reactor cavity and outside of said reactor vessel that is lower than an upper end of the reactor cavity; anda cavity valve provided on the first cavity pipe to open the first cavity pipe when emergency core cooling is performed and thus discharge the vapor generated in the reactor vessel through the first cavity pipe opening to an exterior of the reactor vessel;wherein said first cavity pipe provides a recirculation loop of cooling water by discharging said vapor generated in the reactor vessel and supplying said water collected in said reactor cavity in opposite directions,wherein width of said reactor cavity is less than width of said containment structure, wherein upper most portion of said reactor vessel is located in the reactor cavity below upper most end of the reactor cavity, and wherein the upper most end of the reactor cavity is located below the containment structure. 2. The emergency core cooling system as set forth in claim 1, wherein the containment structure is formed of steel to condense, on a surface of an inner wall of the containment structure, the vapor discharged to the exterior of the reactor vessel from an interior of the reactor vessel. 3. The emergency core cooling system as set forth in claim 1, wherein a heat exchanger is provided in the containment structure to condense the vapor discharged from the reactor vessel on the heat exchanger. 4. The emergency core cooling system as set forth in claim 1, wherein the cavity valve is operated by an alternating current (AC) power supply, or is operated by a direct current (DC) power supply such as a battery when the AC power supply is unable to be used. 5. The emergency core cooling system as set forth in claim 1, wherein the first cavity pipe extends into the reactor vessel at an upper portion thereof. 6. The emergency core cooling system as set forth in claim 5, wherein the first cavity pipe is provided in plurality and the first cavity pipes are placed at the same height. 7. The emergency core cooling system as set forth in claim 1, further comprising:a second cavity pipe extending through the reactor vessel to said interior thereof to be placed at the same height as the first cavity pipe; anda rupture disk provided in the second cavity pipe that ruptures due to an increase in internal pressure of the reactor vessel when the cavity valve is not operated during emergency core cooling to thereby open the second cavity pipe between the interior of the reactor vessel and the exterior of the reactor vessel. 8. The emergency core cooling system of claim 1, wherein said first cavity pipe includes a plurality of pipes that allows said water after being condensed and said vapor from inside said reactor vessel to flow in opposite directions simultaneously. 9. The emergency core cooling system of claim 1, wherein said cooling system includes a path for condensation of said vapor extending from said containment structure to a location that is in said reactor cavity, outside of said reactor vessel and below said opening, wherein said reactor cavity maintains said water from said vapor after being condensed so that the water rises in said reactor cavity from below said first cavity pipe opening to enter said first cavity pipe opening. 10. The emergency core cooling system as set forth in claim 1, wherein an uppermost end of the reactor cavity opens to an upper area contained by the containment structure. |
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description | This application claims the benefit of U.S. Provisional Application No. 60/488,674 filed Jul. 18, 2003. X-radiation is a powerful and commonly used tool in modern society. Specifically, x-radiation is commonly used as a diagnostic tool in medical and industrial (non-destructive testing) fields. However, exposure to radiation can be damaging to human health. In order to protect users, patients and x-ray technicians, steps have been taken to limit their exposure to x-rays. For example, flexible x-radiation attenuating materials worn as protective aprons have been created in order to protect patients and technicians alike. In addition, x-radiation equipment has been designed to incorporate with shielding properties to reduce x-radiation exposure from the source generator. In the field of x-ray equipment, shielding is required or mandated to reduce leakage of stray radiation to below specified maximum levels. Most shielded components of such equipment, such as x-ray tube housings, intensifier housings, collimators and filter devices, typically use a structural outer layer of metal for mechanical strength. This structural component is commonly machined, cast or forged aluminum, brass or steel. Since the aluminum, brass or steel is effectively radiolucent, the structural component is subsequently lined with a second layer of a material, such as lead, for radiation shielding. The lead shielding is typically held in place with an adhesive or by mechanical means, forming a multi-layer final structure with one layer providing strength and structure and the second layer providing x-radiation shielding. Lead is often the material of choice used for x-radiation shielding in medical and industrial x-ray equipment because it is low in cost and readily available. The use of lead, however, poses significant manufacturing challenges as well as health and environmental hazards. There are two major disadvantages of using lead for radiation shielding: toxicity and the heavy weight of the material. The toxicity of lead has been shown to pose significant health risks to humans. Those adversely affected can include both those involved in processing and those using shielding materials and equipment. The environmental impact resulting from the disposal of products containing lead is also well established and a serious modern-day concern. In order to limit lead exposure to humans, many industrialized nations regulate industries that use lead, including x-ray equipment manufacturers. In an effort to control, reduce or eliminate the use of lead, many industrialized nations have eliminated the manufacture and use of lead in products such as gasoline and paint. More recently, there has been a general determination to minimize the exposure of workers in plants which now use lead and, more importantly, to shield the general public from the adverse effects from lead in products and equipment and from the toxic waste resulting from the ultimate disposal of lead-containing products at the end of their useful life. The toxicity hazard can result from direct exposure to lead itself or indirectly: from exposure to an extractable source through groundwater leachate from land-fills (Ref. US EPA Toxicity Leachate Characteristic Procedures, “TCLP”, under US RCRA legislation); from solid residues; or from gaseous emissions from waste incineration. The determination to eliminate lead and certain other toxic materials from all electrical equipment, including x-ray equipment, has been established in a European toxic waste elimination directive known as “W.E.E.E.” (Waste Electrical and Electronic Equipment Initiative, 2000/C365/E13) (Jul. 28, 2000). Not only is lead toxic, but also it is a heavy material that can add significant weight to components such as those required in x-ray equipment. As discussed previously, conventional x-ray equipment contains a lead liner to shield against x-radiation. The excessive weight of lead is especially troublesome because of the mass of lead shielding required to meet mandated radiation leakage standards. Thus, the mass of lead used is a significant proportion of the overall weight of x-ray equipment. Existing manufacturing techniques, which typically involve lining of a separate cast or machined metal structural housing with elemental lead, significantly increase the weight of such equipment. Due to the use of lead, current shielded components are relatively inefficient in terms of mass. They are heavy and complex because the structural metal housing provides insignificant radiation attenuation while the lead shielding, having poor mechanical strength, cannot provide a structural function. Heavy weight is a significant disadvantage for certain types of x-radiation equipment including portable equipment, such as “C-arm” x-ray diagnostic machines, and for equipment whose shielding components are moving or rotating, such as CT tube housings. In CT tube housings, rotational speeds are limited by inertial forces, which are in turn, dependent on their mass. In these applications, for rotational balance, overall shielding mass is further increased by the need for counterweights to preserve static balance. Lighter shielding components allow lower counterweight mass, which can further result in smaller and lighter supporting structures. Therefore, lowering the weight of the shielded structure can have an overall beneficial effect on the size, weight, cost and portability of x-ray units. Reduced mass can also permit higher rotational speeds of moving parts limited by inertial forces. In CT imaging, for example, reduced mass of the moving parts, especially of the tube head and housing, could permit faster revolution speed, which would lower image acquisition time and/or improve image definition. While providing adequate shielding at reduced weight is important, replacement components must still fit existing precise equipment designs and keep overall unit size to a minimum. To keep the volume of the structure small, components having high attenuation and also high density are often preferable. Although mandated radiation leakage testing is usually performed at the worst-case conditions of the peak applied voltage of the machine (typically 70 kVp to 80 kVp for dental x-ray units; 120 kVp to 150 kVp for medical x-ray units; 140 kVp to 160 kVp for CT tube housings; and up to and above 200 kVp for industrial units) shielding must be effective along the entire range of beam energies emanating from the x-ray unit. Shielding components on the receiving end of the radiation, such as intensifier housings, are tested using radiation from the highest voltage from the direct source beam even though they receive only a degraded, filtered and scattered spectrum of radiation in actual practice. Effective substitutes for lead must, therefore, shield radiation not only at the peak voltage of the machine but also along the entire effective range of beam energies and spectra. Several attempts have been made to create materials that provide acceptable shielding properties but which are lightweight, lead-free or both. For instance, flexible x-ray shielding materials have been available for many years and have been discussed by Yaffe, et al. (Health Physics, Vol. 60, No. 5). Yaffe discussed combining metals with flexible elastomers in order to produce lighter weight radiation protection aprons than those made from similar lead-powder filled rubbers or polymers. These compositions, however, are limited to flexible materials and do not anticipate incorporation of complementary metals into resins in order to create lightweight and rigid, lead-free integral radiation shielding structures. Recently, there have been attempts to replace only the lead shielding lining of x-ray equipment with lead-free polymer compositions using a single attenuating element. U.S. Pat. No. 4,157,476 to O'Conner describes a shielding material for a dental x-ray tube consisting of a shielding liner composed of barium sulfate filled polymers. This lead sheeting replacement is contained in and acts as a liner in a conventional structural metal housing. The polymer structure in O'Conner simply replaces the lead, while still requiring a layered structure with separate housing as in conventional equipment. Furthermore, the barium sulfate filled resins are implicitly proposed only for shielding dental tube heads which operate at low kVp (below 80 kVp) where barium is an effective x-radiation absorber. Such a shield would be highly ineffective in terms of mass per unit area relative to lead at the higher kVs found in most medical x-ray units. Although barium in elemental form, is more attenuation efficient than lead per unit mass up to about 100 kVp, in actual practice, one would require higher mass for equivalent attenuation. Higher mass would be required because barium is not available in unreactive elemental form, or in useful high concentration alloy form. Barium sulfate, the only available non-toxic barium salt, contains 41% deadweight of radiolucent sulfate, and has low density which prevents high concentration by weight in compounding. Furthermore, the resulting very low composition density would create much thicker shielding liners, on the order of several times thicker than lead for equivalent shielding. More recently, there have been several additional attempts, both using lead and lead-free formulations, to combine structural and shielding functions in a monolithic polymeric composition. However, these only teach the use of one element for attenuation. For example, U.S. Pat. No. 5,304,792 to Verat describes an x-ray image intensifier tube casing with the outside structural component made from a molded thermoplastic resin loaded with a shielding material such as lead oxide. This technology is specific to intensifier tube housings and uses a single metal or metal oxide (preferably PbO) in an injection moldable thermoplastic resin. Lead-free filled polymer shielding compositions using only a single attenuating element are also described in U.S. Pat. No. 6,048,379 to Bray et al., which teaches the use of tungsten as the attenuating element in a binder. Bray teaches the use of such material as a lead replacement for use in traditional lead applications, such as projectiles, where density equivalents is desired. Bray also claims tungsten powder in a broad variety of resins formed into articles used for radiation shielding, including housings. Single element-based attenuators such as tungsten have a lower shielding efficiency relative (per unit mass) to lead, or conversely require greater elemental mass than lead for equal shielding at most normal medical beam energies, which typically range from 50 kVp to 150 kVp. Single element based attenuators have a lower shielding efficiency due to a number of factors. In the case of tungsten, with the use of energy beams up to 120 kVp, a significant portion of the beam energy spectrum, including the typical emission spike from conventional tungsten-based anodes, falls in the 55 keV to 69 KeV “K-edge” tungsten window causing poor attenuation. At elevated beam energies, such as 120 kVp to 150 kVp, or at lower kVp but with high beam filtration, the attenuation coefficient of tungsten is simply well below that of lead, both overall, and for the greater part of the beam spectrum. Therefore, the tungsten/resin compositions of Bray do not anticipate and cannot produce shielding or complete monolithic shielded components lighter in weight than elemental lead when used for radiation protection. Single element-based attenuating compositions, such as those using barium or tungsten, also exhibit a large variability in their shielding efficiency (per unit mass), along the radiation spectrum, compared to lead. None of the above-cited references addresses this issue, nor do cited test data reflect the existence of this shielding factor variability with beam energy and spectra. In addition, a frequent commercial requirement of such compositions and their components is flame retardancy without the use of toxic or hazardous flame retardants. While the use of such flame retardant agents in polymer compositions is known in the art, their introduction to highly filled, dense shielding compositions requires volumetric space. The use of flame retardant agents displaces and reduces the maximum permissible filler loading of attenuating elements, thereby reducing composition density and adding slightly to the required mass of composition for equivalent shielding in an integral structure. While there have been several attempts at creating lead-free x-ray shielding materials, there remains a need for lightweight and rigid, lead-free, integral, monolithic radiation shielding structures. There is a further need for such x-radiation shielding structures that can shield radiation over a wide range of energies between 50 kVp and 150 kVp, and even up to 200 kVp. The present invention solves the afore-mentioned problems and provides complex molded x-radiation shielding components with varying densities that can be formulated to provide structural strength with x-radiation shielding. This invention provides lightweight radiation shielding structural compositions, which combine the structural and radiation shielding functions in an integral and monolithic structural composition. Another object of this invention is the reduction or elimination of lead from radiation shielding structural compositions. Yet another objective is the production of radiation shielding structural compositions that have fire retardant properties. Yet another object of the present invention is the production of radiation shielding structural compositions with low density. Specifically, the present invention provides lightweight and rigid, lead-free, integral radiation shielding structural compositions comprising at least two radiation shielding elements in elemental or alloyed form, or compounds thereof, having complementary radiation attenuation characteristics, dispersed in a thermoset or thermoplastic resin. The present invention provides both lead-free compositions and those containing lead. More specifically, the present invention provides lightweight and rigid, lead-free integral radiation shielding structural compositions comprising at least two radiation shielding elements selected from the group consisting of antimony, bismuth, iodine, tungsten, tin, tantalum, erbium and barium, or salts, compounds or alloys thereof dispersed in a thermoplastic or thermoset resin that can shield x-rays having energies between 50 kVp and 200 kVp, preferably between 100 kVp and 160 kVp, more preferably between 120 kVp and 150 kVp. The present invention provides components of complex shapes and varying thicknesses. The present invention also provides formulations that include various fillers or bulking agents for creating components requiring greater strength and reduced densities. The present invention is based on the discovery of a group of lead-free and leaded compositions, using two or more specific combinations of radiation attenuation-compatible powdered elements, salts, compounds or alloys thereof, of medium to high density which are mixed with a resin or polymeric carrier or binder at a high filler loading. Each element provides a unique pattern of attenuation versus radiation energy. Combining compatible elements results in a composition with a greater attenuation per unit mass than the individual elements alone. Shielding mass is reduced both by the use of mixtures of powders of elements with complementary radiation attenuating characteristics which have lower combined unit mass at equal shielding properties to lead, and by the forming of those elements in a resin matrix into monolithic rigid components having suitable mechanical and structural strength properties. The overall mass of composition, per unit area, is significantly below the mass of lead required for equivalent shielding, and is even lighter in mass, per unit area, than the whole shielded housing structure of conventional equipment consisting of lead sheet lined aluminum. The present invention provides lightweight and rigid, integral radiation shielding structural compositions comprising at least two radiation attenuating elements or compounds thereof, selected for having complementary radiation attenuating characteristics, dispersed in a thermoplastic or thermoset resin. Such compositions, when formed, shaped or molded into complete components have adequate mechanical properties such as rigidity, tensile and flexural properties and impact strength. Resulting components can have a flexural modulus of from about 300 to about 30,000 MPa and preferably from about 3,000 to about 7,000 MPa. The resulting components can have an ultimate tensile strength of from about 20 MPa with a preferred strength of from about 30 MPa. Formed compositions of the present invention can replace both layers of a desired component, the lead shielding and the supporting structure, with a single-layer, monolithic structural material having integral shielding and having a density such that the thickness is within the range of 25% to 200% of equivalent lead-aluminum housing structures. The resulting structures of the present invention have a preferred density of from about 3.5 g/cc. With the appropriate selection of different combinations of elements, a range of compositions can provide such lower-mass per unit area components to function at different peak energies, as kVp, and having application over the commonly used broad energy ranges below the design peak of the equipment. Such compositions can be flame-retarded as required, for example to provide adequate V-0 per UL 94 tests, while maintaining such lower shielding mass efficiency and, when formed, can be machined, drilled, painted, etc. as required in the commercial use of such components. By appropriate selection of resin matrix, as commonly known in the art, such compositions can form components which can operate at the elevated temperatures required in pressurized, oil-filled x-ray tube housings. The components can withstand physical or chemical degradation of mechanical properties caused by immersion in such commonly used cooling fluids. Components of the present invention can also perform within acceptable resin degradation limits caused by irradiation commonly found with medical or dental x-ray equipment. Structural compositions of the present invention are formulated using a resin component, at least two x-radiation attenuating elements and in some preferred formulations, fillers, reinforcing fibers and other ingredients such as fire or smoke retardants. For consistency and clarity, all ingredients are shown in weight % and elemental weight %. The resin component and the preferred filler components are presented first in each preferred structural composition. The balance of materials is presented next and includes the amounts of attenuating elements. For example, if the resin amount is 20%, then the balance of the structural composition comprises 80% of the overall weight. Of that 80% balance, the structural composition comprises various proportions of attenuating elements. Thus, if the attenuating elements comprise 50% tungsten and 50% bismuth, the amount of tungsten and bismuth each equals 50% of the 80% overall weight balance (or 40% of the overall weight of the structural composition). While the specific elements can be incorporated in elemental or alloyed form or as salts, oxides and compounds thereof, the overall elemental proportion is determined after deducting the resin weight and any dead weight radiolucent cations, such as salt components, radiolucent alloying metals, reinforcing fibers, bulking filler materials or fire and smoke retardants. For example, if a structural composition comprises 10 g of resin and 90 g of tin oxide, with the oxide comprising 10% of the tin oxide, then the resulting elemental weight % of the tin component is 90 g×0.90 or 81 g. The lead-free formulations of the present invention teach the use of several combinations of two or more x-radiation attenuating elements selected for having complementary K-edge radiation attenuating characteristics, including antimony, bismuth, iodine, tungsten, tin, tantalum, erbium and barium in elemental or alloyed form or compounds thereof, in specific weight proportions. Since each element has a specific attenuation, the selection of elements depends upon the desired attenuation in the resulting component. For example, if two elements were selected with similar attenuation characteristics, the resulting component would have roughly the same attenuation of the individual elements. Conversely, by selecting complementary elements, a resulting composition can have improved attenuation per unit mass. Lightweight leaded compositions can be formulated in the same manner. In these formulations, lead substitutes for bismuth at the same weight proportion as defined for bismuth. In addition to complementary attenuation characteristics, the elements are selected with compatible particle size distribution to provide maximum packing fraction and minimum filler volume according to techniques known in the art. The specific weight proportions will depend upon the desired attenuation and other performance characteristics. The specific elements can be added in elemental or alloyed form or compounds thereof including salts and oxides. The choice of elements consists of selecting at least one element from at least two different groups. For example, one x-radiation shielding structure of the present invention includes from about 10% to about 85% in elemental weight % of at least one element selected from the group consisting of antimony, tin, barium and iodine; and from about 15% to about 90% in elemental weight % of at least one element selected from the group consisting of bismuth, tungsten, tantalum and erbium. The selected combination of elements are then mixed with an appropriate resin and molded, cast or formed into a radiation shielding structure. As one skilled in the art is readily aware, the specific choice of resin depends upon the desired formulation and handling characteristics and curing requirements. The resin, or copolymer thereof, can be at least one selected from the group consisting of epoxies, vinyl esters, unsaturated polyesters, phenolics, polyesters, polyamides, polyarylether ketones, polyether ether ketones, polysulfones, poly aryl sulfones, acrylics, polyimides, polyethylene, polypropylene, polyether imides, polyvinylidene fluoride, acrylonitrile-butadiene-styrene, polyurethanes, ethylene copolymers, poly vinyl chlorides, silicones, polycarbonates, polyphenyleneoxide, polycyanates, cyanate esters, bismaleimides and acetals. Preferred embodiments include from about 5% to about 20% by weight resin with a more preferred resin amount of from about 7% to about 12%. In addition, the resin, filler loading and particle size and distribution were selected and designed using known techniques such that the effective viscosity of the mixture was low enough to permit homogeneous mixing while permitting air release and adequate flow during molding. The viscosity was high enough to prevent settling out of the higher-density fillers during both mixing and molding. In order to improve final structural or mechanical properties, glass, other fiber reinforcement or other fillers known in the art can be added to the resin. Typical fiber reinforcement is 5-30 phr, but to avoid taking up too much resin volume, is preferably limited to 5-20 phr, and more preferably limited to 5-10 phr. The fiber reinforcement can be at least one selected from the group consisting of glass, carbon fiber, boron fiber, steel, tungsten, aramid, ultra-high molecular weight polyethylene and polybenzoxazole. Other fillers such as fumed silica, microballoons, or other lightweight non-structural additives can be added to the formulation to manipulate the ultimate density of the structure. Preferred lower density formulations use from about 5% to about 30% resin and up to about 30% by weight non-attenuating fillers. Other desirable functions, such as magnetic shielding or electrical conductivity, can be achieved by incorporating mu-metal or conducting elements, such as high conductivity carbon nano-fibers, into the component during the molding process. The present invention can also incorporate non-toxic and non-hazardous flame and smoke retardant compounds, without adding significant mass or lowering shielding properties. Non-toxic flame retardants which can be used include, but are not limited to aluminum trihydrate, magnesium hydroxide, zinc borate and other salts of boric acid. A single retardant can be used as well as a mixture of more than one retardant. While x-ray equipment is used herein as an example, the compositions of the present invention can be molded or machined into essentially any shape where shielding is desired. FIG. 1 illustrates a CT Tube cathode end cap/cable connector cover. The end cap cover is a one-piece molded component made from x-radiation shielding material of the present invention. FIG. 2 illustrates a cross-section of an image intensifier housing molded from material described in this patent. The figure demonstrates the varying wall thickness that can be produced. FIG. 3 illustrates a CT beam shaper component molded from the material of the present invention and demonstrates the machinability of the material of the present invention. The materials of the present invention can be molded and then precisely drilled or shaped. The ability to form a single monolithic structure with built-in shielding properties also simplifies the manufacturing process by eliminating the handwork required to manufacture and combine several different and separate components of the structure such as the casing, lead liner, and the magnetic and/or electrical shielding. Although the principal applications and weight-saving benefits are envisaged where such structures are provided to shield x-radiation, the principles and teachings can extend to shielding certain gamma radiation, particularly those from commonly used radionucleides in nuclear medicine, such as Cs-131, I-125, Am-241, Tl-201, Hg-197, Co-57, Tc-99m and I-131, with the majority of the radionucleide energy below 200 KeV. Such structures include, but are not limited to, vials, boxes, transport pouches and syringe covers. Other products include gamma ray protective devices for the handling, transport and use of radioactive isotopes used in nuclear medicine. Additionally such structures can shield against the bremsstrahlung secondary x-radiation created by high-energy beta radiation emitted from beta-emitting radiochemicals such as Yttrium-90, for example in syringe covers, or for combination gamma/beta emitters. In addition, components made from the compositions of the present invention can be used for shielding against x-radiation and/or gamma radiation in the nuclear industry, for physics research or in radiation therapy. It should also be understood, that while the greatest weight savings and minimum component thickness occur at maximum attenuating filler loadings, in certain circumstances, for example to modify mechanical structure properties, or to match existing housing wall thickness or exact volume and shape for existing fittings, it may be necessary to compromise this optimum loading by dilution with additional resin or bulking fillers, or both. This thickness bulking, where required, adds little additional overall structure weight, and such matched dimension components still exhibit significant mass-savings over the lead shielding alone, and even greater mass-savings when compared to complete lined housings. The present invention is further illustrated by the following examples. This example shows a dense and lead-free, highly-filled, two-element composition with varying thickness. Two attenuating elements in powder form including 70% by weight antimony, and 30% by weight tungsten were mixed together. The elements were selected with compatible particle size distribution to provide maximum packing fraction and minimum filler volume according to techniques known in the art. The powdered elements were homogeneously mixed with an epoxy resin such that the filler volume represented 50% by volume of the total composition. The mixed composition was compression molded into a series of sheets of different thickness. Each sheet was then divided into samples and tested for radiation shielding properties and for physical and mechanical properties using standard ASTM methods. Sample 1Thickness3.1 mmDensity4.7 gm/ccShielding values1.45 mm Pb @ 120 kVp, HVL 7.6 mm AlUlt. Tensile Strength5100 psi (35 Mpa)Break Elongation1.7%Flex Modulus (10% D)1,500,000 psi (10300 Mpa)Mass per unit area15.0 kg/sq mMass of equivalent lead sheet16.44 kg/sq m The 3.1 mm thick sample was designed for comparison to an x-ray intensifier housing conventionally made as a 2 mm layer of aluminum lined with 1 mm sheet lead. The conventionally made housing provides a lead attenuation equivalence of 1.39 mm Pb. Such intensifiers are commonly operated with primary beam energies in the range 90 kVp to 120 kVp, which after filtration, degradation and scattering approximate to 80 kVp to 110 kVp beams. Sample 1, a single layer measuring 3.1 mm, had excellent rigidity and mechanical properties and had shielding values equivalent to lead sheeting at lower mass. Although the example was made as a flat sheet, the composition was suitable for molding into any complex thin walled shape and can be molded as a replacement for a conventional x-ray intensifier housing or any desired component. This same composition, molded to 2.2 mm thickness, had shielding performance equivalent to a 1 mm Pb lead sheet (at 100 kVp) and weighed 10.2 kg/sq m. The 2.1 mm sample was 10% lower mass per unit area than 1 mm of Pb (11.34 kg/sq m) and 39% lighter in mass than the total housing structure of 1 mm lead plus 2 mm aluminum (16.74 kg/sq m, with average density of 5.58 gm/cc). Its thickness (2.2 mm) is higher than the shielding thickness of lead (1 mm) but less than the 3 mm complete housing thickness. For a cylindrical intensifier housing having a typical shielded area of 0.3-0.5 sq m of material, this composition would reduce overall equipment weight by approximately 2-4 kg, excluding any counterweights, permit a reduced structure (e.g. in a “C-Arm” configuration) and improve portability. This composition would have application in similar medical x-ray machine components, operated at similar kVp, such as filter/collimator housings and shutters. This example shows the effect of filler loading on the mechanical properties of the formed composition and alternative forming techniques. A lead-free, two-element filled composition, as in Example 1, was prepared and tested in the same manner. The loading of metallic powdered elements in this example was 36% by volume. The mixture was poured (cast) into a flat mold for plaques, which were cut up and tested as in Example 1. The epoxy resin used was the same as in Example 1, having a mix viscosity of 580 cps (@72 F) and a pot-life of 21 minutes. Sample 2Thickness3.18 mmDensity3.67 gm/ccShielding values1.1 mm Pb @ 120 kVp, HVL 6.41Ult. Tensile Strength5360 psi (37 Mpa)Break Elongation3.3%Flex Modulus (10% D)960,000 psi (6620 Mpa)Sample Mass per unit area11.67 kg/sq mMass of equivalent lead sheet12.47 kg/sq mMass of 1 mm Pb/2 mm Al16.74 kg/sq m Sample 2 had adequate flexural modulus and mechanical strength as well as greater toughness and impact strength than Sample 1 from Example 1. This sample survived a drop test and still demonstrated mass benefits compared to conventional lead shielded structures. The resulting sample was 7% lighter in weight than 1 mm lead shielding and 33% less area weight than 1 mm lead lined 2 mm aluminum. Despite the high filler loading, the mechanical properties were much closer to that of unfilled resin, which has a tensile strength of 7300 psi, elongation of 4.5%, and flex modulus of 450,000 psi. A lead-free composition, as in Example 2, was prepared and tested in the same manner. The loading of metallic fillers in this example was 36% by volume, but with added chopped glass fiber at 10% by volume of resin. The mixture was pressed into plaques, which were cut up and tested as in Examples 1 and 2. The samples showed improved mechanical strength properties, with greater tensile and flexural strengths and increased flexural modulus This example shows the minimum optimized weight vs. shielding for an antimony-tungsten system (for 100 kVp beam energy). A lead-free, two-element filled composition was prepared and tested in the same manner as Example 1. The loading of the antimony and tungsten metallic fillers was 55% by volume in this example. The epoxy resin system was changed for better mechanical properties and greater pot-life and the compound was flame-retarded using ATH. The final structure was painted. The composition comprised: Antimony61.2%wtTungsten26.2%wtRadiopaque pigment1.4%wtATH1.0%wtEpoxy Resin10.2%wtThe test data is shown below: Sample 3Thickness1.8 mmDensity5.01 gm/ccShielding values1.0 mm Pb @ 85 kVp, Filter 1 mm Al1.0 mm Pb @ 100 kVp, Filter 1 mm Al0.74 mm Pb @ 120 kVp, Filter 1 mm Al0.63 mm Pb @ 140 kVp, Filter 1 mm AlUlt. Tensile Strength7530 psi (52 Mpa)Flexural Strength13650 psi (94 Mpa)Flex Modulus1520000 psi (10480 Mpa)Mass per unit area9.01 kg/sq mMass of equivalent lead sheet11.34 kg/sq mMass of 1 mm Pb/2 mm Al16.74 kg/sq mAverage Density of 1 mm Pb/5.58 gm/cc2 mm Al The resulting component showed a 20% mass saving compared to a 1 mm lead sheet, and a 46% mass saving compared to a housing constructed of 1 mm lead lining 2 mm aluminum with equivalent shielding. The sensitivity to beam energy, kVp, also demonstrates the necessity to customize the selection of attenuating elements and their proportions for shielding against specific beam energies (kVp), in this case 90-120 kVp, suitable for intensifiers and fluoroscopy collimators and filter components operating at or below this limit. There is a clear decrease in shielding value (lead equivalence) at the higher energies tested, making it unsuitable for shielding at high energies, due to the increased weight required. In the above example, to operate at 140 kVp would require 14.3 kg/sq m of this material, instead of the 9.01 required at 100 kVp, making this composition 26% heavier than the lead equivalent and only 15% lighter than a 1 mm lead-lined 2 mm aluminum housing with equivalent shielding performance. These examples show alternative element systems of equal compound density and volumetric filler loading, using tin and bismuth in ratios suitable for 100 kVp energy beams. Two alternative, two-element filled, compositions comparable to Examples 1 in weight and shielding performance in the 90-120 kVp range were prepared and tested, in the same manner as Example 1, using tin and bismuth metallic fillers in different ratios, 55/45% wt and 65/35% wt respectively, with the attenuating fillers 40% by volume of the compound and using a vinyl ester resin system, the second sample, 4-B, being glass reinforced. The compositions were: Sample 4-ASample 4-BTin46.25%wt53.00%wtBismuth37.85%wt28.50%wtEpoxy resin15.90%wt14.30%wtGlass fiber chop0%wt4.20%wtThickness2.72mm2.80mmDensity3.9gm/cc3.9gm/ccShielding values1.0mm Pb1.0mm Pb@ 100 kVp,Mass per unit area10.7kg/sq m11.04kg/sq mMass of equivalent11.34kg/sq mlead sheetMass of 1 mm Pb/16.74kg/sq m2 mm AlAverage density of5.58gm/cc1 mm Pb/2 mm Al The resulting plaques were comparable in weight and shielding performance to Example 1 and showed a 3-6% mass saving compared to 1 mm of lead; and a 34-36% mass savings compared to a 1 mm lead-lined 2 mm aluminum housing with equivalent shielding performance. This example demonstrates that for certain shielding requirements for certain beam energies, there are options as to selection and combinations of elements, in different ratios which can result in similar weight-shielding performance, but may have different costs. Although these samples were made using powders of each individual metal, since tin-bismuth alloys are widely commercially available in these metallic proportions, it would be possible to substitute the corresponding alloy in similar finely divided form with the same result. Since lead and bismuth are adjoining elements in the periodic table, and have correspondingly similar radiation attenuation characteristics per unit mass, lead can be substituted for bismuth in both of the above formulations if a non lead-free composition is required or permitted. Since the density of lead, 11.34 gm/cc is slightly higher than that of bismuth, 9.7 gm/cc, such equivalent leaded compositions would have slightly lower volume and higher density and corresponding less thickness for equal area mass and shielding value. Alternatively, the leaded-filler volume proportion can be equalized to maintain mechanical properties. These examples and the foregoing description are illustrative of this invention. It is understood that those skilled in the art may devise alternatives to those discussed. The present invention is intended to embrace all such alternatives that fall within the scope of the following claims. |
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043269214 | summary | BACKGROUND OF THE INVENTION The invention described herein relates to nuclear reactors and more particularly to improved control rod guide thimbles designed to minimize wear of control rods during reactor operation. Commercial nuclear reactors of conventional design includes a core composed of multiple fuel assemblies. Each fuel assembly includes an array of fuel rods held in spaced relationship with each other by grids of egg-crate configuration spaced along the fuel rod length. Control rod guide tubes or thimbles interspersed among the fuel rods provide a pathway for control rods which reciprocate therein to control the fission process which takes place in the reactor. These guide thimbles are immovably connected to the longitudinally spaced grids and these components thus form the basic structural framework for each fuel assembly. To extract heat from the core, coolant is circulated upwardly in contact with the heat generating fuel rods from which it absorbs heat before being discharged from the reactor. Since the control rod guide thimbles are open at both lower and upper ends, a portion of the coolant also is circulated therethrough during reactor operation. As the coolant flows at high velocity and pressure through the guide thimbles, it causes the control rods therein to vibrate and thus move laterally and cyclically into contact with the inner walls of the guide thimbles. It has been found that this action induces wear which occurs where the tip of the control rod interfaces with the guide thimble inner surfaces. Close examination and analysis of the evidence of wear shows that a scar of triangular geometry occurs in the wear area. This geometry suggests that the control rod experienced lateral vibratory motion which caused wear at the point where point contact is made between the control rod spherical tip and inner walls of the guide thimble. More specifically, as the control rod vibrates, its tip penetrates progressively deeper into the guide thimble wall, and as the control rod slowly advances or moves upwardly during reactor operation, the point of control rod-guide thimble contact also moves upwardly. This effects a change in the wear scar in that it decreases in size and severity because the control rod lateral motion is less as it is withdrawn with changes in reactor reactivity. Nevertheless, inspection of guide thimbles exposed to wear as described above, showed that the guide thimble walls were worn through in some fuel assemblies while others had only partial circumferential wear. Different designs of guide thimbles have been made to alleviate wear caused by the hydraulically induced vibration of the control rods in the guide thimbles. For example, application Ser. No. 102,046 filed Dec. 10, 1979 by S. Kmonk et al. and assigned to the same assignee as the present invention discloses the use of chromeplated stainless steel wear sleeves within the upper end of the guide thimble at the wear location to help minimize wear caused by the vibrating control rods. SUMMARY OF THE INVENTION Briefly stated, the above disadvantages of prior art designs are overcome by this invention by creating a series of local deformations in the form of indentations in the guide thimble and at positions where the control rod walls interface with the guide thimble walls. Such deformations serve to reduce the clearance between the control rod outer surface and the guide thimble inner surfaces and help to promote contact between the control rod walls and the indentations or insets to achieve line-versus-point contact between the interfacing parts. |
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description | The present application is a continuation-in-part of U.S. application Ser. No. 12/348,785, filed Jan. 5, 2009, which is a continuation application of U.S. application Ser. No. 11/796,764, filed Apr. 30, 2007, now U.S. Pat. No. 7,473,919 (issued Jan. 6, 2009), which is a divisional application of U.S. application Ser. No. 10/997,777, filed Nov. 24, 2004, now U.S. Pat. No. 7,211,814 (issued May 1, 2007), the entire disclosures of which are hereby incorporated by reference. The present disclosure relates generally to systems for and methods of attenuating radiation. More particularly, the present disclosure relates to systems for and methods of attenuating radiation during a radiological examination of a patient. Radiation barriers or shields are used to attenuate (e.g., deflect, absorb, etc.) the flux of electromagnetic radiation originating from a radiation source and directed towards a patient. Radiation can have beneficial and/or negative effects. One beneficial effect of radiation relates to radiological examinations. For purposes of this disclosure, the phrase radiological examination refers generally to any procedure wherein radiation is applied to a patient for the purpose of producing an image or representation of the article. Radiological examinations may provide a non-invasive means capable of obtaining an image of the internal composition of the patient. Radiological examinations may be employed in a variety of applications including, but not limited to, medical procedures. A wide array of medical procedures exist where radiological examinations are employed to obtain an image of the anatomy of a patient or portions thereof. For example, portions of a patient's anatomy may be irradiated during: (i) diagnostic procedures (e.g., Computed Tomography (CT) scanning, x-ray photography, or any other imaging procedure) allowing non-invasive investigation of anatomical regions of a patient (e.g., internal tissue, organs, etc.); or (ii) various invasive procedures, such as the fluoroscopic guidance and/or manipulation of instruments during surgical procedures (e.g., CT fluoroscopy, etc.). To obtain an image through a radiological examination, a primary radiation beam (i.e., entrance radiation) is applied to the patient. Preferably, radiation is selectively focused on to those areas to be examined (i.e., target areas) to minimize the patient's overall radiation exposure. Typically, the target areas are irradiated directly without any obstruction or impairment provided between the primary radiation beam and the patient. It is generally known to cover those areas above and/or below the target area that are not being examined (i.e., secondary areas) with a radiation barrier or shield to prevent and/or reduce radiation exposure for those areas. Such shields are formed of a radiation attenuating material and are often placed directly upon the patient. It has been discovered that in certain procedures limited imaging of the patient can still be generated when a barrier or shield (made of a radiation attenuating material) is placed over the target area (i.e., coincident with the primary radiation beam). The radiation attenuation material absorbs much of the primary radiation beam, but allows an amount (sufficient to generate an image of the patient) to penetrate through and subsequently penetrate the patient. Placing the shield over the target area reduces the amount of radiation exposure realized by the patient. This method of reducing radiation exposure may be particularly beneficial during fluoroscopy procedures during which particularly sensitive areas (e.g., male or female reproductive regions, female breast tissue, etc.) of a patient are exposed to a primary radiation beam. However, it has further been discovered that it is often difficult (if not impossible) to sufficiently examine certain regions of the article when a radiation attenuation material is positioned coincident with the primary radiation beam and over the target area. For example, placing a radiation attenuation material on the surface of the patient prevents a clear and/or accurate image of the surface (or regions slightly below the surface) from being obtained. Such examination limitations are due to x-ray glare (e.g., noise, scatter, artifact, etc.), referred to in this disclosure generally as interference, generated when radiation encounters the radiation attenuation material. This interference hinders a user's ability to obtain a clear image of the patient and therefore cannot be used during the radiological examination. Thus, there is a need for a radiation attenuation system that may be used during a radiological examination to reduce the amount of radiation exposure realized by a patient undergoing the examination. Also, there is a need for a radiation attenuation system that may be positioned coincident to the primary radiation beam to protect the target area (i.e., the area of examination) from increased radiation exposure. Further, there is a need for a radiation attenuation system that may be used during a radiological examination without allowing the interference (caused when radiation encounters a radiation attenuation material) from interfering with the clarity and/or accuracy of the generated image of a patient. Further yet, there is a need for a radiation attenuation system that reduces the amount of radiation exposure for personnel present during a radiological examination. Further still, there is a need for a radiation attenuation system that is relatively adaptable for use with a variety of radiological examinations. It would be desirable to provide for a radiation attenuation system capable of satisfying one or more of these or other needs. According to an exemplary embodiment, a system for attenuating a primary radiation beam applied to a target area on a patient for generating an image of the target area during radiological examination includes a barrier formed of a radiation attenuation material and positionable over the target area to partially attenuate the primary radiation beam before the primary radiation beam reaches the target area. The barrier is configured to substantially extend around an entire periphery of the patient. The system also includes a buffer positionable between the barrier and the patient for offsetting the barrier from the patient. The buffer includes at least one flexible bag configured to retain a fluid. The at least one flexible bag is configured to improve the clarity of the image generated during the radiological examination. According to another exemplary embodiment, a system for attenuating a primary radiation beam applied to a target area on a patient for generating an image of the target area during radiological examination includes a barrier formed of a radiation attenuation material and positionable over the target area to partially attenuate the primary radiation beam before the primary radiation beam reaches the target area. The system also includes a buffer positionable between the barrier and the patient for offsetting the barrier from the patient. The buffer includes at least one flexible bag configured to retain a fluid. The system further includes a valve coupled to at least one flexible bag to allow a user to selectively inflate and deflate the at least one flexible bag for adjusting a distance between the barrier and the target area. The at least one flexible bag is configured to improve the clarity of the image generated during the radiological examination According to another exemplary embodiment, a method of performing a radiological examination of a target area on a patient with a primary radiation beam to generate an image of the target area includes placing a radiation attenuation system on the patient. The radiation attenuation system includes a barrier formed of a radiation attenuation material and a buffer formed of at least one flexible bag configured to retain a fluid. The method also includes aligning the barrier to be in-line with the primary radiation beam so that the primary radiation beam passes through the barrier before reaching the target area. The method further includes positioning the at least one flexible bag between the barrier and the target area. Referring generally to the FIGURES, a radiation attenuation system for use during radiological examinations is disclosed according to an exemplary embodiment. The radiation attenuation system is configured to attenuate radiation that would otherwise be received by a patient and allow for a radiological examination in a number of applications, environments, and configurations. Generally the system includes a first portion or layer for attenuating radiation before reaching a patient and a second portion or layer for buffering (e.g., displacing, offsetting, elevating, spacing apart, etc.) the first portion from the patient undergoing the radiological examination. According to an exemplary embodiment, at least the first portion (i.e., the radiation attenuating portion) is configured to extend laterally around the entire periphery of the patient so that the radiation attenuation system can provide at least some level of protection for the patient throughout an entire radiological examination (e.g., throughout a complete revolution of a CT scanner, etc.). As detailed below, the configuration of the first portion (e.g., the shape, the radiation attenuation effectiveness, the thickness, the continuity, etc.) may vary as the first portion extends around the patient. The radiation attenuation system disclosed herein is configured for in-plane shielding wherein a primary radiation beam is partially blocked by the radiation attenuation system before reaching a target area on the patient (i.e., the area on the patient for which an image is to be obtained). The radiation attenuation system reduces the radiation dose realized by the tissue at the target area while allowing enough radiation to pass to be able to generate an image. By providing a buffer region (i.e., the second portion) between the first portion and the patient, improved imaging (e.g., visualization, examination, image capturing, image displaying, etc.) of the target area of the patient can be achieved. For example, providing a buffer region between the radiation attenuating portion and the patient may allow for imaging of internal regions of the patient as well as other regions of the patient (e.g., surface regions, regions slightly below the surface of the article, etc.) that may otherwise be difficult to examine due to glare (e.g., noise, scatter, artifact, etc.), referred to in this disclosure generally as interference, generated when radiation encounters the first portion. The radiation attenuation system may be used with any medical procedure (e.g., fluoroscopy procedures, Computed Tomography (CT) procedures (e.g., invasive (fluoroscopy) and/or noninvasive (scanning)), x-ray photography procedures, and/or any other image producing medical procedure using radiation, etc.) involving a radiological examination wherein radiation is applied to the anatomy of a patient (or portions thereof) to generate an image on an appropriate display (e.g., monitor, screen, x-ray film, etc.). The radiation attenuation system can be placed upon, near, under, or otherwise about the patient undergoing the radiological examination. The radiation attenuation system lessens or otherwise reduces the amount of radiation (e.g., primary radiation beam, incidental scatter radiation, etc.) realized by a patient and/or personnel (e.g., physicians, surgeons, technicians, etc.) present during the procedures. Referring to FIGS. 1 through 3, the radiation attenuation system is shown according to an exemplary embodiment as a shield 10 configured to protect the breast area of a female patient undergoing a CT procedure from undue radiation exposure. Shield 10 provides a relatively convenient and functionally integrated means of attenuating radiation while allowing for a thorough examination of multiple regions of the article. While shield 10 is illustrated as being used as a shield configured to cover the chest and/or abdomen area of a female patient, shield 10 is equally applicable for use with male patients. Further, shield 10 is applicable for use with any radiological examination procedure wherein radiation is applied to a patient for the purposes of producing an image of the patient (e.g., to shield a gonadal region, thyroid region, etc.). Further still, while shield 10 will be described as protecting a patient during a medical procedure, the scope of the appended claims is intended to encompass shields employed in any application (not limited to medical applications) that uses radiation to generate an image of an article. FIG. 4 shows a cross sectional view of shield 10 according to an exemplary embodiment. Shield 10 includes a first portion or layer (e.g., platform, web, matrix, film, pad, radiation attenuating material, etc.), shown as a barrier 20, a second portion or layer (e.g., filler, spacer, lifter, relatively non-radiation attenuating material, etc.), shown as a buffer 40, and a third portion or layer (e.g., housing, casing, coating, skin, outer material, membrane, etc.), shown as a cover 60. The attenuation of radiation is provided by barrier 20, while buffer 40 provides a substantially non-radiation attenuating boundary or zone between barrier 20 and the surface of the patient. Cover 60 forms the exterior portion or surface (e.g., exposed surface, etc.) of shield 10 and may be useful in retaining and/or supporting buffer 40 relative to barrier 20, protecting barrier 20 and/or buffer 40 from contaminants (e.g., fluids, particles, etc.), providing enhanced comfort for a patient, and/or, improving the overall durability of shield 10. Referring back to FIGS. 1 and 2, shield 10 is positioned on the patient so that barrier 20 can extend laterally around the entire periphery of the patient to provide at least some level of protection for the patient throughout a complete revolution of a CT scanner. As such, in addition to being disposed along the chest area of the patient, barrier 20 is also disposed along the sides and back of the patient to further protect the patient from undue radiation exposure. In an application where the patient is lying on a table, such as in FIG. 1, barrier 20 is intended to be positioned between the patient and the table. Shield 10 may be configured to loosely drape around the patient, or alternatively, may be configured to be worn by a patient as shown in FIG. 2 (e.g., by being sized to fit the patient and/or by being adjustable, etc.). Referring to FIG. 5, barrier 20 is intended to be positioned (e.g., disposed, supported, placed, etc.) coincident with (e.g., in line with, in plane with, etc.) a primary radiation beam 12 to attenuate the primary radiation beam before reaching a target area (i.e., the area of examination) on a patient. Barrier 20 attenuates only a portion of the radiation and allows an amount of radiation sufficient to generate an image to penetrate the system (and subsequently the patient) to generate an image that can be viewed by a worker (e.g., surgeon, physician, technician, etc.). In this manner, shield 10 reduces the patient's radiation exposure by protecting the target area of the patient which is traditionally exposed (e.g., uncovered, unprotected, etc.) to the primary radiation beam. In addition to protecting the patient, barrier 20 may also protect one or more individuals present during the radiological examination (e.g., physicians, surgeons, technicians, etc.). Individuals present during a radiological examination may also be susceptible to radiation exposure from the primary radiation beam (e.g., during a fluoroscopy procedure, etc.), but are more likely to be susceptible to radiation exposure from incidental scatter radiation. Barrier 20 protects against scatter radiation by absorbing at least a portion of the primary radiation beam and scatter radiation. Barrier 20 may be configured to attenuate the flux of electromagnetic radiation over a broad wavelength range depending on the intended application. For example, barrier 20 may attenuate radiation from wavelengths of around 1.0×10−15 meters (e.g., cosmic rays) to around 1.0×106 meters (e.g., radiation from AC power lines) including visible and invisible light, and may find incidental uses at relatively low or high frequency extremes (including gamma rays). The degree of radiation transmission attenuation factor by barrier 20 will depend in part on the specific application to which shield 10 is utilized. According to an exemplary embodiment, barrier 20 has a radiation attenuation factor that remains substantially constant throughout the entire layer. According to another exemplary embodiment, the radiation attenuation factor of barrier 20 varies depending on its position within shield 10. For example, a portion of barrier 20 that is intended to cover a target region on a patient may have a first radiation attenuation factor while a portion of barrier 20 that wraps around and covers non-target regions on a patient, but is still in-line with the primary beam 12 as it revolves around the patient (shown as a region 80 in FIGS. 2 through 4), may have a second radiation attenuation factor. Stated another way, the portion of barrier 20 that is offset from the patient by buffer 40 may have a first radiation attenuation factor while a portion of barrier 20 that is closer to the patient may have a second radiation attenuation factor. According to an exemplary embodiment, the second radiation attenuation factor may be less than the first radiation attenuation factor, at least in some areas such as an area opposite the target area, to allow a sufficient amount of the radiation to reach a sensor of the CT scanner used in generating an image of the patient. According to one embodiment, barrier 20 has a radiation attenuation factor of a percent (%) greater than about 10% of a primary 100 kVp x-ray beam. According to other suitable embodiments, barrier 20 has a radiation attenuation factor of a percent of about 10-50%. According to further suitable embodiments, barrier 20 has a radiation attenuation factor greater than about 50%, suitably greater than about 90%, suitably greater than about 95%, at least in the area configured to cover the target area. According to a preferred embodiment, barrier 20 has a radiation attenuation factor of around 20-60%. According to still further suitable embodiments, barrier 20 may have radiation attenuation factors less than 10% or greater than 95% depending on the application. Barrier 20 may also at least partially attenuate gamma rays, and may have a gamma ray attenuation fraction of at least about 10% of a 140 keV gamma radiation source. Barrier 20 may be fabricated from of any radiation attenuation material including, but not limited to, bismuth, barium, lead, tungsten, antimony, copper tin, aluminum, iron, iodine, cadmium, mercury, silver, nickel, zinc, thallium, tantalum, tellurium, and/or uranium. Anyone of the aforementioned attenuation materials alone or in a combination of two or more of the attenuation materials may provide the desired attenuation. Barrier 20 may have a composition that includes only a radiation attenuation material or combinations thereof, or alternatively, barrier 20 may have a composition that includes a combination of a radiation attenuation material and a non-radiation attenuating material. For example, barrier 20 may include one or more radiation attenuation materials compounded (e.g. mixed, blended, alloyed, dispersed, layered, etc.) with a relatively non-radiation attenuating carrier material. According to one embodiment, barrier 20 has a composition similar to the radiation attenuation system disclosed in U.S. Pat. No. 4,938,233, which is hereby incorporated by reference in its entirety. According to another embodiment, barrier 20 has a composition similar to the radiation attenuation system disclosed in U.S. Pat. No. 6,674,087, which is hereby incorporated by reference in its entirety. However, it should be noted that barrier 20 is not limited to such embodiments. Barrier 20 be provided as a relatively single body, or alternatively may include a plurality of members (e.g., multiple layers of attenuating films or sheets stacked (e.g., overlapping) relative to each other). Forming barrier 20 as a plurality of members may provide a simple technique for varying the radiation attenuation factor along the barrier if such variation is desired. Of course, any other technique may also be used to vary the radiation attenuation factor (e.g., forming the material with different radiation attenuation factors, changing the thickness of the material, forming apertures in the material, etc.). According to one embodiment, barrier 20 is a relatively light weight and flexible. Configuring barrier 20 as a flexible member allows provides for optimized workability for processing, bending, folding, rolling, shipping, etc. Barrier 20 may be formable (e.g. deformable) or compliant, and relatively stretchable (e.g. elastic). In this manner, barrier 20 can advantageously conform to the contours of the patient and wrap around the patient when placed thereon. Still referring to FIG. 5, barrier 20 includes a first surface 22 (e.g., outer surface, upper surface, etc.) and a second surface 24 (e.g., inner surface, lower surface, etc.). Primary radiation beam 12 enters shield 10 through first surface 22 of barrier 20 and does not penetrate a target area on the patient until passing through second surface 24 of barrier 20. The amount of radiation penetrating the target area (radiation exiting second surface 24 of barrier 20) is less than if barrier 20 was not provided. The interaction between the primary radiation beam and barrier 20 generates glare (noise, scatter, artifact, etc.), referred to generally as interference. Such interference traditionally limited the use of radiation barriers or shields over or near the target area. To prevent the interference from degrading the clarity and/or accuracy of an image generated by a radiological examination, shield 10 includes buffer 40. As illustrated in FIG. 5, buffer 40 is provided between barrier 20 and the patient. In particular, buffer 40 is provided between barrier 20 and the patient at the target area on the patient. Buffer 40 lifts barrier 20 away from the patient and provides a relatively non-radiation attenuating boundary or zone between barrier 20 and the target area. Providing a non-radiation attenuating zone between barrier 20 and the target area is intended to improve the image quality of the surface regions of the patient or region slightly below the surface that would otherwise be non-viewable due to the interference generated when the radiation encounters barrier 20. Buffer 40 offsets barrier 20 outwardly from the patient a distance sufficient so that the interference does not prevent a readable image from being obtained. Buffer 40 may also advantageously reduce the radiation dose leaving the patient by providing increased absorption. While buffer 40 is only shown at the target area, according to the various alternative embodiments, buffer 40 may extend around the entire shield 10 similar to barrier 20. Buffer 40 is formed of one or more relatively non-radiation attenuating materials. While buffer 40 may attenuate a certain amount of radiation, it is chosen for having relatively low radiation attenuating properties in comparison to barrier 20. According to an exemplary embodiment, buffer 40 comprises one or more receptacles (e.g., containers, pouches, compartments, etc.), show as bags 42, configured to hold a fluid. According to the embodiment illustrated, buffer 40 includes three bags 42, each bag 42 is configured to receive and selectively retain the fluid, such as air or any other gas, liquid or gel suitable for providing a relatively non-radiation attenuation buffer region between barrier 20 and the patient. During use, the three bags 42 are located above the target area on the patient. According to the various alternative embodiments, buffer 40 may be formed a variety of other non-radiation attenuation materials including, but not limited to, a polymeric material such as a foam material (e.g., closed cell foam, open cell foam, etc.), any woven or non-woven textile, cloth, fiber, vinyl, nylon, etc. Anyone of the aforementioned relatively non-radiation attenuation materials alone or in a combination of two or more of the non-radiation attenuation materials may provide the desired buffer 40. Referring to FIG. 7, bag 42 is a flexible bag that includes first 44 and second 46 bag panels having peripheral edges 48 sealed together to define an inflatable chamber therebetween. A bag opening 50 extends through a portion of sealed edges 48 for receiving a fluid (e.g., air, etc.) to inflate the chamber. According to an exemplary embodiment, first 44 and second 46 bag panels are formed of a film material suitable for retaining the gas. First 44 and second 46 bag panels may be formed of any of a variety of suitable materials including, but not limited to, plastics such as a thermoplastic polymer, cellophane, etc. The size, shape, and configuration of bag 42 will vary depending on the intended use of shield 10. According to the embodiment illustrated, bag 42 has a substantially rectangular shape, but accordingly to the various alternative embodiments, bag 42 may be formed of any shape with any number of panels so that bag 42 adequately provides the desired buffering region. According to an exemplary embodiment, bag 42 has a width extending parallel to a long side of shield 10. The width of bag 42 may varying depending on the overall length (i.e., side-to-side dimension) of shield 10. Bag 42 has a length extending parallel to a short side of shield 10 that is approximately equal to the overall width of shield 10 (i.e., top-to-bottom dimension). According to one nonexclusive embodiment, bag 42 has a width that is between approximately 10 and approximately 20 centimeters when inflated, and a length that is between approximately 20 and approximately 40 centimeters when inflated. Dimensioning bag 42 within such ranges is intended to reduce the amount of radiation that is attenuated by buffer 40 by increasing ratio of gas to material used to form bag 42. According to the various alternative embodiments, bag 42 may have a width and/or a length that is less than or greater than the dimensions provided above. Further still, while buffer 40 is shown as utilizing three bags 42, buffer 40 may comprise any number of bags 42, including a single bag 42. However, providing a number of smaller individual bags 42, rather than a single bag as the buffer layer, may improve the ability of buffer 40 to conform to the contours of the patient. Referring to FIG. 7, bags 42 are configured to be received within cover 60 of shield 10 and are shown as being spaced apart in lateral direction along shield 10. As detailed below, cover 60 includes individual openings or compartments that receive bags 42 and separate adjacent bags 42 from each other with a slight space or gap provided therebetween. Providing a space or gap between each bag 42 may further allow buffer 40 to better conform to the patient. According to an alternative embodiment, each bag 42 may interface with an adjacently positioned bag 42 and/or may be coupled to an adjacently positioned bag 42. According to a further alternative embodiment, a bag 42 may be fluidly coupled to one or more of the other bags 42. In such an embodiment, the fluid pressure would be substantially the same within all of the fluidly coupled bags 42. Bag 42 is shown as having a first surface 52 and a second surface 54. According to an exemplary embodiment, second surface 54 of bag 42 is positioned adjacent to second surface 24 of barrier 20, while first surface 52 of bag 42 is intended to be positioned adjacent to the patient. Second surface 54 of bag 42 may contact second surface 24 of barrier 20, or alternatively, an intermediate layer or gap may be provided between second surface 24 of barrier 20 and second surface 54 of bag 42. Similarly, first surface 52 of bag 42 may be configured to contact the patient, or alternatively, an intermediate layer (e.g., a cover material, etc.) or gap may be provided between first surface 52 of bag 42 and the patient. The distance that barrier 20 is offset from the patient depends at least in part on the state of inflation/deflation (e.g., thickness, etc.) of bag 42. This distance may vary depending on whether bag 42 is deflated, partially inflated or fully inflated. Preferably, barrier 20 is offset (e.g., spaced-apart) from the patient a distance sufficient to obtain an image of the patient without undue artifact or noise. That distance depends on a number of factors such as the radiation attenuation factor of barrier 20, physical characteristics of the patient (e.g., size, weight, etc.), and/or the region of the patient being examined (e.g., slightly below the surface, internal portions, etc.). According to an exemplary embodiment, bag 42 is sized to offset barrier 20 between approximately 0.1 centimeters (e.g., when substantially deflated) and approximately 30 centimeters from the patient (e.g., when fully inflated). According to a preferred embodiment, bag 42 is sized to offset barrier 20 up to approximately 10 centimeters from the patient (e.g., when fully inflated). The distance between barrier 20 and the patient may be defined by the thickness of bag 42 alone, or alternatively, shield 10 may include intermediate or supplemental layers or components (e.g., a cover material, etc.) that further add to the distance. Bag 42 may be configured so that the pressure and/or volume of fluid within the bag is adjustable or nonadjustable. Providing a bag 42 wherein the pressure and/or volume is nonadjustable may reduce manufacturing costs by eliminating the need to provide a means for adjustment. However, in certain applications it may be beneficial to allow for the selective control of the pressure and/or volume within bag 42. For example, over time the bag 42 may leak and the pressure and/or volume of the fluid within the bag may lessen or otherwise change (thereby reducing the effective thickness of buffer 40) and sometime thereafter it may be desirable to return bag 42 to its initial state. Further, by selectively increasing or decreasing the pressure and/or volume of the fluid within the bag 42, the thickness of buffer 40 may be controllable thereby allowing the distance between barrier 20 and the patient to be selectively controlled by a user. For various reasons (e.g., type of examination, size of patient, intensity of primary radiation beam, radiation attenuation factor of barrier 20, etc.) it may be beneficial to control the distance between barrier 20 and the patient. By allowing a user to selectively control the pressure and/or volume of the fluid within bags 42, and thereby control the positioning of barrier 20, a single shield 10 may be suitable for use with a variety of applications which call for varying the position of barrier 20. Referring back to FIG. 6, bag 42 is shown as having a device or mechanism (e.g., regulator, etc.), shown as a valve 56, suitable for allowing a user to selectively control the pressure and/or volume of the fluid (e.g., air, etc.) within each bag 42. According to a preferred embodiment, valve 56 can be used by the medical personnel using shield 10 to selectively inflate or deflate bag 42. Valve 56 is selectively moveable between an open position and a closed position. Valve 56 is operably coupled to bag 42 at opening 50 and is shown as being disposed along an edge 48 that faces an edge of shield 10 that is intended to extend substantially perpendicular to the patient. Providing valve 56 along such an edge 48 allows the user (e.g., physician, medical assistant, technician, etc.) to more easily access valve 56 during a radiological examination. To inflate bag 42 (i.e., to increase the distance that barrier 20 is offset from the patient), the user can insert a fluid source (e.g., an air source, etc.) into an opening of valve 56 that is in fluid communication with the chamber of bag 42. For example, the user can insert a straw into the opening of valve 56 and blow air into the chamber. Alternatively, the user can insert a nozzle coupled to a medical facilities air source into the opening. To deflate bag 42 (i.e., to decrease the distance that barrier 20 is offset from the patient), the user can open valve 56 to reduce the pressure and/or volume of the fluid within the chamber. For example, the user can open valve 56 by manipulating the valve with their fingers (e.g., pinching, etc.). Referring back to FIGS. 3 and 4, cover 60 is shown according to an exemplary embodiment. Cover 60 forms an exterior portion or surface of shield 10 and is useful in retaining and/or supporting bags 42, protecting barrier 20 bags 42 from contaminants (e.g., fluids, particles, etc.), providing enhanced comfort for a patient and improving the overall durability of shield 10. Cover 60 is shown as encapsulating both barrier 20 and bags 42 to define the entire exterior portion of shield 10. According to the various alternative embodiments, cover 60 may only cover either barrier 20 or bags 42, and as such, would only partially define the exterior of shield 10. According to the embodiment illustrated, cover 60 includes a plurality of pockets (e.g., envelopes, etc.), shown as compartments 62, for receiving bags 42. Each compartments 62 is defined by a pair of longitudinally extending boundaries, shown as seams 64, and a laterally extending boundary, shown as a seam 66, extending therebetween along at a bottom edge of the compartment. An upper edge of compartment 62 is left open so that bag 42 can be easily added to and removed from compartment 62 as shown in FIG. 7. Seams 64 and 66 may be formed by stitching or any other suitable coupling technique. According to an exemplary embodiment, compartment 63 is sized to receive a single bag 42. If bag 42 includes valve 56, bag 42 should be inserted into compartment 62 in such a manner so that valve 56 is readily accessible through the opening of compartment 62. Positioning bag 42 in this manner will allow a user to adjust the positioning of barrier 20 relative to the patient without requiring the user to remove bags 42 from compartments 62. To conceal or hide valve 56, and/or to simply conceal and retain bag 42, cover 60 includes a supplemental covering or flap 68 movable between a first position wherein valve 56 is accessible to a user and a second position wherein pressure regulator is concealed from the user. Flap 68 may help protect against an inadvertent actuation of valve 56 during a radiological examination. Cover 60 may be provided as a single unitary body integrally formed with barrier 20 and buffer 40, or alternatively, cover 60 may be provided as one or more sections positioned around buffer 20 and/or barrier 40 and coupled together. According to an exemplary embodiment, cover 40 is coupled to (e.g., bonded, fused, adhered, fastened, attached, connected, enclosing, etc.) barrier 20 employing any of a variety of suitable techniques. Cover 60 may be permanently coupled to barrier 20 and/or buffer 40, or alternatively, may be configured to be detachably coupled. Providing cover 60 as a detachable member may allow barrier 20 and/or buffer 40 to be conveniently interchangeable and/or replaceable. According to other suitable alternative embodiments, cover 60 may be disposed about barrier 20 without actually being coupled (either directly or indirectly) to barrier 20. According to an exemplary embodiment, cover 60 may also include a fastening device to allow shield 10 to be secured to a patient. According to the embodiment illustrated, cover includes a hook and loop fastener 70 with corresponding sections provided at opposite lateral free ends of cover 60. Once shield 10 is wrapped around the patient, the corresponding sections of hook and loop fastener 70 can be joined to provide an appropriate fit as shown in FIGS. 2 and 5. According to the various alternative embodiments, hook and loop fastener 70 may be replaced with any of a number of attachment devices including, but not limited to, adhesives, clips, snaps, buttons, zippers, etc.). Cover 60 may be made from a variety of materials. For example, cover 60 may be made of a material that enhances processability, softness or comfort for a user, a material that is substantially impervious to fluid, and/or a material having heat sealing properties to assist in the retention of body heat. Cover 60 may be fabricated from a variety of woven or non-woven materials including, but not limited to, polymers, natural fibers (cotton, wool, silk, etc.), nylon, vinyl, or composite materials. Cover 60 may further include an absorbent layer for maintaining fluid control (e.g., block blood from seeping onto the patient during a surgical procedure, etc.). The absorbent layer may be attached to a relatively liquid impervious layer such as a plastic, polyethylene, etc. The impervious layer may hinder the transmission of fluid from the absorbent layer to cover 60. Referring to FIGS. 8 through 10, further exemplary embodiments of shield 10 are shown. According to the exemplary embodiment of shield 10 shown in FIGS. 1 through 7, barrier 20 is a substantially solid layer as it extends between the lateral free ends of shield 10 even though, as noted above, barrier 20 may be formed of multiple layers and/or may have different thicknesses or compositions to provide for differing radiation attenuation factors. As also noted above, it may be desirable to provide barrier 20 with a radiation attenuation factor that is lower in those regions that are not offset from the patient by buffer 40. Such as region is identified in FIGS. 2, 3 and 7 as a region 80. Reducing the radiation attenuation factor of barrier 40 in these regions may further improve image quality, while still protecting the patient from undue exposure to radiation. The exemplary embodiments shown in FIGS. 8 through 10 provide an alternative approach to reducing the radiation attenuation factor of barrier 20 in region 80. In each embodiment, barrier 20 includes one or more apertures that allow the primary beam to pass through without being attenuated. Such a technique has been found to reduce the effective radiation attenuation factor of barrier 20. In such embodiments, barrier 20 remains a substantially solid layer in the region where barrier 20 is offset by buffer 40 (i.e., those regions intended to cover the target area). According to the embodiment illustrated in FIG. 8, barrier 20 includes a plurality of openings 82 that are arranged to form a checkerboard appearance. According to the embodiment illustrated in FIG. 9, barrier 20 includes a plurality of openings 84 extending substantially parallel to each other in a longitudinal direction of shield 10. According to the embodiment illustrated in FIG. 10, barrier 20 includes a plurality of openings 86 extending substantially parallel to each other in a lateral direction of shield 10. Barrier 20 may be formed with openings 82, 84 and 86, or alternatively, openings 82, 84 and 86 may be removed from barrier 20 after formation (e.g., by cutting, etc.). It is important to note that the construction and arrangement of the elements of the radiation attenuation system as shown in the illustrated embodiments is illustrative only. Although only a few embodiments of the present inventions have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements shown as multiple parts may be integrally formed, the operation of the interfaces may be reversed or otherwise varied, or the length or width of the structures and/or members or connectors or other elements of the system may be varied. Also, for purposes of this disclosure, the term “coupled” means the joining or combining of two members (e.g., portions, layers, materials, etc.) directly or indirectly to one another. Such joining or combining may be stationary in nature or movable in nature. Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate member being attached to one another. Such joining or combining may be permanent in nature or alternatively may be removable or releasable in nature. Further, the size, shape, and configuration of shield 10 may be provided in any number of forms (only a few of which are illustrated in the FIGURES) suitable for at least partially covering an article such as the anatomy of a patient or portions thereof. While shield 10 shown as being a substantially rectilinear cover, shield, or drape having a sufficient width and length to span entirely across the patient and an operating table, shield 10 may be provided as any of a number of shapes and sizes. Further still, shield 10 is configured to be relatively compliant in nature so that it can reside closely next to the body of the patient. Shield 10 is intended to be comfortable and fit positively against the undulating surface of the patient thus improving its stability while the surgical team is operating on the body of the patient. Preferably the coefficient of friction between shield 10 and the surface of the patient adds to that stability, preventing movement of the radiation attenuation system during the surgical procedure and further obviating the need to take extraordinary measures to prevent slippage or movement of the drape. Further still, shield 10 may be configured to be disposable in whole or in part, thereby minimizing ancillary sources of contamination that may arise from multiple uses. For example, shield 10 may be configured to allow barrier 20 and cover 60 to be retained while bags 42 forming buffer 40 can be replaced and/or interchanged as desired. Further, shield 10 may be configured to allow barrier 20 and/or buffer 40 to be retained while cover 60 is replaced. Components of shield 10 are preferably non-toxic, recyclable, and/or biodegradable. According to an alternative embodiment, the articles of radiation attenuation system may be reusable (e.g. for attenuation of radiation from atomic/nuclear disaster, clean up, rescue operations, etc.). According to a preferred embodiment, the articles of shield 10 (e.g., barrier 20, buffer 40, and/or cover 60, etc.) may be sterilized between uses to minimize the likelihood of bacteriological or virus contamination. Sterilization may be performed in any convenient manner, including gas sterilization and irradiation sterilization. It should further be noted that the elements and/or assemblies of the system may be constructed from any of a wide variety of materials that provide sufficient strength or durability, in any of a wide variety of colors, textures and combinations. Accordingly, all such modifications are intended to be included within the scope of the appended claims. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the preferred and other exemplary embodiments without departing from the spirit of the appended claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus-function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and omissions may be made in the design, operating configuration and arrangement of the preferred and other exemplary embodiments without departing from the spirit of the inventions as expressed in the appended claims. |
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description | This application is a continuation of U.S. patent application Ser. No. 14/402,666, filed on Apr. 20, 2015, which is a U.S. National Stage of International Application No. PCT/JP2013/057471, filed on Mar. 15, 2013, which claims priority to Japanese Patent Application No. 2012-115533 filed on May 21, 2012, the contents of which are incorporated herein by reference. The present invention relates to a reflective mirror, a projection optical system, an exposure apparatus, and a device manufacturing method. Relating to exposure apparatuses for use in a photolithography process, EUV exposure apparatuses in which extreme ultraviolet (EUV) light is used as exposure light have been proposed, as disclosed, for example, in the following Patent Document 1. In an optical system of an EUV exposure apparatus, a multilayer-film reflective mirror having a multilayer film capable of reflecting at least a portion of incident light is used. [Patent Document 1] U.S. Patent Application Publication No. 2005/157384 In multilayer-film reflective mirrors, there is a possibility that the reflectance of the multilayer film will change according to the incident angle of the light with respect to the multilayer film. For example, when the reflectance of the multilayer film decreases, there is a possibility that exposure light of a desired intensity will not be irradiated onto a substrate. Consequently, there is a possibility that exposure defects will be generated and defective devices will be manufactured. An object of aspects of the present invention is to provide a reflective mirror with high reflectance. Another object of the aspects of the present invention is to provide a projection optical system and an exposure apparatus which can suppress the generation of exposure defects. Accordingly, the throughput of the exposure apparatus is improved. Still another object of the aspects of the present invention is to provide a device manufacturing method which can suppress the generation of defective devices. Accordingly, the throughput of the device manufacturing is improved. According to a first aspect of the present invention, there is provided a reflective mirror reflecting incident light, the reflective mirror including: a base, and a multilayer film configured to reflect at least a portion of the incident light and having a first layer and second layer that are laminated alternately on the base, the multilayer film being provided with a first portion having a first thickness and with a second portion having a second thickness different from the first thickness, the second portion being provided at a position rotationally symmetric to a position of the first portion about an optical axis of the reflective mirror. According to a second aspect of the present invention, there is provided a projection optical system including a plurality of optical elements, the projection optical system projecting an image of a first surface onto a second surface, and at least one of the optical elements being the reflective mirror according to the first aspect. According to a third aspect of the present invention, there is provided an exposure apparatus for exposing a substrate to exposure light, the exposure apparatus including the reflective mirror according to the first aspect. According to a fourth aspect of the present invention, there is provided a device manufacturing method including exposing a substrate using the exposure apparatus according to the third aspect, and developing the exposed substrate. According to the aspects of the present invention, it is possible to suppress a decrease in reflectance in the multilayer film. In addition, according to the aspects of the present invention, it is possible to suppress the generation of exposure defects and the generation of defective devices. Accordingly, it is possible to use a reflective mirror with high reflectance. In addition, the throughput of the exposure apparatus is improved. Below, description will be given of embodiments of the present invention with reference to the diagrams; however, the present invention is not limited to the description. In the following description, an XYZ rectangular coordinate system is established, and the positional relationship of respective members is described with reference to the XYZ rectangular coordinate system. A predetermined direction within a horizontal plane is made the X axis direction, a direction orthogonal to the X axis direction within the horizontal plane is made the Y axis direction, and a direction orthogonal to both the X axis direction and the Y axis direction (that is, a perpendicular direction) is made the Z axis direction. Rotation (tilt) directions about the X axis, the Y axis, and the Z axis are made the θX, θY and θZ directions, respectively. FIG. 1 is a schematic view showing an example of a multilayer-film reflective mirror 10 (reflective mirror) according to the present embodiment. In FIG. 1, the multilayer-film reflective mirror 10 is provided with a base 5, and a multilayer film 4 having a first layer 1 and second layer 2 laminated alternately on the base 5 and capable of reflecting at least a portion of incident light EL. In the present embodiment, the light EL incident on the multilayer film 4 contains extreme ultraviolet light. Extreme ultraviolet light is, for example, an electromagnetic wave in a soft X-ray region with a wavelength of approximately 11 to 14 nm. Extreme ultraviolet light is reflected by the multilayer film 4. In the following description, extreme ultraviolet light will be referred to as EUV light as appropriate. Here, the light EL incident on the multilayer film 4 may be an electromagnetic wave in a soft X-ray region of approximately 5 to 50 nm or may be an electromagnetic wave of approximately 5 to 20 nm. In addition, the light EL may be an electromagnetic wave with a wavelength of 193 nm or less. For example, the light EL may be vacuum ultraviolet (VUV) light such as ArF excimer laser light (wavelength of 193 nm) or F2 laser light (wavelength of 157 nm). The base 5 is, for example, formed of ultra-low expansion glass. As the base 5, ULE manufactured by Corning Inc., Zerodur (registered trademark) manufactured by Schott AG, or the like is used. The multilayer film 4 includes the first layer 1 and second layer 2 laminated alternately with a predetermined periodic length d. The periodic length d refers to the sum (d1+d2) of the thickness d1 of the first layer 1 and the thickness d2 of the second layer 2. Based on the theory of optical interference, each of the thickness d1 of the first layer 1 and the thickness d2 of the second layer 2 is set such that the reflected waves reflected by each interface with the first layer 1 and the second layer 2 coincide with one another in phase. In the following description, one set of the first layer 1 and the second layer 2 is referred to as a layer pair 7 as appropriate. In the present embodiment, with regard to one layer pair 7, the first layer 1 is arranged on the base 5 side (on the −Z side in the diagram) with respect to the second layer 2. The multilayer film 4 is formed by the layer pair 7 of the first layer 1 and the second layer 2 being laminated on the base 5. For example, there are tens to hundreds of the layer pairs 7 laminated on the base 5. As an example, in the present embodiment, there are 50 layer pairs 7 laminated on the base 5. In the present embodiment, the thickness of the multilayer film 4 includes a thickness Da of the entirety of the multilayer film 4 which is the sum of the thicknesses of the plurality (for example, 50) of the layer pairs 7. In addition, in the present embodiment, the thickness of the multilayer film 4 includes the thickness of one layer pair 7 including one first layer 1 and one second layer 2. That is, in the present embodiment, the thickness of the multilayer film 4 includes the periodic length d (=d1+d2). The first layer 1 is formed of a material with a refractive index differing greatly from the refractive index of vacuum with respect to EUV light. The second layer 2 is formed of a material with a refractive index differing little from the refractive index of vacuum with respect to EUV light. In the present embodiment, the first layer (heavy atom layer) 1 is formed of molybdenum (Mo). The second layer (light atom layer) 2 is formed of silicon (Si). That is, the multilayer film 4 of the present embodiment is a Mo/Si multilayer film where a molybdenum layer (Mo layer) and a silicon layer (Si layer) are laminated alternately. The refractive index of vacuum n is 1. In addition, for example, the refractive index of molybdenum nMo with respect to EUV light with a wavelength of 13.5 nm is 0.92, and the refractive index of silicon nSi is 0.998. In this manner, the second layer 2 is formed of a material where the refractive index with respect to EUV light is substantially equal to the refractive index of vacuum. As shown in FIG. 1, in the present embodiment, there is a distribution in the thickness of the multilayer film 4. In other words, the multilayer film 4 has a plurality of portions with different thicknesses. As shown in FIG. 1, the multilayer film 4 has at least a first portion PA1 with a first thickness and a second portion PA2 with a second thickness which is different from the first thickness. In the present embodiment, the distribution of the thickness of the multilayer film 4 (the thickness distribution of the multilayer film) does not have an axis of rotational symmetry. The multilayer film 4 has a thickness distribution which is not rotationally symmetric (a non-rotationally symmetric thickness distribution). In the present embodiment, the distribution of the thickness of the multilayer film 4 is non-rotationally symmetric with respect to the center of the region to which the light EL is incident on a surface 4S of the multilayer film 4. In the present embodiment, the distribution of the thickness of the multilayer film 4 is non-rotationally symmetric with respect to any position on the XY plane on the surface 4S of the multilayer film 4. In addition, in the present embodiment, the shape of a surface 5S of the base 5 where the multilayer film 4 is formed is determined such that an aberration caused by the distribution of the thickness of the multilayer film 4 are reduced. In the example shown in FIG. 1, the shape of the surface 5S of the base 5 is determined such that a surface 5S2 of the base 5 where the second portion PA2 is formed is arranged at a position further from the surface 4S of the multilayer film 4 than that of a surface 5S1 of the base 5 where the first portion PA1 is formed. FIG. 2 is a diagram schematically showing the surface 4S of the multilayer film 4. In FIG. 2, the thickness of the multilayer film 4 is different in the first position (the first portion PA1) and the second position (the second portion PA2) of the surface 4S. In the example shown in FIG. 2, the first portion PA1 and the second portion PA2 are at an equal distance from an optical axis AX of the multilayer-film reflective mirror 10. That is, the distance between the first portion PA1 and the optical axis AX is equal to the distance between the second portion PA2 and the optical axis AX. In other words, the first portion PA1 and the second portion PA2 are positioned on a circle centered on the optical axis AX. This shows that the second portion PA2 is provided at a position which is rotationally symmetric about the optical axis (reference axis) AX of the multilayer-film reflective mirror 10 with respect to the first portion PA1. In this manner, in the present embodiment, the distribution of the thickness of the multilayer film 4 does not have an axis of rotational symmetry (a point of rotational symmetry). In other words, the distribution of the thickness of the multilayer film 4 is not a rotationally symmetric distribution. This shows that, in the first portion PA1 and the second portion PA2 which are rotationally symmetric about the optical axis (reference axis) AX, the thicknesses of the multilayer film 4 are different from each other. That is, the multilayer-film reflective mirror 10 has a thickness distribution where the thickness of the multilayer film 4 changes in the azimuthal direction of the optical axis AX (for example, the rotation direction around the optical axis AX, the θZ direction, or the like). For example, the multilayer-film reflective mirror 10 has a thickness distribution which continuously changes along the azimuthal direction of the optical axis AX. In addition, in the present embodiment, the distribution of the thickness of the multilayer film 4 is line symmetric with respect to a line which passes through the center of the region to which the light EL is incident on the surface 4S of the multilayer film 4. In addition, in the present embodiment, the distribution of the thickness of the multilayer film 4 is line symmetric with respect to a line which passes through the optical axis AX and the center of the region to which the light EL is incident on the surface 4S of the multilayer film 4. In addition, in the present embodiment, the distribution of the thickness of the multilayer film 4 has a finite number of axes of rotational symmetry in the surface 4S of the multilayer film 4. The multilayer film 4 has a thickness distribution which has a finite number of axes of rotational symmetry in the surface 4S of the multilayer film 4. Note that, in either case, the multilayer-film reflective mirror 10 is provided with the first portion PA1 which has the first thickness and the second portion PA2 which has a second thickness different from the first thickness, second portion PA2 being provided at a position rotationally symmetric about the optical axis AX of the multilayer-film reflective mirror 10 with respect to a position of the first portion PA1. For example, even in a case where the distribution of the thickness of the multilayer film 4 has a finite number of axes of rotational symmetry in the surface 4S of the multilayer film 4, at least a part of the multilayer-film reflective mirror 10 has portions where the thicknesses of the multilayer film are different from each other at positions rotationally symmetric about the optical axis AX. FIG. 3 is a diagram showing a relationship between the incident angle of the light EL with respect to the surface 4S of the multilayer film 4 and the reflectance of the multilayer film 4 with respect to the incident light EL. When the thickness of the multilayer film 4 changes, the reflectance characteristic with respect to the incident angle changes. For example, as shown by lines Ca1 and Cb1 in FIG. 3, the multilayer film 4 with the periodic length da is capable of reflecting the light EL incident at an incident angle of from θah to θar. The multilayer film 4 with a periodic length db is capable of reflecting the light EL incident at an incident angle of from θbh to θbr. In addition, the multilayer film 4 with the periodic length da reflects the light EL, which is incident at the incident angle θam, with a reflectance H1. The multilayer film 4 with the periodic length db reflects the light EL, which is incident at the incident angle θbm, with the reflectance H1. The incident angle θam is a value in the middle of the incident angles of from θah to θar. The incident angle θbm is a value in the middle of the incident angles of from θbh to θbr. The reflectance H1 is the maximum reflectance (peak reflectance) when the light EL is incident at an incident angle of from θah to θar on the surface 4S of the multilayer film 4 with the periodic length da. The reflectance H1 is the maximum reflectance (peak reflectance) when the light EL is incident at an incident angle of from θbh to θbr on the surface 4S of the multilayer film 4 with the periodic length db. Note that, in FIG. 3, the lines Ca1 and Cb1 have bilateral symmetry; however, there is a possibility that the lines will not have bilateral symmetry. In addition, FIG. 3 shows an example where the value in the middle of the incident angles is the maximum reflectance; however, there is a possibility that the value in the middle of the incident angles will not be the maximum reflectance. In this manner, the incident angle where the reflectance H1 is obtained is θam when the light EL is incident on the surface 4S of the multilayer film 4 with the periodic length da, and the incident angle where the reflectance H1 is obtained is θbm when the light EL is incident on the surface 4S of the multilayer film 4 with the periodic length db. In other words, it is possible to obtain the reflectance H1 by setting the periodic length of the multilayer film 4 where the light EL is incident at the incident angle θam to da, and it is possible to obtain the reflectance H1 by setting the periodic length of the multilayer film 4 where the light EL is incident at the incident angle θbm to db. In addition, as shown in FIG. 3, the reflectance is substantially zero even when the light EL is incident on the surface 4S of the multilayer film 4 with the periodic length da at the incident angle θbm. In other words, the light EL is substantially not reflected even when the light EL is incident on the surface 4S of the multilayer film 4 with the periodic length da at the incident angle θbm. In addition, the reflectance is substantially zero even when the light EL is incident on the surface 4S of the multilayer film 4 with the periodic length db at the incident angle θam. In other words, the light EL is substantially not reflected even when the light EL is incident on the surface 4S of the multilayer film 4 with the periodic length db at the incident angle θam. In addition, as shown by line Ca2 in FIG. 3, it is possible to adjust the incident angle (incident angle range) of the light EL which the multilayer film 4 is capable of reflecting by adjusting at least one of the thickness d1 of the first layer 1 and the thickness d2 of the second layer 2. For example, it is possible to increase the incident angle range of the light EL which the multilayer film 4 is capable of reflecting by adjusting at least one of the thickness d1 of the first layer 1 and the thickness d2 of the second layer 2. In addition, it is possible to decrease the incident angle range of the light EL which the multilayer film 4 is capable of reflecting by adjusting at least one of the thickness d1 of the first layer 1 and the thickness d2 of the second layer 2. In the example shown by line Ca2, it is possible for the multilayer film 4 to reflect the light EL which is incident at the incident angles of from θaf to θat. In addition, the maximum reflectance is adjusted by adjusting at least one of the thickness d1 of the first layer 1 and the thickness d2 of the second layer 2. In the example shown in FIG. 3, the reflectance (maximum reflectance) H2 is smaller than the reflectance (maximum reflectance) H1. In addition, it is even possible to adjust the incident angle (incident angle range) which the multilayer film 4 is capable of reflecting by adjusting the thickness Da of the entire multilayer film 4. In addition, it is even possible to adjust the maximum reflectance of the multilayer film 4 by adjusting the thickness Da of the entire multilayer film 4. In this manner, at least one of the incident angle (incident angle range) of the light EL which can be reflected, and the reflectance (maximum reflectance) with respect to the incident angle of the light EL is determined based on the thickness of the multilayer film 4, which includes at least one of the periodic length d of the multilayer film 4, the thickness d1 of the first layer 1, the thickness d2 of the second layer 2, and the thickness Da of the entire multilayer film 4. In addition, it is possible to adjust at least one of the incident angle range and the maximum reflectance by adjusting the thickness of the multilayer film 4. FIG. 4 is a schematic view showing a multilayer film 4J according to a Comparative Example. In FIG. 4, the light EL is incident at a first incident angle θa to a position (portion PAJ1) on a surface 4SJ of the multilayer film 4J, and the light EL is incident at a second incident angle θb to a position (portion PAJ2) which is different from the portion PAJ1. In the multilayer film 4J, the thickness of the portion PAJ1 and the thickness of the portion PAJ2 are equal to each other. The light EL incident on the portion PAJ1 is reflected. On the other hand, the light EL incident on the portion PAJ2 is not reflected. FIG. 5 is a schematic view showing the multilayer film 4 according to the present embodiment. The light EL is incident at the first incident angle θa to a first position (first portion PA1) on the surface 4S of the multilayer film 4, and the light EL is incident at the second incident angle θb to a second position (second portion PA2) which is different from the first portion PA1. In the multilayer film 4, the thickness of the first portion PA1 and the thickness of the second portion PA2 of the multilayer film 4 are different from each other. The first portion PA1 has a thickness capable of reflecting the light EL which is incident at the first incident angle θa. The second portion PA2 has a thickness capable of reflecting the light EL which is incident at the second incident angle θb. In the present embodiment, the thicknesses of the multilayer film 4 in the first portion PA1 and the second portion PA2 are determined such that the reflectances of the light EL in the first portion PA1 (first position) and the second portion PA2 (second position) are high, and the difference between the reflectances is reduced. FIG. 6 is a diagram showing an example of a projection optical system PL according to the present embodiment. The projection optical system PL has a plurality of optical elements and projects an image of a first surface BJ onto a second surface IM. The light EL from the first surface BJ is irradiated onto the second surface IM via the plurality of optical elements of the projection optical system PL. In the present embodiment, at least one of the plurality of optical elements of the projection optical system PL is the multilayer-film reflective mirror 10 having the multilayer film 4. For example, an optical element having the largest incident angle range of the light EL out of the plurality of optical elements of the projection optical system PL may be the multilayer-film reflective mirror 10 according to the present embodiment. In the example shown in FIG. 6, after being reflected by an optical element M1, the light EL from the first surface BJ is irradiated onto the second surface IM via an optical element M2, an optical element M3, an optical element M4, an optical element M5, and an optical element M6. In such a case, for example, the optical element M3 may be the multilayer-film reflective mirror 10, or the optical element M5 may be the multilayer-film reflective mirror 10. Naturally, at least one of the optical elements M1, M2, M4, M6 may be the multilayer-film reflective mirror 10, or all of the optical elements M1 to M6 may be the multilayer-film reflective mirror 10. FIG. 7 and FIG. 8 are diagrams showing examples of distributions of the incident angle of the light EL with respect to the multilayer film 4. As shown in FIG. 7 and FIG. 8, in the present embodiment, the distribution of the incident angle of the light EL with respect to the multilayer film 4 is line symmetric with respect to a line parallel with the Y axis in the diagram. The direction parallel with the Y axis is a scanning direction (scan direction) when a substrate P is exposed in an exposure apparatus EX to be described below. For example, in FIG. 7, the multilayer film 4 has a portion where the incident angle of the light EL is 23.10°. In addition, the multilayer film 4 has a portion where the incident angle of the light EL is 1.155°. FIG. 9 is an example showing a difference in the incident angle distribution of the maximum incident angle of the light EL incident on the multilayer film 4 (for example, FIG. 7) and the incident angle distribution of the minimum incident angle (for example, FIG. 8). The incident angle of the light EL incident on the multilayer film 4 changes in a case where the numerical aperture NA of the projection optical system PL changes, a case where the image height changes, or the like. In the present embodiment, for example, the multilayer film 4 is formed in consideration of the incident angle distribution of the maximum incident angle and the incident angle distribution of the minimum incident angle. In one example, it is possible for the multilayer film 4 to have the thickness distribution shown in FIG. 9. In such a case, in the multilayer-film reflective mirror 10, the thickness of the multilayer film 4 changes according to the gradations shown FIG. 9. For example, the multilayer film 4 has a high film thickness at points in FIG. 9 showing high values, and has a low film thickness at points showing low values. In addition, in the present embodiment, the distribution of the thickness of the multilayer film 4 is line symmetric with respect to a line parallel with the Y axis. The direction parallel with the Y axis is a scanning direction (scan direction) when the substrate P is exposed in the exposure apparatus EX to be described below. The distribution of the thickness of the multilayer film 4 may be represented by the rectangular coordinate system. In addition, the distribution of the thickness of the multilayer film 4 may be represented by the polar coordinate system. For example, the distribution of the thickness of the multilayer film 4 may be represented by a polynomial series representing the distribution of the thickness of the multilayer film 4 using the distance from the optical axis AX on the surface 4S of the multilayer film 4 and polar coordinates. In addition, the distribution of the thickness of the multilayer film 4 may be represented by Zernike polynomials. FIG. 10 is a diagram showing an example of the exposure apparatus EX according to the present embodiment. The exposure apparatus EX of the present embodiment is an EUV exposure apparatus which exposes the substrate P to EUV light. The multilayer-film reflective mirror 10 described above is used as an optical system of the EUV exposure apparatus EX according to the present embodiment. In FIG. 10, the exposure apparatus EX is provided with a mask stage 11 capable of moving while holding a mask M, a substrate stage 12 capable of moving while holding the substrate P onto which exposure light EL is irradiated, a light source apparatus 13 which generates the light (exposure light) EL which includes EUV light, an illumination optical system IL which illuminates the mask M held by the mask stage 11 with the exposure light EL emitted from the light source apparatus 13, the projection optical system PL which projects an image of a pattern of the mask M illuminated by the exposure light EL onto the substrate P, and a chamber apparatus VC which has a vacuum system which forms a predetermined space through which at least the exposure light EL passes and sets the predetermined space to a vacuum state (for example, 1.3×10−3 Pa or less). The substrate P includes a substrate where a photosensitive film is formed on a base such as a semiconductor wafer. The mask M includes a reticle where a device pattern which is projected onto the substrate P is formed. In the present embodiment, EUV light is used as the exposure light EL, and the mask M is a reflective mask which has a multilayer film capable of reflecting EUV light. The multilayer film of the reflective mask includes, for example, a Mo/Si multilayer film, and a Mo/Be multilayer film. The exposure apparatus EX illuminates the reflecting surface (pattern forming surface) of the mask M where the multilayer film is formed with the exposure light EL and exposes the substrate P to reflected light of the exposure light EL reflected by the mask M. The light source apparatus 13 of the present embodiment is a laser-excited plasma light source apparatus which includes a laser apparatus 15 for emitting laser light, and a supply member 16 for supplying a target material such as a xenon gas. The laser apparatus 15 generates laser light with a wavelength in the infrared region and the visible region. The laser apparatus 15 includes, for example, a YAG laser, an excimer laser, or the like using semiconductor laser excitation. In addition, the light source apparatus 13 is provided with a first collection optical system 17 for collecting laser light emitted from the laser apparatus 15. The first collection optical system 17 collects the laser light emitted from the laser apparatus 15 at a position 19. The supply member 16 has a supply port which supplies the target material to the position 19. The laser light collected by the first collection optical system 17 is irradiated onto the target material supplied from the supply member 16. The target material irradiated by the laser light is heated to a high temperature due to the energy of the laser light. Then, the target material is excited into a plasma state and generates light including EUV light during a transition to a low potential state. Note that, the light source apparatus 13 may be a plasma discharge light source apparatus. The light source apparatus 13 generates light (EUV light) which has a spectrum in the extreme ultraviolet region. The exposure apparatus EX is provided with a second light-collection mirror 18 arranged at the periphery of the position 19. The second light-collection mirror 18 includes an elliptical mirror. The second light-collection mirror 18 which includes the elliptical mirror is arranged such that a first focal point and the position 19 are substantially matched. The EUV light (exposure light) EL collected at a second focal point by the second light-collection mirror 18 is supplied to the illumination optical system IL. The illumination optical system IL includes a plurality of optical elements 20, 21, 22, 23, 24 to which the exposure light EL emitted from the light source apparatus 13 is supplied and illuminates the mask M with the exposure light EL emitted from the light source apparatus 13. At least one of the optical elements 20, 21, 22, 23, 24 of the illumination optical system IL may be the multilayer-film reflective mirror 10 described above. The optical element 20 of the illumination optical system IL is a third light-collection mirror functioning as a collimator mirror, to which the exposure light EL from the second light-collection mirror 18 is supplied. The exposure light EL from the second light-collection mirror 18 is guided to the third light-collection mirror 20. The third light-collection mirror 20 includes a parabolic mirror. The third light-collection mirror 20 is arranged such that the focal point thereof and the second focal point of the second light-collection mirror 18 are substantially matched. In addition, the illumination optical system IL has an optical integrator 25. In the present embodiment, the optical integrator 25 includes a reflective fly eye mirror optical system. The reflective fly eye mirror optical system 25 includes an incident side fly eye mirror 21 and an emission side fly-eye mirror 22. The third light-collection mirror 20 supplies the exposure light EL to the incident side fly eye mirror 21 of the reflective fly eye mirror optical system 25, with the exposure light EL substantially collimated. The incident side fly eye mirror 21 includes a plurality of unit mirrors (reflecting element group) having reflecting surfaces disposed in parallel with each other, the reflecting surfaces having an arcuate shape substantially similar to an illumination field as disclosed, in for example, U.S. Pat. No. 6,452,661, and the like. The incident side fly eye mirror 21 is arranged at a position optically conjugate with the reflecting surface of the mask M and the surface of the substrate P, or in the vicinity thereof. In addition, the emission side fly eye mirror 22 includes a plurality of unit mirrors (reflecting element group) corresponding to the plurality of unit mirrors of the incident side fly eye mirror 21. Each of the unit mirrors of the emission side fly eye mirror 22 has a rectangular shape and is arranged in parallel. The emission side fly eye mirror 22 is arranged at a position optically conjugate with the pupil position of the projection optical system PL, or in the vicinity thereof. The collimated light from the third light-collection mirror 20 is incident on the incident side fly eye mirror 21 and undergoes wave front splitting through the incident side fly eye mirror 21. Each of the unit mirrors of the incident side fly eye mirror 21 collects the incident light and forms a plurality of light collection points (light source image). A plurality of unit mirrors of the emission side fly eye mirror 22 are arranged at positions near where the plurality of light collection points are formed. A plurality of light collection points (secondary light source) which correspond to the number of unit mirrors of the emission side fly eye mirror 22 are formed on the emission surface of the emission side fly eye mirror 22 or in the vicinity thereof. In addition, the illumination optical system IL has a condenser mirror 23. The condenser mirror 23 is arranged such that a focal position of the condenser mirror 23 and the position in the vicinity of the secondary light source which is formed by the reflective fly eye mirror optical system 25 are substantially matched. The light from the secondary light source formed by the reflective fly eye mirror optical system 25 is reflected and collected by the condenser mirror 23 and supplied to the mask M via an optical path bending mirror 24. In this manner, the illumination optical system IL including the plurality of optical elements 20 to 24 uniformly illuminates an illumination region on the mask M with the exposure light EL emitted from the light source apparatus 13. The exposure light EL illuminated by the illumination optical system IL and reflected by the mask M is incident on the projection optical system PL. Note that, in order to spatially separate the optical path of the light supplied to the mask M and the optical path of the light reflected by the mask M to be incident on the projection optical system PL, the illumination optical system IL of the present embodiment is a non-telecentric system. In addition, the projection optical system PL is also a mask side non-telecentric system. The mask stage 11 is a stage capable of moving with six degrees of freedom in six directions, which are the X axis, Y axis, Z axis, θX, θY, and θZ directions, while holding the mask M. In the present embodiment, the mask stage 11 holds the mask M such that the reflecting surface of the mask M and the XY plane are substantially parallel. The position information of the mask stage 11 (mask M) is measured by a laser interferometer 41. The laser interferometer 41 measures position information relating to the X axis, Y axis, and θZ directions of the mask stage 11 using a measuring mirror provided in the mask stage 11. In addition, the surface position information of the surface of the mask M held by the mask stage 11 (position information relating to the Z axis, the θX, and the θY) is detected by a focus leveling detection system (not shown). The position of the mask M held by the mask stage 11 is controlled based on the measurement result made by the laser interferometer 41 and the detection result made by the focus leveling detection system. In addition, the exposure apparatus EX of the present embodiment is provided with a blind member 60 arranged at a position opposite to at least a portion of the reflecting surface of the mask M and limits the illumination region of the exposure light EL on the reflecting surface of the mask M as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2004-356415A, and the like. The blind member 60 has an opening through which the exposure light EL can pass and defines the illumination region of the exposure light EL on the reflecting surface of the mask M. The projection optical system PL includes a plurality of optical elements 31, 32, 33, 34, 35, 36 to which the exposure light EL from the mask M is supplied and projects an image of the pattern of the mask M illuminated by the exposure light EL onto the substrate P. At least one of the optical elements 31, 32, 33, 34, 35, 36 of the projection optical system PL may be the multilayer-film reflective mirror 10 described above. The projection optical system PL is provided with a first mirror pair including a first reflecting mirror 31 having a reflecting surface with a concave surface and a second reflecting mirror 32 having a reflecting surface with a concave surface, a second mirror pair including a third reflecting mirror 33 having a reflecting surface with a predetermined shape and a fourth reflecting mirror 34 having a reflecting surface with a concave surface, and a third mirror pair including a fifth reflecting mirror 35 having a reflecting surface with a convex surface and a sixth reflecting mirror 36 having a reflecting surface with a concave surface. In each of the mirror pairs, the first reflecting mirror 31, the third reflecting mirror 33, and the fifth reflecting mirror 35 are each arranged such that the reflecting surfaces face the object plane side (mask M side) of the projection optical system PL, and the second reflecting mirror 32, the fourth reflecting mirror 34, and the sixth reflecting mirror 36 are each arranged such that the reflecting surfaces face the image plane side (substrate P side) of the projection optical system PL. The exposure light EL from the mask M forms an intermediate image after being reflected by the first mirror pair in order of the first reflecting mirror 31 and the second reflecting mirror 32. The light from the intermediate image is reflected by the second mirror pair in order of the third reflecting mirror 33 and the fourth reflecting mirror 34. The light reflected by the second mirror pair is reflected by the third mirror pair in order of the fifth reflecting mirror 35 and the sixth reflecting mirror 36 to be guided to the substrate P. A field stop FS which limits the projection region on the substrate P is arranged at a position where the intermediate image is formed. An aperture stop AS which limits the numerical aperture NA of the projection optical system PL is arranged between the first reflecting mirror 31 and the second reflecting mirror 32 of the first mirror pair. The aperture stop AS has an opening with a variable size (diameter). The size (diameter) of the opening is controlled by an aperture stop control unit 51. The substrate stage 12 is a stage capable of moving with six degrees of freedom in six directions, which are the X axis, Y axis, Z axis, θX, θY, and θZ directions, while holding the substrate P. In the present embodiment, the substrate stage 12 holds the substrate P such that the surface of the substrate P and the XY plane are substantially parallel. Position information of the substrate stage 12 (substrate P) is measured by a laser interferometer 42. The laser interferometer 42 measures position information relating to the X axis, Y axis, and θZ directions of the substrate stage 12 using a measuring mirror provided in the substrate stage 12. In addition, the surface position information of the surface of the substrate P held by the substrate stage 12 (position information relating to the Z axis, the θX, and the θY) is detected by the focus leveling detection system (not shown). The position of the substrate P held by the substrate stage 12 is controlled based on the measurement result made by the laser interferometer 42 and the detection result made by the focus leveling detection system. When exposing the substrate P, the substrate stage 12 holding the substrate P is moved in the Y axis direction in synchronization with the movement of the mask stage 11 holding the mask M in the Y axis direction while the illumination optical system IL illuminates a predetermined illumination region on the mask M with the exposure light EL. As a result, the image of the pattern of the mask M is projected onto the substrate P via the projection optical system PL. As described above, according to the present embodiment, since the thickness of each position (each portion) of the multilayer film 4 is made to be different such that the light EL is reflected based on the incident angle of the light EL with respect to the surface 4S of the multilayer film 4 without the distribution of the thickness of the multilayer film 4 having an axis of rotational symmetry, it is possible for the multilayer film 4 to reflect the incident light EL with high reflectance. Accordingly, it is possible to suppress the generation of exposure defects caused by a decrease in the reflectance in the multilayer film and the generation of defective devices. For example, in a case where portions of a plurality of multilayer films 4 in a circle with the optical axis of the multilayer-film reflective mirror as the center are set to the same thickness, as described with reference to FIG. 3 and FIG. 4, there is a possibility that there will be a portion which is not capable of reflecting the light EL depending on the incident angle of the light EL. In addition, when trying to increase the incident angle range of the light EL in which the light EL can be reflected, for example, there is a possibility that the maximum reflectance will decrease as described with reference to the line Ca2 in FIG. 3. In the present embodiment, for example, the necessary thickness of the multilayer film 4 in each of the first portion PA1 and the second portion PA2 is calculated so as to obtain a target reflectance in each of the first portion PA1 and the second portion PA2. The calculated result is fitted to a function, and then the multilayer film 4 is manufactured. As a result, it is possible to manufacture the multilayer-film reflective mirror 10 having the multilayer film 4 with the desired reflectance. That is, it is possible to manufacture a reflective mirror with high reflectance. In addition, by using the multilayer-film reflective mirror 10 according to the present embodiment in at least one of the illumination optical system IL and the projection optical system PL, it is possible to suppress a decrease in the optical performance of these optical systems IL and PL and in the exposure performance of the exposure apparatus EX. Accordingly, throughput of the exposure apparatus is improved. Note that description was given of an example of a case where the multilayer film 4 is an Mo/Si multilayer film in each of the embodiments described above; however, for example, it is possible to change the material forming the multilayer film 4 according to the wavelength band of the EUV light. For example, in a case of using EUV light of a wavelength band close to 11.3 nm, it is possible to obtain a high reflectance by using an Mo/Be multilayer film where a molybdenum layer (Mo layer) and a beryllium layer (Be layer) are laminated alternately. In addition, in each of the embodiments described above, ruthenium (Ru), molybdenum carbide (Mo2C), molybdenum oxide (MoO2), molybdenum silicide (MoSi2), and the like may be used as the material for forming the first layer 1 of the multilayer film 4. In addition, it is possible to use silicon carbide (SiC) as the material forming the second layer 2 of the multilayer film 4. Alternatively, it is possible for the multilayer-film reflective mirror 10 to use a reflective mirror having a reflecting surface which is an aspherical surface or a free-form surface. In such a case, for example, it is possible to regard a straight line passing through the origin obtained from a formula representing the aspherical surface or free-form surface, or a straight line passing through the center or the center of gravity of the reflecting surface (a reference line or a reference axis) as the “optical axis”. In one embodiment, it is possible to determine the optical axis in the reflective mirror having a spherical reflecting surface or another reflecting surface as a design reference. Alternatively and/or additionally, it is possible to regard a straight line passing through the origin obtained from a formula representing a curved surface of the reflecting surface (a reference line or a reference axis), or a straight line passing through the center or the center of gravity of the reflecting surface (a reference line or a reference axis) as the optical axis, and it is possible to determine the optical axis as a design reference. In addition to a semiconductor wafer for manufacturing a semiconductor device, a glass substrate for a display device, a ceramic wafer for a thin-film magnetic head, an original plate (synthetic quartz or silicon wafer) of a mask or a reticle used in the exposure apparatus, or the like may be applied as the substrate P in the embodiment described above. As for the exposure apparatus EX, in addition to a scan type exposure apparatus of step-and-scan type (scanning stepper) in which while synchronously moving the mask M and the substrate P, the pattern of the mask M is scan-exposed, a step-and-repeat type projection exposure apparatus (stepper) in which the pattern of the mask M is exposed in a batch in the condition that the mask M and the substrate P are stationary, and the substrate P is successively moved stepwise can be used. Furthermore, in the step-and-repeat type exposure, after a reduced image of a first pattern is transferred onto the substrate P by using the projection optical system, in the state with the first pattern and the substrate P being substantially stationary, a reduced image of a second pattern may be exposed in a batch onto the substrate P, the reduced image of the second pattern being partially overlapped on the first pattern, by using the projection optical system, in a state with the second pattern and the substrate P being substantially stationary (a stitch type batch exposure apparatus). In addition, it is also possible to apply the stitch type exposure apparatus to a step-and-stitch type exposure apparatus transferring at least two patterns onto the substrate P in a partially overlapping manner, and moving the substrate P in sequence. In addition, for example, it is also possible to apply the present invention to an exposure apparatus which combines patterns of two masks on a substrate via a projection optical system, and double exposes a single shot region on the substrate at substantially the same time, using a single scan exposure light, as disclosed in U.S. Pat. No. 6,611,316, or the like. In addition, it is also possible to apply the present invention to a twin stage type exposure apparatus provided with a plurality of substrate stages as disclosed in U.S. Pat. No. 6,341,007, U.S. Pat. No. 6,400,441, U.S. Pat. No. 6,549,269, U.S. Pat. No. 6,590,634, U.S. Pat. No. 6,208,407, U.S. Pat. No. 6,262,796, and the like. Furthermore, for example, it is also possible to apply the present invention to an exposure apparatus provided with a substrate stage holding a substrate and a measurement stage on which is mounted a reference member where a reference mark is formed and/or various photoelectric sensors, as disclosed in U.S. Pat. No. 6,897,963 and the like. In addition, it is possible to apply the present invention to an exposure apparatus provided with a plurality of substrate stages and measurement stages. The types of the exposure apparatuses EX are not limited to exposure apparatuses for manufacturing semiconductor elements which expose semiconductor element patterns onto a substrate P, and are widely applicable to apparatuses including exposure apparatuses for manufacturing liquid crystal display elements or for manufacturing displays, and exposure apparatuses for manufacturing thin-film magnetic heads, picture elements (CCD), micromachines, MEMS, DNA chips, reticles, masks, and the like. The exposure apparatus EX of the present embodiment is manufactured by assembling various subsystems including each of the constituent elements listed in the Claims so as to maintain a predetermined mechanical precision, electrical precision, and optical precision. In order to ensure these precisions, adjustments to achieve the optical precision for the various optical systems, adjustments to achieve the mechanical precision for the various mechanical systems, and adjustments to achieve the electrical precision for the various electrical systems are performed before and after this assembly. The process of assembling the various subsystems into the exposure apparatus includes mechanical connections, wiring connections of electrical circuits, piping connections of air pressure circuits, and the like between the various subsystems. Before the process of assembling the various subsystems into the exposure apparatus, it is needless to mention that there are individual assembly processes for each of the subsystems. When the assembly processes of the various subsystems into the exposure apparatus are finished, comprehensive adjustment is performed and the various precisions are ensured for the exposure apparatus as a whole. Note that, it is desirable that the manufacturing of the exposure apparatus be performed in a clean room where the temperature, the cleanliness, and the like are controlled. As shown in FIG. 11, devices such as semiconductor devices are manufactured through: a step 201 of performing function and performance design for the device, a step 202 of creating the mask (reticle) based on this design step, a step 203 of manufacturing the substrate which is a base of the device, a substrate processing step 204 including substrate processing (exposure processing) for exposing the substrate P to exposure light from the pattern of the mask according to the embodiment described above and for developing the exposed substrate, a device assembly step (including treatment process such as a dicing process, a bonding process, and a packaging process) 205, an inspection step 206, and the like. By implementing the aspects of the present invention, the throughput of the device manufacturing is improved. Note that, it is possible to combine the conditions of each of the embodiments described above as appropriate. In addition, there may be cases where some constituent elements are not used. In addition, the disclosures of all of the published patents and US patents relating to apparatuses or the like cited in each of the embodiments and modifications described above are incorporated as a part hereof by reference to the extent permitted by law. 1 FIRST LAYER 2 SECOND LAYER 4 MULTILAYER FILM 4S SURFACE 5 BASE 5S SURFACE 10 MULTILAYER-FILM REFLECTIVE MIRROR (REFLECTIVE MIRROR) EX EXPOSURE APPARATUS |
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044435657 | abstract | A thermoplastic resin composition comprises 100 parts by weight of metal foil fragments, from 1 to 10 parts by weight of a first polymer covering the surfaces of the metal foil fragments and obtained by polymerizing at least one of monomers selected from the group consisting of acrylic acid, methacrylic acid, an alkylacrylate, an aminoalkylacrylate, an alkylmethacrylate and an aminoalkylmethacrylate in the presence of the metal foil fragments, and from 5 to 33 parts by weight of a second polymer obtained by polymerizing a mixture of an aromatic vinyl monomer and a monomer copolymerizable with the atomatic vinyl monomer. Also disclosed is a process for preparing the thermoplastic resin composition containing metal foil fragments. |
summary | ||
description | The present invention relates to a grid for selective transmission of electromagnetic radiation, in particular X-ray radiation, to a method of manufacturing such grid and to a medical imaging device comprising such grid. Grids for selective transmission of electromagnetic radiation may be used for example in medical imaging devices such as computed tomography scanners (CT), standard X-ray scanners like C-arm, mammography, etc., single photon emission computed tomography devices (SPECT) or Positron Emission Tomography scanners (PET). Other devices, such as non-destructive X-ray testing devices, may also use such grids. The grid may be positioned between a source of electromagnetic radiation such as X-ray radiation and a radiation-sensitive detection device. For example, in a CT scanner, the source of electromagnetic radiation may be an X-ray tube whereas in SPECT/PET a radioactive isotope injected into a patient may form the source of electromagnetic radiation. The radiation-sensitive detection device may be any arbitrary radiation detector such as a CCD-device, a scintillator based detector, a direct converter etc. A grid may be used to selectively reduce the content of a certain kind of radiation that must not impinge onto the radiation-sensitive detection device. The radiation reduction is usually being realized by means of radiation absorption. In a CT scanner, the grid may be used to reduce the amount of scattered radiation that is generated in an illuminated object as such scattered radiation may deteriorate the medical image quality. As today's CT scanners often apply cone-beam geometry, hence illuminate a large volume of an object, the amount of scattered radiation is often superior to the amount of the medical information carrying non-scattered primary radiation. For example, scattered radiation can easily amount to up to 90% or more of the overall radiation intensity, depending on the object. Therefore, there is a large demand for grids that efficiently reduce scattered radiation. Grids that do fulfil this demand may be grids that have radiation absorbing structures in two dimensions that are called two-dimensional anti-scatter-grids (2D ASG). As such two-dimensional anti-scatter-grids may need to have transmission channels that are focussed to a focal spot of the radiation source that emits the primary radiation which shall be allowed to be transmitted through the grid, it may be time-consuming and costly to manufacture such grid. WO 2008/007309 A1, filed by the same applicants as the present application, describes a grid for selective transmission of electromagnetic radiation with structural elements built by selective laser sintering. Therein, a method for manufacturing a grid comprises the step of growing at least a structural element by means of selective laser sintering from a powder material, particularly a powder of an essentially radiation-opaque material. Selective laser sintering allows for a large design freedom. Having a structural element that is built by selective laser sintering, the grid can be a highly complex three-dimensional structure that is not easily achievable by conventional moulding or milling techniques. However, the mechanical stability as well as the radiation-absorbing properties of conventional sintered grids may have to be further improved. Furthermore, the manufacturing of such sintered grids may have to be further simplified. Accordingly, there may be a need for a grid for selective transmission of electromagnetic radiation and for a method of manufacturing such grid as well as for a medical imaging device using such grid wherein the mechanical stability and/or the radiation-absorbing properties of the grid are further improved. Furthermore, there may be a need for a method of manufacturing a grid which allows to simplify the manufacturing process. These needs may be met by the subject-matter according to one of the independent claims. Advantageous embodiments of the present invention are described in the dependent claims. According to a first aspect of the present invention a method of manufacturing a grid for selective transmission of electromagnetic radiation is proposed. The method comprises: providing a structural element comprising a plurality of particles comprising a first radiation absorbing material wherein the particles are sintered together and pores are present between neighbouring particles; inserting a liquid second material into the pores; and solidifying the second material. According to a second aspect of the present invention, a grid for selective transmission of electromagnetic radiation is proposed. The grid comprises a structural element comprising a plurality of particles of a first radiation absorbing material wherein the particles are sintered together such that pores are present between neighbouring particles and wherein the pores are at least partially filled with a second solid material. According to a third aspect of the present invention, a medical imaging device such as a CT-scanner, X-ray C-arm system, X-ray mammography system, a SPECT-scanner or a PET-scanner comprising a grid according to the above second aspect of the present invention is proposed. A gist of the present invention may be seen as being based on the following idea: A core of a grid for selective transmission of electromagnetic radiation may be provided as a structural element which is prepared by sintering particles to each other wherein the particles comprise a radiation-absorbing material. For this purpose, the well-known selective laser sintering (SLS) process, sometimes also referred to as direct metal laser sintering (DMLS), may be used. Thereby, complex two-dimensional or three-dimensional structures may be realized for the structural element. However, after the sintering process, pores of non-filled spaces remain between the sintered particles. It is the finding of the inventors of the present invention that such pores may deteriorate the mechanical stability and integrity of the structural element and that, furthermore, these pores may reduce the radiation-absorbing properties of the grid. The inventors therefore propose to fill the pores with a second material. Such filling may be achieved by inserting the second material in a liquid form such that it may flow into the pores. Afterwards, the inserted liquid material may be solidified such that it may enhance the mechanical stability of the entire grid. It may be specifically advantageous to use a radiation absorbing material as the second material such that the second material filled into the pores further adds to increase the radiation absorbing properties of the entire grid. At the surface of the structural element, the inserted second material furthermore may help to smoothen the rough surface provided by the sintered particles of the first material thereby providing smooth wall surfaces for the structural element which then might enhance the radiation absorbing properties of the entire grid. Furthermore, the proposed method allows to start with a rather rough structural element prepared from particles having a large particle size. On the one hand, the use of such large particles may simplify the laser sintering process. On the other side, due to the large size of the particles, also the pores between the particles may have a large size and the surface of the structural element may be very uneven or rough. However, as the pores are subsequently filled with a second material being preferably radiation absorbing, no empty large pores may deteriorate the mechanical stability and/or radiation absorbing properties of the grid. Therefore, the entire manufacturing process may be simplified due to the larger possible particle size while at the same time maintaining or even increasing the mechanical and radiation-absorbing properties. In other words, the proposed concept may be seen as an improved method for precise and cost-effective production of for example two-dimensional anti-scatter-grids for X-ray and computed tomography detectors but also for other applications. The approach combines the use of prefabricated anti-scatter-grids, e.g. manufactured by laser sintering technology. The second manufacturing step may be the dipping of the prefabricated structure in a liquid radiation absorbing metal. The method provides a maximum design freedom and an optimization for X-ray absorption and mechanical stability as well as production speed and costs. The method could be also used for the fabrication of many other small but high precision devices where the combination of prefabricated laser sintered walls dipped into a liquid medium offers more density and/or mechanical stiffness. In the following, further possible features, details and advantages of embodiments of the present invention are mentioned. The structural element provided as a starting core for the grid may be provided in any two-dimensional or three-dimensional geometry which is suitably adapted for selectively transmitting electromagnetic radiation. For example, the structural element may have vertical walls which are slightly tilted such as to be directed to a focal point of a source for the electromagnetic radiation. Surfaces of the structural element may be curved, e.g. spherically shaped. Particularly, a two-dimensional grid having focused channels may have a spatially rather complex structure. The channels may have a rectangular or hexagonal inner shape which requires channel walls having different angulations. The particles from which the structural element is formed by sintering comprise a first radiation-absorbing material, preferably an X-ray absorbing material. Therein, it may depend on the application and/or on the structure size, e.g. the thickness of radiation absorbing channel walls, whether the powder material formed by the particles can be considered as radiation-transparent or radiation-absorbing or radiation-opaque. Herein, the term radiation-transparent shall be defined as absorbing a, referred to a specific application, insignificant portion, e.g. less than 10%, of the incident radiation upon transition through the grid. The term radiation-absorbing shall be defined as absorbing a significant portion, e.g. more than 10%, and the term radiation-opaque shall be defined as absorbing essentially all, e.g. more than 90%, of the incident radiation upon transition through the grid. In mammography applications, X-ray energies of about 20 keV may be used. For these energies, copper (Cu) can be considered as essentially radiation-opaque which means that grid walls fulfilling the requirements of certain geometry parameters like wall thickness (e.g. 20 μm), channel height (e.g. 2 mm) etc. lead to absorption of the kind of radiation that is to be selectively absorbed so that a noticeable improvement of a quality parameter of the radiation detection occurs. A quality parameter may be the scatter-radiation-to-primary-radiation ratio (SPR), the signal-to-noise ratio (SNR) or the like. For CT applications in the range of e.g. 120 keV, molybdenum (Mo) or other refractory materials (e.g. tungsten) can be considered as essentially radiation-opaque but other materials like copper or titanium are likewise essentially radiation-opaque if the structure is made in the appropriate thickness. Consequently, the material particles or powder may be considered as radiation-opaque if the resulting grid has satisfying selective radiation transmission properties. For example, while pure plastic materials are usually to be considered as radiation-transparent for all ranges of medically relevant X-ray energies, metal powder-filled plastics may be considered radiation-opaque provided that the powder content is sufficiently high. As the sintered structural element is directly made from a radiation-absorbing or radiation-opaque material, the required radiation-absorbing properties of the grid are inherent to the sintered structural element. For sintering the radiation-absorbing particles together, the well-known selective laser sintering (SLS) process may be used. In SLS, a powder material is sintered together using a fine laser beam of appropriate energy. The object to be made is sintered layer by layer and the resulting object is subsequently immersed in the powder material so that a next layer of powder material can be sintered on top of the already sintered structures. In this way, rather complex three-dimensional structures can be formed, e.g. having cavities, combinations of convex and concave structural elements, etc. Selective laser sintering allows for generating fine structures from e.g. molybdenum powder by selectively illuminating the top powder layer with a high-intensity laser beam. The grain size of the metal powder may be chosen according to the required structure size and surface roughness. Typical structure sizes (channel wall thickness) for e.g. CT grids are about 50 μm to 300 μm such that grain sizes of about 1 μm-10 μm may suffice. For PET/SPECT devices, typical structure sizes (channel wall thickness) may be about 100 to 1000 μm so that grain sizes of about 5 to 50 μm may suffice. For regular X-ray applications, typical structure sizes may be about 10 to 50 μm so that grain sizes of about 0.1 to 5 μm may suffice. These numbers are only exemplary and shall not be understood as limiting. As a liquid second material to be filled into the pores of the sintered structural element, any material can be used that can be suitably liquefied such that it can flow into the pores. Preferably, the second material should be adapted such that, after solidifying the second material, it can help to enhance the mechanical stability of the structural element. For this purpose, the second material may have sufficient mechanical rigidity and may further be adapted to suitably adhere to the particles of the first radiation absorbing material. Preferably, the second material comprises or consists of a radiation-absorbing material, preferably an X-ray absorbing material, such as for example a metal such as silver, lead or copper and their alloys e.g. tin-antimony-lead alloy (Lettermetal). Such radiation-absorbing material filled into the pores of the structural element may further enhance the radiation-absorbing properties of the structural element and thereby further enhancing the selective transmission of electromagnetic radiation of the entire grid. Furthermore, the liquid second material will not only flow into pores deep inside the structural element but will also at least partially fill open pores at the surface of the structural element thereby reducing the surface roughness of the structural element. The thereby smoothened surface of the structural element may further enhance the transmission properties of the entire grid. The liquid second material may be inserted into the pores by dipping or diving the structural element into a bath of liquefied material. Thereby, the liquid material may flow into the pores or cavities of the sintered structural element and fill these pores up to nearly 100%. The liquid material may be liquefied by melting. For example, a metal having a low melting point can be heated above its melting point thereby creating a liquid melt into which the structural element may then be dipped. It may be advantageous if the melting temperature of the second material is lower than the melting temperature of the first radiation-absorbing material of the particles forming the structural element. The structural element can then be easily dipped into the melted second material and may remain therein until all pores or cavities are essentially filled with the melted second material. The second material will then solidify upon cooling after withdrawal from the melt. Alternatively, the second material may be a liquid or resin comprising small radiation-absorbing particles, e.g. in the nano- or micro-scale. The liquid or resin may be filled into the pores and may subsequently be cured. According to a further embodiment of the present invention, the structural element has minimum structure dimensions and the particles of the first radiation-absorbing material have a maximum particle size being larger than 10%, preferably larger than 20% and even more preferably larger than 25% of the minimum structure dimensions. In other words, the structural element forming the core of the grid may have partial structures having different dimensions in different extension directions. For example, it may have vertical longitudinal walls having a wall thickness wherein the wall thickness is much smaller than the longitudinal extension of the wall and therefore forms a minimum structure dimension. For example, the wall thickness can be between 10 and 1000 μm. Accordingly, the particles which are used to form such partial structures must have a particle size being substantially smaller than the minimum structure dimensions. In conventional grids being formed by selective laser sintering, very small particles are usually used for forming the partial structures in order to avoid large pores or voids within the partial structures. Particle sizes being smaller than 5% of the minimum structure dimensions has been conventionally used. With the manufacturing method proposed herein, the size of the pores between neighbouring particles is much less critical than in the prior art as the pores may be subsequently be filled with a second material. Accordingly, the structural element may be sintered using larger particles having sizes of e.g. 10% or more preferred up to 25% of the wall thickness which may substantially simplify the sintering process. It shall be noted that the “maximum particle size” is referred to as the size the largest particles contained in a powder have. Usually, a powder has particles of different sizes. In conventional grid building techniques it may be preferred to use powders with mainly small particles to reduce the number and size of pores. However, a small portion of larger particles may not significantly deteriorate the overall result whereas to many large particles may lead to a very porous grid structure. With the method presented herein, powders having many large particles, wherein e.g. 90% of all particles are larger than 10% of the minimum structure dimensions of the grid, may be used without significant detrimental effect on the resulting grid. Finally, some features and advantages of the present invention are repeated in another wording. An essential feature of the proposed manufacturing method may be seen in a post-processing of sintered geometries. The “rough” sintered feature may be dipped into a bath of e.g. liquid silver to fill the still porous wall structure. The liquid material would go into the cavities and so the surface would be much smoother. Silver as material also absorbs X-rays and so the efficiency of the wall structure would be higher. The stability may increase and also the production efficiency of the sinter process may be improved. This may be because the grain size could be bigger and also the laser power could be used more efficiently and the laser focus could be bigger. So, the wall may be built with more rough grains and the finishing step may compensate this again. It has to be noted that aspects and embodiments of the present invention have been described with reference to different subject-matters. In particular, some embodiments have been described with reference to the method type claims whereas other embodiments have been described with reference to apparatus type claims. However, a person skilled in the art will gather from the above and the following description that, unless other notified, in addition to any combination or features belonging to one type of subject-matter also any combination between features relating to different subject-matters, in particular between features of the apparatus type claims and features of the method type claims, is considered to be disclosed with this application. The drawings in the figures are only schematically and not to scale. Similar elements in the figures are referred to with similar reference signs. An exemplary embodiment of a method of manufacturing a grid for selective transmission of electromagnetic radiation according to the invention will be described with reference to FIGS. 1, 2 and 4. A grid 1 comprises a 3-dimensional structural element 2 including vertical walls 3 arranged perpendicular to each other. As can be clearly seen in the enlarged portions of FIG. 1, the walls 3 form longitudinal channels 5 though which electromagnetic radiation can easily pass. However, radiation which is irradiated under an angle not parallel to the channels 5 will be absorbed within the walls 3 as the walls 3 comprises a radiation-absorbing material. As schematically shown in FIG. 2, the structural element 2 can be built using a selective laser sintering technique. Therein, particles of a radiation-absorbing material are placed on a substrate 7. The substrate 7 is positioned on a table 9 which can be moved in the y-direction. Using a single laser and, optional, an arrangement for deflecting the laser beam or alternatively using a laser array 11, the particles may be sintered to each other at the location(s) of the focus of one or more laser beams. The laser array 11 may be controlled such that the location(s) of the focus of the one or more laser beams are scanned in x- and z-directions over the surface of the substrate in accordance with a 3-dimensional model 13 stored on a control unit 31 connected both to the laser array 11 and the table 9. After having scribed a first layer 15 of sintered particles, the table 9 can be moved downwards, the particles can be again evenly distributed over the surface of the already existing sintered structure and a second layer 17 of sintered particles can be generated using the laser array 11. Accordingly, the 3-dimensional model 13 stored in the control unit 31 may be reproduced by sintering particles layer-by-layer. After having prepared the structural element 2, the pores between neighbouring particles may be filled by dipping the structural element 2 into a bath of molten metal. In FIGS. 4a and 4b, magnified sectional views of the walls 3, 3′ included in the structural element 2 are shown. The walls may have a rectangular cross-section as shown in FIG. 4a or a wedge-like cross-section as shown in FIG. 4b. Particles 19 of radiation-absorbing material such as molybdenum or tungsten are sintered together. Pores 21 both at the inside of the wall 5, 5′ as well as at its surface are filled with a solidified radiation-absorbing material such as silver or lead. Furthermore, an alternative exemplary embodiment of a method of manufacturing a grid 1′ for selective transmission of electromagnetic radiation according to the invention will be described with reference to FIG. 3. In a first step, a metal sheet 104 which is made for example from molybdenum or tungsten is positioned in a working chamber of a selective laser sintering device. The precise positioning with respect to the position of the laser beam of the SLS device may be achieved by a previous system calibration. The metal sheet may be reversibly glued into the working chamber for fixation. After a layer of metal powder is arranged on the metal sheet, selective laser sintering is used to sinter a first layer of a sintered structure to be manufactured. After the first layer is completed, a next layer of metal powder is arranged on top of the metal sheet and the previously sintered structures. This can be combined with a slight tilt of the working chamber so that the next layer that is sintered has a predetermined angulation with respect to the metal sheet. FIG. 3 shows on the left-hand side a comb-like grid structure 102 that results after several layers of metal powder have been sintered. On the right-hand side of FIG. 3, a magnification M1 of a portion of the comb-like structure as indicated by the circle on the left-hand side of FIG. 3 is shown. The comb-like structure has a base that is formed by a metal sheet 104. Sintered longitudinal wall structures 103 are shown that extend over the length of the metal sheet 104. On top of the walls 103, alignment structures 106 are depicted. It has to be noted that the use of a metal sheet 104 as a base substrate is not mandatory. Alternatively, the entire grid may be made from a structural element which is completely prepared by sintering. In FIG. 5, an example of a medical imaging device 200 is shown. FIG. 5 shows the main features of a CT scanner, namely an X-ray source 220, a radiation detector 210 and a patient couch 230. The CT scanner may rotate around the object to be observed and may acquire projection images by means of radiation detection using the detector 210. A grid as described above according to the invention can be used in the detector 210 to reduce the amount of scatter radiation generated in the object to be observed. Finally, it should be noted that the terms “comprising”, “including”, etc. do not exclude other elements or steps and the terms “a” or “an” do not exclude a plurality of elements. Also, elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims. |
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claims | 1. A coating solution for protecting a surface of a nuclear fuel rod, obtained by dissolving a polymer resin comprising 52-62 wt % of methacrylic acid, 34-42 wt % of 2-hydroxyethyl methacrylate and 0.01-12 wt % of methyl methacrylate in a solvent mixture of isopropanol, ethanol and water. 2. The coating solution of claim 1, comprising 9-12 wt % of the polymer resin and 88-91 wt % of the solvent mixture of isopropanol, ethanol and water. 3. A coating method for protecting a surface of a nuclear fuel rod, comprising:(1) forming a coating film on a surface of a nuclear fuel rod, using a coating solution obtained by dissolving a polymer resin comprising 52-62 wt % of methacrylic acid, 34-42 wt % of 2-hydroxyethyl methacrylate and 0.01-12 wt % of methyl methacrylate in a solvent mixture of isopropanol, ethanol and water;(2) drying the nuclear fuel rod; and(3) loading the dried nuclear fuel rod in a skeleton. 4. The coating method of claim 3, wherein forming the coating film in (1) is performed while a concentration of the coating solution is corrected to be maintained at an initial value by measuring a density of the coating solution using a hydrometer. 5. The coating method of claim 3, wherein drying the nuclear fuel rod in (2) is performed using hot air drying or air drying. |
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046474200 | summary | BACKGROUND OF THE INVENTION Nuclear fission reactors use fuel pins which are loaded with pellets of fissionable nuclear fuel. The amount and concentration of fissionable or fissile material contained within the fuel pin is an important parameter for proper operation and maintenance of a nuclear reactor. Assurance of high quality and adherence to design specifications can advantageously be accomplished by inspecting fuel pins for uniformity and total content of the fissile material. It may also be desirable in certain cases to perform other types of inspections. Fuel pin scanners are currently being used to inspect nuclear fuel pins to assure proper uniformity and amount of fissile material. Current technologies do not, however, provide the production speed or level of accuracy which is now required in producing fuel pins used in liquid metal fast breeder reactors. Plutonium recycle systems used in light water reactors also have similar expected need for high production capability and accuracy in inspecting fuel pins. Fuel pin scanners are already in use in light water reactor fuel manufacturing plants. The early fuel pin scanners used passive systems which simply measured the natural radioactivity of the fuels. Such systems were very slow, thereby requiring large numbers of scanners just to inspect the output of a large light water reactor fuel plant. The economical availability of californium-252 led to the development of nuclear fuel pin scanners which activate the fissile material using radiation. Such fuel pin scanners were capable of processing up to approximately 1,000 uranium oxide fuel pins per day. Such prior pin scanners used a single pass configuration which was relatively slow and provided limited accuracy. The need for fabricating plutonium bearing nuclear fuels on a large scale arose with the liquid metal fast breeder reactor program. Scanning of plutonium bearing fuel pins used in such reactors has created special requirements which were not satisfactorily met by the prior art. Most significant of the problems was the need for greater accuracy in measuring the uniformity of fissionable material contained within the fuel pin. Liquid metal fast breeder reactor fuel pin scanners must not only detect rejectable defects but must also allow characterization of the fuel for identification purposes. Characterization of the fuel allows for the fuel to be more closely monitored during the manufacturing process. This in turn aids in the production of high quality and safe, fast reactor fuels. The typical prior art light water reactor fuel pin scanner consisted of: (1) an irradiator containing one to five milligrams of californium-252; (2) mechanisms for transporting fuel pins sequentially through the irradiator and through one or two fission product gamma ray detectors; (3) sodium iodide, bismuth germanate or plastic scintillators; (4) a gamma ray transmission device for measuring gaps and nuclear fuel density; and (5) an on-line computer for collection and processing of data. All prior art light water reactor fuel pin scanners measured fissile uniformity in a single pass of the fuel pin through the irradiator and detector. In this single pass configuration the fuel pins were passed near a irradiator containing a neutron source such as californium-252 which activates the fissile material to provide increased radioactive emissions therefrom. The activated fuel pin was then passed through a detector in a single pass. Such single pass systems were relatively slow because of the exposure time needed to sufficiently activate the fuel pin and the length over which activation occurred. Decreasing the exposure time to increase capacity required increasing the irradiation power which was not economical. Higher capacity could also be achieved through increased numbers of systems but this also was expensive and indicated the need for high capacity systems which addressed the problem in a new manner. Such single pass activation and detection was also found impractical to achieve the increased accuracy necessary in producing fuel pins used in liquid metal fast breeder reactors. Liquid metal fast breeder reactors use nuclear fuel made with mixed oxides of plutonium and uranium, rather than the uranium dioxide fuels commonly used in light water reactors. Fuel pins made with mixed oxides of plutonium and uranium are more difficult to measure for fissile uniformity because the fissile loading of the fuel pellets is much greater and the thermal neutron activation commonly used with uranium dioxide fuel pins is not effective as an activating source of radiation. Applying known light water reactor fuel pin scanner technology to fuel pins loaded with mixed oxides of plutonium and uranium requires using relatively large amounts (0.1 gram) of californium-252, as compared to 1-5 millgrams used in current light water reactor fuel pin scanners. This amount of californium-252, has a value in excess of $1,000,000 thereby rendering current fuel pin scanner technology uneconomical for fuel pins used in liquid metal fast breeder reactors. SUMMARY OF THE INVENTION It is an object of this invention to provide a nuclear fuel pin scanner which is capable of high production capacity. It is another object of the invention to provide a nuclear fuel pin scanner which accurately and reliably measures fissile uniformity and total fissile loading. It is a further object of this invention to provide a nuclear fuel pin scanner which provides extended irradiation times while maintaining a high production throughput. And it is a still further object of this invention to provide a nuclear fuel pin scanner having improved detector accuracy. Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. To achieve the foregoing and other objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, the nuclear fuel pin scanning system of this invention may comprise a rotary irradiator having a source of activating radiation located centrally thereof. A plurality of spaced positions are provided for supporting a plurality of fuel pins in an arrangement wherein the fuel pins are equally spaced from the source of radiation. The source of radiation advantageously lies along the rotational axis of the irradiator and the fuel pins are slowly rotated thereabout. Means are provided for feeding and discharging the fuel pins to and from their positions in the irradiator. Means are also advantageously provided for axially oscillating the source of activating radiation relative to the fuel pins being activated in the irradiator. Further means are provided for indexing or otherwise rotating the irradiator to advance the fuel pins through a range of positions about the source of radiation. The simultaneous irradiation of a plurality of fuel pins allows for extended activation times when compared to single pass systems and the required throughput rate of the entire system. The nuclear fuel pin scanning system of this invention also includes a detector having a plurality of detector elements arranged in an axial or linear array which receives a fuel pin therein. The detector elements advantageously include a collimating shield defining an annular opening which allows radiation emitted from the activated fuel pins to strike radiation transducers. The radiation transducers can advantageously be a crystal which illuminates when struck by the radiation being detected. The crystal is optically coupled to a photomultiplier or other light transducer which produces an electronic signal representative of the level of radiation striking the crystal. The plurality of detector elements arranged in a linear array allows each element to detect a limited segment of each fuel pin. The fuel pin is oscillated repeatedly over the relative short distance equal to the spacing between adjacent detector elements. Repeated passes using multiple detectors covering short distances of the fuel pin allow detection times which are effectively much longer than if the entire length of the fuel pin was passed by a single detector either in a single pass or multiple passes. Accordingly, the production throughput can be maintained at a high rate even though accurate multiple pass detection is being performed. The multiple detector elements further allow specific accurate readings for each segment of the fuel pin. The invention further comprises a method for inspecting nuclear fuel pins to accurately determine uniformity and total amount of fissile material, while maintaining a relatively high production throughput rate. The method involves arranging a plurality of nuclear fuel pins in an arrangement about a longitudinal axis of rotation with each fuel pin spaced approximately equally from the axis. The arrangement of fuel pins is rotated about the axis of rotation which also is the location of the source of activating radiation. The fuel pins are activated over an extended period of time as the arrangement slowly rotates or is indexed about the source of activating radiation. This form of extended activation provides greater activation and hence improved accuracy in inspecting the fuel pins without decreasing the throughput rate. The source of activating radiation is preferably oscillated back and forth along the longitudinal axis of rotation thereby allowing even irradiation along the length of each fuel pin using a relatively localized source of radiation. Methods according to this invention can further include detecting radiation emissions such as gamma ray emissions from the activated fuel pins. The fuel pins are preferably positioned within a linear array of detector elements each serving to detect emissions occurring over a limited segment of the fuel pin. The fuel pins are then oscillated repeatedly over a distance approximately equal to the spacing of adjacent detector elements. Detection in this manner provides greater effective detection times for a given throughput rate. |
052710548 | abstract | A nuclear fuel perimeter strip grid corner-piece (12) of increased flatness having at least two flat side sections (18,20) on either side of a transverse bend line (22) is provided. The flat side section (20) or sections (20 and 32) which have small cut-outs for arches (34), as opposed to large spring (36) cut-outs, as the fuel support features adjacent to the bend line (22) of variable radii at portions (24 and 26) are stress-relieved by means of slots (30) of length equal to 1/2 to 1/3 of the width of the flat section. The slot (30) is of a width less than twice the material thickness, so as not to weaken the structure near bend (22). |
claims | 1. A system, comprising:focused ion beam (FIB) means for at least partially severing a sample from a substrate;a grasping element configured to mechanically capture the sample;means for mechanically activating the grasping element to mechanically capture the sample; andmeans for separating the captured sample from the substrate. 2. The system of claim 1 further comprising means for transporting the captured sample to a microscope for examination. 3. The system of claim 2 wherein the microscope is a transmission electron microscope. 4. The system of claim 2 wherein the microscope is a scanning electron microscope. 5. The system of claim 2 wherein the microscope is a scanning transmission electron microscope. 6. The system of claim 1 wherein the grasping element includes an integral actuator for mechanically configuring the grasping element between opened and closed positions. 7. The system of claim 1 wherein the grasping element includes a thermally-activated end-effector configured to mechanically capture the sample upon at least one of heating and cooling of the end effector. 8. The system of claim 7 wherein the grasping element includes an integral heater configured to activate the end effector. 9. The system of claim 8 wherein the integral heater is resistively heated. 10. The system of claim 1 wherein the grasping element comprises a malleable end-effector and the means for activating the grasping element includes means for pressing the end-effector against the sample to form a compression bond. 11. The system of claim 1 wherein the grasping element is configured to secure the sample during examination. 12. The system of claim 1 wherein the means for activating the grasping element includes automated means for activating the grasping element to capture the sample via automation. 13. The system of claim 1 wherein the means for separating the captured sample from the substrate includes automated means for separating the captured sample from the substrate via automation. 14. The system of claim 1 further comprising automation means for controlling:the FIB means during the at least partial severing;the activating means during the sample capture; andthe separating means during the sample separation. 15. A grasping element for capturing an FIB-prepared sample, comprising:a body configured to be coupled to a handling assembly;an actuating member coupled to the body; anda grasping member coupled to the actuating member and configured to mechanically capture an FIB-prepared sample in response to mechanical actuation of the actuating member. 16. The grasping element of claim 15 wherein the mechanical actuation is electro-thermal actuation. 17. The grasping element of claim 15 wherein the grasping member is a first one of a plurality of grasping members. 18. The grasping element of claim 17 wherein ones of the plurality of grasping members are substantially mirror images of one another. 19. The grasping element of claim 15 wherein the grasping member includes a first profile corresponding to a second profile of the FIB-prepared sample. 20. The grasping element of claim 19 wherein the first profile is substantially non-rectangular. 21. A grasping element for capturing an FIB-prepared sample, comprising:a body configured to be coupled to a handling assembly;an actuating member coupled to the body; anda grasping member coupled to the actuating member, the grasping member configured to mechanically capture an FIB-prepared sample, the grasping member further configured to release the FIB-prepared sample in response to mechanical actuation of the actuating member. 22. The grasping element of claim 21 wherein the grasping member is configured to passively capture the FIB-prepared sample. 23. The grasping element of claim 21 wherein the mechanical actuation is electro-thermal actuation. 24. The grasping element of claim 21 wherein the grasping member is a first one of a plurality of grasping members. 25. The grasping element of claim 24 wherein ones of the plurality of grasping members are substantially mirror images of one another. 26. The grasping element of claim 21 wherein the grasping member includes a first profile corresponding to a second profile of the FIB-prepared sample. 27. The grasping element of claim 26 wherein the first profile is substantially non-rectangular. 28. An apparatus, comprising:means for cutting a substrate with a focused ion beam (FIB) to at least partially sever a sample from the substrate;means for mechanically activating a grasping element to capture the substrate sample with the grasping element; andmeans for separating the captured sample from the substrate. 29. The apparatus of claim 28 wherein at least a portion of at least one of the cutting means, activating means, and separating means is automated. 30. The apparatus of claim 28 further comprising means positioning the grasping element proximate the substrate sample, wherein the positioning means is at least partially automated. 31. The apparatus of claim 28 further comprising means for transporting the captured sample to an electron microscope, wherein the transporting means is at least partially automated. 32. The apparatus of claim 28 wherein the activating means is configured to activate the grasping element to capture the substrate sample after the substrate sample has been only partially severed from the substrate, and the cutting means is configured to completely sever the partially severed substrate sample from the substrate while the partially severed sample is captured by the grasping element. 33. The apparatus of claim 32 wherein the cutting means is configured to completely sever the partially severed substrate sample by cutting a connection between the partially severed substrate sample and the substrate. 34. The apparatus of claim 33 wherein the cutting means is configured to cut the connection via FIB. 35. The apparatus of claim 28 wherein the separating means is configured to reposition the captured sample relative to the substrate until a connection between the sample and the substrate is compromised. 36. The apparatus of claim 28 wherein the activating means includes means for adjusting an amount of electrical power delivered to the grasping element to mechanically capture the substrate sample with the grasping element. 37. The apparatus of claim 28 wherein the activating means includes means for switching between an electrically powered state and an electrically un-powered state to mechanically capture the substrate sample with the grasping element. 38. The apparatus of claim 28 wherein the activating means includes means for increasing an amount of electrical power delivered to the grasping element to mechanically capture the substrate sample with the grasping element. 39. The apparatus of claim 28 wherein the activating means includes means for substantially ceasing delivery of electrical power to the grasping element to mechanically capture the substrate sample with the grasping element. 40. The apparatus of claim 28 wherein the activating means includes means for actuating the grasping element to mechanically open and close the grasping element. 41. The apparatus of claim 40 wherein the actuating means includes electro-thermal actuating means operable to mechanically open and close the grasping element. 42. The apparatus of claim 40 wherein the actuating means includes electrostatic actuating means operable to mechanically open and close the grasping element. 43. The apparatus of claim 40 wherein the actuating means includes piezoelectric actuating means operable to mechanically open and close the grasping element. 44. The apparatus of claim 28 further comprising the grasping element, wherein the grasping element includes a thermally activated end-effector, and wherein the activating means includes at least one of:means for heating at least a portion of the grasping element, the heating means operable to mechanically open and close the grasping element; andmeans for cooling at least a portion of the grasping element, the cooling means operable to mechanically open and close the grasping element. 45. The apparatus of claim 28 further comprising means for examining the sample while the sample remains captured by the grasping element. 46. The apparatus of claim 28 further comprising means for examining the sample after the sample is released from the grasping element. 47. The apparatus of claim 46 further comprising means for manipulating the grasping element to position the sample on an examination grid prior to the examination of the sample. 48. The apparatus of claim 46 further comprising means for coupling the sample to an examination grid prior to the releasing the sample from the grasping element. 49. The apparatus of claim 28 wherein the grasping element is a mechanically-actuated MEMS element. 50. The apparatus of claim 49 wherein the MEMS element comprises nickel. 51. The apparatus of claim 49 wherein the MEMS element comprises silicon. 52. The apparatus of claim 28 wherein the activating means includes means for pressing the grasping element against the substrate sample. 53. The apparatus of claim 52 wherein the grasping element includes a malleable layer configured to interface with the substrate sample. 54. The apparatus of claim 53 wherein the malleable layer comprises gold. 55. The apparatus of claim 28 wherein:the cutting means includes means for cutting each of a plurality of samples at least partially from a substrate; andthe separating means includes means for separating each of the plurality of samples from the substrate. 56. The apparatus of claim 28 wherein the cutting means, the activating means, and the separating means are each configured for installation into a transmission electron microscope (TEM) and operation within the TEM. 57. The apparatus of claim 28 wherein the cutting means, the activating means, and the separating means are each configured for installation into a scanning electron microscope (TEM) and operation within the SEM. 58. An apparatus, comprising:means for cutting a substrate with a focused ion beam (FIB) to at least partially sever a sample from the substrate;means for positioning an assembly tool proximate the sample, the assembly tool having a compression bond end-effector configured to capture the sample;means for applying a force on the sample through the compression bond end-effector, the force having sufficient magnitude to cause a compression bond to form between the compression bond end-effector and the sample, thereby capturing the sample; andmeans for separating the captured sample from the substrate. 59. The apparatus of claim 58 further comprising means for transporting the captured sample to an electron microscope. 60. The apparatus of claim 58 wherein the force applying means includes means for actuating an actuator to which the compression bond end-effector is coupled. 61. The apparatus of claim 60 wherein actuating includes electro-thermally activating. 62. The apparatus of claim 60 wherein actuating includes electro-statically activating. 63. An apparatus, comprising:means for cutting a substrate with a focused ion beam (FIB) to at least partially sever a sample from the substrate;means for capturing the substrate sample with a grasping element without activating the grasping element; andmeans for activating the grasping element to release the captured substrate sample from the grasping element. 64. The apparatus of claim 63 wherein the capturing means includes means for passively capturing the substrate sample with the grasping element. 65. The apparatus of claim 63 wherein the grasping element is configured to maintain a substantially constant temperature while the substrate sample is being captured with the grasping element. 66. The apparatus of claim 63 wherein the grasping element is configured to passively capture the substrate sample. 67. The apparatus of claim 63 wherein the grasping element is configured to passively capture the substrate sample in the substantial absence of electrical power delivered to the grasping element. 68. The apparatus of claim 63 wherein the capturing means includes means for capturing the substrate sample while the grasping element is in a non-activated state. 69. The apparatus of claim 63 wherein the capturing means includes means for capturing the substrate sample while substantially no electrical power is delivered to the grasping element. |
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claims | 1. A semiconductor inspection equipment comprising:a movable stage for holding a semiconductor sample;a sample image acquisition unit for irradiating the semiconductor sample held on the stage with a charged particle beam and obtaining a sample image through a sample signal discharged from the sample due to irradiation of the charged particle beam;a memory unit for storing CAD data concerning the semiconductor sample; anda display unit capable of displaying the CAD data such that it is superimposed on the sample image obtained by the sample image acquisition unit,wherein the equipment has a grid creation means of generating a grid composed of vertical and horizontal lines having a constant distance and displaying the grid superimposed on the sample image displayed on the display unit, and a means of generating systematic numbers indicating vertical and horizontal positions of a plurality of rectangular areas contained in the grid created by the grid creation means and displaying the numbers in relevant areas in the grid displayed on the display unit. 2. The semiconductor inspection equipment according to claim 1, wherein the grid creation means has a function of generating another grid having a narrower distance between the lines thereof in one rectangular area in the previously created grid. 3. The semiconductor inspection equipment according to claim 1, comprising a means of storing, as CAD data, the grid generated by the grid creation means and superimposed on the sample image displayed on the display unit. 4. The semiconductor inspection equipment according to claim 1, comprising a means of generating characters, symbols, lines, figures, and/or painted figures, and superimposing them on the sample image displayed on the display unit. 5. The semiconductor inspection equipment according to claim 4, comprising a means of copying, as a pattern, the characters, symbols, lines, figures, and/or painted figures contained in a designated area of the sample image displayed on the display screen, a means of performing cutting processing on the pattern, a means of creating an x-axis mirror-inverted copy of the pattern, and a means of creating a y-axis mirror-inverted copy of the pattern. 6. The semiconductor inspection equipment according to claim 4, comprising a means of storing, as CAD data, the characters, symbols, lines, figures, and/or painted figures superimposed on the sample image displayed on the display unit. 7. The semiconductor inspection equipment according to claim 1, comprising a means of superimposing a marker, displayed with the same size irrespective of the display magnification of the sample image, on the sample image displayed on the display unit. 8. The semiconductor inspection equipment according to claim 7, comprising a means of storing, as CAD data, the marker superimposed on the sample image displayed on the display unit. 9. A semiconductor inspection method, comprising;irradiating a semiconductor sample held on a movable stage with a charged particle beam and obtaining a sample image through a sample signal discharged from the sample;generating a grid composed of vertical and horizontal lines having a constant distance and displaying the grid such that it is superimposed on the sample image; andgenerating systematic numbers indicating vertical and horizontal positions of a plurality of rectangular areas contained in the grid and displaying the numbers in relevant areas in the grid. 10. The semiconductor inspection method according to claim 9, wherein the distance of the grid superimposed on the sample image is adjusted. 11. The semiconductor inspection method according to claim 9, wherein another grid having a narrower distance between the lines thereof is generated in one rectangular area in the previously created grid. 12. The semiconductor inspection method according to claim 9, wherein the grid superimposed on the sample image is stored as CAD data. 13. The semiconductor inspection method according to claim 9, wherein characters, symbols, lines, figures, and/or painted figures are superimposed on the sample image displayed on the display unit. 14. The semiconductor inspection method according to claim 13, wherein the characters, symbols, lines, figures, and/or painted figures contained in a designated area of the sample image displayed on the display unit are copied as a pattern. 15. The semiconductor inspection method according to claim 13, wherein an x-axis or y-axis mirror-inverted copy of the characters, symbols, lines, figures, and/or painted figures contained in a designated area of the sample image displayed on the display unit is created as a pattern. 16. The semiconductor inspection method according to claim 13, wherein the characters, symbols, lines, figures, and/or painted figures superimposed on the sample image displayed on the display unit are stored as CAD data. 17. The semiconductor inspection method according to claim 9, wherein a marker displayed with the same size irrespective of the display magnification of the sample image is superimposed on the sample image displayed on the display unit. 18. The semiconductor inspection method according to claim 17, wherein the marker superimposed on the sample image displayed on the display unit is stored as CAD data. 19. A computer readable medium bearing a program for causing a computer to perform the steps of:displaying a grid composed of vertical and horizontal lines having a constant distance such that the grid is superimposed on a sample image obtained through an electron microscope;generating systematic numbers indicating vertical and horizontal positions of a plurality of rectangular areas contained in the grid and displaying the numbers in relevant areas in the grid; andstoring the grid superimposed on the sample image as CAD data. |
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summary | ||
summary | ||
description | In the following discussion, embodiments of a cask and a production method of the cask, and an embedded form according to the present invention will be described in detail with reference to the drawings. It is noted that the present invention is not limited to these embodiments. FIG. 1 is a perspective view showing a cask according to a first embodiment of the present invention. FIG. 2 is a radial sectional view of the cask shown in FIG. 1. FIG. 3 is an axial sectional view of the cask shown in FIG. 1. A cask 100 according to the first embodiment is formed by machining the inner surface of a cavity 102 of a barrel body 101 in agreement with the outside shape of a basket 130. The machining of the inner surface of the cavity 102 is made by the use of a special working apparatus as will be described below. The barrel body 101 and a bottom plate 104 are casts of carbon steel having gamma ray shielding ability. It is also possible to use stainless steel in place of the carbon steel. The barrel body 101 and the bottom plate 104 are connected by welding. Additionally, in order to ensure the hermeticity of a pressure-resistant container, between a primary lid 110 and the barrel body 101 is provided a metal gasket. Between the barrel body 101 and an outer casing 105 is potted a resin 106 which is a polymeric material containing a high proportion of hydrogen and has neutron shielding ability. Furthermore, between the barrel body 101 and the outer casing 105, a plurality of inner fins 107 made of copper for performing heat conduction is welded, and the resin 106 is injected into spaces formed by these inner fins 107 in fluid form and solidified by thermosetting reaction and the like. It is preferable that the inner fins 107 are provided in higher density in the positions where the amount of heat is high so as to enable uniform radiation of the heat. Furthermore, between the resin 106 and the outer casing 105 is provided a heat expansion margin 108 of several mm. A lid portion 109 consists of the primary lid 110 and a secondary lid 111. The primary lid 110 is made of stainless steel or carbon steel which shields gamma rays and is of a disc shape. The secondary lid 111 is also made of stainless steel or carbon steel and of a disc shape, and a resin 112 as a neutron shielding member is sealed in the upper face thereof. The primary lid 110 and the secondary lid 111 are mounted on the barrel body 101 by means of bolts 113 made of stainless steel or carbon steel. Furthermore, between each of the first lid 110 and the secondary lid 111, and the barrel by 101, a metal gasket for keeping the interior hermetically sealed is provided. Further, in the vicinity of the lid portion 109, an auxiliary shielding member 115 in which a resin 114 is sealed is provided. On both sides of a cask body 116 are provided trunnions 117 for suspending the cask 100. FIG. 1 shows the case where the auxiliary shielding member 115 is provided, however, during transportation of the cask 100, the auxiliary shielding member 115 is removed and a buffer member 118 is mounted (See FIG. 2). The buffer member 118 has such a structure that a buffer material 119 such as lumber is incorporated into an outer casing 120 made of stainless steel and the like. A basket 130 consists of 69 square pipes 132 constituting cells 131 for accommodating spent fuel assemblies. The square pipes 132 are made of an aluminum composite material or aluminum alloy in which powder of B or B compound having neutron absorbing ability is added to powder of Al or Al alloy. Furthermore, as the neutron absorbing material, cadmium can be used besides boron. Meanwhile, on the outside surface of the barrel body 101, four chamfered portions 1 are provided at 90xc2x0 intervals. Each chamfered portion 1 is disposed so as to oppose to a flush portion 130a on the outside of the basket 130. The chamfered portion 1 is machined by a special working apparatus as will be described later. That portion has excess thickness thus excess gamma ray shielding ability before subjecting the machine work, however, by subjecting this portion to chamfering work, it is possible to make the thickness of the barrel body 101 substantially uniform and reduce the weight of the barrel body 101. Additionally, the gamma ray shielding ability is ensured in the range of necessary and sufficient. The above-mentioned resin 106 is potted so as to intimately contact with the outside of the barrel body 101, while forming a space portion 2 between the outer casing 105 and the resin 106 at the position corresponding to the chamfered portion 1. This is because the resin 106 of that portion becomes thicker than needed by providing the chamfered portion 1 for the barrel body 101. By providing this space portion 2, it is possible to make the thickness of the resin 106 uniform and to equalize the neutron shielding ability, as well as to reduce the usage of the resin 106. Next, methods for forming the heat expansion margin 108 and the space portion 2 will be described. FIG. 4 is a perspective view showing an embedded form for forming the space portion 2. This embedded form 3 has two types: an embedded form 3a in which a heater 4 is sandwiched between SUS plates 5, and a hot melt adhesive 6 (JET MELT EC-3762LM: manufactured by SUMITOMO 3M) which is a thermoplastic material is provided therearound; and an embedded form 3b in which the heater 4 itself is embedded in the hot melt adhesive 6. The hot melt adhesive 6 comprises vinyl acetate as a main component and has a viscosity at 120xc2x0 C. of 4000 cps. The shape of the embedded form 3 is determined based on the space portion 2 to be arranged. In this case, the space portion 2 is not filled with the resin 106, but the inner fins 107 penetrate therethrough for enabling heat conduction. Therefore, the shape of the embedded form 3 is also restricted by the inner fins 107 and the outer casing 105. In specific, as shown in FIG. 4, two embedded forms 3a having a metal core (SUS plate 5) and one embedded form 3b not having the metal core (5) are prepared for one space portion 2. In this connection, the embedded form 3a having the metal core (5) is used for ensuring large spaces, while the embedded form 3b not having the metal core (5) is used for ensuring small spaces. Since the embedded form 3a has the metal core (5), it has the advantage that the usage of the hot melt adhesive 6 can be reduced and that it can be preferably recycled. FIG. 5 is a perspective view showing an embedded form used for forming a heat expansion margin. This embedded form 3c is so configured that the hot melt adhesive 6 is formed in sheet-like shape and the heater 4 is embedded therein. This embedded form 3c is arranged by spreading on the inner surface of the outer casing 105 between the inner fins 107. After setting the embedded forms 3a, 3b for the space portion 2 and the embedded form 3c for the heat expansion margin, spaces T formed by the barrel body 101, the outer casing 105 and the inner fins 107 are successively potted with the resin 106 in fluid form, to thereby embedding the embedded form 3. Subsequently, after the resin 106 has solidified, the temperature is raised to 140xc2x0 C. by energizing the heater 4. As a result of this, the hot melt adhesive 6 melts to flow out of the lower part of the cask body 116. In this connection, during resin molding, the bottom plate 104 is not mounted on the cask body 116. Through the above process, it is possible to form the space portion 2 and the heat expansion margin 108 between the resin 106 and the outer casing 105. Incidentally, in case there remains a residue after removing the hot melt adhesive 6 by melting, it is preferable to perform finishing by using an apparatus that conducts aspiration while exposing the object to hot air. Meanwhile, as the thermoplastic material, polyethylene, polypropylene, polystyrene, methacrylic resin, nylon and the like that are known as thermoplastic materials can be appropriately used other than the hot melt adhesive 6. FIG. 6 is a flow chart showing a production method of the above-mentioned square pipe. At first, powder of Al or Al alloy is prepared by a quench solidifying method such as atomizing method (step S401), while preparing powder of B or B compound (step S402), and then the both particles are mixed for 10 to 15 minutes by a cross rotary mixer and the like (step S403). As the Al or Al alloy, it is possible to use a pure aluminum base metal, Alxe2x80x94Cu group aluminum alloys, Alxe2x80x94Mg group aluminum alloys, Alxe2x80x94Mgxe2x80x94Si group aluminum alloys, Alxe2x80x94Znxe2x80x94Mg group aluminum alloys, Alxe2x80x94Fe group aluminum alloys and the like. On the other hand, as the B or B compound, it is possible to use B4C, B2O3 and the like. The amount of boron to be added with respect to aluminum is preferably not less than 1.5% by weight and not more than 7% by weight. This range is based on the fact that if the amount is 1.5% by weight or less, it is impossible to achieve sufficient neutron absorbing ability, while on the other hand if the amount is more than 7% by weight, elongation in response to tension will be deteriorated. Next, the mixed powder is enclosed in a rubber case, to which high pressure is uniformly applied from every direction at atmospheric temperatures by CIP (Cold Isostatic Press) for powder molding (step S404). The molding condition of CIP is such that the molding pressure is 200 Mpa, the outer diameter and the length of a molded product are 600 mm and 1500 mm, respectively. By uniformly applying pressure from every direction by the use of the CIP, it is possible to obtain a molded product having high density and less variations in mold density. Subsequently, the powder molded product is vacuum-sealed in a can, and the temperature is raised to 300xc2x0 C. (step S405). Bas components and water in the can are removed at this degassing step. At next step, the molded product HIP degassed under vacuum is remolded by the HIP (Hot Isostatic Press) (step S406). The molding condition of the HIP is such that the temperature is 400xc2x0 C. to 450xc2x0 C., the time is 30 sec, the pressure is 6000 t and the outer diameter of the molded product becomes 400 mm. Subsequently, outside cutting and end surface cutting are conducted so as to remove the can (step S407), and the corresponding billet is hot extruded by using a port hole extruder (step S408). The extrusion condition in this case is such that the heating temperature is 500xc2x0 C. to 520xc2x0 C., and the extrusion speed is 5 m/min. The extrusion condition varies depending on the content of B. Next, after the extrusion molding, tensile sizing is conducted (step S409) and an unsteady portion and an evaluation portion are cut out to complete the product (step S410). The completed square pipe has a square shape as shown in FIG. 7 of which one side of the cross section is 162 mm and the inside is 151 mm. The dimension is held to a minus tolerance of 0 in view of required specifications. In addition, while R of the inner angle is 5 mm, the outer angle is formed into a sharp edge having an R of 0.5 mm. In the case where R of the edge portion is large, when stress is applied to the basket 130, stress concentration occurs in a certain part (vicinity of the edge) of the square pipe 132, which may cause breakage. For this reason, by designing the square pipe 132 to have a sharp edge, a load is directly transmitted to the neighboring square pipe 132, so that it is possible to prevent the stress from concentrating in a certain part of the square pipe 132. FIG. 8 is a perspective view showing an insertion method of the square pipe. The square pipes 132 produced by the above-mentioned process are inserted in turn according to the worked shape within the cavity 102. In connection of this, if there occur a bend and a twist on the square pipe 132, the square pipes 132 are difficult to be inserted when they are tried to be inserted appropriately because of accumulation of tolerances and influence by the bends due to the fact that the minus tolerance of dimension is 0. And if they are tried to be inserted forcefully, excess loads are applied to the square pipes 132. In view of the above, bends and twists of all or part of the produced square pipes 132 are measured beforehand by a laser measuring apparatus and the like and appropriate insertion positions are computed based on the measured data by the use of a computer. In this way, it is possible to readily insert the square pipes 132 into the cavity 102, as well as to make the stress applied to each square pipe 132 uniform. Furthermore, as shown in FIGS. 8 and 3, on both sides of a square pipe line constituting 5 or 7 cells in the cavity 102 are inserted dummy pipes 133. The dummy pipe 133 is directed to make the thickness of the barrel body 101 uniform as well as to reduce the weight of the barrel body 101, while securing the square pipes 132 with accuracy. This dummy pipe 133 is also made of an aluminum alloy containing boron, and produced by the similar process as described above. This dummy pipe 133 may be omitted. Next, work with respect to the cavity 102 of the barrel body 101 will be described. FIG. 9 is a perspective view showing a working apparatus for the cavity 102. This working apparatus 140 comprises a stationary table 141 which is penetrated through the barrel body 101 and placed and fixed in the cavity 102; a movable table 142 which slides in the axial direction on the fixed table 141; a saddle 143 positioned and fixed on the movable table 142; a spindle unit 146 consisting of a spindle 144 and a driving motor 145 disposed on the saddle 143; and a face mill 147 provided on the spindle shaft. On the spindle unit 146 is provided a reaction force receiver 148 of which abutting portion is formed in accordance with the inner peripheral shape of the cavity 102. The reaction force receiver 148 is removable and slides along a dovetail groove (omitted in the drawing) in the direction of the arrow seen in the drawing. Also the reaction force receiver 148 has a clamp device 149 for the spindle unit 146 to enable fixation at a predetermined position. Furthermore, in an under groove of the stationary table 141, a plurality of clamp units 150 are attached. The clamp unit 150 comprises a hydraulic cylinder 151, a wedge-like movable block 152 disposed on the shaft of the hydraulic cylinder 151 and a stationary block 153 abutting on the movable block 152 at an inclined surface, and attached to the inner surface of the groove of the stationary table 141 on the diagonally shaped side in the drawing. Driving the shaft of the hydraulic cylinder 151 causes the movable block 152 to abut with the stationary block 153, resulting in that the movable block 152 is moved downward to some degree due to the effect of the wedge (designated by the dotted line in the drawing). As a result, the lower surface of the movable block 152 is pressed against the inner surface of the cavity 102, so that it is possible to fix the stationary table 141 within the cavity 102. Meanwhile, the barrel body 101 is placed on a rotary supporting base 154 comprising a roller, and is able to rotate in the radial direction. Providing a spacer 155 between the spindle unit 146 and the saddle 143 makes it possible to adjust the height of the face mill 147 on the stationary table 141. The thickness of the spacer 155 is the same as one side of the square pipe 132 in dimension. The saddle 143 is moved in the radial direction of the barrel body 101 by rotating a handle 156 provided for the movable table 142. Movement of the movable table 142 is controlled by a servo motor 157 provided on an end of the stationary table 141 and a ball screw 158. Since the inside shape of the cavity 102 varies as the work proceeds, the shapes of the reaction force receiver 148 and the movable block 152 of the clamp mechanism 150 are changed appropriately. FIG. 10A to FIG. 10D are schematic explanatory views showing working processes of the cavity. At first, the stationary table 141 is secured at a predetermined position in the cavity 102 by the clamp unit 150 and the reaction force receiver 148. Next, as shown in FIG. 10A, the spindle unit 146 is moved at a predetermined cutting speed along the stationary table 141, and then cutting work within the cavity 102 is effected by the face mill 147. After completion of the cutting work at the position in question, the clamp unit 150 is removed to release the stationary table 141. Next, as shown in FIG. 10B, the barrel body 101 is turned 90 degrees on the rotary supporting base 154, and the stationary table 141 is fixed by the clamp unit 150. Then similar to the above described procedure, cutting work is effected by the face mill 147. After that the process as described above is repeated two more times. Next, the spindle unit 146 is turned 180 degrees, and cutting work within the cavity 102 is effected successively as shown in FIG. 10C. Also in this case, similar to the above, the cutting work is repeated while rotating the barrel body 101 90 degrees. Next, as shown in FIG. 10D, the position of the spindle unit 146 is elevated by applying the spacer 155 to the spindle unit 146. Then at this position, the face mill 147 is fed in the axial direction, thereby effecting cutting work within the cavity 102. By repeating the above step while rotating 90 degrees, the shape that is need to accommodate the square piper 132 is substantially completed. Cutting of the portion to which the dummy pipe 133 is to be inserted is also effected in the same way as shown in FIG. 10D. However, the thickness of the spacer for adjusting the height of the spindle unit 146 is designed to be equal to one side of the dummy pipe 133. Additionally, in the case where the chamfered portion 1 of the barrel body 101 is milled, as shown in FIG. 11, the barrel body 101 is secured on the rotary supporting base 154 by a special clamp device 10, and the spindle unit 146 incorporated with the stationary table 141 is arranged on the side of the barrel body 101. Under this condition, the face mill 147 is fed in the axial direction, and cutting work is effected on the chamfered portion 1 of the barrel body 101. After completion of working on one chamfered portion 1, similar to the above, the clamp device 10 is removed and the barrel body 101 is rotated 90 degrees, and the cutting work is continued. This process is repeated two more times to finish the work for the chamfered portion 1 of the barrel body 101. Since spent fuel assemblies to be accommodated in the cask 100 contain fissile materials, fission products and the like and therefore generate radiation and involve decay heat, it is necessary to reliably keep the heat removing ability, shielding ability and criticality preventing ability of the cask 100 during a storage period. In the cask 100 according to the first embodiment, the inside of the cavity 102 of the barrel body 101 is machine worked so that outside of the basket 130 consisting of the square pipes 132 is inserted in a contact state (without space area), and moreover the inner fins 107 are provided between the barrel body 101 and the outer casing 105. Therefore, the heat from a fuel bar is transmitted to the barrel body 101 via the square pipe 132 or helium gas filled therein, to be emitted from the outer casing 105 mainly through the inner fins 107. Accordingly, removal of the decay heat is efficiently conducted, so that it is possible to keep the temperature within the cavity 102 lower than that in the conventional case for the same amount of decay heat. Furthermore, gamma rays generated from a spent fuel assembly are shielded by the barrel body 101, the outer casing 105, the lid portion 109 and the like made of carbon steel or stainless steel. On the other hand, neutrons are shielded by the resin 106, thereby eliminating the affect of exposure to the radiation operator. In specific, the design is made to obtain shielding ability such that the surface dose equivalent rate is not more than 2 mSv/h and the dose equivalent rate at the position of 1 m from the surface is not more than 100 xcexcSv/h. Furthermore, since the square pipes 132 constituting the cells 131 are made of an aluminum alloy containing boron, it is possible to prevent the spent fuel assemblies from absorbing neutrons to go critical. As described above, according to the cask 100 of the first embodiment, since the inside of the cavity 102 of the barrel body 101 is machine worked so that the square pipes 132 constituting the outer periphery of the basket 103 are inserted in contact state, it is possible to improve the heat conduction from the square pipes 132. Furthermore, since a space area within the cavity 102 is eliminated, it is possible to make the barrel body 101 compact and lightweight. Even in such a case, the number of accommodations for the square pipes 132 is not reduced. To the contrary, if the outer diameter of the barrel body 101 is made equal to that of the cask shown in FIG. 17, the number of cells can be kept accordingly, so that it is possible to increase the number of accommodation of the spent fuel assemblies. Moreover, since the barrel body 101 is provided with the space portion 2 as well as the chamfered portion 1 and the resin 106 is formed so as to match with the outside shape of the barrel body 101, it is possible to further reduce the weight of the cask 100 while ensuring the necessary and sufficient thickness required for radiation shielding. Concretely, the cask 100 in question in which the outer diameter of the cask body 116 is, for instance, 2560 mm and the weight is suppressed to 120 tons satisfies the required design condition (the outer diameter of the cask body is no more than 2764 mm, and the weight is no more than 125 tons), while making it possible to increase the number of accommodation of the spent fuel assemblies to up to 69. Next, an alternative of the cask according to the first embodiment will be described. FIG. 12A and FIG. 12B are radial sectional views showing alternatives of the cask. In the above-mentioned cask 100, the chamfered portions 1 of the barrel body 101 are disposed every 90xc2x0 in four positions, however, as shown in FIG. 12A, it is possible to provide chamfered portions 1, 1a every 45xc2x0 to make the barrel body 101 into octagon. In addition, it is also possible to provide the resin 106 with a space portion corresponding to each chamfered portion 1 though it will increase the thickness of the resin 106 (omitted in the drawing). Alternatively, as shown in FIG. 12B, the curved surface of the barrel body 101 may be formed into two chamfered portions 1b. In both cases, it is possible to make the outside shape of the barrel body 101 corresponding to the outside shape of the basket 130, so that it is possible to make the cask 100 more compact and lightweight. FIG. 13 is a radial sectional view showing another alternative of the cask. It is also possible to omit the above-mentioned space portion 2 by changing the shape of an outer casing 201 as in this cask 200. In the actual manufacturing process, since the barrel body 101 and the outer casing 201 are connected by the inner fins 107 before filling with the resin 106, the resin 106 can be potted directly. Therefore, the necessity of the embedded form 3 for forming the space portion as described above is eliminated. However, in order to form the heat expansion margin 108 for absorbing heat expansion of the resin 106, the sheet-like embedded form is still necessary. According to the above configuration, it is possible to make the cask 200 more compact. Further, formation of the space portion 2 can be omitted. FIG. 14 shows a radial section view of a cask 250 having such a configuration. Due to the fact that in the above-mentioned cask 100 the barrel body 101 is made of carbon steel or stainless steel and the resin 106 is made of polymeric materials, the most important factor from the viewpoint of reduction of weight is the shape of the barrel body 101. In view of this, formation of the space portion 2 of the resin 106 is omitted and thereby the manufacturing process is simplified. According to the cask 250 of such configuration, it is possible to simplify the manufacturing process as well as to reduce the weight of the cask 250. FIG. 15 is a radial section view showing a cask according to the second embodiment of the present invention. This cask 300 is characterized in that an auxiliary shielding member 301 is provided at a portion 101a where the gamma ray shielding ability of the barrel body 101 is insufficient, thereby ensuring a predetermined thickness. That is, a portion 101b where the auxiliary shielding member 301 is not formed substantially corresponds to the chamfered portion 1 in the cask 100 of the first embodiment. The auxiliary shielding member 301 is made of carbon steel or stainless steel the same as the barrel body 101 and is produced by casting, forging or machine working. Other configuration is as same as that of the cask 100 of the first embodiment, so that the description thereof is omitted and the same elements are denoted by the same reference numerals. According to this cask 300, similar to the above, it is possible to make the cask 300 compact and lightweight. FIG. 16 is a radial section view showing a cask according to the third embodiment of the present invention. This cask 400 is such that on the outside of the barrel body 501 of the cask 500 shown in FIGS. 17 and 18 are provided four chamfered portions 401 at 90xc2x0 intervals. Similar to the above, each chamfered portion 401 is provided so as to oppose to a flush portion 509a of the outside of the basket 509. This chamfered portion 401 is machine worked by the special working apparatus as described above. Furthermore, the resin 502 is potted in close contact with the outside of the barrel body 501, however, it forms a space portion 402 at the position corresponding to the chamfered portion 401 between the outer casing 503 and the resin 502. This is because when the chamfered portion 401 is provided for the barrel body 501, the thickness of the resin 502 at that position becomes excessively large. By providing this space portion 402, it is possible to reduce the usage of the resin 502. As to other constituents, description will be omitted because they are similar to those of the cask 500. With such configuration, the cask 400 can be made lightweight and compact. As described above, according to the cask of the present invention, since the outside shape of the barrel body is matched to the outside shape of the basket, it is possible to reduce the weight of the cask. Further, according to the cask of the present invention, since the outside shape of the barrel body and the inside shape of the cavity are matched to the outside shape of the basket, it is possible to make the cask lightweight and compact. Also according to the cask of the present invention, since the shape of the neutron shielding member is matched to the outside shape of the basket, it is possible to make the cask compact and to reduce the usage of the neutron shielding member. Also according to the cask of the present invention, since the inside shape of the cavity of the barrel body is matched to the outside shape of the basket, and the outside of the barrel body is worked so that the thickness necessary to shield gamma rays generated by the spent fuel assemblies accommodated in the cells is achieved, it is possible to make the cask lightweight and compact. Also according to the cask of the present invention, since the neutron shielding member is formed on the outside of the barrel body so as to have an approximately uniform thickness, it is possible to reduce the excess neutron shielding member and to make the cask compact. Also according to the cask of the present invention, since the outside shape of the barrel body is matched to the outside shape of the basket by providing a chamfer in the part having excess thickness for shielding gamma rays in the barrel body, it is possible to make the cask lightweight and compact. Also according to the cask of the present invention, since the outside shape of the barrel body is matched to the outside shape of the basket by providing an auxiliary shielding member in the part where the thickness for shielding gamma rays is insufficient in the barrel body, it is possible to make the cask lightweight and compact. Also according to the method of producing a cask of the present invention, an embedded form is arranged in the inner surface of the outer casing beforehand, and after potting the neutron shielding member, the embedded form is removed by heating, thereby forming an expansion margin or other space portions between the outer casing and the neutron shielding member. Therefore, it is possible to facilitate production of the cask. Furthermore, since the embedded form of the present invention is a form for the expansion margin or other space portions to be formed between the outer casing and the neutron shielding member to be potted, and the form is formed of a thermoplastic material and a heater is embedded in the form, and the form is melt removed by heating the heater, it is possible to facilitate production of the cask. Furthermore, since the embedded form of the present invention is formed by providing a thermoplastic material around a metal core and a heater is embedded in the metal core, the form can be easily recycled so that the production efficiency of the cask is improved. Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth. |
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054065950 | claims | 1. An apparatus for closing and sealing a lead-through and which is capable of cleaning the lead-through of solid material deposited therein, said apparatus comprising an annular flange which is attachable to the lead-through, said annular flange defining an internal seating surface, a cone which comprises a head, a rod-shaped part and means forming a sealing surface means located between said head and said rod-shaped part, said rod-shaped part defining an end opposite said sealing surface means which includes a connection means for a flush pipe, said cone being positionable within and movable relative to said annular flange such that, when said annular flange is attached to a lead through, said sealing surface means of said cone abuts said seating surface of said annular flange to close and seal said lead-through, or such that said sealing surface means is spaced from said seating surface and said cone is positioned out of said annular flange and within said lead-through, and a flush pipe defining a first end which is attachable to said connection means and which includes a plurality of holes for emitting flushing water, and a second end which includes means for connecting to a source of flushing water and means for connecting to an operating means, said flush pipe, when connected to said connection means of said rod-shaped part, being capable of moving said cone relative to said annular flange, such that said holes of said flush pipe are positioned within said lead-through. 2. An apparatus according to claim 1, including a detector nut positioned around said rod-shaped part of said cone and a sealing washer positioned between said detector nut and said annular flange to fix said sealing surface means of said cone against said seating surface of said annular flange, said detector nut including a teflon seal positioned against said rod-shaped part and defining drainage openings. 3. An apparatus according to claim 1, including a flush bottle positioned around said flush pipe and movable toward and against said annular flange for drainage of flush water, said annular flange defining a connecting means for connection thereto of said flush bottle. |
description | The invention relates generally to ion implantation, and, in particular, to uniformly implanting an ion beam over a wafer by modifying a relative motion and a relative geometric relation between the wafer and the ion beam. An ion implantation process typically requires a uniform and consistent dose or amount of ions to be implanted into a wafer. Ion implantation processes also typically require a stable and uniform ion beam for implanting into the wafer. The dose is generally a function of ion beam current density and time that the wafer spends in front of an ion beam. Because of larger and larger wafer sizes, recent semiconductor manufactures have moved towards processing one wafer at a time, in so-called single-wafer systems. In general, a so-called ribbon ion beam is employed by the single-wafer ion implantation. Clearly, when the required length of the ribbon beam is continually increased for larger and larger wafer sizes, it becomes more difficult to set up a ribbon ion beam meeting the required levels of uniformity in at least both beam intensities and angles. Therefore, there is a need for an improved method and apparatus capable of achieving uniform implantation in a single-wafer ion implanter without requiring extensive beam uniformity tunes. A conventional technique entails simultaneously moving and rotating a wafer, which is larger than an ion beam, such that different portions of the wafer receive a substantially uniform dose. First, as shown in FIG. 1A, an ion beam 10 is formed with an elongated shape having a length and a width along two independent axes of the ion beam 10, and a wafer 11 is provided with a diameter larger than both the length and the width of the ion beam 10. Second, as shown in FIG. 1B, the wafer 11 is simultaneously rotated and moved across the ion beam 10. Clearly, the rotation of the wafer 11 can be used to ensure the wafer 11 is completely implanted by the ion beam 10, as the ion beam 10 is shorter than the diameter of the wafer 11. Moreover, as shown in FIG. 1C, different points on the wafer may have different rotation trajectories when a projection 12 of the ion beam 10 onto the wafer 11 is moved a unit distance (Δd), as can be discerned with reference to points A, B and C. Significantly, as shown in FIG. 1C, different points may have very different implantations during the different rotation trajectories. Therefore, to ensure that different points on the wafer have essentially equivalent implantation results, it is necessary for each point to be rotated around a center of the wafer at least one time, even integral times, during the unit distance Δd. In other words, the rotation velocity must be significantly higher than the movement velocity. Moreover, as shown in FIG. 1D, by comparison of how the rotary trajectories of points D, E and F are projected by the ion beam 10, the projected ratio of a corresponding rotation trajectory of a point is decreased as the distance between the point and the center of the wafer is increased. Therefore, to achieve subsequently equivalent implantations, the point having lower (higher) projection ratio should be projected for a longer (shorter) period of time. In other words, the movement velocity of the wafer 11 across the ion beam 10 must be higher when the ion beam is near the center of the wafer 11, and lower when the ion beam is near the edge of the wafer 11, as shown in FIG. 1E. Another conventional technique is to scan an ion beam in multiple rotationally-fixed orientations of a wafer at movement velocities, such that different portions of the wafer receive substantially uniform doses. First, as shown in FIG. 2A, an ion beam 20 is formed as an elongated shape having a length and a width along two independent axes, and a wafer 21 is provided having a diameter with no relation to the length and the width. To emphasize the differences between this embodiment and the previous embodiment, the corresponding figures show the case where the diameter is larger than both the length and the width. Second, as shown in FIG. 2B, the wafer 21 is located on the left side of the ion beam 20 and has at least some separate points A, B, C and D. Third, as shown in FIG. 2C, the wafer 21 is moved through the ion beam 20 to the right side of ion beam 20. The wafer 21 is not rotated during the movement of the wafer 21. Fourth, as shown in FIG. 2D, the wafer 21 is rotated, such that the relative geometric relations among the ion beam 20 and the points A, B, C, D are changed. Fifth, as shown in FIG. 2E, the ion beam 20 is moved through the ion beam 20 to the left side of the ion beam 20, when the wafer 21 is not rotated during the movement of the wafer 21. After that, the above “movement-rotation-movement-rotation” process is repeated, until the wafer 21 is essentially uniformly implanted. When the number of repeated times is sufficient, the accumulated implantations on each of points A-D during the multiple rotationally-fixed orientations will essentially be equivalent. In other words, the final implantation result is independent of where the points A-D are in the beginning as shown in FIG. 2B. However, these conventional technologies still have some non-negligible disadvantages. For the former conventional technology, the required rapid rotation may damage the wafer by a couple of different ways. For example, the fine scale structures formed on the wafer may not have sufficient structural integrity to withstand the centripetal acceleration, and the rotation can greatly add to the kinetic energy when particles collide with the wafer surface thus enhancing the destructive potential of the particles. Moreover, the mechanism for simultaneously moving and rotating the wafer is more complex than separately moving and rotating the wafer, especially when the rotation velocity is high. For the later conventional technology, the proper number of repetitions can be less than clear. Here, with more repetitions, implantation uniformity is increased but at the expense of decreased throughput. Clearly, the throughput will be significantly decreased when the ion beam is shorter than the diameter of the wafer or the stable portion of the ion beam is shorter than the diameter of the wafer, because many repeated times will be needed or desired to ensure different portions of the wafer are uniformly implanted. Accordingly, there remains no ideal technology for uniformly implanting a wafer using a ribbon ion beam. A need thus exists to develop such a new technology for achieving this issue, especially to develop a new technology for effectively achieving this issue without significantly having to amend conventional technologies. The present invention provides a method and an apparatus for uniformly implanting a wafer with an ion beam. One feature of the invention is the relative geometric relation between the wafer and the ion beam. The length of the ion beam is not smaller than the diameter of the wafer. Moreover, when the wafer is moved to cross the ion beam, the wafer always is covered by the ion beam along the direction of the ion beam for each portion of the wafer. Therefore, the traditional rapid rotation of wafer for ensuring equivalent implantation over different portions of a wafer with a diameter larger than the ion beam length is not required. Of course, a rotation still is required to average other non-uniformities, such as the non-uniform ion beam current distribution along the length of the ion beam. However, the required rotation velocity is slow, because the rotation is only used to average a variation but is not used to average the implantation and non-implantation over the wafer as with the traditional fast wafer rotation. As a result, the rotation velocity is at most a few times of the movement velocity, and even can be slower than the movement velocity. In another feature of the invention, when the wafer is moved along a scan path intersecting the ion beam with a movement velocity having a movement velocity profile to a position of the wafer, the movement velocity profile is adjustable without any specific limitation. For example, the movement velocity ratio between the center of the wafer and an edge of the wafer is not particularly restricted but can be larger than one, equal to one, or smaller than one. Note that the conventional rapid rotation of wafer requires the ratio always being larger than one, because the ratio that a point of the wafer is implanted by an ion beam during a rotation of the wafer is continuously decreased when projection of the ion beam is moved from the center of the wafer to the edge of the wafer. In contrast, the implanted ions are always distribution over the whole wafer in this invention, because the ion beam length is larger than or equal to the wafer diameter. Therefore, the movement velocity profile can be more variable for precisely adjusting the final implantation result. Accordingly, the invention has a significant advantage in that the rotation velocity is slower than that of the conventional simultaneous movement and rotation, such that conventional defects induced by the fast rotation velocity can be avoided. Also, the wafer is always simultaneously rotated and moved during ion implantation of the wafer, such that conventional defects induced by no-rotation or multiple rotationally-fixed orientations can be improved. In addition, the rotation velocity may be lower than the movement velocity, when said rotation velocity is defined by a tangential velocity parallel to said scan path on an edge of said wafer. Moreover, to further improve the overall uniformity of the implantation, it is optional to rotate the wafer for an angular magnitude 360 P/Q degree during the time when the wafer is moved through a scan path, wherein P is a positive integer and Q also is a positive integer. As example, P can be 1 and Q can be the total scan number. Another feature of the invention is that both the rotation velocity and the movement velocity can be a constant or a velocity profile to a position of the wafer. Hence, the final implantation result over the wafer can be adjusted by adjusting one or more of the movement velocity and the rotation velocity. Another feature of the invention is that each of the movement velocity profile and the rotation velocity profile can be decided using one or more of the following factors: the ion beam current density distribution, especially the distribution along the length of the ion beam, the forecasted final implantation result over the wafer, and the predetermined scan paths. A further feature of the invention is an approach for repairing error during the period of simultaneously moving and rotating the wafer. Whenever an error, such as a glitch or an instability of the ion beam, is detected, the error position is recorded and the ion beam is blocked immediately. After that, both the movement and the rotation of the wafer are continued with the blocked ion beam until an end of the current scan path arrives. Then, both the movement and the rotation are reversed with unblocked ion beam until the error position arrives, such that the whole current scan path is implanted with proper ion beam. Finally, the ion beam is blocked immediately again until the ion beam is projected on the end of the current scan path, such that the whole ion implantation can be performed with little to no error. A related feature of the invention is an approach for repairing secondary error during the above repairing approach. Whenever a secondary error, such as a glitch or an instability of the ion beam, is detected during the reversed movement and reversed rotation, the secondary error position is recorded and the ion beam is blocked immediately. After that, both the reversed movement and the reversed rotation of the wafer with the blocked ion beam are continued until the reversed scan of the current scan path is finished. Next, both the movement and the rotation with blocked ion beam are proceeded again until the error position arrives. Then, the ion beam is not blocked when both the movement and the rotation are proceeded until the secondary error position has arrived, such that the whole current scan path is implanted with proper ion beam. Finally, the ion beam is blocked immediately again until the ion beam is projected on the end of the current scan path, such that the whole ion implantation can be performed without error. A further feature of the invention is that the wafer can be tilted when the wafer is simultaneously moved and rotated. The tilt angle can be fixed or varied within predetermined angle range. During the tilting, the wafer can be rotated around a direction parallel to the ion beam or another direction vertical to the wafer. Hence, the implantation angle of the ion beam on the wafer can be fixed or adjusted. An apparatus for achieving the above features at least has an ion beam assembly for proving the ion beam, a wafer movement driver operative to move the wafer, a wafer rotation driver operative to rotate the wafer, and a controller operative to operate the ion beam assembly, the wafer movement driver and the wafer rotation wafer. The ion beam assembly, the wafer movement driver and the wafer rotation driver can be any commercially available or equivalent product. Herein, a key is the controller that can operate the ion beam assembly, the wafer movement driver and the wafer rotation wafer to achieve the above features. Note that the details of the controller are not limited to those mentioned; it can be an integrated circuit, a program code executed by a computer, another equivalent device, and so on. The apparatus can have some elements for blocking the ion beam, such as blanker, deflector and switch. It also can have a wafer tilting driver for tilting the wafer. Reference will now be made in detail to specific embodiments of the present invention. Examples of these embodiments are illustrated in the accompanying drawings. While the invention will be described in conjunction with these specific embodiments, it will be understood that the intent is not to limit the invention to these embodiments. In fact, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without at least one of these specific details. In other instances, well-known process operations are not described in detail in order not to obscure the present invention. One embodiment is a method of implanting a wafer as shown in FIG. 3. First, as shown in block 301, an ion beam is formed in an elongated shape having a length along a first axis not shorter than a diameter of a wafer and a width along a second axis shorter than the diameter of the wafer. Then, as shown in block 302, a center of the wafer is simultaneously moved along a scan path intersecting the ion beam at a movement velocity and the wafer is rotated, such as around the center of the wafer, at a rotation velocity. As examples, an ion beam longer than a diameter of a wafer can be viewed as the uniform portion of the ion beam being longer than the diameter of the wafer, or viewed as the uniform portion of the ion beam being lower than the diameter of the wafer when the amount of the ion beam current still is detectable on the edge of the wafer. In contrast, in the prior art shown in FIGS. 1A to 1E, the required limitation “an ion beam is shorter than a diameter of a wafer” means that the whole ion beam is dropped to zero, or at least not detectable, on the edge of the wafer. According to an aspect of the invention, an essential mechanism of the method, in addition to that elucidated in the referenced figure, can be further explained as below. First, as shown in FIG. 4A, a wafer 40 is provided with some points A, B, C, and D, and an ion beam 41 is provided beside (e.g., at the right side of) the wafer 40. The length of the ion beam 41 is larger than or equal to the diameter of the wafer 40, but the width of the ion beam 41 is shorter than the diameter of wafer 40. Then, as shown in FIG. 4B, the wafer 40 is simultaneously moved and rotated across the ion beam 41. Here, the movement direction usually is essentially parallel to a short axis of the ion beam 41. Indisputably, the wafer 40 is totally overlapped with the ion beam 41 along the long axis of the wafer 40 when the wafer 40 intersects with the ion beam 41. The wafer 40 may be moved at an angle, as shown in FIG. 4C, but when a point of the wafer 40 is located right under the ion beam 41 all points of the wafer 40 along a line passing the point and parallel to the long axis of the ion beam 41 must be located right under the ion beam 41. In other words, according to a feature of the invention, the case shown in FIG. 4D is not acceptable. Further, the method does not have a preference for clockwise or counterclockwise rotation, with FIG. 4B only showing a sample with clockwise rotation direction. Third, as shown in FIG. 4E, the wafer 40 is located at the other side (e.g., the right side) of the ion beam 41 after the simultaneous movement and rotation. Here, the rotation times during the simultaneous movement and rotation are not limited. Fourth, as shown in FIG. 4F, by simultaneously moving and rotating again by reversing the movement direction but keeping the rotation direction, the wafer 40 is located at the other (e.g., the left) side of the ion beam 41 again. The embodiment only requires reversing the movement direction; whether to reverse, in particular, the rotation direction when the movement direction is reversed is optional for this invention. By repeating the steps shown in FIGS. 4A-4B and 4E-4F several times, full rotation can ensure that the wafer 40 is uniformly implanted by the ion beam 41. One characteristic of the embodiment can be easily found by at least comparing FIG. 1C with FIG. 4B. In the prior art, without rotation, some portions of the wafer 11 will be implanted by the ion beam 10, but other portions of the wafer 40 will never be implanted by the ion beam. Hence, according to a feature of the invention, the required rotation velocity must be high enough so as to let portions of the wafer 40 be implanted and not implanted alternately during the simultaneous moving and rotating step. In contrast, in this embodiment, all portions of the wafer 40 will always be implanted by the ion beam 41 even without rotation. Hence, rotation essentially is only used to average the possible fluctuation of the ion beam current distribution, and then the required rotation velocity will be significantly lower than the prior art. For example, the rotation velocity is at most a few times of the movement velocity. As another example, the rotation velocity is lower than the movement velocity, or the rotation time is less than one when the wafer is moved from one side of the ion beam to another side of the ion beam. A simple way to compare the rotation velocity and the movement velocity is to calculate a difference between a tangential velocity parallel to the scan path on an edge of the wafer and a velocity of the center of the wafer along the scan path. As an example, the rotation velocity is slower than the movement velocity, when the rotation velocity is defined by a tangential velocity parallel to the scan path on an edge of the wafer. As an example, an angular magnitude of the rotation velocity is 360 P/Q degrees during a period that the wafer is moved through the scan path, wherein P is a positive integer and Q is also a positive integer. For example, P is 1 and Q is the total scan number. Another characteristic of the embodiment is evidenced by comparing FIG. 1D with FIG. 4B. In the prior art, during rotation, different portions of the wafer 11 have different implantation ratios, with portions closest to the center of the wafer 11 almost always being implanted during rotation, and portions close to the edge being at most partially implanted during the rotation. Hence, to ensure uniform implantation over the wafer 11, the movement velocity of the wafer 11 must be highest when the center of the wafer 11 is being implanted and lowest when (e.g., gradually decreased until only) the edge of the wafer 11 is being implanted. In contrast, in the current embodiment, the implantation ratios of different portions of the wafer 40 during rotation will always be equivalent. Hence, the movement velocity of the wafer 40 along the scan path across the ion beam 41 need not be adjusted to balance any non-uniformity induced by the different implantation ratios over different portions of the wafer 40. As an example, the simultaneously moving and rotating step can be chosen from one or more of a group comprising or consisting of the following: (a) moving the wafer 40 with a faster movement velocity when the ion beam 41 implants the center of the wafer 40, and with a slower movement velocity when the ion beam 41 only implants an edge of the wafer 40; (b) moving the wafer 40 with a slower movement velocity when the ion beam 41 implants the center of the wafer 40, and with a faster movement velocity when the ion beam 41 only implants an edge of the wafer 40; and (c) moving the wafer 40 with about the same (e.g., an essentially similar) velocity regardless of whether the ion beam 41 is implanting at the center of the wafer 40 or at an edge of wafer 40. Indeed, considering the movement velocity profile and the rotation velocity profile relative to a position of the wafer 40 across the ion beam 41, there is no specific non-uniformity in need of being cancelled by averaging. Thus, not only does the movement velocity have no specific contour as with the prior art shown in FIG. 1E, but also the rotation velocity has no specific contour. Accordingly, both the movement velocity profile and the rotation velocity profile can be flexibly adjusted or fixed, such that implantation of the ion beam 41 over the wafer 40 is improved. The simplest movement velocity profile is a constant movement velocity, which is suitable for a very stable and uniform ion beam 41 and a wafer 40 having very uniform patterns. However, in the practical world, where many factors are non-uniform over different portions of the wafer 40 or non-stable during the simultaneous rotation and movement, the movement velocity is a function of one or more of some possible factors such that non-uniform or non-stable factor(s) can be cancelled by averaging. As an example, possible factors may be a current density distribution of the ion beam 41 along the first axis, a current density distribution of the ion beam 41 along a direction intersecting the first axis, a forecasted implanted dose distribution over the wafer 40, a net current density distribution along the first axis per a predetermined scan path, a net current density distribution along a direction intersecting the first axis per a predetermined scan path, and so on. Similarly, although the rotation velocity usually is a constant velocity, the rotation velocity profile still can be a function of one or more of the above possible factors. One main characteristic of the invention is using one or more of the “predetermined scan path” and the “forecasted implanted dose distribution” as a factor of calculating one or more of the movement velocity profile and the rotation velocity profile. The “ion beam current distribution” and the “quality of the wafer to be implanted” have been popularly used to calculate the velocity profile in the prior art, but the usage of the two factors is newly provided by this invention. Although the wafer 40 is moved along a scan path having a straight-line shape in the above embodiment, the invention is not so limited. Indeed, as with conventional two-dimensional scanning, the shape of the scan path can be straight-line or arcuate. Further, in this embodiment, the wafer 40 is moved along the scan path such that the ion beam 41 implants from an edge of the wafer 40 through the center of the wafer 40 to an opposite edge of the wafer 40. However, the invention also allows for the wafer 40 to be moved along a scan path not from an edge to an opposite edge, but rather from a portion of the wafer 40 to another portion of the wafer 40. Clearly, when the rotation velocity is high enough and/or the repeated times of simultaneous moving/rotating are high enough, the final implantation will still be uniform enough. Furthermore, while the above embodiment describes the wafer being repeatedly backwardly and forwardly moved along only one scan path, the invention allows different scan paths to be used in sequence. Two ends of a next scan path can be different than two ends of a previous scan path when a movement/rotation of the wafer 40 along the previous scan path is finished and a movement/rotation of the wafer along the next scan path is to begin. According to a typical but not required or limiting implementation, the ending point of the previous scan path is the starting point of the next scan path. Besides, different scan paths can correspond to different movement velocity profiles and different rotation velocity profiles, because the implantations among different scan paths are capable of being separately operated. To reduce the amount of channeling, the wafer 40 can be tilted when the wafer 40 is simultaneously moved and rotated. Of course, for this object, it also is possible to tilt the ion beam 41 when the wafer 40 is simultaneously moved and rotated, although it may be preferred or more popular to tilt the wafer 40 but not the ion beam 41. Typically, the wafer 40 is tilted at a fixed tilt angle as shown in FIGS. 5A and 5C, wherein the tilt angle usually is several degrees from vertical or from the direction of the ion beam 41. However, the invention also allows the tilt angle to be varied within a predetermined angle range, as shown in FIGS. 5B and 5D. For varied tilt angle ranges, an advantage is eliminating a risk that all implanted regions over the wafer 40 have a common oblique angle (owing to a non-vertical implanting ion beam 41), but a disadvantage is longer rotation time being required to ensure all implanted regions over the wafer have equivalent implanted regions (with equivalent direction). When the wafer 40 is tilted, the wafer 40 can be rotated around a direction (e.g., axis) parallel to the ion beam 41, as shown in FIGS. 5C and 5D, and also can be rotated around a direction parallel to a vector normal to the wafer surface, as shown in FIGS. 5A and 5B. The former can provide variance relative to the crystal axis with different positions of the wafer 40, but requires a slightly complex mechanism to rotate the wafer 40. The latter may induce varied tilt angles over different positions of the wafer 40, but the required mechanism to rotate the wafer 40 is simpler and cheaper. Furthermore, the ion beam usually is not always stable. Some errors, such as glitches or instabilities of the ion beam, are unavoidable. In the prior art shown in FIGS. 2A to 2E, the scan path for each rotation-fixed orientation is a straight line, and the wafer is not rotated during movement along a rotation-fixed orientation. Hence, the implantation can continue as soon as the repair of the ion beam is complete, because the implantation result is not a function directly of whether a line is implanted going left to right or right to left. In the prior art shown in FIGS. 1A to 1E, the continuous rotation induces a complication caused by having both movement and rotation implemented at the same time, and continuance of the implantation as soon as the repair of the ion beam is attempted cannot properly achieve the same implantation as if the error never happened. However, because the rotation speed is higher than the movement speed in the prior art, the damage induced by the errors may be acceptable if the period of errors is short enough (i.e., the quality of the ion beam is not too bad). However, in the above embodiment, the rotation velocity, which is at most a few times of the movement velocity, can be even slower than the movement velocity. Hence, damage induced by the errors will be significant. Therefore, another embodiment of the invention is a method for repairing error during a period of simultaneously moving and rotating the wafer. As shown in FIG. 6, the embodiment has one or more of the following steps: Initially, as shown in block 601, an error position is recorded, with pausing of the simultaneous moving and rotating step occurring through blocking of the ion beam immediately when an error of the ion beam is detected. Next, as shown in block 602, a movement and a rotation of the simultaneous moving and rotating step are continued until the wafer stops at one end of the scan path (with the ion beam still blocked). Then, as shown in block 603, the ion beam is unblocked, and the direction of both movement and rotation is reversed. After that, as shown in block 604, the ion beam is blocked immediately/precisely at the error position and the reverse movement and the reverse rotation are continued until the wafer stops at the other end of the scan path. Then, as shown in block 605, the wafer is moved and rotated with the ion beam blocked until the wafer stops at one end of the scan path. Finally, as shown in block 606, the ion beam is unblocked and the step of simultaneously moving and rotating the wafer is resumed. Moreover, it is possible that another error may occur during the above steps for repairing error during a period of simultaneously moving and rotating the wafer. Hence, if a secondary error, such as glitch or instability of the ion beam, occurs during the above steps for repairing error, the embodiment may further have one or more of the following steps. Of course, if no secondary error occurs, then the embodiment only continuously monitors the ion beam during the steps of repairing error. By referring to FIG. 7, initially, as shown in block 701, record a secondary error position during the reversed moment and the reversed rotation, and immediately stop the repairing step by blocking the ion beam when a secondary error is detected. Next, as shown in block 702, continue the reversed movement and the reversed rotation of the wafer until the wafer stops at the other end of the scan path with the blocked ion beam. Then, as shown in block 703, perform both movement and rotation until the wafer reaches the error position with the blocked ion beam. After that, as shown in block 704, unblock the ion beam and perform both the movement and the rotation of the wafer until the wafer reaches the secondary error position. Then, as shown in block 705, immediately block the ion beam and continue both the movement and the rotation until the wafer stops at one end of the scan path with the blocked ion beam. Finally, as shown in block 706, unblock the ion beam and resume the simultaneous moving and rotating step. The mechanism of the embodiment can be briefly summarized as follows: keep the scan path fixed but switch the implantation of the ion beam. If an error is found, the scan path will be scanned with blocked ion beam first, and then the scan path will be scanned backwardly and forwardly again to provide a chance for finishing the incomplete implantation. Here, to prevent an ion beam with glitch or instability from implanting, the ion beam is blocked immediately when an error of the ion beam is detected. Then, when the ion beam is moved backwardly and forwardly along the scan path and over a portion of the scan path which should be implanted, the ion beam implants to ensure that whole scan path has a complete implantation. The location of the error and the end (finishing terminal) of the scan path indicates the portion of the scan path which should be implanted but not implanted owing to the appeared error of ion beam. Of course, if another error (namely, a secondary error) occurs during the implantation over the portion, the above mechanism can be applied to repair the secondary error by using the position of the error and the position of the secondary error to indicate another portion of the scan path which should be implanted but not implanted owing to the appeared error and secondary error of ion beam. Without question, no matter how many errors appear, the above mechanism can be repeatedly used to repair these errors. To ensure uniform implantation, it is necessary that the ion beam has essentially similar ion beam current distribution along the scan path. Owing to the period of the glitch or instability usually is very short, the above embodiment directly uses the ion beam after it is blocked to filter out the effect of the error. However, the above embodiment also can use the ion beam only after the state of the ion beam is essentially equal to the state of the ion beam before the error occurs. In other words, the ion beam is monitored before an implantation of the ion beam, especially the unblocked ion beam, is performed. In addition, the way used to block the ion beam is not limited. It can comprise one or more of blanking the ion beam, deflecting the ion beam, or just directly turning-off the ion beam. A further embodiment is an apparatus for ion implantation of a wafer with a center and a diameter. The apparatus is capable of proceeding with and performing all embodiments disclosed above. As shown in FIG. 8, the embodiment at least has an ion beam assembly 801, wafer movement driver 802, wafer rotation driver 803, and controller 804. The ion beam assembly 801 is used to provide an ion beam for implanting a wafer. The wafer movement driver 802 is operative to move the center of the wafer along a scan path intersecting the ion beam at a movement velocity as the wafer crosses the ion beam, wherein the movement velocity has a movement velocity profile relative to a position of the wafer across the ion beam. The wafer rotation driver 803 is operative to rotate the wafer at a rotation velocity as the wafer crosses the ion beam, wherein the rotation velocity has a rotation velocity profile relative to a position of the wafer across the ion beam. The controller 804 is configured to operate the ion beam assembly 801, the wafer movement driver 802, and the wafer rotation wafer 803, such that the ion beam has an elongated shape with a length along a first axis longer than the diameter of the wafer and a width along a second axis shorter than the diameter of the wafer, such that the wafer is totally overlapped with the ion beam along the first axis as the wafer crosses the ion beam and such that the rotation velocity is at most a few times of the movement velocity. As an example, the ion beam assembly 801 usually at least has an ion source and an analysis magnet unit. For instance, the wafer movement driver 802 may have a holder for holding a wafer and both a motor and a roller chain for moving the holder along a rail. In a particular implementation, the wafer rotation driver 803 may embody a motor and a supporting rod for rotating the holder around the supporting rod. However, the prior art disclosed above can move the wafer and rotate wafer, and the above embodiment never requires specific movement or rotation (such as a very high rotation velocity or a very complex movement path). Hence, the details of the ion beam assembly 801, the wafer movement driver 802, and the wafer rotation driver 803 are not key to the embodiment, and thus are not to be limited to the disclosed embodiment. Indeed, any well-known, on-developing or to-be-developed technologies can be used. Clearly, a key according to one feature of the invention is the controller 804. Note that the controller 804 is not intended to be limited by its structure or implementational/nonconsequential functions, i.e., how the controller 804 achieves the method disclosed in the above embodiments, but rather by its ultimate functions such as emphasized and claimed herein. Hence, the details of the controller 804 are not limited; it can be an integrated circuit, a program code executed by a computer, another equivalent device, and so on. As a short summary, the controller 804 is cable of achieving at least one (e.g., or more, or all) of the following functions: (a) Control the ion beam assembly 801 to adjust the length of the ion beam to be larger than the diameter of the wafer. (b) Control the wafer movement driver 802 and the wafer rotation driver 803 to adjust a tangential component of the rotation velocity parallel to the scan path on an edge of the wafer to be at most a few times of a movement velocity. For example, the rotation velocity may be slower than the movement velocity, when the rotation velocity is defined by a tangential velocity parallel to the scan path on an edge of the wafer. For example, an angular magnitude of the rotation velocity may be 360 P/Q degrees during a period that the wafer is moved through the scan path, wherein P is a positive integer and Q is also a positive integer. (c) Control the wafer movement driver 802, such that a movement velocity is flexibly adjusted without the conventional limitation required by the prior art that the movement be higher close to the center of the wafer and lower close to an edge of the wafer. (d) Calculate at least one (e.g., or more, or all) of the movement velocity profile and the rotation velocity profile as at least one (e.g., or more, or all) of the following: a constant; and a function of at least one (e.g., or more, or all) of the following factors: a current density distribution of the ion beam along the first axis, a current density distribution of the ion beam along the direction intersecting the first axis, a forecasted implanted dose distribution over the wafer, a net current density distribution along the first axis per a predetermined scan path, and a net current density distribution along a direction intersecting the first axis per a predetermined scan path. (e) Adjust the movement velocity profile and the rotation velocity profile of each scan path when there are numerous scan paths to be scanned in sequence. (f) Control the ion beam assembly 801, the wafer movement driver 802, and the wafer rotation driver 803 to repair error as the wafer crosses the ion beam. The repairing step is disclosed in FIG. 6 and the corresponding paragraphs. (g) Control the ion beam assembly, the wafer movement driver 802, and the wafer rotation driver 803 to further repair secondary error during the process for repairing error. The error repairing step is disclosed in FIG. 7 and the corresponding paragraphs. Additionally, the embodiment may optionally have a wafer tilting driver for tilting the wafer when the wafer crosses the ion beam, such that the channeling effect can be minimized and implantation uniformity can be improved. The wafer tilting driver can have at least four possible operations as discussed in the above embodiments. The tilt angle can be fixed or varying within a predetermined angle range, and the rotation axis can be parallel to the ion beam or vertical to the wafer. Variations of the methods and the apparatus as described above may be realized by one skilled in the art. Although the methods and the apparatus have been described relative to specific embodiments thereof, the invention is not so limited. Many additional changes in the embodiments described and illustrated can be made by those skilled in the art. Accordingly, it will be understood that the present invention is not to be limited to the embodiments disclosed herein, can include practices other than specifically described, and is to be interpreted as broadly as allowed under the law. |
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039716988 | abstract | A nuclear reactor having a core structure comprising a plurality of closely packed parallel fuel element assemblies. Each assembly comprises a cluster of parallel fuel pins enclosed by a tubular casing through which coolant flow is directed. There is provided barrier means extending longitudinally through the cluster to define inner and outer coolant flow ducts each containing fuel pins. Gagging means for the ducts provides that the temperature of the coolant leaving the outer duct is lower than that leaving the inner duct so that the tubular casing is maintained relatively cool thereby to reduce irradiation growth and consequent bowing of the casing. The fuel pins in the outer duct may be of breeder material further to reduce the operating temperature of the casing. |
summary | ||
052251489 | claims | 1. Method for checking a thickness and cohesion of an interface of a duplex tube comprising a tubular core made from a first alloy and covered with a cladding layer made from a second alloy, a base metal of said second alloy being identical to a base metal of said first alloy, said method comprising successive checking operations in various zones around a circumference or along a length of said duplex tube, each operation comprising the steps of: (a) emitting ultrasonic waves in substantially radial directions from outside to inside said tube in said cladding layer and said core of said tube; (b) detecting reflected ultrasonic waves which have been reflected by surfaces of said tube, by an interface between said core and said cladding layer of said tube and by any flaws at said interface or which are transmitted by said cladding layer; (c) measuring propagation times of said ultrasonic waves radially of said tube along a total thickness of said duplex tube comprising said core and said cladding layer; (d) determining amplitudes and shape of the reflected ultrasonic waves; (e) subjecting said tube from an outer surface of said tube to a magnetic induction created by a multifrequency sinusoidal current; (f) measuring at least one of a phase and an amplitude of eddy currents induced in said tube; (g) calculating therefrom the thickness of said cladding layer; (h) calculating the total thickness of said tube from the measurements of propagation times of said ultrasonic waves and the thickness of said cladding layer; and (i) determining the cohesion of said interface of said tube by analyzing an amplitude and shape of the reflected waves. e.sub.p represents the thickness of said cladding layer, measured by eddy currents, V.sub.p represents the speed of the ultrasonic waves in said cladding layer, V.sub.a represents the speed of the ultrasonic waves in the material constituting said core of said tube, and .delta.t represents the propagation time of the ultrasonic waves in the total thickness of said tube. 2. Method according to claim 1, wherein the frequency of said ultrasonic waves lies between 10 and 20 MHz. 3. Method according to claim 1, wherein said multifrequency sinusoidal current has a main frequency which is determined so as to optimize a sensitivity to variations in thickness of said cladding layer and to minimize variations in signals corresponding to the induced currents caused by variations of an air gap, between said tube and an eddy current probe, subjecting said tube to a magnetic induction created by the multifrequency sinusoidal current, and at least one complementary second frequency which is sensitive to a variation in conductivity of at least one of the alloys constituting said core of said cladding layer of said tube and comparatively less sensitive to variations in thickness of the material of said core or of said cladding. 4. Method according to claim 3, wherein the multifrequency sinusoidal current has a complementary second frequency sensitive to a mean variation in conductivity of the alloys constituting said core and said cladding layer of said tube, and comparatively less sensitive to variations in thickness of said core and of said cladding layer. 5. Method according to claim 3, wherein said multifrequency sinusoidal current has first and second complementary second frequencies, said first frequency being sensitive to a variation in conductivity of the alloy constituting said core of said tube and comparatively less sensitive to variations in conductivity of the alloy constituting said cladding layer and to the variations in thickness of said core and of said cladding layer, and said second frequency being sensitive only to variations in the conductivity of the alloy constituting said cladding layer. 6. Method according to claim 3, wherein said multifrequency sinusoidal current has a complementary frequency sensitive to variations in said air gap. 7. Method according to claim 1, wherein the total thickness e.sub.g of the wall of the duplex tube is determined from the formula: EQU e.sub.g =e.sub.p +(.delta.t-e.sub.p /V.sub.p).times.V.sub.a 8. Method according to claim 1, wherein the cohesion of said tube at said interface is determined by detecting flaws by transmitting ultrasonic waves through said cladding layer and said interface, the presence of a flaw at said interface being manifested by a widening of ultrasonic waves reflected on said outer surface of said tube and at said interface, and by weakening or disappearance of a bottom echo obtained by reflection of ultrasonic waves on the inner wall of said tube. |
048141380 | claims | 1. A replacement rod for replacing a fuel rod retained in a mesh formed in a lattice-like spacer of a nuclear reactor fuel assembly by means of a spring disposed in the mesh, comprising a cladding tube having a shell with an opening formed therein, a sliding body movable inside said cladding tube in two longitudinal directions of said cladding tube, slotted links disposed on said sliding body, a U-shaped retaining leaf spring having two ends, one of said ends of said retaining spring being fixed in the longitudinal direction at said cladding tube and each of said ends of said retaining spring being guided in a respective one of said slotted links, and at least a portion of said spring being displaced radially outwardly through said opening formed in said shell upon movement of said sliding body in one longitudinal direction of said cladding tube and being displaced radially inwardly upon movement of said sliding body in the other longitudinal direction of said cladding tube, and a locking device associated with said sliding body for holding said retaining spring radially outwardly so as to retain the replacement rod in the mesh formed in the spacer. 2. Replacement rod according to claim 1, wherein said cladding tube has a protruding locking shoulder on the inside thereof, and including an actuating rod with an outer shell surface displaceable inside said cladding tube for moving said sliding body, said locking device being in the form of a tongue spring with a given thickness and length disposed on said outer shell surface of said actuating rod, said tongue spring having two ends extending in the longitudinal direction of said actuating rod, one of said ends of said tongue spring facing in the direction of movement of said sliding body being secured on said actuating rod for expulsion of said retaining spring and the other of said ends of said tongue spring being spaced from said outer shell surface of said actuating rod for gripping said protruding locking shoulder from behind, a clamping sheath with a given length disposed inside said cladding tube, a protruding stop shoulder for said clamping sheath disposed inside said cladding tube and spaced apart from said locking shoulder by a given distance in the direction of movement of said sliding body for expulsion of said retaining spring, said clamping sheath being coaxially displaceable in the longitudinal direction of said cladding tube between said locking shoulder and said stop shoulder, said clamping sheath having an inner shell surface protruding beyond said locking shoulder in radial direction and being radially spaced apart from said actuating rod by a distance greater than said given thickness of said tongue spring, and said given distance between said locking shoulder and said stop shoulder being greater than the sum of said given length of said clamping sheath and said given length of said tongue spring in the longitudinal direction of said actuating rod. |
summary | ||
claims | 1. A holding fixture for assisting in assembly of a support grid for nuclear fuel rods and including a plurality of straps each having a plurality of slots extending a portion of a height of the straps and tabs formed beside or between the slots, the holding fixture comprising:an actuation plate;a support plate having a plurality of receiving members structured to receive therein straps of the support grid and having a plurality of cells; anda plurality of cam assemblies structured to move to deflect every other tab of the straps received in the plurality of receiving members,wherein the cam assemblies are disposed in every other cell of the support plate, andwherein when the cam assemblies deflect every other tab of the straps, the slots form V-shapes. 2. The holding fixture of claim 1, wherein the receiving members are notches formed in the support plate. 3. The holding fixture of claim 1, wherein the receiving members are stand- offs extending from a surface of the support plate. 4. The holding fixture of claim 1, wherein the cam assemblies are structured to move to deflect every other tab of the straps based on movement of the actuation plate with respect to the support plate. 5. A holding fixture for assisting in assembly of a support grid for nuclear fuel rods and including a plurality of straps each having a plurality of slots extending a portion of a height of the straps and tabs formed beside or between the slots, the holding fixture comprising:an actuation plate;a support plate having a plurality of receiving members structured to receive therein straps of the support grid and having a plurality of cells; anda plurality of cam assemblies structured to move to deflect every other tab of the straps received in the plurality of receiving members,wherein the cam assemblies are disposed in every other cell of the support plate,wherein the cam assemblies are structured to move to deflect every other tab of the straps based on movement of the actuation plate with respect to the support plate, and wherein the cam assemblies each include:a plurality of cam rods attached to the actuation plate and extending in a direction substantially perpendicular away from the actuation plate; anda plurality of lever members attached to the support plate and being structured to move to deflect or stop deflecting tabs of straps received in the plurality of receiving members,wherein the support plate includes a plurality of openings each structured to allow one of the plurality of cam rods to pass therethrough, andwherein the lever members are structured to move to deflect or stop deflecting tabs of straps received in the plurality of receiving members based on movement of the actuation plate with respect to the support plate. 6. The holding fixture of claim 5, wherein the lever members are structured to move to deflect or stop deflecting tabs of straps received in the plurality of receiving members based on movement of the actuation plate toward or away from the support plate. 7. The holding fixture of claim 1, wherein the actuation plate includes a first actuation plate and a second actuation plate, wherein the first actuation plate and the second actuation plate are structured to move with respect to each other, and wherein the cam assemblies are structured to move to deflect every other tab of the straps based on movement of the first actuation plate with respect to the second actuation plate. 8. The holding fixture of claim 7, wherein the cam assemblies include:a plurality of first cam rods attached to the first actuation plate and extending in a direction substantially perpendicular away from the first actuation plate; anda plurality of second cam rods attached to the second actuation plate and extending in a direction substantially perpendicular away from the second actuation plate,wherein the support plate includes a plurality of openings each structured to allow one pair of the first and second cam rods to pass therethrough, andwherein the first and second cam rods are structured to move toward or away from each other based on movement of the first actuation plate with respect to the second actuation plate. 9. The holding fixture of claim 8, wherein each of the first and second cam rods includes a protrusion formed thereon and structured to abut against and deflect tabs of the straps when the first and second cam rods move away from each other. 10. A holding fixture pair for assisting in assembly of a support grid for nuclear fuel rods and including a plurality of upper straps and a plurality of lower straps each having a plurality of slots extending approximately half a height of the upper or lower straps and tabs formed beside or between the slots, the holding fixture pair comprising:an upper holding fixture comprising:an upper actuation plate;an upper support plate having a plurality of stand-offs structured to receive therein upper straps of the support grid and having a plurality of upper cells; anda plurality of upper cam assemblies structured to move to deflect every other tab of the upper straps received in the plurality of stand-offs,wherein the upper cam assemblies are disposed in every other upper cell of the upper support plate, anda lower holding fixture comprising:a lower actuation plate;a lower support plate having a plurality of notches structured to receive therein lower straps of the support grid and having a plurality of lower cells; anda plurality of lower cam assemblies structured to move to deflect every other tab of the lower straps received in the plurality of notches,wherein the lower cam assemblies are disposed in every other lower cell of the lower support plate. 11. The holding fixture pair of claim 10, wherein the upper cam assemblies are structured to deflect tabs of the upper straps in opposite directions of the directions the lower cam assemblies are structured to deflect tabs of the lower straps. 12. The holding fixture pair of claim 10, wherein when the upper holding fixture and the lower holding fixture face each other, the upper cam assemblies face empty lower cells of the lower holding fixture and the lower cam assemblies face empty upper cells of the upper holding fixture. 13. The holding fixture pair of claim 10, wherein slots are formed between tabs of the upper and lower straps, and wherein when the upper and lower cam assemblies deflect every other tab of the upper and lower straps, the slots form V-shapes. 14. The holding fixture pair of claim 10, wherein the upper cam assemblies are structured to move to deflect every other tab of the upper straps based on movement of the upper actuation plate with respect to the upper support plate and the lower cam assemblies are structured to move to deflect every other tab of the lower straps based on movement of the lower actuation plate with respect to the lower support plate. 15. The holding fixture pair of claim 14, wherein the upper and lower cam assemblies each include:a plurality of cam rods attached to the upper or lower actuation plate and extending in a direction substantially perpendicular away from the upper or lower actuation plate; anda plurality of lever members attached to the upper or lower support plate and being structured to move to deflect or stop deflecting tabs of the upper or lower straps,wherein the upper and lower support plates include a plurality of openings each structured to allow one of the plurality of upper or lower cam rods to pass therethrough, andwherein the lever members are structured to move to deflect or stop deflecting tabs of the upper or lower straps based on movement of the upper or lower actuation plate with respect to the upper or lower support plate. 16. The holding fixture pair of claim 10, wherein the upper actuation plate includes a first upper actuation plate and a second upper actuation plate and the lower actuation plate includes a first lower actuation plate and a second lower actuation plate, wherein the first upper actuation plate is structured to move with respect to the second upper actuation plate and the first lower actuation plate is structured to move with respect to the second lower actuation plate, and wherein the upper cam assemblies are structured to move to deflect every other tab of the upper straps based on movement of the first upper actuation plate with respect to the second upper actuation plate and the lower cam assemblies are structured to move to deflect every other tab of the lower straps based on movement of the first lower actuation plate with respect to the second lower actuation plate. 17. The holding fixture pair of claim 16, wherein the upper and lower cam assemblies each include:a plurality of first cam rods attached to the first upper or lower actuation plate and extending in a direction substantially perpendicular away from the first upper or lower actuation plate; anda plurality of second cam rods attached to the second upper or lower actuation plate and extending in a direction substantially perpendicular away from the second upper or lower actuation plate,wherein the upper and lower support plates include a plurality of openings each structured to allow one pair of the first and second cam rods to pass therethrough, andwherein the first and second cam rods are structured to move toward or away from each other based on movement of the first upper or lower actuation plate with respect to the second upper or lower actuation plate. 18. The holding fixture pair of claim 17, wherein each of the first and second cam rods includes a protrusion formed thereon and structured to abut against and deflect tabs of the upper or lower straps when the first and second cam rods move away from each other. 19. A method for assembling a support grid for nuclear fuel rods, the method comprising:providing the holding fixture of claim 1;providing a plurality of upper straps and a plurality of lower straps each having a plurality of slots extending approximately half a height of the upper or lower straps and tabs formed beside or between the slots;deflecting every other tab of the upper straps;deflecting every other tab of the lower straps;mating the upper straps and the lower straps; andreleasing deflections of the tabs of the upper and lower straps. |
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summary | ||
050874098 | abstract | A multiple shell pressure vessel is fabricated in modular sections comprising a top head module, a nozzle course module and a bottom shell module, each module utilizing telescoping shells with filled interspaces, each shell being removable for inspection and repair with all modular sections and shells being held in compression by a pair of upper and lower single or multilayer tendon skirts held in place by a number of tension members in combination with hydraulic or mechanical jacks or rams. Both tendons and rams are located outside the pressure vessel. Included is a method of arranging the shell flanges and shell radial supports to reduce or eliminate torsional forces on the flanges and flange seals. A leak detection system monitors for leaks in all shells. A method of adjusting shell stresses during operation uses pumps to adjust the pressure of the filler material in the interspaces between shells. The high thermal conductivity of the outer vessel wall, which is due to good thermal bonding provided by the intershell metallic filler-materials, makes it possible to keep the pressure-carrying outer vessel shells cool during service, by cooling the outer shell by plain water, borated water for nuclear reactor vessels, or other coolant. |
claims | 1. A method of molding a composition, comprising the steps of: providing a base polymer matrix material; providing a thermally conductive and electromagnetic interference and radio frequency absorptive carbon flake filler material; coating said filler material with a coating material; mixing said filler material with said base matrix into a mixture; and molding said mixture into a net-shape molded article. 2. The method of claim 1 , wherein said step of providing a base matrix material is providing a liquid crystal polymer. claim 1 3. The method of claim 1 , wherein said step of coating is coating with a thermally conductive and electromagnetic interference and radio frequency reflective material selected from the group consisting of: aluminum, copper and nickel. claim 1 4. A method of molding a thermally conductive electrically insulative composition, comprising the steps of: providing a base polymer matrix material; providing a thermally conductive carbon flake filler material; coating said filler material with an electromagnetic interference and radio frequency reflective material, producing a coated filler material; mixing said filler material with said base matrix into a mixture; and net shape molding said mixture of said coated filler material and said base matrix. 5. The method of claim 4 , wherein said step of providing a base matrix material is providing a liquid crystal polymer. claim 4 6. The method of claim 4 , wherein said step of coating is coating claim 4 |
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description | The present disclosure relates generally to peening of metal assemblies and more specifically to methods of peening nuclear reactor pressure vessel welds. Peening is a process of introducing mechanical stress into the surface layer of a part to compress and strengthen it against future fractures and wear. Peening can be performed in a variety of manners, including shot peening, laser peening and cavitation peening. Cavitation peening involves the application of bubbles onto the surface with the part in a liquid environment. The collapsing of the bubbles imparts impactive forces to the part. When an existing peening apparatus is insufficient to service a specifically shaped part of a metal assembly, a new peening apparatus is often constructed for that specifically shaped part. Peening is performed on a number of metal assemblies, including assemblies in nuclear power plants. A nuclear power plant has a nuclear reactor housed within a pressure vessel and a reactor coolant system (RCS) for removing heat from the reactor and to generate power. Nozzles are attached to the vessels and/or piping for a number of purposes, such as for connecting piping and instrumentation, such as for example Core Exit Thermocouples (CETs), providing vents, and securing control element drive mechanisms and heater elements. The nuclear industry is required to perform inspections of such nozzles, as well as their welds, due to the emergence of primary water stress corrosion cracking (PWSCC). Stress corrosion cracking occurs in a material due to a combination of a corrosive environment and tensile forces placed on the material. Cracking can be induced in materials in different ways including cold forming, welding, grinding, machining, and heat treatment as well as other physical stresses placed on the material. Stress corrosion cracking in nuclear reactor environments is a significant phenomenon that must be carefully monitored for successful operation of a nuclear power plant facility. Without careful monitoring for PWSCC, material defects may begin and may ultimately damage the material. If cracking continues, the materials may be damaged to such an extent that the materials must be removed from service and replaced. In the nuclear reactor environment, such replacement of components is extremely undesirable due to radiological concerns related to worker and facility safety, as well as overall plant economic concerns. WO 2016/085745, WO 2016/085747, EP 0622156 A1 and JP 4831807 disclose methods of peening parts of a closure head of the nuclear reactor pressure vessel. In metal assemblies, peening an obstructed region can be difficult or impossible with an existing peening apparatus and constructing a new peening apparatus, including a specific peening nozzle, can be cost prohibitive and sometimes impossible. More specifically, peening certain surface areas of a nuclear reactor pressure vessel susceptible to PWSCC can be difficult due to parts blocking access to surface area to be peened. In particular, CET nozzle funnels block access to areas susceptible to PWSCC. Additionally, the close proximity of the CET funnel to the Reactor Vessel Closure Head (RVCH) can prevent inspection and repair activities on a low hill side of a J-groove weld. For CET nozzles, the CET funnel itself blocks access to some of the susceptible nozzle material. Inspection or remediation from the outside diameter of the nozzle requires removal and re-installation of the funnel which is costly and radiation intensive. Being able to remove only the blocking areas of the funnel is faster and lower dose than a full removal and replacement. A method for peening an obstructed region of a metal assembly that is obstructed by an obstructing part of the metal assembly is provided. The method includes determining an optimal peening path for treating the obstructed region irrespective of the obstructing part; identifying a portion of the obstructing part within the optimal peening path; determining a section of the portion of the obstructing part that is removable without affecting a mechanical integrity and functionality of the obstructing part; removing, by machining, the section so as to create additional space along the optimal peening path; and peening the obstructed region, a path of the peening at least partially crossing through the additional space. A method for peening a nuclear reactor pressure vessel is also provided. The nuclear reactor pressure vessel includes a part penetrating a sloped wall of the nuclear reactor pressure vessel. A low hill side of the part defines an acute angle with the sloped wall and a high hill side of the part defines an obtuse angle with the sloped wall. The method includes removing, by machining, material of a radially enlarged section of the part at the low hill side of the part. The radially enlarged section forms a free end of the part. The machining creates additional space, which was occupied by the removed material before the machining, between the sloped wall and the part. The method also includes peening the nuclear reactor pressure vessel with a path of the peening at least partially crossing through the additional space. FIG. 1 shows a cross-sectional side view of a portion of a metal assembly in the form of a closure head 10 of a nuclear reactor pressure vessel including a part, in the form of a CET nozzle 12, protruding from a sloped wall 14 of closure head 10. During operation of the nuclear reactor, the closure head is fixed on top of a cylindrical shell. During refueling operations, closure head 10 is removed from a cylindrical shell, at which time maintenance operations may be performed on closure head 10. As is known, closure head 10 is hemispherical in shape and include an inner hemispherical surface 16, which faces an interior of the pressure vessel when closure head 10 is attached to the cylindrical shell, and an outer hemispherical surface 18, which faces away from of the pressure vessel when closure head 10 is attached to the cylindrical shell. Nozzle 12 extends through closure head 10 from outer surface 18 to inner surface 16 by penetrating through sloped wall 14. More specifically, nozzle 12 includes a tubular section 20 passing through sloped wall 14 and guide funnel 22 fixed to a bottom end 24 of tubular section 20 inside closure head 10. In one preferred embodiment, tubular section 20 is formed of Alloy 600 and guide funnel 22 is 304 stainless steel. Nozzle 12 is positioned such that a center longitudinally extending axis 26 of nozzle 12 extends vertically and a high hill side 12a of nozzle 12 at a highest vertical point 28a forms an obtuse angle α1 with respect to of sloped wall 14 and a low hill side 12b of nozzle 12 at a lowest vertical point 28b forms an acute angle α2 with respect to sloped wall 14. The terms axially, radially and circumferentially as used herein are used with respect to center axis 26. As used herein, the high hill side 12a of nozzle 12 is defined as the half of nozzle 12 centered on the highest vertical point 28a of nozzle 12 joining sloped wall 14 and the lower hill side 12b of nozzle 12 is defined as the half of nozzle 12 centered on the lowest vertical point 28b of nozzle 12 joining sloped wall 14. Referring to the view in FIG. 1, high hill side 12a is to the left of center axis 26 and low hill side 12b is the right of center axis 26. Nozzle 12 protrudes from inner surface 16 a maximum height H1 from point 28a to a bottom edge 30 of nozzle 12, which is formed by the bottom edge of funnel 22, and protrudes from inner surface 16 a minimum height H2 from point 28b to bottom edge 30. Guide funnel 22 is radially enlarged with respect to tubular section 20 and thus forms a radially enlarged section of nozzle 12 at a bottom free end 32 of nozzle 12. Guide funnel 22 includes an upper section 34 fixed to bottom end 24 of tubular section 20 and a lower section 36 extends downward from upper section 34 to lower edge 30. Upper section 34 includes a radially extending annular top edge 35 extending perpendicular to a cylindrical outer diameter surface 20a of tubular section 20. Extending axially downward from top edge 35, upper section 34 includes a cylindrical outer diameter surface 34a. On an interior thereof, upper section 34 also includes a stepped inner diameter surface 34b connected to a stepped outer diameter surface 24a of lower end 24 of tubular section 20. Lower section 36 includes a cylindrical outer diameter surface 36a coincident with cylindrical outer diameter surface 34a and a frustoconical outer surface 36b extending downward and radially outward from cylindrical outer diameter surface 36a to define an outermost outer diameter 36d of guide funnel 22. Lower section 36 further includes a frustoconical inner surface 36c extending downward and radially outward from a bottom of stepped inner diameter surface 34b to bottom edge 30. Nozzle 12 is fixed to wall 14 by an annular weld 38 joining cylindrical outer diameter surface 20a of tubular section 20 and inner surface 16 of wall 14 together. In this embodiment, weld 38 is considered a J-groove weld, because when viewed cross-sectionally as in FIG. 1, weld 38 has a J-shaped perimeter 38a. A heat affected zone 40 of wall 14, which surrounds perimeter 38a, also has a J-shape and joins weld 38 with a remaining material 14a of wall 16, i.e., a portion of wall 14 unaffected by the welding. Weld 38 includes an interior facing surface 38b that forms a portion of inner surface 16 of wall 14 that is contiguous with cylindrical outer diameter surface 20a. Due to the radial enlargement of guide funnel 22 with respect to tubular section 20, and the close proximity of top edge 35 to weld 38 at low hill side 12b, peening an entirety of surface 38b of weld 38 is very difficult, if not impossible, as low hill side 12b is an obstructed region that is obstructed by an obstructing part, in the form of guide funnel 22. By inspecting the area of wall 14 around nozzle 12, by for example a visual inspection, to determine the obstructed region of wall 14 that needs to be peened and by considering the peening path of an existing peening nozzle, for example the peening nozzle of WO 2016/085747, and an optimal peening path Popt for treating the obstructed region irrespective of the obstructing part is determined. In other words, the optimal peening path is that which the existing peening apparatus would take if the wall 14 was completely unobstructed. After the optimal peening path is determined, a portion of the obstructing part that is in the path is identified. In this example, upper section 24 of guide funnel 22 is identified as being with the optimal peening path Popt. Next, a section of the portion of the obstructing part that is removable without affecting a mechanical integrity and functionality of the obstructing part is determined. This can be determined by structural analysis of the connection between guide funnel 22 and tubular section Next, a section of the portion of the obstructing part that is removable without affecting a mechanical integrity and functionality of the obstructing part is removed by machining. More specifically, at least a portion of low hill side 12b of guide funnel 22 is removed to allow for peening of surface 38b of weld 38. In a preferred embodiment, the portion of low hill side 12b is removed by machining guide funnel 22, specifically electrical discharge machining (EDM). FIG. 2 shows an embodiment of the EDM of guide funnel 22. A container 41 filled with liquid 42 and sealingly contacting inner surface 16 via seals 44 is provided around guide funnel 22 and an EDM head 44 is provided within the liquid 42 to remove material from guide funnel 22. FIG. 3a shows a side view of an embodiment of guide funnel 22 after a portion of low hill side 12b of guide funnel 22 has been removed and FIG. 3c shows a perspective view of guide funnel 22 after machining, while FIG. 3b shows a perspective view of guide funnel 22 before machining. FIG. 3d shows an enlarged view of the view shown in FIG. 3a. The machining creates additional space 50 (as delimited by dashed lines in FIG. 3a), which was occupied by the removed material before the machining, between sloped wall 14 and nozzle 12. More specifically, a portion of upper section 34, including a portion of top edge 35 and a portion of cylindrical outer diameter surface 34a, has been removed by EDM at the low hill side 12b to create a notch 52 in top edge 35 of guide funnel 22 delimiting the additional space 50. Notch 52 extends axially downward from top edge 35 and extends circumferentially between radially and axially extending walls 54 delimiting the circumferential extent of the additional space 50 for peening surface 38b of weld 38. As shown in FIG. 3c, notch 52 extends at a circumferential angle in a range of 60 degrees to 180 degrees between walls 54. In the embodiment shown in FIG. 3a, wall 54 extends axially away from top edge 35 to a beveled wall 56 of notch 52, with beveled wall 56 extending axially downward to a lowermost circumferentially extending edge 58 of notch 52 that joins cylindrical outer diameter surface 34a or 36a. Beveling of nozzle 52 during the machining provides sufficient additional space 50 for peening, while minimizing the amount of material that is removed from nozzle 22 by machining. In the embodiment shown in FIGS. 3a, 3b, the machining uncovers a portion of lower end 24 of tubular section 20 that was previously covered by guide funnel 22 before the machining. Following the machining of guide funnel 22, a portion of inner surface 16 of closure head 10 previously blocked by guide funnel 22 at the lower hill side 12b can now be peened to prevent or minimize PWSCC. As shown in FIG. 4, a cavitation peening apparatus 60 is provided for peening an entirety of weld surface 38b. Cavitation peening apparatus 60 includes a container 62 filled with liquid 64, which is pressurized at a predetermined pressure, and sealingly contacting inner surface 16 via seals 66, which are provided at an open end of container 62 radially outside of weld 38. Container 62 is provided to surround weld 38 and free bottom end 32 of nozzle 12 such that inner surface 38b of weld 38 is submerged in the liquid 64. A peening nozzle 68 is positioned within the container 62. In this embodiment, the peening nozzle is a cavitation peening nozzle, but in other embodiments the nozzle can be another type of peening nozzle, such as a laser peening nozzle or a shot peening nozzle. In this embodiment, pressurized liquid, such as water, is ejected from peening nozzle 68, causing cavitation bubbles to form. A nozzle flow 70 is directed at weld surface 38b, causing the cavitation bubbles to settle thereon. Nozzle flow 70 has center axis 72 that forms an angle γ1 of between 10 and 60 degrees with inner surface 16 of sloped wall 14 on low hill side 12b. Nozzle flow 70 at least partial crosses through additional space 52 created by machining of guide funnel 22. The collapsing impact of the cavitation bubbles imparts compressive stress in the materials of the weld surface 38b. Peening nozzle 68 is moved around within container 62 to treat the entirety of surface 38b of weld 38. Thus, cavitation peening is performed on weld 38 without closure head 10 being completely submerged in liquid. In one preferred embodiment, peening nozzle 68 is part of a customized ultra-high pressure (UHP) cavitation peening tool. The UHP cavitation peening process includes directing peening nozzle 68 at surface 38b and water at high pressure and high velocity is discharged through a small orifice in nozzle 68. Vapor bubbles are formed in the resulting high velocity water jet stream as it contacts the water at comparatively lower pressure. The pressure within each bubble is below the vapor pressure of the surrounding water medium. The bubbles collapse at the surface, generating high pressure shock waves on the work surface that impart compressive stresses to the surface. Typically, the process requires a back pressure to prevent the bubbles from prematurely collapsing. The UHP cavitation peening process initiates and the peening nozzle 68 is driven to rotate by tooling around the axis of the CRDH nozzle 1 so that the entire surface 38b of weld 38 can be peened. As the peening nozzle 68 rotates, the peening nozzle 68 may also be actuated vertically up and down as needed for the optimal process effectiveness. In this embodiment, due to the minimal amount of material removed from guide funnel 22, further repair of guide funnel 22 is not necessary. Guide funnel 22 has threads and is screwed on to the tubular section 20. Additionally, there are plug welds and tack welds on the other side of guide funnel 22 that keep guide funnel 22 fixed to tubular section 20. An analysis is then performed to confirm that nozzle 12 is in an acceptable connection to operate with the material removed. In the preceding specification, the invention has been described with reference to specific exemplary embodiments and examples thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner rather than a restrictive sense. |
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abstract | The invention comprises a method and apparatus for reducing a kinetic energy of positively charged particles, comprising the steps of: (1) transporting the positively charged particles from an accelerator into an exit nozzle system along a beam line; (2) providing a first chamber of the exit nozzle system, the first chamber comprising: an incident side comprising an incident aperture, an exit side comprising an exit aperture, and a beam path of the positively charged particles from the incident aperture to the exit aperture; (3) filling the beam path in the chamber with a liquid; and (4) using the liquid to reduce the kinetic energy of the positively charged particles. The kinetic energy dissipater is optionally used in combination with a proton therapy cancer treatment system and/or a proton tomography imaging system. |
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